•This work constructs an ultrasensitive electrochemical DNA biosensor.•3D nitrogen-doped graphene (NG) and Fe3O4 composites providing a promising platform for DNA probe immobilization.•DNA was detected sensitively due to the large specific area of 3D NG/Fe3O4 NPs which provide high capturing for molecular recognition elements.•This biosensor proved to hold a good detection capability of DNA in complicated serum samples.Here, we developed a new, sensitive electrochemical deoxyribonucleic acid (DNA) biosensor to detect specific target sequences. The biosensor was constructed using a modified nanocomposite consisting of three-dimensional (3D) nitrogen-doped graphene (NG) and Fe3O4 nanoparticles. These 3D NG-Fe3O4 nanoparticles formed a unique sensing film with strong synergistic effects; the highly porous 3D NG provided a large surface area, whereas Fe3O4 was uniformly deposited on the 3D graphene hydrogel (GH), facilitating electron transfer for sensitive detection of DNA with excellent selectivity, fast responses, and a low detection limit. Immobilization of the probe ssDNA sequences on the electrode was greatly improved owing to the unique synergistic effects of 3D NG and Fe3O4. Differential pulse voltammetry (DPV) was used to survey the DNA hybridization event with methylene blue (MB) as an electrochemical indicator. Under optimal conditions, the proposed biosensor could detect target DNA concentrations down to 3.63 × 10−15 M (signal/noise ratio of 3) with a linear range from 1.0 × 10−14 to 1.0 × 10−6 M, showing high sensitivity. The detection capability of this DNA biosensor in complicated serum samples was also studied. Thus, our biosensor presented a sensitive, simple, and rapid platform for DNA detection and may provide a powerful and versatile tool for medical diagnosis of genetic diseases and mutations.

The rationally designed sensor architecture is very important to improve the sensitivity and selectivity for H2O2 enzyme-free electrochemical sensor. In this work, a sensitive H2O2 biosensor was fabricated by electrochemical deposition of Au-Pt bimetallic nanoparticles (NPs) on molybdenum disulfide nanoflowers (MoS2 NFs). Au-Pt NPs was dispersed or stabilized by the effective support matrix of MoS2 nanosheets, which was effectively enhance the conductivity, catalytic performance and long-term stability. The experimental results show that MoS2-Au/Pt nanocomposites exhibit excellent catalytic activity for specific detection of H2O2, and electrochemical measurement results show that the enzyme-free electrochemical sensor has large linear range of 10 μM to 19.07 mM with high sensitivity of 142.68 μA mM−1 cm−2. This novel sensor produced satisfactory reproducibility and stability, and exhibited superior potential for the practical quantitative analysis of H2O2 in serum samples.

•A 3 × 3 colorimetric sensor array was constructed based on indicator displacement assays;.•The sensor can be used to discriminate Chinese teas of different categories, quality grades, and geographical origins.•HCA and PCA analysis confirmed the good performance of the presented sensor array for tea discrimination.An efficient liquid sensor array was presented for tea differentiation through analysis of amino acid composition based on indicator displacement assays (IDA). After construction and deduction upon response to theanine and six other amino acids abundant in tea leaves, the sensor is capable of distinguishing 70 tea samples within four categories. Statistical analysis including Hierarchy Cluster Analysis (HCA) and Principal Component Analysis (PCA) suggested that successful discrimination of teas depended not only on overall amino acid concentration but also composition of related amino acid. The PCA results even indicated a negative correlation between the loading value in the first principal component and the amino acid content in tea leaves. Besides, differentiation of tea samples of the same category with different quality grades and geographical origins was also realized, demonstrating the versatility of the presented sensor array. Our study offered an alternative method to construct colorimetric sensor for cost-effective surveillance and control of tea related products.Download high-res image (128KB)Download full-size image

Natural polyphenols are important antioxidants closely associated with the health benefits of consuming plant-derived beverages. Herein, we report a simple yet sensitive multilayer sensor based on the colorimetric odor reaction between polyphenols and Fe3+. The sensor was fabricated by alternative assembly of a chitosan layer, Fe3+ complexes and an alginate sodium layer on filter paper modified with a TiO2 membrane. After five times repeated assembly, the resultant sensor achieved good super-hydrophobicity, and together with the specific affinity of chitosan, polyphenols in aqueous samples can be pre-concentrated on the surface of the sensor, leading to improvement of the sensor sensitivity. The detection limits for model polyphenols gallic acid and tannic acid were 1.2 μM and 0.2 μM with a wide linear range between 2 μM and 6.1 mM, and between 2.3 μM and 5.2 μM, respectively. The colorimetric multilayer sensor was further applied to discriminate plant-derived drinks including 5 red wine samples and Chinese green tea samples. Statistical analysis including HCA and LDA showed that it realized successful discrimination within five closely similar red wines and five Chinese green teas of different quality grades. The sensor presented here can serve as a cheap, convenient and simple “electronic tongue” for real-time discrimination of plant-derived drinks of different brands and/or quality grades.

