Fluorescence lifetime imaging study of a thin protein layer on solid surfaces

Understanding the fundamental interactions between proteins and solid surfaces is essential in the area of implantable medical devices. Fluorescence methods offer the sensitivity required to study the formation of the initial thin protein layers that mediate biocompatibility of materials. Thin protein layers (bovine serum albumin labelled with 1-anilino-8-naphthalenesulfonate, BSA–ANS) deposited on several surfaces (glass, silicon, stainless steel, polystyrene, and silver island film) were studied using confocal frequency domain Fluorescence Lifetime Imaging Microscopy (FLIM) and single-point multifrequency lifetime analysis techniques. FLIM provides spatial information about both fluorophores located on the surface and physicochemical parameters of the surface microenvironment. The average fluorescence lifetimes (τav) of the adsorbed BSA–ANS generated by the contact between a protein solution and the material surface were measured by the multifrequency modulation and phase shift. Results indicate that τav values of the albumin complexes on the surfaces (∼ 12 ns) are, in general, shorter than τav found in the bulk solution (∼ 14 ns). For some surfaces, like polystyrene and silver island film the differences in τav of the adsorbed BSA–ANS were found to be much greater. The differences in fluorescence lifetimes may indicate structural changes in the BSA protein induced by contact with the surface.