A solid-phase bioreactor with continuous sample deposition for matrix-assisted laser desorption/ionization...

We report the development of a solid-phase proteolytic digestion and continuous deposition microfluidic chip platform for low volume fraction collection and off-line matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Tryptic peptides were formed in an on-chip bioreactor and continuously deposited onto a MALDI target plate using a motor-driven xyz stage. The bioreactor consisted of a 4 cm × 200 µm × 50 µm microfluidic channel with covalently immobilized trypsin on an array of 50 µm diameter micropost structures with a 50 µm edge-to-edge inter-post spacing. A 50 µm i.d. capillary tube was directly attached to the end of the bioreactor for continuous sample deposition. The MALDI target plate was modified by spin-coating a nitrocellulose solution containing a MALDI matrix on the surface prior to effluent deposition. Protein molecular weight standards were used for evaluating the performance of the digestion and continuous deposition system. Serpentine sample traces 200 µm wide were obtained with a 30 fmol/mm quantity deposition rate and a 3.3 nL/mm volumetric deposition rate.