Fractal Shaped Periodic Metal Nanostructures Atop Dielectric-Metal Substrates for SERS Applications

Abstract

Controlled and reliable field enhancement (FE) effects associated with the excitation of plasmons in resonant metal nanostructures constitute an essential prerequisite for the development of various sensing configurations, especially those utilizing surface-enhanced Raman scattering (SERS) spectroscopy techniques. Leveraging advantages of random nanostructures in providing strong collective resonances in a broad wavelength range with the design flexibility of individual gap plasmon resonators, we experimentally investigate fractal-shaped arrays of gap plasmon resonators and characterize the occurring FE effects by mapping SERS signals from uniformly spread Rhodamine 6G with high-resolution Raman microscopy. In such a geometry, the total FE is expected to benefit from both FE associated with gap plasmon excitation and FE due to constructive interference of the surface plasmon modes reflected and diffracted by fractal-shaped boundaries. Linear reflection imaging spectroscopy is used to verify that the fabricated nanostructures exhibit spatially distributed resonances (bright spots) close to the excitation wavelengths used for the Raman microscopy. The positions of bright spots are argued to be influenced by fractal-shaped boundaries, particle dimensions, polarization, and wavelength of the incident and scattered light. Experimentally obtained SERS images from similar fractal (gold) structures fabricated with different dielectric SiO 2 spacer thicknesses (0, 20, and 40 nm) featured diffraction-limited bright spots corresponding to local SERS enhancements of up to ∼10 7 (relative to Raman signals obtained with a glass substrate) for 40 nm thick SiO 2 layers. Our results indicate that the strategy of combining fractal array geometry with gap plasmon resonances is promising for the design of highly efficient SERS substrates for potential applications in surface-enhanced multichannel sensing, including single-molecule spectroscopy.

Model of the SARS-CoV-2 Virus for Development of a DNA-Modified, Surface-Enhanced Raman Spectroscopy Sensor with a Novel Hybrid Plasmonic Platform in Sandwich Mode

“…The surface of the sensor element is represented with a multilayered structure based on subsequently coated silver mirror film, dielectric film, and Ag nanoparticles, further referred to as film-Ag/SiO 2 /nano-Ag NPs ( Figure 3 a). As noted above, the amplification of the Raman signal for sandwiches in comparison with one-contained-layer nanostructured silver surface is associated with the excitation of both gap plasmons in the SiO 2 layer and local surface plasmon resonances in nano-Ag NPs [ 5 , 6 , 7 , 8 ]. Moreover, the back reflection from the bottom Au layer gives rise to a stronger absorbance and, therefore, the enhancement factor (EF) since the excitation beam passes through the top film twice.…”

“…Such a hybrid scaffold provides efficient work with high-molecule volumetric objects such as live cells and offers sufficient optical transparency for both fluorescence and SERS imaging. The novel hybrid metal-dielectric-metal sandwiched structures [ 5 , 6 ] demonstrate high sensitivity and reproducibility of the SERS signal [ 7 , 8 ]. In this geometry, the overall enhancement factor principally benefits from the combination of two main mechanisms.…”

SERS uncovers the link between conformation of cytochromecheme and mitochondrial membrane potential

“…Plasmon nanostructures allow for the detection of molecules at very low, of the order of nM, concentrations 29,30 . The spectral position of SPRs can be tuned by the geometry, composition, size, and shape of nanoparticles 31,32 . SERS is widely used in biochemistry, pharmacology, and biomedical sciences 33,34 .…”

“…However, RS cannot provide information about certain heme conformations and cannot detect oxidized cytochromes due to their weak Raman scattering. Surface-enhanced Raman spectroscopy (SERS) is known to be a highly effective tool to enhance Raman scattering of molecules 28,29,30,31,32,33 . SERS allows for the study of molecules at very low (below nM) concentrations and is widely used in biochemistry, pharmacology, and biomedical sciences 34,35 .…”

Clustered Regularly Interspaced Short Palindromic Repeats-Mediated Amplification-Free Detection of Viral DNAs Using Surface-Enhanced Raman Spectroscopy-Active Nanoarray

“…could be utilized for sensitive detection to maximize the SERS effect. In particular, strong electromagnetic (EM) fields related to the plasmon resonance properties of noble nanomaterials are used to increase the Raman vibrational signals from target analytes. − With possible enhancement factors up to 10 14 , SERS analytical methods represent an exceptionally sensitive detection method with optimized nanomaterials. − Having their advantages, SERS-integrated amplification-free CRISPR-Cas9 biosensors have been shown to detect multidrug-resistant bacteria with femtomolar sensitivity . However, rapid, sensitive, and selective detection of viral biomarkers is still urgent in preparing for future pandemics.…”