Watanabe Takehiro, Okumura Koji, Kawasaki Hideya, Arakawa Ryuichi
Department of Applied Chemistry, Kansai University, Suita, Osaka 564-8680, Japan.
J Mass Spectrom. 2009 Oct;44(10):1443-51. doi: 10.1002/jms.1628.
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.
我们研究了尿素表面改性和光催化清洁对使用非晶态TiO₂纳米颗粒的表面辅助激光解吸电离质谱（SALDI-MS）的影响，以降低背景噪声并提高灵敏度。在使用高比表面积的纳米颗粒时，环境中的化学背景信号和有机污染物在500 Da以下常常会成为严重问题，这可能会降低无基质方法的优势。在本研究中，通过TiO₂的光催化作用，在SALDI-MS测量前通过紫外线照射可轻松实现污染物的去除和SALDI效率的提高。通过紫外线光催化程序实现的表面清洁降低了背景噪声并增加了肽的峰强度。此外，我们发现TiO₂纳米颗粒的尿素表面改性提高了TiO₂-SALDI-MS的性能。（1）TiO₂的尿素表面改性使得无需柠檬酸盐缓冲液就能产生质子加合物形式，与裸露的TiO₂-SALDI-MS中必须使用柠檬酸盐缓冲液相比，在500 Da以下产生了低背景噪声。（2）与使用裸露的TiO₂纳米颗粒（6 fmol）相比，尿素表面改性使血管紧张素I的检测灵敏度提高到了0.3 fmol。尿素-TiO₂能够电离分子量超过20,000 Da的蛋白质，如胰蛋白酶原（600 fmol）。（3）TiO₂的尿素改性具有在不进行样品净化或对牛血红蛋白的胰蛋白酶消化产物进行预分级分离的情况下选择性检测磷酸肽的优势。
