A new turn-on fluorescence probe for Zn in aqueous solution and imaging application in living cells

We designed and synthesized a new pyrazoline-based turn-on fluorescence probe for Zn²⁺ by the reaction of chalcone and thiosemicarbazide. The structure of the probe was characterized by IR, NMR and HRMS spectroscopy. The probe (L) exhibits high selectivity and sensitivity for detecting Zn²⁺ in buffered EtOH/HEPES solution (EtOH/HEPES = 1/1, pH 7.2) with 80-fold fluorescence enhancement, which is superior to previous reports. Job’s plot analysis revealed 1:1 stoichiometry between probe L and Zn²⁺ ions. The association constant estimated by the Benesi–Hildebrand method and the detection limit were 3.92 × 10³ M⁻¹ and 5.2 × 10⁻⁷ M, respectively. A proposed binding mode was confirmed by ¹H NMR titration experiments and density functional theory (DFT) calculations. The probe is cell-permeable and stable at the physiological pH range in biological systems. Because of its fast response to Zn²⁺, the probe can monitor Zn²⁺ in living cells. Moreover, the selective binding of L and Zn²⁺ was reversible with the addition of EDTA in buffered EtOH/HEPES solution and Zn²⁺ could be imaged in SH-SY5Y neuron cells.     

A 1,8-naphthalimide-derived turn-on fluorescent probe for imaging lysosomal nitric oxide in living cells

Nitric oxide has played an important role in many physiological and pathological processes as a kind of important gas signal molecules. In this work, a new fluorescent probe LysoNO-Naph for detecting NO in lysosomes based on 1,8-naphthalimide was reported. LysoNO-Naph has sub-groups of o-phenylenediamine as a NO reaction site and 4-(2-aminoethyl)-morpholine as a lysosome-targetable group. This probe exhibited good selectivity and high sensitivity (4.57 μmol/L) toward NO in a wide pH range from 4 to 12. Furthermore, LysoNO-Naph can be used for imaging NO in lysosomes in living cells.     

A fluorescence enhanced probe for sulfur dioxide detection and fluorescence imaging in living cellsEI北大核心CSCD

基于香豆素和苯并吡啶基团,构建了用于二氧化硫(SO_(2))高效检测的荧光探针P1,其化学结构通过核磁氢谱(^(1)H NMR)、碳谱(^(13)C NMR)和高分辨质谱(HR-MS)确证。在缓冲溶液体系中,单独的探针P1具有微弱的荧光,识别SO_(2)后荧光发射强度明显增强,能够实现对SO_(2)的专一性裸眼识别,检出限为126 nmol/L。生物应用实验结果表明,该探针具有较低的细胞毒性,可用于生物活细胞中外源性SO_(2)的荧光成像。     

A highly selective and sensitive fluorescence "turn-on" probe for Ag+ in aqueous solution and live cells

A naphthalimide-based fluorescent probe, NPQ, that contains a novel receptor was successfully developed. NPQ exhibited "turn-on" fluorescence and excellent selectivity toward Ag(+) in the presence of various other metal ions in aqueous solution. A series of control compounds were designed and synthesized in order to explore the photoinduced electron transfer (PET) quenching mechanism of NPQ and binding mode of NPQ with Ag(+). Moreover, with the NPQ-Ag(+) complex, I(-) was easily selectively recognized by a marked fluorescence quenching. The live cell imaging experiments demonstrate that NPQ can be used as a fluorescent probe for monitoring Ag(+) in living cells.     

A selective turn-on fluorescent sensor for imaging copper in living cells

We present the synthesis, properties, and biological applications of Coppersensor-1 (CS1), a new water-soluble, turn-on fluorescent sensor for intracellular imaging of copper in living biological samples. CS1 utilizes a BODIPY reporter and thioether-rich receptor to provide high selectivity and sensitivity for Cu+ over other biologically relevant metal ions, including Cu2+, in aqueous solution. This BODIPY-based probe is the first Cu+-responsive sensor with visible excitation and emission profiles and gives a 10-fold turn-on response for detecting this ion. Confocal microscopy experiments further establish that CS1 is membrane-permeable and can successfully monitor intracellular Cu+ levels within living cells.     

