The National Oceanographic Centre (NOC) has a combined lab-on-chip sensor for total alkalinity (TA) and dissolved inorganic carbon (DIC) known as the TADIC sensor. Recent work has now progressed to the stage where it is ready to move towards integration on profiling floats.
This project milestone, led by partner NOC within Work Package 2, supports TRICUSO’s objective of developing new autonomous technologies for observing the Ocean carbon cycle. More specifically, it contributes to Task 2.3, which focuses on optimising lab-on-chip carbonate chemistry sensors for profiling-float applications and preparing them for integration with autonomous float platforms.
Timelapse of the wet-chemical lab-on-chip sensor assembly process. The video illustrates the precision engineering behind the TADIC platform, where pumps, valves, microfluidics, detectors and electronics are brought together into a compact autonomous sensor. Special Thanks to Adrian Nightingale for the video, Pablo Trucco-Pignata and the National Oceanographic Centre (NOC).
Why is this an important milestone?
The Southern Ocean is relatively devoid of in situ observations. It is remote, harsh, and seasonally inaccessible, and remains one of the most difficult regions in which to make sustained, high-quality carbonate chemistry observations, despite the central role it plays in the global carbon cycle absorbing a major share of anthropogenic carbon.
Traditionally, many of the best carbonate chemistry measurements come from ship-based measurements. These observations are highly valuable, but ships cannot be everywhere, all year round. Autonomous profiling floats offer a way to extend observations into remote and under-sampled regions. The challenge is that floats are small, power-limited, and any instruments attached to them must be compact, efficient, robust and capable of operating without human intervention for several years.
However, current float-based estimates of Ocean carbon variables often rely on indirect calculations, for example using measured pH together with estimated alkalinity. These approaches are powerful, but they also introduce uncertainty, especially in regions where reference measurements are sparse.
This is where TADIC becomes important. By measuring TA and DIC from a single autonomous lab-on-chip platform, the sensor provides two core carbonate-system variables directly. Together, TA and DIC can be used to calculate other key carbonate parameters, including pCO2, which is central to estimating air–sea CO2 exchange.
By preparing the combined TADIC lab-on-chip sensor for float integration, TRICUSO is helping to move autonomous carbonate chemistry observations beyond pH-only or algorithm-dependent approaches. This is a key step towards improving carbon observations in the Southern Ocean and other under-sampled regions.
How was this achieved?
The milestone was achieved through a combination of laboratory optimisation, field experience, hardware development and preparation for integration with profiling-float systems.
NOC’s lab-on-chip technology miniaturises analytical laboratory methods into compact autonomous sensors. For this milestone, the focus has been on the TADIC sensor, which combines two carbonate-system measurements within a single autonomous lab-on-chip platform:
Total alkalinity (TA), measured using a single-step titration method with an optical pH indicator.
Dissolved inorganic carbon (DIC), measured by acidifying seawater to convert DIC into CO2, transferring that CO2 across a gas-permeable membrane, and detecting the resulting conductivity change in an alkaline acceptor solution.
The combined TADIC design brings these two measurements into one integrated sensor architecture. This is important for profiling-float applications, where payload space, power, buoyancy, fluidic complexity, reagent storage and waste capacity are all tightly constrained.
Progress towards this milestone has included improved detector integration and calibration, refinements to software and firmware, optimisation of the autonomous state-machine protocol, and continued work to reduce reagent use, waste production and measurement complexity. The TA component has benefited from improved dye characterisation, reduced reliance on certified reference materials and optimisation of the titrant-to-sample ratio. The DIC component has advanced through conductivity-detector calibration, refinement of the gas-exchange and fluidic sequence, and improved temperature characterisation.
These improvements are directly relevant to float integration, where the constraints are much stricter than for laboratory or ship-based operation. A profiling-float sensor must be compact, low-power, mechanically robust, chemically stable, and able to operate with limited reagent and waste capacity over extended periods.
The work also builds on previous deployments of NOC lab-on-chip carbonate sensors on autonomous vehicles, landers and ship-based systems. This field experience has been essential for identifying what must be simplified, strengthened or repackaged before the TADIC sensor can be adapted for profiling-float use.
What happens next?
The next step is to move from sensor readiness into integration and system testing.
Trials are planned for October 2026 in Villefranche-sur-Mer, where the TADIC lab-on-chip system will be tested in preparation for future float-based operation. These trials will focus on the practical integration challenges that determine whether the sensor can operate reliably from a profiling float, including physical configuration, electronics and communication protocols, reagent-cartridge setup, power demand, and autonomous measurement sequencing.
Looking further ahead, the Southern Ocean float deployments will not rely on carbonate chemistry alone. TRICUSO is also developing floats equipped with acoustic wind sensors, which will provide information needed to better constrain air–sea CO2 exchange. In that wider field programme, the TADIC measurements of TA and DIC will form part of a broader autonomous observing package linking carbonate chemistry, float-based observations and surface forcing.
This milestone does not mean that the full float deployment has already taken place. Rather, it confirms that the combined TADIC sensor technology has reached the point where integration trials can proceed.
The results from the Villefranche-sur-Mer trials will inform the next stage of TRICUSO’s work towards autonomous carbonate chemistry observations from profiling floats, including future deployment in the Southern Ocean field programme.
By bringing the TADIC lab-on-chip sensor closer to profiling-float operation, TRICUSO is helping to build the observing capability needed for a denser and more reliable Ocean carbon observing system. This supports the project’s wider goal of strengthening European Research Infrastructure contributions to global greenhouse-gas observation and improving the evidence base for quantifying Ocean carbon uptake.
Milestone story by Pablo Trucco-Pignata.
