Protein adsorption on nano-patterned hydrogenated amorphous carbon model surfaces

Predicting howproteins fold and adsorb onto surfaces is a complex problemof strong relevance to the health and environmental sectors. In thiswork, two nano-patterning techniques, namely focused ion beam(FIB) milling and atomic forcemicroscopy (AFM) nanoindentationwere used to develop hydrogenatedamorphous carbon (a-C:H) model surfaceswith similar nano-topography but different local composition. On the un-patterned surfaces, bovine plasma fibrinogen (BPF) resulted in a thicker and rougher adsorbed film than bovine serumalbumin (BSA), although FTIR analysis indicated that, the secondary structure of the proteins changed similarly, with an increase of the beta-sheet component (+ 27% and + 34% for BSA and BPF, respectively). AFM analysis on the FIB-patterned surfaces indicates that patterning can modify specific protein adsorption behaviors. Moreover, the patternswere compared by imaging the AFM tip/surface adhesive force for BSA adsorbed on either AFM tips or patterned surfaces. The results show an electrostatic interaction between the implanted Ga+ and BSA surface, modifying the adsorption behavior and the adhesive force. Modelling this interaction gave an estimate of the surface charge per protein, a significantly lower value than in dilute solution (-1.8e instead of -18e). This finding is indicative of protein misfolding, as detected in the FTIR analysis. (C) 2016 Published by Elsevier Ltd.