Accurate measurement of airborne biological particle concentration based on laser-induced fluorescence technique

We develop a biological particle counter based on laser-induced fluorescence for accurate measurement of biological particle concentrations in the air. Pure water, NaCl particles, polystyrene latex spheres, and standard fluorescent particles are used as media to evaluate the performance of the counter. Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa are used as representative biological particles to evaluate the measurement accuracy of the counter. In experiments, the results measured by the counter are consistent with he results obtained with the culture method; For each bacterium, good linear agreement is observed between the two results, and the values of the coefficient R2 are all more than 0.97. Because of particle superposition errors, system error, etc., at low concentrations, the number measured by the counter divided by the number measured by the culture method, η = Ncounter/Nculture, is larger than that at high concentrations. For same type of test sample, although the distribution is different, the η values at same concentrations are similar. Finally, the repeatability of the two methods is tested. The results obtained using the counter are found to be more stable, with a relative standard deviation (RSD) of 8.14%; this is less than the RSD of 15% obtained using the culture method.