Mapping interfacial chemistry induced variations in protein adsorption with scanning force microscopy

Area of Science:

• Surface science
• Biophysics
• Materials science

Background:

• Scanning force microscopy (SFM) is a powerful surface analysis technique.
• Understanding protein adsorption at the molecular level is crucial for biomaterials and biosensors.
• Friction force microscopy (FFM) offers high sensitivity to surface properties.

Purpose of the Study:

• To investigate the sensitivity of SFM friction mode to adsorbed protein conformation and orientation.
• To utilize patterned surfaces to differentiate the effects of surface functional groups on protein adsorption.
• To establish SFM friction as a tool for probing the state of adsorbed proteins.

Main Methods:

• Fabrication of patterned alkanethiolate monolayers with distinct functional groups (methyl and carboxylate) on gold substrates.
• Adsorption of bovine fibrinogen (BFG) and other proteins onto the patterned surfaces.
• Imaging of adsorbed proteins using SFM in friction force mode.
• Complementary infrared spectroscopic analysis of protein adsorption.

Main Results:

• Stable, imaging-compatible protein films formed on both methyl- and carboxylate-terminated monolayers.
• Distinct friction contrasts were observed in SFM images of BFG adsorbed on patterned monolayers.
• These friction differences correlate with variations in BFG conformation or orientation induced by the surface functional groups.
• Similar frictional contrasts were observed for other adsorbed proteins.

Conclusions:

• SFM operated in friction force mode is highly sensitive to the conformation and orientation of adsorbed proteins.
• Surface functional groups significantly influence the state of adsorbed proteins.
• SFM friction measurements provide valuable insights into the adsorbed protein state, with implications for surface characterization and bio-interface design.