FIELD

The present disclosure relates to a method of synthesis for colloidal silver.

BACKGROUND

A colloid of silver comprises very small particles of metallic silver suspended in water. The atomic micro-clusters of silver atoms found in colloidal silver range in size between approximately 0.001 and 0.01 microns. This small size with its large surface area to volume ratio enables the surface chemistry of silver which in turn dramatically increases the reactivity of silver with the substances that it comes in contact with. These particles are smaller than the individual cells of bacteria and some of the particles are smaller than even viruses.

Colloidal silver has wide applications in medicines and other areas of research due to its antimicrobial activity. Silver ions denature enzymes of the target cell or organism by binding to reactive groups, resulting in their precipitation and inactivation. Silver inactivates enzymes by reacting with the thiol groups to form silver sulfides. Silver also reacts with the amino, carboxyl, phosphate and imidazole groups and diminish the activities of lactate dehydrogenase and glutathione peroxidase. Colloidal silver is also used as a water disinfecting agent. Silver in a colloidal state produced by electrolysis of silver electrodes in water and colloidal silver in water filters are some of the water disinfection methods specified to provide safe drinking water. One of the most popular uses of colloidal silver is its intake as a supplement to support the immune system in recommended doses.

EXISTING KNOWLEDGE

Various methods of formation of colloidal silver and its use as an antimicrobial agent have been reported in the past. Some of these documents are listed below:

KR20010069644 discloses a method for producing antimicrobial soap containing fine particles of silver produced by using a surfactant in an aqueous solution.

US2009239280 discloses a method for production of colloidal metal compounds including silver or gold nanosize particles by means of a biological process. The aforementioned patent application particularly relates to the use of probiotic bacteria such as Lactobacillus under specific conditions in the production of metallic nanoprecipitates, in particular silver or gold nanoparticles with a goal of improving their anti-microbial efficiency.

US2009068283 discloses a method to provide a silver-based inorganic antimicrobial agent with a silver ion-containing zirconium phosphate type compound.

US2010055199 discloses systems and method for synthesizing silver nanoparticles (SNPs) using Trichoderma fungi; wherein one or more enzymes or metabolites are produced in the biosynthesis of metal nanoparticle by the fungus.

US Patent No. 7968008 disclose methods of preparing metal particles, especially silver particles using capping agents.

The hitherto reported prior art processes however do not allow any process or property control during the synthesis of colloidal silver. Therefore, there is felt a need for a simple and cost effective route for synthesis of colloidal silver that provides stable colloidal silver with variable physical and functional properties.

OBJECTS

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

An object of the present disclosure is to provide a process for synthesis of stable colloidal silver.

Another object of the present disclosure is to provide a simple yet flexible process for synthesis of colloidal silver that provides stable colloidal silver with variable physical and functional properties.

Still another object of the present disclosure is to provide a simple and cost effective method of synthesis of antimicrobial colloidal silver.

An additional object of the present disclosure is to provide a formulation for colloidal silver which is eco-friendly, non-toxic and is cost effective.

Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.

SUMMARY

In accordance with the present disclosure, there is provided a control process for synthesizing colloidal silver particles; said process comprising the following steps:

(a) dissolving a silver salt in a solvent to form a silver ion solution;

(b) adding a capping agent(s) and an enhancing agent (s) in the silver ion solution in controlled manner under stirring at a temperature in the range of 5 C to 250 °C to form a uniform solution;

(c) reducing the uniform solution using a reducing agent(s) in a controlled manner at a temperature in the range of to 5 °C to 250 °C under stirring to form a reaction mixture; and

(d) isolating and purifying stable colloidal silver from the reaction mixture.

In accordance with the present disclosure, at least one product attribute of the stable colloidal silver selected from the group of attributes consisting of color, size, morphology and concentration of the stable colloidal silver particles is controlled by varying at least one process parameter selected from the group consisting of concentrations of silver ion solution, capping agent, enhancing agent, and reducing agent; temperatures in method steps (b) and (c), time of stirring and type of capping agent.

The silver salt used for the synthesis of colloidal silver in the present disclosure is at least one selected from the group comprising of silver chloride, silver bromide, silver iodide, silver sulfate, silver thiocyanate, silver chromate, silver phosphate, silver oxalate, silver carbonate, silver sulfite, silver hydroxide, silver nitrate, silver chlorate, silver acetate and silver nitrite.

