A plasmonic biosensor is a type of optical sensor that utilizes the interaction between light and surface plasmon waves (also known as surface plasmon resonance) to detect biological interactions at the nanoscale. Plasmonic biosensors are widely used in various applications, particularly in label-free detection of biomolecules, such as proteins, DNA, and antibodies.
Operation of a Plasmonic Biosensor:
Principle of Surface Plasmon Resonance (SPR):
Surface plasmon resonance occurs when light (usually from a laser) is directed onto a metal-dielectric interface, typically a thin metal film (e.g., gold or silver) deposited on a glass substrate. When the incident light hits the metal surface at a specific angle, it excites the free electrons on the metal surface, creating collective oscillations known as surface plasmon waves. The angle at which this resonance occurs is called the resonance angle or SPR angle.
Sensing Surface Functionalization:
The metal surface of the biosensor is functionalized with a biologically active layer, such as antibodies, DNA probes, or other ligands, that can selectively bind to specific target molecules of interest. This functionalization step is critical as it enables the sensor to capture and detect the target analyte.
Binding Events:
When a liquid sample containing the target analyte is introduced onto the sensor surface, the target molecules bind to the immobilized bioreceptors. This binding event leads to a change in the local refractive index near the metal surface, causing a shift in the SPR angle.
Detection:
A detector measures the SPR angle in real-time. As the target molecules bind to the bioreceptors, the SPR angle changes, resulting in a shift in the plasmonic resonance curve. The shift in the resonance angle is directly related to the concentration of the bound target molecules, allowing for quantitative analysis.
Applications in Label-Free Detection:
Biomolecular Interaction Studies:
Plasmonic biosensors are extensively used to study the kinetics and affinity of biomolecular interactions. Researchers can investigate protein-protein interactions, protein-ligand binding, antigen-antibody interactions, and DNA hybridization, among others, without the need for fluorescent or radioactive labels.
Drug Discovery and Development:
Label-free plasmonic biosensors enable high-throughput screening of potential drug candidates. Researchers can study how drug compounds interact with specific biomolecular targets, facilitating the identification of promising drug candidates and optimizing drug development processes.
Disease Diagnostics:
Plasmonic biosensors are utilized in medical diagnostics for the detection of disease biomarkers. By detecting specific biomolecules associated with diseases, such as cancer markers or infectious agents, these sensors offer rapid and sensitive diagnosis with potential applications in point-of-care testing.
Environmental Monitoring:
Plasmonic biosensors can be employed to detect environmental pollutants and contaminants in real-time. The sensors can monitor water quality, air pollution, and various chemical analytes with high sensitivity, making them valuable tools for environmental monitoring and remediation.
In summary, plasmonic biosensors are powerful label-free detection tools that offer sensitive and real-time analysis of biomolecular interactions. Their wide range of applications makes them valuable in fields such as biotechnology, medicine, drug discovery, and environmental monitoring.