Isotope-Selective Hydrogen-Bond Network Modulations at Plasmonic Gold Nanoparticle Interfaces Probed by Near-Infrared Spectroscopy

Abstract

Localized surface plasmon resonance (LSPR) in metal nanostructures generates intense, spatially confined electric fields. At the present stage, direct experimental evidence for LSPR-induced perturbations at solid–liquid interfaces remains limited. In this study, we utilize near-infrared spectroscopy to monitor overtone and combination vibrational modes of H₂O/D₂O mixtures, which reflect hydrogen bonding networks, in the presence of colloidal Au nanoparticles under LSPR excitation conditions. Notably, spectral changes were observed exclusively in isotopically mixed H₂O/D₂O solutions (1 : 1 volume ratio) under LSPR excitation. The power and wavelength-dependent spectral variations—most prominently observed at 6900 cm⁻¹, corresponding to the first overtone of the O–H stretch—indicate a selective modulations of HOD vibrational modes. Spectral deconvolution reveals that LSPR predominantly perturbs H-D interactions rather than H-H or D-D interactions. These findings highlight an isotope-selective, field-driven reorganization of the interfacial hydrogen bond network, which may contribute to the anomalous kinetic isotope effects observed in plasmon-induced reactions.