Near-Infrared Light Absorbing Silver-Coated Hollow Gold Nanostars for Surface-Enhanced Raman Scattering Detection of Bovine Serum Albumin Using Capping Ligand Exchange

Abstract

Two novel urchinlike plasmonic nanostructures, hollow gold nanostars (HNSs) and silver-coated hollow gold nanostars (AgHNSs), were synthesized using hollow gold nanospheres (HGNs) as templates. The particle morphology was assessed by transmission electron microscopy (TEM), optical properties were characterized by UV–vis spectroscopy, and elemental composition was evaluated by both inductively coupled plasma-optical emission spectrometry (ICP-OES) and energy-dispersive X-ray (EDX) analysis. Both the HNSs and AgHNSs exhibit tunable structural and optical properties. Their unique star-shaped structure provides the desired “hot spots” for enhancing the electromagnetic (EM) field for surface-enhanced Raman scattering (SERS) applications, while their near-infrared (NIR) absorption is ideal for biomedical applications. A comparative analysis of the relative SERS enhancement using rhodamine 6G (R6G) showed that HNSs reported herein have an order of magnitude higher relative enhancement over previously reported HNSs. Moreover, AgHNSs have a 4-fold increase in the SERS signal compared to HNSs. Discrete dipole approximation (DDA) simulations of electric field enhancement were used to corroborate the experimental findings. The comparison between the experimental and theoretical results suggests that the significant increase in SERS enhancement cannot be completely explained by the larger dielectric constant of silver. The branching of individual spikes, or the increased binding efficacy of the analyte to the nanoparticles, likely also plays an important role. To further explore the applicability of these novel structures, successful capping ligand exchange from citrate to pentanethiol was used to switch the surface charge from negative to positive to facilitate the SERS detection of dried bovine serum albumin (BSA). AgHNSs are stable and effective NIR-absorbing substrates for SERS detection of biological samples. Elemental analyses of AgHNSs, in conjunction with DDA simulations, provide insights into their enhancement mechanism.

Surface-Enhanced Raman Spectroscopy Chips Based on Silver Coated Gold Nanostars

“…More recently, we have used them as an effective substrate for the realization of SERS nanotags for determination of fibroblast activation protein in fibroblasts. Moreover, it has also been demonstrated that the addition of a silver shell to branched gold nano-objects can further enhance their SERS responses, and that the enhancement is strictly connected to the extent of the silver layer [ 24 , 25 , 26 , 27 ]. Inspired by these works, we decided to apply a silver coating layer to our Triton based GNS to increase their SERS response towards environmental pollutants.…”

Facile synthesis of multibranched gold nanostars with precisely tunable sizes for surface-enhanced Raman scattering

“…To achieve high-quality SERS signals, it is essential to design and control the size and morphology of these nanostructures to obtain superior SERS sensitivity, uniformity, and reproducibility. In particular, both experimental results and theoretical calculations indicate that branched Au NPs (such as nanoflowers, nanourchins, nanodendrites, and nanostars) with sharp tips, edges, and corners have intrinsic hotspots, which can generate extremely high electromagnetic field enhancements, [12][13][14] allowing their use in SERS, 15,16 sensing, 17 and photothermal therapy. 18,19 On the other hand, these branched Au NPs have a unique branched structure, which provides a large surface area and numerous sharp tips that can greatly enhance the Raman signal of molecules adsorbed on their surface.…”

Ultra-high SERS detection of consumable coloring agents using plasmonic gold nanostars with high aspect-ratio spikes

“…Among the various metal nanoparticles reported to date, anisotropic gold nanostars (GNS) promise to be a potential candidate due to their excellent SERS enhancement properties, tunable plasmon resonance, and good stability in ambient conditions. [29][30][31][32][33] Anisotropic GNS is an excellent SERS platform than other nanoparticle systems owing to three reasons. First, GNS has 3D sharp protruding spikes, thereby facilitating the generation of multiple hot spots than other nanoparticle systems such as nanospheres, nanorods, and nanocubes.…”