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.     

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.     

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.     

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 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.     

Green synthesis of fluorescence carbon nanoparticles from yum and application in sensitive and selective detection of ATP

Fluorescent carbon nanoparticles (CPs), a fascinating class of recently discovered nanocarbons, have been widely known as some of the most promising sensing probes in biological or chemical analysis. In this study, we demonstrate a green synthetic methodology for generating water‐soluble CPs with a quantum yield of approximately 24% via a simple heating process using yum mucilage as a carbon source. The prepared carbon nanoparticles with an ~10 nm size possessed excellent fluorescence properties, and the fluorescence of the CPs was strongly quenched by Fe³⁺, and recovered by adenosine triphosphate (ATP), thus, an ‘off’ and ‘on’ system can be easily established. This ‘CPs‐Fe³⁺‐ATP’ strategy was sensitive and selective at detecting ATP with the linear range of 0.5 µmol L^?1 to 50 µmol L^?1 and with a detection limit of 0.48 µmol L^?1. Copyright © 2015 John Wiley & Sons, Ltd.     

Highly selective and sensitive ‘on–off’ fluorescent chemosensor for Fe3+ ions crafted by benzofuran moiety in both experimental and theoretical methods

A benzofuran glycinamide-based chemosensor, 3-(2-([4-fluorobenzyl]amino)acetamido)benzofuran-2-carboxamide ( BGA ) was developed and synthesized for the selective and sensitive detection of Fe³⁺ ions. The photophysical properties of the probe BGA were studied using UV–visible light absorption and fluorescence spectrophotometers. The chemosensor BGA showed a marked ‘on–off’ fluorescence response towards Fe³⁺ ions in the presence of other metal ions in DMSO/H₂O solution (9/1, v/v). The very low limits of detection (LOD) were calculated to be 10 nM and 43 nM using UV–visible light absorption and fluorescence spectrophotometers, respectively. Job's plot analysis revealed the formation of a BGA -Fe³⁺ complex with a 1:1 binding stoichiometry ratio using UV–visible light spectroscopy. The sensing mechanism was also demonstrated using density functional theory calculation.     

Green synthesis of fluorescent carbon dots using chloroplast dispersions as precursors and application for Fe3+ ion sensing

Water‐soluble carbon dots (CDs) were synthesized using a one‐step hydrothermal treatment of chloroplast dispersions extracted from fresh leaves as a green carbon source. The CD solution showed an emission peak centred at 445 nm when excited at 300 nm. The synthesized CDs were uniform and monodispersed with an average size of 5.6 nm. When adding ferric(III) ions (Fe³⁺) to the solution of the original CDs, the fluorescence intensity decreased significantly. Based on the linear relationship between fluorescence intensity and concentration of Fe³⁺ ions, an effective method for rapid, sensitive and selective Fe³⁺ sensing in aqueous solution could be established. Under optimum conditions, the extent of the fluorescence quenching of prepared CDs strongly depended on the Fe³⁺ ions over a wide concentration range 1.0–100.0 μM with a detection limit (3σ/k) of 0.3 μM. Furthermore, the quantitative determination of Fe³⁺ ions in environmental water samples was realized.     

A selective determination of copper ions in water samples based on the fluorescence quenching of thiol‐capped CdTe quantum dots

CdTe quantum dots (QDs) capped with different stabilizers, i.e. thioglycolic acid (TGA), 3‐mercaptopropionic acid (MPA) and glutathione (GSH) were investigated as fluorescent probes for the determination of Cu²⁺. The stabilizer was shown to play an important role in both the sensitivity and selectivity for the determination of Cu²⁺. TGA‐capped CdTe QDs showed the highest sensitivity, followed by the MPA and GSH‐capped CdTe QDs, respectively. The TGA‐ and MPA‐capped CdTe QDs were not selective for Cu²⁺ that was affected by Ag⁺. The GSH‐capped CdTe QDs were insensitive to Ag⁺ and were used to determine Cu²⁺ in water samples. Under optimal conditions, quenching of the fluorescence intensity (F₀/F) increased linearly with the concentration of Cu²⁺ over a range of 0.10–4.0 µg/mL and the detection limit was 0.06 µg/mL. The developed method was successfully applied to the determination of Cu²⁺ in water samples. Good recoveries of 93–104%, with a relative standard deviation of < 6% demonstrated that the developed simple method was accurate and reliable. The quenching mechanisms were also described. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Rapid synthesis of titanium(IV)‐immobilized magnetic mesoporous silica nanoparticles for endogenous phosphopeptides enrichment

