•A smartphone-based biosensing system using CVBS was developed for OA detection.•The system presented the good robustness in long-term image capture and analysis.•The system achieved label-free, non-invasive and long-term monitoring of cell viability.•The cost-effective CVBS was constructed by HepG2 cells, MTP and CCK-8 kit for OA detection.•The iPlate Monitor used traversal algorithm to obtain the best detection point-in-time.Okadaic acid (OA), as a diarrheic shellfish poisoning toxin, had wide distribution and frequent occurrence. Therefore, low-cost, high-throughput, wide-range and portable detection of OA was in high demand for food safety and environmental monitoring. In this study, a novel and portable smartphone-based system using cell viability biosensor (CVBS) was developed for label-free, non-invasive and long-term monitoring of cell viability. The variation of cell viability reflected the changes of cell morphology, cell count and cell proliferation indirectly. And this system applied the combination of image analysis and cell counting kit-8 assay (CCK-8) to monitor the reflection. The biosensing system chose HepG2 cells as sensing elements to build CVBS and used it in OA detection. Results showed this system could synchronously detect OA in 96 channels. And this biosensor presented a good performance to various OA concentrations, with a wide linear detection range (10–800 μg/L). Moreover, the point-in-time having best detection performance could be located by the traversal algorithm in the monitoring duration. Thus, this cell-based biosensor system provided a convenient and efficient approach in seafood safety testing such as OA screening.

Okadaic acid (OA) is a marine toxin ingested by shellfish. In this work, a simple, sensitive and label-free gap-based electrical competitive bioassay has been developed for this biotoxin detection. The gap-electrical biosensor is constructed by modifying interdigitated microelectrodes with gold nanoparticles (AuNPs) and using the self-catalytic growth of AuNPs as conductive bridges. In this development, the AuNPs growth is realized in the solution of glucose and chloroauric acid, with glucose oxidation used as the catalysis for growth of the AuNPs. The catalytic reaction product H2O2 in turn reduces chloroauric acid to make the AuNPs grow. The conductance signal amplification is directly determined by the growth efficiency of AuNPs and closely related to the catalytic activity of AuNPs upon their interaction with OA molecule and OA aptamer. In the absence of OA molecule, the OA aptamer can absorb onto the surfaces of AuNPs due to electrostatic interaction, and the catalytically active sites of AuNPs are fully blocked. Thus the AuNPs growth would not happen. In contrast, the presence of OA molecule can hinder the interaction of OA aptamer and AuNPs. Then the AuNPs sites are exposed and the catalytic growth induces the conductance signal change. The results demonstrated that developed biosensor was able to specifically respond to OA ranging from 5 ppb to 80 ppb, providing limit of detection of 1 ppb. The strategy is confirmed to be effective for OA detection, which indicates the label-free OA biosensor has great potential to offer promising alternatives to the traditional analytical and immunological methods for OA detection.

•Detection and screening of bitterness using animal’s gustatory system.•Features of spiking activity as well as LFP are both analyzed.•Fast response and high classification accuracy are achieved.•Interference study is conducted ensuring the high specificity to bitterness.Bitterness detection has attracted increasing attention in science and industry. However, existing methods often suffer from drawbacks such as long detection time and low specificity. Mammalian gustatory systems have been acknowledged as valid chemosensing systems, and thus the potential of utilizing intact rat gustatory system is investigated in bitterness detection and screening. Rat’s gustatory cortex (GC) functions as the central processor of gustation, and GC neurons are coupled with microelectrode array under anesthesia to reduce moving artifacts. By recording extracellular potentials in GC, response patterns evoked by bitterness are widely discovered in both single neuron and neural network activities. As a result, signals are observed to carry abundant information about taste qualities within the first 4 s after bitterness delivery, and the purpose of fast detection is achieved. Based on support vector machine, this biosensor can detect and recognize bitterness with an accuracy of 94.05%. Moreover, the high specificity to bitter compounds is guaranteed by single bitter responsive neuron which can generate highly specific firing patterns in spite of the existence of interference. Quantitative study also reveals that this in vivo system is sensitive enough for further applications. In conclusion, this whole animal-based biosensor is able to detect bitterness especially with strict constrains in time and provides new platform for bitterness screening with high specificity.

•We established two human cancer cell-based impedance biosensors (CIB) to detect DSP toxins in dynamic and real-time way.•Comparative experiments in DSP toxins detection were carried out between CIB and conventional cell-based assay (CCK8).•CIB method presents a good correlation with mouse bioassay (MBA) and LC–MS–MS in DSP toxins detection.Diarrhetic shellfish poisoning (DSP) toxin is a dangerous contamination in seafood worldwide that can threaten human health and fishing. A large number of animal bioassays and chemical analytical methods are employed for DSP toxin detection. However, these toxin detection methods are low-throughput and high-cost which hamper their wide applications. In this study, HeLa and HepG2 cell lines were selected as the sensitive elements to establish the CIBs for monitoring the cytotoxicity induced by a representative DSP toxin, okadaic acid (OA). The limit of detection (LOD) of HeLa- and HepG2-based biosensors are 10.2 μg/L and 3.3 μg/L, respectively, which are both lower than the conventional cell-based assay (21.2 μg/L of HeLa cells and 9.8 μg/L of HepG2 cells). The half maximal inhibitory concentration (IC50) values of OA in HeLa and HepG2 cells which were obtained from CIB (49.9 ± 4.9 and 39.2 ± 4.3 μg/L) are both lower than Cell Counting Kit-8 assay (CCK8) (62.7 ± 7.1 and 45.8 ± 6.7 μg/L). Besides, CIB measurement presents good correlation with mouse bioassay (MBA) and liquid chromatography–tandem mass spectrometry (LC–MS/MS). In summary, all the results indicate that the CIB technology had great potential to be an effective complement in DSP toxins detection.

Based on the inhibition of okadaic acid (OA) on protein phosphatase 2A (PP2A), we developed disposable poly-o-aminophenol-carbon nanotubes (PoAP-CNTs) modified screen print electrode (SPE)-based electrochemical enzyme sensor for OA detection. Electropolymerized PoAP-CNTs composite film was coated on electrode for the immobilization of PP2A. Owing to the excellent physicochemical characteristic of PoAP-CNTs film, the performance of enzyme sensor was enhanced. Under the optimal conditions, the biosensor provides a larger linear range, and lower detection limit for the analysis of OA compared with colorimetric PP2A inhibition assay and PP2A/SPE. The spiked OA shellfish samples were applied to verify the efficiency of method for OA detection. The results shows acceptable recovery rate and low RSD, demonstrating the applicability of this method for in suit OA assessment in the quality and toxicity monitoring of seafood.

•A novel cell-based Love Wave biosensor is established to detect Okadaic acid (OA).•The biosensor can monitor the cell attachment and detect the cell response to OA.•This biosensor has a wide linear detection range (10-100 μg/L).A novel HepG2 cell-based biosensor using Love Wave sensor was developed to implement the real-time and sensitive detection of a diarrheic shellfish poisoning (DSP) toxin, Okadaic acid (OA). Detachable Love Wave sensor unit and miniaturized 8-channel recording instrument were designed for the convenient experimental preparation and sensor response signal measurement. The Love Wave sensor, whose synchronous frequency is around 160 MHz, was fabricated with ST-cut quartz substrate. To establish a cell-based biosensor, HepG2 cells as sensing elements were cultured onto the Love Wave sensor surface, and the cell attachment process was recorded by this biosensor. Results showed this sensor could monitor the cell attachment process in real time and response signals were related to the initial cell seeding densities. Furthermore, cell-based Love Wave sensor was treated with OA toxin. This biosensor presented a good performance to various OA concentrations, with a wide linear detection range (10–100 μg/L). Based on the ultrasensitive acoustic wave platform, this cell-based biosensor will be a promising tool for real-time and convenient OA screening.

Odor detection is a prevalently noninvasive analytical method. To fulfill detecting odor sensitively by taking full advantage of rat's existing olfactory organs, we try using bio-hybrid sensing as pioneer. With developed brain machine interface technique, micro-electrode array is implanted into olfactory bulb to record neural activities in vivo. Acquiring data in vivo preserves integrity of rat's smell perception and bioactivity of odor-sensitive cells. Scents information recorded from olfactory bulb is decoded by maximum likelihood estimation. In this paper, we analyzed selectivity, specificity, repeatability, stability, and discrimination accuracy of sensing system in details. Results suggest that bio-hybrid sensing performs specifically, stably, and discriminates octanol, pentanal, and butyric acid with 92.67% accuracy.

