Figure 2. Adsorption of human IgG onto MoS₂ sensor surface.

(a) 3D AFM topography of multi-layer MoS₂ with thickness of ~80 nm. (b) Transfer characteristics under various concentration of the human IgG from 0 to 100 μg/mL at V_ds = 1 V. (c) Plots of off-current versus human IgG concentration show an increase of off-current with increasing concentration of the human-IgG and abrupt increase of off-current at specific concentration of 10 fg/mL for V_gs = −20 V and V_ds = 1 V. Arrows indicate appropriate axis (red: log-scale, blue: linear-scale). (d), (e) Output characteristics under human IgG conditions of 0 and 100 μg/mL from V_gs = −32 V to V_gs = 0 V in steps of 8 V, respectively. Following adsorption of human IgG on MoS₂ surface, the drain current exhibits 6-fold increase at a high drain voltage and saturation currents disappear due to the immobile charge of human IgG on the MoS₂ nanosheet.