Development of biochromic paper strips from cellulose nanocrystals and anthocyanin extract from pomegranate (Punica granatum L.) for colorimetric determination of urea

An anthocyanin (ACN) spectroscopic probe was extracted and immobilized into a matrix of cellulose nanocrystals (CNC)/urease enzyme to create a colorimetric nanocomposite film sensor. The ACN@CNC composite is a disposable molecular biosensor that uses urease as a catalyst, ACN as a molecular probe, and CNC as a probe carrier with a high surface area. The ACN spectroscopic probe was isolated from the pomegranate peel (Punica granatum L.). A mordant was applied to fix ACN onto CNC by forming nanoparticles (6–14 nm) of mordant/ACN (M/ACN) complexation. CNC showed diameters in the range of 11–21 nm, and crystal lengths of 55–130 nm. Under acid/base conditions, the ACN probe solution in distilled water exhibited a reversible color change, as shown by the UV–Vis absorption spectra. In order to create a biocomposite film, CNC were reinforced with a sodium alginate biopolymer. Upon exposure to urea in an aqueous solution, the ACN@CNC film biosensor changes color from purple (598 nm) to white (432 nm). The detection limit of urea was determined at 25–450 ppm. Various methods were utilized to investigate the morphological properties of CNC and ACN@CNC films.