"Ready-to-use" hollow nanofiber membrane-based glucose testing strips

A novel "ready-to-use" glucose test strip based on a polyurethane hollow nanofiber membrane was fabricated through facile co-axial electrospinning. By utilizing glucose oxidase and horseradish peroxidase in the core-phase solution, and a chromogenic agent either in the core solution (in which case 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) was used) or in the shell-phase solution (in which case o-dianisidine was used) for co-axial electrospinning, in situ co-encapsulation of the two enzymes within the hollow nano-chamber and incorporation of chromogenic agents either inside the nano-chamber or in the shell of the hollow nanofibers was realized. Such unique "all-in-one" feature enabled the prepared hollow nanofiber membrane-based test strips to be applied either as colorimetric sensors in solution or as an optical biosensor operated in the "dip-and-read" mode. When used as a colorimetric biosensor in solution, the test strip with o-dianisidine as chromogenic agent shows an excellent linear response range between 0.01 mM to 20 mM and a high apparent lumped activity recovery of 62.1% as compared to the reaction rate of the free bi-enzyme system. While the activity recovery of the test strip with ABTS as chromogenic agent is only 18.0%, and the test strip is found to be unstable due to spontaneous-oxidation of the ABTS. The o-dianisidine test strip was also applied as an optical biosensor, visible rufous color was quickly developed on the surface of the membrane upon dropping 10 μL of glucose sample, and an excellent correlation between differential diffusive reflectance of the test strip at 440 nm and glucose concentration was obtained in the range of 0.5-50 mM. The test strips also exhibited excellent long-term storage stability with a half-life at 25 °C as long as four months.