Optimization of SWCNT-FET Biosensors by Aptamer Engineering and Toehold-Mediated Strand Displacement

Aptamer-based single-walled carbon nanotube (SWCNT) field-effect transistor (FET) biosensors provide a compact, label-free, and sensitive platform for real-time biomarker detection. To enhance device performance, we employed a truncated DNA aptamer (CSS.3_cut3) with improved conformational switching upon cortisol binding, boosting the sensitivity of SWCNT-FET biosensors. We further optimized the functionalization using a toehold-mediated strand displacement (TMSD) strategy to dynamically integrate the aptamer onto SWCNTs in solution, simplifying the fabrication process and increasing the sensitivity. Interestingly, introducing a partially complementary protection strand during TMSD assembly resulted in bistable, two-level signal outputs upon cortisol sensing, contrasting with the gradual response of unprotected sensors. This effect likely stems from the competition between aptamer-target binding and residual hybridization, modulating signal dynamics via tuneable electrostatic gating. These results underscore the promise of aptamer engineering and DNA nanotechnology for developing high-performance biosensors with programmable behavior, offering new avenues for real-time sensing, dynamic molecular recognition, and integrated diagnostic technologies.