High-Sensitivity Naphthalene-Based Two-Photon Fluorescent Probe Suitable for Direct Bioimaging of H2S in Living Cells

The design of hydrogen sulfide fluorescence probe based on dual nucleophilic reaction and its application for bioimaging

Hydrogen sulfide (H₂S) can undergo dual nucleophilic reaction, which is a wise and effective way to distinguish biothiols and H₂S. A novel H₂S fluorescence probe, 4-{2-[4-(2-disulfide pyridyl-benzoyloxy)-phenyl]-vinyl}-1-methyl-pyridinium[e]iodide (DSPBP), with two nucleophilic reaction sites has been developed. The spectra results showed that DSPBP could detect H₂S in ratiometric and colorimetric signals and has excellent selectivity and sensitivity. The fluorescence ratiometric signals (F₅₂₀/F₄₅₀) displayed a prominent increase from 0.74 to 7.08, the fluorescence color turned to yellow form blue simultaneously. The linear range was 2-14 μM and its detection limit was 25.7 nM. Moreover, the biocompatibility of DSPBP was fine and its toxicity was very low. It has been successfully used for imaging H₂S in cells.

Nanoscale fluorescent metal-organic framework composites as a logic platform for potential diagnosis of asthma

Asthma is a common chronic disorder, and the decreased hydrogen sulfide (H₂S) production in the lung has been considered as an early detection biomarker for asthma. However, the detection of H₂S in biological systems remains a challenge; because it requires the designed sensors to have the following features: nanoscale size, good biocompatibility, real-time detection, high selectivity/sensitivity, and good water stability. Here, we propose the potential of using nanoscale fluorescent metal-organic framework (MOF) composites Eu³⁺/Ag⁺@UiO-66-(COOH)₂ (hereafter denoted as EAUC) as a logic platform for tentative diagnosis of asthma by detecting the biomarker H₂S. This INHIBIT logic gate based on Eu³⁺@UiO-66-(COOH)₂ (EUC) can be produced by choosing Ag⁺ and H₂S as inputs and by monitoring the fluorescent signal (I₆₁₅) as an output. Our fluorescent studies indicate that the EAUC exhibits excellent selectivity, extreme sensitivity (limit of detection: 23.53 μM), and real-time in situ detection of H₂S. Further, MTT analysis in PC12 cells shows that the EAUC possesses low cytotoxicity and favourable biocompatibility that are suitable for the detection of biomarker H₂S in vivo, as demonstrated by the successful detection of spiked H₂S in the diluted serum samples. This work represents the possibility of using MOF-based logic platform for tentative diagnosis of asthma in clinical medicine.

A dinitro-functionalized metal-organic framework featuring visual and fluorogenic sensing of H2S in living cells, human blood plasma and environmental samples

Here, we describe a new dinitro-functionalized Zr(iv) MOF (MOF = metal-organic framework) having a UiO-66 (UiO = University of Oslo) framework topology called UiO-66-(NO₂)₂ (1). It shows fluorescence turn-on behavior towards H₂S in simulated biological medium (HEPES buffer, pH = 7.4). By employing solvothermal conditions, 1 was successfully synthesized by reacting ZrCl₄, H₂BDC-(NO₂)₂ [H₂BDC-(NO₂)₂ = 2,5-dinitro-1,4-benzenedicarboxylic acid] ligand and benzoic acid with a molar ratio of 1 : 1 : 10 in DMF (DMF = N,N-dimethylformamide) at 130 °C for 24 h. The material was characterized by infrared spectroscopy, X-ray powder diffraction (XRPD) and thermogravimetric (TG) analyses. The compound not only displays highly sensitive fluorometric sensing of H₂S but also exhibits a visually detectable colorimetric change towards H₂S in daylight. Moreover, the high selectivity of 1' towards H₂S is retained even when several other biologically intrusive species co-exist in the sensing medium. The limit of detection (LOD) of the compound is 14.14 μM which lies in the range of the H₂S concentration found in biological systems. Fluorescence microscopy studies on J774A.1 cells revealed the efficacy of the probe for imaging H₂S in living cells. Moreover, this material can detect H₂S in human blood plasma (HBP) and monitor the sulfide concentration in real water samples. All these features clearly demonstrate that the material has huge potential for highly selective sensing of both extracellular and intracellular H₂S.

