Isatin analysis using flow injection analysis with amperometric detection - comparison of tetrahedral amorphous carbon and diamond electrode performance
Isatin is an endogenous indole compound in humans and rodents that has a wide range of biological activity. In rat models, isatin concentrations have been shown to increase in the heart, brain, blood plasma, and urine with stress. Studies on patients suffering from Parkinson's disease have indicated a correlation between progress of the disease and urinary output of the molecule. Isatin is electrochemically active and can therefore be detected with electrochemical techniques. In this work, we compared the performance of a nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) and a boron-doped nanocrystalline diamond thin-film electrode for the oxidative detection of this biomolecule using flow injection analysis with amperometric detection. The measurements were performed in 0.1 phosphate buffer pH 7.2. The ta-C:N electrode, like boron-doped nanocrystalline diamond, exhibits some excellent properties for electroanalytical measurements including (i) low background current and noise, (ii) microstructural stability at positive detection potentials, and (iii) good activity for a wide range of bioanalytes without conventional surface pretreatment. The results reveal that both electrodes exhibit a linear dynamic range from 100 to 0.1 mmol L−1, a short-term response variability 3-4 % RSD (30 injections), a sensitivity of 18 mA M-1, and a limit of detection (S/N=3) of 1.0×10−7 mol L−1 (14 ng mL−1 or 2.5 fmol).