colorimetric sensors

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• King Fahd University of Petroleum and Minerals
• Chemistry Department
• CHEM 540 Advanced Analytical Chemistry
• Colorimetric Sensors
• (Applications, merits and advances)
• Student Name Adelabu Isaiah Olabisi
• Student ID 201404120
• 20th December 2014

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OUTLINE

• Introduction
• Colorimetry and Colorimetric Sensors
• Applications
• Merits and Advances
• Conclusion

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Colorimetry refers to the science which
identifies, quantifies and characterizes colour
instrumentally or through the use of human colour
perception. There are lots of reactions or
experiments in which colour is the determining
factor for judging and making calculations
(comparison of colour is very important). The
purpose of colorimetry is the numerical
characterization of colours in a way that two
materials having the same specifications, under
given conditions, are always known to have the
same colour under those conditions.

• Three factors for assessing colour properties
  are
• Source of light or illumination
• Transmission/Absorbance/Reflection of light by
  the object
• Detection/Observation

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It differs from spectophotometry in the sense
that while the later covers the whole
electromagnetic spectrum, it addresses the
visible region of the spectrum by streamlining
spectra to the physical match of colour
perception and related quantities

• Colorimetric sensors are materials, devices,
  molecules and compounds that have the potential
  of detecting changes in colour properties or
  generating changes that can be linked to standard
  colour measurements. They have found wide
  applications in chemistry and other fields
  because of their high sensitivity and selectivity.

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A COLORIMETRIC MICROWELL METHOD FOR BIOCHEMICAL
ANALYSIS

• This is a method of fast, cheap and sensitive
  analysis of creatine, total cholesterol, glucose,
  total protein and triglycerides. Clinical
  analysis and biochemical tests are very important
  for timely diagnosis of diseases and illnesses .
  A good example is that of cholesterol
  determination by the interaction of cholesterol
  oxidase and an assay which yields red coloured
  quinine imine (?500nm). The colour intensity is
  proportional to the concentration of the total
  cholesterol present in the sample.

