1. A colorimetric sensor, for the detection of unhealthy concentration of anion present in a water sample, comprising a composition of atleast an aluminium nanoparticle, copper sulphate and ferrous sulphate; wherein the composition comprises aluminum nanoparticle, ferrous sulphate and copper sulphate present in a ratio of 2:1:1.

2. The sensor as claimed in claim 1, wherein said sensor is in the form of aqueous solution or in a film.

3. The sensor as claimed in claim 1, wherein said anion comprises halide ion.

4. The sensor as claimed in claim 1, wherein said anion comprises Fluoride ion.

5. The sensor as claimed in claim 1, wherein size of nanoparticle ranges from 5 nm to 15 nm.

6. The sensor as claimed in claim 1,wherein said aluminium nanoparticle is synthesized by a green process, comprising following steps: a) Adding seed powder of approximately 5 g seeds of Z. jujubae into 100 ml deionized water followed by boiling at 80⁰ C for approximately 60 min to obtain filtrate seed extract; b) Adding aluminium nitrate (Al(NO3)3) into seed extract obtained in step (a) in approximately 1:4 ratio (w/w) along with constant stirring at room temperature to obtain a mixture; c) Heating the mixture obtained in step (b) at 540 W for approximately 8 min, which yields a yellow brown precipitate that was later centrifuged; d) Washing the precipitate firstly with water followed by methanol and drying the finally obtained precipitate at approximately 100⁰ C to obtain the aluminium nanoparticle.

7. A portable chitosan based glass sensing probe, based on the composition as claimed in claim 1, for the detection of unhealthy concentration of anion present in water prepared by the following steps: a) Dissolving approximately 1.8 wt % chitosan in approximately 2% (v/v) acetic acid solution to obtain final solution; -17- b) Centrifuging the solution resulting from step (a) at approximately 5000 rpm for about 10 minutes to prevent any insoluble flakes; c) Evenly spreading approximately 1.5ml of the chitosan solution obtained from step (b) on a microscope glass slide followed by leaving for 16hours to dry under atmospheric pressure to obtain the chitosan film; d) Dispensing approximately 200 µl of the composition as claimed in claim 1 on the surface of the chitosan film obtained from step ( c).

8. A method for the detection of unhealthy concentration of anion present in a water sample by the colorimetric sensor composition as claimed in claim 1 comprising the steps of: a) Mixing the water sample to be tested with the sensor composition as claimed in claim 1, wherein said composition and water to be tested for the presence of the halide ion is in the ratio of 4:1 followed by incubation for the time period of 1 to 2 minutes; b) observing the color change in the solution by the naked eye wherein the color change from yellow to green shows the presence of anion in the water sample.

9. The method as claimed in claim 7, wherein said method is highly sensitive to detect the fluoride ions concentration as low as 2 ppm.

