A fiber optic immunosensor for rapid bacteria determination

Abstract

Attention is currently focused on fiber optic immunosensor as sensitive and nearly real time protein detector. This kind of sensor is expected to detect bacteria in foods directly by dipping the thin optical fiber dominant area into foods. In the study, an antibody based fiber optic immunosensor to detect Escherichia coli O157:H7 (E.coli O157:H7) was constructed. The principle of the sensor was a sandwich immunoassay on the optical fiber surface. A goat polyclonal antibody was first immobilized on polystyrene optical fiber. E.coli O157:H7 and a cyanine 5 (Cy5) -labeled goat polyclonal antibody were used to generate a specific fluorescent signal. An excitation light (ʎ = 635 nm) was illuminated into the optical fiber, and the Cy5 florescent molecules near the optical fiber (approximately 100 nm) were excited by evanescent wave emitted from the optical fiber. The fluorescent light (ʎ = 670 nm) collected by the optical fiber was measured using a photodiode. The measurement range for E.coli O157:H7 diluted with phosphate buffer (PB) was from 1×102 to 1×107 cells/ml. This method could also detect E.coli O157:H7 in milk artificially inoculated with 1×102 to 1×107 cells/ml. This immunosensor was specific for E.coli O157:H7 and showed significantly higher signal strength than for nonpathogenic E.coli or other bacteria, including Listeria monocytogenes and Vibrio s.p., in pure or in mixed-culture setup. The results could be obtained within about 15 min of sampling.