What color are Gold Nanoparticles?

Why do gold nanoparticles appear red or purple? Let's make some and find out! But please don't drink this 😉
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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.
This property mostly applies to noble metals like Gold or Silver, and can be seen in the famous Lycurgus Cup.
The nanoparticles were generated using a technique known as Laser Ablation in Liquid, or sometimes Laser Synthesis of Colloids. It uses a pulsed laser to ablate metal into a liquid, where the plasma and superheated material is rapidly quenched to form nanoparticles. I synthesized nanoparticles from a range of materials: gold, silver, nickel, copper, titanium, graphite, silicon, and platinum.
==== References ====
- Handbook of Laser Synthesis of Colloids: www.researchgate.net/publicat...
- Carbon nanocube synthesis: Liu, P., et al. "Micro-and nanocubes of carbon with C8-like and blue luminescence." Nano letters 8.8 (2008): 2570-2575. pubs.acs.org/doi/abs/10.1021/...
- Salt effect on Gold nanoparticles: Rehbock, Christoph, et al. "Current state of laser synthesis of metal and alloy nanoparticles as ligand-free reference materials for nano-toxicological assays." Beilstein journal of nanotechnology 5.1 (2014): 1523-1541. www.beilstein-journals.org/bj...
- Lycurgus Cup: en.wikipedia.org/wiki/Lycurgu...
- More about Gold/Silver Dichroicism: Dekker, Floris, et al. "Syntheses of gold and silver dichroic nanoparticles; looking at the Lycurgus cup colors." Chemistry Teacher International 3.1 (2021). www.degruyter.com/document/do...
==== Equipment and techniques ====
- nGauge AFM from ICSPI: www.icspicorp.com/
- Scans are post processed in Gwyddion (gwyddion.net/) and 3D images rendered in Blender
- Generic 50W fiber laser
==== Timeline ====
0:00 Gold and silver nanoparticles
1:10 Laser Ablation in Liquid (LAL)
4:04 LAL advantages and parameters
6:53 Gold particle sizes
7:29 Plasmons
9:36 Plasmon Resonance
11:00 Mie scattering
12:18 Lycurgus Cup
12:59 Noble metals and Conclusion

[@ExplosionsAndFire]

Gold...... that isn't yellow..... I'm in

[@fraserbc]

Have we ruled out ghosts yet?

[@iain3713]

Hi Tom

[@belacickekl7579]

Surely you can fix that by attaching some azides?

[@graealex]

Judging from your last video, you love yellow chemistry.

[@gymprofessor329]

C U B E

[@AppliedScience]

I wish that I could give more than one "like". You're making the videos that I want to watch! I'm inspired to put more time into YT myself. Thanks!

[@SeanJonesYT]

It must be awesome to have Ben commend your work. Ben, I would love to see you two work together on some project - you guys work in such a similar way. It would be absolutely awesome to see, and it's inspiring to have you both spend your time teaching us things we would've otherwise never imagined learning about. Hats off to both of you!

[@lazyman114]

Hey Ben. I noticed that you are here on all the science/engineering youtube videos, which is absolutely fantastic! However, KZbin's algorithm makes it extremely difficult to find such channels on my own. It would be great if you could somehow create a community on discord where we can share and discuss such channels. There are quite a number of youtubers that make groundbreaking content and get 1-3k views at the MOST. Look at Chemical Force. He shows reactions that have never been seen before on video and he is only just now starting to gain traction after 3 years of work. I don't know how youtube's algorithm could be this bad, but there has to be a solution to keep talented content creators from getting discouraged.

[@excitedbox5705]

@@lazyman114 KZbin favors videos that appeal to a wide audience of brainless idiots.

[@notsonominal]

Dont worry Ben, I gave him another like ( .. but you're still the coolest cat on on YT:)

[@NEprimo]

i love you both

[@AppliedScience]

That's so cool! I had no idea short laser pulses to create metal nanoparticles was even a thing.

[@BreakingTaps]

Yeah! I forget how I stumbled onto it... think I was researching laser-induced forward transfer (ablating a thin film with _just enough_ energy to dislodge it from one substrate and fly over to a second nearby substrate) and stumbled onto this. Just seemed so neat and also easy too, my kind of technique :)

[@ThomasAndersonbsf]

@@BreakingTaps I was wondering if the size of the particles would play into smaller deposition to make semiconductors on a substrate or something :)

[@DIYBiotech]

Yall should do a collab where you put the gold nano particles in glass to recreate that Roman cup!

[@travismiller5548]

@@DIYBiotech it's called "fuming." I vaporize gold and silver with a torch and catch it on warm (borosilicate) surfaces all day every day. I feel like a jerk vaporizing precious metals, but all things considered it's a very low business cost. My first gram of gold lasted about 5 years, and I generated over a million dollars of merchandise.

[@athmaid]

@@travismiller5548 what do you do with it if you don't mind me asking?

