Measuring bacterial growth by tapered fiber and changes in evanescent field

Single mode continuous tapered fibers were fabricated with waist diameters of 6–8 μm and of 11 mm waist lengths. The tapered surface was coated with poly-l-lysine and Escherichia coli (E. coli) (JM 101) expressing green fluorescent protein was immobilized. Growth of this culture at 22 and 32 °C was monitored by 480 nm light transmission through the tapered fiber. Change in transmission is a measure of change in absorption of the evanescent field. The transmission decreased exponentially with cell growth on the tapered surface. Growth rate was determined and compared favorably with cells grown on the same medium in multiwell plates. Significance of the results is that a tapered fiber sensor can be used effectively for rapid assessment to determine the presence of bacteria by growth.