A recyclable post-synthetically modified Al(iii) based metal–organic framework for fast and selective fluorogenic recognition of bilirubin in human biofluids

The ultra-fast, highly sensitive and selective sensing features of bilirubin in human biofluids by a post-synthetically modified Al(iii) MOF are presented.

A highly sensitive and selective two-photon fluorescent probe for glutathione S-transferase detection and imaging in living cells and tissues

Design and development of a two-photon fluorescent probe for GST detection and imaging in living cells and deep tissues.

Stepwise dual stimuli triggered dual drug release by a single naphthalene based two-photon chromophore to reverse MDR for alkylating agents with dual surveillance in uncaging steps

A single chromophore based dinitrophenylsulphonyl–naphthalene–chlorambucil conjugate drug delivery system is presented for the dual stimuli controlled release of SO₂and chlorambucil.

A Turn-On Optoacoustic Probe for Imaging Metformin-Induced Upregulation of Hepatic Hydrogen Sulfide and Subsequent Liver Injury

Metformin is currently the most prescribed oral agent for diabetes treatment; however the overdose or long-term use may cause some severe side effects such as liver injury. Researches indicate that metformin-induced liver injury is closely related to upregulation of hepatic H2S. Hence, monitoring hepatic H2S generation induced by metformin could be an effective approach for evaluating hepatoxicity of the drug. Methods: We present a novel turn-on and dual-mode probe for detecting and imaging metformin-induced liver injury by specifically tracking the upregulation of hepatic H2S with fluorescent and optoacoustic methods. After reaction with H2S, the strong electron-withdrawing group dinitrophenyl ether (which acts as both the recognition moiety and the fluorescence quencher) was cleaved and replaced by an electron-donating group hydroxyl. This correspondingly leads to the changes of the probe's electronic state and absorption red-shifting as well as the subsequent turn-on fluorescent and optoacoustic signals. Results: The probe was applied to the colon tumor-bearing mice model and the metformin-induced liver injury mice model to achieve tumor imaging and liver injury assessment. The biosafety of the probe was verified by histological analysis (hematoxylin and eosin staining) and serum biochemical assays. Conclusion: The probe responds quickly to H2S in tumors and the liver, and MSOT imaging with the probe offers cross-secitonal and 3D spatial information of liver injury. This study may provide an effective approach for accessing medication side effects by tracking drug-metabolism-related products.

Detection and Imaging of Hydrogen Sulfide in Lysosomes of Living Cells with Activatable Fluorescent Quantum Dots

The simple, sensitive, and specific detection of hydrogen sulfide (H₂S) is of great importance because of its crucial role in food safety, environmental pollution, and various pathological and physiological processes. Here, we reported activatable fluorescence nanoprobe-based quantum dots (QDs) for sensitive and selective monitoring of H₂S in red wine, environmental water samples, and lysosome of live cancer cells. The nanoprobe was prepared through a strong electrostatic interaction between thioglycolic-acid-stabilized CdTe QDs and p-amino thiophenol capped silver nanoparticles (AgNPs) that resulted in the formation of the assembled nanostructure, called QD/AgNP nanocomplexes. The initial fluorescence of QDs was effectively quenched by the AgNPs because of the inner filter effect. Upon interaction with H₂S, the strong etching ability of H₂S to AgNPs could trigger the disassembly of QD/AgNP nanocomplexes and generate Ag₂S on the surface of QDs, achieving a shell-core Ag₂S/CdTe QDs with remarkable fluorescence as a result of the termination of inner filter effect. The aqueous solution studies displayed that the assembled QD/AgNP nanoprobe was sensitive to detect H₂S, with a detection limit of 15 nM. In addition, this assembled QD/AgNP nanoprobe showed a high specificity toward H₂S over other anions and biologically relevant species. The subsequent fluorescence imaging studies demonstrated that the assembled QD/AgNP nanoprobe exhibited high ability to enter into cellular lysosome and generated an enhancement fluorescence, which was used for endogenous H₂S detection in lysosome of living cancer cells. This proposed nanoprobe revealed a more simple, rapid, time-saving, low-cost, sensitive, and selective process for monitoring of H₂S in further environmental pollution, food safety, and clinical diagnosis of H₂S-related diseases.

