Potential applications of advanced biosensor systems for the real-time monitoring of wastewater treatment plants

CHAPTER 4

Potential applications of advanced biosensor systems for the real-time monitoring of wastewater treatment plants Sujata Sinha*, Guneet Kaur† *

Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology Delhi, New Delhi, India Department of Biology, Hong Kong Baptist University, Kowloon Tong, Hong Kong

†

Contents 1. Introduction 2. Wastewater contaminants 2.1 Contaminants and associated problems 2.2 Discontinuous/traditional methods of WWTP monitoring and their limitations 3. Biosensor tools and technology for WWTPs 4. Advanced biosensors for real-time monitoring of WWTPs 4.1 Microbial cell-based biosensor 4.2 Protein/enzyme/immune biosensor 4.3 Aptamer-based biosensor 5. Examples of advanced techniques for real-time monitoring of wastewater contaminants 5.1 Detection of viral and bacterial contaminants 5.2 Pollutant-based biosensor 5.3 BOD monitoring 6. Conclusions and future outlook Acknowledgments References

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1. Introduction Wastewater treatment plants (WWTPs) are dynamic systems which require long-term expertise and constant monitoring for a reliable, stable, and efficient operation. Maintenance of plant operation against large fluctuations in influent loadings and mechanical breakdown is a critical problem [1]. This problem is further exacerbated by current focus on reduction of operating costs due to which most domestic and industrial WWTPs are forced to operate with fewer and less skilled operators [2]. In such a scenario, development of real-time monitoring system becomes increasingly important, especially to support local operators of small-sized WWTPs. Furthermore, water distribution systems are Tools, Techniques and Protocols for Monitoring Environmental Contaminants https://doi.org/10.1016/B978-0-12-814679-8.00004-2

Copyright © 2019 Elsevier Inc. All rights reserved.

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often plagued with problems emanating from the presence of various types of contaminants. Until the beginning of 1990s, major contaminants in water included nonpolar hazardous compounds, for example, persistent organic pollutants and heavy metals, and biological contaminants which arose because of agricultural and industrial activities [3]. In the recent years, a greater number of municipal derived chemicals described as new or emerging contaminants including human and veterinary pharmaceuticals, personal care products, illicit drugs (e.g., cocaine), plasticizers, and surfactants have been found in urban wastewaters [4] The presence of antibacterial drugs in wastewater has led to dissemination of antibiotic-resistant bacteria which is another major health concern [5]. Among these emerging contaminants, pharmaceuticals are recognized as priority hazardous substances which reach the WWTPs via wastewaters. Pharmaceutical residues are usually present at a concentration range of nanograms or micrograms per liter but their implications to plant and/or human health have already been demonstrated [6, 7]. In addition to wastewaters, the major source of these contaminants in aqueous environment is through release of WWTP effluents due to the lack of efficient and sensitive analytical tools and techniques for their detection which consequently leads to their discharge without any proper treatment [8]. Thus the present times of increasing industrialization and burgeoning population demand more efficient, fast, and sensitive sensing systems to combat the occurrence of these hazardous contaminants and ensure clean water availability. WWTPs are designed on the basis of average concentration of contaminants; however, sudden concentration changes (long- or short-term shocks) can disturb the stability of these plants. Real-time monitoring of contaminants helps in minimizing these shocks and develops strategies for preventing instability and process failure [9]. Traditional monitoring methods in WWTPs include discontinuous method of sample-based analysis of wastewater. This has been gradually replaced by sensor placement approach, microfluidics sensor, electrical impedance spectroscopy (EIS) and dielectric impedance spectroscopy (DIS), light emission luminescence, infrared (IR), mid-infrared (MIR), nearinfrared (NIR) spectroscopy, Raman, surface-enhanced Raman spectroscopy (SERS), model-based event detection methods, and so on, to provide greater sensitivity, accuracy, and more timely detection of irregularities in water quality and possible contamination events [10]. While these earlier methods offer excellent selectivity and detection limits, these suffer from several drawbacks. The latter include nonsuitability for rapid processing of multiple samples, requirement of highly trained operators, time-consuming detection process, use of specific target compounds (e.g., proteins), complex pre- and posttreatment steps, and high cost [11]. Low suitability for in-field studies and in situ monitoring of samples further makes them unattractive. Additionally, these techniques only help in determining the contaminants while providing little information about biological response and chemical analyses which would be more useful in monitoring and controlling the plant operation [12]. Such combined information can be provided by biosensors.

Potential applications of advanced biosensor systems

According to IUPAC, biosensor is defined as a device that uses specific biochemical reactions mediated by isolated enzymes, immunosystems, tissues, organelles, or whole cells to detect chemical compounds usually by electrical, thermal, or optical signals. Compared with other contamination detection methods, the key advantages associated with biosensors include high sensitivity of biological contaminants, suitable for in situ monitoring, requirement of minimum amount of samples, portability, miniaturization, and fast response time [2]. Despite these advantages, biosensors are usually described as the weakest part of the chain in real-time monitoring of WWTPs. Sensor technology is far behind as compared to computer technology for both hardware and software development. However, traditional analytical biosensor techniques can only be operated in laboratory settings which also pose risk for degradation of samples while transporting them to the laboratory. This limitation of off-line techniques can be overcome by providing access to monitoring on-site performing real-time evaluation of contaminants. It also reduces the response time in peak pollution episodes. Biosensors for heavy metals, ammonia, biochemical oxygen demand (BOD), and so on, have been developed and are considered to be fast, sensitive, reproducible, and high on specificity [13–15]. These also overcome the problem of sample transportation and pretreatment while allowing the possibility of direct analyte assay in the sample matrix [16]. In recent times, a number of developments regarding in situ real-time measurements of environmental contaminants have been made, for example, an inferometric biosensor based on bimodal waveguide (BiMW) was able to detect lower concentration of Irgarol 1051, a pollutant in sea water without requirement of sample pretreatment and least interference with sea matrix [17].

2. Wastewater contaminants 2.1 Contaminants and associated problems Contaminants have been classified into various categories such as toxins, environmental polluting hormones, pesticides, pharmaceutical and personal care products, and persistent organic toxic chemicals (inorganic and organic). It has been generalized that the size of these molecules is less than 1000 Da and these are nonimmunogenic in nature [18]. Potential health effects of environmental contaminants on various sectors such as traditional food, health, and wildlife have been summarized from time to time. Levels of contaminants such as chlordane, mercury, polychlorinated biphenyls, and toxaphene in marine/terrestrial mammals, fish, birds, and plants have been summarized in a study by Chan [19]. Heavy metals are widely used in industrial processes and are toxic for living organisms, hence environmental monitoring of these metals through rapid specific and nonspecific detection in drinking water is important. Conventional techniques to analyze heavy metals include precipitation with chemicals, membrane separation, chromatography, ion chelation, coupled plasma mass spectrometry, cold vapor atomic absorption

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spectrometry, X-ray absorption spectrometry, and UV visible spectrometry. These methods are discontinuous in nature and costly although being precise in measurement. Biosensor has been found to be the best alternative for heavy metal monitoring where any biological material in immobilized form is in intimate contact with a compatible transducer and quantifiable electrical signal is generated out of a biochemical signal. New methods in biosensor-based screening of antibiotic in animal-derived food have been recently reviewed [20]. Surface Plasmon resonance (SPR) and whole-cell-based biosensors have been used mainly for detection of antibiotic residues in animal-derived foods [21, 22]. These are portable in nature, have small sample requirement, are highly sensitive, and have higher specificity over other conventional method. However, narrow detection range, lack or robustness, lack of stability, and poor shelf-life have led to limited commercial applications of whole-cell biosensor. SPR-based biosensors have been used for screening of β-lactamase, sulfonamides, tetracyclines antibiotics as they can be monitored real time and are highly sensitive, can be automated, and are robust in operation.

