A rhodamine‐triazole fluorescent chemodosimeter for Cu2+ detection and its application in bioimaging

A rhodamine‐based fluorescent chemodosimeter rhodamine hydrazide‐triazole (RHT) tethered with a triazole moiety was developed for Cu²⁺ detection. In aqueous medium, the RHT probe exhibited high selectivity and sensitivity toward Cu²⁺ among other metal ions. The addition of Cu²⁺ triggered a fluorescence emission of RHT by 384‐fold (Φ = 0.33) based on a ring‐opening process and a subsequent hydrolysis reaction. Moreover, RHT also showed a selective colorimetric response toward Cu²⁺ from colorless solution to pink, readily observed with the naked eye. The limit of detection of RHT for Cu²⁺ was calculated to be 1 nM (0.06 ppb). RHT was successfully demonstrated to detect Cu²⁺ in Chang liver cells by confocal fluorescence microscopy.     

BSA–AuNPs@Tb–AMP metal–organic frameworks for ratiometric fluorescence detection of DPA and Hg2+

An easy and effective strategy for synthesizing a ratiometric fluorescent nanosensor has been demonstrated in this work. Novel fluorescent BSA–AuNPs@Tb–AMP (BSA, bovine serum albumin; AMP, adenosine 5′‐monophosphate; AuNPs, Au nanoparticles) metal–organic framework (MOF) nanostructures were synthesized by encapsulating BSA–AuNPs into Tb–AMP MOFs for the detection of 2,6‐pyridinedicarboxylic acid (DPA) and Hg²⁺. DPA could strongly co‐ordinate with Tb³⁺ to replace water molecules from the Tb³⁺ center and accordingly enhanced the fluorescence of Tb–AMP MOFs. The fluorescence of BSA–AuNPs at 405 nm remained constant. While the fluorescence of BSA–AuNPs at 635 nm was quenched after Hg²⁺ was added, the fluorescence of Tb–AMP MOFs remained constant. Accordingly, a ratiometric fluorescence nanosensor was constructed for detection of DPA and Hg²⁺. The ratiometric nanosensor exhibited good selectivity to DPA over other substances. The F₅₄₅/F₄₀₅ linearly increased with increase of DPA concentration in the range of 50 nM to 10 μM with a detection limit as low as 17.4 nM. F₆₃₅/F₄₀₅ increased linearly with increase of Hg²⁺ concentration ranging from 50 nM to 1 μM with a detection limit as low as 20.9 nM. Additionally, the nanosensor could be successfully applied for the determination of DPA and Hg²⁺ in running water.     

Multifunctional peptide‐based fluorescent chemosensor for detection of Hg2+, Cu2+ and S2− ions

A novel multifunctional fluorescent peptide sensor based on pentapeptide dansyl‐Gly‐His‐Gly‐Gly‐Trp‐COOH (D‐P5) was designed and synthesized efficiently using Fmoc solid‐phase peptide synthesis (SPPS). This fluorescent peptide sensor shows selective and sensitive responses to Hg²⁺ and Cu²⁺ among 17 metal ions and six anions studied in N‐2‐hydroxyethylpiperazine‐N‐2‐ethane sulfonic acid (HEPES) buffer solution. The peptide probe differentiates Hg²⁺ and Cu²⁺ ions by a ‘turn‐on’ response to Hg²⁺ and a ‘turn‐off’ response to Cu²⁺. Upon addition of Hg²⁺ or Cu²⁺ ions, the sensor displayed an apparent color change that was visible under an ultraviolet lamp to the naked eye. The limits of detection (LOD) of DP‐5 were 25.0 nM for Hg²⁺ and 85.0 nM for Cu²⁺; the detection limits for Cu²⁺ were much lower than the drinking water maximum contaminant levels set out by the United States Environmental Protection Agency (USEPA). It is noteworthy that both D‐P5‐Hg and D‐P5‐Cu systems were also used to detect S^2? successfully based on the formation of ternary complexes. The LODs of D‐P5‐Hg and D‐P5‐Cu systems for S^2? were 217.0 nM and 380.0 nM, respectively. Furthermore, the binding stoichiometry, binding affinity and pH sensitivity of the probe for Hg²⁺ and Cu²⁺ were investigated. This study gives new possibilities for using a short fluorescent peptide sensor for multifunctional detection, especially for anions.     

