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

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.