Optical fiber aptasensor for label-free bacteria detection in small volumes

Highly sensitive devices for fast bacteria detection are sought to be developed with the task of quantifying the worldwide problem of pathogenic bacteria and thus helping to take control over spreading bacterial infections. This work concerns a sensing solution based on microcavity in-line Mach-Zehnder interferometer (mu IMZI) induced in an optical fiber. Such a device exhibits ultrahigh sensitivity to refractive index changes in the microcavity. We show that for well-adjusted chemical surface functionalization combined with highly specific low-molecular-weight bioreceptor the mu IMZI can also be used for efficient label-free bacteria detection. The detection capability has been shown for peptide aptamers and pathogenic E. coli O157:H7 bacteria used as a bioreceptor and a target, respectively. We have found that the sensor is capable of detecting bacteria concentrations as low as 10 colony-forming units per mL in a sample which volume may be as small as hundreds of picoliters. The selectivity of the synthesized peptides is additionally confirmed by Enzyme-Linked Immunosorbent Assay (ELISA). Based on the presented performance, the mu IMZI sensor is one of the most sensitive and lowest-analyte-volume label-free biosensors among fiber optical platforms to date.

Automated summary

A highly sensitive device based on a microcavity in-line Mach-Zehnder interferometer induced in an optical fiber has been developed for fast bacteria detection. This device, when combined with specific low-molecular-weight bioreceptors, can efficiently detect bacteria label-free with a detection capability as low as 10 colony-forming units per mL in a sample volume of only hundreds of picoliters. The sensor is one of the most sensitive and lowest-analyte-volume label-free biosensors among fiber optical platforms.