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About this Article
Written by: Winnie Siauw
Written on: December 4th, 2011
Tags: lifestyle, environmental engineering, material science, biomedical engineering
Thumbnail by: S.K. Bajpai and P. Gupta/Journal of Cotton Science
About the Author
Winnie Siauw is a senior at the USC Viterbi School of Engineering, working towards her B.S. in Civil and Environmental Engineering and M.S. in Environmental Engineering in the Progressive Degree Program. She is a member of the Environmental team of American Society of Civil Engineers. Her favorite hobbies include traveling, hiking, singing, cooking, and playing racquet sports.
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Volume XIII Issue III > Silver Nanoparticles: A Valuable Weapon in Microbial Warfare
Nanotechnology is currently being used as a valuable weapon for combating body odor-causing bacteria. Materials can be manufactured at the ‘nano’ scale, one billion times smaller than the world of meters we currently live in. Nanoparticles provide terrific driving forces for diffusion, which allows chemical reactions to occur at a high rate. In the case of odor-resistant clothing, the textile industry recognizes that silver nanoparticles offer distinct properties that combat bacterial growth and reduce body odor. Although nanoparticles can provide tremendous benefits, the potential effects on our health and environment still remains unknown. Some of the primary concerns include the possibilities of nanoparticles penetrating skin and leaking into water systems. Thus, it is crucial for researchers to perform further studies in order to completely understand the impact of nanoparticles on our lives and the environment.
The term “nanoparticle” refers to any particle ranging from 1 to 100 nanometers in size, 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 popular in the scientific community? A single nanoparticle may not be not sufficient to make an impact, but a billion or even a trillion of these nanoparticles can be powerful and beneficial to mankind. Scientists have worked with nanoparticles for centuries. Prior to the recent development of advanced microscopes, such as the Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM), scientists had faced significant limitations in their research due to the inability to see the structure of the nanoparticles. Today, the textile industry has integrated nanotechnology into novel products. Odor-resistant clothing, one of the current consumer products on the market, incorporates silver nanoparticles to help minimize the undesirable odor that results from bacteria in sweat and dirt (Fig. 1).
S.K. Bajpai and P. Gupta/Journal of Cotton Science
Figure 1: A Scanning Electron Microscopic (SEM) picture of silver nanoparticles loaded on grafted cotton fabric.

What's That Smell?

Most people believe body odor is an embarrassing, direct result of sweating or certain body traits. 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, resulting in an unpleasant smell in our feet or armpits. Thus, bacteria thrive in our sweat glands. When bacteria grow on our body, they decompose sweat into acids that produce the odorous chemicals 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 when the bacteria species Staphylococcus epidermidis breaks down fatty acid, causing a cheese-like smell [1].

A Brief History of Silver and Nanoparticles

To minimize body odor, one must prevent the replication of microbes that are generated in our body sweat. Silver has a long history of being an antibacterial agent. Not only did ancient Greek and Roman civilizations use silver to disinfect water and food, but other pioneers also submerged silver coins in water and milk to keep the drinks fresh. By the 1920s, the U.S. Food and Drug Administration approved silver solution as a type of antibacterial agent.
After the discovery of silver as an antibacterial agent, Richard Feyman, a physicist at Caltech, introduced the concept of the “nano-world” in 1959 in his famous lecture “There’s Plenty of Room at the Bottom." 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 could be one 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 experience greater influence by both Van Der Waals interactions and surface tension. His lecture on individual atoms and molecular manufacturing eventually stimulated scientists and engineers worldwide to develop technology to image, fabricate, and manipulate the fundamental structures of atoms and molecules [2].
Feynman's proposition did not transform into a scientific concept until the 1980s and '90s when Eric Drexler, along with other researchers, coined the term “nanotechnology". Thereafter, engineers slowly unwound the mystery inside the nano-world Feynman had constructed in 1959. Along with increasing knowledge of the nano-world, scientists unveiled more unique features of nanoparticles. For instance, engineers noticed that, given their miniscule size, nanoparticles have a high surface-area-to-volu​me ratio, which means these particles also have a high reaction rate.