Electrochemical detection is mainly used for specific target analytes that are
charged, such as ions, which can undergo electron transfer reactions on an electrode.
The detection of neutral molecules using electrochemical method has been a hard
task. The integrated chemical processes involving a redox-responsive receptor which
specifically recognizes and electrochemically detects the signaling molecule are
known as electrochemical molecular recognition (Beer et al. 1999b). By means of
standardized molecular imprinting procedures, a synthetic polymer receptor film
specific for the cancer biomarker, neopterin, was designed and developed as a
recognition unit of a potentiometric chemosensor (Sharma et al. 2016). This
chemosensor worked by measuring the open circuit potential changes that occurred
due to selective binding/sensing of neopterin by the polymer film. It served the
purpose of detecting neopterin in serum samples with a detection limit of 22 μM. A
n-type chemical doping of conducting polyaniline and the formation of Schottky
barrier diode in a chemosensor (Ameen et al. 2016) paved way for electrochemical
detection of hydrazine benzene chemical, with high sensitivity and detection limit of
5.11 μM. Chemosensors employing transducers coated with D- or (L-phenylalanine)-templated molecular imprinted polymer films (Iskierko et al. 2017) following
extended-gate field-effect transistors were also developed for enantioselective determination of (D- or L-) phenylalanine. These were found to have a detection limit of
13 μM. Differential pulse voltammetry of two ligands made up of the diphenyl
derivatives, 3-(2,4-dinitrophenoxy)phenol (L1) and 3-(2-nitrophenoxy)phenol (L2),
was found to exhibit complete quenching of anodic peaks at 1.16 V for L1 and
1.34 V for L2 on adding one equivalent fluoride ions (Sharma et al. 2015). Thereby,
both these ligands serve as a voltammetric chemosensor for sensing fluoride ions.
10.2.3 Colorimetric Chemosensors
Colorimetry is different from fluorescence in the working principle that they work
with respect to absorption with less sensitivity relative to the emission employed in
fluorescence. This method of sensing is not limited by stringent requirements of
fluorophore design; instead, there are several dyes available for sensing applications.
There are two common signal motifs to be considered: (i) a change in absorbance at a
specific wavelength, thereby observing a color appear or fade, or (ii) monitoring the
maximum absorption wavelength to change, such as initial color changes into a new
second color. Sessler and Miyaji reported (Miyaji and Sessler 2001) several commercially available molecules for use as colorimetric anion sensors, including
l-leucine-4-nitroanilide, 1,2-diaminoanthraquinone, 1,8-diaminoanthraquinone,
1-(4-nitrophenyl)-2-thiourea,
4-nitrophenol,
4-nitroaniline,
4-nitro-1,2phenylenediamine, alizarin, 2,2-bi(3-hydroxy-1,4-naphthoquinone) and Direct
Yellow 50.
A recent finding includes a synthesis of a coumarin derivative with benzothiazole
Schiff’s base structure that detects cyanide anions (CN
À ) by nucleophilic addition
mechanism (Fig. 10.2) (Wang et al. 2016b). This detection technique involves
visible colorimetric changes, where there is a color change from reddish brown to
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J. Brindha et al.
charged, such as ions, which can undergo electron transfer reactions on an electrode.
The detection of neutral molecules using electrochemical method has been a hard
task. The integrated chemical processes involving a redox-responsive receptor which
specifically recognizes and electrochemically detects the signaling molecule are
known as electrochemical molecular recognition (Beer et al. 1999b). By means of
standardized molecular imprinting procedures, a synthetic polymer receptor film
specific for the cancer biomarker, neopterin, was designed and developed as a
recognition unit of a potentiometric chemosensor (Sharma et al. 2016). This
chemosensor worked by measuring the open circuit potential changes that occurred
due to selective binding/sensing of neopterin by the polymer film. It served the
purpose of detecting neopterin in serum samples with a detection limit of 22 μM. A
n-type chemical doping of conducting polyaniline and the formation of Schottky
barrier diode in a chemosensor (Ameen et al. 2016) paved way for electrochemical
detection of hydrazine benzene chemical, with high sensitivity and detection limit of
5.11 μM. Chemosensors employing transducers coated with D- or (L-phenylalanine)-templated molecular imprinted polymer films (Iskierko et al. 2017) following
extended-gate field-effect transistors were also developed for enantioselective determination of (D- or L-) phenylalanine. These were found to have a detection limit of
13 μM. Differential pulse voltammetry of two ligands made up of the diphenyl
derivatives, 3-(2,4-dinitrophenoxy)phenol (L1) and 3-(2-nitrophenoxy)phenol (L2),
was found to exhibit complete quenching of anodic peaks at 1.16 V for L1 and
1.34 V for L2 on adding one equivalent fluoride ions (Sharma et al. 2015). Thereby,
both these ligands serve as a voltammetric chemosensor for sensing fluoride ions.
10.2.3 Colorimetric Chemosensors
Colorimetry is different from fluorescence in the working principle that they work
with respect to absorption with less sensitivity relative to the emission employed in
fluorescence. This method of sensing is not limited by stringent requirements of
fluorophore design; instead, there are several dyes available for sensing applications.
There are two common signal motifs to be considered: (i) a change in absorbance at a
specific wavelength, thereby observing a color appear or fade, or (ii) monitoring the
maximum absorption wavelength to change, such as initial color changes into a new
second color. Sessler and Miyaji reported (Miyaji and Sessler 2001) several commercially available molecules for use as colorimetric anion sensors, including
l-leucine-4-nitroanilide, 1,2-diaminoanthraquinone, 1,8-diaminoanthraquinone,
1-(4-nitrophenyl)-2-thiourea,
4-nitrophenol,
4-nitroaniline,
4-nitro-1,2phenylenediamine, alizarin, 2,2-bi(3-hydroxy-1,4-naphthoquinone) and Direct
Yellow 50.
A recent finding includes a synthesis of a coumarin derivative with benzothiazole
Schiff’s base structure that detects cyanide anions (CN
À ) by nucleophilic addition
mechanism (Fig. 10.2) (Wang et al. 2016b). This detection technique involves
visible colorimetric changes, where there is a color change from reddish brown to
272
J. Brindha et al.