Handheld flow cytometer for monitoring bacteria in water

Abstract

Water-quality monitoring is an essential priority for global health. It is estimated that worldwide more than 5000 people die daily from drinking contaminated water. With microorganisms a primary cause for the occurrence of infectious diseases, the concentrations of harmful bacterial cells should be routinely monitored to maintain microbiological quality control of drinking water. Because of the difficulty and cost of directly measuring all microbial pathogens in water samples, organisms like E.coli, Giardia and cryptosporiduim that indicate the presence of sewage and fecal contamination have been targeted for measurement. Bacterial quantitation is currently performed by labs that primarily use plate-culture assay techniques which can take up to 24 hours to produce test result. In order to achieve more timely assessment of water quality, we have developed and tested a hand-held, opto-fluidic-chip-based flow cytometer that promises to meet the requirements for point-of-need microbiological testing of water. The enabling technique is termed spatially modulated fluorescence detection and delivers high signal-to-noise discrimination without precision optics. Relative movement between analyte and a predefined patterned environment generates a time-dependent signal, and correlating the detected signal with the known pattern achieves high discrimination of the particle signal from background noise. The detection technique has been extensive evaluated and benchmarked against a commercial flow cytometer with measurements of absolute CD4+ and percentage CD4 counts in human blood, which are required for screening, initiation of treatment, and monitoring of HIV-infected patients. We have also assembled a first-generation, compact, handheld, single-parameter instrument based on the spatial modulation technique. The performance of this prototype provides a clear existence proof that a multi-parameter, high-performance, compact instrument for bacterial monitoring in water is fully realizable.