A plasmonic biosensor is a type of optical sensor that utilizes surface plasmon resonance (SPR) to detect and analyze biological interactions at the molecular level. It is a label-free detection technique, meaning it does not require any chemical or fluorescent labels to detect the target molecules, making it particularly advantageous for various applications in biochemistry, molecular biology, and medical diagnostics.
Here's how a plasmonic biosensor works and its applications in label-free detection:
Principle of Plasmonic Biosensor (Surface Plasmon Resonance):
Surface plasmon resonance occurs when light (typically from a laser) is directed at a metal surface (often gold or silver) through a prism or grating at a specific angle. The metal surface is coated with a thin layer of a biologically active material, such as antibodies, DNA, or other ligands, which can specifically bind to the target molecules.
When light hits the metal surface at a specific angle, it induces the collective oscillation of free electrons at the metal-dielectric interface, forming surface plasmon waves. The angle at which this resonance occurs is highly sensitive to changes in the refractive index of the surrounding medium. When target molecules bind to the biologically active layer, it causes a change in the refractive index at the surface, leading to a shift in the resonance angle. This shift can be precisely measured and correlated with the binding events between the target molecules and the immobilized ligands on the metal surface.
Operation of Plasmonic Biosensor:
Sensing Surface Preparation: The metal surface (usually gold or silver) is coated with a thin layer of a biologically active material. This material can be antibodies, DNA, proteins, peptides, or other ligands, depending on the specific application.
Sample Application: The sample containing the analyte (target molecules) is introduced onto the sensing surface. If the analyte molecules are present in the sample and can bind to the immobilized ligands, they will do so.
Light Interaction: A light beam, typically from a laser, is directed at the metal-dielectric interface at a specific angle. This induces surface plasmon resonance at the metal surface.
Detection: The change in the refractive index at the metal-dielectric interface due to the binding of analyte molecules is detected as a shift in the resonance angle. This shift is monitored in real-time and is directly related to the concentration and kinetics of the molecular interactions.
Data Analysis: The data obtained from the sensor is processed and analyzed to determine the binding affinity, kinetics, and concentration of the target molecules in the sample.
Applications in Label-Free Detection:
Plasmonic biosensors have a wide range of applications due to their label-free detection capabilities, which offer several advantages:
Biological Interactions: Plasmonic biosensors are widely used to study molecular interactions such as antigen-antibody interactions, protein-protein interactions, DNA hybridization, receptor-ligand binding, and enzyme-substrate interactions.
Drug Discovery: Plasmonic biosensors are utilized in drug discovery processes to identify and analyze potential drug candidates by studying their interactions with target biomolecules.
Medical Diagnostics: They are employed in clinical diagnostics for the detection of various disease biomarkers, pathogens, and viral infections in patient samples.
Environmental Monitoring: Plasmonic biosensors can be used to detect pollutants, toxins, and contaminants in environmental samples.
Food Safety: They can be employed in the food industry to detect allergens, pathogens, and adulterants in food products.
Pharmaceutical Quality Control: Plasmonic biosensors play a crucial role in ensuring the quality and consistency of pharmaceutical products by detecting impurities and verifying the composition.
Biomedical Research: Plasmonic biosensors are widely used in various research areas to gain insights into molecular interactions and study complex biological processes.
Overall, the label-free detection capability of plasmonic biosensors makes them a powerful and versatile tool for sensitive, real-time, and quantitative analysis of biomolecular interactions, with widespread applications in diverse scientific and industrial fields.