Adsorption kinetics of bovine serum albumin on fused silica: population heterogeneities revealed by single-molecule fluorescence microscopy

The adsorption of bovine serum albumin (BSA) on fused silica at neutral pH was investigated at the single-molecule level by total internal reflection fluorescence microscopy. Dye-labeled BSA molecules that adsorbed on the quartz surface lit up as discrete, fluorescent dots which eventually disappeared upon desorption. Movies of these events offered unprecedented details for kinetics modeling. The results suggested that 99.3% of the BSA was not sticky, and even if adsorbed, it would desorb in minutes. In contrast, the remaining 0.7% was not only sticky, but would anchor in due course. Such population heterogeneity, otherwise masked in ensemble measurements, sheds new light on our understanding of protein adsorption. The methodology is also generally applicable to the studies of macromolecules at interfaces.