Near-infrared Fluorescent Turn-on Probe Research Articles

Near-Infrared Fluorescent Turn-On Probe for Selective Detection of Hypochlorite in Aqueous Medium and Live Cell Imaging.

Hypochlorite, as an important reactive oxygen species (ROS), plays a vital role in many physiological and pathological processes, but an excess concentration of hypochlorite (ClO-) may become toxic to humans and cause disease. Hence, the selective and rapid detection of hypochlorite (ClO-) is necessary for human safety. Here, we report a novel near-infrared (NIR) fluorescence "turn-on" and highly selective benzophenoxazinium chloride-based fluorescent probe, BPH (benzophenoxazinium dihydroxy benzaldehyde), for hypochlorite detection. Due to hypochlorite-induced vicinal diol oxidation to the corresponding ortho benzoquinone derivative, the photoinduced electron transfer (PET) process, which was operating from vicinal diol to the benzophenoxazinium chloride receptor moiety, was suddenly inhibited, as a result of which strong NIR fluorescence "turn-on" emission was observed. The detection limit of BPH was found to be 2.39 × 10-10 M, or 0.23 nM. BPH was successfully applied for exogenous and endogenous hypochlorite detection in live MDA-MB 231 cells.

Live Cell Imaging and Real-Time Monitoring of Nucleolus Morphology and Mitophagy with a Red Fluorescent and Photostable rRNA-Specific Probe in Human Cancer Cells.

rRNAs are prevalent in living organisms. They are produced in nucleolus and mitochondria and play essential cellular functions. In addition to the primary biofunction in protein synthesis, rRNAs have been recognized as the emerging signaling molecule and drug target for studies on nucleolus morphology, mitochondrial autophagy, and tumor cell malignancy. Currently, only a few rRNA-selective probes have been developed, and most of them encounter the drawbacks of low water solubility, poor nuclear membrane permeability, short emission wavelength, low stability against photobleaching, and high cytotoxicity. These unfavorable properties of rRNA probes limit their potential applications. In the present study, we reported a new rRNA-selective and near-infrared fluorescent turn-on probe, 4MPS-TO, capable of tracking rRNA in live human cancer cells. The real-time monitoring performance in nucleolus morphology and mitochondrial autophagy is demonstrated in HeLa cells. The probe shows great application potential for being used as a rRNA-selective, sensitive, and photostable imaging tool in chemical biology study and drug screening.

Highly selective near-infrared fluorescent turn-on probe with a large Stokes shift for the detection of hydrogen sulfide and imaging in live cells

The signalling molecules of hydrogen sulphide (H2S) play an important role in a variety of physiological and pathological processes, and its abnormal concentration causes Down's syndrome, Alzheimer's disease and diabetes mellitus. Thus, the development of an effective detection tool is of vital importance and challenge. In this paper, we synthesized a new “turn-on” hydrogen sulfide near-infrared fluorescent probe (DCM-H2S). Remarkably, this probe demonstrated an unanticipated level of selectivity for hydrogen sulfide (H2S) over other analytes, rendering it suitable for the precise determination of H2S in both in vitro and in vivo settings. Expectedly, the probe exhibited unexpectedly heightened selectivity for H2S compared to other analytes, making it a viable option for the specific determination of H2S in both in vitro and in vivo applications. With the addition of H2S, the probe exhibited distinct turn-on near-infrared (NIR) fluorescence intensity alterations in the DMSO/H2O system, together with a high sensitivity (LOD = 0.13 μM) and large Stokes shift (121 nm). More importantly, the probe has been successfully applied to bioimaging for real-time, dynamic tracking of exogenous and endogenous H2S. The outcomes showed that the probe (DCM-H2S) provides a rapid and effective detection tool for monitoring H2S in vivo.

Application of a Specific and Sensitive NQO1 Turn-On Near-Infrared Fluorescence Probe for Live Cancer Cell and Xenografted Tumor Imaging in Nude Mice.

