Multi-doped carbon dots (C-dots) were synthesized using a facile one-pot solvothermal method, and the C-dots can be used as a ratiometric pH probe directly without integrating with other dyes, which was demonstrated by monitoring the proton-producing enzyme catalytic reactions.

•A photoelectrochemical AChE biosensor based on semiconductor nanocomposite was developed.•The combination of ZnO and TiO2 enhanced the photoelectrochemical activity.•Cd2 + showed dose-dependent effects on AChE activity.Acetylcholinesterase (AChE) is a well-known serine hydrolase and its dysfunction could disturb cholinergic neurotransmission which is related to the pathogenesis of neurodegenerative disorders. In this report, a photoelectrochemical biosensor based on metal oxide semiconductor nanocomposite was fabricated to investigate the effect of cadmium ion (Cd2 +) on the activity of AChE. The photoelectrochemical nanocomposite was prepared by anodic oxidation of titanium (Ti) foil to form titanium dioxide (TiO2) nanotubes (TNs) array followed by cathodic deposition of zinc oxide nanorods (ZnONRs) onto the TNs. AChE was immobilized on the obtained nanocomposites and the biosensor showed enhanced photoelectrochemical response under visible light irradiation. The experimental results showed that Cd2 + exhibited interesting dose-dependent and time-dependent effects on AChE activity. Specifically, high concentration of Cd2 + inhibited while low level of Cd2 + could stimulate the activity of AChE. These findings are of great significance for the study of enzyme activity influenced by metal ions and related pathogenesis investigation of neurodegenerative disorders.A photoelectrochemical biosensor based on metal oxide semiconductor nanocomposite was developed to investigate the effect of Cd2 + on AChE activity.

A label-free molecular beacon (MB) system integrated with enzyme-free amplification strategy was developed for simple and highly selective assay of Aβ oligomers.Highly selective response for Aβ oligomers.The method could monitor the Aβ aggregation process.Without the organic fluorophore labeling for signaling.Without the use of enzyme for amplification assay.Amyloid-beta (Aβ) oligomers are highly toxic species in the process of Aβ aggregation and are regarded as potent therapeutic targets and diagnostic markers for Alzheimer's disease (AD). Herein, a label-free molecular beacon (MB) system integrated with enzyme-free amplification strategy was developed for simple and highly selective assay of Aβ oligomers. The MB system was constructed with abasic site (AP site)-containing stem-loop DNA and a fluorescent ligand 2-amino-5,6,7-trimethyl-1,8-naphyridine (ATMND), of which the fluorescence was quenched upon binding to the AP site in DNA stem. Enzyme-free amplification was realized by target-triggered continuous opening of two delicately designed MBs (MB1 and MB2). Target DNA hybridization with MB1 and then MB2 resulted in the release of two ATMND molecules in one binding event. Subsequent target recycling could greatly amplify the detection sensitivity due to the greatly enhanced turn-on emission of ATMND fluorescence. Combining with Aβ oligomers aptamers, the strategy was applied to analyze Aβ oligomers and the results showed that it could quantify Aβ oligomers with high selectivity and monitor the Aβ aggregation process. This novel method may be conducive to improve the diagnosis and pathogenic study of Alzheimer's disease.

Based on melamine binding-triggered triplex formation and subsequent activation of Mg2+-dependent DNAzymes, a novel strategy for DNAzyme regulation was proposed and developed for melamine recognition.

