High-Throughput Electrochemistry - a new approach to the rapid development of modified carbon electrodes

电化学广泛应用于我们周围的世界，从大大小小的不同类型的电池，到用于制造氯和氢氧化钠的工业过程，以及沉积用于装饰效果的金属和制造微芯片的方法，再到糖尿病患者每天使用几次的便携式设备来测量他们的血糖。电化学反应发生在表面上，其最大的优点之一是施加在电极上的电压直接用来驱动化学反应，而流动的电流是反应速度的直接量度。在许多情况下，挑战在于设计电极表面以进行特定的化学反应，这样我们就可以利用这些优势。在裸露的金属或碳表面，反应是通过一次一个电子的转移而发生的。因此，在许多我们想要进行的反应中，会形成不稳定的中间体，然后再进行进一步的反应，导致电极表面的污染和不良副产物的产生。克服这个问题的一种方法是通过附加分子来修饰电极表面，这些分子在整个反应中充当中间体或介质。然后通过首先将电子一次一个地转移到（或从）附着在电极表面的介质中，在电极表面发生反应。然后，在第二步中，这些介质与溶液中的分子反应，从而催化我们希望在电极上进行的反应。这种方法的最大优点是，原则上，我们可以选择我们选择的分子附着在电极表面，这样它们就可以快速地与电极交换电子，并选择性地与溶液中的分子发生反应——我们可以根据我们想要的反应设计电极表面。挑战在于找到合适的分子，并以正确的方式将它们附着在电极表面。在过去20年左右的时间里，人们一直在努力做这件事，他们采用了一些有灵感的猜测方法，选择一两个分子进行尝试，然后制备出附着这些分子的电极表面。在这个项目中，我们将以一种更有效的方式解决这个问题。我们将在电极表面合成数百或数千种相关的，但每一种都略有不同的分子，然后筛选这些分子，以找到最适合我们感兴趣的特定反应的分子。为此，我们将开发制备电极表面的新方法和筛选表面活性的新方法。我们选择了三种特殊的反应来研究。首先是NADH的氧化，这是一种常见的辅酶。自然界中有数百种酶使用NADH。如果我们能找到氧化NADH的好电极，我们就可以用这些不同的酶来制造传感器和燃料电池。特别是，一种用于NADH氧化的良好修饰电极对于开发更好的传感器以使糖尿病患者能够测量他们的血糖非常重要。第二个反应是抗坏血酸（维生素C）的氧化。当试图氧化NADH时，抗坏血酸是一个重要的可能的干扰，因为抗坏血酸存在于血液和许多生物样本中。因此，对于NADH电极，我们希望找到修饰过的表面，使NADH比抗坏血酸反应更好。另一方面，抗坏血酸本身也很重要，因为我们需要能够测量它在饮料和食品中的浓度，所以我们也将寻找对抗坏血酸氧化非常好的改良电极。最后一个目标是多巴胺，一种参与大脑神经元之间信号传递的分子。许多催化NADH反应的分子也催化多巴胺的氧化。我们将筛选我们生产的不同分子，看看是否有特别适合检测多巴胺的分子，这样我们就可以生产出微小的电极，用于在大脑研究中测量多巴胺。

Electrochemistry is widely used in the world around us from batteries of different types both large and small, through the industrial processes used to make chlorine and sodium hydroxide and methods to deposit metals for decorative effects and to make microchips, to the portable devices used several times a day by diabetics to measure their blood glucose. Electrochemical reactions occur at surfaces and one of their great advantages is that the voltage applied to the electrode is used directly to drive the chemical reaction and the current that flows is a direct measure of the speed of the reaction. In many cases the challenge is to design the surface of the electrode to carry out a particular chemical reaction so that we can exploit these advantages. At bare metal, or carbon, surfaces reactions occur by the transfer of electrons one at a time. As a result in many reactions that we would like to carry out unstable intermediates are formed which then undergo further reactions that lead to fouling of the electrode surface and the production of undesirable side products. A way to overcome this problem is to modify the electrode surface by attaching molecules which act as intermediates or mediators in the overall reaction. The reaction at the electrode surface then occurs by first transferring the electrons one at a time to (or from) the mediator attached to the electrode surface. Then, in a second step these mediators react with molecules in solution, thus catalysing the reaction that we wish to carry out at the electrode. The big advantage of this approach is that, in principle, we can select the molecules we choose to attach to the surface of the electrode so that they exchange electrons rapidly with the electrode and react selectively with the molecules in solution - we can design the electrode surface for the reaction we want. The challenge is to find the right molecules and the right way to attach them to the electrode surface. For the last 20 years or so efforts to do this have used inspired guesswork to pick one or two molecules to try and then prepared electrode surfaces with these molecules attached. In this project we will tackle this problem in a much more effective way. We will synthesise hundreds or thousands of related, but each slightly different, molecules on electrode surfaces and then screen these to find the best for the particular reactions we are interested in. To do this we will develop new ways of preparing the electrode surfaces and new ways to screen the surfaces for activity. We have chosen three particular reactions for our study. The first is the oxidation of NADH, a common coenzyme. There are hundreds of enzymes in nature which use NADH. If we can find good electrodes for the oxidation of NADH we can then use these different enzymes to make sensors and in fuel cells. In particular a good modified electrode for NADH oxidation could be important in developing better sensors to allow diabetics to measure their blood glucose. The second reaction is the oxidation of ascorbate (vitamin C). Ascorbate is an important possible interference when trying to oxidise NADH because ascorbate is present in blood and many biological samples. Therefore for the NADH electrodes we want to find modified surfaces at which NADH reacts much better than ascorbate. On the other hand ascorbate is also important in its own right as we need to be able to measure its concentration in drinks and foodstuffs so we will also be looking for modified electrodes which are very good for ascorbate oxidation. The final target is dopamine, a molecule involved in signalling between neurones in the brain. Many of the molecules which catalyse the reaction of NADH also catalyse the oxidation of dopamine. We will screen the different molecules we produce to see if any are especially good for the detection of dopamine so that we can produce minute electrodes that can be used to measure dopamine in studies of the brain.