Silicon micropillar array electrospray chip for drug and biomolecule analysis

We have developed a lidless micropillar array electrospray ionization chip (µPESI) combined with mass spectrometry (MS) for analysis of drugs and biomolecules. The µPESI 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 µm, 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 µPESI chip can be used for a fast analysis using single sampling or for continuous infusion measurements using a syringe pump for sample introduction. The µPESI‐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 µL. 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 µPESI‐MS is shown to be a very potential method for direct analysis of drugs and biomolecules. Copyright © 2007 John Wiley & Sons, Ltd.