| United States Patent Application |
20030185889
|
| Kind Code
|
A1
|
|
Yan, Jixiong
; et al.
|
October 2, 2003
|
Colloidal nanosilver solution and method for making the same
Abstract
The present invention provides a colloidal nanosilver solution which
contains nanosilver particles having diameters between 1 nm and 100 nm.
The silver content in the colloidal solution is between 0.001% to 0.4% by
weight. The colloidal nanosilver solution also contains a gelling agent
which includes, but is not limited to, starch or its derivative,
cellulose or its derivative, polymer or copolymer of acrylate or acrylate
derivative, polyvinyl pyrrolidone, alginic acid, and xanthogenated gel.
The present invention also provides a method for making the colloidal
nanosilver solution. The colloidal nanosilver solution prepared by this
method does not contain any toxic or impure substances.
| Inventors: |
Yan, Jixiong; (Wuhan, CN)
; Cheng, Jiachong; (Beijing, CN)
|
| Correspondence Name and Address:
|
VENABLE, BAETJER, HOWARD AND CIVILETTI, LLP
P.O. BOX 34385
WASHINGTON
DC
20043-9998
US
|
| Serial No.:
|
106053 |
| Series Code:
|
10
|
| Filed:
|
March 27, 2002 |
| U.S. Current Class: |
424/484 |
| U.S. Class at Publication: |
424/484 |
| Intern'l Class: |
A61K 009/14 |
Claims
We claim:
1. A colloidal nanosilver solution comprising a nanosilver particle with
diameter ranged between 1 nm and 100 nm; wherein said colloidal
nanosilver solution contains 0.001% to 0.4% by weight of silver.
2. The colloidal nanosilver solution according to claim 1, further
comprising a gelling agent.
3. The colloidal nanosilver solution according to claim 2, wherein said
gelling agent is starch or starch derivative.
4. The colloidal nanosilver solution according to claim 3, wherein said
starch derivative is at least one selected from the group consisting of
sodium carboxymethyl starch, hydroxyethyl starch, and pregelatinized
starch.
5. The colloidal nanosilver solution according to claim 2, wherein said
gelling agent which is cellulose or cellulose derivative.
6. The colloidal nanosilver solution according to claim 5, wherein said
cellulose derivative is at least one selected from the group consisting
of methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl
cellulose, and hydroxyethyl cellulose.
7. The colloidal nanosilver solution according to claim 2, wherein said
gelling agent is polymer or copolymer of acrylate or acrylate derivative.
8. The colloidal nanosilver solution according to claim 7, wherein said
polymer or copolymer of acrylate or acrylate derivative is Carbopol 934P.
9. The colloidal nanosilver solution according to claim 2, wherein said
gelling agent is polyvinyl pyrrolidone, alginic acid, or xanthogenated
gel.
10. The colloidal nanosilver solution according to claim 2, wherein said
gelling agent is at a concentration of 0.2 to 5% by weight of the total
solution.
11. The colloidal nanosilver solution according to claim 1, wherein said
colloidal nanosilver solution inhibits growth of bacteria, fungi, or
chlamydia.
12. The colloidal nanosilver solution according to claim 6, wherein said
bacteria, fungi or chlamydia are at least one selected from the group
consisting of Escherichia coli, Methicillin resistant Staphylococcus
aureus, Chlamydia trachomatis, Providencia stuartii, Vibrio vulnificus,
Pneumobacillus, Nitrate-negative bacillus, Staphylococcus aureus, Candida
albicans, Bacillus cloacae, Bacillus allantoides, Morgan's bacillus
(Salmonella morgani), Pseudomonas maltophila, Pseudomonas aeruginosa,
Neisseria gonorrhoeae, Bacillus subtilis, Bacillus foecalis alkaligenes,
Streptococcus hemolyticus B, Citrobacter, and Salmonella paratyphi C.
13. A method for making the colloidal nanosilver solution according to
claim 2 comprising: dissolving silver oxide (Ag.sub.2O) in ammonia water
(NH.sub.3.H.sub.2O) to form a solution containing silver ammino ion
[Ag(NH.sub.3).sup.+]; dissolving said gelling agent in water to form a
gelling medium; mixing said silver ammino ion-containing solution with
said gelling medium to form a colloidal nanosilver ammino ion-containing
solution; and mixing said colloidal nanosilver ammino ion-containing
solution with hydrazine hydrate (NH.sub.2NH.sub.2.H.sub.2O) to form the
colloidal nanosilver solution.
