Synthesis and In Situ Application of a New Fluorescent Probe for Visual Detection of Copper(II) in Plant Roots

A new rhodamine-based fluorescent probe (RDC, rhodamine-based derivative) was rationally designed and synthesized for the highly selective, sensitive, and quantitative detection of Cu²⁺. The probe demonstrated outstanding specificity toward Cu²⁺, even in the presence of competing metal ions (e.g., Al³⁺, Fe³⁺, Cr³⁺, Na⁺, and K⁺), exhibiting negligible interference and confirming its robust anti-interference capability. A spectroscopic analysis revealed that Cu²⁺ induced spirocyclic ring cleavage, resulting in a colorless-to-pink colorimetric transition and enhancement of the yellow-green fluorescence at 590 nm. Upon addition of Cu²⁺, the fluorescence spectrum showed a linear response in the concentration range of 0.4-20 μM, with a correlation coefficient (R²) of 0.9907 and the limit of detection (LOD) calculated to be 0.12 μM. Meanwhile, Job's plot analysis verified that the binding stoichiometry between RDC and Cu²⁺ was 1:1. The probe exhibits rapid response kinetics (<5 min) and non-destructiveness properties, enabling in vivo imaging. Under stress conditions, Cu²⁺ accumulated predominantly in root tips (its primary target tissue), with the following distribution hierarchy: root tips > maturation zone epidermis > xylem vessels > cortical cell walls. In conclusion, RDC is a well-characterized, high-performance tool with high accuracy, excellent selectivity, and superior sensitivity for plant Cu²⁺ studies, and this work opens new technical avenues for rhodamine-based probes in plant physiology, environmental toxicity monitoring, and rational design of phytoremediation strategies.