A ratiometric fluorescence sensor for Fe3+ based on FRET and PET processes

A rhodamine/coumarin‐based ratiometric fluorescent Fe³⁺ sensor has been designed and synthesized. The sensor exhibits a good response to Fe³⁺ ions with high sensitivity, selectivity and a large shift in the emission spectra (>100 nm), which shows Fe³⁺‐induced FRET OFF–ON and PET ON–OFF behavior. Copyright © 2015 John Wiley & Sons, Ltd.     

Hg2+‐selective ratiometric and colorimetric probe based on dansyl–rhodamine and its staining function in cell imaging

A new ratiometric probe composed of a dansyl–rhodamine dyad for the detection of Hg²⁺ via fluorescence resonance energy transfer was designed and synthesized. Rhodamine, dansyl chloride, and hydrazide were selected as the acceptor, donor, and reaction site, respectively. It displayed high selectivity and sensitivity to Hg²⁺ with obvious colour change and fluorescence change due to Hg²⁺‐assisted hydrolysis of rhodamine hydrazide. A good linear relationship ranging from 0 to 16 μM and 0–28 μM for the Hg²⁺ concentration was found based on absorbance and fluorescence assay, respectively. Detection limits of absorbance and fluorescence for Hg²⁺ were calculated to be 1.22 μM and 9.10 μM, respectively.     

A selective and sensitive fluorescent sensor for cysteine detection based on bi‐8‐carboxamidoquinoline derivative and Cu2+ complex

In this paper, a novel fluorescent sensor 1 for selective and sensitive detection of cysteine was developed based on a complex between bi‐8‐carboxamidoquinoline derivative ligand ( L ) and Cu²⁺. The interaction of Cu²⁺ with the ligand causes a dramatic fluorescence quenching most likely due to its high affinity towards Cu²⁺ and a ligand–metal charge transfer (LMCT) process. The in situ generated L–Cu ² complex was utilized as a chemosensing ensemble for cysteine. In the presence of cysteine, the fluorophore, L , was released from L–Cu ² complex because of the strong affinity of cysteine to Cu²⁺ via the Cu–S bond, leading to the fluorescence recovery of the ligand. The proposed displacement mechanism was confirmed by the results of mass spectrometry (MS) study. Under optimized conditions, the recovered fluorescence intensity is linear with cysteine concentrations in the range 1 × 10^?6 mol/l to 8 × 10^?6 mol/l. The detection limit for cysteine is 1.92 × 10^?7 mol/l. Furthermore, the established method showed a highly sensitive and selective response to cysteine among the 20 fundamental α‐amino acids used as the building blocks of proteins, after Ni²⁺ was used as a masking agent to eliminate the interference of His. The proposed sensor is applicable in monitoring cysteine in practical samples with good recovery rate.     

A highly selective fluorescent chemosensor for Cu2+: synthesis and properties of a rhodamine B‐containing diarylethene

A diarylethene bearing a triazole‐linked rhodamine B unit was synthesized. Its fluorescent emission was significantly enhanced in the presence of protons or Cu²⁺ due to transformation from the pirocyclic form to open‐ring form. The fluorescence was quenched sequentially upon irradiation with 297 nm light based on the intramolecular fluorescence resonance energy transfer mechanism. In an acetonitrile: water binary solvent (1: 1 v /v), the compound showed significant fluorescent enhancement for Cu²⁺ compared with a wide range of tested metal ions with a fast response and a limit of detection of 2.86 × 10^?8 mol L^?1. Using Cu²⁺ and UV light as the chemical inputs, and fluorescence intensity at 597 nm as the output, a logic gate was developed at the molecular level. Moreover, the compound can be used with a high accuracy to detect Cu²⁺ in a natural water sample.     

Facile synthesis,cytotoxicity and bioimaging of Fe3+ selective fluorescent chemosensor

The designing and development of fluorescent chemosensors have recently been intensively explored for sensitive and specific detection of environmentally and biologically relevant metal ions in aqueous solution and living cells. Herein, we report the photophysical results of alanine substituted rhodamine B derivative 3 having specific binding affinity toward Fe³⁺ with micro molar concentration level. Through fluorescence titration at 599 nm, we were confirmed that ligand 3 exhibited ratiometric fluorescence response with remarkable enhancement in emission intensity by complexation between 3 and Fe³⁺ while it appeared no emission in case of the competitive ions (Sc³⁺, Yb³⁺, In³⁺, Ce³⁺, Sm³⁺, Cr³⁺, Sn²⁺, Pb²⁺, Ni²⁺, Co²⁺, Cu²⁺, Ba²⁺, Ca²⁺, Mg²⁺, Ag⁺, Cs⁺, Cu⁺, K⁺) in aqueous/methanol (60:40, v/v) at neutral pH. However, the fluorescence as well as colorimetric response of ligand–iron complex solution was quenched by addition of KCN which snatches the Fe³⁺ from complex and turn off the sensor confirming the recognition process was reversible. Furthermore, bioimaging studies against L-929 cells (mouse fibroblast cells) and BHK-21 (hamster kidney fibroblast), through confocal fluorescence microscopic experiment indicated that ligand showed good permeability and minimum toxicity against the tested cell lines.     