14. The method according to claim 13, wherein said gelling agent is at
least one selected from the group consisting of starch or starch
derivative, cellulose or cellulose derivative, polymer or copolymer of
acrylate or acrylate derivative, polyvinyl pyrrolidone, alginic acid, and
xanthogenated gel.
15. The method according to claim 14, wherein said starch derivative is
sodium carboxymethyl starch, hydroxyethyl starch, or pregelatinized
starch.
16. The method according to claim 14, wherein said cellulose derivative is
methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl
cellulose, or hydroxyethyl cellulose.
17. The method according to claim 14, wherein said polymer or copolymer of
acrylate or acrylate derivative is Carbopol 934P.
18. The method according to claim 13, wherein said colloidal nanosilver
ammino ion-containing solution is mixed with hydrazine hydrate
(NH.sub.2NH.sub.2.H.sub.2O) at about 0 to 45.degree. C. for about 0.5 to
2 hours.
19. The method according to claim 13, wherein after the formation of said
colloidal nanosilver solution, further comprising a step of contacting
said colloidal nanosilver solution with air for about 0.5 to 5 hours.
20. The method according to claim 13, wherein said ammonia water is at a
concentration of about 28% by weight.
21. The method according to claim 13, wherein said silver oxide and said
ammonium water is at a ratio of about 1:7 to about 1:10, w/v.
22. The method according to claim 13, wherein said silver oxide and said
hydrazine hydrate is at a ratio of about 1:0.087 to about 1:0.26, w/v.
23. A colloidal nano silver solution which is prepared according to claim
13.
24. The antibacterial or antifungal agent comprising the colloidal
nanosilver solution according to claim 1.
25. The antibacterial or antifungal agent according to claim 24, wherein
said antibacterial or antifungal agent is used to treat patients with
burn and scald-related skin infection, wound-related skin infection,
dermal or mucosal bacterial or fungal infection, surgery cut infection,
vaginitis, and acne-related infection.
26. A method for disinfection or sanitation comprising applying the
colloidal nanosilver solution according to claim 1 to areas in need of
disinfection or sanitation.
27. A method for suppressing bacterial or fungal growth in patients
comprising applying the colloidal nano silver solution to said patients.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a colloidal nanosilver solution
containing nanosilver particles with sizes ranged from 1 to 100 nm in
diameter. The silver content in the colloidal nanosilver solution is
about 0.001% to 0.4% by weight. The colloidal nanosilver solution also
contains a gelling agent which includes, but is not limited to, starch or
its derivatives, cellulose or its derivative, polymer or copolymer of
acrylate or acrylate derivative, polyvinyl pyrrolidone, alginic acid, and
xanthogenated gel. The colloidal nanosilver solution is characterized by
not containing toxic or impure substances and is suitable for use in
sanitation, disinfection, or as antimicrobial agent for treatment of
patients. The present invention also relates to a method for making the
colloidal nanosilver solution by interacting silver oxide first with
ammonia water then with hydrazine hydrate.
DESCRIPTION OF THE RELATED ART
[0002] It has been known for centuries that silver possesses germicidal
properties and has been employed as germicide before modern antibiotics
were developed. During those days, users would shave silver particles
into their drinking water, or submerge whole silver pieces in the
drinking water, for the purpose of ingesting silver by drinking the
water. Even after the onset of modem antibiotics era, silver remains to
be used as antimicrobial agent, particularly because microorganisms
treated by silver do not acquire resistance to the metals, while the
conventional antibiotics often induce the formation of
antibiotic-resistant microorganisms.
[0003] Silver is a safe and effective antimicrobial metal. In the late
eighteenth century, western scientists confirmed that silver, which had
been used in oriental medicine for centuries, was an effective
antibacterial agent. Scientists also knew that the human body fluid is
colloidal. Therefore,
colloidal silver had been used for antibacterial
purposes in the human body. By the early nineteenth century,
colloidal
silver was considered the best antibacterial agent until the discovery of
the antibiotics. Due to the potency and revenue-driven advantages of
antibiotics, the antibiotics gradually substituted
colloidal silver as
the main choice for antibacterial agent. However, thirty years into the
discovery of the antibiotics, scientists began to discover that
antibiotics induced the development of antibiotic-resistant bacterial
strains which significantly affected the efficiency of antibiotics.
Therefore, since 1870s, silver has again been recognized as a preferred
antibacterial use, particularly due to its non-toxic and non-induction of
bacterial-resistant characteristics.
[0004] There are many reasons why administering silver suspended in
solution (e.g.,
colloidal silver) would enhance an individual's health.
