A Novel, Standalone and Low-cost System for In-Situ Chemical Imaging with Planar Optodes

In order to better understand soils heterogenous nature, we can apply chemical imaging to visualize microscale spatiotemporal dynamics of important soil parameters such as oxygen or pH in real-time. However, the use of chemical imaging with planar optodes is mostly limited to laboratory experiments, due to practical constraints of the current applied equipment.

To address these challenges, we have developed a novel and low-cost multi analyte real time in-situ imaging system (MARTINIS)[1]. Specifically designed for operating in-situ or in mesocosm applications. MARTINIS significantly downscales imaging components, fitting them into a 25 cm in diameter and 70 cm long transparent tube. The system can be deployed into the soil profile with planar optodes attached to the tube’s exterior to create an interface for direct chemical imaging in the field. We show how we developed our proof-of-concept system by applying low-cost, off the shelf components and 3d printing, while maintaining high spatial (< 100 um) and temporal resolution (≥ minutes). To demonstrate the functionality of MARTINIS we have deployed the system in various in-situ environments and mesocosm applications in soil or sediments to obtain “panoramic” imaging of oxygen, pH and temperature dynamics. By incorporating a simplified temperature planar optode directly to the imaging system we are able to compensate for soil temperature changes along depth gradients when measuring oxygen or pH.

In one application, MARTINIS operated semi-autonomously over three months to monitor 2D soil oxygen conditions in a 16 cm deep soil profile. The system captured dynamic changes in oxygen levels linked to specific rainfall events and demonstrated reliable performance across various weather conditions, from snow to sun. In another application for short-term deployment, we measured heterogeneous soil pH gradients in wildfire-affected remote locations, highlighting the systems portability and adaptability. Deployment versatility was extended to waterlogged sediments in a mesocosm setup to observe the effect of bioturbation on oxygen dynamics. Measuring 2D oxygen and pH dynamics directly in the field is crucial, as these parameters drive many biogeochemical processes in soils and are tightly linked to rapidly changing environmental conditions. Conditions, which are often impossible to replicate in the laboratory. Enabling in-situ chemical imaging can be especially valuable in agricultural settings, where microscale soil oxygen dynamics leads to “hot spots” or “hot moments” of greenhouse gas production such as N₂O.

With MARTINIS we present a proof-of-concept system that aims to overcome current barriers of applying planar optodes in-situ and increase accessibility to researchers by applying low-cost equipment, a modular platform and user-friendly software.  

 

[1]           M. R. Rasmussen et al., "A novel, standalone and low-cost system for in-situ chemical imaging with planar optodes in soils," Sensors and Actuators B: Chemical, vol. 424, p. 136894, 2025/02/01/ 2025, doi: https://doi.org/10.1016/j.snb.2024.136894.