An anti-passivation ink for the preparation of electrodes for use in electrochemical immunoassays.

p-Nitrophenylphosphate (PNPP) is usually employed as the substrate for enzyme-linked immunosorbent assays. p-Nitrophenol (PNP), the product of PNPP, with the catalyst alkaline phosphatase (ALP), will passivate an electrode, which limits applications in electrochemical analysis. A novel anti-passivation ink used in the preparation of a graphene/ionic liquid/chitosan composited (rGO/IL/Chi) electrode is proposed to solve the problem. The anti-passivation electrode was fabricated by directly writing the graphene-ionic liquid-chitosan composite on a single-side conductive gold strip. A glassy carbon electrode, a screen-printed electrode, and a graphene-chitosan composite-modified screen-printed electrode were investigated for comparison. Scanning electron microscopy was used to characterize the surface structure of the four different electrodes and cyclic voltammetry was carried out to compare their performance. The results showed that the rGO/IL/Chi electrode had the best performance according to its low peak potential and large peak current. Amperometric responses of the different electrodes to PNP proved that only the rGO/IL/Chi electrode was capable of anti-passivation. The detection of cardiac troponin I was used as a test example for electrochemical immunoassay. Differential pulse voltammetry was performed to detect cardiac troponin I and obtain a calibration curve. The limit of detection was 0.05 ng/ml.

[Rapid detection of Escherichia coli O157 : H7 using surface plasmon resonance (SPR) biosensor].

A biosensor based on surface plasmon resonance (SPR) was developed for rapid detection of Escherichia coli O157 : H7. BIACORE 3000 SPR instrument and a dextran-modified sensor chip (CM5) were used. After activation with EDC/NHS, anti-E. coli O157 : H7 antibody was immobilized on the gold surface of the SPR sensor, and then following ethanolamine was injected, and the chip was ready for E. coli O157 : H7. Regeneration was achieved using NaOH in order to detect several samples. The limit of detection was found to be 3 x 10(5) CFU x mL(-1) for E. coli O157 : H7, and the change of RU was linearly correlated with the concentration of E. coli O157 : H7 cells (R2 = 0.99). The detection time ranged from 5 to 7 min, and the result of regeneration was effective which allowed the chip to be reused for more than 50 samples. This method is convenient, and stable, and shows potentials for applications in food areas.

[Application of near-infrared spectroscopy to detection of pesticide phoxim residues].

Near-infrared (NIR) spectroscopy technique was applied directly to the detection of pesticide phoxim residues. A sample pretreatment method was introduced. Samples were mixed with silica gel. Silica gel as a sorbent was employed to extract and enrich the low-concentration samples. Subsequently, diffuse reflection spectrum was measured on silica gel. Calibration models were developed using partial least square regression (PLSR) algorithm. Leave-one-out cross-validation was used to evaluate and compare the models. Two experiments were carried out, and the results show that 21 samples with the concentration gradient of 0.5 mg x L(-1) exhibited a high correlation coefficient of cross-validation of 0. 958, and a root mean square error of cross validation (RMSECV) of 0.872 mg x L(-1), while 41 samples with the concentration gradient of 0.25 mg x L(-1) gave a correlation coefficient of cross-validation of 0.924 and RMSECV of 1.15 mg x L(-1). It is indicated that with the reduction in concentration gradient, the prediction capacity of models dropped, but there still existed a high correlation coefficient with the concentration of phoxim in the samples. The experiments proved that the sample pretreatment method with the introduction of silica gel as an absorber to enrich low concentration analyte was effective. The method was able to lower the detection limit of NIR. The developed technique has a potential application in low-concentration sample detection by NIR spectroscopy, such as pesticide residues.

[Application of immunomagnetic separation to E. coli O157 : H7 detection].

In the present paper, the capture efficiencies of four different proportions of E. coli O157 : H7 and immunomagnetic beads (IMB) (1 : 6.34, 1 : 12.69, 1 : 25.38 and 1 : 30.07) and three different proportions of E. coli O157 : H7 and Bacillus subtilis (0.3 mL : 0.1 mL, 0.2 mL : 0.2 mL and 0.1 mL : 0.3 mL) were compared, with the total volume and capacity of IMB remaining constant. It was revealed that the capture efficiency could reach 100% when the proportion of E. coli O157 : H7 and IMB was 1 : 30, meaning that almost all targets E. coli O157 : H7 could be captured at 1 : 30, and that the capture efficiency decreased and then increased with the number of Bacillus subtilis increasing. Moreover, the combination of ATP bioluminescence and IMS was correlated well with conventional culture methods, R2 = 0.9882, and the detection limit was as low as 10(2) CFU x mL(-1).

[Studies on detection of E. coli O157:H7 by ATP bioluminescence].

In the present paper, a quantitative linear model betweena series of concentrations of E. coliO157 : H7 and counts by BPCL ultra weak luminescence analyzer was built up. And the influences of four different buffers with the same pH (pH = 7.4), Tris-HCl, PBS, KH2PO4-NaOH and Na2 HPO4-C6H8O7, and five different chemical substances with the same mass concentration (10 g x L), NaCl, KCl, NaOH, MgCl2 and NaH2PO4 on ATP bioluminescence were compared. The results showed that Tris-HCl was a suitable buffer for dilution, since it could distinguish well between different concentrations and had the lowest background signals. And MgCl2 could intensify luminescence distinctly, while the other four chemical substances decreased luminescence, of which NaOH decreased luminescence most obviously. Moreover, ATP bioluminescence was correlated well with conventional culture methods (r = 0.96), and the detection limit was 10(3) cells x mL(-1).