Figure 1.

(a) Schematic of typical SPR device. Light is directed onto a gold film and the reflection is monitored with a detector. At a certain angle, the light does not reflect but generates surface plasmon resonance (SPR). In a flow cell above the film, receptors are linked to the film and analyte solution is flowed past the receptors. If the analyte binds to the receptors, the angle at which SPR is generated shifts, and this angle is tracked over time as the reaction progresses. (b) Simulated SPR binding curves of four different molecules (A,B,C,D) with identical K_D values (10 nM), but different rate constants, k_on and k_off. Analyte concentration was 100 nM for all molecules. Units for k_on are M⁻¹s⁻¹ and for k_off, s⁻¹. This plot demonstrates the significance of knowing the kinetic constants. Molecule A would bind quickly and dissociate quickly, whereas molecule D would bind slowly but dissociate very slowly. The half-lives (t_1/2 = ln 2/k_off) of the bound complexes are roughly (from A–D): 12 min, 2 hr, 20 hr, and 8 days. (a) is adapted from Cooper [9] and used with permission of Macmillan Publishers Ltd.