Preparation of green and sustainable colorimetric cotton assay using natural anthocyanins for sweat sensing

Herein, we develop a novel smart cotton swab as a diagnostic assay for onsite monitoring of sweat pH changes toward potential applications in monitoring human healthcare and drug exam. Anthocyanin (Ac) can be extracted from Brassica oleracea var. capitata f. rubra using a simple procedure. Then, it can be used as a direct dye into cotton fibers using potash alum as mordant (M) to fix the anthocyanin dye onto the surface of the cotton fabric (Cot). This was monitored by generating mordant/anthocyanin nanoparticles (MAcNPs) onto the fabric surface. The cotton sensor assay demonstrated colorimetric changes in the ultraviolet-visible absorbance spectral analysis associated with a blueshift from 588 to 422 nm with increasing the pH of a perspiration simulant fluid. The biochromic performance of the dyed cotton diagnostic assay depended essentially on the halochromic activity of the anthocyanin spectroscopic probe to demonstrate a color change from pink to green due to intramolecular charge transfer occurring on the anthocyanin chromophore. After dyeing, no significant defects were detected in air-permeability and bend length. High colorfastness was investigated for the dyed cotton fabrics.