The solvent used for the synthesis of colloidal silver in the present disclosure is at least one selected from the group comprising of methanol, ethanol, propanol, butanol, pentanol, hexanol, glycols and the like.
The capping agent used for the synthesis of stable colloidal silver in the present disclosure is at least one selected from the group consisting of co-polymers of polyvinylpyrrodiline and its derivatives, sodium salt of maleic and acrylic acid copolymer, and its derivatives; ammonium bromides and its additives; surfactants and their additives.

Typically, the capping agent is selected from the group consisting of polyvinylpyrrodiline, sodium salt of maleic and acrylic acid copolymer, surfactants, ammonium bromide and the like.

The enhancing agent used for the synthesis of stable colloidal silver in the present disclosure is selected from the group consisting of citrates, peroxides, carbonates and the like.

Typically, the enhancing agent is selected from the group of citrate compounds consisting of sodium citrate, potassium citrate, citric acid and the like.

Typically, the enhancing agent is selected from the group of peroxide compounds consisting of hydrogen peroxide, alkali metal peroxide, organic peroxides and the like.

Typically, the enhancing agent is selected from the group of carbonate compounds consisting of calcium carbonate, potassium carbonate, sodium carbonate and the like.

The process of the present disclosure optionally involves heating the reaction mixture in the method step (c) at a temperature ranging between 5°C and 250 °C.

The reducing agent is selected from the group consisting of borohydrides, alkalies sugars and the like.

In accordance with the present disclosure, the reducing agent is at least one borohydride selected from the group of borohydride compounds consisting of sodium borohydride, lithium aluminium borohydride, sodium cyanoborohydride, potassium borohydride, sodium triacetoxyborohydride and the like.

The reducing agent is at least one sugar selected from the group of sugars consisting of glucose, glyceraldehyde, galactose, lactose, maltose and the like.

The reducing agent is at least one alkali selected from the group of alkali compounds consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide.

The stable colloidal silver particles synthesized in accordance with the process of the present disclosure is separated using at least one separating method from the group consisiting of filtration, extraction and the like

The purification of the separated stable colloidal silver in accordance with the process of the present disclosure is carried out by at least one purification method selected from the group consisting of recrystallization, solvent purification and the like.

Typically, the size of the stable colloidal silver obtained ranges between 1.0 nm to 400 nm.

Typically, the shape of the stable colloidal silver particles is selected from the group consisting of spherical, prisms, and the like.

Typically, the concentration of the stable colloidal silver particles is in the range of 0.001% to 10%.

The yield of stable colloidal silver prepared by the process of the present disclosure as determined gravimetrically is between 95% and 100%.

In accordance with the present disclosure, the process is carried out using manual or robotic procedure.
In accordance with a second aspect of the present disclosure, there is provided stable colloidal silver prepared by the process of the present disclosure.

Typically, the stable colloidal silver is in metallic or ionic form with absence of free individual silver ions.

In accordance with the present disclosure, there is provided a formulation comprising stable colloidal silver particles as prepared by the process of the present disclosure.

Typically, the formulation comprises at least one pharmaceutical excipient selected from the group consisting of preservatives, cryoprotectants, tonicity adjusting agents, solubilizing agents, pH adjusting agents, buffering agents, taste masking agents, sweeteners, flavours, diluents, disintegrants, lubricants, glidents, binders, solvents, matrix forming agents, coating polymers, effervescent agents, wetting agents and dispersing agents.

Typically, the formulation is at least in one dosage form selected from the group consisting of soaps, pills, powder, granules, tablet, capsule, lozenges, solution, liquid suspension, sprays, foam, aerosols and the like.

Typically, the percent biodegradability of the formulation is more than 72%.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure will now be described with reference to the accompanying drawings, in which:

Fig. 1 illustrates a plot of size distribution of colloidal silver against its intensity. It shows the nanosized nature of the colloidal silver prepared by the process of the present disclosure.

Fig. 2 illustrates a plot of size distribution of colloidal silver against its intensity. It shows the microsized nature of the colloidal silver prepared by the process of the present disclosure.

Figure 3 illustrates the spherical shape of the colloidal silver prepared by the process of the present disclosure as determined by Transmission Electron Microscopy.

Figure 4 illustrates the prism shape of the colloidal silver prepared by the process of the present disclosure as determined by Transmission Electron Microscopy.

