Winnie Siauw
WRIT 340
Illumin Article
11/4/2011
Nanoparticle: A Valuable Weapon That Attacks Microbial Colonies
The term “nanoparticle” refers to any particle with size ranging from 1 to 100
nanometers, where a nanometer is one-billionth of a meter. To put the size of a nanoparticle in
perspective, the diameter of a human hair is equivalent to 80,000 of the smallest nanoparticles
combined. So what makes this miniature particle so impressive and attractive to the scientific
community? Of course, a single nanoparticle is not sufficient to make an impact, but a billion or
even a trillion of these nanoparticles can be very powerful and beneficial to mankind. Scientists
have worked with nanoparticles for centuries. Prior to the recent development of advanced
microscopes, such as Scanning Electron Microscope (SEM) and Transmission Electron
Microscopy (TEM), scientists had faced significant limitations on their research due to the
inability to see the structure of the nanoparticles. Today, the textile industry has integrated
nanotechnology into their products. Odor-resistant clothing, one of the consumer products in the
current market, has incorporated the use of silver nanoparticles into clothing to help achieve its
goal of minimizing the undesirable odor which results from bacteria in sweat and dirt.
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What Causes Body Odor?
In popular culture, most people perceive body odor as shameful, a direct result of
sweating or intrinsic body trait. However, sweat itself is odorless. Body odors are actually
caused by bacterial activity. Many microorganisms, such as bacteria, mold, mildew, and fungus,
prefer to grow in moist environments. For example, the unpleasant smell from stinky feet or
armpits results from rapid multiplication of bacteria, which uncontrollably thrive in a pool of
sweat. When bacteria grow on our body, they decompose sweat into acids that produce the
odorous chemicals which we perceive as body odor. Propionic Acid and Isovaleric Acid are
two common types of acids generated when bacteria break down the human body's sweat. When
amino acids are broken down by Propionibacteria into Propionic Acid, the acid produces a
vinegar-like smell. Similarly, Isovaleric acid is produced by the action of the
bacteria Staphylococcus epidermidis breaking down fatty acid, which causes a cheese-like smell
[8].
Brief History of Silver and Nanoparticles
In order to minimize the undesirable body odor, it is necessary to abolish the replication
of microbes that are generated in our body sweat. Silver has a long history of being an
antibacterial agent. Not only had ancient Greek and Roman civilizations used silver to disinfect
water and food, other pioneers also used to submerge silver coins in water and milk to keep them
fresh. By 1920s, the US Food and Drug Administration had even approved silver solution as a
type of antibacterial agent.
After the discovery of silver as an antibacterial agent, the concept of the “nano-world”
was introduced in 1959 from a famous lecture titled “There’s Plenty of Room at the Bottom” by
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Richard Feynman, a physicist at Caltech. Feynman suggested that in principle, it was possible to
develop “nano-scale” machines capable of producing smaller products. Feynman suggested that
if microscopic “machine shops” were created, then materials can be divided into billion times
smaller than the current size to reach an unprecedented nano-scale level. Feynman proposed that
smaller particles, with their lower mass, encounter less gravitational force, but greater influence
by both Van Der Waals attraction and surface tension. His lecture on individual atoms and
molecular manufacturing had eventually stimulated scientists and engineers worldwide to
develop technology to image, fabricate and manipulate the fundamental structures of atoms and
molecules [3].
Feynman's proposition did not transform into a scientific concept until the 80s and 90s
when Eric Drexler, along with other researchers, derived the term “nanotechnology". Thereafter,
they slowly unwound the mystery inside the nano-world which Feynman had constructed in
1959. Along with increasing knowledge of the nano-world, scientists unveiled more unique
features of nanoparticles. For instance, given their miniscule size, nanoparticles have a high
surface-area-to-volume ratio, which means these particles also have a high rate of chemical
reaction.