[@BreakingTaps]

*Addendum* - Commenters have pointed out that Pauli Exclusion is not for free electrons (electrons gas), it's only for electrons in atomic or molecular states. Oops! Addendum to the addendum: read comments in this thread for more clarification :) - I misdescribed the absorption vs transmission vs scattering phenomenon a bit. @Matthew Reavley says "the specific resonant frequency that you mentioned absorbs light of that frequency, that light isn't reflected back the direction it came, but rather the energy that's absorbed gets re-emitted in all directions. As a result, the intensity of that colour is reduced when you have a light source shining through it (eg. When the lycurgus cup is red, its because the intensity of the green light travelling in the same direction is now significantly reduced), and in all other directions (like when the light it outside the cup) , you only see the absorbed and emitted colour (green)"

[@kevinmartin7760]

I'm pretty sure it still applies, it is just that there are so many states available, forming a near-continuum of energy levels, that it makes no difference.

[@aaronclair4489]

@@kevinmartin7760 Kevin is absolutely correct. The Pauli exclusion principle holds for all fermions, such as electrons, protons, and neutrons. No two identical fermions can have the same quantum numbers (such as energy and spin). In essence, no two electrons can be at the same place at the same time with the same characteristics. In solids, the energy levels of electrons smear out. Instead of one orbital having one discrete energy in one atom, all the orbitals at that energy overlap, and their different energies shift minutely up or down to form energy bands. This is Band Theory, which describes electrons in solids. In a conductor, the valence band (full of electrons) and the conduction band (full of empty slots for electrons) touch, which is how electrons can flow from place to place. This is the origin of the electron sea. At least, this is my understanding of electrons in solids.

[@BreakingTaps]

​@@kevinmartin7760 ​ @Aaron Clair Ah ok, interesting! I remember seeing some information about levels "splitting" but I didn't quite understand at the time. But in context of your epxlanations that makes a lot more sense now, and describes why the "electron sea" actually can exist. Man I really need to go dig up my old physics books and re-read all this stuff, it's been far too long and I really struggled to put together a coherent explanation haha. Was definitely at the edge of my knowledge here :)

[@DanielHeineck]

@@BreakingTaps, exactly -- the density of states of a metal is characteristically very high around the Fermi energy, making them "practically equal" but not, technically. I think older versions of Kittel's "Solid State Physics" book are available online -- it'll have a pretty good explanation (it's also *every* English-speaking person's introduction to solid state physics)

[@alexdaharp]

@@BreakingTaps. IMO, what @Aaron Clair wrote is the typical explanation for band structure (more of a thing for crystals, the explanations for small molecules follow a similar theory called MO theory. When stuff is in between w.r.t size, stuff become a mess). The big thing is that plasmons need a partially filled conduction band. If you have a full valence band (a filled conduction band by definition is a valence band) you actually make Quantum Dots instead! In that case you can control the smearing of the electrons through controlling the size. A cool field is what happens when you get really small noble metal nanoparticles. When you get small enough, band structure doesn't really work anymore and you get some really weird effects. It's a really interesting field, you literally can count the number of atoms in the particles! I'm curious, have you checked the stability of your nanoparticles? I have heard that they tend to be a bit unstable unless you control the ionic strength or chuck something like a ligand (a molecule that bonds with the surface of the nanoparticle) into the mixture.

[@SarahKchannel]

Now put a vial onto a peltier cooler/heater.. cycle the temp and see if there is a color shift when particles change size according to temperature... Likewise if you flash them with a laser or light source.

[@dddwidovich3514]

He dissolved it with iodine! or iodists. Then halogen,manganese as a catalyst?

[@patti441]

@@dddwidovich3514 what are you tanking about ?

[@patti441]

none of those cgemicals are present its just super fine metal dust in an suspension of water

[@dddwidovich3514]

@@patti441 ooookay, what do you like to hear, ambasador muchacha jalapenia

[@dddwidovich3514]

Lala

[@SwitchAndLever]

KZbin actually recommends something I want to watch for once! Well produced, engaging topic without becoming too entrenched in the scientific literature. Lovely stuff!

[@BreakingTaps]

Thanks! ❤

[@KeesHessels]

Man, your channel should have way more subscrtibers...

[@4n2earth22]

Patience, patience. Oh, and tell a lot of peeps....

[@morkovija]

Share the goodness - do your part

[@WaffleStaffel]

Agreed. One of the most underrated channels. I'd say that in due time he'd be big, but he's already a rockstar.

[@notsonominal]

True story (and this is just a mindless comment to feed the beast..:)

[@Tahira204]

Just discovered this channel, super educative, I love it.

[@eulemitbeule5426]

That stuff might be really interesting as catalysts in chemical reactions: You usually use palladium on charcoal because it has a really big surface area, but you might be able to use a solution of Pd nanoparticles instead since that stuff seems to be able to tolerate organic solvents. Would be interesting to see what happens to the Pd nanoparticles during the reaction

[@carltauber2939]

The reason that the catalyst is adsorbed on a solid is so that the liquid or gaseous reactants can flow through the solid and be separated from it mechanically. If the catalyst is in solution you have to find a way to separate it from the products so you can continue to use it.

