Gold-Coated Nanoelectrospray Emitters Fabricated by Gravity-Assisted Etching Self-Termination and Electroless Deposition

To improve the stability and sensitivity of nanoelectrospray for liquid chromatography-mass spectroscopy (LC-MS) analysis, we present a new method to fabricate gold-coated emitters. Via gravity-assisted etching self-termination, the emitter with a tapered outer surface and a straight inner surface is prepared with good reproducibility, without the need of fluid introduced to protect internal surface during etching. Followed by electroless deposition, the emitter is further coated with gold film homogeneously, by which the relative standard deviation (RSD) value of total ion current in 160 h is <5%, showing good stability. Compared to that obtained by a commercial emitter, the identified protein number from 2 mu g HeLa cell digests is increased over 10%, contributed by the stable electrospray and improved signal intensity of peptides. Furthermore, the integrated gold-coated emitter is prepared at the end of the ultranarrow-bore packed column (inner diameter of 25 mu m), and 218 proteins are identified from 2 ng HeLa cell digests. All of these results demonstrate the great promise of such emitters for use in ultrasensitive proteome analysis.