10. The method as claimed in claim 7, wherein the anion comprises fluoride ion.

The present invention relates to the field of colorimetric sensor for detection of anion/ halide ion.
More specifically the invention provides a colorimetric fluoride sensor.
Background of the Invention:
The following background discussion includes information that may be useful in understanding
the present invention. It is not an admission that any of the information provided herein is prior
art or relevant to the presently claimed invention, or that any publication specifically or
implicitly referenced is prior art.
Anions play a major role in our daily life, being crucial to physiological function as well as
various industrial processes. Consequently, in the environment, anionic species can be either
essential to sustain growth or act as harmful pollutants. Colorimetric sensors for anions have
become a very active area of research due to various processes based on anion involved in
various applied field.
The monitoring of halide anion more particularly fluoride becomes a necessity nowadays
because of vital importance for various environmental and health-care issues as well as in
industrial and scientific applications. Fluoride is an essential trace elements for humans and
beneficial to maintain dental health and the treatment of osteoporosis. However, excess intake of
fluoride is harmful as it causes fluorosis, acute stomach, bone related diseases, thyroid activity,
nephrotoxic effects, metabolic and neurological disorders in humans and animals (Wan et al.,
2016). Fluoride also cause attention deficit hyperactivity disorder (ADHD) (Malin et al., 2015).
For a large proportion of the world, groundwater is the main resource of drinking water that is
contaminated with fluoride (K. Brindha et al., 2013). World health organization puts the
guideline valve of the fluoride anion in drinking water as 1.5 mg/L (Zhang et al., 2009). Hence,
monitoring of fluoride becomes a necessity nowadays. As of now, several analytical fluoridedetecting and sensing techniques have been reported such as Ion selective electrode, Ion
chromatography, NMR analysis, Fluorescent or colorimetric sensing but all these available
techniques are costly, time consuming, lesser sensitive, have lower specificity, requires large
sample volume and requires skilled personnel, which limit their utility. Colorimetric detection
-3-
method proves to be more rapid, easy to operate, cost-effective, sensitive and highly selective
method.
As of now, several analytical fluoride-detecting and sensing techniques have been reported and
available in prior art such as ion selective electrode, ion chromatography, NMR analysis and
fluorescent or colorimetric sensing but high cost, time consuming, sensitive, low specificity,
large sample volume and skilled personnel limit their utility (Hutchinson et al., 2007). Further,
some of the colorimetric sensor for fluoride or anion detection uses various hazardous chemicals/
materials which are harmful for the human as well as for the environment.
Consequently, there is a need of a simple, effective and on site detection of anion/ halide ion
without resorting or minimal use of any spectroscopic instrumentation.
There is a need of a method and a sensor which is highly sensitive, selective, provides quick
response (i.e. time saving), cost- effective, user-friendly method of detecting the presence of
fluoride in a water. There is also an urgent requirement of an efficient sensor and a method
which requires less amount of sample, which is independent of electricity requirement and which
does not require skilled worker. There is also a need of a green method for sensor devolvement
for the detection of halide ion.
Object/s of the present Invention
The primary object of the present of the present invention is to overcome the limitation of prior
art.
Another object of the present invention is to provide a composition for the colorimetric detection
of anion/ halide sensor.
Yet another object of the present invention is to provide a method of detection of anion /halide
sensor based on the sensor composition as described above.
Yet another objective of the present invention is to provide green and cost effective method for
synthesis of Aluminium nanoparticles (NPs) used in the detection of anion and halide sensor.
Yet another aspect of the present invention is to provide a composition for green synthesis of
aluminium nanoparticle which is used in the preparation of sensor composition.
-4-
Yet another objective of the present invention is to provide a suitable accessible sensing probe
for F ion detection.
Yet another object of the present invention is to provide cost effective and efficient sensor for
detection of anion/ halide ion.
Yet another object of the present invention is to provide halide fluoride sensor, more particularly
