(Biology research) How to: Get uniform distribution of viscous solution on glass?

[bserbiak]

Hey all, need some help. I'm running an experiment exposing Vicia Faba (beans) to UVA and UVB light, observing chromosome breaks, and repeating the process with sunscreen added.

 

I need to find a way to introduce the sunscreen somewhere in between the path of the light and the plants (whether this involves application to the leaves, some sort of glass plate or other)

 

whatever the solution entails, the following must be true:

1)The sunscreen must be uniformly administered to all plants at once

(ie: no gradients in distribution, no "by hand" application, etc...)

 

Any ideas? I've already attempted to press the sunscreen between two glass plates to spread it uniformly, but this doesn't work because of the viscosity of the sunscreen. Optimally, I would like to be able to use the sunscreen agent on glass, but need a fix for this problem.

 

Thanks to anyone willing to read that and reply

[iNow]

Perhaps you can add the sunscreen to a spray bottle, get a consistent spray out of the bottle prior to applying to the glass, then you have all glass applied with the same number of sprays.

 

Get bottle.

Add sunscreen.

Pump several times to the trash until spray is even and consistent.

Apply X number of pumps to each glass.

 

As long as you are sure to clean thoroughly the spray bottle and nozzle prior to adding the sunscreen, you should be okay.

 

 

 

EDIT: Or, are you asking for something else on which to apply the sunscreen as the glass won't work at all? If that's the case, I presume you could spray the beans directly with your spray bottle.

[Klaynos]

Spin coating.

 

It's commonly used for creating very regular thin films, you spin the sample with the fluid on it which spreads out, spinners allow for different ramp speeds, top speeds, holding pressures (normally the hold the substrate down using a vacuum in my experience) etc...

 

So what I'd probably do in your case is build the settup with a glass side in the light path, this slide can then be replaced by one that has been spin coated. But if you're just trying to reduce the light intensity why not use something like ND filters which are FAR more reproducible.

[bserbiak]

Thanks for the input.

@inow- I think the idea of some type of diffuser could work...just not a human driven spray bottle...there's too much space for error and inconsistency there. The glass as a surface shouldn't be a problem in itself- I like it personally because it reflects very little light by itself. Thank you for your contribution though

 

@Klaynos- awesome idea...I'll be looking into this...unfortunately I may not have the resources to accomplish this in the labs here (Certainly will seek this out though). And as far as your comment about the use of filters rather than a OTC sunscreen goes; I'm testing the efficacy of a specific set of sunscreen agents, that need to remain in product form. But god do I wish that filters could be used here to make this all so much easier. Thank you for the help

[Mr Skeptic]

Maybe cotton dampened with sunscreen and rubbed on the plates might work. Since sunscreen is normally applied by rubbing it on, this might be closer to real life, inaccurate as it may be. How accurate does this need to be? In any case, be sure to take into account how much UV gets absorbed by the glass.

[bserbiak]

Checked the UV absorption of the glass- all set with that. Unfortunately, it needs to be near perfect uniformity. The last time this type of research was presented at the regional conferences, the issue of consistent application of the sunscreen was brought up again and again; the research was torn to bits over that. A realistic application (rubbing with cotton or not) would only work if it was guaranteed to provide uniformity.

[Klaynos]

Yeah, I think spin coating is the way forward it's used alot in physics for sample preparation so if you've got a physics dept you might want to try contacting someone there, semiconductors or optics people use them ALOT. You will have to watch the absorption of the glass you use, in the UV it varies greatly, my masters project we had to buy all UV fused silica lenses so we could use the UV part of our light sourse.

[iNow]

Well, I'm not sure how tech savvy/able you are, or what people/resources you have access to in your lab, but you could use a simple ink jet print cartridge.

 

In short, you get a clean cartridge and put the sunscreen where the ink would go. You can then use the printers existing functionality and software to lay down a very consistent thickness and converage of the sunscreen.

 

I've seen this type of "drop-on-demand" inkjet used in biology via science programs. They essentially dropped one tiny drop at a time at exact locations and in exact thicknesses to build up home grown organs for transplant.

 

I imagine you could adapt this layer-by-layer biomanufacturing technology to your purposes, and it would certainly overcome any concerns at the conference about consistent thickness and/or application.

 

http://www.futuremedicine.com/doi/abs/10.2217/17460751.3.1.93

 

 

 

EDIT: There may be some ideas here, too: http://www.liebertonline.com/doi/abs/10.1089/ten.2006.12.1169?cookieSet=1&journalCode=ten

[Mr Skeptic]

Wouldn't it be easier to directly measure how much the plate + sunscreen blocks, than to indirectly measure it via bean mutations? If someone already measured the mutation rates for beans given a certain exposure to UV light, you could just measure how much UV is blocked and extrapolate how many mutations there should be.

[John Cuthber]

Get 2 plates of glass, put thin spacers between them. Seal round most of the edges to give a big flat very thin glass box.

Dissolve the sunscreen up in something- alcohol will probably work, and pour it into the gap between the plates.

Seal the last bit of the edge and you have a filter with a known amount of sunscreen distributed evenly over a known area. Just getting hold of the active ingredient in the sunblock might make it easier to get a clear solution.

Incidentally, as has been pointed out before, glass blocks a lot of UV. Big sheets of fused quartz are going to cost a fortune.

You might want to look up the UV spectra of, for example, perspex, and PVC. Perspex won't survive alcohol indefinitley, but it might give you time to grow some plants.

 

I'd not like to be there when someone trys to spin coat a big glass plate.

[CharonY]

You won't get mine to do that, that's for sure.

[Klaynos]

How big are we talking?

[DrDNA]

I vote in favor Klaynos' suggestion.

Spin coating is the gold standard.

You don't even necessarily have to spend a lot of cash.

I've even built one out of an old hard drive motor.....it works nice for small substrates.

[CharonY]

How large is the lamp? If it ain't that big you could really spin-coat a smallish plate with that and still cover it.

 

//edit: apparently my already low writing abilities have been gone to hell completely. Guess sleep is not that much overrated after all.

[Mr Skeptic]

Myself, I'd use a spectral photometer and known dilutions of the sunscreen, then adjust the brightness of the lamp.