Sulfide-Induced Concentration-Dependent Distinct Optical Response: Unique Chromogenic Probe Developed for Analyzing Fecal Contamination in Water and Intracellular Imaging Applications
Rikitha S. Fernandes, Sanjay Ch, Balaram Ghosh, Nilanjan Dey
Abstract
Herein, we report the design and synthesis of a red luminescent ruthenium (Ru) complex with imidazophenanthroline as the chelating ligand. The metal complex showed a unique concentration-dependent distinct optical response in the presence of the target analyte, Na 2 S. At the lower concentration (micromolar range), the addition of Na 2 S resulted in the decrease of absorption maximum with a diminution of luminescence intensity. On the contrary, a bathochromic shift in the UV–visible spectrum with a turn-on luminescence response was noticed upon the addition of excess Na 2 S (millimolar range). The detailed mechanistic investigation indicated the formation of a hydrogen-bonded complex with sulfide (HS̅) ions at lower concentrations involving imidazole nitrogen ends. On the other hand, excess Na 2 S led to the reduction of nitro to amino group, which facilitated the extent of intramolecular charge transfer. Furthermore, we used the Ru(II) complex for analyzing H 2 S in toilet water samples, as it is the indicator of fecal contamination. Also, it was observed that chemically modified paper strips could detect H 2 S in contaminated water samples without involving any sophisticated instruments (sustainable approach). Finally, the imaging of H 2 S inside living breast cancer cells (MCF-7) was achieved under various stimulated conditions. Moreover, H 2 S-induced, concentration-dependent alternation in the luminescence signal was also noticed under intracellular conditions.