One man’s trash is another man’s treasure, and that includes a man’s (or woman’s) urine. Scientists have figured out how to transform your pee into tiny semiconducting nano crystals they’ve dubbed “quantum pee-dots.”
Quantum dots have been around since about 1990. If you took a wafer of silicon and cut it in half over and over and over again until all that was left was an teensy dot made up 100,000 or so atoms — congratulations, you’d have a quantum dot. They’re so tiny that billions of them could fit on the head of a pin. The smaller, the better, because it’s all those weird quantum effects that kick in at smaller scales that give quantum dots their superior electrical and optical properties.
The nano crystals glow brightly when they are zapped by light, and size determines exactly what color of light a given dot will emit. The bigger the dot, the redder the light it emits; that light becomes shorter and shorter in wavelength, and higher in energy, as the dots shrink in size. This gives quantum dots a property called “tunability.” Scientists love tunability, because it means you can pretty much tailor your quantum dots to give off whatever frequency of light you want, just by altering their size.
A novel, one-step process for recycling urine into quantum dots is detailed in a paper accepted for publication in the journal Green Chemistry. It’s not as silly as it sounds, lead author Gary Baker of the University of Missouri-Columbia told Gizmodo via email. Using “up cycled” urine as a base material to make things is becoming a staple of green chemistry. Sweden, Finland, and the Netherlands are already experimenting with “pee” cycling efforts. Urine also makes a terrific fertilizer.
The urea is the key ingredient, since it’s such a nitrogen rich source of carbon. “It is the most prevalent organic species in human urine, and it’s a decent precursor for making carbon,” he said. Using a liquid rather than a solid source means you can bypass severe processing steps, plus there’s no need for chemical reagents or specialized equipment.
Back in 2011, Ioannis Ieropoulos and his colleagues at Bristol Robotics Laboratory built fuel cells that run on recycled urine, and then used them to power cell phones two years later. “There is no longer a need to think about expensive or difficult source materials to generate [quantum] dots,” Ieropoulos told Chemistry World about the significance of Baker et al’s research. “One only needs urine.” Other groups have isolated quantum dots from foodstuffs like bread, caramel, cornflakes, fruit peels, beer, tea, and coffee grounds.
In fact, pretty much anything that contains carbon can be used to make quantum dots. That’s how Baker et al. got the idea in the first place. He was chatting with his graduate students about different possible carbon precursors, and naturally, given grad student humor, the conversation turned to urine. Thus quantum “pee-dots” were born.
Physicists already knew you could dope quantum dots with nitrogen or sulfur, for instance, and thereby alter their electronic and optical properties. But Baker and his students were surprised to find that “pee-dots” reflect what you eat. Certain foods will change the dots’ size, thereby changing the color of the light they emit.
In particular, Vitamin C just happens to be a handy carbon source and is readily excreted from the body via urine. And consuming asparagus is widely known to change the odor of one’s pee in some people, thanks to the presence of sulfur in the vegetable. (As Marcel Proust observed in 1913, asparagus “transforms my chamber-pot into a flask of perfume.” Most people don’t find the odor pleasant.)
One of Baker’s students valiantly offered himself as a test subject, consuming an entire pound of asparagus in a single sitting, lightly steamed. The poor guy was at least allowed a small pat of butter to help the asparagus go down. And it did have an unmistakable effect on the resulting sulfur-doped “pee-dots,” although it didn’t alter the optical properties as much as they had hoped. (There were also more speculative hints that the resulting “pee-dots” may offer clues as to the donor’s health, but that definitely requires further study.)
Since they are water soluble and chemically inert, quantum dots are biocompatible. So they’re a promising replacement for the organic dyes used to tag the reactive agents in biosensors — you know, the kind that light up when a harmful toxin is present. But the dyes degrade rapidly, limiting their usefulness. Quantum dots don’t degrade that much, and they come in a broader spectrum of colors for good measure.
That’s why Baker’s team tested their “pee-dots” by bioimaging mouse cells (pictured above). He also hopes the “pee-dots” might prove useful in test strips to monitor water quality. Other promising applications for quantum dots include using them for light harvesting, catalysis, solar cells, and LEDs, including LEDs used in televisions. There’s already a prototype quantum-dot TV, as Wired reported in January of this year.
Baker doesn’t think folks will just start mass-producing quantum dots from their recycled urine any time soon, but he is hopeful that this kind of research might help sway the public mindset toward better stewardship of energy and related resources. “Once you get over the ‘ick’ factor, the separation of liquid and solid wastes is not as significant a challenge as it first appears,” he said.
Ekimov, A.I. and Onushchenko, A.A. (1981) “Quantum size effect in three-dimensional microscopic semiconductor crystals,” JETP Letters 34: 345-349.
Essner, J.B. et al. (2015) “Pee-dots: biocompatible fluorescent carbon dots derived from the up cycling of urine,” Green Chemistry [Advance article, published online September 21, 2015].
Ieropoulos, I., Greenman, J. and Melhuish, C. (2012) “Urine utilization by microbial fuel cells; energy fuel for the future,” Phys. Chem. Chem. Phys. 14: 94-98.
Ieropoulos, I., et al. (2013) “Waste to real energy: the first MFC powered mobile phone,” Phys. Chem. Chem. Phys. 15: 15312-15316.
Liao, H. et al. (2015) “2 fluorescent nano particles from several commercial beverages: their properties and potential application for bioimaging,” J. Agric. Food. Chem. 63: 8527.
Images: (top) Quantum dots of many colors made by PlasmaChem Gmbh. Source: User:Antipoff/Wikimedia. (bottom) Gary Baker et al/University of Missouri/Columbia.