Atomic force microscopy of deoxyribonucleic acid strands adsorbed on mica: The effect of humidity on apparent width and image contrast

We have investigated the effect of relative humidity on the apparent width and contrast of isolated strands of deoxyribonucleic acid (DNA) imaged with atomic force microscopy (AFM). Due to convolution of the tip with DNA, the apparent width of DNA molecules observed with AFM was broader than the known width of DNA. Also, the apparent width of DNA increased with increasing humidity while the contrast of the DNA images decreased with increasing humidity. This phenomenon is completely reversible and can be attributed to non-normal forces causing a buckling of AFM cantilever.