# Photo-induced-photo-catalytic SERS with silver-deposited TiO2 nanorods for ultrasensitive and sustainable detection of low Raman cross-section molecules

## TL;DR

A new SERS technique using silver-deposited TiO2 nanorods improves detection of hard-to-measure molecules and allows the sensor to clean itself for reuse.

## Contribution

The novel PI-PC SERS method combines photo-induced enhancement and photocatalytic degradation for ultrasensitive and reusable detection.

## Key findings

- PI-PC SERS enhanced detection sensitivity tenfold compared to normal SERS.
- The technique enabled self-cleaning by removing residual analytes after measurement.
- It successfully detected low Raman cross-section molecules like 4-nitrophenol and urea.

## Abstract

Surface-enhanced Raman spectroscopy (SERS) offers significant advantages, including label-free, non-invasive analysis and ultrasensitivity down to the single-molecule level, making it widely applicable in analytical chemistry and biology. However, its effectiveness is limited when detecting molecules with inherently low Raman scattering cross-sections, restricting its broader applications. In this study, we apply the photo-induced-photo-catalytic SERS (PI-PC SERS) technique, utilizing an Ag-deposited TiO2 nanorod (Ag/TiO2 NR) substrate to overcome this limitation. The PI-PC SERS technique combines two optoelectronic effects: photo-induced enhanced Raman scattering (PIERS) and the photocatalytic activity of the metal/semiconductor substrate. PIERS amplifies Raman signals beyond normal SERS, while the photocatalytic effect facilitates the removal of residual analytes. The PI-PC SERS process follows three sequential irradiation steps: (i) pre-irradiation with 365 nm UV light to activate PIERS, (ii) laser excitation at 785 nm to capture the enhanced Raman signal, and (iii) post-irradiation with 365 nm UV light to trigger photocatalytic degradation. Two low Raman cross-section molecules, 4-nitrophenol (a widely used pesticide) and urea (an important biomarker), were selected to evaluate the performance of the PI-PC SERS technique on the Ag/TiO2 NR substrate. The results demonstrated that PI-PC SERS not only enhanced detection sensitivity tenfold compared to normal SERS but also enabled self-cleaning by efficiently removing residual analytes after measurement, ensuring substrate reusability. These findings pave the way for advancing SERS-based techniques for detecting low Raman cross-section molecules while broadening their potential applications in chemical and biological sensing fields.

In this study, we introduce a PI-PC SERS strategy based on Ag-deposited TiO2 nanorods (Ag/TiO2 NRs), integrating PIERS and photocatalysis effects to achieve ultrasensitive, renewable detection of low-Raman-cross-section molecules.