Potential of TiO2 Nanoparticles for Mass Spectrometric Detection and Quantification of Biologically-Relevant Small Molecules

INTRODUCTION: Matrix-assisted laser desorption and ionization mass spectrometry (MALDI MS) is suitable for clinical applications because of its performances. On the other hand, if organic matrices are used, analysis of small molecules (mass <1000 Da) becomes difficult due to a high number and intensity of matrix –related signals. Certain physiologically important molecules, such as hormones, carbohydrates, drugs, and others, belong to the small molecule group. Application of TiO2 nanoparticles as substrates for surface-assisted laser desorption and ionization (SALDI) MS is, in these cases, promising tool. OBJECTIVES: To test the suitability of TiO2 nanoparticles with various sizes and shapes as substrates for SALDI MS of various classes of small biologically-relevant molecules. METHODS: The following TiO2 nanoparticles are prepared: colloidal nanoparticles (NPs, round, diameters of 5 nm), prolate nanospheroids (PNSs, 40-50 nm length) and nanotubes (NTs, approximately 100 nm long, 10 nm diameter). Samples (amino acids, steroid hormons, vitamins, carbohydrates) at various concentration were analyzed in positive and negative mode, whereas reproducibility and day-to-day repeatability was tested by ANOVA statistical analysis. RESULTS: By tested organic matrices, 63% of samples could not be detected, whereas by using any of nanoparticles, only 33% of analytes were not detectable. The spectra acquired with TiO2 nanoparticles, were characterized by lower number of well defined signals, which did not overlap with the signals from analytes. Analyte signals are simple, and the number of analyte-generated adducts is low when TiO2 substrates are used. Moreover, in some cases, also molecular ions could be detected. Generally, spectra were better reproducible when acquired with nanoparticles compared to organic matrices, as judged by the standard deviations in the signal-to-noise ratio (standard deviations are smaller when nanoparticles are used). In that sense, PNSs demonstrated