Toward a highly sensitive and selective indole-rhodamine-based light-up probe for Hg2+ and its application in living cells

We herein designed and synthesized a light-up fluorescent probe L1 for Hg²⁺ species, which is based on indole derivative and Rhodamine fluorophore. The new probe can show a linear response to Hg²⁺ with high sensitivity and selectivity. As the Hg²⁺ concentration changed from 0 to 450 μM, the fluorescence intensity of L1 at 575 nm changed from 50 to 6181 (～120-fold). The detection limit of the probe was 5.0 × 10^?8 M. Besides, we have successfully applied L1 to monitor Hg²⁺ species in living MCF-7 cells by way of fluorescence imaging.     

Anthroneamine based chromofluorogenic probes for Hg2+ detection in aqueous solution

Anthroneamine derivatives 1–3 (H₂O:DMSO; 9:1, HEPES buffer, pH 7.0 ± 0.1) undergo highly selective fluorescence quenching with Hg²⁺. The observed linear fluorescence intensity change allows the quantitative detection of Hg²⁺ between 200 nM/40 ppb—12 μM/2.4 ppm even in the presence of interfering metal ions viz. Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Cr³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺, Pb²⁺. Probes 1–3 and their Hg²⁺ complexes also show the broad pH resistance for their practical applicability.     

A benzothizole-based fluorescent probe for Hg2+ recognition utilizing ESIPT coupled AIE characteristics

A new benzothizole-based fluorescent probe 1 for Hg²⁺ recognition utilizing “ESIPT+AIE” strategy has been developed. In THF/H₂O (1:1, v/v, PBS 20 mM, pH = 8.5) mixed solution, probe 1 displays rapid fluorescence responses to Hg²⁺ ions with high selectivity and sensitivity through Hg²⁺-triggered releasing of a compound possessing “ESIPT+AIE” characteristics. Cell imaging investigations indicate that probe 1 is cell permeable with low toxicity to MCF-7 cells, and applicable to detect Hg²⁺ ions in living MCF-7 cells.     

A highly selective fluorescence turn-on detection of Al3+ and Ca2+ based on a coumarin-modified rhodamine derivative

A fluorescent chemosensor 1 was synthesized containing a coumarin moiety bound to rhodamine B hydrazide. Compound 1 displayed different fluorescence emission responses to Al³⁺ and Ca²⁺ ions with high quantum yields (0.64 and 0.15, respectively) and low detection limits (3.0 × 10^–8 and 9.4 × 10^–8 M, respectively). The possible binding modes of compound 1 with Al³⁺ and Ca²⁺ ion were calculated using a Job plot, HRMS, ¹H NMR spectroscopic titration and IR spectroscopy. Moreover, the calcium in 1-Ca²⁺ could be displaced by Al³⁺ ions, resulting in another ratiometric sensing signal output, which indicates that 1-Ca²⁺ could detect Al³⁺ ions in a ratiometric way. Bioimaging results also demonstrated that compound 1 could act as an intracellular Al³⁺ ion imaging sensor.     

Cu2+-selective turn-on fluorescence signaling based on metal-induced hydrolysis of pyrenecarbohydrazide

We developed a simple Cu²⁺-selective turn-on fluorescence signaling probe based on the hydrolysis of 1-pyrenecarbohydrazide (1) to 1-pyrenecarboxylic acid. Probe 1 exhibited prominent fluorescence signaling of Cu²⁺ ions in a 10% aqueous Tris-buffered (pH 7.0) DMSO solution with a detection limit of 5.93 × 10^?8 M. Signaling with control compounds derived from pyreneacetic acid and pyrenebutyric acid showed that the fluorescence signal became less pronounced as the distance between the hydrazide functionality and the pyrene fluorophore increased. As a practical application, this probe was employed for the determination of Cu²⁺ in a simulated semiconductor wastewater.     