•Detection of bitterness using behaving rat's gustatory system and brain–machine interface.•High accuracy in discrimination between bitter and non-bitter substances.•Dependence found between power of LFP oscillations and bitterness concentration.•Detection of bitterness is achieved with high sensitivity and the limit of detection is 0.076 μM.Animals' gustatory system has been widely acknowledged as one of the most sensitive chemosensing systems, especially for its ability to detect bitterness. Since bitterness usually symbolizes inedibility, the potential to use rodent's gustatory system is investigated to detect bitter compounds. In this work, the extracellular potentials of a group of neurons are recorded by chronically coupling microelectrode array to rat's gustatory cortex with brain–machine interface (BMI) technology. Local field potentials (LFPs), which represent the electrophysiological activity of neural networks, are chosen as target signals due to stable response patterns across trials and are further divided into different oscillations. As a result, different taste qualities yield quality-specific LFPs in time domain which suggests the selectivity of this in vivo bioelectronic tongue. Meanwhile, more quantitative study in frequency domain indicates that the post-stimulation power of beta and low gamma oscillations shows dependence with concentrations of denatonium benzoate, a prototypical bitter compound, and the limit of detection is deduced to be 0.076 μM, which is two orders lower than previous in vitro bioelectronic tongues and conventional electronic tongues. According to the results, this in vivo bioelectronic tongue in combination with BMI presents a promising method in highly sensitive bitterness detection and is supposed to provide new platform in measuring bitterness degree.

Bitter detection has attracted extensive attention in industries and researches due to pharmacological and/or food safety issues. Common electronic tongues constructed with electrochemical, optical or mass sensors are often subjected to the drawback of low-specificity in detecting a wide range of bitter compounds with diverse chemical structures and functions. However, biological gustatory components present unique specificity to bitter compounds, which may provide a promising approach in bitter detection. The activation of G protein coupled receptors (GPCRs) by ligands will affect cell morphology in a specific manner, which can be monitored by cell-impedance sensor. Thus cells expressing bitter receptors (a subfamily of GPCRs) can be used as sensing material in specific bitter detection. In this study, we explored the feasibility of utilizing male mouse germ cells in testis and cell-based impedance sensors (CIS) to build a cell-based bitter biosensor. Male mouse germ cells express bitter receptor T2Rs, which can sensitively and specifically respond to bitter compounds. To verify bitter sensing capacity of the germ cells, calcium responses of germ cells to three bitter compounds were examined prior to cell impedance response measurement. Furthermore, a bitter receptor blocker, probenecid, was used to verify the specificity of T2R-mediated impedance responses in germ cells. Cell-impedance response profiles of germ cells to four bitter compounds were investigated by analyzing the response intensity under various concentrations. Finally, impedance responses to five basic tastes were examined to evaluate the performance of cell-based bitter biosensor in bitter detection. The results revealed that this hybrid bitter biosensor could respond to those bitter compounds in a dose-dependent manner. The detection threshold for quinine was 0.125 mM, lower than our previous cell-based bitter biosensor. The calcium imaging tests and use of probenecid confirmed that T2R activation contributed to the cell impedance responses of this cell-based biosensor. Moreover, this germ cell-based cell could specifically detect bitter compounds among five taste stimuli, which may provide a promising and valuable approach for detection of various bitter compounds.

Biosensors utilizing living tissues and cells have recently gained significant attention as functional devices for chemical sensing and biochemical analysis. These devices integrate biological components (i.e. single cells, cell networks, tissues) with micro-electro-mechanical systems (MEMS)-based sensors and transducers. Various types of cells and tissues derived from natural and bioengineered sources have been used as recognition and sensing elements, which are generally characterized by high sensitivity and specificity. This review summarizes the state of the art in tissue- and cell-based biosensing platforms with an emphasis on those using taste, olfactory, and neural cells and tissues. Many of these devices employ unique integration strategies and sensing schemes based on sensitive transducers including microelectrode arrays (MEAs), field effect transistors (FETs), and light-addressable potentiometric sensors (LAPSs). Several groups have coupled these hybrid biosensors with microfluidics which offers added benefits of small sample volumes and enhanced automation. While this technology is currently limited to lab settings due to the limited stability of living biological components, further research to enhance their robustness will enable these devices to be employed in field and clinical settings.

Herein, we present a novel miniaturized multisensor chip integrated with a nanoband electrode array (NEA) for lead and copper detection and a light addressable potentiometric sensor (LAPS) for pH sensing. By this means, pH information could be provided before electrochemical analysis to ensure high performance in heavy metal quantification due to the significant effects of solution acidity on electrochemical analyses. The fabrication processes of the multisensor chip are described in detail and the electrochemical behaviour of NEA was characterized using cyclic voltammetry in sulfuric acid and acetate buffer. For the detection of lead and copper qualitatively and quantitatively, square wave anodic stripping voltammetry (SWASV) was applied with the standard addition method. Deposition potential and deposition time were optimized to be −0.6 V and 120 s, respectively. NEA exhibited a sensitivity of 0.510 μA pbb−1 and 0.678 μA ppb−1 towards lead and copper, respectively, with high correlation coefficients. The repetitive and long-term experiments also demonstrated the good reproducibility and stability of NEA in heavy metal detection. Moreover, the silicon nitride modified LAPS showed a pH sensitivity of 56.49 mV pH−1 with a high correlation coefficient of 0.9999. The reproducibility of LAPS was also investigated and a deviation of less than 2 mV was obtained in both the samples. These results indicate that the miniaturized multisensor chip demonstrates good electrochemical performance in heavy metal and pH sensing.

With growing concern about human health, relevant drug and food toxicity has drawn more and more attention. However, traditional methods like mouse bioassays cannot meet the sharply increasing demand for drug and food toxicity assessment. In this study, a multifunctional cell-based impedance biosensor system is established for drug and toxin analysis, using a cell-based impedance biosensor (CIB) as the sensitive element. Cellular growth and beating experiments were carried out to verify the multifunctionality of the system. Four typical heart-related compounds including verapamil, bay K8644, chromanol 293B, and adriamycin were used for cardiotoxicity analysis function tests of the CIB system. Also, one typical marine diarrhetic toxin, okadaic acid (OA), was used for cytotoxicity analysis function tests of the CIB system. From the results, the CIB system can reflect the drug function and toxicity directly through the cell growth and beating status. According to the results, the multifunctional CIB system may provide a high-throughput and useful method for effective screening of cardiovascular drugs and marine toxins in vitro.

•A portable cardiomyocyte-based potential biosensor is established to rapidly detect saxitoxin (STX) and brevetoxin (PbTX-2).•The potential biosensor can record high consistent and quite regular cardiomyocytes extracellular field potential (EFP) signals for 60 h.•The potential biosensor can detect 0.35 ng/ml STX and 1.55 ng/ml PbTX-2 within 5 min.Saxitoxin (STX) and brevetoxin (PbTX-2), which are produced by marine dinoflagellates, are highly-toxic marine toxins targeting separate sites of the α subunit of voltage-dependent sodium channels (VDSCs). In this work, a portable cardiomyocyte-based potential biosensor is designed for rapid detection of STX and PbTX-2. This potential biosensor is constructed by cardiomyocyte and microelectrode array (MEA) with a label-free and real-time wireless 8-channel recording system which can dynamically monitor the multisite electrical activity of cardiomyocyte network. The recording signal parameters, spike amplitude, firing rate and 50% of spike potential duration (SPD50) extracted from extracelluar field potential (EFP) signals of the potential biosensor is analyzed to quantitatively evaluate toxicological risk of STX and PbTX-2. Firing rate of biosensor signals presents high sensitivity to STX with the detection limit of 0.35 ng/ml within 5 min. SPD50 shows high sensitivity to PbTX-2 with the detection limit of 1.55 ng/ml within 5 min. Based on the multi-parameter analysis, cardiomyocyte-based potential biosensor will be a promising tool for rapid detection of these two toxins.

•A hippocampal neuronal network-based biosensor is designed and applied it in detecting 5-hydroxytryptamine (5-HT).•This biosensor is sensitive and specific in detecting 5-HT, which may provide promising approaches for neurotransmitter studies.5-hydroxytryptamine (5-HT) is an important neurotransmitter in regulating emotions and related behaviors in mammals. To detect and monitor the 5-HT, effective and convenient methods are demanded in investigation of neuronal network. In this study, hippocampal neuronal networks (HNNs) endogenously expressing 5-HT receptors were employed as sensing elements to build an in vitro neuronal network-based biosensor. The electrophysiological characteristics were analyzed in both neuron and network levels. The firing rates and amplitudes were derived from signal to determine the biosensor response characteristics. The experimental results demonstrate a dose-dependent inhibitory effect of 5-HT on hippocampal neuron activities, indicating the effectiveness of this hybrid biosensor in detecting 5-HT with a response range from 0.01 μmol/L to 10 μmol/L. In addition, the cross-correlation analysis of HNNs activities suggests 5-HT could weaken HNN connectivity reversibly, providing more specificity of this biosensor in detecting 5-HT. Moreover, 5-HT induced spatiotemporal firing pattern alterations could be monitored in neuron and network levels simultaneously by this hybrid biosensor in a convenient and direct way. With those merits, this neuronal network-based biosensor will be promising to be a valuable and utility platform for the study of neurotransmitter in vitro.

