Cellulose-derived cholesteric liquid crystal: Towards smart and sustainable colorimetric sensors

The omnipresence of cholesteric liquid crystals (ChLC) in living matter and its associated optical properties in close linkage to structural colors in nature has inspired present development of colorimetric sensors. The sensors perform a vital, dominate and irreplaceable role in a host of monitor applications across our daily lives. Therefore, the major assessment of current sensor quality mainly focused on the context of smartness in data readouts and sustainability issues. During the past few years, ChLC has drawn increasing attention due to its remarkable and perfect stimuli-responsive structure-color. The recent progress of the evolution for cellulose, chitin, or protein-based ChLC is reviewed based on their colors, bio-identities and sensor varieties. The mechanism underlying their unique structure-related optical phenomena and its implications in sensoric applications has been elucidated. Particularly, there has been tremendous attention towards cholesteric cellulose-derivatives and cellulose nanocrystals (CNC) due to their outstandingly unrivaled superior qualities, sustainable alternatives rather than conventional sensors for dynamic sensing practices. Hence, it is highly prospected the broad utilization of cholesteric cellulose as economically novel sensors with cost-optimality, visually tangible instant color readouts, fast turnaround time and reversibility at low-value energy.