A FRET-based fluorescent Zn2+ sensor: 3D ratiometric imaging, flow cytometric tracking and cisplatin-induced Zn2+ fluctuation monitoring

A simulated microgravity-oriented AIE probe-ECM hydrogel-integrated chip for cell culture and superoxide anion radical detection

Human space activities have been continuously increasing. Astronauts experiencing spaceflight are faced with health problems caused by special space environments such as microgravity, and the investigation of cell injury is fundamental. The development of a platform capable of cell culture and injury detection is the prerequisite for the investigation. Constructing a platform suitable for special conditions in space life science research is the key issue. The ground-based investigation is an indispensable part of the research. Accordingly, a simulated microgravity (SMG)-oriented integrated chip platform capable of 3D cell culture and in situ visual detection of superoxide anion radical (O2•-) is developed. SMG can cause oxidative stress in human cells, and O2•- is one of the signaling molecules. Thus, a O2•--responsive aggregation-induced emission (AIE) probe is designed, which shows high selectivity and sensitivity to O2•-. Moreover, the probe exhibits abilities of long-term and wash-free staining to cells due to the AIE behavior, which is precious for space cell imaging. Meanwhile, a chip with a high-aspect-ratio chamber for adequate medium storage for the lack of the perfusion system during the SMG experiment and a cell culture chamber which can integrate the extracellular matrix (ECM) hydrogel for the bioinspired 3D cell culture is fabricated. In addition, a porous membrane is introduced between the chambers to prevent the hydrogel from separating during the SMG experiment. The afforded AIE probe-ECM hydrogel-integrated chip can achieve 3D culturing of U87-MG cells and in situ fluorescent detection of endogenous O2•- in the cells after long-term staining under SMG. The chip provides a powerful and potential platform for ground-based investigation in space life science and biomedical research.

ZNT1 and Zn 2+ control TLR4 and PD-L1 endocytosis in macrophages to improve chemotherapy efficacy against liver tumor

BACKGROUND AND AIMS

HCC is closely associated with inflammation and immune modulation, and combined chemotherapy with other strategies is under extensive investigation to achieve better efficacy. HCC is accompanied by zinc (Zn) deficiency. This study aims to understand how Zn could affect macrophage function and its application for HCC therapy.

APPROACH AND RESULTS

Zn 2+ and the Zn transporter 1 (ZNT1, solute carrier family 30 member 1) were markedly reduced in intrahepatic macrophages from patients with HCC and from mouse liver tumors. Lower ZNT1 expression was associated with higher IL-6 production and shorter survival time in patients with HCC. Critically, ZNT1 regulated endosomal Zn 2+ levels for endocytosis of toll-like receptor 4 and programmed cell death ligand 1, thereby decreasing macrophage-induced inflammation and immunosuppression to protect from liver tumors. Myeloid-specific deletion of ZNT1 in mice increased chronic inflammation, liver fibrosis, tumor numbers, and size. Notably, Zn supplementation could reduce inflammation and surface programmed cell death ligand 1 expression in macrophages with the increased CD8 + T cell cytotoxicity, which synergized the antitumor efficacy of Sorafenib/Lenvatinib.

CONCLUSIONS

Our study proposes a new concept that ZNT1 and Zn regulate endosome endocytosis to maintain surface receptors, and Zn supplements might be synergized with chemotherapy to treat inflammation-associated tumors, especially those containing programmed cell death ligand 1 + myeloid cells.

