Abstract
A facile seed-mediated method was developed to modify core-shell Ag nanosphere@PSPAA with another Ag layer for achieving an enhancement of their surface-enhanced Raman scattering (SERS) activity. Interestingly, an Ag bridge in the polymer shell connected the inner and outer Ag layers, resulting in a mushroom-like nanostructure. The outer Ag grew around the polymer shell to form the cap of the nanomushrooms (NMs) with the extension of the reaction time. The epitaxial growth mechanism of this novel nanostructure was investigated by tuning the type of seed from nanosphere to nanocube and nanorod. With the growth of the outer Ag cap, the SERS intensity of these Ag NMs increased significantly together with the red-shifting and broadening of their typical localized surface plasmon resonance band. Such a phenomenon can be attributed to the formation of SERS hotspots between the inner and outer Ag layers. The Ag NMs were then wrapped with a graphene oxide (GO) shell via static interactions. The GO-wrapped Ag NMs exhibited a further better SERS performance in terms of sensitivity, homogeneity and stability compared with non-wrapped ones, indicating that the heterostructure could be potentially useful for SERS-based immunoassay.
Highlights
Over the past two decades, surface-enhanced Raman scattering (SERS) has evolved into a notably promising analytical method in the fields of life care, environmental monitoring, food safety, and state security due to its single-molecule sensitivity[1,2,3,4,5]
These core-shell NPs were used as seed for in-situ reducing AgNO3 on their surface to grow outside Ag layer
Ag NMs were prepared by a seed-mediated growth method using core-shell Ag NS@polystyrene-block-poly(acrylic acid) (PSPAA) as core under the assistance of surfactant sodium citrate
Summary
Over the past two decades, surface-enhanced Raman scattering (SERS) has evolved into a notably promising analytical method in the fields of life care, environmental monitoring, food safety, and state security due to its single-molecule sensitivity[1,2,3,4,5]. Among the various SERS-based materials, noble metal nanostructures have demonstrated superior activity since the generation of extremely strong electromagnetic field under the excitation of their localized surface plasmon resonance (LSPR)[6,7,8]. Among all these noble metals, Ag stands out due to its easy fabrication process and excellent SERS performance[9]. Recent advances in wet-chemical synthesis further enable the fabrication of various Ag nanostructures with engineered complex size, shape, and composition, such as nanorods[10], nanoplates[11], nanocubes[12], and nanostars[13] These nanostructures have been extensively prepared by using different types of surfactant to effectively tune their plasmonic properties. After exposing to ambient air for one month, the GO-wrapped sample exhibited a more stable SERS signal with decrease ratio of only 15%
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