It is widely acknowledged that sialic acid (SA) overexpression on cell surfaces has been thought to be a characteristic feature associated with many malignant diseases. In this paper, we report a new strategy for SA expression evaluation and electrochemical cytosensing of living cells. High selectivity and sensitivity were achieved by combining 3-aminophenylboronic acid (APBA) modified carbon nanospheres (CNS-APBA) for SA recognition and horseradish peroxidases (HRP) decorated on gold nanoparticles (Au-HRP NPs) for signal amplification. The HRP labels can effectively catalyze the oxidation of aniline in the presence of H2O2 to form polyaniline (PAn). The relatively positive detection potential range for PAn completely excluded the conventional interference from dissolved oxygen. Based on the dual signal amplification by functionalized carbon nanospheres and enzymatically produced polyaniline, the designed cytosensor can be used for SA evaluation on cancer cell surfaces and highly sensitive cell detection with a wide calibration range (from 5.0 × 102 to 1.0 × 106 cells per mL for MCF-7 cells and from 1.0 × 103 to 1.0 × 106 cells per mL for BGC-823 cells) and a low detection limit (25 cells per mL for MCF-7 cells and 800 cells per mL for BGC-823 cells). This strategy provides a valuable tool for the evaluation of sialic acid on cancer cells and great potency for cancer study.

Human sirtuin1 (SirT1), which is a member of the sirtuin family, plays an important role in a wide range of cellular processes. Here we demonstrate a new strategy for the photoelectrochemical assay of SirT1 in different cell lines based on a semiconductor–polymer hybrid system consisting of Au–polymer and TiO2-Au nanocomposites. Au–polymer (GC-HBAP) hybrids were synthesized from crosslinked hyperbranched azo-polymer and gold colloids and then used as an immobilization platform for SirT1 antibody. Gold-doped TiO2 (TiO2-Au) nanocomposites were prepared as the photoelectrochemical labels for signal readout in the sandwiched immunoassay. The integration of GC-HBAP with TiO2-Au facilitated the electron transfer and the photoelectrocatalytic reaction, resulting in good analytical performance with high sensitivity, selectivity and rapid response for the analysis of SirT1 levels in different cell lines. This proposed semiconductor–polymer system might open a new perspective for the development of a highly sensitive photoelectrochemical immunosensor, and have potentially promising applications in assays of other proteins.

Here we report a label-free colorimetric method for protein assay based on the intrinsic peroxidase-like catalytic activity of DNA-hemin-graphene (DNA-GH) composite. By using aptamers as protein recognition elements, protein-mediated aggregation of the DNA-GH composite leads to the decrease or increase of the colorimetric signal depending on the sandwich or competitive design strategy. Thrombin and PDGF-BB were chosen as model analytes and the detection limits (LOD) by this method were estimated to be 0.5 nM and 5 nM, respectively. Compared to traditional ELISA method for protein detection, this method possesses the advantages of high sensitivity, simplicity, and low cost. In addition, by designing different DNA-modified hemin-graphene (GH) constructs, using proteins as inputs, the “OR” and “INHIBIT” logic gates were built. This procedure does not require chemical modification on the aptamer probes or analytes and circumvents the limitation associated with the number of target binding sites. Given the attractive analytical characteristics and distinct advantages of DNA-GH composite, the universal approach can be widely applied for the detection of diverse proteins and for the design of versatile logic gates.

•A highly sensitive immunosensor adopting a dual-layered enzyme strategy was proposed.•This immunosensor exhibited satisfactory analytical performances for CaM detection.•It was successfully applied to the CaM analysis in two cancer cells (HepG2 and MCF-7) with high sensitivity, which has shown great potency for cancer study.Calmodulin (CaM) is a ubiquitous protein in eukaryotic cells, and it plays an important role in cancer progression. In this paper, a highly sensitive immunosensor adopting a dual-layered enzyme strategy was proposed for electrochemical detection of CaM. This immunosensor was constructed by introducing honeycomb-like mesoporous carbon (HMPC) as a sensor platform to sequentially immobilize antibody (Ab1), CaM and a multi-functionalized label. The label (HRP-PAupc-Ab1) was synthesized by covalently binding Ab1 and horseradish peroxidase (HRP) to poly(acrylic acid)-functionalized Au popcorn (PAupc) nanoparticles. A novel dual-layered enzyme strategy was employed by incubating HRP-secondary antibody (HRP-Ab2) onto the label surface and the enhanced biocatalyzed precipitation was therefore induced. This immunosensor exhibited satisfactory analytical performances for CaM detection with a linear response ranging from 5.0 pg mL−1 to 100 ng mL−1 and a detection limit of 1.5 pg mL−1. The immunosensor has also been successfully applied to the CaM analysis in two cancer cells (HepG2 and MCF-7) with high sensitivity, which has shown great potency for cancer study.

