In recent years, surface-enhanced Raman scattering (SERS) of a molecule/metal–semiconductor hybrid system has attracted considerable interest and regarded as the synergetic contribution of the electromagnetic and chemical enhancements from the incorporation of noble metal into semiconductor nanomaterials. However, the underlying mechanism is still to be revealed in detail. Herein, we report an irreversible accumulated SERS behavior induced by near-infrared (NIR) light irradiating on a 4-mercaptobenzoic acid linked with silver and silver-doped titanium dioxide (4MBA/Ag/Ag-doped TiO 2 ) hybrid system. With increasing irradiation time, the SERS intensity of 4MBA shows an irreversible exponential increase, and the Raman signal of the Ag/Ag-doped TiO 2 substrate displays an exponential decrease. A microscopic understanding of the time-dependent SERS behavior is derived based on the microanalysis of the Ag/Ag-doped TiO 2 nanostructure and the molecular dynamics, which is attributed to three factors: (1) higher crystallinity of Ag/Ag-doped TiO 2 substrate; (2) photo-induced charge transfer; (3) charge-induced molecular reorientation.
As a highly functional platform, lab-on-fiber (LOF) has exhibited amazing potential to be used in ultrasensitive surface-enhanced Raman spectroscopy (SERS) detection. However, the low detection efficiency and high cost of most SERS-based LOF platforms have severely limited their further applications in environmental monitoring, biomedicine, etc. Here, we report a reusable SERS-based LOF platform through a Au-coated optical fiber integrated into a patterned microfluidic chip. With the assistance of laser-induced thermophoresis, we successfully obtained rich “hot spots” on the Au-coated optical fiber by reversible accumulation of gold nanoparticles within 5 min. Experimental results indicate that it has a low detection limitation of 10–10 mol/L (M) for environmental pollutant molecules. Fortunately, with the dynamic and reversible accumulation of gold nanoparticles controlled by laser on/off, the platform shows excellent reversibility and stability under multiple detection–cleaning cycles, which are better than those of the LOF platform based on chemical modification and photochemical deposition. The thermophoresis-based LOF platform with the advantages of easy operation, miniaturization, and high reusability provides a cost-effective approach for SERS detection.
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