Not many people guess that I'm a chemist. Yes, I even have a PhD that I just finished at the University of Birmingham (UK). I want to share an article that I wrote for www.satnavmag.org (Satnav magazine, a student run scientific magazine for the general public), it was published in July 2010.
Nanoparticles and you
What comes to mind when you hear the word nanoparticles? Some people might think of killer nanobots that will attack the planet, such as in The Prey by Michael Crichton, where they infect our brains and create a zombie infested world. The truth is far from that. In actual fact, nanoparticles are all around us right now, found in some of the things that we use every day.
So what are they?
Nanoparticles are usually defined as particles that range between 1 and 100 nm in size. A nanometre (nm) is one thousand millionth of a metre or 0.000000009 m, so it is pretty small! To illustrate this, the size of a human hair is between 25000 nm and 180000 nm wide, and bacteria are around 100 nm in diameter. Approximately ten hydrogen atoms in a line make up one nanometre.
How long have they been around?
Nanoparticles have been used for a very long time. It is just that we have only recently begun to understand what they are. Gold nanoparticles, which are red when they are as small as nanometres, were used in the past to stain glass. Medieval artisans made stained glass by mixing gold chloride into molten glass. They created tiny gold spheres that absorbed and reflected sunlight in a way that produced a variety of colours, without truly knowing what they were making. The artisans knew that by putting varying and tiny amounts of gold and silver in the glass, they could produce the effects found in stained-glass windows.
The Lycurgus Cup, which was made by the Romans, dates to the fourth century AD (Shown bellow). When viewed in reflected light (in daylight), it appears green, and when a light is shone into the cup and transmitted through the glass, it appears red.
The Lycurgus Cup from Roman times containing gold nanoparticles exhibited at the British
Museum, here displayed under different light sources.
When were nanoparticles first synthesised?
Nanoparticles were first synthesised by Anthony Turkevich in the early 1950s, who incidentally was the same man that first determined the composition of the moon’s surface. Ever since then they have been widely used as contrast agents for electron microscopy (used during imaging examinations to highlight specific parts of the body and make them easier to see), cancer research and as carriers for drugs.
Silver antibacterial nanoparticles
Silver nanoparticles are widely used because of their antibacterial properties; silver acts against the bacteria by destroying or deactivating the enzymes that allow oxygen intake of the organism, and by destroying the cell membrane. As a result, the organism’s DNA cannot make replicas of itself, let alone create possible resistant strains. Silver nanoparticles are also non-toxic and don’t suppress the immune system. Socks, paints, bandages, and food containers incorporate nanosilver to exploit its antimicrobial properties. In clothing such as socks, nanosilver may restrict the growth of pungent bacteria.
Nanoparticles in clothes
Garments coated by silver, gold and palladium nanoparticles were shown at a fashion show in New York in 2007. The work was performed by designer Olivia Ong (Department of Fiber Science and Apparel Design from the College of Human Ecology), and the nanoparticle coated fabrics were made by Professor Juan Hinostroza.
One garment is claimed to prevent colds and flu and never needs washing (as bellow on the left of the image), and another destroys harmful gases and protects the wearer from smog and air pollution (as shown below on the right of the image).
The dress (left) is made of cotton covered with silver nanoparticles that can deactivate bacteria. The hood, sleeves and pockets of the jacket (right) contain palladium nanoparticles that act as catalysts to reduce the negative effects of pollution.
Dipping positively charged cotton into a negatively charged silver nanoparticle solution resulted in the particles clinging to the cotton fibers. Firstly, positively charged cotton fibers were made by using ammonium and epoxy based reactions, which served to induce positive ionization. The silver particles, which are about 10-20 nanometres across, were synthesized in citric acid which prevented the nanoparticles from sticking together. The resultant colors are not the product of dyes, but are instead reflections of manipulation of particle size or arrangement. The problem with these types of fabrics is their price; for 90 cm2 of the fabric you would have to shell out 10,000 American dollars!
Nanoparticles in appliances
In addition, Samsung has incorporated silver nanoparticles into a washing machine, which is known to release the particles during washing. They penetrate deeply into all kinds of fabrics, creating a protecting coat of sterilisation for a maximum of 99.99% disinfection, as well as an added antibacterial effect which can last for up to 30 days after washing. These nanoparticles are also used in fridges and air-conditioning, in order to prevent bad smells.
Other uses
Another commonly used nanoparticle is silicon oxide. Silicon oxide nanoparticles are used in the cosmetic industry, for biomedical applications and also in solar cells. Cerium oxide nanoparticles have recently been used in the petrol industry where they are added to diesel to reduce fuel consumption, greenhouse gas emissions (CO2), and particulate emissions.
Nanoparticles of iron oxide are very interesting because of their magnetic properties, and are widely used for medical applications. Over 300 sun creams in the market today contain titanium oxide and zinc oxide nanoparticles. By replacing traditional forms of ZnO and TiO2 with nanoparticles of these substances, manufacturers can reduce the visibility of the cream paving the way for ‘invisible’ sun cream.
What are the effects of nanoparticle use?
One of the biggest issues with nanoparticles is their possible toxicity and effect on the environment after they have been disposed. Regulatory bodies in the U.S. and Europe have started dealing with the potential risks
posed by nanoparticles, however neither engineered nanoparticles, nor the products and materials that contain them are subject to any special regulation regarding production, handling or labelling. It is therefore highly important to study the adverse effects and to both quantify and minimize them, both for environmental protection and to ensure the long term sustainability of the nanotechnology industry, along with its associated benefits. A lot of research is being done at the moment to assess those effects on humans, animals and the environment. Every day new uses for these tiny particles are found, and soon they may play a much bigger part in our lives than could have ever have been previously imagined.
