spectroscopic and chromatographic techniques. These disadvantages is usually due
to high background noise and in case of naked eye observation, color perception
can vary person to person. In order to increase the accuracy and achieve the low
limit of detection by colorimetric techniques, many research groups today combining these methods with digital imaging techniques.
This chapter intends to provide an overview of the design of colorimetric sensors
which includes principle of colorimetry and various sensing mechanisms on which
sensors are based Also, the recent developments in the materials utilized for the
colorimetric sensing of the water pollutants. Nevertheless, a discussion on the
commercially available colorimetric sensors.
2 Principles, and Sensing Mechanisms of Colorimetric
Sensors
2.1 Principle of Colorimetric Sensors
In order to design the colorimetric sensors for the detection of analyte, there are two
major principle factors which are considered i.e. the change in absorbance value at
particular wavelength and second is the shift in maximum absorption wavelength.
These two factors can be studied and confirmed with the help of UV/Vis spectroscopy and observed by naked eyes. The sensors based upon the first principle,
appears to fade or darken when the analyte is introduced based upon its concentration and in second case, the change of color to the new color is observed. There
are times, when color changes are not observed by naked eyes, even when these
changes are observed with the help of UV/Vis spectroscopy. The rhodamine
based copolymer poly(2, 3-dihydroxybutylene-alt-2,3-dihydroxybutylenedithioether) [P(DHB-a-DHBDT)] self-assembled onto 2-(5-bromopyridine-2-yl)-3′,6′-bis
(diethylamino)spiro-[isoindoline-1,9′-xanthene]-3-thione shows the sensitivity
towards the Hg(II) ions, in which color change from colourless to pink color
observed by naked eyes as shown in Fig. 2. The said probe utilizes the second
principle of colorimetry and its sensing mechanism is based upon the shifting of
aromatic protons in the presence of metal ions [1].
Apart from these above-mentioned principles there are practical considerations
which needs to be considered i.e. solubility of the sensor and matrix of the analyte,
pH of the medium and behaviour of analyte in that pH, and medium does not have
spectral overlap with the analyte to avoid interference while analysis.
Further, there are four major transduction methods or parameters which are
considered or evaluated while designing colorimetric sensors i.e. aggregation
observed while using metal nanoparticles, pH in case of organic dyes, in case of
polymers conjugation geometry, and analyte induced reactions when dependent on
irreversible chemical change. These transduction parameters cause the color
changes upon the addition of the analyte to the matrix.
Materials in Colorimetric Detection of Water Pollutants
127
to high background noise and in case of naked eye observation, color perception
can vary person to person. In order to increase the accuracy and achieve the low
limit of detection by colorimetric techniques, many research groups today combining these methods with digital imaging techniques.
This chapter intends to provide an overview of the design of colorimetric sensors
which includes principle of colorimetry and various sensing mechanisms on which
sensors are based Also, the recent developments in the materials utilized for the
colorimetric sensing of the water pollutants. Nevertheless, a discussion on the
commercially available colorimetric sensors.
2 Principles, and Sensing Mechanisms of Colorimetric
Sensors
2.1 Principle of Colorimetric Sensors
In order to design the colorimetric sensors for the detection of analyte, there are two
major principle factors which are considered i.e. the change in absorbance value at
particular wavelength and second is the shift in maximum absorption wavelength.
These two factors can be studied and confirmed with the help of UV/Vis spectroscopy and observed by naked eyes. The sensors based upon the first principle,
appears to fade or darken when the analyte is introduced based upon its concentration and in second case, the change of color to the new color is observed. There
are times, when color changes are not observed by naked eyes, even when these
changes are observed with the help of UV/Vis spectroscopy. The rhodamine
based copolymer poly(2, 3-dihydroxybutylene-alt-2,3-dihydroxybutylenedithioether) [P(DHB-a-DHBDT)] self-assembled onto 2-(5-bromopyridine-2-yl)-3′,6′-bis
(diethylamino)spiro-[isoindoline-1,9′-xanthene]-3-thione shows the sensitivity
towards the Hg(II) ions, in which color change from colourless to pink color
observed by naked eyes as shown in Fig. 2. The said probe utilizes the second
principle of colorimetry and its sensing mechanism is based upon the shifting of
aromatic protons in the presence of metal ions [1].
Apart from these above-mentioned principles there are practical considerations
which needs to be considered i.e. solubility of the sensor and matrix of the analyte,
pH of the medium and behaviour of analyte in that pH, and medium does not have
spectral overlap with the analyte to avoid interference while analysis.
Further, there are four major transduction methods or parameters which are
considered or evaluated while designing colorimetric sensors i.e. aggregation
observed while using metal nanoparticles, pH in case of organic dyes, in case of
polymers conjugation geometry, and analyte induced reactions when dependent on
irreversible chemical change. These transduction parameters cause the color
changes upon the addition of the analyte to the matrix.
Materials in Colorimetric Detection of Water Pollutants
127