TiO2 Aerogel Decorated with Pt Nanoparticles for the Analysis of Hardly Ionizable Metabolites Using Laser Desorption/Ionization Mass Spectrometry

Abstract

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS) conventionally uses organic matrices for analyte ionization under ultraviolet-laser irradiation. For the effective analysis of small molecules (m/z < 500), nanostructured inorganic matrices have been developed to eliminate background noise from fragmented organic matrices as well as to enhance analyte ionization. Despite their potential, achieving high ionization efficiency without compromising the inherent porosity of the matrix remains a challenge. Herein, a TiO2 aerogel decorated with Pt nanoparticles (PtNP-TiO2 aerogel) was developed as an interface-mediated solid-state inorganic matrix using a nanoparticle-based incorporation strategy to preserve the network-derived textural porosity of the framework. The interfacial coupling between PtNPs and TiO2 simultaneously promoted photocatalytic ionization through an elongated carrier lifetime and enhanced analyte desorption by the localized photothermal conversion of the PtNPs. Specifically, structural analysis revealed that the incorporated PtNPs induced phase transformation and lattice distortion by forming metal–semiconductor interfaces at the aerogel framework. The photothermal behavior of the decorated PtNPs was verified using preionized dyes as desorption probes, confirming efficient local heat transfer. Furthermore, the enhanced surface ionization of the PtNP-TiO2 aerogel was attributed to the Schottky barrier formation at the PtNP-TiO2 aerogel interface. These interfaces facilitated efficient charge carrier separation through lattice distortion-induced shallow trap states, leading to improved ionization. Finally, PtNP-TiO2 aerogel-based LDI-MS demonstrated versatility in the quantitative analysis of small metabolites with inherently low ionization efficiencies.