Recent Advances in Organic Small-Molecule Fluorescent Probes for the Detection of Zinc Ions (Zn2+)

Zinc(II) ions (Zn2g) play crucial roles in the growth, propagation, and metabolism of animals, plants, and humans. Abnormal concentrations of Zn2+ in the environment and living organisms pose potential risks to environmental protection and human health. Therefore, it is imperative to develop rapid, reliable and in-situ detection methods for Zn2+ in both environmental and biological contexts. Furthermore, effective analytical methods are required for diagnosing diseases and understanding physiological metabolic mechanisms associated with Zn2+ concentration levels. Organic small-molecule fluorescent probes offer advantages such as fast, reliable, convenient, non-destructive detection capabilities and have significant application potential in Zn2+ detection and bioimaging; thus garnering extensive attention. Over the past two years alone, various organic small-molecule probes for Zn2+ based on different detection mechanisms and fluorophores have been rapidly developed. However, these probes still exhibit several limitations that need further resolution. In light of this context, we provide a comprehensive summary of the detection mechanisms, performance characteristics, and application scope of Zn2+ fluorescence probes since year 2022 while highlighting their advantages. We also propose solutions to address existing issues with these probes and outline future directions for their advancement. This review aims to serve as a valuable reference source offering insights into the development of advanced organic small-molecule-based fluorescence probes specifically designed for detecting Zn2+.

Photoactivatable Engineering of CRISPR/Cas9-Inducible DNAzyme Probe for In Situ Imaging of Nuclear Zinc Ions

DNAzyme-based fluorescent probes for imaging metal ions in living cells have received much attention recently. However, employing in situ metal ions imaging within subcellular organelles, such as nucleus, remains a significant challenge. We developed a three-stranded DNAzyme probe (TSDP) that contained a 20-base-pair (20-bp) recognition site of a CRISPR/Cas9, which blocks the DNAzyme activity. When Cas9, with its specialized nuclear localization function, forms an active complex with sgRNA within the cell nucleus, it cleaves the TSDP at the recognition site, resulting in the in situ formation of catalytic DNAzyme structure. With this design, the CRISPR/Cas9-inducible imaging of nuclear Zn2+ is demonstrated in living cells. Moreover, the superiority of CRISPR-DNAzyme for spatiotemporal control imaging was demonstrated by integrating it with photoactivation strategy and Boolean logic gate for dynamic monitoring nuclear Zn2+ in both HeLa cells and mice. Collectively, this conceptual design expands the DNAzyme toolbox for visualizing nuclear metal ions and thus provides new analytical methods for nuclear metal-associated biology.

Revealing the elevation of Zn2+ in the brain of depressed mice by a ratiometric fluorescent probe with dual near-infrared emissions

A mitochondria-targeted ratiometric fluorescent probe (Mito-Zn) was first designed and synthesized with dual emissions both located in the near-infrared region, for Zn2+ detection with high sensitivity and selectivity. By using the developed Mito-Zn, a high level of Zn2+ in the depressed mouse brain was discovered for the first time.

Recent advances in Zn2+ imaging: From organelles to in vivo applications

Zn2+ is involved in various physiological and pathological processes in living systems. Monitoring the dynamic spatiotemporal changes of Zn2+ levels in organelles, cells, and in vivo is of great importance for the investigation of the physiological and pathological functions of Zn2+. However, this task is quite challenging since Zn2+ in living systems is present at low concentrations and undergoes rapid dynamic changes. In this review, we summarize the design and application of fluorescent probes for Zn2+ imaging in organelles, cells, and live organisms reported over the past two years. We aim to provide inspiration for the design of novel Zn2+ probes for multi-level monitoring and deepen the understanding of Zn2+ biology.

Comparison of Three Low-Molecular-Weight Fluorescent Probes for Measuring Free Zinc Levels in Cultured Mammary Cells

