Miniaturized sensor system for continuous soil-nutrient monitoring based on integration of a lab-on-a-chip microfluidic cartridge with an optoelectronic detection unit

Project Information

SOILMONITOR

Grant agreement ID: 101097989

DOI

10.3030/101097989

Project closed

EC signature date 26 October 2022

Start date 1 November 2022

End date 31 January 2026

Funded under

• The European Innovation Council (EIC)

Total cost

€ 2 499 716,25

EU contribution

€ 2 499 716,00

Coordinated by

CHRISTIAN-ALBRECHTS-UNIVERSITAET ZU KIEL
Germany

Periodic Reporting for period 1 - SOILMONITOR (Miniaturized sensor system for continuous soil-nutrient monitoring based on integration of a lab-on-a-chip microfluidic cartridge with an optoelectronic detection unit)

Reporting period: 2022-11-01 to 2023-10-31

Summary of the context and overall objectives of the project

The SOILMONITOR proposes a highly miniaturized sensor system for continuous monitoring of soil nutrients. Through time series monitoring of nitrate, phosphate, and ammonium, the SOILMONITOR is aimed at contributing to a balance in the supply of soil nutrients. The sensor is intended to spend one year maintenance-free in the soil, where it takes nutrient concentration measurements in soil water at regular intervals when there is sufficient soil moisture. For this, soil water is drawn into a microfluidic through the ceramic of the inlet. In the microfluidic system, the solution is stained with a nutrient-specific assay and its concentration is determined by photometry using an organic light-emitting diode - organic photodetector (OLED-OPD) pair. Once the concentrations have been determined, the mixture will be pumped into a waste reservoir. The determined concentrations are to be sent to a station via a Lo-Ra WAN network. In the first development phase, nitrate will be measured; the measurements will then be extended to ammonium and phosphate.

The project is intended to deliver seven complementary and synergistic benefits: quick and informed decisions on fertilization, higher fertilizer efficiency, soil-quality improvements, easier compliance with environmental standards, reduced management efforts, less nutrient leaching, and reduced N2O-emis-sions. The SOILMONITOR project is divided into six work packages aimed at the following main achievements:
• Development and optimization of a prototype to ensure the broadest possible applicability of accurate soil nutrient measurement, and test for these results.
• Development, test and optimization of water extraction and demonstration that the average sensor water extraction radius is equivalent to plant root water extraction radius.
• Demonstration of a maintenance-free sensor lifetime of at least one year.
• Preparation of private investment and/or funding to transition and progress the sensor along the commercialization roadmap.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In the first year of the SOILMONITOR project work was carried out on the individual components necessary for the system.

1. Soil water extraction
Since photometric measurements require a water matrix, the first step is to extract soil water from the ground. Using a porous alumina ceramic, extraction experiments were conducted in preliminary tests for three soil types using a peristaltic pump. The easiest extraction was obtained for sandy soil, and the most difficult extraction for silt (Böckmann et al., 2021). In the first project year these tests were extended to three types of well-specified typical test soils. It was found that a stronger suction is necessary for soil solution extraction in soils with a lower water content.

2. Photometric nutrient measurement
For a year-long nutrient measurement with small sample volumes in a microfluidic a stable chemical assay and a matched photometric readout system are necessary. In an interdisciplinary approach we worked on a new type of nitrate-sensitive assay and the matching optoelectronic readout system. In particular we demonstrated color-sensitive OPDs suitable for differential measurements in an integrated system. We demonstrated the integration of nanostructures in the OPD stack for this purpose.

3. Design of microfluidic
We decided to fabricate microfluidic systems by photolithographic master design and replication in the silicone polydimethylsiloxane (PDMS). In this method, a silicon wafer is coated with a negative photoresist and structures are selectively cured with UV light via a photomask. The uncured photoresist is dissolved with the aid of a developer, thus producing a positive for casting with silicone. This process is particularly suitable for producing microstructures in one plane. The structures are sealed with a glass lid that will later include the OLED-OPD measurement system. A multi-level approach will be used for liquid storage. In the first project year, the process was established and inlets, mixer geometries, valves, test chambers and actuation approaches were investigated.

4. Economic progress
SOILMONITOR made significant strides in developing a business proposal for pioneering an automated nutrient sensing solution for agriculture. Our strategy aims to solve the specific needs and problems of farmers and agricultural businesses through a unique, user-friendly and cost-effective system. Based on customer surveys and market analysis, a business model has been developed that is in line with the long-term strategy. SOILMONITOR is based on a robust foundation with patents covering innovative technologies related to the sensor. This IP protection ensures our exclusivity in the field.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

1. Economic benefits
The capability to quantify soil nutrients directly within water extracted from the soil and thus available to growing crops is pertinent to determine proper amounts of fertilization. More accurate and efficient fertilization practices can result in cost savings for farmers by allowing them to apply the right amount of nutrients at the right time, reducing waste and overuse of fertilizers. The SOILMONITOR can thus enhance fertilizer efficiency and improve cost-effectiveness for farmers.

2. Impacts on the agricultural industry
SOILMONITOR advances the growing use of data-driven decision-making in agricultural practices. Continuous monitoring over an entire season provides farmers with real-time data to make informed decisions about fertilizer use, planting, and soil management. The project further encourages and facilitates the adoption of sustainable agricultural practices through its aim to provide critical data for nutrient management and crop growth and quality optimization at a low cost and maintenance-free. As a technological innovation, SOILMONITOR has the potential to increase the overall competitiveness and resilience of agriculture and offers the opportunity to set EU and global standards in precision agriculture.