@conference{
author = "Popović, Iva and Nešić, Maja and Šaponjić, Zoran and Petković, Marijana",
year = "2015",
abstract = "The important factor that determines the process of the laser-induced desorption and ionization of molecules for the mass spectrometric analysis is the interaction between the laser light and the substrate. It is of importance that substrate efficiently absorbs laser energy, which will be further rapidly transferred to the analyte. The overall goal in this process is to obtain good quality mass spectrum with low degree of fragmentation. Whereas the application of organic matrices instead of substrates results in the numerous undesired polymerization reactions, which complicate the spectra, and in some cases, even prevent the detection of the ions of interests, nanoparticles as substrates are convenient due to a lower number of background signals and low onset of fragmentation reactions in the gas phase. Titanium dioxide (TiO2) is semiconductor-based and widely used substrate for laser desorption and ionization ((SA)LDI), and when it is in the excited state it transfers an electron or energy into the ground state molecule. This process is called sensitized photoreaction [1]. The desorption/ionization processes on TiO2 nanoparticles are related to the physical properties of the substrate such as ability to absorb and dissipate energy from the irradiating laser light source [2]. TiO2 has a large band gap (bulk anatase: 3.2 eV), and can therefore be used as a SALDI matrix with the N2 laser (337 nm) [3]. The aim of our study is to investigate the influence, which the interaction of the UV laser with TiO2 nanoparticles of various shapes and size has on the quality of the mass spectra of carbohydrates: D-(+)-glucose, D-(+)-maltose, raffinose, arabinose, β-ciclodextrine, substances which are otherwise difficult for mass spectrometric analysis. For this purpose, we used small, nearly spherically shaped colloidal TiO2 nanoparticles (average diameter ~ 5 nm), prolate nanospheroids (length: 40–50 nm, the lateral dimension: 14–16 nm) and nanotubes (length: 100-150 nm, average diameter 11 nm). For comparison, the spectra are acquired also with traditionally used organic matrices. The spectra of carbohydrates with organic matrices are overloaded with matrix signals, in which case the signals arising from the analyte of interest are suppressed, or it is possible to detect only adducts with matrix. Laser-induced ionization on nanostructures offers alternative ionization pathways through the formation of Na+ and K+ adducts with appreciable yield [4]. TiO2 nanotubes showed extraordinary properties for detection of carbohydrates. Arabinose was detectable only with TiO2, and D-(+)-glucose and D-(+)-maltose were detected in negative ion mode, which was not the case with other organic matrices and substrates. Not only the highest intensities of mass peaks but also the smallest coefficient of variation was achieved with TiO2 nanotubes. Taken toghether, TiO2 nanotubes, due to their size and the shape, have the most suitable physical properties for the substrate in the SALDI technique. The laser intensity was kept as low as possible in order to prevent fragmentaion. Higher laser intensity is required for the process of desorption/ionization when TiO2 NPs are used (2400 i.u.), but for TiO2 PNSs and TiO2 nanotubes were lower and nearly the same 1950 and 2000 i.u., respectively. In conclusion, larger, tube-shaped TiO2 substrates more efficiently absorb the laser energy and transfer it to the carbohydrates, enabling their desorption/ionization and preventing their fragmentation.",
publisher = "Belgrade : Vinča Institute of Nuclear Sciences",
journal = "PHOTONICA2015 : 5th International School and Conference on Photonics and COST actions: MP1204, BM1205 and MP1205 : book of abstracts; August 24-28, 2015; Belgrade",
title = "The interaction between variously shaped TiO2 nanoparticles with UV laser determines the quality of the mass spectra of carbohydrates",
pages = "101-102",
url = "https://hdl.handle.net/21.15107/rcub_vinar_12008"
}