Free zinc is a critical regulator in signal transduction and affects many cellular processes relevant to cancer, including proliferation and cell death. Acting as a second messenger, altered free intracellular zinc has fundamental effects on regulating enzymes such as phosphatases and caspases. Therefore, the determination of free intracellular zinc levels is essential to assess its influence on the signaling processes involved in cancer development and progression. In this study, we compare three low-molecular-weight fluorescent probes, ZinPyr-1, TSQ, and FluoZin-3, for measuring free zinc in different mammary cell lines (MCF10A, MCF7, T47D, and MDA-MB-231). In summary, ZinPyr-1 is the most suitable probe for free Zn quantification. It responds well to calibration based on minimal fluorescence in the presence of the chelator TPEN (N,N,N',N'-Tetrakis(2-pyridylmethyl)ethylenediamine) and maximal fluorescence by saturation with ZnSO₄, resulting in the detection of free intracellular zinc in breast cancer subtypes ranging from 0.62 nM to 1.25 nM. It also allows for measuring the zinc fluxes resulting from incubation with extracellular zinc, showing differences in the zinc uptake between the non-malignant MCF10A cell line and the other cell lines. Finally, ZinPyr-1 enables the monitoring of sub-cellular distributions by fluorescence microscopy. Altogether, these properties provide a basis for the further exploration of free zinc in order to realize its full potential as a possible biomarker or even therapeutic target in breast cancer.

Synthesis and anticancer mechanisms of zinc(II)-8-hydroxyquinoline complexes with 1,10-phenanthroline ancillary ligands

Twenty new zinc(II) complexes with 8-hydroxyquinoline (H-Q1-H-Q6) in the presence of 1,10-phenanthroline derivatives (D1-D10) were synthesized and formulated as [Zn(Q1)₂(D1)] (DQ1), [Zn(Q2)₂(D2)]·CH₃OH (DQ2), [Zn(Q1)₂(D3)] (DQ3), [Zn(Q1)₂(D4)] (DQ4), [Zn(Q3)₂(D5)] (DQ5), [Zn(Q3)₂(D4)] (DQ6), [Zn(Q4)₂(D5)]·CH₃OH (DQ7), [Zn(Q4)₂(D6)] (DQ8), [Zn(Q4)₂(D3)]·CH₃OH (DQ9), [Zn(Q4)₂(D1)]·H₂O (DQ10), [Zn(Q5)₂(D4)] (DQ11), [Zn(Q6)₂(D6)]·CH₃OH (DQ12), [Zn(Q5)₂(D2)]·5CH₃OH·H₂O (DQ13), [Zn(Q5)₂(D7)]·CH₃OH (DQ14), [Zn(Q5)₂(D8)]·CH₂Cl₂ (DQ15), [Zn(Q5)₂(D9)] (DQ16), [Zn(Q5)₂(D1)] (DQ17), [Zn(Q5)₂(D5)] (DQ18), [Zn(Q5)₂(D10)]·CH₂Cl₂ (DQ19) and [Zn(Q5)₂(D3)] (DQ20). They were characterized using multiple techniques. The cytotoxicity of DQ1-DQ20 was screened using human cisplatin-resistant SK-OV-3/DDP ovarian cancer (SK-OV-3CR) cells and normal hepatocyte (HL-7702) cells. Complex DQ6 showed low IC₅₀ values (2.25 ± 0.13 μM) on SK-OV-3CR cells, more than 3.0-8.0 times more cytotoxic than DQ1-DQ5 and DQ7-DQ20 (≥6.78 μM), and even 22.2 times more cytotoxic than the standard cisplatin, the corresponding free H-Q1-H-Q6 and D1-D10 alone (>50 μM). As a comparison, DQ1-DQ20 displayed nontoxic rates against healthy HL-7702 cells. Furthermore, DQ6 and DQ11 induced significant apoptosis via mitophagy pathways. DQ6 also significantly inhibited tumor growth in an in vivo SK-OV-3-xenograft model (ca. 49.7%). Thus, DQ6 may serve as a lead complex for the discovery of new antitumor agents.