Figure 5 illustrates the formation of a silver mirror when solution of silver sulphate is treated with Tollen's reagent due to the presence of silver ions.

Figure 6 illustrates complete absence or negligible quantity of free silver ions in the colloidal silver as no silver mirror is formed when yellow colloidal silver is treated with Tollen's reagent.

Figure 7 illustrates complete absence or negligible quantity of free silver ions in the colloidal silver as no silver mirror is formed when blue colloidal silver is treated with Tollen's reagent.

Figure 8 illustrates a plot of size distribution of colloidal silver against its intensity. It shows the presence of colloidal silver of size ranging between 40 nm to 400 nm.

DETAILED DESCRIPTION

The description herein after the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

The use of silver as an antimicrobial agent has been known from several years. The efficiency of silver to destroy microbes including bacteria is high. Oligodynamic silver ions destroy bacteria, viruses and other germs by at least three key ways that lead to permanent inactivation (denaturing) of essential bacterial protein and DNA without harming host tissues via:

1) Disrupting a germ's outer membrane proteins;

2) Inactivation of bacterial enzymes; and

3) Inhibition of bacterial replication via DNA binding.

However, the use of silver ion solution as such is not recommended because of its side effects like argyria. Properties of the metal vary on account of their particle size. Colloidal silver with micro and nano size has better efficacy than the silver ions in the solution. Thus micro and nano sized silver is used in the formulation comprising silver for better efficacy. The antimicrobial and medicinal powers of any silver containing formulation are governed by one or more of the following variables:

1) Particle size (Surface area & energy);

2) Particle concentration (Therapeutic Index);

3) Particle charge (Oligodynamic quality); and

4) Particle Shape (Catalytic activity).

Accordingly, in accordance with a first aspect of the present disclosure there is provided a simple yet flexible method of synthesis of stable colloidal silver particles.

The control process for synthesizing stable colloidal silver particles of the present disclosure comprises the following steps:

(a) dissolving a silver salt in a solvent to form a silver ion solution;

(b) adding a capping agent(s) and an enhancing agent (s) in the silver ion solution in controlled manner under stirring at a temperature in the range of 5 C to 250 C to form a uniform solution;

(c) reducing the uniform solution using a reducing agent(s) in a controlled manner at a temperature in the range of5 °C to 250 °C under stirring to form a reaction mixture; and

(d) isolating and purifying stable colloidal silver from the reaction mixture.

The formation of colloidal silver of varying functional properties depends on the reaction parameters for the synthesis of the colloidal silver. Thus the properties of the final colloidal silver synthesized are governed by the type and concentrations of the reactants; temperature and time for which the reaction is carried out.

In accordance with the present disclosure, at least one product attribute of the stable colloidal silver selected from the group of attributes consisting of color, size, morphology and concentration of the stable colloidal silver particles is controlled by varying at least one process parameter selected from the group consisting of concentrations of silver ion solution, capping agent, enhancing agent, "and reducing agent; temperatures in method steps (b) and (c); time of stirring and type of capping agent.

Various silver salts are used for the formation of silver ion solution. The silver salts used for the synthesis of stable colloidal silver in the present disclosure includes silver chloride, silver bromide, silver iodide, silver sulfate, silver thiocyanate, silver chromate, silver phosphate, silver oxalate, silver carbonate, silver sulfite, silver hydroxide, silver nitrate, silver chlorate, silver acetate, silver nitrite and the like.

The silver salt is dissolved in a suitable solvent to produce silver ions. The solvent used for the synthesis of stable colloidal silver in the present disclosure is at least one selected from the group consisting of methanol, ethanol, propanol, butanol, pentanol, hexanol, glycols and the like.

One of the challenges in the synthesis of stable colloidal silver is the selection of capping agent. The capping agent plays an important role in producing the colloidal silver with desired morphology, color and size. The capping agent should be effective to isolate the particle and limit the size of its growth.

Various capping agents are used for the synthesis of stable colloidal silver. The capping agent used in the present disclosure includes co-polymers of polyvinylpyrrodiline and its derivatives, sodium salt of maleic and acrylic acid copolymer, and its derivatives; ammonium bromides and its additives; surfactants and their additives.

Typically, the capping agent is at least one selected from the group consisting of polyvinylpyrrodiline, sodium salt of maleic and acrylic acid copolymer, surfactants, ammonium bromide and the like.

