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 unique two-photon fluorescent probe based on ICT mechanism for imaging palladium in living cells and mice

Palladium(0) as one of the vital transition metals, is employed in numerous industries, such as drug synthesis, aerospace high-tech field and automobile industry. When the Pd(0) enter into the body, it will bind with thiol-containing amino acids, DNA, RNA, and other biomolecules damaging to human health. Thus, developing a novel tool for monitoring and imaging of Pd(0) in vivo is very urgent. In the work, based on a intramolecular charge transfer (ICT) mechanism a two-photon fluorescent probe NIPd had been designed and synthesized for the recognition Pd(0). In vitro experiments data displayed that probe NIPd exhibited a 13-fold fluorescent increase for Pd(0) in 30 min in the aqueous solution with a detection limit of 16 nmol/L. It also showed the outstanding selectivity and antijamming performance. More importantly, NIPd could be served as a two-photon fluorescent probe for real-time monitoring Pd(0) in living cells and mice.     

A unique two-photon fluorescent probe based on ICT mechanism for imaging palladium in living cells and mice

Palladium(0) as one of the vital transition metals, is employed in numerous industries, such as drug synthesis, aerospace high-tech field and automobile industry. When the Pd(0) enter into the body, it will bind with thiol-containing amino acids, DNA, RNA, and other biomolecules damaging to human health. Thus, developing a novel tool for monitoring and imaging of Pd(0) in vivo is very urgent. In the work, based on a intramolecular charge transfer (ICT) mechanism a two-photon fluorescent probe NIPd had been designed and synthesized for the recognition Pd(0). In vitro experiments data displayed that probe NIPd exhibited a 13-fold fluorescent increase for Pd(0) in 30 min in the aqueous solution with a detection limit of 16 nmol/L. It also showed the outstanding selectivity and antijamming performance. More importantly, NIPd could be served as a two-photon fluorescent probe for real-time monitoring Pd(0) in living cells and mice.     

Squaraine-based colorimetric and fluorescent sensors for Cu-specific detection and fluorescence imaging in living cells

New squaraine-based chemosensors SQ1 and SQ2 functionalized with 2-picolyl units were first synthesized and used as highly selective and sensitive colorimetric and fluorometric dual-channel sensors for Cu²⁺-specific recognition in aqueous systems. Among a series of individual metal ions, only Cu²⁺ could result in dramatic color changes. We also evaluated their capability of biological applications and found that SQ2 could be successfully employed as a Cu²⁺-selective probe in the fluorescence imaging of living cells.     

A highly sensitive fluorescent probe for tracking intracellular zinc ions and direct imaging of prostatic tissue in mice

A highly sensitive fluorescent sensor ZnDN was designed, synthesized and used for tracking intracellular zinc ions in various living cells and direct imaging of prostatic tissue in mice. ZnDN was prepared from the heterocyclic-fused naphthalimide fluorophore, and the zinc receptor, N,N-bis(2-pyridylmethyl)ethylenediamine (BPEN). Upon addition of Zn²⁺ to the solutions of ZnDN, a remarkable fluorescence enhancement was observed, which could be attributed to the photo-induced electron transfer (PET) mechanism. Since ZnDN exhibited high sensitivity toward Zn²⁺ in phosphate buffer solution, with a limit of detection of 4.0 × 10⁻⁹ mol/L, it was further applied for the imaging of exogenous and endogenous Zn²⁺ in different living cells. Living cells imaging experiments suggested that ZnDN could image the changes of intracellular free zinc ions, and could be used for two-photon imaging. Moreover, flow cytometry suggested that ZnDN could distinguish cancerous prostate cells from normal cells. Animal experiments indicated that ZnDN had the potential in imaging prostate tissue in vivo.     

A borondipyrrolemethene-based turn-on fluorescent probe for silver ion with high sensitivity and selectivity and its application in water samples and living cells

A borondipyrrolemethene-based compound (1) is synthesized and used as a “turn-on” fluorescent probe for silver ions (Ag⁺). The probe displays highly sensitive fluorescence response toward Ag⁺ with a 40-fold fluorescence enhancement when 60 μM of Ag⁺ is added. The fluorescence intensity of the probe is linearly dependent on Ag⁺ concentration ranging from 0.05 to 60 μM. And the detection limit (LOD) can reach 0.02 μM, which complies with the standard of World Health Organization (WHO) for drinking water (0.9 μM). Moreover, the probe shows remarkable selectivity for Ag⁺ over other metal ions. Furthermore, the response behavior of 1 toward Ag⁺ is pH independent in the neutral range from 6.0 to 8.0. The response of 1 toward Ag⁺ is fast (response time is less than 2 min) and reversible chemically. What’s more, the sensing mechanism of probe 1 toward Ag⁺ is verified by mass spectra (MS) and density functional theory (DFT) calculations. In particular, the probe is applied for detection of Ag⁺ in water samples and living cells successfully.     

