A highly sensitive and selective rhodamine-semicarbazide based fluorescent sensor for Cu²⁺ detection in real water...

A colorimetric and fluorescent sensor, selective for Cu²⁺ ions, was synthesized in two steps using a rhodamine-based compound attached to the semicarbazide-picolylamine moiety (RBP). Spectroscopic measurements, including UV-Vis absorption and fluorescence emission, were conducted in the semi-aqueous medium containing acetonitrile/4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, denoted as MeCN/HEPES buffer (2:8, v/v, pH 7.0). The sensor exhibited high selectivity towards Cu²⁺ ions compared to other cations and demonstrated remarkable sensitivity towards Cu²⁺ ions, with a limit of detection at the nanomolar level. The calculated transitions indicated a 1:1 stoichiometric binding of RBP to Cu²⁺ ions based on a 4-coordination mode involving additional chelation in the semi-aqueous medium. The sensing mechanism for the detection of Cu²⁺ ions was investigated using high-resolution mass spectroscopy. The sensor could be employed as a real-time chemosensor for monitoring Cu²⁺ ions. Furthermore, the sensor has the potential for utilization in the detection of Cu²⁺ ions in actual water samples with the high precision and accuracy, as indicated by the small relative standard derivation values. The 50^th percentile cytotoxicity concentration of RBP was found to be 22.92 μM. Additionally, the fluorescence bioimaging capability of RBP was demonstrated for the detection of Cu²⁺ ions in human hepatocellular carcinoma (HepG2) cells.