A visible multi-response electrochemical sensor based on cellulose nanocrystals

Cellulose nanocrystals (CNCs), a renewable material extracted from plants, algae, and bacteria, form iridescent films with chiral nematic order. Here, we report stimuli-responsive CNC / polyaniline (PANI) composite films for use in optical and electrochemical sensing. CNC-PANI and CNC-glucose-PANI films with bright structural color were obtained by an optimized self-assembly process. The films responded to humidity, pH and organic solvents with a change in the reflection wavelength, change in visible structural color, and changes in conductivity. A two-layer, conductive CNC-PANI film was prepared and incorporated into a circuit, where it could respond to stimuli with a change in color and increased conductivity. Moreover, a PANI electrochromic device (ECD) with CNC films was fabricated for information encryption. With voltages up to 1.5 V, the color of the ECD changed from green to blue within 1 s, and the CNC pattern hidden inside appeared with good cyclability. The ECD can also be used for anti-counterfeiting due to the chiral nematic CNC pattern. This novel iridescent CNC-PANI film demonstrates the potential of visible electrochemical multi-sensing using natural, sustainable materials.