Cell surface glycans are a class of sophisticated biomolecules related to cancer development and progression, and their analysis is of great significance for early cancer diagnosis and treatment. In this paper, we proposed a fluorescence assay to evaluate glycan expression on living cancer cells based on a competitive strategy coupled with dual-functionalized nanobiocomposites. The competitive assay was conducted between living cancer cells and thiomannosyl derivatives using concanavalin A (Con A)-modified electrode as the interaction platform. To impart fluorescence signaling ability to competitive derivatives, quantum dots (QDs) were anchored on BSA-protected Au nanoparticles, and thiomannosyl derivatives were further immobilized on the nanoparticle surface through Au–S binding. Due to the spacing between QDs and Au nanoparticles by BSA, the {QDs–Au–BSA–mannose} nanobiocomposites maintained the fluorescence of QDs and showed binding ability with the Con A-modified electrode. Au nanorods (AuNRs)-modified electrode was used as an effective substrate to immobilize Con A. This assay was successfully applied to the analysis of two cancer cells lines (A549 and QGY-7701). The method is simple and shows promise for the study of glycan expression on living cancer cells.

In this report, a novel visible-light-activated photoelectrochemical biosensor was fabricated to study the inhibition of acetylcholinesterase (AChE) activity induced by two endogenous neurotoxins, 1(R)-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline [(R)-Sal] and 1(R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetra-hydroisoquinoline [(R)-NMSal], which have drawn much attention in the study of the pathogenesis of neurodegenerative diseases such as Parkinson's disease. The photoelectrode was prepared by three steps, as follows. At first, nitrogen and fluorine co-doped TiO2 nanotubes (TNs) were obtained by anodic oxidation of a Ti sheet. Secondly, silver nanoparticles (AgNPs) were deposited onto the TNs through a microwave-assisted heating polyol (MAHP) process. At last, AChE was immobilized on the obtained photoelectrode and the biosensor was marked as AChE/Ag/NFTNs. Due to the nitrogen and fluorine co-doping, the photoelectrochemical biosensors can produce high photocurrent under visible light irradiation. Moreover, the presence of AgNPs greatly increased the photocurrent response of the biosensor. AChE/Ag/NFTNs hybrid system was used to study AChE inhibition induced by (R)-Sal and (R)-NMSal. The result proved that both (R)-Sal and (R)-NMSal exhibited mixed and reversible inhibition against AChE. This strategy is of great significance for the development of novel photoelectrochemical biosensors in the future.Highlights► A novel visible-light-activated photoelectrochemical biosensor was fabricated. ► The inhibition of acetylcholinesterase activity induced by two endogenous neurotoxins was studied. ► Both (R)-Sal and (R)-NMSal exhibited mixed and reversible inhibition against AChE.

A novel electrochemical immunosensor for sensitive detection of α-synuclein (α-SYN), a very important neuronal protein, has been developed based on dual signal amplification strategy. Herein, G4-polyamidoamine dendrimer-encapsulated Au nanoparticles (PAMAM-Au nanocomposites) were covalently bound on the poly-o-aminobenzoic acid (poly-o-ABA), which was initially electropolymerized on the electrode surface to perform abundant carboxyl groups. The formed immunosensor platform, PAMAM-Au, was proved to provide numerous amino groups to allow highly dense immobilization of antigen, and facilitate the improvement of electrochemical responses as well. Subsequently, the enhanced gold nanoparticle labels ({HRP-Ab2-GNPs}) were fabricated by immobilizing horseradish peroxidase-secondary antibody (HRP-Ab2) on the surface of gold nanoparticles (GNPs). After an immunoassay process, the {HRP-Ab2-GNPs} labels were introduced onto the electrode surface, and produced an electrocatalytic response by reduction of hydrogen peroxide (H2O2) in the presence of enzymatically oxidized thionine. On the basis of the dual signal amplification of PAMAM-Au and {HRP-Ab2-GNPs} labels, the designed immunosensor displayed an excellent analytical performance with high sensitivity and stability. This developed strategy was successfully proved as a simple, cost-effective method, and could be easily extended to other protein analysis schemes.

