A Review of Nanocomposite-Modified Electrochemical Sensors for Water Quality Monitoring

Abstract

Electrochemical sensors play a significant role in detecting chemical ions, molecules, and pathogens in water and other applications. These sensors are sensitive, portable, fast, inexpensive, and suitable for online and in-situ measurements compared to other methods. They can provide the detection for any compound that can undergo certain transformations within a potential window. It enables applications in multiple ion detection, mainly since these sensors are primarily non-specific. In this paper, we provide a survey of electrochemical sensors for the detection of water contaminants, i.e., pesticides, nitrate, nitrite, phosphorus, water hardeners, disinfectant, and other emergent contaminants (phenol, estrogen, gallic acid etc.). We focus on the influence of surface modification of the working electrodes by carbon nanomaterials, metallic nanostructures, imprinted polymers and evaluate the corresponding sensing performance. Especially for pesticides, which are challenging and need special care, we highlight biosensors, such as enzymatic sensors, immunobiosensor, aptasensors, and biomimetic sensors. We discuss the sensors' overall performance, especially concerning real-sample performance and the capability for actual field application.

Keywords: electrochemical sensor; emergent contaminants; impedance spectroscopy; in-situ applications; inorganic compounds; pesticides; square wave voltammetry; water contaminants.

Figure 1

Primary sources of water contaminants in the environment.

Figure 2

Simultaneous detection of the mixture of methyl parathion (MP) and carbendazim (CBM). The concentration ranges are (3–25) × 10³ μM for MP and (10–70) × 10³ μM for CBM. The insert profiles show the calibration curves between the peak current density and the target pesticide concentration. Reprinted from [70].

Figure 3

Preparation of molecularly imprinted materials.

Figure 4

Comparison of the EIS responses for the GCE modified with different nanomaterials before and after aptamer immobilization and acetamiprid detection: (A) AuNPs/GCE, (B) MWCNT-rGONR/GCE, (C) Au/MWCNT-rGONR/GCE; (D) EIS responses of bare GCE (a), Au/MWCNT-rGONR/GCE (b), aptamer/Au/MWCNT-rGONR/GCE (c), MCH/aptamer/Au/MWCNT-rGONR/GCE (d) in 0.1 M PBS (pH 7.0) containing 5 mM [Fe(CN)₆]^3−/4− and 0.1 M KNO₃, and EIS responses of MCH/aptamer/Au/MWCNT-rGONR/GCE (e) after 100 nM acetamiprid captured on the modified electrode in 0.1 M PBS (pH 7.0) containing 5 mM [Fe(CN)₆]^3−/4− and 0.1 M KNO₃. Reprinted from [145].

Figure 5

Spider diagram for the overall performance of different electrochemical biosensors for pesticide detection (1—bad, 5—very good). Remark: We do not consider sensors based on living cells.

Figure 6

Redrawing of (a) self-assembled graphene and copper nanoparticles composite sensor structure following reference [190], (b) fabrication process of CG/PPy/CS/GCE for sensitive detection of NO₂⁻ following reference [201]. (c) the construction process of graphene oxide (GO)-chitosan (CS)-Au nanoparticles (AuNPs)/glassy carbon electrode (GCE) [177] and (d) Growth process of PEDOT/PEDOT-SH/Au on electrode surface [210].

Figure 7

Redrawing of (a) Pencil graphite sensor coated with Molybdenum blue functionalized poly(vinyl chloride) following [212], (b) Nozzle-Jet-Printed Silver/Graphene Composite/Field-Effect Transistor Sensor following [212] and (c) ISFET structure with the phosphate selective membrane following [219].

Figure 8

Redrawing of (a) GCE-GR reduced-Fe₂O₃/Chitosan following reference [255], and (b) Chemical sequence of electro polymerization of AgNPs/ZnONPs onto Au electrode and chemical reaction of immobilization of enzyme onto modified electrode following reference [286].