The quantity of these biochemical samples can be
determined by measuring the absorbance where
analyte also form characteristic complexes that
absorb in the visible region of the
electromagnetic spectrum. Each analyte has a
specific absorption band which can be interpreted
quantitatively
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Experimental arrangement to collect and analyze
images to determine the concentration of glucose,
triglycerides, total cholesterol, creatine and
total protein in a blood sample.
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Mirowells on microplates with standard chemical
analysis miniaturized on them provides a modern
approach to analytical techniques. These include
methods that make use of optical scanners and
photo assisted techniques on computer screen.
Digital images obtained from these sensors ( e.g
video camera or plate) which act as
charge-coupled devices (CCD) can be analyzed and
translated into millions of colours and compared
to standard measurements. The aim of this work is
to use a 64-microwell plate design and a scanner
to quantitatively characterize biochemical assays
in the blood using a two dimensional analysis
array. In this method, there appears to be an
addition of a form of user friendly interface
(Graphical User Interface) which is made in a
laboratory to improve analytical curves and to
program the statistical, mathematical
calculations that will improve the analytical
result of the biochemical analysis.
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1. Image loading. 2. Selection of image for
statistical data 3. Concentration prediction of
selected sample parameter. A. Micro well plate
main view showing rows and columns. B. Selected
image view. C. Curve of predicted concentration
against measured concentration. D. Graphical
display of result. E. Predicted concentration
value.
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Curves of Absorbance against Concentrations
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The data analysis can be done by uploading into
computational software such as MATLAB, the pixels
of the Red, Green and Blue colours can be
analyzed and the intensities correlated with a
standard measurement(absorbance value). This
employs the use of the Beer Lamberts law which
can be represented mathematically as A -Log
(I/I0) A ECL Where A Absorbance, I
intensity of R,G,B I0 maximum pixel value. C
concentration, L path length. The micro well
plates show characteristic colour value that can
be matched to each biochemical assay thereby
presenting an effective and efficient analytical
result using colorimetric sensors.
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SILVER NANOPLATES-BASED COLORIMETRIC SENSORS
Silver nanostructures having varying shapes and
sizes possess characteristic optical properties .
These nanostructures can be nanowires , nanobelts
, nanoplates , nanocrystals , nanocubes e.t.c.
This shows a colorimetric method for determining
and sensing Iodide ions (I-) by utilizing the
reactions between iodide ions and triangular
silver nanoplates (TAg-NPs) using sodium
thiosulfate as a sensitizer (Na2S2O3). The role
of the sensitizer is to improve the sensitivity
and selectivity of the silver nanostructure as a
sensor. The interesting surface Plasmon
properties are applicable for surface-enhanced
raman scattering , biological sensing, optical
label and chemical sensing . Triangular silver
nanoplates (TAg-NPs) have drawn attention over
the past few decades as a result of their
characteristic plasmonic properties across
visible and near infrared regions.
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In this review, specific morphological changes
and transformation of optical properties of
TAg-NPs to sense traces of Iodide was based on
the chemical interactions between TAg-NPs and
Iodide ion (I-) in the presence of Na2S2O3 . The
introduction of Na2S2O3 to TAg-NPs and Iodide ion
(I-) mixture increases the detection limit and
selectivity for iodide ions detection. Its
concentration as low as 1.010-9molL-1 can be
determined compared to the range for UV-visible
spectroscopy which is 1.010-9molL-1 to
1.010-6molL-1. Reactions of TAg-NPs and Iodide
ion (I-) only and in the presence of Na2S2O3 are
shown below
It was observed that the absorption peak of
TAg-NPs slowly blue -shifted from 666nm to 427nm
with increase in concentration of Na2S2O3. In
addition, the TAg-NPs colour changes from blue to
yellow.
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UVVis spectra of TAg-NPs by the addition of I
, the concentrations of I are 0, 0.05, 0.1,
0.25, 0.5, 0.75, 1.0, 1.75, and 2.5 µM,
respectively for spectra 19. (b) TEM image of
TAg-NPs after reaction with 2.5 µM I . pH 7.96,
n 1, reacted for 40 min under room
temperature.
(a) UVVis spectra of TAg-NPs in the presence of
different concentrations of Na2S2O3 (b) TEM
of TAg-NPs in the presence of Na2S2O3
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DETECTION OF Hg2 IN AQUEOUS SYSTEM USING PLANT
EXUDATE REDUCED SILVER NANOPARTICLES
This has proven to be a highly sensitive and
selection analytical technique for the
colorimetric detection of the presence of toxic
Hg2 in aqueous system. The Silver Nanoparticles
(Ag-NPs) used was produced using a reducing and
stabilizing exudates of gum kondagogu (GK). The
bright yellow colour characteristic of the Ag-NPs
fades away upon the addition of various
concentrations of Hg ions. The fading can be
directly linked to the increasing concentrations
of Hg2 in the system. The metal sensing
mechanism is described based on X-ray diffraction
and turbidometric analysis of GK-Ag NPs with
Hg2. This analysis employs the use of UV-Visible
spectrophotometer, X-ray diffraction,
Transmission electron microscope analysis and
Scanning electron microscopy-energy dispersive
X-ray .
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UVvisible spectra of as synthesized GKAg NPs
and Ag NPs in the presence of 1200 nM of Hg2
ions. Inset Photograph showing colour change of
Ag NPs from yellow to colourless after Hg2
addition.
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SEM micrographs of Ag NPs (a) before addition and
(b) after addition Hg2 and corresponding EDAX
profiles
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UVvisible spectra of GKAg NPs recorded in the
presence of various cations, (b) the colorimetric
response of GKAg NPs to various cations and (c)
spectroscopic response of GKAg NPs to CH3Hg
before and after irradiation.
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UVvisible spectra of GKAg NPs after addition of
Hg2 ions of various concentrations (0500 nM)
(b) Graphical plot between absorbance at 400
nm versus concentration of Hg2 ions in nM.
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The synthesized GK-AgNP was found to be
relatively stable at various concentrations as
there was no observable change in the UV-Visible
spectra, also it was stable within pH ranges of
6-11 because at lower pH value there was
significant difference in absorption intensity.
The limit of quantification show high detection
as shown in table 1, also comparison with CVAAS
show high accuracy of AgNPs as mercury ions
detector as shown in table 2.
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CONCLUSION Colorimetric sensors have proven to be
an alternative to other analytical techniques
because of its portability, ease of usage, cheap
cost and analysis run time among several other
factors. In biochemical analysis, they reduce the
relative amount of solvent/ analytes used for
analysis. It serves as a mean of early detection
of diseases/ illnesses by applying readily
available test kits. Researches are on-going in
this field to continually develop colorimetric
sensors to replace complex analytical techniques
without compromising sensitivity and selectivity
which are of paramount importance in analytical
chemistry.
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• REFERENCES
• Hou, X., Chen, S., Tang, J., Xong, Y, Long, Y.
  (2014). Silver nanoplates-based colorimetric
  iodide recognition and sensing using sodium
  thiosulphate as a sensitizer. Analytica Chimica
  Acta, 825, 57-62. dio10.1016/j.aca.2014.03.038.
• Lori Rastogi, R.B. sashidhar, D.Karunasagar,
  J.Arunachalam (2014). Gum Kondagogu
  reduced/stabilized silver nanoparticles as direct
  colorimetric sensor for the sensitive detector of
  Hg2 in aqueous system. Analytica Chimica Acta
  ,118, 111-117.
• Medeiros de Morais, C.D.L, de Lima, K.M.G.
  (2014). A Colorimetric microwell method using a
  desktop scanner for biochemical assays. Talanta,
  126, 145-50. dio 10.1016/j.talanta.2014.03.066.

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