a fluoride sensor, which can detect the anion in solution as well as in the solid phase or in a film.
Summary of the Invention:
In an aspect of the present invention there is provided a colorimetric sensor, for the detection of
unhealthy concentration of anion present in a water sample, comprising a composition of atleast
an aluminium nanoparticle, copper sulphate and ferrous sulphate;
wherein the composition comprises aluminum nanoparticle, ferrous sulphate and copper sulphate
present in a ratio of 2:1:1.
In an aspect of the present invention, there is provided a green process for synthesizing
aluminium nanoparticle. In an embodiment, the process comprises following steps:
a) Adding seed powder of approximately 5 g seeds of Z. jujubae into 100 ml deionized
water followed by boiling at 80⁰ C for approximately 60 min to obtain filtrate seed
extract;
b) Adding aluminium nitrate (Al(NO3)3) into seed extract obtained in step (a) in
approximately 1:4 ratio (w/w) along with constant stirring at room temperature to
obtain a mixture;
c) Heating the mixture obtained in step (b) at 540 W for approximately 8 min, which
yields a yellow brown precipitate that was later centrifuged;
d) Washing the precipitate firstly with water followed by methanol and drying the
finally obtained precipitate at approximately 100⁰ C to obtain the aluminium
nanoparticle.
-5-
In an aspect of the Invention, there is provided a portable chitosan based glass sensing probe,
based on the composition as described above, for the detection of unhealthy concentration of
anion present. In an embodiment, the chitosan based glass sensing probe comprises following
steps:
a) Dissolving approximately 1.8 wt % chitosan in approximately 2% (v/v) acetic
acid solution to obtain final solution;
b) Centrifuging the solution resulting from step (a) at approximately 5000 rpm for
about 10 minutes to prevent any insoluble flakes;
c) Evenly spreading approximately 1.5ml of the chitosan solution obtained from step
(b) on a microscope glass slide followed by leaving for 16hours to dry under
atmospheric pressure to obtain the chitosan film;
d) Dispensing approximately 200 µl of the composition as claimed in claim 1 on the
surface of the chitosan film obtained from step ( c).
In another aspect of the Invention, there is provided a method for the detection of unhealthy
concentration of anion present in a water sample by the colorimetric sensor composition. In an
embodiment, the method comprises following steps:
a) Mixing the water sample to be tested with the sensor composition as claimed in claim
1, wherein said composition and water to be tested for the presence of the halide ion
is in the ratio of 4:1 followed by incubation for the time period of 1 to 2 minutes;
b) observing the color change in the solution by the naked eye wherein the color change
from yellow to green shows the presence of anion in the water sample.
Brief Description of the Drawings:
To further clarify advantages and features of the present invention, a more particular description
of the invention will be rendered by reference to specific embodiments thereof, which is
illustrated in the appended drawings. It is appreciated that these drawings depict only typical
embodiments of the invention and are therefore not to be considered limiting of its scope. The
invention will be described and explained with additional specificity and detail with the
accompanying drawings in which:
-6-
Figure 1: illustrates schematic diagram to represent the formation of Al2O3 NPs
Figure 2: illustrates the change in absorbance of ACF solution upon addition of F and other
anionic solutions and values of (A560/240) of ACF solution upon addition of 100 ppm F and other
100 ppm anions. Error bars represent standard deviations based on three independent
measurements.
Figure 3: illustrates the UV-vis spectra of ACF solution in presence of increasing F ions
concentration and absorbance dependence of F ions.
Figure 4: illustrates the schematic representation of sensing probe fabrication.
Figure 5: illustrates the schematic representation of possible mechanism for F detection through
developed colorimetric detector.
Detailed description of the present invention:
In the present document, the word "exemplary" is used herein to mean "serving as an example,
instance, or illustration." Any embodiment or implementation of the present subject matter
described herein as "exemplary" is not necessarily to be construed as preferred or advantageous
over other embodiments.
While the disclosure is susceptible to various modifications and alternative forms, specific
embodiment thereof has been shown by way of example in the drawings and will be described in
detail below. It should be understood, however that it is not intended to limit the disclosure to the
specific forms disclosed, but on the contrary, the disclosure is to cover all modifications,
