SitS: Wireless, sustainable, and automated sensory system for in-situ monitoring of soil heavy metals

This award was made through the "Signals in the Soil (SitS)" solicitation, a collaborative partnership between the National Science Foundation and the United States Department of Agriculture National Institute of Food and Agriculture (USDA NIFA). With the rapid growth of industrialization and urbanization, elevated levels of non-essential heavy metals in soils and irrigation water pose major threats to ecosystem health, food safety, and human and animal health, due to their toxicity, bioaccumulation, and environmental persistence.

To closely monitor and manage heavy metal contaminated soils for ensuring food safety and human health, researchers at Michigan State University and Fraunhofer USA Center Midwest are collaborating to develop a novel wireless sensor platform for continuous field measurement of heavy metal concentrations in soils. In addition, the research team will integrate the research topics into diverse educational and outreach activities, including teacher training opportunities, secondary education opportunities through summer programs, and communications through various social media platforms and YouTube channels.

If successful research outcomes will have a significant positive impact on soil sensing science and technology, soil quality, food safety, and public health.

The overarching goal of this project is to develop an environmentally friendly, sustainable, wireless, automated microfluidic-sensor platform, capable of in-situ detection, continuous monitoring, and remote reporting of soil pH and concentrations of major heavy metal elements. Metal elements of interest include, but are not limited to, lead, mercury, cadmium, nickel, and lithium.

The proposed platform will synergistically integrate several multifunctional modules in a hermetically sealed and compact package, including: 1) a self-renewable microelectrode sensor array; 2) highly-efficient microfluidics with an integrated porous ceramic filter, active mixers, and parallel fluidic channels; 3) a high-performance, eco-friendly solar energy harvester; 4) low power electronic circuitry for power management, microfluidic control, and multichannel electrochemical sensing; 5) a zero-energy Internet of Things (IoT) networking module capable of both above- and underground wireless data communication; and 6) real-time signal processing and quantification for the end-user. The prototype platform will be demonstrated in a pilot study to investigate the episodic release of metals from soil microsites that are driven by fluctuating and preferential distribution of soil water content, leading to an in-depth understanding of the dynamic behaviors of heavy metals in heterogeneous soil matrixes.

The proposed platform will provide distinct advantages over existing approaches for heavy metal sensing in soils. In particular, material selection, soil sample processing, power management, and device/system packaging are carefully considered as part of the system design to achieve the best sensing performance while minimizing disturbance to soil environments.

Boron-doped polycrystalline diamond as a new sensing material allows for highly sensitive and selective, long-term stable electrochemical measurements. Integration of microelectrode sensors with automated parallel microfluidics enables high-throughput, simultaneous detection of multiple analytes with minimal sample volume. Deliberately designed multi-step sample processing can reduce sample matrix complexity, provide consistent test conditions, and prevent leaching of wastewater into the soil environment.

The zero-energy IoT communication enables secure and energy-efficient wireless data transmission within a large network while eliminating tethered configuration and line of sight between sensors and data aggregators. The use of a solar energy harvester as a power source is environmentally-friendly, self-sustainable, and cost-effective. Besides the significant contributions to soil sensing science and technology, this project is expected to have a great impact on engineering- and agriculture-related STEM education through integration of research with diverse educational and outreach activities, such as annual workshops, outreach publication, teacher training, K-12 summer programs, new SitS courses, social media and YouTube channels.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.