Photoinduced Enhanced Raman Spectroscopy for the Ultrasensitive Detection of a Low-Cross-Section Chemical, Urea, Using Silver–Titanium Dioxide Nanostructures

Abstract

Surface-enhanced Raman scattering (SERS) is a powerful analysis technique that allows both the identification and detection of analytes at trace levels. However, the low rate of charge transfer (CT) between noble-metal nanoparticles and several analytes prevents them from being effectively detected by SERS-based sensors. They are regarded as low Raman crosssection molecules. In this study, we enhanced the performance of the silver nanoparticles (AgNPs)-based SERS sensing platform for a low Raman cross-section molecule, urea, focusing on improving the rate of CT. First, a set of Ag/titanium dioxide (TiO 2 ) nanocomposites were synthesized. The presence of TiO 2 improved the intensity of the SERS signal of urea, in comparison to the use of bare AgNPs. Second, a photoinduced enhanced Raman spectroscopy (PIERS) technique was employed to further elevate the Raman signal of urea. Thanks to the step of preirradiation using UV light at λ = 365 nm, with the use of the substrates containing 25%, 33%, and 50% TiO 2 content, enhancements of 1.93, 3.42, and 7.45 times were achieved, respectively, compared to the use of Ag/TiO 2 composites without UV irradiation. Through modification of the substrate, combined with application of the PIERS technique, the SERS system for urea detection using Ag/3TiO 2 (50% TiO 2 ) achieved a competitive detection limit of 4.6 × 10 −6 M. It also allowed the detection of urea in milk at concentrations down to 10 −5 M. This substrate modification and PIERS technique are promising for improvement of the sensing performance of other low-cross-section molecules.

A manganese dioxide–silver nanostructure-based SERS nanoplatform for ultrasensitive tricyclazole detection in rice samples: effects of semiconductor morphology on charge transfer efficiency and SERS analytical performance

“…It allowed more hot electrons to be transferred to the LUMO level of the analyte. This strategy was adopted using Ag/TiO 2 nanostructures, [6][7][8] Au@WS 2 nanocomposites, 9 AuNPdiphenylalanine peptide nanotubes, 10 etc., exhibiting improvements in the SERS performance of the sensing systems. However, it requires an additional step of UV excitation before SERS measurement.…”

Photoactivated plasmonic nanohybrid fibers with prolonged trapping of excited charge carriers for SERS analysis of biomolecules

“…[44][45][46] There have been instances where preirradiation of the SERS substrate with light has helped in achieving higher enhancement for molecules with low scattering cross sections. 22,24 Specifically, this photoactivation method has been observed for Ag-TiO 2 nanocomposites with (254 nm)-UVC radiation. The oxygen vacancy produced on the surface due to radiation creates donor states below the conduction band edge, tuning the optical absorption to the visible range.…”

“…23 The subsequent net charge transfer to the silver nanoparticles (AgNPs) leads to higher SERS chemical enhancement. 24 However, introducing core-shell or non-transparent supporting substrates does not aid the system's efficient molecular absorption or light-harnessing efficiency. 22 Herein, we propose a new type of transparent support for plasmonic nanoparticles for photo-induced SERS through preradiation or photoexcitation of the dielectric medium.…”

Emergence of Raman Spectroscopy as a Probing Tool for Theranostics

“…RS has an inherently low scattering cross section, much lower than fluorescence 174 , 175 . The autofluorescence background often makes it challenging to get a discernible spectrum and complicates the Raman spectral analysis under in vivo conditions, specifically under slow imaging 176 . However, these problems can be overcome by using a near-IR laser which ensures a much lower fluorescence background, and also by using a fast scanning spectrometer which can either do point, line, or raster scanning using a rotating galvo-mirror 177 .…”