Graphene based pH microsensor networks for Blue Carbon monitoring
Lead Research Organisation:
University of Plymouth
Department Name: Sch of Geog Earth & Environ Sciences
Abstract
The rising acidity in the oceans from CO2 in the atmosphere contributes to dissolved inorganic carbon (DIC) in the shallow surface waters. DIC can be considered as the dissolved carbon bound to oxygen in small molecules (i.e. dissolved CO2, bicarbonate and carbonate). DIC is in balance with both the atmospheric CO2 and what is termed 'Blue Carbon', which is carbon in the ocean bound up as carbon chains, plants and animals (i.e. organic carbon) in coastal and marine ecosystems. Important to this project, pH is one of the few critical parameters that can be measured continuously in rivers and oceans to observe DIC and help us control and monitor the impact and effect of our carbon emissions.
Our aim is to directly address the current lack of pH sensors available that can withstand the harsh conditions of rivers and oceans by making low cost graphene materials that are sufficiently 'robust' and 'sensitive' to become the mainstream environmental sensor networks of the future. The proposal takes a problem-driven, multidisciplinary approach to develop a cost-effective solution to monitoring DIC and the impacts of carbon released into rivers and coastal waters. Our interdisciplinary team intend to advance sensors for pH measurement via focused graphene sensor development aligned with this major societal challenge, with readiness to be interfaced with leading industry-led technology.
Our aim is to directly address the current lack of pH sensors available that can withstand the harsh conditions of rivers and oceans by making low cost graphene materials that are sufficiently 'robust' and 'sensitive' to become the mainstream environmental sensor networks of the future. The proposal takes a problem-driven, multidisciplinary approach to develop a cost-effective solution to monitoring DIC and the impacts of carbon released into rivers and coastal waters. Our interdisciplinary team intend to advance sensors for pH measurement via focused graphene sensor development aligned with this major societal challenge, with readiness to be interfaced with leading industry-led technology.
Technical Summary
Global carbon dioxide (CO2) fluxes and rising acidity in rivers and oceans are buffered by the dissolved inorganic carbon (DIC) equilibrium in surface waters. pH is therefore a critical parameter needed to monitor DIC and the measurement of pH and DIC will ultimately allow us to monitor and control aquatic carbon emissions that leak from land to the ocean or diffuse across the sea surface.
The proposal takes a problem-driven, collaborative, multidisciplinary approach to develop a cost-effective solution to monitor emissions and impacts of carbon released into riverine and coastal waters. To deliver this project we have assembled a team of experts spanning the fields of marine and environmental science, analytical chemistry, graphene sensors, electronics and nanotechnology.
Our aim is to directly address current field pH sensor limitations by synthesizing functionalized graphene materials that are suitably robust and sensitive to become the mainstream environmental sensors of the future. We will then trial sensors and evaluate current sensor networks and field platforms for graphene sensors in both catchment and marine settings in the UK. The University of Plymouth (UoP) and Plymouth Marine Laboratory (PML) teams will link industry project partners (ProMare, IBM, Silicon Austria), higher education and environmental intelligence experts. The integrated approach ensures 'systems thinking' towards the development of large-scale pH sensor networks for application in catchments and coastal regions.
The proposal takes a problem-driven, collaborative, multidisciplinary approach to develop a cost-effective solution to monitor emissions and impacts of carbon released into riverine and coastal waters. To deliver this project we have assembled a team of experts spanning the fields of marine and environmental science, analytical chemistry, graphene sensors, electronics and nanotechnology.
Our aim is to directly address current field pH sensor limitations by synthesizing functionalized graphene materials that are suitably robust and sensitive to become the mainstream environmental sensors of the future. We will then trial sensors and evaluate current sensor networks and field platforms for graphene sensors in both catchment and marine settings in the UK. The University of Plymouth (UoP) and Plymouth Marine Laboratory (PML) teams will link industry project partners (ProMare, IBM, Silicon Austria), higher education and environmental intelligence experts. The integrated approach ensures 'systems thinking' towards the development of large-scale pH sensor networks for application in catchments and coastal regions.
