A cyclic-olefin-copolymer microfluidic immobilized-enzyme reactor for rapid digestion of proteins from dried blood spots

•Production of a cyclic-olefin-copolymer immobilized-enzyme reactor (IMER).•Trypsin immobilisation on a polymer monolith by vinylazlactone chemistry.•Short protein digestion times, in the order of minutes to seconds.•High repeatability in terms of protein-sequence coverage and number of peptides.•Ultra-fast IMER-facilitated workflow for dried-blood-spot (DBS) protein analysis.

A critical step in the bottom-up characterization of proteomes is the conversion of proteins to peptides, by means of endoprotease digestion. Nowadays this method typically uses overnight digestion and as such represents a considerable bottleneck for high-throughput analysis. This report describes protein digestion using an immobilized-enzyme reactor (IMER), which enables accelerated digestion times that are completed within seconds to minutes. For rapid digestion to occur, a cyclic-olefin-copolymer microfluidic reactor was constructed containing trypsin immobilized on a polymer monolithic material through a 2-vinyl-4,4-dimethylazlactone linker. The IMER was applied for the rapid offline digestion of both singular protein standards and a complex protein mixture prior to liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-ESI-MS/MS) analysis. The effects of protein concentration and residence time in the IMER were assessed for protein standards of varying molecular weight between 11 and 240 kDa. Compared to traditional in-solution digestion, IMER-facilitated protein digestion at room temperature for 5 min yielded similar results in terms of sequence coverage and number of identified peptides. Good repeatability was demonstrated with a relative standard deviation of 6% for protein-sequence coverage. The potential of the IMER was also demonstrated for a complex protein mixture in the analysis of dried blood spots. Compared to a traditional workflow a similar number of proteins could be identified, while reducing the total analysis time from 22.5 h to 4 h and importantly omitting the sample-pre-treatment steps (denaturation, reduction, and alkylation). The identified proteins from two workflows showed similar distributions in terms of molecular weight and hydrophobic character.