In Vivo Imaging of Endogenously Produced HClO in Zebrafish and Mice Using a Bright, Photostable Ratiometric Fluorescent Probe

An endoplasmic reticulum-targeted two-photon fluorescent probe for bioimaging of HClO generated during sleep deprivation

With the development of social society, sleep deprivation has become a serious and common issue. Previous studies documented that there is a correlation between sleep deprivation and oxidative stress. However, the information of sleep deprivation related ROS has rarely been obtained. Also, it has been demonstrated that sleep deprivation can induce endoplasmic reticulum (ER) stress. As such, for a better understanding of sleep deprivation as well as its related diseases, it is important to develop probes with ER-targeting ability for detecting ROS generated in this process. Herein, a novel two-photon fluorescent molecular probe, JX-1, was designed for sensing HClO in live cells and zebrafish. The investigation data showed that in addition to real-time response (about 150 s), the probe also exhibited high sensitivity and selectivity. Moreover, the probe JX-1 demonstrated two-photon fluorescence, low cytotoxicity and ER targeting ability. These prominent properties enabled the utilization of the probe for monitoring exogenous and endogenous HClO in both live cells and zebrafish. Using this useful tool, it was found that sleep deprivation can induce the generation of HClO in zebrafish.

Aggregation-enhanced emission enables phenothiazine coumarin as a robust ratiometric fluorescent for rapid and selective detection of HClO

By taking advantage of phenothiazine moiety as an electron-donating group, a novel donor-acceptor (D-A) type coumarin dye, PTZ-Et, was developed. The introduction of phenothiazine moiety not only caused emission red-shifting and Stokes shift enlarging, but also endowed PTZ-Et with significant aggregation-enhanced emission (AEE) features, thereby enabled PTZ-Et as a robust ratiometric fluorescent probe for HClO detection. Upon oxidation of the sulfur atom on phenothiazine into sulfoxide, PTZ-Et displayed remarkable ratiometric fluorescence response (over 150 folds variations of F₅₃₄/F₆₂₆) toward HClO with rapid response time (<30 s) and ultra-sensitivity (LOD = 15 nM). Additionally, the corresponding sensing mechanism of PTZ-Et for HClO was fully elucidated through the successful purification and well characterization (¹H NMR, ¹³C NMR, HRMS, and single crystal data) of the corresponding reaction product between PTZ-Et and HClO. Significantly, PTZ-Et was capable of monitoring both exogenous and endogenous HClO in living RAW 264.7 cells by ratiometric fluorescence imaging.

Dimethylamino naphthalene-based fluorescent probes for hydrogen sulfide detection and living cell imaging

Hydrogen sulfide shows great importance in various physiological and biochemical processes. The development of fluorescence probes for facile and efficient detection of H₂S has attracted increasing attention of researchers. Herein, we synthesized two fluorescence probes based on simple naphthalene structure for detection of H₂S. Upon reaction with H₂S, the probe DN-DM exhibited a red fluorescence emission with large Stokes shift. The probe showed high sensitivity, pH insensitivity and good selectivity for H₂S over other analytes including common biothiols. The detection mechanism was based on the thiolysis of the dinitrophenyl ether moiety, which was confirmed by ¹H NMR spectral analysis. The DFT calculation was also performed for a deeper understanding of the photophysical properties. In addition, these probes showed good cell-membrane permeability and could be utilized for detection of H₂S in living cells.

Ratiometric Fluorescent Quantum Dot-Based Biosensor for Chlorothalonil Detection via an Inner-Filter Effect

