Toshihiko Yoshioka

Quantitative and Single-step Enzyme Immunosensing Based on an Electrochemical Detection Coupled with Lateral-flow System

A single-step electrochemical immunochromatography has been developed: the device was based on two pieces of nitrocellulose membrane, a sample pad with anti-mouse IgG antibody labeled with glucose oxidase (GOx-labeled antibody), a conjugate pad with glucose, and a Pt working electrode. Either antibody or antigen was immobilized on the membrane. The addition of a solution containing mouse IgG, a model target, allows for the dissolution of GOx-labeled antibody in the sample pad to form an immunocomplex. The produced immunocomplex was automatically separated by capturing to the antibody immobilized on the membrane with the sandwich structure or by passing through the membrane modified with an antigen for the competitive reaction. The separated GOx label arrived at the conjugate pad with glucose to undergo the enzyme reaction. Hydrogen peroxide generated by this reaction was detected at the Pt electrode prepared on the second nitrocellulose membrane downstream from the conjugate pad. The results demonstrated that the designed immunochromatography can be applied to quantitative detection with a single-step procedure, because both the GOx-labeled antibody for revealing the immunoreactions and the substrate for the enzyme reaction were prepared in the device. Moreover, the initial concentration of the GOx-labeled antibody permitted control of the detectable concentration for mouse IgG.

Improvement of Electrochemical Response of Cocaine Sensors Based on DNA Aptamer by Heat Treatment

We report on a biosensor for cocaine based on the conformation change of DNA aptamer by capturing the cocaine molecules. The oxidation current of ferrocene conjugated on the terminal end of aptamer immobilized on an Au electrode increased with increasing cocaine concentration. The sensor response has been improved by a simple heat treatment after immobilization, since the aggregates of DNA aptamer generated during the immobilization step could be dissociated and rearranged on the electrode.