In this paper, an electrochemical acetylcholinesterase (AChE) inhibition assay based on three-dimensional ordered macroporous (3DOM) composite was conducted. The 3DOM composite was first fabricated on the glassy carbon electrode by electropolymerization of aniline in the presence of ionic liquid (IL) on a sacrificial silica nanospheres template. After the silica nanospheres were etched, an IL-doped polyaniline (IL-PANI) film with 3DOM morphology was formed. Then, gold nanoparticles (AuNPs) were decorated on the IL-PANI film by electrodeposition. The immobilized AChE on the 3DOM composite displayed favorable affinity to substrate acetylthiocholine chloride (ATCh), and the 3DOM composite showed excellent electrocatalytic effect on thiocholine, the hydrolysis product of ATCh. The presence of IL and AuNPs could improve the sensitivity by accelerating the electron transfer. The designed AChE biosensor was successfully applied to evaluate the AChE inhibition induced by endogenous neurotoxin 1(R),2N-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline [(R)-NMSal]. The results demonstrate that (R)-NMSal exerts a considerable effect on AChE activity, and the inhibition is reversible. The developed method offers a new approach for AChE inhibition assay, which is of great benefit in understanding the mechanism behind neurotoxin-induced neurodegenerative disorders.

In this paper, we report a novel lectin-based electrochemical biosensor constructed by functionalized multiwalled carbon nanotubes (CNTs) for a competitive assay of glycan expression on living cells. The biosensor was fabricated by adsorbing poly(diallyldimethylammonium chloride) (PDDA)-functionalized CNTs (PDCNTs) onto a glassy carbon working electrode (GCE), followed by adsorbing glutathione (GSH)-protected gold nanoparticles (AuNPs). The resulting GCE/PDCNT/Au–GSH offers an effective platform for concanavalin A (Con A, a lectin) immobilization with high stability and bioactivity. A thiol-derivatized carbohydrate (thiomannosyl dimer) was synthesized to construct {CNT/thionine/Au–S–mannose} biocomposites, which exploit CNTs as carriers to load enormous amounts of thionine for generating an electrochemical signal and AuNPs for anchoring the thiomannosyl dimer. These two applications of the functionalized CNTs as a biosensing platform and biocomposites play important roles in signal enhancement for glycan detection. Using a competitive assay, the electrochemical biosensor shows good analytical performance with high sensitivity, selectivity and a rapid response for the analysis of mannose on human lung cancer cells as a model glycan. This proposed strategy possesses promising application for the assay of other glycans on living cancer cells with the selection of more lectins with the biosensor development.

