WASHINGTON, D.C. — Our lives are bursting with bacteria. The bugs are inside our bodies, on our skin and on most surfaces we touch. That’s not necessarily a bad thing. But some places need to be bacteria-free, such as bandages for wounds or food packaging. Jessica Tian, 17, has come up with a way to keep bacteria away. She created germ-free papers by dunking them in a special chemical bath.
The senior at Del Norte High School in San Diego, Calif., showed off her method at theRegeneron Science Talent Search. The science competition is run by Society for Science & the Public. It is sponsored by Regeneron, a company that designs and makes medicines. The event brings together high school students each year to share their science projects with the public. The 40 finalists also compete for cash awards totaling almost $2 million. (Society for Science & the Public also publishes Science News for Students and this blog.)
Jessica’s chemical bath was developed to leave a germ-killing coating on cellulose. The outer wall of plant cells contain cellulose. But that's not all. “Cellulose is versatile,” Jessica explains. “It’s in our clothing, in food packaging, in pretty much every aspect of our daily life.”
Each molecule of cellulose is a long chain built from sugars. These chains bond easily with water. That’s good; it helps paper towels soak up spills. But this is also why wet cellulose is a great home for bacteria. And some of those germs may pose a risk to health. That’s especially true when they grow on a bandage or food wrapper. Scientists have been trying to invent antimicrobial coatings to stop bacteria from sticking to cellulose. However, Jessica notes, “most methods require heat and pressure. And some lead to air pollution.”
“I wanted to create a method that could [add] antibacterial properties to cellulose in a simple way,” the teen says. She wanted it to be inexpensive. It also had to be easy to apply on a large scale and pose little risk to the environment.
To figure out how to do this, Jessica traveled across the country to spend a summer in the lab of Benjamin Hsaio. He’s a chemist at Stony Brook University in New York. The Simons Summer Research Program for high school juniors connected Jessica with Hsaio. “This was the first time I got to work in a lab,” she says. “I really enjoyed the whole atmosphere.”
The teen worked to add titanium dioxide and silver nanoparticles to cellulose paper. Titanium dioxide is a white pigment. When exposed to ultraviolet light, the negatively charged electrons in it can become excited. The titanium oxide then breaks down water. This produces free radicals. These are charged molecules that can attack and kill bacteria cells.
Usually, Jessica says, titanium dioxide requires a lot of energy to activate its germ-killing prowess. She thought she saw a way to lower the energy needed, though: add silver nanoparticles. These are tiny particles of silver that are only billionths of a meter in diameter. They reduce the energy needed to excite the electrons in titanium dioxide. Adding an ingredient, this way, is known as “doping.” The doped silver should let titanium dioxide kill bacteria using only light from the sun, Jessica hypothesized.
In the lab, Jessica created a colloid (KOLL-oid) solution. Tiny particles of titanium dioxide and silver nanoparticles were spread fairly evenly throughout the liquid. She created three versions. Each had different amounts of titanium dioxide and silver. Then the teen dipped cellulose papers into one of the solutions and dried them in an oven. Other papers were covered in titanium dioxide alone or nothing at all. These served as controls.
Once the papers were dry, Jessica dipped them in solutions of bacteria. Then she rubbed the papers onto lab plates containing agar — a gel containing the nutrients needed for bacteria to grow. After 24 hours, she checked the plates.
The titanium dioxide and silver colloid had killed 99 percent of the bacteria, compared with untreated cellulose. The coating of titanium dioxide alone did not work as well.
“I knew that silver and titanium dioxide could work together,” Jessica says. There had been a lot of research on silver and an titanium dioxide, she notes, "but not much on both of them together [on] cellulose.”
The best part, Jessica says, is that her treatment poses no threat to the environment. Other methods need high temperatures or pressures to create a germ-killing coating. All Jessica’s needed was a slow dip in the chemical bath. The simple, low-cost coating "could be applied to clothing so it could have antibacterial properties,” she says. “I think it could be applied even in developing countries.”