•We have developed a neuro-2a cell-based impedance biosensor to detect PSP toxins.•STX could be detected by this method with a detection limit as low as 0.1 nM.•This improved method has excellent specificity in marine toxins detection.Paralytic shellfish poisoning (PSP) toxins are well-known sodium channel-blocking marine toxins, which block the conduction of nerve impulses and lead to a series of neurological disorders symptoms. However, PSP toxins can inhibit the cytotoxicity effect of compounds (e.g., ouabain and veratridine). Under the treatment of ouabain and veratridine, neuroblastoma cell will swell and die gradually, since veratridine causes the persistent inflow of Na+ and ouabain inhibits the activity of Na+/K+-ATPases. Therefore, PSP toxins with antagonism effect can raise the chance of cell survival by blocking inflow of Na+. Based on the antagonism effect of PSP toxins, we designed an improved cell-based assay to detect PSP toxins using a neuroblastoma cell-based impedance biosensor. The results demonstrated that this biosensor showed high sensitivity and good specificity for saxitoxins detection. The detection limit of this biosensor was as low as 0.03 ng/ml, which was lower than previous reported cell-based assays and mouse bioassays. With the improvement of biosensor performance, the neuroblastoma cell-based impedance biosensor has great potential to be a universal PSP screening method.

Mammalian olfactory systems have extraordinary ability to sense and identify various trace odorants. Taking advantages of cell culture and micro-fabrication technologies, olfactory cell- or tissue-based biosensor represent a promising platform for in vitro odorant detection. However, in vitro conditions lead to shortened cell/tissue survivals, and the working life of neuron chips is short. The purpose of this study is to develop an in vivo recording and analyzing method for long-term and repeatable detection of odor stimulation. In this study, we implanted penetrating micro-wire array electrode into the olfactory bulb of conscious rats to obtain odor-evoked electrophysiological activities. Then, we investigated the response of ensembles of mitral/tufted cells to stimulation with carvone at a number of concentrations in time and frequency domains. The stable, repeatable odorant responses from up to 16 neural regions could be obtained for at least 3 weeks. Further, we explored the concentration detection sensitivity limitation of developed method, and found the detection low limit of carvone was below 10−10 mol/L. The result demonstrates that the concentration range of in vivo odorant detection method is much wider than in vitro method.

It has been reported that detection of exhaled breath condensate (EBC) is available for studies of pulmonary diseases, especially lung disease. In order to detect lung cancer (LC) at early stage, a point-of-care testing system suitable for measurement of tumor markers in EBC is developed. The assay, based on gold nanoparticle sandwich immunoassay and subsequent gold staining, was performed on a Love-wave sensor packaged inside a chip cartridge. Benefit from high sensitivity of Love-wave sensor, oriented immobilization of coating antibodies and immunogold staining enhancement, the present immunosensor could provide a sensitive, specific and rapid measurement. Carcinoembryonic antigen (CEA), neuron specific enolase (NSE) and squamous cell carcinoma antigen (SCC) in EBC collected from 17 patients with LC and 13 healthy volunteers were detected by this system. Results were compared with commercial chemiluminescence immunoassay and showed high correlation between two methods. Additionally, it revealed significantly statistical differences existing between two groups of subjects. These results indicate that the present system is suitable for detection of tumor markers in EBC and could be used as assistant tools for early detection of LC.

It is of substantial interest to mimic mechanisms of biological sensing systems for the development of novel biosensors. This paper presents a novel biomimetic bitter receptor-based biosensor for the detection of specific bitter substances, in which bitter receptors were used as sensitive elements for the first time. A simple and practical self-assembled aptamer-based strategy was proposed for functional immobilization and purification of bitter receptors. A human bitter receptor, T2R4, was expressed on the plasma membrane of HEK-293 cells and fused with a His6-tag on its C-terminal. The membrane fractions containing the expressed T2R4 were extracted and immobilized on the gold surface of a quartz crystal microbalance (QCM) pretreated with a monolayer of self-assembled aptamers that can specifically recognize and capture biomolecules labeled with His6-tags. The QCM device was used to monitor the responses of T2R4 to various bitter stimuli. The results indicate that this biosensor can detect denatonium with high sensitivity and specificity, which is the specific target of T2R4. In addition, this biosensor shows dose-dependent responses to a certain concentration range of denatonium. The sensitivity of bitter receptor-based biosensors prepared by an aptamer-based method is 1.21 kHz mM−1, which is 2 times higher than that prepared by a SAM-based method. The major advances on bitter receptor immobilization and purification presented in this work could substantially be very useful for developing other membrane receptor-based biosensors and molecular sensor arrays. This bitter receptor-based biosensor has great potential to be used as a valuable tool for bitter detection as well as for the research of taste signal transduction.

Microelectrode array (MEA) was used for in situ heavy metal determination in aquatic environments due to its characteristics of high sensitivity, large current density and fast mass transfer rate, while interferences caused by background factors and complex external environment were inevitable in analysis leading to inaccurate results. Hence, two algorithms, partial least square regression and local optimum method were employed in different situations for electrochemical analysis to eliminate interference. Partial least square regression was superior to local optimum method thanks to convenient operations and good outcomes for in situ determination, which was proved to be effective in low interference samples. Nevertheless, inaccurate results were obtained in samples of complicated composition because of negative impacts on working electrode. Local optimum method was proposed aiming at those situations, by which severe interference was ignored and better results were acquired to prove the reasonability and validity of the algorithm. The determination of cadmium and lead was improved effectively combined PLS with local optimum method.

•The electric cell-substrate impedance sensing (ECIS) system was used to study the cellular changes induced by chemicals.•The Cd2+-induced hepatotoxicity was concentration dependent and time dependent.•Appropriate amount of Zn2+ had a hepatoprotective effect toward Cd2+-induced hepatotoxicity, whereas excessive intake may be toxic to cells.•The self-assembled poly-l-lysine was applied to immobilize L-02 cells on electrodes for improving the detection sensitivity of the ECIS system.Cadmium (Cd) is a toxic environmental pollutant which creates risks to human health. Liver is one of the major sites of Cd accumulation in the organism and target organs under chronic and acute exposure of Cd. It was estimated that Zn2+ supplementation can prevent apoptosis induced by a variety of agents such as Cd2+. In this paper, an improved electric cell-substrate impedance sensing (ECIS) assay was developed to investigate the Cd2+-induced hepatotoxicity and the effects of Zn2+ at different concentrations on it in vitro. Normal liver L-02 cells were cultured onto interdigitated electrodes. With ECIS technology the dynamic responses of L-02 cells were monitored in a non-invasive and label-free manner. The results showed a clear dose- and time-depending toxic effect of Cd2+ on L-02 cells. The half-inhibition concentration of Cd2+ was 20 μM after 24 h of exposure. The results also revealed that enhanced Zn2+ consumption (10–20 μM) may be beneficial for preventing Cd2+-induced hepatotoxicity. However, its excessive intake (40 μM) may intensify the hepatotoxicity. Furthermore, for improving the detection sensitivity of the system, a cell immobilization approach using self-assembly techniques was applied to bind cells on electrodes for improving the detection sensitivity of the system. This study demonstrated that the ECIS system holds promise as a utility platform for real-time studying cell status and evaluating chemical effect with high detection sensitivity.

In this study a potentiometric glucose sensor is constructed with the application of an enzyme–metal–insulator–silicon (EMIS) structure. Glucose biosensing is realized by modifying the metal layer of the sensor with an ultra-thin (<100 nm) film of polypyrrole (PPy)–glucose oxidase (GOD) through an electropolymerization process. The optimum film formation conditions can be provided with 0.1 M pyrrole, 100–200 U/mL GOD, an applied current density of 0.01–0.05 mA/cm2 and an electrical charge of 20–30 mC/cm2. The applicability of the surface photovoltage technology for potential determination is confirmed with an improved sensitivity (106.3 mV/dec) and widened linear range (0.04–10 mM) compared with the traditional two-electrode cell measurement. Good selectivity, stability and lifetime of the potentiometric glucose sensor are also shown. The usage of the ultra-thin PPy–GOD film is advantageous in reducing the response time (from several seconds to less than 80 s) of the sensor, which guarantees its potential in rapid determination of plasma glucose concentration. With ease of fabrication and miniaturization, the photoelectric hybrid glucose sensor can be used in glucose monitoring of extracellular microenvironment.

The aim of the present study was to investigate the electrophysiological characteristics of the different layers of the olfactory bulb (OB). We used an in vitro OB slice coupled onto a microelectrode array (MEA) for simultaneous detection of spontaneous activities of OB neurons at different sites. Different frequency oscillations dominated the different layers of the OB slice, and the gamma frequency oscillations mainly appeared in the glomerular layer. The waves consisted of negative, positive, and bidirectional spikes, and were distributed at the different layers of the OB slice. Thus, combination of the OB slice with MEA is a useful technique for identifying signal oscillations by multi-site synchronous measurement, and will allow further studies on olfactory information coding and processing function.

