Stacking paper sheets into multi-purpose quick response sensing code with built-in nitrocellulose-membrane-free lateral flow assay for detecting tetracycline in food samples.

Lateral flow assays (LFAs) have found extensive applications in food safety and quality monitoring. Now, smartphone technology is redefining how tests are conducted at the point of use. At the same time, quick response (QR) codes enhance digital connectivity for information transmission, data collection, and response linkage. Here, we present a versatile QR code conversion strategy for LFAs that streamlines detection and response workflows, ensuring high user-friendliness and minimal operational requirements for on-site food safety detection. It combines visual cues from test and control zones with QR code generation into a multifunctional smartphone-based scanning and detection system. The proposed QR-coded LFA utilizes low-cost filter paper instead of nitrocellulose membrane and exhibits its applicability and flexibility in sandwich/competitive/multiplexed formats and various scenarios. As a demonstration, the QR-coded LFA, coupled with a companion mobile application, was applied to simultaneously determine tetracycline in food samples and perform the QR code functions.