A transferrin-responsive fluorescent probe based on Zn-doped carbon dots for selective Fe³⁺ detection in serum

The detection of Fe³⁺ and Cu²⁺ in biological fluids is crucial for clinical diagnostics, yet remains challenging due to severe matrix interference in complex environments like serum. Current methods often lack real-time capability and struggle with selectivity, while fluorescent probes are frequently compromised by unpredictable biomolecular interactions. There is a pressing need for robust sensors that can overcome these physiological barriers. This study addresses this gap by developing a dual-functional probe designed to maintain reliable performance within biological systems, enabling accurate metal ion quantification.

In this work, zinc-doped plant-derived carbon dots (Zn-PECDs) were synthesized via a one-pot solvothermal method using plant extract as a green carbon source. The Zn-PECDs functioned as a dual-responsive fluorescent probe, exhibiting: (1) A unique dual-mode response in aqueous solution-selective "turn-on" fluorescence enhancement toward Cu²⁺ and "turn-off" quenching toward Fe³⁺; (2) A transformed response in serum, where Cu²⁺ detection was hindered by precipitation, while Fe³⁺ induced a distinct "turn-on" signal due to the formation of a stable Zn-PECDs@transferrin (Tf) complex; (3) Shielding by serum Tf that prevented direct electron transfer-mediated quenching, enabling selective Fe³⁺ detection in 50-fold diluted human serum with a linear range of 1-90 μM and a detection limit of 1.5 μM. The probe demonstrated excellent reproducibility and biocompatibility, underscoring its potential in complex biological matrices.

This study presents Zn-PECDs as a robust dual-functional probe for monitoring Cu²⁺ and Fe³⁺, addressing key challenges in physiological metal ion detection. The discovery of a protein-mediated shielding mechanism offers novel insights into the design of bio-compatible nanosensors and enhances the capability for accurate metal ion quantification in clinical diagnostics. This approach paves the way for advanced sensor platforms that can operate reliably in complex biological environments.