Integrated Electrochemical Biosensors for Detection of Waterborne Pathogens in Low-Resource Settings

Abstract

More than 783 million people worldwide are currently without access to clean and safe water. Approximately 1 in 5 cases of mortality due to waterborne diseases involve children, and over 1.5 million cases of waterborne disease occur every year. In the developing world, this makes waterborne diseases the second highest cause of mortality. Such cases of waterborne disease are thought to be caused by poor sanitation, water infrastructure, public knowledge, and lack of suitable water monitoring systems. Conventional laboratory-based techniques are inadequate for effective on-site water quality monitoring purposes. This is due to their need for excessive equipment, operational complexity, lack of affordability, and long sample collection to data analysis times. In this review, we discuss the conventional techniques used in modern-day water quality testing. We discuss the future challenges of water quality testing in the developing world and how conventional techniques fall short of these challenges. Finally, we discuss the development of electrochemical biosensors and current research on the integration of these devices with microfluidic components to develop truly integrated, portable, simple to use and cost-effective devices for use by local environmental agencies, NGOs, and local communities in low-resource settings.

Keywords: electrochemical biosensors; in-situ monitoring; low and middle-income countries (LMICs); low-resource settings; microbial pollution; point-of-care.

Figure 1

Classification of new main spectra with the Biotyper™ database. The highest matching scores of the new main spectra were divided into ranges reflecting highly probable species identifications (>2.3), probable species identifications (2.0–2.3), secure genus identifications (1.7–2.0), and unreliable identifications (<1.7). Strains with Biotyper™ species classifications are different from the species assignment for VibrioBase main spectra. (Re-printed from Erler et al. [28]. Copyright (2015), with permission from Elsevier).

Figure 2

(a) Schematic illustration of the pyrosequencing reaction with four enzymes (DNA polymerase, ATP sulfurylase, luciferase, and apyrase). Nucleotides are added one at a time to form the complementary strand of the single-stranded template, to which a sequencing primer has been annealed. Each nucleotide incorporation event is accompanied by the release of pyrophosphate (PPi). ATP sulfurylase converts the PPi into ATP. The ATP is then converted to visible light by luciferase and the produced light signal is detected. Unincorporated nucleotides and ATP are degraded by apyrase between each cycle. (b) Major steps in the metagenomic detection of microbial pathogens in water by pyrosequencing. (Modified from Aw and Rose [38] Copyright (2011), with permission from Elsevier).

Figure 3

Schematic for a portable microfluidic platform composed of printed circuit board (PCB) technology with SU-8 photoresist. Schematic shows the impulsion system containing inlet, automated microchannels, and pressurized chambers combined with electronics followed by micromixer serpentine design and sample outlet. (Re-printed from Aracil et al. [61]. Copyright (2015), with permission from Elsevier).

Figure 4

Schematic depiction of the experimental setup used for step one of the two-step preconcentration process for virus recovery from fresh and wastewater samples. (Re-printed from Farkas et al. [67]. Copyright (2018), with permission from MDPI AG).

Figure 5

Self-assembled monolayers (SAMs) with DNA aptamers on a gold surface before and after incubation with PSA. (a) Thiolated aptamer with MCH; (b) amine-terminated aptamer with sulfo-betaine; (c) structure of the thiol-modified sulfo-betaine. (Re-printed from Jolly et al. [79]. Copyright (2015), with permission from Elsevier).

Figure 6

Schematic of a proposed anti-biofouling mechanism. Where an oscillating electric field exists, the surface double layer was disturbed leading to unstable organic and microbe attachment. (Re-printed from Long et al. [80]. Copyright (2019), with permission from Elsevier).

Figure 7

Tag design (110 mm × 35 mm) based on a development kit for printing onto different substrates. A to B and C to D show the longest path over which resistance measurements are made for each antenna arm, while E to F and G to H show the centre paths over which resistance is measured. (Re-printed from Smith et al. [86]. Copyright (2018), with permission from IOP Publishing Ltd.).

Figure 8

Standard components of a biosensing device. (Re-printed from Bhalla et al. [89]. Copyright (2016)).

Figure 9

Typical 3-electrode cell setup with a working electrode usually made of gold, a reference electrode, which may be Ag/AgCl, Hg/HgSO4, or SCE, and a thin-wire Pt counter electrode.

Figure 10

Randles equivalent circuit.

Figure 11

Guidelines for selecting a biomarker in wastewater diagnostics. (Re-printed from Gracia-Lor et al. [99]. Copyright (2017), with permission from Elsevier).

