Discrimination of protein receptors through quantitative adhesion force maps
Atomic Force Microscopy (AFM) is the only technique able to measure topography and intermolecular forces of biomolecules mimicking the physiological conditions with nanometer resolution. Working in the force based AFM Jumping mode (JM) is possible to take images without damaging soft samples. JM produces topography and tip-sample maximum adhesion images. Working in a repulsive regime applying very low forces the adhesion images become molecular recognition maps. Using this methodology it is possible to discriminate between avidin and streptavidin single receptors on hybrid samples. The adhesion maps obtained with biotin-PEG-tips showed features identified as avidin molecules, in the range of 40–80 pN, meanwhile streptavidin molecules gave 120–170 pN at the working conditions. Adhesion maps of enzymatic ferredoxin-NADP+ reductase samples imaged with ferredoxin and flavodoxin functionalized tips were also obtained. Molecular recognition maps showed a high homology with topography features when FNR was attached in an oriented manner facing up the interacting surface [PEDS 11, 715-23, 2012]. This evidences that repulsive JM allows identifying biomolecules through the intermolecular specific force being very efficient when protein molecules are immobilized in an oriented manner.