Extracellular redox potential is an important regulator of cell–microenvironmental interactions. It works in concert with intracellular redox state to control the electron transport in redox signaling. The redox regulation can influence cell surface proteins such as receptors, transport proteins, and enzymes that contain thiol moieties, and then cause significant impact on cell proliferation, differentiation and apoptosis. The present work employs an electrochemical potentiometric means to probe extracellular redox potential of living cells. A metal–insulator–semiconductor structured sensor is used based on an AC photovoltage technique. The sensor has a sensitivity of 53.2 mV/log([Fe(II)]/[Fe(III)]) for Fe(II)/Fe(III) redox couple and 25.4 mV/log([CySS]/[Cys]2) for Cys/CySS couple. Then kidney cells are incubated on the sensor surface for physiological redox potential study. The potential is found to be reduced at physiological activity and the reduction rate is related with cell density. The reduction rate decreases after the inhibition of mitochondrial complex I. Evidence is presented that the mitochondrial electron transport chain has significant influence on the extracellular reduction rate.

This study presents an in vivo biosensing system for odorant detection. Taking advantage of mammal's extraordinarily sensitive olfactory systems, we extract the odorant information from conscious rats’ olfactory bulb (OB) using microelectrode array. By chronically implanting the microelectrode into OB, high-quality mitral/tufted (M/T) cell activity evoked by odorants could be obtained for at least three weeks. The responses of multiple M/T cells broadly represent information about the presented odorants. Six odorants (carvone, citral, isobutyl alcohol, diacetyl, anisole and isoamyl acetate) used in this study could be discriminated by analyzing the neuronal activity. What is more, we found the concentration detection limit of system is below 10−15 mol/L for carvone. These results demonstrate that in vivo biosensing system has characteristic of high sensitivity, continuous recording, specificity, which presents a promising platform for specific trace odorant detection in many fields.

Inspired by the very high sensitivity and specificity of biological olfactory system, engineers pay much attention to biomimetic olfactory biosensors due to their excellent performance and great commercial prospects. In this study we presented an olfactory receptor (OR)-based piezoelectric biosensor with high sensitivity and specificity for the odorant detection, in which aptamers were employed for the specific and effective olfactory receptor immobilization to improve the overall performance of biosensors. An olfactory receptor of C. elegances, ODR-10, was expressed heterologously in HEK-293 cells with a hexahistidine (His6) tag on the N terminus. His6-tagged ODR-10 was extracted from the plasma membrane of transfected HEK-293 cells and used as the sensing element of biosensors. Anti-His6 aptamers were immobilized covalently onto the gold surface of piezoelectric quartz crystal microbalance (QCM) electrode to capture the His6-tagged ODR-10 specifically, as well as achieve the purification of ODR-10 simultaneously. The immobilization procedures were characterized by electrochemical methods and scanning probe microscopy (SPM). Additionally, physical adsorption method was used as a control method to illustrate the influences of immobilization methods on the performances of OR-based biosensors. The results demonstrated that the piezoelectric biosensor prepared by aptamer-assisted immobilization method showed high specificity and improved sensitivity. The detection limit was as low as 1.5 ppm (v/v). Additionally, the aptamer-assisted receptor immobilization method has great potential to become a universal protein immobilization technique in biosensing, and be applied into the development of OR-based biosensor array for the simultaneous detection of several odorants. This aptamer-assisted olfactory receptor biosensor has great application prospects in many fields, such as food safety, environmental monitoring, and disease diagnosis.

Electrical cell–substrate impedance sensor (ECIS) and light-addressable potentiometric sensor (LAPS) are becoming powerful tools for monitoring the cell growth status and cell metabolism. This work describes the ECIS- and LAPS-type cardiomyocyte-based biosensors. The working principle and detection systems of transducers were presented. In particular, our investigation is devoted to some basic characteristic tests of these transducers for the purpose of comparing their performance related to cardiomyocyte-based biosensors evaluation. Finally, cardiomyocyte-based biosensors performance was displayed and analyzed. From the results, both of transducers are promising tools to establishing the cardiomyocyte-based biosensors.

•Cell growth and metabolism were continuously and synchronously monitored by cellular impedance sensing and LAPS based on the same sensor structure.•Electrolyte-insulator-semiconductor (EIS) structure was used as the sensor structure.•Equivalent circuit model for cellular impedance sensing was build.•Cytotoxicity of heavy metal Cadmium (Cd) was evaluated.Light-addressable potentiometric sensor (LAPS) can be used as a sensitive pH-meter with its electrolyte-insulator-semiconductor (EIS) structure. Previous LAPS practices in cell-based assays, which were limited to pH detection of extracellular microenvironment, seemed to be insufficient since the cell physiology is reflected by various parameters, such as energy metabolism and cell morphology. In this paper, the feasibility of monitoring cell growth status based on the same sensor structure of LAPS was investigated and testified. A novel real-time biosensor system was established, which could monitor the cell growth and metabolism synchronously. In the cellular experiment, the normal growth of mouse embryonic fibroblast 3T6 cells and their apoptosis in the presence of heavy metal cadmium (Cd) were investigated. The results showed that the normal growth of cells could lead to an increase of 2.65 in cell index (CI). And, CI decreased from 1.96 in normal growth condition to 0.64 24 h after the treatment of Cd and fell to 0.16 after 48 h. The extracellular acidification rate (ECAR) experienced a similar change to CI. The combination of cellular impedance sensing with LAPS will bring out new opportunities for LAPS to be more utility in cell-based assays, such as cytotoxicity detection and drug evaluation.

The study presented a novel integrated cell-based biosensor with light-addressable potentiometric sensor (LAPS) and electrical cell-substrate impedance sensor (ECIS). The integrated cell-based biosensor was fabricated in order to monitor the cellular metabolism and growth status by LAPS and ECIS. Moreover, the specific instrument was established for controlling the detection processes. Sensor test and cell experiments were carried out to determine the performance of integrated sensor. The result showed that integrated biosensor can monitor the change of cell electrical impedance and extracellular acidification simultaneously which can be used for drug evaluation by monitoring cell growth status (e.g. cell number, adhesion, and morphology) and cell energy metabolism status (e.g. extracellular acidification) in real time. With the development of sensor technology, the integrated cell-based biosensor will be a utility platform to study the mechanism of cellular metabolism and in vitro drug analysis.

The biological olfactory system can recognize and discriminate thousands of volatile organic compounds (VOCs) with extremely high sensitivity and specificity. The most fundamental elements are olfactory receptors (ORs) in the cilia of olfactory sensory neurons (OSNs), which contribute greatly to the high-performance olfactory system. The excellent properties of ORs are generally recognized in the development of biomimetic OR-based biosensors. Over the past two decades, much work has been done in developing OR-based biosensors due to their promising potential in many applications. In this article, we will outline the latest advances of OR-based biosensors. Two current crucial issues in this field will be discussed, namely, the production methods and immobilization techniques of ORs. We will also elaborate on various OR-based biosensors and their latest developments. Finally, current research trends and future challenges in this field will be discussed.Highlights► This review paper introduces the history of olfactory receptor-based biosensors comprehensively. ► Two hot issues in the development of olfactory receptor-based biosensors are discussed in detail. ► The latest developments of various olfactory receptor-based biosensors are presented. ► The future research trends are pointedout.

•We developed a novel bioelectronic nose based on BMI technology.•Neural responses of olfactory bulb to four different odorants were recorded by implanted electrodes in vivo.•We found neural activities were modulated by animal's respiration and odorants.•Odorants could be classified by an olfactory decoding methods.The mammalian olfactory system has merits of higher sensitivity, selectivity and faster response than current electronic nose system based on chemical sensor array. It is advanced and feasible to detect and discriminate odors by mammalian olfactory system. The purpose of this study is to develop a novel bioelectronic nose based on the brain–machine interface (BMI) technology for odor detection by in vivo electrophysiological measurements of olfactory bulb. In this work, extracellular potentials of mitral/tufted (M/T) cells in olfactory bulb (OB) were recorded by implanted 16-channel microwire electrode arrays. The odor-evoked response signals were analyzed. We found that neural activities of different neurons showed visible different firing patterns both in temporal features and rate features when stimulated by different small molecular odorants. The detection low limit is below 1 ppm for some specific odors. Odors were classified by an algorithm based on population vector similarity and support vector machine (SVM). The results suggested that the novel bioelectonic nose was sensitive to odorant stimuli. The best classifying accuracy was up to 95%. With the development of the BMI and olfactory decoding methods, we believe that this system will represent emerging and promising platforms for wide applications in medical diagnosis and security fields.

