Ag@C Core–Shell Colloidal Nanoparticles Prepared by the Hydrothermal Route and the Low Temperature Heating–Stirring Method and Their Application in Surface Enhanced Raman Scattering

Abstract

Silver nanoparticles (AgNPs) with diameters in the range 40–80 nm have been synthesized by the hydrothermal route and the low temperature heating–stirring method. The influences of reaction time, reactant concentration, and temperature on the AgNP growth have been systemically studied. Experimental surface enhanced Raman scattering (SERS) results show that AgNPs prepared under different temperature and time exhibit a large difference in enhanced SERS signals for rhodamine 6G (10–6 M). Ag@C core–shell NPs have been proved to be formed by using the above two methods, and the carbon shell thickness is gradually increased with increasing reaction time and temperature. It is found that Ag@C NPs with a thick shell (more than 3 nm) have a very low SERS activity, while those with an ultrathin film (less than 1 nm) have a high SERS activity, indicating that carbon shell thickness is a key factor affecting the SERS, which has also been evaluated by finite-difference time-domain simulation. The existence of an ultrathin carbon shell around the AgNP can decrease its surface electric property; then Ag@C NP aggregates are easily formed which may produce the higher hot spots than the bare AgNPs. In addition, this kind of Ag@C NPs exhibits a long SERS-active shelf life (6 months), because the carbon shell can protect AgNPs from oxidation.

Plasmonic Core/Satellite Heterostructure with Hierarchical Nanogaps for Raman Spectroscopy Enhanced by Shell‐Isolated Nanoparticles

“…[ 28,63,64 ] First, PVP (0.5 g) was dissolved in DI water (10 mL); 10 mL of an aqueous solution containing NaOH (0.1 M ) and glucose (0.1 M ) were successively put into the PVP solution and stirred for 5 min. [ 28,63,64 ] First, PVP (0.5 g) was dissolved in DI water (10 mL); 10 mL of an aqueous solution containing NaOH (0.1 M ) and glucose (0.1 M ) were successively put into the PVP solution and stirred for 5 min.…”

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Au and Ag nanoparticles coated with an ultrathin inert shell to act as tips that are similar to the tips used in a TERS system; this new system was named shell-isolatednanoparticle-enhanced Raman spectroscopy (SHINERS). [ 2,[22][23][24][25][26][27][28][29][30][31][32][33][34] Nevertheless, it is still challenging to obtain high-quality Raman spectra from liquid-phase samples on nonmetallic surfaces for ultrasensitive detection due to the limited enhancement from shell-isolated Au nanoparticles.Recently, plasmonic core/satellite structures as a new type of nanostructure have attracted a great deal of attention because of the strong plasmonic coupling formed between satellite nanoparticles. The enhanced Raman signals from the SHINs were as strong as a combined signal resulting from thousands of TERS tips.

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Shell‐Isolated Nanoparticle‐Enhanced Raman and Fluorescence Spectroscopies: Synthesis and Applications

“…Then, CTAB adsorption and carbonization process were alternatively carried out several times, affording carbon‐shell coated Ag nanoparticles. The hydrothermal process can also be used to prepare carbon‐shell‐isolated Ag nanoparticles . For carbon‐shell‐isolated Ag nanoparticles, AgNO 3 and glucose were mixed in DI water and hydrothermally treated at different temperatures and reaction times.…”

Study of Preparation, Growth Mechanism and Catalytic Performance of Carbon Based Embedded Silver Nano Composite Materials

“…By comparing of the peak intensities from Ag/CSs and CSs, we can find that the peak intensity of the former is much more than that of the latter. This may due to the Surface Enhancement Raman Scattering effect of Ag nanoparticles [17]. In addition, both spectrum can be divided into two peaks (G-peak and D-peak) by Gaussian fitting.…”