A 1,8-Naphthalimide-based Tripodal Fluorescent Chemosensor to Selectively Detect Copper Ions

A 1,8-naphthalimide-based tripodal fluorescent ligand (L3) was synthesized through the copper (I) catalyzed Huisgen azide-alkyne cycloaddition reaction of 2-(2-azidoethyl)-6-morpholino-1 H-benzo[de]isoquinoline-1,3(2 H)-dione with triproparagylamine. Naphthalimide acts as the fluorophore while the triazole and amine nitrogens chelate the metal ion. L3 showed a selective fluorescence turn-off for Cu(II) over other metal ions in aqueous acetonitrile solution. A Job's plot, Benesi-Hildbrand plot and high-resolution mass spectrometry data confirm a 1:1 binding stoichiometry with a binding constant of 7.8 х105 M- 1 while addition of disodium EDTA demonstrates its reversibility. The structure and stability of the complex was supported by theoretical calculations. The limit of detection for Cu(II) was calculated to be 0.3 µM which is considerably lower than WHO recommended Cu(II) limit in drinking water.

Fluorescent Probes and Quenchers in Studies of Protein Folding and Protein-Lipid Interactions

Fluorescence spectroscopy provides numerous methodological tools for structural and functional studies of biological macromolecules and their complexes. All fluorescence-based approaches require either existence of an intrinsic probe or an introduction of an extrinsic one. Moreover, studies of complex systems often require an additional introduction of a specific quencher molecule acting in combination with a fluorophore to provide structural or thermodynamic information. Here, we review the fundamentals and summarize the latest progress in applications of different classes of fluorescent probes and their specific quenchers, aimed at studies of protein folding and protein-membrane interactions. Specifically, we discuss various environment-sensitive dyes, FRET probes, probes for short-distance measurements, and several probe-quencher pairs for studies of membrane penetration of proteins and peptides. The goals of this review are: (a) to familiarize the readership with the general concept that complex biological systems often require both a probe and a quencher to decipher mechanistic details of functioning and (b) to provide example of the immediate applications of the described methods.

A functional cobalt-organic framework constructed by triphenylamine tricarboxylate: Detect nitroaromatics by fluorescence sensing and UV-shielding

Luminescent metal-organic frameworks (LMOF) with ligand-modified are a promising strategy to be applied to fabricate chemical sensors. Herein, a novel Co (II) metal-organic framework (Co-MOF), namely Co [(NTB) bpy] (NTB = 4,4'4″-tricarboxylic acid triphenylamine, bpy = 4,4 '-bipyridyl), was successfully synthesized with excellent water stability and fluorescence properties. Due to the propeller structure of NTB ligands, a special topological structure of Co-MOF was shown: {2⁴.4¹⁶.6⁸}{2}4. It was proved that Co-MOF has great stability by soaking in different solvents for two weeks. Remarkably, the fluorescence quenching experiment verified that Co-MOF has excellent fluorescence sensor performance. Trinitrophenol, 2,4-dinitrophenol, and 2-amino-4-nitrotoluene (10^-5 M) with LOD of 9.00 × 10^-5, 5.40 × 10^-5 and 5.07 × 10^-6 M can be detected via the process of fluorescence enhancement and quenching. Throughout the investigation, the mechanics of fluorescence quenching was performed. Due to the excellent UV absorption capacity of Co-MOF, it was a promising application to combine low-dimensional nanomaterials with sustainable biomass materials. A hybrid films of Co-MOF and cellulose acetate (CA) was generated. The hybrid films had highly transparency in the visible wavelength range and excellent UV-shielding ability owing to the CA/Co-MOF hybrid films enhanced the UV absorption capacity of Co-MOF.

Fluorescent probes for the detection of disease-associated biomarkers

Fluorescent probes have emerged as indispensable chemical tools to the field of chemical biology and medicine. The ability to detect intracellular species and monitor physiological processes has not only advanced our knowledge in biology but has provided new approaches towards disease diagnosis. In this review, we detail the design criteria and strategies for some recently reported fluorescent probes that can detect a wide range of biologically important species in cells and in vivo. In doing so, we highlight the importance of each biological species and their role in biological systems and for disease progression. We then discuss the current problems and challenges of existing technologies and provide our perspective on the future directions of the research area. Overall, we hope this review will provide inspiration for researchers and prove as useful guide for the development of the next generation of fluorescent probes.

An inner-filter-effect based ratiometric fluorescent sensor for the detection of uranyl ions in real samples

In this work, a ratiometric fluorescence system was designed for the detection of trace UO₂²⁺ in water based on the inner filter effect (IFE) between gold nanoparticles (AuNPs) and gold nanoclusters (AuNCs). IFE-induced fluorescence quenching was achieved due to the enhanced complementary overlap between the absorption spectra of AuNPs and the emission spectrum of AuNCs after the addition of UO₂²⁺. Blue carbon dots (B-CDs) were added to serve as reference fluorophores to expand the color tonality and make human eye recognition easier. The ratiometric fluorescent sensor demonstrated a unique fluorescence color change from red to blue when different doses of UO₂²⁺ were added, with a detection limit of 8.4 nM. Furthermore, the ratiometric fluorescent sensor was effectively used for UO₂²⁺ determination in real-world water samples, with acceptable recoveries.

