Photophysical properties of rhodamine isomers: A two-photon excited fluorescent sensor for trivalent chromium cation (Cr)

We introduce a new rhodamine-based fluorescent chemosensor, FD8 which exhibits a distinct two-photon excited fluorescence (TPEF) on/off characteristic upon binding Cr³⁺ ions. By coordination with metal cation, conformation of FD8 changes from spirocyclic to open-ring, resulting in remarkable enhancement of absorption and fluorescence both in one- and two-photon excitations. As a result, a 29-fold enhancement of two-photon excited fluorescent intensity was observed when 10 eq. Cr³⁺ was added to the FD8 solution. The detection limit of Cr³⁺ cation concentration down to 1 μM (0.01 eq. of FD8) was achieved under our experimental condition. Besides the excitation within ultraviolet regime by fluorescence resonance energy transfer (FRET) mechanism, the TPEF on/off behavior further extends the excitation to near infrared regime (the biological optimal window of 700-1200 nm), and shows more effective sensitivity. The broad excitation wavelength, on/off fluorescence and high selectivity to Cr³⁺ enable FD8 to be a powerful Cr³⁺ cation sensor with potential application, especially in biological detection. To the best of our knowledge, this is the first report about two-photon fluorescent sensor for Cr³⁺ ions.     

Fluorescent oligomer as a chemosensor for the label-free detection of Fe and dopamine with selectivity and sensitivity

In this article, a sensitive and selective turn-off fluorescence chemosensor, Tyloxapol (one kind of water soluble oligomer), was developed for the label-free detection of Fe³⁺ ions in aqueous solution. Fluorescence (FL) experiments demonstrated that Tyloxapol was a sensitive and selective fluorescence sensor for the detection of Fe³⁺ directly in water over a wide range of metal cations including Na⁺, K⁺, Ag⁺, Hg²⁺, Cd²⁺, Co²⁺, Cu²⁺, Cr³⁺, Mn²⁺, Ba²⁺, Zn²⁺, Ni²⁺, Mg²⁺, Ca²⁺, and Pb²⁺. Moreover, the fluorescence intensity of Tyloxapol has shown a linear response to Fe³⁺ in the concentration range of 0–100 μmol L⁻¹ with a detection limit of 2.2 μmol L⁻¹ in aqueous solution. Next, based on a competition mechanism, another turn-on sensing application of the Tyloxapol/Fe³⁺ platform to probe dopamine (DA) against various other biological molecules such as other neurotransmitters or amino acids (norepinephrine bitartrate, acetylcholine chloride, alanine, valine, phenylalanine, tyrosine, leucine, glycine, histidine) were also investigated. It is expected that our strategy may offer a new approach for developing simple, cost-effective, rapid and sensitive sensors in biological and environmental applications.     

Ratiometric fluorescence probe for two-photon bioimaging of Cr in living cells

We presented a ratiometric fluorescent probe dansylamide–rhodamine dyad (DANS–RB) for selectively detecting Cr³⁺ in semi-aqueous solution. The detection mechanism relies on the fluorescent resonance energy transfer (FRET) process from the dansylamide (energy donor) to the rhodamine (energy acceptor) after the addition of Cr³⁺. The cell-permeability of DANS–RB was confirmed by the two-photon fluorescence microscopy experiments, which demonstrated DANS–RB was a good candidate for monitoring the intracellular Cr³⁺ level with the ratiometric fluorescent method. Combining the excellent selectivity, the ratiometric quantitative detection, and the cell-permeability, DANS–RB may find a broad application in the investigation on biologically relevant species in living cells.     

An ‘off-on’ fluorescent chemosensor of selectivity to Cr and its application to MCF-7 cells

A ‘switching-on’ fluorescent chemosensor for the selective and sensitive signaling of intraceullar Cr³⁺ has been designed and synthesized exploiting the guest-induced prohibition of the photoinduced electron transfer process between naphthyridine moiety and 7,10-diphenylfluoranthene moiety, the system shows a Cr³⁺-selective chelation-enhanced fluorescence response not only in ethanol but in cell.     

