pesticides were found to have quenching effects on the characteristics emission peak
for europium (III) (λ ¼ 614 nm). Selectivity of this chemosensor was also ensured by
studying the possible interferents, and also, the quenching mechanism was of
dynamic type for the pesticides chlorfenvinphos, diazinon, and isofenphos, while
it is static for azinphos ethyl.
Fluorescence detection in chemosensors is known for its sensitivity and wide
usage, though it has limitations as well. The major one is its sensitivity to the
surroundings, including the solvents, temperature, and interfering species. It needs
designing of one or more fluorophores that respond with a change in fluorescence on
binding, and it is important to maintain the photostability of these fluorophores used.
In this regard, organic dyes are not so preferred, while the metal complexes and
quantum dots possess good stability and fluorescent intensity.
10.2.2 Electrochemical Chemosensors
A commonly exploited method of detection in chemosensors is electrochemical
detection. There are different ways to detect species using electrochemical methods
that include ion-selective electrodes (ISEs) for sensing toxic pollutants and pH
analysis in water test samples and a general research technique of cyclic
voltammetry (CV) that helps in the study of thermodynamics and kinetics of electron
transfer reactions apart from sensing the presence or concentration of a specific
target. These methods change the physicochemical information of a specific analyte
like a molecule or ion, into appropriate electrical signal possessing particular potential/current or both that could be displayed as the output according to the chemical
information. The electrochemical detection is based on a chemical or physical
change induced by the target analyte interacting with the electrode, on its surface,
or in particular the interfacial area between the electrode and its electrolyte. These
electric signals are monitored as either potential/current change or both, based on
which detection is done called potentiometry, amperometry (also called coulometry),
and voltammetry, respectively. Ion-selective electrodes (ISEs) are classic potentiometric sensors that help in converting the target ion’s concentration into a readable
output potential signal response. Membrane-based ISEs with ion-selective
conducting membrane leading to an electric field generation and hence potential
difference are available in market; however, most of them detect only the inorganic
ions. Ion-selective membrane can also be constructed by exclusive coating of an
electrode surface with an ion-selective agent. These coating-based ISEs are easy to
develop and possess high selectivity and rate of response. Another new electrode
includes the ion-selective (or sensitive) field-effect transistors (ISFETs), which
belong to a broader class of chemically modified field-effect transistors
(CHEMFETs) which are beneficial especially in equipment miniaturization and
gives more data for enhanced reliability. There have been several research in the
past two decades, with the aim to develop electrochemical-based molecular probes
or sensors with high specificity for cationic, anionic, or neutrally charged analyte
molecules (Beer 1996; Beer et al. 1999a).
10 Environment Remediation Tools: Chemosensors and Biosensors
271
for europium (III) (λ ¼ 614 nm). Selectivity of this chemosensor was also ensured by
studying the possible interferents, and also, the quenching mechanism was of
dynamic type for the pesticides chlorfenvinphos, diazinon, and isofenphos, while
it is static for azinphos ethyl.
Fluorescence detection in chemosensors is known for its sensitivity and wide
usage, though it has limitations as well. The major one is its sensitivity to the
surroundings, including the solvents, temperature, and interfering species. It needs
designing of one or more fluorophores that respond with a change in fluorescence on
binding, and it is important to maintain the photostability of these fluorophores used.
In this regard, organic dyes are not so preferred, while the metal complexes and
quantum dots possess good stability and fluorescent intensity.
10.2.2 Electrochemical Chemosensors
A commonly exploited method of detection in chemosensors is electrochemical
detection. There are different ways to detect species using electrochemical methods
that include ion-selective electrodes (ISEs) for sensing toxic pollutants and pH
analysis in water test samples and a general research technique of cyclic
voltammetry (CV) that helps in the study of thermodynamics and kinetics of electron
transfer reactions apart from sensing the presence or concentration of a specific
target. These methods change the physicochemical information of a specific analyte
like a molecule or ion, into appropriate electrical signal possessing particular potential/current or both that could be displayed as the output according to the chemical
information. The electrochemical detection is based on a chemical or physical
change induced by the target analyte interacting with the electrode, on its surface,
or in particular the interfacial area between the electrode and its electrolyte. These
electric signals are monitored as either potential/current change or both, based on
which detection is done called potentiometry, amperometry (also called coulometry),
and voltammetry, respectively. Ion-selective electrodes (ISEs) are classic potentiometric sensors that help in converting the target ion’s concentration into a readable
output potential signal response. Membrane-based ISEs with ion-selective
conducting membrane leading to an electric field generation and hence potential
difference are available in market; however, most of them detect only the inorganic
ions. Ion-selective membrane can also be constructed by exclusive coating of an
electrode surface with an ion-selective agent. These coating-based ISEs are easy to
develop and possess high selectivity and rate of response. Another new electrode
includes the ion-selective (or sensitive) field-effect transistors (ISFETs), which
belong to a broader class of chemically modified field-effect transistors
(CHEMFETs) which are beneficial especially in equipment miniaturization and
gives more data for enhanced reliability. There have been several research in the
past two decades, with the aim to develop electrochemical-based molecular probes
or sensors with high specificity for cationic, anionic, or neutrally charged analyte
molecules (Beer 1996; Beer et al. 1999a).
10 Environment Remediation Tools: Chemosensors and Biosensors
271