The MALDI‐TOF MS has already been a main platform for phosphoproteome analysis. However, there are some weaknesses in direct analysis of endogenous phosphopeptides by MALDI‐TOF MS because of the serious suppression effect and poor ionization efficiency, which is brought by the excess of nonphosphopeptides and protein. It is essential to enrich endogenous phosphopeptides from complex biosamples efficiently prior to MALDI‐TOF MS analysis. Herein, we present a time‐saving and detailed protocol for the synthesis of titanium(iv)‐immobilized magnetic mesoporous silica nanoparticles (denoted as Fe₃O₄@mSiO₂‐Ti⁴⁺), the subsequent enrichment process, and MALDI‐TOF MS analysis. We tested the LOD, size‐exclusive effect, reproducibility, and stability of Fe₃O₄@mSiO₂‐Ti⁴⁺ nanoparticles. Furthermore, the ability of this protocol for identifying endogenous phosphopeptides in healthy human serum and saliva was investigated.     

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).     

Preparation and application of solvent‐modulated self‐doped N–S multicolour fluorescence carbon quantum dots

In this paper, two types of carbon quantum dot (CQDs) were prepared using biocompatible l ‐methionine as the carbon source and urea as the nitrogen source and a one‐step hydrothermal treatment. By changing the reaction solvents (deionized (DI) water and dimethylformamide (DMF)), the maximum emission of the resulting CQDs shifted from blue to red light. Specifically, the emission wavelength of the CQDs moved from 433 nm to 625 nm following embedding of a new functional group (–CONH–) on the surface of the CQDs. Photoluminescence quantum yields of the CQDs with blue and red emission reached 64% and 61%, respectively. The R‐CQDs were used to detect metal ions and a linear relationship was demonstrated between ln(F/F₀) and Fe³⁺ concentration in the range 0–0.5 mmol/L with a detection limit of 0.067 μM. Therefore these R‐CQDs have great potential as fluorescent probes for Fe³⁺ detection. We expect that the excellent water‐soluble, biocompatible and optical properties of the CQDs developed in this work mean that they will be widely used to detect biological cells.     

Luminescent and hydrophilic LaF3–polymer nanocomposite for DNA detection

Luminescent LaF₃–Ce³⁺/Tb³⁺ nanocrystals have been successfully prepared via a simple wet chemical technique. For the next bioapplication, these nanoparticles dispersed in cyclohexane have also been functionalized with poly(St‐co‐MAA), based on a designed oil‐in‐water microemulsion system. These polymer‐coated nanospheres are water‐soluble and bioconjugable. Unlike semiconductor quantum dots, the as‐prepared lanthanum fluoride nanocrystals possess non‐size‐dependent emissions and completely stable photocycles. With functionalized LaF₃ nanospheres as fluorescence probes, a fluorescence method was developed for the rapid quantitative analysis of DNA, due to the quenching effect of fluorescence by the DNA. Under optimum conditions, the fluorescence intensity was proportional to the concentration of the introduced DNA over the range 2.5–35 µg/mL for calf thymus DNA (ctDNA) and 2.5–30 µg/mL for fish sperm DNA (fsDNA), respectively. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

Fluorescent sensors based on quinoline‐containing styrylcyanine: determination of ferric ions,hydrogen peroxide,and glucose,pH‐sensitive properties and bioimaging

A novel styrylcyanine‐based fluorescent probe 1 was designed and synthesized via facile methods. Ferric ions quenched the fluorescence of probe 1, whereas the addition of ferrous ions led to only small changes in the fluorescence signal. When hydrogen peroxide was introduced into the solution containing probe 1 and Fe²⁺, Fe²⁺ was oxidized to Fe³⁺, resulting in the quenching of the fluorescence. The probe 1/Fe²⁺ solution fluorescence could also be quenched by H₂O₂ released from glucose oxidation by glucose oxidase (GOD), which means that probe 1/Fe²⁺ platform could be used to detect glucose. Probe 1 is fluorescent in basic and neutral media but almost non‐fluorescent in strong acidic environments. Such behaviour enables it to work as a fluorescent pH sensor in both the solution and solid states and as a chemosensor for detecting volatile organic compounds with high acidity and basicity. Subsequently, the fluorescence microscopic images of probe 1 in live cells and in zebrafish were achieved successfully, suggesting that the probe has good cell membrane permeability and a potential application for imaging in living cells and living organisms. Copyright © 2014 John Wiley & Sons, Ltd.     

Facile synthesis of anthracene-appended amino acids as highly selective and sensitive fluorescent Fe3+ ion sensors

We designed new fluorescent chemical sensors for Fe³⁺ ion detection, by conjugating amino acids as receptors into an anthracene fluorophore. The conjugates were synthesized in solid phase by Fmoc-chemistry. Fluorescence sensors containing Asp (1) and Glu (2) both had exclusive selectivity for Fe³⁺ in 100% aqueous solution and in a mixed organic–aqueous solvent system. Other metal ions did not interfere with the detection ability of the sensors for Fe³⁺. The sensors detect Fe³⁺ ions via a chelation-enhanced fluorescent quenching effect. The binding affinity, reversible monitoring, and pH sensitivity of the sensors were investigated. In addition, detection of fluoride ion among halide ions was done by a chemosensing ensemble method with 1–Fe³⁺ and 2–Fe³⁺ complexes.     

