Dry-mass Sensing for Microfluidics

Label-free detection of analytes in solution is of great importance for a wide range of microfluidic (and bulk) applications ranging from biophysical research to point of care diagnostics. Here, we present an approach for interfacing an electromechanical sensor with a microfluidic device for the accurate quantification of the dry mass of analytes within microchannels [1,2]. We show experimentally that by depositing solutes onto the active surface of a quartz crystal microbalance by means of an on-chip microfluidic spray nozzle and subsequent solvent removal we can determine dry solute mass in real time. Moreover, this lab-on-two chips detection scheme does not suffer from the decrease in the sensor's quality factor and the viscous drag present if the measurement is performed in a liquid environment, yet allows solutions to be analysed. We demonstrate the sensitivity and reliability of our approach by controlled deposition of nanogram levels of salt and protein from a micrometer-sized channel.