Distance-based ratio metric assay using thread-based devices for Karaya gum detection in food samples

Karaya gum, a natural food-grade thickener, is an adulterant that compromises product quality and consumer safety. Herein, we develop a low-cost, rapid and portable device that employs thread-based microfluidics integrated with ratio-metric displacement to detect and quantify Karaya gum, with a limit of detection of 0.1%w/v. The interaction between the cellulose in the bamboo viscose thread and the chlor-zinc-iodide reagent causes the thread to turn blue immediately. On addition of simulated Karaya gum samples, a brown region appears beyond the blue region due to hydrogen bond formation between the hydroxyl groups of the thread and the complex sugars in the gum, thereby causing the displacement of iodine, which was confirmed by FTIR analysis. Higher gum concentrations increase viscosity and result in less displacement of iodine, with the blue-to-brown colorimetric ratio being directly proportional to the gum concentration. These observations were confirmed by measuring the viscosity of the Karaya gum and correlating it with the structure and nature of the gum. Furthermore, the variation in the iodine release was quantified using grayscale values utilizing Fiji software. The device was implemented for field trial using commercial basil drink. This approach offers an efficient alternative to conventional cumbersome detection strategies and has enormous potential for onsite food safety and quality control.