Sensitive activity stains for enzymes selectively expressed in human cancers offer valuable tools for imaging with wide applications in experimental, diagnostic, and therapeutic settings. The scant expression of the antioxidant enzyme NQO1 in normal tissues and its great abundance in malignant counterparts due to the increased redox stress and hypoxia is one such example. Previously, we described a potent nontoxic probe that remains nonfluorescent but releases an intense fluorogenic compound after intracellular cleavage by NQO1 catalysis. This infrared probe with a 644nm emission has excellent tissue penetrating ability and low background absorption. Described here are methods (fluorescence microscopy, flow cytometry, and in vivo animal imaging) to rapidly image NQO1 activity in hypoxic and non-hypoxic cancer cells and tumors developed in live mouse xenograft models. The specificity of the dye for NQO1 in all three procedures was verified, and the methods should be useful for both in vitro and in vivo studies.

An environmentally sensitive zinc-selective two-photon NIR fluorescent turn-on probe and zinc sensing in stroke

A two-photon near infrared (NIR) fluorescence turn-on sensor with high selectivity and sensitivity for Zn2+ detection has been developed. This sensor exhibits a large Stokes' shift (∼300 nm) and can be excited from 900 to 1000 nm, with an emission wavelength of ∼785 nm, making it ideal for imaging in biological tissues. The sensor's high selectivity for Zn2+ over other structurally similar cations, such as Cd2+, makes it a promising tool for monitoring zinc ion levels in biological systems. Given the high concentration of zinc in thrombi, this sensor could provide a useful tool for in vivo thrombus imaging.

A Near-Infrared Colorimetric Fluorescent Probe for Ferrous Ion Detection and Imaging.

Based on the N-redox mechanism, a turn-on near-infrared fluorescence probe (SWJT-15) with cyano isophorone as skeleton was designed and synthesized for the detection of ferrous ions (Fe2+). The probe has a lower detection limit (83 nM) and fast response (200s) to Fe2+ ions. And the probe has unique selectivity and good anti-interference performance against Fe2+ ions compared to other metal ions. Moreover, the probe has been successfully applied to imaging Fe2+ ions in HeLa cells.

A near-infrared fluorescence-on fluorescent probe for formaldehyde imaging in Arabidopsis thaliana

As a reactive carbonyl molecule, formaldehyde (FA) plays an important part in plant physiological and pathological activities. It is necessary to probe FA in plant for the study of its functions. In this paper, we report DISE, a dicyanoisophorone-based turn-on near-infrared fluorescent probe, which exhibits a highly sensitive response to FA. In addition, confocal imaging experiments showed that DISE could image endogenous and exogenous FA in Arabidopsis root tissue. It demonstrates that the probe has the potential to be an imaging tool to research the FA's biological roles in plant.

Rational design of a turn-on near-infrared fluorescence probe for the highly sensitive and selective monitoring of carboxylesterase 2 in living systems.

In vivo selective fluorescence imaging of carboxylesterase 2 (CES2) remains a great challenge because existing fluorescence probes can potentially suffer from interference by other hydrolases. In addition, some fluorescent probes that have been separately reported for measuring CES2 activity in vitro are affected by autofluorescence and absorption of the biological matrix due to their limited emission wavelength or short Stokes shift. Herein, based on the substrate preference and catalytic performance of CES2, a novel and NIR fluorescent probe was developed, in which a hemi-cyanine dye ester derivative was used as the basic fluorescent group. In the presence of CES2, the probe was hydrolyzed to expose the fluorophore CZX-OH (λabs ∼ 675 nm, λem ∼ 850 nm), which led to a notable red-shift in the fluorescence (∼175 nm) spectrum. Confocal imaging of cells and live mice demonstrated that the fluorescent signal of this probe was related to the real activities of CES2 in cancer cells. All these results will powerfully promote the screening of CES2 regulators and the analysis of CES2-related physiological and pathological processes.

