Co-encapsulation of enzyme and tricyanofuran hydrazone into alginate microcapsules incorporated onto cotton fabric as a biosensor for colorimetric recognition of urea

One of the major consequences resulting from chronic kidney failure is a considerable increase in the level of metabolism waste products in blood, including urea that is naturally released by kidney. Herein, we report a novel practical colorimetric test gauze strip for an efficient recognition of urea in serum was developed. The prepared testing gauze strip was based on a composite composed of urease enzyme co-encapsulated in alginate biopolymer, supported on cotton gauze assay, with artificial tricyanofuran hydrazone (TCFH) receptor sites. A cross-linked calcium alginate microcapules containing tricyanofuran hydrazone molecules and urease enzyme, were successfully prepared and employed on cotton fibers creating a colorimetric cotton strip to act as a color changeable sensor for determining urea. The readout limit achieved for urea was as low as ~250 ppm at room temperature and atmospheric pressure. The sensor responded linearly relying on the urea concentration in the range from 0.1 to 250 ppm. The chromogenic cotton platform response depended on the acid-base characteristic effects of the tricyanofuran hydrazone probe. The protonated form of tricyanofuran hydrazone molecules immobilized within the alginate microcapsules (1.7–12.9 μm) were in a microenvironment demonstrating a light yellow color. When binding to ammonia produced by urease/urea reaction, the tricyanofuran hydrazone spectroscopic probe was deprotonated and exhibited higher absorption wavelength and a purple color. The simple fabrication and abovementioned characteristics of such naked-eye colorimetric cotton gauze sensor are such that they should be applicable for monitoring of urea. A thin alginate microcapsules layer was created on the surface of cotton strip using dip-coating technique. We studied the distribution of the colorimetric cross-linked alginate microcapsules onto cotton strip. Its distribution was investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) as well as Fourier-transform infrared spectroscopic (FT-IR) analysis. Colorimetric measurements of the solid state cotton gauze were applied to monitor the color changes. •Simple colorimetric test-system for detection of urea was developed.•Cotton sensor was loaded by a pH responsive probe and an active enzyme as a core co-encapsulated in a biopolymer shell.•Chromogenic biosensor was characterized by a detection limit in the concentration range 0.1–250 ppm.•Test cotton exhibits color cha