Fluorescent Probes as a Tool in Diagnostic and Drug Delivery Systems

Over the last few years, the development of fluorescent probes has received considerable attention. Fluorescence signaling allows noninvasive and harmless real-time imaging with great spectral resolution in living objects, which is extremely useful for modern biomedical applications. This review presents the basic photophysical principles and strategies for the rational design of fluorescent probes as visualization agents in medical diagnosis and drug delivery systems. Common photophysical phenomena, such as Intramolecular Charge Transfer (ICT), Twisted Intramolecular Charge Transfer (TICT), Photoinduced Electron Transfer (PET), Excited-State Intramolecular Proton Transfer (ESIPT), Fluorescent Resonance Energy Transfer (FRET), and Aggregation-Induced Emission (AIE), are described as platforms for fluorescence sensing and imaging in vivo and in vitro. The presented examples are focused on the visualization of pH, biologically important cations and anions, reactive oxygen species (ROS), viscosity, biomolecules, and enzymes that find application for diagnostic purposes. The general strategies regarding fluorescence probes as molecular logic devices and fluorescence–drug conjugates for theranostic and drug delivery systems are discussed. This work could be of help for researchers working in the field of fluorescence sensing compounds, molecular logic gates, and drug delivery.

Fluorescent Probes for Biological Species and Microenvironments: from Rational Design to Bioimaging Applications

Some important biological species and microenvironments maintain a complex and delicate dynamic balance in life systems, participating in the regulation of various physiological processes and playing indispensable roles in maintaining the healthy development of living bodies. Disruption of their homeostasis in living organisms can cause various diseases and even death. Therefore, real time monitoring of these biological species and microenvironments during different physiological and pathological processes is of great significance. Fluorescent-probe-based techniques have been recognized as one of the most powerful tools for real time imaging in biological samples. In this Account, we introduce the representative works from our group in the field of fluorescent probes for biological imaging capable of detecting metal ions, small bioactive molecules, and the microenvironment. The design strategies of small molecule fluorescent probes and their applications in biological imaging will be discussed. By regulating the design strategy and mechanism (e.g., ICT, PeT, and FRET) of the electronic and spectral characteristics of the fluorescent platforms, these chemical probes show high selectivity and diverse functions, which can be used for imaging of various physiological and pathological processes. Through the exploration of the rational response mechanism and design strategy, combined with a variety of imaging techniques, such as super-resolution imaging, photoacoustic (PA) imaging, etc., we have realized multimode imaging of the important biological analytes from the subcellular level to the in vivo level, which provides powerful means to study the physiological and pathological functions of these species and microenvironments. This Account aims to offer insights and inspiration for the development of novel fluorescent probes for biological imaging, which could provide powerful tools for the study of chemical biology. Overall, we represent a series of turn-on/turn-off/ratiometric fluorescent/PA probes to visually and dynamically trace biological species and microenvironments in cells and even in vivo that seek higher resolution and depth molecular imaging to improve diagnostic methods and clarify new discoveries related to chemical biology. Our future efforts will be devoted to developing multiorganelle targeted fluorescent probes to study the mechanism of subcellular organelle interaction and employing various dual-mode probes of NIR II and PA imaging to investigate the development of related diseases and treat the related diseases at subcellular and in vivo levels.

Fluorescent probes for the detection of disease-associated biomarkers

Fluorescent probes have emerged as indispensable chemical tools to the field of chemical biology and medicine. The ability to detect intracellular species and monitor physiological processes has not only advanced our knowledge in biology but has provided new approaches towards disease diagnosis. In this review, we detail the design criteria and strategies for some recently reported fluorescent probes that can detect a wide range of biologically important species in cells and in vivo. In doing so, we highlight the importance of each biological species and their role in biological systems and for disease progression. We then discuss the current problems and challenges of existing technologies and provide our perspective on the future directions of the research area. Overall, we hope this review will provide inspiration for researchers and prove as useful guide for the development of the next generation of fluorescent probes.

