A fiber optic biosensor for specific identification of dead Escherichia coli O157:H7

•We develop a compact all-fiber biosensor to specifically identify dead bacteria.•The common multi-mode fiber devices increase compactness of biosensor.•We establish and optimize the overall procedure of dead bacteria identification.•The minimum detectable concentration of PI solution is lower than 1 ng mL−1.•The detection limit of dead E. coli O157:H7 is 104 cfu mL−1.

A compact and low-cost fiber optic biosensor was developed to specifically identify dead Escherichia coli (E. coli) O157:H7 with an antibody-activated combination tapered fiber as probe and propidium iodide (PI) as the fluorescent dye. The combined common multi-mode fiber devices and correlation detection significantly reduced the cost and increased the compactness of the instrument. The minimum detectable concentration of PI solution was lower than 1 ng mL−1. Identification of dead bacteria was completed in 30 min, with 10 min allocated for the fiber probe to capture bacteria and 15 min for PI staining. The detection limit of dead E. coli O157:H7 was 104 cells mL−1 without interference from live E. coli O157:H7 and six other E. coli serotypes at 107 cfu mL−1 or cells mL−1. Quantitation was achieved from 104 cells mL−1 to 107 cells mL−1 with r of 0.996 (p < 0.0002). This method integrating specific detection and dead cell identification could also be used to analyze other bacteria by coupling the biosensor with various antibodies and dyes.