A novel near-infrared fluorimetric method for point-of-care monitoring of Fe2+ and its application in bioimaging

Iron is one of the essential trace elements in the human body, which is involved in many important physiological processes of life. The abnormal amount of iron in the body will bring many diseases. Therefore, a novel near-infrared fluorimetric method was developed. The method is based on a fluorescent probe (E)-4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl)-N, N-diethylaniline oxide (DDED) which uses N-oxide as a recognition group to real-time monitoring and imaging of Fe²⁺ in vivo and in vitro. The method exhibits excellent selectivity and high sensitivity (LOD = 27 nM) for Fe²⁺, fast reaction rate (< 4 min), extremely large Stokes shift (＞ 275 nm), low cytotoxicity. The strip test strongly illustrates the potential application of DDED in real environment. In particular, DDED has been successfully applied to real-time monitoring and imaging of Fe²⁺ in HepG² cells and zebrafish. That is, the method has great potential for the detection of Fe²⁺ in living systems.

FRET based ratiometric switch for selective sensing of Al3+ with bio-imaging in human peripheral blood mononuclear cells

FRET based ratiometric switch for selective sensing of Al³⁺ with bio-imaging in human peripheral blood mononuclear cells (PBMCs).

Reaction-based highly selective and sensitive monomer/polymer probes with Schiff base groups for the detection of Hg2+ and Fe3+ ions

It is urgent and important to detect heavy metals in environments. In this work, novel reaction-based fluorescent probes were obtained by Schiff base reaction. The probes with Schiff base moiety (-C=N-) undergo irreversible hydrolysis in the presence of Hg²⁺ and Fe³⁺. They exhibit perfect high selectivity and sensitivity to Hg²⁺and Fe³⁺ ions. Upon the addition of Hg²⁺and Fe³⁺, fluorescence intensity of the probes increased notably. And the color of the probe changes from brown to bright green under UV light, which can realize "naked eye" detection. In addition, Schiff base group was introduced into polyurethane chain through condensation polymerization reaction. As expected, the fluorescent polyurethane probe (P2) maintained the detection performance of its original small molecules (BSD). Even more P2 showed a more sensitive detection effect than BSD, and the detection limits of P2 for Hg²⁺ and Fe³⁺ reach 0.19 μM and 0.21 μM, respectively. It indicates that Reaction-based probes could be a useful tool for the detection of Hg²⁺ and Fe³⁺.

A flexible tripod fluorescent probe for multiple cations detection and its application in living cells

To the flexible tripod platform tren (tris(2-aminoethyl)amine), a Rhodamine and two naphthalene fluorophores were introduced. The resulting fluorescence probe named TRN was fully characterized and employed in cell imaging. Probe TRN exhibited high selectivity and excellent sensitivity for the simultaneous fluorescence detection of Zn²⁺/Hg²⁺/Al³⁺/Cu²⁺. The significant changes in the fluorescence color make naked-eye detection possible. Furthermore, fluorescence imaging experiments of Zn²⁺/Hg²⁺/Al³⁺/Cu²⁺ in living PC3 cells demonstrated its value for practical applications in biological systems.

One-step synthesis of rhodamine-based Fe3+ fluorescent probes via Mannich reaction and its application in living cell imaging

Four rhodamine-based fluorescent probes M1-M4 were synthesized in one step using Mannich reaction. The Mannich reaction based approach has the advantages of simplicity, good yield and excellent atomic economy. The structures were determined by ¹H NMR, ¹³C NMR, IR and HRMS. The probe M3 as a representative compound was characterized by single-crystal X-ray analyses. The fluorescence and absorbance spectra research of the probes demonstrated that they could be used as Fe³⁺-selective fluorescent probes with good sensitivity, excellent linearity, and outstanding anti-interference in acetonitrile/Tris-HCl buffer solution (3:7, V/V; pH = 7.4). Moreover, confocal laser scanning microscopy experiments have proven that the probe M3 was successfully used for fluorescence imaging in MCF-7 cells.

Multichromophoric COO-BODIPYs: an advantageous design for the development of energy transfer and electron transfer systems

Synthesis and photonics avails a new design for multichromophoric arrays.

