Cellulose nanofibers as effective mediator for optical chemical sensors for heavy metal ions detection

Two forms of nanocellulose-based sensing materials were developed for heavy metal ions (HMIs) detection: all-solid-state and suspension. In these materials, cellulose nanofibers (CNF), isolated from cellulose bleached pulp via homogenization, were employed as a support matrix. For all-solid-state optodes development free-base 5,10,15,20-tetraphenylporphyrin (TPP) and zinc-porphyrin derivative (ZnPC) were deposited on CNF support. Moreover, CNF suspension enriched with silver nanoparticles (AgNPs) bearing 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPP(SO3)4) was tested for HMIs assessment in solution. The solid-state platform enabled fast and low-cost optical detection of multiple HMIs in individual and multicomponent solutions; a smartphone digital camera was used for optical signal acquisition, while chemometric methods were employed for data analysis. Among tested HMIs, the highest attention was focused on Cd2+ and Pb2+ ions detection, for which the low detection limit (LDL) was estimated 0.0018 and 0.0033 mgL−1, respectively. These values are lower than the WHO provisional guideline values of 0.003 and 0.01 mgL−1 for natural waters. CNF suspension was characterized by SEM, IR and UV–vis spectroscopy, showing a successful loading of TPP(SO3)4 and incorporation of AgNPs into CNF. The effective assessment of HMIs in individual solutions through the naked eye detection, and by UV–vis tests demonstrate the potential of CNF-based sensing materials for environmental monitoring applications.