Surface plasmon resonance (SPR) is a powerful optical technique that enables real time, label-free detection of biomolecular interactions. In this article, we discuss the principle behind SPR, applications in various fields like biomedical research, drug discovery and food safety testing.

What is Surface Plasmon Resonance?

Surface plasmon resonance is an optical phenomenon that occurs when light hits the interface between two media with different dielectric constants, typically a metal and a dielectric. When light hits this interface at a specific angle known as the resonance angle, it excites electromagnetic waves known as surface plasmons that travel along the interface. This resonance causes a dip in the intensity of reflected light at a specific angle which is very sensitive to changes in the refractive index near the metal surface. Any interaction-binding event or molecular adsorption on the surface causes a change in local refractive index which can be detected in real time without any labels.

Principal and Instrumentation

A typical SPR setup comprises of a prism coupled with a thin gold film on one side. Monochromatic, polarized light from a laser source is passed through the prism and reflected at the gold film interface. At a precise angle called the resonance angle, resonance occurs and surface plasmons are excited which interact strongly with the evanescent field. This causes a sharp dip in the reflected light intensity. Any change in mass deposited on the sensor surface causes a shift in resonance angle which is proportional to change in refractive index. This angular shift is continuously monitored during an interaction which provides quantitative data on binding kinetics and affinity.

Applications in Biomedical Research

SPR is widely used to study biomolecular interactions like protein-protein, protein-ligand, antigen-antibody binding etc. It allows characterization of affinity, kinetics, concentration analysis in real time without labelling. In drug discovery, it is used for screening ligand binding, determining affinity constants and evaluating structure-activity relationships of drug candidates. It is also suited for epitope mapping to understand antigen-antibody binding sites.

In the biomedical field, SPR is applied for pathogen detection, disease diagnosis and monitoring disease progression or treatment response. It enables detection of biomarkers for various cancers, viruses, bacteria with high sensitivity without complex sample preparation. Development of biosensors for quick pathogen detection has applications in food safety testing, epidemiology and public health management.

Uses in Other Areas

Apart from biomedicine, SPR finds numerous applications in various other fields due to its inherent sensitivity, real time analysis capabilities. In materials science, it is used to study thin film deposition, corrosion, nanoparticle binding to surfaces etc. It aids understanding of material synthesis, functionalization and modification processes.

In environmental monitoring, SPR biosensors allow detection of toxins, pollutants, heavy metals in water samples. This helps evaluate water quality for drinking purposes or industrial use. Food safety testing employs SPR for quick detection of pathogens, allergens, toxins in food products to guarantee quality and prevent outbreaks.

SPR sensing has opened up new opportunities in many other emerging areas like homeland security for explosives detection at airports/borders, agricultural testing for GMOs, pesticides and fertilizer analysis. Miniaturized portable SPR devices also enable on-site, point-of-care diagnostics and testing in resource limited settings.

Advantages over other Techniques

Some key advantages of SPR over other techniques like fluorescence, radioactive labeling include its non-destructive, real-time and label-free nature. It does not require complex sample preparation or separation steps. The evanescent field allows high sensitivity detection of molecular interactions occurring very close to the sensor surface. SPR provides both qualitative and quantitative data on binding affinity, kinetics, concentration that aids deeper understanding of biological systems. Its applications continue to expand with the development of improved sensor surfaces, microfluidics integration and portable devices. Overall, SPR is emerging as a valuable optical technique with diverse utilities across various fields.

Future Prospects and Conclusions

Technological advancements are further expanding the applications of SPR. Integration with microfluidics enables automation, reduced sample volumes and high-throughput screening. Advances in nanostructures and nanoplasmonics are pushing the sensitivity limits to single molecule detection levels. Development of compact, field portable SPR devices would facilitate point-of-care testing and on-site environmental/agricultural monitoring.

Combining SPR with other techniques like mass spectrometry, fluorescence, ELISA offers multi-parameter analysis. Applications in new disciplines like food/fermentation industry, electrochemistry, nanotechnology are likely to emerge. Overall, surface plasmon resonance continues to prove itself as a powerful real-time, label-free analytical method for studies of molecular interactions and development of advanced biosensors with diverse utilities. Its non-invasive capabilities complements other techniques and holds immense potential for addressing challenges across biomedical, industrial and environmental domains.

In summary, this article provided an overview of the principles and wide scope of surface plasmon resonance technique and its applications across various fields. The label-free, real-time analysis capabilities have made it extremely valuable for biomolecular interaction studies and development of advanced biosensors. Continued technological advances promise to further expand the utilities of this powerful optical sensing platform.