Highly Selective Dual-Modal Probe for Photoacoustic and Magnetic Resonance Imaging of the Labile Cu²⁺ Pool in the Liver

Copper ions (Cu2+) play vital roles in human physiology, and their dyshomeostasis is associated with diseases such as hepatocellular carcinoma, Alzheimer's disease, and Wilson's disease. Cu2+ imaging technologies facilitate the investigation of Cu2+ dynamics in biological systems. However, developing highly selective and sensitive Cu2+ probes that can overcome interference from physiologically abundant Zn2+ remains a key challenge. In this study, we design and synthesize a Cu2+-activated dual-modal probe (BHGd) for photoacoustic (PA) and magnetic resonance (MR) imaging, which exhibits remarkable specificity for Cu2+. Impressively, BHGd demonstrates exceptional selectivity for Cu2+ even in the presence of a 1000-fold excess of Zn2+. BHGd binds Cu2+ in a 1:1 stoichiometry, forming a stable ternary complex in the presence of human serum albumin (HSA), which enhances PA signals by 5.9-fold and increases longitudinal relaxivity (r1) by 114.9%. Furthermore, in vivo experiments demonstrate that BHGd enables precise monitoring of labile Cu2+ fluctuations in the liver of mice, achieving a remarkable 59% increase in PA signal intensity and a 30% enhancement in MR signal contrast. The systematic investigation demonstrates that BHGd can serve as a powerful molecular probe for investigating copper metabolism in living systems. Our breakthrough addresses the long-standing challenge of Cu2+/Zn2+ discrimination and provides a design principle for next-generation metal ion probes, with significant potential for diagnosing Cu2+ imbalance-related disorders, monitoring therapeutic responses, and advancing biomedical research.