Figure 20.

(a) Schematics illustrating the principles of the fluorescence affinity hollow fiber sensor. In the absence of glucose, fluorochrome-labeled Concanavalin A is bound to the fixed glucose residues inside the porous beads (A-i). The beads are colored with dyes that prevent the excitation light from inducing Con A to fluoresce, keeping the fluorescence emission at 520 nm. After diffusion of glucose through the hollow fiber membrane (molecular weight cutoff, 10 kDa), Con A is displaced from the beads and diffuses out of them. Fluorochrome-labeled Con A becomes exposed to excitation light, resulting in a strong increase in fluorescence (A-ii). (b) Spectra of fluorescence and absorption of the various chromophoric components of the bead-based affinity sensor. (1) Excitation spectrum of fluorescein, (2) emission spectrum of fluorescein, (3) absorption spectrum of dye-labeled Sephadex beads. (c) Light microscopy picture of a small section of the hollow fiber that was filled with dye-colored Sephadex G150 beads. A bead fraction having a bead diameter of less than 25 µm was used in this study; the beads were obtained by sieving the original material (mesh size of 25 µm) [58].