A two-photon fluorescent turn-on probe for imaging of SO2 derivatives in living cells and tissues

SO₂ and its derivatives (bisulfite/sulfite) play crucial roles in several physiological processes. Therefore, development of reliable analytical methods for monitoring SO₂ and its derivatives in biological systems is very significant. In this paper, a FRET-based two-photon fluorescent turn-on probe, A-HCy, was proposed for specific detection of SO₂ derivatives through the bisulfite/sulfite-promoted Michael addition reaction. In this FRET system, an acedan (2-acetyl-6-dialkylaminonaphthalene) moiety was selected as a two-photon donor and a hemicyanine derivative served as both the quencher and the recognition unit for bisulfite/sulfite. A-HCy exhibited excellent selectivity and rapid response to HSO₃⁻ with a detection limit of 0.24 μM. More importantly, probe A-HCy was first successfully applied in two-photon fluorescence imaging of biological SO₂ derivatives in living cells and tissues, suggesting its great potential for practical application in biological systems.     

A naked-eye rhodamine-based fluorescent probe for Fe(III) and its application in living cells

A naked-eye turn-on fluorescent Fe³⁺ probe (RQ6) was developed by linking a new conjugated quinoline fluorescent group to the rhodamine platform. The probe can detect Fe³⁺ with high selectivity over other metal ions. Bioimaging studies indicated that RQ6 was cell permeable and suitable for detecting Fe³⁺ in the living cells by confocal microscopy.     

A novel HPQ-based turn-on fluorescent probe for detection of fluoride ions in living cells

2-(2′-Hydroxyphenyl)-4(3H)-quinazolinone (HPQ) has been reported as a precipitating fluorescent molecule with excellent optical properties, such as large Stokes shift and strong fluorescence intensity. HPQF, a novel HPQ-based turn-on probe for localizable detection of fluoride ions, was designed, synthesized and fully characterized by ¹H NMR, ¹³C NMR and HRMS. As a chemogenic fluoride probe, the tert-butyldiphenylsilane moiety of HPQF can be easily cleaved by fluoride. After spontaneous 1,6-elimination, HPQ molecule was generated to emit fluorescence under the excitation light. Further study shows that HPQF exhibited high selectivity and sensitivity for detection of fluoride. In addition, HPQF was utilized for the detection of fluoride in living cells.     

A fluorescent turn-on probe for the detection of alkaline phosphatase activity in living cells

Fluorescent probe 1, showing a high fluorescence turn-on signal ratio, enables the real-time imaging of endogenous alkaline phosphatase (ALP) activity in living cells, and the fast and quantitative analysis of enzyme activity at the single-cell level.     

Amphiphilic diarylethene as a photoswitchable probe for imaging living cells

This communication reports a unique example of water-soluble and fluorescent-switchable amphiphilic diarylethene. This compound performs stable vesicle aggregation in water and shows aggregation-dependent emission in its open form. The fluorescence can be effectively switched by alternating between UV and visible light irradiation. This compound thus can stain KB cells for switchable living cell imaging with excellent resistance to fatigue.     

A fluorescent "turn-on" probe for the dual-channel detection of Hg(II) and Mg(II) and its application of imaging in living cells

A novel rhodamine-based fluorescent chemosensor (RND) was synthesized that contains two independent fluorophores and acts as a very sensitive, selective and reversible off-on probe for Hg(II). Importantly, this newly developed sensing system exhibited different fluorescent responses toward Hg(II) and Mg(II) at 589 nm and 523 nm, respectively. RND also displayed detectable color change upon treatment with Hg(II). Results from confocal laser scanning microscopy experiments demonstrated that this chemosensor is cell permeable and can be used as a fluorescent probe for monitoring Hg(II) or Mg(II) in living cells. This probe can also indirectly detect glutathione (GSH) and cysteine (Cys) with good linear relationships.     

