Waterborne protozoan parasite detection using two-frequency impedance flow cytometry†

Abstract

Waterborne parasitic protozoa are common causes of gastrointestinal diseases in both humans and farm animals, even with standardized water treatment in place. This creates a need for continuous water monitoring to detect the presence of these micron-sized parasites in water sources to prevent potential outbreaks. This paper proposes a monitoring system consisting of a microfluidic channel embedded with micromachined microelectrodes to detect and evaluate protozoa at the individual (oo)cyst level in flowing water. To identify and discriminate between the (oo)cysts of Giardia and Cryptosporidium, two frequency-based impedance flow cytometry (IFC) is employed, where a high and a low frequency are applied to obtain the amplitude and phase variances of the samples. Using combination of amplitude and phase measurements at tested frequencies, the parasites and non-parasites (polystyrene) are identified, and a high degree of discrimination is also demonstrated for samples suspended in both DI water and filtered creek water. While impedance flow cytometry was utilized to detect waterborne protozoa, the system proposed in this paper is distinctive in the following ways. It employs differential coplanar electrodes instead of parallel electrodes to achieve a limit detection of <0.1% volume ratio between volume of a single (oo)cyst and the volume the electrodes occupy in the channel. It applies a low and high frequency simultaneously to obtain amplitude ratios to characterize sample populations instead of amplitude vs. phase at a single fixed frequency, potentially improving sample discrimination. This work also demonstrates detection and identification of protozoan (oo)cysts suspended in a natural water source, instead of in purified water, showing the proposed system's potential as a continuous waterborne parasitic protozoa monitoring system in a real environment.