Dual-mode ratiometric electrochemical and turn-on fluorescent probe for reliably detecting H2O2 in Parkinson's disease serum

• A dual-mode probe Re-B for detection of H 2 O 2 were designed and synthesized. • The ratiometric electrochemical strategy based on a single probe molecule possessed a self-calibration function. • The Re-B probe exhibits a ``turn-on'' response to H 2 O 2 and maintains low background fluorescence. • The dual-mode signals are cross-validated, minimizing the risk of false positives and negatives. Accurate diagnosis and effective treatment of Parkinson's disease (PD) rely on the accurate detection of the corresponding biomarkers. The build-up of reactive oxygen species (ROS), for instance, hydrogen peroxide (H 2 O 2 ), resulting in oxidative stress inside cells is closely related to the pathogenesis of PD. In this study, two compounds, Re-B and Re-OB, were synthesized through a simple one-step reaction. Upon reacting with H 2 O 2 , the borate ester group in Re-B is selectively cleaved, restoring the phenol group. This leads to both a dual-signal ratiometric electrochemical response and a ``turn-on'' fluorescence effect. The Re-B probe demonstrates a clear ``turn-on'' electrochemical current response at −311.1 mV, followed by a ``turn-off'' response at −257.6 mV when interacting with H 2 O 2 on a single-walled carbon nanotube-modified screen-printed carbon electrode (SPCE/SWCNTs). Concurrently, the fluorescence spectrum shows a ``turn-on'' response with an emission peak at 586 nm. The fluorescence and ratiometric electrochemical methods developed in this study show exceptionally high sensitivity and selectivity for H 2 O 2 , with detection limits as low as 0.5 μM for the electrochemical method and 0.1 μM for fluorescence. The consistency between the results from both electrochemical and fluorescence quantification of H 2 O 2 levels in serum underscores its reliability. This approach has significant potential as a point-of-care diagnostic device for PD early detection, providing valuable information for timely diagnosis and treatment.