2.2 Discontinuous/traditional methods of WWTP monitoring and their limitations Multiple tube fermentation (MTF) and conventional culture-based method are traditional methods used for obtaining microbiological parameters of water to monitor the biological contaminants [2]. However, membrane filtration (MF) technique recognized by United States Environmental Protection Agency (USEPA)/World Health Organisation (WHO) has been recommended for detection of contaminants in potable water. PCR amplification and Fluorescence in situ hybridization (FISH) have also been used for detection of biological contaminants. On the other hand, nonbiological contaminants which are mainly categorized into two categories including chemical- and nanoparticle-based contaminants are detected using capillary electrophoresis, gas and/or -liquid chromatography mass spectrometry (GC-MS/LC-MS), and other spectroscopic techniques.

3. Biosensor tools and technology for WWTPs Biosensors are analytical devices which convert the presence of a molecule or compound into useful and measurable signal due to a specific mechanism. Biosensors can be divided into two broad categories on the basis of (1) transduction element and (2) biorecognition element. On the basis of transducing element, biosensors can be divided into optical, piezoelectric, thermal, bioluminescence, and electrochemical [23]. Thermal or calorimetric biosensors detect materials on the basis of heat evolved due to biochemical reaction when for, for example, the analyte reacts with enzyme, and so on. In a piezoelectric biosensor (quartz crystal microbalance biosensor), the surface is coated with biologically active substance to provide real-time output, simplicity, broader pH range, and lower cost.

Potential applications of advanced biosensor systems

Bioanalytic or bioluminescence biosensors work on the principle that certain enzymes are used to radiate photon as a by-product of ensuing reactions. Compact instruments comprising electrochemical biosensor can be created which can be used for monitoring toxicity and water quality and can operate even in turbid media. Electrochemical type can be divided into conductometric, potentiometric, amperometry, impedance biosensor, and so on. Optical fiber and SPR biosensor falls under the category of optical sensor. On the basis of biorecognition element, biosensors can be classified as immunosensor, aptasensor, genosensor, and enzymatic biosensors where antibodies, aptamers, nucleic acids, and enzymes, respectively, are used as biorecognition element. Of these, immune and enzymatic biosensors are most commonly used for environmental purposes. However, the uses of aptamer sensors are increasing due to certain advantages associated with them such as ease of modification, in vitro synthesis, thermal stability, ease in distinguishing targets with different functional groups, and so on. An overview of types of biosensors and their detection mechanism is shown in Fig. 4.1.

4. Advanced biosensors for real-time monitoring of WWTPs Biosensor development for analysis of environmental contaminants has recently been reviewed [11]. Sensitivity, specificity, and detection time are the most important factors which are instrumental in selection of appropriate biosensor for any analyte. Higher sensitivity with less detection time gives an edge to biosensors over other techniques including electrochemical and spectroscopic techniques which are widely practiced for sensing and detection applications. Various traditional and updated methods for chromium detection in potable water have been recently reviewed [24]. These include the electrochemical techniques which are preferable over others due to their superior selectivity, sensitivity, and stability. Among four categories of electrochemical biosensors, amperometric based on transduction mechanism was found to be best method due to their better sensitivity and lesser response time. Furthermore, a porous silica-based biosensor has been newly developed [25, 26]. It mainly consists of three components, that is, a sensing layer made of enzyme immobilized porous silica, a light source coherent in nature, and a detector. In principle, changes in surface refractive index occur as a result of chromium ions coming in contact with porous-silicon sensing surface. Fourier transform is used for analyzing and detecting spectral interference pattern of porous silica film and changes in optical effective thickness which in turn changes in the presence of analyte.

4.1 Microbial cell-based biosensor Microbial fuel cell technology (MFC) has been reported as a potential tool for monitoring of water quality. A novel bioelectrochemical device, MFC, has been developed using electrogenic bacteria which convert wastewater to electricity [27, 28]. MFCs convert chemical energy in organic matter to electricity through metabolic process of

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Fig. 4.1 Overview of types of biosensors and their detection mechanism for real-time monitoring of WWTPs.

microorganism. An electroactive bacterial film develops at the anode of this device which transfers electron after oxidation of organic compounds to electrode so that the current generation can directly be related to metabolic activity of bacteria present in the anodic film. Change in metabolic activity which could be the result of disturbances, like the presence of bioactive compounds, organic toxins, organic load, and so on, results in change of generated electricity. This principle is very straightforward and has been used for detection of toxins such as pesticides, for example, diazinon and polychlorinated biphenyls, acephate, glyphosate, formaldehyde, p-nitrophenol, and so on, in water [29]. MFC possess certain unique features which can act as smart water sensor. Firstly, shocks in wastewater can cause a jump or drop in voltage output and can act as real-time shock indicator. Secondly, these devices include no requirement of external transducer as opposed to other types of sensors which leads to cost reduction of instrument, improved simplicity, and sustainability. Thirdly, MFC-based devices are self-sustainable and do not require external power supply like other devices. MFCs have been developed for measurement of BOD, chemical oxygen demand (COD), toxins, and organic substances. A schematic diagram of MFC is shown in Fig. 4.2. Traditional MFC still uses tubular bioreactor, single chamber and cube shape which makes its use difficult for real-time assays. Therefore its use as sensor is restricted due to lack of portability as tubes and pumps are required in the devices and use of expensive manufacturing material. In a recent work, a biosensor based on paper MFC has been

Potential applications of advanced biosensor systems

Fig. 4.2 Diagram of a typical microbial fuel cell consisting of an anode, a cathode, a proton exchange membrane, and an electrical circuit.

