Simultaneous Quantification of Hg2+ and MeHg+ in Aqueous Media with a Single Fluorescent Probe by Multiplexing in the Time Domain

Imaging gastrointestinal damage due to acute mercury poisoning using a mitochondria-targeted dual near-infrared fluorescent probe

Mercury (Hg) is one of the most widespread pollutants that pose serious threats to public health and the environment. People are inevitably exposed to Hg via different routes, such as respiration, dermal contact, drinking or diet. Hg poisoning could cause gingivitis, inflammation, vomiting and diarrhea, respiratory distress or even death. Especially during the developmental stage, there is considerable harm to the brain development of young children, causing serious symptoms such as intellectual disability and motor impairments, and delayed neural development. Therefore, it's of great significance to develop a specific, quick, practical and labor-saving assay for monitoring Hg2+. Herein, a mitochondria-targeted dual (excitation 700 nm and emission 728 nm) near-infrared (NIR) fluorescent probe JZ-1 was synthesized to detect Hg2+, which is a turn-on fluorescent probe designed based on the rhodamine fluorophore thiolactone, with advantages of swift response, great selectivity, and robust anti-interference capability. Cell fluorescence imaging results showed that JZ-1 could selectively target mitochondria in HeLa cells and monitor exogenous Hg2+. More importantly, JZ-1 has been successfully used to monitor gastrointestinal damage of acute mercury poisoning in a drug-induced mouse model, which provided a great method for sensing Hg species in living subjects, as well as for prenatal diagnosis.

A Formyl Chromone Based Schiff Base Derivative: An Efficient Colorimetric and Fluorescence Chemosensor for the Selective Detection of Hg2+ Ions

A novel chromone-based Schiff base L was designed and synthesized by condensing an equimolar amount of 3-formyl chromone and 2,4-dinitro phenyl hydrazine. Schiff base L was developed as a potent colorimetric and fluorescent molecular probe to recognize Hg2+ ions over other competitive metal ions. In the presence of Hg2+, Schiff base L displays a naked-eye detectable color change under day and UV365 nm light. Various UV-Vis and fluorescence studies of L were performed in the absence and presence of Hg2+ to determine the sensitivity and the sensing mechanism. With high selectivity and specificity, the detection limit and association constant of L for Hg2+ were estimated at 1.87 µM and 1.234 × 107 M-1, respectively. The developed sensor L was applied to real soil samples for the detection of Hg2+.

Monitoring Hg2+ and MeHg+ poisoning in living body with an activatable near-infrared II fluorescence probe

Noninvasively imaging mercury poisoning in living organisms is critical to understanding its toxicity and treatments. Especially, simultaneous fluorescence imaging of Hg²⁺ and MeHg⁺in vivo is helpful to disclose the mysteries of mercury poisoning. The key limitation for mercury imaging in vivo is the low imaging signal-to-background ratio (SBR) and limited imaging depth, which may result in unreliable detection results. Here, we designed and prepared a near-infrared II (NIR II) emissive probe, NIR-Rh-MS, leveraging the "spirolactam ring-open" tactic of xanthene dyes for in situ visualization of mercury toxicity in mice. The probe produces a marked fluorescence signal at 1015 nm and displays good linear responses to Hg²⁺ and MeHg⁺ with excellent sensitivity, respectively. The penetration experiments elucidate that the activated NIR-II fluorescence signal of the probe penetrates to a depth of up to 7 mm in simulated tissues. Impressively, the probe can monitor the toxicity of Hg²⁺ in mouse livers and the accumulation of MeHg⁺ in mouse brains via intravital NIR-II imaging for the first time. Thus, we believe that detecting Hg²⁺ and MeHg⁺ in different organs with a single NIR-II fluorescence probe in mice would assuredly advance the toxicologic study of mercury poisoning in vivo.