Organelle-Level Labile Zn2+ Mapping Based on Targetable Fluorescent Sensors

Although many Zn²⁺ fluorescent probes have been developed, there remains a lack of consensus on the labile Zn²⁺ concentrations ([Zn²⁺]) in several cellular compartments, as the fluorescence properties and zinc affinity of the fluorescent probes are greatly affected by the pH and redox environments specific to organelles. In this study, we developed two turn-on-type Zn²⁺ fluorescent probes, namely, ZnDA-2H and ZnDA-3H, with low pH sensitivity and suitable affinity (K_d = 5.0 and 0.16 nM) for detecting physiological labile Zn²⁺ in various cellular compartments, such as the cytosol, nucleus, ER, and mitochondria. Due to their sufficient membrane permeability, both probes were precisely localized to the target organelles in HeLa cells using HaloTag labeling technology. Using an in situ standard quantification method, we identified the [Zn²⁺] in the tested organelles, resulting in the subcellular [Zn²⁺] distribution as [Zn²⁺]_ER < [Zn²⁺]_mito < [Zn²⁺]_cyto ∼ [Zn²⁺]_nuc.

Benzimidazole–acid hydrazide Schiff–Mannich combo ligands enable nano–molar detection of Zn2+ via fluorescence turn–on mode from semi–aqueous medium, HuH–7 cells, and plants

Herein, we have synthesized two unsymmetrical and dipodal Schiff–Mannich combo ligands, benzoic acid (3–benzoimidazol–1–ylmethyl–2–hydroxy–5–methyl–benzylidene)–hydrazide (H2BBH) and the hydroxyl analogue, 2–hydroxy–benzoic acid (3–benzoimidazol–1–ylmethyl–2–hydroxy–5–methyl–benzylidene)–hydrazide (H3BSH) for selective detection of Zn2+ in semi–aqueous...

Tracking Labile Copper Fluctuation In Vivo/Ex Vivo: Design and Application of a Ratiometric Near-Infrared Fluorophore Derived from 4-Aminostyrene-Conjugated Boron Dipyrromethene

Specimen differences, tissue-dependent background fluorescence and scattering, and deviated specimen position and sensor concentration make optical imaging for labile copper fluctuation in animals questionable, and a signal comparison between specimens is infeasible. We proposed ratiometric optical imaging as an alternative to overcome these disadvantages, and a near-infrared (NIR) ratiometric sensor, BDPS1, was devised therefore by conjugating boron dipyrromethene (BODIPY) with 4-aminostyrene and modifying the 4-amino group as a Cu+ chelator. BDPS1 possessed an excitation ratiometric copper-sensing ability to show the ratio of NIR emission (710 nm) upon excitation at 600 nm to that at 660 nm, Fex600/Fex660, increasing from 2.8 to 10.7. This sensor displayed still the opposite copper response of its internal charge transfer (ICT; 670 nm) and local (581 nm) emission bands. Ratiometric imaging with this sensor disclosed a higher labile copper region near the nucleus apparatus, and HEK-293T cells were more sensitive to copper incubation than MCF-7 cells. Dual excitation ratiometric imaging with this sensor realized tracking of labile copper fluctuation in mice, and the whole-body imaging found that tail intravenous injection of CUTX-101, a therapeutical agent for Menkes disease, led to a distinct labile copper increase in the upper belly. The ex vivo imaging of the resected viscera of mice revealed that CUTX-101 injection enhanced the labile copper level in the liver, intestine, lung, and gall bladder in sequence, yet the kidney, heart, and spleen showed almost no response. This study indicated that modifying BODIPY as an extended ICT fluorophore, with its electron-donating group being derived as a metal chelator, is an effective design rationale of NIR ratiometric sensors for copper tracking in vivo/ex vivo.

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.

NBD-based synthetic probes for sensing small molecules and proteins: design, sensing mechanisms and biological applications

Compounds with a nitrobenzoxadiazole (NBD) skeleton exhibit prominent useful properties including environmental sensitivity, high reactivity toward amines and biothiols (including H2S) accompanied by distinct colorimetric and fluorescent changes, fluorescence-quenching ability, and small size, all of which facilitate biomolecular sensing and self-assembly. Amines are important biological nucleophiles, and the unique activity of NBD ethers with amines has allowed for site-specific protein labelling and for the detection of enzyme activities. Both H2S and biothiols are involved in a wide range of physiological processes in mammals, and misregulation of these small molecules is associated with numerous diseases including cancers. In this review, we focus on NBD-based synthetic probes as advanced chemical tools for biomolecular sensing. Specifically, we discuss the sensing mechanisms and selectivity of the probes, the design strategies for multi-reactable multi-quenching probes, and the associated biological applications of these important constructs. We also highlight self-assembled NBD-based probes and outline future directions for NBD-based chemosensors. We hope that this comprehensive review will facilitate the development of future probes for investigating and understanding different biological processes and aid the development of potential theranostic agents.

