Plasma amplifiers: multiscale light-enhanced uniform SERS composite substrates for breaking through resonance limitations.

A phenomenon known as plasmon resonance constitutes a unique optical effect that can induce an enhancement in localized electromagnetic fields, resulting in a substantial increase in the electromagnetic field intensity surrounding metallic nanostructures. In this work, the coupling effect of excitation of surface plasmon polaritons and local surface plasmons in nanoparticles is deeply studied under the background of nanoparticles/one-dimension grating composite structures through grating matching. By employing finite-difference time-domain simulations as our methodological approach, we discern gratings with a periodicity of 1.5 µm support surface plasmon bound states between the gratings. Furthermore, the modulation of SPs along the vertical sidewalls of the grating due to standing wave effects exhibits oscillatory behavior with varying grating heights. Experimental results obtained from the nanoparticle/grating composite SERS substrate validate theoretical predictions, demonstrating higher enhanced Raman signals at 633 nm compared to 532 nm. Remarkably, this structure exhibits good performance, with R6G detection sensitivity down to concentrations as low as 10-10 M and mapping achieving a relative standard deviation of 7.79%, underscoring its uniformity and capability of electromagnetic field enhancement.

N-glycosylation of the SARS-CoV-2 spike protein at Asn331 and Asn343 is involved in spike-ACE2 binding, virus entry, and regulation of IL-6.

The coronavirus disease 2019 (COVID-19) pandemic is an ongoing global public health crisis. The causative agent, the SARS-CoV-2 virus, enters host cells via molecular interactions between the viral spike protein and the host cell ACE2 surface protein. The SARS-CoV-2 spike protein is extensively decorated with up to 66 N-linked glycans. Glycosylation of viral proteins is known to function in immune evasion strategies but may also function in the molecular events of viral entry into host cells. Here, we show that N-glycosylation at Asn331 and Asn343 of SARS-CoV-2 spike protein is required for it to bind to ACE2 and for the entry of pseudovirus harboring the SARS-CoV-2 spike protein into cells. Interestingly, high-content glycan binding screening data have shown that N-glycosylation of Asn331 and Asn343 of the RBD is important for binding to the specific glycan molecule G4GN (Galß-1,4 GlcNAc), which is critical for spike-RBD-ACE2 binding. Furthermore, IL-6 was identified through antibody array analysis of conditioned media of the corresponding pseudovirus assay. Mutation of N-glycosylation of Asn331 and Asn343 sites of the spike receptor-binding domain (RBD) significantly reduced the transcriptional upregulation of pro-inflammatory signaling molecule IL-6. In addition, IL-6 levels correlated with spike protein levels in COVID-19 patients' serum. These findings establish the importance of RBD glycosylation in SARS-CoV-2 pathogenesis, which can be exploited for the development of novel therapeutics for COVID-19.

Fabrication of silver nanostructure array patterns (SNAPs) on silicon wafer for highly sensitive and reliable SERS substrates.

Metal nanostructure arrays with large amounts of nano-gaps are important for surface enhanced Raman scattering applications, though the fabrications of such nanostructures are difficult due to the complex and multiple synthetic steps. In this research, we report silver nanostructure array patterns (SNAPs) on silicon wafer, which is fabricated with semiconductor manufacturing technology, Cu2O electrochemistry deposition, and Ag In-situ oxidation-reduction growth. Benefiting from the dense and uniform distribution of Ag nanowires, the fabricated SNAPs demonstrate a very strong and uniform surface-enhanced Raman scattering (SERS) effect. The efficiency of SNAPs was investigated by using rhodamine 6G (R6G) dye as an analyte molecule. The results show that the minimum detectable concentration of R6G can reach as low as 10-11 M, and the Raman signals in the random region show good signal homogeneity with a low relative standard deviation (RSD) of 4.77 %. These results indicate that the SNAPs perform a great sensitivity and uniformity as a SERS substrate. Furthermore, we used the SNAPs substrate to detect antibiotic sulfadiazine. The main peaks in sulfadiazine Raman and vibration modes assignments were obtained and the quantitative analysis model was established by principal component analysis (PCA). The detection and application results of sulfadiazine indicate that the SNAPs substrate can be applied for trace detection of antibiotics. In addition, we have cited the application of the SNAPs substrate in anti-counterfeiting labels. These practical applications demonstrate that the fabricated SNAPs can potentially provide a way to develop low-cost SERS platforms for environmental detections, biomedicine analysis, and commodities anti-counterfeiting.

Investigation of high-order resonant modes for aluminium nanoparticles (arrays) using the finite-difference time-domain method.

The optical properties of aluminum nanoparticles are simulated and calculated using the finite-difference time-domain (FDTD) method. Our research has given a comprehensive explanation of how the substrate's dielectric coefficients impact the surface plasmon resonance effect. Furthermore, it offers valuable insights into the role of substrate materials with different dielectric coefficients in modulating the surface plasmon resonance effect of aluminum nanoparticles. The simulation demonstrates the high sensitivity of the structure's surface plasmon resonance (SPR) to the particle size of aluminum nanoparticles. Primarily due to the short-wavelength resonance characteristics, as the particle size increases in the presence of a substrate, there is an overall red shift in the peak position compared to the case without a substrate. A non-metallic kind of substance, which is weakly coupled to the aluminum nanoparticles, has weak electric field enhancement; nevertheless the metal substrates confer significant electrically powered field enhancement to the system, and the height of the particles placed on the substrate also affects the SPR properties of the structure. For various specific needs or possible applications requiring different characteristic peaks, the SPR properties of the aluminum nanoparticle-substrate structure can be tuned by particle size and height.