Extended coverage of screen-printed graphite electrodes by spark discharge produced gold nanoparticles with a 3D positioning device. Assessment of sparking voltage-time characteristics to develop sensors with advanced electrocatalytic properties

Highlights: • Highly reactive "naked" spark discharge produced gold nanoparticles. • Extended coverage of SPEs by sparked AuNPs (sAu-SPE) with a 3D positioning device. • At sAu-SPE the response of the graphitic underlying substrate is suppressed. • Assessment of sparking voltage-time characteristics to develop advanced sensors. • Simultaneous DPV sensing of ascorbic and uric acids in human urine. -- Abstract: Graphite screen-printed electrodes (SPEs) were modified with gold nanoparticles (AuNPs) produced by electric spark discharge between the SPE and a gold-silicon eutectic alloy (eAu/Si) tip electrode, under atmospheric conditions at 1.2 kV DC using a fully automated procedure. The automation was based on a 3D positioning device, which allowed to precisely adjust the sparking distance and to achieve regular spacing of a predetermined number of sparks across the surface of SPEs (d = 3 mm) by controlling the movement of the eAu/Si tip. Moreover, the effect of voltage-time characteristics of the produced discharges on the morphological and electroanalytical properties of the sparked-modified SPEs was investigated by setting the values of capacitors in the high voltage multiplier cascade, and at the power supply output. It is shown that under specific variables the underlying carbon layer is not appreciably damaged by the spark discharges and does not contribute to electrochemical responses of sparked SPEs, i.e., the active electrode surface has been entirely covered by AuNPs. Sparked surfaces were extensively characterized by scanning electron microscopy and various electrochemical techniques, while the electroanalytical utility of eAu/Si-sparked SPE was investigated with ascorbic acid as a pilot analyte. Advanced electrocatalytic activity is documented by an extreme shift of ascorbate oxidation overpotential (E_p = 89 mV at eAu/Si-sparked SPE) with respect to both bare SPE (E_p = 503 mV) and bulk gold electrode (E_p = 358 mV). Simultaneous differential pulse voltammetric sensing of ascorbic and uric acids in human urine is also demonstrated.