Black Light World

Uranium marbles glow with a greenish hue under ultraviolet light, but they're said to be safe — despite the radioactive sticker on the container.

Glow-in-the-dark uranium marbles have emerged as the top Science Geek Gift of 2011, but you don't have to go radioactive to get that greenish glow.

To be sure, there's something slightly subversive about marbles that are slightly radioactive.  "Definitely geeky, but non-geeks would also love them because they glow and have a risk factor appeal," one commenter wrote.

That's probably a big reason why the suggestion from Richard-1971294 won out over Joel Davis' Star Trek pizza cutter in this year's 10th annual Science Geek Gift roundup.

The totally unscientific tally was close: The margin of victory was less than 50 votes out of more than 3,000 cast. But the green glow of victory means that Richard is eligible to receive a pile of geek-friendly books, including "The Cult of Lego," "Science Ink," "The Physics Book" and "The Case for Pluto." Because Joel came so close, I'm sending him an autographed copy of "The Case for Pluto" as well.

Now, about that uranium: In the old days, pigments containing uranium used to be found in things ranging from ceramic tiles to dinnerware and glassware. Today, uranium isn't used as a coloring agent, but probably not for the reason you'd suppose. Natural, unprocessed uranium isn't all that radioactive — but because it's a heavy metal, it's as toxic as lead. And we all know what happened to lead paint. On the Health Physics Society website, Washington State University's Ron Kathren says "chemical toxicity is the overriding consideration" when it comes to limiting the use of natural uranium.

Uranium marbles, which glow green under ultraviolet light, are still available from Black Light World as well as eBay vendors. If you're serious about the nuclear option — for example, in the form of a spinthariscope toy or a chunk of trinitite — you'll want to check out United Nuclear's wares as well.

A healthier glow
The health risks of radioactive inks and paints have been known since the 1920s, due to the illnesses suffered by the "Radium Girls" who painted the dials on glow-in-the-dark watches. Today, few manufactured items make use of radioluminescence, which involves converting radioactive emissions into visible light. (Exceptions include some types of watch dials, keychains and gunsights that glow due to paints containing tritium or promethium rather than radium.) Virtually all of the glow-in-the-dark items you see today take advantage of electroluminescence, chemiluminescence or photoluminescence.

Electroluminescence is behind the greenish glow in pushbutton timepieces such as Timex's Indiglo line. Chemiluminescence relies on a chemical process — for example, the mixing of chemicals in a glow stick. Photoluminescence involves "charging up" a chemically treated object such as a glow-in-the-dark Godzilla by shining a light on it.

The key substances in most glow-in-the-dark items are phosphors, chemical compounds that are good at taking in energy and emitting it as light. Zinc sulfide and strontium aluminate are the most commonly used glow-in-the-dark ingredients, and new glow-in-the-dark compounds continue to be developed. They're relatively safe: That's why you see so many kids' toys that glow in the dark, as well as these geekier items:

• Glow chemistry lab in a bag from ImagineToys.
• Glow-in-the-dark spitballs from Scientifics Online.
• Glowing science projects from About.com
• Glow-in-the-dark ties from Zazzle.
• Glowing "Uranium" soap from Perpetual Kid.
• Luminescent lingerie from Lumino Glow.
• Glow-in-the-dark condoms from Night Light.
• Glow-in-the-dark toilet paper from ThinkGeek.

You can set your own environment aglow with phosphorescent paint from ThinkGeek or United Nuclear. For the final frontier in glow-in-the-dark geekery, check out this ghostly green space shuttle at MakerBot's website. If it's bioluminescence you're into, GloFish has been offering fluorescent fish for years, but don't look for glowing kittens or puppies to enter the market anytime soon. In fact, ethical debates over genetically altered organisms like glow-in-the-dark zebrafish have been raging for years. The prudent product for your kids might be a glow-in-the-dark coloring book that teaches them about totally natural bioluminescence.

Speaking of bioluminescence...

