Building a blue light transilluminator (for viewing DNA)

[Sirtalis]

Hi All,
It's been a while since I have built anything fun, so I decided to try my hand at making a good blue light DNA transilluminator. Commercial versions of these are available, but small/cheap ones run over $500, and 'good' ones run closer to $2000. These systems are effectively just LEDs with the proper wavelength mounted under a diffuser and a glass sheet, then a filter over the top. All scientific equipment is ridiculously marked up, but these seem particularly expensive for a box with lights in it.

** Yes, I could just buy one. I am doing this more for fun than any real need. I thought this forum might have fun thinking, designing and testing this contraption! **

The concept:
DNA is separated by size within an agarose gel matrix and stained with a fluorescent marker. To visualize the location of DNA within the gel, it is placed on top of the transilluminator, and light of a specific wavelength is passed through the gel. The fluorescent marker is excited by shorter wavelengths, and emits a longer wavelength. The gel is viewed through a long pass filter allowing you to see the emission wavelengths of the marker while blocking the shorter wavelengths used for excitation.

The somewhat obsolete versions of these use UV (301nm) as an excitation wavelength end the markers emit green (603nm) light. These don't need an additional filter for viewing (because we can't see UV light) however, since UV is extremely damaging to DNA, using to visualize important samples is problematic.

Blue light transilluminators use a marker with an excitation range of about 450nm-550nm with a peak at about 497nm and an emission range of about 490-670nm with a peak around 520nm (https://www.thermofisher.com/content/dam/LifeTech/Documents/spectra/images/7567dna.jpg)
The "long pass filter" that is normally used is a piece of acrylic (color code #2422) which is very efficient at blocking everything below about 540nm (it's just a piece of plexiglass, but it works really well for this purpose and costs about $10 sq/ft).

So, (finally) here's what I am trying to build:

1) An LED panel able to provide bright light peaking around 470nm-495nm (preferably closer to 490nm). The illuminated surface will be about 9x9 inches, so the panel should be close to that size. Are there inexpensive blank PCBs that big on which to solder a bunch of LEDs? (I can't find anything like that). Are there other options for building this panel? Shoot me suggestions!

2) A short pass filter to clean up the raw LED light allowing for nearly 0 transmittance through the long pass filter used above it. This is probably necessary unless the LED outputs very clean light with nothing above 540nm but most LEDs in this range output some higher wavelengths, even though their peaks are lower.

3) I already have the long pass acrylic filter. This component is sufficient, so I don't really need suggestions for this (https://www.eplastics.com/img/Plexiglas 2422 TP Amber Wavelength Chart.jpg).

I am decent at building electronics and soldering, but I really need suggestions on specific LEDs and acrylic to use for this purpose. My first attempt used a cheap "ice blue" LED strip from amazon ($15) and a piece of acrylic #2114 ($10) as a short pass filter/diffuser. This setup results in a LOT of very, very blue light with great diffusion. When the long pass filter is placed on top, the blue is completely blocked (it looks black and dark -i.e. perfect). However, I think this setup produces closer to a 450nm peak. This MIGHT work, but it's not close to the optimal excitation wavelength, so it will not be very efficient, and will not work well for viewing very small amounts of DNA.

How do I get this rig to output closer to 470nm-490nm while still being completely blocked by the long pass filter and still be relatively inexpensive?

Does anyone have (or know how to borrow/rent) a spectrometer to test this rig?
(Thinking of building a spectrometer... you know, because I "need" one)

Again, let me reiterate, that this project is just for fun. If you aren't here for a fun thinking/design challenge, please be nice anyway

I'll post some pictures soon to show what I have so far and as this project goes forward.

Thanks!

 

[DaveTheDude]

Your project is waaaaay beyond my paygrade...

 

[desert.snake]

That is, in fact, you need 2 filters - one to cut off the extra frequencies of the LEDs, and the second to cut off the extra frequencies after the light passes through the substance under study, or do you want LEDs that give a very narrow peak around 490 nm?

You already have filter 2, so you need filter 1, which will cut off all waves, shorter than ~ 450-480 nanometers, right or did I mix something up??

I have seen glasses for sale that have a certain spectral transmittance, but there is one drawback, they are only 3 * 3 inches.

D here -

 

[desert.snake]

Or you can find suitable high-power LEDs in China, they are not very expensive, cyan 490 nm

4 large chips at 100 watts each will be enough to cover 9 by 9 inches + add a diffuser film so that the light is uniform (diffusing film can be taken from broken liquid crystal displays, which are sometimes thrown away)

Or order 50 pieces of 3W LEDs on individual boards and fix them on a sheet of metal

something like that, but square 7 pcs * 7 pcs LED, and one left in stock

 

[Sirtalis]

Thanks for the replies! I Also posted this over at BudgetLightForum, and received helpful replies. I wasn't sure anyone would reply at all, haha.

Desert.Snake,
Yes, your first schematic is exactly what I need, I couldn't have stated it better myself.

I actually do have good candidates for both filter 1 (short-pass) and filter 2 (long-pass). The Acrylic #2114 is an opaque blue that works fairly well to block nearly all light below about 520-530nm(or thereabouts). Acrylic #2422 is a transparent amber (orange) that works very well, and blocks everything below about 540nm. When I put these filters together, they look black. When I put them together and look directly at the sun (probably not a recommended method to test filters), I can see a faint greenish light, but very little makes it through.

I currently only have a cheap spectroscope to estimate these spectra, but I've been working on this for a few days now, and I have decided that I need something more accurate that can quantify these spectra, so I'm working on building this spectrometer.

My first attempt at a cheap light panel (the lazy way) is to make a panel similar to this out of LED strip lights. I got a roll of "Ice Blue" LEDs and a roll of "Cyan 490nm" LEDs.

These are the spectra I have so far (490nm LED strip to come shortly). Sorry for the poor quality, this was taken through my phone with a cheap spectroscope. I aligned them as best I could, but they aren't perfect. There is also some blueish aberration, this is not part of the spectrum. I'll hopefully get some better pics and quantified spectra later.

Looks like the "Ice Blue" LEDs are actually white LEDs with a spike in the blue region. They emit light way out into the red as well as blues.

Note that the filter pass-through wavelengths do not overlap much at all. The cutoff for the long-pass is 540nm give or take a few. So it looks like these filters will actually work really well for my purpose. The bottom picture is the excitation/emmission of the DNA dye.

The short pass filter cuts about 70% of the light, so I need the panel to be bright.
I think my only hangup here is whether the LED strip lights produce enough light in the proper wavelengths to excite the dye without producing TOO much green that makes it through the filter set together).

The 100W LEDs would do the trick, haha! They would also probably cook an egg over the panel. Good for breakfast, bad for sensitive DNA samples.

I am interested in the idea of just using individual single LED PCBs attached to a panel. This looks like it might be the best (most professional looking) option.

Thanks again for the suggestions thus far! I'll keep you all posted as this goes forward.

 

[desert.snake]

Very cool! Looking forward to more news.

Your filters seem to work very well for this.

The problem with heating from powerful LEDs is easily solved, it is necessary to increase the distance

or

Rotate it through a mirror so that most of the heat goes up, then you can use a few pieces, something like this lamp, but 490 nm. There will be a lot of light losses, but it will be cold and in the right place.