Two new rhodamine‐based fluorescent chemosensors for Fe3+ in aqueous solution

Two new rhodamine‐based fluorescent probes were synthesized and characterized by NMR, high resolution mass spectrometer (HR‐MS) and IR. The probes displayed a high selectivity for Fe³⁺ among environmentally and biologically relevant metal ions in aqueous solution (CH₃OH–H₂O = 3 : 2, v/v). The significant changes in the fluorescence color could be used for naked‐eye detection. Job's plot, IR and ¹H NMR indicated the formation of 1: 1 complexes between sensor 1 and Fe³⁺. The reversibility establishes the potential of both probes as chemosensors for Fe³⁺ detection. The probe showed highly selectivity in aqueous solution and could be used over the pH range between 5 and 9. A simple paper test‐strip system for the rapid monitoring of Fe³⁺ was developed, indicating its convenient use in environmental samples. Copyright © 2014 John Wiley & Sons, Ltd.     

Selective and sensitive fluorescent turn‐off chemosensors for Fe3+

Two novel chemosensors (2a and 2b) were synthesized by facile condensation of the binding unit (l ‐histidine) and the fluorophores (anthracene and dansyl groups). Both of them displayed high selectivity and sensitivity towards Fe³⁺ over other metal ions in aqueous solution. The sensing mechanism was based on the paramagnetic property of Fe³⁺ that would lead to fluorescence quenching of the fluorophores when Fe³⁺ was bound to the recognition units. The results showed that l ‐histidine was a good coordination motif for Fe³⁺ and both the anthracene and dansyl groups can sensitively report the sensing information. Copyright © 2012 John Wiley & Sons, Ltd.     

Formation of fluorescent carbon nanodots from kitchen wastes and their application for detection of Fe3+

This work reports a scalable synthesis of water‐dispersible fluorescent carbon nanodots based on the simple hydrothermal method (180 °C for 6 h) of kitchen wastes (grape peel for example). We discuss the feasibility of synthesis from kitchen wastes both experimentally and theoretically, and the as‐prepared nanodots have high selectivity for Fe³⁺ ions based on fluorescence quenching which is due to the complexes between nanodots and metal ions. Copyright © 2014 John Wiley & Sons, Ltd.     

A novel colorimetric fluorescence sensor for Fe3+ based on quinoline Schiff base

A novel fluorescent sensor bearing a quinoline and an anisidine moiety has been developed for highly selective detection of Fe³⁺, which shows photo‐induced electron transfer (PET) behavior induced by Fe³⁺. Binding of Fe³⁺ to the sensor induced the electron of C = N group transfer from quinoline to iron, the result exhibits fluorescent enhancement. With the features of easy synthesis, simple structural skeleton and excellent sensing ability, the newly synthesized chemosensor also applied as a highly selective fluorescent probe in complex samples containing various competitive metal ions. The probe could fulfill various needs in biological and environmental fields.     

A selective and sensitive turn-on chemosensor for detection of Fe3+ in aqueous solution and its cell imaging in dorsal root ganglia neurons and MKN-45 cells

A new turn-on fluorescent chemosensor (RBTM) for Fe³⁺ was designed based on Rhodamine B and a thiocarbonylimidazole moiety. The spectroscopic probe used for characterization of the synthesized system showed 300-fold fluorescence enhancement for the detection of Fe³⁺ with a 1:1 stoichiometry in EtOH/H₂O solution (2:1, v/v, HEPES buffer, 1 mM, pH 7.30). Upon addition of Fe³⁺ in aqueous ethanol, the probe displayed a significant fluorescence enhancement and a distinct color change (colorless to pink) that can be detected by the naked eye. The binding constant between the probe and Fe³⁺ was determined to be 1.16 × 10⁴ M⁻¹ and the corresponding detection limit was calculated to be 0.256 µM. In addition, the energy gaps between the HOMO and LUMO in RBTM and RBTM-Fe³⁺ were calculated using DFT calculations to be 92.93 kcal/mol and 37.49 kcal/mol, respectively. The results indicate that binding of Fe³⁺ to RBTM lowered the HOMO–LUMO energy gap of the complex and stabilized the system. Fluorescence imaging experiments demonstrated that RBTM can be used as a fluorescent probe to detect Fe³⁺ in MKN-45 cells and dorsal root ganglia, thus revealing that RBTM could be used for biological applications.     