Organisations
- University of Plymouth (Lead Research Organisation)
- Natural Environment Research Council (Co-funder)
- Zimmer and Peacock (Collaboration)
- IBM (Collaboration)
- Silicon Austria Labs GmbH (SAL) (Collaboration)
- Silicon Austria Labs (Project Partner)
- IBM Research GmBh (Project Partner)
- Plymouth Marine Laboratory (Project Partner)
- ProMare (Project Partner)
| Title | Continued testing and development of GFET sensors |
| Description | Melanin has been identified as a problem interfering with the graphene channel, microscopic analysis appears to show that the channel degrades as a result of the functionalisation step. Therefore work has commenced into investigating alternative approaches to functionalising the channel involving using either graphene oxide or reduced graphene oxide in place of DMSO-melanin. |
| Type Of Material | Technology assay or reagent |
| Year Produced | 2025 |
| Provided To Others? | No |
| Impact | Being able to determine that the DMSO-melanin damages the graphene channel of the GFET sensors confirms that this material is not a suitable candidate for sensor functionalisation. Other potential candidates may now undergo assessment. |
| Title | Development of a 3D printed protective housing |
| Description | In order to increase the robustness of the sensor a prototype protective housing has been developed that holds a protective layer over the sensor which prevents it from coming into direct contact with the sample. While sensitivity to pH changes was reduced following the addition of this protective layer and housing, the sensor was still able to detect changes in pH. |
| Type Of Material | Technology assay or reagent |
| Year Produced | 2025 |
| Provided To Others? | No |
| Impact | Given the well-documented issue of biofouling in marine environments, which can compromise sensor performance, the use of protective housing with the sensors is a promising approach. By incorporating a thin glass barrier, these housing designs enable the sensors to detect pH changes while maintaining their own structural integrity, potentially leading to improved robustness and extended operational lifespan in the field. |
| Title | Electrochemical characterisation of DMSO-melanin pH sensors |
| Description | The pH sensors developed by functionalising screen printed carbon electrodes by drop casting DMSO-melanin onto the working electrode have been characterised using electrical and electrochemical techniques (cyclic voltammetry and electrochemical impedance spectroscopy) before and after undergoing functionalisation. |
| Type Of Material | Technology assay or reagent |
| Year Produced | 2025 |
| Provided To Others? | No |
| Impact | This characterisation has revealed that the resistance and the capacitance of the sensors changes as a result of functionalisation. This helps to increase understanding in how these sensors operate. |
| Title | Electrochemical pH sensor for detecting shifts in the pH of artificial seawater |
| Description | Screen printed pH sensors have been developed that are able to detect shifts in the pH of artificial seawater via the use of open circuit potentiometry. The sensors consist of a three electrode system consisting of a graphene working electrode and silver/silver chloride counter and reference electrodes. These sensors have been functionalised by drop casting a pH sensitive material onto the working electrode of the sensor and allowing this material to dry before use. This material is called Dimethyl sulphoxide (DMSO) melanin. Testing has shown that these sensors are able to respond to small changes in the pH of artificial seawater in a predictable manner. |
| Type Of Material | Technology assay or reagent |
| Year Produced | 2024 |
| Provided To Others? | No |
| Impact | These sensors are simple to fabricate and are inexpensive. That they are able to respond to small changes in the pH of artificial seawater where there is a high concentration of sodium chloride is positive and suggests that they are possible candidates for the deployment in real world marine pH monitoring applications. Furthermore the DMSO-melanin being pH sensitive in the artificial seawater makes it a potentially useful material to functionalise the surface of the graphene field effect transistor should functionalisation be required. |
| Title | Initial GFET sensors produced |
| Description | The first version of the GFET devices have been produced. This method involves using sputter coating and plasma etching in order to produce the features of the GFET device. These features include gold contact pads that are connected to a graphene channel which runs through the centre of the device. |
