Streptavidin binding as a function of SBP concentration was investigated as described above. Briefly, SBP (0–5 mM) was deposited on TiO2 thin films, BSA was added to block any remaining unmodified TiO2 sites, followed by streptavidin, and then finally interrogated with FITC-anti-strept antibody. Increasing the SBP concentration in the solution used to modify the TiO2 film must bind more streptavidin, as evidenced by the resultant increase in the relative fluorescence intensity from bound FITC-anti-strept antibody (Fig. 5b). This series of images clearly demonstrates the ability of surface bound SBP to bind streptavidin from solution, followed by detection of the sorbed streptavidin with FITC-anti-strept antibody. The relative integrated fluorescence intensity over the TiO2 spot Radotinib（IY-5511) plotted in Fig. 5c, where the data is plotted on an arbitrary 0–100% intensity scale, setting the 0 μM SBP relative fluorescence intensity to 0% and the 5 μM SBP relative fluorescence intensity to 100%. The 0 μM added SBP followed by BSA also served as the background, and its fluorescence intensity was subtracted from all other measurements. Increasing concentrations of SBP used to modify the TiO2 surface result in a sharp increase in streptavidin binding, however, by 1.25 mM SBP, the relative fluorescence intensity plateaus, suggesting either the maximum amount of streptavidin has bound to the surface despite an increasing amount of surface SBP (shown in Fig. 4), or the maximum amount of FITC-anti-strept antibody bladder can sterically fit at the surface has been reached. The data of Fig. 5c appear to fit a simple Langmuir isotherm, indicating that either a monolayer of streptavidin accumulates at the SBP surface or the FITC-anti-strept antibody is useful to detect only the outermost surface-bound layer of streptavidin. Use of 5 mM SBP solution to modify the TiO2 surface ensured complete surface coverage of the photocatalyst and was used for the subsequent illumination studies.