Comparing the plasmonic properties of laser and chemically synthesized SeNPs for Localized surface plasmon resonance detection.

Localized Surface Plasmon Resonance (LSPR) sensing offers a rapid, label-free, and highly sensitive approach for detecting biomolecular interactions. This study investigates the LSPR characteristics of selenium (Se) nanoparticles synthesized via two distinct approaches: pulsed laser ablation in liquid (PLAL) and chemical reduction, for the development of an optical sensor to detect Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). The laser ablation method produced ligand-free Se nanoparticles with high purity and narrow size distribution, while the chemical reduction route yielded nanoparticles with tunable morphology and surface functionalization capability. The SeNPs were characterized by Ultraviolet-Visible (UV-Vis) spectroscopy, Dynamic Light Scattering (DLS), and High-Resolution Transmission Electron Microscopy (HR-TEM). Raman spectroscopy was used to determine the functional groups on the surfaces of SeNPs. Thereafter, an optical biosensing substrate pre-coated with 3-aminopropyltriethoxysilane (APTES) was functionalized with the SeNPs and conjugated with SARS-CoV-2 monoclonal antibodies (SARS-CoV-2 mAb) to offer specificity for SARS-CoV-2. After characterization, the biosensing substrate was used for detecting SARS-CoV-2 pseudovirus (analyte) using LSPR. In the presence of SARS-CoV-2, the local refractive index around the SeNPs functionalized with the antibody increased, leading to a red shift in the LSPR peak when compared to the control sample. Furthermore, when the antibody captured the SARS-CoV-2 antigen, the SeNPs synthesized by the chemical reduction approach (C-SeNPs) exhibited a higher redshift compared to laser-synthesized SeNPs (L-SeNPs), indicating that C-SeNPs are good candidates for biosensing applications in optical techniques. The difference in LSPR shifts between the two types of nanoparticles reflects their unique sensitivity to biomolecular interactions. These findings demonstrate that synthesis method selection influences LSPR sensor performance, and highlight the potential of Se nanoparticles, particularly those prepared by the chemical reduction method, as promising plasmonic transducers for fast and cost-effective COVID-19 diagnostics.