Taste receptor cells in taste buds can generate action potentials in response to taste stimuli. The spatiotemporal patterns of the potentials have great value in both biomedical and engineering researches. In the present study, by fixing the biological epithelium onto the surface of microelectrode arrays (MEA), we established a novel taste sensor to record action potentials from the taste receptor cells of rat in response to taste stimuli. By this multi-channel recording method, we examined the electrophysiological activities of taste receptor cells in taste buds to stimuli representing the basic taste qualities (sour, salt, bitter, sweet and umami). The recorded action potentials corresponding to five tastes displayed different spatiotemporal patterns. The multi-channel results demonstrated that taste buds released the spontaneous signals simultaneously and displayed different responses to different tastes stimulations. The temporal characteristics were derived by time-domain and frequency-domain analysis, and the signals fired in different stimuli could be distinguished into different clusters by principal component analysis (PCA). The study provides an effective and reliable platform to recognize and distinguish basic taste qualities.Highlights► A bioelectronic tongue was designed to record action potentials of taste cells to taste stimuli. ► By multi-channel recording, electrophysiological activities of cells were examined. ► Spatiotemporal patterns of sour, salt, bitter, sweet and umami were analyzed. ► Basic tastes distinguished into different clusters by principal component analysis (PCA). ► The study provides a platform to recognize and distinguish basic taste qualities.

•A cell-based biosensor can monitor the cardiomyocyte growth and beating status.•The RTCA technology was a high temporal resolution ECIS technology.•The performance of cell-based biosensor was tested by verapamil and flecainide.Drug-induced cardiotoxicity greatly endangers the human health and results in resource waste. Also, it is a leading attribution to drug withdrawal and late-stage attrition in pharmaceutical industry. In the study, a dual function cardiomyocyte-based biosensor was introduced for rapid drug evaluation with xCELLigence RTCA Cardio system. The cardiomyocyte-based biosensor can monitor the cardiomyocyte growth and beating status simultaneously under the drug effects. Two typical cardiovascular drug, verapamil and flecainide were selected as treatment agents to test the performance of this biosensor. The experiment results showed that the performance of cardiomyocyte-based biosensor verified the basic drug effects by beating status and also tested the drug cytotoxicity by the cell index curves of cardiomyocyte growth. Based on the advanced sensor detection technology and cell culture technology, this cardiomyocyte-based biosensor will be a utility platform for the drug preclinical assessment.

Responses of 302 mitral/tufted (M/T) cells in the olfactory bulb were recorded from 42 anesthetized freely breathing rats using a 16-channel microwire electrode array. Saturated vapors of four pure chemicals, anisole, carvone, citral and isoamyl acetate were applied. After aligning spike trains to the initial phase of the inhalation after odor onset, the responses of M/T cells showed transient temporal features including excitatory and inhibitory patterns. Both odor-evoked patterns indicated that mammals recognize odors within a short respiration cycle after odor stimulus. Due to the small amount of information received from a single cell, we pooled results from all responsive M/T cells to study the ensemble activity. The firing rates of the cell ensembles were computed over 100 ms bins and population vectors were constructed. The high dimension vectors were condensed into three dimensions for visualization using principal component analysis. The trajectories of both excitatory and inhibitory cell ensembles displayed strong dynamics during odor stimulation. The distances among cluster centers were enlarged compared to those of the resting state. Thus, we presumed that pictures of odor information sent to higher brain regions were depicted and odor discrimination was completed within the first breathing cycle.

The immobilization efficiency of molecular detectors is of great importance with regard to the performances of biosensors such as the sensitivity, stability, and reproducibility. This paper presents a biomimetic olfactory receptor-based biosensor with better performances by improving the immobilization efficiency of molecular detectors for odorant sensing. A mixed self-assembled monolayers (SAMs) functionalized with specific olfactory receptors (ODR-10) was constructed on the sensitive area of surface acoustic wave (SAW) chip. The immobilization of ODR-10 was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The responses of this biosensor to various odorants were recorded by monitoring the resonance frequency shifts of SAW, which is correlated to the mass loading on its sensitive area. All the results demonstrate this biosensor can specifically respond to the natural ligand of ODR-10, diacetyl, with high sensitivity and stability. The sensitivity is 4 kHz/ng, which is 2× higher than that of previous work. The detection limit is 1.2 × 10−11 mM. The major advances on immobilization efficiency of molecular detectors presented in this work could substantially promote and accelerate the researches and applications of olfactory receptor-based biosensors with different transducers, such as quartz crystal microbalance (QCM), surface plasma resonance (SPR), and field effect transistors (FET).Highlights► A biomimetic olfactory receptor-based biosensor was developed. ► High efficiency immobilization of molecular detectors was achieved by SAMs. ► The performance of this biosensor was enhanced.

Vesicular exocytosis plays an important role in many physiological processes. The dense-core vesicles release of chromaffin cells is a suitable model for the presynaptic process in neurosecretory cells. In this study, light-addressable potentiometric sensor (LAPS) was introduced as a label-free recording method for vesicle release by the local extracellular acidification. The chromaffin cells are directly cultured on the sensor surface. After cells and LAPS hybrid system is established, the events of vesicular exocytosis are recorded. Protons stored in the vesicles and co-released with transmitters, induced a brief acidic shifts in the cell-sensor cleft. Under the stimulation of the KCl and acetylcholine (Ach), the signals presented the different amplitude and exocytosis rate, and reflected the specific features of the exocytosis. The result indicates that neurosecretory cell-based biosensor will provide a useful platform for neurosecretion mechanism research by monitoring the exocytotic activities with extracellular acidification sensing.Highlights► Light-addressable potentiometric sensor (LAPS) used as a recording method for vesicle release. ► The extruded matrix of vesicles release protons lowered the extracellular pH on sensor. ► LAPS with Chromaffin cell is a kind of neurosecretory cell-based biosensor. ► The sensor will provide a useful platform for neurosecretion mechanism research.

Adenosine triphosphate (ATP) is considered as the key neurotransmitter in taste buds for taste signal transmission and processing. Measurements of ATP secreted from single taste receptor cell (TRC) with high sensitivity and specificity are essential for investigating mechanisms underlying taste cell-to-cell communications. In this study, we presented an aptamer-based biosensor for the detection of ATP locally secreted from single TRC. ATP sensitive DNA aptamer was used as recognition element and its DNA competitor was served as signal transduction element that was covalently immobilized on the surface of light addressable potentiometric sensor (LAPS). Due to the light addressable capability of LAPS, local ATP secretion from single TRC can be detected by monitoring the working potential shifts of LAPS. The results show this biosensor can detect ATP with high sensitivity and specificity. It is demonstrated this biosensor can effectively detect the local ATP secretion from single TRC responding to tastant mixture. This biosensor could provide a promising new tool for the research of taste cell-to-cell communications as well as for the detection of local ATP secretion from other types of ATP secreting individual cells.

Bio-hybrid systems provide an opportunity for integrating a living bio-active unit and a proper biosensing system, to employ the unique properties of the bio-active unit. The biological olfactory system can sense and identify thousands of trace odors. The purpose of this study is to combine olfactory epithelium with microelectrode array (MEA) to establish an olfactory epithelium-MEA hybrid system to record the odor-induced electrophysiological activities of the tissue. In our experiments, extracellular potential of olfactory receptor neurons in intact epithelium were measured in the presence of ethyl ether, acetic acid, butanedione, and acetone, respectively. After the odor-induced response signals were analyzed in the time and frequency domain, the temporal characteristics of response signals were extracted. We found that olfactory epithelium-MEA hybrid system can reflect the in vitro odor information of different signal characteristics and firing modes in vitro. The bio-hybrid sensing system can represent a useful instrument to sense and detect the odorant molecules with well recognizing patterns. With the development of sensor technology, bio-hybrid systems will represent emerging and promising platforms for wide applications, ranging from health care to environmental monitoring.

To eliminate measurement error caused by fluctuation, distortion and noise of light source output in a light-addressable potentiometric sensor (LAPS) system, LAPS system based on precise light intensity modulation is presented in this study. A superluminescence LED (SLED) module, with a home-made multi negative feedback SLED driver, is proposed as the precise light source in this system. A high-speed optical fiber spectrometer is introduced for on-line monitoring and long period intensity compensation. The precise light source provides light output to LAPS, and keeps light intensity on sensitive surface to meet sine rules with low distortion and low noise. Furthermore, it is immune from variation of ambient temperature. Detailed optical parameters of precise light source are presented and compared with conventional light source. H+ measurements for LAPS system based on precise light intensity modulation were given and compared with system with conventional light source. From contrast experiments, it can be deduced that LAPS system based on precise light intensity modulation has better linearity, higher accuracy and lower noise than LAPS system with conventional light source.

Cellular metabolism is ubiquitous biological mechanism involved in many significant physiological processes, and most of the biological cascade reactions are tightly coupled. Non-invasive measurement of cellular metabolism is important to study the metabolism mechanism and drug effect in a long-term detection. In this study, the two processes of heavy doping and thick oxidation fabricated a new light-addressable potentiometric sensor array, which was applied to detect the cellular metabolism induced pH change. The performance of the LAPS was tested by the basic characteristic experiments and renal cell experiments. The result showed that the stability and pH resolution of LAPS array were greatly improved. With the development of the sensor design and fabrication, the LAPS will be a utility tool in the field of biological metabolism.

