Abstract
For high-precision biochemical sensing, surface-enhanced Raman spectroscopy (SERS) has been demonstrated to be a highly sensitive spectroscopic analytical method and Ag is considered to be the best material for SERS performance. Due to the high surface activity of Ag nanoparticles, the high stability of Ag nanostructures, especially in moist environments, is one of the key issues that need to be solved. A method for silica (SiO2) cladding of Ag nanoparticles (NPs) is demonstrated here for high sensitivity and long-term stability when putted in aqueous solution. The chemically inert, transparent, hydrophilic, and bio-compatible SiO2 surface acts as the protection layer for the Ag nanoparticles, which can also enhance the Raman intensity to a certain extent. In our study, the Ag@SiO2 core-shell substrate can detect crystal violet solutions with molar concentrations down to 10−12 M. After 24 h of immersion, the reduction in Raman scattering intensity is about 85 % for sole Ag NP films, compared to 12 % for the Ag coated with a 10-nm SiO2 layer. This thickness was found to be optimum for Ag@SiO2 core-shell substrates with long-term stability and high SERS activity.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1604-5) contains supplementary material, which is available to authorized users.
Highlights
As a powerful spectroscopic technique, surface-enhanced Raman spectroscopy (SERS) has shown promising applications in surface adsorption, biochemical sensing, and tracelevel analysis as a result of its high sensitivity, rapid response, and the advantages of nondestructive detection [1,2,3,4]
Morphology Characterization of Ag@SiO2 Nanostructure Different film thickness of the SiO2 layers can be achieved by controlling the SiO2 deposition time, and the morphology of the Ag@SiO2 nanostructure was characterized by scanning electron microscopy (SEM), as shown in Fig. 1 and Additional file 1: Figure S1
SERS Characterization of Ag@SiO2 Core-Shell Nanostructure and Research on the Enhancement Mechanism The samples were immersed into 10−6 M crystal violet (CV) solution, which acted as the probe molecule for 30 min, and dried in air
Summary
As a powerful spectroscopic technique, surface-enhanced Raman spectroscopy (SERS) has shown promising applications in surface adsorption, biochemical sensing, and tracelevel analysis as a result of its high sensitivity, rapid response, and the advantages of nondestructive detection [1,2,3,4]. The mechanism for SERS is mainly attributed to the electromagnetic field enhancement caused by the localized surface plasmon resonance of noble metal nanoparticles (NPs). Ag is considered to be one of the most promising candidates for SERS applications due to its low loss in optical frequency and high plasmonic efficiency, as well as its lower cost compared to Significant efforts have been devoted to improve the chemical stability of Ag NPs, and core-shell nanostructures are one of the most popular methods, which have been reported in literatures [11, 12]. Li et al [17] reported the use of a single-atom-thick monolayer of graphene for the protection of Ag NPs that can function as a highly stable SERS substrate for nearly 1 month with ambient aerobic exposure
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