Figure 12

Example of a modular lab on a chip for stem cell studies. Several microfluidic components and sensing modules are integrated together for cell isolation, detection and counting, viability or migration assays, and differentiation studies. (Re-printed from Primiceri et al. [111]. Copyright (2013), with permission from The Royal Society of Chemistry).

Figure 13

Layout of the gold array-embedded gradient chip. (Re-printed from Lee et al. [117]. Copyright (2020), with permission from The Royal Society of Chemistry).

Figure 14

(left) Computational setup of the magnetic mixer. (right) Comparison of mixing efficiency between pure diffusion (a) and magnetic mixer without channel flow after 100 bead revolutions (b). The concentration is averaged over channel height. The back circles denote the position of static discs, whereas the green circles indicate the instant position of rotating beads. In (b), left, 2 beads rotation per disk with 2a spacing; middle, 1 bead per disk with 2a spacing; right, 1 bead per disk with 1.5a spacing. (Re-printed from Owen et al. [119]. Copyright (2013), with permission from MDPI AG).

Figure 15

Microfluidic filter device for tissue specimens. (a) Schematic of the microfluidic filter device containing two microporous membranes. The first membrane is located in the centre of the device and is intended to restrict large tissue fragments and aggregates from passing through to the effluent outlet (direct filtration). If desired, some of the sample can be passed over the surface of the first membrane for collection from the crossflow outlet (tangential filtration). The second membrane is immediately upstream of the effluent outlet and is intended to restrict smaller aggregates from reaching the effluent outlet. (b) Exploded view showing seven PET layers, including three channel layers, two via layers, and two layers to seal the top and bottom of the device. (Re-printed from Qiu et al. [121]. Copyright (2018), with permission from The Royal Society of Chemistry).

Figure 16

Schematic design of the microfluidic device for continuous-flow magnetically-controlled capture and separation of microparticles. The device consists of an incubator that employs the target acquisition by repetitive traversal (TART) of magnetic beads and a separator that uses magnetic fractionation. The incubation and separator are serially connected and placed next to a bar-shaped permanent magnet. Particle distributions are analysed in the observation regions at the Y-junction, the end of the incubator, and the end of the separator. These regions are each divided into ten lanes to facilitate the analysis. (Re-printed from Zhou et al. [122]—permission pending).

Figure 17

(top) Integration of electrical concentration of leukaemia cells and electrical lysing of red blood cells in the microchannel constriction: (a) experimentally recorded snapshot image with the trapped leukaemia cells highlighted with circles for clarity and (b) numerically predicted trapping zone for leukaemia cells and trajectories for red blood cells. The block arrow indicates the flow direction. (bottom left) Superimposed image of two red blood cells (highlighted as cell 1 and cell 2) illustrating the typical process of electrical lysis in the microchannel constriction. The block arrow indicates the flow direction in the channel. (bottom right) Picture of the microfluidic chip and dimensions of the constriction microchannel. (Re-printed from Church et al. [131]. Copyright (2010), with permission from The American Institute of Physics).

Figure 18

A simplified example of magnetic protein separation using functionalized-magnetic beads in a single tube. (Re-printed from Zhou et al. [142]. Copyright (2018), with permission from Elsevier).

Figure 19

IEF concept schematic. Amphoteric molecules are driven along the pH gradient towards their PI. (Reprinted from Sommer and Hatch, 2009 [138], with permission from Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim).

Figure 20

Schematic design of the μPAD used by Yu et al. The device was placed on a cooling pad and the connections were fixed to the anolyte and catholyte soaked paper. (Re-printed from Yu et al. [147], with permission from Springer Nature).

Figure 21

Polymerase chain reaction (PCR) standard protocol involves raising the temperature of the reaction to 95 °C to separate the DNA strands, lowering it to the annealing temperature for the oligonucleotide primers to hybridize, and then raising it to the optimal DNA polymerase temperature of 72 °C for primer extension. This process is repeated cyclically, creating exponential copies of the target sequence. (Re-printed from Lui et al. [150]. Copyright (2009), with permission from MDPI AG).

Figure 22

Photograph of the fabricated PCR-on-chip device. (Re-printed from Moschou et al. [154]. Copyright (2013), with permission from Society of Photo-Optical Instrumentation Engineers (SPIE)).

Figure 23

(a) Exploded view of the self-driven microfluidic chip consisting of a polydimethylsiloxane (PDMS) microfluidic structure layer, a hydrophilic film, a PDMS hydrophobic layer, and a glass substrate. (b) A photograph of the chip. (c) Schematic illustration of the chip design. The area enclosed by the red dotted line represents the LAMP reaction module (module B), with the other area being used for sample treatment (module A). (Re-printed from Ma et al. [159]. Copyright (2019), with permission from The Royal Society of Chemistry).