A FRET-based ratiometric fluorescent probe for Hg2+ detection in aqueous solution and bioimaging in multiple samples

Mercury ion, as a metal cation with great toxic effect, is widely present in various production and living environments. It seriously threatens human health and environmental safety. It is of great significance to develop convenient and effective methods for mercury ion detection. Here, we designed and synthesized a new ratiometric fluorescent probe (namely APS-NA) for the detection of mercury ions in the environment and multiple biological samples. The probe is constructed by covalently connecting two fluorophores with lipolic acid to achieve fluorescence resonance energy transfer (FRET). In the molecular structure of APS-NA, acridone is used as an energy donor, 1,8-naphthalimide is used as an energy acceptor, and a dithioacetal group is used as the reaction site for Hg²⁺. The intact APS-NA mainly shows the green fluorescence from the acceptor moiety 1,8-naphthalimide; the presence of Hg²⁺ ions would break the dithioacetal linkage between acridone and 1,8-naphthalimide; the defunctionalization of FRET would lead to bright blue fluorescence emission of acridone; thus ratiometric fluorescent detection of Hg²⁺ can be achieved by this recognition process. The probe not only has a large Stokes shift (Δλ = 110 nm), but also has high selectivity, high sensitivity (low detection limit 30 nM) and naked eye visualization. In addition, we have successfully used this probe for the detection Hg²⁺ of actual samples and imaging of a variety of organisms. These results indicate that the probe has broad application prospects.

Kinetically Orthogonal Probe for Simultaneous Measurement of H2S and Nitroreductase: A Refined Method to Predict the Invasiveness of Tumor Cells

The concentrations of nitroreductase and H₂S have been widely used to predict the invasiveness of tumors. However, the above two substrates always interfere with the measurement of each other as both substrates react with the typical nitroaromatic probe with the same process. Moreover, the above interferences may lead to the misjudgment of the tumor invasiveness. We used a strategy combining kinetical distinguishing and signal amplification to construct a kinetically orthogonal probe labeled KOP. The above strategy expanded the gap between the reactivity of KOP to H₂S and nitroreductase with an acceptable reactivity and could determine the concentration of coexisting nitroreductase and H₂S on a kinetic curve with a breakpoint. KOP could also indicate the correct invasiveness tendency in the cellular model with a complex H₂S generation pathway, while the traditional kinetically nonorthogonal probe could not indicate invasiveness correctly.

Small-molecule fluorescent probes based on covalent assembly strategy for chemoselective bioimaging

In this review, we comprehensively summarize the recent progress in the development of small molecular fluorescent probes based on the covalent assembly principle. The challenges and perspective in this field are also presented.

"Covalent-Assembly"-Triggered Striking Far-Red to near-Infrared Emitting Fluorescent Probe for Abrupt Detection of Nerve-Agent Mimic (DCP): Real Time Application in Monitoring the Presence of Trace Amounts in Soil and Live Cells

Detection of chemical warfare agents (CWA) by simple and rapid methods with real-sample applications are quite inevitable in order to ease the threats to living systems caused by uncertain terror attacks and wars. Herein we have developed the first far-red to near infra-red (NIR) probe based on a covalent assembly approach for the detection of trace amounts of nerve agent mimic diethyl chloro phosphate (DCP) in soil and their fluorescent bio imaging in live cells. The probe features abrupt fluorescence turn on sensing of DCP with fluorescence quantum yield Φ = 0.622. It senses DCP selectively over other analytes in excellent sensitivity with a detection limit of 6.9 nM. In real time, the probe treated strips were employed to detect the DCP vapor effectively with eye catching fluorescence response. The presence of trace amounts of these acute warfare agents in the environment were monitored by soil analysis. Further fluorescent bio imaging was carried out to monitor trace level DCP in living cells using the HeLa cell line.