A new sensitive sensor for detecting chlorothalonil (CHL) based on the inner-filter effect (IFE) between gold nanoparticles (AuNPs) and ratiometric fluorescent quantum dots (RF-QDs) was developed. Here, RF-QDs were designed by two different color CdTe QDs. Based on the IFE, the AuNPs can quench the fluorescence of the RF-QDs. Because of the electrostatic attraction between protamine (PRO) and the AuNPs, the PRO can restore fluorescence effectively. Papain (PAP) can easily hydrolyze PRO and causes the quench of fluorescence quenching. The addition of CHL can inhibit PAP activity and restore the fluorescent signal. Through the characterization of the structural changes of PAP, the inhibition and mechanism of CHL on PAP activity were studied. The ability of CHL to inhibit PAP activity was evaluated by measuring the fluorescence of the RF-QDs. Under the optimal conditions, this sensing platform shows a response to CHL in the range of 0.34-2320 ng/mL and a detection limit of 0.0017 ng/mL. Based on the CHL inhibition of PAP activity, the RF-QDs showed good selectivity for CHL. The practical application of the proposed system was demonstrated by detecting CHL in food and environmental samples with satisfying results.

Selective Detection and Visualization of Exogenous/endogenous Hypochlorous Acid in Living Cells using a BODIPY-based Red-emitting Fluorescent Probe

Herein, a red-emitting fluorescent probe DM-BDP-OCl containing a para-DMTC benzyl pyridinium moiety at the meso position of BODIPY as self-immolative portion for the detection of HOCl was designed and synthesized. DM-BDP-OCl exhibited excellent specificity and a fast response for HOCl beyond other ROS/RNS. It was used for the accurately measurable detection of HOCl with a linear range from 0 μM to 50 μM, and the detection limit for HOCl reached 60 nM. Moreover, the probe could directly monitor fluctuations of exogenous and endogenous HOCl in living HeLa and RAW 264.7 cells. This work provided a powerful and convenient imaging tool for probing pathological and physiological actions of HOCl.

A lysosome specific, acidic-pH activated, near-infrared Bodipy fluorescent probe for noninvasive, long-term, in vivo tumor imaging

Long-term, in vivo, fluorescent cell tracking probes are useful for understanding complex cellular processes including tissue regeneration, communication, development, invasion, and cancer metastasis. A near-infrared fluorescent, water-soluble probe is particularly important for studying these biological events and processes. Herein, a lysosome specific, near-infrared Bodipy probe with increased fluorescent intensity in the acidic, lysosome environment is reported. This Bodipy probe is packaged in a nanoparticle using DSPE-PEG₂₀₀₀. The resulting nanoparticle is intravenously delivered to a tumor xenograft, where the fluorescent Bodipy becomes useful for non-invasive, long-term, in vivo fluorescent tumor imaging for periods greater than 36 days. These long-term, in vitro and in vitro tracking data indicate that the described Bodipy nanoparticles hold great potential for monitoring biological processes.

Series of Mitochondria/Lysosomes Self-Targetable Near-Infrared Hemicyanine Dyes for Viscosity Detection

Six mitochondria/lysosomes self-targetable and viscosity-sensitive dyes (1a-1f) were developed via simple structure modification on cyanine-derived dyes. They all showed remarkable OFF-ON fluorescent response to viscosity in the near-infrared region (652-690 nm) and exhibited good linear relationship with solution viscosity. The transient absorption spectra were used to evaluate the excited-state lifetime of dye 1a in different viscosity environments. Furthermore, cellular imaging assays indicated that different derivatives (1a-1f) with the same chromophore core exhibited different organelle-targeting abilities. Among them, dyes 1a-1c could sense lysosomal viscosity fluctuations while dyes 1d-1f could be applied in mitochondrial viscosity detections.

Incorporating Thiourea into Fluorescent Probes: A Reliable Strategy for Mitochondrion-Targeted Imaging and Superoxide Anion Tracking in Living Cells

Three aggregation-induced emission active fluorescent compounds, TPA-Pyr-Octane, TPA-Pyr-Br, and TPA-Pyr-Thiourea (TPA = triphenylamine pyridinium), are synthesized; their tiny differences in chemical structures result in a huge difference in cell-imaging applications. Especially, incorporating thiourea into fluorescent probes is found as a reliable strategy for mitochondrion-targeted imaging and superoxide anion tracking in living cells, which is possibly due to the presence of hydrogen bonding between thiourea and mitochondrion proteins. This finding is very useful for the design of biosensors and delivery carriers in disease treatment.

