The combination of electrochemistry and nanotechnology leads to spatiotemporal control at the nanoscale for nonequilibrium chemical and biological systems in liquid solutions.

The combination of electrochemistry and nanotechnology leads to spatiotemporal control at the nanoscale for nonequilibrium chemical and biological systems in liquid solutions. Over the past decades, electrochemistry has transformed our society. Batteries loaded with nanomaterials now allow us to drive cars without the humming of an internal combustion engine; chemical synthesis is being electrified with the benefits from nanomaterial-based catalysts with greener feedstocks and energy sources; and miniaturized electrochemical sensors sit in the center of gadgets that monitor the sugar level in your body. With such remarkable achievements from electrochemistry, one might ask the following: is there anything else that electrochemistry can help with? For researchers in the field of nanoscience and nanotechnology, one might ask more specifically this question: are there any other synergies by integrating electrochemistry and nanotechnology? This Viewpoint is meant to offer some pondering in this context from a junior faculty who is excited about both electrochemistry and nanoscience. Electrochemistry, by its own very nature, offers a method of spatiotemporally controlling the concentration profiles of chemical species and hence their free energies μ and entropies S in solution (Figure 1). Electrochemical charge transfer at the material–liquid interface transduces electronic signal into concentration gradients away from the electrode’s surface. While such a mass transport limitation is often less desirable as it strains performances in some devices, fundamentally those electrochemically created concentration gradients lead to nonequilibrium chemical systems that will be temporally modulated by electrochemical signals. Under a given electrode geometry and electrochemical boundary conditions, well-defined differential equations that include reaction kinetics and mass transport allow quantitative control of the established nonequilibrium systems.(1,2) Steady-state or kinetic systems near equilibrium can be maintained, and complex time-dependent dissipative systems can be generated, too. Those features in electrochemistry contribute to the fact that the classic oscillatory Belousov–Zhabotinsky (BZ) reaction was first quantitatively monitored and modulated by electrochemistry.(3) The gradient-generating nature of electrochemistry allows researchers to create and control nonequilibrium systems in chemistry and biology. We live in a world away from equilibrium, and spatiotemporal heterogeneity is ubiquitously critical to biological processes. Here, we just list a few examples: the heterogeneous local microenvironment of soil and root nodules dictates the microbiota composition in agriculture;(4) the temporally dynamic O₂ and nutrient gradients radially and axially in the intestine offer the metabolic diversity of gut microbiomes;(5) and it is the interdependence among microbes in different microenvironments that leads to the difficulty of enriching and culturing the predominant majority of natural microorganisms.