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  • [♩INTRO]

  • When you look around the world, things seem to fall into two categories:

  • There's stuff that produces light, like the Sun or your computer monitor,

  • and there's stuff that only reflects it, like the walls of your room or your face.

  • At a molecular level, that first kind of thing uses energy to create light.

  • The second only absorbs and reflects certain wavelengths of light,

  • which give it color.

  • But there's a type of molecule that bends these rules: fluorophores.

  • Fluorophores get their name from the process of fluorescence.

  • That's when a molecule absorbs incoming light

  • and then emits it at a different wavelength.

  • And since different wavelengths correspond to different colors,

  • fluorophores are secret color-converting workshops.

  • But it's more than just, like, cool in theory:

  • Fluorescence turns out to be a kind of chemical superpower

  • that lets us tackle all kinds of problems

  • from solving crimes, to saving lives, and even helping you look your best.

  • First, in 1961, researchers at the University of Princeton were studying a jellyfish

  • off the coast of North America that glowed green around its edge.

  • To learn more about this, they ended up taking samples

  • from thousands of jellyfish.

  • And they isolated a protein called aequorin.

  • Exceptaequorin produces blue light from a chemical process.

  • Which wasn't the same as the green light they saw in the live jellyfish.

  • So, something must have been changing that light from blue to green.

  • The answer to the puzzle was green fluorescent proteins, or GFPs.

  • These glow green when exposed to blue or ultraviolet light.

  • And in the 1970s, researchers figured out why:

  • It's a combination of how these molecules absorb energy,

  • along with the way they're structured.

  • So, molecules are made up of atoms,

  • and atoms are just a central nucleus surrounded by some number of electrons.

  • And in an atom, there are different orbitals that electrons can occupy.

  • For a rough analogy, you can think of them as floors of a building

  • electrons can exist on one level or another,

  • but they can't hover in-between floors.

  • When GFP molecules absorb light, that energy pushes electrons up

  • to a higher energy orbital.

  • Then, eventually, the electrons relax and fall back down to their original state.

  • But when they do, they release some light

  • but it's not exactly the same light the molecule first absorbed.

  • Some of that original energy might have gone into moving the whole molecule

  • around a little, or twisting or rotating it.

  • So, the light that's released has less energy than before.

  • Less energetic light has a longer wavelength, and that wavelength

  • is what determines its color.

  • So, ultimately, high-energy blue light goes into the GFP,

  • and less-energetic green light comes out.

  • This is how all fluorescence works in general.

  • But it specifically works in these GFP molecules because of how they're shaped.

  • They're essentially built like a soda can,

  • with a combination of three amino acids hanging out inside.

  • On their own, those three amino acids don't seem to fluoresce.

  • But when they're inside a GFP, the surroundingcanof proteins

  • holds them in place and shields them from their environment.

  • That means when light falling into the can gets absorbed,

  • it's harder for these amino acids to convert that energy into movement,

  • or transfer it to other molecules nearby.

  • Instead, they're more likely to lose the energy by releasing it as light.

  • All in all, this allows GFPs to convert ultraviolet and blue light into visible green light.

  • And that was a huge breakthrough, it turns out, for biology.

  • By the 1990s, scientists had managed to take the gene for producing GFPs

  • and put it into E. coli bacteria.

  • Then, when scientists observed the bacteria under a microscope

  • and shined UV light on them, the bacteria glowed green!

  • This introduced a groundbreaking tool for studying life.

  • See, at a molecular level, life is basically just a bunch of genes

  • that switch on and off, and those genes tell the cell to make or not make proteins

  • that control biological processes.

  • So, by placing GFP genes alongside other genes,

  • scientists can actuallyseecells switching certain processes on and off.

  • And when I saysee,” I mean with their eyes!

  • In fact, by tweaking the segment of genes that produces GFPs,

  • they even managed to get the proteins to shine in colors other than green

  • which has been hugely helpful.

  • Like, in 2007, a study used different-colored GFPs

  • to tag the nerve cells in a mouse's brain as it developed.

  • Afterward, the resulting nerve cells could be individually traced with different

  • rainbow colors, which the researchers obviously called theBrainbow”.

  • The next year, the Nobel Prize in chemistry went to the researchers

  • who discovered, isolated the genes for, and created new colors of GFPs.

  • GFPs are used for a bunch of different stuff, too.

  • Since whole organs, like skin, can be made to produce GFPs, we're also able to

  • make genetically-modified animals that glow under the UV light from a blacklight.

  • It's all very retro.

  • Nowadays, people can stock their aquariums withGloFish”,

  • which are pet fish genetically engineered to glow in different colours.

  • We still don't quite know why that original jellyfish evolved to fluoresce

  • the way it does, but we've definitely learned a whole lot from its ethereal glow.

  • Fluorophores don't just tell us about the mysteries of life.

  • We can also use them to solve the mysteries ofdeath.

  • Fluorescein is a chemical that looks like reddish-brown brick dust to the naked eye.

  • But as the name hints, deep down, it has fluorescent powers, too.

  • It's made of organic molecules whose whole structure consists of several rings.

  • In that arrangement, each of the atoms in fluorescein has strong chemical bonds

  • with its neighbors, making the molecule rigid and stiff.

  • And like the GFP soda-can structure, that stiffness gives fluorescein its abilities.

  • When blue light gets absorbed by a fluorescein molecule,

  • the energy is stored by the electrons.

  • But because the molecule is rigid, the electrons can't easily give up their energy

  • to the molecule through movement or deformation.

  • So the molecule ends up releasing most of its energy in the form of light

  • specifically, a bright, yellowish-green color.

