Snail slime + gold could boost the power of sunscreens and more_yuxing tio2
2022-05-25 05:16:35

Chemistry

Snail slime + gold could boost the power of sunscreens and more

The pair could make skin-care products that are better for our skin and the environment

Snail-slime skincare products and cosmetics have been around for more than 1,000 years. But adding gold nanoparticles could give these personal-care products a new edge.

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By Katie Grace Carpenter

Two unlikely materials — snail slime and gold — may be the secret to better sunscreens.

Suncreens often contain tiny particles that reflect sunlight. Usually those are bits of the metals zinc or titanium. But nanoparticles of gold could work better due to their high reflectivity and low toxicity. To make such nanobits, researchers in Italy used snail slime to clump gold atoms together. The mucus made the process eco-friendly and also could help personal-care products last longer.

Explainer: What is a metal?

The researchers hope their slimy gold specks will be used one day in sunscreens and other cosmetics. And these innovative products may not only be great for our skin but also safer for our planet.

The study describing the new tech appeared in the November Journal of Photochemistry and Photobiology B: Biology.

Spas and snails and slimy trails

Snail slime might sound like the last thing you’d want to smear on your face. But snail-based skincare is far from new. Even the ancient Romans used it. Today, some spas offer “snail facials.” Live snails ooze across the face. The goopy trails they leave can hydrate skin. They also can apparently lighten age spots.

For their new study, researchers in Bari, Italy, used slime that had been harvested from the brown garden snail (Helix aspersa Müller). A special ozone-filled chamber had encouraged the snails to ooze slime. “But in a mild way,” adds Pinalysa Cosma — “not in a way that hurts the snails.” Cosma is a chemist on the team. She works at the University of Bari Aldo Moro.

Explainer: Ions and radicals in our world

Her team mixed that slime into a flask with gold atoms dissolved in water. Snail slime changed those gold atoms from one form, called Au3+, into a type called Au0.

“The main component of snail slime — a protein — is a reduction agent,” explains Vito Rizzi. He’s another chemist on the team at the University of Bari Aldo Moro. A reduction agent, he explains, gives up electrons to chemical ions.

When the snail-slime protein gives electrons to Au3+, the gold is no longer an ion. It turns it into Au0, Cosma says, which “is the metal form of gold.” Unlike Au3+, this form doesn’t dissolve in water. So individual atoms of this gold now clump into nanoparticles.

Companies often make gold nanoparticles with chemicals that are “not eco-friendly,” Rizzi notes. Those chemicals can release pollutants into the environment. Snail slime doesn’t. (Other natural substances have also been used as a “greener” way to make nanoparticles, such as extracts from plants or fungi.)

diagram showing how gold atoms and snail slime make nanoparticles
Gold nanoparticles are small clumps of gold (Au) atoms. To make nanoparticles, gold atoms drifting in water are combined with snail slime. The slime changes the gold atoms from a form that dissolves in water (Au3+) to a form that doesn’t dissolve (Au0). Nondissolved gold atoms now clump into nanoparticles.Vito Rizzi

Sunscreen of the future?

Gold is really shiny. Imagine a bright gold coin gleaming in the sun. The gold bits reflect sunlight like nanomirrors. (So do other metals. That’s why the back of your sunscreen bottle might list “zinc oxide” or “titanium dioxide” among the ingredients.) But gold reflects more light than reflective ingredients currently used in sunscreens.

an illustration showing a gold nanoparticle, with gold atoms clumped together into a sphere
This illustration of a gold nanoparticle shows how the individual gold atoms might clump together.LAGUNA DESIGN/SCIENCE PHOTO LIBRARY/iStock/Getty Images Plus

Snail slime itself also appears to boost gold’s sun-screening abilities. This is probably because the mucus absorbssome light at the same time the gold is reflectinglight. Many sunscreens contain ingredients that do both.

Cosma’s team dissolved its nanogold in water and then measured how much light the mix absorbed. Compared with plain gold nanoparticles, the team’s snail-slimed particles absorbed more. That’s important. It means adding slime-coated gold could boost a sunscreen’s protection even more than plain gold bits. This should give sunscreens a higher sun-protection factor, or SPF.

Snail slime offers another benefit, too. It boosts the gold nanoparticles’ ability to mop up harmful chemicals called oxygen radicals, also known as oxidants. Many normal chemical reactions in the body produce these radicals. But too many can cause problems. For example, they can kill cells. Oxygen radicals also can react with and break down sunscreen ingredients. That’s why companies add antioxidant chemicals to to fight the radicals. The Italian study reports its nanoparticles also act as antioxidants.

Explainer: What Are Antioxidants?

“This is a very good study,” says Bipinchandra Salunke. He’s a biotechnologist in Dhule, India (where he’s currently helping to develop a start-up company). Salunke was not involved in the new research, but he has made gold nanoparticles in the past. Back in 2014, he was part of a team that used a plant extract to do that. His group described its technique in the International Journal of Cosmetic Science.

The Bari group is “adding one new biological agent to the library,” Salunke says. “And they are showing biomedical applications, also.” He refers to a previous study by the Bari team. It showed that slimy gold nanoparticles could help wounds heal faster. The researchers reported those results in the December 2020 issue of Soft Matter.

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Challenges to overcome

The slime-gold duo may not be ready for widespread use just yet. The reason: A particle’s structure affects which chemicals it can react with. So nanoparticles of different shapes and sizes can have different traits. Some nanogold bits may work better for particular uses.

