DIY Spectrophotometer

[Jeswin John]

Antoher DIY tool for research. I'm still reading the article but if someone knows, tell me how we get the data, like optical density?

http://www.rsc.org/Education/EiC/issues/2007Sept/BuildYourOwnSpectrophotometer.asp

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[Bryan Bishop]

On Tue, Feb 10, 2009 at 3:12 PM, Jeswin John <phill...@gmail.com> wrote:
> Antoher DIY tool for research. I'm still reading the article but if someone
> knows, tell me how we get the data, like optical density?
>
> http://www.rsc.org/Education/EiC/issues/2007Sept/BuildYourOwnSpectrophotometer.asp

You might also be interested in the "open source spectrophotometer"-
http://openwetware.org/wiki/Citizen_Science/Open_Spectrophotometer_Project

- Bryan
http://heybryan.org/
1 512 203 0507

[Jeswin John]

That one is arduino based so more sophisticated. Looks good. The one I posted might be a good hands on approach for primary or secondary school children.

[Dan]

It's worth keeping in mind that OD is a fairly arbitrary unit of
measurement. IIRC, 1 OD is a 10-fold attenuation of light. Now, most
specs are calibrated to that with a 1 cm pathlength glass reference
neutral density filter. As long as you're sample is non-scattering,
that should be pretty consistent from spec to spec. If you can get a
set of OD calibration standards, one can simply measure the signal and
create a calibration curve.

However, for things like measuring cell density which rely upon
scattering, all bets are off. Scattering is very dependent on the
angle of incidence of the light, the distance from sample to detector,
cuvette geometry, etc. In my experience, cell density OD600
measurements vary 20%+ from spec to spec, sometimes even more. An old
lab I worked in did OD 690 measurements because that wavelength gave
overall results consistent with the numbers they got from an older
spec most of their historical data was from.

The point here is if you want to do cell titers, forget OD as a fixed
unit of measure and just calibrate it with a cell viability curve and
go from there.

[Douglas Ridgway]

On Wed, Feb 11, 2009 at 12:16 PM, Dan <dan.h...@gmail.com> wrote:

> The point here is if you want to do cell titers, forget OD as a fixed
> unit of measure and just calibrate it with a cell viability curve and
> go from there.

There's also the Klett colorimeter, which measures transmission of a
filtered light (not single wavelength, like OD). Klett is routinely
measured straight through a culture tube, avoiding the need to sample
your culture. The one I've used looks like it was built pre-1950, but
something similar might be an easy DIY build.

[Tom Knight]

The Klett is great, but what the world really needs is a high tech
stir-bar, able to be autoclaved, which can measure OD while a culture
is growing and report out to a readout device. There is no reason that
this cannot be made, and made cheaply. The world would beat a path to
your door, similar to the rapid adoption of the Nanodrop spec. Power
can come from the magnetic field and liquid drag (you don't need much)
and I/O through an IR path, e.g.

Let's not concentrate on making duplicates of old technology; let's
make something better.

[Aaron Hicks]

What we've done in the past for measuring OD during reactions involving synthetic chemistry is to use a probe that has a sensor in the tip. Certainly not dual-purpose like a magnetic stir bar, but certainly functional. I forget the name of the manufacturer; I seem to recall they were out of Tucson, AZ. They could take the temperature of autoclaving.

-AJ

[Nathan McCorkle]

How about a stir-bar with a mirror or prism on it, and the light source and sensor on the outside of the flask? The mirror could alternatively be at the bottom of the flask, and the light and sensor be at the top, in the stopper.