Novel Mitochondria-Targeting and Naphthalimide-based Fluorescent Probe for Detecting HClO in Living Cells

Abstract

As a key reactive oxygen species (ROS), hypochlorous acid (HClO) plays an important role in many physiological and pathological processes. The mitochondria-targeting probes for the highly sensitive detection of HClO are desirable. In present work, we designed and synthesized an original mitochondria-localizing and turn-on fluorescent probe for detecting HClO. 4-Aminonaphthalimide was employed as the fluorescent section, the (2-aminoethyl)-thiourea unit was utilized as a typical sensing unit, and the quaternized pyridinium moiety was used as a mitochondria-targeted localization group. When HClO was absent, the probe showed weak fluorescence. In the existence of HClO, the probe revealed a blue fluorescence. Moreover, the turn-on fluorescent probe was able to function in a broad pH scope. There was an excellent linearity between the fluorescence emission intensity at 488 nm and the concentrations of HClO in the range of 5.0 × 10–7 to 2.5 × 10–6 mol·L–1. Additionally, the probe had almost no cell toxicity and possessed an excellent mitochondria-localizing capability. Furthermore, the probe was able to image HClO in mitochondria of living PC-12 cells. The above remarkable properties illustrated that the probe was able to determine HClO in mitochondria of living cells.

Fluorescent Probes for HOCl Detection in Living Cells

“…(a) In mitochondria, FHZ (in cytoplasm and mitochondria) [67], HKOCl-4m [79], and compound (VII) [84], NSSN [93].…”

“…In early 2021, Xu and coauthors presented a mitochondria-targeted probe of the turn-on type, compound (VII) [84]. The naphthalimide residue was used as a fluorophore, (2-aminoethyl)-thiourea was used as the reaction site, and the quaternized pyridine fragment was used as a mitochondria-targeting group.…”

“…Interaction with HOCl results in intramolecular cyclization of the thiourea group of the probe, which is accompanied by an increase in fluorescence intensity (λ ex = 370 nm; λ em = 488 nm). The probe is characterized by selectivity to HOCl compared to other active forms, relatively high sensitivity (LOD 230 nM), and large operating pH range (pH 2-9); fluorescence intensity reaches a plateau within 60 s. The chemosensor was used to visualize exogenous HOCl in mitochondria of PC-12 cell line (cells of rat pheochromocytoma), as well as for recording the formation of endogenous HOCl in RAW264.7 cells upon their stimulation with PMA [84].…”

An ICT-FRET-based fluorescent probe for the ratiometric sensing of hypochlorous acid based on a coumarin–naphthalimide derivative

“…Peroxynitrite (ONOO − ) was obtained by the interaction of hydrogen peroxide and sodium nitrite, and its concentration is determined by its UV absorption at 302 nm ( ε = 1670 L mol −1 cm −1 ). 26 Tert -Butoxy radical (˙O t Bu) was obtained by the reaction of 1 mM Fe 2+ with 200 μM TBHP. HClO was standardized at pH 12 ( ε 292nm = 350 L mol −1 cm −1 ).…”

“…[20][21][22] Up to now, numerous fluorescent probes have been developed and applied to the detection of hypochlorous acid. [23][24][25][26][27][28][29][30] Most of these fluorescent probes respond only at a single wavelength, and the fluorescence intensity changes with the concentration of the target analyte, which is easily affected by many factors, such as instrument, environment, probe concentration, photobleaching and excitation intensity. [31][32][33] The ratiometric probes can overcome these shortcomings.…”