It is possible that such a solution operates to inhibit the growth of
bacteria, fungi, viruses, and other unwanted organisms, as well as
eradicating such existing bacteria, fungi, viruses, and other organisms.
It is also possible that a solution of silver can have an
anti-inflammatory effect, sufficient to reduce symptoms of asthma. Silver
in solution might also act in a similar fashion to a homeopathic remedy.
[0005] There have been numerous attempts to produce silver-based
solutions, including
colloidal silver. However, many of the silver-based
products fail to maintain the silver particles in suspension, either
because the silver solution is not a true colloid or because it is
otherwise unstable. When the suspension of the silver particles fails,
the particles fall to the bottom of the solution, thereby reducing the
solution's concentration of silver and rendering it less effective.
[0006] In the invention to be presented in the following sections, a
colloidal nanosilver solution will be disclosed. The colloidal nanosilver
solution of the present invention can maintain the colloidal nanosilver
particles in suspension for a long period of time. It also has the
advantages of not containing toxic or impure substances so that it is
particularly suitable for medicinal and healthcare use.
SUMMARY OF THE INVENTION
[0007] The present invention provides a colloidal nanosilver solution
containing nanosilver particles with sizes ranged between 1 nm and 100 nm
in diameter, the silver content in the colloidal nanosilver solution is
about 0.00% to 0.4% by weight.
[0008] The colloidal nanosilver solution also comprises a gelling agent,
which is starch or its derivative, cellulose or its derivative, polymer
or copolymer of acrylate or acrylate derivative, polyvinyl pyrrolidone,
alginic acid, or xanthogenated gel. Examples of starch derivative
include, but are not limited to, sodium carboxymethyl starch,
hydroxyethyl starch, and pregelatinized starch. Examples of cellulose
derivative include, but are not limited to, methyl cellulose,
hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl
cellulose. An example of polymer or copolymer of acrylate derivative is
carbomer, which is a carboxy vinyl polymer. Carbomer generally are high
molecular weight ("MW") polymers (MW above 1,000,000). Carbomer is
commercially available. B. F. Goodrich Company currently sells carbomer
using the tradename of Carbopol. Carbopol 934P has a MW of about
3,000,000 and Carbopol 940 is about 4,000,000. The preferred Carbopol is
Carbopol 934P. The preferred concentration of the gelling agent is at
about 0.2 to 5% by weight of the total solution.
[0009] The colloidal nanosilver solution has antimicrobial activity,
particularly for inhibiting growth of bacteria, fungi, or chlamydia.
Examples of microorganisms which can be inhibited by the colloidal
nanosilver solution include, but are not limited to, Escherichia coli,
Methicillin resistant Staphylococcus aureus, Chlamydia trachomatis,
Providencia stuartii, Vibrio vulnificus, Pneumobacillus, Nitrate-negative
bacillus, Staphylococcus aureus, Candida albicans, Bacillus cloacae,
Bacillus allantoides, Morgan's bacillus (Salmonella morgani), Pseudomonas
maltophila, Pseudomonas aeruginosa, Neisseria gonorrhoeae, Bacillus
subtilis, Bacillus foecalis alkaligenes, Streptococcus hemolyticus B,
Citrobacter, and Salmonella paratyphi C.
[0010] The present invention also provides a method for making the
colloidal nanosilver solution. The method includes the following steps:
(1) dissolving silver oxide (Ag.sub.2O) in ammonia water
(NH.sub.3.H.sub.2O) to form a solution containing silver ammino ion
[Ag(NH.sup.3).sup.+]; (2) dissolving a gelling agent in water to form a
gelling medium; (3) mixing the silver ammino ion-containing solution with
the gelling medium to form a colloidal nanosilver ammino ion-containing
solution; and (4) mixing the colloidal nanosilver ammino ion-containing
solution with hydrazine hydrate (NH.sub.2NH.sub.2.H.sub.2O) to form the
colloidal nanosilver solution. The ammonia water used in step (1) is
preferred to be at a concentration of 28% by weight. Also, the silver
oxide and the ammonium water in step (1) is preferred to be at a ratio of
about 1:7 to about 1:10 (w/v). In addition, the silver oxide and the
hydrazine hydrate in step (4) is preferred to be at a ratio of about
1:0.087 to about 1:0.26 (w/v).
[0011] It is preferred that the colloidal nanosilver ammino ion-containing
solution is mixed with hydrazine hydrate (NH.sub.2NH.sub.2.H.sub.2O) at
about 0 to 45.degree. C. for about 0.5 to 2 hours. Also, after the
formation of the colloidal nanosilver solution, it is preferred to let
the colloidal nanosilver solution be in contact with air for about 0.5 to
5 hours.
