Simultaneous Imaging of Temperature and Oxygen by Utilizing Thermally Activated Delayed Fluorescence and Phosphorescence of a Single Indicator

Abstract

Chemical gradients are essential in biological systems, affecting processes like microbial activity in soils and nutrient cycling. Traditional tools, such as microsensors, offer high-resolution data but are limited to one-dimensional measurements. Planar optodes allow for two-dimensional (2D) and three-dimensional (3D) chemical imaging but are often sensitive to temperature changes. This study presents an advanced dual-emission optical sensor that simultaneously measures temperature and oxygen using a modified platinum(II) meso-tetrakis(3,5-ditert-butylphenyl)-tetra(2-tert-butyl-1,4-naphthoquinono)porphyrin. The ratio between thermally activated delayed fluorescence and phosphorescence was optimized by modifying platinum(II) naphthoquinonoporphyrin with tert-butyl groups which simultaneously improved solubility in apolar solvents and polymer matrix (polystyrene). This dual-function sensor enables two-parameter chemical imaging with a consumer-grade RGB camera or a hyperspectral camera. We demonstrated 2D visualization of temperature and oxygen distribution in a model soil system. The RGB camera provided rapid and cost-effective imaging, while the hyperspectral camera offered more detailed spectral information despite some limitations. Our findings revealed the formation of a stable temperature gradient and oxygen depletion, driven by water content and temperature-sensitive microbial activity. This dual O₂/T sensor, with further potential improvements, shows considerable promise for advanced multiparameter sensing in complex biological and environmental studies, providing deeper insights into dynamic microenvironments.