Silver nanoparticles
Encyclopedia
Silver nanoparticles are nanoparticles of silver
, i.e. silver particles of between 1 nm and 100 nm in size. While frequently described as being 'silver' some are composed of a large percentage of silver oxide due to their large ratio of surface-to-bulk silver atoms.
, ion implantation
, or wet chemistry.
with a reducing agent like sodium borohydride
in the presence of a colloidal stabilizer. Sodium borohydride has been used with polyvinyl alcohol
, poly(vinylpyrrolidone), bovine serum albumin (BSA), citrate and cellulose as stabilizing agents. In the case of BSA, the sulfur-, oxygen- and nitrogen-bearing groups mitigate the high surface energy of the nanoparticles during the reduction. The hydroxyl groups on the cellulose are reported to help stabilize the particles. Polydopamine coated magnetic-bacterial cellulose contains multifunctional groups, which acts as a reducing agent for in situ preparation of reusable antibacterial Ag-nanocomposites Article . Citrate and cellulose have been used to create silver nanoparticles independent of a reducing agent as well. An additional novel wet chemistry method used to create silver nanoparticles took advantage of ß-D-glucose as a reducing sugar and a starch as the stabilizer.
Also, it is important to note, not all nanoparticles are created equal. The size and shape have been shown to have an impact on its efficacy. Additionally, crystal facet size, oxide content and several other factors could also affect the antimicrobial properties.
, optics
, electronics
and other areas due to their unique size-dependent optical, electrical and
magnetic properties. Currently most of the applications of silver nanoparticles are in antibacterial/antifungal agents in biotechnology and bioengineering,
textile engineering, water treatment
, and silver-based consumer products.
There is also an effort to incorporate silver nanoparticles into a wide range of medical devices, including but not limited to
Samsung
has created and marketed a material called Silver Nano
, that includes silver nanoparticles on the surfaces of household appliances.
Silver nanoparticles have been used as the cathode in a silver-oxide battery
.
Ionic silver has a long history of use in topical medical applications, and it has been shown that ionic silver, in the right quantities, is suitable in treating wounds. The US Food and Drug Administration has approved the use of a range of different silver-impregnated wound dressings. Silver nanoparticles are now replacing silver sulfadiazine as an effective agent in the treatment of wounds.
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
, i.e. silver particles of between 1 nm and 100 nm in size. While frequently described as being 'silver' some are composed of a large percentage of silver oxide due to their large ratio of surface-to-bulk silver atoms.
Synthesis
There are many different synthetic routes to silver nanoparticles. They can be divided into three broad categories: physical vapor depositionPhysical vapor deposition
Physical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces...
, ion implantation
Ion implantation
Ion implantation is a materials engineering process by which ions of a material are accelerated in an electrical field and impacted into another solid. This process is used to change the physical, chemical, or electrical properties of the solid...
, or wet chemistry.
Ion implantation
Although it may seem counter-intuitive, ion implantation has been used to create silver nanoparticles. This process has been shown to produce silver particles embedded in glass, polyurethane, silicone, polyethylene, and polymethylmethacrylate. The particles grow in the substrate with the bombardment of ions. The existence of nanoparticles is proven with optical absorbance, though the exact nature of the particles created with this method is not known.Wet chemistry
There are several wet chemical methods for creating silver nanoparticles. Typically, they involve the reduction of a silver salt such as silver nitrateSilver nitrate
Silver nitrate is an inorganic compound with chemical formula . This compound is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides...
with a reducing agent like sodium borohydride
Sodium borohydride
Sodium borohydride, also known as sodium tetrahydridoborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a versatile reducing agent that finds wide application in chemistry, both in the laboratory and on a technical scale. Large amounts are...
in the presence of a colloidal stabilizer. Sodium borohydride has been used with polyvinyl alcohol
Polyvinyl alcohol
Polyvinyl alcohol is a water-soluble synthetic polymer .-Properties:...
, poly(vinylpyrrolidone), bovine serum albumin (BSA), citrate and cellulose as stabilizing agents. In the case of BSA, the sulfur-, oxygen- and nitrogen-bearing groups mitigate the high surface energy of the nanoparticles during the reduction. The hydroxyl groups on the cellulose are reported to help stabilize the particles. Polydopamine coated magnetic-bacterial cellulose contains multifunctional groups, which acts as a reducing agent for in situ preparation of reusable antibacterial Ag-nanocomposites Article . Citrate and cellulose have been used to create silver nanoparticles independent of a reducing agent as well. An additional novel wet chemistry method used to create silver nanoparticles took advantage of ß-D-glucose as a reducing sugar and a starch as the stabilizer.
