Rapid on-site detection of gaseous methylarsines using a portable surface-enhanced Raman spectrometer based on Ag-As interaction

Gaseous methylarsines (monomethylarsine, MMA; dimethylarsine, DMA; and trimethylarsine, TMA) are toxic and widespread in the environment. Traditional off-site methods for analyzing gaseous methylarsines are not suitable for field deployment, and the integrity of these gases may be compromised during sample collection, preservation, and transportation. The development of on-site gaseous methylarsine detection techniques is crucial and urgent for understanding the biogeochemical cycle and associated risk of arsenic. Here we present a portable device designed for in-field detection of gaseous methylarsines, composed of a portable Raman spectrometer, an air pump, and a substrate for surface-enhanced Raman spectroscopy (SERS). The substrate was prepared conveniently by loading silver dendrites onto the surface of a copper mesh via a Cu-Ag substitution reaction, allowing specific adsorption of gaseous methylarsines based on the Ag-As interaction. Based on density functional theory (DFT) calculations, we found that the adsorption energies of methylarsines on the Ag(111) surface ranged from −0.28 to −0.50 eV, indicating thermodynamically favorable adsorption. The favorable adsorption energy is attributed to the hybrid coupling between the As and Ag orbitals near the Fermi level, with the interaction strength increasing with the degree of methylation. With the portable SERS device, the limits of detection for MMA, DMA, and TMA gases were 0.11, 0.10, and 0.09 mg/m 3 (as As), respectively. Real gas samples from the Yangbajing Hot Spring on the Tibetan Plateau were typically analyzed on-site, and TMA was detected at 30.28 mg/m 3 (as As). The result was validated using traditional liquid chromatography-hydride generation-atomic fluorescence spectroscopy (LC-HG-AFS) analysis.