developed and tested for sensing capacity of toxins in water. Widely tested formaldehyde was used as model bioactive compound for development of MFC-based biosensor. Increased sensor sensitivity and baseline current was achieved by simple design modification by folding back-to-back two paper MFCs electrically connected in parallel system [30]. Paper-based devices have been found to be user-friendly, portable, miniature size, and relatively cheaper than another biosensor. Three main categories of paper-based devices are microfluidic paper analytical devices, dipstick assay, and lateral flow assay [11]. Paper-based nano-sensors based on synergy between biosensing and nanotechnology have great potential for environmental monitoring. Membrane-less MFC-based biosensor for monitoring of wastewater quality has also been reported recently [31]. Performance of such devices in terms of device current output was tested with various substrate concentrations in wastewater. This membrane-less device (SCMFC) was able to survive long starvation and repeatability of current output was good. Simultaneous generation of bioelectricity and organic compound degradation was possible with this device, while detection time was short and a good correlation between low concentration of wastewater and current output was achieved. Additionally, genetically modified bacteria are being employed in the whole-cell biosensor by fusing promoter less reporter gene to pollutant-responsive gene for improving its selectivity and specificity against its intended target. Such biosensors have been reported for phenolic compounds and organochloride pesticides, for example, Lindane

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[32, 33]. Escherichia coli cells carrying the LZCapR plasmid having β-galactosidase reporter gene sequence sensitive for phenolic compounds were attached to agarose gel and were used for analysis of phenolic compounds from untreated hospital wastewater samples [33]. Similarly, for the detection of neurotoxic organophosphate compounds a recombinant E. coli containing periplasmic expressing organophosphorus hydrolase enzyme was immobilized on 96-well plates coated with mussle adhesive protein [32]. Stress-responsive bacterial strain has also been used in the wastewater biotreatment plants as minibioreactor [34]. However, this was limited by overloading of toxic chemicals which was further removed by adding two minibioreactors in a series. The use of genetically modified microbes as biosensors for in situ monitoring of environmental pollution has been covered in detail [35]. Use of microorganisms as biosensing element over enzyme, antibodies, and subcellular components has some advantages which include capability to grow in relatively cheaper media, detection of large number of chemicals, ease of genetic modification, and adaptability to a number of conditions. Reporter gene (lux/luc/gfp) is fused with natural regulatory gene with or without constitutive promoter and toxicity of target compound is assayed by decrease in reporter gene activity. Additionally, activation of regulator by specific chemicals results in a dosedependent enhancement in signal of reporter gene which is easily detected by the chemical-specific biosensor. Whole-cell biosensor has been broadly divided into constitutive and inducible expression on the basis of bacterial cells involved. In case of nonspecific whole-cell biosensor, a bacterial strain carries constitutively expressed operon (e.g., luxCDABE) or some other operon for sensing contaminants such as polyaromatic hydrocarbons, antibiotics, various metal pollutants, and so on, which has been taken from Vibrio fischeri to sense environmental contaminants. Reporter genes are highly expressed in case of strains if no contaminants are present; however, lower or decreased production of reporter gene signifies the exposure to pollutants as these compounds or samples have an inhibitory effect on the strain [36]. Various strains carrying reporter genes like Pseudomonas fluorescence and Rhizobium leguminosarum have been developed carrying reporter genes for other samples such as naphthalene, salicylate, and metal pollution [37, 38]. Measurements using these strains are considered to be nonspecific as pollutants which decrease metabolic activity also reduce the production of light. However, other factors such as salinity, pH, other metals, xenobiotics, and so on, also decrease light production, and therefore the nature and assessment of toxicity becomes difficult. Nevertheless, measurement of nitric oxide, metals, xenobiotics, and some antibiotics has been done using nonspecific whole-cell biosensors. On the other hand, specific whole-cell biosensor produces specific response to different compounds. Genetic engineering is used to transcriptionally fuse inducible promoter to different reporter genes and inducing transcription or relieving repression.

Potential applications of advanced biosensor systems

Any external stimulus can induce reporter gene expression which in turn leads to an increase in quantifiable signal. When stimulus is received from promoter only then the regulatory protein is released. Tetracycline residue screening from animal-derived food has been done using whole-cell biosensor comprising the construct tetR-tetA fusion luxCDABE [39, 40]. Transformed competent cells of Shigella flexneri and Shigella sonnei with pLUX plasmid were evaluated for their ability to monitor wastewater quality by undergoing degradation and measuring bioluminescence response using microplate luminometer. These were found to be extremely sensitive to wastewater samples and formed different patterns in sync with COD removal shown at different days of degradation. Generally higher levels of bioluminescence (571.76%) were observed at later stages (5 days) of degradation as compared to initial days at 0.1% (v/v) effluent concentration [41]. With increase in exposure of biosensor to wastewater effluent, a decrease in bioluminescence was observed. This biosensor could analyze environmental pollutants in a way which was not possible with chemical analysis, while it could also be used for in situ monitoring of biodegradation. Their other advantages include real-time monitoring every 15 min along with rapid warning, generation of consistent pattern useful as indicator of the level of degradation, rapid and reliable bioluminescence response, stability at room temperature, low cost and ability to cope with large number of samples, portability, and potential for their use in on-line monitoring. With the help of disposable modular biochip, a flow-through biosensor for continuous on-line monitoring of toxicity of wastewater was developed [42]. Biochip containing agar-immobilized bioluminescent recombinant reporter bacteria was connected with single-photon avalanche diode (SPAD) detector. Biochip was harbored both with constitutive and inducible reporter strain and was exposed to continuous water flow for 10 days. During this period, biosensor was also exposed to various water contaminants/pollutants along with industrial wastewater. It was able to detect all simulated contamination within 0.5–2.5 h and response was indicative of nature of contaminating chemicals in water. Damage both by oxidative and DNA damage, heavy metal toxicity (As/Sb), and cytotoxicity stress was detected using these reporter strains. Biosensor device contained four flow-through chambers, where each chamber consisted of a glass layer, a poly(dimethoxysilane) (PDMS) chip, and polymethyl methacrylate (PMMA) cover. PDMS chip is perforated 4 mm diameter and 5 mm dip each, 3  4 cavities cylindrical in nature, giving a total volume of 60 μL. A serpentine channel is carved on PMMA cover which is 2 mm deep with 2 mm in diameter. Four flow-through chambers are connected to four feeding tubes at 40°C and a screw system presses against glass, PDMS (perforated) and carved PMMA against each other and forming a flow channel having 12 wells in its path. Waste fluid is discharged in the container through feed tubes and signal generated in the form of light is quantified and detected through three aligned SPAD device. Single axis linear motor stepper is connected to the detector which scans through flow chambers as water passes

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Fig. 4.3 Schematic representation of a whole-cell biosensor.

through immobilized reporters and stops above each well to measure the signal. LabVIEW program is specially dedicated to record the light signal and detector movement. A wooden box is used to keep flow-through and detector inside it as appropriate dark conditions for photon counting. A schematic diagram of whole-cell biosensors is shown in Fig. 4.3. A novel on-line monitoring and alert system for activated sludge (AS) has been developed, which is composed of a single chamber MFC, a signal acquisition subsystem, and an alert subsystem with self-diagnosis function. Single chamber MFC without cathode exchange membrane (CEM) which is present in the core of online system was assembled and submersed into AS reactor. Submersible MFC process was established for AS process where oxygen acted as an electron acceptor and organic substrates as electron donors, respectively. This setting provided evaluation of AS reactor status and gave reliable and early warning for risks involved. For evaluation of reliability and sensitivity of this on-line monitoring and alert system, various shocks were imposed to AS reactor and response of submersible MFC was examined [43]. Two bacterial biosensors based on S. sonnei and E. coli were constructed which were found to be sensitive against toxicity of wastewater effluents. Competent cells were transformed with pLUX plasmid with Lux-CDABE operon using gene pulser apparatus. Transformed cells were selected by plating on LB-agar plates supplemented with ampicillin. A linear increase in cell luminescence was observed with increase in heavy metal and other inorganic pollutants and a high correlation coefficient up to 0.995–0.997 was obtained. These bacterial biosensors were found to be the best alternative for rapid, sensitive, and cheap method of wastewater monitoring [44].