Near-infrared fluorescent turn-on probe for hydrazine detection: environmental samples and live cell imaging.

An acetoxy naphthaldehyde conjugated benzophenoxazinium chloride chromophore-based-donor-π-acceptor (D-π-A) fluorescent probe BPN (benzophenoxazinium naphthoxy imine) displaying near-infrared (NIR) emission was reported for hydrazine detection. The chosen water-soluble benzophenoxazinium chloride chromophore has excellent photostability, a high molar extinction coefficient and fluorescence quantum yield (Φ = from 0.0075 to 0.6193), higher selectivity towards hydrazine and a longer fluorescence lifetime. In the presence of hydrazine, BPN exhibits near infrared fluorescence emission at 725 nm along with color change from light blue to red, as detected by the naked eye. Moreover, the BPN probe can selectively detect hydrazine (DL = 4.5 × 10-10 M) in a 90% aqueous DMSO solution without interfering with other analytes. As proof of real samples, the probe is successfully applied to sense hydrazine in thin layer chromatography (TLC) paper strips (both solution and vapor phases) and water and soil samples, suggesting its significant potential application. Also, due to its NIR emission and aqueous solubility, the BPN probe can be successfully used in live cell imaging with low cytotoxicity.

DNA Minor Groove-Induced cis-trans Isomerization of a Near-Infrared Fluorescent Probe.

The discovery of small molecules that exhibit turn-on far-red or near-infrared (NIR) fluorescence upon DNA binding and understanding how they bind DNA are important for imaging and bioanalytical applications. Here we report the DNA-bound structure and the DNA binding mechanism of quinone cyanine dithiazole (QCy-DT), a recently reported AT-specific turn-on NIR fluorescent probe for double-stranded DNA. The nuclear magnetic resonance (NMR)-derived structure showed minor groove binding but no specific ligand-DNA interactions, consistent with an endothermic and entropy-driven binding mechanism deduced from isothermal titration calorimetry. Minor groove binding is typically fast because it minimally perturbs the DNA structure. However, QCy-DT exhibited unusually slow DNA binding. The cyanine-based probe is capable of cis-trans isomerization due to overlapping methine bridges, with 16 possible slowly interconverting cis/trans isomers. Using NMR, density functional theory, and free energy calculations, we show that the DNA-free and DNA-bound environments of QCy-DT prefer distinctly different isomers, indicating that the origin of the slow kinetics is a cis-trans isomerization and that the minor groove preferentially selects an otherwise unstable cis/trans isomer of QCy-DT. Flux analysis showed the conformational selection pathway to be the dominating DNA binding mechanism at low DNA concentrations, which switches to the induced fit pathway at high DNA concentrations. This report of cis/trans isomerization of a ligand, upon binding the DNA minor groove, expands the prevailing understanding of unique discriminatory powers of the minor groove and has an important bearing on using polymethine cyanine dyes to probe the kinetics of molecular interactions.

A turn-on near-infrared fluorescent probe for visualization of endogenous alkaline phosphatase activity in living cells and zebrafish.

Alkaline phosphatase (ALP) is an essential hydrolase and widely distributed in living organisms. It plays important roles in various physiological and pathological processes. Herein, a turn-on near-infrared (NIR) fluorescent probe (DXMP) was developed for sensitive detection of ALP activity both in vitro and in vivo based on the intramolecular charge transfer (ICT) mechanism. Upon incubation with ALP, DXMP exhibited a strong fluorescence increment at 640 nm, which was attributed to the fact that ALP-catalyzed cleavage of the phosphate group in DXMP induced the transformation of DXMP into DXM-OH. The probe exhibited prominent features including outstanding selectivity, high sensitivity, and excellent biocompatibility. More importantly, it has been successfully used to detect and image endogenous ALP in living cells and zebrafish.

