Abstract
Surface-enhanced Raman scattering technique, as a powerful tool to identify the molecular species, has been severely restricted to the noble metals. The surface-enhanced Raman scattering substrates based on semiconductors would overcome the shortcomings of metal substrates and promote development of surface-enhanced Raman scattering technique in surface science, spectroscopy, and biomedicine studies. However, the detection sensitivity and enhancement effects of semiconductor substrates are suffering from their weak activities. In this work, a semiconductor based on Nb2O5 is reported as a new candidate for highly sensitive surface-enhanced Raman scattering detection of dye molecules. The largest enhancement factor value greater than 107 was observed with the laser excitation at 633 and 780 nm for methylene blue detection. As far as literature review shows, this is in the rank of the highest sensitivity among semiconductor materials; even comparable to the metal nanostructure substrates with “hot spots”. The impressive surface-enhanced Raman scattering activities can be attributed to the chemical enhancement dominated by the photo-induced charge transfer, as well as the electromagnetic enhancement, which have been supported by the density-functional-theory and finite element method calculation results. The chemisorption of dye on Nb2O5 creates a new highest occupied molecular orbital and lowest unoccupied molecular orbital contributed by both fragments in the molecule-Nb2O5 system, which makes the charge transfer more feasible with longer excitation wavelength. In addition, the electromagnetic enhancement mechanism also accounts for two orders of magnitude enhancement in the overall enhancement factor value. This work has revealed Nb2O5 nanoparticles as a new semiconductor surface-enhanced Raman scattering substrate that is able to replace noble metals and shows great potentials applied in the fields of biology related.
Highlights
Surface-enhanced Raman scattering (SERS) has inspired researchers’ great interests because of its highly sensitive, efficient, and nondestructive characters for detection of traces amount of target molecules
The X-ray diffraction (XRD) pattern of Nb2O5 NPs (Fig. 1a) indicates that all the peaks can be indexed to orthorhombic Nb2O5 (PDF #71-0336).[29]
The high resolution transmission electron microscope (HRTEM) micrograph in Fig. 1c further indicates the spacing of adjacent lattice fringes as 0.391 nm, which is corresponding to the (001) lattice planes
Summary
Surface-enhanced Raman scattering (SERS) has inspired researchers’ great interests because of its highly sensitive, efficient, and nondestructive characters for detection of traces amount of target molecules. This enables promising applications in the fields of surface science, spectroscopy, chemical analysis, and biochemical detection.[1,2,3,4,5] Generally, the noble metals of Au and Ag, because of their unique and remarkable surface plasmon resonance effect, are widely used as SERS sensors with high sensitivity.[6,7,8,9] the SERS technique as a new analytical methodology has not vanished as far as initially predicted.[10] It is one of the most profound difficulties that only several limited noble metals possess a significant Raman enhancement capability, but can hardly satisfy the applications involving other non-metal materials. It is of great significance to explore alternative non-metal SERS substrates for a better applicability
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