How Silver Nanoparticles Work on Clothing
Knowing that silver is an effective antimicrobial agent and that nanoparticles provide
terrific driving force for diffusion, how can we take advantage of these fantastic properties and
integrate them into our everyday life to benefit us? From the antibacterial properties of silver
and the applications of nanoparticles, scientists derived the “silver nanoparticles” to combine the
major benefits offered by silver and nanoparticles alone. Silver nanoparticles can be assembled
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into many different shapes, such as spheres, rods, cubes, wires, film and coatings. Moreover,
silver nanoparticles can be integrated into a variety of materials like metals, ceramics, polymers,
glass and textiles via fine spraying of silver nanoparticle solution [9]. As a result of the vast
possibilities, the market of athletic products increasingly emphasizes on the famous advertising
labels of "antibacterial" and "odor controlling". Strolling down a sporting products store in the
neighborhood, we can easily identify shoe products, sports clothing, and towels labeled
"antibacterial" or "odor controlling", which usually refers to the use of silver nanoparticles in
destroying odor-causing bacteria [4].
The benefits of nanoparticles surely appeal to the public, but
how do these tiny particles actually destroy microbial colonies?
Bacteria, approximately 1000 nanometers, use enzymes to metabolize
nutrients and create energy in a similar fashion as any other living
organisms. They are unicellular with only one compartment of protein,
which stores all the elements of the cell. Thus, in order to
stop the exponential rate of bacterial replication, it is
Source: El-Rafie, M.H., Mohamed, A.A., Shaheen, T.I., Hebeish, A.
"Antimicrobial effect of silver nanoparticles produced by fungal
process on cotton fabrics." Carbohydrate Polymers. 2010. Volume 80,
issue 3. p. 779-782.
necessary to disrupt the bacterial enzymes and energy
metabolism.
To counter bacterial growth, the textile industry first
inserts silver nanoparticles into its products to allow the
particles to attach to the filaments. Once the silver
nanoparticles encounter the sweat from human body or any
Source: http://www.smartsilver.com/apparel/applications/footwear
other source of moisture, they naturally release a low
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concentration of silver ions into the moist environment. Unlike traditional antibiotics, which only
concentrate on one of the pathways that kill bacteria, silver ions attack microbes in three
different pathways: respiration, replication, and cell wall synthesis.
The figure on the right shows how silver nanoparticles
penetrate the bacterial cell membrane and change their structural
composition by interacting with the bacteria's sulfate-groups, which
are the active site of enzymes. Silver ions disrupt the underlying
means of bacterial survival by blocking some of the bacterial
Source: http://www.trevira.com
enzymes responsible for energy metabolism and electrolyte transport. The lack of enzyme
activity ultimately suffocates the bacteria. As an additional means of attack, these powerful
silver ions also deter the bacterial replication process by reacting with their backbone of DNA.
Finally, silver ions bind to the bacterial cell wall to weaken
the protection and structure of the cell, thereby creating
structural imperfections within the protective layers in
bacteria and speeding the collapse or burst of the bacteria
[1]. Therefore, by destroying these three areas, silver ions
prevent bacteria by establishing a defense system, slowing
bacterial growth, and eventually killing them.
SEM image. Source: Guggenbichler, J.P., Boswald, M., Lugauer,
S., Krall, T. "A New Technology of Microdispersed Silver in
Polyurethane Induces Antimicrobial Activity in Central Venous
Catheters." Infection. 1999. Volume 27. p. 16-23.
Primary Concerns over Nanoparticles
Despite the useful properties in silver nanoparticles, there are underlying environmental
and health concerns that must be addressed in order for the nanoparticles to comply with safety
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requirements. The Swiss Federal Laboratories for Materials Testing and Research conducted an
experiment to examine the reduction of the amount of silver nanoparticles in fabrics that had
been subjected to washing. They discovered that silver nanoparticles were gradually stripped
away from the fabrics in the washing machines and consequently discharged to the wastewater
treatment plant [10]. Since the silver material is highly toxic to microbes, these silver
nanoparticles can reduce the efficiency of biological decomposition at the wastewater treatment
plant. More importantly, they can also spread into the environment, polluting our soil and water
and damaging drinking water safety [6].
If the nanoparticles are leaked to the environment from treated wastewater or recycled
water, they could pose a significant threat on the growth of plants by killing beneficial soil
microbes needed to keep the plants healthy. As a result, the nanoparticles can potentially
damage the production of vegetables, crops, fruits, etc. In addition, if enough nanoparticles
accumulate in the bio-solids at the wastewater treatment plant, then the fertilizers composed of
bio-solids would also contain nanoparticles. Hence, the serial contamination of water and soil by
nanoparticles can bring adverse effects [5].