A two-photon fluorescent probe with a large turn-on signal for imaging hydrogen sulfide in living tissues

A two-photon fluorescence turn-on H₂S probe GCTPOC–H₂S based on a two-photon platform with a large cross-section, GCTPOC, and a sensitive H₂S recognition site, dinitrophenyl ether was constructed. The probe GCTPOC–H₂S exhibits desirable properties such as high sensitivity, high selectivity, functioning well at physiological pH and low cytotoxicity. In particular, the probe shows a 120-fold enhancement in the presence of Na₂S (500 μM), which is larger than the reported two-photon fluorescent H₂S probes. The large fluorescence enhancement of the two-photon probe GCTPOC–H₂S renders it attractive for imaging H₂S in living tissues with deep tissue penetration. Significantly, we have demonstrated that the probe GCTPOC–H₂S is suitable for fluorescence imaging of H₂S in living tissues with deep penetration by using two-photon microscopy. The further application of the two-photon probe for the investigation of biological functions and pathological roles of H₂S in living systems is under progress.     

Highly selective and sensitive fluorescence turn-on probe for proline

A weakly fluorescent coumarinyl aldehyde was transformed into a strongly fluorescent aldol product by a catalytic amount of proline. The aldehyde probe has shown a highly selective fluorescence turn-on response toward proline over other amino acids with micromolar sensitivity.     

Coumarin-malonitrile conjugate as a fluorescence turn-on probe for biothiols and its cellular expression

A nonfluorescent coumarin-malonitrile conjugate (1) was transformed into a strongly fluorescent molecule through the Michael addition of a thiol group to the α,β-unsaturated malonitrile of 1. The molecular probe has exhibited a highly selective fluorescence response toward biothiols (Cys, Hcy, GSH) with micromolar sensitivity both in vitro and in vivo.     

Highly selective, naked-eye and fluorescent "off-on" probe for detection of histidine/histidine-rich proteins and its application in living cell imaging

A highly selective colorimetric and fluorescence enhanced probe S1 (M2@Cu) for histidine and histidine-rich proteins has been developed. In neutral aqueous ethanol solution, probe S1 can selectively detect histidine out of twenty DNA encoded amino acids by showing a color change from brownish red to light green, and with a fluorescence enhancement up to 99-fold at 537 nm, simultaneously.     

Selective turn-on fluorescent probes for imaging hydrogen sulfide in living cells

Hydrogen sulfide (H(2)S) is an important biological messenger but few biologically-compatible methods are available for its detection. Here we report two bright fluorescent probes that are selective for H(2)S over cysteine, glutathione and other reactive sulfur, nitrogen, and oxygen species. Both probes are demonstrated to detect H(2)S in live cells.     

A turn-on chemosensor for Hg2+ in aqueous media and its application in "MCT" imaging in living cells

A turn-on chemosensor L1, which exhibits high selectivity and sensitivity toward Hg(2+) over other common metal ions in aqueous media under a physiological pH window via a 1:1 binding mode, had been synthesized and characterized. L1 provides good fluorescent imaging of Hg(2+) in living cells. Particularly, we adopted the "micro computed tomography (MCT)" technology, successfully demonstrating the method of Hg(2+) sensing by L1 in cell lines, also the cell permeability of L1 and its imaging position in the cells.     

A reaction based chromofluorogenic turn-on probe for specific detection of fluoride over sulfide/thiols

A new reaction based probe fluorescein nosylate (R1) has been designed and synthesized for selective recognition of F⁻ in acetonitrile (CH₃CN) by exploiting both its nucleophilic and basic character. Probe R1 consists of fluorescein dye as a signalling unit while 4-nitrobenzenesulfonyl chloride as the masking unit. The F⁻ plays the role of de-masking agent to set free the fluorescein moiety in its open form from R1 leading to significant changes in its absorption/emission profile. The detection of F⁻ amidst of sulfide/thiols through receptors undergoing nucleophilic scission is a tedious job due to similarity in their extent of basicity/nucleophilicity. Here, we present a convenient solution for the same in the form of R1 which detects F⁻ selectively over sulfide/thiols in CH₃CN with a high detection limit of 4.6 × 10⁻⁷ M and 2.75 × 10⁻⁸ M determined through UV–visible and fluorescence titration data, respectively.     

Highly sensitive naked-eye and fluorescence "turn-on" detection of Cu(2+) using Fenton reaction assisted signal amplification

Increase of pH induced by Cu(2+)-catalyzed Fenton reaction promoted ring-opening of triazole-linked fluorescein lactone, which enabled selective "turn-on" fluorescent detection of Cu(2+), along with ultralow naked-eye detection limit down to 200 nM.