Team:Dundee/Project/DetectionComparison

Introduction

The current method for regulating toxic levels of microcystin does not involve directly detecting microcystin, but instead uses cyanobacteria cell counts. One direct method for detecting microcystin is to take water samples and carry out high performance liquid chromatography (HPLC). This process takes approximately 24 hours. Using our biological detector we hope to reduce this time. We examine the affect that this lengthy detection time can have on the change in numbers of cyanobacteria and microcystin found in the water body that is being tested. This then allows us to determine whether faster detection methods are necessary.

Theory

Making the following assumptions:

• t = 0 is the time water samples are taken
• b0 is the initial number of cyanobacteria at t=0
• t is the time in hours after the water samples are taken
• cyanobacteria undergo binary fission every hour
• cyanobacteria growth is uninhibited
• each cyanobacteria releases N microcystin molecules

We arrive at these equations:

where b(t) is the number of cyanobacteria at time t and MC(t) the number of microcystin molecules.
HPLC results are obtained 24 hours after the water samples are taken i.e. t=24. We compare this against our aim of a 1 hour detection time t=1 by evaluating equation (2).

Dividing MC(24) by MC(1) we recover an expression for MC(24) in terms of MC(1).