Adhesion forces of the blood plasma proteins on self-assembled monolayer surfaces of alkanethiolates with different functional groups measured by an atomic force microscope

To determine the adhesion force of representative blood plasma proteins (albumin (Alb), immunoglobulin G (IgG), and fibrinogen (Fib)) to foreign material surfaces, force-versus-distance curves were measured using an atomic force microscope (AFM) between the protein covalently immobilized AFM tips and the well-defined model surfaces of self-assembled monolayers (SAMs) of alkanethiolates terminated with different functional groups (CH3, NH2, OH, and COOH). From the f-d curves measured between the protein-immobilized tip and the SAM surface, the mechanical adhesion forces of the protein to the SAM surface (detachment force of protein from the surface) were determined. From the adhesion forces determined between the protein tip and the SAM surface and between like SAM-coated tips and surfaces (i.e., tip/surface combinations: CH3/CH3, NH2/NH2, OH/OH, and COOH/COOH),the thermodynamic adhesion strength (work of adhesion and surface pressure of SAM on a protein surface) was also determined according to the Dupre equation and Johnson, Kendall, and Roberts adhesion theory. The relative strength of thermodynamic adhesion of the proteins to the SAM surfaces was found with statistical significance to be in the following orders: (a) For Alb and IgG, CH3- much greater than (OH-, NH2-) > COOH-SAM surface; for Fib, CH3 much greater than) OH > NH2 > COOH. (b) On CH3-, NH2-, and OH-SAM surfaces, Fib exhibits higher adhesion than Alb and IgG.