Public Lab Research note

Ultra micro cuvette tests, UV LED and low-temperature fluorescence

by warren | August 19, 2014 17:56 19 Aug 17:56 | #11063 | #11063

What I want to do

Just posting a variety of small tests I've done over the past few days, based a bit on the literature I've been looking through recently (this, this, and this).

Temperature and fluorescence

I'd read that temperature could affect intensity of fluorescence (Carstea, 2012), and since we're really trying to get fluorescence to be brighter, i tried preparing 3 identical samples of crude oil I ordered online, one drop each diluted in 1/4 oz of mineral oil:



That turned out to be a lot of oil, and the laser didn't really make it evenly through multiple bottles of it, which kind of ruined my experiment:


However, I'm really curious -- this was just to the naked eye, and I haven't validated with a spectrometer at all, but it seemed to me that the color of the cold (middle) cuvette was a bit more blue. Hmm. Not at all definitively, but I would love to try scanning this with a more dilute set of samples. Maybe it's an example of fluorescence saturation, which I read about in this article by Patsayeva (2000).


Ultra micro cuvettes

As a followup to this discussion on sample containers, I also tried out some new round-topped "ultra micro" cuvettes, which both reduce the amount of sample needed (they narrow to 2mm wide at the bottom) and since they have round caps, we hope they'll seal very well, unlike the square topped ones which leak. I'd read here and here that since the sample itself can absorb/block/filter out some wavelengths, it's best to use as thin and minimal a sample as possible, so the light emitted doesn't have to travel through more of the sample before reaching the camera.

I filled a couple with olive oil and one with the not-quite-dilute-enough crude oil from the temperature test above, and shot a laser through them:


Not bad! Also, the higher concentration doesn't seem to be a problem with such a thin (2mm) layer of sample. And it only took about 10 drops before the narrow part of the cuvette was full.


I also tried using a big UV LED, which is either 385 nanometer or 395 nanometers -- I can't remember but will dig up the packaging again. It worked OK, although it wasn't that bright. Maybe it needs more power... not sure. I used 2 AA batteries, but I think it called for 3.5-4.5v. Still, if we could get this bright enough, it'd be much more compact than the big laser pointer.



Note the pink fluorescence from the olive oil vs. the blue from the crude oil sample. Cool!

Questions and next steps

One big question is: do the round-topped cuvettes seal? I've left them upside down and on their sides on a piece of cardboard and will be watching them for a day or two. Then I'll put them in my backpack and carry them around town wrapped in a towel and a ziploc bag for another couple days. We'll see, but the seal seems pretty good and no leaks yet after a couple hours! I should also try filling them with just mineral oil and shipping them somewhere.

If they work, they're <$1 each, and compact and lightweight!


What happens if you unscrew the lens on the laser and put it in front of the LED? can you concentrate the light to make a brighter point?

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@ygzstc - pointing you at this note since you've ordered some very bright UV LEDs.

Oops, missed your comment mathew - we'll have to try that, though at this point the switch to the Infragram-type camera has sort of solved our dimness issues. If Yagiz is able to get LEDs to work, someday we could switch to LEDs with a knob dimmer. That'd be rad.

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Crap, those are only in quantities of 400+ or 1000+. I'll keep looking.

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These look good too, and come with a spectrum datasheet:


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