Biological processes are regulated by the interaction of molecules through specific molecular contacts, forming stable yet irreversible complexes. These interactions are highly determined by the principles of thermodynamics as well as biomolecular structure and recognition. Thus, finding the binding site and quantifying the strength (i.e., binding affinity) interaction is essential to understanding biological processes, and designing of drugs.

Biomolecular interaction analysis, often referred to as BIA, is a scientific method used to study and analyze the interactions between biomolecules, such as proteins, nucleic acids, and small molecules, in order to better understand their binding affinities, kinetics, and other important characteristics. This technique is fundamental in fields like biochemistry, molecular biology, and drug discovery, as it provides insights into the mechanisms and strengths of molecular interactions. BIA is widely applied in drug screening and development due to its focus on the quantification of interactions between biomolecules. The outcome of such detailed studies help us understand how potential agonists or antagonists interact with a drug target, as well as quantify the binding affinity of a ligand to its receptor.

The primary technique used in biomolecular interaction analysis is surface plasmon resonance (SPR). SPR is a label-free and real-time analytical technique that allows researchers to monitor the binding between molecules without the need for fluorescent or radioactive labels. Here's how it works:

• Immobilization: One of the interacting molecules is immobilized on a sensor surface, often through covalent attachment or other binding techniques.
• Flow System: A solution containing the second molecule (the analyte) is flowed over the immobilized surface.
• Detection: Changes in the refractive index at the surface are monitored in real time. When the analyte binds to the immobilized molecule, it causes a shift in the resonance angle, which is detected as a change in the reflected light.
• Data Analysis: The resulting sensorgrams are analyzed to extract information about the interaction, including association and dissociation rates, equilibrium constants, and affinity.

Apart from SPR, other techniques and instruments used in biomolecular interaction analysis include:

• Isothermal Titration Calorimetry (ITC): This measures heat changes associated with biomolecular interactions, providing information on binding stoichiometry and thermodynamics.
• Surface Plasmon Resonance Imaging (SPRi): An extension of SPR, this technique offers spatial information on binding events and is useful for studying interactions on surfaces.
• Microscale Thermophoresis (MST): This technique is based on the movement of molecules in temperature gradients and is used to study interactions in solution.
• Bio-layer Interferometry (BLI): It measures changes in the interference pattern of white light reflected from a biosensor tip to determine binding kinetics and affinity.
• Fluorescence-based techniques: Various fluorescence-based assays, such as fluorescence resonance energy transfer (FRET), can be used to study biomolecular interactions.
• Mass Spectrometry: MS can provide information about binding stoichiometry and changes in mass resulting from binding events.

These techniques and instruments enable researchers to gain insights into the fundamental aspects of molecular interactions, which is critical for understanding biological processes, developing new drugs, and advancing fields like structural biology, immunology, and molecular genetics.