Tuneable, Pre-stored Paper-Based Electrochemical Cells (μPECs): an Adsorptive Stripping Voltammetric Approach to Metal Analysis

Abstract

The development of point-of-care (POC) devices for the detection of environmental contaminants and the early monitoring of disease outbreaks in the health and food sectors has steadily grown in recent times. The real-time analysis offered by POC devices is pivotal in developing areas where access to skilled labor is often lacking. Chelating agent–based signal amplification methods have previously been employed in conjunction with electroplated metallic films to improve electrode sensitivity in trace metal analysis. Here, we describe a method for the dry storage of electrochemical reagents: ammonia/ammonium chloride (NH3/NH4Cl) buffer as a supporting electrolyte, dimethylglyoxime (DMG) as a chelating agent, and mercury in paper-based electrochemical cells (PECs), fabricated from commercial filter paper. The stored PECs were applied to the trace, microliter analysis of nickel in water samples by adsorptive cathodic stripping voltammetry (AdCSV) in conjunction with screen-printed electrodes. The method relies on the single-step accumulation/adsorption of microvolumes of the metallic analyte onto stored DMG ligands to form [Ni(dmgH)2] complexes in the presence of mercury films. By integrating the AdCSV techniques with paper-based analytical devices, detection of Ni2+ in water samples with good resolution was achieved at 20 μL sample volumes in the low parts per billion range. The mechanism for pre-concentration and its subsequent reduction was demonstrated as it differs from bulk electroanalysis. Instrumental parameters of the PECs, accumulation time, and deposition potential were optimized along with reagent storage introduction and concentrations. Further, the PECs were investigated in the absence and presence of mercury and had shown good possibility for metal-free sensors in future work. The prepared PECs showed good reproducibility (4.36%, n = 4) and no intermetallic interferences in the presence of 100 μg L−1 Zn2+, Cd2+, Pb2+, Co2+, and In2+. Detection and quantitation limits were calculated and recorded as 6.27 μg L−1 and 18.8 μg L−1, respectively, for Ni2+ determination and 13.1 μg L−1 and 39.3 μg L−1 for the Hg-free derivative at the 90-s accumulation time. The pre-stored paper-based electrochemical cells were then applied to the detection of Ni2+ in real tap water samples and showed good recovery values of ± 94%. Further, the infusion of PECs with a range of chelating agents (dimethylglyoxime, nioxime, and morin hydrate) demonstrates the possibility for tuning PECs to specific applications and improving selectivity in metal analysis applications.