Mesoporous Silica Thin Films for Improved Electrochemical Detection of Paraquat

Abstract

An electrochemical method was developed for rapid and sensitive detection of the herbicide paraquat in aqueous samples using mesoporous silica thin film modified glassy carbon electrodes (GCE). Vertically aligned mesoporous silica thin films were deposited onto GCE by electrochemically assisted self-assembly (EASA). Cyclic voltammetry revealed effective response to the cationic analyte (while rejecting anions) thanks to the charge selectivity exhibited by the negatively charged mesoporous channels. Square wave voltametry (SWV) was then used to detect paraquat via its one electron reduction process. Influence of various experimental parameters (i.e., pH, electrolyte concentration, and nature of electrolyte anions) on sensitivity was investigated and discussed with respect to the mesopore characteristics and accumulation efficiency, pointing out the key role of charge distribution in such confined spaces on these processes. Calibration plots for paraquat concentration ranging from 10 nM to 10 μM were constructed at mesoporous silica modified GCE which were linear with increasing paraquat concentration, showing dramatically enhanced sensitivity (almost 30 times) as compared to nonmodified electrodes. Finally, real samples from Meuse River (France) spiked with paraquat, without any pretreatment (except filtration), were analyzed by SWV, revealing the possible detection of paraquat at very low concentration (10-50 nM). Limit of detection (LOD) calculated from real sample analysis was found to be 12 nM, which is well below the permissible limits of paraquat in drinking water (40-400 nM) in various countries.

Critical Effect of Film Thickness on Preconcentration Electroanalysis with Oriented Mesoporous Silica Modified Electrodes

“…Surfactant-containing films have been used as permselective sensors for lipophilic analytes (e. g., pharmaceutical drugs [17] or trace nitroaromatic explosives and pesticides [18]) based on their extraction in the surfactant phase and subsequent detection onto the electrode surface while rejecting ionic interferences [19]. Applications of surfactant-extracted films include preconcentration electroanalysis of redox cations (via electrostatic binding to the negatively charged silica surface) [20,21], permselective coatings (based on charge selectivity [22], hydrophobic/ hydrophilic balance [23] or gated molecular transport [24]), or molecular sieving membranes [25] which are also likely to be exploited as antifouling surfaces [26]. Oriented mesoporous silica films bearing organo-functional groups can be also prepared [27].…”

“…Finally, free-standing mesoporous silica membranes can be used for molecular filtration [34]. In a previous work [21], we have shown that perpendicularly oriented mesoporous silica thin films electrogenerated by EASA on glassy carbon electrode can be successfully applied to the preconcentration electroanalysis of paraquat, a cationic 4,4'-bipyridinium-based pesticide likely to bind quickly to the negatively charged silica surface. Here we discuss the critical effect of film thickness of the sensor's sensitivity, on the basis of deposits obtained after distinct synthesis durations.…”

“…The optimum sensitivity (2.1 A cm À2 M À1 ) was obtained for the film deposited for 16 s (corresponding to ca. From the sensor point of view, since the recognition/preconcentration is based just on the binding of cationic species to the negatively charged silica surface, the selectivity of this approach in view of practical applicability in samples where other cations may coexist can be questionable but we have shown in a previous work that analysis of real water samples (i.e., river water) by the standard addition method is indeed possible [21]. In this case, a preconcentration factor of almost 30 can be achieved with respect to bare ITO.…”

“…Good adhesion to the support is ensured for films generated as such onto electrode surfaces bearing surface hydroxyl groups, whereas using "molecular glue" is mandatory for other electrode substrates (such as electrografting of 3-aminopropyltriethoxysilane on glassy carbon [16]) prior to film deposition. Applications of surfactant-extracted films include preconcentration electroanalysis of redox cations (via electrostatic binding to the negatively charged silica surface) [20,21], permselective coatings (based on charge selectivity [22], hydrophobic/ hydrophilic balance [23] or gated molecular transport [24]), or molecular sieving membranes [25] which are also likely to be exploited as antifouling surfaces [26]. Surfactant-containing films have been used as permselective sensors for lipophilic analytes (e. g., pharmaceutical drugs [17] or trace nitroaromatic explosives and pesticides [18]) based on their extraction in the surfactant phase and subsequent detection onto the electrode surface while rejecting ionic interferences [19].…”

Platinized Silica Nanoporous Membrane Electrodes for Low‐Fouling Hydrogen Peroxide Detection

“…For example, nanoporous gold electrodes have been employed for the detection of DNAs in diluted biofluids . SNM modified electrodes have also illustrated excellent antifouling ability and allowed the direct detection of a variety of targets in complex samples and rat brain with high sensitivities . Our previous study shows that the SNM modified carbon fiber microelectrode (SNM/CFME) can work stably in rat brain up to 2 h .…”