Low-cost sensor to detect long-term ocean acidity

The new technology, designed to measure pH levels in seawater, was developed by engineers from the National Oceanography Centre, in collaboration with oceanographers from University of Southampton Ocean and Earth Science, which is based at the centre.

The team tested the new device aboard the RRS Discovery, and presented their results in Anaytica Chimica Acta.

In its current form it can be used for on-board analysis of seawater samples, but the ultimate aim is to further develop the design so that it can be deployed for longer, in situ measurements.

Ocean acidification is occurring as a consequence of rising levels of atmospheric carbon dioxide (CO2), which is absorbed by the oceans. When it dissolves in seawater, CO2 forms a mild acid, which is decreasing ocean pH globally and has the potential to impact marine ecosystems.

‘We need to monitor seawater pH to a high level of precision and accuracy, and over long periods of time, in order to detect changes in the carbon system,’ said Dr Victoire Rérolle, lead author and researcher with NOC’s Sensors group.

As well as monitoring global change, the sensors can be used to measure more localised human impact. The micro sensors could be deployed to detect leakages from carbon capture and storage sites by measuring any proximal fluctuations in pH. The oil industry is also interested in this technology for monitoring seawater acidity around drilling sites.

The microfluidic chip within the sensor is claimed to offer advantages as it is robust, small, reasonably cheap to produce, and uses small amounts of reagents, an key factor for in situ deployment.

The sensor uses a dye which changes colour with pH. The dye is added to the sample, then the colour is measured using an LED light source and a spectrometer. The microfluidic element describes the component needed to mix the seawater sample with the dye and the cell to measure the colour.

‘Now that we know that the bench top system works, we can use the technology from other systems to create in situ pH micro sensors,’ Dr Rérolle said in a statement. ‘This is what we are working on now, in collaboration with oceanographers based at NOC.’

The development work was funded by SENSEnet, an EU Framework 7 project for the development of aquatic sensors, and the research expedition aboard the RRS Discovery was funded by the UK Ocean Acidification Research Programme.

Collaborating institutes were the National Oceanography Centre, University of Southampton Ocean and Earth Science, the Norwegian Institute for Water Research, the Uni Bjerknes Centre Norway and the University of Bergen.