Enhancement of the Aggregation-Induced Emission by Hydrogen Bond for Visualizing Hypochlorous Acid in an Inflammation Model and a Hepatocellular Carcinoma Model

As an important reactive oxygen species, hypochlorous acid (HClO) is produced in various physiological processes. The abnormal rise of the HClO level is associated with a large number of inflammatory diseases. In this work, we develop a simple, aqueous-soluble aggregration-induced emission (AIE) probe for sensing HClO with significant aggregation-induced fluorescence (>1000 times). Two probes, CH₃O-TPE-Py⁺-N⁺ (COTN) and OH-TPE-Py⁺-N⁺ (HOTN) (TPE, tetraphenylethylene), are synthesized for sensing HClO by the cleavage of the Py⁺-N⁺ group; the reaction products are CH₃O-TPE-CHO (COT) and OH-TPE-CHO (HOT), respectively. The hydrophobicity of the probes is changed with the increased aggregation-induced emission. During the process, HOTN shows significantly better response than COTN. The slightly different chemical structures of COTN and HOTN result in a significant response to HClO. The theoretical calculation data support the theory that the hydrogen bond contributes to the excellent sensitivity for HClO. On the basis of the good response to HClO in vitro, HOTN is used to image inflammation and hepatocellular carcinoma in vivo because these diseases always produce high HClO levels.

BODIPYS and aza-BODIPY derivatives as promising fluorophores for in vivo molecular imaging and theranostic applications

Since their discovery in 1968, the BODIPYs dyes (4,4-difluoro-4-bora-3a, 4a diaza-s-indacene) have found an exponentially increasing number of applications in a large variety of scientific fields. In particular, studies reporting bioapplications of BODIPYs have increased dramatically. However, most of the time, only in vitro investigations have been reported. The in vivo potential of BODIPYs and aza-BODIPYs is more recent, but considering the number of in vivo studies with BODIPY and aza-BODIPY which have been reported in the last five years, we can now affirm that this family of fluorophores can be considered important as cyanine dyes for future in vivo and even clinical applications. This review aims to present representative examples of recent in vivo applications of BODIPYs or aza-BODIPYs, and to highlight the potential of these dyes for optical molecular imaging.

A bright NIR-II fluorescent probe for breast carcinoma imaging and image-guided surgery

A novel bright near-infrared II (NIR-II, 1000-1700 nm) fluorescent probe with excellent water-solubility, superior photostability, and excellent in vitro and in vivo biocompatibility was facilely synthesized for in vivo biomedical imaging of xenograft breast tumor and chemically induced spontaneous breast carcinoma. To the best of our knowledge, it is the first time that the superior practical applications of this NIR-II probe in dimethylbenzanthracene (DMBA)-induced rat mammary carcinoma imaging and image-guided rat carcinoma surgery were demonstrated.

Aggregation-induced emission luminogens for RONS sensing

The development of AIE bioprobes for RONS sensing in living systems is now summarized. We discuss some representative examples of AIEgen based bioprobes in terms of their molecular design, sensing mechanism and sensitive sensing in vitro and in vivo.

A mitochondria-targeted fluorescent probe for hypochlorite sensing and its application in bioimaging

A coumarin-diaminomaleonitrile derivative was prepared and used for detecting OCl⁻ in living cells and zebrafish. Its high selectivity, sensitivity and low toxicity indicate that it is an ideal tool for biological applications.

Ratiometric fluorescent probe with aggregation-induced emission features for monitoring HClO in living cells and zebra fish

Herein, we present a ratiometric fluorescent probe, PTZ-HClO, with unique optical performance and aggregation-induced emission features that can simultaneously detect HClO.