Also, it is important to note, not all nanoparticles are created equal. The size and shape have been shown to have an impact on its efficacy. Additionally, crystal facet size, oxide content and several other factors could also affect the antimicrobial properties.
Uses
Over the last decades silver nanoparticles have found applications in catalysisCatalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
, optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
, electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
and other areas due to their unique size-dependent optical, electrical and
magnetic properties. Currently most of the applications of silver nanoparticles are in antibacterial/antifungal agents in biotechnology and bioengineering,
textile engineering, water treatment
Water treatment
Water treatment describes those processes used to make water more acceptable for a desired end-use. These can include use as drinking water, industrial processes, medical and many other uses. The goal of all water treatment process is to remove existing contaminants in the water, or reduce the...
, and silver-based consumer products.
There is also an effort to incorporate silver nanoparticles into a wide range of medical devices, including but not limited to
- bone cementBone cementBone cements have been used very successfully to anchor artificial joints for more than half a century. Artificial joints are anchored with bone cement. The bone cement fills the free space between the prosthesis and the bone and plays the important role of an elastic zone...
, - surgical instruments,
- surgical masks,
- wound dressings.
Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...
has created and marketed a material called Silver Nano
Silver Nano
Silver Nano is a trademark name of an antibacterial technology which uses silver nanoparticles in washing machines, refrigerators, air conditioners, air purifiers and vacuum cleaners introduced by Samsung in April 2003....
, that includes silver nanoparticles on the surfaces of household appliances.
Silver nanoparticles have been used as the cathode in a silver-oxide battery
Silver-oxide battery
A silver oxide battery , not to be confused with a similar but different silver–zinc battery, which is a secondary cell, is a primary cell with relatively very high energy/weight ratio. They are costly due to the high price of silver...
.
Health concerns
Exposure to silver nanoparticles has been associated with "inflammatory, oxidative, genotoxic, and cytotoxic consequences"; the silver particulates primarily accumulate in the liver. but have also been shown to be toxic in other organs including the brain.Ionic silver has a long history of use in topical medical applications, and it has been shown that ionic silver, in the right quantities, is suitable in treating wounds. The US Food and Drug Administration has approved the use of a range of different silver-impregnated wound dressings. Silver nanoparticles are now replacing silver sulfadiazine as an effective agent in the treatment of wounds.
- Allergic reaction: While there is anecdotal evidence suggesting the possibility of a silver allergy, an extensive review of the medical literature does not lend any credence to this possibility. Some silver alloys that include nickel do elicit an allergic reaction.
- Argyria and staining: Ingested silver or silver compounds, including colloidal silver, can cause a condition called argyriaArgyriaArgyria is a condition caused by improper exposure to chemical forms of the element silver, silver dust, or silver compounds. The most dramatic symptom of argyria is that the skin becomes blue or bluish-grey colored. Argyria may be found as generalized argyria or local argyria...
, a discoloration of the skin and organs.In 2006, there was a case study of a 17-year-old man, who sustained burns to 30% of his body, and experienced a temporary bluish-grey hue after several days of treatment with Acticoat, a brand of wound dressing containg silver nanoparticles. Argyria is the deposition of silver in deep tissues, a condition that cannot happen on a temporary basis, raising the question of whether the cause of the man’s discoloration was argyria or even a result of the silver treatment. Silver dressings are known to cause a “transient discoloration” that dissipates in 2–14 days, but not a permanent discoloration.
- Silzone heart valve: St. Jude MedicalSt. Jude MedicalSt. Jude Medical, Inc. is a $16 billion global medical device company, with headquarters in Little Canada, Minnesota, United States, a suburb of St. Paul. The company sells products in more than 100 countries and has over 20 operations and manufacturing facilities worldwide. Its principal...
released a mechanical heart valve with a silver coated sewing cuff (coated using ion beam-assisted deposition) in 1997. The valve was designed to reduce the instances of endocarditisEndocarditisEndocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves . Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or even on intracardiac devices...
. The valve was approved for sale in Canada, Europe, the United States, and most other markets around the world. In a post-commercialization study, researchers showed that the valve prevented tissue ingrowth, created paravalvular leakage, valve loosening, and in the worst cases explantation. After 3 years on the market and 36,000 implants, St. Jude discontinued and voluntarily recalled the valve.