Electrically induced fluorescence Fe sensing behavior of nanostructured Tiron doped polypyrrole

Nanostructured polypyrrole (PPy) film doped with Tiron was electrodeposited from aqueous solution on the surface of transparent electrode and used for sensitive, selective and rapid electrically controlled fluorescence detection of Fe³⁺ in aqueous media. The fluorescence intensity of PPy-Tiron film decreases linearly in the presence of Fe³⁺ by applying negative potential over a concentration range from 5.0 × 10⁻⁸ to 1.0 × 10⁻⁶ mol L⁻¹, with a relatively fast response time of less than 30 s at pH 7.4. The detection is not affected by the coexistence of other competitive metal ions such as Al³⁺, Ce³⁺, Tl³⁺, La³⁺, Bi³⁺, Cr²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺. The proposed electro-fluorescence sensor has a potential application to the determination of Fe³⁺ in environmental and biological systems. The fluorescent thin film sensor was also used as a novel probe for Fe³⁺/Fe²⁺ speciation in aqueous solution.     

Study on the synthesis of novel fluorescent macrocyclic sensors and their sensitive properties for Cu2+ and Fe3+ in aqueous solution

In this work, we synthesised and characterised three novel fluorescence macrocyclic sensors containing optically active dansyl groups. The studies for the interaction of the synthesised compounds with various mental ions (Li⁺, Na⁺, K⁺, Ag⁺, Mg²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Zn²⁺, Co²⁺, Cd²⁺, Hg²⁺, Ni²⁺, Cu²⁺, Mn²⁺, Cr³⁺, Al³⁺, Fe³⁺) were performed by fluorescence titration, Job’s plot, ESI-MS and DFT calculations. The results showed that the sensors 1a–1c displayed selective recognition for Cu²⁺ and Fe³⁺ ions and formed stoichiometry 1:1 complex through PET mechanism in DMSO/H₂O solution (1:1, v/v, pH 7.4 of HEPES). The binding constant (K) and detection limit were calculated.     

Etodolac:β-cyclodextrin inclusion complex as a novel fluorescent chemosensor probe for Ba2+

The inclusion complex of etodolac (ETD) with β-CD was investigated by UV-visible and fluorescence spectroscopy. The chemosensory ability of ETD:β-CD complex for various metal cations was investigated thoroughly, and we found that the emission of the complex showed a drastic increase in the intensity for Ba²⁺. Competitive experiments of ETD:β-CD complex with Ba²⁺ showed that no significant variation was found in the fluorescence intensity of the ETD:β-CD/Ba²⁺ complex upon adding other cations, such as Na⁺, Ag⁺, Hg²⁺, Cd²⁺, Al³⁺, Cr³⁺, Fe³⁺, Se⁴⁺, and Ti⁴⁺. The linearity range, limit of detection (LOD), and limit of quantitation (LOQ) were determined from the selectivity and sensitivity studies.     

A new rhodamine-based dual chemosensor for Al and Cu

A new rhodamine B derivative bearing a hydrazone group has been designed and prepared. The synthesized colorimetric and fluorescent molecular chemosensor can be used as a dual probe, selectively detecting Al³⁺ and Cu²⁺ in acetonitrile solution by monitoring changes in the absorption and fluorescence spectral patterns. The results show that Al³⁺ ions can induce a greater fluorescence enhancement, while the addition of Cu²⁺ ions induces a strong UV–vis absorption enhancement with weak fluorescence. The limits of detection of Cu²⁺ and Al³⁺ were estimated to be 2.9 × 10⁻⁷ M and 8.3 × 10⁻⁹ M, respectively.     