Water-soluble fluorescent probe for simultaneous detection of cyanide, hypochlorite and bisulfite at different emission wavelengths

A fluorescent probe that responds at distinct wavelengths upon exposure to cyanide, hypochlorite, and bisulfite was synthesized. As a result, an easy to apply analytical methodology was developed for the detection of these ions. The feasibility of this method was evaluated by theoretical calculations. The probe exhibited excellent solubility in the test solution (H₂O: DMF = 99: 1, v: v) with low detection limits for cyanide, hypochlorite and bisulfite (4.5 × 10 ^-8 M, 4.9 × 10 ^-7 M and 4.3 × 10 ^-8 M respectively) showing distinct emission wavelengths for each ion without interference in practical application. Furthermore, the probe had low toxicity and was applied for the imaging experiments of cyanide, hypochlorite and bisulfite in living HeLa and MDCK cells.

Tumor microenvironment-activated nanosystems with selenophenol substituted BODIPYs as photosensitizers for photodynamic therapy

NIR-light-absorbing photosensitizers with the capability of selective localization and activation in tumor regions are of great importance for practical photodynamic therapy (PDT). Here, selenophenol substituted BODIPYs were designed and synthesized as new photosensitizers for PDT. One of these obtained BODIPYs, IBSeOV, possesses an intense and low energy absorption with a high singlet oxygen quantum yield (Φ_Δ = 60%). Considering manganese dioxide (MnO₂) nanosheets as versatile nanocarriers in cancer theranostics, nanosystem IBSeOV/MnO₂ was then fabricated to furnish tumor environment selective activation. Such designed nanoplatform allowed for GSH-controllable ¹O₂ production and exhibited low cytotoxicity in dark but good photocytotoxicity to cancer cells. The in vivo antitumor outcome suggested the high treatment efficiency of IBSeOV/MnO₂ for tumor therapy.

Endoplasmic Reticulum Targeting Ratiometric Fluorescent Probe for Carboxylesterase 2 Detection in Drug-Induced Acute Liver Injury

Carboxylesterase 2 (CES2), an endoplasmic reticulum (ER) located phase I enzyme, plays a vital role in the metabolism of various endogenous and exogenous substances, and is regarded as an important target for the design of prodrugs. Unfortunately, superior highly selective ER targeting fluorescent probes for monitoring of CES2 are not currently available. Herein, we report an ER targeting CES2 selective and sensitive ratiometric fluorescent probe ERNB based on the ER localizing group p-toluenesulfonamide. ERNB possessed high specificity, sensitivity, and exhibited excellent subcellular localization when compared to commercial ER tracker, and was used to image CES2 in the ER of living cells. Additionally, using ERNB we evaluated the CES2 regulation under d,l-dithiothreitol and tunicamycin-induced ER stress. Furthermore, we determined the down regulation of CES2 activity and expression in the acetaminophen-induced acute liver injury model. On the basis of these results, we conclude that ERNB is a promising tool for highlighting the role of CES2 in the ER and in exploring the role of CES2 in the development of diseases associated with ER stress.

A mitochondria-targeted fluorescent probe based on coumarin-pyridine derivatives for hypochlorite imaging in living cells and zebrafish

Hypochlorite plays a critical role in various physiological processes and is involved in many diseases. Thus, real-time, rapid, and accurate monitoring of hypochlorite has important medical and physiological significance. Herein, a novel coumarin-pyridine derivative (CPD) probe was designed and synthesized, which exhibited fantastic advantages, such as a rapid response (within 10 s), naked eye recognition, large Stokes shift (185 nm), dual-channel detection, and high selectivity and sensitivity toward OCl^- (detection limit 0.012 μM, S/N = 3). Furthermore, the current CPD probe was successfully used to image OCl^- in the mitochondria of both A549 cells and zebrafish, which further demonstrated its suitability for practical applications in biological systems.

A selective cascade reaction-based probe for colorimetric and ratiometric fluorescence detection of benzoyl peroxide in food and living cells

A novel colorimetric and ratiometric fluorescent probe (Cou-BPO) was readily prepared for specific detection of harmful benzoyl peroxide (BPO). The probe Cou-BPO reacted with BPO via a selective oxidation cleavage-induced cascade reaction of the pinacol phenylboronate group, which resulted in an observable colorimetric and ratiometric fluorescence response towards BPO with a fast response time (<15 min) and a low detection limit (56 nM). For practical application, facile, portable and sensitive test paper of Cou-BPO has been prepared for visual detection of BPO. Furthermore, we employed Cou-BPO as a probe to determine BPO in food samples and living cells.

