Novel halochromic cellulose nanowhiskers from rice straw: Visual detection of urea

•Facile development of chromogenic biosensor for determination of urea.•Cellulose nanowhiskers were loaded with a spectroscopic probe and urease enzyme.•Detection limit was in the concentration range 50−1100 ppm.•Response time of about 5–10 min.•Color shift from light yellow to pink was monitored upon detection of urea. Colorimetric nanocomposite film sensor was fabricated by incorporating TCFH spectroscopic probe into cellulose nanowhiskers (CNW)/Urease enzyme matrix. CNW-TCFH can be used as disposable molecular biosensor in which CNW is the probe carrier comprising high surface area-to-volume ratio, urease is the catalyst and TCFH is the molecular probe. Tricyanofuran-hydrazone (TCFH) spectroscopic probe was prepared. UV–vis absorption spectra demonstrated solvatochromic behavior and a reversible color change of the tricyanofuran-hydrazone probe solution in acetone under acid/base conditions. CNW were reinforced with sodium alginate biopolymer to introduce biocomposite film. This CNW-TCFH film biosensor responds through visible color shift from light yellow to pink when exposed to urea in aqueous media. The morphology properties of CNW and CNW-TCFH films were examined by different tools. The photophysical properties of the prepared TCFH probe, including solvatochromism and pH sensory, were also studied.