[0012] The colloidal nanosilver solution can be used as an antibacterial
or antifingal agent for treatment of patients with bum and scald-related
skin infection, wound-related skin infection, dermal or mucosal bacterial
or fungal infection, surgery cut infection, vaginitis, and acne-related
infection, by applying or spraying the solution onto the wounds. It can
also be used as a disinfectant or sanitary agent to clean areas in need
of disinfection or sanitation.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The present invention provides a colloidal nanosilver solution
which contains nanosilver particles having diameters with sizes ranged
between 1 nm and 100 nm. A colloid is a gelatinous or mucinous dispersion
medium that consists of particles which are larger than an ordinary
crystalloid molecule, but are not large enough to settle out under the
influence of gravity. These particles normally range in size from 1 to
100 nm. There are generally two kinds of colloids: (1) Suspension
colloids (suspensoids), in which the dispersion medium consists of
particles that are insoluble, such as a metal, and the dispersion medium
may be gaseous, liquid, or solid. (2) Emulsion colloids (emulsoids), in
which the dispersion medium is usually water and the disperse phase
consists of highly complex organic substances, such as starch or glue,
which absorb much water, swell, and become uniformly distributed
throughout the dispersion medium. The suspension colloids tend to be less
stable than the emulsion colloids. The colloidal nanosilver solution of
the present invention is a hybrid of both the suspension and the emulsion
colloids.
[0014] The colloidal nanosilver solution of the present invention is
further characterized by its non-toxic and purity nature, as well as its
stability. The silver content in the colloidal solution is between 0.001%
to 0.4% by weight. It is also stable at room temperature (about
25.degree. C. or 77.degree. F.) for at least 110 days. Because of these
characteristics, the colloidal nanosilver solution is particularly
suitable for use in healthcare related matters such as sanitization and
disinfection.
[0015] The colloidal nanosilver solution of the present invention can be
used in sanitary products, which include, but are not limited to,
solutions for cleansing agents for clothing, women hygiene, acne or
pimples, and soaking solution for tooth brush. It can also be used in
healthcare products, which include, but are not limited to, treating
patients with all kinds of injuries and/or burns, bacterial and fungal
infections (including gynecological infections such as vaginitis),
gastrointestinal bacterial infection, and sexually transmitted diseases.
In addition, the colloidal nanosilver solution of the present invention
can be used in industrial products, which include, but are not limited
to, food preservatives especially for fruits and vegetables, drinking
water disinfectants, paper and construction filling materials
preservation (especially to prevent mold formation).
[0016] The colloidal nanosilver solution of the present invention
possesses a broad spectrum of antibacterial and antifungal ability. It
can kill and suppress growth of bacteria and fungi, such as Escherichia
coli, Methicillin resistant Staphylococcus aureus, Chlamydia trachomatis,
Providencia stuartii, Vibrio vulnificus, Pneumobacillus, Nitrate-negative
bacillus, Staphylococcus aureus, Candida albicans, Bacillus cloacae,
Bacillus allantoides, Morgan's bacillus (Salmonella morgani), Pseudomonas
maltophila, Pseudomonas aeruginosa, Neisseria gonorrhoeae, Bacillus
subtilis, Bacillus foecalis alkaligenes, Streptococcus hemolyticus B,
Citrobacter, and Salmonella paratyphi C.
[0017] The antibacterial and antifungal activity of the colloidal
nanosilver solution of the present invention has advantage over the
conventional antibiotics in killing and suppressing bacterial growth, as
it does not induce drug-related resistance in the bacterial or fungal
strains.
[0018] Conventionally, a
colloidal silver solution is prepared by reducing
silver nitrate (AgNO.sub.3) to metallic silver with reducing agent such
as glucose, ascorbic acid, hydrazine hydrate, hydrazine sulfate, and
formaldehyde. The term "
colloidal silver solution" as used in this
context refers to a colloidal solution containing silver particles where
the sizes of the silver particles are not necessarily within the
nanometer range in the "colloidal nanosilver solution" as described in
the present invention.
[0019] Under this preparation method, other than silver, oxidized products
of the reducing agents, which are possibly toxic, are generated. The
presence of these oxidized products not only affect the purity of the
colloidal silver solution but also make the
colloidal silver solution
unsuitable for use in healthcare related industry due to its toxicity.
Also, although the oxidized products of the reducing agents can be
removed from the
colloidal silver solution by conventional methods, such
as dialysis, the method of dialysis involves excessive steps which not
only is time-consuming but also adds more difficulties and expenses to
the industrial-scale manufacturing process.
