Silver nanoparticles

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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.

Synthesis

There are many different synthetic routes to silver nanoparticles. They can be divided into three broad categories: physical vapor deposition, ion implantation, or wet chemistry.

Ion implantation

Although it may seem counter-intuitive, ion implantation has been used to create silver nanoparticles.^[1] 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 nitrate 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 ^[2]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

See also: Medical uses of silver

Over the last decades silver nanoparticles have found applications in catalysis, 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

• bone cement,
• surgical instruments,
• surgical masks,
• wound dressings.

Samsung has created and marketed a material called Silver Nano, that includes silver nanoparticles on the surfaces of household appliances.^[3]

Silver nanoparticles have been used as the cathode in a silver-oxide battery.

Health concerns

Exposure to silver nanoparticles has been associated with "inflammatory, oxidative, genotoxic, and cytotoxic consequences"; the silver particulates primarily accumulate in the liver.^[4] but have also been shown to be toxic in other organs including the brain.^[5]

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.^{[6][7][8][9][10]} 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.^[10][11]

• 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.^[12] 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 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.^[13] 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.^[14] Silver dressings are known to cause a “transient discoloration” that dissipates in 2–14 days, but not a permanent discoloration.^{[citation needed]}

• Silzone heart valve: St. Jude Medical released a mechanical heart valve with a silver coated sewing cuff (coated using ion beam-assisted deposition) in 1997.^[15] The valve was designed to reduce the instances of endocarditis. 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.

References

1. ^ Stepanov, A. L.; Popok, V. N.; Hole, D. E. (2002). Glass Physics and Chemistry 28 (2): 90. doi:10.1023/A:1015377530708. 
2. ^ Magnetic antimicrobial nanocomposite based on bacterial cellulose and silver nanoparticles Manthiriyappan Sureshkumar, Dessy Yovita Siswanto and Cheng-Kang Lee, J. Mater. Chem., 2010, 20, 6948-6955.http://pubs.rsc.org/en/Content/ArticleLanding/2010/JM/c0jm00565g
3. ^ Samsung's Silver Nano Washer Ads Reportedly Exaggerated, Nov 21, 2005
4. ^ Johnston HJ, Hutchison G, Christensen FM, Peters S, Hankin S, Stone V (April 2010). "A review of the in vivo and in vitro toxicity of silver and gold particulates: particle attributes and biological mechanisms responsible for the observed toxicity". Crit. Rev. Toxicol. 40 (4): 328–46. doi:10.3109/10408440903453074. PMID 20128631. 
5. ^ Ahamed M, Alsalhi MS, Siddiqui MK (December 2010). "Silver nanoparticle applications and human health". Clin. Chim. Acta 411 (23–24): 1841–8. doi:10.1016/j.cca.2010.08.016. PMID 20719239. 
6. ^ Qin, Yimin (2005). "Silver-containing alginate fibres and dressings". International Wound Journal 2 (2): 172–6. doi:10.1111/j.1742-4801.2005.00101.x. PMID 16722867. 
7. ^ MRSA Silver
8. ^ Hermans MH (2006). "Silver-containing dressings and the need for evidence". The American journal of nursing 106 (12): 60–8; quiz 68–9. PMID 17133010. 
9. ^ Chopra, I. (2007). "The increasing use of silver-based products as antimicrobial agents: a useful development or a cause for concern?". Journal of Antimicrobial Chemotherapy 59 (4): 587–90. doi:10.1093/jac/dkm006. PMID 17307768. 
10. ^ ^{a b} Atiyeh BS, Costagliola M, Hayek SN, Dibo SA (2007). "Effect of silver on burn wound infection control and healing: review of the literature". Burns 33 (2): 139–48. doi:10.1016/j.burns.2006.06.010. PMID 17137719. 
11. ^ Lansdown AB (2006). "Silver in health care: antimicrobial effects and safety in use". Current Problems in Dermatology 33: 17–34. doi:10.1159/000093928. PMID 16766878. 
12. ^ Holmstrup, P (1991). "Reactions of the oral mucosa related to silver amalgam: a review". Journal of Oral Pathology & Medicine 20 (1): 1–7. PMID 2002442. 
13. ^ Trop, Marji, Michael Novak, Siegfried Rodl, Bengt Hellbom, Wolfgang Kroell, and Walter Goeseeler (2006). "Silver-coated dressing acticaot caused raised liver enzymes and argyris-like symptoms in burn patient". The Journal of Trauma, Injury, Infection and Critical Care 60 (3): 648–652. doi:10.1097/01.ta.0000208126.22089.b6. 
14. ^ Parkes, A. (2006). "Silver-coated dressing Acticoat". Journal of Trauma-Injury Infection & Critical Care 61 (1): 239–40. doi:10.1097/01.ta.0000224131.40276.14. 
15. ^ Horstkotte, D; Bergemann, R (2001). "Thrombogenicity of the St. Jude medical prosthesis with and without silzone-coated sewing cuffs". The Annals of thoracic surgery 71 (3): 1065. doi:10.1016/S0003-4975(00)02363-8. PMID 11269440.