Fast Chemical Analysis of Droplets Unlocked by Ultra-Fast Ion Mobility Spectrometry

This study presents the first coupling of high-throughput droplet microfluidics to an ultra-fast ion mobility spectrometer (IMS), providing a method for the label-free and comprehensive analysis of droplet contents at very high speeds. Building on the core strengths of IMS ─ compactness, simplicity, and cost-effectiveness ─ the added ability to capture full spectra at exceptionally short cycle times of less than 2 ms positions the technique as an exceptional platform for spectrometric analysis. The combination of a custom electrospray interface, a purpose-built monolithic fused-silica droplet generator chip, and an ultra-fast IMS enabled the chemical analysis of individual droplets in segmented flow at speeds of up to 120 Hz. The approach of droplet-based high-throughput ion mobility spectrometry (DHT-IMS) was also applied for reaction screening in nanoliter-sized droplets, exemplified by a hydrazone formation reaction between 5-methylisatin and phenylhydrazine.