[0020] To avoid producing unwanted toxic products, at least two methods
are disclosed which produce a
colloidal silver solution containing
harmless side products from the reducing agents. For example:
[0021] (1) Reacting silver oxide (Ag.sub.2O) with hydrogen gas to form
metallic silver and water:
Ag.sub.2O+H.sub.2.fwdarw.2Ag+H.sub.2O
[0022] (2) Reacting silver oxide (Ag.sub.2O) with hydrazine hydrate
(NH.sub.2NH.sub.2.H.sub.2O) to form metallic silver, nitrogen gas, and
water.
2Ag.sub.2O+NH.sub.2NH.sub.2.H.sub.2O.fwdarw.4Ag+N.sub.2+3H.sub.2O
[0023] Because the above reactions produce metallic silver, nitrogen gas,
and water, which are non-toxic in nature so that no additional steps are
necessary for removing the unwanted toxic products, theoretically, they
should be suitable for the production of
colloidal silver solution.
However, the reactions as shown above are not practical in manufacturing
industrial-scale colloidal nanosilver solution. For example, in the
reaction as described in (1), which requires the silver oxide to interact
with hydrogen gas, a multiphase reaction is involved which make it very
difficult to carry out. See V. Kohlschuetter Strassburg (Z. Elektrochem.,
14, 49-63. CA: 2: 1379-1380). When the silver oxide and hydrogen are
sealed in a glass tube and reacted at 18.degree. C. or lower, the
reduction reaction takes place very slowly. On the other hand, if the
reaction is carried out at 60.degree. C. or lower, the hydrogen gas is
discharged into the saturated silver oxide solution, which results in
yielding a
colloidal silver solution with silver particles partially in
suspension and partially precipitated. A
colloidal silver solution
prepared in this way is not suitable for use in sanitation or healthcare
products due to precipitation of silver.
[0024] Also, in the reaction as described in (2) above, the interaction of
silver oxide with hydrazine hydrate in water is limited by the low
solubility of the silver oxide in water. See J. Voigt et al. (Z. Anorg.
Allgem. Chem. 164, 409-419, CA21:3512). Therefore, in order to obtain a
soluble silver oxide solution, the silver content of the silver oxide
solution must be no more than 0.001% by weight. Using such a diluted
silver oxide solution as starting material, the resulting silver content
in the
colloidal silver solution is too low to be effective for
sanitation or healthcare use.
[0025] The present invention provides a method for making a colloidal
nanosilver solution which is distinctively different from the prior art
methods. Based on this method, a colloidal nanosilver solution which
contains high silver concentration (i.e., containing 0.001% to 0.4% by
weight of silver), high stability in the colloidal state (i.e., stable at
room temperature for no less than 110 days), and no toxic substances, is
formed.
[0026] The method for preparing the colloidal nanosilver solution of the
present invention contains the following reactive steps:
[0027] (1) Dissolution of Silver Oxide in Ammonia Water
(N.sub.3.H.sub.2O).
[0028] Silver oxide (Ag.sub.2O) is dissolved in concentrated ammonia water
(NH.sub.3.H.sub.2O) to obtain a silver ammino oxide
[Ag(NH.sub.3).sup.+].sub.2O solution where the silver ion is in the form
of silver ammino ion [Ag(NH.sub.3).sup.+] in as follows:
Ag.sub.2O+2NH.sub.3.H.sub.2O.fwdarw.[Ag(NH.sub.3).sup.+].sub.2O+2H.sub.2O
[0029] The concentrated ammonia water is preferred to be about 28%. The
preferred ratio of silver oxide and ammonium water is at about 1:7 to
about 1:10, w/v. This procedure has the advantage of increasing the
solubility and concentration of silver in the solution.
[0030] (2) Dissolution of Gelling Agent in Water to Form a Gelling Medium.
[0031] A gelling medium is provided by dissolving a gelling agent in
water. This gelling medium serves as a protective gel/colloid mechanism
for keeping the nanosilver particles suspended in the colloidal
nanosilver solution and preventing the nanosilver particles from
aggregating with each other to form bigger pellets and precipitate.
Preferably, the concentration of the gelling agent is between 0.2% to 5%
by weight.
[0032] The gelling agent can be a synthetic or natural polymer or a
combination thereof, which can be readily dissolved in water. Examples of
the gelling agent include, but are not limited to, starch or starch
derivatives, cellulose or cellulose derivatives, polymer or copolymer of
acrylate or acrylate derivatives, polyvinyl pyrrolidone (PVP), alginic
acid, and xanthogenated gel. The starch derivatives include, but are not
limited to, sodium carboxymethyl starch, hydroxyethyl starch, and
pre-gelatinized starch. The cellulose derivatives include, but are not
limited to, methyl cellulose, hydroxypropyl cellulose, hydroxypropyl
methyl cellulose, and hydroxyethyl cellulose. The polymer or copolymer of
acrylate or acrylate derivative is preferred to be Carbomer.
