A High-affinity Near-infrared Fluorescent Probe for Interference-resistant Cu²⁺ Determination in Real Samples and Living Plant Imaging.

Copper ions (Cu²⁺) play important roles in crop growth and agricultural production, but excessive Cu²⁺ accumulation in crops and their growth environments may pose risks to crop quality, food safety, and human health. In view of increasing copper contamination in agricultural environments, developing rapid, sensitive, and reliable methods for Cu²⁺ determination in real agricultural matrices is highly desirable. In this work, a high-affinity near-infrared (NIR) fluorescent probe, DCI-Cu, was successfully developed for interference-resistant Cu²⁺ determination. The probe exhibited NIR emission at 670 nm, a large Stokes shift of approximately 200 nm, broad pH tolerance, favorable photostability, high selectivity, and strong anti-interference capability toward common coexisting species, especially sulfur-containing species, biological thiols, and ethylenediaminetetraacetic acid (EDTA). Benefiting from these properties, DCI-Cu enabled ultrafast and sensitive Cu²⁺ detection with a fluorescence "turn-off" response within 3 s and a low detection limit of 136 nM. Mechanistic studies supported a 1:1 binding model between DCI-Cu and Cu²⁺, and the high coordination constant of 8.42 × 10⁷ M⁻¹ was associated with a proposed six-coordinate coordination model. DCI-Cu was successfully applied to accurate quantitative detection of Cu²⁺ in real water, soil, and crop samples, with satisfactory recoveries of 96.5%-105.5% and low RSDs of 1.43%-2.51%. Moreover, DCI-Cu was successfully used for in situ fluorescence imaging of Cu²⁺-related changes in living triticale leaves. Consequently, DCI-Cu provides a promising NIR fluorescence tool for rapid, sensitive, and interference-resistant Cu²⁺ analysis in crop-associated environmental and plant matrices.