Make Your Own Quantum Dots

Quantum dots certainly sound as if they should be something cool, but carry the hazardous baggage of being sometimes made from cadmium which can be dangerous. What are they? In essence, they are nanometer-scale particles, so small that when high energy light hits them, the photons will be absorbed and re-emitted at a lower energy state. You can easily make non-toxic quantum dots in your kitchen. Apart from the cool factor, they can be used as fluorescent dyes, inks, and possibly paints. [StrangelyAmusing] explains how in the video below.

You don’t need much in the way of equipment. A microwave oven, a Pyrex (borosilicate) container, and gloves. You’ll also need plastic pipettes and a blacklight — possibly the most exotic two items on the list. The ingredients are equally mundane: vinegar, baking soda, water, and sugar.

The vinegar allows the sugar to breakdown (or invert) faster and the baking soda neutralizes the vinegar once its done its job. You are left with fructose and glucose. Once the sugar solution is at the right pH, it remains a matter of heating it again to cause quantum dots to form. The dots will glow green under a blacklight.

According to [StrangelyAmusing] the whole process takes about ten minutes. Other than glowing, what can you do with them? We aren’t quite sure. Commercially, quantum dots have applications (or potential applications) in lasers, solar cells, light emission devices, and even biological markers. However, we don’t have any idea how you’d go from fluorescent sugar solution to any of those devices. If you figure it out, be sure to drop us a tip.

We’ve looked at making different sized dots before. We don’t recommend dealing with the cadmium dots, but we have seen it done in a proper lab.

17 thoughts on “Make Your Own Quantum Dots

  1. Sorry, for some reason I can only think about homeopathic quantum dots now.

    I have a friend that uses these for his bio test on paper systems. They are pretty awesome and there is a market just for making/selling the quantum dots.

  2. quite interesting.
    I wonder why they glow green. I don’t know much about q-dots, but I heard they can fluoresce white. According to an article about their potential use in LED lights.

    If the object of the initial steps is to get fructose & glucose, I wonder if high-fructose corn syrup could be used to skip them?

    1. I’ve seen setups with a rainbow of colors given off by quantum dots. I’m not a chemist, but from what I read it is the size of the q-dots that directly affect what wavelength of light is given off (different mechanism, but kinda similar to how the bandgap of doped silicon in a LED affects the color).

    2. About the high fructose corn syrup question, seems it would indeed work and allow you to skip the acid (vinegar) step.

      Interestingly, the paper that StrangelyAmusing references, “Fast, energy-efficient synthesis of luminescent carbon quantum dots”, doesn’t use acid, or heat at all. I guess StrangelyAmusing was just making a more kitchen and time friendly project, which is great for letting people get a taste of the process.

      Anyway, the paper uses either fructose or disaccharides. For a base, it uses either sodium hydroxide (lye) or sodium bicarbonate (baking soda). It calls for fairly precise solutions at 500mM of sugar-water and base-water, mix them, wait a week and then separate a quantum dot solution via dialysis. Supposedly if you get the solutions correct it will spontaneously (although slowly) form carbon quantum dots and yellow/darken over the days.

  3. How do we know these are quantum dots? Just because it is fluorescent doesn’t mean it is made of quantum dots. Tonic water is also fluorescent because of the quinine molecule. Quantum dots have size dependent properties, including photoluminescent energy (color). Can this sugar derived substance be synthesized at different sizes to produce different colors, for example by growing at higher temperature or longer times?

  4. I noticed this post on instructables the other day and immediately had to try it. Yeah, it works — at least it fluoresces green when hit with light from a UV LED I have.

    About QD’s question: are these really quantum dots? I’d guess so, but would like to verify it somehow. The only thing I’ve found is a post on the sciencemadness forum where someone mentions: “At least with green i would try extraction with non polar solvent to confirm it´s really not just some organic compound.”

    The problem is, I don’t know what that means. Any ideas folks? What’s a good nonpolar solvent that’s easily procured? Or can acetone be used even though it apparently has both polar & nonpolar characteristics??

    Anyway, carbon quantum dots apparently have semiconductor properties, which immediately makes me wonder if they can be doped and turned into diodes, transistors, etc. If only for playing around with the idea.

    Really keen on finding some reading material, but unfortunately almost everything seems to be research level papers which aren’t very impressive and often very poorly written. There IS an ebook “Carbon Quantum Dots: Synthesis, Properties and Applications” which costs $40 as an ebook and (from the free sample) written much like the papers mentioned above… Any ideas for where we can discuss or get more info — at least for technically minded nerds who aren’t necessarily chemists?

    1. Here are some common solvents listed from non-polar to polar-

      Hexane – Toluene – Tetrahydrofuran – Methylene Chloride – Acetonitrile – 2-Propanol (rubbing alcohol) – Ethanol – Methanol – Water

      The emission spectrum of a quantum dot is determined by its size and structure. So if it really is quantum dots, then varying time and temperature of the reaction will cause the emission center wavelength to change, because the size will change.

      The best way to determine if you have quantum dots is to evaporate off the solvent (which may require a vacuum and further cleaning to do in this case) and then look at the residue in a scanning electron microscope. Quantum dots or nano-crystals will be readily visible, but a fluorescent organic compound will just look like a coating of random stuff.

      1. Great info. Thanks! Unfortunately I don’t have access to an electron microscope. I wonder if the evaporated matter could be tested for electrical resistivity to determine whether it’s indeed quantum dots? Any old organic fluorescing matter I would guess would have a very high resistivity, whereas quantum dots might have a pretty low resistance, similar to graphene or graphite? Or would surface passivation (dot “coating”?) affect that?

        Anyway, if they can conduct electricity through contact, they might make for a pretty interesting Franklin Bell experiment with a Van de Graaff generator and UV light…

  5. can you eat them, would you be able to get them in the same size in your bloodstream (fluorescing your blood), can you watch them get broken down by observing a change in fluorescence in the blood?

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