Laser scanning cytometry for enumeration of fluorescent microspheres

As surrogates for viruses, bacteria, and protozoa, fluorescent microspheres can be used to challenge pathogen-removal technologies and determine their efficacy in removing contaminants of interest. In addition, microspheres are helpful in quantifying flow patterns and mixing characteristics. However, the most common microsphere enumeration method - direct count by fluorescence microscopy - requires skilled operators and expensive equipment. In the research discussed here, a prototype device that used laser scanning cytometry and that was constructed of relatively inexpensive components performed at least as well as the microscope for the range of ∼5-200 μS/mm². Among the many challenges facing water providers today are increasingly stringent regulations and the threat of intentional contamination of water sources with pathogens. A device such as the prototype described here would offer utility managers a way to test their water supply technologies with more accuracy and precision. It represents a building block toward more advanced (but still low-cost) technologies that can detect pathogens and help reduce risks.