Figure 2.

Evaporation of 10 μL PBS droplets on a Teflon AF coated surface (115° contact angle) leads to the expected linear decrease (R² = 0.997) in droplet height with time (open diamonds, N = 3). The evaporating 10 μL PBS droplet red-shifts the WGM resonance (squares, N = 10) of embedded resonators as the decreasing volume concentrates the buffer ions. As shown, evaporation negligibly affects the WGM resonance (≤2 pm shift in first 10 min) early in the evaporative process. Control experiments using 10 μL PBS droplets covered in silicon oil (open circles, N = 2) shows the stability of the WGM resonance in the absence of evaporation. Error bars represent inter assay variability.