Naphthalene, a versatile platform in medicinal chemistry: Sky-high perspective

Naphthalene, a cytotoxic moiety, is an extensively explored aromatic conjugated system with applications in various pathophysiological conditions viz. anticancer, antimicrobial, anti-inflammatory, antiviral, antitubercular, antihypertensive, antidiabetic, anti-neurodegenerative, antipsychotic, anticonvulsant, antidepressant. Naphthalene epoxides and naphthoquinones are most reactive metabolites of naphthalene and are responsible for the covalent interaction with cysteine amino acid of cellular proteins for cytotoxic nature. Many naphthalene derived bioactive phytoconstituents are present in nature including podophyllotoxins (Etoposide, teniposide), bis-ANS 82, Rifampicin, Justiprocumin A, B, Patentiflorin A. The naphthalene-based molecules, viz. Naphyrone, tolnaftate, naftifine, nafcillin, terbinafine, propranolol, nabumetone, nafimidone, naproxen, duloxetine, lasofoxifene, bedaquiline etc. have also been approved by FDA and are being marketed as therapeutics. Thus, the naphthalene scaffold emerges as an important building block in drug discovery owing to its broad spectrum of biological activities through varying structural modifications. This review incorporates the pharmacological aspects of different types of chemically modified naphthalene-based molecules along with their activity profile. This compiled information may serve as a benchmark for the alteration of existing ligands to design novel potent molecules with lesser side effects.

Imaging of intracellular sulfane sulfur expression changes under hypoxic stress via a selenium-containing near-infrared fluorescent probe

Hypoxia is a significant global issue affecting the health of organisms. Oxygen homeostasis is critical for mammalian cell survival and cellular activities. Hypoxic stress can lead to cell injury and death, which contributes to many diseases. Sulfane sulfur is involved in crucial roles in physiological processes of maintaining intracellular redox state and ameliorating oxidative damage. Therefore, real-time imaging of changes in sulfane sulfur levels is important for understanding their biofunctions in cells. In this study, we develop a new near-infrared (NIR) fluorescent probe BD-diSeH for imaging of sulfane sulfur changes in cells and in vivo under hypoxic stress. The probe includes two moieties: an NIR azo-BODIPY fluorophore equipped with a strong nucleophilic phenylselenol group (-SeH). The probe is capable of tracing dynamic changes of endogenous sulfane sulfur based on a fast and spontaneous intramolecular cyclization reaction. The probe has been successfully used for imaging sulfane sulfur in 3D-multicellular spheroid and mouse hippocampus under hypoxic stress. The overall levels of sulfane sulfur are affected by the degree and length of hypoxic stress. The results reveal a close relationship between sulfane sulfur and hypoxia in living cells and in vivo, allowing better understanding of physiological and pathological processes involving sulfane sulfur. Moreover, to investigate the effects of environmental hypoxia on aquatic animals, this probe has been applied for sulfane sulfur detection in hypoxic zebrafish.

