Chapter 17

Nanosensors for water safety

Mohammad Ramezani1,2, Seyed Mohammad Taghdisi3, Rezvan Yazdian-Robati4, Fatemeh Oroojalian5,6,Khalil Abnous1,7 and Mona Alibolandi1

1Pharmaceutical Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran, 2Department of

Pharmaceutical Biotechnology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran, 3Targeted Drug Delivery Research

Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran, 4Molecular and Cell Biology Research

Center, Faculty of Medicine, Mazandaran University of Medical Sciences, Sari, Iran, 5Department of Advanced Sciences and Technologies, School of

Medicine, North Khorasan University of Medical Sciences, Bojnurd, Iran, 6Natural Products and Medicinal Plants Research Center, North Khorasan

University of Medical Sciences, Bojnurd, Iran, 7Department of Medicinal Chemistry, School of Pharmacy, Mashhad University of Medical Sciences,

Mashhad, Iran

Chapter Outline

17.1 Introduction 285

17.2 Applications of nanobiosensors in water safety 286

17.3 Nanosensors for the detection of heavy metals in water 286

17.3.1 Electrochemical nanosensors for the detection of

heavy metals in water 286

17.3.2 Optical nanosensors for the detection of heavy

metals in water 288

17.4 Nanobiosensors for the detection of infectious agents

(virus, bacteria, etc.) in water 291

17.4.1 Electrochemical nanobiosensors for the detection

of infectious agents in water 291

17.4.2 Optical nanobiosensors for the detection of

infectious agents in water 292

17.5 Nanosensors for the detection of chemical contaminants

(including toxins, antibiotics, and insecticides) in water 294

17.5.1 Electrochemical nanosensors for the detection of

chemical contaminants in water 294

17.5.2 Optical nanosensors for the detection of chemical

contaminants in water 295

17.6 Conclusion 298

References 298

17.1 Introduction

Nowadays, rapid and accurate monitoring of pollutant contamination in water is increasing to safeguard the supply of

contaminant-free potable water to the public [1]. Since waterborne diseases pose major threats to global health, it is of

great significance to develop accurate, simple, and fast-detection analytical techniques to monitor water resources [2].

Drinkable water should be free from various contaminants, and its quality should meet the applied national

potable water standards [3]. Wastewater consists of different harmful materials including microorganisms, nonessential

heavy metals, drugs, and other toxic pollutants that have been adversely produced through different channels including

domestic, industrial, commercial, and agricultural activities and released water [4]. Development of different types of

biosensors, such as immunosensors or aptasensors, as impressive alternatives for conventional sensing systems is in

response to increasing demand for fast, highly sensitive, and selective methods for detecting and monitoring of water

pollutants [5,6]. Over the past few decades a wide range of rapid, highly sensitive and specific, and robust biosensors

have been introduced for the detection of the aforementioned contaminants in water. The first biosensor was reported

by Leland C. Clark in 1956 for the detection of glucose levels in serum samples using a membrane-bound biologically

sensitive element [7]. Biosensors and affinity sensor devices are compact analytical instruments, which basically contain

two important functional parts: sensing element and transducer element, which can be employed to detect and measure

a broad spectrum of target analytes in simple or complex sample matrixes by transforming the recognition of targets

into physicochemically detectable optical, electronic, or magnetic signals [8]. Considering the two main biorecognition

elements (aptamer or antibody), different types of biosensors are categorized in this chapter into electrochemical and

285Nanosensors for Smart Cities. DOI: https://doi.org/10.1016/B978-0-12-819870-4.00016-5

© 2020 Elsevier Inc. All rights reserved.

optical including colorimetric, fluorescence, and surface plasmon resonance (SPR) based on their transducing

mechanisms. Aptamers, known as chemical antibodies, are short, artificial single-stranded nucleic acid sequences or

peptide molecules, which specifically identify a wide variety of targets including small molecules, proteins, toxins,

virus-infected cells, and cancer cells with remarkable affinity and selectivity. Aptamers are classically identified and

separated with specific properties through an in vitro technology called systematic evolution of ligands by exponential

enrichment (SELEX) through a large DNA or RNA library containing up to 1015 different sequences [9,10]. Aptamers

offer a set of unique properties as a rival of antibodies in terms of high stability, ease of synthesis, cost-effectiveness,

lack of immunogenicity, low molecular weight, and fast refolding to its original structure, no limitations on their tar-

gets, and finally high resistance against denaturation. Moreover, aptamers can be simply modified with different tags

without affecting their affinities in order to label them with fluorophores as well as quenchers to produce different

aptamer-based biosensors [11]. Aptasensors are a kind of biosensor with aptamer as the recognition element to capture

the target. The integration of aptamers and various nanomaterials has been investigated broadly to develop novel, selec-

tive, and sensitive sensing methods [12]. Immunosensors or antibody-based biosensors are a class of biosensors exploit-

ing antibodies as the biological recognition element. These types of biosensors act based on the fact that specific

antibodies have high affinity toward their corresponding antigens in which the transducer detects, either directly or

indirectly, the immunochemical reaction and converts it into a measurable signal [13]. This chapter presents a general

summary on both aptamer- and antibody-based biosensors for monitoring of three main categories of pollutants in

wastewater (organic materials, heavy metals, and microorganisms) with a special focus on the effect of nanotechnology

in this area.

17.2 Applications of nanobiosensors in water safety

Progress in the field of nanoscience has introduced various emerging nanomaterials with unique properties, which have

been widely applied for the development of different sensors named “nanobiosensors” [14]. The unique characteristics

of nanomaterials in combination with suitable sensing ligands propose unique opportunities to develop ultrasensitive

detection approaches.

17.3 Nanosensors for the detection of heavy metals in water

Heavy metals are discharged into water in many developing countries through natural process, industrial, chemical, and

agricultural activities, mining, nuclear wastes, manufacturing processes, and other anthropogenic activities [15].

Although some metals (Co, Cu, Fe, Mn, Mo, Ni, Se, and Zn) are necessary for biochemical reactions in living organ-

isms, excess amounts of these heavy metals can have negative effects on human health. Lead (Pb), chromium (Cr), cad-

mium (Cd), mercury (Hg), arsenic (As), and antimony (Sb) are nonessential heavy metals that are highly toxic,

nonbiodegradable, universally distributed in nature, carcinogenic even at a trace level, which may lead to serious health

concerns by generating free radicals [16]. Several studies have noted various chronic and subchronic effects of these

heavy metals in drinking water. To lessen the effects of heavy metals on human health, regulatory agencies have

suggested the maximum allowable limits of few heavy metals in drinking water [17]. Herein, we report several nanobio-

sensors for monitoring of heavy metals in water.