[@BE-dj6cp]

@@carltauber2939 perhaps a semi-permeable membrane (not permeable to nanoparticles) then use chromatography column to separate substrate from product. Not sure what that would be good for besides research. Alternatively, attaching nanoparticle to a porous membrane somehow w/o losing catalytic properties would be ideal for fuel cell application if cheap to produce. The major drawback of fuel cell tech is the catalyst is expensive platinum. If catalyst could be made cheaply = low sticker price production EV that runs on tank of methanol or H2 w/o big expensive environmentally unfriendly lithium ion battery pack

[@edoars46]

Man, ur explanation of nanomaterial synthesis is like telling me how to cook instant noodle, u made it really understandable, cheers 👍

[@combin8or]

Suggestion- make an aerogel with nanoparticle inclusions. Semiconductor aerogels also exhibit surface plasmon resonance by virtue of their pore sizes. I’ve always wondered if one could dope silica (or another dielectric) aerogel with nanoparticles to exhibit some interesting properties. These days, particularly lithium or sodium.

[@DerPancake234]

Looking at the nanoparticles under a dark field microscope makes really cool pictures. Using a polarization filter and measuring the scattered wavelength shows how spherical or oval the particles are. Great video as always.

[@BreakingTaps]

Oh nifty, I didn't realize you could see them under a reglar optical microscope. This is not helping my microscope-hoarding predilection however :P

[@raymondbiju437]

can you explain this a bit more? sounds neat

[@florianf4257]

This is a common misconception about optical microscopes. The Theory doesn't state that you can't see things smaller than the Abbe limit, you just can't locate them more accurate. The biggest problem with seing such small particles is that their scattering crossections are quite small too, so they won't be very bright. For that reason darkfield microscopy ist the method of choice, where you can even see scattered light for 20nm nanoparticles. You just can't really tell if you see only one or maybe multiple that are very close to each other due to the Abbe limit (or in this case the Rayleigh's criterion, as Abbe doesn't apply for darkfield).

[@excitedbox5705]

I use copper and silver nanoparticles for printing circuits, but you can also use copper as a thermal paste or add it to liquid coolant to increase the cooling properties. One of the coolest things about metal nanoparticles is that at really small sizes (

[@robbystokoe5161]

I learned an amazing amount from this video. Your explanation of the concept of a plasmon with the wave analogy was fantastic. I'd heard of plasmon resonance before but didn't know what it was until now. This is just the second video of yours I've watched, and I'm excited to keep learning from them.

[@colepearson2605]

I’m in a class called “Nanotechnology” right now, and this video got recommended to me right after I had a lecture on these nano particles! This really helped to explain surface plasmon resonance to me.

[@DoingItOurselvesOfficial]

I’ve seen red colloidal gold turn that purple colour when the particles start to conglomerate. Usually when contaminated by another mineral or from UV exposure. You should be drinking the Colloidal gold. It’s amazing for your health providing the particles are small enough.

[@matthewreavley]

Also, another interesting thing you can do to tighten down your range of particle sizes is to use the fact that as nanoparticles get smaller, their melting point reduces (there's some unfriendly maths that show it's because surface energy increases relative to bulk energy). In short, with your 30-100nm particles, you could find the temperature where particles below 80nm melt and agglomerate, leaving behind those 80nm and larger nanoparticles. I believe this effect was first found in gold nanoparticles, and had something to do with someone forgetting to turn a hotplate off!

[@Gainn]

If you put gold into solution with aqua regia and then boil it off it agglomerates into a solid.

[@oportillo02]

I'm a non born english speaker architect, and i understood everything. Congratulations and greetings!

[@22391pranav]

Your nanoparticles have a high polydispersity index, which is probably due to the method. You can use silver nanoparticles as antibacterial agent

[@albyboy4278]

Yes, nice to use silver nanoparticles to kill bacteria ... But don't let them touch your skin because they give you the silver skin disease ... Basically the skin absorbs the silver creating silver salts and replacing the skin color with the color of silver, metal color of silver . Once combined with the skin, the silver does not come off and remains with you for life. You have to be careful with the silver particles. There are examples of women left with silver-colored faces because the creams they used had silver salts.

[@angiasaa]

Actually, silver can be fatal, though admittedly you'd need a lot of silver to be killed by it. Silver nanoparticles absorb into the skin easily and will turn the skin blue. Silver poisoning is a thing. Look for Argyria or Argyrosis for more info on that. You have a good point however, people think they're being clever, but have no clue what it is doing to themselves. Beauty products.. :)

[@lastofthebest5102]

@@angiasaa LOL, ok. Whatever you say. Funny how you forgot to mention that flatwear (silverware) and plates/cups used by discerning people are constantly shedding nanoparticles each time they are used which mixes with food and is ingested. You must be one of those feds attempting to dissuade others from getting silver into their bodies so as to keep a population from figuring out how to collect more spiritual gains. Perhaps you have never heard of the Lycurgus cup?

