Description:FIELD OF THE INVENTION
[0001] The present disclosure pertains to the field of chemical analysis or sensing technology. More particularly, the present disclosure relates to a chemical sensor composed of hemicyanine dye represented by the formula (1). The present disclosure also relates to a method of detection of ammonia by using hemicyanine dye represented by the formula (1).

BACKGROUND OF THE INVENTION
[0002] Background description 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.
[0003] Ammonia is a basic volatile compound that readily dissolves in water. Ammonia plays a very crucial role in several fields due to its chemical properties and wide range of applications such as in fertilizer production, chemical industries, refrigeration, fuel and energy, water treatment, in explosive production, textiles and plastic industry. However ammonia is a toxic gas. Presence of ammonia causes severe respiratory irritation. Ammonia emissions from agriculture, industrial and waste treatment can cause significant health and environmental risks. An accurate real time liquid ammonia sensor (ammonia in the dissolved form) allows for the detection of hazardous concentrations preventing human exposure and ensuring compliance with safety. Additionally it helps to monitor air and water pollution and safe guarding ecosystems. It poses a potential hazard for humans as well as other life forms even at a very low concentration. It is important to sense ammonia with selective and low cost chemo-sensors. Various types of ammonia sensors have been designed for the detection of ammonia with different stimuli response mechanism. However a sensor with continuous monitoring of ammonia concentration in the ppm level is of high demand. There are many different sensors available to detect the gaseous ammonia such as IR based detection, electrochemical sensors, and semi-conductor based solid state sensors. Even though ammonia gas sensors are numerous, the sensors for the detection of ammonia in aqueous media are less explored. Precise detection of ammonia with optical chemo-sensors are in the spotlight due to their cost effective production, strong EMI-resistance, high reproducibility, long life time, and compatibility with biological and explosive environments.
[0004] The optical sensors responding to ammonia uses its Lewis base properties. Ammonia deprotonates triphenylmethane type dyes, xanthane dyes, coumarine based dyes bringing about easily detectable optical changes. Bromocresol purple, phenol red, fluorescein, and their derivatives have already been employed in sensor fabrication. Even though several classes of dyes have been used as ammonia sensors, a good photostability and sensitivity still exists as a challenge. Recently Seong-Min Ji et al developed two hemicyanine dyes with dihydroxybenzene donor as gaseous sensor of volatile compound ethylamine (EtNH2).
[0005] The development of low cost sensitive and durable ammonia sensors is essential for ensuring public health, environmental protection and enhancing industrial process control.

OBJECTS OF THE INVENTION
[0006] An objective of the present invention is to provide a hemicyanine dye represented by the formula (1).
[0007] Another objective of the present invention is to provide a method of preparation of a hemicyanine dye represented by the formula (1).
[0008] Another objective of the present invention is to provide a chemical sensor for detection of ammonia.
[0009] Still another objective of the present invention is to provide a method of detection of ammonia.
[0010] Another objective of the present invention is to provide a dye coated paper strips.
[0011] Yet another objective of the present invention is to provide a cost effective, environment friendly sensor for selectively detection of ammonia.

SUMMARY OF THE INVENTION
[0012] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0013] An aspect of the present disclosure is to provide a hemicyanine dye represented by the formula (1) comprising:

(Formula 1)
[0014] Another aspect of the present disclosure is to provide a method of preparation of a hemicyanine dye represented by the formula (1) comprising: a) refluxing 0.02 mmol of 2-methylbenzothiazole and 0.05 mmol of bromo acetic acid in a dioxane under condition followed by precipitation with diethyl ether, filtering and washing with a mixture of 2-propanol and diethyl ether to obtain a solid compound of Formula (A); and b) refluxing 0.005 mmol of compound of Formula (A) with of 0.005 mmol of 4-hydroxy benzaldehyde of Formula (B) in methanol and piperidine under condition followed by filtering and washing with methanol and diethyl ether to obtain a hemicyanine dye represented by the formula (1).

