(292c) Mechanistic Optimization of Floating Gate Transistors for Biosensing Applications

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

The detection mechanism of FGTs has been attributed previously to surface charge and capacitance changes at the sensing surface. In this work, we demonstrate charge vs. capacitance based optimization of the sensing pad to provide maximum sensitivity for different types of targets. Self-assembled monolayers of MUA and alkanethiols were utilized to systematically alter the charge state and capacitance of the sensing surface, and the results obtained allowed us to optimize the sensing area with regard to both the charge and size of target molecules. We further optimized the microfluidic channels used for target delivery in terms of height and aspect ratio to increase target molecule flux at the surface and enhance detection times for the device. Our study provides general conclusions regarding testing protocols, sensing areas, and target delivery methods that are applicable to a wide range of transistor based biosensors, which are a promising class of sensing devices for food safety and point of care diagnostics.