Dual-chromic cellulose paper modified with nanocapsules containing leuco dye and spiropyran derivatives: A colorimetric portable chemosensor for detection of some heavy metal cations

Heavy metal cations are important in our daily life and may cause serious disorders and diseases. Colorimetric portable cellulosic sensors with high selectivity and sensitivity toward metal cations are preferred relative to those based on small molecules which operate mostly in organic media and difficult test methods. Here, dual-chromic stimuli-responsive cellulose paper (TPL@T-Cell) was produced by modification of the paper with the designed and prepared epoxy-functionalized polyacrylic nanocapsules via dip-coating and subsequent heat treatment processes. The capsules contained thermochromic leuco-dye derivative and photochromic hydroxyl-functionalized spiropyran and were prepared through semi-continuous miniemulsion polymerization. Chemical structure of the synthesized dyes, nanocapsules and modified cellulose fibers were identified by FTIR and UV-Vis analyses. Spherical morphology of the prepared nanocapsules with average particles size of 121 nm were observed by SEM and DLS analyses. The effective wetting of the cellulose fibers by nanocapsules with proper diffusion and deposition through the establishment of physical and chemical interactions were evaluated by SEM and ATR-FTIR analyses, respectively. The prepared TPL@T-Cell sensor revealed distinct color changes toward Fe2+, Pb2+ and Sn2+ ions. Opto-chemical results indicated that detection limit of TPL@T-Cell for Sn2+ (0.0028 µM, 0.326 ppb), Fe2+ (0.0013 µM, 0.15 ppb), and Pb2+ (0.0023 µM, 0.268 ppb) are lower than their critical permitted levels announced by WHO. These exhibited applicability of TPL@T-Cell sensor for determining trace amount of some heavy metal ions with instant responsivity, wide linear detection range, high sensitivity, and low detection limit via colorimetric and spectroscopic responses.