Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, 1628601, Japan.
Sci Rep. 2023 Mar 24;13(1):4833. doi: 10.1038/s41598-023-31927-8.
Although various conjugates of single-walled carbon nanotubes (SWNTs) and biomolecules, such as nanobiosensors and nanobiodevices, have been reported, the conjugation of papain and SWNTs have not been reported because of the formation of unexpected aggregates. In this study, atomic force microscopy (AFM) in liquid was used to investigate the interactions between papain and DNA-wrapped SWNTs (DNA-SWNTs) at two different pH values (pH 3.0 and 10.5). The direct AFM observation of the mixture of papain and DNA-SWNTs confirmed the aggregation of papain molecules with DNA-SWNTs in the buffer solutions. The numerous and non-uniform adsorption of papain molecules onto DNA-SWNTs was more pronounced at pH 3.0 than that at pH 10.5. Furthermore, thick conjugates appeared when papain and DNA-SWNTs were simultaneously mixed. The near-infrared photoluminescence spectra of the SWNTs drastically changed when the papain molecules were injected into the DNA-SWNT suspension at pH 3.0. Thus, the regulation of electrostatic interactions is a key aspect in preparing optimal conjugates of papain and DNA-SWNTs. Furthermore, although previous papers reported AFM images of dried samples, this study demonstrates the potential of AFM in liquid in evaluating individual bioconjugates of SWNTs.
尽管已经报道了各种单壁碳纳米管（SWNTs）和生物分子的缀合物，例如纳米生物传感器和纳米生物器件，但由于形成了意想不到的聚集体，因此尚未报道木瓜蛋白酶和 SWNTs 的缀合物。在这项研究中，使用原子力显微镜（AFM）在液体中研究了两种不同 pH 值（pH 3.0 和 10.5）下木瓜蛋白酶和 DNA 包裹的 SWNTs（DNA-SWNTs）之间的相互作用。直接 AFM 观察到木瓜蛋白酶和 DNA-SWNTs 的混合物证实了缓冲溶液中木瓜蛋白酶分子与 DNA-SWNTs 的聚集。在 pH 3.0 时，DNA-SWNTs 上的木瓜蛋白酶分子的大量且不均匀的吸附比在 pH 10.5 时更为明显。此外，当同时混合木瓜蛋白酶和 DNA-SWNTs 时，会出现厚的缀合物。当将木瓜蛋白酶分子注入 DNA-SWNT 悬浮液中时，SWNTs 的近红外光致发光光谱在 pH 3.0 时发生了剧烈变化。因此，调节静电相互作用是制备木瓜蛋白酶和 DNA-SWNTs 最佳缀合物的关键方面。此外，尽管以前的论文报道了干燥样品的 AFM 图像，但本研究表明 AFM 在液体中评估 SWNTs 个体生物缀合物的潜力。