17.3.1 Electrochemical nanosensors for the detection of heavy metals in water

Despite the accuracy of conventional analytical methods, such as atomic absorption spectroscopy, ultraviolet�visible

spectroscopy, and chromatography for the detection of heavy metals, their uses are limited due to practical disadvan-

tages such as complexity, time-consuming procedure, high cost, and need for preconcentration procedures. Therefore

developing simple and sensitive techniques for the determination of heavy metal ions in water has received considerable

attention. Electrochemical biosensors can address the aforementioned issues due to their advantages such as simplicity,

fast response, portability, easy operation, and low production cost. This part highlights electrochemical nanosensors for

the detection of heavy metals in water [6].

17.3.1.1 Aptamer-based electrochemical nanosensors for the detection of heavy metals in water

Application of aptamers in construction of electrochemical biosensors has opened a new field for highly sensitive and

selective determination of heavy metals in water. In electrochemical aptasensors, aptamer as a recognition element

selectively reacts with the target analyte [6], leading to generation of an electrical signal that is proportionally related to

286 PART | III Nanosensors for healthy cities

the concentration of analyte. Compared to the optical sensors, electrochemical aptasensors detect lower concentration of

target analyte. In addition, electrochemical techniques are label-free, which can decrease both cost and limit of detection

(LOD) of electrochemical aptasenors [18�20]. Application of nanomaterials in electrochemical biosensors can improve

the electron conductivity, thereby increasing the sensitivity of sensors. Being benefitted from interactions between oligo-

nucleotides and metal ions, aptamers are considered the powerful recognition elements in the construction of electro-

chemical aptasensors for the detection of heavy metals in water [21]. Pb21 is one of the most toxic heavy metals, and

excessive exposure to lead ion may increase incidence of numerous health problems especially brain damage and kidney

failure in both humans and animals. Moreover, long-term exposure to Pb21 may result in serious disorders such as ane-

mia, memory deterioration, cardiovascular disease, and even death. Thus detection and efficient separation of Pb21 from

water is of utmost value. In this regard an electrochemical aptasensor was fabricated by our team for the selective and

ultrasensitive detection of Pb21 in tap water with detection limit of 326 pM. The designed aptasensor was based on gold

nanoparticles (AuNPs), hairpin structure of thiolated complementary strand of aptamer and thionine as a redox label. The

incorporation of AuNPs in electrochemical aptasensors has the potential to significantly enhance electrochemical signal

based on unique features of AuNPs such as their large surface area, high electron conductivity, and high redox activity

[22]. In this aptasensor, in the presence of target, the complementary strand forms a hairpin structure, resulting in a weak

electrochemical signal. In the absence of Pb21, thionine�AuNPs complex is conjugated to the complementary strand on

the surface of the electrode, leading to a strong electrochemical signal. The aptasensor response for Pb21 detection was

in the linear range from 0.6 to 50 nM with the detection limit of 326 pM (Fig. 17.1) [23].

In another study, AuNPs were used to enhance the surface area in order to immobilize a maximum number of apta-

mers on the surface of electrode and thus to improve the electrochemical signal for the ultrasensitive detection of cop-

per (Cu21) in lake samples. In this aptasensor, two partial complementary DNA strands (DNA1 as sensing strand and

ferrocene (Fc)-labeled DNA2 as anchoring strand) were attached to the AuNPs and immobilized on the surface of gold

electrode via �SH of 4-aminothiophenol. In the presence of Cu21, self-cleavage happens at two different locations of

the DNA1 (aptamer) producing three fragments, leading to Fc as redox tag reaches onto the surface of electrode and

produces a very strong redox signal. Using square-wave voltammogram (SWV), LOD of 0.1 pM with 94.7% and 108%

recovery for the spiked samples could be achieved using this aptasensor [24].

FIGURE 17.1 Schematic illustration of the electrochemical aptasensor for the detection of Pb21 based on AuNPs and thionine. Aptasensor function

in the absence (A) and presence of target (B). AuNPs, Gold nanoparticles. Adapted with permission from S.M. Taghdisi, N.M. Danesh, P. Lavaee, M.

Ramezani, K. Abnous, An electrochemical aptasensor based on gold nanoparticles, thionine and hairpin structure of complementary strand of aptamer

for ultrasensitive detection of lead, Sens. Actuators, B: Chem. 234 (2016) 462�469. Copyright 2016 Elsevier.

Nanosensors for water safety Chapter | 17 287

17.3.1.2 Other electrochemical nanosensors for the detection of As(III) in water

In order to detect the presence of heavy metals, various nanomaterials have been applied to modify the working electro-

des of electrochemical sensors. Among different nanomaterials, carbon nanotubes (CNTs) with advantages of biocom-

patibility, high surface area coverage, and fast heterogeneous electron transfer have been extensively applied to develop

nanobiosensors in the last decade [6,25]. In a study, multiwalled CNTs (MWCNTs) were decorated with AuNPs (hybrid

composite) as sensing materials and applied for the electrochemical sensing of As(III) in water. Arsenic is a highly

toxic element, which is a relatively widespread water pollutant. Au-CNT was immobilized on a glassy carbon (GC)

electrode as a working electrode. The benefit of Au-CNT electrode is the high surface area in comparison to Au depos-

ited on a normal size GC electrode. An LOD of 0.1 μg/L was obtained using SWV as the analytical technique in an

optimized condition with a deposition time of 120 seconds [26].

17.3.2 Optical nanosensors for the detection of heavy metals in water

Optical sensors are a broad type of analytical methods for detecting light intensity. Unique features of optical sensors,

including high sensitivity, fast response, and simple use, lead to extensive application of optical aptasensors for moni-

toring pollutants in water. Moreover, the engineering of nanomaterials for application in selective sensing platform has

emerged as one of the most powerful options for the improvement of assays based on optical detection. Colorimetric,

fluorescent, and surface-enhanced Raman scattering (SERS) are three main types of optical aptasensors, which have

been used to develop aptasensors for pollutant detection in water [27].

