In situ single bio-molecule recognition by atomic force microscopy using functionalized tip

Atomic force microscopy is a powerful and widely used imaging technique that can visualize single molecules both in air and solution. In this paper, by functionalizing the AFM tip with antibodies, atomic force microscopy is able to identify specific types of receptors such as angiotensin II type I receptors on cells´ membrane. The antibody is tethered to the AFM tip through a spacer to form a strong but flexible binding. Due to the flexibility of the spacer, the antibody bond to the AFM tip has much more chance to interact with the antigen (receptor) on cell´s surface than a direct antibody coating method. Because the AFM phase image is very sensitive to the interaction force between tip and surface, the single receptors can be easily identified by passing the phase information to a band-pass filter to remove the low frequency topography signal. After adding more antibodies to the solution to block all the specific type receptor, the disappearance of the receptors in the image verify the effectiveness of this method.