Phenothiazine–rhodamine‐based colorimetric and fluorogenic ‘turn‐on' sensor for Zn2+ and bioimaging studies in live cells

A phenothiazine–rhodamine (PTRH) fluorescent dyad was synthesized and its ability to selectively sense Zn²⁺ ions in solution and in in vitro cell lines was tested using various techniques. When compared with other competing metal ions, the PTRH probe showed the high selectivity for Zn²⁺ ions that was supported by electronic and emission spectral analyses. The emission band at 528 nm for the PTRH probe indicated the ring closed form of PTRH, as for Zn²⁺ ion binding to PTRH, the λ_em get shift to 608 nm was accompanied by a pale yellow to pink colour (under visible light) and green to pinkish red fluorescence emission (under UV light) due to ring opening of the spirolactam moiety in the PTRH ligand. Spectral overlap of the donor emission band and the absorption band of the ring opened form of the acceptor moiety contributed towards the fluorescence resonance energy transfer ON mechanism for Zn²⁺ ion detection. The PTRH sensor had the lowest detection limit for Zn²⁺, found to be 2.89 × 10^?8 M. The sensor also demonstrated good sensing application with minimum toxicity for in vitro analyses using HeLa cells.     

Zero and second‐derivative synchronous fluorescence spectroscopy for the quantification of two non‐classical β‐lactams in pharmaceutical vials: Application to stability studies

The formation of metal chelates with various ligands may lead to the production of fluorescent chelates or enhance the fluorescence of the chelating agent. This paper describes two sensitive, selective and computer‐solved methods, namely, zero order (SF) and second‐derivative synchronous spectrofluorimetry (SDSFS) for nano‐quantitation of two carbapenems; meropenem (MP) and ertapenem (EP). The methods are based on the chelation of MP with Tb³⁺ and EP with Zr⁴⁺ in buffered organic medium at pH 4.0 to produce fluorescent chelates. In the zero order method, the relative synchronous fluorescence intensity is measured at 327.0 nm at Δλ = 70.0 and 100.0 nm for MP and EP, respectively. The second method utilizes a second‐derivative technique to enhance the method selectivity and emphasize a stability‐indicating approach. The peak amplitudes (²D) of the second‐derivative synchronous spectra were estimated to be 333.06 and 330.06 nm for MP and EP, respectively. The proposed synchronous spectrofluorimetric methods were validated according to the International Conference on Harmonization (ICH) guidelines and applied successfully for the analysis of MP and EP in pure forms, pharmaceutical vials and in synthetic mixtures with different degradants of both drugs. Under optimum conditions, the mole‐ratio method was applied and the co‐ordination ratios of MP–Tb³⁺ and EP–Zr⁴⁺chelates were found to be 1:1 and 1:3. The formation constants for the chelation complexes were evaluated using the Benesi–Hildebrand's equation; the free energy change (ΔG) was also calculated. The results indicated that EP–Zr⁴⁺ was more stable than the MP–Tb³⁺ chelate. Moreover, the developed methods were found to be selective and inexpensive for quantitative determination of both drugs in quality control laboratories at nano‐levels.     

A N‐(2‐hydroxyethyl)piperazine dangled 2,5‐diphenyl‐1,3,4‐oxadiazole‐based fluorescent sensor for selective relay recognition of Cu2+ and sulfide in water

A new 2,5‐diphenyl‐1,3,4‐oxadiazole‐based derivative (L) was synthesized and applied as a highly selective and sensitive fluorescent sensor for relay recognition of Cu²⁺ and S^2? in water (Tris–HCl 10 mM, pH = 7.0) solution. L exhibits an excellent selectivity to Cu²⁺ over other examined metal ions with a prominent fluorescence ‘turn‐off’ at 392 nm. L interacts with Cu²⁺ through a 1:2 binding stoichiometry with a detection limit of 4.8 × 10^–7 M. The on‐site formed L–2Cu²⁺ complex exhibits excellent selectivity to S^2? with a fluorescence ‘off–on’ response via a Cu²⁺ displacement approach. Copyright © 2016 John Wiley & Sons, Ltd.     

