A Continuous Microfluidic Concentrator for High-Sensitivity Detection of Bacteria in Water Sources

Abstract

Water contamination is a critical issue that threatens global public health. To enable the rapid and precise monitoring of pathogen contamination in drinking water, a concentration technique for bacterial cells is required to address the limitations of current detection methods, including the culture method and polymerase chain reaction. Here we present a viscoelastic microfluidic device for the continuous concentration of bacterial cells. To validate the device performance for cell concentration, the flow characteristics of 2-μm particles were estimated in viscoelastic fluids at different concentrations and flow rates. Based on the particle flow distributions, the flow rate factor, which is defined as the ratio of the inlet flow rate to the outlet flow rate at the center outlet, was optimized to achieve highly concentrated bacterial cells by removal of the additional suspending medium. The flow characteristics of 0.5-, 0.7-, and 1.0-μm-diameter particles were evaluated to consider the effect of a wide spectrum of bacterial size distribution. Finally, the concentration factor of bacterial cells, Staphylococcus aureus, suspended in a 2000-ppm polyethylene oxide solution was found to be 20.6-fold at a flow rate of 20 μL/min and a flow rate factor of 40.

Keywords: bacteria; concentration; viscoelastic fluid; water contamination.

Figure 1

Schematic of the continuous bacterial concentration using viscoelastic fluid. (a) Bacteria suspended in a viscoelastic fluid are randomly introduced to the inlet. (b) Due to the elastic force, bacteria cells are focused at the center of the microchannel. At the outlet, tightly focused cells are collected at the center outlet (outlet A) and suspending medium is removed to the side outlets (outlet B). (c) Image of the fabricated device used in this study for bacterial concentration. Microscopic images of (d) the filter zone, (e) the inlet, and (f) the outlet region of the microchannel.

Figure 2

Evaluation of (a) the effect of the polymer concentration (1000, 2000, and 3000 ppm) at the fixed flow rate of 50 μL/min and (b) the effect of the flow rate (20, 60, and 100 μL/min) in the 2000-ppm PEO solution on flow characteristics of 2-μm fluorescent polystyrene particles. White dotted lines show the position of fluorescent intensity measurement. The X and Y axes indicate the normalized fluorescence intensity of 0–1 and channel width of 0–100 μm, respectively.

Figure 3

Evaluation of the effect of the flow rate factors (FF) determined by the suction flow rate from outlet A on the flow characteristics of the 2-μm fluorescent particles in 2000-ppm PEO solution. (a) FF = 8, (b) FF = 13, (c) FF = 20, (d) FF = 40. (e) Recovery rate and concentration factor at various FF values. The standard deviations depict the measured values from five different experiments (n = 5).

Figure 4

(a–c) Flow characteristics of nanoparticles with 500, 700, and 1000 nm diameters, suspended in 2000-ppm PEO solution at 20 μL/min and FF = 40. (d) Recovery rate and concentration factor of the nanoparticles. The standard deviations depict the measured values from five different experiments (n = 5).

Figure 5

Concentration of bacteria cells at an injection flow rate of 20 μL/min and FF of 40 at the (a) inlet and (b) outlet after the concentration process. (c) Flow cytometric scattergrams before and after the concentration process at the inlet, outlet A, and outlet B, respectively. (d) Ct values of RT-LAMP assay before and after the concentration process.