Numerical Analysis and Simulation of Fluidics in Nanogap-Embedded Separated Double-Gate Field Effect Transistor for Biosensor

Abstract

For detection of diverse biomolecules, researchers have developed a wide variety of biosensors, using, for example, fluorescent imaging (Oh et al., 2005), piezoelectric properties (Yang et al., 2006), nano-mechanical properties (Fritz et al., 2000), electrochemical properties (Drummond et al., 2003), conducting properties (Reed et al., 1997; Cui et al., 2001; Patolsky et al., 2007), and so on. Although some of these techniques show ultra-high sensitivity, they require labelling processes for analytes or bulky and expensive equipment for measurement. Label-free detection without necessity of an external apparatus is important in point-of-care testing (POCT) devices (Kost et al., 1999; St-Louis 2000; Tierney et al., 2000), which enable fast and easy on-site detection of biomolecules for health monitoring. In terms of integration with peripheral CMOS circuitry for realizing a more affordable POCT system, biosensors based on a field-effect transistor (FET) scheme have notable advantages (Schoning & Poghossian, 2002). Hence, FET-based biosensors have been actively studied (Begveld, 2003; Schoning & Poghossian, 2002) since the first report of an ionsensitive solid-state device (Begveld, 1970). In most FET-based biosensor devices (Schoning & Poghossian, 2002; Kim et al., 2006; Sakata et al., 2007), variation of threshold voltage on a scale of tens of mV was obtained in the detection of biomolecules, and the fabrication process was not fully compatible with conventional CMOS technology. Recently, our group reported a new concept for a FET-based biosensor utilizing dielectric constant change inside nanogaps embedded in a FET device (Im, H. et al., 2007). In our previous work (Im et al., 2011), we successfully detected the antigen and antibody of avian influenza (AI), which can cause human fatality. Avian influenza antigen (AIa) and antibody (anti-AI) showed a large degree of signal change (i.e. a high signal-to-noise ratio) with a fabricated nanogap-embedded separated double-gate field effect transistor (hereafter referred to as “nanogap-DGFET”), shown in Fig. 1 (Im et al., 2011). Fig. 2 shows scanning