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 fluorescence turn-on probe for the detection of thiol-containing amino acids in aqueous solution and bioimaging in cells

A turn-on fluorescent probe, based on a water-soluble terphenyl derivative, for the detection of cysteine and homocysteine is reported. The aldehyde groups in the probe play crucial roles in providing reaction with thiol groups in the amino acids, leading to a formation of thiazolidine (from cysteine) or thiazinane ring (from homocysteine). As a result, the new formation of such rings alters the electronic property of the conjugated system in the probe and results in emission enhancement. The probe in aqueous solution exhibits a remarkable increase in its quantum yield upon exposure to cysteine (up to 20-fold) and to homocysteine (up to 700-fold), while slight quenching is observed in the presence of glutathione. Moreover, an investigation on time-resolved fluorescence spectra of the probe in the presence of cysteine and homocysteine reveals potential discriminatory detection of cysteine and homocysteine. Bioimaging of the thiols in live HeLa cells was successfully applied.     

A highly sensitive fluorescent probe for tracking intracellular zinc ions and direct imaging of prostatic tissue in mice

A highly sensitive fluorescent sensor ZnDN was designed, synthesized and used for tracking intracellular zinc ions in various living cells and direct imaging of prostatic tissue in mice. ZnDN was prepared from the heterocyclic-fused naphthalimide fluorophore, and the zinc receptor, N,N-bis(2-pyridylmethyl)ethyl-enediamine (BPEN). Upon addition of Zn²⁺ to the solutions of ZnDN, a remarkable fluorescence enhancement was observed, which could be attributed to the photo-induced electron transfer (PET) mechanism. Since ZnDN exhibited high sensitivity toward Zn²⁺ in phosphate buffer solution, with a limit of detection of 4.0×10^-9 mol/L, it was further applied for the imaging of exogenous and endogenous Zn²⁺ in different living cells. Living cells imaging experiments suggested that ZnDN could image the changes of intracellular free zinc ions, and could be used for two-photon imaging. Moreover, flow cytometry suggested that ZnDN could distinguish cancerous prostate cells from normal cells. Animal experiments indicated that ZnDN had the potential in imaging prostate tissue in vivo.     

A colorimetric and fluorescent turn-on chemosensor for Zn based on an azobenzene-containing compound

This paper presents a new colorimetric reversible fluorescent turn-on chemosensor molecule for zinc ion based on an azobenzene derivative. The basal fluorescence intensity of the chemosensor molecule is little affected under physiological pH 5-9, whilst the excitation (507 nm) and emission (610 nm) wavelength of the molecular probe for zinc ion is in the visible range.     

A quick response fluorescent probe based on coumarin and quinone for glutathione and its application in living cells

We have designed and synthesized a simple but effective fluorescent probe for sensing glutathione (GSH) by PET process based on coumarin and quinone, which worked as fluorophore and reaction site, respectively. The probe could discriminate GSH from cysteine and homocysteine within 1 min in PBS-buffered solution. The sensing mechanism was confirmed by density functional theory (DFT), viscosity test, fluorescence spectrum analysis and HRMS, respectively. The probe has a low limit of detection (0.1 μM) and finally been used in cell imaging successfully.     

Salicylaldehyde hydrazones as fluorescent probes for zinc ion in aqueous solution of physiological pH

Salicylaldehyde hydrazones of 1 and 2 were synthesized and their potential as fluorescent probes for zinc ion was investigated in this paper. Both of the probes were found to show fluorescence change upon binding with Zn²⁺ in aqueous solutions, with good selectivity to Zn²⁺ over other metal ions such as alkali/alkali earth metal ions and heavy metal ions of Pb²⁺, Cd²⁺ and Hg²⁺. They showed 1:2 metal-to-ligand ratio when their Zn²⁺ complex was formed. By introducing pyrene as fluorophore, 2 showed interesting ratiometric response to Zn²⁺. Under optimal condition, 2 exhibited a linear range of 0-5.0 μM and detection limit of 0.08 μM Zn²⁺ in aqueous buffer, respectively. The detection of Zn²⁺ in drinking water samples using 2 as fluorescent probe was successful.     