Stability of the capped colloidal silver is further increased by the addition of enhancing agents during the synthesis of the stable colloidal silver as described in the present disclosure. The enhancing agent used for the synthesis of stable colloidal silver in the present disclosure is at least one compound selected from the group consisting of citrates, peroxides, carbonates and the like.

Typically, the enhancing agent is at least one citrate selected from the group of citrate compounds consisting of sodium citrate, potassium citrate, citric acid and the like..

Typically, the enhancing agent is at least one carbonate selected from the group of carbonate compounds consisting of calcium carbonate, potassium carbonate, sodium carbonate and the like..

The reducing agent is added to the capped colloidal silver for producing metallic colloidal silver. The reducing agent is at least one compound selected from the group consisting of borohydrides, alkalies, sugars and the like..

In accordance with the present disclosure, the reducing agent is at least one borohydride selected from the group of borohydride compounds consisting of sodium borohydride, lithium aluminium borohydride, sodium cyanoborohydride, potassium borohydride, sodium triacetoxyborohydride and the like..

The reducing agent is at least one sugar selected from the group of sugars consisting of glucose, glyceraldehyde, galactose, lactose, maltose and the like..

The reducing agent is at least one alkali selected from the group of alkali compounds consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide and the like..

The stable colloidal silver is separated using at least one separating method from the group consisiting of filtration, extraction and the like.

The stable colloidal silver obtained by the process of the present disclosure is purified to remove all residual reactants.

The purification is carried out by at least one purification method selected from the group consisting of recrystallization, solvent purification and the like.

The yield of stable colloidal silver prepared by the process of the present disclosure as determined gravimetrically is between 95% and 100%.

Typically, a sharp and homogeneous distribution of particle size is achieved by adding at least one additive selected from the group consisting of capping agents, enhancing agents and/or modifying agents.

Typically, the size of the stable colloidal silver obtained ranges between 1.0 nm to 400 run.

Typically, the shape of the stable colloidal silver particles is selected from the group consisting of spherical, prisms and the like...

Typically, the concentration of the stable colloidal silver is in the range of 0.001% to 10%.

Typically, manual or robotic procedure is used for carrying out the process of the present disclosure.
In accordance with a second aspect of the present disclosure, there is provided stable colloidal silver prepared by the process of the present disclosure.

Typically, the stable colloidal silver is in metallic or ionic form with absence of free individual silver ions.
In accordance with a third aspect of the present disclosure, there is provided a formulation comprising stable colloidal silver particles as prepared by the process of the present disclosure.

Typically, the formulation comprises at least one pharmaceutical excipient selected from the group consisting of preservatives, cryoprotectants, tonicity adjusting agents, solubilizing agents, pH adjusting agents, buffering agents, taste masking agents, sweeteners, flavours, diluents, disintegrants, lubricants, glidents, binders, solvents, matrix forming agents, coating polymers, effervescent agents, wetting agents and dispersing agents.

Depending on the intended application, the formulation of the present disclosure is formulated in several dosage forms including soaps, pills, powder, granules, tablet, capsule, lozenges, solution, liquid suspension, sprays, foam, aerosols, and the like.

Typically, the formulation exhibits at least one property selected from the group consisting of anti microbial, anti-leaching, non-toxicity, stability, durability, compatibility and the like.

The formulation prepared in accordance with the present disclosure shows excellent antimicrobial properties due to oligodynamic effect of the stable colloidal silver.

Depending on the type and concentration of the stable colloidal silver used for application, the colloidal silver acts both as a bacteriostatic product with no zone of inhibition; and non - leaching and bactericidal with zone of inhibition and leaching property.

The percent biodegradability of the formulation of the present disclosure is more than 72%.

The formulations provided by the present disclosure is suitable for a wide range of applications including but not limited to stem cell cleaning, drug delivery carrier and semiconducting. The durability of the formulations is high for the application specific wear and tear. A wide range of applications for the antimicrobial property is addressed by the formulations in accordance with the present disclosure. These applications ranges from textiles, cosmetics and personal care, home care, paints,

plastics, industrial applications, hospital application, disinfection, agriculture, poultry, medical applications, foot wear, furnishings, pet care, automotive, construction, food and beverages, preservatives, packaging and not limited to it. In accordance with the present disclosure, the formulations are compatible with a majority of the substrates. These substrates include fabric, glass, wood, plastic, steel, metal, paper, cement, leather, rubber, and ceramics and not limited to it.

