Probing the kinetics of chemical reactions in ultra-small droplet samples using digital microfluidic nuclear magnetic resonance spectroscopy

In this study, we present a digital microfluidic (DMF) system that connects analyte droplets with planar microcoils in a high-field nuclear magnetic resonance (NMR) spectrometer for in situ photoreaction analysis. Transparent indium tin oxide glass was employed in fabricating the DMF electrode chips. NMR spectroscopy was utilized for its superior sensitivity and ability to detect small changes in molecular structure, making it highly advantageous for chemical analysis. Utilizing Computer Simulation Technology Studio Suite, we designed a plane annular microstrip coil that accurately matches droplet shape to optimize detection sensitivity and increase filling factor. An advanced DMF control circuit remotely manages droplet samples and facilitates precise mixing for in situ reaction analysis. Our results demonstrate improved sensitivity in the in situ experimental analysis, such as the aldehyde amine reaction (sodium benzaldehyde-2-sulfonate solution and aniline solution) and photopolymerization reaction (polyethylene glycol ester). The integration of DMF and NMR technologies provides a promising approach for increasing efficiency and accuracy in chemical analysis.