Bimetallic Mn–Fe Bentonite Electrodes for Enhanced Electrochemical Detection of Uric Acid

A novel Mn/Fe co-doped bentonite composite (Fe–Mn–Bent) modified carbon paste electrode exploits synergistic Mn 2+ /Mn 4+ and Fe 2+ /Fe 3+ redox cycling to enhance electron transfer, increase active sites, and significantly improve electrocatalytic two-electron uric acid oxidation. The optimal composition was 30 wt% Fe-Mn-Bent obtained after calcination at 300 °C. XRD confirmed spinel-type Fe-Mn oxides with reflections at 34.92°, 40.4°, and 61.7°, while FTIR bands at 693–448 cm −1 corresponded to Fe-O and Mn-O vibrations. SEM–EDS showed a rough nanoparticle-decorated surface, and XPS indicated Fe 3+ at 714.12 and 727.7 eV and Mn 4+ at 643.78 eV, attributed to surface oxidation or MnO 2 -like domains. Linear Sweep Voltammetry (LSV) provided the best performance at pH 6, –1.0 V, 200 s, and 100 mV s −1 , yielding a peak current of 88 μA, electrochemically active surface area of 0.122 cm 2 , and the lowest charge-transfer resistance (R ct = 792 Ω) for the 30 wt% Fe-Mn-Bent. The modified electrode exhibited a linear range of 0.5–1000 μM, LOD = 0.11 ± 0.006 μM, and LOQ = 0.37 ± 0.02 μM, with repeatability of 1.01% RSD, reproducibility of 1.21% RSD, and 91.7% stability after one week. Recovery in human serum was 84.4%–95.1%, confirming applicability for point-of-care clinical diagnostics.