pH‐Controlled Nanoparticles Formation and Tracking of Lysosomal Zinc Ions in Cancer Cells by Fluorescent Carbazole–Bipyridine Conjugates

Abstract

Fluorescent probes for simultaneous detection of multiple organelle specific analytes in cancer cells are essential for bioimaging applications. During abnormalities in cells, among other important parameters (metal ions, reactive oxygen species (ROS), enzymes, etc.) pH and Zn2+ are also altered in cells. Herein, we report the formation of nanoparticles of the fluorescent molecules based on carbazole‐bipyridine conjugates (CBL1‐3) and their use as nanoprobes to simultaneously detect Zn2+ and pH variations in lysosome. Upon increasing the pH from 4–6, these probes form nanoparticles with increased size and enhanced fluorescence at 510 nm. Among CBL1‐3, nanoparticles of CBL2 upon Zn2+ binding, exhibit pH responsive intensity change only at lysosomal pH window at 610 nm and become silent above pH 7. Fluorescent imaging experiments on cancer cells revealed that the CBL2 nanoprobe is capable of localizing at lysosomes and facilitates the detection of endogenous Zn2+ and pH variations. Furthermore, the lysosomal Zn2+ variation with external stimuli induced programmed cell death was visualized using the nanoprobe.

Review on Lysosomal Metal Ion Detection Using Fluorescent Probes

“…Following iron, the transition metal ion Zn 2+ is the second most abundant metal ion in the human body. It plays a vital role in regulating immune function, signal transduction, and the operation of metalloenzymes . In healthy individuals, the concentration of Zn 2+ in serum typically falls within the range of 1–10 μM.…”

“…Recently, Ajayaghosh and co-workers reported the synthesis of a series of self-assembled fluorescent nanoprobes based on carbazole-bipyridine derivatives CBL1–3 and CBG ( 14 ), as shown in Figure a . The authors found that compared to the monomers of CBL1 and CBL3, the CBL2 nanoprobes exhibit promising results in the simultaneous detection of Zn 2+ and pH variations in lysosomes.…”

“…It plays a vital role in regulating immune function, signal transduction, and the operation of metalloenzymes. 20 In healthy individuals, the concentration of Zn 2+ in serum typically falls within the range of 1–10 μM. In mammalian cells, the Zn 2+ ions form stable complexes with numerous enzymes, metabolites, and proteins, collectively constituting a labile Zn 2+ concentration in the picomolar range.…”

“…Recently, Ajayaghosh and co-workers reported the synthesis of a series of self-assembled fluorescent nanoprobes based on carbazole-bipyridine derivatives CBL1–3 and CBG ( 14 ), as shown in Figure 7 a. 20 The authors found that compared to the monomers of CBL1 and CBL3, the CBL2 nanoprobes exhibit promising results in the simultaneous detection of Zn 2+ and pH variations in lysosomes. The efficiency of the probe to monitor endogenous Zn 2+ ions was confirmed by treating cervical cancer cells with the zinc chelator N,N,N,N -tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) under oxidative stress conditions ( Figure 7 b).…”

“…(b) Fluorescence microscopic images of HeLa cells initially treated with TPEN, H 2 O 2 , and TPEN + H 2 O 2 followed by incubation with CBL2 for 30 min (i) and counter-stained with Hoechst 33342 (ii). Reprinted with permission from ref ( 20 ). Copyright 2018, Wiley VCH.…”