Electrochemical Sensors Developed for Gathering Microscale Chemical Information

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).

In-vivo electrochemical monitoring of H2O2 production induced by root-inoculated endophytic bacteria in Agave tequilana leaves

A dual-function platinum disc microelectrode sensor was used for in-situ monitoring of H₂O₂ produced in A. tequilana leaves after inoculation of their endophytic bacteria (Enterobacter cloacae). Voltammetric experiments were carried out from 0.0 to -1.0V, a potential range where H₂O₂ is electrochemically reduced. A needle was used to create a small cavity in the upper epidermis of A. tequilana leaves, where the fabricated electrochemical sensor was inserted by using a manual three-dimensional micropositioner. Control experiments were performed with untreated plants and the obtained electrochemical results clearly proved the formation of H₂O₂ in the leaves of plants 3h after the E. cloacae inoculation, according to a mechanism involving endogenous signaling pathways. In order to compare the sensitivity of the microelectrode sensor, the presence of H₂O₂ was detected in the root hairs by 3,3-diaminobenzidine (DAB) stain 72h after bacterial inoculation. In-situ pH measurements were also carried out with a gold disc microelectrode modified with a film of iridium oxide and lower pH values were found in A. tequilana leaves treated with bacteria, which may indicate the plant produces acidic substances by biosynthesis of secondary metabolites. This microsensor could be an advantageous tool for further studies on the understanding of the mechanism of H₂O₂ production during the plant-endophyte interaction.

Determination of microcystin-LR in waters in the subnanomolar range by sol-gel imprinted polymers on solid contact electrodes

The present work reports new sensors for the direct determination of Microcystin-LR (MC-LR) in environmental waters. Both selective membrane and solid contact were optimized to ensure suitable analytical features in potentiometric transduction. The sensing layer consisted of Imprinted Sol-Gel (ISG) materials capable of establishing surface interactions with MC-LR. Non-Imprinted Sol-Gel (NISG) membranes were used as negative control. The effects of an ionic lipophilic additive, time of sol-gel polymerization, time of extraction of MC-LR from the sensitive layer, and pH were also studied. The solid contact was made of carbon, aluminium, titanium, copper or nickel/chromium alloys (80 : 20 or 90 : 10). The best ISG sensor had a carbon solid contact and displayed average slopes of 211.3 mV per decade, with detection limits of 7.3 × 10(-10) M, corresponding to 0.75 μg L(-1). It showed linear responses in the range of 7.7 × 10(-10) to 1.9 × 10(-9) M of MC-LR (corresponding to 0.77-2.00 μg L(-1)), thus including the limiting value for MC-LR in waters (1.0 μg L(-1)). The potentiometric-selectivity coefficients were assessed by the matched potential method for ionic species regularly found in waters up to their limiting levels. Chloride (Cl(-)) showed limited interference while aluminium (Al(3+)), ammonium (NH(4)(+)), magnesium (Mg(2+)), manganese (Mn(2+)), sodium (Na(+)), and sulfate (SO(4)(2-)) were unable to cause the required potential change. Spiked solutions were tested with the proposed sensor. The relative errors and standard deviation obtained confirmed the accuracy and precision of the method. It also offered the advantages of low cost, portability, easy operation and suitability for adaptation to flow methods.