Label-Free Neuropeptide Detection beyond the Debye Length Limit

Abstract

Biosensors with high selectivity, high sensitivity, and real-time detection capabilities are of significant interest for diagnostic applications as well as human health and performance monitoring. Graphene field-effect transistor (GFET) based biosensors are suitable for integration into wearable sensor technology and can potentially demonstrate the sensitivity and selectivity necessary for real-time detection and monitoring of biomarkers. Previously reported DC-mode GFET biosensors showed a high sensitivity for sensing biomarkers in solutions with a low salt concentration. However, due to Debye length screening, the sensitivity of the DC-mode GFET biosensors decreases significantly during operation in a physiological fluid such as sweat or interstitial fluid. To overcome the Debye screening length limitation, we report here alternating current (AC) mode heterodyne-based GFET biosensors for sensing neuropeptide-Y (NPY), a key stress biomarker, in artificial sweat at physiologically relevant ionic concentrations. Our ACmode GFET biosensors show a record ultralow detection limit of 2 × 10 −18 M with an extensive dynamic range of 10 orders of magnitude in sensor response to target NPY concentration. The sensors were characterized for various carrier frequencies (ranging from 30 kHz to 2 MHz) of the applied AC voltages and various salt concentrations (10, 50, and 100 mM). Contrary to DC-mode sensing, the AC-mode sensor response increases with an increase in salt concentration in the electrolyte. The sensor response can be further enhanced by tuning the carrier frequency of the applied AC voltage. The optimum response frequency of our sensor is approximately 400−600 kHz for salt concentrations of 50 and 100 mM, respectively. The saltconcentration-and frequency-dependent sensor response can be explained by an electrolyte-gated capacitance model.

Deterministic Single-Row-Droplet Catalyst Formation for Uniform Growth Integration of High-Density Silicon Nanowires

“…For comparison, the FET fabricated by random SiNW arrays (black curve in Figure 5g) showed only an I on/off ratio >10 5 and high SS of 396 mV dec −1 . Since the off current and SS performances of the FET device are highly dependent on the diameter of the SiNW channel, considering the influence of Debye screening on the control of mobile charge carrier in the semiconductor channel, 48,49 the current in the thin channel is easier to close than that in the large and random channel diameter. This can also be experimentally demonstrated by the performances of FET device fabricated by using thicker SiNW arrays with diameter of ∼45 nm and ∼100 nm in Figure S5, with I on/off ratio >10 5 and high SS of 320 mV dec −1 .…”