Self-assembled gold decorated polydopamine nanospheres as electrochemical sensor for simultaneous determination of ascorbic acid, dopamine, uric acid and tryptophan.

Herein, a new sensor based on screen-printed carbon electrodes covalently modified with self-assembled gold-decorated-polydopamine nanospheres (Au-PDNs) is reported. The sensor was applied to the simultaneous determination of the biologically significant molecules ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (TR). The Au-PDNs were anchored to gold nanoparticles electrodeposited onto the bare electrodes via cysteamine-glutaraldehyde bridges, and were characterized by scanning and transmission electron microscopies. The stepwise fabrication of the electrodes and their electrochemical responses were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry. The response of the new device to these analytes is pH-dependent, which allows selecting the best working conditions as a function of the sample characteristics. At pH values of 3.0 and 8.0, it was possible to determine simultaneously AA, UA and TR in presence of DA, and DA, UA and TR in presence of AA respectively, with very wide linear ranges and high sensitivities. The simultaneous determination of AA, DA, UA and TR was possible at pH 6.0 with competitive sensitivities in two consecutive linear ranges, between 10-80 μM and 80-240 μM; 1-160 μM and 160-350 μM; 10-120 μM and 120-350 μM; and 1-160 μM and 160-280 μM, respectively. The obtained limits of detection were 0.2 nM, 0.1 nM, 0.1 nM and 0.1 nM, respectively.