Consumption of H2S from Our Daily Diet: Determination by a Simple Chemosensing Method

A unique method has been developed for comparative analysis of H₂S produced from food samples from our daily diet, both qualitatively and quantitatively. The selective detection of H₂S has been executed by introducing a simple chemodosimeter (PN-N ₃ ) that gives response on the basis of intramolecular charge transfer. UV-vis, fluorimetric, and NMR titrations were performed to demonstrate the sensing mechanism and electronic environment of PN-N ₃ in the presence of H₂S. Density functional theory calculations were performed to validate the mechanism of azide (PN-N ₃ ) reduction to amine (PN-NH ₂ ) by the strong reducing power of H₂S. The potentiality of this chemosensing method is that it could be treated as a simple, less-time-consuming, and cost-effective method for determining H₂S in biological samples in the nanomolar range.

A two-photon fluorescent probe for bio-imaging of formaldehyde in living cells and tissues

Formaldehyde (FA) plays an important role in living systems as a reactive carbonyl species (RCS). An abnormal degree of FA is known to induce neurodegeneration, cognitive decrease and memory loss owing to the formation of strong cross-link DNA and protein and other molecules. The development of efficient methods for biological FA detection is of great biomedical importance. Although a few one-photon FA fluorescent probes have been reported for imaging in living cells, probes excited by two photons are more suitable for bio-imaging due to their low background fluorescence, less photobleaching, and deep penetration depth. In this study, a two-photon fluorescent probe for FA detection and bio-imaging in living cells and tissues was reported. The detection is based on the 2-aza-Cope sigmatropic rearrangement followed by elimination to release the fluorophore, resulting in both one- and two-photon excited fluorescence increase. The probe showed a high sensitivity to FA with a detection limit of 0.2 μM. Moreover, enabled the two-photon bio-imaging of FA in live HEK-293 cells and tissues with tissue-imaging depths of 40-170 μm. Furthermore, could be applied for the monitoring of endogenous FA in live MCF-7 cells, presaging its practical applications in biological systems.

Ultrathin two-dimensional covalent organic framework nanoprobe for interference-resistant two-photon fluorescence bioimaging

A two-photon fluorescent covalent organic framework nanopore is designed for the first time for H₂S interference-resistant bioimaging.

The complex environment of living organisms significantly challenges the selectivity of classic small-molecule fluorescent probes for bioimaging. Due to their predesigned topological structure and engineered internal pore surface, covalent organic frameworks (COFs) have the ability to filter out coexisting interference components and help to achieve accurate biosensing. Herein, we propose an effective interference-resistant strategy by creating a COF-based hybrid probe that combines the respective advantages of COFs and small-molecule probes. As a proof of concept, a two-photon fluorescent COF nanoprobe, namely TpASH-NPHS, is developed for targeting hydrogen sulfide (H₂S) as a model analyte. TpASH-NPHS exhibits limited cytotoxicity, excellent photostability and long-term bioimaging capability. More importantly, compared with the small-molecule probe, TpASH-NPHS achieves accurate detection without the interference from intracellular enzymes. This allows us to monitor the levels of endogenous H₂S in a mouse model of cirrhosis.

Evaluating Drug-Induced Liver Injury and Its Remission via Discrimination and Imaging of HClO and H2S with a Two-Photon Fluorescent Probe

Drug-induced liver injury (DILI) has aroused wide concern. Finding new markers or indicators as well as detoxification molecules for DILI is of great significance and good application prospect, which can help develop effective preclinical screening methodology and corresponding treatment protocols. Herein, in this article, DILI caused by antidepressant drugs of duloxetine and fluoxetine and its remission were evaluated by a two-photon fluorescent probe, RPC-1, through discriminating and imaging HClO and H₂S simultaneously. By being applied both in vitro and in vivo, RPC-1 revealed slight up-regulation of HClO and negligible liver damage after administration of either of the two drugs. In contrast, an apparent up-regulation of HClO and obvious liver damage was observed after combined administration of the drugs. Meanwhile, the pretreatment of N-acetyl cysteine (NAC) resulted in the increasing of endogenous H₂S level, which contributed to the remission of DILI. The histological analysis and serological test both gave good consistency with the imaging results. These findings demonstrate that HClO may be an appropriate indicator of DILI, and H₂S plays an important role in the antidotal effect of NAC. We envision that RPC-1 can be used as a powerful tool to predict clinical DILI and study the effect of antidote, as well as explore the molecular mechanisms involved.

