Immobilized optical fiber microprobe for selective and sensitive Escherichia coli detection.

Escherichia coli (E. coli) bacteria have been found to be responsible for various health outbreaks caused by contaminated food and water. Accurate and rapid test of E. coli is thus crucial for protecting the public health. A fast-response, label-free bacteriophage-based detection of E. coli using multimode microfiber probe is proposed and demonstrated in this paper. Due to the abrupt taper and subwavelength diameter, different modes are excited and guided in the microfiber as evanescent field that can interact with surrounding E. coli directly. The change of E. coli concentration and corresponding binding of E. coli bacteria on microfiber surface will lead to the shift of optical spectrum, which can be exploited for the application of biosensing. The proposed method is capable of reliable detection of E. coli concentration as low as 103 cfu/mL within the range of 103 to 107  cfu/mL. Owing to the advantages of high sensitivity and fast response, the microfiber probe has great potential application in the fields of environment monitoring and food safety.