Multi-site recording is the important component for studies of the neural networks. In order to investigate the electrophysiological properties of the olfactory bulb neural networks, we developed a novel slice-based biosensor for synchronous measurement with multi-sites. In the present study, the horizontal olfactory bulb slices with legible layered structures were prepared as the sensing element to construct a tissue-based biosensor with the microelectrode array. This olfactory bulb slice-based biosensor was used to simultaneously record the extracellular potentials from multi-positions. Spike detection and cross-correlation analysis were applied to evaluate the electrophysiological activities. The spontaneous potentials as well as the induced responses by glutamic acid took on different electrophysiological characteristics and firing patterns at the different sites of the olfactory bulb slice. This slice-based biosensor can realize multi-site synchronous monitoring and is advantageous for searching after the firing patterns and synaptic connections in the olfactory bulb neural networks. It is also helpful for further probing into olfactory information encoding of the olfactory neural networks.

Drug-induced prolongation of ventricular repolarization with arrhythmia is a major concern in clinic safety pharmacology, and has been a common reason for the withdrawal of several promising drugs from the market. Therefore, novel techniques should be developed to evaluate cardiotoxicity of new drugs in preclinical research. A cardiomyocyte based biosensor was developed using the light addressable potentiometric sensor (LAPS). Mouse embryonic stem cells cultured on the surface of LAPS were induced to differentiate into synchronized spontaneity beating cardiomyocytes. Changes of extracellular potentials and cell shapes with their mechanical beatings could induce modulation of photocurrents in the LAPS system, and finally change the output of the sensor. With the characteristics of light addressability, LAPS can record cell clusters at any desired position. The sensor can be used to record the prolongation of ventricular action potentials with the cardiotoxicity induced by drugs such as amiodarone, levofloxacin, sparfloxacin, and noradrenaline. The quick and on time characteristics of the sensor were promising to establish a high-throughput platform for pharmacological toxicity investigation.

In olfactory biosensors, microelectronic sensor chips combined with biological olfactory cells are a promising platform for odor detection. In our investigation, olfactory epithelium stripped from rat was fixed on the surface of microelectrode arrays (MEAs). Electrophysiological activities of olfactory receptor neurons in intact epithelium were measured in the form of extracellular potentials. Based on multi-channel recording performance of MEA and structural and functional integrality of native olfactory epithelium, the spatiotemporal analysis was carried out to study the extracellular activity pattern of neurons in the tissue. The variation of spatiotemporal patterns corresponding to different odors displayed the signals firing image characteristic intuitionally. It is an effective method in the form of patterns for monitoring the state of tissue both in time and space domain, promoting the platform for olfactory sensing mechanism research.

In this paper, impedance measurement of electrolyte–insulator–semiconductor (EIS) structure with high spatial resolution was proposed to monitor cell adhesion. The light addressing ability of this work overcomes the geometrical restrict of cell culture on conventional impedance detection devices such as interdigitated electrode (IDE) and electric cell-substrate impedance sensing (ECIS). Instead of studying cells on predetermined sites of IDE and ECIS, cells cultured anywhere on EIS sensor surface can be addressed and selected as target cells. Principle and primary models for high resolution impedance detection were described and tested by experiments. The EIS sensor was investigated in terms of its intrinsic characteristics, like impedance behavior, voltage characteristic, frequency dependency and photovoltaic effect. Optimized working condition was studied for cell experiments. Cell adhesion under treatment of 0.1% Triton X-100 was monitored using rat kidney cells as the source. Results showed good sensitivity (10% change of impedance) and resolution (40 μm) for cell adhesion impedance detection and suggested this work should be suitable for monitoring cell impedance. Further improvements on sensitivity, spatial resolution were discussed as well as the further applications for single cell monitoring and cell adhesion imaging.

Taste receptor cells are the taste sensation elements for sour, salty, sweet, bitter and umami sensations. It was demonstrated that there are cell-to-cell communications between type II (sour) and type III (sweet, bitter and umami) taste cells. Serotonin (5-HT) is released from type III cells, which is the only type of taste cells that has synaptic process with sensory afferent fibers. Then, taste information is transmitted via fibers to the brain. During this process, 5-HT plays important roles in taste information transmission. In order to explore a sensor to detect 5-HT released from taste cell or taste cell networks, we develop a 5-HT sensitive sensor based on LAPS chip. This sensor performs with a detection limit of 3.3 × 10−13 M and a sensitivity of 19.1 mV per concentration decade. Upon the stimuli of sour and mix (bitter, sweet and umami) tastants, 5-HT released from taste cells could be detected flexibly, benefit from the addressability of LAPS chip. The experimental results show that the local concentration of 5-HT is around several nM, which is consistent with those from other methods. In addition, immunofluorescent imaging technique is utilized to confirm the functional existence of both type II and III cells in a cluster of isolated taste cells. Different types of taste cells are labeled with corresponding specific antibody. This 5-HT sensitive LAPS chip provides a potential and promising way to detect 5-HT and to investigate the taste coding and information communication mechanisms.

Excitation–contraction coupling, a process of linking electrical activity to contraction, is the basis of cardiac function at cellular level. Here we developed a multi-scale electrode array (MSEA) as an in vitro platform to synchronously monitor excitation and contraction of cultured cardiomyocytes. The electrodes of MSEA were with sizes ranging from several tens of micrometers to about 1 mm and were classified into type_1, type_2 and type_3 by their electrode area. The former two types of electrodes were electroplated with platinum black to reduce baseline noise and no extra treatment was done on type_3 electrodes. In experiment, the micrometer-scale electrodes recorded extracellular field potentials like generally used multielectrode arrays and especially, the millimeter-scale electrodes recorded a “hump” followed after extracellular field potential. By analyzing temporal behavior of hump and observing its change under treatment of microtubule inhibitor vinblastine, it was verified that the hump expressed mechanical contraction of cardiomyocytes. In addition, we analyzed that the pathway of contraction recording was through cell–electrode contractile coupling, in which charges at electrode–electrolyte interface were reestablished due to contractile behavior of cellular layer and then the hump was formed. Finally, the dependence of amplitude and time duration of hump on electrode area, electrode property and contractile strength was also explored.

Neurochip based on light-addressable potentiometric sensor (LAPS), whose sensing elements are excitable cells, can monitor electrophysiological properties of cultured neuron networks with cellular signals well analyzed. Here we report a kind of neurochip with rat pheochromocytoma (PC12) cells hybrid with LAPS and a method of de-noising signals based on wavelet transform. Cells were cultured on LAPS for several days to form networks, and we then used LAPS system to detect the extracellular potentials with signals de-noised according to decomposition in the time-frequency space. The signal was decomposed into various scales, and coefficients were processed based on the properties of each layer. At last, signal was reconstructed based on the new coefficients. The results show that after de-noising, baseline drift is removed and signal-to-noise ratio is increased. It suggests that the neurochip of PC12 cells coupled to LAPS is stable and suitable for long-term and non-invasive measurement of cell electrophysiological properties with wavelet transform, taking advantage of its time-frequency localization analysis to reduce noise.

Nowadays, cardiotoxicity induced by clinical drugs presents a high prevalence and has aroused great attention onto the effective and reliable drug evaluation before clinical treatment. Doxorubicin (Adriamycin), as a type of anthracycline chemotherapy agent for cancer treatment, was restricted in the clinical use because of its cardiotoxicity. In the present work, a dual functional biochip ExCell integrated with microelectrode arrays and interdigitated electrodes was designed to study the electrophysiological function and physical state of cardiomyocytes under the treatment of doxorubicin. Extracellular field potentials and cell–substrate impedance were measured to respectively express these two functions simultaneously in the same culture. The result detected by ExCell presented a portrait of cardiotoxicity induced by doxorubicin. The amplitude of extracellular field potentials decreased to 93%, 82% and 50% at 50 min treatment of doxorubicin with concentrations of 20 μM, 100 μM and 200 μM, respectively. Successively, beating rate decrease, beat-to-beat variation and Ca2+ flux manifested severe abnormality. The cell–substrate impedance declined continuously in the depressing process of electrophysiological function and cell death was induced in high concentration treatment. All these result indicate that the biochip ExCell has the potential to be a fast-response and subtle tool for high-throughput drug evaluation assays.

Olfactory systems of human beings and animals have the abilities to sense and distinguish varieties of odors. In this study, a bioelectronic nose was constructed by fixing biological tissues onto the surface of light-addressable potentiometric sensor (LAPS) to mimic human olfaction and realize odor differentiation. The odorant induced potentials on tissue–semiconductor interface was analyzed by sensory transduction theory and sheet conductor model. The extracellular potentials of the receptor cells in the olfactory epithelium were detected by LAPS. Being stimulated by different odorants, such as acetic acid and butanedione, olfactory epithelium activities were analyzed on basis of local field potentials and presented different firing modes. The signals fired in different odorants could be distinguished into different clusters by principal component analysis (PCA). Therefore, with cellular populations well preserved, the epithelium tissue and LAPS hybrid system will be a promising neuron chip of olfactory biosensors for odor detecting.