equivalents, and alternative falling within the spirit and the scope of the disclosure.
The terms “comprises”, “comprising”, “includes”, or any other variations thereof, are intended to
cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of
components or steps does not include only those components or steps but may include other
components or steps not expressly listed or inherent to such setup or device or method. In other
words, one or more elements in a system or apparatus proceeded by “comprises... a” does not,
without more constraints, preclude the existence of other elements or additional elements in the
system or method.
-7-
The present invention relates to the detection of unhealthy concentration of Fluoride (F) in water
samples.
The present invention provides a colorimetric sensor for detection of anion, particularly fluoride
ions. The colorimetric sensor/ detectors according to the present invention is able to detect and
provide quick visual response to halide ions, more specifically fluoride ion above permissible
limit. The colorimetric sensor can detect presence of anion/halide ion concentration by changing
the color.
It involves the development of a chitosan based colorimetric sensing probe by utilizing Al2O3
nanoparticles that were synthesized using Ziziphus jujubae waste seeds. Chitosan being as
natural poycationic linear polysaccharide exhibit specific characteristics such as inexpensive,
eco-friendly, selective, biodegradable and form stable water insoluble films. Due to the presence
of amine group, chitosan is recognized as good chelate for anions in nearly neutral solutions and
considered as an ideal candidate in sensing applications.
In an embodiment, the present invention demonstrates the utilization of Ziziphus jujubae waste
seed extract as both reducing and stabilizing agent for synthesis of Al2O3 NPs. As compared to
previously reported high temperature and complicated instruments involved techniques, applied
green methodology for NPs synthesis using Ziziphus jujubae seed waste is very simple and costeffective. The striking color change associated with F ion induced NPs aggregation has been
successfully employed for the naked eye detection of F. The developed detector shows color
change from yellow to green after addition of F ions as low as 2 ppm instantly. Selectivity of
developed process with other anions such as Cl-
, Br-
, Iand HPO4
-2 has done and no spectral
response was observed.
The Inventors further develops chitosan based glass sensing probe for F to make it more
accessible for human being as it is user-friendly and portable. The detector has also been utilized
for the detection of different F ions concentration in water samples. Easy synthesis,
biocompatibility and low level detection of F ions make it an efficient sensing probe which is
easy to apply in real water systems.
In an aspect of the present invention, there is provided a composition for the colorimetric
detection of anion. In an embodiment, the colorimetric sensor composition comprises atleast an
-8-
aluminium nanoparticle, copper sulphate and ferrous sulphate (also referred as ACF solution
hereinafter); wherein the composition comprises aluminum nanoparticle, ferrous sulphate and
copper sulphate present in a ratio of 2:1:1.
In an embodiment, the sensor is in the form of aqueous solution or in a film.
In an embodiment, the size of nanoparticle ranges from 5 nm to 15 nm.
In an embodiment, the aluminium nanoparticle is synthesized by a green process. The method
comprises following steps:
a) Adding seed powder of approximately 5 g seeds of Z. jujubae into 100 ml deionized
water followed by boiling at 80⁰ C for approximately 60 min to obtain filtrate seed
extract;
b) Adding aluminium nitrate (Al(NO3)3) into seed extract obtained in step (a) in
approximately 1:4 ratio (w/w) along with constant stirring at room temperature to
obtain a mixture;
c) Heating the mixture obtained in step (b) at 540 W for approximately 8 min, which
yields a yellow brown precipitate that was later centrifuged;
d) Washing the precipitate firstly with water followed by methanol and drying the
finally obtained precipitate at approximately 100⁰ C to obtain the aluminium
nanoparticle.
In another aspect of the Invention, there is provided a portable chitosan based glass sensing
probe, based on the composition as described above for the detection of unhealthy concentration
of anion present in water.
In an embodiment, the chitosan based glass sensing probe is prepared by the following steps:
a) Dissolving approximately 1.8 wt % chitosan in approximately 2% (v/v) acetic
acid solution to obtain final solution;
b) Centrifuging the solution resulting from step (a) at approximately 5000 rpm for
about 10 minutes to prevent any insoluble flakes;
-9-
c) Evenly spreading approximately 1.5ml of the chitosan solution obtained from step
(b) on a microscope glass slide followed by leaving for 16hours to dry under
