Figure 1. smFET device characteristics.

(a) To-scale illustration of the smFET device structure. An amine-modified oligonucleotide probe is covalently coupled to a single defect site, generated on a single-walled carbon nanotube (SWCNT) sidewall via diazonium chemistry. The CNT acts as the channel of a field-effect transistor, transducing biomolecular charge into a conductance change in the smFET. Binding and melting reactions of a complementary oligonucleotide generate random telegraph signals (RTSs, shown in inset), which correspond to hybridization and melting events. Experiments are performed at a constant source–drain bias (V_s) of 100 mV, while the electrolytic gate bias is modulated by an on-chip pseudo-reference electrode. (b) Representative transfer (I–V) characteristics of four CNT devices before and after point functionalization and DNA attachment. V_g is the bias on the platinum pseudo-reference electrode relative to the device. V_g is varied from −1.5 V to +1.5 V (in acetonitrile solution supported by 0.1 M tetrabutylamonium hexafluorophosphate). (c) The power spectral densities (PSDs) of the devices from b showing a strong flicker (1/f) noise component before (black line) and after (red line) modification. While the newly formed defect dominates transfer characteristics, the CNT sidewall becomes less sensitive to charge traps, leading to lower flicker noise.