In this paper, a novel dual enzymatic-biosensor is described for simultaneous determination of glucose and cholesterol in serum and peritoneal macrophages (PMs) of diabetic mice to evaluate the risk of diabetes-accelerated atherosclerosis. The biosensor was constructed by a three-step method. First, a poly-thionine (PTH) film was assembled on the surface of glassy carbon electrode by cyclic voltammetric electropolymerization of thionine, which serves as an electron transfer mediator (ETM). Second, gold nanoparticles (GNPs) were covered on the surface of PTH facilitating the electron transfer between glucose oxidase (GOx), cholesterol oxidase (ChOx) and electrode. Finally, the enzymes, GOx, cholesterol esterase (ChE), and ChOx, were covalently attached to the PTH layer through a chitosan (CH) linker. The PTH coupled with GNPs provides good selectivity, high sensitivity and little crosstalk for the dual enzymatic-biosensor. The developed biosensor had good electrocatalytic activity toward the oxidations of glucose and cholesterol, exhibiting a linear range from 0.008 mM to 6.0 mM for glucose with a detection limit of 2.0 μM, and a linear range from 0.002 mM to 1.0 mM for cholesterol with a detection limit of 0.6 μM. The results of the diabetic mice demonstrated that the cholesterol level did not change obviously with the increase of glucose level in serum, while the cholesterol level was induced with the increase of the glucose level in PMs. Previous studies have shown that the large accumulation of cholesterol in macrophage could lead to macrophage foam cell formation, which is the hallmark of early atherosclerosis. This study provides useful further evidences for the development of diabetes-accelerated atherosclerosis.Graphical abstractIn this paper, we reported a novel dual enzymatic-biosensor for simultaneous determination of glucose and cholesterol in serum and peritoneal macrophages (PMs) of diabetic mice to evaluate the diabetes-accelerated atherosclerosis risk. The biosensor was firstly modified with a poly-thionine (PTH) film as electron transfer mediator (ETM), then the gold nanoparticles (GNPs) were covered on the surface of PTH to act as tiny conduction centers for facilitating the electron transfer between enzymes and electrode. The schematic of the dual biosensor is shown in figure. The developed dual biosensor had good electrocatalytic activity toward the oxidations of glucose and cholesterol, exhibited a linear range from 0.008 mM to 6.0 mM for glucose with a detection limit of 2.0 μM, and a linear range from 0.002 mM to 1.0 mM for cholesterol with a detection limit of 0.6 μM. The results of the diabetic mice demonstrated that the cholesterol level was not changed obviously with the increase of glucose level in serum, while the cholesterol level was enhanced together with the increase of the glucose level in PMs. Previous studies have shown that the large accumulation of cholesterol in macrophage could lead to macrophage foam cell formation, the hallmark of early atherosclerosis. These findings indicated the possibility that high glucose induced by diabetes might increase the macrophage cholesterol level to further accelerate atherosclerosis development.Highlights► A novel biosensor was developed to determine glucose and cholesterol simultaneously. ► The dual enzymatic-biosensor has good selectivity and high sensitivity. ► We determined glucose and cholesterol in the real samples of diabetic mice. ► The results showed that high glucose might increase the macrophage cholesterol level. ► It provided useful experimental evidences for diabetes-accelerate atherosclerosis.

A novel amplified electrochemical immunoassay based on ferrocene (Fc)-functionalized ZnO nanorods (NRs) was developed in the present work. The detection antibody (dAb) and Fc were immobilized onto the surface of ZnO NRs, denoted as {dAb–ZnO–Fc} bioconjugates. The amount of dAb and Fc in the bioconjugates was investigated using the copper reduction/bicinchoninic acid reaction (BCA protein assay) and inductive coupled plasma-atomic emission spectroscopy (ICP-AES), respectively. Greatly amplified signal was achieved in the sandwich-type immunoassay when dAb and Fc linked to ZnO NRs at a proper ratio. Using Escherichia coli (E. coli) as a model antigen, the designed immunoassay showed an excellent analytical performance, and exhibited a wide dynamic response range of E. coli concentration from 102 to 106 cfu/mL with a detection limit of 50 cfu/mL (S/N = 3). By introducing a pre-enrichment step, the detection of 5 cfu/10 mL E. coli in hospital sewage water was realized. This proposed signal amplification strategy was promising and could be easily extended to monitor other biorecognition events.Highlights► {dAb-ZnO-Fc} bioconjugates were prepared by employing ZnO NRs as efficient carriers of dAb and Fc. ► We investigated and optimized the ratio of dAb to Fc loaded on the surface of ZnO NRs. ► A sandwich-type electrochemical immunoassay was developed based on {dAb-ZnO-Fc} bioconjugates. ► The designed immunoassay exhibited a wide dynamic response range of E. coli concentration from 102 to 106 cfu/mL with a detection limit of 50 cfu/mL. ► 5 cfu/10mL E. coli in hospital sewage water was detected by introducing a pre-enrichment step.