atmospheric pressure to obtain the chitosan film;
d) Dispensing approximately 200 µl of the composition as claimed in claim 1 on the
surface of the chitosan film obtained from step ( c).
In another aspect of the present invention there is provided a method for the detection of
unhealthy concentration of anion present in a water sample by the colorimetric sensor
composition as described above.
In an embodiment, the method of detection comprises the steps of mixing the water sample to be
tested with the sensor composition as described above. In an embodiment, the composition and
water to be tested for the presence of the halide ion is in the ratio of 4:1. After the step of mixing,
the final solution is incubated for the time period of 1 to 2 minutes. Thereafter, the color change
in the solution is observed through naked eye. The color change from yellow to green shows the
presence of anion in the water sample. The method is highly sensitive to detect the fluoride ions
concentration as low as 2 ppm.
Figure 8 illustrates an embodiment showing Fluoride detection through colorimetric detector
provided by the present invention. The visual color alteration in ACF solution is due to the
interaction of functional groups present on the surface of NPs with anion. This interaction is
responsible for aggregation of nanoparticles. The ACF solution showed the involvement of OH
functionality in the F detection method. Firstly, in the presence of sulfate ions the aluminium in
solution may be complexed with sulfate (Fig. 5). Further, the appearance of green color after
addition of F salt is due to the exchange of F ions with hydroxyl ions. Bonding of the F anion to
the H+
of the surface, forms an anion to dipole (-O---H
+
---F
-
) complex structure. Thus the color
developed from yellow to green reveal the metal ligand interaction. This occurred because of the
similarity in ionic radius of the iso-electronic OH and F ions.
-10-
The below table shows comparison of the conventional technique versus the technique provided
by the present Invention.
Available techniques (F detection) Chitosan/Al2O3 NPs based sensing
probe
Chemical based visual detection Green synthesized Nanoparticles based
detection
High Energy requirement Less Energy requirement
Low sensitivity High sensitivity
Non-portable Portable
Complex process / mechanism Easy process/ mechanism
Require functional group for sensing probe No functional group require
Electricity independent Electricity independent
High cost Low cost
The Inventor is further described with the help of non-limiting examples:
Example 1:
Synthesis of aluminium oxide nanoparticles
The Z. jujubae seeds were used for green synthesis of Al2O3 NPs because these are common
household waste produced in the local area, affordable and environment friendly. Firstly, 5 g
seeds of Z. jujubae were washed several times with distilled water and crushed with motor
pestle. The resulting seed powder was added into 100 ml deionized water and boiled at 80 ⁰ C
for 60 min. After cooling, the procured suspension was filtered with the help of Whatman’s filter
paper and stored at 4 ⁰ C. Further, the filtrate seed extract was used as a reducing and stabilizing
agent for NPs synthesis.
-11-
For Al2O3 NPs synthesis aluminium nitrate (Al(NO3)3) was added into seed meal extract with
1:4 ratio (w/w) and allowed constant stirring at room temperature. The mixture obtained was
microwave heated at 540 W for 8 min, which yield a yellow brown precipitate that was later
centrifuged. The precipitate was washed with Millipore water followed by methanol and dried at
100 ⁰ C in oven. Finally, the nanoparticles were characterized through SEM, EDX and XRD.
Example 2:
Characterization of NPs
The surface morphology and elemental composition of synthesized Al2O3 NPs was characterized
by using FESEM and EDX spectrum analysis. Figure 1 (a to d) clearly indicates the formation of
Al2O3 NPs. The FESEM image illustrates appearance of green synthesized Al2O3 NPs as flakes
with irregular shapes (Fig. 1a). The EDX measurements of Al2O3 NPs showed the presence of O
(53.11%), Al (25.09%) and Si (21.80%) (Fig.1b). Based on the EDX spectrum analysis, it was
confirmed the presence of Al elements in the samples.
Phase purity and crystallinity of the prepared Al2O3 NPs was recognized through XRD analysis.
The XRD patterns of synthesized Al2O3 NPs are shown in Fig. 1c. The three major diffraction
peaks of synthesized Al2O3 NPs were detected at 2 θ = 66.80 ⁰ , 45.62 ⁰ and 36.94 ⁰ (Fig. 1c)
which are corresponded to the crystal planes of (240), (-422) and (221), respectively. The XRD
patterns declared the monoclinic crystal phase of Al2O3 NPs (00-011-0517). The average
crystalline size of NPs can be determined using the Debye-Scherrer equation (Homaeigohar et
al., 2014). Debye-Scherrer equation is shown as:
D= kλ/ βhkl cosθhkl

