Effect of urea surface modification and photocatalytic cleaning on surface‐assisted laser desorption ionization mass spectrometry with amorphous TiO₂ nanoparticles

Abstract

We have investigated the effect of urea surface modification and the photocatalytic cleaning on surface-assisted laser desorption ionization mass spectrometry (SALDI-MS) with amorphous TiO2 nanoparticles for the reduction of the background noise and the improvement of the sensitivity. In the use of nanoparticles of high surface area, chemical background signals arising from ambient environments and organic contaminants can frequently be serious problems below 500 Da, possibly reducing the advantages of the matrix-free approach. In this study, removal of contaminants and enhanced SALDI efficiency were easily achieved with UV irradiation via the photocatalyst effect of TiO2 before SALDI-MS measurements. The surface cleaning achieved by the UV photocatalytic procedure reduced the background noise and increased the peak intensities of peptides. In addition, we found that urea surface modification of TiO2 nanoparticles increased the performance of the TiO2-SALDI-MS. (1) The urea-surface modification of TiO2 made it possible to produce proton-adduct forms without citrate buffer, resulting in low background noises below 500 Da, in contrast to the essential use of a citrate buffer in the bare TiO2-SALDI-MS. (2) The detection sensitivity of angiotensin I increased to 0.3 fmol with the urea-surface modification, as compared to the use of bare TiO2 nanoparticles (6 fmol). The urea-TiO2 could ionize proteins of more than 20,000 Da such as trypsinogen (600 fmol). (3) The urea modification of TiO2 had the advantage of selective detection of phosphopeptides without sample clean up, or prefractionation in tryptic digest products of bovine hemoglobin.

Influence of Crystalline Forms of Titania on Desorption/Ionization Efficiency in Titania-Based Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

“…6). Under the UV-laser irradiation on titania based SALDI-MS, it was reported that electrons are excited from the valence band to the conduction band of titania, producing oxidative holes to drive in-source oxidation reactions and reductive electrons to induce in-source reactions of analytes in SALDI-MS. 33), 48), 49) In this study, such UV-laser induced photocatalytic oxidation reactions were observed in the case of amorphous (or titania)-type titania with strong photocatalytic e#ects, but not for rutile-type titania with weak photocatalytic e#ects. As shown in Fig.…”

“…Among the various types of materials proposed for SALDI-MS, titania (TiO 2 ) appears to be a promising candidate, because its physicochemical properties permit SALDI performance to be improved: (1) a high UV absorbance with a large bandgap (bulk anatase: 3.2 eV), (2) good chemical stability under a variety of pH conditions and under ambient air, (3) surface modification with various functional groups, 33) and (4) possible morphology control of titania such as porous structures with a high surface area. 18), 19) In addition, in contrast to DIOS-MS that is used for analyzing analytes with a molecular weight of ῑ6 kDa, 34) titaniabased SALDI-MS can be used to analyze high molecular weight proteins (ῑ24 kDa) as well as small molecules and has the advantage that phosphopeptides are specifically adsorbed.…”

Study on the use of 3‐aminopropyltriethoxysilane and 3‐chloropropyltriethoxysilane to surface biochemical modification of a novel low elastic modulus Ti–Nb–Hf alloy

“…Nowadays, organosilane precursors bearing functional groups such as amino [12][13][14][15][16][17][18][19][20][21][22], thiol, carboxyl, phosphate, vinyl [23][24][25], cyanide [26], phenyl [24,27] or sulphhydryl groups are readily available. Despite the wide variety of silane precursors available for surface modification, the majority of studies have employed aminosilanes, in particular 3-aminopropyltriethoxysilane (APTES) [11][12][13][14][15][16][17][18][19][20][21][22].…”

Imaging mass spectrometry with silver naeoparticles reveals the distribution of fatty acids in mouse retinal sections

“…The core metal and functional groups of the NPs can be modified to ionize analytes on the basis of specific chemical properties. The core metals gold [11], silver [12][13][14], titanium dioxide [15], and their mixture [16] have been used in SALDI-MS analysis. SALDI-MS analyses using their NPs have detected analytes that are different from those used in general matrices or to enhance the signal intensities from the molecules.…”