Quartz crystal microbalance study of bovine serum albumin adsorption onto self-assembled monolayer-functionalized gold with subsequent ligand binding

Adsorption characteristics of the model protein bovine serum albumin (BSA) onto gold surfaces were examined using a 5 MHz quartz crystal microbalance. Protein immobilization was executed in the presence and absence of a homogenous self-assembled monolayer (SAM) of NHS-terminated alkanethiols. BSA concentrations in the range of 3.2 × 10−6 to 1.0 × 10−3 mol/L were found to saturate both SAM-functionalized and non-functionalized surfaces with similar densities of 450 ± 26 ng/cm2. The lack of functionalization dependence is attributed to the large protein size relative to the density of available binding sites in either surface condition. The BSA ligand 8-anilino-1-naphthalenesulfonic acid (ANS) was subsequently introduced to the immobilized BSA to determine any effects of the protein immobilization conditions on ligand binding. The rate of ANS binding to BSA was found to increase with increasing BSA concentration used in the immobilization step. This suggests that protein concentration affects morphology and ligand binding affinity without significantly altering adsorption quantity.