High Performance Zinc Oxide Nanorod-Doped Ion Imprinted Polypyrrole for the Selective Electrosensing of Mercury II Ions

Abstract

A biomimetic, ion-imprinted polymer (IIP) was prepared by electropolymerization of pyrrole at the surface of gold electrodes decorated with vertically grown ZnO nanorods. The vertical growth of the nanorods was achieved via an ultrathin aryl monolayer grafted by reduction of diazonium salt precursor. Pyrrole was polymerized in the presence of L-cysteine as chelating agent and Hg2+ (template). Hg2+-imprinted polypyrrole (PPy) was also prepared on a bare gold electrode in order to compare the two methods of sensor design (Au-ZnO-IIP vs. Au-IIP). Non-imprinted PPy was prepared in the same conditions but in the absence of any Hg2+ template. The strategy combining diazonium salt modification and ZnO nanorod decoration of gold electrodes permitted us to increase considerably the specific surface area and thus improve the sensor performance. The limit of detection (LOD) of the designed sensor was ~1 pM, the lowest value ever reported in the literature for gold electrode sensors. The dissociation constants between PPy and Hg2+ were estimated at [Kd1 = (7.89 ± 3.63) mM and Kd2 = (38.10 ± 9.22) pM]. The sensitivity of the designed sensor was found to be 0.692 ± 0.034 μA.pM-1. The Au-ZnO-IIP was found to be highly selective towards Hg2+ compared to cadmium, lead and copper ions. This sensor design strategy could open up new horizons in monitoring toxic heavy metal ions in water and therefore contribute to enhancing environmental quality.

Towards Clean and Safe Water: A Review on the Emerging Role of Imprinted Polymer-Based Electrochemical Sensors

“…Some used, in this regard, L-cystein and acrylic acid which served both as co-dopants and ligands [127]. The resulting ion imprinted polymer permitted to achieve picomolar LOD for a lead as reported by Ait-Touchente et al [14]. This is the lowest LOD ever reported for Hg(II) detection.…”

“…The rationale for making MIPs by electropolymerization lies in the fact that the technique permits to synthesize the thin film, to characterize its redox properties and to use the same electrode and the same apparatus for electrosensing measurements. Electropolymerization is also suitable for nanostructuration of MIP films [14,58]. This is particularly important for directly coating electrodes at the polymer synthesis stage.…”

“…Moreover, advances on transducers, for example carbon based nanostructured materials, enable achieving outstanding performances of MIPs [12]. From our perspective, with past and present active research on polymer thin film preparation, surface interactions and applications in sensor science, we wished to address the crucial point of three kinds of toxic pollutants: organics represented by pesticides (for example, the glyphosate case [13]), metal ions owing to their growing occurrence in water and soils [14], and finally bacteria due to the sanitary issues they raise [15] as well as the increasing demand for food security [16] on the one hand, and the ever-lasting problem of nosocomial diseases, on the other hand [17]. The three types of pollutants differ in composition and size, and require completely different imprinting techniques as will be discussed at length in Section 5.…”

Electropolymerised Polypyrroles as Active Layers for Molecularly Imprinted Sensors: Fabrication and Applications

“…An interesting application of molecularly imprinted polymers is for the detection of heavy metal ions, such as mercury (II) cations [38]. Sensors were fabricated on Au transducers, decorated with ZnO nanorods, using both imprinted and non-imprinted polypyrrole, with L-cysteine being present in the polymerisation solution and being incorporated into the PPy, in order to act as a mercury chelating agent.…”

Role of Functional Monomers upon the Properties of Bisphenol A Molecularly Imprinted Silica Films

“…Furthermore, the resulted MIPs are robust, exhibiting reusability, long-term stability and low production cost [14,15]. Using this MI technique and the various polymerization procedures, MIPs in different shapes and sizes were developed, e.g., pearls [16], particles [17,18], membranes [19][20][21], thin films [22,23], nanospheres/nanofibers [24,25], or electrochemical sensing receptors [13,17,26]. Nevertheless, depending on the polymerization procedure (for instance bulk polymerization [27]), MIPs can still present some inherent drawbacks, such as heterogeneous distribution of binding sites, low binding capacity, and poor site accessibility, which is why a great deal of attention should be focused on finding the proper procedure for delivering performant MIPs adequate for the targeted application.…”