Synthesis of novel 1,10-phenanthroline derivatives and it used as probes for sensitive detection of Zn2+ and Cd2+ metal ions - Spectroscopic and theoretical approach

A novel class of unexpected 1,10-phenanthrolinederivatives were synthesized from 2,3-dihydroacridin-4(1H)-ones with 3-aminonaphthalen-2-carboxylic acid in presence of phosphorus oxychloride at 130°C and simple perceptive emission intensity increasing assay was developed effectively to detect the very low concentrations of Zn²⁺ and Cd²⁺ ions. Emission intensity of compounds 3(a-c) directly related to the concentrations of Zn²⁺ and Cd²⁺ ions was due to metal chelating enhanced fluorescence (CHEF) effect and also its further validated by fluorescence lifetime measurement. Furthermore, the sensing mechanism for compounds 3(a-c) of Zn²⁺ and Cd²⁺ were sustained by theoretical calculations. Computational analysis results reveals that compounds 3(a-c) are more interested in Zn²⁺ ions than that of Cd²⁺ ions, while, compound 3c is more interested with Zn²⁺ and Cd²⁺ ions than those of the rest of the compounds. In addition, this proposed detection analysis has the direct application for monitoring Zn²⁺ and Cd²⁺ concentrations in tap and drinking water samples.

Lysosome imaging in cancer cells by pyrene-benzothiazolium dyes: An alternative imaging approach for LAMP-1 expression based visualization methods to avoid background interference

A series of pyrene-benzothiazolium dyes (1a-1d) were experimentally investigated to study their internalization mechanism into cellular lysosomes as well as their potential imaging applications for live cell imaging. The lysosome selectivity of the probes was further compared by using fluorescently tagged lysosome associated membrane protein-1 (LAMP-1) expression-dependent visualization in both normal (COS-7, HEK293) and cancer (A549, Huh 7.5) cell lines. These probes were successfully employed as reliable lysosome markers in tumor cell models, thus providing an attractive alternative to LAMP-1 expression-dependent visualization methods. One advantage of these probes is the elimination of significant background fluorescence arising from fluorescently tagged protein expression on the cell surface when cells were transfected with LAMP-1 expression plasmids. Probes exhibited remarkable ability to stain cellular lysosomes for long-term experiments (up to 24 h) and the highly lipophilic nature of the probe design allowed their accumulation in hydrophobic regions of the cellular lysosomes. Experimental evidences indicated that the probes are likely to be internalized into lysosomes via endocytosis and accumulated in the hydrophobic regions of the lysosomes rather than in the acidic lysosomal lumen. These probes also demonstrated significant stability and lysosome staining for fixed cell imaging applications as well. Lastly, the benzothiazolium moiety of the probes was identified as the key component for lysosome selectivity.

Development of a Concise Rhodamine-Formylhydrazine Type Fluorescent Probe for Highly Specific and Ultrasensitive Tracing of Basal HOCl in Live Cells and Zebrafish

Hypochlorous acid (HOCl) has received special attention by virtue of its pivotal antimicrobial nature, and the appropriate amount of HOCl is beneficial to innate immunity of host to cope with microbial invasion. However, the uncontrollable accumulation of HOCl is implicated in many human diseases and even cancers. Thus, to determine its deeper biological functions, it is significantly important to specifically monitor intracellular HOCl in biosystems. Herein, we rationally designed a simple fluorescent probe FH-HA on the basis of the formylhydrazine recognition receptor and rhodamine B fluorophore. It is worth noting that the formylhydrazine moiety for the first time is adopted as the recognition receptor for specifically recognizing HOCl. Additionally, probe FH-HA also exhibited excellent performance in many areas including satisfactory water-solubility, high specificity, and excellent sensitivity. Notably, probe FH-HA could quickly respond to HOCl (within 3 s), which facilitates the tracing of transient HOCl. More importantly, probe FH-HA was capable of specifically tracing the fluctuations of endogenous HOCl in living cells and zebrafish, and it could monitor basal HOCl in cancer cells to distinguish cancer cells from normal ones.

