In situ electrochemical enzyme immunoassay on a microchip with surface-functionalized poly(dimethylsiloxane) channel

This paper reports a rapid microchip-based electrochemical enzyme immunoassay with surface-functionalized poly(dimethylsiloxane) (PDMS) channel. The microchip fabricated on a glass substrate by photolithography consists of a three-electrode system for electrochemical detection and is assembled with the antibody-immobilized PDMS channel by plasma treatment. For effective immobilization of target antibodies, the internal surface of the PDMS channel is chemically modified into the silane monolayer containing poly(ethyleneglycol) (PEG) groups, which minimize non-specific binding. Due to low height (50 μm) of the channel dimensions, the microchip provides a rapid immunoassay by reducing the mass transfer resistance between electrodes and immobilized antibodies, and it takes about 8 min for total analysis time including sampling, reaction and washing step. In this study, sandwich immunoassays for mouse IgG are performed as a model system and result in a low detection limit of 485 pg mL−1 with 95% confidence level. All immunoassay procedures for liquid handling such as sampling, reaction and washing are carried out using conventional syringe pumps, preserving an internal channel volume of 0.7 μL constant. Such an on-chip integration of immunological and enzymatic reactions, amperometric detection, and microchip operations allows performing immunoassays more rapidly, easily, and economically.