With the ease that people can travel around the world, viruses spread through droplet transmission are one of the most dangerous causes of infectious diseases. The COVID-19 pandemic made this point quite clear. One of the obvious responses to prevent a reoccurrence of this type of situation is effective virus detection technology to prevent the global spread of viruses.
A technique thought to be useful as next-generation detection methods involves surface plasmon resonance (SPR) in microscale and localized SPR (LSPR) in nanoscale virus sensing systems. Many studies have been conducted on ultra-sensitive technologies, especially those based on signal amplification. In some cases, it has been reported that even a low viral load can be measured, indicating that the virus can be detected in patients in the early stages of the viral infection. These findings corroborate that SPR and LSPR are effective in minimizing false-positives and false-negatives that are prevalent in the existing virus detection techniques.
Existing polymerase chain reaction (PCR)-based detection methods provide highly effective methods for virus detection, but their use is limited by (1) the cost of equipment, (2) the need for skilled technicians, and (3) the time required for detection. By automating the PCR system, the next-generation technologies should have a reliable single-step detection of the target virus and require minimum time for detection.
SPR provides another detection technology. In surface plasmon resonance, surface charge oscillations are coupled with electromagnetic waves. The quantum of these oscillations is called surface plasmon polariton (SPP) and the excitation of SPP is an essential step in SPR biosensors.
Compared to SPR on a thin metal film, plasmon phenomenon produced by irradiating light on metal nanoparticles is described as localized SPR. In this case, the plasmon generated on the nanoparticle surface produces a strong electric field in the vicinity of the nanoparticles. Within the plasmon region, the interaction of light with molecules and other types of fluorescent nanomaterials is enhanced. A significantly enhanced electric field forms between the particles, when the nanoparticles in the electric field are in close proximity to each other or bind together. In this electric field, Raman scattering of certain chemical species is electromagnetically enhanced.
The LSPR-based virus detection technique involves an optimized thin metal film modified on a prism for coupling light. To be effective, LSPR requires meticulous nanoparticle control technology to detect virus particles because more localized plasmons emit highly strong signal responses. However, since SPR does not require a prism, a detection system can be constructed using only a light source and a detector that can irradiate specific light.
Other LSPR Research
When LSPR sensors using metallic nanoparticles are used for refractive index (RI) measurements in chemical and biological studies, their sensitivity is highly influenced by the material and structure of the nanoparticle. Recent advances in the improvement of LSPR sensitivity have been found by fabricating plasmonic array nanostructures with high uniformity and site-selective immobilization. In addition, the use of a simple mathematical approach with LSPR inflection point has been found to improve the RI sensitivity in gold nanoparticles with different shapes, sizes, shells and more.
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