Just looping in @ethanbass, @ygstcu, @matej, & @tonyc who were part of this discussion/design process, @stevie and @gretchen, and @stoft because of the possibilities I mentioned at the end about pairing this with a light sensor to try to get an absolute measurement of input light brightness, and possibilities re: absolute intensity calibration. What do you think?

Just a note that I found this interesting article (not peer-reviewed; Photonics is an industry trade journal, I think) which discusses LED input light:

http://www.photonics.com/Article.aspx?AID=47915

The UV probe fired a xenon flashlamp at 254 nm, and the visible-range device used an LED to provide excitation at 370 to 460 nm. The researchers tested the probes using phenanthrene as the key standard to help determine the concentration of diesel fuel, gasoline, gear oil and motor oil in a water sample. They found that the LED-based probe did not respond at all to the diesel fuel, whereas the UV sensor picked out diesel at less than 1 mg/l and was sensitive to all of the other potential pollutants as well.

So, the LED we're using is close to what they're calling a "visible-range device." More:

In a paper published in Power Plant Chemistry in 2010, Malkov and his colleague, Dietmar Sievert, also of Hach Co., focused their attention on polycyclic aromatic hydrocarbons (PAHs). They set out to show how well UV fluorescence would provide a correlation between oil concentration and the sensor readings they acquired. They compared the results of the UV probe with those from a device using visible wavelengths.

“The biggest challenges [are] that UV sensors are too specific to PAH and therefore won’t see natural oils in water, while [visible] sensors are not specific enough and will suffer from interference provided by natural organic matter in water,” Malkov said.

So, it sounds like whether we continue to use a 405nm laser or a 405nm LED, we really do have to take organic matter seriously, as we'd expected, as a false positive.

Very cool.

If you're going to try to make a cuvette frame, another line of thought is the minimal version, which tucks into the DSK housing itself for "rigidity" [sarcastic quotation marks intentional, but only half kidding, as it does lock it in to some extent).

Anyway, here are some photos of a quick little version I mocked up then almost recycled on accident. It's more tape than craft, but it would be light tight and reusable with a simple lid.

Here are some images, shoudl speak for themselves:

this is just a tube formed to the cuvette, then pinched at the bottom to set a depth to it for demo purposes. Window cut out of front and side to allow light to come in, then fluoresce out.

shoves in from the top.

from inside the DSK

whole think took 5 mins to build. Also, the whole thing fits assembled inside our new DSK box. this may all be off topic, but hopefully cool to someone t

Hey Warren, thanks for your comment on my lab set up. Yeah I'm trying to do oil contamination testing here were I live (city point hopewell va) there are a couple of big chemical plants here right on the appomattox river(shore line,) a lot of people still fish off the shore even with the warning signs posted. I have learned that gas and diesel will fluoresce under a UV light but I want to see if I can detect smaller amounts of contaminants with UV-VIS and Raman spectrophotometry.

Very interesting. A new board from seeed is intriguing- though a bit pricey - seems like it could be turned into an auto-monitoring system. https://www.seeedstudio.com/Hamamatsu-C12880MA-MEMS-u-Spectrometer-and-Breakout-Board-p-2916.html

Can a 405 nm led be used to visualize heating oil stains?