One-pot pyrene-functionalized UiO-66-NH₂ enables pH-Gated speciation of serum copper: Exchangeable versus total...

Metal ion dysregulation, particularly involving copper, has been implicated in neuropsychiatric disorders including depression. Herein, we report a pyrene-functionalized UiO-66 platform (UiO-66-NH-PCA) prepared by a facile one-pot solvothermal strategy that avoids complicated pyrene-ligand presynthesis and tedious post-synthetic modification. Spectroscopic analyses supported amidation-consistent chemical anchoring of the pyrene unit onto UiO-66-NH₂, affording a fluorescent MOF that retained its framework integrity under acidic conditions. UiO-66-NH-PCA acted as a turn-off fluorescence probe for Cu²⁺, and control experiments further indicated that the Cu²⁺ response depended on the immobilized interfacial state of PCA on the MOF rather than on free PCA or simple physical mixing. By leveraging pH-dependent copper accessibility, the platform enabled pH-gated serum copper speciation, allowing determination of probe-accessible exchangeable copper (Cu_ex) at neutral pH and total copper (Cu_total), including both exchangeable and protein-bound fractions released under acidic conditions (pH 2). The detection limits were 0.48 nM at pH 7 and 0.55 nM at pH 2. Application to serum from chronic unpredictable mild stress (CUMS) rats revealed an elevated Cu_ex/Cu_total ratio, which decreased markedly after paroxetine treatment. The analytical results were in good agreement with inductively coupled plasma-mass spectrometry (ICP-MS). Collectively, this work establishes a sensitive fluorescence platform for pH-gated copper speciation in complex biofluids and provides a useful analytical tool for studying depression-related copper homeostasis.