A Selective, Nontoxic, OFF–ON Fluorescent Molecular Sensor Based on 8‐Hydroxyquinoline for Probing Cd²⁺ in Living Cells

Abstract

In spite of the fact that cadmium(II) has been recognized as a highly toxic element and that excessive exposure to this metal ion has been reported to have many adverse effects on human health, very few selective and specific fluorescent probes are available for imaging Cd(2+) in living cells. Herein, we report the spectroscopic and photochemical characterization of 5-(5-chloro-8-hydroxyquinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a fluorescent sensor for the selective imaging of Cd(2+) in living cells. In particular, the response of L to Cd(2+) was first assessed in aqueous solutions, sodium dodecyl sulfate micelles, and liposomes, and subsequently in living cells by fluorescence microscopy techniques. Cytofluorimetric analyses of leukemic HL-60 cells loaded with L also allowed evaluation of the toxicity of the probe and the selective analysis of its intracellular fluorescence in the presence of Cd(2+). Furthermore, the 1:1 complex species [Cd(L)H(2)O](2+) responsible for the OFF-ON chelation enhancement of fluorescence (CHEF) effect on L was structurally characterized; time-dependent DFT calculations allowed the prediction of theoretical excitations, which were comparable with the experimental ones.

Fluorescent Sensors for Measuring Metal Ions in Living Systems

“…234 Another cell permeable compound based on 8-hydroxyquinoline was applied to imaging Cd 2+ in cultured cells, but this sensor (Mameli Cd-1) showed a low dynamic range. 235 …”

A Quinoline-Based Ratiometric and Reversible Fluorescent Probe for Cadmium Imaging in Living Cells

“…Many of these probes can not reduce the fluorescence interference of Zn 2+ due to the similar coordination properties of Zn 2+ and Cd 2+ . 19,20) As a result, only few of them have been utilized for in vivo imaging. Moreover, many of these reported probes detect cadmium via the variety of fluorescent intensity, 14,[21][22][23][24][25][26] which limits its application in quantitative analysis of Cd 2+ in vivo, as the strong autofluorescence of biomolecules background would lead to low signal-to-noise ratio.…”

“…19,20) As a result, only few of them have been utilized for in vivo imaging. Moreover, many of these reported probes detect cadmium via the variety of fluorescent intensity, 14,[21][22][23][24][25][26] which limits its application in quantitative analysis of Cd 2+ in vivo, as the strong autofluorescence of biomolecules background would lead to low signal-to-noise ratio. Through monitoring the fluorescence intensity ratios at two different wavelengths before and after the coordination event, the target concentration can be quantitatively determined by ratiometric fluorescent probe without the influence of artifacts in principle.…”

“…To the best of our knowledge, several fluorescent probes for cadmium have been reported. [13][14][15][16][17][18] In these probes, however, their practical application is still limited as their poor water solubility (need more than 30% organic solvent as co-solution) or need complicated synthesis steps to obtain these probes. Many of these probes can not reduce the fluorescence interference of Zn 2+ due to the similar coordination properties of Zn 2+ and Cd 2+ .…”

From yellow to pink using a fluorimetric and colorimetric pyrene derivative and mercury (II) ions

“…However, for human and environmental welfare, they must exist in optimal quantities. Otherwise, they can promote metabolic disorders, since they are easily absorbed and accumulated from the environment [39].…”