Department of Chemical Engineering , University of Rhode Island , Kingston , Rhode Island 02881 , United States.
ACS Appl Mater Interfaces. 2019 Jan 16;11(2):2225-2233. doi: 10.1021/acsami.8b16478. Epub 2019 Jan 4.
Single-walled carbon nanotubes (SWCNTs) functionalized with short single-stranded DNA have been extensively studied within the last decade for biomedical applications due to the high dispersion efficiency and intrinsic biocompatibility of DNA as well as the photostable and tunable fluorescence of SWCNTs. Characterization of their physical properties, particularly their length distribution, is of great importance regarding their application as a bioengineered research tool and clinical diagnostic agent. Conventionally, atomic force microscopy (AFM) has been used to quantify the length of DNA-SWCNTs by depositing the hybrids onto an electrostatically charged flat surface. Here, we demonstrate that hybrids of DNA-SWCNTs with different oligomeric DNA sequences ((GT) and (GT)) differentially deposit on the AFM substrate, resulting in significant inaccuracies in the reported length distributions of the parent solutions. Using a solution-based surfactant exchange technique, we placed both samples into a common surfactant wrapping and found identical SWCNT length distributions upon surface deposition. Additionally, by spin-coating the surfactant-wrapped SWCNTs onto a substrate, thus mitigating effects of electrostatic interactions, we found length distributions that did not depend on DNA sequence but were significantly longer than electrostatic deposition methods, illuminating the inherent bias of the surface deposition method. Quantifying the coverage of DNA molecules on each SWCNT through both absorbance spectroscopy and direct observation, we found that the density of DNA per SWCNT was significantly higher in short (GT)-SWCNTs (length < 100 nm) compared to long (GT)-SWCNTs (length > 100 nm). In contrast, we found no dependence of the DNA density on SWCNT length in (GT)-SWCNT hybrids. Thus, we attribute differences in the observed length distributions of DNA-SWCNTs to variations in electrostatic repulsion induced by sequence-dependent DNA density.
单壁碳纳米管（SWCNTs）经短链单链 DNA 功能化后，由于 DNA 具有高分散效率和固有生物相容性，以及 SWCNTs 具有光稳定性和可调谐荧光性，在过去十年中被广泛研究用于生物医学应用。表征其物理性质，特别是其长度分布，对于它们作为生物工程研究工具和临床诊断剂的应用非常重要。传统上，原子力显微镜（AFM）已被用于通过将杂交体沉积在带静电的平面上来量化 DNA-SWCNTs 的长度。在这里，我们证明具有不同寡聚 DNA 序列（(GT)和(GT)）的 DNA-SWCNT 杂交体在 AFM 基底上以不同的方式沉积，从而导致母体溶液报告的长度分布存在显著的不准确性。使用基于溶液的表面活性剂交换技术，我们将两种样品都放入一种常见的表面活性剂包裹中，并在表面沉积时发现 SWCNT 的长度分布相同。此外，通过将包裹有表面活性剂的 SWCNT 旋涂到基底上，从而减轻静电相互作用的影响，我们发现长度分布不依赖于 DNA 序列，但明显长于静电沉积方法，这说明了表面沉积方法的固有偏差。通过吸收光谱和直接观察来量化每个 SWCNT 上 DNA 分子的覆盖度，我们发现短（GT）-SWCNTs（长度<100nm）中 DNA 分子的密度明显高于长（GT）-SWCNTs（长度>100nm）。相比之下，我们发现（GT）-SWCNT 杂交体中 DNA 密度与 SWCNT 长度无关。因此，我们将 DNA-SWCNTs 观察到的长度分布差异归因于序列依赖性 DNA 密度引起的静电排斥的变化。
