A micro-nib nanoelectro spray source for mass spectrometry

The design, fabrication and testing of a novel interface resembling a micro-nib for nano-electrospray ionisation-mass spectrometry (ESI-MS) applications is reported in this paper. The micro-nibs are fabricated in a planar topology using the negative photoresist SU-8 deposited onto silicon substrates. In order to direct the liquids to the nib tip, capillary slots with dimensions of 8 mum x 35 mum and 16 mum x 35 mum are included in the micro-nib design. The micro-nibs are fabricated so that they overhang from the edge of a silicon substrate in order to provide a reliable free-standing planar interface from a micro-fluidic circuit to a mass spectrometer. The micro-nib sources are tested on an ion trap mass spectrometer using standard peptide samples at concentrations down to 1 muM and with a typical ionisation voltage of around 1 kV. In addition, the nibs function well when the voltage supply was decreased to a value of 0.8kV. The resulting mass spectra are seen to have a good signal-to-noise ratio (S/N) comparable to those observed using classical emitter tips. The micro-nibs demonstrate state-of-the-art performances with respect to current micro-machined electrospray interfaces and are comparable to those obtained for stand-alone fused-silica-based emitter tips. (C) 2003 Elsevier B.V. All rights reserved.