Evanescent sensing of biomolecules and cells

A technique using the evanescent field of tapered fibers is developed for rapid, convenient, and accurate sensing of biomolecules and cells using small volumes of analytes in the range of 150 μl. A tapered optical fiber was fabricated by heat pulling with a flame. A simple fiber-mounting device was developed to accommodate the optical fiber and provide a reaction chamber for analytes to interact with the tapered region. Using an analytical grade spectrofluorometer nicotinamide adenine dinucleotide (NADH), nicotinamide adenine dinucleotide phosphate (NADPH), and Chinese Hamster Ovary (CHO) cells at various concentrations were measured. A parameter, namely, the product of extinction coefficient and light path, is used to characterize detection sensitivity. Results from biomolecules and cells show that the sensitivity of the tapered fiber is at least an order of magnitude higher than that obtained in a cuvette arrangement.