A novel fluorescent probe based on biphenyl and rhodamine for multi-metal ion recognition and its application

At present, the design of multi ion sensing receptors is a new area of research due to their potential application in the recognition of analytes. Herein, a novel fluorescent probe for the detection of multi metal ions was designed and synthesized based on the fluorophores of biphenyl and rhodamine. Probe 1 exhibits multiple fluorescence responses to various metal ions (Zn²⁺, Al³⁺, Cr³⁺ and Fe³⁺) and is accompanied by different optical signal outputs. Moreover, the interference between the target ions can also be effectively solved by the introduction of probe 2 and the addition of the corresponding anions. Probe 1 was also successfully used to detect trace metal ions in real water samples and silicone plate test strips were prepared for the rapid qualitative detection of target metal ions. In addition, in order to better understand the multiple response mechanism of probe 1, geometry optimizations and electronic calculations were carried out at the B3LYP/6-31G*/LANL2DZ level of theory. And harmonic vibrational frequency calculations were also carried out to ensure that all optimized structures were at energy minima on the potential energy surface.

Chemically reversible binding of H2S to a zinc porphyrin complex: towards implementation of a reversible sensor via a "coordinative-based approach"

Binding of hydrogen sulfide (H₂S) to a zinc porphyrin complex and the stabilization of the related zinc hydrosulfido adduct are explored. High-resolution MALDI Fourier transform ion cyclotron resonance mass spectrometry (HR MALDI-FT-ICR) and ¹H NMR experiments provide evidence that HS^- coordination occurs at the zinc centre. The coordination of HS^- occurs in a reversible manner and modulates fluorescence emission of a tetra(N-methylpyridyl)porphine zinc complex (TMPyPZn). The results highlight the potential of TMPyPZn and related systems for the implementation of fast and simple H₂S sensors via a coordinative-based approach.

Living cell imaging and sensing of hydrogen sulfide using high-efficiency fluorescent Cu-doped carbon quantum dots

A simple Cu-doped carbon quantum dot-based fluorescent sensor for H₂S sensing and intracellular bioimaging was constructed.

Synthesis and Properties of D–π–A Structural Imidazole-Triphenylamine Derivatives

Four novel D-π-A structural 1-aryl-2-[4-(N,N-diphenyl)phenyl]-4,5-diphenyl-1H-imidazoles have been synthesised. Their synthesis, thermal stability, optical properties and electrochemical behaviour have also been investigated. These compounds exhibit increased thermal stability, blue emissions and intramolecular charge transfer. The HOMO and LUMO energy levels of these compounds were calculated from electrochemical measurements.

Dynamic mapping of spontaneously produced H2S in the entire cell space and in live animals using a rationally designed molecular switch

A rationally designed molecular switch created to detect and dynamically map spontaneous production of H₂S in whole cells and the organs of live zebrafish.

Hydrogen sulfide induced supramolecular self-assembly in living cells

A gasotransmitter mediated reduction instructs supramolecular self-assembly in multiple living cell lines, revealing the variation in intracellular H₂S production.

Pyrrolopyrrole aza boron dipyrromethene based two-photon fluorescent probes for subcellular imaging

A series of two-photon-absorbing pyrrolopyrrole aza boron dipyrromethenes have been prepared which can serve as fluorescent probes for subcellular imaging.

