Ruthenium(II) Complex-Based Luminescent Bifunctional Probe for Ag+ and Phosphate Ions: Ag+-Assisted Detection and Imaging of rRNA.

A new bis-heteroleptic Ru(II) complex (1) of benzimidazole-substituted 1,2,3-triazole pyridine ligand has been designed and constructed for the photoluminescent detection of cationic and anionic analytes, Ag+ and phosphate ions. Compound, 1[PF6]2 was fully characterized by various spectroscopic techniques and the solid-state structure was determined via single-crystal X-ray diffraction. The cation and anion sensing properties in 50% aqueous buffer (pH 9.2) and pure acetonitrile were carefully examined in photoluminescence (PL) spectroscopy. The 1[PF6]2 was found to be highly selective to pyrophosphate; PPi/HP2O73- and H2PO4- ions in CH3CN. It showed ∼10-fold PL intensity enhancement at 583 nm in the presence of only 1 and 2 equiv of PPi and H2PO4- ions, respectively. The PL titrations of 1[PF6]2 with PPi and H2PO4- in CH3CN furnished the association constant (Ka = 3.3 × 103 M-1 and 6.8 × 103 M-1) and the detection limit was as low as 5.73 and 5.19 ppb, respectively. The 1[PF6]2 also selectively detected Ag+ over other competitive cations through the luminescence light up in 50% aqueous buffer (pH 9.2) media. The PL titration of 1[PF6]2 with Ag+ showed ∼8-fold luminescence enhancement at 591 nm and yielded association constant, Ka = 3.5 × 104 M-1 and the detection limit was determined to be 5.05 ppb. A new cation sensing mechanism has been established where the Ag+ ion is detected in photoluminescence spectroscopy through the unique cyclometalated Ag+-triazolide complex formation. The high selectivity of 1[PF6]2 for phosphates and Ag+ was established by PL in the presence of various competing ions. Finally, for biological application, the cytotoxicity study was performed. The probe showed low cytotoxicity and was suitable for intracellular Ag+ imaging. The cell imaging and in vitro photoluminescence study revealed that the probe stained the cell nucleoli and specifically bind with ribosomal RNA (rRNA) and, therefore, it can also serve as a luminescent probe for rRNA in the presence of Ag+.