(Formula A) (Formula B) (Formula 1)
[0015] Still another aspect of the present disclosure is to provide a chemical sensor for detection of ammonia comprising: a sensing element composed of the hemicyanine dye represented by the formula (1) as defined above.
[0016] Yet another aspect of the present disclosure is to provide a method of detection of ammonia comprising: dissolving the hemicyanine dye represented by the formula (1) as defined above in water to obtain a dye solution; exposing the ammonia in presence of dye solution; and interacting the hemicyanine dye represented by the formula (1) with ammonia undergoes a rapid interaction bringing a measurable and visible change in the optical properties which is monitored spectrophotometrically.
[0017] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

DESCRIPTION OF THE FIGURES
[0018] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0019] Figure 1 illustrates absorption spectra of dye in solvents of different polarity. Concentration of dye: 3.5x10-5M.
[0020] Figure 2 illustrates plot of absorption maximum (cm-1) vs dielectric constant (ε) of dye in solvents of different polarity.
[0021] Figure 3 illustrates TGA of the dye.
[0022] Figure 4 illustrates Calibration curve for the photostability studies.
[0023] Figure 5 illustrates a) the frontier molecular orbital distribution for Formula 1 and Formula 2; b) the topological diagram depicting the bond critical point between the dye and NH3 for the intermediate formed after the addition of NH3 to Formula 1; c) the TD-DFT simulated absorption spectral features for Formula 1 and Formula 2.
[0024] Figure 6 illustrates addition of various analytes to the solution of the dye in aqueous solution: photo images of colour changes observed with naked eye.
[0025] Figure 7 illustrates a schematic representation of sensor.
[0026] Figure 8 illustrates response curve.
[0027] Figure 9 illustrates calibration curve.
[0028] Figure 10 illustrates real time monitoring of bacterial growth as function of ammonia concentration.
[0029] Figure 11 illustrates effect of pH.
[0030] Figure 12 illustrates repeatability studies of the sensor.
[0031] Figure 13 illustrates interference studies.

DETAILED DESCRIPTION OF THE INVENTION
[0032] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0033] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising,” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0034] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[0035] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in the light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0036] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it is individually recited herein.
[0037] All processes described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0038] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0039] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0040] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0041] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description that follows, and the embodiments described herein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[0042] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0043] The present disclosure provides a novel ammonia sensor capable of detecting trace amounts of liquid ammonia in liquid or gaseous forms. The sensor is based on a hemicyanine dye that interacts selectively with ammonia molecules and generates a visible colour change from yellow to pink as a function of ammonia concentration. This sensor is designed for real time monitoring with high sensitivity fast response time and excellent thermal and photo stability. This can easily integrate with the existing industrial monitoring systems. The key invention in the sensor lies in its use of hemicyanine dye which enhances its selectivity towards ammonia with no interference from other molecules of same kind.
[0044] An embodiment of the present disclosure is to provide a hemicyanine dye represented by the formula (1) comprising:

(Formula 1).
[0045] Another embodiment of the present disclosure provides a method of preparation of a hemicyanine dye represented by the formula (1) comprising: a) refluxing 0.02 mmol of 2-methylbenzothiazole and 0.05 mmol of bromo acetic acid in a dioxane under condition followed by precipitation with diethyl ether, filtering and washing with a mixture of 2-propanol and diethyl ether to obtain a solid compound of Formula (A); and b) refluxing 0.005 mmol of compound of Formula (A) with of 0.005 mmol of 4-hydroxy benzaldehyde of Formula (B) in methanol and piperidine under condition followed by filtering and washing with methanol and diethyl ether to obtain a hemicyanine dye represented by the formula (1).

(Formula A) (Formula B) (Formula 1)

