Toothpaste Diode

While reading the back of a tube a toothpaste [Underling] noticed that one of the ingredients was hydrated silica, gears turned, sparks flew and he wondered if he could possibly make a transistor out of the stuff. After thinking about it he decided that making a diode out of toothpaste would be easier and still prove the idea.

The quick n dirty explanation of this is he smeared some toothpaste on a bit of chrome and set it on fire with a propane torch. When set on fire the result is silica and sodium, heat causes the sodium to bond with the silica and since sodium is negatively charged this forms an n-type semiconductor or half of the diode. Chrome is used for the second half of the diode, for a few reasons, he had some lying around, its positivity charged, and the toothpaste contains a little bit of lye which oxidizes the chrome and burns off, bonding the silica to the metal.

What is left is a thin layer of chrome doped silicon under a layer of sodium doped silicon, which in spots where everything is perfect, acts like a diode, blocking current in one direction but not the other.


  1. IJ Dee-Vo says:

    best use for toothpaste I ever seen!

  2. SRV says:

    I understand the hard work and theory that went into this, but in the end what do you really have? Bragging rights?

  3. Awexome idea! Congrats on getting it working :)

  4. Andy7 says:

    Bragging rights? Yes of course he gets bragging rights – what more do you need?

    Nice experiment!

  5. SRV says:

    I don’t understand why reinventing the wheel is considered a ‘hack’, that’s all.

  6. Philippe says:


    @SRV: Zzzzzzzzzzzzzzzzzzzzzzzzzz….

  7. colecoman1982 says:

    @SRV: I’m sorry, I think you have the wrong site. I think you were looking for

  8. jaqen says:

    @SRV: Making a wheel yourself from toothpaste is more “hacky” than buying a wheel from the store I guess :-)

  9. Freax says:

    If you could get transistors to work, we could use a makerbot or something similar to print our own toothpast-ICs… cool

  10. ChemE says:

    umm…Na is used to dope the silica because it is a positively charged ion. You may want to fix that mistake.

  11. IJ Dee-Vo says:

    @SRV obvious user not a Maker. How is it not a hack? What is wrong with bragging rights, or doing something to see if it can be done or satsify ones curisty? seriosly? Well those that can’t do anything cool, obviosly troll

  12. s1500 says:

    filed under: Macgyver

  13. mic says:

    *A wild troll appears!*
    *Uses Ignore*
    It’s super effective!

    Bragging rights? No it is in case MacGyver needs a diode of course…. You didn’t see that episode?

  14. detectorgadget says:

    this is the best type of hack if you ask me… nothing better than making home-brew components.

    would love to see this being used as a detector in a crystal radio.

  15. Wolfton says:

    Okay. Those who think this is not a hack need to be hacked themselves.

    Without these somewhat-simple hacks, who would ever take things further? To your discerning eyes, must this have been included in a larger build in order to be particularly ‘worthy’ of hackaday?

  16. alan says:

    those complaining about the people complaining about how it’s not a hack.

    it was 1 person who said something about it. we don’t need 10 people b****ing him out.



  17. Adrian says:

    If he powers this with a potato, full geek-cred.

  18. yetihehe says:

    Now – make arduino out of toothpaste :D

  19. furan says:

    Excellent! HaD needs more like this, not less! Srv needs to look up the meaning of the word hack…

  20. mike bradley says:

    Not reinventing, experimenting. Braging rights well deseved. Imagine if it gave off light? What if it was a new form of diode? This is how new technologies are born.

  21. SRV says:

    Hack = taking something and modifiying it in a way that was not originally intended, no? Making homemade diode = cool, but not hack.

  22. 0x4368726973 says:

    Definitely need to encorage this work. I may try picking up some little samples or travel packs of different kinds of toothpaste, and see if I can figure out different properties of different ones. I have a little analyzer for different types. Perhaps my cinnamon toothpaste I currently am using at home will show something interesting…

  23. IJ Dee-Vo says:

    @srv=instant fail by stating proof that it is indeed a hack, then denying the proof. Tooth paste not intended to be a diode. then used as one.