[@davesmith440]

can you use gold particles as a antibacterial agent as well

[@tamasmihaly1]

You're a good teacher. Clear and logical. I look forward to your future work. Thank you very much.

[@LaserEngraving911]

Love it Thanks for the deep dive!!

[@jonc133]

Great video and thanks for sharing. Back in my PhD days, I was working with gold chloride solutions and coating them on to nylon. When I did x-ray photoelectron spectroscopy on them, I noticed the sample came out different colours, depending on how long the xrays had been on them. The x-ray source was breaking down the gold chloride and gold particles were forming - the longer the x-ray were on, the larger the particles that formed, eventually forming a completely gold film.

[@dogodogo5891]

hi i read somewhere gold np can produces some invisible effect by combination of plasmon resonance stuff n metamaterial structue is that true?

[@gaiustesla9324]

just found your channel mate and its bloody good.

[@johnmanderson2060]

Thanks for the plasmon resonance explanation, it was top notch ! 👍🏻

[@supergiantbubbles]

Fantastic video. Very well explained.

[@mastershooter64]

man this channel's content is amazing! this guy should have tens of millions of subscribers and views and I don't understand why he does!

[@TeamStevers]

Love your videos! So many subjects and in depth while being digestible. You are the science teacher for the modern age. Production quality is top notch. Get an agent and pitch a show to Netflix. You have that X factor.

[@BreakingTaps]

I think that's the nicest thing anyone has ever said to me! Thanks for watching, and the kind words! ❤

[@TeamStevers]

@@BreakingTaps you deserve it my dude!

[@joeshmoe7967]

This video and other on your channel, just go to show there sooooo many things one can learn, but with our short life spans we can't learn them all. Channels like this at least allows us to pick up some crumbs. Great content. - Cheers

[@dantesmith3664]

great video. I really enjoyed it

[@scootergem]

I feel very comfortable with what you tell us, I trust you. Please continue being so forthright . That's very important in science. So many times the facts are contaminated by "facts" that confuse or mislead. The job you are doing is above that and I thank you. Good information isn't always easy to find. 🦉

[@whitebeard1807]

Learn new thing today! Thank you.

[@maku6087]

Basically it is the same principle as with a resonating dipole antenna. Just on a much smaller scale with much shorter wavelengths.

[@VincentGroenewold]

Super interesting, you always present things that likely just interest you, but are quite unknown for the general audience (and even me being a former scientist). :) I wish you a million subscribers.

[@VincentGroenewold]

Also, this channels warrants a new Patreon I think, so hi! :)

[@hadinossanosam4459]

Would be really interesting to take transmission (and maybe reflection) spectra of these particles, I wonder whether they show a nice resonance pattern and/or let one identify the average particle size Also, how do you manage to find such above-and-beyond-awesome topics so consistently? The only other channel that manages that regularly is AppliedScience, and he uploads once a season ;)

[@BreakingTaps]

Agreed! I wanted to include some UV-Vis spectra in this video but my spectrophotometer is reaaaaaally old and didn't want to behave. Also it only prints out on thermal paper and I ran out :) Gold has a really well characterized set of transmission curves which are commonly used to identify the nanoparticle size without resorting to SEM/AFM images. It's not perfect, gold has a weird property of shifting the response if there is a mixture of sizes (rather than showing bimodal or a flatter curve) but it's generally Good Enough. Here's a good example: cdn.shopify.com/s/files/1/0256/1107/5658/files/gold_nanoparticle_absorbance_93074e71-b7d1-4b6c-bba1-171f028c4d5f.jpg?v=1570803718 And thanks, appreciate it! Sorta stumbled into this one on accident :) I wanted to try out the laser ablation technique, then did some more reading and saw how gold and silver behaved and the video sorta pivoted to talking about that since it was so cool :)

[@niki40935]

A more peculiar effect even is that anisotropic nanoparticles display multiple resonance peaks - each usually corresponding with some symmetric axis of the particle. With colloidal synthesis nano-triangles, nanorods, and cubes can be quite reliably produced (and it's quite fun:))). To respond to Hadinos, yes exactly! You can use absorption spectra to estimate both the average size but also the dispersity of your synthesis, if you have a good theoretical model for the size and shape dependent absorption of the nanoparticle! Great Video!

[@4n2earth22]

@@BreakingTaps "it only prints out on thermal paper" and "reaaaaaally old" kinda mean the same thing..... ;-)

[@BreakingTaps]

@@4n2earth22 Hehehe.... I do have a soft spot for thermal paper though, very satisfying :D

[@BreakingTaps]

@@niki40935 Oh, that explains some of the images I saw of rods and "stars" which had really interesting color variations. I guess each dimension of the particle can give rise to a different resonant frequency, which when combined gives you different colors not possible with just the spherical particles alone?