[0046] In an embodiment, the condition in step a) includes temperature in the range of 80 to 120 °C for a period in the range of 6 to 10 hrs. Preferably, the temperature is in the range of 90 to 110 °C for a period in the range of 7 to 9 hrs. More preferably, the temperature is 100 °C for a period of 8 hrs.
[0047] In an embodiment, the condition in step b) includes temperature in the range of 50 to 80 °C for a period in the range of 10 to 14 hrs. Preferably, the temperature is in the range of 60 to 70 °C for a period in the range of 11 to 13 hrs. More preferably, the temperature is 64 °C for a period of 12 hrs.
[0048] Still another embodiment of the present disclosure provides a chemical sensor for detection of ammonia comprising: a sensing element composed of the hemicyanine dye represented by the formula (1) as defined above.
[0049] In an embodiment, the chemical sensor operates in the range of 0.056 pm to 2.08 pm with LOD of 0.263 ppm.
[0050] In an embodiment, the chemical sensor as and when used for preparing dye coated paper strips for sensing ammonia in liquid or gaseous forms.
[0051] Yet another embodiment of the present disclosure provides a method of detection of ammonia comprising: dissolving the hemicyanine dye represented by the formula (1) as defined above in water to obtain a dye solution; exposing the ammonia in presence of dye solution; and interacting the hemicyanine dye represented by the formula (1) with ammonia undergoes a rapid interaction bringing a measurable and visible change in the optical properties which is monitored spectrophotometrically.
[0052] In an embodiment, the hemicyanine dye represented by the formula (1) interacts with ammonia molecules generating a visible colour change from yellow to pink as a function of ammonia concentration.
[0053] In an embodiment, the hemicyanine dye represented by the formula (1) shows high selectivity toward ammonia molecules in presence of other interfaces.
[0054] Synthesis of 3-(carboxymethyl)-2-methylbenzo[d]thiazol-3-ium bromide is shown in Scheme 1. A mixture of 2-methylbenzothiazole (2.98g, 0.02mmol) and bromo acetic acid (6.94g, 0.05mmol) in dioxane (10ml) was refluxed for 8hrs. A pink colour solid was obtained after precipitation with diethyl ether, filtered off, and washed with a mixture of 2-propanol and diethyl ether to obtain 3-(carboxymethyl)-2-methylbenzo[d]thiazol-3-ium bromide.

(Formula A1) (Formula A2) (Formula A)
Scheme 1: Synthesis of 3-(carboxymethyl)-2-methylbenzo[d]thiazol-3-ium bromide
[0055] Synthesis of (Z)-3-(carboxymethyl)-2-(4-hydroxystyryl)benzo[d]thiazol-3-ium bromide is shown in Scheme 2. A mixture of benzothiazolium salt (1.5g, 0.005mmol) and 4- hydroxy benzaldehyde (0.61g, 0.005mmol) in 20 ml of methanol along with 1 ml of piperidine was refluxed at 64oC for 12 hrs in inert atmosphere of nitrogen. The dye obtained after 12 hrs was filtered and washed with methanol and diethyl ether to obtain the pure product.

(Formula A) (Formula B) (Formula 1)
Scheme 2: Synthesis of dye.
[0056] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions, or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
EXAMPLES
[0057] The present invention is further explained in the form of the following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.
Example 1:
(A) Synthesis of 3-(carboxymethyl)-2-methylbenzo[d]thiazol-3-ium bromide:
[0058] A mixture of 2-methylbenzothiazole (2.98g, 0.02mmol) and bromo acetic acid (6.94g, 0.05mmol) in dioxane (10ml) was refluxed for 8hrs. A pink colour solid was obtained after precipitation with diethyl ether, filtered off, and washed with a mixture of 2-propanol and diethyl ether. The yield was 6.8g (68%) : mp. 139 ±1oC. The FTIR spectrum exhibited absorption bands at 3305, 2895, 2729, 2516, 1946, 1734, 1439, 1351, 1227, 768 cm-1; 1HNMR (MeOD, 400MHz) 8.25 (dd, J = 8Hz, 1H) 8.10 (d, J = 8.4Hz, 1H) 7.83 (dddd,J=7.8Hz 1H) 7.75 (dddd, J =7.7Hz1H) 5.65 (s, 2H) 3.17 (m, 3H) 13CNMR (MeOD, 400MHz) 178.85, 166.02, 141.52, 129.90, 128.84, 128.58, 124.03, 116.05, 49.45, 15.45 ppm.
(B) Synthesis of (Z)-3-(carboxymethyl)-2-(4-hydroxystyryl)benzo[d]thiazol-3-ium bromide
[0059] A mixture of benzothiazolium salt (1.5g, 0.005mmol) and 4- hydroxy benzaldehyde (0.61g, 0.005mmol) in 20 ml of methanol along with 1 ml of piperidine was refluxed at 64oC for 12 hrs in inert atmosphere of nitrogen. The dye obtained after 12 hrs was filtered and washed with methanol and diethyl ether to obtain the pure product. The yield was 1.89g (89%): mp: 206 ±10 oC. FTIR spectrum showed an absorption band at 3459, 2962, 2498, 1699, 1544, 1438, 1344, 842, 744 cm-1; 1HNMR (DMSO,400MHz) 10.5(s,1H) 8.3(d, J=8Hz, 1H) 8.2(q, J=16Hz, 2H) 7.8(d, J=8Hz, 1H) 7.7(m, 4H) 6.8(d, J=8Hz, 2H) 5.2(s, 2H) 13C-NMR (DMSO, 400MHz) 166.59, 158.76, 144.90, 142.12, 135.02, 130.35, 130.03, 128.84, 127.73, 124.80, 121.21, 120.24, 117.13, 117.00, 113.02, 51.28, 49.07.
(C) Photophysical Properties
[0060] The absorption spectra of the dye was recorded in solvents of different polarities (Figure 1). The dye exhibited hypsochromic shifts with increase in solvent polarity. The absorption maxima, molar extinction coefficients of the dye in different solvents are tabulated (Table 1). The high intensity absorption bands in the visible region is attributed to the charge transfer transitions. It occurs through a charge transfer from hydroxyl moiety to the benzothiazolium ring via the conjugated chain. The absorption maximum is found to be at 414nm in water. Decrease in the solvent polarity, brought about a red shift in the absorption maximum. The excited state of the dye is less polar in polar solvents than the ground state, hence blue shift occurs as solvent polarity is increased. The negative solvatochromism in the ICT absorption maximum in chloroform, acetonitrile, methanol, and water is evident from the results. Figure 2 showed the plot of the absorption maxima of the dye in solvents of varying polarity against its dielectric constant exhibits a moderately good correlation which in turn shows the influence of solvent polarity on the absorption maxima of the dye. In case of more polar solvents like water other specific interactions also influenced which exhibit a deviation from the linearity. Compared to other similar hemicyanine dyes, the dye under consideration is weakly fluorescent due to high ICT. In this study the molar extinction coefficient of the dye was correlated to the oscillator strength by Strickler-Berg relations. The radiative rate constant (k0e) was calculated using the equation (1), where the integral is the area under the absorption curve corresponding to single electron oscillator.