  • And that's come in handy for medicine.

  • For instance, doctors occasionally need to inspect blood vessels

  • in the back of the eye for damage that might diagnose certain conditions.

  • Like, diabetic patients might have narrow or blocked vessels in their eye

  • that could impair their vision or cause blindness.

  • To inspect those blood vessels,

  • they use a procedure called fluorescein angiography.

  • The first step is to inject fluorescein dye into a patient's bloodstream.

  • After a short while, the dye will be circulating in all of their blood vessels,

  • including the ones in their retina.

  • Then, the doctors can project blue light onto the retina

  • to get those fluorescein compounds glowing,

  • and then they can check out the shape of the blood vessels

  • with a filtered camera.

  • Meanwhile, fluorescein can also detect blood even when it's outside the body,

  • which gives it a slightly more gruesome use in police work.

  • Investigators can detect tiny droplets of blood using a modified form

  • of fluorescein that doesn't glow on its own.

  • They mix it with hydrogen peroxide, then spray it over a suspected crime scene.

  • If their mixture comes in contact with even a small amount of blood,

  • the hydrogen peroxide reacts with iron in the blood, which releases oxygen.

  • And when the oxygen reacts with the fluorescein,

  • it can convert it back to a form that fluoresces as usual.

  • Then, an investigator can shine blue or UV light over everything

  • and look for that telltale yellowish-green glow.

  • And luckily, the DNA within the blood won't be affected by the process, either,

  • which allows investigators to extract samples to identify suspects.

  • Blood and crime scenes might sound grim,

  • but fluorophores also play a role in saving lives.

  • Daylight fluorescent pigments are a whole family of artificial molecules

  • that fluoresce in different colors.

  • Like fluorescein, their general molecular structure consists of rings of molecules,

  • which create strong chemical bonds between neighboring atoms

  • and absorb UV light in a similar way.

  • But they can also be made to absorb visible light,

  • by adding rings of carbon atoms or a long chain of atoms.

  • These extra atoms change how the electrons jump around inside the molecules,

  • which ultimately changes what colors of light the molecules release.

  • So, this idea can be used to create fluorescent dyes in pretty much any color.

  • Even in normal light, the colors of daylight fluorescent dyes seem brighter

  • than normal objects of the same color because... they are!

  • In addition to reflecting light,

  • they add even more light to their natural color through fluorescence.

  • The fact that they shine visibly in daylight is what gives the dyes their name.

  • And since the colors seem to almost leap off the material,

  • daylight pigments make materials extremely visible.

  • And that is useful in lots of scenarios.

  • Safety jackets, road signage, and lifeboats benefit

  • from the vibrant, bright colors of fluorescent dyes.

  • Fire trucks and ambulances are covered with fluorescent pigments

  • so they can be spotted from far away, too.

  • But bright colors aren't just for safety.

  • Lots of clothing, face paint, and accessories are also made with

  • daylight fluorescent dyes in them.

  • As well as looking bright and colorful in the sun,

  • those same clothes will shine just as brightly under a blacklight.

  • So, file that away for a future trip to the nightclub.

  • I know we're all going to go face paint and rave out as soon as the COVID's over.

  • Finally, while fluorescent pigments might bring some color to a Saturday night,

  • it's a different kind of fluorophore that shows up at the office on Monday morning.

  • Optical brighteners are organic molecules with rigid,

  • chemical bonds between their atoms.

  • Like other fluorophores, that allows them to absorb UV light.

  • But brighteners tend to emit blue light, specifically.

  • Now based on that, you might think we'd use them to make things look blue.

  • But actually, we more often use them to make things look white.

  • On their own, materials like paper become yellow over time

  • as the organic compounds in them break down,

  • reacting with oxygen in the air to become yellow.

  • White laundry can also turn yellow over time because of factors

  • like nitrogen dioxide in the air reacting with the material of the fabric.

  • And it's not easy to get rid of the yellow, but a bit of blue can cover it up.

  • That's because colors of light add together when you mix them,

  • with white light being an even mixture of colors from across the spectrum.

  • So you can compensate for the extra yellow by adding some extra blue.

  • The overall effect is that the material looks white again!

  • And that's why optical brighteners are added to laundry detergent

  • and the paper-making process.

  • The brighteners allow the material to appear brighter and whiter for longer.

  • Weirdly enough though, brighteners might not keep working

  • as well as they once did.

  • The brighteners rely on the presence of UV light

  • to make the molecules fluoresce, but LED lights don't produce UV.

  • So the more we switch to efficient lights like LEDs,

  • the less effective fabric brighteners will be.

  • The good news is that, if history is anything to go by,

  • new innovations with fluorophores will continue improving different areas of life,

  • including laundry, but probably also things like medicine and forensics as well.

  • But for now, if your white shirt looks a little yellow in the office,

  • try blaming science.

  • If you like watching SciShow, you might also like our podcast,

  • it's called SciShow Tangents.

  • It's a lightly-competitive knowledge showcase where the hosts rack up points

  • for teaching everyone the most mind-blowing science facts.

  • If you liked this video, you might want to start with our episode

  • calledGlowing Things,” which includes talks of death fluorescence.

  • I'm not going to tell you what that is.

  • You have to listen to the podcast to find out.

  • If you like science, and laughing, and lighthearted, nerdy competitions,

  • you can find SciShow Tangents anywhere you get your podcasts.

  • [♩OUTRO]

[♩INTRO]

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发光的鱼和你的正装衬衫有什么共同点(What Glowing Fish and Your Dress Shirt Have in Common)

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