Real-time detection and imaging of exogenous and endogenous Zn2+ in the PC12 cell model of depression with a NIR fluorescent probe

Depression is closely related to overactivation of N-methyl-d-aspartic acid (NMDA) receptors, and Zn2+ is a vital NMDA receptor modulator involved in the pathophysiological and physiological processes of depression. Therefore, quantitative and real-time detection of Zn2+ is very important for understanding the pathogenesis of depression. In this work, a near-infrared (NIR) fluorescent probe ISO-DPA was designed and synthesized for Zn2+ detection with a large Stokes shift (185 nm), high quantum yield (up to 44%), high sensitivity (LOD = 0.106 μM) and good pH stability. The probe showed rapid response within 10 s, accompanied by a distinct fluorescence change from faint to bright pink with the fluorescence intensity increasing 4.5-fold. Moreover, the sensing mechanism of ISO-DPA towards Zn2+ was supported by MALDI-TOF-MS and Job's plot. The probe ISO-DPA could detect instantaneous variation of exogenous and endogenous Zn2+ in PC12 cells. The bioimaging results reveal the increase of the endogenous Zn2+ concentration in PC12 cells under the oxidative stress induced by glutamate and confirm that overactivation of NMDA receptors results in an increase of the Zn2+ level. All the results proved that ISO-DPA is an excellent probe for detecting Zn2+ in solution and living cells and could help us better understand Zn2+ associated pathogenesis of depression.

FRET processes of bi-fluorophoric sensor material containing tetraphenylethylene donor and optical-switchable merocyanine acceptor for lead ion (Pb2+) detection in semi-aqueous media

A novel aggregation-induced emission (AIE) structure containing a tetraphenylethene (TPE) unit covalently linked with a merocyanine (MC) unit was synthesized and investigated in semi-aqueous solutions with 90% water fraction. The open-form structure of red-emissive MC unit combined with TPE unit was utilized as a bi-fluorophoric sensor to detect lead(II) ion, which could be transformed from the close-form structure of non-emissive SP unit upon UV exposure. Moreover, the TPE unit as an energy donor with the blue-green photoluminescence (PL) emission at 480 nm was combined with the MC unit as an energy acceptor with the red PL emission at 635 nm. Due to the Förster resonance energy transfer (FRET) processes, the bi-fluorophoric sensor produced more efficient ratiometric PL behavior to induce a stronger red PL emission than that of the mono-fluorophoric MC unit. Hence, the PL sensor responses of the AIE bi-fluorophoric structure toward lead(II) ion could be further amplified via the FRET-OFF processes to turn off red PL emission of the coordinated MC acceptor and to recover blue-green PL emission of the TPE donor. Accordingly, the best LOD value for the AIE sensor detection toward Pb2+ was 0.27 μM. The highest red MC emission with the optimum FRET process of AIE sensor could be utilized in cell viability tests to prove the non-toxic and remarkable bio-marker of AIE sensor to detect lead(II) ion in live cells. The developed FRET-OFF processes with ratiometric PL behavior of the bi-fluorophoric AIE sensor can be utilized for future chemo- and bio-sensor applications.