[0033] Carbomer is a polymer of acrylic acid (or a carboxy vinyl polymer).
It is currently sold under the tradename of Carbopol by B. F. Goodrich
Company. The preferred carboxy vinyl polymer is a high molecular weight
(preferably MW above 1,000,000; and most favorably MW above 3,000,000)
polymer, such as Carbopol 934P which has a molecular weight of about
3,000,000.
[0034] Carbopol is the trademark of B. F. Goodrich Company's carboxy vinyl
polymers, which generally are high molecular weight ("MW") polymers (MW
above 1,000,000). Specifically, Carbopol 934P has a MW of about 3,000,000
and Carbopol 940 is about 4,000,000. The preferred Carbopol is Carbopol
934P.
[0035] (3) Mixing Silver Ammino Oxide Solution with the Gelling Medium.
[0036] The silver ammino oxide [Ag(NH.sub.3).sup.+].sub.2O solution is
thoroughly mixed with the gelling medium to form a uniformly dispersed
silver ammino oxide-gelling solution to be used for the next reaction.
The silver ammino oxide-gelling medium is preferred to be controlled at
about 0.degree. to 45.degree. C.
[0037] (4) Reaction of Silver Ammino Ion with Hydrazine Hydrate.
[0038] The silver ammino ion is further interacted with hydrazine hydrate
in the presence of oxygen gas to form metallic silver, nitrogen gas, and
water as follows:
[Ag(NH.sub.3).sup.+].sub.2O+NH.sub.2NH.sub.2.H.sub.2O+2O.sub.2.fwdarw.2Ag.-
sub.(metallic)+2 N.sub.2+6H.sub.2O
[0039] The preferred temperature for the above reaction is at about
0.degree. C.-45.degree. C. The reaction is preferred to be conducted in
about 0.5 to 2 hours. The silver ammino oxide and hydrazine hydrate are
preferred to be at a ratio of 1:0.087 to 1:0.26 by weight. The nanosilver
particles prepared by the reactive steps (1)-(4) have diameter of 1 nm to
100 nm.
[0040] Because hydrazine hydrate is toxic, after the completion of step
(4), the colloidal nanosilver solution is preferred to be kept in the
presence of air for additional 0.5 to 5 hours so that the residue of
hydrazine hydrate in the final colloidal nanosilver solution can be
decomposed into nitrogen and water by the following oxidative reaction:
NH.sub.2NH.sub.2.H.sub.2O+O.sub.2.fwdarw.N.sub.2+3H.sub.2O
[0041] The resulting nitrogen gas and water are non-toxic so that no
removal of the side products is necessary.
[0042] Moreover, the present invention provides a method for making the
colloidal nanosilver solution of high silver concentration, high
stability in the gel state, and no toxic ingredients. The above mentioned
problems associated with the reaction are solved in the present
invention: the solubility of silver oxide and final concentration of
silver in the colloidal solution are improved, the colloidal nanosilver
is stabilized as the gel state in the solution, and the toxic reactant,
hydrous ammonia, is carefully removed from the colloidal nanosilver
solution by further decomposition reaction with oxygen in the air. The
colloidal nanosilver solution of the present invention is suitable for
healthcare purposes and serves as an effective antimicrobial agent.
[0043] The following examples are illustrative, but not limiting the scope
of the present invention. Reasonable variations, such as those occur to
reasonable artisan, can be made herein without departing from the scope
of the present invention.
EXAMPLE 1
Preparation of the Colloidal Nanosilver Solution of the Present Invention
[0044] The colloidal solution containing nanosilver particles of the
present invention was prepared according to the following steps:
[0045] 1. 60 g of sodium carboxymethyl starch 60 g was dissolved in 1600
ml of distilled water. The dissolved sodium carboxymethyl starch solution
was added to a 5000 ml flask. The flask was heated to and maintained at
70.degree. C. until the solution became gelatinized. The gelatinized
solution was cooled down to room temperature.
[0046] 2. 3 g of silver oxide was added to and mixed with 22 ml of 28%
ammonia water to form a silver ammino oxide (i.e.,
[Ag(NH.sub.3).sup.+].sub.2O)-solution.
