Rezek Bohuslav, Shin Dongchan, Nebel Christoph E
Diamond Research Center, AIST, Central 2, Tsukuba 305-8568, Japan.
Langmuir. 2007 Jul 3;23(14):7626-33. doi: 10.1021/la0636661. Epub 2007 Jun 5.
Properties of hybridized deoxyribonucleic acid (DNA) arrays on single-crystalline undoped and boron-doped diamonds are studied at the microscopic level by atomic force microscopy (AFM) in buffered electrolytic solutions. DNA is linked to diamond via aminodecene molecules (TFAAD) that are attached to undoped diamonds by a photochemical reaction and via nitrophenyl-diazonium molecules attached electrochemically to boron-doped diamonds. Both H-terminated and oxidized diamond surfaces are used in this process. On H-terminated surfaces, AFM measurements detect compact DNA layers. By analyzing phase and height contrast in AFM, a DNA layer height of 76 A is determined on the photochemically functionalized diamonds and a DNA layer height of up to 92 A is determined on the electrochemically functionalized diamonds. Based on the layer thickness, the DNA chains are tilted under the angle of 31 degrees . The morphology of the DNA layers exhibits long-range (30-50 nm) undulations of 20 A in height and a nanoroughness of 8 A. Using Hertz's model for calculating the contact area of the AFM tip on a DNA layer and a geometrical model of DNA arrangement on diamond yields the DNA density on diamonds of 6 x 10(12) cm(-2) on both photochemically and electrochemically functionalized diamonds. The structure of these dense DNA layers is not significantly influenced by variations in buffer salinity of 1-300 mM NaCl. DNA molecules can be removed from the diamond surface by contact-mode AFM with forces >or= 45 nN and >or= 76 nN on photochemically and electrochemically functionalized diamonds, respectively, indicating that DNA is bonded covalently and stronger on diamond than on gold substrates. The DNA arrangement and bonding strength are similar on oxidized diamond surfaces when using an electrochemical process. On oxidized surfaces after photochemical processing, DNA is bonded noncovalently as deduced from the removal force < 6 nN. The presence of hybridized DNA as well as the selective removal of DNA by AFM scanning are corroborated by fluorescence microscopy.
在缓冲电解液中，通过原子力显微镜（AFM）在微观层面研究了单晶未掺杂和硼掺杂金刚石上杂交脱氧核糖核酸（DNA）阵列的性质。DNA通过氨基癸烯分子（TFAAD）与金刚石相连，TFAAD通过光化学反应附着在未掺杂的金刚石上，并通过电化学方式附着在硼掺杂金刚石上的硝基苯基重氮分子相连。在此过程中使用了氢终止和氧化的金刚石表面。在氢终止的表面上，AFM测量检测到紧密的DNA层。通过分析AFM中的相位和高度对比度，在光化学功能化的金刚石上确定DNA层高度为76埃，在电化学功能化的金刚石上确定DNA层高度高达92埃。基于层厚度，DNA链倾斜角度为31度。DNA层的形态表现出高度为20埃的长程（30 - 50纳米）起伏和8埃的纳米粗糙度。使用赫兹模型计算AFM针尖在DNA层上的接触面积以及DNA在金刚石上排列的几何模型，得出在光化学和电化学功能化的金刚石上DNA密度均为6×10¹²厘米⁻²。这些致密DNA层的结构不受1 - 300 mM NaCl缓冲盐度变化的显著影响。通过接触模式AFM，在光化学和电化学功能化的金刚石上分别施加≥45 nN和≥76 nN的力时，DNA分子可以从金刚石表面去除，这表明DNA在金刚石上共价结合且比在金基底上更强。当使用电化学过程时，在氧化的金刚石表面上DNA排列和结合强度相似。从去除力<6 nN推断，在光化学处理后的氧化表面上，DNA以非共价方式结合。荧光显微镜证实了杂交DNA的存在以及通过AFM扫描对DNA的选择性去除。
