Two near-infrared highly sensitive cyanine fluorescent probes for pH monitoring

Two near-infrared(NIR) p H-activated heptamethine indocyanine probes with quaternary ammonium unit were designed and synthesized. The absorption and emission titrations indicate that cationic structure improves the cyanine dye's aqueous solubility and these two probes exhibit highly sensitive response to p H in acid condition. Their fluorescence intensities both gradually increase about 25-fold from p H 7.60 to 3.00 with p Ka values of 4.72 and 4.45 respectively, which are suitable for studying acidic organelles in living cells. Moreover, their fluorescence intensities are linearly proportional to p H values in the range of 5.50–4.00. These results are probably attributed to the protonation of the indole nitrogen atoms, which are verified by 1H NMR spectra. Furthermore, these two probes can achieve real-time imaging of cellular p H and detection of p H in situ in living He La cells due to their excellent properties,including good reversibility, desirable photostability, high selectivity, low cytotoxicity and remarkable membrane permeability.     

Nile-red and Nile-blue-based near-infrared fluorescent probes for in-cellulo imaging of hydrogen sulfide

Hydrogen sulfide has recently been identified as a biologically responsive species. The design and synthesis of fluorescence probes, which are constructed with Nile-red or Nile-blue fluorophores and a fluorescence-controllable dinitrophenyl group, for hydrogen sulfide are reported in this paper. The Nile-red–dinitrophenyl-ether-group-based probe (1a) is essentially non-fluorescent because of the inhibition of the photo-induced electron-transfer process; when the dinitrobenzene moiety is removed by nucleophilic substitution with the hydrosulfide anion, probe 1a is converted into hydroxy Nile red, eliciting a H₂S-induced fluorescence turn-on signal. Furthermore, probe 1a has high selectivity and sensitivity for the hydrosulfide anion, and its potential for biological applications was confirmed by using it for real-time fluorescence imaging of hydrogen sulfide in live HeLa cells. The Nile-blue–dinitrobenzene-based probe (1b) has gradually diminishing brightness in the red-emission channel with increased hydrogen-sulfide concentration. Thus, this paper reports a comparative study of Nile-red and Nile-blue-based hydrogen-sulfide probes. Graphical Abstract

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Intracellular pH measurements made simple by fluorescent protein probes and the phasor approach to fluorescence lifetime imaging

A versatile pH-dependent fluorescent protein was applied to intracellular pH measurements by means of the phasor approach to fluorescence lifetime imaging. By this fit-less method we obtain intracellular pH maps under resting or altered physiological conditions by single-photon confocal or two-photon microscopy.     

A fluorophore's electron-deficiency does matter in designing high-performance near-infrared fluorescent probes

The applications of most fluorescent probes available for Glutathione S-Transferases (GSTs), including NI3 which we developed recently based on 1,8-naphthalimide (NI), are limited by their short emission wavelengths due to insufficient penetration. To realize imaging at a deeper depth, near-infrared (NIR) fluorescent probes are required. Here we report for the first time the designing of NIR fluorescent probes for GSTs by employing the NIR fluorophore HCy which possesses a higher brightness, hydrophilicity and electron-deficiency relative to NI. Intriguingly, with the same receptor unit, the HCy-based probe is always more reactive towards glutathione than the NI-based one, regardless of the specific chemical structure of the receptor unit. This was proved to result from the higher electron-deficiency of HCy instead of its higher hydrophilicity based on a comprehensive analysis. Further, with caging of the autofluorescence being crucial and more difficult to achieve via photoinduced electron transfer (PET) for a NIR probe, the quenching mechanism of HCy-based probes was proved to be PET for the first time with femtosecond transient absorption and theoretical calculations. Thus, HCy2 and HCy9, which employ receptor units less reactive than the one adopted in NI3, turned out to be the most appropriate NIR probes with high-sensitivity and little nonenzymatic background noise. They were then successfully applied to detecting GST in cells, tissues and tumor xenografts in vivo. Additionally, unlike HCy2 with a broad isoenzyme selectivity, HCy9 is specific for GSTA1-1, which is attributed to its lower reactivity and the higher effectiveness of GSTA1-1 in stabilizing the active intermediate via H-bonds based on docking simulations.

