Making Gold Nanoparticles with Lasers

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The color of gold nanoparticles depends on their physical size, ranging from light red to a dark bluish/purple. This phenomenon is caused by Plasmon Resonance. There is a cloud of delocalized electrons flying around a metal, and these electrons can react in a coordinated manner to electromagnetic fields (like light). But when the surface of the metal is very small -- like in a nanoparticle -- the electron cloud is can begin to oscillate across the surface.

If the wavelength of light is just right it will resonate with the electron cloud, and that wavelength of light is reflected while all others are transmitted or absorbed. This causes the particle to look a specific color.

Or... Ghosts.

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I wish yt would suggest me more of these type of shorts instead of all the garbage..

AriesSupertramp
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Fun fact: these colloidal gold particles are used in pregnancy tests, COVID tests, drug tests, etc.! That's why the line looks purplish-reddish! The particles are attached to antibodies that detect these substances :)

eucamong
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This is a colloidal solution of gold popularly known as ’Gold Sol’.
Due to its specific purple colour it's also called as ’Purple of Cassius’...

techsiastic
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Purple and yellow being complimentary makes this such an aesthetic

seanholm
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Excellent video! We are performing this daily in our lab, I'm always captivated by the magical appeal that astonishes students and even children.

By maintaining laser parameters, a simple switch of liquids in which the laser ablation is performed can alter the color of the produced liquid. For instance, using tap water from different locations introduces variations in salts, minerals, etc., impacting nanoparticle size and modifying surface plasmon resonance, ultimately changing the liquid's color.

MAM-BUW
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So that’s why gold-fumed glass looks amethyst. Amazing.

alecwhatshisname
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You can do this for almost all metals - the only thing being that the nanoparticles absorb wavelengths in the UV range and our eyes don't see this.
Silver turns a weird yellow colour as its right on the edge of UV and visible.
I did my PhD on copper nanoparticles - the solutions were anything from blue to murky green - depending not only the size but also how oxidised the nanoparticles are

usherly
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Wow... What's really gold here is a YT short with a proper ending and a few seconds of pause at the end. Great work sir!

thomasi
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Cool, now put that colloidal solution into, say a smaller container like a cuvette and shoot it with laser around 532nm wavelength and check out the output on the other side of a wall about 2 feet away or more. You should see a cool effect: thermal self diffraction fringe patterns on the far-field. They'll look like concentric rings. If you don't see anything at first, you may have to increase the laser power, or the size of the nanoparticles are not resonant with the 532nm laser. Ideally, you want the particles to be about 80nms in size. Anyways, I hope you play around with it and post a video of it here. Super cool.

heribertovasquezcarrasco
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Back in the old days glass was colored red by adding gold. Railroad switch lamps were red or green made by adding either gold or copper to the glass.

JohnRay
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"The particles are purple because of surface plasmon resonance which is the same level of voodoo horseshit as alchemy. Is it purple because of ghosts or is it purple because of surface plasmon resonance" -explosions&fire

georgeh
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I love how you break things down. Makes it so easy to understand!

minidocss
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It's so interesting to see full atoms behaving like ions! Gold ions often take on a reddish hue when in solution, and these nanoparticles do something similar despite having all their electrons.

flitterlys
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This is how all stained glass colors were and still are made. Copper silver gold cadmium and others all create different colored powers depending on the size of individual particles.

Pickledill
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Fantastic to see this kind of thing on youtube! I actually make gold nanoparticles as part of my PhD and it's beautiful to see the colours you can create! 💜
I've made NPs right out to deep blues and cyans, and if you make elongated particles you can actually see multiple colours, like the solution will look blue when you shine light through it, but scatter some deep red back at you when lit from above

carolynelliott
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This is seriously the stuff we need to be seeing on our shorts.

banditoincognito
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Sometimes you learn things that make you go “Huh “

Neuranet
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I love how you caught the sound of the laser hitting the gold. That was cool.

Mysucculentchinesemeal
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As a kid I was in Venice. I visited a glass factory. They used gold to produce the red color inside the glass.

Red-Feather
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I got to make these in college. I still have the bottle, and it's stable 6 years later. We used a reaction to parcipitate the gold into solution though not a laser. How does the laser eching ensure all the particles are the same size?

isaac