[@billymonday8388]

absolutely amazing video

[@squelchstuff]

Great video, and yet another fascinating out of band (youtube) subject. Being able to produce your own nanoparticles inexpensively, besides equipment layout, could be very useful indeed. I was going to suggest using nanoparticles in a fuel cell ion exchange membrane, but then remembered you said you had trouble with platinum and your laser - oh well. My other suggestion is to take a foray into ferro-fluids. There's all kinds of interesting properties to play with there.

[@BreakingTaps]

Yeah it's a shame the platinum didn't really work, I was hoping it would work since Pt is such a great catalyst for all kinds of things. I thought it didnt work at all, but on reviewing the footage you can see a _tiny_ amount ablated, so I guess you could let it run a long time. But heating the solution to boiling becomes a problem (for the bigger batches I ran it in a water bath which helps)

[@lastofthebest5102]

10k for a near IR pulsed laser is not what I would consider "inexpensively". Funny how he forgot to mention that the machine he is using cost more than most peoples cars.

[@Khodazmoon]

that was really cool. I didn't know about that but i have synthesised the gold nanoparticles by Citrate method. very cool channel

[@irvingmarquez1106]

Thanks so much for sharing

[@McImTheBear]

I love this channel so much

[@lnaesll]

You are an incredible teacher.

[@AlsoDave]

On what to do with them: it'd be incredible to see conductive transparent thin films with silver ones, apparently it's a potential alternative to ITO

[@fapasaurusrex]

Damn this a pretty cool video, perhaps you could try making lighting gels with these

[@Anar10n]

Great vid

[@abj9121]

To short video! 😭😭😭 Love it!

[@romit45612]

in my undergrad chem labs we made magnetic nanoparticles to create a ferrofluid, was pretty fun and looks cool too!!

[@NB-ro5vo]

How do you deactivate Nano particles

[@Slimysock-td6oq]

Yo can I get a procedure?

[@andymouse]

Interesting stuff ! you could try and recreate the optical properties of the glass ?...cheers.

[@ian6083]

This is amazing work! Thank you so much for sharing! Use the particles in suspension in an MHD apparatus. Apparently, even gold can be magnetized under certain conditions. This would be a great science demonstration.

[@BreakingTaps]

Interesting! Added to my list of things to read more about, thanks for the tip!

[@donwp]

Interesting video. Thanks. The scattering vs reflecting effect might allow you to create a stained glass window that shows a different scene in daytime vs nighttime. And, maybe even different again as the inside lights are altered in colour.

[@James-ri3fd]

What a good idea!!!

[@Alexander_Sannikov]

Wow the scanning laser beam looks really futuristic, love it!

[@tootalldan5702]

Cool demo. I would think Tungsten could create a rainbow of colors similar to the different heating points color pattern. Looking forward to the next video.

[@elektronikzmbrtlar1586]

Metal nanoparticles can be a really good chemical catalysts

[@logicalfalse]

Gold nanoparticles are used as a dopant in semiconductors. You could make a DIY LED that uses the nanoparticles as both a dopant and a plasmon colour filter. Great channel!

[@lostlithium4687]

Till now I only read it in the books, thanks for the demonstration

[@LanceMcCarthy]

You just blew my mind, plasmon resonance is awesome.

[@CrazyLabs]

I'd like to see lanthanides nanoparticles. Lanthanides have very strange electrons configurations

[@travismiller5548]

When working hot glass, I sometimes "drill" holes with hot tungsten welding electrodes which are "thoriated" and "lanthanated"- alloyed with very small percentages of thorium and lanthanum. Obviously most of the captured vapors are burnt back off the surface of the glass to clean it up once the hole is generated. Tungsten being the main ingredient, the colors are silvery, and a creamy white.

[@JayeDiesel]

Figure out a way to add the nanoparticles from any of them and fuse or coat them to another metal. Or add them to some nail polishes to get some crazy effects... so many ideas. A fuel additive, possibly use them in a heat pipe to help move heat better. Or for it to move more heat due to overall density etc... Ok, I'm done. For now... Awesome video. Really felt like I learned something! Thank you!

[@denisdelgadokikumotogracia7938]

Great video! Would be nice to see if the nanoparticles can function as a catalyst for an heterogeneous chemical reaction

[@gavendb]

really neat. i wish i could do cool stuff like this!

[@ronaldorme6375]

fascinating. especially the Lazor obliteration technique

[@TheAruruu]

use suggestion: you know those oil and water moving sculptures you used to find in doctors offices? could you make one of those using the red gold nanoparticles and have it change colors while moving?

[@smash5967]

Wait, you're telling me the wave/particle duality thing doesn't apply to the ocean?

[@erbalumkan369]

Any wave needs a medium to pass through.