17.3.2.1 Aptamer-based optical nanosensors for the detection of heavy metals in water

Aptamer-based colorimetric nanosensors

Among different analytical approaches, colorimetric sensors using various smart materials have been extensively used

because of their low cost, simplicity, and easy color change read out by the naked eye without expensive or sophisti-

cated instrumentation [28]. Different smart materials, including nanoparticles, magnetic nanoparticles (MNPs), CNTs,

graphene oxides, and conjugated polymers with robust physical or chemical properties, have been employed to trans-

form the detection events into color [29�31]. In recent years, AuNPs have been broadly exploited for the fabrication of

colorimetric aptasensors. AuNPs display unique optical features, such as high extinction coefficients at the visible

wavelength and potent localized SPR (LSPR), which improve the sensitivity of colorimetric assays [32,33]. AuNPs of

around 13 nm in diameter possess a maximum absorbance at 520 nm in dispersion state while the color of the solution

is red. Upon aggregation of AuNPs the absorbance shifts to around 650 nm and a purple color is observed [33].

Exploiting this phenomenon of AuNPs, our team fabricated a colorimetric aptasensor for the sensitive and selective

detection of Pb21 in tap water with a detection limit of 2.4 nM. This sensing platform was based on exonuclease I (Exo

I), dsDNA (aptamer/complementary strand of aptamer), and AuNPs as transducer elements. Exo I is an enzyme that

selectively digests the 30 end of ssDNAs. One of the main great advantages of this aptasensor is the protection of

AuNPs against salt-induced aggregation by dsDNA structure instead of ssDNA, improving the sensitivity of the assay.

Modifying the surface of AuNPs with dsDNA avoids the aggregation of AuNPs at high salt concentrations. In the

absence of lead, upon addition of Exo I, dsDNA remains intact on the surface of the AuNPs and protects the AuNPs

from salt-induced aggregation. Once Pb21 is introduced, the aptamer leaves the surface of AuNPs due to its better affin-

ity for Pb21 compared to its complementary strand. Therefore the single-stranded complementary strand is digested by

Exo I; and following the addition of NaCl, AuNPs are aggregated leading to observation of purple/blue color and

change in the absorbance spectra [34]. Using polyethylenimine (PEI)-induced aggregation of AuNPs, a colorimetric

aptasensor was presented for Pb21 detection in tap water with an LOD of 0.7 nM by our team [35]. In this sensing plat-

form, PEI as a cationic polymer was used instead of salt because AuNP-based analytical methods that use salt-induced

aggregation usually show higher detection limit [36]. Unmodified AuNPs have high catalytic activity toward peroxidase

substrates. AuNPs in the presence of H2O2 can catalyze peroxidase substrates such as 3,30,5,50-tetramethylbenzidine sul-

fate (TMB) accompanied with color change [37]. Using this principle, a colorimetric triple-helix molecular switch

(THMS) aptasensor was developed for the detection of Pb21 in water with detection limit of 708 pM [38]. THMS pos-

sesses unique characteristics, such as high sensitivity and stability as well as maintaining the selectivity of the original

aptamer, over known double-helix DNA molecular switches and molecular beacon-based signaling aptamers [39].

THMS contains a label-free target selective aptamer sequence with two arm segments and an oligonucleotide as a signal

transduction probe (STP), which is trapped between two arm segments. In the absence of target, THMS is stable and

intact thus could not bind to AuNPs owing to its very rigid structure. Therefore AuNPs show their peroxidase-like

288 PART | III Nanosensors for healthy cities

activity and oxidize the colorless TMB into a purplish-blue product. However, in the presence of Pb21, THMS is disas-

sembled, and STP is released, leading to adsorption of the STP as an ssDNA on the surface of AuNPs. Thus AuNPs

lose their catalytic activity and the solution remains colorless [40].

Aptamer-based fluorescent nanosensors for the detection of heavy metals in water

Fluorometric sensing, as one of the most prevalent optical techniques, has wide applications in the construction of apta-

sensors due to its flexibility in quantitative analysis, high sensitivity and high efficiency, and wide response range. A

number of fluorophores and quenchers have been extensively investigated in various fluorescent aptasensors, including

quantum dots (QDs), upconversion nanoparticles (UCNPs), CNTs, and nanoclusters (NCs), which can easily be conju-

gated with aptamers [8]. Based on the superquenching capability of CNTs and unique properties of ATTO 647N as a

fluorophore, a fluorescent aptasensor was employed for the detection of Pb21 in tap water by our group. In the absence

of Pb21, ATTO 647N-labeled aptamer was wrapped around single-walled CNTs (SWCNTs) by π�π stacking interac-

tions between the DNA bases of the aptamer and SWCNTs leading to the fluorescence quenching of ATTO 647N-

labeled aptamer. In the presence of target, ATTO 647N-labeled aptamer left the SWCNTs and bound with Pb21. Pb21

induced the conformational change of aptamer forming a G-quadruplex aptamer/Pb21 complex. Thus fluorescence

emission was turned on. This simple and sensitive aptasensor exhibited high selectivity toward Pb21with an LOD of

0.42 nM (Fig. 17.2) [41].

Based on the application of silica nanoparticles (SNPs) coated with streptavidin (SNPs-streptavidin) as solid supports

and fluorescence amplifiers and target-induced conformational change of complementary strand of aptamer 1 (CS1), our

team developed a fluorescent aptasensor for the determination of As(III) in tap water. Two complementary strands of

aptamer were modified with biotin and fluorescein (FAM) (CS1) and black hole quencher 1 (BHQ1, CS2). In this apta-

sensor, BHQ1 was used as an acceptor dye and FAM as a fluorophore. CS1 was attached on the surface of SNPs-

streptavidin. Then, CS2 was in close proximity of CS1 using the aptamer as a linker. In the presence of target, aptamers

interacted with As(III) and were released from SNPs-streptavidin. Consequently, CS2 was separated from SNPs-

streptavidin and CS1 formed a hairpin structure on the surface of SNPs-streptavidin, which brought FAM close to SNPs-

streptavidin, leading to a strong fluorescence signal. Without introduction of As(III), aptamer was hybridized with CS1

and CS2, and a weak fluorescence signal was detected. This aptasensor showed a wide linear range between 2 and

500 nM and was successfully applied to detect As(III) in tap water with detection limit of 0.46 nM (Fig. 17.3) [42].

Aptamer-based surface plasmon resonance nanosensor for the detection of As(III) in water

SPR is an optical phenomenon that happens when an incident beam of polarized light beats a prism covered by a thin

metal film. Incident light photons are absorbed by free electrons at the surface of the biochip thereby changing the sur-

face plasmon waves. Any alteration in the metal surface, including interactions between the target and immobilized

probe molecules, changes the SPR, which can be measured. The most important advantage of SPR method is that it is a

FIGURE 17.2 Schematic diagram

of the sensing platform for the detec-

tion of Pb21 based on CNTs and

ATTO 647N-labeled aptamer. CNTs,

Carbon nanotubes. Adapted with

permission from S.M. Taghdisi,

S.S. Emrani, K. Tabrizian, M.

