Conjugated Polyelectrolytes-based Fluorescent Thermal Sensors for Versatile Applications

Abstract

Temperature monitoring is crucial in various scientific and industrial fields, where precise detection can drive advancements in research and technology. With continuous progress in material science, thermal sensors are becoming increasingly versatile. In this work, we present three novel fluorescent thermal sensing systems based on conjugated polyelectrolytes (CPEs), designed for accurate and reversible temperature detection. The first system involves the complexation of polygalacturonic acid (PGA) with poly(phenylene ethynylene) (PPE-CO2-108), studied in both solution and thin-film forms. The thermal sensitivity and reversibility of this sensor were optimized by adjusting PGA concentrations and the ionic strength of the solution. Furthermore, the temperature of dried PGA films was successfully monitored using a smartphone application developed in-house, showcasing potential applications such as early infection detection through PGA-based sutures. In another approach, a sensor was developed based on PPE-CO2-108 assembled into polyvinylpyrrolidone-co-polystyrene (PVP-co-PS) nanoparticles, with thermochromic response, characterized by a shift in maximum intensity with change in temperature. The sensor showed good reversibility and cyclability upon exposure to heating and cooling cycles. In addition to the observed spectral shift, the nanothermometer also exhibited a lifetime-based thermal response over a wide temperature range. To further explore CPEs in thermal sensing, a system was designed, utilizing interactions between two conjugated polymers—poly(2,5-bis(3-sulfonatopropoxy)-1,4-phenylene, disodium salt-alt-1,4-phenylene) (OPS) and poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene] (MPS-PPV) in a matrix of PVP-co-PS. A ratiometric thermal response, characterized by the emission ratio of these polyelectrolytes, was obtained, with good thermal sensitivity for accurate temperature monitoring.