A Schiff base fluorescence probe for highly selective turn-on recognition of Zn2+

A simple Schiff base CTS, synthesized between 2-hydroxy-1-naphthaldehyde and 2-benzylthio-ethanamine, was found to be a good turn-on fluorescence probe for the detection of Zn²⁺, due to the restriction of the rotation of the bond between CN and naphthalene ring and/or the blocking of the photo-induced electron transfer (PET) mechanism of the nitrogen atom to naphthalene ring. Excellent selectivity for Zn²⁺ was evidenced, over many other competing ions, including Fe³⁺, Cr³⁺, Ni²⁺, Co²⁺, Fe²⁺,Mn²⁺, Ca²⁺, Hg²⁺, Pb²⁺, Cu²⁺, Mg²⁺, Ba²⁺, Cd²⁺, Ag⁺, Li⁺, K⁺, and Na⁺, in EtOH/HEPES buffer (95:5, v/v, pH = 7.4). It was noteworthy that Cd²⁺ had no interference with Zn²⁺. The stoichiometric complex of CTS-Zn²⁺ was determined to be 2:1 for CTS and Zn²⁺ in molar, based on the Job plot and single crystal X-ray diffraction data. The binding constant of the complex was 85.7 M^?2 with a detection limit of 5.03 × 10^?7 M. The fluorescence bio-imaging capability of CTS to detect Zn²⁺ in live cells was also studied. These results indicated that CTS could serve as a favorable probe for Zn²⁺.     

A fast,highly selective and sensitive dansyl-based fluorescent sensor for copper (II) ions and its imaging application in living cells

Since the copper ions (Cu²⁺) play a fatal role in many foundational physiological processes, it is important to develop a simple, highly sensitive and selective sensor for Cu²⁺ detection in living systems. Herein, an intramolecular charge transfer (ICT) and dansyl-based fluorescent chemosensor 1 was designed, synthesized and characterized for the sensitive and selective quantification of Cu²⁺. It exhibited remarkable fluorescence quenching upon addition of Cu²⁺ over other selected metal ions, attributed to the complex formation between 1 and Cu²⁺ with the association constant 6.7 × 10⁵ M^?1. The sensor 1 showed a fast and linear response towards Cu²⁺ in the concentration range from 0 to 12.5 × 10^?6 mol L^?1 with the detection limit of 2.5 × 10^?7 mol L^?1. This detection could be carried out in a wide pH range of 5.0–14. Furthermore, sensor 1 can be used for detecting Cu²⁺ in living cells.     

A new colorimetric chemodosimeter for mercury ion via specific thioacetal deprotection in aqueous solution and living cells

A sensitive and selective new chemodosimeteric chemosensor (DIBT) for mercury ions was successfully devised and characterized. Upon addition of Hg²⁺ to DIBT, a red-edge absorption band at 972 nm was observed. An important feature for the new chemodosimeter is its high selectivity toward mercury ions over the other competitive species due to Hg²⁺-triggered specific C–S cleavage, making the ‘naked-eye’ detection of mercury ions possible in aqueous solution and living cells such as Candida albicans.     

Design and synthesis of novel rhodamine-based chemodosimeters derived from [2.2]paracyclophane and their application in detection of Hg2+ion

For a better insight into the spectroscopic properties of [2.2]paracyclophane in fluorescent probes, a novel rhodamine-based chemodosimeter bearing [2.2]paracyclophane 4a has been designed and synthesized. The probe 4a exhibits a highly selective and sensitive response to Hg²⁺ over other transition metal ions in aqueous solution. Its detection limit is determined to be 77 nM. The significant changes in the fluorescence color could be used for the naked-eye detection. Furthermore, the probe 4a shows good membrane permeability and can be applied to detect intracellular Hg²⁺ in human lung adenocarcinoma cells (A549 cells). The crystal structure and spectral properties of its congener 4b that contains one 12-bromo [2.2]paracyclophane group and rhodamine moiety are also investigated for a comparison.     

A sensitive tetraphenylethene-based fluorescent probe for Zn2+ ion involving ESIPT and CHEF processes

A new tetraphenylethene-based fluorescent probe 2-(quinolin-8-yliminomethyl)-4-triphenylvinyl-phenol (HL) for detecting Zn²⁺ ion through the excited state intramolecular proton transfer (ESIPT) and chelation enhanced fluorescence (CHEF) processes has been designed and synthesized. The results show that HL emits relatively strong blue fluorescence at 460 nm without Zn²⁺ ion, however, probe HL displays highly pink fluorescent emission at 600 nm when adding Zn²⁺ ion. The fluorescent emission of HL appears an extremely large Stokes shift, which effectively reduces the interference of background signal. The limit of detection of HL for Zn²⁺ ion can reach to 9.0 × 10^–8 M.     

