Engineering of bioinspired cellulose nanowhisker-reinforced alginate hydrogel platform for colorimetric urea biosensing

Abstract Colorimetric urea biosensors have been significant analytical tools for the potential determination of urea in biological fluids, environmental samples, and industrial processes. An extract of Aloe barbadensis Miller ( aloe vera L.) encloses a high content of anthraquinone (AQ) derivatives that have been applied as chromogenic sensors. Schonteten’s method was applied to the aloe vera extract to produce a green emission, confirming the presence of anthraquinone adducts. An anthraquinone probe was immobilized into a nanocomposite of alginate hydrogel, cellulose nanowhiskers (CNW), and urease enzyme to produce a colorimetric sensory film. The developed nanocomposite is a disposable biosensor that uses anthraquinone as a molecular probe, urease as a catalyst, and CNW as a high surface area transporter. A mordant was applied to fix AQ onto CNW by forming nanoparticles (10–28 nm) of an AQ/Al complex. CNW showed crystal lengths of 45–95 nm and crystal diameters of 9–25 nm. Under acid/base conditions, an aqueous solution of anthraquinone displayed a reversible colorimetric shift, as indicated by the absorbance spectra. Upon immersion in an aqueous solution of urea, the biosensor film displayed a colorimetric switch from white (399 nm) to yellow (479 nm). The detection limit of urea was monitored in the range of 5-300 ppm. Diverse analytical methods were employed to examine the morphological features of CNW and AQ@CNW films.