Where D is the crystallite size, k is Scherrer constant (0.9), λ is the X-ray wavelength of
radiation for Cu Kα (0.154 nm), βhkl is the full-width at half maximum (FWHM) and hkl is the
diffraction angle. The calculated crystallite size of Al2O3 NPs was 11.64 nm.
The synthesized material in this study is designed to be potentially used in water purification
system and thus require the property to withstand a temperature range of 20-175 ⁰ C. The
thermal stability of Al2O3 NPs expressed in weight (mg) of the samples and temperature range of
30-700 ⁰ C. The thermogravimetric curve (TG) (Fig. 1d) of synthesized Al NPs showed a sharp
-12-
weight loss in the range of 240-270 ⁰ C. This weight loss could be attributed to the volatilization
of organic residues attached on the surface of NPs. After the volatilization of organic residues
there was no weight loss at melting region of aluminium (650 ⁰ C). This result suggested the
higher stability of Al2O3 NPs.
Example 3:
Development of detector
A stock solution of F (100 mgL-1
) was prepared by addition of 0.0221 g NaF to 100 ml double
distilled water. Colorimetric detection of F ions was done to identify the selectivity and low
concentration limit of detector. For the detection, 500 µL of different concentrations of F ion (2
ppm, 4 ppm, 6 ppm, 8 ppm, 10 ppm and above) was added in ACF solution (2000 µL) to identify
the lowest naked eye detection limit. Selectivity tests for F ion were carried with some other
anions. F colorimetric detection was done using ACF solution (Al NPs-CuSO4-FeSO4). Firstly,
ACF solution was prepared with composition of 1000 µL Al NPs (1mgml-1
), 500 µL CuSO4, 500
µL FeSO4 (1.2 g in 50 ml distilled water) till solution color become yellow. Next, 2000 µL of
ACF solution was mixed with 500 µL of different concentration of F ion. After incubation for 1-
2 min, green color of solution was observed by naked eye. All selectivity tests were carried out
with some other anions such as chloride (Cl-
), bromide (Br-
), iodide (I-
), phosphate (P-
) and
nitrate (NO3-
) (100 ppm). UV- vis spectrum was also recorded for different F ion concentrations.
Example 4:
Detection of F ion
For the practical utilization of colorimetric detectors, they should be able to detect and provide
quick visual response to F ions above permissible limit. To validate the application of the
developed colorimetric detector for application in detection in biological samples, the selectivity
of the detector was tested for F ions. This was achieved by monitoring the color response of ACF
solution upon addition of F and other anions such as Cl, Br, I, PO4 and NO3. A distinct color
change from yellow to green was observed upon addition of different concentration as 2 ppm, 4
ppm, 6 ppm, 8 ppm, 10 ppm and above in ACF solution. Results depicted a notable color change
-13-
on addition of 2-4 ppm F solution in ACF mixture from yellow to green. Next, more distinct
color change was observed on addition of 6 ppm, 8 ppm and above F solution from yellow to
green and dark green, respectively. In contrast, no observable color change was observed with
other anions. Thus, notable sensing ability of ACF solution was observed towards F ions at
concentration as low as 2 ppm.
The maximum absorbance wavelength (λmax) of ACF solution was observed at 240 nm and the
addition of F solution significantly changed the absorbance spectrum. The absorbance at 240 nm
was reduced and a new band observed at about 560 nm with the color change from yellow to
dark green (Fig. 2a). The maximum wavelength of ACF at 240 nm can be attributed to
photoexcitation of aluminium electrons from valence band to conduction band (Prashanth et al.,
2015). Addition of F ions caused formation of other peak at around 560 nm which is due to
bathochromic shift witnessed probably due to the formation of hexafluoroaluminate. In this
complex, bonding between F anion and H+ ion caused the color formation. However, slight
change in absorbance at 240 was observed and no new band was reported on addition of other
anions, such as Cl-
, Br-
, Iand HPO4
-2
.
For analyzing the selectivity of ACF solution for other anions, the absorption titration of ACF
solution against other anions was performed (Fig. 2b). We analyzed the variation in values of
absorption ratio (A560/240) for ACF solution that considered after 5 min upon the addition of the F
and other metal ions. The concentration of other metal ions analyzed after 5 min at 100 times of
F ions. Upon ACF solution interaction with several anions, both the absorption spectral changes
and the absorbance ratio A560/240 changes of ACF solution are presented in Fig. 2b. Only F ions
were observed with significant A560/240 value. Thus, it can be concluded that developed
colorimetric detector is highly selective for F ions as compared to all other anions.
Next, for sensitivity evaluation of ACF solution, UV titration was performed by varying the F
ions concentration (Fig. 3a). Notable sensitivity of ACF solution was observed towards F ions at
concentration as low as 2 ppm. The Al NPs containing ACF solution displayed absorption band
at around 240 nm which is assigned to OH functional group. Further, on addition of F ions to
ACF solution, band reduction was observed in the studied region. This gradual decrease in
absorption band attributed to the involvement of –OH groups in detection process. Next, new
absorption band at 560 nm was observed with bathochromic shift of 320 nm attributed to the
-14-
intramolecular charge transfer (ICT) transition between the ACF solution and F ion complex
(Fig. 3a). Thus, the F ion concentrations in the solution could be identified through changes in
the absorbance intensity at particular peaks (Fig. 3b). As shown in fig. 3b, the F ions
concentration is linearly dependent on the absorbance intensity. A linear relationship between the
R-value and the concentrations of F ions could be obtained in the range of 2 ppm to 14 ppm
(R2
=0.990). Therefore, F ions concentration in different water or plant samples could be
examined through colorimetric detector.
Example 5:
Fabrication of sensing probe
The sensing probe was fabricated by first preparing Chitosan film on the glass surface. The
Chitosan films were prepared as described by the Lauto et al., without the addition of other
chemicals. Chitosan (medium molecular weight, 85% deacetylation) was dissolved at 1.8 wt %
in 2% (v/v) acetic acid solution. The solution was centrifuged at 5000 rpm for 10 min to get rid
of any insoluble flakes. Chitosan solution (1.5 ml) was evenly spread on a microscope glass slide
(7cm× 2 cm) and left for 16hrs to dry under atmospheric pressure. Then 200 µl of ACF solution
was dispensed on the surface of the chitosan film.
Example 6:
The experiment is performed with different concentration of colorimetric sensor constituents.
The results are mentioned in the below table. The results clearly shows the significance of ratio.
Only the ratio where aluminum nanoparticle, ferrous sulphate and copper sulphate is present in a
ratio of 2:1:1 provides visible detection.

