Screen-printed digital microfluidics combined with surface acoustic wave nebulization for hydrogen-deuterium exchange measurements

• DMF and SAWN were combined to mix and ionize microliter-sized droplets for HDX analysis in a peptide.
• This novel workflow is rapid, minimizes biofouling, and provides soft ionization for HDX-MS.
• SAWN-HDX alone of ubiquitin revealed very low back exchange rates (up to 6%).
• SAWN-HDX of ubiquitin revealed similar kinetics to previously published predictions.

An inexpensive digital microfluidic (DMF) chip was fabricated by screen-printing electrodes on a sheet of polyimide. This device was manually integrated with surface acoustic wave nebulization (SAWN) MS to conduct hydrogen/deuterium exchange (HDX) of peptides. The HDX experiment was performed by DMF mixing of one aqueous droplet of angiotensin II with a second containing various concentrations of D2O. Subsequently, the degree of HDX was measured immediately by SAWN-MS. As expected for a small peptide, the isotopically resolved mass spectrum for angiotensin revealed that maximum deuterium exchange was achieved using 50% D2O. Additionally, using SAWN-MS alone, the global HDX kinetics of ubiquitin were found to be similar to published NMR data and back exchange rates for the uncooled apparatus using high inlet capillary temperatures was less than 6%.