[0047] 3. The silver ammino oxide solution was then mixed thoroughly with
the gelatinized solution of (2) to form a silver ammino oxide-gelling
medium.
[0048] 4. 0.5 g of 80% hydrazine hydrate was mixed with and dissolved in
200 ml of distilled water to form a hydrazine hydrate solution.
[0049] 5. The hydrazine hydrate solution was added to the flask containing
silver ammino oxide-gelling medium. An additional 115 ml of distilled
water was then added to and mixed with the rest of the solution. The
solution was then reacted at room temperature for 1.5 hours under seal.
The flask was then opened to allow the reactants to be in touch with air
for additional 3.0 hours.
EXAMPLE 2
Preparation of the Colloidal Nanosilver Solution of the Present Invention
[0050] The colloidal solution containing nanosilver particles of the
present invention was prepared according to the following steps.
[0051] 1. 1600 ml of distilled water was added to a 5000 ml flask and
heated to and maintained at 70.degree. C.
[0052] 2. 50 g of methyl cellulose was gradually added to the flask
containing the heated distilled water. After thorough mixing of the
methyl cellulose with the distilled water, the temperature of the
solution was gradually reduced to around 30.degree. C. until a
gelatinized solution was formed.
[0053] 3. 3 g of silver oxide was added to and mixed with 22 ml of 28%
ammonia water to form a silver ammino oxide solution.
[0054] 4. The silver ammino oxide solution was then added to and mixed
with the gelatinized solution to form a silver ammino oxide-gelling
medium.
[0055] 5. 0.6 g of 80% hydrazine hydrate was dissolved in 200 ml of
distilled water to form a hydrazine hydrate solution.
[0056] 6. The hydrazine hydrate solution was then added to the flask
containing silver ammino oxide-gelling medium. An additional 125 ml of
distilled water was then added to and mixed with the rest of the
solution. The solution was then reacted at room temperature for 1 hour
under seal. The flask was then opened to allow the reactants to be in
touch with air for additional 4.0 hours.
EXAMPLE 3
Preparation of the Colloidal Nanosilver Solution of the Present Invention
[0057] The colloidal solution containing nanosilver particles of the
present invention was prepared according to the following steps.
[0058] 1. 1600 ml of distilled water was added to a 5000 ml flask and
heated to and maintained at 70.degree. C.
[0059] 2. 4.5 g of carboxypropyl methyl cellulose was gradually added to
the flask containing the heated distilled water. After thorough mixing of
the carboxypropyl methyl cellulose with the distilled water, the
temperature of the solution was gradually reduced to around 30.degree. C.
until a gelatinized solution was formed.
[0060] 3. 4.5 g of silver oxide was added to and mixed with 33 ml of 28%
ammonia water to form a silver ammino oxide solution.
[0061] 4. The silver ammino oxide solution was then added to and mixed
with the gelatinized solution to form a silver ammino oxide-gelling
medium.
[0062] 5. 1 g of 80% hydrazine hydrate was dissolved in 260 ml distilled
water to form a hydrazine hydrate solution.
[0063] 6. The hydrazine hydrate solution was added to the silver ammino
oxide-gelling medium and 76 ml of distilled water was further added to
and mixed with the rest of the solution. The flask was then sealed and
kept at room temperature for about 1 hour.
[0064] 7. The flask was then unsealed to allow the solution to be in touch
with air for 4 hours to obtain the colloidal nanosilver solution of the
present invention.
EXAMPLE 4
Preparation of the Colloidal Nanosilver Solution of the Present Invention
[0065] The colloidal solution containing nanosilver particles of the
present invention was prepared according to the following steps.
[0066] 1. 1600 ml of distilled water was added to a 5000 ml flask.
[0067] 2. 1 g of polyvinylpyrrolidone (PVP) was gradually added into the
flask at room temperature and dissolved therein to form a gelatinized
solution.
[0068] 3. 6 g of silver oxide was dissolved in 44 ml of 28% ammonia water
to form a silver ammino oxide solution.
[0069] 4. The silver ammino oxide solution of step (3) was add to and
thoroughly mixed with the gelatinized solution of (2) to form a silver
ammino oxide-gelling medium.
[0070] 5. 1.5 g of 80% hydrazine hydrate was dissolved in 270 ml of
distilled water to form a hydrazine hydrate solution.
[0071] 6. The hydrazine hydrate solution was then mixed with the silver
ammino oxide-gelling medium of (4) in the flask with 73 ml of additional
distilled water added to and mixed into the rest of the solution. The
flask was sealed and kept at 30.degree. C. for 1.5 hours.