Bovine serum albumin functionalized blue emitting Ti3C2 MXene quantum dots as a sensitive fluorescence probe for Fe3+ ion detection and its toxicity analysis

In the present work, an improved class of protein functionalized fluorescent 2D Ti₃C₂ MXene quantum dots (MXene QDs) was prepared using a hydrothermal method. Exfoliated 2D Ti₃C₂ sheets were used as the starting precursor and transport protein bovine serum albumin (BSA) was used to functionalize the MXene QDs. BSA-functionalized MXene QDs exhibited excellent photophysical property and stability at various physiological parameters. High-resolution transmission electron microscopy analysis showed that the BSA@MXene QDs were quasispherical in shape with a size of ~2 nm. The fluorescence intensity of BSA@MXene QDs was selectively quenched in the presence of Fe³⁺ ions. The mechanism of fluorescence quenching was further substantiated using time-resolved fluorescence and Stern–Volmer analysis. The sensing assay showed a linear response within the concentration range 0–150 μM of Fe³⁺ ions with excellent limit of detection. BSA@MXene QDs probe showed good selectivity toward ferric ions even in the presence of other potential interferences. The practical applicability of BSA@MXene QDs was further tested in real samples for Fe³⁺ ion quantification and the sensor had good recovery rates. The cytotoxicity studies of the BSA@MXene QDs toward the human glioblastoma cells revealed that BSA@MXene QDs are biocompatible at lower doses and showed significant cytotoxicity at higher dosages.     

Development of highly selective fluorescent ferrocenyl-iminopyridine chemosensor for biologically relevant Fe3+

Design, synthesis, characterization, and ion detection studies of two ferrocene-appended Schiff bases namely N-(2-[ferrocenylamino]ethyl)-5-nitropyridin-2-amine ( 1 ) and ferrocenylamino-1H-imidazole-4-carboxamide ( 2 ) been reported. Both the chemosensors have been thoroughly characterized using Fourier transfer infrared, ¹H and ¹³C nuclear magnetic resonance, high resolution mass spectrometry, and ultraviolet/visible (UV/visible) and fluorescence spectral techniques. Probes 1 and 2 were designed with the aim of appending the ferrocenyl group with pyridine ring having an amine substitution (for 1 ) and imidazole ring with an amide substitution (for 2 ). Interaction of these probes with a series of cations and anions was examined through UV/vis and fluorescence spectral techniques. Probe 2 exhibited an insignificant response towards anions and loss of selectivity for cations, whereas 1 displayed highly selective detection towards biologically important Fe³⁺ in 2:1 (probe:cation) stoichiometry. Notably, none of the cations and anions could interfere the selectivity of Fe³⁺ ensured by 1 in aqueous medium. The limit of detection for Fe³⁺ detection using 1 was determined to be 0.2 ppm. The results strongly suggest that 1 could find promising future application as a chemosensor for Fe³⁺ in biological systems for quantification and qualitative analysis.     

Sensitive determination of DNA based on the interaction between prulifloxacin–terbium(III) complex and DNA

A simple spectrofluorimetric method is described for the determination of DNA, based on its enhancement of the fluorescence intensity of prulifloxacin (PUFX)–Tb³⁺. The luminescence intensity of the PUFX–Tb³⁺ complex increased up to 10‐fold after adding DNA. The excitation and emission wavelengths were 345 and 545 nm, respectively. Under optimum conditions, variations in the fluorescence intensity showed a good linear relationship with the concentration of hsDNA in the range of 3.0 × 10^‐9 to 1.0 × 10^‐6 g/mL, with a correlation coefficient (R) of 0.997, and the detection limit was 2.1 × 10^‐9 g/mL. The method was successfully applied to the determination of DNA in synthetic samples, and recoveries were in the range 97.3–102.0%. The mechanism of fluorescence enhancement of the PUFX–Tb³⁺ complex by DNA is also discussed. The mechanism may involve formation of a ternary complex mainly by intercalation binding together with weak electrostatic interaction, which will increase the energy transition from ligand to Tb³⁺, increasing the rigidity of the complex, and decreasing the radiationless energy loss through O–H vibration of the H₂O molecule in the PUFX–Tb³⁺ compl+osed method is not only more robust and friendly to the environment, but also of relatively higher sensitivity. Copyright © 2013 John Wiley & Sons, Ltd.