Silicon micropillar array electrospray chip for drug and biomolecule analysis

We have developed a lidless micropillar array electrospray ionization chip (mu PESI) combined with mass spectrometry (MS) for analysis of drugs and biomolecules. The mu PESI chip, made of silicon, contains a sample introduction spot for a liquid sample, an array of micropillars (diameter, height, and distance between pillars in the range of 15-200, 20-40, and 2-80 mu m, respectively), and a sharpened tip for direct electrospray formation. The microchips were fabricated using deep reactive ion etching (DRIE) which results in accurate dimensional control. The chip, providing a reliable open-channel filling structure based on capillary forces and a electrospray emitter tip for ionization, allows an easy operation and reliable, non-clogging liquid transfer. The mu PESI chip can be used for a fast analysis using single sampling or for continuous infusion measurements using a syringe pump for sample introduction. The mu PESI-MS shows high sensitivity, with limit of detection 30 pmol/L (60 amol or 28 fg) for verapamil measured with tandem mass spectrometry (MS/MS) and using a sample volume of 2.5 mu L. The system shows also good quantitative linearity (r(2) > 0.99) with linear dynamic range of at least six orders of magnitude and good ion current stability (standard deviation <5%) in 1-h continuous flow measurement. The mu PESI-MS is shown to be a very potential method for direct analysis of drugs and biomolecules. Copyright (C) 2007 John Wiley & Sons, Ltd.