A new type of DNA sequence-specific electrochemical biosensor based on magnetic beads for the detection of Escherichia coli is reported in the present work. Alginic acid-coated cobalt magnetic beads, capped with 5′-(NH2) oligonucleotide and employed not only for magnetic separation but also as the solid adsorbent, were used as DNA probes to hybridize with the target E. coli DNA sequence. This assay was specific for E. coli detection depending on the uid A gene, which encodes for the enzyme β-d-glucuronidase produced by E. coli strains. When daunomycin (DNR) was used as DNA hybridization indicator, the target sequences of E. coli hybridized with the probes resulted in the decrease of DNR reduction peak current, which was proportional to the E. coli concentration. The optimization of the hybridization detection was carried out and the specificity of the probes was also demonstrated. This DNA biosensor can be employed to detect a complementary target sequence for 3.0 × 10−10 mol/L and denatured PCR products for 0.5 ng/μL. The linear range of the developed biosensor for the detection of E. coli cells was from 1.0 × 102 to 2.0 × 103 cells/mL with a detection limit of 50 cells/mL. After a brief enrichment process, a concentration of 10 cells/mL E. coli in real water samples was detected by the electrochemical biosensor.

In this article, we report a novel lectin-based biosensor for electrochemical assay of cancer-associated glycosylation by comparative study of mannose and sialic acid expression on normal and cancer cells derived from human lung, liver, and prostate. Using a sandwich format, high sensitivity and selectivity were achieved by combining the lectin-based biosensor with the {lectin−Au−Th} bioconjugates featuring lectin and thionine (Th) labels linked to gold nanoparticles (AuNPs) for signal amplification. The proposed strategy demonstrated that mannose exhibited high expression levels in both normal and cancer cells, while sialic acid was more abundant in cancer cells as compared to normal ones. The results were in good agreement with those from fluorescent microscopy studies. The differences in the two glycan expression indicated that sialic acid could serve as a potential biomarker for early cancer detection. The lectin-based biosensor was also successfully used to quantify cancer cells and evaluate the average amount of sialic acid on single cell surface, which could supply significant information on glycan functions in cancer progression. Overall, the lectin-based electrochemical biosensor provides an effective pathway to analyze glycan expression on living cells and may greatly facilitate the medical diagnosis and treatment in early process of cancer.

The integration of Au-doped TiO2 nanotubes with biomolecule acetylcholinesterase (AChE) yields a novel AChE–Au–TiO2 hybrid system, which provides a new rapid and valid photoelectrochemical approach to the determination of AChEinhibition induced by endogenous neurotoxin.

Acetylcholine (ACh) and choline (Ch) play a critical role in cholinergic neurotransmission and the abnormalities in their concentrations are related to several neural diseases. Therefore, the in vivo determination of ACh and Ch is important to the research on neurodegenerative disorders. In this work, electrochemical biosensors based on poly(m-(1,3)-phenylenediamine) (pmPD) and polytyramine (PTy) modified enzyme electrodes were fabricated. The electropolymerized pmPD polymer was used to exclude interfering substances and the PTy layer facilitated the immobilization of acetylcholinesterase (AChE) and choline oxidase (ChOx). Then, ACh/Ch sensor and Ch sensor were coupled with microdialysis to produce a novel device, which provides a sensitive and selective method for simultaneous determination of ACh and Ch. This method has detection limits of 63.0 ± 3.4 nM for ACh and 25.0 ± 1.2 nM for Ch. The integrated device was successfully applied to assessing the impact of endogenous neurotoxin N-methyl-(R)-salsolinol [1(R),2-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, (R)-NMSal] on ACh and Ch concentration, which is of great benefit to understand the pathogenesis of Parkinson's disease.