A novel highly selective ratiometric fluorescent sensor for relay recognition of Zn2+ and H2PO4−

A novel fluorescent sensor (AQTF1) based on the N-(quinolin-8-yl) tetrahydrofuran-2-carboxamide was designed and synthesized. This new sensor demonstrated high selectivity for the Zn²⁺ without the interference from Cd²⁺. The detection limit of this probe was calculated to be 10.8 nM for Zn²⁺. The in situ prepared AQTF1-Zn²⁺ complex was used for detection of H₂PO₄^? and displayed good selectivity from the common anions. Furthermore, the AQTF1 displayed good ratiometric response for the relay recognition for Zn²⁺ and H₂PO₄^?.     

Synthesis and evaluation of two novel rhodamine-based fluorescence probes for specific recognition of Fec+ ion

Two low cytotoxic fluorescence probes Rb1 and Rb2 detecting Fe³⁺ were synthesized and evaluated. Rb1 and Rb2 exhibited an excellent selectivity to Fe³⁺, which was not disturbed by Ag⁺, Li⁺, K⁺, Na⁺, NH₄⁺, Fe²⁺, Pb²⁺, Ba²⁺, Cd²⁺, Ni²⁺, Co²⁺, Mn²⁺, Zn²⁺, Mg²⁺, Hg²⁺, Ca²⁺, Cu²⁺, Ce³⁺, AcO^?, Br^?, Cl^?, HPO₄^2?, HSO₃^?, I^?, NO₃^?, S₂O₃^2?, SO₃^2? and SO₄^2? ions. The detection limits were 1.87 × 10^?7 M for Rb1 and 5.60 × 10^?7 M for Rb2, respectively. 1:1 stoichiometry and 1:2 stoichiometry were the most likely recognition mode of Rb1 or Rb2 towards Fe³⁺, and the corresponding OFF–ON fluorescence mechanisms of Rb1 and Rb2 were proposed.     

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 highly sensitive and selective resonance Rayleigh scattering method for Hg2+ based on the nanocatalytic amplification

In 0.2 mol/L HCl–0.22 mol/L HNO₃ medium, trace Hg²⁺ catalyzed NaH₂PO₂ reduction of HAuCl₄ to form gold nanoparticles (AuNPs), which exhibited a strong resonance Rayleigh scattering (RRS) effect at 370 nm. With increasing of [Hg²⁺], the RRS effect enhanced due to more AuNP generated from the catalytic reaction. Under the chosen conditions, the enhanced RRS intensity at 370 nm is linear to Hg²⁺ concentration in the range of 5.0–450 × 10⁻⁹ mol/L, with a detection limit of 0.1 nmol/L. This RRS method was applied for the determination of Hg in water samples, with high sensitivity and good selectivity, and its results were agreement with that of atomic fluorescence spectrometry.     

Non-chromatographic speciation analysis of mercury by flow injection on-line preconcentration in combination with chemical vapor generation atomic fluorescence spectrometry

A novel non-chromatographic approach for direct speciation of mercury, based on the selective retention inorganic mercury and methylmercury on the inner wall of a knotted reactor by using ammonium diethyl dithiophosphate and dithizone as complexing agents respectively, was developed for flow injection on-line sorption preconcentration coupled with chemical vapor generation non-dispersive atomic fluorescence spectrometry. With the sample pH kept at 2.0, the preconcentration of inorganic mercury on the inner walls of the knotted reactor was carried out based on the exclusive retention of Hg–DDP complex in the presence of methylmercury via on-line merging the sample solution with ammonium diethyl dithiophosphate solution, and selective preconcentration methylmercury was achieved with dithizone instead of ammonium diethyl dithiophosphate. A 15% (v/v) HCl was introduced to elute the retained mercury species and merge with KBH₄ solution for atomic fluorescence spectrometry detection. Under the optimal experimental conditions, the sample throughputs of inorganic mercury and methylmercury were 30 and 20 h^− 1 with the enhancement factors of 13 and 24. The detection limits were found to be 3.6 ng l^− 1 for Hg²⁺ and 2.0 ng l^− 1 for CH₃Hg⁺. The precisions (RSD) for the 11 replicate measurements of each 0.2 μg l^− 1 of Hg²⁺ and CH₃Hg⁺ were 2.2% and 2.8%, respectively. The developed method was validated by the analysis of certified reference materials (simulated natural water, rice flour and pork) and by recovery measurements on spiked samples, and was applied to the determination of inorganic mercury and methylmercury in biological and environmental water samples.     