[@neillcoetzer9133]

You should look into cadmium Selenide quantum dots. Doing bachelor's project on it now and it has some very interesting properties and optimization problems in the synthesis. The synthesis itself also isn't particularly difficult, which is nice when you need to do the synthesis like 50 times

[@James-ri3fd]

Interesting

[@reamageorge9648]

Very interesting and beautifully explained. Just wondering if you have tried to view the morphology of the nanoparticles you've made.

[@BreakingTaps]

Thanks! Just those few AFM scans that I showed in the middle of the video somewhere. I'm looking to see if I can get some SEM or TEM of them at some point :)

[@matthewreavley]

I'm trying to recall from my nanomaterials course, but with surface plasmon resonance, the specific resonant frequency that you mentioned absorbs light of that frequency, that light isn't reflected back the direction it came, but rather the energy that's absorbed gets re-emitted in all directions. As a result, the intensity of that colour is reduced when you have a light source shining through it (eg. When the lycurgus cup is red, its because the intensity of the green light travelling in the same direction is now significantly reduced), and in all other directions (like when the light it outside the cup) , you only see the absorbed and emitted colour (green)

[@BreakingTaps]

Ahhhh ok that makes a lot more sense! I admit I spent a _long time_ debating if it was being absorbed or reflected or just elastically scattered or something else. I couldn't find a good layman explanation, and all the papers were mostly over my head. Cheers for the explanation! Will add this to the addendum!

[@avialexander]

That purple doesn't look like any particular wavelength of light, do harmonics of the base frequency also get reflected off the nanoparticles?

[@BreakingTaps]

Good eye :) I glossed over that, mainly because I couldnt get my UV-Vis spectrophotometer working to show the absorbance spectra. As the particles get larger (or start to aggregate) the absorbance starts to red-shift and broaden out. So more longer wavelengths are absorbed and the shorter purple/blues are transmitted. Until you get big enough that it starts behaving like bulk metal gold again. There are charts of the spectra online if you're interested, like this one: cdn.shopify.com/s/files/1/0256/1107/5658/files/gold_nanoparticle_absorbance_93074e71-b7d1-4b6c-bba1-171f028c4d5f.jpg?v=1570803718 E.g. at 20nm, nearly all green is absorbed and half of blue/purple is absorbed, leaving just red. But by time you get to 400nm particles it's a pretty flat profile, transmitting just a bit more blue/purple than red.

[@avialexander]

@@BreakingTaps Ah cool, thanks! So it looks like the harmonics effect exists, but is kind of overshadowed by the statistical distribution of particle size producing a wider spectral response. So the plateaus on the shorter wavelength side of those spectra would be the harmonics, if I am not mistaken?

[@BreakingTaps]

@@avialexander To be honest, I'm not sure! we've reached the edge of my knowledge here, so you probably have a better intuition of the effect than me. From my very loose understanding that sounds pretty reasonable though :)

[@Psychx_]

This seems like a super material efficient way to prepare precious metals for use as catalysts.

[@tedv5379]

Nano particle can be used to create “solar blind” UV-C light passing filters. A solar-blind filter that passes wavelengths less than about 300nm while blocking all visible light and longer wavelength UV-B and UV-A light can be used with various semiconductor detectors view corona discharge, welder flash, detect hot flames and even see non-line of sight scattering of UV-C sources, even in broad daylight. These types of filters are very difficult to fabricate and are quite valuable. I’d love to see some experiments to fabricate one. Thanks for your content.

[@moonstreetlabs]

Yay, plasmon resonance

[@chbu7081]

I'm doing that now.

[@travismiller5548]

It would be neat to see what ti pen looks like on glass under a microscope. Titanium can be used to mark glass and artists us it to sign glassware. I've had mixed results creating a conductive path and electroplating it. Had to use a conductive paint to bridge to the fine titanium lines and bring it into the plating circuit. What I found was copper would plate the line, then loose adhesion to the titanium and lift up on one end of the line, and the process would begin again, creating a series of fractal-like curled fingers.

[@MisterIkkus]

I fucking love your channel.

[@seanmcelwee5034]

Early pandemic I was watching a series of lectures on nonlinear optics. They mentioned gold has nonlinear properties but due to high absorption, cant be used as thin film layers or bulk material like other nonlinear materials. They instead use solutions of gold nano particles. Might be interesting

[@rynther]

This is pretty cool stuff, and in regard to color, relates to dichroic glass, and "diffused" gemstones. Created by surface coating or flash plating glass for dichroic, or diffusion of a compound into the upper one or two molecular layers of a gem to change it's optical properties. A fun and easy to get sample of this is "aqua aura" or "rainbow aura" quartz, produced by flash plating clear quartz with either gold or titanium respectively. (fun fact, if you sand off the coating on one face of an "aqua aura" quartz piece, you can see the red transmission light, instead of the blue reflection.) Diffused stones are much more diverse, as the body material interacts with the surface layer in many different ways, but it's generally used to enhance what would otherwise be uninteresting or less valuable stones. A prime example being iron diffused into aluminum oxide to enhance the blue in white or very pale sapphires. Meanwhile, thanks for the great content, I would love to see if these nano particles could be used for color filters.

