Coumarin–lipoic acid conjugates on silver nanoparticle-supported nanopipettes for in situ dual-mode monitoring of intracellular Cu(II) and potential chemodynamic therapy applications

Abstract

Intracellular Cu(II) in the human body is essential to many physiological functions, and its disruption is connected to several diseases. Synthetic coumarin–lipoic acid (Cou-LA) conjugate-functionalized silver-nanoparticles decorated on nanopipettes (CSNs) were fabricated herein for the determination of intracellular Cu(II) via in situ dual Raman/fluorescence spectroscopy. The CSNs selectively sensed Cu(II) over other metal ions to induce enhanced Raman intensities and fluorescence quenching. The determination of Cu(II) in single HeLa cells was achieved in accordance with changes in the ratio of Raman intensities at 500 and 597 cm^-1 and fluorescence at 469 nm, which was ascribed to the capturing of Cu(II) by the CSNs. The Raman signals exhibited a good linear relationship with Cu(II) concentration from 10 to 75 μM with R² = 0.956. The calibration curve indicated a local Cu(II) concentration of ~42.6 ± 8.6 μM in a single HeLa cell after pretreatment with 100 μM Cu(II) for 1 h. Cou-LA exhibited negligible cytotoxicity in both normoxic and hypoxic HeLa cells. However, a significant reduction in cell viability occurred with the Cu(II)–Cou-LA complex. This cytotoxicity was attributed to the generation of reactive oxygen species via a Cu-catalyzed Fenton-like process in tumor microenvironments and was found to be applicable to chemodynamic therapy (CDT). The system fabricated in this study represents a novel strategy for intracellular dual-mode Cu(II) detection and CDT applications in cancer research.