Abstract
One of the main challenges for highly sensitive surface-enhanced Raman scattering (SERS) detection is the noise interference of fluorescence signals arising from the analyte molecules. Here we used three types of gold nanostars (GNSs) SERS probes treated by different surface modification methods to reveal the simultaneously existed Raman scattering enhancement and inhibiting fluorescence behaviors during the SERS detection process. As the distance between the metal nanostructures and the analyte molecules can be well controlled by these three surface modification methods, we demonstrated that the fluorescence signals can be either quenched or enhanced during the detection. We found that fluorescence quenching will occur when analyte molecules are closely contacted to the surface of GNSs, leading to a ~100 fold enhancement of the SERS sensitivity. An optimized Raman signal detection limit, as low as the level of 10−11 M, were achieved when Rhodamine 6 G were used as the analyte. The presented fluorescence-free GNSs SERS substrates with plentiful hot spots and controllable surface plasmon resonance wavelengths, fabricated using a cost-effective self-assembling method, can be very competitive candidates for high-sensitive SERS applications.
Highlights
Surface-enhanced Raman scattering (SERS) active substrate is currently a hot topic in highly sensitive optical spectral sensing applications because of its short time-consumption and reproducibility[1,2,3,4]
We chemically synthesized gold nanostars (GNSs) with well-controlled morphology as surface-enhanced Raman scattering (SERS) probes combined from previously reported methods[24,25,26,27,28,29,30,31]
The fast Fourier transform (FFT) patterns obtained from the above high-resolution transmission electronic microscopy (TEM) (HRTEM) image shows a hexagonal symmetry diffraction pattern, which indicates that the tips of GNSs are single-crystal with the growth direction of Au
Summary
Surface-enhanced Raman scattering (SERS) active substrate is currently a hot topic in highly sensitive optical spectral sensing applications because of its short time-consumption and reproducibility[1,2,3,4]. Metal nanostructures with densely packed sharp tips, such as nanostars[7,8,9,10] and nanoplates[11,12,13,14,15] are the best promising candidates for high-performance SERS probes To obtain such nanostructures with well controlled morphology and size for SERS application, chemical synthesis methods were usually used[4, 9, 12, 16]. Such chemically synthesized metal nanostructures containing organic shells (capping agents, or modifier)[17] always generate serious background fluorescence noise which limits the SERS detection sensitivity greatly. We showed various technologies including precise control of GNSs morphology, large-scale and uniform preparation of GNSs substrates and several surface modification methods for molecules distance control, which can be widely applied in the fields of optical sensing, processing and display
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