A Highly Selective and Ultrasensitive Fluorescent Probe for Monitoring Hg2+ and Its Applications in Real Water Samples

Mercury ions as high toxic pollutants have received wide-spread attention because of their poisonousness, persistence and enrichment. To better understand the distribution of mercury species and supplement more detailed toxicological research, it is necessary to develop some methods for monitoring mercury ions with high sensitivity and selectivity. Therefore, a simple rhodol-based highly selective fluorescent probe, RH-Hg, has been developed for monitoring Hg²⁺ with thiocarbamate as the recognition receptor. The probe RH-Hg can quantificationally detect mercury ions in aqueous solution assisted by hydrogen peroxide (H₂O₂), and it can discriminate Hg²⁺ through "naked-eye" observation of the color changes from light orange to dark pink. Finally, the practical applications of the probe RH-Hg in the river water further demonstrated that it will be an effective and economical tool for monitoring the distribution of Hg²⁺ in the environment.

A mitochondria-oriented fluorescent probe for ultrafast and ratiometric detection of HSO3− based on naphthalimide–hemicyanine

The chemodosimeter was a FRET-based probe for detecting HSO₃⁻ selectively.

A selective cascade reaction-based probe for colorimetric and ratiometric fluorescence detection of benzoyl peroxide in food and living cells

A colorimetric and ratiometric fluorescent probe (Cou-BPO) was prepared for food analysis and cell imaging; it showed high selectivity, sensitivity, visible and fast response towards BPO via a selective oxidation cleavage-induced cascade reaction.

A colorimetric and ratiometric fluorescent probe for cyanide sensing in aqueous media and live cells

A mitochondria-targeting ratiometric fluorescent probe for cyanide was reported.

Construction of a two-photon fluorescent probe for ratiometric imaging of hypochlorous acid in alcohol-induced liver injury

A ratiometric two-photon fluorescent probe for HClO was deliberately constructed to reveal the generation of HClO in alcohol-induced liver injury.

A selective cascade reaction-based probe for colorimetric and ratiometric fluorescence detection of benzoyl peroxide in food and living cells

A colorimetric and ratiometric fluorescent probe (Cou-BPO) was prepared for food analysis and cell imaging; it showed high selectivity, sensitivity, visible and fast response towards BPO via a selective oxidation cleavage-induced cascade reaction.

A FRET-based two-photon probe for in vivo tracking of pH during a traumatic brain injury process

Traumatic brain injury (TBI) is a cause of neurodegenerative diseases accompanied by intracellular pH decrease. Herein, a FRET-based ratiometric two-photon fluorescent pH probe is designed to monitor pH change and understand TBI process.

Novel fluorescent probe with a bridged Si–O–Si bond for the reversible detection of hypochlorous acid and biothiol amino acids in live cells and zebrafish

Herein, we report the design of a novel fluorescent probe consisting of a naphthalimide fluorophore and a silicone small molecule for the reversible detection of hypochlorous acid and biothiol amino acids.

A colorimetric and fluorescent lighting-up sensor based on ICT coupled with PET for rapid, specific and sensitive detection of nitrite in food

A colorimetric and fluorogenic sensor exhibiting rapid, specific and sensitive detection of potentially toxic nitrite in food is described.

A general strategy for development of a single benzene fluorophore with full-color-tunable, environmentally insensitive, and two-photon solid-state emission

We report here a single-benzene based fluorescent framework, amino-terephthalonitrile, denoted SB-Fluor.

A simple sensor based on 1,8-naphthalimide with large Stokes shift for detection of hypochlorous acid in living cells

Probe 1shows excellent selectivity to HOCl among different ions including common ROS, high sensitivity, high fluorescence quantum yield (Φ= 0.93), low detection limit (0.237 μM) and successfully used for the detection of HOCl in cells.