(397bk) Robust SERS Substrate With Hot Spots Derived From Massive Nanogaps Between Silver Nanoparticles and Nanowires

Robust SERS substrates with hotspots on a large scale from massive nanogaps can be fabricated by assembling Ag nanocubes around nanowires on the ITO glass. Noble metal nanomaterials are commonly used as SERS-active substrates and referred to hotspots because the localized surface plasmon resonance (LSPR) occurs on the surface of metal nanoparticles, especially when nanoparticles are gathered together. Herein, Ag nanowires and nanocubes are synthesized by polyol method and then nanowires and nanocubes were put on the ITO glass step by step. Massive nanogaps form strong LSPR would lead to link Ag surfaces in a nano-scale gap for incurring the substantial increase with several orders of magnitude in SERS signals due to the plasmonic interaction.

The plasmonic interaction of substrate was corroborated by UV-Vis spectra because the frequency change of plasmon resonance indicates the coupling of plasmon. Since Ag nanowire can form large area porous network on the ITO glass, Ag nanocubes could be dispersed homogeneously on the substrate. The adhesion of two metallic surfaces would bring Ag nanocubes and nanowires closely to form lots of nanogaps, which can lead to strong LSPR. From the spectra of UV-Vis, the strength and frequency change of plasmon resonance indicate the strong electrical field coupling occurred on our substrate. Since the intensity of Raman is proportional to the fourth power of the electric field strength, the huge changes in the electromagnetic field of our substrate would result in the substantial increase in SERS signals. In order to clarify the performance of our substrate, the rhodamine 6G (R6G), tryptophan, Lysozyme (LYZ), and Bovine Serum Albumin (BSA) are used as model compounds to confirm SERS results.

Table 1 shows the Raman results for different analytes. With the hot spot on a large scale, and strong LSPR, the SERS results prove the supreme performance of the robust substrate by detecting rhodamine 6G solution with high sensitivity (enhancement factor 5×10⁸) on the basis of 1 cm × 2 cm area. Furthermore, several biomolecules were detected in low concentration (as list in Table1), indicating highly potential in analysis by using our substrate.

SERS is a useful and rapid tool for low concentration detection. Our robust substrate, prepared by assembling Ag nanocubes around Ag nanowires represents the homogeneous distribution of nanogaps, possessing the high enhancement factor on a large scale, indicating highly potential application in biomolecules measurements.