Robust, Ion-Selective Thick-Film Sensors for Long Term Field Deployment

The source of all water in land based water courses and water systems is rain, which in turn predominantly arises due to evaporation from seas and oceans. It is therefore not surprising that the most abundant electroactive species present in land based water bodies is the chloride ion although the concentration of chloride varies with the distance from the sea. A chloride sensor would therefore be an invaluable tool for hydrology since it offers a direct and simple method to track and map the flow of water as it moves through the terrain. Moreover selective and considered spatial distribution of chloride sensors (networks) will enable quantitative measures of the chloride retention capacity of different soil types and is therefore a useful tool for soil scientists. Furthermore, a chloride sensor gives a qualitative measure of soil salinity; a particularly important indicator for agricultural management. In addition, at the plant level a miniaturised array of chloride sensors would facilitate real-time studies of chloride fluxes in the root rhizosphere enabling new bioscience to be achieved. Other major species present in the environment include nitrate, which can be viewed as beneficial or as a contaminant depending on its location and concentration. Currently it is not possible to measure nitrate reliably in the field in real-time. A nitrate sensor has obvious benefits in the fields of agriculture, soil science and plant science. Again, at the root level it allows real-time measurements of nutrient fluxes to and from the plant.

We shall use thick-film screen printing technology to produce an array of sensors that measure chloride ions and nitrate ions with respect to an integrated reference electrode.

We shall develop an array of electrodes to measure chloride and nitrate ions with respect to an integral reference electrode. This shall be implemented using some novel developments in thick-film technology. Screen printing technology (thick-film) involves the layer by layer construction of a sensor on a common substrate using different materials deposited in patterns that define the required structure. Typically the printable materials are glass based and are processed at temperatures of the order of 850 degC, though lower temperatures are necessary for some materials. The majority of the screen printable materials employed are commercially available, but novel sensing materials will need to be developed in-house. With this technology, resulting sensors are inherently low cost due to the nature of the batch printing process and robust due to the glassy construction on a ceramic substrate.

When these sensors are coupled with emerging technologies in wireless networks, wide scale real-time measurement systems become truly viable for the first time. This project will demonstrate a simple proof of concept to show that such sensors can be employed in real environmental applications.

Impact Summary


Who might benefit from this research?

As the output from this project is an enabling technology, there are many potential beneficiaries. The enabling technology is sensors that can be deployed at different scales, allowing both temporal and spatial data to be collected. The obvious beneficiaries are those who would like to make use of the data that these sensors can generate, and these include scientists operating in the fields of biology, soil science, hydrology and environmental science. Specifically, there are many beneficiaries in the theme area of food sustainability. For example, detailed studies of plant behaviour in the presence of the selected measurands can be evaluated (e.g. assessing salt tolerance of plants) leading to developments allowing poor quality land to be used for agriculture.

The new science enabled by these sensors will indirectly benefit government agencies, regulators, policy makers and other stakeholders. For example, the mapping of the movement of fertiliser elements through different soil types will allow holistic, catchment area scale measurements to inform land use planning.

How might they benefit?

In the themes of food sustainability, soil science and hydrology, scientists benefit because the sensors (coupled with networks) allow unprecedented spatial and temporal data collection, allowing the effects of transient events to be monitored for the first time. This will allow scientific insights into such effects as diurnal variations in nutrient levels, impact of significant rainfall events (storms and floods), preferential use of nutrients due to local changes around a root, etc.

Other stakeholders (such as farmers and local populations) will benefit from the more intelligent use of resources, such as fresh water and fertilisers. Irrigation systems can be made more responsive and could potentially use brackish water for irrigation at certain times of the year. Real-time measurements of nutrient levels and their distribution will help farmers manage their fertiliser requirements with the added benefit of reducing eutrophication of waterways due to excess nutrient run off.

Moreover, there is a potential socioeconomic impact as well. The ability to measure environmental parameters at this level potentially allows field monitoring to a higher level than previously possible. Such potential impacts resulting from this include feedback systems allowing brackish water to be used for irrigation, thus reducing the strain on potable water supplies for parts of the world where potable water and irrigation are in competition, and as previously mentioned, informing on efficient farming practices to increase the amount of useable land, thus benefitting the population of these areas in general.

Impact within BBSRC Strategic Priorities

Soil science and agri-systems approaches: This work will allow improved understanding of agricultural systems as it enables research- based management systems at a range of scales (farm, catchment, regional) to optimise food production in ways that are reconciled with maintaining biodiversity. It also enables agri-ecosystem approaches to land management practices that enhance biodiversity conservation in agricultural and associated ecosystems.

Crop science: The developed sensors will have application in enhancing crop productivity and quality by allowing the optimised and efficient use of resources (e.g. water, fertiliser and human resources).

Living with environmental change: Increasing competition for water resources, coupled with reduced rainfall and increasing temperatures due to climate change are exacerbating water quality problems in many developed and developing countries. These sensors will allow hydrological models to be validated thus creating opportunities that bridge climate and ecosystems science, for example in the interaction of soil and water.