Simultaneous in Vitro Detection of DA, UA, and AA with an rGO/AuNPs-Modified Carbon Fiber Ultramicroelectrode for ex Vivo Dopamine Monitoring

Biomolecules such as dopamine (DA), uric acid (UA), and ascorbic acid (AA) play essential roles in maintaining physiological homeostasis. Dysregulation of their concentrations can disrupt neurotransmission and metabolic balance, potentially leading to neuropsychiatric disorders, gout, and oxidative stress. An electrochemical sensor was developed for simultaneous detection of DA, UA, and AA using a reduced graphene oxide/gold nanoparticle-modified carbon fiber ultramicroelectrode (rGO/AuNPs-CFUME). The nanocomposite was comprehensively characterized by scanning electron microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), and X-ray diffraction (XRD), confirming successful integration of AuNPs with rGO. The modified electrode exhibited enhanced electrocatalytic activity toward these analytes, enabling their simultaneous determination with well-resolved oxidative peaks. In phosphate buffered saline (PBS, 0.01 M, pH 7.0), the sensor exhibited linear responses for DA (linear ranges: 0.2−10.0 μM and 10.0−50.0 μM, sensitivity: 7.88 μA and 2.08 μA μM−1 cm−2, limit of detection (LOD): 24.0 nM), UA (linear ranges: 2.0−10.0 μM and 100.0−200.0 μM, sensitivities: 2.15 and 0.81 μA μM−1 cm−2, LOD: 0.38 μM), and AA (linear ranges: 50.0−1200.0 μM, sensitivity: 0.61 μA μM−1 cm−2, LOD: 8.9 μM), with all detection limits determined at S/N = 3. The composite electrode exhibited long-term stability, good reproducibility, and excellent anti-interference capability. The developed sensor successfully demonstrated quantitative DA detection in ex vivo rat brain tissue slices, offering a robust platform for future neurochemical monitoring applications.