Abstract
Metallic nanoparticles (MNPs) and metallic nanostructures are both commonly used, independently, as SERS substrates due to their enhanced plasmonic activity. In this work, we introduce and investigate a hybrid nanostructure with strong SERS activity that benefits from the collective plasmonic response of the combination of MNPs and flow-through nanohole arrays (NHAs). The electric field distribution and electromagnetic enhancement factor of hybrid structures composed of silver NPs on both silver and gold NHAs are investigated via finite-difference time-domain (FDTD) analyses. This computational approach is used to find optimal spatial configurations of the nanoparticle positions relative to the nanoapertures and investigate the difference between Ag-NP-on-Ag-NHAs and Ag-NP-on-Au-NHAs hybrid structures. A maximum GSERS value of 6.8 × 109 is achieved with the all-silver structure when the NP is located 0.5 nm away from the rim of the NHA, while the maximum of 4.7 × 1010 is obtained when the nanoparticle is in full contact with the NHA for the gold-silver hybrid structure. These results demonstrate that the hybrid nanostructures enable hotspot formation with strong SERS activity and plasmonic enhancement compatible with SERS-based sensing applications.
Highlights
Metallic nanostructures that support surface plasmon resonance (SPR) have been extensively researched in the past decade and employed in several sensing and biosensing applications, including cell analysis [1], the detection and quantification of infectious diseases [2,3,4], and cancer biomarker quantification [5]
SPR is based on the collective oscillation of conduction electrons, which promotes an enhancement of the electromagnetic field at the metal-dielectric interface [6]
We investigate the electromagnetic field enhancement achieved by the combination of two nanoplasmonic-enabling structures, metallic nanoparticles and nanohole arrays, as a hybrid structure for a potential surface-enhanced Raman scattering (SERS) substrate with hot spots
Summary
Metallic nanostructures that support surface plasmon resonance (SPR) have been extensively researched in the past decade and employed in several sensing and biosensing applications, including cell analysis [1], the detection and quantification of infectious diseases [2,3,4], and cancer biomarker quantification [5]. In the context of (bio)sensing, this phenomenon has found applications in techniques such as SPR spectroscopy [1,2,7,8], SPR imaging [3,4,9], and surface-enhanced Raman scattering (SERS) spectroscopy [10,11,12]. SERS is a light scattering-based technique that enables the detection of chemical and biological analytes in a label-free fashion owing to the inherent and unique vibrational modes of the molecules. SERS-active nanostructures enhance the vibrational excitation of molecules due to a confined enhancement of electromagnetic field at the metal surface, so-called “hotspots”, which translates into a stronger signal due to the high level of light scattering from the sample [13,14]. SERS has been demonstrated to boost the Raman sensitivity by several orders of magnitude, even in small amounts of analytes
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