Fully polymeric integrated microreactor/electrospray ionization chip for on-chip digestion and mass spectrometric analysis

We have developed, fabricated and tested a lidless polymeric microchip which integrates a microreactor with an electrospray ionization (ESI) tip for mass spectrometric (MS) analysis. The microchip contains a microreactor spot, a micropillar-filled channel and an electrospray tip, all made of an SU-8 epoxy polymer. The fabrication process of the microchips required just two lithographic steps, making it simple, cost-effective, rapid, and well-suited for mass production. The lidless structure of the chip provides easy sampling of reagents and samples. On-chip trypsin protein digestion of bovine heart cytochrome c (CytC) and bovine serum albumin (BSA) was performed on the microreactor in a solvent drop without the need for immobilization of the enzyme to the microreactor. The digestion was accomplished in the microreactor within 8 min, after which the digestion products were measured directly by an integrated on-chip ESI combined to MS. The whole procedure was rapid as the total time for on-chip digestion and measurement was less than 10 min. An average sequence coverage obtained with CytC was 90% and with BSA it was 82%. The microchip can also be used as a stand-alone electrospray ionization tip for mass spectrometric analysis.