Low-cost screen-printed sensors on-demand: Instantly prepared sparked gold nanoparticles from eutectic Au/Si alloy for the determination of arsenic at the sub-ppb level

We report on the straightforward preparation of gold nanoparticles (AuNPs) through a direct metal-to-substrate electric discharge at ambient conditions at 1.2 kV between the source metal (gold) and low-cost graphite screen-printed electrodes (SPEs). Considering that sparked nanoparticles are generated on the basis of an evaporation-condensation process, comparative experiments by using Au and a eutectic Au/Si (97/3 wt%) alloy were conducted. The so-modified sparked AuNP-SPE and eAuNP-SPE, respectively, were characterized by scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Data revealed a 2.4-fold electro active surface of AuNPs in the case of eAuNP-SPE. Compared with the unmodified SPEs, sparked electrodes exhibited two distinct electrode-electrolyte interfaces, characterized by different time-constants. EIS data were successfully modeled to an equivalent electric circuit that considers sparked-induced morphological features of the sensing surface and concomitant alterations of the diffusion process. Both types of sparked electrodes endowed sensitivity to otherwise inactive plain SPEs to the anodic stripping voltammetric detection of arsenic. Compared with AuNP-SPE, eAuNP-SPE exhibited ca. 5-fold sensitivity and offered fast (30 s preconcentration time) measurements, linear response over the concentration range from 0.5 to 12 ppb and a limit of detection (3 sigma/m criterion) of 0.22 ppb. Moreover, eAuNP-SPEs were successfully applied to the determination of arsenic in drinking water. Results demonstrated a new type of AuNP-modified low cost electrodes lend themselves to extremely simple preparation while offering enhanced detection capabilities and a wide-scope of applicability.