Bioinspired structural color sensors based on self-assembled cellulose nanocrystal/citric acid to distinguish organic solvents

Cellulose nanocrystals (CNCs) have gained much interest due to their unique optical properties and environmental friendliness. Many beetles, butterflies, and birds have spectacularly unique structural colors in the natural world. The most straightforward sensor signal is a rapid and immediately recognizable color shift. Inspired by this, solvent test films based on self-assembled CNC structures are designed to detect and distinguish different organic solvents. The citric acid (CA) is added to tune the helical pitch of the composite films. When added as stimuli, CA acts as a plasticizer, and the resulting films are mechanically durable. CNC/CA nanocomposite films can serve as discrimination sensors by showing an apparent color change when dipped in organic solvents due to different solubility and the magnifying effect caused by increasing CA concentration. The testing films were optically characterized with Polarized Light Microscopy (POM) and a UV-Visible Spectrophotometer. The demand for a solvent-responsive sensor was met by the structural color change in CNC/CA nanocomposite films. CNC/CA nanocomposite films provide a simple but effective foundation for developing green and inexpensive test sheets for organic solvent detection.