Fig. 6 Glucose detection with enzyme-loaded microfibers. (a) The effect of HRP/GOX weight ratio on the absorption of mixture of glucose and TMB after catalysis with HRP and GOX-loaded microfibers. (b) The effect of glucose concentration on the absorption of the aqueous solution containing enzymes, glucose, and TMB. (c) Visual detection of glucose (0, 0.25, 0.5, 1, 2 mM) with enzymes and TMB-loaded microfibers.
Prior to the glucose analysis with microfibers, the chromogenic reaction in aqueous solution were investigated at selected concentrations of glucose (Fig. 6b ). Data showed that the absorption (652 nm) of the mixture increased with glucose concentration. But the relationship between the absorption and the concentration was not linear in the selected range of glucose concentration. The slope of the curve was smaller when the glucose concentration was higher than 2 mM, indicating that the color change was less sensitive to glucose with too high concentrations. For visual detection of glucose, microfibers with enzymes and TMB were fabricated under the optimal conditions and wrapped on a glass slide (Fig. 6c ). The aligned fibers turned to blue after dropwise adding with 20 μL of glucose solution. The blue color remarkably became deeper with the increase of glucose concentration from 0 to 2 mM. The catalysis reaction was triggered by the addition of glucose and the penetration into the pores of the hydrogel network followed by the rapid generation of OxTMB, which causes the visible blue color in the microfibers. The knittability and the modulability in the composition and size enabled great potentials of the microfluidic microfibers in the construction of portable devices for the simultaneous detection of multiple markers.