Fluorescent sensing using biconical tapers

Single mode fibers were heat drawn to into biconical tapers with a waist diameter of 3.69 mum, and a waist length of 7.1 mm. The taper is shown experimentally to eject 460 nm light and collect the emitted fluorescent light at 516 nm. Flourescein solution at concentration of 10 to 60 muM was placed in the waist region, and excitation light of 460 nm was launched at one of the fiber, and 516 urn light intensity was measured at the other end of the fiber. The 516 nm fluorescence signal was found to be proportional to the fluorescein concentration. The results reported in this paper show in practical terms, the feasibility of measuring fluorescence through evanescent coupling, thus demonstrating the use of tapered fibers as fluorescence sensors with potential applications in medical and biomedical areas. (C) 2003 Elsevier B.V. All rights reserved.