Photothermal Confinement SERS: Interplay between Nanostructure Reconstruction and Molecular Adsorption

Abstract

The high sensitivity of surface-enhanced Raman spectroscopy (SERS) originates from the synergistic interplay among laser irradiation, nanostructures, and molecules. During SERS measurements, laser-induced photothermal effects can promote nanostructure reconstruction and electromagnetic coupling, thereby enhancing the SERS responses. However, they may simultaneously induce molecular desorption and SERS signal attenuation. How these opposing processes are balanced to determine SERS sensitivity remains unclear. Herein, we reveal that the photothermal confinement SERS (PC-SERS) in solid SERS substrates is governed by the interplay among support-mediated photothermal confinement, nanostructure reconstruction, and molecular adsorption affinity. Low-thermal-conductivity supports enable localized photothermal confinement, inducing plasmonic nanostructure reconstruction, narrowing interparticle gaps, and enhancing electromagnetic coupling. Under wet conditions, strongly adsorbed molecules (e.g., 4-mercaptobenzoic acid, 4-MBA) effectively utilized the reconstructed hot spots, achieving a 2−4 orders of magnitude improvement in sensitivity, whereas weakly adsorbed molecules (e.g., benzo[a]anthracene, BaA) suffered depletion from hot spots, resulting in a 1−2 orders of magnitude decrease. This work establishes a mechanistic framework for understanding and controlling photothermal effects in SERS through the coupled evolution of nanostructures and molecular adsorption.