(6) By creating concentration gradients electrochemically, a digitally controlled electrochemical device has the potential of establishing and spatiotemporally modulating extracellular microenvironments at will. Such devices can mimic the natural microenvironment and offer a customizable perturbation for fundamental studies and applications noted above. Also, the spatiotemporal control of biochemical processes inspires researchers to design new chemical transformation pathways. For example, it is proposed that the O₂ gradient within micrometer-sized aerobic diazotrophic bacteria enables microbial N₂ fixation in air with O₂-sensitive nitrogenase and O₂ as the terminal electron acceptor;(7) can we establish new chemical transformations with similar seemingly incompatible steps? Since it is shown that local concentrations of reaction intermediates are paramount to the reaction rate in cascade tandem reactions,(8) can we leverage the local concentrations generated electrochemically and design faster cascades? Electrochemically generated chemical gradients will lead to the successful demonstrations of such new reaction cascades that we may never see in homogeneous solutions. So, what can nanotechnology and nanoscience help with under the forgoing argument for electrochemically controlled nonequilibrium systems? Fundamentally, electrochemistry’s capability of controlling concentration gradients is determined and limited by the electrodes’ dimension and boundary conditions. It is challenging if not impossible to control a gradient of nanometer-scale resolution with a micrometer-sized electrode. The diffusion at nanoscale shortens the time to establish the desirable gradients and hence increases temporal resolution. As demonstrated in the porous-electrode model developed by Newman in the 1960s,(9) nanomaterial electrodes create exponential gradients for chemical species, which is different from the simple linear gradients from planar electrodes. Finally, the interfacial engineering at the nanoscale will yield selective electrochemical reactions that precisely modulate the gradients of targeted species but do not interfere with others, which is particularly important for biological applications when a myriad of chemicals are in the solution. Therefore, the introduction of nanomaterials and nanotechnology will allow electrochemistry to modulate gradients in chemistry and biology with higher spatiotemporal resolutions, more varied gradient shapes, and more selective control for the targeted species. Because it is the microscopic spatiotemporal gradients that govern the examples noted above, the benefits generated by nanotechnology are mission-critical for the control of those nonequilibrium scenarios. Excited by such a prospect, the author’s research group has made a few advances synergistically combining electrochemistry and nanotechnology (see Figure 1). With the use of a nanowire array electrode, we created a CH₄-to-CH₃OH catalytic cycle of seemingly incompatible steps in which ambient CH₄ activation by O₂-sensitive Rh^II metalloradicals is followed by O₂-driven hydroxylation that yields CH₃OH.(10,11) We also mimicked the O₂ gradient in root nodules and housed O₂-sensitive symbiotic rhizobia for electricity-driven N₂ fixation in air.