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Related Experiment Video

Updated: Jun 19, 2026

Measurement of Particle Size Distribution in Turbid Solutions by Dynamic Light Scattering Microscopy

Measurement of Particle Size Distribution in Turbid Solutions by Dynamic Light Scattering Microscopy

Published on: January 9, 2017

A PHOTOELECTRIC DENSITOMETER FOR USE WITH SUSPENSIONS.

T J Stier¹, W Arnold, J N Stannard

¹Laboratory of General Physiology, Harvard University, Cambridge.

The Journal of General Physiology

|October 30, 2009

Summary

This study introduces a novel device for accurately measuring microorganism population density. The photoelectric cell-based apparatus achieves high precision, crucial for preparing yeast suspensions with minimal error.

Area of Science:

Microbiology
Biotechnology
Instrumentation Engineering

Background:

Accurate enumeration of microbial populations is essential for various biological and industrial applications.
Existing methods for measuring population density can be time-consuming or lack precision.
Standardization of microbial suspensions is critical for reproducible experimental results.

Purpose of the Study:

To develop and validate a rapid and accurate device for measuring microorganism population density.
To enable the preparation of yeast suspensions with a high degree of accuracy (within 1% error).
To overcome limitations of existing methods in terms of speed and precision.

Main Methods:

Construction of a device utilizing two Visitron photoelectric cells, a high-intensity light source, and a Wheatstone bridge.

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Employing a ratio method to minimize the impact of the photocell's characteristic constant.

Utilizing Pyrex milk culture tubes and precisely aligned slits to direct light beams onto photocells.

Main Results:

The developed apparatus accurately measures the population density of microorganism suspensions.
The device allows for the preparation of yeast suspensions with an error margin of 1%.
The method of ratios effectively eliminates a significant unmeasurable variable (photocell constant).

Conclusions:

The constructed device offers a rapid and accurate solution for measuring microorganism population density.
This apparatus surpasses the accuracy of previously available methods for specific applications.
The technology is particularly effective for cultures of similar age and optical characteristics.