Human beings and animals have sensitive olfactory systems that can sense and identify a variety of odors. The purpose of this study is to combine biological cells with micro-chips to establish a novel bioelectronic nose system for odor detection by electrophysiological sensing measurements of olfactory tissue. In our experiments, 36-channel microelectrode arrays (MEAs) with the diameter of 30 μm were fabricated on the glass substrate, and olfactory epithelium was stripped from rats and fixed on the surface of MEA. Electrophysiological activities of olfactory receptor neurons in intact epithelium were measured through the multi-channel recording system. The extracellular potentials of cell networks could be effectively analyzed by correlation analysis between different channels. After being stimulated by odorants, such as acetic acid and butanedione, the olfactory cells generate different firing modes. These firing characteristics can be derived by time-domain and frequency-domain analysis, and they were different from spontaneous potentials. The investigation of olfactory epithelium can provide more information of olfactory system for artificial olfaction biomimetic design.

A novel biosensor based on single-stranded DNA (ssDNA) probe functionalized aluminum anodized oxide (AAO) nanopore membranes was demonstrated for Escherichia coli O157:H7 DNA detection. An original and dynamic polymerase-extending (PE) DNA hybridization procedure is proposed, where hybridization happens in the existence of Taq DNA polymerase and dNTPs under controlled reaction temperature. The probe strand would be extended as long as the target DNA strand, then the capability to block the ionic flow in the pores has been prominently enhanced by the double strand complex. We have investigated the variation of ionic conductivity during the fabrication of the film and the hybridization using cyclic voltammetry and impedance spectroscopy. The present approach provides low detection limit for DNA (a few hundreds of pmol), rapid label-free and easy-to-use bacteria detection, which holds the potential for future use in various ss-DNA analyses by integrated into a self-contained biochip.

Taste receptor cell, the taste sensation organ with its intrinsic advantage of high sensitivity, specificity, fast response and powerful ability of information processing from taste system, can recognize taste substances. In order to investigate the electrophysiological signals of taste receptor cells and realize acidic sensation in a biomimetic manner, a cell-based biosensor platform of neuron–silicon interface was designed and characterized. Acid-sensing taste receptor cells were cultured on light-addressable potentiometric sensor (LAPS) to recognize sour stimuli as compared with non-acid solutions. A computational model of acid-sensing taste receptor cells was constructed to simulate the action potentials of taste receptor cells and to help decode the extracellular signals recorded by LAPS. The temporal firing and characteristic features from LAPS recordings upon acidic solutions demonstrate that this kind of hybrid biosensor based on taste receptor cells and LAPS can realize acidic sensation. This study also provides a prototype of a novel biosensor which deploys the sensory transduction and decoding mechanism from biology to realize chemosensing, potentially in a non-invasive and long-term manner.

The paper discussed a novel design of multifunctional cell-based biosensors for simultaneously detecting cell acidification and extracellular potential. Employing living cells such as cardiac myocytes as a source for the light addressable potentiometric sensor (LAPS) array, this cell-based biosensor was able to monitor both the acidification and extracellular potential in parallel. For LAPS array fabrication, part of the silicon base was heavily doped with boron to form separate testing areas. Detecting system was built involving lock-in amplifier and digital demodulation with FFT methods. This LAPS array showed a good sensitivity of 53.9 mV/pH to H+ with good linearity. Each testing area for extracellular potential detection was decreased to 200 μm × 200 μm in size to obtain a better sensitivity. Experiment results showed that this LAPS array could monitor the acidification of cells as well as the extracellular potential with good sensitivity. This novel integrated biosensor will be useful for multi-parameter extracellular monitoring and can possibly be a platform for drug screening.

This paper presents a novel biomimetic olfactory biosensor for the study of olfactory transduction mechanisms on the basis of light addressable potentiometric sensor (LAPS), in which rat olfactory sensory neurons (OSNs) are used as sensing elements. Rat OSNs are cultured on the surface of LAPS chip. To validate the origin of the electrical signals recorded by LAPS, the inhibitory effect of MDL12330A to the olfactory signals of OSNs is tested, which is the specific inhibitor of adenylyl cyclase. The enhancive effect of LY294002 to the responses of OSNs is also investigated, which is the specific inhibitor of phosphatidylinositol 3-kinase (PI3K). The results show that this hybrid biosensor can record the responses of OSNs to odours efficiently in a non-invasive way for a long term, and the responses can be inhibited by MDL12330A and enhanced by LY294002. All these results demonstrate that this hybrid biosensor can be used to monitor electrophysiology of OSNs in a non-invasive way and suggest it could be a promising tool for the study of olfactory transduction mechanisms.

Taste receptor cells are the taste sensation elements expressing sour, salty, sweet, bitter and umami receptors, respectively. There are cell-to-cell communications between different types of cells. Nevertheless, the mechanism of taste sensation and taste information coded by taste receptor cell is not well understood at present and it is a long-standing issue. In order to explore taste sensation and analyze taste-firing responses from another point of view, we present a promising biomimetic taste receptor cell-based biosensor. The temporal firing responses to different tastants are recorded. Meanwhile, we investigate the firing rate and temporal firing of taste receptor cells. The experimental results are consistent with that from patch clamp and molecular biology experiment. Firing rate is dependent on the concentration of stimulus. PCA analysis (principal component analysis) of the temporal firing responses shows that the responses from different types of taste receptor cells can be distinguished. Furthermore, exogenous ATP is applied to mimic the effects of transmitter ATP (adenosine triphosphate) released from type II cells onto type III cells. Both enhanced and inhibitory effects on spontaneous firing are observed. This novel biomimetic hybrid biosensor provides a potential solution to investigate the taste sensation and coding mechanisms in a non-invasive way.

Based on patch clamp data on the ionic currents of rat taste receptor cells, a mathematical model of mammalian taste receptor cells was constructed to simulate the action potentials of taste receptor cells and their corresponding ionic components, including voltage-gated Na+ currents and outward delayed rectifier K+ currents. Our simulations reproduced the action potentials of taste receptor cells in response to electrical stimuli or sour tastants. The kinetics of ion channels and their roles in action potentials of taste receptor cells were also analyzed. Our prototype model of single taste receptor cell and simulation results presented in this paper provide the basis for the further study of taste information processing in the gustatory system.

A patch clamp chip, as a novel cell-based chip for electrophysiological recordings, has many prominent advantages such as high resolution, accuracy, high throughput and automation. It can be used to perform multivariate and real-time measurements of cell networks in situ. Therefore, this technology will dramatically promote the research on ionic channels, neuronal networks and the application of this technology in drug screening. This paper reviews the development of planar patch clamp technology and its applications in detail. The latest progress in the research of taste cells electrophysiology and taste transduction is also presented. Finally, this paper analyzes the methodology of neural chips. Based on the current research of our laboratory, the prospective applications of a patch clamp chip in the research of taste sensation and transduction mechanisms at molecular and cellular levels are discussed.

Titanium dioxide (TiO2) thin film was deposited on the surface of the light addressable potentiometric sensor (LAPS) to modify the sensor surface for the non-labeled detection of DNA molecules. To evaluate the effect of ultraviolet (UV) treatment on the silanization level of TiO2 thin film by 3-aminopropyltriethoxysilane (APTS), fluorescein isothiocyanate (FITC) was used to label the amine group on the end of APTS immobilized onto the TiO2 thin film. We found that, with UV irradiation, the silanization level of the irradiated area of the TiO2 film was improved compared with the non-irradiated area under well-controlled conditions. This result indicates that TiO2 can act as a coating material on the biosensor surface to improve the effect and efficiency of the covalent immobilization of biomolecules on the sensor surface. The artificially synthesized probe DNA molecules were covalently linked onto the surface of TiO2 film. The hybridization of probe DNA and target DNA was monitored by the recording of I-V curves that shift along the voltage axis during the process of reaction. A significant LAPS signal can be detected at 10 µmol/L of target DNA sample.

This paper presents a novel strategy for the response enhancement of olfactory sensory neurons (OSNs)-based biosensors by monitoring the enhancive responses of OSNs to odorants. An OSNs-based biosensor was developed on the basis of the light addressable potentiometric sensor (LAPS), in which rat OSNs were cultured on the surface of LAPS chip and served as sensing elements. LY294002, the specific inhibitor of phosphatidylinositol 3-kinase (PI3K), was used to enhance the responses of OSNs to odorants. The responses of OSNs to odorants with and without the treatment of LY294002 were recorded by LAPS. The results show that the enhancive effect of LY294002 was recorded efficiently by LAPS and the responses of this OSNs-LAPS hybrid biosensor were enhanced by LY294002 by about 1.5-fold. We conclude that this method can enhance the responses of OSNs-LAPS hybrid biosensors, which may provide a novel strategy for the bioelectrical signal monitor of OSNs in biosensors. It is also suggested that this strategy may be applicable to other kinds of OSNs-based biosensors for cellular activity detection, such as microelectrode array (MEA) and field effect transistor (FET).

