In this study, we examined the in vitro electrochemical detection of Vascular Endothelial Growth Factor (VEGF) as cancer biomarker using p-type field-effect transistor (FET) biosensor. We demonstrated the high-performance FET sensor, which could detect ca. 400 fM of VEGF concentration, based on anti-VEGF RNA aptamer conjugated carboxylated polypyrrole nanotubes (CPNTs). The CPNTs used as high-performance transducers of this FET system were successfully fabricated by cylindrical micelle templates in a water-in-oil emulsion system. The functional carboxyl group (-COOH) was effectively incorporated into the polymer backbone during the polymerization by using pyrrole-3-carboxylic acid (P3CA) as a co-monomer. Two types of CPNTs (CPNT1: ca. 200 nm in diameter, CPNT2: ca. 120 nm in diameter) demonstrated the excellent conductivity performance in this FET system. Based on CPNTs conjugated with anti-VEGF RNA aptamer (CPNTs-aptamer), VEGF (target molecule) acts as the gate dielectrics of p-type FET sensor and specifically interacts with anti-VEGF aptamer attached to CPNT surfaces. Importantly, the VEGF detection limit of the FET sensor based on CPNT2-aptamer was found to be near 400 fM in real-time. Moreover, the CPNTs-aptamer FET sensors can be repeatedly used for various concentrations of the target molecule (VEGFs) through the washing and rinsing processes.
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