An OFF–ON–OFF type fluorescent probe based on a naphthalene derivative for Al3+ and F− ions and its biological application

A novel fluorescent probe‐based naphthalene Schiff, 1‐(C2‐glucosyl‐ylimino‐methyl)‐naphthalene‐2‐ol (L) was synthesized by coupling d ‐glucosamine hydrochloride with 2‐hydroxy‐1‐naphthaldehyde. It exhibited excellent selectivity and highly sensitivity for Al³⁺ in ethanol with a strong fluorescence response, while other common metal ions such as Pb²⁺, Mg²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Fe²⁺, Mn²⁺, Hg²⁺, Li⁺, Na⁺, K⁺, Fe³⁺, Cr³⁺, Zn²⁺, Ag⁺, Ba²⁺ and Ca²⁺ did not cause the same fluorescence response. The probe selectively bound Al³⁺ with a binding constant (K_a) of 5.748 × 10³ M^?1 and a lowest detection limit (LOD) of 4.08 nM. Moreover, the study found that the fluorescence of the L ? Al³⁺ complex could be quenched after addition of F^? in the same medium, while other anions, including Cl^?, Br^?, I^?, NO₂^?, NO₃^?, ClO₄^?, CO₃^2?, HCO₃^?, SO₄^2?, HSO₄^?, CH₃COO^?, PO₄^3?, HPO₄^2?, S^2? and S₂O₃^2? had nearly no influence on probe behaviour. Binding of the [L ? Al³⁺] complex to a F^? anion was established by different fluorescence titration studies, with a detection limit of 3.2 nM in ethanol. The fluorescent probe was also successfully applied in the imaging detection of Al³⁺ and F^? in living cells.     

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.     

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.     

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.     

Pyrazolone as a recognition site: Rhodamine 6G‐based fluorescent probe for the selective recognition of Fe3+ in acetonitrile–aqueous solution

Two novel Rhodamine–pyrazolone‐based colorimetric off–on fluorescent chemosensors for Fe³⁺ ions were designed and synthesized using pyrazolone as the recognition moiety and Rhodamine 6G as the signalling moiety. The photophysical properties and Fe³⁺‐binding properties of sensors L¹ and L² in acetonitrile–aqueous solution were also investigated. Both sensors successfully exhibit a remarkably ‘turn‐on’ response, toward Fe³⁺, which was attributed to 1: 2 complex formation between Fe³⁺ and L¹/L². The fluorescent and colorimetric response to Fe³⁺ can be detected by the naked eye, which provides a facile method for the visual detection of Fe³⁺. Copyright © 2014 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.     

Colorimetric chiral fluorescent sensors for Eu3+ and sequential enantioselective sensing of malate anion

Novel phenanthroline Schiff base fluorescent sensors L1 , L2 , and D1 were designed and synthesized. The sensing abilities of the compounds in the presence of metal cations (Li⁺, Na⁺, K⁺, Ag⁺, Mg²⁺, Ba²⁺, Ca²⁺, Mn²⁺, Pb²⁺, Hg²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Co²⁺, Cu²⁺, Cr³⁺, Fe³⁺, Fe²⁺, Al³⁺, and Eu³⁺) were studied by UV‐vis and fluorescent spectroscopy. The compounds L1 , L2 , and D1 could act as Eu³⁺ ion turn‐off fluorescent sensors based on ligand‐to‐metal binding mechanism in DMSO‐H₂O solution (v/v = 1:1, 10 mM Tris, pH = 7.4). Additionally, the L1 –Eu³⁺ and D1 –Eu³⁺ complexes could be applied as turn‐on enantioselective sensors sensing of malate anion isomers with color changes. Furthermore, biological experiments using living PC‐12 cells demonstrated that L1 and D1 had excellent membrane permeability and could be used as effective fluorescent sensors for detecting Eu³⁺ and malate anion in living cells.     

