Abstract
The long-term aim of this work is to develop a biosensing system that rapidly detects bacterial targets of interest, such as Escherichia coli, in drinking and recreational water quality monitoring. For these applications, a standard sample size is 100 mL, which is quite large for magnetic separation microfluidic analysis platforms that typically function with <20 µL/s throughput. Here, we report the use of 1.5-µm-diameter magnetic microdisc to selectively tag target bacteria, and a high-throughput microfluidic device that can potentially isolate the magnetically tagged bacteria from 100 mL water samples in less than 15 min. Simulations and experiments show ~90% capture efficiencies of magnetic particles at flow rates up to 120 µL/s. Also, the platform enables the magnetic microdiscs/bacteria conjugates to be directly imaged, providing a path for quantitative assay.
Highlights
Detection of bacteria indicative of fecal contamination is central to water quality monitoring for ensuring safe water for human contact and/or drinking
As reported in the National Outbreak Reporting System (NORS) from the Center for Disease Control and Prevention (CDC), between 2009 and 2017 there were a total of 33 outbreaks associated with exposure to fecal contaminated (Escherichia, Enterococcus, and Streptococcus) water, which resulted in 436 cases of illness, 65 hospitalizations, and 1 death in the United States [1,2]
It is recommended that recreational waters have a geometric mean (GM) below 35 CFU/100 mL for Enterococci and below 126 CFU/100 mL for E. coli, as specified by the Recreational Water Quality Criteria from the U.S Environmental Protection Agency (EPA) [3]
Summary
Detection of bacteria indicative of fecal contamination is central to water quality monitoring for ensuring safe water for human contact and/or drinking. We demonstrate the use of a much improved microfluidic magnetic separation (μFMS) device that offers flow rates of up to 120 μL/s with capture efficiencies of ~94%. This device is capable of analyzing 100 mL water samples in less than 15 min, a significant advancement towards rapid bacteria detection. Instead of integrating the magnets into the microfluidic platform as in [16,28,30], our device utilizes an external magnet array placed below the microfluidic platform, drastically simplifying the device fabrication and lowering the per-unit test cost This proof-of-concept demonstrates isolation of microdisc/particle or microdisc/bacteria conjugates using a μFMS device, which uses a single filtration step protocol, providing an imaging-ready substrate for subsequent fluorescent microscopy. The concentration of the magnetic particles in the stock (before filtration) and the filtrate (after filtration) of each of these samples (except E. coli sample) were quantified in order to estimate capture efficiencies, as will be described
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