Single-molecule techniques allow for the direct observation of long-chain macromolecules, and these methods can provide a molecular understanding of chemically heterogeneous and stimuli-response polymers. In this work, we report the synthesis and direct observation of thermoresponsive DNA copolymers using single-molecule techniques. DNA-PNIPAM copolymers are synthesized using a two-step strategy based on polymerase chain reaction (PCR) for generating linear DNA backbones containing non-natural nucleotides (dibenzocyclooctyne-dUTP), followed by grafting thermoresponsive side branches (poly(N-isopropylacrylamide), PNIPAM) onto DNA backbones using copper-free click chemistry. Single-molecule fluorescence microscopy is used to directly observe the stretching and relaxation dynamics of DNA-PNIPAM copolymers both below and above the lower critical solution temperature (LCST) of PNIPAM. Our results show that the intramolecular conformational dynamics of DNA-PNIPAM copolymers are affected by temperature, branch density, and branch molecular weight. Single-molecule experiments reveal an underlying molecular heterogeneity associated with polymer stretching and relaxation behavior, which arises in part due to heterogeneous chemical identity on DNA copolymer dynamics.

中文翻译：

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热响应 DNA 共聚物的合成和直接观察

单分子技术允许直接观察长链大分子，这些方法可以提供对化学异质和刺激反应聚合物的分子理解。在这项工作中，我们报告了使用单分子技术合成和直接观察热响应 DNA 共聚物。DNA-PNIPAM 共聚物是使用基于聚合酶链式反应 (PCR) 的两步策略合成的，用于生成含有非天然核苷酸 (二苯并环辛炔-dUTP) 的线性 DNA 主链，然后接枝热响应侧支链 (poly( N-isopropylacrylamide), PNIPAM) 使用无铜点击化学作用到 DNA 主链上。单分子荧光显微镜用于直接观察低于和高于 PNIPAM 的较低临界溶解温度 (LCST) 的 DNA-PNIPAM 共聚物的拉伸和松弛动力学。我们的研究结果表明，DNA-PNIPAM 共聚物的分子内构象动力学受温度、支链密度和支链分子量的影响。单分子实验揭示了与聚合物拉伸和松弛行为相关的潜在分子异质性，这部分是由于 DNA 共聚物动力学上的异质化学特性所致。