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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.

Articles you may be interested inUnderstanding the relationship between molecular order and charge transport properties in conjugated polymer based organic blend photovoltaic devices Band bending in the surface layer of amorphous selenium induced by contact with an insulating organic polymer was detected by photoelectric signals generated at the interface under no external bias. The magnitudes and polarities of the signal varied among samples involving different polymers, and also among samples involving the same polymer with and without doping by an electropositive organic impurity. Details of this behavior, along with the observation that the polarity of the signal was reversed when the method of making the contact between selenium and polymer was altered, indicate that the preferred orientation of polymer molecules containing dipole moments on the selenium surface is the principal cause of the surface potential gradient in the selenium.

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Articles you may be interested inIn situ investigations of the metal/silicon reaction in Ti/Si thin films capped with TiN: Volumetric analysis of the C49-C54 transformation

By measuring the charge pumping current (I CP) and the subthreshold swing, we examined the front- and back-interface trap densities (D fit and D bit) of long channel N-type metal-oxide-semiconductor transistors fabricated on separation-by-implanted-oxygen (SIMOX) substrates, as a function of the total oxygen implantation dose. The front-channel subthreshold swing (S f) measured in the coupled condition was larger than that calculated with D fit and D bit obtained from I CP. However, dose dependences of the D fit and D bit obtained from I CP were consistent with those of the front- and back-channel peak mobilities, while those obtained from the subthreshold swings were not. These seemingly contradictory results can be satisfactorily explained by the existence of lateral nonuniformities (LNU) in the front- and the back-channel local threshold voltages. We propose that the experimentally determined S f can be used as an index of LNU in the SIMOX and other silicon-on-insulator substrates, just by comparing it with the theoretical value of S f.

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The applicability of matrix-free surface-assisted laser desorption/ionization mass spectrometry using porous silicon (DIOS-MS) and TiO2 nanoparticles (TiO2-SALDI-MS) was examined by analyzing an antioxidant added to insoluble polypropylene (PP) materials. The optimized solvent extraction, which involved freezing and crushing the PP, results in a good recovery, 89ῌ4 and 97ῌ8῍ for 0.5 wt῍ of the added antioxidant, tetrakis[methylene3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (commercial name; Irganox1010) in laboratory-produced and commercial PP composites, respectively. The positive ion measurements in DIOS and TiO2-SALDI-MS yielded sodium adduct ions without any interference from other signals. Using an internal standard with a similar structure, a good calibration curve linearity was established in the Irganox1010 concentration range of 0.01῍2.0 mg/mL in PP, which was su$cient for monitoring the plastic additives. However, TiO2-SALDI-MS was superior to DIOS-MS in terms of mass resolution and easiness of sample preparation. A solvent extraction method followed by TiO2-SALDI-MS appears to be a anticipated method for the analysis of additives in insoluble plastics.