Quinoline-based highly selective and sensitive fluorescent probe specific for Cd2+ detection in mixed aqueous media

Quinoline-based fluorescent probe as a recognition unit was designed and synthesized in this study. The probe R1 displayed excellent selectivity and sensitivity for cadmium ions (Cd²⁺) over a wide range of metal ions in acetonitrile-water (MeCN-H₂O) mixed solution. In order to better understand the recognition mechanism between probe and Cd²⁺, the density functional theory calculations were performed. Finally, the colorimetric experiment result was observed and conveniently monitored by the naked eye, and a visual detection limit of 4 × 10^?6 mol L^?1 was achieved. These experimental results indicated the promising potential of the probe to detect Cd²⁺ in biological system. Furthermore, the probe R1 was successfully used for the highly sensitive detection of Cd²⁺ in living cells.     

Fluorescence “turn-on” chemosensor for the selective detection of zinc ion based on Schiff-base derivative

N,N′-phenylenebis(salicylideaminato) (L) has been used to detect trace amounts of zinc ion in acetonitrile–water solution by fluorescence spectroscopy. The fluorescent probe undergoes fluorescent emission intensity enhancement upon binding to zinc ions in MeCN/H₂O (1:1, v/v) solution. The fluorescence enhancement of L is attributed to the 1:1 complex formation between L and Zn(II), which has been utilized as the basis for selective detection of Zn(II). The linear response range for Zn(II) covers a concentration range of 1.6 × 10^?7 to 1.0 × 10^?5 mol/L, and the detection limit is 1.5 × 10^?7 mol/L. The fluorescent probe exhibits high selectivity over other common metal ions, and the proposed fluorescent sensor was applied to determine zinc in water samples and waste water.     

Coumarin-based fluorescent chemosensor for the selective quantification of Zn2+ and AcO− in an aqueous solution and living cells

In this work, we report a novel fluorescence chemosensor HM based on the coumarin fluorophore for the quantification of Zn²⁺ and AcO^?. HM specifically binds to Zn²⁺ in the presence of other competing cations, and evident changes in UV–vis and fluorescence spectra in HEPES buffer are noticed. The in situ generated HM-Zn²⁺ complex solution exhibit a high selectivity toward AcO^? via Zn²⁺ displacement approach. The detection limits of HM for Zn²⁺ and HM-Zn²⁺ for AcO^? were estimated to be 7.24 × 10^?8 M and 9.41 × 10^?8 M, respectively. HM and the resultant complex HM-Zn²⁺ exhibit low cytotoxicity and cell-membrane permeability, which makes them capable of Zn²⁺ and AcO^? imaging in living Hep G2 cells. A B3LYP/6-31G(d,p) basis set was employed for optimization of HM and HM-Zn²⁺ complex.     

Syntheses,crystal structures and magnetic properties of coordination polymers Ni(NO2)2 and Ni(4,4′-bipy)(NO2)2

Two new coordination polymer frameworks Ni(NO₂)₂ (1) and Ni(4,4′-bipy)(NO₂)₂ (2) (4,4′-bipy = 4,4′-bipyridine) were synthesized by solvothermal reaction in formamide, and were characterized by elemental analysis, IR spectroscopy, single crystal X-ray diffraction, and magnetic measurement. In compound 1, each Ni²⁺ ion is linked with four neighboring Ni²⁺ ions through μ_1,3-nitrito bridges forming 2D layered structure. In compound 2, each Ni²⁺ ion is bridged with six neighboring Ni²⁺ ions through four μ_1,3-nitrito groups and two 4,4′-bipy ligands forming 3D structure. Magnetic measurements show weak ferromagnetism within framework of the two compounds with T_N = 19 K (1) and 21 K (2).     

A new “naked-eye” colorimetric and ratiometric fluorescent sensor for imaging Hg2+ in living cells

A new oligothiophene-based sensor 3 TH for monitoring Hg²⁺ has been designed and synthesized based on the intramolecular charge transfer (ICT) mechanism. The 3 TH shows the significant specificity toward Hg²⁺ through “naked-eye” colorimetric detection as well as via ratiometric fluorescence enhancement response with low detection limit of 62 nM. In addition, sensor 3 TH shows high selectivity and sensitivity for Hg²⁺ with fast response in a suitable pH range. Moreover, the 3 TH-based test strips was used to conveniently detect Hg²⁺ ions in water. Furthermore, considering its good ‘‘turn-on’’ fluorescent sensing behavior and low cell cytotoxicity, 3 TH was successfully applied to detect and image Hg²⁺ in real water samples and living cells, which shows great potentials for application in environmental and biological systems.