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Kill them all! Or at least prevent their birth.
April 5, 2012 4:26 PM   Subscribe

I need to keep scientific samples (chips) in solution for weeks at a time, and they're growing bacteria. I suspect biologists have a good way of dealing with this, since they tend to do more solution work than I do; are any of you out there able to point me in the right direction in terms of UV lamps or something similar?

Specifics: the chips are fused silica with graphene and gold on their surface. I'm storing them in deionized water and a little bit of surfactant. They can't be dried out once they're wet.

I did some preliminary searches for UV lamps, but I'm getting swamped by sterilizing cabinets for salons. Thanks!
posted by you're a kitty! to Science & Nature (14 answers total) 1 user marked this as a favorite
 
Using sterile containers & sterile medium with a growth disinhibitor plus refrigeration would be my first suggestions, not UV lamps. I've never seen UV lamps used that way (not to say they aren't but I haven't seen it).
posted by fshgrl at 4:37 PM on April 5, 2012 [1 favorite]


I don't really understand nature of your samples, and I think the specifics will probably have an effect on how you handle this. The question you'll have to ask yourself is "is the method I'm using to prevent bacterial growth going to affect my samples in any way which is significant to my process?"

So, first, is there any possibility that UV light could alter them? If so, I would consider simply starting with sterile materials (sterile containers, solution reagents and water), some method of sterilizing the chips (could be as simple as a wash with ethanol or 2-propanol, possibly followed by a rinse in sterile water) and good aseptic technique. Depending on how many times you'll be replicating this procedure, it might be cheaper than a UV sterilizer. I don't think this will rise to the level of needing a controlled environment such as a laminar flow hood, assuming you don't need them to be sterile sterile, just not growing enough bacteria to interfere.
posted by pullayup at 4:38 PM on April 5, 2012 [1 favorite]


Oh, and any major supplier (e.g. Fisher) can sell you all of these things. If you're working in a lab there are probably catalogs already floating around.
posted by pullayup at 4:41 PM on April 5, 2012


The simplest thing is to use bacteriostatic solutions like alcohol or sodium azide, as mentioned. Do you really need absolute sterility? (As opposed to "not rotting in the fridge" low bioburden). If so, would your chips survive autoclaving? You could keep them in liquid while you cook 'em, and they'll stay sterile until you open the container.
posted by Quietgal at 4:43 PM on April 5, 2012 [1 favorite]


Also, are you sure its bacteria growing on them and not, for example, algae?
posted by fshgrl at 4:46 PM on April 5, 2012 [1 favorite]


Also: make sure whatever you're keeping them in is tightly covered. That's a thing that is important.
posted by Jon_Evil at 4:47 PM on April 5, 2012 [1 favorite]


Also: make sure whatever you're keeping them in is tightly covered.

This is a good idea but less critical than you might think. Since they need to respire, microbiologists routinely use unsealed containers (petri dishes, tubes with lids that just kind of sit on top) to grow their cultures, and depend on the bacteria to generally stay put. In this kind of "sterile enough" scenario you really just need to start with a low bioburden and prevent particulates in the air from settling or being blown into your container. You don't need heroics to get a hermetic seal if it isn't trivial to achieve.
posted by pullayup at 4:55 PM on April 5, 2012


Microorganisms need nutrients, and the only thing in your setup that sounds like nutrient to me is your surfactant. Could you substitute e.g. ethanol for that and still have things work?
posted by flabdablet at 4:55 PM on April 5, 2012 [4 favorites]


Like others here, I would either add 0.02% sodium azide or 10% ethanol or another bacteriostatic compound to the solution. Sterile filtering all solutions through a 0.2 micron filter will remove any bacteria or algae in the solution. If you do that and put your samples into sterile containers, not much should grow, assuming your samples themselves aren't contaminated.
posted by pombe at 5:27 PM on April 5, 2012


The thing about sterility is that once you have a sterile material, it'll stay sterile until you do something to mess that sterility up. So once you get them sorted they should be okay until someone goes and sneezes on them.

I don't think that graphene gets damaged by autoclaving, and it won't add complexities to your setup in the way changing your storage solution might. If you're just storing samples and aren't transferring them back and forth again, you could put them into the solution you're using now, run them through an autoclave (find a bio friend, they'll have access to one, or find your nearest clinical/bio facility for assistance). Once they've been sterilized, they'll be good for as long as they're well covered. You'll probably want to have them in a container with a screw-top cap--loosen the cap a little before putting it in the autoclave lest you have a fun demo of PV=nrT.

You could also just autoclave your DI water/surfactant solution. Or put it through a filter, as mentioned above. If the possiblity of a very slight contamination wouldn't wreck your surfaces, simply popping them in the fridge will slow growth down considerably.

I'm not sure how well UV would work--since your surfaces are not perfectly transparent in the UV, you wouldn't be killing anything on the undersides.
posted by tchemgrrl at 6:41 PM on April 5, 2012 [1 favorite]


Yup, azide or ethanol should do it. Ethanol is (relatively) non-toxic so that would be my first choice unless it interferes with the chips.

Another option might be sodium benzoate, a bacterio- and fungistatic under moderately acidic conditions. Less effective than azide, probably, but also less dangerous, since sodium benzoate is a common food additive.
posted by en forme de poire at 6:44 PM on April 5, 2012


Are these for a Biacore or the like?

Azide would be my first choice so long as you're not doing anything involving Horseradish Peroxidase with them at a later date.

If you have some freedom about which surfactant you're using you might consider going with Proclin.
posted by Kid Charlemagne at 9:46 PM on April 5, 2012


For UV, I think you need good circulation of the solution - its penetration depth in water is shallow. How about a UV unit meant for an aquarium? You need to put it inline with a pump though.

This is speculation from my side, but I'd be a bit cautious with UV sterilization not to produce any ozone. At least in atmosphere, that should eat graphene in an instant, so I imagine you don't want any dissolved in the water either.

If this is just for storage (not a controlled experiment in itself), could you just put in a dip-heater and bring the liquid close to boiling temperature once a day? I can't see that that would degrade the graphene. Perhaps just boil it once and then seal tight?
posted by springload at 5:16 AM on April 6, 2012


The answer to this depends a lot on what your samples can and can't tolerate. Sodium azide would be *this* biologist's go-to solution, but please don't use it unless you can do so safely. Supply companies sell all kinds of antimicrobials that are intended to keep water baths clean for long periods sitting open at 37 C. If your samples are sensitive to potentially having residue deposited on them, I'd stay away from those kinds of things. Depending on how long you're storing these things and how fast you're seeing contamination, sterile-filtering your storage solutions plus refrigeration during storage might completely solve your problem.
posted by juliapangolin at 1:25 PM on April 6, 2012


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