Figure 6

Conic measurement of BSA physisorption on the QW-SPR device. (a) The dispersion relation of the SPR is projected on a skewed set of axes I(E–k_y,k_x).¹⁵ The image reveals the projection of two ellipses, obtained from the projection of the SPR dispersion on the E–k_y space. Measuring the distance in k_x between the two ellipses provides direct information on the SPR conditions. In this case, the quality of the signal as a function of E–k_y depends on the luminescence intensity of the QW. (b) Δ_SPR as a function of E–k_y and time, as the BSA solution is injected over the device and rinsed. The periodic modulations in E–k_y are attributed to the interactions of the SPs with the grating as predicted in the literature.^15,16 (c) Cumulative SPR shift in time for the BSA physisorption, where the SNR, bulk shift (Δ_B) and surficial shift (Δ_S) are measured. BSA, bovine serum albumin; QW, quantum well; SNR, signal-to-noise ratio; SP, surface plasmon; SPR, surface plasmon resonance.