Immobilization of anthocyanin-based red-cabbage extract onto cellulose fibers toward environmentally friendly biochromic diagnostic biosensor for recognition of urea

Simple, green, sustainable, portable, wearable, cheap, reversible, flexible, comfortable, real time and highly sensitive viscose (Vis) fabric was developed for visual colorimetric recognition of urea in fluids. Natural anthocyanin (Ac) spectroscopic probe extracted from red-cabbage as well as urease enzyme as a catalyst were subjected to co-encapsulation process into the matrix of the calcium alginate biopolymer, which in turn was immobilized in situ into viscose fibers as a host matrix. Calcium alginate nanocapsules were generated on viscose surface utilizing the anthocyanin extract in combination with urease enzyme as the interior materials and the crosslinked calcium alginate as a shell. This co-encapsulation process was carried out in situ employing the pad dry-cure method under ambient conditions. Both high sensitivity and small molecular size of this anthocyanin probe made it suitable for encapsulation within calcium alginate nanoparticles biosensor assay (Vis-Ac). The anthocyanin receptor encapsulated into calcium alginate displayed ratiometric variations in the absorbance spectra to the degree of a 127 nm hypsochromic blue-shift from 567 nm to 440 nm with the increasing the total content of urea in an aqueous medium. The colorimetric changes of Vis-Ac were monitored between purple and greenish-yellow in relative to increasing the concentration of urea. Those colorimetric changes were studied using CIE Lab chromogenic parameters, UV-visible absorbance spectra and colorimetric strength (K/S). HPLC-MS was utilized to describe the colored solution extracted from red-cabbage. Transmission electron microscopic (TEM) images were used to explore the generated Vis-Ac nanocapsules to display diameters in the range of 50-65 nm. The morphologies of Vis-Ac immobilized on viscose fabrics were investigated with energy-dispersive X-ray patterns (EDS), Fourier-transform infrared spectra (FT-IR) and scan electron microscope (SEM). The current biochromic sensor barcode showed a comparatively quick responsiveness (6-9 min) with a detection limit in the range of 300-1000 ppm. The comfortability of the treated viscose was studied by exploring its bend length, air-permeability and fastness properties.