Laser-Modified Black Titanium (IV) Oxide Nanospheres as a Matrix for Signal Enhancement in Visible Laser Desorption Post-Ionization Mass Spectrometry

Laser desorption post-ionization mass spectrometry (LDPI-MS) acts as a powerful analytical platform and has emerged as an essential tool for the highly sensitive and direct characterization of complex chemical and biological samples. Herein, laser-modified black titanium dioxide (TiO2) was applied as a novel matrix for sensitive analysis and imaging of small-molecule analytes. A wide variety of representative compounds containing ferulic acid, bisphenol A, niacin, and acetaminophen were examined by LDPI-MS utilizing black TiO2 as the matrix. Compared with conventional matrices and unmodified white TiO2, LDPI-MS with the black TiO2 matrix exhibits superior desorption performance due to enhanced photothermal conversion. Quantitative analysis utilizing this matrix also allows the determination of acetaminophen with an excellent linear range of 20.0–2000 ng/spot (R2 = 0.99866) and a limit of detection of 20.0 ng/spot. With a 532 nm laser employed as the desorption source, the spatial distribution of acetaminophen in mouse kidney tissue sections was visualized at a 100–200 μm spatial resolution utilizing the black TiO2 matrix. These successful applications confirm that laser-modified black TiO2 represents a highly effective substrate for tissue imaging and sensitive molecular detection.