Visualization of endogenous β-galactosidase activity in living cells and zebrafish with a turn-on near-infrared fluorescent probe

β-Galactosidase (β-gal) is an important biomarker for primary ovarian cancers. Developing noninvasive bioimaging probes for studying the activity of β-gal is highly desirable for cancer diagnosis. Herein, a turn-on near-infrared (NIR) fluorescent probe， 2-((6-(((2S, 3R, 4S, 5R, 6R)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran -2-yl)oxy)-2,3-dihydro-1H-xanthen-4-yl)methylene)malononitrile named DXM-βgal, was rationally designed based on enzymatic reaction for the detection of β-gal activity both in vitro and in vivo. Upon incubating with β-gal, DXM-βgal displayed a significant fluorescence enhancement at 640 nm, accompanying by a color change of solution color from red to purple. DXM-βgal exhibited high selectivity and sensitively to β-gal with low limit of detection (2.92 × 10−4 U mL−1). Besides, based on its advantages of long-wavelength emission and excellent biocompatibility, DXM-βgal was successfully applied to imaging β-gal in living cells and zebrafish. Given these prominent properties, we believe that DXM-βgal will be a potential tool for investigating β-gal activity in biomedical research.

A turn-on near-infrared fluorescent probe with rapid response and large Stokes shift for the selective and sensitive detection of zinc(ii) and its application in living cells

Herein, a new near-infrared turn-on fluorescent probe, YPT, was designed and synthesized for the rapid detection of Zn2+, which exhibited low limit of detection for Zn2+ (12 nM) as well as a favorable large Stokes shift (λem − λex = 168 nm).

A turn-on near-infrared fluorescent probe for detection of cysteine over glutathione and homocysteine in vivo

Cysteine (Cys) has emerged as a significant sensing target in recent years.

Iminocoumarin-based red to near-infrared fluorescent turn-on probe with a large Stokes shift for imaging H2S in living cells and animals

The development of organic dye-based fluorescent probes for detection of H2S in living systems has attracted considerable attention in recent years. In this work, a novel tetrahydroquinoxaline iminocoumarin-based red to near-infrared (red-to-NIR) fluorescent probe was developed for detection of H2S. This probe shows a rapid and distinct red-to-NIR fluorescent turn-on detection process for H2S with high selectivity and sensitivity (the detection limit was determined to be as low as 10 nM at physiological pH). In addition, this probe exhibits a remarkable large Stokes shift (128 nm) and low cytotoxicity, and can be applied for imaging H2S in living cells and animals. All these results demonstrated that this new probe is promising for detection of H2S both in vitro and in vivo.

A dual colorimetric and near-infrared fluorescent turn-on probe for Hg2+ detection and its applications

The increasing Hg2+ contamination in environment and ecosystem has gained wide attention and thus demands for its facile and effective detection. In this study, we constructed a new fluorescent probe (E)-2-(2-(3-(1,3-dithian-2-yl)-4-hydroxystyryl)- 4H-chromen-4-ylidene)malononitrile (DCM-Hg) for Hg2+ detection by incorporating the 1, 3-dithiane group to the dicyanomethylene-4H-pyran fluorophore for the first time. This probe can selectively detect Hg2+via the Hg2+-triggered deprotection reaction of thioacetals, which leads to a distinct color change from purple to pink and obvious fluorescence enhancement in the near-infrared (NIR) region. The NIR fluorescence intensity increased linearly with Hg2+ level within the range from 0 to 100 μM and the detection limit of DCM-Hg for Hg2+ was found to be 6.8 × 10−8 mol/L. Moreover, the probe could sense Hg2+ on paper strips and image Hg2+ in living cells with low cytotoxicity, which demonstrates its potential application in environment and biological science.

