Nanostructured zinc-coordination supraparticles on cellulose fibers: A 3D-Printed μ-FAD integrated smartphone platform for multiplexed salivary metabolic monitoring

Existing multiplexed salivary diagnostics struggle to achieve a delicate balance between high sensitivity, low cost, and portability. This balance is essential for practical at-home diabetes monitoring. To address this challenge, we developed an integrated smartphone-based 3D paper sensor for multiplexed salivary metabolic monitoring featuring in situ-formed supraparticle zinc-coordination assemblies (SP-ZnCA) on wax-printed microzones. This design combines ratiometric fluorescence-using a DABSA probe with large Stokes shift and a multi-enzyme cascade (glucose oxidase, uricase, and cholesterol oxidase-horseradish peroxidase) for simultaneous quantification of salivary glucose, uric acid, and cholesterol with ultra-low detection limits (0.83-1.67 μM). We developed a custom modular micro fluorescence analysis device (μ-FAD) equipped with a 254 nm UV-LED, a 3D-printed dark chamber, and smartphone-based imaging. Through an optimized coaxial optical pathway, the μ-FAD enables rapid on-site testing within 8 min. Remarkably, the system reduces equipment costs to just 1/200 of those of conventional fluorometers. Clinical validation using 18 human saliva samples demonstrated high accuracy (R² > 0.97) relative to ELISA, at a mere $0.05 per test. By harmonizing material innovation, enzymatic signal amplification, and accessible diagnostics, our work successfully resolves the sensitivity-cost-portability trade-off and offers a scalable, affordable platform for decentralized diabetes management.