An autonomous lab-on-chip sensor for in situ measurements of seawater total alkalinity
Allison Schaap a, Stathys Papadimitriou a, Socratis Loucaides a, Matthew Mowlem a
a National Oceanography Centre, European Way, Southampton, United Kingdom
Proceedings of Emerging Investigators in Microfluidics Conference (EIMC)
Online, Spain, 2021 July 20th - 21st
Organizers: Adrian Nightingale, Darius Rackus and Claire Stanley
Oral, Allison Schaap, presentation 029
DOI: https://doi.org/10.29363/nanoge.eimc.2021.029
Publication date: 5th July 2021

Total alkalinity (TA) is one of the four parameters which characterize the oceanic carbonate system. TA data with high spatial coverage and high temporal frequency can contribute to better measurements, modelling, and understanding of the carbon cycle in water, providing insights into problems from global climate change to ecosystem functioning.  To provide this data, we present an autonomous sensor capable of in situ measurements of TA, based on a generic oceanographic lab-on-chip platform which has been implemented for a number of chemical assays.

This sensor implements a benchtop TA assay on a small portable device. The system is based a generic ocean chemical lab-on-chip hardware platform with integrated microfluidics, optics, pumps, valves, and electronics.  The TA sensor samples seawater, mixes it with reagents, degasses the resulting solution, and performs an optical measurement.  It can carry multiple calibration materials on board, allowing for routine re-calibration and quality checks in the field. The scientific applications of this sensor require reliable accuracy (~0.1%-0.5%) during deployments lasting months in harsh and varying conditions. 

This sensor has been tested and demonstrated both in the lab and in the field.  Field deployments have included a carbon storage experiment in the North Sea, an ecosystem study in a Mediterranean seagrass meadow, a coral reef health study in Australia, and most recently a carbon uptake study off the coast of Antarctica.  The results from lab and sea trials show that the technology is in a strong position to be able to meet the scientific needs for TA measurements.

To close, I’ll discuss some of the general engineering challenges that we’ve faced in creating microfluidic technology that has to survive at sea.

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