Scientists recently developed a portable sensing platform to detect nutrients (PO43−, NO2−, NO3−) in natural waters in the Arctic. Rapid prototyping, colorimetric chemistry, advanced electronics, and LED-based optical detection all contributed to the sensor platform’s development. The sensors have been used in the CNR Dirigibile Italia Arctic Research Station in Ny-Ålesund in Svalbard, Norway, since 2016, and researchers have published results of the study in Frontiers in Sensors in 2021.
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Why Are Researchers Studying Nutrient Levels?
Nutrients like phosphate (PO43−), nitrite (NO2−), and nitrate (NO3−) are key determinants of many ecological processes in the marine environment. Natural water’s nutrient levels influence critically important microbial, plant, and animal metabolic processes.
Scientists rely on nutrient level data for environmental monitoring and research. Nutrient levels have been included as a major observational variable for several international global ocean expeditions since the 1970s.
However, measuring nutrients in marine environments is challenging. Compared to physical parameters observed for environmental monitoring like temperature, salinity, and pH levels, nutrient levels require much more complex sampling, detection, and analysis technology.
Marine nutrient measurements are typically obtained with manual sampling, transportation, and subsequent analysis in the laboratory. Samples are often collected in remote locations and then spend a protracted period in storage and transportation as a result.
Researchers have been interested in autonomous, in situ nutrient-sensing for some time, as it offers the potential for lower cost measurements with enhanced analytical relevance.
The portable sensing platform described in the recent paper can help enhance our understanding of global nutrient distribution and ultimately lead to better environmental modeling and decision-making.
The Portable Sensing Platform
Researchers developed a modular sensing platform that incorporates interchangeable optical detection units. Crucially, each interchangeable unit has a small form factor (20 cm × 6 cm × 3.5 cm) and costs only around €300 to produce.
The platform used an Arduino Mega 2,560 microcontroller board for electronic control. An LCD displayed raw data in binary values, while a data logger connected an 8 GB SD card to store data.
LED colorimetric techniques were employed, with a pulse width modulation driver optimizing LED intensity for the chosen method. This system was developed as a sensing platform for detecting PO43−, NO2−, and NO3− in natural waters, with low cost being a key design concern.
An Epilog Zing laser cutter fabricated 4 mm thick black polymethylmethacrylate (PMMA) panels to form the platform’s structure. The panels were solvent bonded together with 1,2-Dichloroethane.
Four detection chambers were used in the unit: two for detecting PO43− and one each for detecting NO2− and NO3−.
The lambda max (λmax) specific for each colorimetric chemistry informed which LEDs would be used for detection. A 375 nm LED was utilized in the PO43− chamber, while a 540 nm LED was used in both the NO2− and NO3− chambers. A photodiode carried out absorbance detection in each chamber.
LEDs and photodiodes were aligned with a 3D printed custom-designed holder. The LED photodiode could be easily removed and replaced through the holder without affecting the alignment. This meant that the detector was more stable and cheaper to produce. It also means that maintenance and servicing needs are greatly reduced – critical for field deployments in remote locations.
Engineers subjected the new sensor platform to rigorous testing both in the laboratory and on pilot field expeditions in the Mediterranean Sea. Results from the laboratory tests showed excellent linear response for the sensors, with a limit of detection of 0.03 μm for PO43− and 0.05 μm for NO2− and NO3−.
The cost-effective sensors developed for this research can be deployed for up to a month in harsh Arctic conditions, collecting nutrient levels data every hour for that whole time. Crucial to getting this level of data was driving down the cost of the sensors.
Using Portable Sensors in the Arctic Wilderness
The portable sensing platform was deployed at the CNR Dirigibile Italia Arctic Research Station, Ny-Ålesund, Norway. This environment is extremely challenging for sensing operations but also highly important for building up our knowledge of global water nutrient levels.
As well as providing in situ nutrient levels analysis at the research center, the portable sensing platform also analyzed samples taken on nearby field trips. A field campaign in Kongsfjorden in June 2016 acquired 55 water samples in 10 L Niskin bottles aboard the MS Teisten research vessel. The adaptive sensing platform at the Ny-Ålesund research station was then used to analyze the samples for PO43−, NO2−, and NO3− levels.
This research is part of the EU-wide Commonsense project and is a joint effort from EU countries to develop and install a network of environmental sensors around the entire continent.
With this network in place, researchers will be able to closely monitor changes in levels of polluting chemicals, acidity, microplastics, noise, and many other factors, including nutrient concentrations.
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References and Further Reading
McCaul, M. et al. (2021) Nutrient Analysis in Arctic Waters Using a Portable Sensing Platform. Frontiers in Sensors. Available at: https://doi.org/10.3389/fsens.2021.711592.
O’Connell, C. (2016) DCU researcher senses marine change in extreme conditions. Silicon Republic. [online] Available at: https://www.siliconrepublic.com/innovation/marine-research-margaret-mccaul-sensors-dcu.
O’Connell, C. (2016) The importance of keeping a close eye on the Arctic. The Irish Times. [online] Available at: https://www.irishtimes.com/news/science/the-importance-of-keeping-a-close-eye-on-the-arctic-1.2898243.