Figure 1: A scheme of a possible experimental set up for a surface plasmon resonance (SPR)-based instrument (using flow conditions). (A) A glass prism is coated with a thin layer of a noble metal (usually gold) to create a biosensor surface. Antibody or another type of biomolecule (named “ligand”) is immobilized on the sensor surface (A). The metal layer possesses surface mobile electrons. At certain incidence angle the incoming beam of light disturbs these electrons causing changes in surface plasmon waves (A). Electrons “resonate” giving a name to SPR phenomena. This particular incidence angle is called SPR angle. At the SPR angle reflectivity drops to a minimum (B). However, the binding of antibody to free analyte onto sensor’s surface (A) leads to accumulation of biomolecules onto surface and subsequently affects SPR conditions (B). Refractive index increases and a shift of SPR angle occurs (B). SPR-based methods offer two opportunities to measure the efficiency of binding to sensor’s surface: 1) measuring the shift of SPR angle during binding of biomolecules; 2) when SPR angle remains fixed- measure changes of reflectivity (ΔR%) (B).