Electrochemical detection of dopamine at the poly-alanine/sulfosalicylic acid modified glassy carbon electrode

A novel and simple sensor was constructed based on the glassy carbon electrode (GCE) modified with poly-alanine/sulfosalicylic acid layer-by-layer composite film by electrochemical deposition method, and the electrochemical behavior of dopamine (DA) on the electrode was studied in detail by using cyclic voltammetry and differential pulse voltammetry. Under the optimal conditions, the poly-alanine/sulfosalicylic acid/GCE exhibited a higher catalytic activity for dopamine compared with poly-sulfosalicylic acid/GCE, poly-alanine/GCE and bare GCE, which was attributed to its good synergistic effect between alanine and sulfosalicylic acid and the electrostatic attraction between sulfonate groups and dopamine cations. The detection limit of the composite film modified electrode for dopamine was 0.12 μmol/L with a linear range from 0.7 to 300 μmol/L. At the same time, the diffusion coefficient was estimated to be 6.16×10-6 cm2/s and the number of the electrons transferred during the heterogeneous reaction was calculated as 1.9, indicating that the redox reaction of dopamine on modified electrode involved two protons and two electrons. Moreover, the sensor was not interfered by ascorbic acid (AA) and uric acid (UA), and the peak potentials of AA, DA, UA were 0.109V, 0.281V and 0.427V, respectively, which was vital to improve the selectivity of the sensor for DA detection. The prepared electrochemical sensor was successfully used to detect dopamine in pharmaceutical dopamine hydrochloride injection with satisfactory results.