Dual-channel colorimetric fluorescent probe for determination of hydrazine and mercury ion

Hydrazine and mercury (Hg) poisoning represented a serious hazard to human health. So, developing method to detect and recognize them is highly desirable. Here, we prepared a multifunctional colorimetric and fluorescent probe (PI-Rh) consisting of a phenanthroimidazole (PI) dye conjugated with a Rhodamine (Rh) group for the effective recognition of hydrazine and Hg²⁺, induvidually and collectively, with different colorimetric and fluorescence outputs. Probe PI-Rh displays low detection limits measured to be 0.0632 μM (~2 ppb) and 0.0101 μM (~2 ppb) respectively for hydrazine and Hg²⁺ with high selectivity and excellent sensitivity. Moreover, the experimental results indicated that the superiority of this probe lied in its wide applications, for example, successful response in real water, and soil analysis. Interestingly, an visual, rapid, and real-time detection of gaseous hydrazine can be realized with 0.2793 μM detection limit using the facile PI-Rh-impregnated test paper.

Bicolour fluorescent molecular sensors for cations: design and experimental validation

Molecular entities whose fluorescence spectra are different when they bind metal cations are termed bicolour fluorescent molecular sensors. The basic design criteria of this kind of compound are presented and the different fluorescent responses are discussed in terms of their chemical behaviour and electronic features. These latter elements include intramolecular charge transfer (ICT), formation of intramolecular and intermolecular excimer/exciplex complexes and Förster resonance energy transfer (FRET). Changes in the electronic properties of the fluorophore based on the decoupling between its constitutive units upon metal binding are also discussed. The possibility of generating fluorescent bicolour indicators that can capture metal cations in the gas phase and at solid-gas interfaces is also discussed.

A reaction-based ratiometric fluorescent probe for mercury ion detection in aqueous solution

Mercury ions are crucially harmful to ecosystem and human being due to their characters of bioaccumulation and difficulty of biochemical degradation. Therefore, development of mercury ion detection methods has attracted increasing interests recently. In this study, we successfully synthesized a hydroxyphenylbenzothiazole (HBT)-based fluorescent probe HBT-Hg in an extremely simple manner for mercuric ions detection. The spectral studies revealed that the probe HBT-Hg could react with Hg²⁺ selectively and sensitively in PBS buffer (10 mM, pH = 7.40), showing ratiometric fluorescent changes from blue to light green. The response mechanism of the probe HBT-Hg and Hg²⁺ was finally confirmed by HPLC analysis, viz., the probe HBT-Hg converted to its precursor compound 1. Finally, the probe HBT-Hg was successfully applied in monitoring Hg²⁺ in living A549 cells.

A novel near-infrared fluorescent sensor for zero background nitrite detection via the "covalent-assembly" principle

Different chemical states of nitrogen are present in many freshwater and marine ecosystems, and nitrite ions are one of the most toxic water-soluble nitrogen species. Developing an effective and convenient sensing method to constantly detect the concentration of nitrite has become a wide concern. Here, a novel near-infrared fluorescent probe (AAC) was designed and synthesized via the "covalent assembly" principle, showing excellent selectivity and high sensitivity for nitrite. A new nitrite-quantitative method was established with the help of AAC, and the detection limit of nitrite using the new method was as low as 6.7 nM. AAC was successfully applied for the quantitative detection of nitrite in real-world environmental and food samples (including river water and Chinese sauerkraut), and the detection results were essentially identical to the results obtained from the traditional Griess assay. Moreover, AAC was successfully applied for tracking nitrite in Escherichia coli by fluorescence imaging. Since nitrite can have devastating effects, the method established with AAC allowed us to "see" effectively about the water quality, food quality, etc.

Colorimetric detection of Hg2+ with an azulene-containing chemodosimeter via dithioacetal hydrolysis

Azulene is a bicyclic aromatic chromophore that absorbs in the visible region. Its absorption maximum undergoes a hypsochromic shift if a conjugated electron-withdrawing group is introduced at the C1 position. This fact can be exploited in the design of a colorimetric chemodosimeter that functions by the transformation of a dithioacetal to the corresponding aldehyde upon exposure to Hg2+ ions. This chemodosimeter exhibits good chemoselectivity over other metal cations, and responds with an unambiguous colour change clearly visible to the naked eye. Its synthesis is concise and its ease of use makes it appropriate in resource-constrained environments, for example in determing mercury content of drinking water sources in the developing world.

