Single-molecule Förster Resonance Energy Transfer was used to observe the adsorption of fluorescently-labeled "target" DNA oligonucleotides and their association and hybridization with complementary DNA "probes" tethered to the surface as a function of surface grafting density. Ionic strength was varied systematically to disentangle the potentially competing effects of probe accessibility and electrostatic repulsion. At high ionic strength, when the Debye length was ~1 nm, the adsorption of target DNA was not significantly inhibited by the presence of tethered probe DNA, even at high grafting density, and the fraction of adsorbed target strands undergoing hybridization increased systematically with grafting density, leading to a dramatic increase in the net hybridization rate at high grafting density. However, at lower ionic strength, when the Debye length was ≥3 nm, the adsorption rate of target DNA decreased and the fraction of adsorbed target strands undergoing hybridization saturated at high probe grafting density (≥7,000 strands/µm2), presumably due to electrostatic repulsion. As a result, the net rate of hybridization exhibited a maximum as a function of grafting density. This has important consequences for the design of systems that optimize surface-mediated DNA hybridization under low-salt high-stringency conditions.

中文翻译：

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表面介导的DNA杂交中静电排斥力和表面接枝密度之间的相互作用。

使用单分子Förster共振能量转移来观察荧光标记的“靶标” DNA寡核苷酸的吸附以及它们与拴系在表面上的互补DNA“探针”的缔合和杂交，这是表面嫁接密度的函数。系统地改变了离子强度，以消除探针可及性和静电排斥的潜在竞争作用。在高离子强度下，当Debye长度为〜1 nm时，即使在高嫁接密度下，系留探针DNA的存在也不会显着抑制目标DNA的吸附，并且随着嫁接的进行，系统杂交的目标链吸附比例会系统地增加密度，导致高嫁接密度下的净杂交率急剧增加。然而，在较低的离子强度下，当Debye长度≥3nm时，目标DNA的吸附速率降低，并且在高探针接枝密度（≥7,000条/μm2）下，进行杂交的吸附目标链的比例饱和，可能是由于静电排斥。结果，杂交的净速率表现出最大的嫁接密度。这对优化在低盐高严格条件下表面介导的DNA杂交的系统的设计具有重要的意义。杂交的净速率表现出最大的嫁接密度函数。这对于在低盐高严格条件下优化表面介导的DNA杂交的系统设计具有重要意义。杂交的净速率表现出最大的嫁接密度函数。这对于在低盐高严格条件下优化表面介导的DNA杂交的系统设计具有重要意义。