Bimetallic Core–Shell Nanostars with Tunable Surface Plasmon Resonance for Surface-Enhanced Raman Scattering

Abstract

Noble metal complex nanomaterials were widely investigated in bioscientific systems for surface-enhanced Raman scattering (SERS) imaging. Silver (Ag) has higher enhancement factors, arising from better optical properties, in comparison to gold (Au), which has better chemical stability and a broader localized surface plasmon resonance (LSPR) region extending to red-NIR, and both should be taken into account to enhance SERS performance. Among them, nanostars (NSs) have emerged as one promising geometry because of their strong enhanced electromagnetic fields induced by the lightning-rod effect from their branches. Therefore, core–shell NSs have been employed as efficient SERS substrates for trace detection because bimetallic nanoparticles provide richer plasmonic modes from their integrated material-dependent and size/shape-correlated plasmonics. Herein, we prepared two uniform and tunable core–shell NSs with different cores (Ag or Au) and the same Au shell, tailoring size and branch morphology to investigate their induced LSPR properties. As a result, their extinction spectra nearly coincide when the size and shape of two NSs become similar. A parallel electric field distribution and response wavelength were obtained as the shells are alike. Thus, it strongly suggests that the shell dominates its LSPR region in the core–shell NS. Meanwhile, an improved SERS activity with an enhancement factor of 1.5 × 107 was achieved in Ag@Au compared to Au@Au NSs because of the addition of Ag. This work offered certain theoretical and experimental references for the plasmonic metal NS with extensively enhanced electromagnetic fields, providing an effective SERS substrate for imaging and detection in life sciences.

Universal Fabrication of Highly Efficient Plasmonic Thin‐Films for Label‐Free SERS Detection

“…The metal composition of the NPs is a key parameter affecting the SERS efficiency. [ 31 ] A representative example is the one of bimetallic NPs with a core@shell structure which provides richer plasmonic modes, thanks to the combined material‐ and size/shape‐dependent plasmonics. [ 32 ] Bimetallic core@shell NPs have been the subject of SERS studies in solution as a function of the size of both core and shell and also excitation wavelength.…”

Nanomaterials for the Diagnosis and Treatment of Inflammatory Arthritis

“…Gold nanostructures including injectable auranofin for RA have been used for medicinal purposes for decades [ 105 ]. Gold nanostructures have been widely evaluated in a number of imaging techniques, including CT, MRI, Raman spectroscopy, fluorescence, and photoacoustic imaging owing to its unique light scattering abilities and configurable surface plasmon resonance [ 106 ]. The desirable imaging features and simplicity of gold nanomaterial preparation make it a good substrate for selective inflammation and arthritis imaging [ 107 ].…”

General Background of SERS Sensing and Perspectives on Polymer‐Supported Plasmon‐Active Multiscale and Hierarchical Sensor Particles

“…[ 9 ] In the SERS, the amplification of electromagnetic fields (intensity enhancement) is not only generated by increasing the concentration of the sample (target analyte) but mainly due to the excitation of localized surface plasmons at a metal surface. [ 31 ] Ideally, the surface of noble metals such as silver or gold can be fabricated with nanoscale roughness where adsorption of analyte molecules takes place, which allows concentrating incident light and enhances scattering outcome. [ 30 ]…”

“…Besides the dimers and controllably assembled nanoparticles, a core–shell architecture is an important configuration that can be utilized as an efficient SERS substrate for high enhancement factors. [ 31,105–106,110–114 ] In this regard, tunable‐sized Au–Ag core–shell nanoparticles were synthesized by either varying the size of Au core or Ag shell, and their SERS activities were performed by different laser lines. [ 111 ] Besides, Au–Ag nanoshuttles with sharp tips and tunable shell thickness were synthesized by using Au nanorods as core materials, and applying Ag shell on its surface in presence of glycine buffer shows improved SERS activity.…”