Development of an electrochemical immunoassay for detection of gatifloxacin in swine urine

To detect gatifloxacin （GAT） residue in swine urine, an electrochemical immunoassay was established, An indirect competitive immunoassay was developed, in which the coating antigen is immobilized in an enzyme-linked immunosorbent assay （ELISA） plate and GAT residue from the sample competes with the limited binding sites in added anti-GAT antibody. Horseradish peroxidase （HRP） conjugated to goat anti-rabbit IgG was used as the enzymatic label. A carbon fiber working electrode was constructed and current signals were detected by using hydrogen peroxide as a substrate and hydroquinone as an electrochemical mediator. The electrochemical immunoassay was evaluated by analysis of GAT in buffer or swine urine and an average value of half inhibition concentration （IC50） of 8.9 ng/ml was obtained. Excellent specificity of the antibody was achieved with little cross-reaction with Iomefloxacin （3.0%）, ciprofloxacin （3.0%）, and ofloxacin （1.9%） among commonly used （fluoro）quinolones. In conclusion, the im- munoassay system developed in this research can be used as a rapid, powerful and on-site analytical tool to detect GAT residue in foods and food products.

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/Ghi） 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/Ghi electrode had the best performance according to its low peak potential and large peak current. Amperometdc 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.

Electrochemical detection of human ferritin based on gold nanorod reporter probe and cotton thread immunoassay device

In this study,a natural cotton thread immunoassay device combined with gold nanorod（GNR） reporter probe is developed for the rapid,sensitive and quantitative electrochemical determination of human ferritin,a lung cancer related biomarker.Human ferritin as an analyte and a pair of monoclonal antibodies are used to demonstrate the proof-of-concept on the cotton thread immunoassay device.An enhancement of the sensitivity is achieved by using gold nanorod as an electroactive report probe compared with a traditional gold nanoparticle（GNP） report probe.The device was capable of measuring 1.58 ng/mL ferritin in 30 min by anodic stripping voltammetry（ASV） testing,which meet the requirement for clinical diagnosis.

High-density single antibody electrochemical nanoarrays

The fabrication and electrochemical interrogation of very high density single-antibody nanoarrays is reported.Gold nanodots,15 nm in diameter,arranged in large(cm2)square arrays with a pitch of 200 nm,are used as carriers for primary antibodies(immunoglobulin G(IgG)),further recognized by secondary redox-labeled detection antibodies.Ensemble scale interrogation of the antibody array by cyclic voltammetry,and nanoscale interrogation of individual nanodots by mediator tethered atomic forcescanning electrochemical microscopy(Mt/AFM-SECM),enable the occupancy of nanodots by single antibody molecules to be demonstrated.Experiments involving the competitive adsorption of antibodies of different species onto the nanodots evidence the possibility of using single-antibody nanoarrays for digital electrochemical immunoassays.