title: Effects of geometry on transmission and sensing potential of tapered fiber sensors.
abstract: Geometry of tapered fiber sensors critically affects the response of an evanescent field sensor to cell suspensions. Single-mode fibers (nominally at 1300 nm) were tapered to symmetric or asymmetric tapers with diameters in the range of 3-20 microm, and overall lengths of 1-7 mm. Their transmission characteristics in air, water and in the presence of Escherichia coli (JM101 strain) at concentrations of 100, 1000, 7000 and 7 million cells/mL were measured in the 400-800 nm range and gave rich spectral data that lead to the following conclusions. (1) No change in transmission was observed due to E. coli with tapers that showed no relative change in transmission in water compared to air. (2) Tapers that exhibited a significant difference in transmission in water compared to air gave weak response to the presence of the E. coli. Of these, tapers with low waist diameters (6 microm) showed sensitivity to E. coli at 7000 cells/mL and higher concentration. (3) Tapers that showed modest difference in water transmission compared to air, and those that had small waist diameters gave excellent response to E. coli at 100-7000 cells/mL. In addition, mathematical modeling showed that: (1) at low wavelength (470 nm) and small waist diameter (6 microm), transmission with water in the waist region is higher than in air. (2) Small changes in waist diameter (approximately 0.05 microm) can cause larger changes in transmission at 470 nm than at 550 nm at waist diameter of 6 microm. (3) For the same overall geometry, a 5.5 microm diameter taper showed larger refractive index sensitivity compared to a 6.25 microm taper at 470 nm.
authors.affiliation: Department of Chemical and Biological Engineering, Drexel University, Philadelphia, PA 19104, USA.
authors.forename: Angela
authors.initials: A
authors.lastname: Leung
authors.forename: Kishan
authors.initials: K
authors.lastname: Rijal
authors.forename: P Mohana
authors.initials: PM
authors.lastname: Shankar
authors.forename: Raj
authors.initials: R
authors.lastname: Mutharasan
mesh_terms: D015374:Biosensing Techniques / Q000295:instrumentation* / Q000379:methods; D015169:Colony Count, Microbial / Q000295:instrumentation* / Q000379:methods; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D004926:Escherichia coli / Q000302:isolation & purification*; D005240:Feasibility Studies; D005336:Fiber Optic Technology / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000295:instrumentation*