Effect of Surface Potential on the Adsorption of Proteins

Extracellular matrix (ECM) proteins such as fibronectin, laminin and collagen play an important role in many cellular behaviors including cell adhesion, cell spreading, etc. Understanding their adsorption behavior on surfaces of different nature is helpful for studying the cellular response to environments. It is known that by tailoring the chemical composition in binary amine and carboxylic acid terminated self-assembled monoalyers (SAMs) modified gold substrate, different surface potentials can be obtained. To examine how the surface potential affects the interaction between ECM proteins and the substrates, a quartz crystal microbalance with dissipation detection (QCM-D) using binary-SAMs-modified Au on quartz crystal is used. The ionic strength and pH are controlled by phosphate buffer solution at 37 °C and the zeta-potential of modified Au and protein is determined with electrokinetic analyzer and dynamic light scattering, respectively. During adsorption, the shift of resonate frequency (f) and the energy dissipation (D) are acquired simultaneously and the weight change is calculated using the viscoelastic model. The result reveals that the low charge-density protein can be adsorbed on highly charged SAM even both surfaces are negatively charged. This behavior is attributed to the highly charged SAM polarized the protein microscopically and the Debye interaction allows the adsorption although the macroscopic electrostatic interaction discourage the adsorption. For SAM-modified surface of moderate potential, proteins are not polarized and electrostatic interaction dominated hence less adsorption is observed. Besides, the intermolecular force that allows protein to self-assemble into macroscopic structure also lead to change in adsorption morphology and kinetics. This difference can also be identified from the D-f plot.