Bottom-up approach is an additive process, and involves sensor preparation by
one by one assembly of individual molecules or atoms into particular positions using
tools like atomic force microscopes (AFM). But this method is mainly used to build
starting molecules for self-assembling sensors.
The third and fastest method for nanosensors fabrication is self-assembly, which
entails growing specific nanostructures for sensors applications. In this method,
mostly set of components that are already complete, are automatically assembled
to give finished products. This technique is more accurate, cost-effective and fast
than the other methods, as it involves assembly of numerous molecules with
minimum or no outer influence.
5.3
Classification of Nanosensors
Nanosensors can generally and broadly be classified on the basis of:
1. Structure and type of nanomaterials used for fabrication of nanosensors.
2. Transduction principle.
3. Applications.
4. Various types of analytes for which the nanosensors are used.
Figure 5.1 represents main components of nanosensors and their various types for
environmental applications.
5.3.1 On the Basis of Transduction Principle
Nanosensors can be classified on the basis various techniques employed for transduction of signal. There are different methods for signal transduction but the
nanosensors can be categorized on the basis of main transduction mechanisms:
(1) optical nanosensors, (2) electrochemical nanosensors (3) mechanical/acoustic
nanosensors (Munawar et al. 2019) and (4) magnetic nanosensors.
5.3.1.1 Optical Nanosensors
Optical nanosensors are based on the distinctive optical behaviour displayed by
nanomaterials upon interaction of light signals. The sensitivity of the optical
nanosensors depends mainly on the techniques for detecting the optical phenomenon
(Qu et al. 2012). These nanosensors respond to variation in optical signal transduction and can be further classified according to their particular optical properties like
absorption and emission, surface plasmon resonance (SPR), light scattering,
fluorescence, etc.
Many fluorescence-based nanosensors are designed on the either properties of
non-fluorescent nanomaterials to quench the fluorescence of fluorophores or fluorescence quenching of the fluorescent nanomaterials by other species. The Jablonski
diagram for fluorescence, and fluorescence quenching in the presence of quencher
5 Development of Environmental Nanosensors for Detection Monitoring. . .
95
one by one assembly of individual molecules or atoms into particular positions using
tools like atomic force microscopes (AFM). But this method is mainly used to build
starting molecules for self-assembling sensors.
The third and fastest method for nanosensors fabrication is self-assembly, which
entails growing specific nanostructures for sensors applications. In this method,
mostly set of components that are already complete, are automatically assembled
to give finished products. This technique is more accurate, cost-effective and fast
than the other methods, as it involves assembly of numerous molecules with
minimum or no outer influence.
5.3
Classification of Nanosensors
Nanosensors can generally and broadly be classified on the basis of:
1. Structure and type of nanomaterials used for fabrication of nanosensors.
2. Transduction principle.
3. Applications.
4. Various types of analytes for which the nanosensors are used.
Figure 5.1 represents main components of nanosensors and their various types for
environmental applications.
5.3.1 On the Basis of Transduction Principle
Nanosensors can be classified on the basis various techniques employed for transduction of signal. There are different methods for signal transduction but the
nanosensors can be categorized on the basis of main transduction mechanisms:
(1) optical nanosensors, (2) electrochemical nanosensors (3) mechanical/acoustic
nanosensors (Munawar et al. 2019) and (4) magnetic nanosensors.
5.3.1.1 Optical Nanosensors
Optical nanosensors are based on the distinctive optical behaviour displayed by
nanomaterials upon interaction of light signals. The sensitivity of the optical
nanosensors depends mainly on the techniques for detecting the optical phenomenon
(Qu et al. 2012). These nanosensors respond to variation in optical signal transduction and can be further classified according to their particular optical properties like
absorption and emission, surface plasmon resonance (SPR), light scattering,
fluorescence, etc.
Many fluorescence-based nanosensors are designed on the either properties of
non-fluorescent nanomaterials to quench the fluorescence of fluorophores or fluorescence quenching of the fluorescent nanomaterials by other species. The Jablonski
diagram for fluorescence, and fluorescence quenching in the presence of quencher
5 Development of Environmental Nanosensors for Detection Monitoring. . .
95