Colloidal TiO2 nanoparticles as substrates for M(S)ALDI mass spectrometry of transition metal complexes

Abstract

RATIONALE Nanoparticles as substrates for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) have advantages over organic matrices, since they enable acquisition of spectra in the low-mass range. It has been previously shown that TiO2 nanoparticles can be used as substrate for MALDI-TOF MS analysis of phospholipids and for other types of molecules, but none of them was applied to the analysis of transition metal complexes. METHODS The MALDI-TOF mass spectra of potential anti-tumor drugs [AuCl2(bipy)]Cl, [PtCl4(bipy)], and [RuCl2(bipy)2]Cl acquired with organic matrices have been compared with spectra acquired with colloidal titanium dioxide nanoparticles. Colloidal TiO2 nanoparticles (NPs) with average diameter of 5 nm were synthesized and characterized by microscopy. For some experiments, the TiO2 NPs were treated at 60 degrees C. Suspensions of matrix and the analyte were premixed, applied to the MALDI target and left at room temperature. Mass spectra were acquired with a 50-Hz pulsed nitrogen laser emitting at a wavelength of 337 nm. RESULTS The MALDI spectra of transition metal complexes acquired with TiO2 NPs exhibited somewhat lower sensitivity than those with organic matrices; on the other hand, they are characterized by significantly lower number of signals arising from the tested complexes than the organic matrices. Whereas adducts between organic matrices and the analytes were detectable in the spectra, this was not the case for the TiO2-assisted mass spectra. CONCLUSIONS We have shown that colloidal TiO2 NPs can be used as substrates for MALDI-TOF MS of transition metal complexes. Although the sensitivity of this approach in comparison with the use of organic matrices might still be a problem, the potential of the applications of NPs for the mass spectrometric characterization of transition metal complexes is clearly demonstrated.