• Gallery: Bioluminescence lights up the oceans
• Glow-in-the-dark shark can become invisible
• These mushrooms glow in the dark
• Glow-in-the-dark jellyfish on display

Previous Science Geek Gift Guides:

• The gift of science (2002)
• For the scientist who has everything (2002)
• Toy traditions go back to the future (2003)
• Your toys will be assimilated (2004)
• Gifts for space geeks (2004)
• Find your star (2005)
• The top gift for science geeks (2006)
• Season's readings for kids ... and for grown-ups (2007)
• The top geek gift of 2008
• Gifts from the sixth dimension (2009)
• Make your own geeky goodness (2010)

More science gifts:

• Edmund Scientific: The classic science store
• Educational Innovations
• Exploratorium Science Gift Guide 2011
• GeekDad Holiday Gift Guide 2011
• Home Science Tools gift guide
• Imagination Soup math and science gifts
• MakeZine Holiday Gift Guide
• Robot Snob suggestions for robotics fans
• Sheldon Shirts: Big Bang Theory gifts
• ThinkGeek: Stuff for smart masses
• xkcd store
• Zazzle gifts for geeks ... and "Big Bang" fans

You don't need to buy me a present. All I ask is that you connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Malte Gather / Nature Photonics

A human kidney cell produces green laser light inside a resonator.

Physicists and molecular biologists have created the world's first biological laser, with live, glowing kidney cells at its core.

At the heart of a laser is a substance that can absorb, amplify and emit light in a single focused beam. This role has been played by a string of characters over the years: semiconductors, crystals, dyes and even gases. Until now, living cells weren't part of that cast lineup. There's a good reason for that: Most living things, with the exception of some bioluminescent jellyfish, don't naturally trap or emit light.

But recently, other organisms have acquired the ability to shine. The researchers behind these glow-in-the-dark animals owe their thanks to Osamu Shimomura, who extracted the green fluorescence protein and the genes that make GFP from the glowing guts of those jellyfish. (Coincidentally, he started work on the bioluminescent crystal jellyfish in 1960 — the same year that the laser was invented.) 

Since then, molecular biologists have gone gaga over the GFP gene and other fluorescence genes. They use them as visual signals indicating that the other genes they study have been successfully transferred into different organisms (such as cats and dogs). The ever-expanding popularity of fluorescence genes among molecular biologists earned its discoverers a shiny Nobel in 2008. Now the GFP gene itself is stealing the spotlight.

"Almost any organism, from bacteria to higher mammalians, can be programmed to synthesize such luminescent proteins, so we wondered if GFP could be used to amplify light and build biological lasers," Malte Gather and Seok Hyun Yun, the two physicists behind the "biolaser," wrote in a Q&A interview with Nature Photonics. The journal published their paper online on Sunday.  

Guiliano Scarcelli

Malte Gather and Seok Hyun Yun are the inventors of the biological laser.

The researchers reprogrammed a line of human embryonic kidney cells with an enhanced version of the GFP gene. Then they sandwiched those cells between highly reflective mirrors and pulsed a blue light through the chamber.

In their optically active compartment, the cells absorbed and re-emitted a laser-worthy green light for several minutes. The mirrors amplified the light to create a coherent beam, just as they do in non-biological lasers.

The cells survived for a few hours after the lasing ordeal, and seemed to be actively producing and reabsorbing the green fluorescence protein. This could mean that, unlike regular lasers which wear out with use, "the laser can self-heal," they told Nature Photonics.

The two physicists are now working on ways to tweak the setup so that it can be used as a living imaging tool. Such lasers may shed new light, so to speak, on biological processes within the cell, Gather told me: "The pattern of the laser light seems to carry information about the insides of the cell."

Biolasers could also have medical applications. Some treatments, such as photodynamic therapy for cancer patients, use external lasers to stimulate drugs to be released close to a tumor. "You have a drug that attacks a tumor when you apply light," Gather said. "Using a laser light force from the inside would make this more efficient."

Ultimately, the researchers want to free the lasing cell from its optical chamber, and somehow include tiny reflective mirrors within the cell itself. "For medical applications, that would be crucial," Gather said.  

More on lasers:

• Laser eyed to remove space junk
• It's a golden year for lasers
• X-ray laser lights up small wonders
• 'Star Wars' creator fumes over laser lightsaber

Nidhi Subbaraman is the science and tech news intern at msnbc.com. Find Nidhi on Twitter, and connect with the Cosmic Log on Facebook.