because of the faster electron transfer rates. The modified electrode sensor with a
longer spacer was used to detect melamine and trichlorfon residues by CV and
differential pulse voltammetry (DPV) techniques. The sensor had a good linear
relationship over a wide concentration range, a maximal recovery of ca. 112.4%
and a low detection limit of about 1.5 Â 10
À7 and 3.5 Â 10
À8 mol L
À1 , respectively.
Turan et al. (2016) have used an innovative approach for the fabrication of a
biosensor utilizing a conducting polymer and silver nanowires. To obtain immobilization platform for butyrylcholinesterase (BChE), a graphite electrode was modified with the poly(5,6-bis(octyloxy)-4,7-di(thieno[3][3,2-b]thiophen-2-yl)benzo[c]
[1,2,5]oxoadiazole) (PTTBO) which has a hydrophobic alkyl chain as the pendant
group providing hydrophobic nature to the matrix. Since biomolecules contain both
hydrophobic and hydrophilic parts in their structure, alkyl chains interact with the
proteins which provide an enhanced stability. Biosensor performance was improved
through the deposition of silver nanowires on the polymer-coated surfaces which
enhances the charge transfer rate. This enabled the development of rapid, highly
sensitive, and stable amperometric sensors for the quantitative determination of
organophosphorus pesticide, paraoxon. Fabricated biosensor showed two linear
ranges between 0.5–8 μM and 10–120 μM with a low detection limit of 0.212 μM
when butyrylthiocholine iodide is used as the substrate.
Zhang et al. (2013) have developed novel nanobiosensing principles for organophosphorus pesticides. Thiocholine generation by AChE catalysis leads to the
aggregation of AuNPs, resulting in the recovery of fluorescence resonance energy
transfer (FRET) between AuNPs and NaYF4: Yb, upconversion NPs (Long et al.
2015). Immobilization of AChE in fenugreek hydrogel-agarose matrix with AuNPs
results in high enzyme retention efficiency of 92% and a significantly prolonged
half-life of the AChE (55 days) (Kestwal et al. 2015). Apart from AChE, pesticides
can also inhibit other enzyme activity such as trypsin and tyrosinase (Yan et al.
2015). Trypsin easily hydrolyzes protamine covered on the surface of AuNPs,
leading to fluorescence quenching of QDs.
Electrochemical and photochemical properties of pesticides such as omethoate,
malathion, lindane, carbofuran, carbaryl, etc. are being used for the development
of nanobiosensors (Yang et al. 2016). Nanobiosensors based on copper oxide
nanowires-CNTs, AgNPs decorated polyaniline-nanocrystalline zeolite organicinorganic hybrid material, cobalt oxide (CoO)-reduced GOx, zirconia-ordered
macroporous polyaniline, and other nanosystems, have already been reported to
improve the sensitivity of the nanosensors (Huo et al. 2014; Kaur et al. 2015, Wang
et al. 2014, 2015; Wu et al. 2014). In addition to electrochemical methods, a few
NP-enhanced surface-enhanced Raman spectroscopy (SERS) methods have been
developed, but these methods have limitations in terms of low affinity. Such
problems can be overcome by optimizing metal NPs, for example, the type, molecular linker, surface coverage, and laser excitation wavelength of NPs (Kubackova
et al. 2015).
Immunoassay-based nanobiosensing systems are most widely being used in the
detection of pesticides (Belkhamssa et al. 2016; Sun et al. 2015; Xiao et al. 2016).
The application of nanometal organic framework and other materials can greatly
114
H. V. Raghu et al.
longer spacer was used to detect melamine and trichlorfon residues by CV and
differential pulse voltammetry (DPV) techniques. The sensor had a good linear
relationship over a wide concentration range, a maximal recovery of ca. 112.4%
and a low detection limit of about 1.5 Â 10
À7 and 3.5 Â 10
À8 mol L
À1 , respectively.
Turan et al. (2016) have used an innovative approach for the fabrication of a
biosensor utilizing a conducting polymer and silver nanowires. To obtain immobilization platform for butyrylcholinesterase (BChE), a graphite electrode was modified with the poly(5,6-bis(octyloxy)-4,7-di(thieno[3][3,2-b]thiophen-2-yl)benzo[c]
[1,2,5]oxoadiazole) (PTTBO) which has a hydrophobic alkyl chain as the pendant
group providing hydrophobic nature to the matrix. Since biomolecules contain both
hydrophobic and hydrophilic parts in their structure, alkyl chains interact with the
proteins which provide an enhanced stability. Biosensor performance was improved
through the deposition of silver nanowires on the polymer-coated surfaces which
enhances the charge transfer rate. This enabled the development of rapid, highly
sensitive, and stable amperometric sensors for the quantitative determination of
organophosphorus pesticide, paraoxon. Fabricated biosensor showed two linear
ranges between 0.5–8 μM and 10–120 μM with a low detection limit of 0.212 μM
when butyrylthiocholine iodide is used as the substrate.
Zhang et al. (2013) have developed novel nanobiosensing principles for organophosphorus pesticides. Thiocholine generation by AChE catalysis leads to the
aggregation of AuNPs, resulting in the recovery of fluorescence resonance energy
transfer (FRET) between AuNPs and NaYF4: Yb, upconversion NPs (Long et al.
2015). Immobilization of AChE in fenugreek hydrogel-agarose matrix with AuNPs
results in high enzyme retention efficiency of 92% and a significantly prolonged
half-life of the AChE (55 days) (Kestwal et al. 2015). Apart from AChE, pesticides
can also inhibit other enzyme activity such as trypsin and tyrosinase (Yan et al.
2015). Trypsin easily hydrolyzes protamine covered on the surface of AuNPs,
leading to fluorescence quenching of QDs.
Electrochemical and photochemical properties of pesticides such as omethoate,
malathion, lindane, carbofuran, carbaryl, etc. are being used for the development
of nanobiosensors (Yang et al. 2016). Nanobiosensors based on copper oxide
nanowires-CNTs, AgNPs decorated polyaniline-nanocrystalline zeolite organicinorganic hybrid material, cobalt oxide (CoO)-reduced GOx, zirconia-ordered
macroporous polyaniline, and other nanosystems, have already been reported to
improve the sensitivity of the nanosensors (Huo et al. 2014; Kaur et al. 2015, Wang
et al. 2014, 2015; Wu et al. 2014). In addition to electrochemical methods, a few
NP-enhanced surface-enhanced Raman spectroscopy (SERS) methods have been
developed, but these methods have limitations in terms of low affinity. Such
problems can be overcome by optimizing metal NPs, for example, the type, molecular linker, surface coverage, and laser excitation wavelength of NPs (Kubackova
et al. 2015).
Immunoassay-based nanobiosensing systems are most widely being used in the
detection of pesticides (Belkhamssa et al. 2016; Sun et al. 2015; Xiao et al. 2016).
The application of nanometal organic framework and other materials can greatly
114
H. V. Raghu et al.