its been a long time since ive posted here. ive been focusing a lot of my energy on microbiology latley. and thats why im back.
at my university lab, we go through tons of non reusable polystyrene petri dishes everyday. they can not be autoclaved. so everyone just throws them
away.
im a poor student so i cant afford to buy tons of pyrex plates or lots of disposable plates, so i cean the used ones and attempt to use them again.
after all my attempts, i get contamination maybe 70% of the time when reusign these dishes, thats a lot of wasted time and agar. so i want to put
together an apparatus for sterilizing these dishes without heat.
cobalt 60 would be an amazing thing to have! too bad. so ive been looking into electron beam irradation. i havent searched long but i cant seem to
find many details on the actual electron beam generator. does it work similar to an x ray vacuum tube? all i can find is people trying to sell me the
service of using theirs.
could a xray tube be used for irradiation? theres an obvious reason that we limit exposure to xrays. would longer exposure with a overcharged (or not)
xray tube be good enough to kill of the remaining gunk on hand clean petri plates?
im very worried about endospores, they get me everytime.
Uv lights that we use in the lab for mutations and what not, dont seem to cut it. i dont have one, and they are suprisingly expensive for any unit
that would work well enough.
so im asking for your help. how would you guys go about building a unit like im describing, that would be cheap, mildly safe and would work?
thanks for the help. im sure many of us could use somethign like this.watson.fawkes - 12-11-2009 at 12:44
What chemical means have you already tried? Bleach? Many washing processes are ineffective commercially because they take too long (slow reaction
rates) but are otherwise effective. These are perfectly appropriate for amateur use, to whom time is generally cheaper.kafka - 12-11-2009 at 14:38
i have been most succesful with washing out the petri dish with soap and water, then i usualy wipe it down with alcohol and dump in a very
concentrated bleach solution. usually 1:1 bleach water.
ive yet to try simply dumping pouring the bleach out of the plates then pouring the agar. i worry it would be too strong for the fungus or whatever i
grow on it. i usually spray it down with isoalcohol to wash off the bleach then i let most if not all of the alcohol evaporate.
i should try washing with bleach then less and less concentrated dips. i wonder what concentration would be ok to not wash off.
i also have some star san which i use for brewing. it is simply an acid, i think phosphoric. i havent tried it yet but it may work.
either way though i would really like to make this machine. it would be great to not use up so many chemicals, much less work, cleaner agar and i
would be able to sterilize things like syringes, scalpales etc.
do you think x rays would be strong enough? Eclectic - 12-11-2009 at 15:36
Nope. Prolly better to use an iodophor disinfectant. tentacles - 12-11-2009 at 15:50
I'd suggest at least adding some acetic acid to give the bleach a fighting chance to disinfect. I'd suggest like a 5% bleach 5% vinegar solution to
start with. I wouldn't recommend using it too strong, hypochlorous acid is pretty nasty. I'd suggest going with electic's suggestion, you should be
able to find it at most home brew shops. Sedit - 12-11-2009 at 16:57
Have you tryed microwaves by any chance? They should be transparent to the plastic dish for the most part yet heat up any water present in the spores
and/or bacteria present destroying the cell walls and possibly sterilizing the petri dish. watson.fawkes - 12-11-2009 at 18:34
It's uncommon for any plastic to be completely impervious, to have eliminated all porosity. Whatever you use, it may take longer than you think. Think
of soon-to-die bacteria as having a half-life, depending on your cleaning process. It may just be that you need longer. You could consider measuring
this by timing a wash, rinsing with sterile water, and plating plain agar. You should be able to measure how fast you're killing bacteria.
Agitation will make anything go faster. Ultrasonic even better.
either way though i would really like to make this machine.
Whatever that machine would be, it would be
cheaper to buy some glass and an autoclave. Irradiation with Co-60 is just kind of screw-loose for a beginner to deal with. I think about doing some
crazy-style things, but being around gamma-activated materials is not one of them. And autoclaves are cheaper than X-ray machine.kafka - 12-11-2009 at 19:33
i already have a good sized pressure cooker that i use as an autoclave, glass dishes would be a cheaper route proably. im justinterested in the
contraption.
i have not tried the microwave. its so simple that im going ot have to give it a try. iodine is worth a try, ill go to the homebrew shop and pick some
up.
im only dreaming of worring with cobalt 60. i realize its extreme. meanwhile x ray tubes are pretty damn cheap online which is why i considered it.
ill try out the microwave, iodine and acidic bleach first. thanks guysgarage chemist - 13-11-2009 at 01:09
Ethylene oxide would be the perfect sterilizer for this, it's used widely in hospitals and in the production of hypodermic needles.