Separation of Cr ions from Co and mn ions by poly (bis(phenoxy) phosphazene) membranes

Poly(bis (phenoxy)phosphazene) was synthesized and cast by knife techniques into membranes supported on porous Inconel plates for separation testing. A solution of Cr³⁺, Co²⁺ and Mn^2/t+ nitrates was used as the feed solution in diffusion experiments conducted from 25 to 180°C. It was discovered that Co²⁺ and Mn²⁺ ions had much higher diffusion coefficients than Cr³⁺ ions through the membrane, with a maximum difference occurring near 100°C. The lower diffusion associated with Cr³⁺ ions is believed to be due to formation of polymerized hydrated Cr³⁺ ions that are too large to penetrate the membranes. Diffusion activation energies are reported.     

Highly sensitive and selective reversible sensor for the detection of Cr

A new fluorescent sensor capable of sensing Cr³⁺ has been synthesized. Complexing with Cr³⁺ triggers the formation of a highly fluorescent ring-open form which is pink in color. The sensor shows extremely high fluorescence enhancement upon complexation with Cr³⁺ and it can be used as a ‘naked eye’ sensor. Binding of Cr³⁺ was found to be reversible as the pink color disappears with excess EDTA.     

A near-infrared emissive Al sensing platform for specific detection in solution,cells and probing DNase activity

A new tricarbocyanine-based chemosensor exhibited a dramatic Al³⁺-specific fluorescence turn-on response in the near-infrared (NIR) region. The receptor was found to be highly selective towards Al³⁺ over other metal ions in physiological condition. The sensor was non-toxic and could thus be employed as an imaging probe for detecting intracellular Al³⁺ in live cells. Interestingly, upon interaction with DNA in solution, the L–Al³⁺ ensemble rendered tracking of DNase activity in solution through a systematic reduction in the fluorescence emission intensity.     

A ratiometric fluorescent chemosensor for Al in aqueous solution based on aggregation-induced emission and its application in live-cell imaging

A ratiometric fluorescent chemosensor 1 was developed for the detection of Al³⁺ in aqueous solution based on aggregation-induced emmision (AIE). The chemosensor showed the fluorescence of its aggregated state and Al³⁺-chelated soluble state in the absence and in the presence of Al³⁺, respectively, and resulted in a fluorescence ratio (I₄₆₁/I₅₃₇) response to Al³⁺ in neutral aqueous solution at a detection limit as low as 0.29 μmol L⁻¹. The method was also highly selective to Al³⁺ over other physiological relevant metal ions investigated in this study. Taking advantage of its AIE characteristics, the chemosensor was successfully applied on test papers for simple and rapid detection of Al³⁺. Moreover, the application of 1 for the imaging of Al³⁺ in living cells by ratiometric fluorescence changes was also achieved.     

A novel Cr turn-on probe based on naphthalimide and BINOL framework

Naphthalimide and BINOL framework based fluorescent probe NP-B was rationally designed and synthesized. NP-B exhibited ‘turn-on’ fluorescence for Cr³⁺ and high selectivity over other metal ions. 1:1 binding mode between NP-B and Cr³⁺ was proposed and the mode was verified through MALDI-TOF mass spectrum. The detection limit was calculated to be 0.20 μM, which indicated the good sensitivity for Cr³⁺.     

Multi-Responsive Sensor Based on Porous Hydrogen-Bonded Organic Frameworks for Selective Sensing of Ions and Dopamine Molecules