Ramezani, K. Abnous, A.S. Emrani,

Ultrasensitive detection of lead(II)

based on fluorescent aptamer-

functionalized carbon nanotubes,

Environ. Toxicol. Pharmacol. 37

(3) (2014) 1236�1242. Copyright

2014 Elsevier.

Nanosensors for water safety Chapter | 17 289

label-free sensing technique. However, there are some drawbacks to using the conventional SPR and LSPR biosensors,

which include the requirement of bulky and expensive optical equipment and data analysis device [43]. Combining

AuNPs with cetyltrimethylammonium bromide (CTAB) as a binder provided a new way to design a novel and facile

analytical platform to achieve a sensitive SPR aptasensor for measuring target molecules at trace levels. Nguyen et al.

presented a colorimetric aptasensor for the detection of As(III) in water using synergistic molecular assembly of apta-

mer and CTAB on AuNPs. The sensing platform displayed an LOD of 16.9 ppb and a linear range between 1 and

100 ppb using SPR. Upon binding of As(III) ion to the aptamer�AuNPs, in the presence of CTAB, AuNPs were aggre-

gated and a red-shift in the SPR band and a visual change in the color occurred. Other chemical species did not prompt

these changes at all, which is one of the advantages of the designed aptasensor. The presented aptasensor is highly spe-

cific for As(III) sensing [44].

Other optical sensors for the detection of heavy metals in water

Presence of mercury ion (Hg) in drinking water mostly originates from packaging of bottled water, industrial activities,

corrosion of pipe materials and coatings, amalgam in teeth, and powder laundry detergents. In addition, Hg ions can be

deposited in the soil around the reservoir and then enter the water [17]. A novel visual sensor was designed by Li et al.

using unmodified Au@Ag core�shell NPs with good monodispersity based on a redox reaction between Ag�shell and

Hg21. In the presence of Hg21 in water sample, Ag�shell reduced Hg21 into Hg(0). The reduced Hg(0) was deposited

on the surface of Au core to form Au�Hg alloy and thus induced NP aggregation. Therefore the color solution changed

from bright yellow to purplish red, and the SPR spectra of Au@Ag core�shell NPs were red-shifted. The visual sensor

could selectively detect Hg21 as low as 0.4 μM with the naked eye and 5.0 nM by UV�Vis spectral analysis methods.

The proposed visual sensor was successfully applied for the detection of Hg21 in tap and lake water samples [45].

Semiconductor QDs (with a diameter of 2�10 nm) are nanoscale semiconducting crystals that offer unique optical and

electrical features. Application of QDs in different biosensors, especially aptasensors, has attracted considerable interest

due to the excellent properties of these nanomaterials including wide absorption range, narrow and symmetric size-

tunable photoluminescent emission spectra, broad excitation range, high quantum yields, multiplexed staining, long flo-

rescent lifetime, and great resistance to photo bleaching [46]. Growing interest for chemical and biological detection

using QD-based sensors led to the design of several biosensors, for instance, Hai et al. proposed a “signal-on” sensing

strategy for the detection of lead ions in water samples with great application value. They used graphene/AuNPs elec-

trode and CdTe QDs as electrochemical luminescent markers to produce an electrochemiluminescence (ECL) aptasen-

sor. When Pb21 was present in the test solution, the aptamer configuration changed and formed a G-quadruplex and

was covalently linked to a carboxyl group on the surface of the CdTe QDs. Therefore the QDs could be immobilized

FIGURE 17.3 Schematic illustration of the optical nanobiosensor for As(III) detection based on SNPs-streptavidin, As(III) aptamer and target-

induced conformational change of CS1. CS1, Complementary strand of aptamer 1; SNPs, silica nanoparticles. Aptasensor function in the absence (A)

and presence of target (B). Adapted with permission from S.M. Taghdisi, N.M. Danesh, M. Ramezani, A.S. Emrani, K. Abnous, A simple and rapid

fluorescent aptasensor for ultrasensitive detection of arsenic based on target-induced conformational change of complementary strand of aptamer and

silica nanoparticles, Sens. Actuators, B: Chem. 256 (2018) 472�478. Copyright 2018 Elsevier.

290 PART | III Nanosensors for healthy cities

on the surface of electrode and subsequently, strong ECL was detected. This aptasensor had a good linear relationship

with respect to the concentration of Pb21 and could detect Pb21 as low as 3.8 pM [47].

17.3.2.2 Antibody-based optical nanobiosensor for the detection of Pb21 in water

Lead ion in drinking water was also detected using lateral flow strip. A simple lateral flow test contains four sections

(sample pad, conjugate pad, nitrocellulose membrane, and absorbent pad) attached onto a sheet of plastic backing

orderly. Choosing the selective format depends on the kind of target analytes [48]. A strip immunosensor was devel-

oped by Kuang et al. for the detection of Pb21 in drinking water. The immunosensor contained the respective monoclo-

nal antibodies immobilized on two heterogeneously sized AuNPs as the detection reagents. The nitrocellulose

membrane-based immunostrip consisted of a test zone containing Pb21-ITCBE conjugated to bovine serum albumin

(BSA) and a control line with goat antimouse immunoglobulin G (IgG). In the strip, colored lines were formed on the

nitrocellulose membrane by using red AuNPs coated with anti-Pb(II)-ITCBE antibody and goat antimouse IgG as the

signaling reagents for easy visual detection of Pb21. The color intensity was reduced as the concentration of the target

analyte increased [49]. The visual LOD for qualitative detection of the amplified method was found to be 2 ng/mL and

the LOD for semiquantitative detection was as low as 0.19 ng/mL using a scanning reader that was four times more sen-

sitive than the conventional lateral flow strip.

17.4 Nanobiosensors for the detection of infectious agents (virus, bacteria, etc.)in water

17.4.1 Electrochemical nanobiosensors for the detection of infectious agents in water

In this section, we will focus on the uses of different nanomaterials for the fabrication of biosensors for infectious

agents.

17.4.1.1 Aptamer-based electrochemical nanobiosensor for the detection of Staphylococcusaureus in water

Silver nanoparticles (AgNPs) are clusters of silver atoms, normally within a size range of ,100 nm at one dimension.

They are attracting interest as suitable NPs for bioapplications [50]. The main feature of AgNPs is their ultrasmall size,

leading to considerable increase in the ratio of surface area to volume, and thus a large number of atoms are readily

available for reaction. AgNPs can be applied in many fields, such as molecular diagnostics, therapies, and in devices

that are utilized in different medical procedures [51].

