Project:OD600 Measurement

In the molecular biology of bacteria, OD600 is often used to estimate the current growth phase of a bacteria, or other cells in suspension. The measured OD600 gives an estimate of the concentration of the cells in the liquid, which can be used to estimate the growth phase of the population. 600nm is in the visible wavelength an is approximately orangey-red.

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The idea is to take a 600 nm source, (or a source including 600 nm and a BP filter) and a level detector, and calibrate it to match 0.4 at OD600 on a proper spectrophotometer..

The initial attempt was to use a white led with a filter for something approximating 600nm

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At the moment the main issue is that the LDR (light dependent resistor) only sees about 20 ohms of difference between the initial inoculation and the mid-log phase, which shows as 0.4 OD600 on a spectrophotometer.

If you don't have access to a spectrophotometer, (or even if you do), this should be a convenient way to estimate OD600 values for your sample

A secondary project is to cast some 10mm x 10mm resin blocks to be used for calibration against a system that takes a cuvette.

Here is a document describing various methods for calibrating spectrophotometers;

http://www.perkinelmer.co.uk/CMSResources/Images/44-136839TCH_Validating_UV_Visible.pdf

alternative ideas

use a stain that binds to a protein that is only expressed during exponential growth phase

DNA Pol II is only expressed during the stationary period of growth, and so might be used as a marker for the end of exponential growth

omp regulates response to osmolarity is expressed in postexponential phase; (Connell et al 1987)