Intrinsically coupled colorimetric–fluorescence dual-mode lateral flow immunoassay for procalcitonin via AuNP–AuNC proximity quenching

Intrinsically coupled dual-mode LFIA: color rise as fluorescence quenches. • Reciprocal signals enables built-in self-verification and internal calibration. • ATT–Arg Au nanoclusters provide bright, stable green emission (QY 65.8%). • LODs: 0.079 ng mL −1 (color) and 0.006 ng mL −1 (fluorescence) for PCT. Procalcitonin (PCT) is a clinically important biomarker for bacterial infections and sepsis, motivating rapid and sensitive point-of-care quantification. Herein, a colorimetric–fluorescence dual-mode lateral flow immunoassay (LFIA) was developed by integrating gold nanoparticles (AuNPs) and arginine/6-Aza-2-thiothymine-stabilized gold nanoclusters (ATT-Arg-AuNCs). AuNPs conjugated with detection antibodies served as colorimetric reporters, while AuNCs associated with capture antibodies formed an immobilized fluorescent donor layer on the test line. Upon PCT-mediated sandwich assembly, AuNP enrichment intensified the colorimetric band and simultaneously imposed nanoscale AuNP–AuNC co-localization, activating metal-induced nonradiative dissipation and proximity-regulated fluorescence quenching (intrinsically coupled “color-on/fluorescence-off” transduction). Under optimized conditions, the colorimetric mode (T/C) exhibited a linear response over 0.5–10 ng mL −1 with a limit of detection (LOD) of 0.079 ng mL −1 , whereas the fluorescence mode (ΔF) provided a wider linear range of 0.05–10 ng mL −1 with a lower LOD of 0.006 ng mL −1 . In spiked serum samples ( n  = 3), recoveries were 95.1%–105.1% (colorimetric) and 92.3%–116.4% (fluorescence), with relative standard deviations <10%, demonstrating acceptable accuracy and precision in complex matrices. This intrinsically coupled dual-mode LFIA combines visual screening with sensitive quantification in a single strip and offers a generalizable strategy for extending proximity-gated dual-readout LFIAs to other biomarkers via antibody substitution. Download: Download high-res image (210KB) Download: Download full-size image Graphical abstract of the dual-mode colorimetric–fluorescence lateral flow immunoassay for procalcitonin (PCT) detection.