A sensitive and highly selective dual aptamer�based sandwich aptasensor was introduced for the detection of

Staphylococcus aureus in tap and river water by measuring the electrochemical signal of AgNPs [52]. In this platform,

as shown in Fig. 17.4, a biotin-labeled aptamer 1 specific to S. aureus was immobilized on streptavidin-coated magnetic

FIGURE 17.4 Schematic representation of the electrochemical sandwich aptasensor for the detection of Staphylococcus aureus using Apt-MBNPs as

capture probes, and AgNPs act as a reporter. Adapted with permission from A. Abbaspour, F. Norouz-Sarvestani, A. Noori, N. Soltani, Aptamer-

conjugated silver nanoparticles for electrochemical dual-aptamer-based sandwich detection of Staphylococcus aureus, Biosens. Bioelectron. 68 (2015)

149�155. Copyright 2015 Elsevier.

Nanosensors for water safety Chapter | 17 291

beads (Apt-MBNPs), which served as capture probes. Thiolated aptamer 2 (with the same sequence) was conjugated to

silver nanoparticles (Apt-AgNPs), which was employed as reporter probe. Upon interaction of aptamer 1 with S. aureus,

the Apt-AgNPs were immobilized on magnetic beads. Then, magnetic beads containing the affinity complex were sepa-

rated, and electrochemical signal of HNO3-dissolved AgNPs was recorded using anodic stripping voltammetry (ASV)

on the surface of an electrode. External magnetic separation of target bacteria and signal amplification by AgNPs low-

ered the detection limit down to 1 cfu/mL. Moreover, the proposed aptasensor exhibited a linear response to S. aureus

concentration over an extended dynamic range of 10�13 106 cfu/mL.

17.4.1.2 Genosensor-based electrochemical nanobiosensor for the detection of Aeromonas inwater

The genus Aeromonas bacteria has been linked with acute gastroenteritis infection and life-threatening diseases such as

prostatitis, septicemia, hemolytic�uremic syndrome, and meningitis [53]. So, there is an urgent need for sensitive and

selective analytical methods for the detection of Aeromonas. Fernandes et al. proposed an electrochemical nanosensor

to identify Aeromonas in tap water [54]. According to this report, the aptasensor improved bacterial sensing using

MWCNT�chitosan�bismuth complex and lead sulfide nanoparticles (PbNPs). Here, signaling DNA (sz-DNA) probe

was attached on PbNPs. Thiol-modified sequence was utilized as fixing probe DNA (fDNA). After hybridization of tar-

get Aeromonas DNA (tDNA) sequence with these two probes, the hybridized structure was dissolved in nitric acid to

release the lead ion from sz-DNA. The released lead ions were electrodeposited on the MWCNT�Chi�Bi coated on

glass carbon electrode (GCE) surface, and the interaction of bacterium DNA and probe DNA was recorded using differ-

ential pulse voltammetry (DPV). This sensing platform could detect lower than 100 cfu/mL of Aeromonas in spiked tap

water.

17.4.1.3 Antibody-based electrochemical nanobiosensors for the detection of infectious agentsin water

Escherichia coli is a prevalent intestinal bacterium of animals and human. Some strains of E. coli can make severe

bloody diarrhea, vomiting, and urinary tract infections [55]. Based on World Health Organization (WHO) guidelines,

E. coli is as an indicator for drinkable water [56]. An electrochemical immunoassay was developed for the fast determi-

nation of E. coli in surface water using ASV based on Cu@Au nanoparticles as antibody labels [57]. In this report the

immunosensor was fabricated by immobilization of E. coli on polystyrene-modified ITO (indium-doped tin oxide) chip.

After that, Cu@Au-labeled antibody reacted with E. coli. Then, Cu@Au NPs were dissolved by oxidation to the metal

ionic forms, and the isolated Cu21 ions were detected by ASV. The amount of detected Cu21 was directly proportional

to the amount of pathogenic E. coli in sample. This technique could detect E. coli with a detection limit of 3 cfu/

10 mL. For larger targets, such as marine pathogenic bacterium, ECL blocking assays are appropriate. A good example

using this technique was presented by Sha et al. They fabricated a label-free ECL immunosensor for ultrasensitive and

rapid detection of Vibrio parahaemolyticus in seawaters [58]. V. parahaemolyticus is a Gram-negative bacterium found

in marine and coastal water. In this immunosensor the magnetic Fe3O4/GO nanocomposite was activated using N-(3-

Dimethylaminopropyl)-N0-ethylcarbodiimide hydrochloride (EDC)/N-Hydroxysuccinimide (NHS) and iso-luminol

(ABEI), and V. parahaemolyticus antibody was covalently grafted. The ECL signal was reduced with increasing

amounts of V. parahaemolyticus in the range of 10�108 cfu/mL with LOD of 5 cfu/mL in seawater samples. Simple

instrumentation, good stability, and high sensitivity and specificity are the main advantages of this designed

immunosensor.

17.4.2 Optical nanobiosensors for the detection of infectious agents in water

17.4.2.1 Aptamer-based optical nanobiosensors for the detection of infectious agents in water

Aptamer-based colorimetric nanobiosensors for the detection of infectious agents in water

MNPs have been recently exploited in bioanalysis systems for the separation and signal production. Apart from large sur-

face area and good biocompatibility, the remarkable advantage of MNPs is that the location and transport can be con-

trolled using an external magnetic field. Wu et al. took advantage of MNPs and AuNPs to detect V. parahaemolyticus in

water samples [59]. MNPs were conjugated with specific biotin-labeled aptamers against target and served as capture

probe. Also, AuNPs were modified with horseradish peroxidase (HRP) and thiolated aptamer, which was employed as

the signal probe. Through specific recognition of target by aptamers, MNPs�aptamer�target�aptamer�HRP�AuNPs

292 PART | III Nanosensors for healthy cities

sandwich complex was formed. Upon additions of TMB and H2O2 into the reaction, HRP molecules catalyzed the

enzyme substrate and generated an optical signal. This analytical system provided increased signal amplification by sim-

ple concentration of target molecules using magnetic beads, which improved the specificity of the biosensor by elimina-

tion of various interfering elements in biological samples [60]. Using this assay, a good linear relationship with V.

parahaemolyticus in the concentration range from 10 to 106 cfu/mL was obtained, and the detection limit was found to

be 10 cfu/mL.

