Nanoclusters prepared from ruthenium(II) and quercetin for fluorometric detection of cobalt(II), and a method for screening their anticancer drug activity.

Ruthenium-quercetin conjugated nanoclusters (Ru-QC NCs) were synthesized via a one-pot reflux reaction. As inhalation of heavy metal ions like cobalt can lead to lung cancer, a fluorescent probe was designed for the determination of Co(II) both in aqueous solutions and living cells. The probe consists of hybrid nanoclusters with an average size of 2 nm that were prepared from ruthenium(II) ions and the flavonoid quercetin. These are termed as Ru-QC NCs. They display strong orange-colored emission with a peak at 558 nm under 465-nm excitation. The Ru-QC NCs are cell viable and enable imaging of cells and intracellular fluorometric detection of Co(II). The anticancer properties of Ru-QC NCs were screened by using non-small cell lung cancer (A549) and human dermal fibroblast (HDFa) cell lines. The Ru-QC NCs exert considerable cytotoxicity in A549 cells (at levels of 20-50 μg·mL-1), whereas no significant cytotoxicity was observed in case of HDFa cells. The anticancer properties of Ru-QC NCs were screened via MTT assay, live-dead staining, and ROS assay, respectively. Morphological changes of cancer cells were observed using atomic force microscopy. The fluorescent probe can detect Co(II) with a detection limit of 9.28 nM and with a linear response in the 0.03-100 μM concentration range. Graphical abstract Schematic representation of ruthenium-quercetin nanoclusters with potential anticancer properties. They are promising fluorescent probes for intracellular sensing of cobalt (Co2+) and bio-imaging. They exhibited efficient fluorometric detection of Co2+ with the limit of detection (LOD) of 9.28 nM.