effective analytical tool. NPs of gold and silver have shown enhancement in the
SERS factor by upto 10
14 (Fritzsche and Taton 2003; Kneipp et al. 1999). Recently,
SERS technique based nano-dielectrophoretic microfluid device biosensors were
prepared and these were used for the sensing of water contaminating pathogens
(Wang et al. 2017).
5.3.1.2 Electrochemical Nanosensors
Voluminous research has been done of the development of electrochemical-based
detection techniques due to low cost, high sensitivity, ease of operation, lesser time
consumption, and ease of miniaturization and portability of electrochemical devices.
Hence, these techniques offer a convenient approach towards nanosensors development for detection of environmental contaminants. The basic operating principle
behind electrochemical based sensors is the detection of measurable change in
current or potential, which takes place upon the chemical reaction of the analyte,
which involves any kind of electron transfer between the analyte and the sensor
material. Electrochemical nanosensors can be categorized mainly into: (1) conventional three or two electrode electrochemical systems, (2) chemiresistive/field-effect
transistor (FET) systems (Nehra et al. 2019).
Three and Two Electrode Systems These types of electrochemical nanosensors
can be designed by fabrication of nanomaterials modified electrodes which can be
used as working electrodes for three electrode or two electrode (for I–V method)
electrochemical systems. Different materials, usually conductive materials like gold,
silver, platinum, glassy carbon, indium tin oxide (ITO) and graphite can be used as
substrates for deposition or growth of nanomaterials. Various methods for surface
modification of these substrates using nanomaterials can be applied, like dip coating,
drop casting, polymer-based coatings, direct growth on substrate, screen printing,
use of binders (like Nafion). The analytes undergo redox reactions on the electrode
surface and can be detected by electrochemical techniques like amperometry,
voltammetry, impedance, potentiometry, etc. The nanomaterials act as electro
catalysts by providing greater surface for analyte adsorption, improving the electron
transfer properties between the analyte and electrode, and decreasing the over
potential for electrochemical reactions taking place on the electrode surface. A
number of different types of nanomaterials like metal, metal oxides, carbon-based,
etc., have been used for fabrication of electrochemical nanosensors. The surfaces of
these nanomaterials could further be chemically or biologically modified to show
specificity for a particular analyte. Thus, these nanomaterials modified electrode
surfaces display higher sensitivity, greater selectivity and much lower limit of
detection for analytes.
Screen-printed electrodes (SPE) are designed to integrate the working, reference and counter electrodes into small, compact, low cost and disposable electrochemical strips. These devices are based on inks like silver, platinum, carbon
nanotubes (CNTs). Similar to the conventional system, the working electrode can
be modified with various nanomaterials to devise nanosensors. SPE are designed to
detect samples in microvolume and provide convenient, cheap and portable
5 Development of Environmental Nanosensors for Detection Monitoring. . .
101
SERS factor by upto 10
14 (Fritzsche and Taton 2003; Kneipp et al. 1999). Recently,
SERS technique based nano-dielectrophoretic microfluid device biosensors were
prepared and these were used for the sensing of water contaminating pathogens
(Wang et al. 2017).
5.3.1.2 Electrochemical Nanosensors
Voluminous research has been done of the development of electrochemical-based
detection techniques due to low cost, high sensitivity, ease of operation, lesser time
consumption, and ease of miniaturization and portability of electrochemical devices.
Hence, these techniques offer a convenient approach towards nanosensors development for detection of environmental contaminants. The basic operating principle
behind electrochemical based sensors is the detection of measurable change in
current or potential, which takes place upon the chemical reaction of the analyte,
which involves any kind of electron transfer between the analyte and the sensor
material. Electrochemical nanosensors can be categorized mainly into: (1) conventional three or two electrode electrochemical systems, (2) chemiresistive/field-effect
transistor (FET) systems (Nehra et al. 2019).
Three and Two Electrode Systems These types of electrochemical nanosensors
can be designed by fabrication of nanomaterials modified electrodes which can be
used as working electrodes for three electrode or two electrode (for I–V method)
electrochemical systems. Different materials, usually conductive materials like gold,
silver, platinum, glassy carbon, indium tin oxide (ITO) and graphite can be used as
substrates for deposition or growth of nanomaterials. Various methods for surface
modification of these substrates using nanomaterials can be applied, like dip coating,
drop casting, polymer-based coatings, direct growth on substrate, screen printing,
use of binders (like Nafion). The analytes undergo redox reactions on the electrode
surface and can be detected by electrochemical techniques like amperometry,
voltammetry, impedance, potentiometry, etc. The nanomaterials act as electro
catalysts by providing greater surface for analyte adsorption, improving the electron
transfer properties between the analyte and electrode, and decreasing the over
potential for electrochemical reactions taking place on the electrode surface. A
number of different types of nanomaterials like metal, metal oxides, carbon-based,
etc., have been used for fabrication of electrochemical nanosensors. The surfaces of
these nanomaterials could further be chemically or biologically modified to show
specificity for a particular analyte. Thus, these nanomaterials modified electrode
surfaces display higher sensitivity, greater selectivity and much lower limit of
detection for analytes.
Screen-printed electrodes (SPE) are designed to integrate the working, reference and counter electrodes into small, compact, low cost and disposable electrochemical strips. These devices are based on inks like silver, platinum, carbon
nanotubes (CNTs). Similar to the conventional system, the working electrode can
be modified with various nanomaterials to devise nanosensors. SPE are designed to
detect samples in microvolume and provide convenient, cheap and portable
5 Development of Environmental Nanosensors for Detection Monitoring. . .
101