| Type Of Material | Technology assay or reagent |
| Year Produced | 2024 |
| Provided To Others? | No |
| Impact | The GFET devices can be taken forward for further development into a pH sensor. This next stage of this involves performing electrical testing on the devices in order to assess the quality of the contacts and the graphene channel. Once this is complete the devices can be tested with pH buffer solutions in order to assess pH sensitivity and assess whether any further functionalisation protocols need to be developed. |
| Title | Laser cut physical masks designed and produced |
| Description | The laser cut masks that are required for the fabrication of the GFET pH sensor have been designed and produced. This allows for the process of sensor fabrication to begin. |
| Type Of Material | Technology assay or reagent |
| Year Produced | 2023 |
| Provided To Others? | No |
| Impact | GFET sensor fabrication is able to commence. |
| Title | Testing susceptibility to temperature changes |
| Description | The temperature of the ocean varies across the globe and the influence of temperature on pH measurements obtained using classical glass electrode pH meters. Therefore the effect of temperature on the measured signal has been tested using modified seawater at various environmentally relevant temperatures ranging from 4°C to 35°C. The sensor performed well with there being no significant difference in the measured signal as a result of these temperature differences. |
| Type Of Material | Technology assay or reagent |
| Year Produced | 2025 |
| Provided To Others? | No |
| Impact | This adds further confidence that the sensors are capable of detecting pH changes in seawater samples across a wide range of different temperatures. The temperature range that was tested covers much of what the senors are likely to be exposed to once deployed. |
| Title | Testing with real seawater samples |
| Description | As the initial testing with standard reference buffers and artificial seawater was successful, the DMSO-melanin pH sensors were tested with real seawater samples where the pH was modified with either hydrochloric acid or sodium hydroxide. This testing was also successful with sensitivity being displayed both over a wide (pH4, pH7, pH10) and narrow (pH7, pH7.8, pH8.3) range of pH values that are relevant to monitoring changes in marine pH. |
| Type Of Material | Technology assay or reagent |
| Year Produced | 2025 |
| Provided To Others? | No |
| Impact | The ability of the sensors to accurately detect changes in pH over both small and significant variations suggests their utility for monitoring subtle, long-term changes associated with ocean acidification, as well as detecting more pronounced shifts that could signal a major environmental incident, such as a chemical spill. This capability enables early intervention, potentially mitigating the effects of such events. |
| Title | Voltage/current testing protocol for GFET devices developed |
| Description | A protocol for testing the GFET devices using the B1500A Keysight semiconductor device parameter analyser that is able to test the quality of the gold contact pads and graphene channel on these devices. This protocol uses a four probe arrangement with two probes being responsible for feeding a current through the device and the other two probes measure the voltage which allows for the resistance to be calculated so that the quality of the various parts of the devices can be assessed. This protocol can also be used for detecting any potential changes in resistance with solutions that are of a different pH thereby also functioning as a sensing protocol. |
| Type Of Material | Technology assay or reagent |
| Year Produced | 2024 |
| Provided To Others? | No |
| Impact | The development of this protocol results in the quality of the fabricated GFET devices to be assessed and provides the protocol necessary for pH sensitivity testing to begin. |
| Description | Collaboration with IBM with partner Patrick Ruch |
| Organisation | IBM |
| Department | IBM Research Zurich |
| Country | Switzerland |
| Sector | Private |
| PI Contribution | Collaborative opportunities for (i) exchange of marine and environmental data from cutting edge sensor networks and autonomous platforms and (ii) consultation to ensure developed sensors align with the latest formats, |
| Collaborator Contribution | data exchange and consultation, leveraging our ongoing collaboration around the Mayflower Autonomous Ship AI and networking that are currently being developed in this field. |
