Claims:We claim:
1. A cysteine functionalized gold nanorods, comprising:
a) Areca catechu leaf extract reduced gold nanoparticles; and
b) cysteine,
wherein the molar ratio of Areca catechu leaf extract reduced gold nanoparticles and cysteine is 0.1:1;
wherein the size of cysteine-functionalized gold nanorods are in the range of 5 to 100 nm.
2. A process for preparing cysteine-functionalized gold nanorods, comprising:
i) heating aqueous solution of 0.5 mM Gold (III) chloride trihydrate (HAuCl4.3H2O) till boiling,
ii) adding leaf extract of Areca catechu to the solution obtained in step i),
iii) stirring the mixture prepared in step ii) at room temperature until the solution turns pale red colored,
iv) purifying solutions obtained in step iii) by centrifugation to form gold nanorods,
v) discarding the supernatants obtained in step iv) to form pellets,
vi) redispersing the pellets obtained in step v) in deionized water,
vii) drying the pellets obtained in step vi) to obtain powdered gold nanorods,
viii) dispersing powder obtained in step vii) in a solution of 5 mM cysteine,
ix) allowing to stand the solution obtained in step viii) for overnight at room temperature,
x) removing the unreacted cysteine obtained in step ix) by dialyzing process to give cysteine-functionalized gold nanorods.
3. The process for preparing cysteine-functionalized gold nanorods as claimed in claim 2, wherein the cysteine-functionalized gold nanorods are useful for detection of mercury in the range of 5 to 65 µM.
4. The process for preparing cysteine-functionalized gold nanorods as claimed in claim 2, wherein the size of cysteine-functionalized gold nanorods is in the range of 5 to 100 nm.
Dated this 15th day of August, 2021
To be signed digitally by
(Prabhakar R Sharma)
Agent for the Applicant
Patent Agent (IN/PA 4122)
, Description:Technical Field of the Invention
The present invention relates to a cysteine-functionalized gold nanorods. The present invention also relates to an improved process for the preparation of cysteine-functionalized gold nanorods. The cysteine-functionalized gold nanorods of the present invention has usefulness in mercury detection.
Background of the Invention
Heavy metal pollution is a serious threat for human, plants and other living organisms. It is a source of environmental poisoning of land, air as well as water. Heavy metal poisoning is easy to spread to nearby surfaces and hard to remove from infected surfaces. They tend to accumulate for long in the environment and creates life threating diseases.
Nanomaterials are widely used as a chemical sensor due to their property of stability, unique optical properties, good biocompatibility and easy modifications. To prepare gold nanoparticles, a highly toxic reducing agent sodium borohydride is used which is unfavorable to the environment. CN107024463A discloses method of preparation of gold nano-cluster fluorescence ratio detection test strip with bovine serum albumin coated gold nano-cluster and cysteine coated gold nano-cluster for selective and sensitive detection of mercury ion in range is 50 nM-3 µM. CN105598465A discloses preparation method of fluorogold nanoparticles using N-acetyl-L-cysteine, chloroauric acid and methanol/glacial acetic acid solution and application for mercury ion detection.
CN102706866B discloses detection reagent of water-soluble gold nanoparticle solution modified with cetyltrimethylammonium bromide and dithizone for rapid detection of multiple single metal ions and preparation method thereof.
There is a need for natural reducing agent in preparation of gold nanoparticles and easily available chemical sensors for the selective and sensitive detection mercury.
Objects of the Invention
The main object of the present invention is to provide a cysteine-functionalized gold nanorods.
Another object of the invention is to provide a cysteine-functionalized gold nanorods for selective detection of mercury.
Another object of the invention is to provide a cysteine-functionalized gold nanorods for sensitive detection of mercury.
Yet another object of the invention is to provide a process for preparation of cysteine-functionalized gold nanorods.
Summary of the Invention
Accordingly, the present invention provides a cysteine functionalized gold nanorods which comprises Areca catechu leaf extract reduced gold nanoparticles and cysteine.
In an embodiment of the invention the molar ratio of Areca catechu leaf extract reduced gold nanoparticles and cysteine is 0.1:1.
In an embodiment of the invention the size of cysteine-functionalized gold nanorods are in the range of 5 to 100 nm.
In an embodiment of the invention the cysteine-functionalized gold nanorods are useful for selective and sensitive detection of mercury in the range of 5 to 65 µM.
The present invention also relates to a process for preparing cysteine-functionalized gold nanorods which comprises heating aqueous solution of 0.5 mM Gold (III) chloride trihydrate (HAuCl4.3H2O) till boiling, adding to this solution leaf extract of Areca catechu, stirring the formed mixture at room temperature until the solution turns pale red colored, purifying gold nanorods from the formed pale red colored solution by centrifugation, discarding the supernatants obtained by centrifugation to form pellets, redispersing the obtained pellets in deionized water, drying the pellets to give powdered gold nanorods, dispersing the formed powder in a solution of cysteine, allowing to stand the solution obtained for overnight at room temperature, removing the unreacted cysteine by dialyzing process to give cysteine-functionalized gold nanorods.