[0061] Additionally the pure radiative lifetime τ0 was also calculated by taking the reciprocal of k0e. It was found that the electronic transitions of the dye are fully spin and symmetry allowed which is assigned to 1π- π* transitions from the correlation between extinction coefficient and calculated τ0 values. The pure radiative lifetime shows a decrease from a non-polar to polar solvent as shown in the tabular column. The constant radiative lifetime of the dye (calculated) which indicates that the same excited state is populated.
Table 1: Photophysical properties of the dyes.
Solvent Dielectric constant (F m-1) Absorption Maximum (nm) Molar Extinction coefficient (x 103 M-
1cm-1) Calculated Oscillator strength Calculated radiative rate constant
(x 108 s-1) Pure radiative lifetime (ns)
Chloroform 4.7 432 1.96 0.38 1.36 7.30
Methanol 33 430 2.22 0.38 1.39 7.14
Acetonitrile 37.5 416 2.36 0.47 1.82 5.48
Water 80 414 2.10 0.55 2.15 4.63

(D) Thermal studies
[0062] Thermo gravimetric analysis (TGA) of the dye was performed at the rate of 10 °C min-1 as shown in Figure 3. TGA curve of the dye shows that the thermal degradation takes place in two steps. In the first step at 193.6-220 °C the degradation is due to the removal of acetic acid (15.11%) from the dye. At 220.3-446.4°C) the degradation is due to the loss of C9H10NS+ (64.03%). These mass loses are seen in the DSC curves at 206.68°C and 341.60°C as endothermic peaks (Figure 3).
(E) Photostability studies
[0063] The photostability studies of the dye in water was conducted by placing it in a borosil glass bottle under a mercury vapour lamp of power with high illuminance of 16000 lux. Even when subjected to a strong light source, the colour change of the dye is remarkably less as shown in Figure 4. The photodegradation study of the dye was repeated in quartz cuvettes to include the effect of UV radiation on the degradation of the dye and similar results were obtained. This is evident from the low photodegradation rate as seen in the UV-Vis absorption spectra of the dye taken before irradiation and after 1hrs, 2hrs, and 5hrs of exposure. Quantitative assessment of the photodegradation of the dye was done using the first-order kinetic model. The pseudo-first order kinetic model is used to plot the rate kinetics curve denoting the photodegradation of the dye using the equation
ln(C0/Ct)=Kappt
[0064] where C0 is the initial concentration, Ct is the concentration at time t, Kapp is apparent degradation constant in min-1 and t is time in minutes. Figure 4b shows the photodegradation rate kinetics of the dye under the UV-Vis light irradiation. The apparent degradation constant Kapp of dye is found to be very low, Kapp= 5.44 x 10-5 min-1 compared to methyl orange (2.13 x 10-4 min-1), which indicates the greater photostability of the dye.
(F) Computational studies
[0065] Density functional calculations were performed using the Gaussian 16 (Revision C.01) suite of quantum chemical programs. The geometry optimization was carried out using w-B97XD functional in conjugation with 6-311++G(d, p) for all other atoms. Relativistic effective core potential SDD was used for the Br atom. Topological analyses of the electron densities were performed using the Bader's atoms in molecule (AIM) formalism by using the Multiwfn software to analyze the weak interatomic interactions for the intermediate. The optimized structure and the frontier molecular orbitals of hemicyanine dyes represented by Formula 1 and Formula 2 are given in Figure 5a.
[0066] The molecular orbital analysis revealed that for Formula 1 the electron density distribution is mainly delocalized on the COO- fragment and the LUMO is extended to the other counterpart of the molecule. However, upon the addition of NH3, to form Formula 2, electron distribution for both the HOMO and LUMO is extended over the entire molecule. The presence of bond critical point between the 4-hydroxy part of the dye and NH3 as shown in Figure 5b, confirms the weak non-covalent interaction and could form intermolecular proton transfer complexes with ammonia. A decreased HOMO-LUMO gap for Formula 2, resulted in a redshift which can be attributed to the delocalization of the π-electrons over the molecule. These trends are reflected in the absorption spectral features, and corroborates well with the experimental findings as shown in Figure 5c.
(G) Optical response
