Letter pubs.acs.org/ac
Quinoline-Based Two-Photon Fluorescent Probe for Nitric Oxide in Live Cells and Tissues Xiaohu Dong,†,§,∥ Cheol Ho Heo,‡,∥ Shiyu Chen,† Hwan Myung Kim,*,‡ and Zhihong Liu*,† †
Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, Hubei 430072, China ‡ Division of Energy Systems Research, Ajou University, Suwon, Gyeonggi-do 443-749, Korea § Xi’an Modern Chemistry Research Institute, Xi’an, Shaanxi 710065, China S Supporting Information *
ABSTRACT: A two-photon fluorescent probe (QNO) for nitric oxide is reported. The probe is designed with a photoinduced electron transfer (PeT) mechanism and shows 12-fold fluorescence enhancement toward NO. Adopting a quinoline derivative as the fluorophore, QNO has a large twophoton action cross section value of 52 GM and long-wavelength emission. It also features high selectivity, low cytotoxicity, and pH insensitivity. By utilizing two-photon microscopy (TPM), QNO can detect NO in live cells and live tissues at a depth of 90−180 μm.
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it is still in great need to develop new species of TP probes for direct imaging of endogenous NO produced in both live cells and intact tissues, so as to facilitate their applications. Herein, we designed and prepared an efficient TP probe for NO (named as QNO, Scheme 1) composed of a quinoline derivative as the fluorophore and an o-phenylenediamine moiety as the receptor for NO, linked with glycinamide. This probe can detect NO in live cells and tissues in a depth of more than 100 μm for long periods of time without photobleaching and cytotoxicity issues. The preparation of QNO is summarized in Scheme 2. The quinoline intermediate (2) was prepared by cyclization of 4aminophenol with crotonaldehyde followed by Bucherer reaction. Subsequent alkylation and oxidation by SeO 2 produced 3. The key intermediate 4 was synthesized in 71% overall yield by condensation of 3 with 2-aminobenzenethiol followed by hydrolysis. QNO was obtained by the coupling of 4 and 2-nitro-1,4-phenylenediamine followed by reduction in 28% overall yield. The detailed synthetic procedure is described in the Supporting Information. The solubility of QNO in 0.1 M phosphate-buffered saline solution (pH = 7.4) was approximately 2.0 μM, which was sufficient to stain the cells (Figure S1 in the Supporting Information). The photophysical data of QNO were determined in phosphate-buffered saline (0.1 M PBS, pH = 7.4, containing
itric oxide (NO) is a small uncharged free radical, playing a vital role as a signaling molecule in a variety of physiological and pathological processes that take place in the cardiovascular, nervous, and immune systems.1,2 Misregulation of NO production has a crucial relationship with various diseases such as cancer, neurodegenerative injury, and inflammation.3 NO is reactive, lipid-soluble, and easy to diffuse, which makes it difficult to capture and detect. An attractive approach to detect NO in real time is fluorescent probes. As yet, a number of NO fluorescent probes have been developed for bioimaging,4 which mainly include the o-phenylenediaminebased probes contributed by Nagano5 and the transition metalbased probes developed by Lippard.6 Although lots of the probes are useful for bioimaging, most of them can only be employed under one-photon microscopy (OPM), which limits their application due to short excitation wavelengths (
