Dual channel chemosensor for successive detection of environmentally toxic Pd2+ and CN- ions and its application to cancer cell imaging

Abstract

Background: Detecting and neutralizing Pd²⁺ ions are a significant challenge due to their cytotoxicity, even at low concentrations. To address this issue, various chemosensors have been designed for advanced detection systems, offering simplicity and the potential to differentiate signals from different analytes. Nonetheless, these chemosensors often suffer from limited emission response and complex synthesis procedures. As a result, the tracking and quantification of residual palladium in biological systems and environments remain challenging tasks, with only a few chemosensing probes available for commercial use.

Results: In this paper, a straightforward approach for the selective detection of Pd²⁺ ions is proposed, which involves the design, synthesis, and utilization of a propargylated naphthalene-derived probe (E)-N'-((2-(prop-2-yn-1-yloxy)naphthalen-1-yl)methylene)benzohydrazide (NHP). The NHP probe exhibits sensitive dual-channel colorimetry and fluorescence Pd²⁺ detection over other tested metal ions. The detection process is performed through a catalytic depropargylation reaction, followed by an excited state intramolecular proton transfer (ESIPT) process, the detection limit is as low as 11.58 × 10^-7 M under mild conditions. Interestingly, the resultant chemodosimeter adduct (E)-N'-((2-hydroxynaphthalen-1-yl)methylene)benzohydrazide (NHH) was employed for the consecutive detection of CN^- ions, exhibiting an impressive detection limit of 31.79 × 10^-8 M. Validation of both detection processes was achieved through ¹H nuclear magnetic resonance and density functional theory calculations. For real-time applications of the NHP and NHH probes, smartphone-assisted detection, and intracellular detection of Pd²⁺ and CN^- ions within HeLa cells were studied.

Significance: This research presents a novel naphthalene derivative for visually detecting environmentally toxic Pd²⁺ and CN^- ions. The synthesized probe selectively binds to Pd²⁺, forming a chemodosimeter. It successfully detects CN^- ions through colorimetry and fluorimetry, offering a low detection limit and quick response. Notably, it's the first naphthalene-based small molecule to serve as a dual probe for toxic analytes - palladium and cyanide. Moreover, it effectively detects Pd²⁺ and CN^- intracellularly in cancer cells.

Keywords: Chemodosimeter; Colorimetric; Cyanide; ESIPT; Fluorimetric; Palladium.