A new fluorescent turn-on chemodosimeter for mercury ions in solution and its application in cells and organisms

Using the Hg²⁺-induced desulfurization reaction of thiosemicarbazide derivative, we designed and synthesized a novel “turn on” coumarin-based fluorescent probe L with a simple structure for detecting mercury ion (II). Spectroscopy revealed that the probe responds selectively to mercury ions over other metal ions with marked fluorescence enhancement. Detection of Hg²⁺ was effective at pH 7.0–9.5, with high selectivity and significant effect in HeLa cells, human umbilical vein endothelial cells and Escherichia coli, but no cytotoxicity. This probe could be an ideal and practical Hg²⁺ probe with important biological significance.     

A fluorescence turn-on probe for cysteine and homocysteine based on thiol-triggered benzothiazolidine ring formation

We synthesized a new coumarin-based probe TP, containing a disulfide moiety, to detect biothiols in cells. A fluorescence turn-on response is induced by the thiol–disulfide exchange of the probe, with subsequent intramolecular benzothiazolidine ring formation giving rise to a fluorescent product. The probe exhibits an excellent selectivity for cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH) and other amino acids. The fluorescent probe also exhibits a highly sensitive fluorescence turn-on response to Cys and Hcy with detection limits of 0.8 μM for Cys and 0.5 μM for Hcy. In addition, confocal fluorescence microscopy imaging using RAW264.7 macrophages demonstrates that the probe TP could be an efficient fluorescent detector for thiols in living cells.     

A highly sensitive fluorescence probe for thiophenol in living cells via a substitution-cyclization strategy

A novel fluorescent probe 1 was synthesized for the detection of thiophenol on the basis of a unique thiophenol-mediated substitution-cyclization reaction. The probe 1 displayed 420-fold fluorescence intensity enhancement and highly selective and sensitive response for thiophenol over other competing sulfur species. This probe showed an excellent linear relationship in 10–140 μM and the low detection limit of 29 nM. The recognition mechanism of probe 1 toward PhSH was supported by the NMR spectrum and ESI-MS. Furthermore, the probe 1 was successfully applied for detection of thiophenol in living HepG2 cells.     

A simple and fast-response fluorescent probe for hypochlorite in living cells

A novel fluorophore pyrido[1,2-a]benzimidazole was synthesized and used as a fluorescent probe for hypochlorite based on the oxidation of hydrazine to carboxyl group. The detection limit was measured to be as low as 7.0?nM. The probe can realize fast-detection for hypochlorite within 60?s. Furthermore, it could be used for imaging in living cells.     

A TCF-based colorimetric and fluorescent probe for palladium detection in an aqueous solution

A new fluorescent probe (TCF-AC) that contains 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) skeleton has been developed. Probe TCF-AC exhibits highly selective and sensitive detection toward Pd⁰ in EtOH/H₂O (1:1, v/v, PBS 20?mM, pH?=?7.4) solution with fluorescence “turn on” and colorimetric changes. The Pd⁰ detection by TCF-AC holds some advantages including good anti-interference ability, a relative large Stokes shift (>100?nm), and a low detection limit (7.05?×?10^?7?M). Cell imaging studies demonstrate that TCF-AC is applicable to detect Pd⁰ in living HeLa cells.     

A new fluorescent probe with ultralow background fluorescence for imaging of endogenous cellular selenol under oxidative stress

A new fluorescent probe (Rhod-Sec) for selenol detection with ultralow background fluorescence have been developed in this paper, which showed a 380-fold off-on fluorescence response, and can be applied to visualize the fluctuation of selenol in HepG2 cells through LPS-induced cells oxidation resistance.     

A new ESIPT-based fluorescent probe for highly selective and sensitive detection of HClO in aqueous solution

A new ESIPT-based fluorescent probe, PHC2, for the detection of hypochlorous acid has been rationally designed and developed. Endowed by the specific reaction between hypochlorous acid and phenyl azo group, PHC2 features high degree of selectivity and sensitivity for HClO with a low detection limit (13.2 nM) under physiological conditions in neutral aqueous solution.     

A NBD-based simple but effective fluorescent pH probe for imaging of lysosomes in living cells

NBDlyso with lysosome-locating morpholine moiety has been developed as a high selective and sensitive fluorescent pH probe. This probe can respond to acidic pH (2.0–7.0) in a short time (less than 1 min) and not almost change after continuously illuminated for an extended period by ultraviolet light. The fluorescence intensity of NBDlyso enhanced 100-fold in acidic solution, with very good linear relationship (R² = 0.996). The pK_a of probe NBDlyso is 4.10. Therefore, NBDlyso was used to detect lysosomal pH changes successfully. Besides, X-ray crystallography was used to verify the structure of NBDlyso, and the recognition mechanism involving photo-induced electron transfer was interpreted theoretically by means of DFT and TDDFT calculations skillfully when NBDlyso comes into play under the acidic condition. This probe showed good ability to sense pH change in living cell image.