A Rhodamine B-based fluorescent probe for imaging Cu2+ in maize roots

A new Rhodamine B-based fluorescent probe (RBO) is successfully designed and synthesized, which is a higher selective and sensitive chemosensor for Cu²⁺ than other ions. Under physiological conditions (pH = 7.0), the non emission RBO displays a rapid fluorescence increase together with a color change after addition of Cu²⁺ and the detection limit is down to 28 nM, which can clearly illustrate the distribution of Cu²⁺ with the help of laser scanning confocal microscope in plant tissues. Eventually, it confirmed that the Cu²⁺ accumulates mostly in the vascular cylinder and very less in the epidermal cells of maize roots, which is important to understand how the plants take up, transport and store in the Cu²⁺.     

A cataluminescence gas sensor for ammonium sulfide based on Fe3O4–carbon nanotubes composite

In the present work, Fe₃O₄–carbon nanotubes (CNTs) composite was explored as a sensing material candidate for ammonium sulfide. Intense chemiluminescence emission can be observed during the catalytic oxidation of ammonium sulfide on the surface of Fe₃O₄–CNTs composite. Based on this phenomenon, a selective and sensitive gas sensor for the determination of ammonium sulfide was demonstrated. Under the optimized conditions, the linear range of cataluminescence intensity vs concentration of ammonium sulfide gas was 1.4–115 µg mL^?1 (R = 0.998) with a limit of detection (S/N = 3) of 0.05 µg mL^?1. The relative standard deviation (n = 5) for 14.3 µg mL^?1 ammonium sulfide was 1.9%. There was no response to common foreign substances, such as sulfur dioxide, toluene, aether, ethanol, acetone, hydrogen sulfide, carbon bisulfide, benzene and ammonia. The proposed sensor was successfully applied for the determination of ammonium sulfide in artificial air samples. Copyright © 2009 John Wiley & Sons, Ltd.     

An aqueous fluorescent probe for Hg2+ detection with high selectivity and sensitivity

An aqueous fluorescent probe, 1, was developed for the rapid detection of Hg²⁺ with high sensitivity and excellent selectivity. Upon the addition of Hg²⁺ in pure aqueous media, the Hg²⁺‐mediated hydrolysis of vinyl ether and subsequent cyclization reactions converted probe 1 into the corresponding iminocoumarin dye, which is strongly fluorescent when excited. The application of this probe for the detection of intracellular Hg²⁺ was successfully demonstrated in living cells. Copyright © 2015 John Wiley & Sons, Ltd.     

Construction of a novel turn‐on–off fluorescence sensor used for highly selective detection of thiamine via its quenching effect on o‐phen‐Zn2+ complex

In this work, a simple and selective fluorescence sensor approach called ‘turn‐on–off’ for the determination of thiamine (TM) has been developed. As known, the o‐phenanthroline (o‐phen) has inner fluorescence, though when reacted with zinc ions to form the o‐phen–Zn²⁺ complex the fluorescence intensity was enhanced effectively, while upon addition of TM into the o‐phen–Zn²⁺ complex solution, the intensity of the system was gently quenched, which was termed the ‘turn‐on–off’ probe. Notably, the method possessed highly selective, sensitive determination for TM with a detection limit of 0.25 μmol L^?1 and the reduced fluorescence intensity was proportional to the concentration of TM in the range 0.84–80.0 μmol L^?1. Besides, the proposed mechanism was also investigated through exploring the Fourier transform infrared (FT‐IR), nuclear magnetic resonance (NMR) spectroscopy. Furthermore, this manner was successfully applied into practical samples for TM detection with satisfactory results.     