In an embodiment of the invention the cysteine-functionalized gold nanorods are useful for selective and sensitive detection of mercury in the range of 5 to 65 µM.
In an embodiment of the invention the size of cysteine-functionalized gold nanorods are in the range of 5 to 100 nm.
Brief Description of drawings
In the drawings accompanying the specification, figure 1 shows TEM images of cysteine-functionalized gold nanorods.
In the drawings accompanying the specification, figure 2 shows HR-TEM images of cysteine-functionalized gold nanorods.
In the drawings accompanying the specification, figure 3 shows colorimetric sensing behaviour of cysteine-functionalized gold nanorods in presesnce of various metal ions.
Detailed description of the Invention
According to the present invention, the invention provides a cysteine functionalized gold nanorods which comprises Areca catechu leaf extract reduced gold nanoparticles and cysteine.
The molar ratio of Areca catechu leaf extract reduced gold nanoparticles and cysteine in the present invention is 0.1:1.
The size of cysteine-functionalized gold nanorods in the present invention are in the range of 5 to 100 nm.
The cysteine-functionalized gold nanorods useful for selective and sensitive detection of mercury in the present invention is in the range of 5 to 65 µM.
The present invention further provides a process for preparing cysteine-functionalized gold nanorods which comprises heating aqueous solution of 0.5 mM Gold (III) chloride trihydrate (HAuCl4.3H2O) till boiling, adding to this solution leaf extract of Areca catechu, stirring the formed mixture at room temperature until the solution turns pale red colored, purifying gold nanorods from the formed pale red colored solution by centrifugation, discarding the supernatants obtained by centrifugation to form pellets, redispersing the obtained pellets in deionized water, drying the pellets to give powdered gold nanorods, dispersing the formed powder in a solution of cysteine, allowing to stand the solution obtained for overnight at room temperature, removing the unreacted cysteine by dialyzing process to give cysteine-functionalized gold nanorods.
The cysteine-functionalized gold nanorods in the present invention are useful for selective and sensitive detection of mercury in the range of 5 to 65 µM.
The size of cysteine-functionalized gold nanorods in the present invention are in the range of 5 to 100 nm.
The cysteine-functionalized gold nanorods of present invention has colorimetric sensory behavior for mercury detection.
The cysteine-functionalized gold nanorods sensor of the present invention are useful for determination of the presence or concentration of mercury (Hg2+) ions in a sample.
Unless otherwise specified, following abbreviations are used for denoting various terms in the present invention, mM is millimole, µM is micromole, mL is milliliters, µg is microgram, rpm is rotation per minute and nm is nanometer.
Examples
The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.
Method of preparation of cysteine-functionalized gold nanorods
Gold (III) chloride trihydrate is reduced in presence of Areca catechu left extract to gold. Importantly, pre-cleaning of all glass wares with aqua-regia and then deionized water was done to avoid and completely remove potential artificial nucleation sites. In brief, 0.5 mM of 20 mL solution of HAuCl4.3H2O (in water) was heated to boiling for 15 minutes and 5 mL of 20 µg/mL of Areca catechu leaf extract was added and the reaction mixture was stirred at room temperature for 30 minutes until a pale red colored solution was observed. The solution containing gold nanorods was purified by centrifugation at 15,000 rpm for 15 minutes. The supernatant was discarded, and the pellet was redispersed in deionized water, followed by drying to get powdered gold nanorods. Further, the as obtained gold nanorods was dispersed in a solution of cysteine (5 mM in 50 mL water) and allowed to stand for overnight at room temperature. Following this, the unreacted cysteine was removed by dialyzing process to give cysteine-functionalized gold nanorods. Figure 1 and figure 2 shows TEM images and HR-TEM images of cysteine-functionalized gold nanorods respectively
Sensitivity and selectivity studies
The colorimetric detection of mercury (Hg2+) ion by cysteine-functionalized gold nanorods was performed by mixing aqueous solutions of Mercuric chloride (HgCl2) in different concentrations (0–65 µM) with 1.0 mL of cysteine-functionalized gold nanorods (in aqueous solution) at room temperature. The efficiency of cysteine-functionalized gold nanorods to probe mercury (Hg2+) ions was quantitatively estimated by adding 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 and 65 µM to 1.0 mL of cysteine-functionalized gold nanorods dispersion in separate 5 mL glass vials. All samples were allowed to stand at room temperature to change color and the Surface Plasmon Resonance band intensity was monitored using UV-Visible spectroscopy. The selectivity of cysteine-functionalized gold nanorods towards Hg2+ ion was assessed under identical conditions individually with various common metal ions such as Cu2+, Co2+, Pb2+, Mg2+ and Na+. Surprisingly, the color of cysteine-functionalized gold nanorods solution remained the same in the presence of other metal ions, whereas with the addition of solution of Hg2+, the color of the mixture turned to pale blue indicating their interaction as shown in figure 3.