Potential applications of advanced biosensor systems

4.2 Protein/enzyme/immune biosensor Enzyme-based biosensor can be divided into two categories on the basis of their interaction with target analytes. In the first case, enzyme metabolizes the analyte and its concentration can be determined through catalytic transformation of analyte by immobilized enzyme. Other type of enzyme-based biosensor is enzyme inhibition based in which the activity of enzyme is inhibited by analyte. The latter is measured by decrease in enzymatic product formation [11]. Some of the reported enzyme biosensors for detection of phenolic compounds are based on enzymes such as peroxidase, tyrosinase, and laccase enzyme [45]. Acetylcholinesterase- and colin oxidase enzymebased biosensors have been constructed for detection of organophosphorus and carbamate pesticides. These biosensors were based on compounds having inhibitory properties on the enzymes. Similarly, degradation of parathion and carbaril pesticide by hydrolase and acetylcholinesterase enzyme was the basis of development of amperometric biosensor [46]. A biosensor based on tyrosinase enzyme immobilization was developed on photo cross linkable polyvinyl alcohol polymer. Whole system was inserted in computercontrolled flow system that was attached besides photocatalytic reactor and included a photocatalyst, that is, titanium dioxide (TiO2). This biosensor was able to accurately monitor the timely paracetamol degradation and was comparable with traditional HPLC assay. It provided real-time information on reaction advancement and allowed better control of photodegradation process [47].

4.3 Aptamer-based biosensor Aptamers are short single-stranded DNA or RNA oligonucleotides which bind their target molecules with high affinity and specificity due to their three-dimensional structure. This property makes them particularly useful as molecular recognition element in biosensors wherein they allow fast and easy detection of environmental contaminants such as pharmaceutical residues [48, 49]. Development of aptamer-based biosensors for pharmaceutical detection is advantageous since enzyme- or antibody-based biosensors targeting toxic molecules are mostly unavailable while aptamer development is possible for such toxic targets. This can be explained by the fact that pharmaceuticals are often shown to have poisonous effects, especially at high concentrations and therefore development of antibodies for targeting them is difficult. Furthermore, binding of antibodies to small targets can be tedious and complicated [18]. By their mode of action, aptamers resemble antibodies by demonstrating specific affinity to target molecules. Standard methods for pharmaceuticals detection include high performance liquid chromatography (HPLC), gas chromatography (GC), GC-mass spectrometry (GC-MS), LC-MS which are time consuming, laborious, and require highly skilled personnel [50]. Aptamer-based system offers an alternative fast and easy detection approach. Additionally, aptamer can be coupled with other easy detection

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system, for example, calorimetric assays to allow development of in-field screening of specific contaminants [51]. In other words, flexibility, stability, cheap to produce, and easy to modify are interesting properties offered by aptamers for real sample applications [52]. With respect to WWTPs, aptamer-based sensing could be used for various purposes, including automatic monitoring of pharmaceutical degradation, inspection of incoming water, and construction of components for WWTPs, such as filters to test the filtration efficacy using specific markers. The increasing use of aptasensors for monitoring of low molecular weight pollutants (emerging contaminants) in water sources, wastewater, and WWTPs effluents has been recently reviewed by Zhang et al. [53]. The synthesis of aptamers occurs by the process called SELEX, that is, systematic evolution of ligands by exponential enrichment which was first developed in 1990. A modification of this method, Capture-SELEX was developed by Stoltenburg et al. [54] which allows the selection of DNA aptamers with high affinity and a secondary structure fitting to the target. In a recent study, this method was used to demonstrate the functionality of quinolone-specific aptamers in real water samples in local tap water and in effluents of sewage plants [54, 55]. High specificity, binding affinity, and functional stability of aptamers for quinolones in real water samples make them suitable for real-time monitoring and analysis applications in WWTPs. Traditionally, apta-sensing relied on optical-based read-out methods following an aptamer-binding event. This required high precision, expensive instrumentation, and sophisticated algorithms to interpret the data and was therefore replaced by electrochemical aptasensors. In the latter, the changes in electric current produced by redox reactions occurring on the transducer electrode surface are measured by an electrochemical device. Compared to optical, piezoelectric, or thermal detection, electrochemical transduction offers a simple, rapid, highly sensitive, cost-effective, miniaturized, robust, and highthroughput method which is desirable for environmental sample sensing such as in WWTPs [56]. For labeling in electrochemical aptasensing, enzymes (horse radish peroxidase, glucose oxidase, etc.) and electroactive compounds (ferrocene, ferrocyanide, methylene blue, etc.) have been used. Aptamers conjugated with fluorophores and quenchers are more useful for real-time detection [57, 58]. The recent years have witnessed a great number of reports involving development and use of various types of aptasensors for detection of different molecules; however, only some reports have dealt with real-time applications. Nevertheless, the high specificity and selectivity of aptamer-based sensors demonstrated in these reports make them promising and powerful tools for realtime, on-site analysis of wastewaters. Some of these reports are discussed later. Rapid development of industry and agriculture has led to serious problems of heavy metal pollution in environment including water systems. Lead (II) is one of the most toxic heavy metals which is commonly found in wastewaters. The use of fluorescein-based aptamers for Pb (II) was attempted by Chen et al. who demonstrated a high specificity of this sensor even in the presence of interfering metal ions [20]. Real-time detection of