A sensitive electrochemical immunoassay for rapid detection of Escherichia coli has been developed by anodic stripping voltammetry (ASV) based on core–shell Cu@Au nanoparticles (NPs) as anti-E. coli antibody labels. The characteristics of Cu@Au NPs before and after binding with antibody were confirmed by transmission electron microscopy (TEM). After Cu@Au-labeled antibody reacted with the immobilized E. coli on Polystyrene (PS)-modified ITO chip, Cu@Au NPs were dissolved by oxidation to the metal ionic forms, and the released Cu2+ ions were determined at GC/Nafion/Hg modified electrode by ASV. The utilization of GC/Nafion/Hg modified electrode could enhance the sensitivity for Cu2+ detection with a concentration as low as 9.0 × 10−12 mol/L. Since Cu@Au NPs labels were only present when antibody reacted with E. coli, the amount of Cu2+ directly reflected the number of E. coli. The technique could detect E. coli with a detection limit of 30 CFU/mL and the overall analysis could be completed in 2 h. By introducing a pre-enrichment step, a concentration of 3 CFU/10 mL E. coli in surface water was detected by the electrochemical immunoassay.

An electrochemical impedance immunosensor for the detection of Escherichia coli was developed by immobilizing anti-E. coli antibodies at an Au electrode. The immobilization of antibodies at the Au electrode was carried out through a stable acyl amino ester intermediate generated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydrosuccinimide (NHS), which could condense antibodies reproducibly and densely on the self-assembled monolayer (SAM). The surface characteristics of the immunosensor before and after the binding reaction of antibodies with E. coli were characterized by atomic force microscopy (AFM). The immobilization of antibodies and the binding of E. coli cells to the electrode could increase the electro-transfer resistance, which was directly detected by electrochemical impedance spectroscopy (EIS) in the presence of Fe(CN)63−/Fe(CN)64− as a redox probe. A linear relationship between the electron-transfer resistance and the logarithmic value of E. coli concentration was found in the range of E. coli cells from 3.0 × 103 to 3.0 × 107 cfu mL−1 with the detection limit of 1.0 × 103 cfu mL−1. With preconcentration and pre-enrichment steps, it was possible to detect E. coli concentration as low as 50 cfu/mL in river water samples.

A novel electrochemical detector with an acetylcholine film has been developed for HPLC. The chemically modified electrode is an efficient electrocatalyst of (R)-salsolinol ((R)-Sal), (R)-N-methylsalsolinol ((R)-NMSal), and monoamine neurotransmitters, enabling highly sensitive detection. The electrode is also stable and long-lived. Combined with microdialysis sampling, HPLC with the novel detector enabled successful study of changes in the concentrations of monoamine neurotransmitters in rat brain after the injection of (R)-salsolinol and (R)-N-methylsalsolinol.

A new method for rapid detection of Escherichia coli (E. coli) was developed by flow injection analysis (FIA) using bismuth nano-film modified glassy carbon electrode (BiNFE) in this paper. The method depended on a good marker β-d-glucuronidase which is found in E. coli strains. β-d-Glucuronidase was produced by the induction of methyl-β-d-glucuronide sodium (MetGlu), then released from E. coli cells through the permeabilization of cell membrane caused by polymyxin B nonapeptide and lysozyme. The released β-d-glucuronidase could catalyze the hydrolysis of the substrate 4-nitrophenyl β-d-glucuronide (PNPG) in the culture medium to produce 4-nitrophenol. Since 4-nitrophenol is electroactive and its quantity is proportional to the concentration of E. coli, E. coli could be determined by electroanalysis of 4-nitrophenol. The BiNFE was fabricated by an electrodeposition of metallic bismuth onto a glassy carbon electrode, which showed a high sensitivity in determination of 4-nitrophenol when used in conjunction with FIA system. Experimental results showed that the amplified response current of 4-nitrophenol obtained at the BiNFE was linear with the concentration of E. coli ranging from 1.5 × 102 to 1.0 × 106 cfu/ml, the detection limit of this method for E. coli is 100 cfu/ml, and the complete assay was performed in 3 h.