Supramolecular assembly affording a ratiometric two-photon fluorescent nanoprobe for quantitative detection and bioimaging

Fluorescence quantitative analyses for vital biomolecules are in great demand in biomedical science owing to their unique detection advantages with rapid, sensitive, non-damaging and specific identification. However, available fluorescence strategies for quantitative detection are usually hard to design and achieve. Inspired by supramolecular chemistry, a two-photon-excited fluorescent supramolecular nanoplatform (TPSNP) was designed for quantitative analysis with three parts: host molecules (β-CD polymers), a guest fluorophore of sensing probes (Np-Ad) and a guest internal reference (NpRh-Ad). In this strategy, the TPSNP possesses the merits of (i) improved water-solubility and biocompatibility; (ii) increased tissue penetration depth for bioimaging by two-photon excitation; (iii) quantitative and tunable assembly of functional guest molecules to obtain optimized detection conditions; (iv) a common approach to avoid the limitation of complicated design by adjustment of sensing probes; and (v) accurate quantitative analysis by virtue of reference molecules. As a proof-of-concept, we utilized the two-photon fluorescent probe NHS-Ad-based TPSNP-1 to realize accurate quantitative analysis of hydrogen sulfide (H₂S), with high sensitivity and good selectivity in live cells, deep tissues and ex vivo-dissected organs, suggesting that the TPSNP is an ideal quantitative indicator for clinical samples. What's more, TPSNP will pave the way for designing and preparing advanced supramolecular sensors for biosensing and biomedicine.

Graphitic nanocapsules: design, synthesis and bioanalytical applications

Graphitic nanocapsules are emerging nanomaterials which are gaining popularity along with the development of carbon nanomaterials. Their unique physical and chemical properties, as well as good biocompatibility, make them desirable agents for biomedical and bioanalytical applications. Through rational design, integrating graphitic nanocapsules with other materials provides them with additional properties which make them versatile nanoplatforms for bioanalysis. In this feature article, we present the use and performance of graphitic nanocapsules in a variety of bioanalytical applications. Based on their chemical properties, the specific merits and limitations of magnetic, hollow, and noble metal encapsulated graphitic nanocapsules are discussed. Detection, multi-modal imaging, and therapeutic applications are included. Future directions and potential solutions for further biomedical applications are also suggested.

Theoretical Studies on Two-Photon Fluorescent Hg2+ Probes Based on the Coumarin-Rhodamine System

The development of fluorescent sensors for Hg²⁺ has attracted much attention due to the well-known adverse effects of mercury on biological health. In the present work, the optical properties of two newly-synthesized Hg²⁺ chemosensors based on the coumarin-rhodamine system (named Pro1 and Pro2) were systematically investigated using time-dependent density functional theory. It is shown that Pro1 and Pro2 are effective ratiometric fluorescent Hg²⁺ probes, which recognize Hg²⁺ by Förster resonance energy transfer and through bond energy transfer mechanisms, respectively. To further understand the mechanisms of the two probes, we have developed an approach to predict the energy transfer rate between the donor and acceptor. Using this approach, it can be inferred that Pro1 has a six times higher energy transfer rate than Pro2. Thus the influence of spacer group between the donor and acceptor on the sensing performance of the probe is demonstrated. Specifically, two-photon absorption properties of these two probes are calculated. We have found that both probes show significant two-photon responses in the near-infrared light region. However, only the maximum two-photon absorption cross section of Pro1 is greatly enhanced with the presence of Hg²⁺, indicating that Pro1 can act as a potential two-photon excited fluorescent probe for Hg²⁺. The theoretical investigations would be helpful to build a relationship between the structure and the optical properties of the probes, providing information on the design of efficient two-photon fluorescent sensors that can be used for biological imaging of Hg²⁺ in vivo.