The monitoring of folate receptor levels in living cancer cells has attracted increasing interest; however, the present fluorescent probes used often suffer from interference from nonspecific adsorption on the surface of non-target cells. In the present study, the probe is readily prepared by using folic acid as a template molecule, a mesoporous silica nanoparticle as an imprinting material, and a CdTe quantum dot as a signal transducer for the recognition of folate receptors. This system is expected to offer specific recognition of folate receptors over other substances based on the high affinity of folic acid and folate receptors. The probe is stable and monodispersed in an aqueous suspension, and has little toxicity to living cells and thus can be utilized for targeted A549 cell imaging. The living cell imaging experiments further demonstrate its value in bioimaging cell-surface folate receptors by virtue of its superior biocompatibility, lower cytotoxicity and membrane permeability.

There is an obvious pressing need for the rapid, sensitive and highly portable identification of toxic gases. In this study, a battery-operated, low-cost and portable embedded gas detection device is fabricated with ARM9 S3C2440A core as the main application processor. And a quite simple and effective cross-responsive sensor array is utilized here for toxic gases detection based on cross-reactive recognition mechanism. This device shows how the discriminatory capacity of sensor arrays utilizing pattern recognition operating in environments. It collects images of chemical sensors before and after exposing to the target gas, and then processes those images to extract the unique characteristic for each gas. The gas chamber model was optimized by simulating with FLUENT software, to ensure a sufficiently reaction between toxic gases and cross-responsive sensor arrays. Then five toxic gases were detected by the proposed device and experiments showed the validity of the system for the qualitative and quantitative identification of toxic gases. It has shown successful classification of the five toxic gases by HCA and PCA analysis at ppb level. Importantly, this developed equipment provides a potential method for the qualitative and quantitative identification of toxic gases.

Artificial tongue systems are multisensory devices which are highly desirable for the analysis and recognition of complicated composition samples. Herein, a low-cost and simple colorimetric sensor array for identification and quantification of proteins were reported. Using prophyrin, porphyrin derivatives (mainly metalloporphyrins) and chemically responsive dyes as the sensing elements, the developed sensor array of artificial tongue showed a unique pattern of colorific change upon its exposure to proteins. The composite pattern for each sample was subjected to principal component analysis (PCA), thus providing a clustering map for more practical visualization. All the pure and mixed proteins, as well as denatured proteins, gave distinct patterns, thus resulting in their unambiguous identification. The PCA analysis also suggested that the unique pattern of colorific change may be due to the change of protein conformation and local environmental pH. These results demonstrate that the developed colorimetric artificial tongue system is an excellent sensing platform for identification and quantitative analysis of protein samples.

In this study, a practicable method for the detection of Riemerella anatipestifer (R. anatipestifer) using biosensor based on imaging ellipsometry (BIE) is described. The method is performed by immobilizing anti-R. anatipestifer egg yolk immunoglubilin (IgY) onto modified chemistry surface to form sensing layer. Antigen captured by sensing layer can then be quantitatively measured through imaging ellipsometry in grayscale format. The results demonstrate that it can detect R. anatipestifer as low as 5.2 × 103 CFU/mL. Furthermore, the proposed method can realize specific discrimination for multiple serotypes of 1, 2, 4, and 14 of R. anatipestifer. It has the advantages of rapid, simple, high sensitivity and low cost.Highlights► Biosensor based on imaging ellipsometry is utilized to detect Riemerella anatipestifer. ► The strategy of direct detection without labeling is adopted. ► The proposed method can detect R. anatipestifer as low as 5.2 × 103 CFU/mL. ► It also realized specific discrimination 1, 2, 4 and 14 serotypes in single experiment. ► But, the detection time is only 20 min required.

The molecular interactions of monosulfonate tetraphenylporphyrin (TPPS1) and meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) with dimethyl methylphosphonate (DMMP) have been investigated by UV–vis and fluorescence spectroscopies. The association constants and interaction stoichiometries of the bindings were obtained through Benesi–Hildebrand (B–H) method. Particularly, both linear and nonlinear fitting procedures were performed to evaluate the possible 1:2 interactions. Experimental results showed that hydrogen-bonding interactions existed in both of the two systems, resulting in regular changes in the absorbance and fluorescence characteristics of the porphyrins. The association constants and stoichiometries determined from absorbance and fluorescence studies were in excellent agreement. Using a nonlinear fitting method, we demonstrated that the one-step 1:2 interaction took place in the TPPS1–DMMP system, and the association constants were determined to be 71.4 M−1 by absorbance measurements and 70.92 M−1 by fluorescence measurements. The interaction stoichiometry of the TPPS–DMMP system was 1:1, and the association constants were determined to be 16.06 M−1 by absorbance measurements and 16.03 M−1 by fluorescence measurements. It was concluded that the interaction between TPPS1 and DMMP was stronger than that between TPPS and DMMP.

The monitoring of folate receptor levels in living cancer cells has attracted increasing interest; however, the present fluorescent probes used often suffer from interference from nonspecific adsorption on the surface of non-target cells. In the present study, the probe is readily prepared by using folic acid as a template molecule, a mesoporous silica nanoparticle as an imprinting material, and a CdTe quantum dot as a signal transducer for the recognition of folate receptors. This system is expected to offer specific recognition of folate receptors over other substances based on the high affinity of folic acid and folate receptors. The probe is stable and monodispersed in an aqueous suspension, and has little toxicity to living cells and thus can be utilized for targeted A549 cell imaging. The living cell imaging experiments further demonstrate its value in bioimaging cell-surface folate receptors by virtue of its superior biocompatibility, lower cytotoxicity and membrane permeability.