Public Lab Research note

Fluorescence of BP oil with UV laser: success!

by warren | November 08, 2013 21:48 | 380 views | 15 comments | #9750 | 380 views | 15 comments | #9750 08 Nov 21:48

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What I want to do

Scott Eustis and I and others have made a number of attempts to get clear fluorescence spectra by shining a green laser through mineral oil which has had small amounts of crude oil dissolved in it. But we've struggled to get enough brightness into a Desktop Spectrometer.

My attempt and results

Today over lunch I was fiddling with a UV laser (~405 nanometers: buy on Amazon here for $8) with Matt Hirsch and we suddenly realized that it produces a much stronger spectrum than green lasers had. This may be because a laser can only create fluorescence at longer (lower energy) wavelengths than its own -- so green lasers could never create blue fluorescence. See the setup in the lead image for how we did it -- it was pretty easy. But PLEASE be careful not to shine this in your eye, and don't look at the laser dot directly as this could be a strong UV laser and could damage your eye even though it's hard to see with the naked eye.

The spectra were remarkably strong:


This is very exciting because it has a pretty good signal to noise ratio, and it's a lot to work with for potentially matching oils.

Questions and next steps

We were also able to measure the spectrum of Bertolli olive oil and an unidentified fuel liquid which is probably paraffin. So one thing we should do is take a lot of spectra of different oils and see if we can reliably distinguish them! If you do this, tag your spectra with "oil" please!


Finally, I created a little black cardboard box with the whole setup taped down inside to streamline the process. It includes space to store your laser pointer and samples, and standardizes the position and orientation of the laser and sample container. It's VERY helpful in doing these sorts of tests, especially for reducing stray light:


Update: Link to sample containers I used:


Jeff, nice experiment. Yes, UV is the right choice -- the shorter the wavelength the better. I'm assuming that the UV-light 'reference' was with water and the oil tests were with some small amount added to the water. Right? What is interesting is the dramatic drop in the UV carrier signal. This would make quantitative measurements difficult. At least there appears to be sufficient signal outside of the UV carrier signature. -Dave

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I would love to be able to characterize oils, olive oil in particular. Two areas of characterization: Adulteration and Quality.

A very high percentage of Extra Virgin Olive Oils (60% in a UC Davis study 4 years ago) are blended with either oils not from olives or from olive oil that has been extracted using solvents that are still in the oil. That Bertolli you tested probably has those solvents in it. I'd like to see a way for consumers to detect this easily, or at least a techy consumer. Palm oil is a very common blending oil in EVOO.

Another high percentage problem in store purchased EVOO is the oil is not really EVOO. The most common problem is storage failure: Too old, to high or low temperature during storage, or exposure to UV light that destroys the monounsaturated bonds in olive oil. Most of these defects show up as the presence of free fatty acids or in loss of polyphenol levels.

Disclaimer - I produce EVOO, and I try my best to make it the best, so finding a tool that makes it easy to see quality difference would benefit me and others like me.

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@stoft - the reference was just the UV laser. I didn't have an empty vial at the time but you're right that we should do that test. The sample is a very small amount of residue dissolved in mineral oil, which itself does not visibly fluoresce under UV laser illumination. You can see the preparation here:

@greggbone - great -- well, i think the first step is to begin scanning lots of oils with this technique -- to check for consistency and standardization. Questions:

  • does the same oil scanned by 2 different UV laser setups generate very similar spectra?
  • do two different brands generate distinct spectra?
  • do two different bottles of the same brand generate similar spectra?
  • does the type of sample container make a big difference? (i'm using these: )

All of the above would be good tests to run on crude oil samples as well, and on a variety of common petroleum pollutants, like motor oils. Interestingly, DTE Heavy oil (which we did test) did not fluoresce. I'll post that and a couple others soon, but I'll also have to dig out the "known samples" -- positive controls -- which I ordered some months ago

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Very nice experiment, and a great set-up for measurements. I bought a 405-nm laser a couple of months ago, and that's a much better wavelength for inducing fluorescence. I've been having fun just pointing it at things in the house and seeing what fluoresces. I need to haul the spectrometer out and see what it shows.

The wavelength is visible to the eye, and is technically violet, but the eye is only weakly sensitive so it looks like a faint violet spot on a surface that does not fluoresce, such as a metal (illuminate the surface at a glancing angle, don't try to reflect the beam back at yourself). Most white paper fluoresces white, showing a brighter spot. Colored plastics also fluoresce brightly to very brightly. So don't be deceived by its apparent faintness; it only looks faint because your eye does not respond well at that very-close to ultraviolet wavelength.

Look for "blue laser" on eBay and the like - they are surprisingly cheap. Most of them emit at 405 nm, the wavelength used for BluRay readers, which is mass produced. Those sold as "true blue" usually are more expensive at emit at 445 nm, the wavelength of the blue LEDs used in solid-state lighting. I bought a "UV flashlight," but its output looked violet to the eye and showed up as a broad peak around 405 nm, so I suspect cheap "UV lasers" you see on eBay may also emit at 405 nm.

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@jeffh - do you think it'd be possible to do such analysis using a blue or ultraviolet LED, instead of a laser? I wonder if it would be safer (for the eyes) and also cheaper/easier? It'd certainly be easier to build it into a smaller testing setup -- maybe even something that fits on the mobile phone version of the spectrometer.

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There are tradeoffs, but it's certainly worth trying violet/UV LEDs. The wavelengths are roughly equivalent, but the LED emits across a broader range of wavelengths than the laser. It's easy to measure that with the spectrometer.

Lasers produce smaller focal spots, so they can concentrate light on a tiny sample or detect lower concentrations of pollutants. But their more directional light is more of an eye hazard.

The violet LED flashlight may emit more light overall from a broader area, but I have not measured the actual power so I'm not sure. Like a standard white LED flashlight, it emits from an array of LEDs, so it might not make a smaller device.

Just checked ebay, and packages of 100 ultraviolet LEDs are on sale for $5-$10. No details on the packaging, but I would guess it's a couple of bare wires and a lens, and that price is so cheap they could be designed into a spectrometer.

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Scott has ordered some laser pointers and is going to try to reproduce.

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Sorry -- he is going to try to reproduce this experiment.


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Note to self: found possibly-suitable boxes:

9" x 6 1/2" x 2 3/4", black, $0.21 each. I guess we should look for foam blocks too, now, or some kind of rigid black lasercut thing to fold up to hold the sample containers in place.

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I'm also trying to reproduce. it's on an much longer time frame, though, than this experiment.

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Hey guys- I'm new here and apologize if this has already been stated. If you want to see the maximum fluorescence, you must first look at its absorption spectra to determine the wavelength of maximum absorption. If your camera doesn't detect UV light, remove all filters in the camera lens assy that are blocking/ absorbing UV/ IR light so that the absorption reading will cover the widest range. There are LED's available for most any wavelength.

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hey guys..i am trying to do the same experiment but i am not getting any result. it seems that the uv light can't enter the spectrometer in order to detect it by the camera. does the type of sample container matter to detect uv. And why the laser is not pointed directly to spectrometer kit? i put it in the same direction as it is in the picture but no signal at all unless if i pointed directly to camera and the sample is in between. Thanks in advance

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Hmm, do you have enough UV light? No, the sample container shouldn't matter, as long as you are seeing a glow coming from the sample. Can you post photos of your own results, and your setup? I'm excited to see other people try it out. I hope your samples are concentrated enough.

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