MXene-Mediated Charge Modulation in Plasmonic Metal-Semiconductor Heterojunctions for Photo-Induced Enhanced Raman Spectroscopy.

The smart integration of nanoparticles with tailored semiconductors, followed by UV illumination prior to Raman measurements, activates photo-induced enhanced Raman spectroscopy (PIERS), enabling ultrasensitive detection. This photo-mediated modulation of charge transfer is a special case of surface-enhanced Raman spectroscopy (SERS), where enhancement is tuned via chemical-interaction-induced charge transfer between the analyte and substrate. Herein, photoinduced charge transfer dynamics are explored by tuning the work function of the supporting material embedding plasmonic nanostructures and creating an interfacial light-mediated charge-transfer system. Using two distinct nanoparticles supported on a two-dimensional material revealed directional charge transport behaviour, reflecting Fermi-level equilibration at heterojunctions. Titanium carbide-based MXene (Ti₃C₂Tx; Tx = -OH, -F) is introduced as a charge-transfer modulator due to its tunable work function, significantly influencing carrier transport direction and efficiency. Notably, Au-based hybrids exhibit PIERS enhancement upto five orders of magnitude, unlike Ag-based hybrids that show quenching. This confirms that optimized nanoparticle-MXene hybrids facilitate hot electron movement across interfaces, leading to differential PIERS responses. Additionally, density functional theory calculations elucidate electronic structures and photogenerated electron migration. This study provides valuable insights into photo-induced charge transfer, emphasizing its pivotal role in enhancing chemical contributions in SERS, advancing future optical sensing and molecular recognition platforms.