A Pyridyl-Benzimidazole Based Ruthenium(II) Complex as Optical Sensor: Targeted Cyanide Detection and Live Cell Imaging Applications

TL;DR

This study introduces a ruthenium(II) complex that acts as a highly selective, sensitive, and practical optical sensor for cyanide detection in water, cells, and food, with potential environmental and biomedical applications.

Contribution

The paper reports a novel Ru(II) complex with high selectivity and sensitivity for cyanide detection, including its application in live cell imaging and on paper strips for visual detection.

Findings

Detected cyanide with a limit of 12.8 nM in water.

Successfully applied the sensor for live cell imaging of cyanide.

Developed paper strips for naked-eye cyanide detection under UV light.

Abstract

The extreme toxicity of cyanide (\ce{CN^-}) ions in diverse environmental media has garnered significant attention toward the design of well-organized molecular probes for their selective and sensitive detection. In this context, we present a monometallic Ru(II) complex (Ru-1), based on the 2-(pyridin-2-yl)-1H-benzo[d]imidazole moiety, acting as a highly selective luminescent probe for \ce{CN^-} recognition in pure water. Additionally, Ru-1 also functions as an efficient sensor for \ce{F^-}, \ce{AcO^-}, and \ce{H2PO4^-} ions, along with \ce{CN^-}, when acetonitrile is used as the solvent system. The binding constant ($K_b$) and detection limit (LoD) for \ce{CN^-} were determined to be $3.05 \times 10^6$~M$^{-1}$ and 12.8~nM, respectively, in water. The close proximity of the N--H site to the Ru(II) center, along with its notable acidity, were identified as the primary factors responsible for the high selectivity of Ru-1 toward \ce{CN^-} in aqueous media. Job's plots and density functional theory (DFT) analyses were conducted to support the anion binding mechanism. Furthermore, time-resolved fluorescence (TRF) spectroscopy was employed to evaluate the \ce{CN^-}-induced emission lifetime change of Ru-1 in water. To explore practical applicability, the Ru-1 probe was developed into paper-based strips capable of detecting \ce{CN^-} ions in the millimolar range via the naked eye under 365~nm UV illumination. It was also effectively applied for the detection of \ce{CN^-} in human breast cancer MCF-7 cell lines and natural food sources, such as apple seeds and sprouting potatoes.