Topology-guided magneto-fluorescent nanoprobes with core-confined AuAg nanocluster emitters and surface-anchored Fe3O4 nanodots for matrix-tolerant lateral flow immunoassays.

Magneto-fluorescent nanoprobes are attractive labels for lateral flow immunoassays (LFIAs) because they integrate magnetic enrichment with fluorescence-based signal amplification. However, conventional magnetic-core/fluorescent-shell nanoprobes often suffer from a structure-dependent optical-magnetic trade-off: internally embedded Fe3O4 domains show limited magnetic-field accessibility, whereas increasing magnetic loading can cause magnetic-component-induced optical attenuation and compromise fluorescence readout. To address this limitation, we developed a topology-guided magneto-fluorescent nanoprobe, DMSN@AuAgNCs@SiO2@Fe3O4 (DASF), featuring core-confined AuAg nanocluster emitters and surface-anchored Fe3O4 nanodots. The confined AuAg nanoclusters provided high emitter loading and AIE-like confinement-enhanced fluorescence, whereas the surface-anchored Fe3O4 nanodots improved magnetic field accessibility while limiting Fe3O4-induced optical attenuation. DASF retained 94.1% of its fluorescence output after Fe3O4 anchoring and achieved complete magnetic enrichment within 3 min under optimized Fe3O4 loading. A location-swapped control, DMSN@Fe3O4@SiO2@AuAgNCs (DFSA), was constructed to validate the structural rationale. Compared with DFSA, DASF exhibited stronger fluorescence output, higher effective magnetic responsiveness, improved component-normalized optical/magnetic performance, and enhanced LFIA signal generation. Using C-reactive protein as a model biomarker, DASF-LFIA improved detection sensitivity through magnetic enrichment of target-bound probes and reduced serum matrix interference through magnetic separation. The assay achieved limits of detection of 0.19 μg mL-1 using a portable fluorescence analyser and 0.47 μg mL-1 using smartphone-assisted readout. Clinical serum analysis showed good agreement with immunoturbidimetry, with Pearson's correlation coefficients of 0.994 and 0.980, respectively. This work establishes a topology-guided probe design for balancing fluorescence output and magnetic enrichment in matrix-tolerant LFIA biosensing.