This paper reports a novel phenomenon that the ZnO nanorod arrays hydrothermally grown on the UV-treated area of the ZnO seeding layer exhibit different surface morphology and photoluminescence characteristics compared with those grown on the non-UV-treated area. The diameter distribution of the nanorods on the different areas is different too. The UV treatment makes the ZnO seeding layer hydrophilic, which is the exhibition of the change of the surface energy status. This change will affect the growth behavior of the ZnO nanorod arrays. Patterned ZnO nanorod arrays with different structures on the same substrate can be realized by hydrothermal method employing UV treatment of the ZnO seeding layer. This kind of UV treatment can find other applications in other preparation methods for 1D nanostructures of ZnO and other kinds of materials, and for the research of the hydrothermal growth mechanism of these nanostructures.

Recent advantages in electrophysiological technique on detecting potential and ion changes of taste cells make great progress in developing taste transduction mechanisms of taste receptor cells (TRCs). Light-addressable potentiometric sensor (LAPS) is used to detect extracellular potential of TRCs cultured on the silicon chip and to test the taste cell response to taste stimuli of NaCl, HCl, MgSO4, sucrose and glumate. Results show that the system composed of LAPS and TRCs is sensitive to gustatorius changes, which has great potential to monitor electrophysiology property of living TRCs. It is a novel non-invasive method to study taste transduction mechanisms in vitro for a long term.

This paper presents development of a quartz crystal microbalance (QCM) biosensor for real-time detection of E. coli O157:H7 DNA based on nanogold particles amplification. Many inner Au nanoparticles were immobilized onto the thioled surface of the Au electrode, then more specific thiolated single-stranded DNA (ssDNA) probes could be fixed through Au-SH bonding. The hybridization was induced by exposing the ssDNA probe to the complementary target DNA of E. coli O157:H7 gene eaeA, then resulted in a mass change and corresponding frequency shifts (Δf) of the QCM. The outer avidin-coated Au nanoparticles could combine with the target DNA to increase the mass. The electrochemical techniques, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were adopted to manifest and character each step. The target DNA corresponding to 2.0×103 colony forming unit (CFU)/mL E. coli O157:H7 cells can be detected by this biosensor, so it is practical to develop a sensitive and effective QCM biosensor for pathogenic bacteria detection based on specific DNA analysis. The piezoelectric biosensing system has potential for further applications, such as food safety and environment monitoring, and this approach lays the groundwork for incorporating the method into an integrated system for in-field bacteria detection.

By means of the specific immuno-recognition and ultra-sensitive mass detection, a quartz crystal microbalance (QCM) biosensor for Escherichia coli O157:H7 detection was developed in this work. As a suitable surfactant, 16-mercaptohexadecanoic acid (MHDA) was introduced onto the Au surface of QCM, and then self-assembled with N-hydroxysuccinimide (NHS) raster as a reactive intermediate to provide an active interface for the specific antibody immobilization. The binding of target bacteria with the immobilized antibodies decreased the sensor’s resonant frequency, and the frequency shift was correlated to the bacterial concentration. The stepwise assembly of the immunosensor was characterized by means of the electrochemical techniques. Using the immersion-dry-immersion procedure, this QCM biosensor could detect 2.0×102 colony forming units (CFU)/ml E. coli O157:H7. In order to reduce the fabrication time, a polyelectrolyte layer-by-layer self-assembly (LBL-SA) method was adopted for fast construction. Finally, the reproducibility of this biosensor was discussed.

Olfaction is a very important sensation for all animals. Recently great progress has been made in the research of olfactory transduction. Especially the novel finding of the gene superfamily encoding olfactory receptors has led to rapid advances in olfactory transduction. These advances also promoted the research of biomimetic olfactory-based biosensors and some obvious achievements have been obtained due to their potential commercial prospects and promising industrial applications. This paper briefly introduces the biological basis of olfaction, summarizes the progress of olfactory signal transduction in the olfactory neuron, the olfactory bulb and the olfactory cortex, outlines the latest developments and applications of biomimetic olfactory-based biosensors. Finally, the olfactory biosensor based on light addressable potentiometric sensor (LAPS) is addressed in detail based on our recent work and the research trends of olfactory biosensors in future are discussed.

Biosensors incorporating mammalian cells have a distinct advantage of responding in a manner which offers insight into the physiological effect of an analyte. To investigate the potential applications of cell-based biosensors on heavy metal toxicity detection, a novel biosensor for monitoring electrophysiological activity was developed by light-addressable potentiometric sensor (LAPS). Extracellular field potentials of spontaneously beating cardiomyocytes could be recorded by LAPS in the range of 20 μV to nearly 40 μV with frequency of 0.5–3 Hz. After exposed to different heavy metal ions (Hg2+, Pb2+, Cd2+, Fe3+, Cu2+, Zn2+; in concentration of 10 μM), cardiomyocytes demonstrated characteristic changes in terms of beating frequency, amplitude and duration under the different toxic effects of ions in less than 15 min. This study suggests that, with the physiological monitoring, it is possible to use the cardiac cell-based biosensor to study acute and eventually chronic toxicities induced by heavy metal ions in a long-term and no-invasive way.

A review of an olfactory and taste cell sensor is presented in this article. Olfactory and taste cell sensor is one kind of cell-based on biosensors which are based on the electronic nose and electronic tongue research, trying to culture olfactory and taste living cell on the surface of chips. This is a really mimicking bioelectronic nose and tongue technology, which can detect odors and taste by using chips such as light-addressable potentiometric sensor to record action potential representing the odorants and taste in cell membrane. Now, several kinds of cells from olfactory bulb and taste bud on chip have been cultured, while the experiments and analysis about the detection of olfactory and taste and its action potential under the stimulus of different odors and taste also are in progress.

Recent advantages in electrophysiological technique on detecting potential and ion changes of taste cells make great progress in developing taste transduction mechanisms of taste receptor cells (TRCs). Light-addressable potentiometric sensor (LAPS) is used to detect extracellular potential of TRCs cultured on the silicon chip and to test the taste cell response to taste stimuli of NaCl, HCl, MgSO4, sucrose and glumate. Results show that the system composed of LAPS and TRCs is sensitive to gustatorius changes, which has great potential to monitor electrophysiology property of living TRCs. It is a novel non-invasive method to study taste transduction mechanisms in vitro for a long term.

Microelectrode array (MEA) was used for in situ heavy metal determination in aquatic environments due to its characteristics of high sensitivity, large current density and fast mass transfer rate, while interferences caused by background factors and complex external environment were inevitable in analysis leading to inaccurate results. Hence, two algorithms, partial least square regression and local optimum method were employed in different situations for electrochemical analysis to eliminate interference. Partial least square regression was superior to local optimum method thanks to convenient operations and good outcomes for in situ determination, which was proved to be effective in low interference samples. Nevertheless, inaccurate results were obtained in samples of complicated composition because of negative impacts on working electrode. Local optimum method was proposed aiming at those situations, by which severe interference was ignored and better results were acquired to prove the reasonability and validity of the algorithm. The determination of cadmium and lead was improved effectively combined PLS with local optimum method.

Herein, we present a novel miniaturized multisensor chip integrated with a nanoband electrode array (NEA) for lead and copper detection and a light addressable potentiometric sensor (LAPS) for pH sensing. By this means, pH information could be provided before electrochemical analysis to ensure high performance in heavy metal quantification due to the significant effects of solution acidity on electrochemical analyses. The fabrication processes of the multisensor chip are described in detail and the electrochemical behaviour of NEA was characterized using cyclic voltammetry in sulfuric acid and acetate buffer. For the detection of lead and copper qualitatively and quantitatively, square wave anodic stripping voltammetry (SWASV) was applied with the standard addition method. Deposition potential and deposition time were optimized to be −0.6 V and 120 s, respectively. NEA exhibited a sensitivity of 0.510 μA pbb−1 and 0.678 μA ppb−1 towards lead and copper, respectively, with high correlation coefficients. The repetitive and long-term experiments also demonstrated the good reproducibility and stability of NEA in heavy metal detection. Moreover, the silicon nitride modified LAPS showed a pH sensitivity of 56.49 mV pH−1 with a high correlation coefficient of 0.9999. The reproducibility of LAPS was also investigated and a deviation of less than 2 mV was obtained in both the samples. These results indicate that the miniaturized multisensor chip demonstrates good electrochemical performance in heavy metal and pH sensing.

With growing concern about human health, relevant drug and food toxicity has drawn more and more attention. However, traditional methods like mouse bioassays cannot meet the sharply increasing demand for drug and food toxicity assessment. In this study, a multifunctional cell-based impedance biosensor system is established for drug and toxin analysis, using a cell-based impedance biosensor (CIB) as the sensitive element. Cellular growth and beating experiments were carried out to verify the multifunctionality of the system. Four typical heart-related compounds including verapamil, bay K8644, chromanol 293B, and adriamycin were used for cardiotoxicity analysis function tests of the CIB system. Also, one typical marine diarrhetic toxin, okadaic acid (OA), was used for cytotoxicity analysis function tests of the CIB system. From the results, the CIB system can reflect the drug function and toxicity directly through the cell growth and beating status. According to the results, the multifunctional CIB system may provide a high-throughput and useful method for effective screening of cardiovascular drugs and marine toxins in vitro.