(698b) Role of Interfacial Charge Concentration on Biosensing By Electrolyte Gated Transistors 

Electrolyte gated transistors (EGTs) have been identified as promising transducers for biosensing applications due to fast and sensitive signal transduction, low voltage operation, and facile fabrication. A floating gate EGT (FGT) is a derivative of this device utilizing a floating gate to physically separate and electronically couple the active sensing area with the transistor. This eliminates the degradation and optimization issues associated with interactions of the semiconductor or the dielectric with the analyte medium, typically seen in traditional transistor based detection systems. Previous work has demonstrated the utility of FGTs for the fast and reliable detection of ssDNA and ricin in media such as orange juice, milk and aqueous buffer.

While the FGT strategy has yielded promising results, questions remain regarding its fundamental operating mechanism for detecting biomolecules. In this work, we implement well-established self-assembled monolayer (SAM) chemistry on the sensing area to create a charged surface and hence characterize the role that interfacial charge concentration plays in relation to potentiometric changes. Carboxylic acid terminated SAMs were exposed to buffers of different pH and the response of the device was studied. The results agree with theoretical predictions from Grahame’s equation from conventional double layer theory, thereby rationalizing the nonlinear responses obtained at high analyte concentrations in previous work with this platform. Our study further elucidates an important effect in the sensing mechanism of floating gate EGTs, which are seen as portable, low cost biosensors that could perform well in distributed systems, bringing the sensitivity and functionality of conventional biodetection methods to field applications.