The needles are actually gassed while already inside their thin plastic wrap and cardboard box- the EO molecule is so small that it diffuses through
thin plastic.
The downside is that some of the EO can remain inside thick plastic pieces like silicone tubing, later causing toxicity problems.
How does the manufacturer of the polystyrene dishes sterilize them? On individually wrapped hypodermic needles, you often find the imprint "sterile
EO", which means EO has been used on it.
For your application, iodine would probably be best. watson.fawkes - 13-11-2009 at 08:00
How does the manufacturer of the polystyrene dishes sterilize them?
At least one uses gamma irradiation. I
acquired a box of these recently, and there's a special color-changing indicator that says "I've been through the machine", ensuring sterility
as-shipped.entropy51 - 13-11-2009 at 10:24
Clean the dishes thoroughly and dry them. Store them for 24 hours in a dessicator over 37% formaldehyde (formalin). Transfer them to a dessicator
and store 24 hours over a strong ammonia solution. Then thoroughly air them out with the lids on for about a week. They will be sterile.Satan - 14-11-2009 at 06:39
Electron beam irradiation is quite excellent, but a LINAC isn't exactly homebrew equipment.
It would be pretty fucking awesome to have a 5MeV horn of blue-glowing power in your house though. And break soooo many international restrictions
too. Sedit - 14-11-2009 at 10:56
What kind of power are we talking here needed to sterilize the dish using electrons? There are means of creating extremely high powers using Voltage
multipliers and what not. Combine these with a vacume chamber and creation of an electron beam is a snap. Magnetic fields can focus the "beam" if
higher power concentrations are needed.aonomus - 14-11-2009 at 11:11
The only thing that might be an issue when using a electron beam is forcing charge into the plastic. If you look up on youtube Lichtenberg figure
production, they irradiate blocks of acrylic plastic with a multi-MeV beam, and then use a sharp metal rod (grounded and insulated) to discharge all
the stored charge. If you charge up the plastic, and no way exists for it to bleed out, it might decide to discharge all of a sudden, shocking you, or
damaging/killing your cultures...
That being said, polystyrene is not acrylic plastic, so take the above with a grain of salt. The effect exists where plastics store charges upon
irradiation, but I'm not sure if polystyrene will behave the same way as acrylic.12AX7 - 14-11-2009 at 13:50
Polystyrene is an excellent insulator, too.
Charge can possibly be baked out. It may not be conductive enough even at the softening temperature, I don't know. Moisture might help, too (steam
it?).
You can't have anything over 200 or 500keV without holding a particle accelerator license (and appropriate facilities for it). I don't know if
anything less is as useful. Relativistic electrons are nice because their cross section drops, giving deeper penetration. X-rays in the 10 to 50keV
range are fairly easy to produce, but at low efficiency; this might be why electrons are preferred for sterilization. You'd have to cook it with,
say, a surplus dental machine for many days to get enough dosage.
Chemically, I wonder what happens to polystyrene under radical stress. Everything else turns color and darkens, from the formation of color centers
and whatnot. I can imagine some interesting reactions, like cross linking (making it brittle), conjugation (knock hydrogens out of place, form chains
of alternating double bonds -- which would be colored, if enough occur in a single stretch) and other substitutions occuring inside the plastic.
Probably insignificant at sterilization doses.
Timentropy51 - 14-11-2009 at 17:50
Sterilization requires doses in the 50 kilogray range, minimum. Nothing that amateurs have access to would come even close.
You'd have to cook it with, say, a surplus dental machine for many days to get enough dosage.
Dental x-ray
machines deliver milligray per pulse, are not sufficiently penetrating, and would burn out if run continuously. They are rated for a few pulses per
hour.
What would be required would be a LINAC used for radiotherapy in cancer centers. They are sometimes used for sterilization of blood products and will
do the job.
[Edited on 15-11-2009 by entropy51]
[Edited on 15-11-2009 by entropy51]chemoleo - 14-11-2009 at 18:51
Surely industrial alcohol (which is cheap) at 70%, a soak for an hour in a bucket, and put them to dry into a sterile fumehood with the UV on (these
UV lamps are present in all tissue culture hoods, otherwise get one)? Or, first a soak in bleach, then ethanol, then dry under UV?
You are trying to shoot sparrows with a cannon!
[Edited on 15-11-2009 by chemoleo]Mr. Wizard - 14-11-2009 at 19:21
No doubt the previous suggestions are more practical, but for an interesting site that explains how x-rays can be made at home, you can check here.
