pubs.acs.org/Langmuir © 2009 American Chemical Society
Matrix-Free Laser Desorption/Ionization Mass Spectrometry on Silicon Nanowire Arrays Prepared by Chemical Etching of Crystalline Silicon Gaelle Piret,† Herve Drobecq,‡ Yannick Coffinier,† Oleg Melnyk,‡ and Rabah Boukherroub*,† †
Institut de Recherche Interdisciplinaire (IRI, CNRS-USR 3078), Parc de la Haute Borne, 50 Avenue de Halley, BP 70478, 59658 Villeneuve d’Ascq and Institut d’Electronique, de Micro electronique et de Nanotechnologie (IEMN, UMR CNRS 8520), Cit e Scientifique, Avenue Poincar e - BP 60069, 59652 Villeneuve d’Ascq, France, and ‡Institut de Biologie de Lille (IBL, CNRS-UMR 8161), Universit e de Lille Nord de France, IFR142, 1 rue du Pr. Calmette, 59021 Lille, France Received June 24, 2009. Revised Manuscript Received August 12, 2009 This paper reports on the use of silicon nanowires (SiNWs), easily prepared in a single step by chemical etching of crystalline silicon in HF/AgNO3 aqueous solution, as a highly sensitive substrate for laser desorption/ionization mass spectrometry (LDI-MS) analysis. The SiNWs’ diameter and length depend on the etchant concentration and dissolution time. Optimized LDI substrate consists of nanowires with an average diameter in the range of 20-100 nm and 2.5 μm in length. The optimized SiNWs’ surface morphology coupled to a controlled surface chemistry allowed a significant LDI-MS performance through measurements of a broad range of analytes, including small molecules, peptides, and a bovine serum albumin (BSA) digest. A signal-to-noise ratio of 250 was ascertained for a 10 fmol bradykinin pick, in reflector mode acquisition. Likewise, the sutent, a small tyrosine kinase inhibitor, could be observed down to 10 fmol, as compared to 500 fmol limit detection using the classical matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). We have further investigated the optical properties of the nanowires, and our results suggest that they have a small or no effect on the desorption/ionization (D/I) process. On the contrary, the surface morphology and thermal properties of the silicon nanostructures are found to be the essential features contributing to the D/I performance.
Introduction Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a soft ionization technique, developed in the late 1980s, for mass analysis of analytes. MALDI allows the analysis of a wide variety of compounds, including polymers, peptides, and proteins.1 However, due to a competitive desorption of parasitic ions from the matrix, it is difficult to detect low molecular weight compounds (
