Force spectroscopy by dynamic atomic force microscopy on bovine serum albumin proteins changing the tip hydrophobicity, with piezoelectric tuning fork self-sensing scanning probe

A tuning fork AFM (atomic force microscope) scanning probe has been used to study the chemical grafting between a functionalized tip and BSA (bovine serum albumin) protein. A non-conventional chemistry based on diazonium salts has been applied to control the hydrophobicity and hydrophilicity of the tip termination, and to graft proteins on surface. Unfolding signatures during the protein stretching have been observed, using amplitude modulation (AM-AFM) control of the probe. We propose a methodology to obtain quantitative information of the withdrawal forces from the amplitude and phase signals. Our results demonstrate the great potential of this new piezoelectric probe combined in term of sensitivity and versatility of the chemical functionalization of the tip to analyze biological materials.