[@ProtonOne11]

One thing that would interest me about the production process: I guess at some point the suspended particles in the liquid are interacting so much with the laser beam and cavitation that the production of new particles is significantly slowed down. Did you just stop at that point, or did you increase the particle concentration by evaporating parts the solvent. And what happens for example with the red liquid if you completely dry it out? Do you get a red gold powder, or does the color change back to gold at some point?

[@BreakingTaps]

Ah, good question! I wanted to mention that but completely forgot. You're right, at some point the suspended particles start eating up too much of the laser power and production really dies down. I side-stepped that to some degree by ablating the vials on their side, so that there was less liquid in between the laser and metal. But that's the main reason the "continuous flow" setups are preferred for batch production (it also carries away bubbles which helps too). A high NA / short focus lens really helps as well, less laser fluence is lost pre-focus. I mostly stopped once density started to get too high, but also just at the point where I liked the color (which was around 5min for me) so not super scientific :) That said, there's a neat trick you can do once the suspended density gets high enough: you can re-focus the laser "inside" the liquid and start ablating the nanoparticles themselves. I didn't do much rigorous study of it, but some papers claim it helps reduce particle size since you're re-ablating the nanoparticles. The circular motion supposedly helps since it helps swirl larger particles towards the center. I haven't dried enough solution to tell unfortunately (only small amounts for AFM, and that was done on mica which is yellow'ish anyway). But I have read that these particles "red-shift" due to different index of refraction of air vs water, so they would probably skew more/darker red once dried. I don't think they return to a gold coloring unless there is sufficient density to really start agglomerating, and even then it's probably more a dark blue.

[@CS-kk4tm]

Great video! What is the make/model of your laser?

[@kolloidal]

very good info. What laser machine you are using, where to buy, how much it cost - (a lot I think).

[@aklb43]

You can achieve the same effect in lampworking glass by fuming the gold or silver onto the glass. It will change the color of glass to the colors you have depending on variables.

[@omsingharjit]

if the colour is mix of two phenomenon resonance and Scattering .than it will be nice to do little experiment with it like shining perticular wavelengths of light one by one to see which one Is Reflected best vs other absorbed . shining with higher wavelengths blue or uv to see how much scattering occurred

[@panama_dan]

Regarding what to do with the nanoparticles, maybe cast some in a plastic so you can have an indefinitely suspended sample? Might take a lot of trial and error, but it would be a nice souvenir for the work you have put in. Further, I did some undergrad research in SERS using gold and silver nanoparticles. You could use them as a means for amplifying the signals of analytes that may be too dilute to detect under normal conditions. This requires diving in and setting up a Raman spectrometer (gratings, optics, lasers, detectors) and you seem relatively well equipped for it. Morphology also affects this and could be an interesting exploration in the analytical side of chemistry. Heck, you could just play around with surfactant/capping agent effects on morphology for fun to get rods, stars, cubes, maybe even tubes. Hopefully this will spur some idea for you to pursue that won't be an Sisyphean endeavor!

[@MD-qh6ld]

or have them suspended in molten glass, kind of like the lycurgus cup

[@nadimfetaih3841]

I know this video was 2 years ago now. But it would be super cool for you to use the nano particles to create a large version of a QLED tv. Like, make a few pixels that are large enough to see the separation of them, and have them emit light in the same way as a TV does to get a better understanding of QLED technology!

[@icebluscorpion]

You could do dye lasers too with this with the right material

[@ciaduck]

You could use them for electroplating perhaps, or creating a thin film on something. Maybe explore use in an electrolyte? I don't know enough about batteries to know if that would be good at all.

[@ramous5182]

Awesome! How did the romans get nanoparticles for the lycurgus cup? Did they use a gold salt that was reduced in place?

[@BreakingTaps]

Unknown! :) Apparently there is still a lot of debate how they managed to get the gold-silver alloy in the glass. Some historians think it was accidental contamination from silver/gold work elsewhere in the shop. But other historians discredit that since it's clearly a decorative piece, so they think it was intentional. There are some other broken fragments of glassware that has a similar trait from the same time period iirc. Gold chloride and silver nitrate were commonly used for stained glass in later time periods, so it's entirely possible they knew the same trick and incorporated it. I personally suspect it was a chemical synthesis route like you suggest, rather than physically generating the nanoparticles since they'd also need a way to purify out the larger nanoparticles to get that color.

[@4n2earth22]

They got reallllllly tiny midgets to work on that project, if memory serves....

[@ellogroresearch2072]

Hello, thank you very much for sharing the information with us. Super important to know more about this topic of nanoparticles of snoble minerals. I understood that we can use sodium chloride (could you say how much per liter?) One of the problems that arises from the stability of colloidal gold is precisely the time in which or the moment in which the particles come together again. That is why the stability of the products obtained is extremely important. That is, how long is the stability of the products made by Laser? Thanks !!!