Aptamer-based fluorescent nanobiosensors for the detection of infectious agents in water

In an investigation developed by Wang’s group, carboxyl-modified carbon dots (CDs) by hydrothermal method with

good biocompatibility and high fluorescence quantum yield were synthesized and served as the fluorophore for the

detection of Salmonella typhimurium. S. typhimurium is a pathogenic Gram-negative bacterium, which can be found in

water samples. It can cause gastroenteritis in humans and even death. In this fluorescence aptasensor, carboxyl-

modified CDs were attached to amino groups of aptamers selective for S. typhimurium. In the presence of bacteria,

CDs�Apt complexes attached to S. typhimurium, and a strong fluorescence intensity was observed, which was related

to the concentration of S. typhimurium in the linear range of 103�105 cfu/mL, and the detection limit was 50 cfu/mL in

tap water [61].

In another study, Salmonella paratyphi A could be detected using SWCNTs wrapped with a DNAzyme-labeled apta-

mer conjugate (probe) with the detection limit of 104 cfu/mL and a linear range of 104�108 cfu/mL in city water sam-

ples. The DNAzyme sequence was utilized as a label to strengthen detection signals. In the presence of the target

bacterium and hemin, they were selectively attached to the probe, leading to the aptamer sequence becoming far away

from SWCNTs, and a self-assembly of hemin/G-quadruplex HRP mimicking DNAzyme was formed. This self-

assembled DNAzyme led to the generation of chemiluminescence (λ5 420 nm) by the oxidation of luminol using

H2O2 [62].

17.4.2.2 Antibody-based optical nanobiosensors for the detection of infectious agents in water

Antibody-based fluorescent nanobiosensors for the detection of infectious agents in water

A nanobiosensor using a fluorescent dye and an anti-E. coli antibody-anchored silver�silica core�shell nanoparticles

was reported for rapid and sensitive detection of E. coli in water samples where E. coli could be quantitatively mea-

sured in the range of 10�100 cfu/mL. In this immunosensor, Ag@SNPs served as a carrier for a fluorescent label. The

developed dual-labeled core shell�based optical immunosensor was able to efficiently detect the presence of E. coli as

low as 5 cfu/mL within 60 minutes [63]. In an attempt to improve the performance of a fluorescent immunosensor using

QDs as a fluorescence label, Yang and Li immobilized biotin-labeled anti-Salmonella antibody onto a streptavidin-

coated QD for quantitative detection of S. typhimurium. At first, they separated the target from wash water using anti-

Salmonella antibody-coated magnetic beads and allowed them to react with secondary biotin-labeled anti-Salmonella

antibody. Measurement of the intensity of fluorescence generated by QDs provided a quantitative technique for S. typhi-

murium detection. The linear response between logarithm of S. typhimurium cell number and fluorescence intensity was

in the range of 103�107 cfu/mL with the detection limit of 103 cfu/mL [64].

Antibody-based surface plasmon resonance nanobiosensor for the detection of Escherichia coli in water

Among noble-metal nanomaterials, AgNPs can commonly be useful in the construction of SPR biosensors because of

their interesting physicochemical properties including the SPR and large effective scattering cross-section of individual

AgNPs. In comparison to gold nanoshells, Ag nanoshells exhibit a stronger and sharper plasmon resonance band at the

shorter wavelength end of the visible range [43,63]. Kalele et al. proposed a rapid and highly selective sensor based on

the SPR band (443 nm) shift and silver nanoshells for the extremely specific detection of E. coli in the range of 5�109

cells in water samples. In this work, rabbit IgG antibody was conjugated to silver nanoshells (silica particle coated with

silver shells) via their amino groups. In the presence of E. coli the SPR-band intensity was shifted and decreased dra-

matically [65].

17.4.2.3 Other optical nanobiosensors for the detection of Escherichia coli in water

AgNPs were also effectively exploited for the detection of bacteria using SERS in drinking water. Zhou et al. demon-

strated the SERS-based label-free detection of living bacteria in drinking water by direct deposition of AgNPs on the

cell wall of bacteria. Using a modified version of the Leopold and Lendl protocol, after several washing steps and

Nanosensors for water safety Chapter | 17 293

centrifugation, AgNPs were synthesized in the bacterial suspension. With this approach the SERS enhancement from

AgNPs on the surface of bacteria in water was about 9-fold higher than in PBS solution and approximately 30-fold

more than the simple mixture of AgNPs�bacterial suspension. Detection limit of 2.53 102 cells/mL was achieved

when the Ag-coated bacteria were exploited on a chip surface (hydrophobic glass slide), and SERS mapping was

applied for detection. In addition, the authors demonstrated that this approach combined with hierarchy cluster analysis

was able to discriminate between three different E. coli strains and one strain of Staphylococcus epidermidis [66].

17.5 Nanosensors for the detection of chemical contaminants (including toxins,antibiotics, and insecticides) in water

Pharmaceutical compounds have been broadly considered by the researchers because such contaminants are originated

from manufacturing and their excessive applications in human and veterinary clinical practice. These analytes and tox-

ins can result in severe environmental impacts and likely enter drinking-water supplies [67].

17.5.1 Electrochemical nanosensors for the detection of chemical contaminants in water

17.5.1.1 Aptamer-based electrochemical nanosensors for the detection of chemicalcontaminants in water

Graphene, as a two-dimensional sheet of sp2 atomic carbon, is an ideal nanomaterial for the preparation of carbon-

based electrochemical biosensors because of its excellent conductivity, electrocatalytic activity, and its ability for

immobilizing different nanoparticles, ligands, and aptamers [68]. Combination of AgNPs with graphene oxide leads to

development of new generation of biosensors. For example, Jiang et al. developed an aptasensor composed of AgNPs

anchored on nitrogen-doped graphene oxide (Ag/NG nanocomposites) for the detection of acetamiprid as a neonicoti-

noid insecticide in wastewater samples. Ag/NG nanocomposites were placed onto GCE. Then, the aptamer was immobi-

lized onto Ag/NG nanocomposites. In the presence of target, Aptamer/Acetamiprid complex was formed and

impedance increased. Due to excellent electrical characteristics and large surface area of Ag/NG nanocomposites, an

effective electron transfer and high loading capacity were achieved. LOD of 3.33 10214 M was estimated based on

electrochemical impedance spectroscopy (EIS) [69].

It is important to develop techniques to determine cylindrospermopsin (CYN) at trace levels in freshwater sources

since CYN is considered one of the most hazardous cyanobacterial toxins in water sources. Zhao et al. fabricated a

label-free impedimetric aptasensor for CYN by covalently grafting the amino anti-CYN aptamer on a thionine/graphene

nanocomposite-modified GCE using glutaraldehyde as a cross linker. EIS measurements of [Fe(CN)6]42/32 as redox

agent were utilized to detect CYN and an LOD of 0.374 nM with linear range of 1.0�150 nM [70].

