A six-membered-ring incorporated Si-rhodamine for imaging of copper(ii) in lysosomes

Abstract

The regulation of copper homeostasis in lysosomes of living cells is closely related to various physiological and pathological processes. Thus, it is of urgent need to develop a fluorescent probe for selectively and sensitively monitoring the location and concentration of lysosomal Cu(2+). Herein, a six-membered ring, thiosemicarbazide, was incorporated into a Si-rhodamine (SiR) scaffold for the first time, affording a SiR-based fluorescent probe SiRB-Cu. Through the effective Cu(2+)-triggered ring-opening process, the probe exhibits fast NIR chromogenic and fluorogenic responses to Cu(2+) within 2 min as the result of formation of a highly fluorescent product SiR-NCS. Compared with a five-membered ring, the expanded ring retains great tolerance to H(+), ensuring the superior sensitivity with a detection limit as low as 7.7 nM and 200-fold enhancement of relative fluorescence in the presence of 1.0 equiv. of Cu(2+) in pH = 5.0 solution, the physiological pH of lysosome. Moreover, the thiosemicarbazide moiety acts not only as the chelating and reactive site, but also as an efficient lysosome-targeting group, leading to the proactive accumulation of the probe into lysosomes. Taking advantage of these distinct properties, SiRB-Cu provides a functional probe suitable for imaging exogenous and endogenous lysosomal Cu(2+) with high imaging contrast and fidelity.

Silicon‐substituted Xanthene Dyes and Their Unique Photophysical Properties for Fluorescent Probes

“…reported a Rhodamine B analogue of Si‐rhodamine, which possesses bathochromic shifts in the absorption and fluorescence maxima compared to the tetramethylrhodamine analogue, SiR650, (Figure ; compound 20 , Table ) and they also established an efficient synthetic scheme for this scaffold . This fluorophore was derivatized to afford fluorescent probes for nitric oxide, Cu 2+ and Hg 2+ , based on the spirocyclization mechanism . Lavis et al.…”

An NIR-emitting lysosome-targeting probe with large Stokes shift via coupling cyanine and excited-state intramolecular proton transfer

“…Current molecular design in NIR probes uses BODIPY, 5,6,7 benzofuran, 8 rhodamine, 9 and cyanine 10 as fluorophores, which typically exhibit small Stoke’s shift. In addition, most NIR lysosome probes are including an amine group in the probe design.…”

A highly selective fluorescent probe for the sensing of Cu2+ based on the hydrolysis of a quinoline-2-carboxylate and its application in cell imaging

“…10 Furthermore, high levels of A highly selective fluorescent probe for the sensing of Cu 2+ based on the hydrolysis of a quinoline-2-carboxylate and its application in cell imaging copper ions accumulating in lysosomes in the higher oxidative state (Cu 2+ form) cause serious damage to living cells. [11][12][13][14] Therefore, it is desirable to design new methods and tools for the sensing of intracellular copper ions.…”

“…As shown in Scheme 1, probe 1 was obtained in high yield by the esterification of compound 2 with quinoline-2-carboxylic acid. The product was fully characterized by 1 H NMR, 13 C NMR, and high-resolution mass spectrometry (HRMS) (see Figures S1-S5, Supporting Information). Further studies revealed that probe 1 exhibits high selectivity and sensitivity for Cu 2 over other cations and anions with a low detection limit of 0.2 μM.…”