Porous TiO₂ Film Immobilized with Gold Nanoparticles for Dual-Polarity SALDI MS Detection and Imaging

Abstract

Surface-assisted laser desorption/ionization (SALDI) mass spectrometry (MS) has become an attractive complementary approach to matrix-assisted laser desorption/ionization (MALDI) MS. SALDI MS has great potential for the detection of small molecules because of the absence of applied matrix. In this work, a functionalized porous TiO2 film immobilized with gold nanoparticles (AuNPs-FPTDF) was prepared to enhance SALDI MS performance. The porous TiO2 films were prepared by the facile sol–gel method and chemically functionalized for dense loading of AuNPs. The prepared AuNPs-FPTDF showed superior performance in the detection and imaging of small molecules in dual-polarity modes, with high detection sensitivity in the low pmol range, good repeatability, and low background noise compared to common organic MALDI matrixes. Its usage efficiently enhanced SALDI MS detection of various small molecules, such as amino acids and neurotransmitters, fatty acids, saccharides, alkaloids, and flavonoids, as compared with α-cyano-4-hydroxycinnamic acid, 9-aminoacridine, and the three precursor substrates of AuNPs-FPTDF. In addition, the blood glucose level in rats was successfully determined from a linearity concentration range of 0.5–9 mM, as well as other biomarkers in rat serum with SALDI MS. More importantly, the spatial distribution of metabolites from the intact flowers of the medicinal plant Catharanthus roseus was explored by using the AuNPs-FPTDF as an imprint SALDI MS substrate in dual-polarity modes. These results demonstrate wide applications and superior performances of the AuNPs-FPTDF as a multifunctional SALDI surface with enhanced detection sensitivity and imaging capabilities.

Mass spectrometry imaging for direct visualization of components in plants tissues

“…Imprinting [62] has been applied in recent years, mainly used for inorganic matrix deposition. Its principle is that placing tissue slice on the surface of the nanomaterial, covered by porous Teflon, TLC plate [63,64], or other nanomaterials [65,66] with certain pressure. Compounds on the sample surface would be transferred to the nanomaterial, then analyzed directly on the nanomaterial plate after removing the sample slice.…”

Imaging Metabolites in Agar‐Based Bacterial Co‐Cultures with Minimal Sample Preparation using a DIUTHAME Membrane in Surface‐Assisted Laser Desorption/Ionization Mass Spectrometry**

“…One of the alternative workflows includes surface‐assisted laser desorption/ionization (SALDI) MSI [3,24–26] combined with an imprinting or blotting sample preparation in which the analytes are transferred from the sample to an appropriate support prior to analysis [24,27–29] . SALDI‐MSI offers several advantages over MALDI‐MSI, such as a clear background in the low m/z range enabling the analysis of small molecules, a higher signal reproducibility, and the ability to carry out analyses in both ionization modes with the same nanostructured substrate [3,24,30,31] . SALDI‐MS has already been used with the aim of discovering new bioactive compounds excreted by microorganisms, including fungi [32] and molds [33] .…”

“…[24,[27][28][29] SALDI-MSI offers several advantages over MALDI-MSI, such as a clear background in the low m/z range enabling the analysis of small molecules, a higher signal reproducibility, and the ability to carry out analyses in both ionization modes with the same nanostructured substrate. [3,24,30,31] SALDI-MS has already been used with the aim of discovering new bioactive compounds excreted by microorganisms, including fungi [32] and molds. [33] In particular, SALDI-MSI imprinting methods have been used to image the metabolic interactions between microbial colonies, using nanostructured silicon substrates [16,34] and TiO 2 nanowires, [35] for example.…”

A Polymer-Based Matrix for Effective SALDI Analysis of Lipids

“…7,9,10 Although the mechanism of SALDI was still indefinite, many inorganic and carbon-based organic materials in the consideration of UV absorption and interaction between analytes and surfaces have been developed in the last decades. Silicon-based (DIOS, 11 SiNWs 12 ), carbonbased (graphene, 13−15 N-doped graphene 16 and carbon nanosphere, 17 carbon dots 18 ), and metal (Ag, 19−21 Au 22 nanoparticles) or metal oxide (TiO 2 , 23,24 ZnO 25 ) based materials have been widely reported as effective matrices for SALDI MS or imaging. 26−29 Due to the strict conditions in the synthesis of common inorganic matrices and their application limitation for SALDI MS analysis, polymer-based materials show their potential as SALDI matrices.…”

“…In addition, fatty acids, another biologically important category of lipids, are difficult to be identified because of the heavy interference caused by matrix self-desorption in MALDI ion source. , Surface-assisted laser desorption/ionization mass spectrometry (SALDI MS), based on different materials, was proposed to replace the traditional MALDI strategies for the detection of low m / z range molecules (<1000 Da) owing to its clean background. ,, Although the mechanism of SALDI was still indefinite, many inorganic and carbon-based organic materials in the consideration of UV absorption and interaction between analytes and surfaces have been developed in the last decades. Silicon-based (DIOS, SiNWs), carbon-based (graphene, − N-doped graphene and carbon nanosphere, carbon dots), and metal (Ag, − Au nanoparticles) or metal oxide (TiO 2 , , ZnO) based materials have been widely reported as effective matrices for SALDI MS or imaging. − …”