| Impact | None yet |
| Start Year | 2025 |
| Description | Collaboration with Zimmer & Peacock for pH sensors and measurement instrumentation |
| Organisation | Zimmer and Peacock |
| Country | United Kingdom |
| Sector | Private |
| PI Contribution | Use of Z&P pH sensors and instrumentation. |
| Collaborator Contribution | Provision of pH sensors for use in the project. |
| Impact | Collaboration covers electrochemical sensors and their use in pH sensing for Blue Carbon monitoring. |
| Start Year | 2023 |
| Description | Silicon Austria Ltd. with partner Sabine Lengger |
| Organisation | Silicon Austria Labs GmbH (SAL) |
| Country | Austria |
| Sector | Private |
| PI Contribution | Discussions about sensor development |
| Collaborator Contribution | Discussions relating to production of materials, sensors and latest 2D materials |
| Impact | None yet |
| Start Year | 2020 |
| Description | International Meeting |
| Form Of Engagement Activity | A formal working group, expert panel or dialogue |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | GOA-ON Week. Seession on 'Technology gaps and new tools for OA research', Thursday 21 November 2024 at 13:00 UTC. In this community discussion session, researchers working on the development of new techniques and technology for the observation and measurement of ocean acidification introduce their tools. Our talk was entitled 'Automating TA/DIC Measurements for High Frequency Sampling' by Dr. Simon Whelan & Simon Ussher |
| Year(s) Of Engagement Activity | 2024 |
| URL | https://www.goa-on.org/webinars/OaWeek2024/webinar.php |
| Description | Presentation / Panel discussion at UNFCCC COP29 |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Policymakers/politicians |
| Results and Impact | Side event at UNFCCC COP29 on polar oceans - triple threats to polar oceans Side event at UNFCCC COP29 on mCDR - panel discussion |
| Year(s) Of Engagement Activity | 2024 |
| Description | Stakeholder Meeting |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Industry/Business |
| Results and Impact | A project meeting invliting stakeholders and project partners to disseminate some of the findings of the pH sensors developed (graphene and functionalised carbon) |
| Year(s) Of Engagement Activity | 2024 |
| Description | Wepal-Quasimeme Workshop on Quality Assurance for inorganic carbon system measurements in context of monitoring for ocean acidification and marine carbon dioxide removal technologies |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Co-organiser and presenter at the workshop. 8 years after the first Wepal-Quasimeme Ocean Acidification (OA) workshop in Southampton and after 3 years of the AQ15 Wepal-Quasimeme intercalibration exercise, it's time to bring the Ocean Acidification community back together. We also welcome the growing marine carbon dioxide community (mCDR), who are interested in monitoring (MRV) mCDR technologies. Many of the methodologies, instrumentation, developments and quality control overlap between these issues. The first OSPAR QSR on OA was published in 2023 but there is still, more than ever before, a need for high quality data (TA, DIC, pH, pCO2) to strengthen all scientific output on OA. OSPAR, as well as other international initiatives such as ICOS, GOA-ON and AMAP, indicate that strong international collaborative monitoring programmes on OA need to continue, to facilitate meaningful data gathering, collation and assessment. A consistent approach to sampling, sample pre-treatment, analysis, quality control, validation of methods, calculation of derived variables and an understanding of methodological limitations is required; methods should be fit for purpose. Many monitoring agencies, with varying levels of experience, are analysing samples for carbonate chemistry parameter on different types of instruments but also using new techniques, as more sensors are installed on buoys or ships, or more automated analysers are set up. There's still a gap in availability of CRMs, standards, buffers for quality control and calibrations when analysing marine samples. Worldwide, Scripps reference materials are used for QC or calibration for total alkalinity (TA), dissolved inorganic carbon (DIC) and pH analysis without having a separate way of ensuring that their measurement system is in control and has a calibration with known linearity. Thus, even when reference materials are used, there are likely to be unidentified uncertainties showing up on a well-designed proficiency study like the QUASIMEME AQ15. |
| Year(s) Of Engagement Activity | 2025 |