[0067] The optical response of the dye was primarily monitored by adding various analytes such as aniline, picric acid, 4-aminophenol, ammonia, nitrobenzene, Hg2+, Zn2+,Mg2+, Metal carbonates to the aqueous solution of the dye. The concentration of stock solution of the dye is 5mM. Except in the case of ammonia there was no colour change for other analytes as shown in the Figure 6. A schematic representation of sensor is shown in Figure 7. The absorption spectra of the dye in presence of ammonia revealed a notable shift in the absorption maximum, changing from 414 nm (pure dye) to 425 nm (dye + ammonia) is shown in Figure 8. Interestingly, after adding ammonia, the intensity of the absorption peak at 414 nm decreased, accompanied by the appearance of a new peak at 525 nm, which demonstrates the sensing activity of dye towards ammonia.
[0068] To examine the sensing behaviour of the dye towards ammonia, UV-Vis titrations of the aqueous solution of dye was carried out. As indicated in the Figure 8 upon addition of 2.18 equivalents of ammonia, the intensity of the original absorption band at 414nm was found to decrease gradually. In addition, a new peak at 525nm is observed along with an isobestic point at 455nm. Emergence of isobestic points implies the existence of two forms- a) dye and b) complexed form of dye with ammonia. The binding of ammonia to the phenolate oxygen of the aldehyde in the dye increases the intramolecular charge transfer character. This in turn results in a change in electronic arrangement of the dye leading to a quinonoid form. Correspondingly a red shift in absorption maximum is observed. The peak intensity at 525nm increases progressively on increasing the concentration of ammonia up to 2.18 equivalents after which it reaches a saturation. The limit of detection (LOD) of ammonia was determined by plotting the absorbance maxima of the dye vs concentration of ammonia as shown in the Figure 9. The LOD was estimated using the equation LOD=3σ/S where, σ is the standard deviation of the measurements and S is the slope of the linear plot obtained. The linear range of the absorbance maxima was observed within the range 0.056ppm to 2.08ppm. The LOD is then calculated to be 0.263ppm (The lowest ammonia concentration for which the null hypothesis of equal mean signals for the blank and the LOD could be rejected by a two-sample students T-test with one sided alternative with α= 0.005).
[0069] A real time monitoring of bacterial growth as function of ammonia concentration as shown in Figure 10.
(H) Effect of pH on absorbance
[0070] Detection of ammonia was investigated at different pH as well. Different pH solutions were prepared using standard acetate (pH=4) and phosphate buffer (pH=7) solutions, by adding suitable amount of sodium hydroxide (0.2M) and hydrochloric acid (0.2M). The absorption spectra of the dye was recorded with and without the addition of ammonia in different pH range 2-14 (Figure 11). On increasing the pH up to 10.6 there is not much change in the absorbance value of the dye at wavelength 525nm. After this pH there is slight increase on absorbance observed. This is attributed to the fact that at highly alkaline medium the absorbance increment is due to ICT mechanism of the phenoxide tautomer in the deprotonated dye in the ground state. On adding ammonia the peak at 525nm increases considerably, where the absorbance remains unchanged without much variations. After pH 10.6 a slight decrease in absorbance was observed and this is due to the competition between OH- ions and NH3 in aqueous media for the complexation and subsequent deprotonation to the quinonoid form.
(I) Repeatability studies
[0071] To determine the repeatability of the sensor the absorbance was measured at 2 min, 3 min, 5 min, 10 min, 20min, and 30 min from the time of adding 12μL of aqueous solution of ammonia of concentration 16.6μM. It is evident from the graph that there is no observable change in absorbance at 525 nm with respect to time, which indicates the repeatability of the sensor (Figure 12).
(J) Interference Studies
[0072] Under the same conditions and same concentrations of selected interferons (all 50μM) detailed absorbance measurements were carried out to explore the anti-interference ability of the sensor. The results showed that the dye possess a good selectivity towards NH3 detection. The coexistence of interferons with ammonia does not affect the latter’s absorbance (Figure 13).
[0073] The foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.