Visualizations of Mercury Methylation and Dynamic Transformations by In Vivo Imaging

Visualization of Hg(II) and MeHg in their native contexts is significant for examining mercury poisoning, while it is challenging because of indistinguishable fluorescent (FL) signals during FL imaging. Herein, visualizations of mercury methylation and dynamic transformations of Hg(II) and MeHg are achieved in living biological systems. Well distinguishable FL responses (blue emission for Hg(II), yellow emission for MeHg) are obtained by a double-response FL probe (DPAHB) without any interference. As demonstrated by experimental and computational studies, the distinguishable signals are attributed to selective binding with DPAHB and different inhibition of excited-state proton transfer. Through control tests for live-dead markers, mercury methylation is demonstrated to be employed in living biological systems. Therefore, the methylation and dynamic transformations of both ions are monitored in zebrafish by imaging, and these results are confirmed by traditional high-performance liquid chromatography-based methods. The methylation of Hg(II) to MeHg, dynamic transformations and final accumulations of both species in zebrafish tissues are visualized successfully. This method is also convenient for fast evaluation of detoxification reagents. This is the first visualization of in vivo mercury methylation and dynamic transformation of both species and is effective for studying pathological processes in their native contexts.

Molecular probe designviathe “covalent-assembly” principle

Fluorescent probes are useful molecular tools. We summarize the recent progress with the “covalent-assembly” design principle, which warrants high-performance fluorescence probes exhibiting a highly sensitive turn-on signal from the dark background.

Anthracene-Based Highly Selective and Sensitive Fluorescent "Turn-on" Chemodosimeter for Hg2

Three π-extended anthracene-bearing thioacetals (1-3) have been synthesized, and their fluorescence "turn-on" responses to Hg2+ ions are studied. The chemodosimetric fluorescence-sensing behavior and their resulting hydrolysis via a desulfurization reaction mechanism leads to the formation of highly fluorescent respective aldehyde substitutions. Furthermore, this mechanism was supported by increase in the quantum yields of their resulting aldehydes and is correlated to their molecular substitution. The chemosensors 1-3 have exhibited to be promising receptors toward Hg2+ ions in the presence of other competitive metal ions. Moreover, the detection limits of 1-3 have been found to be in the nanomolar range (94, 59, and 235, respectively). Fluorescence microscopic imaging studies show that 1-2 have been found to be effective for fluorescence imaging in live cells. Moreover, compounds 1-3 act as potential candidates for the detection of Hg2+ in environmental and biological systems as well as real samples.

A reaction-based ratiometric fluorescent sensor for the detection of Hg(ii) ions in both cells and bacteria

A novel reaction-based fluorescent probe (ATC-Hg) was designed and synthesized via the "covalent assembly" principle, which exhibited excellent selectivity and high sensitivity for Hg2+ and CH3Hg+. Moreover, it is the first Hg(ii) sensitive fluorescent probe that has been successfully applied in imaging in both cells and Escherichia coli.

A thiocoumarin-based colorimetric and ratiometric fluorescent probe for Hg2+ in aqueous solution and its application in live-cell imaging

A new intramolecular charge transfer (ICT) based colorimetric and ratiometric fluorescent chemodosimeter for the detection of Hg²⁺ has been rationally designed and developed.

A novel ESIPT-based fluorescent chemodosimeter for Hg2+ detection and its application in live-cell imaging

A novel ESIPT-based fluorescent chemodosimeter for the detection of Hg²⁺ has been rationally designed and developed.

In situ formation of pyronin dyes for fluorescence protease sensing

A cutting-edge strategy for fluorogenic sensing of proteases (leucine aminopeptidase for the proof of concept) and based on the “covalent-assembly” principle is reported. Non-fluorescent mixed bis-aryl ethers are readily converted into a fluorescent pyronin through a domino process triggered by the peptide bond cleavage event caused by the targeted enzyme.