Tetrasubstituted cyclopentenone‐based fluorescent chemosensors for the selective detection of Fe3+ and Cu2+ ions

Fluorescent chemosensors based on 4‐hydroxy cyclopentenones were synthesized by the base catalyzed reaction of 1,5‐diphenyl‐pentane‐1,3,5‐trione with benzil and thenil. The molecule obtained by the benzil reaction was found to be useful for the selective detection of Fe³⁺ by fluorescence turn‐off, while the molecule synthesized by the thenil reaction was useful for selective detection of Cu²⁺ by fluorescent turn‐on. Details of the synthesis, complexation mode, nature of binding, reversibility, and pH studies of the two sensors are discussed. The studies revealed that the sensors were suitable for determining Fe³⁺ and Cu²⁺ content in real water samples.     

A Phenazine based colorimetric and fluorescent chemosensor for sequential detection of Ag+ and I− in aqueous media

A new colorimetric and fluorescent probe MNTPZ based on 1H‐imidazo[4,5‐b]phenazine derivative has been designed and synthesized for successive detection of Ag⁺ and I^?. The probe MNTPZ shows selective colorimetric response by a change in color from yellow to orange and “turn‐off” fluorometric response upon binding with Ag⁺ in DMSO: Water (pH = 7, 1:1, v/v) over other cations. The binding mode of probe MNTPZ to Ag⁺ was studied by Job's plot, ¹H NMR studies, FT‐IR spectroscopy and DFT calculations. Moreover, the situ generated probe MNTPZ + Ag⁺ complex acted as an efficient fluorometric “turn‐on” probe for I^? via Ag⁺ displacement approach. The detection limit of probe MNTPZ for Ag⁺ and the resultant complex probe MNTPZ + Ag⁺ for I^? were determined to be 1.36 μmol/L and 1.03 μmol/L respectively. Notably, the developed probe was successfully used for quantitative determination of I^? in real samples with satisfactory results.     

A new Rhodamine B-based ‘on–off’ chemical sensor with high selectivity and sensitivity toward Fe3+ and its imaging in living cells

A new fluorescent chemosensor based on a Rhodamine B and pyrrole conjugate (RBPY) has been designed and synthesized. UV–vis absorption and fluorescence spectroscopic studies show that RBPY exhibits a high selectivity and sensitivity toward Fe³⁺ among many other metal cations in a MeOH/H₂O solution (3:2, v/v, pH 7.10, HEPES buffer, 0.1 mM) by forming a 1:1 complex with Fe³⁺. Furthermore, results reveal that the formation of the RBPY–Fe³⁺ complex is fully reversible in the presence of sulfide anions and could also be used as an efficient sensor for S²⁻. Importantly, fluorescence microscopy experiments further demonstrated that RBPY can be utilized as a fluorescent probe for the detection of Fe³⁺ in human liver (L-02) cells.     

Resonance light‐scattering enhancement effect of the protein–Y3+–TTA–SLS system and its analytical application

In this paper, a sensitive resonance light scattering (RLS) method for the determination of protein is reported. In the Tris–HCl (pH 7.50) buffer, protein enhanced the RLS intensity of the Y³⁺–2‐thenoyltrifluoroacetone (TTA)–sodium dodecyl sulphate (SLS) system. The enhanced RLS intensities were in proportion to the concentrations of proteins in the range 8.0 × 10^?9–1.0 × 10^?5 g/mL for BSA, 1.0 × 10^–8–1.0 × 10^?5 g/mL for HSA and 1.0 × 10^–8–1.0 × 10^?6 g/mL for EA, and their detection limits were 5.0, 5.4 and 6.7 ng/mL, respectively. Actual samples were satisfactorily determined. The interaction mechanism was also studied. Copyright © 2008 John Wiley & Sons, Ltd.