Droplet microfluidic based sensors for high resolution chemical sensing on autonomous underwater vehicles

海洋中的化学过程支撑着地球生命的自然循环。例如，海洋生态取决于营养物质（如硝酸盐和磷酸盐）在哪里和以多少运输，因为这些构成了食物链的最终基础。海洋也与大气处于动态平衡状态，并且是世界如何适应人为二氧化碳影响的内在因素。因此，更好地了解海洋化学动力学不仅具有学术意义，而且还将有助于更好地保护海洋生物，改进模型以了解和预测气候变化。然而，为了正确地理解海洋化学，我们必须能够准确地测量环境中化学物质的时空分布，以及它们如何响应不同的刺激而变化。然而，浩瀚的海洋带来了一个后勤问题——我们如何才能描述这样一个庞大而复杂的水体？一个令人信服的答案是使用配备化学传感器的自主水下航行器（auv）。auv可以在不需要人类干预的情况下一次航行到偏远地区数月，因此提供了一种高效的方法来收集有关海洋化学动力学的信息。目前最先进的化学传感器（使用小型实验室分析自动取样和分析水）提供了最高级的分析性能（准确性、精密度、灵敏度），但存在资源（电力、流体）使用效率低下和测量频率低的问题，限制了它们在auv上的适用性。为此，在此期间，我将开发一种基于液滴微流体的新型化学传感器。液滴微流体涉及产生、操纵和测量分散在沿着数百微米宽的油管流动的油流中的离散液滴。由于液滴体积非常小（亚微升），可以快速准确地进行化学处理和测量，这意味着液滴微流体为环境的连续采样和化学分析提供了快速高效的途径。虽然液滴微流体是一种经过验证且广泛应用于实验室分析化学的工具，但它现在才进入第一个现场部署设备。在这项研究中，我将推动提高现场可部署液滴微流体的灵敏度，测量频率和适用性，以开发适合在auv上使用的液滴微流体传感器。这些传感器将是高效的（低功耗和流体使用），能够以高灵敏度测量几种不同的化学参数（这意味着它们可以在广泛的海洋环境中使用）和高测量频率（在移动车辆上使用时转化为丰富详细的空间数据）。这个项目将是朝着传感器在海洋环境中监测化学变化的广泛、常规使用迈出的关键一步，特别是在auv上。这将导致化学传感器在未来成为环境科学中无处不在的工具，最终在整个海洋中大量部署在静态系泊和远洋自动驾驶车辆上。

Chemical processes within the oceans underpin the planet's natural cycles of life. Marine ecology, for example, depends on where and in what quantity nutrients (such as nitrate and phosphate) are transported, as these constitute the ultimate base of the food chain. The oceans are also in dynamic equilibrium with the atmosphere and are intrinsic to how the world will adjust to the effects of anthropogenic carbon dioxide. Thus better understanding of oceanic chemical dynamics is not only of academic interest, but will also lead to better protection of marine life and improved models to understand and predict climatic change.To properly understand ocean chemistry, however, we must be able to accurately measure the temporal and spatial distributions of chemical species within the environment and how they change in response to different stimuli. The vastness of the oceans provides a logistical problem however - how can we possibly characterise such a large and complex body of water? One compelling answer to this is to employ autonomous underwater vehicles (AUVs) equipped with chemical sensors. AUVs can travel to remote locations for months at a time without need of human interaction and as such offer a highly efficient way to gather information about the chemical dynamics of the ocean.The current state-of-the-art chemical sensors (which automatically sample and analyse the water using miniaturised laboratory assays) provide superlative analytical performance (accuracy, precision, sensitivity) but suffer from inefficient use of resources (power, fluid) and low measurement frequencies - limiting their applicability to AUVs. In response to this, during this fellowship I will develop a new type of chemical sensor based around droplet microfluidics. Droplet microfluidics involves the generation, manipulation and measurement of discrete droplets of water dispersed within a stream of oil flowing along tubing hundreds of microns in width. As the droplet volumes are so small (sub-microlitre), chemical treatments and measurements can be quickly and precisely performed, meaning droplet microfluidics offers a rapid and highly efficient route to continuous sampling and chemical analysis of the environment.While droplet microfluidics is a proven and widely used tool for laboratory-based analytical chemistry, it is only now making its way into the first field-deployable devices. In this fellowship I will drive improvements in the sensitivity, measurement frequency and applicability of field-deployable droplet microfluidics to develop droplet microfluidic sensors suitable for use on AUVs. The sensors will be highly efficient (low power and fluid use), capable of measuring several different chemical parameters with high sensitivity (meaning they can be used in a wide range of marine environments) and at high measurement frequencies (which translates into richly detailed spatial data when used on moving vehicles). This project will be a key step towards the widespread, routine usage of sensors to monitor chemical change in the marine environment, in particular on AUVs. It will lead to chemical sensors being a ubiquitous tool in environmental science in the future, eventually deployed in large volumes throughout the oceans on static moorings and ocean-going autonomous vehicles.