From household appliances to personal care products and medication, humans are
exposed to increasing amount of nanoparticles. According to scientific research, if the
commercial industry continues to release mass amount of products in which nanoparticles are
integrated, then the toxicity concentration from ions can negatively affect the aquatic ecosystem
and potentially human beings as well. Gordon Shetler, an environmental news journalist, states,
"In one new experiment, Furgeson, a professor of pharmaceutical sciences, exposed zebrafish
embryos to silver nanoparticles in a laboratory, and found that some died and others were left
with dramatic mutations [7]." Even though scientists have not confirmed the actual threat
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induced by nanoparticles on mankind, the concern revolves around the possibility of
nanoparticles seeping into human skin and reaching into the organs. Once the nanoparticles
enter the human anatomy, they can potentially leave us with long-term health effects. As a result,
the EPA has enforced numerous regulations on the applications of nanotechnology in
commercial industries to hopefully prevent health and ecological problems.
Future of Nanotechnology
"Nanotechnology is projected to be a trillion-dollar industry by 2015, with some saying it
will be the focus of the next industrial revolution. The number of products – including
sunscreens, paints, vitamins, food additives, electronics, vehicles and appliances – that use nanomaterials has increased by nearly 380 percent since 2006, according to the Project on Emerging
Nanotechnologies, a non-profit group based in Washington, D.C. that tracks nanotechnology
[7]." Since nanotechnology is such a powerful discovery that offers various applications, it is
essential to understand all aspects of their impact on our ecosystem.
Existing methodologies can greatly benefit from process improvements designed to better
evaluate the hazards of nanoparticles. We should never underestimate the influence of
nanoparticles, since any misuse can lead to long-lasting health effects. Nanoparticle, a particle
invisible to the human eyes, can be such a valuable weapon against microbial colonies and
undesirable bacterial growth. Yet, it could also infiltrate and defeat the immune system in the
human body. After all, like many other technology and scientific discoveries, members of the
science and engineering fields own the responsibility of thoroughly understanding the power and
implication of nanoparticles to ensure that we safely integrate this foreign substance into our
daily lives.
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Sources:
[1] 2011. How SmartSilver Works[Online]. Available: http://www.smartsilver.com/how
[2] A. R Barron, S. Maguire-Boyle and S. Desai et al. (2011). Nanotechnology for the Oil and Gas Industry [Online],
Available: http://cnx.org/content/col10700/1.11/
[3] L. Liu, "Background," in Emerging Nanotechnology Power: Nanotechnology R&D and Business Trends in the Asia
Pacific Rim, Singapore, World Scientific Publishing Co. Pte. Ltd., 2009 pp. 1-3.
[4] E. Boysen and N. Boysen. Introduction to Nanotechnology [Online], Available :
http://www.understandingnano.com/introduction.html
[5] E.S. Papazoglou and A. Parthasarathy, "Is Bionanotechnology a Panacea?," in BioNanotechnology, 1st ed. San
Rafael: Morgan & Claypool, 2007 ch. 6, sec. 6.3.4, pp. 113-114.
[6] N. Zeliadt. (2010 August 9). Silver Beware: Antimicrobial Nanoparticles in Soil May Harm Plant Life [Online].
Available: http://www.scientificamerican.com/article.cfm?id=silver-beware-antimicrobial-nanoparticles-in-soilmay-harm-plant-life
[7] G. Shetler (2009 Nov. 17). Nanosilver in consumer products: No silver lining for fish [Online]. Available:
http://www.environmentalhealthnews.org/ehs/news/nanosilver
[8] C. Nordqvist. What Is Body Odor (B.O.)? What Causes Body Odor? [Online]. Available:
http://www.medicalnewstoday.com/articles/173478.php
[9] Dr R. Senje and I. Illuminat. (2009 June). NANO& BIOCIDAL SILVER[Online]. Available Telnet:
http://www.foe.org/sites/default/files/Nano-silverReport_US.pdf
[10] (2010 Sept 1). Silver – and other – nanoparticles in fabrics[Online]. Available:
http://oecotextiles.wordpress.com/category/chemicals/silver/
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