Development of a piperazinyl-NBD-based fluorescent probe and its dual-channel detection for hydrogen sulfide

To selectively detect H₂S based on the thiolysis reaction of 7-nitro-1,2,3-benzoxadiazole (NBD), amines attracted increasing attention since NBD amine is regarded as a new H₂S reaction site. Herein, a novel fluorescent probe, triphenylamine piperazine NBD (TPA-Pz-NBD), was developed. The results showed that it exhibited high selectivity towards H₂S via fluorescence spectroscopy and solution color. Furthermore, TPA-Pz-NBD not only detected H₂S by a dual-channel, turn-on fluorescence signal at 500 nm and turn-off fluorescence signal at 545 nm, respectively, but also displayed a wide detection range of 0-125 μM. In addition, living cell imaging results indicated that TPA-Pz-NBD holds potential for the detection of intracellular H₂S.

Highly sensitive naphthalimide based Schiff base for the fluorimetric detection of Fe3

A simple 1,8-naphthalimide based Schiff base probe (E)-6-((4-(diethylamino)-2-hydroxybenzylidene)amino)-2-(2-morpholinoethyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NDSM) has been designed and synthesized for the specific detection of Fe3+ based on a fluorimetric mode. The absorbance of NDSM at 360 nm increased significantly in acetonitrile : water (7 : 3, v/v) medium only in the presence of Fe3+ ions with a visible colour change from yellow to golden yellow. Likewise, fluorescence emission intensity at 531 nm was almost wholly quenched in the presence of Fe3+. However, other competitive ions influenced insignificantly or did not affect the optical properties of NDSM. Lysosome targetability was expected from NDSM due to the installation of a basic morpholine unit. The LOD was found to be 0.8 μM with a response time of seconds. The fluorescence reversibility of NDSM + Fe3+ was established with complexing agent EDTA. Fe3+ influences the optical properties of NDSM by complexing with it, which blocks C[double bond, length as m-dash]N isomerization in addition to the ICT mechanism. The real-time application of Fe3+ was demonstrated in test paper-based detection, by the construction of a molecular logic gate, quantification of Fe3+ in water samples and fluorescence imaging of Fe3+.

The application of amide units in the construction of neutral functional dyes for mitochondrial staining

To develop a new class of neutral fluorescent dyes with mitochondrial staining capacity, a series of functional dyes were obtained from Nile red (2a–e) and coumarin (3a–e) with different amide compounds via Suzuki coupling reactions.

A photoacoustic Zn2+ sensor based on a merocyanine/xanthene-6-ol hybrid chromophore and its ratiometric imaging in mice

HD-Zn was constructed for reversible ratiometric PA Zn²⁺ imaging in vivo. Zn²⁺ titration experiments together with a theoretical study suggests that Zn²⁺ chelation-induced ICT alteration in HD-Zn is responsible for its ratiometric PA sensing ability.

Investigation of thiolysis of 4-substituted SBD derivatives and rational design of a GSH-selective fluorescent probe

In order to evaluate 7-sulfonamide benzoxadiazole (SBD) derivatives for the development of fluorescent probes, herein we investigated the thiolysis reactivity and selectivity of a series of SBD compounds with different atoms (N/O/S/Se) at the 4-position. Both SBD-amine and SBD-ether are stable toward biothiols in buffer (pH 7.4), while SBD-selenoether can react efficiently with biothiols GSH/Hcy, Cys, and H2S to produce SBD-SG/S-Hcy, SBD-NH-Cys, and SBD-SH, respectively, with three different sets of spectral signals. Therefore, the SBD-selenoether compounds should be useful platforms for the differentiation of these biothiols. Though SBD-alkylthioether shows much lower reactivity than SBD-selenoether, SBD-arylthioether is a tunable motif and structural modifications at the aryl moiety enable the rate of thiol-mediated thiolysis to be modified. To this end, an ER-targeted GSH-selective fluorescent probe 7 was rationally designed via thiolysis of SBD-arylthioether. Compared with control probe SBD-Cl, probe 7 exhibits improved GSH selectivity and better biocompatibility. In total, this study highlights that the modification at the 4-position of SBD is an efficient strategy for the development of new fluorescent probes with tunable reactivity and selectivity.