An integrated microfluidic chip for the analysis of biochemical reactions by MALDI mass spectrometry
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Using an integrated microfluidic chip combined with mass spectrometry is an attractive method for parallel and multiple analyses because of its inherent simplicity, low sample consumption, and high sensitivity. To realize an effective microfluidic chip for the rapid analysis of biochemical reactions by matrix assisted laser desorption/ionization (MALDI)–mass spectrometry (MS), the basic operations on microfluids, namely loading, metering, cutting, transporting, mixing, and injecting, must be integrated. This study describes an integrated microfluidic chip with MALDI–MS that performs the on-chip analysis of biochemical reactions, such as enzymatic reactions. For on-chip multiple reactions, we present sequential fluidic manipulations with nanoliter-sized droplets, based on the precise control of wettability and the capillary pressure of a microchannel. The microfluidic chip we have developed successfully performed biochemical reactions and can dispense a droplet of a few hundred nanoliters on the MALDI target plate according to the designed multiple reaction procedure. Finally, the MS spectrum showed accurate and clear characteristic peaks for reaction products. Our investigations into reaction efficiency showed that the microfluidic chip could reduce the reaction time to one third, and the volume to one hundredth, of off-chip methods using conventional labware such as the micropipette and Eppendorf tube.