Figure 2. Calibration of nanosensor response to recombinant protein.

(a) Concentration-response curve for RAP1 protein shows two regimes of response. Above 0.15 μg/mL RAP1, a bulk sensor response starts being observed for the integrated sensor response for all sensors in the field of view (red), whereas below 0.15 μg/mL RAP1, individual sensor responses are observed (blue). (b) Example nIR intensity response upon addition of RAP1, and corresponding integrated intensity curves for RAP1 concentrations from 0 to 25 μg/mL. (c) First passage time until first sensor turn-on response at various RAP1 concentrations within the single-senor response regime. First passage times show a decaying exponential, as expected by protein diffusion-limited kinetics, with semilog(y) plot inset. (d) Example single-sensor nIR intensity response upon addition of RAP1 protein (red box). Sample traces are shown to demonstrate variance in first passage times for two sample RAP1 concentrations, 0.25 μg/mL (blue) and 0.06 μg/mL (green). All error bars are standard error. Sensor sensitivity can measure individual binding events in the single-sensor regime.