Aptamer-integrated DNA nanostructures for biosensing, bioimaging and cancer therapy

The combination of nanostructures with biomolecules leading to the generation of functional nanosystems holds great promise for biotechnological and biomedical applications. As a naturally occurring biomacromolecule, DNA exhibits excellent biocompatibility and programmability. Also, scalable synthesis can be readily realized through automated instruments. Such unique properties, together with Watson-Crick base-pairing interactions, make DNA a particularly promising candidate to be used as a building block material for a wide variety of nanostructures. In the past few decades, various DNA nanostructures have been developed, including one-, two- and three-dimensional nanomaterials. Aptamers are single-stranded DNA or RNA molecules selected by Systematic Evolution of Ligands by Exponential Enrichment (SELEX), with specific recognition abilities to their targets. Therefore, integrating aptamers into DNA nanostructures results in powerful tools for biosensing and bioimaging applications. Furthermore, owing to their high loading capability, aptamer-modified DNA nanostructures have also been altered to play the role of drug nanocarriers for in vivo applications and targeted cancer therapy. In this review, we summarize recent progress in the design of aptamers and related DNA molecule-integrated DNA nanostructures as well as their applications in biosensing, bioimaging and cancer therapy. To begin with, we first introduce the SELEX technology. Subsequently, the methodologies for the preparation of aptamer-integrated DNA nanostructures are presented. Then, we highlight their applications in biosensing and bioimaging for various targets, as well as targeted cancer therapy applications. Finally, we discuss several challenges and further opportunities in this emerging field.

Real-Time Monitoring ATP in Mitochondrion of Living Cells: A Specific Fluorescent Probe for ATP by Dual Recognition Sites

Adenosine triphosphate (ATP) is mainly produced in the mitochondrion and used as a universal energy source for various cellular events. Various fluorescent probes for ATP have been established successfully, but most of them are not appropriate for monitoring the fluctuation of the mitochondrial ATP level. Herein, a fluorescent probe named Mito-Rh is first synthesized and used to recognize ATP in mitochondrion. In the probe, rhodamine, diethylenetriamine, and triphenylphosphonium are selected as fluorophore, reaction site, and mitochondrion-targeting group, respectively. Probe Mito-Rh shows high sensitivity to ATP with 81-fold fluorescence enhancement, and the detection range (0.1-10 mM) can match the concentration level of ATP in the mitochondrion. Moreover, Mito-Rh provides excellent selectivity toward ATP over other biological anions (ADP, AMP, GTP, CTP, UTP) owing to a concurrent effect of dual recognition sites (hydrogen bond and π-π stacking). In particular, the probe can localize in mitochondrion specifically and demonstrates utility in the real-time detection of mitochondrial ATP concentration changes.

A novel two-photon fluorescent probe for hydrogen sulfide in living cells using an acedan–NBD amine dyad based on FRET process with high selectivity and sensitivity

The first NBD amine based two-photon fluorescence probe L using a FRET strategy was developed for the H₂S detecting in vitro and in vivo. The probe L not only afforded high selectivity and sensitivity for H₂S detecting, but also dispalyed a linear response to H₂S with a low detection limit 24 nM.

Selective visualization of endogenous hydrogen sulfide in lysosomes using aggregation induced emission dots

The AIE dots (AIED) with superior sensor properties have been developed for selective imaging of lysosomal H₂S in living cells.

An efficient two-photon fluorescent probe for measuring γ-glutamyltranspeptidase activity during the oxidative stress process in tumor cells and tissues

We have developed a novel TP excited fluorescent probe for GGT detection and bioimaging in an oxidative stress model in living cells and tissues.

A targetable fluorescent probe for imaging exogenous and intracellularly formed nitroxyl in mitochondria in living cells

We have developed a new mitochondrial-targeted turn-on fluorescent HNO probe (Mito-HNO). Fluorescence imaging shows that Mito-HNO is suitable for ratiometric visualization of HNO within mitochondria in living cells.

