Lithographically patterned siliconnanowire arrays for matrix free LDI-TOF/MS analysis of lipids

Abstract

Silicon nanowire arrays were patterned onto silicon chips by a combination of lithography and chemical vapor deposition using the vapor-liquid-solid growth method. Thus, highly reproducible sample deposition zones were obtained that were used for laser desorption ionization (LDI) mass spectrometric analysis of lipidic species with lithium salts as dopants. Using a conventional UV laser (337 nm), hydrocarbons and numerous lipids (triglycerides, diglycerides, wax esters) could be effectively lithiated yielding [M + Li]⁺ ions. Upon doping with lithium hydroxide the SiNW arrays yielded high signal-to-noise ratios with low limits of detection (e.g. 750 pg tripalmitin on target with S/N 5) and efficient ionization for a range of fatty acids (FA), mono-, di- and triglycerides and hydrocarbons (HC), in the form of [FA − H + 2Li]⁺, [mono- or diglyceride − H₂O + Li]⁺, or [triglyceride + Li]⁺ and [HC + Li]⁺, respectively. It is expected that these chips will find a broad range of applications in the analysis of natural compounds and food control.