Potential applications of advanced biosensor systems

most toxic form of arsenic (III) has been reported with field effect transistor (FET)-type aptasensor based on carboxylic polypyrrole-coated flower-like MoS2 nanospheres (CFMNSs) [59]. Extraordinary performances with rapid response were possible by integrating arsenic-binding aptamer-conjugated CFMNSs into liquid-ion gated FET system. System was highly sensitive toward As (III) even at very low concentration and recognized among various numerous other metal ions mixed in a solution even from a real sample derived from river water. Other reports for fluorescence aptasensors (DNA based) based on detection of ampicillin and kanamycin A from polluted river water and clean wastewater are available [60, 61]. In addition to heavy metals, another category of frequently found contaminants in wastewaters is endocrine disrupting compounds (EDCs) such as pharmaceuticals, pesticides, plasticizers, and personal care products. EDCs including Bisphenol A (BPA), 17βestradiol (E2), and 17α-ethynylestradiol (EE) are commonly found in natural and treated waters. A portable optic fiber DNA-based aptasensor for rapid, highly selective, on-site detection of BPA has been developed [62]. The sensor exhibited an impressive sensitive response to BPA in the range of 2–100 nM with a low detection limit of 1.86 nM and was also successfully employed for wastewater sample analysis. In another report, improved designs of DNA aptamers for enhanced aptamer selectivity and sensitivity were developed by in vitro selection method and used for the detection of E2 and EE [63]. Strong selectivity for E2 and structural analog (estrone) over EE, or with strong selectivity for EE over E2 and estrone, this sensor was considered suitable for real-time detection of E2 and EE in wastewaters. In a recent report, impedimetric sensor for selective detection of two pesticides, acetamiprid and atrazine, based on aptamer-modified platinum nanoparticles was developed [64]. The sensor demonstrated a low detection limit of 1 pM and 10 pM for acetamiprid and atrazine, respectively, with a potential to be used for analysis of wastewater in a real-time manner. Some other recent nonconventional applications of high sensitive aptasensors have been in the field of wastewater-based epidemiology, for evaluation of disease/biomarker, community-wide drugs, alcohol, and tobacco use [65, 66]. In one such application, human-specific mitochondrial DNA (mtDNA)-based electrochemical apatasensor was developed to assess human fecal contamination in wastewater and evaluate water quality [67]. The developed sensor could detect complementary DNA at concentrations as low as 10 pM while also enabling the detection of single nucleotide mismatches and high feasibility for wastewater analysis in real time. In another report, the use of DNA-based community sewage sensor for rapid and cost-efficient estimation of cocaine use trends has been attempted [68]. The sensor was made by immobilization of DNA aptamer on gold electrode surface for electrochemical detection of cocaine. Although not applied in a real-time manner, the sensor was successfully employed for quantification of cocaine in wastewater samples collected from WWTPs and considered for potential implementation as a miniaturized portable tool for on-site, real-time monitoring of wastewater.

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5. Examples of advanced techniques for real-time monitoring of wastewater contaminants 5.1 Detection of viral and bacterial contaminants For detection of viral and bacterial pathogens, a variety of biosensors such as electrochemical (amperometric, impedimetric), quartz crystal microbalance type piezoelectric, and optical SPR types have been developed [69, 70]. Integrated and sensitive SPR-based biosensors have been reviewed in detail [71]. Wide variety of SPR-based biosensors have been developed for studying and quantifying protein-protein interactions; however, improved SPR techniques have also been used for detection of hormones and pesticides using chromatographic, spectroscopic techniques, and classical immunoassays. SPR can give a real-time binding information including binding kinetics and enhanced quantification of response. SPR protocols for virus detection have also been reported; however, these have been restricted to animal virus particle rather than the complete virus. Bacterial viruses or bacteriophages detection in water samples has been investigated on the basis of interaction between viruses and bacteria [72]. A gold sensor chip was used for immobilization of model bacterium E. coli WG5 using avidin biotin linkages and bacteriophages extracted from wastewater were added for testing. Initial binding only at high concentration was observed but even at a low concentration, a time-delayed cell lysis event could be observed. This two-channel microfluidic SPR sensor device was able to detect as low as 1 pfu/mL (plaque forming unit/mL) bacteriophage after 2 h of incubation. Detection was explained by the fact that virus-bacteria interaction causes structural change in bacteria bound on surface due to cell collapse and increase in mass density of sensor chip. It was found to have a potential for future biosensor technology primarily due to its ability to sense bacteriophage concentration. Real-time optical detection of E. coli (used as model indicator for bacterial species) in process water containing complex mixture of contaminants from food industry has also been reported [73]. A nanostructured, oxidized porous silicon (Psi) functionalized with specific antibodies against E. coli was exposed to water samples and reflectivity spectra were collected in real time. Complex natural microflora, soil particles and debris present in water were characterized with the biosensor, when exposed to water spiked with culture-grown E. coli induced remarkable changes in thin film optical interferences spectrum of the biosensor. Highly specific and selective quantification of target cell was confirmed by real-time PCR even while target cell concentration was of the order of magnitude lower than that of other bacterial species. A cantilever biosensor exploiting electrokinetic capture for real-time detection of E. coli was recently developed [74]. Integrated electrode with piezoelectric actuation was used for fabrication of this biosensor. It showed a signal-to-noise ratio of up to 82 for a cell concentration of 107 cells/mL for stagnant samples and a ratio of 26 for flowing cells with a cell concentration of 105 cells/mL of flowing samples and a higher order

Potential applications of advanced biosensor systems

resonant mode. From dried image, it was observed that most of the cells were captured along the outermost edge of the spiral electrode. Reduction of electrode mass and gap for cantilever biosensor can be reduced using sandwich electrode and it was suggested that more improvement in designs was further possible.

5.2 Pollutant-based biosensor Novel cell-based assays for pharmaceuticals beta-blocker and cyclooxygenase inhibitors (nonsteroidal antiinflammatory/NSAIDs) were developed, which could assess these compounds real time in surface water extract as well as in given wastewater [75]. Both assays were done by biosensor cell line expressing appropriate sensor and fluorescent reporter proteins to enhance specificity and sensitivity. Beta blocker measurement is directly related to inhibition of the beta-1 adrenergic receptor and NSAIDS were checked by cyclooxygenase (cox) inhibition activity and the time range was seconds to minutes. In complex mixture like effluents from wastewater treatment effluent treatment plant (WWETP), NSAIDS and beta-blocker inhibition can be measured by diclofenac (DicEQ) lead substance metoprolol (MetEQ). Both methods are highly sensitive and can detect up to a limit of 0.5 and 2.0 μg/L, respectively. These devices have found great potential for large-scale monitoring of WWTPs. It was suggested in this study that these sensors could be used for monitoring of similar compounds (other beta blockers and NSAIDs group of compounds) in future as same mode of action could be applied to similar compounds.

5.3 BOD monitoring Bioelectrochemical devices are providing new platform for various applications. MFC for electricity generation and microbial electrolysis cell for hydrogen production are two important examples of such devices. A novel open-type bioelectrochemical device for in situ BOD biomonitoring was developed which could be used during intermittent aeration [76]. Traditional bioelectrochemical BOD sensors required anaerobic settings for anodic reactions. Generally, they are closed type where a closed chamber is used to pack anode to avoid exposure to oxygen. However, in this study an open-type anode without any protection from exposure to oxygen and air was placed in a tank filled with livestock wastewater aerated intermittently. A potentiostat was used for controlling anodic potential and it interestingly generated similar level of currents both in presence (aerating condition) and absence of oxygen (nonaerating condition). Generally, traditional BOD biosensors which are bioelectrochemical in nature require anaerobic condition for their operations (anodic reactions) and are not used directly in aerobic conditions like aeration tanks [27, 77]. There was a logarithmic correlation between BOD concentration (up to 250 mg/L) and current generation. It was presumed that whole anode in the setting was covered with suspended solid in wastewater and created anaerobic condition due to biological oxygen removal. This was further confirmed by detecting the

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presence of an exoelectrogenic anaerobe Geobacter sp. inside the covered anode using 16srRNA gene sequencing method. Automatic control of aeration intensity and in situ monitoring of natural water environments was also possible with this device [76]. Numerous examples of ex situ monitoring of BOD under anaerobic conditions are available in various reports [78, 79]. A BOD biosensor, based on mediator-less MFC using bacterial consortium was also developed which showed strong linear correlation of charge with BOD up to 206 mg/L [80].

