Smart microfibrillated cellulose as swab sponge-like aerogel for real-time colorimetric naked-eye sweat monitoring

Collecting sweat sample for onsite testing is a sophisticated process as the analysis process must be completed in a real-time with a highly absorptive and sensitive device in order to gain a useful assessment of its content. Thus, we developed a chemical probe incorporated into microfibrillated cellulose to introduce a novel, simple, robust and flexible aerogel. This chromogenic sponge-like aerogel assay demonstrated a color change from yellow to orange, red and blue depending on the sweat biochemical changes. Novel pH sensitive tricyanofuran hydrazone probe was prepared, characterized and encapsulated in-situ within microfibrillated cellulose to follow up sweat pH changes. The solvatochromic performance in several solvents of different polarities and the reversible pH correlated color change of this tricyanofuran hydrazone probe in an acetonitrile solution was explored by UV-Vis absorption spectra. The microporous and microfibrillated sponge-like cellulose substrate was fabricated by activation of wood pulp using phosphoric acid followed by freeze-drying process. Morphological characterization, thermal stability and fiber crystallinity of the prepared aerogel were explored using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The visual color change was explored by studying the CIE LAB color space coordinates and color strength values. The cytotoxicity of the sponge-like aerogel sensor was also evaluated.