Three-Dimensional Hierarchical Plasmonic-Semiconductor Heterostructure for High-Performance SALDI-MS Detection

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is a powerful technique for small-molecule analysis but is often limited by inefficient laser-energy utilization and weak interfacial interactions. Herein, we report a three-dimensional hierarchical plasmonic-semiconductor heterostructure that enables the efficient capture, localization, and conversion of laser energy, thereby enhancing laser desorption/ionization efficiency. Vertically aligned CuO nanorods provide a high-surface-area photothermal architecture, while discretely distributed Ag nanoparticles generate localized electromagnetic hotspots, form Ag/CuO Schottky interfaces, and increase nanoscale roughness. Photothermal measurements, transient photovoltage analysis, finite-difference time-domain simulations, photoluminescence spectroscopy, and density functional theory calculations reveal a synergistic enhancement mechanism. Enhanced photon harvesting and plasmonic electromagnetic confinement promote nonradiative energy conversion, generating a transient thermal field that drives analyte desorption. Ion formation is likely facilitated by surface-assisted protonation/deprotonation processes and possible interfacial charge-transfer processes associated with charge separation at the Ag/CuO interface. Roughness-induced hydrophobicity and moderately strengthened analyte-substrate interactions further facilitate analyte enrichment while maintaining efficient desorption. As a result, the developed substrate exhibits a wide linear dynamic range (10-7-10-3 M, R2 > 0.99) and low detection limits of 0.4-0.8 nM for carbendazim, imidacloprid, and thiabendazole. It also demonstrates high reproducibility, spatial uniformity, and long-term stability. Reliable quantitative analysis is achieved in complex matrices, with results consistent with those obtained by UV-vis spectroscopy, demonstrating its potential for rapid and sensitive pesticide detection. This work provides a rational design strategy for high-performance plasmonic-semiconductor SALDI-MS substrates by integrating efficient laser-energy utilization and controlled interfacial carrier dynamics.