6. Conclusions and future outlook Biosensors undoubtedly provide a powerful and promising tool for real-time monitoring of WWTPs. Progress in development and potential applications of various types of biosensors in this regard has been increasing in the recent years. However, while a lot of examples exist for microbial-, protein-, and aptamer-based biosensors for detection of contaminants in wastewater, only few reports are available which deal with in situ and real-time monitoring. These are largely focused on microbial-based biosensors which have been used since long time and undergone great improvements to allow a real-time and continuous use. In this regard, specific whole-cell biosensors equipped with detection of response from a specific reporter gene and biochip design offer the possibility of a flow-through biosensor which could be easily used in a real-time manner. Furthermore, latest developments in the detection mechanism for aptamer-based sensors such as electrochemical transduction and label-free methods help to debottleneck some of the previous problems associated with optical-based sensing. This opens opportunities for miniaturized, sensitive, high throughput, easy-to-handle tools for in-line and real-time measurements. Progress in these kinds of biosensor development in the near future is believed to pave the way for large-scale, real-time applications of biosensors in monitoring of WWTPs.

Acknowledgments Sujata Sinha is thankful to the Department of Science & Technology, Government of India, for providing grant (SR/WOS-A/LS-1004/2015) in form of WOS-A.

References [1] M.W. Lee, S.H. Hong, H. Choi, J.-H. Kim, D.S. Lee, J.M. Park, Real-time remote monitoring of small-scaled biological wastewater treatment plants by a multivariate statistical process control and neural network-based software sensors, Process Biochem. 43 (2008) 1107–1113. [2] S.N. Zulkifli, H.A. Rahim, W.J. Lau, Detection of contaminants in water supply: a review on state-ofart monitoring technologies and their applications, Sensors Actuators B Chem. 255 (2018) 2657–2689. [3] M. Petrovi
c, S. Gonzalez, D. Barcelo´, Analysis and removal of emerging contaminants in wastewater and drinking water, TRAC Trend. Anal. Chem. 22 (2003) 685–696.

Potential applications of advanced biosensor systems

[4] B. Petrie, R. Barden, B. Kasprzyk-Hordern, A review on emerging contaminants in wastewaters and the environment: current knowledge, understudied areas and recommendations for future monitoring, Water Res. 72 (2015) 3–27. [5] C.G. Daughton, T.A. Ternes, Pharmaceuticals and personal care products in the environment: agents of subtle change, Environ. Health Perspect. 107 (1999) 907. [6] O.A. Jones, N. Voulvoulis, J.N. Lester, Potential ecological and human health risks associated with the presence of pharmaceutically active compounds in the aquatic environment, Crit. Rev. Toxicol. 34 (2004) 335–350. [7] W. Schmidt, K. O’Rourke, R. Hernan, B. Quinn, Effects of the pharmaceuticals gemfibrozil and diclofenac on the marine mussel (Mytilus spp.) and their comparison with standardized toxicity tests, Mar. Pollut. Bull. 62 (2011) 1389–1395. [8] N.H. Tran, M.R. Karin, Y.-H. Gin, Occurrence and fate of emerging contaminants in municipal wastewater treatment plants from different geographical regions—a review, Water Res. 133 (2018) 182–207. [9] P.A. Vanrolleghem, D.S. Lee, On-line monitoring equipment for wastewater treatment processes: state of the art, Water Sci. Technol. 47 (2003) 1–34. [10] A.F. Chrimes, K. Khoshmanesh, P.R. Stoddart, A. Mitchell, K. Kalantar-zadeh, Microfluidics and Raman microscopy: current applications and future challenges, Chem. Soc. Rev. 42 (2013) 5880–5906. [11] X. Wang, X. Lu, J. Chen, Development of biosensor technologies for analysis of environmental contaminants, Trends Environ. Anal. Chem. 2 (2014) 25–32. [12] J. Chouler, M.D. Lorenzo, Water quality monitoring in developing countries: can microbial fuel cells be the answer, Biosensors 5 (2015) 450–470. [13] F. Amaro, A.P. Turkewitz, A. Martin-Gonzalez, J.C. Gutierrez, Whole-cell biosensors for detection of heavy metal ions in environmental samples based on metallothionein promoters from Tetrahymena thermophila, Microb. Biotechnol. 4 (2011) 513–522. [14] A. Bollman, N.P. Revsbech, An NH4+ biosensor based on ammonia oxidising bacteria for use under anoxic condition, Sensors Actuators B Chem. 105 (2005) 412–418. [15] N. Verma, A.K. Singh, Development of biological oxygen demand biosensor for monitoring the fermentation industry effluent, ISRN Biotechnol. 2013 (2013) 1–6. [16] B. Chocarro-Ruiz, A. Ferna´ndez-Gavela, S. Herranz, L.M. Lechuga, Nanophotonic label-free biosensors for environmental monitoring, Curr. Opin. Biotechnol. 45 (2017) 175–183. [17] B. Chocarro-Ruiz, S. Herranz, et al., Inferometric nanoimmunosensor for label-free and real-time monitoring of Irgarol 1051 in sea water, Biosens. Bioelectron. 117 (2018) 47–52. [18] V.-T. Nguyen, Y.S. Kwon, M.B. Gu, Aptamer-based environmental biosensors for small molecule contaminants, Curr. Opin. Biotechnol. 45 (2017) 15–23. [19] H.M. Chan, A database for environmental contaminants in traditional foods in northern and Arctic Canada: development and applications, Food Addit. Contam. 15 (1998) 127–134. [20] T. Chen, G. Cheng, S. Ahmed, Y. Wang, X. Wang, H. Hao, Z. Yuan, New methodologies in screening of antibiotic residues in animal-derived foods: biosensors, Talanta 175 (2017) 435–442. [21] P.J. Vikesl, K.R. Wigginton, Nanomaterial enabled biosensors for pathogen monitoring, Environ. Sci. Technol. 44 (2010) 3656–3669. [22] V. Dumont, A.C. Huet, I. Traynor, C. Elliott, P. Delahaut, A surface plasmon resonance biosensor assay for the simultaneous determination of thiamphenicol, florefenicol, orefenicol amine and chloramphenicol residues in shrimps, Anal. Chim. Acta 567 (2006) 179–183. [23] M. Saleem, Biosensors a promising future in measurement, IOP Conf. Ser. Mater. Sci. Eng 51 (2013). [24] P. Biswas, A.K. Karn, P. Balasubramanian, P.G. Kale, Biosensor for detection of dissolved chromium in potable water: a review, Biosens. Bioelectron. 94 (2017) 589–604. [25] A. Janshoff, K.P.S. Dancil, C. Steinem, D.P. Greiner, V.S.Y. Lin, C. Gurtner, K. Motesharei, M.J. Sailor, M.R. Ghadiri, Macroporous p-type silicon Fabry-Perot layers. Fabrication, characterization and applications in biosensing, J. Am. Chem. Soc. 120 (1998) 12108–12116. [26] M.B. de La Mora, M. Ocampo, R. Doti, J.E. Lugo, J. Faubert, Porous silicon biosensor, in: State of the Art in Biosensor, INTECH Open Access Publ, 2013, pp. 141–161.

