研究人员首次成功地在范德华基底（在这种情况下为石墨烯）上生长出均匀的二维丝蛋白片段层。这一壮举将对开发基于丝绸的电子器件至关重要，因为迄今为止，由于控制丝绸纤维结构固有的无序性很困难，因此一直受到限制。丝绸是一种基于蛋白质的材料，人类已经使用了 5000 多年。近年来，研究人员一直在寻求利用其两种主要成分之一——丝素蛋白（由蛋白质片段组成）——在电子和生物电子应用中。这是因为它可以自组装成一系列基于纤维的结构，这些结构具有优异的机械和光学性能。事实上，丝素蛋白薄膜与范德华固体、金属或氧化物界面化的器件似乎特别有希望用于制造下一代薄膜晶体管、存储器晶体管（或忆阻器）、人机界面和传感器。然而，问题在于，丝绸不能以其天然形式用于此类器件，因为其纤维以无序、缠结的方式排列。这意味着它不能均匀或准确地调制电子信号。

😁 研究人员通过控制丝绸纤维的无序排列，成功在石墨烯上生长出均匀的二维丝蛋白片段层。

🤩 他们利用原子力显微镜、纳米傅里叶变换红外光谱和分子动力学计算，观察到这些薄膜由丝素蛋白分子的稳定层状结构组成，其结构与天然丝绸的纳米晶体相同。

😊 这些丝素蛋白在该基底上以精确的平行β-折叠片（自然界中常见的一种蛋白质形状）排列，这种排列方式使其具有高度的稳定性和均匀性。

🥳 该研究团队利用丝绸分子与基底的固有相互作用及其结晶性，迫使丝绸分子在两种材料的界面处组装成一个晶体层。然后，他们调节丝蛋白溶解的水溶液的浓度，以限制形成的丝绸层的数量。通过这种方式，他们能够组装单层、双层或更厚的多层。

🥰 由于这种材料高度有序，因此其特性是均匀的。此外，由于β-折叠片排列中强烈的分子间相互作用以及与基底的强相互作用，它非常稳定。研究人员希望他们的研究结果将有助于开发利用化学修饰的天然丝绸基层来提供不同电子功能的二维生物电子器件。

😉 他们还计划使用他们的起始材料来创建完全合成的类似丝绸的层，这些层由模仿丝绸分子氨基酸序列的人工、序列定义的聚合物组装而成。

😌 重要的是要注意，在这项工作中开发的系统是无毒且水性的，这对生物相容性至关重要。

🤓 他们相信，这种材料可以用于制造记忆电阻器，用于基于神经网络的计算。这些网络可以使计算机模仿大脑的功能。

Researchers have succeeded in growing a uniform 2D layer of silk protein fragments on a van der Waals substrate – in this case, graphene – for the first time. The feat should prove important for developing silk-based electronics, which have been limited until now because of the difficulty in controlling the inherent disorder of the fibrillar silk architecture.

Silk is a protein-based material that humans have been using for over 5000 years. In recent years, researchers have been looking to exploit one of its two main components, silk fibroin (which is made up of protein fragments), in electronic and bioelectronic applications. This is because it can self-assemble into a range of fibril-based architectures that boast excellent mechanical and optical properties. Indeed, devices in which silk fibroin films are interfaced with van der Waals solids, metals or oxides appear to be particularly promising for making next-generation thin-film transistors, memory transistors (or memristors), human–machine interfaces and sensors.

There is a problem, however, in that silk cannot be used in its natural form for such devices because its fibres are arranged in a disordered, tangled fashion. This means it cannot uniformly or accurately modulate electronic signals.

Controlling natural disorder

A team of researchers, led by materials scientist and engineer James De Yoreo of the PNNL and the University of Washington, has now found a way to control this disorder. In their work, the researchers grew highly organized 2D films of silk fibroins on graphene, a highly conducting sheet of carbon just one atom thick.

Using atomic force microscopy, nano-Fourier transform infrared spectroscopy and molecular dynamics calculations, the researchers observed that the films consist of stable lamellae of silk fibroin molecules that have the same structure as the nano-crystallites of natural silk. The fibroins pack in precise parallel beta-sheets – a common protein shape found in nature – on this substrate.

Thanks to scanning Kelvin probe measurements, De Yoreo and colleagues also found that the films modulate the electric potential of the graphene substrate’s surface.

The researchers say that they took advantage of the inherent interactions of the silk molecules with the substrate and its crystallinity to force the silk molecules to assemble into a crystalline layer at the interface between the two materials. They then regulated the concentration of the aqueous solution in which the silk proteins had been dissolved to limit the number of silk layers that form. In this way, they were able to assemble single monolayers, bilayers or much thicker multilayers.

Uniform properties

Since the material is highly ordered, its properties are uniform, says De Yereo. What’s more, because of the strong intermolecular interactions in the beta-sheet arrangement and the strong interactions with the substrate, it is highly stable. “In its pure state, it can regulate the surface potential of the underlying conductive substrate, but there are techniques for doping silk to introduce both optical and electronic properties that can greatly expand its useful properties,” he explains.

The researchers hope their results will help in the development of 2D bioelectronic devices that exploit natural silk-based layers chemically modified to provide different electronic functions. They also plan to use their starting material to create purely synthetic silk-like layers assembled out of artificial, sequence-defined polymers that mimic the amino acid sequence of the silk molecule. “In particular, we see potential for using these materials in memristors, for computing based on neural networks,” De Yereo tells Physics World. “These are networks that could allow computers to mimic how the brain functions.”

It is important to note that the system developed in this work is nontoxic and water-based, which is crucial for biocompatibility, adds the study’s lead author Chenyang Shi.

The research is detailed in Science Advances.

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