Hybrid paper–fabric sandwich structure-based micro-analytical device for detection of iodine

This study presents a novel method for manufacturing microfluidic paper–fabric hybrid analytical devices (μPFADs), which play a vital role in conducting diagnostic tests at the point of care (POC), especially in resource-limited environments. By circumventing the need for complex machinery or highly skilled operators, our method presents a practical solution for scaling up these POC devices. The approach involves the utilization of a folded paper structure featuring a specific pattern like a circular well or liner microchannel on either side of the fold as a mirror image, followed by inserting a piece of fabric in between the paper fold, thereby creating a sandwich-like structure. Subsequently, a PDMS (polydimethylsiloxane) elastomer with base and curing agents in a 10:1 ratio would be coated over the entire top paper and allowed to settle, enabling the penetration of PDMS down to the bottom paper through the sandwiched fabric. When sufficient PDMS penetration is achieved through visual changes on the back side of the paper, the sandwiched assembly is heated for polymerization of the PDMS. An embedded fabric-based POC device is obtained within the paper whose structure is defined by the designs on the folded paper itself. This micro paper–fabric hybrid analytical device (μPFAD) offers several noteworthy advantages as it boasts rapid fabrication times and is cost-effective, without the need for any printing machines, thereby further enhancing its suitability for no- or low-resource environments. Experimental studies with these μPFADs were conducted for the colorimetric detection of iodine, whose deficiency is a leading cause of thyroid disorders, particularly hypothyroidism. Here, starch acts as the chromogenic agent, which forms a blue-colored complex that shifts the color from purple to deep blue–black with increasing iodine concentration. The initial experimental results reveal contrasting color changes for varying levels of iodine using the proposed μPFADs, which would be useful for the early diagnosis and management of thyroid disorders