EXAMPLES:

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

Example 1:

40.0 g of silver salt was dissolved to obtain a silver ion solution. Sodium salt of maleic and acrylic acid copolymer, sodium citrate and hydrogen peroxide was added to the silver ion solution in a controlled manner under stirring to obtain a uniform solution. The uniform mixture was reduced using sodium borohydride in a controlled manner under stirring to form a reaction mixture. The reaction mixture was further heated at a temperature of 65°C to obtain a stable colloidal silver solution. The stable colloidal silver was separated from the colloidal silver solution by filtration and puriifed.

The colour of the sample observed was violet.

Example 2

40.0 silver salt was dissolved to obtain a silver ion solution. Polyvinylpyrrolidine, sodium citrate and hydrogen peroxide was added to the silver ion solution in a controlled manner under stirring at a temperature to obtain a uniform solution. The uniform mixture was reduced using using sodium borohydride in a controlled manner under stirring to form a reaction mixture. The reaction mixture was further heated at a temperature of 63°C obtain a stable colloidal silver solution. The stable colloidal silver was separated from the colloidal silver solution by filtration and purified.

The colour of the sample observed was blue.

Analysis Data

1) Determination of concentration of colloidal silver:

The concentration of stable colloidal silver was determined by Intracouple Plasma Optical Emission Spectroscopy (ICP-OES) and the data is as shown in Table 1.

2) Detection of Silver ions in the colloidal silver by Silver Mirrror Test:

Two of the methods used for testing the presence of silver ions are Tollen's reagent test for qualitative testing and Ion Chromatography (determinative of trace silver ions using hydrophilic resins with chemiluminescence detection) for quantitative testing.

The presence of silver ions in the stable colloidal silver was detected using the Tollen's reagent test.

Figure 5 shows the formation of a silver mirror when solution of silver sulphate was treated with Tollen's reagent due to presence of silver ions.

Figure 6 illustrates complete absence or negligible quantity of free silver ions in the stable colloidal silver as no silver mirror is formed when yellow colloidal silver was treated with Tollen's reagent.

Figure 7 illustrates complete absence or negligible quantity of free silver ions in the stable colloidal silver as no silver mirror is formed when blue colloidal silver was treated with Tollen's reagent.

Thus it is concluded that no silver ion is present in the stable colloidal silver prepared by the process of the present disclosure.

3) Determination of efficacy of the formulation of the present disclosure:

Over 700 viral, bacterial, fungal and protozoan pathogens succumb to colloidal silver without developing resistance against the colloidal silver range provided in the present disclosure. The test details are provided in table 2.

Table 2

The results show that the colloidal silver has six fold efficacy on bacteria and excellent efficacy against various types of fungi, viruses (encapsulated and non-encapsulated).

4) Wash Durability of the formulation of the present disclosure on a textile fabric

The results showing the durability of the formulation of the present disclosure is as shown in Table 3.
Table 3.

Thus the above results show that the formulation provided by the present disclosure is highly durable.

5) Surface Residual Test of the formulation of the present disclosure:

The surface residual test for the formulation was carried out using the following process:

Firstly, the user was made to apply the product on a surface continuously for a week. In the following week, user was made to clean the surface with plain water. At the end of the 2nd week, swabs of the residue from the cleaned surface were collected. These swabs were submitted to a local third party lab for the estimation of quantity of residual silver left on the cleaned surface.

The results are as shown in Table 4.

Table 4:

Results: - Test reports showed that a week after cessation of the use of the formulation of the present disclosure, there was a residual disinfectant activity due to the presence of residual silver.

Thus the results show that the surfaces continued to have protection against microbes beyond the period of a week.

The residual silver at the end of the 2 week was only 50 ppb or 0.05ppm, too low to cause any environmental effects but good enough to give residual disinfectant activity to the surface.

6. Tests for the compatibility of the formulation of the present disclosure:

The formulation was tested for its compatibility on some of the substrates as shown in Table 5.
Table 5:

Table 5 shows that the formulation of the present disclosure has a high compatibility with various substrates.

7. Tests for determination of cytotoxicity of the colloidal silver of the present disclosure:

The active ingredient colloidal silver in the formulation of the present disclosure has negligible toxicity due to its particle size. The concentration of colloidal silver used is very low, much below the toxicity limits defined by Environmental Protection Agency (EPA) in use and application. The silver further aggregates to form higher particles when left to atmosphere, which is non-toxic and non-hazardous to environment.