Multifunctional organic–inorganic composite luminescent nanospheres

A simple general strategy was successfully developed for the preparation of magnetic–luminescent multifunctional nanocomposites by incorporating fluorescent (pyrene) and magnetic (Fe₃O₄) components simultaneously into a poly(styrene‐co‐methacrylic acid) [poly(St‐co‐MAA)] copolymer matrix. The nanospheres so prepared were characterized using scanning electron microscopy (SEM), powder X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The prepared magnetic–fluorescent inorganic–organic nanocomposites have excellent magnetic and photoluminescent properties. They can be used in magnetic separation of trace amounts of sample, fluorescence detection and imaging applications, including magnetic resonance imaging (MRI) and fluorescence imaging. The fluorescence quenching of the nanospheres in the presence of different amounts of Cu²⁺ ions was also investigated. Under optimal experimental conditions, the relative fluorescence intensity of the composite nanosphere colloidal solution is proportional to the concentration of Cu²⁺ ions, which indicates that these multifunctional nanocomposites can be used for the magnetic separation and fluorescence detection of Cu²⁺ ions. Copyright © 2011 John Wiley & Sons, Ltd.     

Terbium (III) coordination polymer–copper (II) compound as fluorescent probe for time‐resolved fluorescence ‘turn‐on’ detection of hydrogen sulfide

With recognition of the biological importance of hydrogen sulfide (H₂S), we present a simple and effective fluorescent probe for H₂S using a Tb³⁺ coordination polymer–Cu²⁺ compound (DPA/Tb/G–Cu²⁺). Dipicolinic acid (DPA) and guanosine (G) can coordinate with Tb³⁺ to form a macromolecular coordination polymer (DPA/Tb/G). DPA/Tb/G specifically binds to Cu²⁺ in the presence of coexisting cations, and obvious fluorescence quenching is observed. The quenched fluorescence can be exclusively recovered upon the addition of sulfide, which is measured in the mode of time‐resolved fluorescence. The fluorescence intensities of the DPA/Tb/G–Cu²⁺ compound enhance linearly with increasing sulfide concentrations from 1 to 30 μM. The detection limit for sulfide in aqueous solution is estimated to be 0.3 μM (at 3σ). The DPA/Tb/G–Cu²⁺ compound was successfully applied to sense H₂S in human serum samples and exhibited a satisfactory result. It displays some desirable properties, such as fast detection procedure, high selectivity and excellent sensitivity. This method is very promising to be utilized for practical detection of H₂S in biological and environmental samples.     

Ratiometric and selective fluorescent chemodosimeter for Cu(II) by Cu(II)‐induced oxidation

A new rhodamine derivative, rhodamine B 4‐N,N‐dimethylaminobenzaldehyde hydrazone (1), was designed for ratiometric sensing of Cu(II) selectively. A red‐shift from 515 to 585 nm was observed in the fluorescence spectrum when Cu(II) was added to 1 in acetonitrile. Other metal ions of interest showed no ratiometric response. The interaction between Cu(II) and 1 was found to be the Cu(II)‐induced oxidation of 1. Copyright © 2008 John Wiley & Sons, Ltd.     

d‐penicillamine capped cadmium telluride quantum dots as a novel fluorometric sensor of copper(II)

d ‐penicillamine‐capped cadmium telluride quantum dots (DPA‐capped CdTe QDs) were synthesized as the new fluorescent semiconductor nanocrystal in aqueous solution. Fourier transmission infrared spectroscopy, X‐ray diffraction, transmission electron microscopy, ultraviolet‐visible and photoluminescence spectroscopy were used for characterization of the QDs. Based on the quenching effect of Cu²⁺ ions on the fluorescence intensity of DPA‐capped CdTe QDs, a new fluorometric sensor for copper(II) detection was developed that showed good linearity over the concentration range 5 × 10^–9–3 × 10^–6 m with the detection limit 0.4 × 10^–9 m . Owing to the strong affinity of the DPA to copper(II), the sensor showed appropriate selectivity for copper(II) compared with conventional QDs. The DPA‐capped CdTe QDs was successfully applied for determination of Cu²⁺ concentration in river, well and tap waters with satisfactory results. Copyright © 2013 John Wiley & Sons, Ltd.     

A new Schiff base as a turn‐off fluorescent sensor for Cu2+ and its photophysical properties

A new Schiff base receptor 1 was synthesized and its photophysical properties were investigated by absorption, emission and excitation techniques. Furthermore, its chromogenic and fluorogenic sensing abilities towards various metal ions were examined. Receptor 1 selectively detects Cu²⁺ ion through fluorescence quenching and detection was not inhibited in the presence of other metal ions. From fluorescence titration, the limit of detection of receptor 1 as a fluorescent ‘turn‐off’ sensor for the analysis of Cu²⁺ was estimated to be 0.35 μM.     

