Synergizing PIERS and photocatalysis effects in a photo-responsive Ag/TiO2 nanostructure for an ultrasensitive and renewable PI-PC SERS technique

Abstract

Surface-enhanced Raman spectroscopy (SERS) is a renowned analytical technique for non-invasive molecular identification. Advancements in SERS technology pivot on designing nano-structured substrates to enhance sensitivity and reliability. A key emerging trend involves integrating pre-treatment and post-treatment techniques on these substrates, leveraging advanced nanostructures to bring unique features, such as ultrasensitivity or reusability, to bridge the gap between laboratory and real-world applications of the SERS technique. Despite these advances, the synergistic application of pre- and post-treatment techniques on a single SERS substrate to fully exploit unique physicochemical effects remains underexplored. To address this, we introduce photo-induced-photo-catalytic SERS (PI-PC SERS), a novel technique that synergistically combines photo-induced enhanced Raman scattering (PIERS) and photocatalysis using a single Ag/TiO₂ nanocomposite structure. This method aims to deliver ultrasensitive sensing capabilities and reusability. The PI-PC SERS technique involves pre-irradiating the SERS substrate with UV light to amplify the Raman signal and post-irradiating to remove fouled analytes. Pre-irradiation enhances the SERS signal by several orders of magnitude compared to normal SERS, attributed to the PIERS effect. Consequently, the detection sensitivity for methylene blue (MB) using PI-PC SERS reaches 1.02 × 10⁻¹⁴ M, significantly better than the 3.04 × 10⁻¹¹ M achieved with normal SERS. Similar enhancements are observed for thiram, with a limit of detection (LOD) of 1.02 × 10⁻¹¹ M for PI-PC SERS compared to 2.19 × 10⁻⁹ M for normal SERS. Additionally, post-irradiation facilitates the removal of analyte molecules via photocatalysis, restoring the substrate to its pristine state, as the byproducts – water and CO₂ gas – are easily managed. Our findings demonstrate that PI-PC SERS creates ultrasensitive sensors and ensures substrate cleanliness and longevity. This method shows great promise for ultrasensitive, sustainable, and cost-effective applications in chemical sensing and molecular diagnostics.