Nanoparticles made with snail slime aren’t just one size or shape. Yet for store-bought products, Cosma says, it’s important to closely control their form and function. For now, current snail-slime nanoparticles remain a mixed bag.

That’s may be due to snail slime containing lots of molecules. Several of them may play a role in changing Au3+to Au0. Proteins are thought to be responsible. But snail slime also contains peptides, carbohydrates and more. Any of these may have the ability to help produce nanoparticles, says Salunke.

Jennifer Gubitosa is yet another chemist on the Bari team. She points out that things other than the slime recipe can “also affect the shape or morphology of the nanoparticles.” Among them, she notes, are temperature and pH. The good news: Such things “can be easily controlled.”

It’s even possible that the different types of nanoparticles in a jumble could be sorted out. Salunke suggests using a centrifuge (SEN-trih-fewj). It rotates a container of liquid fast. This creates pressure on its particles, pushing them outward. (You may have felt a similar pressure push you to the outside of your seat on a spinning carnival ride.) Smaller particles move through a liquid easier, collecting at the bottom. Bigger particles stay closer to the top.

Salunke suggests putting the nanoparticle mix into sugar water. It’s thicker than plain water. That improves the layering. Then centrifuge the mix “and in each layer,” he suspects, “you’ll get a particular size or shape.”

Power Words

More About Power Words

agent: A person or thing (it can be a chemical or a form of energy) that play's some role in getting something done.

antioxidant: Any of many chemicals that can shut down oxidation — a biologically damaging reaction. They do this by donating an electron to a free radical (a reactive molecular fragment) without becoming unstable. Many plant-based foods are good sources of natural antioxidants, including vitamins C and E.

atom: The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

biology: The study of living things. The scientists who study them are known as biologists.

biomedical: Having to do with medicine and how it interacts with cells or tissues.

biotechnologist: A scientist who uses living cells to make useful things.

carbohydrates: Any of a large group of compounds occurring in foods and living tissues, including sugars, starch and cellulose. They contain hydrogen and oxygen in the same ratio as water (2:1) and typically can be broken down in an animal’s body to release energy.

cell: (in biology) 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.

centrifuge: A device that rapidly spins a container. The forces created by that spinning acts on whatever is inside the container, forcing its most dense parts to collect at the bottom.

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 also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemical reaction: A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).

dissolve: To turn a solid into a liquid and disperse it into that starting liquid. (For instance, sugar or salt crystals, which are solids, will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water.)

electron: A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids.

environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

extract: (v.) To separate one chemical (or component of something) from a complex mix. (noun) A substance, often in concentrated form, that has been removed from some source material.

factor: Something that plays a role in a particular condition or event; a contributor.

flask: A type of container with a narrow neck. In the laboratory, sterile flasks made from glass are used for conducting chemical and biological experiments.

fungi: (sing: fungus) Organisms with one or more cells that reproduce via spores and feed on living or decaying organic matter. Examples include mold, yeasts and mushrooms.

hydrate: (noun: hydration) To restore the proper level of fluids in the body.

ion: (adj. ionized) An atom or molecule with an electric charge due to the loss or gain of one or more electrons. An ionized gas, or plasma, is where all of the electrons have been separated from their parent atoms.

metal: Something that conducts electricity well, tends to be shiny (reflective) and is malleable (meaning it can be reshaped with heat and not too much force or pressure).

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).

mucus: A slimy substance produced in the lungs, nose, digestive system and other parts of the body to protect against infection. Mucus is made mainly of water but also includes salt and proteins such as mucins. Some animals use mucus for other purposes, such as to move across the ground or to defend themselves against predators.

oxygen: A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).

peptide: A short chain of amino acids (usually fewer than 100).

photochemistry: (adj. photochemical) A branch of science that deals with the chemical reactions that are triggered by exposure to light.

pressure: Force applied uniformly over a surface, measured as force per unit of area.

protein: A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

reduction: (in chemistry) A process in which an atom gains an electron by stealing it from another atom or molecule. Reduction is the opposite of oxidation.

titanium dioxide: A white, unreactive, solid material that occurs naturally as a mineral and is used extensively as a white pigment.

toxicity: A measure of the potential for some substance to poison or cause harm to living things. The harm may not occur immediately. Depending on the dose, organism and the toxic material, any harm may not show up for days, weeks or even years.

trait: A characteristic feature of something

zinc oxide: A chemical — with the formula ZnO — made when one atom of zinc bonds to an atom of oxygen. Its reflective properties make it useful in a range of products, from paints to sunscreens. Its germ-killing properties make it useful in some medicines or cosmetics. It can even be used as a source of the mineral zinc in foods.

Citations

Journal:​ ​​V. Rizzi et al. ​Snail slime-based gold nanoparticles: An interesting potential ingredient in cosmetics as an antioxidant, suneliscreen, and tyrosinase inhibitor.​ ​​Journal of Photochemistry and Photobiology B: Biology.​ ​​Vol.​ ​224,​ November 2021, p. 112309. doi:​ ​10.1016/j.jphotobiol.2021.112309.

Journal: J. Gubitosa et al. Biomolecules from snail mucus (Helix aspersa) conjugated gold nanoparticles, exhibiting potential wound healing and anti-inflammatory activity. Soft Matter. Vol. 16, December 2020, p. 10876. doi: 10.1039/d0sm01638a.

Journal: H.P. Borase et al. Phytolatex synthesized gold nanoparticles as novel agent to enhance sun protection factor of commercial sunscreens. International Journal of Cosmetic Science.Vol. 36, December 2014, p. 571. doi: 10.1111/ics.12158.

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