single-stranded DNA or RNA library. Aptamers are preferred over proteins for
detection elements as they show higher stability and tolerance for temperature and
pH. The application of aptamers based biosensor for determination of water contaminants can range from lake water, tap water, seawater and wastewater. They are
widely used for detection of molecular toxins [20], heavy metals [21], drugs [22],
pesticides [23] and EDCs [24].
A toxin known as microcystins is a toxin secreted by cyanobacteria found in the
aquatic ecosystem was found to contaminate food products [25]. Zhao et al.
developed an aptamer-based biosensor for the detection of microcystins. Surface
Enhanced Raman Scattering (SERS) was used to activate a bi-metallic nanosystems
consisting of gold nanoflower (Au-NF) and silver nanoparticle (Ag-NP). This
coupling of SERS active nanosystem led to the enhancement of the electromagnetic
field for identification of microcystins with high sensitivity in lake water. This type
of device may be developed to become a choice for portable biosensors for both
qualitative and quantitative detection [26].
A temperature-based aptamer sensor was developed by Gao et al., for the
detection of heavy metals such as lead and mercury. In this technique, the sample
enters the capillary channel of a chip and reaches an exothermic reservoir containing sodium hydroxide as the exothermic agent. The entrance to the reservoir is
guided by a microvalve made of an aptamer coupled hydrogel. When the analyte
interacts with the aptamer the hydrogel shrinks, this leads to enhanced flow, causing
a rise in the temperature due to heat dissolution. A thermometer detects this increase
in temperature leading to quantitative analysis of heavy metals [27].
Aptamer-based biosensor is also used for the detection of drugs and other
pharmaceutical ingredients found as water contaminants. A biosensor using an
aptamer which was obtained using Capture-SELEX procedure was developed by
Nikolaus et al., for detection of kanamycin A. The specificity and affinity of the
analyte for the aptamer were analysed. Beads and microplate-based assay were
carried out, and the fluorescence was measured. The affinity results were confirmed
using a surface plasmon resonance (SPR) system. Thus an aptamer-based biosensor
was proposed for the detection of aminoglycoside antibiotics in water [28].
Bala et al. developed an aptamer-based biosensor for detection of organophosphorus pesticide known as malathion. This sensing device used a cationic polyelectrolyte known as Polydiallyldimethylammonium chloride (PDDA) and an
unmodified gold nanoparticle for the detection of malathion.
In another study, aptamers sensor for specific Bisphenol A determination using
AC electrokinetics (ACEK) capacitive detection method was proposed by Lin et al.
In this method an AC signal is given to an array of microelectrodes fabricated on
silicon wafers. This signal causes microflows for binding of the analyte to the
aptamers. This binding causes interfacial capacitance change, which is measured.
This sensor was able to sense the presence of Bisphenol A within 30 s and had a
limit of detection as 1.0 femtomolar [29].
Materials in Bio-Sensing of Water Pollutants
193
detection elements as they show higher stability and tolerance for temperature and
pH. The application of aptamers based biosensor for determination of water contaminants can range from lake water, tap water, seawater and wastewater. They are
widely used for detection of molecular toxins [20], heavy metals [21], drugs [22],
pesticides [23] and EDCs [24].
A toxin known as microcystins is a toxin secreted by cyanobacteria found in the
aquatic ecosystem was found to contaminate food products [25]. Zhao et al.
developed an aptamer-based biosensor for the detection of microcystins. Surface
Enhanced Raman Scattering (SERS) was used to activate a bi-metallic nanosystems
consisting of gold nanoflower (Au-NF) and silver nanoparticle (Ag-NP). This
coupling of SERS active nanosystem led to the enhancement of the electromagnetic
field for identification of microcystins with high sensitivity in lake water. This type
of device may be developed to become a choice for portable biosensors for both
qualitative and quantitative detection [26].
A temperature-based aptamer sensor was developed by Gao et al., for the
detection of heavy metals such as lead and mercury. In this technique, the sample
enters the capillary channel of a chip and reaches an exothermic reservoir containing sodium hydroxide as the exothermic agent. The entrance to the reservoir is
guided by a microvalve made of an aptamer coupled hydrogel. When the analyte
interacts with the aptamer the hydrogel shrinks, this leads to enhanced flow, causing
a rise in the temperature due to heat dissolution. A thermometer detects this increase
in temperature leading to quantitative analysis of heavy metals [27].
Aptamer-based biosensor is also used for the detection of drugs and other
pharmaceutical ingredients found as water contaminants. A biosensor using an
aptamer which was obtained using Capture-SELEX procedure was developed by
Nikolaus et al., for detection of kanamycin A. The specificity and affinity of the
analyte for the aptamer were analysed. Beads and microplate-based assay were
carried out, and the fluorescence was measured. The affinity results were confirmed
using a surface plasmon resonance (SPR) system. Thus an aptamer-based biosensor
was proposed for the detection of aminoglycoside antibiotics in water [28].
Bala et al. developed an aptamer-based biosensor for detection of organophosphorus pesticide known as malathion. This sensing device used a cationic polyelectrolyte known as Polydiallyldimethylammonium chloride (PDDA) and an
unmodified gold nanoparticle for the detection of malathion.
In another study, aptamers sensor for specific Bisphenol A determination using
AC electrokinetics (ACEK) capacitive detection method was proposed by Lin et al.
In this method an AC signal is given to an array of microelectrodes fabricated on
silicon wafers. This signal causes microflows for binding of the analyte to the
aptamers. This binding causes interfacial capacitance change, which is measured.
This sensor was able to sense the presence of Bisphenol A within 30 s and had a
limit of detection as 1.0 femtomolar [29].
Materials in Bio-Sensing of Water Pollutants
193