Titania Microparticles and Nanoparticles as Matrixes for in Vitro and in Situ Analysis of Small Molecules by MALDI-MS

TiO2 microparticles (TMs) and nanoparticles (TNs), prepared by hydrolysis of Ti butoxide and maintained in aqueous solution, were evaluated as matrixes for the detection of small molecules. With aqueous suspensions of TMs, positive-ion spectra collected for phospholipids (PLs) extracted from soybeans showed high sensitivity and no matrix interferences. Negative-ion traces had a suitable signal-to-noise ratio (S/N) but showed high levels of phosphatidic acid caused by the loss of die headgroup in other PLs. The hydrolysis was more pronounced when TNs were used. In situ studies performed by applying TM suspensions directly onto 50-mu m thick soybean slices did not yield satisfactory results as TMs formed a crusty layer that precluded desorption/ionization. When a TN suspension was used instead, PLs and triacylglycerols were detected. Only minor PI, hydrolysis was observed. TNs also enabled the coverage of rose petals and the detection of different levels of flavonols/anthocyanins and their glycosides as the color changed from yellow to orange-red. Although the hydrolysis of PLs limits the use of TMs or INS for in vitro PL analysis, TNs offer a suitable alternative for the analysis of other molecules of low molecular weight, and their small size (average of similar to 200 nm) facilitates their penetration into tissue for in situ imaging.