Efficient Two-Photon Fluorescence Nanoprobe for Turn-On Detection and Imaging of Ascorbic Acid in Living Cells and Tissues

Ascorbic acid (AA) serves as a key coenzyme in many metabolic pathways, and its abnormal level is found to be associated with several diseases. Therefore, monitoring AA level in living systems is of great biomedical significance. In comparison with one-photon excited fluorescent probes, two-photon (TP) excited probes are more suitable for bioimaging, as they could afford higher imaging resolution with deeper imaging depth. Here, we report for the first time an efficient TP fluorescence probe for turn-on detection and imaging of AA in living cells and tissues. In this nanosystem, the negatively charged two-photon nanoparticles (TPNPs), which were prepared by modifying the silica nanoparticles with a two-photon dye, could adsorb cobalt oxyhydroxide (CoOOH) nanoflakes which carried positive charge by electrostatic force, leading to a remarkable decrease in their fluorescence intensity. However, the introduction of AA could induce the fluorescence recovery of the nanoprobe because it could reduce CoOOH into Co(2+) and result in the destruction of the CoOOH nanoflakes. The nanosystem exhibits a high sensitivity toward AA, with a LOD of 170 nM observed. It also shows high selectivity toward AA over common potential interfering species. The nanoprobe possessed both the advantages of TP imaging and excellent membrane-permeability and good biocompatibility of the silica nanoparticles and was successfully applied in TP-excited imaging of AA in living cells and tissues.

Target-Activated Modulation of Dual-Color and Two-Photon Fluorescence of Graphene Quantum Dots for in Vivo Imaging of Hydrogen Peroxide

The development of nanoprobes suitable for two-photon microscopy techniques is highly desirable for mapping biological species in living systems. However, at the current stage, the nanoprobes are restricted to single-color fluorescence changes, making it unsuitable for quantitative detection. To circumvent this problem, we report here a rational design of a dual-emission and two-photon (TP) graphene quantum dot (GQD(420)) probe for imaging of hydrogen peroxide (H2O2). For specific recognition of H2O2 and lighting the fluorescence of TPGQD(420), a boronate ester-functionalized merocyanine (BMC) fluorophore was used as both target-activated trigger and the dual-emission fluorescence modulator. Upon two-photon excitation at 740 nm, TPGQD(420)-BMC displays a green-to-blue resolved emission band in response to H2O2 with an emission shift of 110 nm, and the H2O2 can be determined from 0.2 to 40 μM with a detection limit of 0.05 μM. Moreover, the fluorescence response of the TPGQD(420)-BMC toward H2O2 is rapid and extremely specific. The feasibility of the proposed method is demonstrated by two-photon ratiometrically mapping the production of endogenous H2O2 in living cells as well as in deep tissues of murine mode at 0-600 μm. To the best of our knowledge, this is the first paradigm to rationally design a dual-emission and two-photon nanoprobe via fluorescence modulation of GQDs with switchable molecules, which will extend new possibility to design powerful molecular tools for in vivo bioimaging applications.

Two-dimensional graphitic carbon nitride nanosheets for biosensing applications

Two-dimensional graphitic carbon nitride nanosheets (CNNSs) with planar graphene-like structure have stimulated increasingly research interest in recent years due to their unique physicochemical properties. CNNSs possess superior stability, high fluorescence quantum yield, low-toxicity, excellent biocompatibility, unique electroluminescent and photoelectrochemical properties, which make them appropriate candidates for biosensing. In this review, we first introduce the preparation and unique properties of CNNSs, with emphasis on their superior properties for biosensing. Then, recent advances of CNNSs in photoelectrochemical biosensing, electrochemiluminescence biosensing and fluorescence biosensing are highlighted. An additional attention is paid to the marriage of CNNSs and nucleic acids, which exhibits great potentials in both biosensing and intracellular imaging. Finally, current challenges and opportunities of this 2D material are outlined. Inspired by the unique properties of CNNSs and their advantages in biological applications, we expect that more attention will be drawn to this promising 2D material and extensive applications can be found in bioanalysis and diseases diagnosis.