  24. elcomol says:

    @srv, dude what the heck, speaking against yourself.
    Are you joking or what…

    Very nice Macgyver hack, love this stuff.

  25. The troll factor around is annoying.

    I’m trying to get my head wrapped around the chemistry, but I have a feeling this might be forming a liquid diode with the moisture in the air.

    Liquid diode –

  26. brad says:

    [quote]Chrome is used for the second half of the diode, for a few reasons, he had some lying around, its positivity charged, and the toothpaste contains a little bit of lye which oxidizes the chrome and burns off, bonding the silica to the metal.[/quote]

    holy run-on sentence, batman.

  27. Underling says:

    Your right it does have a positive charge. I dug a little deeper and found a better explanation for how it worked. Next time I’ll do more research before I post my findings.

  28. Underling says:

    @ brad
    I disagree for three reasons:
    1. The breakdown voltage is to low
    2. There are not enough spots on the metal that act as a diode. Very few spots are actually diode on the metal. I think that a rectifier like that would work over more of the metal.

  29. DanH03 says:

    I agree a toothpaste diode is not a hack, but it is a build, and very notable one. This is innovative. Isn’t innovation and creativity the point behind the HaD site??

    Congrats for a great project, you’ve got some awesome ideas and projects, not to mention bragging rights!!

  30. zumax says:

    It may be a hack, and a cool one at that. But the offered theory is utter nonsense. First: you need far more power than that of a torch to reduce silica (SiO_2) to silicon; then sodium as a dopant — forget that. And so on.

    Most probably some of the multiple metal oxide layers formed in the process have semicouducting properties (many have).

  31. SRV says:


    Yep, that’s exactly what I said – in all of my posts I recognized the hard work that went into this and said that it’s definitely a cool project, and yet people are jumping down my throat and calling me a troll because I point out it’s not a hack? Making a diode out of alternative materials is still not a “hack”, in the literal sense of the word. Any time you create something from nothing it is not a “hack” as it is defined here.

  32. Andy7 says:

    Rather than powering it with a potato wouldn’t it be better to use the alcohol in MOUTHWASH to build a fuel cell to power his toothpaste IC?

    Seriously, I want to see someting made from this – it’s GOT to happen.

  33. Pilotgeek says:

    Wow, some people just need to the hack.

  34. Underling says:

    I’m still working on trying to make a better Cat’s-whisker detector and refining the diode. Once I’ve perfected it I have every intention on building a Cristal radio with one of my diodes. If you check my website in about a week I’ll probably post a photo. If i ever get a transistor working I can use it to amp the radio.

  35. Underling says:

    Sodium Hydroxide when reciting with chrome creates heat and combustible grasses. This is what probably created the silicon. If you bothered to look at my sight you would know that after others pointing out that sodium would not work i researched further and revised my theory. You would have also read that I have very little knowledge of chemistry and as such asked people to suggest flaws in my theory not get on another website and bash it without pointing it out them me so I can possibly correct it.

  36. Underling says:

    Thats setting aside the fact that propane buns at 1995 °C and silica melts at 1700°C so you can melt small amounts of silica with a propane torch.

  37. Vis1-0n says:

    Would I be able to pick up AM radio when I brush my teeth with that brand toothpaste?

  38. snowdruid says:

    what zumax was pointing out is that silica and silicon are two different compound. silica is actualy silicon dioxide.while silica might melt at 1700 it wont magicaly become silicon (wich is used as semiconductor not silica). so basically i have no clue how your diode works but its still very nice work :P

  39. Silicon Alley says:

    Freax posted:
    > If you could get transistors to work, we could
    > use a makerbot or something similar to print our > own toothpast-ICs… cool

    Guess the project makers would have a choice as to whether to polish their projects or to brush them up. :)

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