A novel, standalone and low-cost system for in-situ chemical imaging with planar optodes in soils

Planar optodes are optical sensors that provide microscale 2D visualization of various chemical analytes in environmental and biological samples in real-time. The application of planar optodes to study the spatiotemporal dynamics in particular of oxygen, pH or ammonia is a valuable tool for investigating the drivers of many biogeochemical processes in soils. However, such applications are mainly limited to laboratory experiments due to practical limitations of the method that hinder accessibility for field measurements. This study describes a novel and low-cost multi analyte real time in-situ imaging system (MARTINIS) designed for in-situ or mesocosm applications. We show that imaging equipment used in traditional laboratory setups can be significantly scaled down to fit into a Ø250mm cylinder that can be deployed in soils. To illustrate the functionality of MARTINIS, we demonstrate imaging of oxygen and temperature planar optodes to acquire “panoramic” images with high spatial (≈ 10 µm) and temporal (intervals ranging from minutes up to hours and days) resolution in a laboratory setup and in-situ. MARTINIS aims to increase accessibility for in-situ applications of planar optodes with a standalone solution for both hardware and software. In-situ applications are especially valuable in agricultural settings, where microscale soil dynamics leading to greenhouse gas emissions such as N 2 O are affected by changing environmental conditions. Tools such as the system described in this study, which aims at long-term online monitoring of spatiotemporal in-situ soil conditions, could thus lead to new insights in the field of soil science. • Novel imaging system enables planar optodes to be applied in-situ in soils. • Spatiotemporal soil oxygen dynamics are visualized with low-cost equipment. • In-situ temperature compensation is achieved with planar optodes for temperature. • Modular system design and open-source software widens environmental applications.