Surface plasmon resonance (SPR) is a spectroscopic technique that can be used to study the interaction between light and metal surfaces as well as the properties of thin metal films. When light strikes the interface between a metal and a dielectric medium (such as air or water), surface plasmons are generated – density oscillations of the electrons at the metal interface. The surface plasmon resonance effect occurs when surface plasmons are excited by light through an optical phenomenon known as total internal reflection.
How Does SPR Work?
In an SPR experiment, light from a monochromatic light source is directed towards a prism. One side of the prism is coated with a thin film of metal, usually gold or silver, and the other side contacts a liquid sample solution. When light strikes the internal face of the prism at a specific angle, total internal reflection occurs and an evanescent wave is generated at the metal boundary. This evanescent wave penetrates the metal film and can couple with surface Surface Plasmon Resonance under the proper conditions. By detecting the angle at which surface plasmons are excited based on the minimum in reflected light, information about the local refractive index at the metal surface can be ascertained.
Sensing Molecular Interactions with SPR
One of the most common applications of SPR is to detect and analyze biomolecular interactions. In a typical experiment, one binding partner is immobilized on the metal surface while the other binding partner is flowed over in liquid phase as the analyte. As analyte molecules interact with and bind to the immobilized ligands, a change in local refractive index at the sensor surface occurs. This leads to a change in the angle of resonance that can be directly monitored and quantified in real-time. SPR has proven to be highly sensitive for various binding studies, allowing researchers to measure KD values, binding kinetics, concentrations of analytes, and more.
Applications in Drug Discovery and Development
Due to its label-free, real-time capabilities, SPR has found widespread utility in drug discovery and development. It has become a mainstay technology for high-throughput screening of compound libraries against protein targets of interest. SPR can rapidly evaluate thousands of potential drug candidates for binding affinity and activity. Additionally, SPR biosensors have facilitated mechanistic studies to identify lead compounds, optimize drug candidates, and characterize drug-target interactions. This information aids in deciding go/no-go decisions, selecting appropriate molecules for further development, and gaining biological insights critical for developing effective therapeutics.
Detecting Viruses, Bacteria and Toxins
The high sensitivity of SPR also enables its use as a biosensing platform for detecting various pathogens. Functionalized metal surfaces can specifically capture viruses, bacteria, or toxins from complex samples. By measuring the change in SPR signal, extremely low analyte concentrations down to the single-digit picomolar range can be accurately quantified. This has enabled the development of SPR-based assays for detecting food/water contaminants, disease biomarkers, and biowarfare agents. Portable SPR sensors show promise as a rapid, on-site testing method in applications like environmental monitoring, clinical diagnostics, and biothreat detection.
Quality Control and Food Safety Testing
Beyond research uses, SPR biosensors see application in quality control testing within various industries. For the food and beverage industry, SPR assays can test for allergens, spoilage microbes, and food authenticity. This allows producers to ensure safety, meet regulations, verify labeling claims, and manage recalls more effectively if issues arise. SPR is also well-suited for authenticating high-value goods and monitoring counterfeiting within industries like pharmaceuticals, luxury goods, and electronics. Its label-free screening promotes non-destructive testing while providing quantifiable results useful for documentation and certification purposes.
Advancing Fundamental Plasmonics Research
While the analytical power of SPR makes it indispensable for applications, it also drives fundamental plasmonics research. By controlling variables like metal properties and evanescent fields, scientists leverage SPR platforms to conduct investigations into localized SPR, propagating surface plasmons, plasmonic coupling effects, and more. Novel SPR-based sensing architectures continue to be developed with the goal of improving sensitivity, selectivity, and multiplexing capabilities. Advances in plasmonics may one day enable the integration of SPR into miniaturized, low-cost lab-on-a-chip devices with widespread point-of-care applications. Overall, SPR technique remains an active area of interdisciplinary research spanning physics, engineering, chemistry and biology.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it