91

92

Tools, techniques and protocols for monitoring environmental contaminants

[27] H. Liu, R. Ramnarayanan, B.E. Logan, Production of electricity during wastewater treatment using a single chamber microbial fuel cell, Environ. Sci. Technol. 38 (2004) 2281–2285. [28] D. Pant, A. Singh, G.V. Bogaert, S.I. Olsen, P.S. Nigam, L. Diels, K. Vanbroekhoven, Bioelectrochemical systems (BES) for sustainable energy production and product recovery from organic wastes and industrial wastewaters, RSC Adv. 2 (2012) 1248–1263. [29] T. Zhou, Microbial fuel-cell based biosensors for toxicity detection: a review, Sensors 17 (2017) 2230–2251. [30] J. Chouler, A.C. Izquierdo, S. Rehgaraj, J.L. Scott, M.D. Lorenzo, A screen-printed paper microbial fuel biosensor for detection of toxic compounds in water, Biosens. Bioelectron. 102 (2018) 49–56. [31] P. Tanikkul, N. Pisutpaisal, Membrane-less MFC based biosensor for monitoring wastewater quality, Int. J. Hydrogen Energ. 43 (2018) 483–489. [32] C.S. Kim, B.H. Choi, J.H. Seo, G. Lim, H.J. Cha, Mussel adhesive protein-based whole cell array biosensor for detection of organophosphorous compounds, Biosens. Bioelectron. 41 (2013) 199–204. [33] H.J. Shin, Agarose-gel-immobilised recombinant bacterial biosensors for simple and disposable on-site detection of phenolic compounds, Appl. Microbiol. Biotechnol. 93 (2012) 1895–1904. [34] M.B. Gu, P.S. Dhurjati, T.K. Van Dyk, R.A. LaRossa, A miniature bioreactor for sensing toxicity using recombinant bioluminescence E. coli cells, Biotechnol. Progress 12 (1996) 393–397. [35] H.J. Shin, Genetically engineered microbial biosensors for in situ monitoring of environmental pollution, Appl. Microbiol. Biotechnol. 89 (2011) 867–877. [36] L.H. Hansen, B. Ferrari, A.H. Sørensen, D. Veal, S.J. Sørensen, Detection of oxytetracycline production by Streptomyces rimosus in soil microcosms by combining whole-cell biosensors and flow cytometry, Appl. Environ. Microbiol. 67 (2001) 239–244. [37] J. Tr€ ogl, A. Chauhan, S. Ripp, A.C. Layton, G. Kuncova´, G.S. Sayler, Pseudomonas fluorescens HK44: lessons learned from a model whole-cell bioreporter with a broad application history, Sensors 12 (2012) 1544–1571. [38] G.I. Paton, G. Palmer, M. Burton, E.A.S. Rattray, S.P. McGrath, L.A. Glover, K. Killham, Development of an acute and chronic ecotoxicity assay using lux-marked Rhizobium leguminosarum biovar trifolii, Lett. Appl. Microbiol. 24 (1997) 296–300. [39] H. Hong, W. Park, TetR repressor-based bioreporters for the detection of doxycycline using Escherichia coli and Acinetobacter oleivorans, Appl. Microbiol. Biotechnol. 98 (2014) 5039–5050. [40] T.S. Moller, M. Overgard, S.S. Nielsen, V. Bortolaia, M.O. Sommer, Relation between tetR and tetA expression in tetracycline resistant Escherichia coli, BMC Microbiol. 16 (2016) 39. [41] A.O. Olaniran, R.M. Motebejane, B. Pillay, Bacterial biosensor for rapid and effective monitoring of biodegradation of organic pollutants in wastewater effluents, J. Environ. Monit. 10 (2008) 889–893. [42] T. Elad, R. Almog, S.Y. Kroll, K. Levkov, S. Melamad, Y.S. Diamand, S. Belkin, Monitoring of water toxicity by use of bioluminescent reporter bacterial biochips, Environ. Sci. Technol. 45 (2011) 8536–8544. [43] G.H. Xu, Y.K. Wang, G.P. Sheng, Y. Mu, H.Q. Yu, An MFC-based online monitoring and alert system for activated sludge process, Sci. Rep. 4 (2014) 6779. [44] A.O. Olaniran, L. Hiralal, B. Pillay, Whole-cell bacterial biosensors for rapid and effective monitoring of heavy metals and inorganic pollutants in waste water, J. Environ. Monit. 13 (2011) 2914–2920. [45] V.K. Nigam, P. Shukla, Enzyme based biosensor for detection of environmental pollutants: a review, J. Microbiol. Biotechnol. 25 (2015) 1773–1781. [46] G.A. Mostafa, Electrochemical biosensors for the detection of pesticides, Open Eletrochem. J. 2 (2010) 22–42. [47] C.C. Blanchard, G. Istamboulie, M. Bontoux, G. Plantard, V. Goetz, T. Noguer, Biosensor based realtime monitoring of paracetamol photocatalytic degradation, Chemosphere 131 (2015) 124–129. [48] F. Pfeiffer, G. Mayer, Selection and biosensor application of aptamers for small molecules, Front. Chem. 4 (2016) 1–21. [49] A. Hayat, J.L. Marty, Aptamer based electrochemical sensors for emerging environmental pollutants, Front. Chem. 2 (2014) 1–9. [50] L. Jia, M. Su, X. Wu, H. Sun, Rapid selective accelerated solvent extraction and simultaneous determination of herbicide atrazine and its metabolites in fruit by ultra high performance liquid chromatography, J. Sep. Sci. 39 (2016) 4512–4519.

