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Electrospray interfacing of polymer microfluidics to MALDI‐MS

The off‐line coupling of polymer microfluidics to MALDI‐MS is presented using electrospray deposition. Using polycarbonate microfluidic chips with integrated hydrophobic membrane electrospray tips, peptides and proteins are deposited onto a stainless steel target followed by MALDI‐MS analysis. Microchip electrospray deposition is found to yield excellent spatial control and homogeneity of deposited peptide spots, and significantly improved MALDI‐MS spectral reproducibility compared to traditional target preparation methods. A detection limit of 3.5 fmol is demonstrated for angiotensin. Furthermore, multiple electrospray tips on a single chip provide the ability to simultaneously elute parallel sample streams onto a MALDI target for high‐throughput multiplexed analysis. Using a three‐element electrospray tip array with 150 µm spacing, the simultaneous deposition of bradykinin, fibrinopeptide, and angiotensin is achieved with no cross talk between deposited samples. In addition, in‐line proteolytic digestion of intact proteins is successfully achieved during the electrospray process by binding trypsin within the electrospray membrane, eliminating the need for on‐probe digestion prior to MALDI‐MS. The technology offers promise for a range of microfluidic platforms designed for high‐throughput multiplexed proteomic analyses in which simultaneous on‐chip separations require an effective interface to MS.