A rapid responsive colorimetric and near-infrared fluorescent turn-on probe for imaging exogenous and endogenous peroxynitrite in living cells

Rapid, specific and sensitive near-infrared (NIR) fluorescent probes for endogenous peroxynitrite (ONOO−) are valuable tools for the research of ONOO− in living systems. In this paper, we developed a new colorimetric and NIR fluorescent turn-on probe for ONOO− by using a NIR fluorescent chromenylium-cyanine hybrid as the fluorophore and a hydrazide as the reactive site. This probe exhibits prominent features during detecting ONOO− including rapid response (<2 s), high selectivity and sensitivity, long excitation wavelength (640 nm), distinct colorimetric (colorless to blue) and significant NIR fluorescent turn-on signal changes as well as low cytotoxicity. The fluorescence enhancement at 698 nm is more than 100-fold and the detection limit is as low as 25 nM for ONOO−. We also showed that this probe could be used for bioimaging of both exogenous and endogenous peroxynitrite in living cells, indicating it can be used as a powerful tool for the biological research of peroxynitrite in living systems.

Ultrasensitive Tyrosinase-Activated Turn-On Near-Infrared Fluorescent Probe with a Rationally Designed Urea Bond for Selective Imaging and Photodamage to Melanoma Cells.

Melanoma is a highly aggressive malignancy and early monitoring and diagnosis are challenging at present. Tyrosinase is overexpressed in melanoma and regarded as an important biological marker for diagnosis and treatment. Thus, the selective and sensitive detection of tyrosinase is of great significance. To date, a few fluorescent probes have been reported for the detection of tyrosinase in vitro or in vivo. However, a highly sensitive near-infrared probe for tyrosinase monitoring is still missing. In this study, the Gibbs free energy change of different urea bonds during spontaneous hydrolysis is analyzed with the aid of chemical thermodynamic computation. On the basis of this analysis, we modified the dye methylene blue with a rationally designed urea bond to specifically create a probe, called MB1, for rapid detection of tyrosinase. Our experimental results demonstrated that MB1 can serve as a highly sensitive near-infrared responsive fluorescent probe for the monitoring and bioimaging of tyrosinase. In addition, the activated MB1 probe can effectively kill melanoma cells by photodynamic therapy. Thus, the near-infrared probe has great potential for monitoring and treating melanoma.

Highly selective near-infrared fluorescent probe with rapid response, remarkable large Stokes shift and bright fluorescence for H2S detection in living cells and animals

The detection of hydrogen sulfide (H2S) in living systems has received considerable attention in recent years. Although many probes have been reported for detection of cellular H2S, the creation of rapid, highly selective and sensitive near-infrared (NIR) probe for in vivo detection of H2S still remains a challenging target. Herein, a novel dicyanoisophorone-based NIR fluorescent turn-on probe for H2S was reported. This probe uses a sulfonamide group for the first time as a selective reaction site for H2S and more importantly, it displays a rapid (<1 min), highly selective and sensitive (detection limit: 6 nM) response for H2S, giving bright NIR fluorescence output (fluorescence enhancement >130-fold) with a remarkable large Stokes shift (221 nm). Moreover, it has low cytotoxicity and can be used for tracking and imaging of H2S in living cells and animals. Overall, this work provided a very promising NIR fluorescent probe with a new reaction site and excellent sensing properties for rapid detection of H2S both in vitro and in vivo.

A simple but effective colorimetric and far-red to near-infrared fluorescent probe for palladium and its application in living cells

In this work, a new colorimetric and far-red to near-infrared fluorescent turn-on probe for rapid detection of palladium was reported. This probe uses a readily available seminaphthorhodafluor dye as the fluorophore and an allylcarbonate moiety as the reaction site. Based on the Pd0-triggered cleavage reaction, this probe shows rapid (within 2 min), selective, and sensitive response for palladium with different oxidation states (Pd0, or Pd2+ and Pd4+ in the presence of PPh3) in almost wholly aqueous solution under mild conditions, accompanied by distinct color changes and significant fluorescent turn-on signal in the far-red to near-infrared region. The detection limit of this probe for Pd0 was determined to be as low as 1.6 nM in solution. In addition, a sensitive bioimaging of palladiun in living cells can be achieved with a low level of this probe (2 μM), indicating the new developed probe has great potential for palladium detection in both solution and living systems.