Development of colorimetric cotton swab using molecular switching hydrazone probe in calcium alginate

Abstract

Smart cotton fabric was developed to function as a swab for sweat pH monitoring in real-time toward a potential application for drug testing and monitoring human healthcare. A wearable, flexible and disposable microencapsulated chemical barcode was incorporated onto the highly absorptive cotton fabric to monitor sweat biochemical variations. A pH-responsive tricyanofuran hydrazone molecular switch encapsulated inside calcium alginate (Ca-alginate) microcapsule was loaded onto a cotton fabric matrix to keep an eye on sweat pH variations. Calcium alginate sensor microcapsules were prepared using tricyanofuran-hydrazone receptor sites as the core material and cross-linked calcium alginate biopolymer as the wall-former. The cotton fabric was dyed in-situ with a microencapsulated tricyanofuran-hydrazone in calcium alginate using the pad-dry-cure technique at room temperature. The chromogenic activity of the cotton detection tool depended mainly on the halochromic performance of the tricyanofuran hydrazone spectroscopic probe, which demonstrated color shift from light yellow to darker yellow, orange and purple due to protonation/deprotonation reversible mechanism of the tricyanofuran hydrazone chromophore. The visible color shift was monitored by CIELAB coordinates. The surface morphology, distribution and composition of fabrics were explored employing scanning electron microscopic (SEM) images, energy dispersive X-ray (EDX) spectra, and mapping analytical techniques. Microencapsulated tricyanofuran-hydrazone sensor probe on fabrics was characterized in terms of their air-permeability, stiffness and colorfastness.