[@w__a__l__e]

complete shot in the dark run a current through it, may be there will be different conductivity/ check the resistance of the different nano particle configurations

[@gristlevonraben]

Does your platinum nano particles glow under uv light? very cool video!

[@josealvarenga1623]

Hi, great information, can you post the fiber laser you use, thank you

[@_Reverse_Flash]

Man I hate it too when my plasma reactor starts to fail in the middle of a home movie.

[@Obsidian0Knight]

This reminds me of my fountain pen ink. This makes me think of shimmering ink. What happens when you dry one of these solutions? And also what happens at higher concentrations? Would the nano particles coldweld and fall out of suspension as the solvent evaporated?

[@omsingharjit]

colour change due to different nano size may be because of nano particles light interaction with different different wavelengths differently like Quantum dots may be

[@thrustin64]

Not sure if you found a use for this but you could do surface enhanced Raman spectroscopy if you have access to a Raman spectrometer.

[@TheLightningStalker]

I'm slightly concerned that the algorithm knows that I am a nanoparticle.

[@georgewashington90]

To improve the video put on the dark rounded plate white piece of paper. It will make deference in colors of your test tubes more visible.

[@realcygnus]

👍 We don't need no stinking applications. 🤣

[@johnmanderson2060]

I wonder if your metallic nanoparticles could be Infused in layers inside aerogel in order to create some useful device, like a catalyst apparatus or a solid state battery ? (my favorite topic, i am an EV fan) i wonder if metallic nanoparticles and electrolyte infused aerogel could be a good battery inner nanomatrix capable to block dendritic formations. Thanks for your great videos. 👍🏻

[@WaffleStaffel]

CoeLux artificial skylights are an interesting application of titanium oxide nanoparticles. I wonder if a DIY version could be made with the liquid sandwiched between two sheets of glass. I've made silver nanoparticles in water in varying concentrations. It has a diffuse yellow-greenish tint. At the most concentrated, it looks like antifreeze.

[@BreakingTaps]

Ooh, I like this idea! I remember seeing that artificial skylight made with soapy water (on DIY Perks iirc?), would be cool to replicate the commercial version. I'll start digging around to see if I can find any of their patents or how it workswith TiO2

[@OutOfNamesToChoose]

@@BreakingTaps Yes please! Ever since I saw that DIY Perks video, I'm disappointed not to have seen much more mention of it elsewhere. I'd love to see a nanoparticle commercial version (and who knows? It could turn into a very handy little project!)

[@josephf6785]

This would be a pretty interesting application!

[@WaffleStaffel]

@@BreakingTaps I was unaware of the DIY Perks video, thanks! He did a beautiful job. I believe the relevant patent is USRE47363. They describe a number of processes, but it looks like they're using cast PMMA. In section 20 they describe mixing in the particles, sonicating, then centrifuging the material before casting it. That's a big undertaking. One way or another it would be worth it. I live in the PNW, and it's often times as dark and rainy as the DIY Perks video.

[@BreakingTaps]

@@WaffleStaffel Oh awesome, thanks for digging up that patent! I found some related patents from different companies, but couldn't locate theirs. Just had a skim over the patent, surprisingly accessible and easy to read for a patent! And lots of good background information/explanation... I think I can adapt this. Cheers!

[@Jandodev]

Lasers, plasmas, gold what else could we ask for!

[@kreynolds1123]

Collect a bunch, dry it out, then get in touch with glass blower or do by self and dust the particles on to molten glass surface and or blended into the glass.

[@predatoryanimal6397]

check if the particles have any adsorptive properties maybe they can be used in quantitative assays for proteins, other colloids, or surfaces

[@peetiegonzalez1845]

This is awesome. I'm not sure if it's the same mechanism exactly but it looks very similar to what happens with Quantum Dots. Could you finely control the colour produced by your nanoparticles by finely controlling the size?

[@franciscojavierramirezaren4722]

Thanx for sharing, great video! Pauli exclusion is not for free electrons (electrons gas) its only for electrons in atomic or molecular states. 🤔

[@BreakingTaps]

Gah! I was on the fence about that but decided to include it. Time to start an addendum with corrections! Thanks for the note :)

[@franciscojavierramirezaren4722]

@@BreakingTaps Thanx you! Keep doing, great content!!

[@psyneur9182]

The Pauli exclusion principle applies to all fermions: no 2 or more identical fermions can exist in the same quantum state. Atomic/molecular states are just one instance when the principle applies. Although I'm not sure mentioning it was necessary for explaining plasmon resonance.

[@franciscojavierramirezaren4722]

@@psyneur9182 Electron gas is a Boltzman gas at ambient temperature (in fact follows Boltzman distribution) and behave like a clasical gas, so no relevant the fermi exclusion. Collective electrons oscillations are the core explanation of phenomenom.

[@namenotshown9277]

as a very general rule, waves and other phenomena occur at boundaries eg water/air interface, basically boundaries are very interesting places