[DIYbio] Re: permittistat ( was DIY Turbidostat)

On 10/28/2011 10:13 AM, Jt wrote:
>   Though the
> current iteration is probably a little more sophisticated than a lot
> of hobbyists would want to get into, there are pared down versions
> which are totally within grasp.

Thanks for the offer to free publish.

I was researching the state of the art of various "stats" and came across
a nice concept from 1991, (patent expired) that could help do some culture growth-stat
functions.

==========
  The permittistat: a novel type of turbidostat
http://mic.sgmjournals.org/content/137/4/735.full.pdf
==========
"Baker's yeast was grown in a novel type of turbidostat in which the steady-state biomass level was controlled not by
the optical turbidity but by the dielectric permittivity of the suspension at appropriate radio frequencies. Dry
weight, fresh weight, the optical density at 600 nm, percentage viability (from methylene blue staining), bud count
and ethanol concentration were measured off-line and the cell size distribution was recorded using flow cytometry.
Any changes in the physiological properties of the yeast had a negligible effect on the ratio between the permittivity
set (and measured) and the steady-state dry weight, fresh weight or optical density of the cultures. The permittistat
was found to provide an extremely convenient means for carrying out turbidostatic culture."
==========

The method they talk of is using an oscillating voltage to measure the permittivity of the space
between electrodes as frequency is varied. They used a four-terminal dielectric spectrometer designed for the
registration of microbial biomass, a BugmeterTM, produced by Aber
Instruments, Aberystwyth, UK.  We all know how easy it is to control volt signals
with an Arduino or similar now, so this kind of "stat" could get around any fouling up of
OD detector windows by growing bugs with low costs and fairly low complexity of control code and
instrumentation gear.  The frequencies used in the above paper were 400 kHz and 9.5 MHz, which
are easy for some inexpensive chips to output.

Besides keeping a batch at a constant mass density of bugs in water/nutrient mix, when you sweep
the frequency along you can tell other subtle qualities of the mix.  Search on "dielectric spectroscopy".

John