Recent Advances in Photo-Induced Enhanced Raman Spectroscopy for Ultrasensitive Molecular Detection: Mechanisms, Substrate Engineering, and Irradiation Effects

Abstract Photoinduced enhanced Raman spectroscopy (PIERS) has emerged as an important extension of surface enhanced Raman spectroscopy (SERS), providing enhanced sensitivity through the synergistic effect of electromagnetic field amplification and photoinduced charge transfer (CT) processes. In a typical PIERS configuration, photoactive semiconductor substrates such as TiO2, ZnO, or WO3 are decorated with plasmonic nanoparticles (NPs) and subjected to UV pre-irradiation, which generates oxygen vacancies and sub-bandgap defect states. These defects facilitate efficient interfacial CT from the semiconductor through the plasmonic nanostructure to the adsorbed analyte, thereby amplifying the Raman scattering cross-section beyond what can be achieved through electromagnetic enhancement alone. This review systematically examines PIERS across four dimensions: (i) the stepwise enhancement mechanism involving defect-mediated UV/photoirradiation and interfacial CT; (ii) substrate architectures spanning noble metal-semiconductor nanocomposites, noble-metal-free defect-engineered platforms, and hybrid systems incorporating MXenes, perovskites, and piezoelectric materials; (iii) excitation parameters, including Raman laser excitation and UV irradiation conditions such as power, wavelength, and duration and (iv) signal stability, oxygen vacancy dynamics, and long-lived PIERS responses arising from Schottky barrier formation at metal-semiconductor interfaces. The review concludes with practical guidelines for benchmarking and standardizing PIERS data to enable meaningful cross-laboratory comparison.