Hydrogen-bonded organic frameworks (HOFs), as an emerging porous material, have attracted increasing research interest in fluorescence sensing due to their inherent fluorescence emission units with unique physicochemical properties. Herein, based on the organic building block 3,3′,5,5′-tetrakis-(4-carboxyphenyl)-1,1′-biphenyl (H₄TCBP), the porous material HOF-TCBP was successfully synthesized using hydrogen bond self-assembly in a DMF solution. The fluorescence properties of the HOF-TCBP solution showed that when the concentration was high, excimers were easily formed, the PL emission was red-shifted, and the fluorescence intensity became weaker. HOF-TCBP showed good sensitivity and selectivity to metal ions Fe³⁺, Cr³⁺, and anion Cr₂O₇²⁻. In addition, HOF-TCBP can serve as a label-free fluorescent sensor material for the sensitive and selective detection of dopamine (DA). HOF-based DA sensing is actually easy, low-cost, simple to operate, and highly selective for many potential interfering substances, and it has been successfully applied to the detection of DA in biological samples with satisfactory recoveries (101.1–104.9%). To our knowledge, this is the first report of HOF materials for efficient detection of the neurotransmitter dopamine in biological fluids. In short, this work widely broadens the application of HOF materials as fluorescent sensors for the sensing of ions and biological disease markers.     

A Significant Fluorescence Turn-On Probe for the Recognition of Al3+ and Its Application

An easy prepared probe, BHMMP, was designed and synthesized, which displayed a significant fluorescence enhancement (over 38-fold) and obvious color change in the recognition of Al³⁺. The binding ratio of probe BHMMP to Al³⁺ was determined as 1:1, according to Job plot. The binding mechanism was fully clarified by the experiments, such as FT-IR spectrum, ESI–MS analysis, and ¹H NMR titration. A DFT study further confirmed the binding mode of BHMMP to Al³⁺. The limit of detection (LOD) for Al³⁺ was determined as low as 0.70 µM, based on the fluorescence titration of BHMMP. Moreover, the results from real sample experiments, including real water samples, test papers, and cell images, well-demonstrated that BHMMP was capable of sensing Al³⁺ in environmental and biological systems.     

Photo-Physical Properties of a New Norfloxacin-Containing Polymer for Protons and Fe3+ Sensing

A novel norlfoxacin-containing fluorescent polymer was synthesized via copolymerization of two derivatives of norfloxacin and methylmetacrylate (MMA). It could emit blue fluorescence in both the solution and film states. Fluorescence characteristics of the polymer as a function of pH were investigated in aqueous solution. The polymer solution showed weaker fluorescence between pH 5-9. When the pH of the solution was higher than 9 or lower than 5, stronger fluorescence could be seen. Responses of metal cations (Mn^{2 +}, Fe^{3 +}, Co^{2 +}, Ni^{2 +}, Cu^{2 +} and Zn^{2 +}) to the fluorescence intensity of this polymer were obtained that only Fe^{3 +} could quench efficiently the fluorescence intensity of the polymer in solution and film state. The results suggested the possibility that this newly synthesized compound might work as a polymeric sensor responding to water polluted by protons and Fe^{3 +}.     

An efficient and selective flourescent chemical sensor based on 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane as a new fluoroionophore for determination of iron(III) ions. A novel probe for iron speciation

A novel fluorescent chemical sensor for the highly sensitive and selective determination of Fe³⁺ ions in aqueous solutions is prepared. The iron sensing system was prepared by incorporating 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a neutral Fe³⁺-selective fluoroionophore in the plasticized PVC membrane containing sodium tetraphenylborate as a liphophilic anionic additive. The response of the sensor is based on the strong fluorescence quenching of L by Fe³⁺ ions. At pH 5.5, the proposed sensor displays a calibration curve over a wide concentration range from 6.0 × 10⁻⁴ to 1.0 × 10⁻⁷ M, with a relatively fast response time of less than 2 min. In addition to a high stability and reproducibility, the sensor shows a unique selectivity toward Fe³⁺ ion with respect to common coexisting cations. The proposed fluorescence optode was applied to the determination of iron(III) content of straw of rice, spinach and different water samples. The fluorescent sensor was also used as a novel probe for Fe³⁺/Fe²⁺ speciation in aqueous solution.     

