(163h) Sensing Mechanisms of Floating Gate Transistors

Transistors have been utilized extensively for biodetection due to their fast and sensitive signal transduction. The Electrolyte-Gated Transistor (EGT) is a variant of the field effect transistor where the conventional gate dielectric is replaced with an electrolyte. The EGT is especially attractive for biosensing applications because it offers the added advantage of low voltage operation, and can be fabricated using fast and potentially inexpensive manufacturing techniques such as printing. The Floating Gate Electrolyte-Gated Transistor (FG-EGT, or FGT) incorporates a floating gate that physically separates and electronically couples the active sensing area with the transistor. This design eliminates degradation and optimization issues associated with interactions of the semiconductor/dielectric with the analyte medium, and allows for an independent choice of electronic materials and capture chemistry. The floating gate therefore allows this device to overcome many drawbacks of traditional transistor-based sensors that directly utilize the semiconductor or dielectric surface for molecular capture. Previous work has shown the utility of FGTs for the fast and reliable detection of ssDNA in buffers, ricin in potable liquids, and gluten from different grain sources.

In this work, self-assembled monolayers of MUA and alkanethiols were utilized to systematically alter the charge state and capacitance of the sensing surface, demonstrating the ability of the device to detect changes in both interfacial charge and capacitance. Further, a simple inverter amplification circuit was used to obtain higher signals from the device when compared to previous work using transfer curves. By varying the sensing area along during these experiments, we were able to deduce an optimum area that maximizes the signal obtained from the device. This enables us to identify the best device architectures for the detection of charge-based and capacitance-based signals. The capacitance values obtained from our experiments are compared to literature and cyclic voltammetry for further confirmation of our findings. Our study provides general conclusions regarding testing protocols and sensing areas that are applicable to a range of transistor-based biosensors, which are a promising class of sensing devices for food safety and point-of-care diagnostics.