Active ingredient Colloidal Silver passed the following toxicity testing (tested at ISO 13025):

a. Acute Oral Toxicity in Rats

b. Primary Skin Irritation in Rabbits

c. Eye Irritation Study in rabbits

d. Skin Sensitization study in Guinea Pigs

e. 28 day Repeated Dose Dermal toxicity study - 14 days recovery period -
in Rats

f. Bacterial Reverse Mutation test using Salmonella typhimurium Tester
strain.

g. In Vitro Mammalian Chromosomal Aberration test in cultured Human
peripheral blood lymphocytes.

h. Bacterial Reverse Mutation test that proves the formulation does not allow bacteria to develop resistance against the formulation of the present disclosure.

8. Absence of toxic residues in the formulation of the present disclosure:

The formulation comprising stable colloidal silver of the present disclosure was free from following toxic residues:

a) heavy metals like arsenic, lead, cadmium, mercury, copper, cobalt, nickel, chromium, antimony, tin, zinc, barium, iron, manganese and selenium;

b) toxic nonylphenolethoxylates (NPEOs) and OctylphenolEthoxylates (OPEOs); biological active products like premethrin, dimethyl fumarate, triclosan, TBT, trichloro phenols all isomers, which are considered to be toxic to humans and environment;

c) Ortho-phenylphenol (OPP), pentachlorophenol, all tetrachloro phenols, Perfiuorooctane sulphonic acid (PFOS), Perfluorooctanoic Acid (PFOA), Organo tin compounds like tributyl tin, monobutyl tin,, dibutyl tin, , triphenyl tin, dioctyl tin compounds which are toxic substances; and

d) Pesticides, azoamines, formaldehydes, chloro-organic carriers, phthalates and poly aromatic hydrocarbons (PAH) including Benzo(a)pyrene.

The formulation of the present disclosure was proven non toxic to fresh water fish (eg. Branchydaniorerio). The biodegradability of the formulations was found to be more than 72%.

From Fig. 6 and 7, it is clear that the formulation of the present disclosure is free from silver ions and hence there is no possibility of cosmetic effect of Argyria by its usage.

TECHNICAL ADVANTAGES

A control process for synthesis of colloidal silver, particularly highly stable colloidal silver with variable physical and functional properties; the synthesis and the formulation for colloidal silver as described in the present disclosure have several technical advantages including but not limited to the realization of:

• the process provides formation of colloidal silver with particle size ranging from 1.0 nm to 400 nm;

• the process provides formation of colloidal silver with uniformity in the particle size in the formulation which is greater than 99 %;

• the process provides formation of colloidal silver with concentrations ranging from as low as 0.001% to as high as 10%;

• the process provides formation of colloidal silver with flexibility in its colour ranging anywhere in the complete visible spectrum;

• the process provide formation of colloidal silver with flexibility in its morphology and shape;

• the process provides a formulation for colloidal silver which is compatible with a majority of the substrates;

• the formulation development for the colloidal silver involves a parallel manual or robotic process for synthesis.

• the process provides a highly durable, eco-friendly and non-toxic formulation for colloidal silver with wide industrial applications for its antimicrobial property and

• an easily scalable process at the industrial scale.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated

element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other modifications in the nature of the disclosure or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

We Claim:

1. A control process for synthesizing colloidal silver; said process comprising the following steps:

a) dissolving a silver salt in a solvent to form a silver ion solution;

b) adding a capping agent(s) and an enhancing agent (s) in the silver ion solution in controlled manner under stirring at a temperature in the range of.5 °C to 250 °C form a uniform solution;

c) reducing the uniform solution using a reducing agent(s) in a controlled manner at a temperature in the range of 5 °C to 250 °C under stirring to form a reaction mixture; and

d) isolating and purifying stable colloidal silver from the reaction mixture.

2. A process as claimed in claim 1, wherein at least one product attribute of the colloidal silver selected from the group of attributes consisting of color,

size, morphology and concentration of the stable colloidal silver particles is controlled by varying at least one process parameter selected from the group consisting of concentration of silver ion solution, capping agent,

enhancing agent, and reducing agent; temperatures in method steps (b) and (c), time of stirring and type of capping agent.