A carbonothioate‐based highly selective fluorescent probe with a large Stokes shift for detection of Hg2+

Mercury (Hg) is one of the heavy metal pollutants in the environment. Even a very small amount of mercury can cause serious harm to human beings. Herein, we reported a new carbonothioate‐based fluorescent probe for the detection of Hg²⁺ without interference from other metal ions. This probe possessed a very large Stokes shift (192 nm), which could improve the detection sensitivity by minimizing the interferences resulted from self‐absorption or auto‐fluorescence. With the addition of Hg²⁺ to the probe solution, considerable fluorescence enhancement was observed. Additionally, the Hg²⁺ concentration of 0–16 μM and fluorescence intensity showed a good linear relationship (y = 22106× + 53108, R² = 0.9955). Finally, the proposed probe was used to detect Hg²⁺ in real water samples, and its result was satisfactory. Therefore, our proposed probe would provide a promising method for the determination of Hg²⁺ in the environment.     

Ratiometric fluorescence detection of superoxide anion based on AuNPs‐BSA@Tb/GMP nanoscale coordination polymers

A novel ratiometric fluorescence nanosensor for superoxide anion (O₂^??) detection was designed with gold nanoparticles‐bovine serum albumin (AuNPs‐BSA)@terbium/guanosine monophosphate disodium (Tb/GMP) nanoscale coordination polymers (NCPs) (AuNPs‐BSA@Tb/GMP NCPs). The abundant hydroxyl and amino groups of AuNPs‐BSA acted as binding points for the self‐assembly of Tb³⁺ and GMP to form core‐shell AuNPs‐BSA@Tb/GMP NCP nanosensors. The obtained probe exhibited the characteristic fluorescence emission of both AuNPs‐BSA and Tb/GMP NCPs. The AuNPs‐BSA not only acted as a template to accelerate the growth of Tb/GMP NCPs, but also could be used as the reference fluorescence for the detection of O₂^??. The resulting AuNPs‐BSA@Tb/GMP NCP ratiometric fluorescence nanosensor for the detection of O₂^?? demonstrated high sensitivity and selectivity with a wide linear response range (14 nM–10 μM) and a low detection limit (4.7 nM).     

UV light‐tunable fluorescent inks and polymer hydrogel films based on carbon nanodots and lanthanide for enhancing anti‐counterfeiting

Novel water‐soluble green fluorescent carbon nanodots (CNs) using methacrylic acid and m‐phenylenediamine as precursors were first synthesized using a one‐pot hydrothermal method. Red fluorescent lanthanide complexes were prepared using lanthanide ion Eu³⁺ and pyridine‐2,6‐dicarboxylic acid. The optical properties of CNs were characterized using ultraviolet visible (UV) spectra and fluorescence spectra, microscopic morphology was characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS), and the elemental composition was characterized using Fourier transform‐infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectra (XPS). The fluorescence spectra of the lanthanide complexes were also measured. A simple strategy was developed to prepare UV light‐tunable fluorescent inks and polymer hydrogels films based on CNs and lanthanide complexes. The fluorescent inks and polymer hydrogels films could be repeatedly switched between green and red fluorescence. The change of color depended on luminescence of the CNs and the lanthanide complexes under 254 and 365 nm UV light, respectively. The UV light‐tunable fluorescent inks and polymer hydrogels films could enhance its anti‐counterfeiting function for data and information.     

Multi‐functional ion‐sensor based on a photochromic diarylethene with a 1H‐imidazo [4,5‐f][1,10] phenanthroline unit

A new asymmetrical diarylethene containing a 1H‐imidazo [4,5‐f][1,10] phenanthroline unit was synthesized. The compound showed typical photochromism and functioned as a notable fluorescence switch upon alternating irradiation with ultraviolet (UV) and visible light. Its closed‐ring isomer could be used as a selective ‘naked‐eye’ colorimetric sensor for Cu²⁺, accompanied by a notable color change from blue to colorless. Furthermore, the compound was found to be selective towards Ca²⁺, Mg²⁺, and Sr²⁺ with significant fluorescence changes. On the basis of this characteristic, a logic circuit was constructed by utilizing both light and chemical stimuli as inputs and fluorescence intensity at 487 nm as output. Copyright © 2015 John Wiley & Sons, Ltd.