Submicron 3,4-dihydroxybenzoic acid-TiO 2 composite particles for enhanced MALDI MS imaging of secondary metabolites in the root of differently aged baical skullcap.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) has become an attractive technique for the localization and visualization of small molecules in various biological tissue sections. In this work, submicron 3,4-dihydroxybenzoic acid-TiO 2 composite particles (3,4-DHB-TiO 2 CPs) were synthesized for enhanced MALDI MSI of secondary metabolites in the root of Scutellaria baicalensis Georgi (baical skullcap). Submicron TiO 2 particles were synthesized as starting materials by using a facile sol-gel method and chemically modified with six analogs of dihydroxybenzoic acids (DHB) (2,3-DHB, 2,4-DHB, 2,5-DHB, 2,6-DHB, 3,4-DHB, and 3,5-DHB). Among them, 3,4-DHB-TiO 2 CPs provided superior performance in MALDI MSI of small molecules. Compared with conventional matrices, such as 2,5-dihydroxybenzoic acid (2,5-DHB) and α-cyano-4-hydroxycinnamic acid (CHCA), 3,4-DHB-TiO 2 CPs exhibited low background noise and high detection sensitivity for the visualization of spatial distribution patterns of secondary metabolites in the roots of differently aged S. baicalensis by using MALDI MSI. The age-related spatial and content changes of flavonoids in S. baicalensis roots were demonstrated and further validated by liquid chromatography-mass spectrometry (LC-MS). This work provides a potential organic-inorganic hybrid matrix for MALDI MSI of secondary metabolites in plant tissues.