An amperometric method for the rapid detection of Escherichia coli (E. coli) by flow injection analysis (FIA) using an IrO2–Pd chemically modified electrode (CME) was developed in this paper. The method is based on a good marker β-d-galactosidase which was found in E. coli strains. β-d-galactosidase was produced by the induction of isopropyl β-d-thiogalactopyranoside (IPTG) and released from E. coli cells through the permeabilization of both polymyxin B nonapeptide and lysozyme to E. coli cells wall. The released β-d-galactosidase could catalyze the hydrolysis of the substrate p-aminophenyl β-d-galactopyranoside (PAPG) in the culture medium to produce 4-aminophenol which was proportional to the concentration of E. coli. Hence, E. coli could be detected by the determination of 4-aminophenol. An IrO2–Pd CME, which showed high sensitivity in determination of 4-aminophenol, was prepared as the electro-detector in FIA. The amplified response current of 4-aminophenol obtained at the IrO2–Pd CME was linear with the concentration of E. coli ranging from 2.0 × 102 to 1.0 × 106 cfu/mL, the detection limit of this method to E. coli was 150 cfu/mL and the complete assay could be performed in 3 h.

The integration of Au-doped TiO2 nanotubes with biomolecule acetylcholinesterase (AChE) yields a novel AChE–Au–TiO2 hybrid system, which provides a new rapid and valid photoelectrochemical approach to the determination of AChEinhibition induced by endogenous neurotoxin.

In this paper, we report a novel lectin-based electrochemical biosensor constructed by functionalized multiwalled carbon nanotubes (CNTs) for a competitive assay of glycan expression on living cells. The biosensor was fabricated by adsorbing poly(diallyldimethylammonium chloride) (PDDA)-functionalized CNTs (PDCNTs) onto a glassy carbon working electrode (GCE), followed by adsorbing glutathione (GSH)-protected gold nanoparticles (AuNPs). The resulting GCE/PDCNT/Au–GSH offers an effective platform for concanavalin A (Con A, a lectin) immobilization with high stability and bioactivity. A thiol-derivatized carbohydrate (thiomannosyl dimer) was synthesized to construct {CNT/thionine/Au–S–mannose} biocomposites, which exploit CNTs as carriers to load enormous amounts of thionine for generating an electrochemical signal and AuNPs for anchoring the thiomannosyl dimer. These two applications of the functionalized CNTs as a biosensing platform and biocomposites play important roles in signal enhancement for glycan detection. Using a competitive assay, the electrochemical biosensor shows good analytical performance with high sensitivity, selectivity and a rapid response for the analysis of mannose on human lung cancer cells as a model glycan. This proposed strategy possesses promising application for the assay of other glycans on living cancer cells with the selection of more lectins with the biosensor development.

Multi-doped carbon dots (C-dots) were synthesized using a facile one-pot solvothermal method, and the C-dots can be used as a ratiometric pH probe directly without integrating with other dyes, which was demonstrated by monitoring the proton-producing enzyme catalytic reactions.

Human sirtuin1 (SirT1), which is a member of the sirtuin family, plays an important role in a wide range of cellular processes. Here we demonstrate a new strategy for the photoelectrochemical assay of SirT1 in different cell lines based on a semiconductor–polymer hybrid system consisting of Au–polymer and TiO2-Au nanocomposites. Au–polymer (GC-HBAP) hybrids were synthesized from crosslinked hyperbranched azo-polymer and gold colloids and then used as an immobilization platform for SirT1 antibody. Gold-doped TiO2 (TiO2-Au) nanocomposites were prepared as the photoelectrochemical labels for signal readout in the sandwiched immunoassay. The integration of GC-HBAP with TiO2-Au facilitated the electron transfer and the photoelectrocatalytic reaction, resulting in good analytical performance with high sensitivity, selectivity and rapid response for the analysis of SirT1 levels in different cell lines. This proposed semiconductor–polymer system might open a new perspective for the development of a highly sensitive photoelectrochemical immunosensor, and have potentially promising applications in assays of other proteins.