Synergistic dual-strategy immunoassays using carbon dots@MOF enable ultrasensitive procalcitonin stratification

Highly sensitive point-of-care testing (POCT) with an extended dynamic range is critical for accurate serum procalcitonin (PCT) quantification in grading diagnosis. However, conventional single-fluorescence POCT assays face inherent limitations in balancing trace-level sensitivity with broad detection spans. Herein, we demonstrate a dual-strategy POCT system based on the synergistic integration of homogeneous immunoassay and lateral flow immunoassay. Via rational design of blue/near-infrared carbon dots@metal-organic framework (CDs@MOF) functional probes (Tris-CDs@ZIF-8/NIR-CDs@ZIF-8), ultrasensitive detection of PCT with an ultra-wide dynamic range spanning from pg to ng levels was achieved, facilitating stratified diagnosis. Under the confinement effect of MOF, both Tris-CDs and NIR-CDs exhibited enhanced fluorescence intensity and stability. In the homogeneous immunoassay, leveraging fluorescence resonance energy transfer and signal amplification, Tris-CDs@ZIF-8 (donor) and NIR-CDs@ZIF-8 (acceptor) enabled direct detection of PCT in raw serum ranging from 0 to 100 ng/mL with a limit of detection (LOD) of 0.2 ng/mL, which is well-suited for rapid screening at ≥10 ng/mL. In the lateral flow immunoassay, a portable UV analyzer equipped with highly fluorescent Tris-CDs@ZIF-8 probes achieved semi-quantitative visualization (threshold: 0.01 ng/mL) and quantitative detection (LOD: 0.001 ng/mL) of PCT, enabling precise stratification at ≤10 ng/mL concentrations. The dual-strategy synergistic system significantly overcomes the performance limitations of conventional single-fluorescence POCT assays, providing a novel approach for the immediate graded detection of disease markers.