Potential applications of advanced biosensor systems

[51] B. Strehlitz, C. Reinemann, S. Linkorn, R. Stoltenburg, Aptamers for pharmaceuticals and their application in environmental analytics, Bioanal. Rev. 4 (2012) 1–30. [52] A. Sett, S. Das, P. Sharma, U. Bora, Aptasensors in health, environment and food safety monitoring, Open J. Appl. Biosens. 1 (2012) 9–19. [53] W. Zhang, Q.X. Liu, Z.H. Guo, J.S. Lin, Practical application of aptamer-based biosensors in detection of low molecular weight pollutants in water sources, Molecules 23 (2018) 344. [54] R. Stoltenburg, N. Nikolaus, B. Strehlitz, Capture-SELEX: selection of DNA aptamers for aminoglycoside antibiotics, J. Anal. Methods Chem. 2012 (2012) 415697. [55] C. Reinemann, U.F. von Fritsch, S. Rudolph, B. Strehlitz, Generation and characterization of quinolonespecific DNA aptamers suitable for water monitoring, Biosens. Bioelectron. 77 (2016) 1039–1047. [56] C.I.L. Justino, A.C. Duarte, T.A.P. Rocha-Santos, Recent progress in biosensors for environmental monitoring: a review, Sensors 17 (2017) 2918. [57] N. Xia, Y. Zhang, K. Chang, X. Gai, Y. Jing, S. Li, L. Liu, G. Qu, Ferrocene-phenylalanine hydrogels for immobilization of acetylcholinesterase and detection of chlorpyrifos, J. Electroanal. Chem. 746 (2015) 68–74. [58] C. Perez-Gonzalez, D.A. Lafontaine, J.C. Penedo, Fluorescence-based strategies to investigate the structure and dynamics of aptamer-ligand complexes, Front. Chem. 4 (2016) 33. [59] J.H. An, J. Jang, A highly sensitive FET type aptasensor using flower-like MoS2 nanospheres for realtime detection of arsenic (III), Nanoscale 9 (2017) 7483–7492. [60] N. Nikolaus, B. Strehlitz, DNA-aptamers binding aminoglycoside antibiotics, Sensors 14 (2014) 3737–3755. [61] Z. Luo, Y. Wang, X. Lu, J. Chen, F. Wei, Z. Huang, C. Zhou, Y. Duan, Fluorescent aptasensor for antibiotic detection using magnetic bead composites coated with gold nanoparticles and a nicking enzyme, Anal. Chim. Acta 984 (2017) 177–184. [62] N. Yildirim, F. Long, M. He, H.-C. Shi, A.Z. Gu, A portable optic fiber aptasensor for sensitive, specific and rapid detection of bisphenol-A in water samples, Environ. Sci. Process Impact 16 (2014) 1379–1386. [63] S.U. Akki, C.J. Werth, S.K. Silverman, Selective aptamers for detection of estradiol and ethynylestradiol in natural waters, Environ. Sci. Technol. 49 (2015) 9905–9913. [64] L. Madianos, G. Tsekenis, E. Skotadis, L. Patsiouras, D. Tsoukalas, A highly sensitive impedimetric aptasensor for the selective detection of acetamiprid and atrazine based on microwires formed by platinum nanoparticles, Biosens. Bioelectron. 101 (2018) 268–274. [65] Y. Du, C. Chen, J. Yin, B. Li, M. Zhou, S. Dong, E. Wang, Solid-state probe based electrochemical aptasensor for cocaine: a potentially convenient, sensitive, repeatable, and integrated sensing platform for drugs, Anal. Chem. 82 (2010) 1556–1563. [66] A. Mokhtarzadeh, J. Ezzati Nazhad Dolatabadi, K. Abnous, M. de la Guardia, M. Ramezani, Nanomaterial-based cocaine aptasensors, Biosens. Bioelectron. 68 (2015) 95–106. [67] Z. Yang, M.A. d’Auriac, S. Goggins, B. Kasprzyk-Hordern, K.V. Thomas, C. G. Frost, P. Estrela, A novel DNA biosensor using a ferrocenyl intercalator applied to the potential detection of human population biomarkers in wastewater, Environ. Sci. Technol. 49 (2015) 5609–5617. [68] Z. Yang, E. Castrignano`, P. Estrela, C.G. Frost, B. Kasprzyk-Hordern, Community sewage sensors towards evaluation of drug use trends: detection of cocaine in wastewater with DNA-directed immobilization aptamer sensors, Sci. Rep. 6 (2016) 21024. [69] J.J. Gau, E.H. Lan, B. Dunn, C.M. Ho, J.C. Woo, A MEMS based amperometric detector for E. coli bacteria using self-assembled monolayers, Biosens. Bioelectron. 16 (2001) 745–755. [70] S. Kurosawa, J.W. Park, H. Aizawa, S. Wakida, H. Tao, K. Ishihara, Quartz crystal microbalance immunosensors for environmental monitoring, Biosens. Bioelectron. 22 (2006) 473–481. [71] X.D. Hoa, A.G. Kirk, M. Tabrizian, Towards integrated and sensitive surface plasmon resonance biosensor: a review of recent progress, Biosens. Bioelectron. 23 (2007) 151–160. [72] C.G. Aljaro, X.M. Berbel, A.T. Jenkins, A.R. Blanch, F.X. Munoz, Surface plasmon resonance assay for real time monitoring of somatic coliphages in waste waters, Appl. Environ. Microbiol. 74 (2008) 4054–4058.

93

94

Tools, techniques and protocols for monitoring environmental contaminants

[73] N.M. Massad-Ivanir, G. Shtenberg, N. Raz, C. Gazenbeek, D. Budding, M.P. Bos, E. Segal, Porous silicon-based biosensors: towards real-time optical detection of target bacteria in the food industry, Sci. Rep. 6 (2016) 38099. [74] S. Leahy, Y. Lai, A cantilever biosensor exploiting electro kinetic capture to detect Escherichia coli in real time, Sensors Actuators B Chem. 238 (2017) 292–297. [75] K. Bernhard, C. Stahl, R. Martens, H.R. Kohler, R. Triebskorn, M. Scheurer, M. Frey, Two novel real-time cell-based assays quantify beta-blocker and NSAID specific effects in effluents of municipal waste-water treatment plants, Water Res. 115 (2017) 74–83. [76] T. Yamashita, N. Ookawa, M. Ishida, H. Kanamori, H. Sasaki, Y. Katayose, H. Yokoyama, A novel open-type biosensor for the in-situ monitoring of biochemical oxygen demand in an aerobic environment, Sci. Rep. 6 (2016) 38552. [77] H. Wang, H. Luo, P.H. Fallgren, S. Jin, Z.J. Ren, Bioelectrochemical system platform for sustainable environmental remediation and energy generation, Biotechnol. Adv. 33 (2015) 317–334. [78] S. Jouanneau, L. Recoules, M.J. Durand, A. Boukabache, V. Picot, Y. Primault, A. Lakel, M. Sengelin, B. Barillon, G. Thouand, Methods for assessing biochemical oxygen demand (BOD): a review, Water Res. 49 (2014) 62–82. [79] G.J. Chee, Y. Nomura, I. Karube, Biosensor for the estimation of low biochemical oxygen demand, Anal. Chim. Acta 379 (1999) 185–191. [80] B.H. Kim, I.S. Chang, G.C. Gil, H.S. Park, H.J. Kim, Novel BOD (biological oxygen demand) sensor using mediator-less microbial fuel cell, Biotechnol. Lett. 25 (2003) 541–545.