An abnormal and intriguing phenomenon that the fluorophore''s electron-deficiency could affect a probe''s performance is now revealed for the first time.     

Gold nanocluster-based fluorescent probes for near-infrared and turn-on sensing of glutathione in living cells

In this study, a novel Au nanocluster (NC)-based fluorescent sensor has been designed for near-infrared (NIR) and turn-on sensing of glutathione (GSH) in both living cells and human blood samples. The large Stokes-shifted (140 nm) fluorescent Au NCs with NIR emission and long-wavelength excitation have been rapidly synthesized for 2 h by means of a microwave-assisted method in aqueous solution. The addition of Hg(II) leads to an almost complete emission quenching (98%) of Au NCs because of the interaction of Hg(II) and Au(I) on the surface of Au NCs. After introducing GSH to the Au NC-Hg(II) system, a more than 20 times fluorescent enhancement is obtained because of the preferable affinity of GSH with Hg(II). Under optimum conditions, the fluorescence recovery is linearly proportional to the concentration of GSH between 0.04 and 16.0 μM and the detection limit is as low as 7.0 nM. This Au NC-based sensor with high sensitivity and low spectral interference has been proven to facilitate biosensing applications.     

萘酰亚胺类荧光分子探针的研究进展

荧光分子探针作为一种有效的金属离子检测手段,不仅使用方便,而且具有高灵敏度,高选择性等突出的优点.作者综述了萘酰亚胺类荧光分子探针的最新研究进展;指出萘酰亚胺化合物具有独特的荧光化学性质(如荧光量子产率高、荧光发射波长适中、斯托克斯位移大、光稳定性好、结构易于修饰等),因此被广泛应用于荧光探针研究领域,并且在合成、离子识别、检测及细胞成像等方面不断取得新的应用.     

Hypoxia-sensitive fluorescent probes for in vivo real-time fluorescence imaging of acute ischemia

Based on the findings that the azo functional group has excellent properties as the hypoxia-sensor moiety, we developed hypoxia-sensitive near-infrared fluorescent probes in which a large fluorescence increase is triggered by the cleavage of an azo bond. The probes were used for fluorescence imaging of hypoxic cells and real-time monitoring of ischemia in the liver and kidney of live mice.     

Synthesis and evaluation of polyhydroxylated near-infrared carbocyanine molecular probes

[reaction: see text] A new near-infrared (NIR) fluorescent molecular probe derived from indocarbocyanine dye and galactose was prepared, and the procedure was optimized. The presence of a nonionic polyhydroxyl moiety between hydrophobic groups enhances solubility and possibly minimizes aggregation in aqueous solutions. The structural framework of this molecule provides multivalent sites for labeling diverse molecules.     

Fine-tailoring the linker of near-infrared fluorescence probes for nitroreductase imaging in hypoxic tumor cells

Fine-tailoring the linker of nitroreductase fl uorescence probes with a given recognition unit and reporting unit is found to be able to achieve the best sensing performance.     

Ratiometric probes for hydrogencarbonate analysis in intracellular or extracellular environments using europium luminescence

A series of six, cationic, zwitterionic and anionic Eu complexes has been examined for the analysis of hydrogencarbonate concentration in the intracellular and extracellular ranges; an anionic complex incorporating three glutarate residues and a sensitising acridone chromophore (lambda exc = 410 nm) exhibits a 69% change in the intensity ratio of the 618/588 nm Eu emission bands between 5 and 15 mM HCO3- in a cell lysate medium.     

Recent advances in molecular fluorescent probes for organic phosphate biomolecules recognition

This review provided a systematic overview of the recent researches on the small-molecule fluorescent probes for recognition various organic phosphate biomolecules (OPBs) including nucleotides, NAD(P)H, FAD/FMN and PS. The general strategies and the recognition mechanisms for these OPBs probe designs were described and emphasized to inspire the better design for fluorescent probes in the future.     

