Nanoliter Droplet Characterization using Vibrating Crystal Sensor with Surface-attached Polymer Hydrogel Coating

AbstractThis paper presents a novel method for nanoliter droplet characterization using a polymer coated sensor of a low-cost quartz crystal microbalance (QCM). The gold electrode of the crystal sensor was coated by a surface-attached polymer hydrogel film of about 2μm thickness using simple spin casting and photocrosslinking procedure [1,2]. The resonance frequency of the coated crystal sensor was continuously recorded at the sample rate of 2Hz over 90seconds before and after loading a micro droplet of filtered double-distilled water. Good repeatability (max. CV = 3.8%) and good linearity (r(x,y)= 0.995) of the maximum resonance frequency shift have been observed during 144 dispenses for 6 different droplet volumes in the range from 3 nl to 13 nl. A calibration line for the measured domain of the maximum frequency shift in relation to droplet mass was established according to the gravimetric calibration of the used dispenser with an ultra-microbalance