Ultrasensitive electrochemical immunoassay based on graphene oxide-Ag composites for rapid determination of clenbuterol.

We report the development of an ultrasensitive amperometric biosensor based on Ag nanoparticles-decorated graphene oxide nanosheets (GO) (Ag-GO) for the rapid detection of clenbuterol (CLB). The morphology and structure of the Ag-GO labeled CLB (Ag-GO-CLB) were characterized by transmission electron microscope (TEM), atomic force microscope (AFM), and ultraviolet-visible spectroscope (UV-vis). The immunosensor was prepared by covalently immobilizing capture antibodies on a multi-walled carbon nanotubes-modified glassy carbon electrode. Through competitive immunoreactions, the Ag-GO-CLB nanocomposites were captured on the immunosensor and the silver was measured by positive differential pulse voltammetry (DPV) in KCl solution for the detection of antigen. The experimental results show a linear response over the range from 0.01 to 10.0 ng mL(-1) with a lower detection limit of 6.8 pg mL(-1) (signal-to-noise ratio of 3). The Ag-GO based immunosensor offers a simple and convenient route for metal-immunoassay labels, which can avoid the complicated and time-consuming dissolving of metal component for ultrasensitive determination. Moreover, the electrochemical immunoassay shows acceptable specificity and stability and is suitable for the determination of CLB in real samples.

Label-free immunoassay for chloramphenicol based on hollow gold nanospheres/chitosan composite.

A novel label-free electrochemical immunosensor for rapid determination of chloramphenicol (CAP) was fabricated by entrapping monoclonal antibody to chloramphenicol (anti-CAP) in hollow gold nanospheres (HGNs)/chitosan composite modified on a glassy carbon electrode. The hollow gold nanospheres (HGNs) were prepared by using Co nanoparticles as sacrificial templates and characterized by transmission electron microscopy (TEM). The changes of the electrode behavior after each fabrication step were investigated by electrochemical impedance spectroscopy (EIS) technique. Under optimal conditions, the proposed immunosensor has a sensitive response to CAP in a linear range of 0.1-1000 ng mL(-1) with the detection limit of 0.06 ng mL(-1). Accurate detection of CAP in real meat samples was demonstrated by comparison with conventional HPLC method. The proposed method was proven to be a feasible quantitative method for CAP analysis with the properties of simple preparation, stability, high sensitivity and selectivity.

A monoclonal antibody-based immunosensor for detection of Sudan I using electrochemical impedance spectroscopy.

Sudan I monoclonal antibodies (Mabs) were prepared by hybridoma technique and firstly used to develop a Sudan I immunosensor by immobilizing the Mabs on a gold electrode. o-Mercaptobenzoic acid (MBA) was covalently conjugated on the gold electrode to form a self-assembled monolayer (SAM). The immobilization of Sudan I Mabs to the SAM 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 SAM. The changes of the electrode behavior after each assembly step were investigated by cyclic voltammetric (CV) technique. The Sudan I concentration was measured through the increase of impedance values in the corresponding specific binding of Sudan I and Sudan I antibody. A linear relationship between the increased electron-transfer resistance (Ret) and the logarithmic value of Sudan I concentrations was found in the range of 0.05-50 ng mL(-1) with the detection limit of 0.03 ng mL(-1). Using hot chili as a model sample, acceptable recovery of 96.5-107.3% was obtained. The results were validated by conventional HPLC method with good correlation. The proposed method was proven to be a feasible quantitative method for Sudan I analysis with the properties of stability, highly sensitivity and selectivity.

Ultrasound-radiated synthesis of PAMAM-Au nanocomposites and its application on glucose biosensor.

Hybrid nanocomposites of carboxyl-terminated generation 4 (G 4) poly(amidoamine) dendrimers (PAMAM) with gold nanoparticles (AuNPs) encapsulated inside them were synthesized under ultrasound irradiation. The obtained nanocomposites were used to fabricate highly sensitive amperometric glucose biosensor which exhibited a high and reproducible sensitivity of 2.9 mA/mM/cm(2), response time less than 5 s, linear dynamic range from 0.1 to 15.8 microM, correlation coefficient of R(2)=0.9988, and limit of detection (LOD), based on S/N ratio (S/N=3) of 0.05 microM. A value of 2.7 mM for the apparent Michaelis-Menten constant K(M)(app) was obtained. The high sensitivity, wider linear range, good reproducibility and stability make this biosensor a promising candidate for portable amperometric glucose biosensor.