For now, she’s only applied her mix to small bits of cellulose paper. But if the dip works on clothing, bandages or paper, it could help keep them germfree when they need to be.
(for more about Power Words, click here)
activate (in biology) To turn on, as with a gene or chemical reaction.
agar A gelatinous material made from certain marine algae used as a material (and food source) in which to grow bacteria.
antibacterial Having properties that tend to destroy or limit the growth or reproduction of bacteria.
antimicrobial A substance used to kill or inhibit the growth of microbes. This includes naturally derived chemicals, such as many antibiotic medicines. It also includes synthetic chemical products, such as triclosan and triclocarban.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Some organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
cellulose A type of fiber found in plant cell walls. It is formed by chains of glucose molecules.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical can also be an adjective to describe properties of materials that are the result of various reactions between different compounds.
colloid A material in which tiny insoluble particles have spread throughout a larger volume of another substance. Colloids take many forms. Smoky air is a colloid. So is fog. Milk is a colloid, with tiny globs of butterfat suspended throughout the liquid. Whipped cream is a colloid too. Colloids typically don’t separate into their individual components over time.
control A part of an experiment where there is no change from normal conditions. The control is essential to scientific experiments. It shows that any new effect is likely due only to the part of the test that a researcher has altered. For example, if scientists were testing different types of fertilizer in a garden, they would want one section of it to remain unfertilized, as the control. Its area would show how plants in this garden grow under normal conditions. And that gives scientists something against which they can compare new experimental data.
doping (in materials) The deliberate insertion of something into a crystalline semiconductor or other material.
environment The sum of all of the things that exist around some organism or some device and the condition those things create for that organism or device. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature, humidity and placement of components in some electronics system or product.\
free radical A charged molecule (typically highly reactive and short-lived) having one or more unpaired outer electrons. It will attempt to steal electrons to make itself whole again through a process known as oxidation.
gel A gooey or viscous material that can flow like a thick liquid.
germ Any one-celled microorganism, such as a bacterium, fungal species or virus particle. Some germs cause disease. Others can promote the health of higher-order organisms, including birds and mammals. The health effects of most germs, however, remain unknown.
high school A designation for grades nine through 12 in the U.S. system of compulsory public education. High-school graduates may apply to colleges for further, advanced education.
hypothesis (v. hypothesize) A proposed explanation for a phenomenon. In science, a hypothesis is an idea that must be rigorously tested before it is accepted or rejected.
liquid A material that flows freely but keeps a constant volume, like water or oil.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
nanoparticle A small particle with dimensions measured in billionths of a meter.
particle A minute amount of something.
pigment A material, like the natural colorings in skin, that alter the light reflected off of an object or transmitted through it. The overall color of a pigment typically depends on which wavelengths of visible light it absorbs and which ones it reflects. For example, a red pigment tends to reflect red wavelengths of light very well and typically absorbs other colors. Pigment also is the term for chemicals that manufacturers use to tint paint.
pressure Force applied uniformly over a surface, measured as force per unit of area.
Science Talent Search An annual competition created and run by Society for Science & the Public. Since 2016, it has been sponsored by Regeneron Pharmaceuticals. Begun in 1950, this event brings 40 research-oriented high school seniors to Washington, D.C., to showcase their research to the public and to compete for awards.
society An integrated group of people or animals that generally cooperate and support one another for the greater good of them all.
solution A liquid in which one chemical has been dissolved into another.
sun The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Sun is also the term for some other sunlike star.
titanium dioxide A white, unreactive, solid material that occurs naturally as a mineral and is used extensively as a white pigment.
ultraviolet light A type of electromagnetic radiation with a wavelength from 10 nanometers to 380 nanometers. The wavelengths are shorter than those of visible light but longer than X-rays.
wave A disturbance or variation that travels through space and matter in a regular, oscillating fashion.