A novel approach to study the structure-property relationships and applications in living systems of modular Cu(2+) fluorescent probes

A series of Cu²⁺ probe which contains 9 probes have been synthesized and established. All the probes were synthesized using Rhodamine B as the fluorophore, conjugated to various differently substituted cinnamyl aldehyde with C=N Schiff base structural motif as their core moiety. The structure-property relationships of these probes have been investigated. The change of optical properties, caused by different electronic effect and steric effect of the recognition group, has been analyzed systematically. DFT calculation simulation of the Ring-Close and Ring-Open form of all the probes have been employed to illuminate, summarize and confirm these correlations between optical properties and molecular structures. In addition, biological experiment demonstrated that all the probes have a high potential for both sensitive and selective detection, mapping of adsorbed Cu²⁺ both in vivo and environmental microbial systems. This approach provides a significant strategy for studying structure-property relationships and guiding the synthesis of probes with various optical properties.

Nile Red Derivative-Modified Nanostructure for Upconversion Luminescence Sensing and Intracellular Detection of Fe(3+) and MR Imaging

Iron ion (Fe(3+)) which is the physiologically most abundant and versatile transition metal in biological systems, has been closely related to many certain cancers, metabolism, and dysfunction of organs, such as the liver, heart, and pancreas. In this Research Article, a novel Nile red derivative (NRD) fluorescent probe was synthesized and, in conjunction with polymer-modified core-shell upconversion nanoparticles (UCNPs), demonstrated in the detection of Fe(3+) ion with high sensitivity and selectivity. The core-shell UCNPs were surface modified using a synthesized PEGylated amphiphilic polymer (C18PMH-mPEG), and the resulting mPEG modified core-shell UCNPs (mPEG-UCNPs) show good water solubility. The overall Fe(3+)-responsive upconversion luminescence nanostructure was fabricated by linking the NRD to the mPEG-UCNPs, denoted as mPEG-UCNPs-NRD. In the nanostructure, the core-shell UCNPs, NaYF4:Yb,Er,Tm@NaGdF4, serve as the energy donor while the Fe(3+)-responsive NRD as the energy acceptor, which leads to efficient luminescence resonance energy transfer (LRET). The mPEG-UCNPs-NRD nanostructure shows high selectivity and sensitivity for detecting Fe(3+) in water. In addition, benefited from the good biocompatibility, the nanostructure was successfully applied for detecting Fe(3+) in living cells based on upconversion luminescence (UCL) from the UCNPs. Furthermore, the doped Gd(3+) ion in the UCNPs endows the mPEG-UCNPs-NRD nanostructure with effective T1 signal enhancement, making it a potential magnetic resonance imaging (MRI) contrast agent. This work demonstrates a simple yet powerful strategy to combine metal ion sensing with multimodal bioimaging based on upconversion luminescence for biomedical applications.

Fluorescent theranostic agents for Hg2+detection and detoxification treatment

Two novel small-molecule based theranostic agents encompassing the dual functions of detection and detoxification of mercury ion poisoning are developed.

A switch-on MRI contrast agent for noninvasive visualization of methylmercury

The first Gd(iii)-based T₁ MRI contrast agent, o-MeHgGad, is demonstrated for noninvasive visualization of CH₃Hg⁺.

Dual enzyme-responsive “turn-on” fluorescence sensing systems based on in situ formation of 7-hydroxy-2-iminocoumarin scaffolds

We herein report a novel class of dual enzyme-responsive fluorogenic probes based on two orthogonal deprotection reactions via the “covalent assembly” principle. Sensing of two different enzymes (hydrolase and nitroreductase) through domino reactions, producing the push–pull backbone of a fluorescent 3-substituted 7-hydroxy-2-iminocoumarin dye, is reported.