Rant Ulrich, Arinaga Kenji, Fujiwara Tsuyoshi, Fujita Shozo, Tornow Marc, Yokoyama Naoki, Abstreiter Gerhard
Walter Schottky Institut, Technische Universitaet Muenchen, Munich, Germany.
Biophys J. 2003 Dec;85(6):3858-64. doi: 10.1016/S0006-3495(03)74800-0.
We present experiments on the bias-induced release of immobilized, single-stranded (ss) 24-mer oligonucleotides from Au-surfaces into electrolyte solutions of varying ionic strength. Desorption is evidenced by fluorescence measurements of dye-labeled ssDNA. Electrostatic interactions between adsorbed ssDNA and the Au-surface are investigated with respect to 1), a variation of the bias potential applied to the Au-electrode; and 2), the screening effect of the electrolyte solution. For the latter, the concentration of monovalent salt in solution is varied from 3 to 1600 mM. We find that the strength of electric interaction is predominantly determined by the effective charge of the ssDNA itself and that the release of DNA mainly occurs before the electrochemical double layer has been established at the electrolyte/Au interface. In agreement with Manning's condensation theory, the measured desorption efficiency (etarel) stays constant over a wide range of salt concentrations; however, as the Debye length is reduced below a value comparable to the axial charge spacing of the DNA, etarel decreases substantially. We assign this effect to excessive counterion condensation on the DNA in solutions of high ionic strength. In addition, the relative translational diffusion coefficient of ssDNA in solution is evaluated for different salt concentrations.
我们展示了关于在不同离子强度的电解质溶液中，偏压诱导固定在金表面的单链（ss）24聚体寡核苷酸释放的实验。通过对染料标记的单链DNA进行荧光测量来证明解吸现象。针对以下两点研究了吸附的单链DNA与金表面之间的静电相互作用：1）施加于金电极的偏压电位的变化；2）电解质溶液的屏蔽效应。对于后者，溶液中单价盐的浓度在3至1600 mM之间变化。我们发现电相互作用的强度主要由单链DNA本身的有效电荷决定，并且DNA的释放主要发生在电解质/金界面处建立电化学双层之前。与曼宁凝聚理论一致，在很宽的盐浓度范围内，测得的解吸效率（etarel）保持恒定；然而，当德拜长度减小到与DNA的轴向电荷间距相当的值以下时，etarel会大幅下降。我们将这种效应归因于高离子强度溶液中DNA上过量的反离子凝聚。此外，还评估了不同盐浓度下溶液中单链DNA的相对平动扩散系数。
