Oh. Willemsen et al., SIMULTANEOUS HEIGHT AND ADHESION IMAGING OF ANTIBODY-ANTIGEN INTERACTIONS BY ATOMIC-FORCE MICROSCOPY, Biophysical journal, 75(5), 1998, pp. 2220-2228
Specific molecular recognition events, detected by atomic force micros
copy (AFM), so far lack the detailed topographical information that is
usually observed in AFM. We have modified our AFM such that, in combi
nation with a recently developed method to measure antibody-antigen re
cognition on the single molecular level (Hinterdorfer, P., W. Baumgart
ner, H. J. Gruber, K. Schilcher, and H. Schindler, Proc. Natl. Acad. S
ci. USA 93:3477-3481 (1996)), it allows imaging of a submonolayer of i
ntercellular adhesion molecule-1 (ICAM-1) in adhesion mode. We demonst
rate that for the first time the resolution of the topographical image
in adhesion mode is only limited by tip convolution and thus comparab
le to tapping mode images. This is demonstrated by imaging of individu
al ICAM-1 antigens in both the tapping mode and the adhesion mode. The
contrast in the adhesion image that was measured simultaneously with
the topography is caused by recognition between individual antibody-an
tigen pairs. By comparing the high-resolution height image with the ad
hesion image, it is possible to show that specific molecular recogniti
on is highly correlated with topography. The stability of the improved
microscope enabled imaging with forces as low as 100 pN and ultrafast
scan speed of 22 force curves per second. The analysis of force curve
s showed that reproducible unbinding events on subsequent scan lines c
ould be measured.