ADVANTAGES OF THE PRESENT INVENTION
[0074] High sensitivity: Detect ppm levels with high accuracy
[0075] Rapid response: provide real- time data enabling industrial and environmental monitoring applications.
[0076] Cost – effective: Reduce the need of costly equipment for ammonia detection.
[0077] Stability: High photostability and thermal stability.
, Claims:1. A hemicyanine dye represented by the formula (1) comprising:


(Formula 1).

2. A method of preparation of a hemicyanine dye represented by the formula (1) comprising:
a) refluxing 0.02 mmol of 2-methylbenzothiazole and 0.05 mmol of bromo acetic acid in a dioxane under condition followed by precipitation with diethyl ether, filtering and washing with a mixture of 2-propanol and diethyl ether to obtain a solid compound of Formula (A); and
b) refluxing 0.005 mmol of compound of Formula (A) with of 0.005 mmol of 4-hydroxy benzaldehyde of Formula (B) in methanol and piperidine under condition followed by filtering and washing with methanol and diethyl ether to obtain a hemicyanine dye represented by the formula (1).

(Formula A) (Formula B) (Formula 1)
3. The method as claimed in claim 2, wherein the condition in step a) includes temperature in the range of 80 to 120 °C for a period in the range of 6 to 10 hrs.
4. The method as claimed in claim 2, wherein the condition in step b) includes temperature in the range of 50 to 80 °C for a period in the range of 10 to 14 hrs.
5. A chemical sensor for detection of ammonia comprising: a sensing element composed of the hemicyanine dye represented by the formula (1) as claimed in claim 1.
6. The method as claimed in claim 5, wherein the chemical sensor as and when used for preparing dye coated paper strips for sensing ammonia in liquid or gaseous forms.
7. A method of detection of ammonia comprising:
dissolving the hemicyanine dye represented by the formula (1) as claimed in claim 1 in water to obtain a dye solution;
exposing the ammonia in presence of dye solution; and
interacting the hemicyanine dye represented by the formula (1) with ammonia undergoes a rapid interaction bringing a measurable and visible change in the optical properties which is monitored by spectrophotometrically.
8. The method as claimed in claim 7, wherein the hemicyanine dye represented by the formula (1) interacts with ammonia molecules generating a visible colour change from yellow to pink as a function of ammonia concentration.
9. The method as claimed in claim 7, wherein the hemicyanine dye represented by the formula (1) shows high selectivity toward ammonia molecules in presence of other interfaces.
10. The method as claimed in claim 7, wherein the hemicyanine dye represented by the formula (1) is able to operate in the range of 0.056 pm to 2.08 pm with LOD of 0.263 ppm.