Turbidity meter?

[Yuriman]

I could use a bit of Anandtech HT help.


Let's say you have a small container, maybe 4x4x6cm, completely enclosed. You will be growing bacteria inside it, and want to know the growth rate. What is your method for counting the little bugs, without cracking the box open? Easiest/cheapest/most accurate?

I'm thinking a home-brew turbidity meter might work, maybe a small LED and camera with a white strip on the opposite side of the container.


Also, where would one go to find some tiny optics with around 400x magnification, and a very short focal length?

Thanks in advance.

 

[CycloWizard]

Depends on the kind of "bugs" you're looking at. Transmission sensors for measuring things like suspended solids concentrations exist and should work, but how well they work depends on whether your bugs are suspended or colonize on the wall of your container. Sounds like a wastewater treatment project, which is also where I learned about such sensors (though mine were never purchased due to a lack of funds ).

As for where you might buy the optics, it depends: where are you doing this?

 

[Yuriman]

Florida, USA

We're going to use a strain of Shewanella, about 2.5 x 0.5 microns, and we're going to be launching them in a box, piggy-back on a satellite early next year. The idea is to find out if they behave oddly in microgravity, so direct imaging would be fantastic, but simply measuring the growth rate with a turbidity meter would give us a lot of data.

We're going to try and keep them off the walls of the box, so just assume that won't be an issue.

Now that I think of it, an LED with a photosensor on the opposite side of the box would probably be the simplest.


How would you suggest looking at our bugs in a box?

 

[Gibsons]

usually this sort of thing is done over a 1cm path with a known wavelength, 590-600nm. Not sure how a LED compares in terms of wavelength.

Do you know how dense your culture might get? If OD's get pretty high the readout might get flaky/non linear, specially over a 4 cm wavelength.

I assume you're going to monitor pH of the solution? that might give some indication of growth, though not particularly accurate. Unless your media is buffered.

 

[Rubycon]

Might want to look at uncollimated visible laser radiation in the 630-670nm range. It would be more sensitive and have a much narrower spectral width than an LED.

You can also measure oxidation-reduction potential of the supporting fluid. It will change quite rapidly (down) with increase of head count.

 

[Yuriman]

A great idea, Ruby. ^^

I'm not a bio or chem major, just asking the smartest people I know for some ideas. How easy is it to measure the orp?

I'm not sure how dense it will get, I'll ask next time our group meets.

 

[Gibsons]

Any reason you can't use a GFP producing strain? You could maybe even get them from these guys
http://aem.asm.org/cgi/content/full/72/11/7324

If so, that might get rid of the need for a light source, and would make visualizing them much easier. Depending on what you want to see of course.

 

[Rubycon]

ORP is measured with a platinum band electrode either immersed (high maint) or mounted inline on a fitting of one of the lines carrying the fluid to the column. Any standard ORP meter will work and average ocean water reference is approximately +350mV. At +650mV water is considered sterile, for example.

 

[Yuriman]

The bacteria we're going to send up are already decided on, no chance of using glow-bugs. Our strain of Shewanella eats waste and can be used in fuel cells to generate electricity, it frees electrons through some metabolic process, so I don't know if your ORP meter would work; at the least, we'd have to calibrate it. Otherwise, that would be a great way to measure population, since we could toss out the vibrator-motor.

We are also sending up 3 symbiotic extremophile bacteria, I'll get some more information on them.

Simplicity is top priority here. I'll try the electrode, but I'm not sure how to wire that in with our other electronics. Can you link me to some example hardware?



Also, any thoughts on a tiny microscope, or camera + matching optics? The smaller the better.