How Portable Sensors Track Aquatic Nutrients

The portable sensor can be used to easily track aquatic nutrients. Nutrients like PO43, NO2, and NO3 in natural waters can be identified by combining rapid prototyping techniques with colorimetry, electronics, and LED-based optical detection to create a highly portable and robust sensor.

If you think of a sensor as a system or instrument that detects changes in its environment and communicates that information to other electrical devices for additional processing, you’ve got it. 

Sensors to track nutrients in fluids

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According to Dickson Data, use of portable sensors to track micro-components in water can have critical implications for compliance and regulation. This is especially important for business enterprises in the food and industry, though it has wide-scale application. 

With interchangeable optical detection units, a component cost of around €300 per unit, and a tiny form factor, the sensing platform is a modular design that incorporates interchangeable optical detection units. 

Fifty-five water samples were collected at Kongsfjorden, Ny-Aselund (78.5–79°N; 11.6–12.6°E) during a field campaign on the MS Teisten research vessel on June 22, 2016. It also used a 19plus V2 Seacat Profiler CTD probe with turbidity and dissolved oxygen sensors for 23 hydrological casts, which were also documented. The adaptive sensing platform evaluated water samples at the CNR Dirigible Italia Arctic Research Station Laboratory for PO43, NO2, and NO3.

Concentrations of nutrients 

It was determined that various factors, including hydrology, influence the Fjord’s nutrient concentrations. An excellent linear response was observed with a detection limit of 0.05 micromoles (NO2, NO3) and 0.03 micromoles of phosphate (PO43). This study shows how the adaptive sensing platform can be used in remote places as a standalone platform or for validating deployable environmental sensor networks.

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Concentrations of NO2, NO3, and PO43 (0–20 uM) were used to evaluate the analytical performance of the sensing platform Using ultra-pure water (MilliQ, Millipore, Burlington, MA, USA). Analytical-grade chemicals, all reagents, and test solutions were created (Sigma Aldrich, St. Louis, MO, United States). 

Eppendorf vials of 1.5 ml capacity were used to transfer 900 L of sample and test solutions for NO2 measurement. Once the Griess reagent was added to each vial, the selection was thoroughly mixed for 20 minutes at room temperature (about 20°C). After that, the keys were incubated for 20 minutes at 60°C. It was found that VCl3 (Garci-Robledo et al., 2014) was used to measure NO3 in the samples and test solutions.

Fabrication of platforms

A microcontroller board called an Arduino Mega 2,560 was used for the electronic control (Radionics, Ireland). An LCD (Radionics, Ireland) presented raw data in BIT values while an 8 GB SD card attached through a Data Logger was displayed. Pulse Width Modulation driver was used to adjust the LED intensity on the platform so that it could be used by the colorimetric approach selected for the experiment. 

To detect NO2, NO3, and PO43 in natural waters, the benchtop sensing platform depicted in Figure 4 was created. Used an Epilog Zing Laser cutter to laser cut black polymethylmethacrylate (PMMA) panels that were solvent glued together using 1,2-Dichloroethylene, and the platform was assembled (Sigma Aldrich). 

Each of the four detection chambers (one and two for PO43, two and three for NO2, and three for NO3) is 20 cm x 6 cm x 3.5 cm in size. Lighting was chosen for each chamber based on the max (lambda max), particularly for each colorimetric chemistry. The optical detection within each section was done using LEDs of 375 and 540 nm wavelengths (Roithner, Wien, Austria) for PO43 and NO2 and NO3, respectively. To measure absorbance in each chamber, the photodiode (PD) was utilized (Roithner, Wien, Austria).

Using a 3D printer (Stratasys Objet260 Connex1) to create a custom-designed holder for the LED and photodiode, the alignment of these two components was achieved (Figures 4C, D). When deployed in remote regions, a field deployment is necessary, which increases detector stability, reduces unit cost, and simplifies servicing of the detection unit.

Distribution of nutrients

Distributions of nutrients are critical to preserving marine environments. As glacier discharge influences the availability of nutrients in polar habitats, this is one method through which glacial discharge impacts marine primary productivity. Fjords are the primary conduits via which glacial runoff enters the ocean in much of the Arctic and Sub-Antarctic. 

Consequently, glacial runoff significantly influences these coastal environments, which is anticipated to continue growing as global temperatures rise. Finally, the marine-terminating glaciers Kronebreen and Kongsvegen in Kongsfjorden are predicted to transition to land-terminating, further affecting the ecosystem’s nutrient balance. Must reliably measure water quality metrics on a near-daily basis to be possible. 

Because of the high cost and difficulty of shipping, it’s not practical to use older, more traditional instruments for nutrient analysis like NO2, NO3, and PO4. The ability to analyze samples on-site eliminates the requirement to treat and store models for further research, damaging the sample integrity. Analytical assessments for nutrients may be conducted quickly and accurately using the low-cost sensing technology provided in this study.

Transport and use in remote areas with complicated logistics are now possible because of the platform’s analytical performance, robustness, and mobility. The modular design incorporates interchangeable optical detecting units, enabling the detection of most colorimetric reagent-based tests, readily replacing the LEDs and PD. The 3D-printed holder assures continued alignment and eliminates movement artifacts. 

Sample analysis and results

The platform analyzed 56 water samples collected during a sampling campaign on June 22, 2016, and correlated with hydrological data collected during the same movement. A correlation between turbidity and an increase in nutrient contents was seen along with the inner and outer glacial fjords’ surface measurements; this was particularly evident with a rise in water depth. 

More detailed sample campaigns, such as those carried out by Cantoni, are needed to better understand the highly varied nature of the nutrient distribution in the Fjord’s water column. In developing and validating autonomous sensing networks, this study’s technology provides a valuable framework for further exploration. 

Every component of a platform that generates an analytical response must operate reliably for an autonomous sensor to function in-situ. 

We have used and updated the sensing platform given in this study to test and evaluate optical components, 3D printed structures, and fluidics that have been integrated into autonomous sensing platforms after the conclusion of this study. 

The HOLIFAB project has embraced emerging fabrication technologies to improve analytical performance, reduce costs, and accelerate the development of in-situ chemical sensors that are analytically reliable and autonomous for weeks or months.


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