Development of SPEEK-Coated IrOx Sensor for High-Biomass Aquatic pH Monitoring.

Instability is a key challenge for current pH sensors in practical applications, especially in aquatic environments with high biomass and redox substances. Herein, we present a novel approach that uses a highly stable IrOx sensing layer enveloped in a composite film of SPEEK doped with a silicon-stabilized ionic liquid (SP-IrOx). This design mitigates drift due to sensitive layer variations and minimizes interference from complex external conditions. After exhibiting robustness under moderately reducing conditions caused by S2-, I-, and ascorbic acid, the SP-IrOx sensor's efficacy was validated through real-time pH measurements in demanding aquatic settings. These included laboratory algal culture medium, sediment substrates, and mussel aquaculture areas. The sensor sustained accuracy and stability over extended periods of 6-8 days when compared to calibrated commercial electrodes. The deviations from reference samples were minimal, with a variance of no more than 0.03 pH units in mussel aquaculture areas (n = 17) and 0.07 pH units in an algal culture medium (n = 37). As a potentiometric, this solid-state electrode features a compact structure and low energy consumption, making it an economical and low-maintenance solution for precise pH monitoring in diverse challenging environments with high biomass and turbidity.

High anti-interference ability induced by the SP/SiOx/ImIL composite film on IrOx pH electrodes.

High concentrations of redox substances in the solution may cause severe electrode potential drift, resulting in the inaccuracy of in situ measurements. Sulfide anion, a highly reductive substance, is the killer of all metal oxide electrodes because of its small size and strong surface activity. We first proposed to use SPEEK (SP) with silica-stabilized imidazole-type ionic liquid (ImIL) to fabricate a composite film (SP/SiOx/ImIL) to achieve a high anti-interference ability for metal electrodes. The composite film was especially designed to address the interference caused by sulfide anions and other small-sized anions (i.e., I-, F- and ascorbic acid). The reduced proton conductivity was restored by introducing ImIL into SPEEK matrix. Open circuit potential tests showed that the potential of the SP/SiOx/ImIL modified IrOx electrode fluctuated within 0.3 mV in 30 min continuous test at a concentration of 10-3 M Na2S, exhibiting good stability in moderately high sulfide solution. It also exhibited fast response and good reversibility. In addition, no potential drift was measured under other anions interferences. XPS survey verified that the Ir4+/Ir3+ ratio of the IrOx electrode did not change before and after application in sulfide-containing solution, indicating that the SP/SiOx/ImIL composite film has good anion isolation capacity.

A Long-Term Stable Sensor Based on Fe@PCN-224 for Rapid and Quantitative Detection of H2O2 in Fishery Products.

Hydrogen peroxide (H2O2) has been reported to be used for the illegal treatment of fishery products in order to obtain "fake" freshness. Residues of H2O2 in food may be of toxicology concern. In this study, a nonenzymatic sensor was developed based on Fe@PCN-224 metal-organic frameworks wrapped by Nafion to detect H2O2 concentration. The hybrid structure of Fe@PCN-224 was fabricated by incorporated free FeIII ions into the center of PCN-224, which was ultra-stable due to the strong interactions between Zr6 and the carboxyl group. Scanning electron spectroscopy images exhibited that Nafion sheets crossed together on the surface of Fe@PCN-224 nanoparticles to form a hierarchical and coherent structure for efficient electron transfer. Electrochemical investigations showed that the Fe@PCN-224/Nafion/GCE possessed good linearity from 2 to 13,000 µM (including four orders of magnitude), low detection limits (0.7 µM), high stability in continuous monitoring (current remained nearly stable over 2300 s) and in long-term measurement (current decreased 3.4% for 30 days). The prepared nanohybrid modified electrode was effectively applied to H2O2 detection in three different fishery products. The results were comparable to those measured using photometrical methods. The developed electrochemical method has a great potential in detecting the illegal management of fishery products with H2O2.