We Claim:

1. A colorimetric sensor, for the detection of unhealthy concentration of anion present in a
water sample, comprising a composition of atleast an aluminium nanoparticle, copper
sulphate and ferrous sulphate;
wherein the composition comprises aluminum nanoparticle, ferrous sulphate and copper
sulphate present in a ratio of 2:1:1.
2. The sensor as claimed in claim 1, wherein said sensor is in the form of aqueous solution
or in a film.
3. The sensor as claimed in claim 1, wherein said anion comprises halide ion.
4. The sensor as claimed in claim 1, wherein said anion comprises Fluoride ion.
5. The sensor as claimed in claim 1, wherein size of nanoparticle ranges from 5 nm to 15
nm.
6. The sensor as claimed in claim 1,wherein said aluminium nanoparticle is synthesized by a
green process, comprising following steps:
a) Adding seed powder of approximately 5 g seeds of Z. jujubae into 100 ml deionized
water followed by boiling at 80⁰ C for approximately 60 min to obtain filtrate seed
extract;
b) Adding aluminium nitrate (Al(NO3)3) into seed extract obtained in step (a) in
approximately 1:4 ratio (w/w) along with constant stirring at room temperature to
obtain a mixture;
c) Heating the mixture obtained in step (b) at 540 W for approximately 8 min, which
yields a yellow brown precipitate that was later centrifuged;
d) Washing the precipitate firstly with water followed by methanol and drying the
finally obtained precipitate at approximately 100⁰ C to obtain the aluminium
nanoparticle.
7. A portable chitosan based glass sensing probe, based on the composition as claimed in
claim 1, for the detection of unhealthy concentration of anion present in water prepared
by the following steps:
a) Dissolving approximately 1.8 wt % chitosan in approximately 2% (v/v) acetic
acid solution to obtain final solution;
-17-
b) Centrifuging the solution resulting from step (a) at approximately 5000 rpm for
about 10 minutes to prevent any insoluble flakes;
c) Evenly spreading approximately 1.5ml of the chitosan solution obtained from step
(b) on a microscope glass slide followed by leaving for 16hours to dry under
atmospheric pressure to obtain the chitosan film;
d) Dispensing approximately 200 µl of the composition as claimed in claim 1 on the
surface of the chitosan film obtained from step ( c).
8. A method for the detection of unhealthy concentration of anion present in a water sample
by the colorimetric sensor composition as claimed in claim 1 comprising the steps of:
a) Mixing the water sample to be tested with the sensor composition as claimed in claim
1, wherein said composition and water to be tested for the presence of the halide ion
is in the ratio of 4:1 followed by incubation for the time period of 1 to 2 minutes;
b) observing the color change in the solution by the naked eye wherein the color change
from yellow to green shows the presence of anion in the water sample.
9. The method as claimed in claim 7, wherein said method is highly sensitive to detect the
fluoride ions concentration as low as 2 ppm.
10. The method as claimed in claim 7, wherein the anion comprises fluoride ion.