Tip Functionalization by Biotin Linkers: A Technique for DNA Elasticity Measurement Studied by Atomic Force Microscopy T. H. Nguyen 1 , V.C. Bui 1 , Y. U. Kim 2 , and S. S. Choi 1,* 1 Department of Physics and Nanoscience, 2 Department of Biology, Sun Moon University, Ahsan, Chungnam, 336-708, South Korea Email: nthuong@sunmoon.ac.kr Abstract We have investigated the mechanical properties of a double strands deoxyribonucleic acid (dsDNA) in deionized water and in 10 mM NaCl solution by using atomic force microscopy (AFM). In order to do this, a number of the force vs. displacement (F-D) curves between the AFM tip functionalized by biotin linkers and the dsDNA immobilized on 3-aminopropyltriethoxysilane treated glass substrate has been measured. These force curves will be compared to those measured by untreated tip to compare the difference of the adhesion forces between the two tip types. The retraction parts of the force curves reveal that the binding force between the DNA and the biotin treated tip is increased up to four times compared to those measured by the untreated one. Analysis of the force curves measured by biotin treated tip shows that the dissipated force for the molecular stretching in salt solution (702 ± 19 pN) is greater than that in DI water (558 ± 21 pN) due to the effect of electrostatic attraction generated by the Na + ions around the DNA segments. It also shows that the Young’s modulus and the persistence length of the dsDNA measured in DI water are smaller than those measured in NaCl medium which implies that the salt solution increased the rigidity of the biological system. Keywords: dsDNA, AFM, stretching, Young’s modulus, persistence length, WLC model. 1