A microfluidic system for the separation and detection of E. coli O157:H7 in soil sample using ternary interactions between humic acid, bacteria, and a hydrophilic surface

• The tertiary interactions among bacteria, HA, and solid surface are investigated.
• E. coli was simply separated from fertilized soil sample by the adsorption control.
• E. coli was detected by performing 4 processes in single micro chip.

The removal of humic acid from soil samples is of great importance for the nucleic acid based detection of pathogenic bacteria because it is one of the main enzyme (polymerase) reaction inhibitors. A simple and effective detection tool that detects pathogens in fertilized soil samples was developed here by the combination of sample preparation steps (the concentration of bacteria and removal of humic acid) and micro amplification steps in a microfluidic pillar chip with a single chamber. The pH dependent ternary interactions between E. coli O157:H7, humic acid, and solid surface were investigated and optimized for maximum adsorption of E. coli O157:H7 and desorption of humic acid on a solid surface to perform serial processes ((1) concentration of bacteria, (2) removal of humic acid, (3) nucleic acid extraction/amplification, and (4) fluorescent detection) in a microfluidic chip. These serial processes were successfully performed in a microfluidic PDMS chip with 400 micro pillars, resulting in the 87.5% rate of success in detection of 103 cfu of E. coli O157:H7 in fertilized soil (15 g) containing humic acid (up to 5000 ppm) for 2 h.