Open Sandwich-Based Immuno-Transistor for Label-Free and Noncompetitive Detection of Low Molecular Weight Antigen

In this study, we proposed a new detection method, open sandwich-based immuno-field effect transistor (OS-FET) for label-free and noncompetitive detection of low molecular weight antigen. The principle of OS-FET is based on the detection of intrinsic molecular charges caused by the small antigen-dependent interchain interaction of separated V(L) and V(H) chains from a single antibody variable region using the field effect. Introducing V(H) chain and small antigen bisphenol A into the OS-FET with the immobilized V(L) chain on the gate, we could detect electrically and directly the binding of bisphenol A by V(H) and V(L) chains. Although the detection limit of OS-FET was 1 nM to detect bisphenol A for the standard deviation of control signal, the addition of isothiocyanobenzyl-EDTA with negative charges to the V(L) chain enhanced the detection limit to 1 pM. We could directly transduce the charge density changes based on the capture of target on the gate into the electrical signals using the OS-FET. The platform based on the FETs is suitable for a label-free, noncompetitive, and quantitative detection system for small antigen analysis in environmental, food, and clinical research.