Recent advances in molecular fluorescent probes for organic phosphate biomolecules recognition

Organic phosphate biomolecules (OPBs) are indispensable components of eukaryotes and prokaryotes, such as acting as the fundamental components of cell membranes and important substrates for nucleic acids. They play pivotal roles in various biological processes, such as energy conservation, metabolism, and signal modulation. Due to the difficulty of detection caused by variety OPBs, investigation of their respective physiological effects in organisms has been restrained by the lack of efficient tools. Many small fluorescent probes have been employed for selective detection and monitoring of OPBs in vitro or in vivo due to the advantages of tailored properties, biodegradability and in situ high temporal and spatial resolution imaging. In this review, we summarize the recent advances in fluorescent probes for OPBs, such as nucleotides, NAD(P)H, FAD/FMN and PS. Importantly, we describe their identification mechanisms in detail and discuss the general strategies for these OPBs probe designs, which provide new insights and ideas for the future probe designs.     

Examination of chlorin-bacteriochlorin energy-transfer dyads as prototypes for near-infrared molecular imaging probes

Abstract New classes of synthetic chlorin and bacteriochlorin macrocycles are characterized by narrow spectral widths, tunable absorption and fluorescence features across the red and near-infrared (NIR) regions, tunable excited-state lifetimes (<1 to >10 ns) and chemical stability. Such properties make dyad constructs based on synthetic chlorin and bacteriochlorin units intriguing candidates for the development of NIR molecular imaging probes. In this study, two such dyads (FbC-FbB and ZnC-FbB) were investigated. The dyads contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. In both constructs, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of approximately (5 ps)(-1) and a yield of >99%. Thus, each dyad effectively behaves as a single chromophore with an exceptionally large Stokes shift (85 nm for FbC-FbB and 110 nm for ZnC-FbB) between the red-region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (lambda(f) = 760 nm, Phi(f) = 0.19, tau approximately 5.5 ns in toluene). The long-wavelength transitions (absorption, emission) of each constituent of each dyad exhibit narrow (相似文献   

Highly sensitive near-infrared fluorescent probes for nitric oxide and their application to isolated organs

Novel near-infrared (NIR) fluorescent probes for nitric oxide (NO) have been designed, synthesized, and evaluated. Their NIR fluorescence was increased in an NO concentration-dependent manner under physiological conditions, and their reaction efficiency with NO was at least 53 times higher than that of a widely used NO probe, DAF-2. They were confirmed to function in isolated intact rat kidneys. Because NIR light can penetrate deeply into tissues, these probes may have potential for in vivo NO imaging.     

Imaging intracellular viscosity by a new molecular rotor suitable for phasor analysis of fluorescence lifetime

The arsenal of fluorescent probes tailored to functional imaging of cells is rapidly growing and benefits from recent developments in imaging strategies. Here, we present a new molecular rotor, which displays strong absorption in the green region of the spectrum, very little solvatochromism, and strong emission sensitivity to local viscosity. The emission increase is paralleled by an increase in emission lifetime. Owing to its concentration-independent nature, fluorescence lifetime is particularly suitable to image environmental properties, such as viscosity, at the intracellular level. Accordingly, we demonstrate that intracellular viscosity measurements can be efficiently carried out by lifetime imaging with our probe and phasor analysis, an efficient method for measuring lifetime-related properties (e.g., bionalyte concentration or local physicochemical features) in living cells. Notably, we show that it is possible to monitor the partition of our probe into different intracellular regions/organelles and to follow mitochondrial de-energization upon oxidative stress.     

The chronological evolution of small organic molecular fluorescent probes for thiols

Abnormal concentrations of biothiols such as cysteine, homocysteine and glutathione are associated with various major diseases. In biological systems, the structural similarity and functional distinction of these three small molecular thiols has not only required rigorous molecular design of the fluorescent probes used to detect each thiol specifically, but it has also inspired scientists to uncover the ambiguous biological relationships between these bio-thiols. In this minireview, we will discuss the evolution of small organic molecular fluorescent probes for the detection of thiols over the past 60 years, highlighting the potent methodologies used in the design of thiol probes and their particular applications in the semi-quantification of cellular thiols and real-time labelling. At the same time, the present challenges that limit their further application will be discussed. We hope that this minireview will promote future research to enable deeper insight into the crucial role of thiols in biological systems.

The chronological evolution of small organic molecular fluorescent probes for thiols: from separation dependency analysis to cellular specific analysis, what''s next?