[0072] 7. The flask was unsealed to allow the solution to be in touch with
air for 5 hours to obtain the colloidal nanosilver solution of the
present invention.
EXAMPLE 5
Examination of the Dimension and Stability of the Colloidal Nanosilver
Solution
[0073] I. Purpose:
[0074] The colloidal solution containing nanosilver particles of the
present invention was examined for the dimension of the nanosilver
particles and stability of the colloidal nanosilver solution over time
(days) in terms of suspension by electron microscopy.
[0075] II. Method:
[0076] In accordance with the standard procedures for JY/T011-1996
transmission electron microscope, JEM-100CXII transmission electron
microscope was used under the testing conditions of accelerating voltage
at 80 KV and resolution at 0.34 nm. The colloidal nanosilver solutions
produced by Examples 1-4 of the present invention were observed for the
size and distribution of the nanosilver particles therein. Aliquots of
the samples from Examples 1-4 were taken out from the solutions either
being freshly made or after being stored at room temperature for 110
days.
[0077] III. Results:
[0078] For the freshly made colloidal nanosilver samples, the diameters of
all the silver particles contained therein were below 35 nm, among which,
most particles (37%) had a diameter of 15 nm.
[0079] For the colloidal solution stored after 110 days, the diameters of
all the silver particles contained therein were kept below 35 nm, among
which, most particles (38%) had a diameter of 15 nm.
[0080] IV. Conclusion:
[0081] The colloidal solution of the present invention containing
nanosilver particles which had a size range of 1 nm to 100 nm and was
very stable after storage of 110 days at room temperature. There was no
visible increase in size of the silver particles contained therein and no
precipitation of silver particles. The colloidal solution of the present
invention was stable for further processing and adopted for use, storage,
and transportation.
EXAMPLE 6
Antimicrobial Activity of the Colloidal Nanosilver Solution of the Present
Invention
[0082] I. Purpose:
[0083] The colloidal solution of the present invention was tested for the
antimicrobial ability.
[0084] II. Method:
[0085] Microbial strains tested were Escherichia coli, Methicillin
resistant Staphylococcus aureus, Chlamydia trachomatis, Providencia
stuartii, Vibrio vulnificus, Pneumobacillus, Nitrate-negative bacillus,
Staphylococcus aureus, Candida albicans (ATCC 10231), Bacillus cloacae,
Bacillus allantoides, Morgan's bacillus (Salmonella morgani), Pseudomonas
maltophila, Pseudomonas aeruginosa, Neisseria gonorrhoeae, Bacillus
subtilis, Bacillus foecalis alkaligenes, Streptococcus hemolyticus B,
Citrobacter, and Salmonella paratyphi C. These strains were either
isolated from clinical cases or purchased as standard strains from
Chinese Biological Products Testing and Standardizing Institute.
[0086] A typical example of the test, as illustrated by Candida albicans
(ATCC 10231), was as follows:
[0087] Colloidal nanosilver solutions of examples 1-4 (each contains a
concentration of 1370 .mu.g/ml of silver) were tested for its antifungal
activity against Candida albicans. The colloidal nanosilver solutions
were diluted in distilled water to make the final concentrations of 137
.mu.g/ml, 68.5 .mu.g/ml, 45.7 .mu.g/ml, 34.2 .mu.g/ml, and 27.4 .mu.g/ml.
In the control group, no colloidal nanosilver solution was added. Candida
albicans was added to each tested and control groups, respectively, and
the viability of the fungus in each group was examined 2 minutes after
incubation with the colloidal nanosilver solutions of examples 1-4.
[0088] Typically, due to the resilience of Candida Albicans, a higher
concentration of disinfectant is required to kill or suppress the growth
of Candida albicans than for killing bacteria such as Staphylococcus
aureus and Escherichia coli.
[0089] III. Results:
[0090] There was an average of 99.99% killing rate (1.78.times.10.sup.6
cfu/mu) for all of the colloidal nanosilver solution tested (Examples
1-4) after 2 minutes of incubation. Among the same example, the most
diluted sample demonstrated about the same fungicidal activity as the
least diluted one.
[0091] IV. Conclusion:
[0092] The colloidal solution containing nanosilver particles of the
present invention was effective as antimicrobial agent even at a diluted
concentration of 27.4 .mu.g/ml of silver.
[0093] While the invention has been described by way of examples and in
terms of the preferred embodiments, it is to be understood that the
invention is not limited to the disclosed embodiments. On the contrary,
it is intended to cover various modifications as would be apparent to
those skilled in the art. Therefore, the scope of the appended claims
should be accorded the broadest interpretation so as to encompass all
such modifications.