17.5.1.2 Antibody-based electrochemical nanosensors for the detection of chemicalcontaminants in water

Dendrimers are highly branched macromolecules with three-dimensional structures. They have been used in different

aspects of biomedical applications including gene and oligonucleotide delivery, targeting of anticancer chemotherapy,

oral and transdermal delivery, scaffolds for tissue engineering, and diagnostic application [71]. Poly(propylene imine)

(PPI) dendrimer has been widely utilized for clinical and industrial applications as well as development of biosensor

[72]. A novel electrochemical immunosensor containing PPI dendrimer�gold nanocomposite was reported for the

detection of cholera toxin in water. AuNPs in this nanocomposite platform enhanced the electrode conductivity and

charge transfer at the biosensor interface. Also, the dendrimer scaffold formed a host�guest interaction with the biore-

ceptor, which facilitated trap of cholera toxins. Detection limits of 7.23 10213 and 4.23 10213 g/mL were achieved

from the square-wave and EIS measurements, respectively. The merits of this assay are its capability to monitor the tar-

get with two different electrochemical techniques and its good stability up to 2 weeks [73].

Taking advantage of gold nanorods (AuNRs), an electrochemical sensor with very low LOD of 5 pg/mL was intro-

duced for the detection of microcystin-LR (MC-LR) in real lake water samples. Microcystins are a group of monocyclic

hepta-peptide metabolites produced by blooming cyanobacteria. MC-LR is the most prevalent of this family and is a

type of hepatotoxin that can disrupt the function of liver [74]. In addition, MC-LR is a human carcinogen and inhibits

intracellular serine/threonine phosphatases 1 and 2A (PP1 and PP2A) leading to illnesses and deaths [75]. Thus it is

considered a toxic biological substance. This electrochemical immunosensor was based on gold electrode modified with

a composite, containing molybdenum disulfide/AuNRs (MoS2/AuNRs). Extremely low LOD in this assay could be

294 PART | III Nanosensors for healthy cities

associated with the synergistic effect between MoS2 and AuNRs, which provided a larger surface area on the electrode

with better electrochemical performance and high electrical conductivity. Another advantage of this immunosensor was

its regeneration in glycine�HCl solution (pH 3.0), which dissociated the antigen�antibody complex [76]. Use of bio-

compatible nanomaterials has been broadly studied and exploited in biosensing analysis systems. A three-dimensional

CNT/cobalt (CNT@Co) silicate core�shell nanostructure was designed to be utilized as the substrate for immobiliza-

tion of the MC-LR antigen. In this platform, Fe3O4 NCs/polydopamine/AuNPs (Fe3O4@PDA-AuNPs) core�shell mag-

netic nanocomposites were exploited as the label carrier to be attached to the detection secondary antibody (Ab2) and

HRP. Large surface area of the three-dimensional villiform-like structure in CNT@Co silicate and high electrochemical

cyclic voltammogram signals produced by Fe3O4@PDA-AuNPs-HRP-Ab2 in the presence of hydroquinone (HQ), pro-

vided a linear response to MC-LR in the 0.005�50 μg/L range with a detection limit of 0.004 μg/L [77]. Regarding the

WHO guideline, this immunosensor provides the opportunity to measure MC-LR in drinking water with

acceptable LOD value [78].

17.5.1.3 Other electrochemical nanosensors for the detection of dihydroxybenzene isomers inwater

Recent development in screen-printing knowledge has opened up new exciting opportunities to apply electrochemical

sensing techniques for environmental analyses such as routine water-quality tests for organic contaminants and heavy

metals outside a laboratory. In portable electrochemical sensors, screen-printed electrode (SPE) is used as a support and

offers several advantages in terms of linear output, low cost, low power requirement, portability, high sensitivity, low

sample volume, quick response, and easy handling [79,80]. Benefiting from the mentioned advantages of SPE, a novel

modified electrode was successfully proposed by electrodepositing AuNPs on MWCNT-decorated SPE to determine

three types of dihydroxybenzene isomers including HQ, catechol (CC), and resorcinol (RC), which are main environ-

mental contaminants because of their high toxicity and resistance to degradation in water samples. Deposition of

AuNPs on the SPE surface can improve the biocompatibility and conductibility of electrochemical nanobiosensors [81].

Using DPV, the authors simultaneously detected HQ, CC, and RC at the modified SPE with the detection limits of

3.93 1027, 2.63 1027, and 7.23 1027 M, respectively [82].

17.5.2 Optical nanosensors for the detection of chemical contaminants in water

17.5.2.1 Aptamer-based optical nanosensors for the detection of chemical contaminants inwater

Aptamer-based colorimetric nanosensor for the detection of malathion in water

In AuNP-based colorimetric aptasensors, the aptamer is bound onto the surface of AuNPs and therefore inhibits AuNP

aggregation against salt-induced aggregation or other substances, which have positive charge [83]. A novel and highly

sensitive colorimetric aptasensor was designed for the detection of malathion as an organophosphorus pesticide in lake

water using AuNPs and a positively charged polymer called polyelectrolyte poly(diallyldimethylammonium chloride)

(PDDA) by Bala et al. [84]. Free PDDA can induce the aggregation of AuNPs. As is shown schematically in Fig. 17.5,

in the absence of malathion, the aptamer interacts with the PDDA. So, the AuNPs are well dispersed due to the lack of

PDDA and the color of sample remains red. Upon addition of malathion, the aptamer interacts with the malathion as

target and thus free PDDA helps in aggregating AuNPs. Consequently, the color of solution changes from red to blue.

The designed sensor indicated a very high sensitivity toward malathion with a detection limit of 0.06 pM.

Aptamer-based fluorescent nanosensor for the detection of microcystin-LR in water

In a study conducted by our team, a novel ultrasensitive fluorescent aptasensor was introduced for the selective detec-

tion of MC-LR using SWCNTs. In this aptasensor, two different kinds of aptamers were immobilized on the surface of

SWCNTs. One of them was dapoxyl 10 (DAP-10) aptamer, which targets a fluorescent dye called dapoxyl, and the

other was unmodified MC-LR aptamer, which binds to MC-LR. In the absence of MC-LR, MC-LR aptamer remains on

the surface of SWCNTs, thus leaving no available space for DAP-10 aptamer on the surface of SWCNTs. Therefore

DAP-10 aptamer forms a complex with dapoxyl dye, producing a strong fluorescence signal. When MC-LR is present,

the MC-LR aptamer is bound to MC-LR and leaves the surface of SWCNTs. So, DAP-10 aptamer can attach on the

free SWCNTs surface, resulting in a very weak fluorescence intensity observed by the free dapoxyl dye. The presented

fluorescent aptasensor could effectively detect MC-LR with a detection limit of 135 pM (0.137 μg/L) in tap water [85].

