Matrix-assisted laser desorption/ionization of small biomolecules impregnated in silica prepared by a sol-gel process

Abstract

Sol-gel chemistry is emerging as an important tool for immobilizing enzymes and other biomolecules. Investigation of the reactions between enzymes and substrates in the resulting porous solids has been limited primarily to molecular spectroscopy. Herein, we demonstrate the interrogation of these solids by matrix-assisted laser desorption/ionization in conjunction with reflectron time-of-flight mass spectrometry. Small di-and tri-peptides such as phenylalanylmethionine (PheMet), diphenylalanine (PhePhe), triphenylalanine (PhePhePhe), and glutathione (γ-GluGlyCys) were chosen as the target analytes. The matrix, α-cyano-4-hydroxycinnamic acid (CHCA), was incorporated into the sol-gel process to obtain isotopically resolved peaks in the mass spectra. With the matrix and target analyte 'doped' in the dried gel, a Nd:YAG laser was used to expel the biomolecule from the confines of the silica. The presence of the matrix CHCA greatly enhanced peptide ion intensity and also, by use of matrix ions as internal calibrants, led to increased mass accuracy. Using internal calibration, the percent relative error for the monoisotopic peak of glutathione in a thin silica film (m/z of 308.04) was approximately 0.02%, while for triphenylalanine in a monolith (m/z of 460.22) the error was less than 0.01%. Variations in the pore size of the silica gel did not affect signal intensity or mass accuracy.

Exciting new directions in the intersection of functionalized sol–gel materials with electrochemistry

“…A matrix-assisted laser desorption/ionization (MALDI) mass spectrometry method was developed to determine species in sol-gels. 345,346 The MALDI results verified the formation of the dimer and dione in mesoporous and microporous silica, respectively. The agreements of the masses with the hypothesis were 0.15% (dimer; mesoporous) and 0.04% (dione; microporous).…”

Conformational Stability of Adsorbed Insulin Studied with Mass Spectrometry and Hydrogen Exchange

“…Another advantage of mass spectrometry is the possibility of probing proteins in a nonaqueous environment. This has, for example, been demonstrated by mass determination of proteins electroblotted into polymeric membranes, 10 peptides incorporated into silica gels, 11 or small DNA strands hybridized to complementary DNA strands covalently attached to a surface. 12 Developments in biotechnology have led to an enormous increase in the exposure of proteins to nonbiological solid surfaces.…”

Sol–Gel-Derived Silver-Nanoparticle-Embedded Thin Film for Mass Spectrometry-Based Biosensing

“…Alternatively, the sol–gel method has recently gained considerable attention as a simple means for producing effective MS platforms via the incorporation of organic matrices and optically active metal nanoparticles (NPs) that serve as UV energy absorbers. Separate studies utilizing thin films impregnated with α-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB) were capable of detecting a number of small molecules and proteins, respectively. , Several oligonucleotides were successfully analyzed by doping 3,4-diaminobenzoic acid (DABA) or 3,5-DABA into sol–gel solutions during the preparation of thin films, a method that also proved to be effective in reducing interference signals associated with alkali metal salts without desalting steps prior to analysis . Incorporating TiO 2 into the sol–gel allowed for the detection of surfactants, peptides, and tryptic digest products; however, the addition of a proton source in the form of citrate buffer was necessary for useful MS data …”