Azalea Petal-Derived Porous Carbon–Thionine Based Ratiometric Electrochemical Sensor for the Simultaneous Determination of Ascorbic Acid and Uric Acid

The design of the electrode materials for electrochemical sensors is crucial for the simultaneous fast detection of ascorbic acid (AA) and uric acid (UA). A hierarchical porous carbon material (KACM) was prepared via high-temperature calcination and KOH activation using azalea (a species of rhododendron) biomass as the carbon source. KACM and thionine (Thi) were simultaneously assembled on a glassy carbon electrode (GCE) to construct a porous carbon/thionine ratiometric electrochemical biosensor for the detection of ascorbic acid and uric acid. Electrochemical evaluation showed that the Thi/KACM/GCE has good electrochemical performance, strong catalytic activity toward AA and UA oxidation, and good separation of the two oxidation peaks. Under the optimized conditions, Thi/KACM/GCE has a wide linear range (0.05–9 mM) and low detection limit (6.4 μM for AA and 10 μM for UA). Additionally, the biosensor exhibited good selectivity, stability, and reproducibility. Thi/KACM/GCE was used for the simultaneous detection of AA and UA in human urine with 99.4–101.0% recovery of the compounds. This study reports for the first time the use of azaleas in electrochemical biosensors, and the results show that small changes in the structural properties of biomass materials can affect their electrochemical properties.