Trace enrichment of metal ions in aquatic environments by Saccharomyces cerevisiae

Sorption properties of baker’s yeast cells, characterised as Saccharomyces cerevisiae were evaluated for trace enrichment of metal ions: Cd²⁺, Cr³⁺, Cr⁶⁺, Cu²⁺, Pb²⁺ and Zn²⁺ from aqueous environments. Metal concentration was determined by flame atomic absorption spectrometry (FAAS). Parameters affecting metal uptake such as solution pH, incubation time, amount of yeast biomass and effect of glucose concentration (energy source) were optimised. Further studies were carried out to evaluate the effects on metal uptake after treating yeast with glucose as well as with an organic solvent. The results showed that trace enrichment of the metals under study with yeast, depends upon the amount of yeast biomass, pH and incubation time. Treatment of yeast cells with 10-20 mM glucose concentration enhanced metal uptake with exception to Cr⁶⁺, whose metal enrichment capacity decreased at glucose concentration of 60 mM. Of the investigated organic solvents THF and DMSO showed the highest and lowest capacity, respectively, to enhance metal uptake by yeast cells. Trace enrichment of metal ions from stream water, dam water, treated wastewater from a sewage plant and wastewater from an electroplating plant achieved enrichment factors (EF) varying from 1 to 98, without pre-treatment of the sample. pH adjustment further enhanced the EF for all samples. The results from these studies demonstrate that yeast is a viable trace metal enrichment media that can be used freely suspended in solution to achieve very high EF in aquatic environments.     

Equilibrium study on the reactions of boric acid with some cis -diaqua CrIII-complexes

Substitution inertcis-diaqua Cr^III complexes: cis-[(L^x−)Cr^III(H₂O)₂]^(3−x)+ derived from N-donor ligands (L^x−) viz., bipyridine and 1,10-phenanthroline (x = 0) and N,O-donor ligands viz., nitrilotriacetate and anthranilate N,N-diacetate (x = 3) titrate as diprotic acids in aqueous solution and enhance the acidity of otherwise weakly acidic boric acid (H₃BO₃) producing mononuclear and binuclear mixed ligand Cr^III-borate complexes: [(L)Cr(H₂BO₄)]^x− and [(L)Cr(BO₄)Cr(L)]^(1−2x)+ respectively through coordination of the H₂O and/or OH⁻ ligands, cis-coordinated in the Cr^III-complexes on the electron deficient B^III-atom in H₃BO₃ with release of protons. Deprotonation of the parent Cr^III-complexes and their reactions with H₃BO₃ have been investigated by potentiometric method in aqueous solution,I = 0.1 mol dm⁻³ (NaNO₃) at 25 ±0.1°C. The equilibrium constants have been evaluated by computerized methods and the tentative stoichiometry of the reactions have been worked out on the basis of the speciation curves     

Kinetics and mechanism of the chromic oxidation of 3-O-methyl-d-glucopyranose

The oxidation of 3-O-methyl-d-glucopyranose (Glc3Me) by Cr^VI in acid medium yields Cr^III, formic acid and 2-O-methyl-d-arabinose as final products when a 50-times or higher excess of Glc3Me over Cr^VI is used. The redox reaction takes place through the combination of Cr^VI → Cr^IV → Cr^II and Cr^VI → Cr^IV → Cr^III pathways. Intermediacy of free radicals and Cr^II in the reaction was demonstrated by the observation of induced polymerization of acrylamide and detection of CrO₂²⁺ formed by reaction of Cr^II with O₂. Intermediate oxo-Cr^V–Glc3Me species were detected by EPR spectroscopy. In 0.3–0.5 mol/L HClO₄, intermediate Cr^V rapidly decompose to the reaction products, while, at pH 5.5–7.5, where the redox processes are very slow, five-coordinate Cr^V bis-chelates of the pyranose and furanose forms of Glc3Me remain more than 15 h in solution. The C1–C2 bond cleavage of Glc3Me upon reaction with Cr^VI distinguishes this derivative from glucose, which is oxidized to gluconic acid.