Current perspectives, challenges, and future directions in the electrochemical detection of microplastics

Abstract

Microplastics (5 μm) are a developing threat that contaminate every environmental compartment. The detection of these contaminants is undoubtedly an important topic of study because of their high potential to cause harm to ecosystems. For many years, scientists have been assiduously striving to surmount the obstacle of detection restrictions and minimize the likelihood of receiving results that are either false positives or false negatives. This study covers the current state of electrochemical sensing technology as well as its application as a low-cost analytical platform for the detection and characterization of novel contaminants. Examples of detection mechanisms, electrode modification procedures, device configuration, and performance are given to show how successful these approaches are for monitoring microplastics in the environment. Additionally included are the recent developments in nanoimpact techniques. Compared to electrochemical methods for microplastic remediation, the use of electrochemical sensors for microplastic detection has received very little attention. With an overview of microplastic electrochemical sensors, this review emphasizes the promise of existing electrochemical remediation platforms toward sensor design and development. In order to enhance the monitoring of these substances, a critical assessment of the requirements for future research, challenges associated with detection, and opportunities is provided. In addition to-or instead of-the now-in-use laboratory-based analytical equipment, these technologies can be utilized to support extensive research and manage issues pertaining to microplastics in the environment and other matrices.

Fig. 1. MPs pathways.

Fig. 2. MPs and their effect on human health.

Fig. 3. Classification of visual inspection methods.

Fig. 4. Classification of thermal analysis methods.

Fig. 5. Sources of MPs and illustration of sensor design for their electrochemical detection.

Fig. 6. Diagram showing how MPs are measured for impedance while going through a flow cell. Variation in impedance according to the type of particle: plastic, seeds, or organisms.

Fig. 7. SEM images for the carbon fiber electrode with and without MPs (a). An enhanced view of a transient current–time signal resulting from a collision event between MPs and electrode can be seen in the inset of the chronoamperogram (b), in which the blue line represents the PE MPs and the black line represents the MP-free state. Histogram showing the distribution of integrated charges extracted from spikes resulting from chronoamperometric measurements (c).

Fig. 8. (a) Schematic of the microfluidic configuration used for serial faradaic ion concentration polarization experiments. For frames (b–e), only BPE1 was active. For frames (f) and (g), both BPE1 and BPE2 were active. (b–g) Series of optical and fluorescence micrographs showing the location of mP1 and BODIPY2_ during serial faradaic ion concentration polarization. With reference to the three dotted lines at the bottom of (a), the micrographs were captured along the portion of the channel length indicated by (b and c) the dotted black line; (d) the dotted green line; and (e–g) the dotted red line. The curved black arrow in (b) indicates the location and rotation direction (counterclockwise) of the vortex downstream of the cathodic pole of BPE1.

Fig. 9. (a) Design of the device, (b) image of the assembled device, (c) an optical microscope image of the sensing zones circled in part (a), (d) silver wire embedded within a pipette tip, and (e) schematic of the sensing zone when using an acetate film, a flat lid, and a ridge lid.

Fig. 10. Schematic of exoelectrogenic biofilm on an electrode surface and its interactions with MPs.

Fig. 11. Schematic of the EPD process.

Fig. 12. (a) Illustration of SURMOF film formation via an LBL assembly. (b) Schematic of the LBL assembly of Au NPs/graphene electrode. Reproduced with permission from ref. .

Fig. 13. Top image shows a schematic of the common printing techniques: (A) direct ink writing (DIW), (B) fused deposition modeling (FDM), (C) stereolithography (SLA), and (D) binder jetting.

Fig. 14. (a) Schematic of Ag/rGO hybrid ink formulation, (b) nozzle-jet-printed Ag/rGO-based FET sensor, and (c) optical image of printed Ag/rGO-based FET sensors on a PET substrate.

Fig. 15. Example of roll-to-roll gravure-printed electrodes on flexible PET substrates (a) with optical images showing an array of 3 mm-diameter electrodes consisting of carbon (working electrode), silver (reference electrode) and carbon (counter electrodes), and insulation layer (b) with SEM images showing the cross section of hierarchical carbon ink over silver ink (c), carbon electrode surfaces, and silver electrode (d) with nanostructured ink components (e).

Ayman H. Kamel