A microsystem for extraction, capture and detection of E-coli O157:H7

This paper presents use of a microsystem for extraction, capture and detection of pathogenic bacteria such as E-coli O157:H7 in soil sample. The assay protocol considers Enzyme-linked Immunosorbent Assay (ELISA), with each bacterium sandwiched between a magnetic bead and a horseradish peroxidase (HRP) enzyme. The system employs three different chips, the soil extraction and mixing chip, retention and reaction chip, and the detection chip. The extractor chip extracts bacterial solution directly from soil sample and mixes with magnetic beads (Dynabeads). The retention chip traps bacteria attached to beads in a microfluidic chamber using a bar magnet. Subsequently, bacteria are bound to HRP which finally reacts with substrate solution to generate a fluorophore. The detection chip relies on a microfluidic flow cell and a pair of fibers to measure fluorescence due to the fluorophore that is related to the concentration of bacteria in the soil sample. Use of the microsystem for detection of pathogenic bacteria extracted directly from the soil sample has been demonstrated. Variation of fluorescence with concentration of bacteria in the sample is studied. The limit of detection (LOD) of the system is evaluated.