Nanosensors for water safety Chapter | 17 295

17.5.2.2 Antibody-based optical nanosensors for the detection of chemical contaminants inwater

Antibody-based colorimetric nanobiosensor for the detection of microcystin-LR in water

Exploiting the high peroxidase activity of G-quadruplex�hemin complexes, a simple immunoassay, with high detection

sensitivity and selectivity toward MC-LR residues in water samples, was presented by Zhu et al. [86]. This sensor could

specifically detect MC-LR at concentrations less than 0.05 ng/mL in a wide dynamic working linear range of

0.1�10 ng/mL. The detection of MC-LR was performed through a competitive-type immunoassay. The major concept

was that the G-quadruplex catalyzed the H2O2-mediated oxidation of 2, 20-azino-bis (3-ethylbenzothiazoline-6-sulfonicacid) diammonium salt to produce colored products. Upon addition of MC-LR, it rivals for antibody with coated anti-

gen. The colored products decreased when the antibody�antigen immune complex decreased. Importantly, the simplic-

ity and facile operation used in this immunosensor provided a promising immunosensing platform for rapid screening

of toxins in polluted water.

Antibody-based fluorescent nanobiosensor for the detection of microcystin-LR in water

Benefiting from the fluorescence properties of QDs, an indirect competitive fluorescent immunoassay based on QD hap-

tens was reported for the sensitive and rapid analysis of MC-LR in a portable optofluidic platform by Feng et al. [87].

For constructing of QD�hapten nanoprobes, the carboxyl-coated QDs were coupled with aminoethyl-MC-LR and used

as donors for the recognition of the Cy5.5-labeled anti-MC-LR antibody in water samples (Fig. 17.6). Using this

approach, the detection limit of 0.03 μg/L and the linear working range of 0.10�4.0 μg/L for MC-LR were obtained.

Antibody-based luminescence nanosensor for the detection of diclofenac in water

Lanthanide-doped UCNPs, which emit a higher and shorter-energy photon after excitation with multiple low-energy

photons have provided a new generation of luminescent labels for sensitive immunochemical detection. Relative to

QDs and organic dyes, UCNPs display advantages including large anti-Stokes shifts that can separate excitation and

detection channels, sharp emission bandwidths allowing for multiplexed detection of analytes, long excited-state life-

times, minimal autofluorescence, very high photochemical stability, and low cytotoxicity [88]. The direct use of

UCNPs as reporters for heterogeneous bioanalytical assays make them comparable to those that are routinely detected

by conventional ELISAs (enzyme-linked immunosorbent assays) or radioimmunoassays. For example, in a competitive

heterogeneous assay for the detection of diclofenac as an antiinflammatory drug in water samples, a detection limit of

0.05 ng/mL was obtained, which was five times higher than the one detected with an ELISA assay. In this sensing plat-

form, BSA-DCF conjugate was coated in a microtiter plate. Then, the binding of anti-diclofenac antibody was assessed

by an antimouse IgG-UCNP secondary antibody conjugate. The upconversion luminescence was measured under

FIGURE 17.5 Schematic design of a colorimetric aptasensor for the detection of malathion based on AuNPs and PDDA. AuNPs, Silver nanoparti-

cles; PDDA, poly(diallyldimethylammonium chloride). Adapted with permission from R. Bala, M. Kumar, K. Bansal, R.K. Sharma, N. Wangoo,

Ultrasensitive aptamer biosensor for malathion detection based on cationic polymer and gold nanoparticles, Biosens. Bioelectron. 85 (2016)

445�449. Copyright 2016 Elsevier.

296 PART | III Nanosensors for healthy cities

980 nm laser excitation. The merit of this assay is to avoid the enzymatic-mediated signal amplification step, providing

a faster and more straightforward assay [89].

Antibody-based surface-enhanced Raman scattering nanobiosensor for the detection of chemicalcontaminants in waters

Aflatoxin B1 (AFB1) is a prominent carcinogenic pollutant in foods. It is recognized as an extremely dangerous substance

due to its high toxicity to the human nervous system. This aflatoxin is generated by two species of Aspergillus. Combination

of immunochemistry methods with SERS offers the opportunity for improving the performance of the bioanalytical methods.

Ko et al. designed a highly sensitive SERS-based immunoassay for AFB1 detection in tap water using silica-encapsulated hol-

low AuNPs (SEHGNs) as SERS-encoding nanoprobes and magnetic beads as supporting substrates (Fig. 17.7). Quantitative

FIGURE 17.6 Schematic diagram of QD-FRET-based competitive immunoassay for the detection of MC-LR. FRET, Forster resonance energy

transfer; MC-LR, Microcystin-LR; QD, quantum dot. Adapted with permission from L. Feng, A. Zhu, H. Wang, H. Shi, A nanosensor based on

quantum-dot haptens for rapid, on-site immunoassay of cyanotoxin in environmental water, Biosens. Bioelectron. 53 (2014) 1�4. Copyright 2014

Elsevier.

FIGURE 17.7 Schematic description of AFB1 detection based on SERS-based immunoassay platform. AFB1, Aflatoxin B1; SERS, surface-enhanced

Raman scattering. Adapted with permission from J. Ko, C. Lee, J. Choo, Highly sensitive SERS-based immunoassay of aflatoxin B1 using silica-

encapsulated hollow gold nanoparticles, J. Hazard. Mater. 285 (2015) 11�17. Copyright 2015 Elsevier.

Nanosensors for water safety Chapter | 17 297

determination of AFB1 in water sample was achieved by monitoring the intensity change of the characteristic peaks of

Raman reporter molecules. The detection process could be completed within 30 minutes with an LOD of 0.1 ng/mL [90].

17.6 Conclusion

This chapter has summarized the promising and powerful role of nanosensors in the field of water analysis. In this chap-

ter, we have discussed different types of nanosensors, including genosensors, immunosensors, and aptasensors, based

on different transduction approaches such as electrochemical and optical nanosensors. Although nanosensors improve

the performance of analytical tools including specificity, sensitivity as well as reliability for water monitoring, they still

need to be further optimized to provide confidence to users.

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