(12) Finally, machine-learning-based algorithms have been developed to model the yielded concentration gradients from nanowire arrays.(13) The author contends that those demonstrated works will introduce more examples of nanoscopically controlled nonequilibrium systems in chemistry and biology. Taking such a road less traveled will yield a different yet beautiful scenery. Figure 1. Combining electrochemistry and nanotechnology will lead to spatiotemporally controlled nonequilibrium systems at the nanoscale. C.L. thanks Prof. Long Luo for constructive inputs. C.L. acknowledges the financial support of the National Institute of Health (R35GM138241). This article references 13 other publications.

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非平衡系统的微观控制：当电化学遇到纳米技术

电化学和纳米技术的结合导致在纳米尺度上对液体溶液中的非平衡化学和生物系统进行时空控制。

电化学和纳米技术的结合导致在纳米尺度上对液体溶液中的非平衡化学和生物系统进行时空控制。在过去的几十年里，电化学改变了我们的社会。装有纳米材料的电池现在可以让我们在没有内燃机嗡嗡声的情况下驾驶汽车；化学合成正在电气化，受益于基于纳米材料的催化剂以及更环保的原料和能源；微型电化学传感器位于监测您体内糖分水平的小工具的中心。鉴于电化学取得了如此显着的成就，人们可能会问：电化学还有什么可以帮助的吗？对于纳米科学和纳米技术领域的研究人员，有人可能会更具体地问这个问题：整合电化学和纳米技术是否还有其他协同作用？这个观点旨在为一位对电化学和纳米科学都感到兴奋的初级教师提供一些在此背景下的思考。电化学，就其本质而言，提供了一种时空控制化学物质浓度分布的方法，从而控制它们的自由能 μ 和熵小号在溶液中（图 1）。材料-液体界面处的电化学电荷转移将电子信号转换为远离电极表面的浓度梯度。虽然这种传质限制通常不太理想，因为它会影响某些设备的性能，但从根本上说，那些电化学产生的浓度梯度会导致非平衡化学系统，这些系统将在时间上受到电化学信号的调制。在给定的电极几何形状和电化学边界条件下，定义明确的微分方程（包括反应动力学和质量传递）允许对已建立的非平衡系统进行定量控制。(1,2) 可以保持接近平衡的稳态或动力学系统，并且可以复杂化也可以生成与时间相关的耗散系统。电化学中的这些特征有助于经典的振荡 Belousov-Zhabotinsky (BZ) 反应首先通过电化学进行定量监测和调节。(3) 电化学的梯度产生性质使研究人员能够在化学和生物学中创建和控制非平衡系统. 我们生活在一个远离平衡的世界，时空异质性对生物过程至关重要。在这里，我们只列举几个例子：土壤和根瘤的异质局部微环境决定了农业中的微生物群组成；（4）时间动态 O (3) 电化学的梯度产生特性使研究人员能够在化学和生物学中创建和控制非平衡系统。我们生活在一个远离平衡的世界，时空异质性对生物过程至关重要。在这里，我们只列举几个例子：土壤和根瘤的异质局部微环境决定了农业中的微生物群组成；（4）时间动态 O (3) 电化学的梯度产生特性使研究人员能够在化学和生物学中创建和控制非平衡系统。我们生活在一个远离平衡的世界，时空异质性对生物过程至关重要。在这里，我们只列举几个例子：土壤和根瘤的异质局部微环境决定了农业中的微生物群组成；（4）时间动态 O₂和肠道中径向和轴向的营养梯度提供了肠道微生物群的代谢多样性；（5）不同微环境中微生物之间的相互依赖导致了大多数天然微生物的富集和培养困难。（6）通过以电化学方式产生浓度梯度，数控电化学装置具有随意建立和时空调节细胞外微环境的潜力。这种设备可以模仿自然微环境，并为上述基础研究和应用提供可定制的扰动。此外，生化过程的时空控制激发研究人员设计新的化学转化途径。例如，建议 O ₂微米大小的需氧固氮细菌内的梯度使微生物能够利用 O ₂敏感固氮酶和 O ₂在空气中固定N ₂作为末端电子受体；(7) 我们可以用类似的看似不相容的步骤建立新的化学转化吗？由于表明反应中间体的局部浓度对级联串联反应的反应速率至关重要，(8) 我们能否利用电化学产生的局部浓度并设计更快的级联反应？电化学产生的化学梯度将导致我们在均相溶液中可能永远不会看到的这种新反应级联的成功演示。那么，在上述电化学控制的非平衡系统的论点下，纳米技术和纳米科学能提供什么帮助呢？从根本上说，电化学控制浓度梯度的能力取决于电极的尺寸和边界条件。使用微米级电极控制纳米级分辨率的梯度即使不是不可能，也是具有挑战性的。纳米级的扩散缩短了建立理想梯度的时间，从而提高了时间分辨率。正如 Newman 在 1960 年代开发的多孔电极模型中所证明的，(9) 纳米材料电极为化学物质产生指数梯度，这与平面电极的简单线性梯度不同。最后，纳米级的界面工程将产生选择性的电化学反应，精确调节目标物质的梯度，但不干扰其他物质，这对于溶液中存在大量化学物质时的生物应用尤为重要。所以，纳米材料和纳米技术的引入将使电化学能够以更高的时空分辨率、更多样化的梯度形状和对目标物种的选择性控制来调节化学和生物学中的梯度。因为控制上述示例的是微观时空梯度，所以纳米技术产生的好处对于控制那些非平衡情景至关重要。对这样的前景感到兴奋，作者的研究小组在电化学和纳米技术的协同结合方面取得了一些进展（见图1）。通过使用纳米线阵列电极，我们创建了一个 CH 因为控制上述示例的是微观时空梯度，所以纳米技术产生的好处对于控制那些非平衡情景至关重要。对这样的前景感到兴奋，作者的研究小组在电化学和纳米技术的协同结合方面取得了一些进展（见图1）。通过使用纳米线阵列电极，我们创建了一个 CH 因为控制上述示例的是微观时空梯度，所以纳米技术产生的好处对于控制那些非平衡情景至关重要。对这样的前景感到兴奋，作者的研究小组在电化学和纳米技术的协同结合方面取得了一些进展（见图1）。通过使用纳米线阵列电极，我们创建了一个 CH₄ -to-CH ₃ OH 催化循环看似不相容的步骤，其中环境中的 CH ₄被 O ₂敏感的Rh ^II金属自由基激活，然后是 O ₂驱动的羟基化，产生 CH ₃ OH。(10,11) 我们还模拟了根瘤中的O ₂梯度和用于电驱动 N _{2的 O 2敏感共生根瘤菌}(12) 最后，已经开发了基于机器学习的算法来模拟纳米线阵列产生的浓度梯度。(13) 作者认为，这些展示的工作将介绍更多的化学和纳米级控制的非平衡系统的例子生物学。走这样一条人迹罕至的路，会带来不一样的美景。图 1. 结合电化学和纳米技术将导致时空控制的纳米级非平衡系统。CL 感谢罗龙教授的建设性意见。CL 感谢美国国立卫生研究院 (R35GM138241) 的财政支持。本文引用了其他 13 种出版物。