Microenvironment-mediated oxidative enhancement of conjugated polyelectrolytes for the detection of hydrogen peroxide

The sensitive detection of hydrogen peroxide is important for many applications, including biomedical diagnostics and environmental monitoring. In this work, we report a simple turn-on fluorescent platform based on conjugated polyelectrolytes (CPEs), specifically poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene] (MPS-PPV), complexed with polyvinylpyrrolidone (PVP) for the detection of hydrogen peroxide (H₂O₂). MPS-PPV alone exhibits weak fluorescence enhancement in response to the incremental addition of H₂O₂. However, when PVP is added, a sixfold increase in fluorescence is observed. Mechanistically, this enhancement is attributed to the dual role of PVP: (1) its complexation with hydrogen peroxide increases the local oxidant concentration, promoting oxidative attack on the CPE backbone, and (2) it stabilizes the resulting oxidized polymers, thus reducing aggregation and enhancing their emission. Changes in the ionic strength further confirm that the CPE conformation and its complexation with PVP are key to the observed fluorescence enhancement. Time-resolved fluorescence measurements in the presence of ascorbic acid, a radical scavenger, demonstrate that hydroxyl radicals are the active species responsible for the sensing response. Finally, as a proof of concept, the sensor was successfully applied to the enzymatic detection of glucose, enabling quantitative detection over a physiologically relevant range (3.5-10.5 mM). This work demonstrates how microenvironmental control of conjugated polyelectrolytes can play a critical role in developing CPE-based fluorescent sensors and enhancing their sensitivity.