Nano-Bio Research Center, Korea Institute of Science and Technology, Seoul, Korea.
Nanotechnology. 2010 Feb 19;21(7):75101. doi: 10.1088/0957-4484/21/7/075101. Epub 2010 Jan 21.
The mechanical properties of a small fragment (30 bp) of an individual double-stranded deoxyribonucleic acid (dsDNA) in water have been investigated by atomic force microscopy (AFM). We have stretched three systems including ssDNA, double-fixed dsDNA (one strand of the dsDNA molecules was biotinylated at the 3'-end and thiolated at the 5'-end, this was reversed for the other complementary strand) and single-fixed dsDNA (one strand of the dsDNA molecules was biotinylated at the 3'-end and thiolated at the 5'-end, whereas the other complementary strand was biotinylated at only the 5'-end). The achieved thiolation and biotinylation were to bind ds- or ssDNA to the gold surface and streptavidin-coated AFM tip, respectively. Analysis of the force versus displacement (F-D) curves from tip-DNA-substrate systems shows that the pull-off length (L(o)) and stretch length (delta) from the double-fixed system were shorter than those observed in the ssDNA and the single-fixed system. The obtained stretch force (F(st)) from the single-fixed dsDNA was much greater than that from the ssDNA even though it was about 10 pN greater than the one obtained in the double-fixed system. As a result, the Young's modulus of the double-fixed dsDNA was greater than that of the single-fixed dsDNA and the ssDNA. A more reliable stiffness of the dsDNA was observed via the double-fixed system, since there is no effect of the unpaired molecules during stretching, which always occurred in the single-fixed system. The unpaired molecules were also observed by comparing the stiffness of ssDNA and single-fixed dsDNA in which the end of one strand was left free.
通过原子力显微镜（AFM）研究了水中单个双链脱氧核糖核酸（dsDNA）小片段（30bp）的机械性能。我们拉伸了三个系统，包括 ssDNA、双固定 dsDNA（dsDNA 分子的一条链在 3'端被生物素化，在 5'端被硫醇化，另一条互补链则相反）和单固定 dsDNA（dsDNA 分子的一条链在 3'端被生物素化，在 5'端被硫醇化，而另一条互补链仅在 5'端被生物素化）。实现的硫醇化和生物素化分别是将 dsDNA 或 ssDNA 结合到金表面和链霉亲和素涂层 AFM 尖端。分析尖端-DNA-基底系统的力与位移（F-D）曲线表明，双固定系统的拉开长度（L(o)）和拉伸长度（delta）比 ssDNA 和单固定系统观察到的要短。尽管单固定 dsDNA 的拉伸力（F(st)）比 ssDNA 大约 10pN，但它比双固定系统获得的拉伸力大得多。因此，双固定 dsDNA 的杨氏模量大于单固定 dsDNA 和 ssDNA。通过双固定系统观察到了更可靠的 dsDNA 刚度，因为在拉伸过程中没有未配对分子的影响，而在单固定系统中总是会发生这种情况。通过比较 ssDNA 和单固定 dsDNA 的刚度也观察到了未配对分子，其中一条链的末端是自由的。