Through bond energy transfer (TBET)-operated fluoride ion sensing via spirolactam ring opening of a coumarin–fluorescein bichromophoric dyad

The detection of fluoride ions in a competitive environment often poses several challenges. In this work, we have designed and synthesized a coumarin functionalized fluorescein dyad (R3) which represents an ideal through bond energy transfer (TBET) fluorophore with the coumarin unit as donor and fluorescein unit as acceptor. The bichromophoric dyad demonstrates the detection of fluoride ions in the parts per billion (ppb) concentration level (22.8 ppb) with high selectivity via a TBET emission signal at 548 nm with a diagnostic bright yellow colour fluorescence output. Based on UV-visible, fluorescence, ¹H NMR and DFT studies, it is shown that the fluoride ion induces the opening of the spirolactam ring of the fluorescein moiety and provides a π-conjugation link between the donor and acceptor units enabling a TBET phenomenon with a larger pseudo-Stokes shift of 172 nm. To the best of our knowledge, this is the first report where the fluoride ion is detected via a TBET signal between the coumarin and fluorescein units in a bichromophoric dyad.

A coumarin–fluorescein based bichromophoric dyad detects fluoride ions in parts per billion concentration level via a TBET emission signal at 548 nm with a diagnostic bright yellow fluorescence.

A new fluorescent hemicryptophane for acetylcholine recognition with an unusual recognition mode

The ammonium of the target interacts with the south part of the hemicryptophane probably because the cyclotriveratrylene's electronic density is altered by the extension of conjugation.

Ratiometric fluorescent nanoprobes for visual detection: Design principles and recent advances - A review

Signal generation techniques for visual detection of analytes have received a great deal of attention in various sensing fields. These approaches are considered to be advantageous when instrumentation cannot be employed, such as for on-site assays, point-of-care tests, and he althcare diagnostics in resource-constrained areas. Amongst various visual detection approaches explored for non-invasive quantitative measurements, ratiometric fluorescence sensing has received particular attention as a potential method to overcome the limitations of intensity-based probes. This technique relies on changes in the intensity of two or more emission bands (induced by an analyte), resulting in an effective internal referencing which improves the sensitivity of the detection. The self-calibration, together with the unique optophysical properties of nanoparticles (NPs) have made the ratiometric fluorescent nanoprobes more sensitive and reliable, which in turn, can result in more precise visual detection of the analytes. Over the past few years, a vast number of ratiometric sensing probes using nanostructured fluorophores have been designed and reported for a wide variety of sensing, imaging, and biomedical applications. In this work, a review on the NP-based ratiometric fluorescent sensors has been presented to meticulously elucidate their development, advances and challenges. With a special emphasis on visual detection, the most important steps in the design of fluorescent ratiometric nanoprobes have been given and based on different classes of analytes, recent applications of fluorescent ratiometric nanoprobes have been summarized. The challenges for the future use of the technique investigated in this review have been also discussed.

The Applicability of 2-amino-4,6-diphenyl-pyridine-3-carbonitrile Sensors for Monitoring Different Types of Photopolymerization Processes and Acceleration of Cationic and Free-Radical Photopolymerization Under Near UV Light

The performance of a series of 2-amino-4,6-diphenyl-pyridine-3-carbonitrile derivatives as fluorescent molecular sensors for monitoring photopolymerization processes of different monomers by the Fluorescence Probe Technique (FPT) was studied. It has been shown that the new derivatives are characterized by much higher sensitivity than the commercially available 7-diethylamino-4-methylcoumarin (Coumarin 1) and trans-2-(2',5'-dimethoxyphenyl)ethenyl-2,3,4, 5,6-pentafluorobenzene (25ST) probes. It has been discovered that the 2-amino-4,6-diphenyl-pyridine-3-carbonitrile derivatives accelerate the cationic photopolymerization process initiated with diphenyliodonium photoinitiators at the wavelength where the photoinitiator alone does not work. They are particularly efficient for the photoinitiation of cationic photopolymerization of an epoxide and vinyl monomers. Consequently, the application of the 2-amino-4,6-diphenyl-pyridine-3-carbonitrile derivatives in a dual role: (a) as fluorescent sensors for monitoring the free-radical, thiol-ene and cationic polymerization progress, and (b) as long-wavelength co-initiators for diphenyliodonium salts initiators, is proposed.

Rapid "turn-on" photoluminescence detection of bisulfite in wines and living cells with a formyl bearing bis-cyclometalated Ir(iii) complex

A new photoluminescence (PL) probe based on a formyl bearing bis-cyclometalated Ir(iii) complex, [Ir(ppy)2phen-CHO]+PF6- (1), is synthesized and applied to the selective detection of a bisulfite anion (HSO3-). Probe 1 is prepared using 2-phenylpyridine (ppy) as the C^N main ligand and 1,10-phenanthroline-5-carboxaldehyde (phen-CHO) as the N^N ancillary ligand. Probe 1 displayed excellent selective PL enhancement in response to HSO3- in acetic acid-sodium acetate buffer solution (pH = 5.0). The increase of PL signal is directly proportional to the concentration of HSO3- in the range of 2 μM to 45 μM with a detection limit of 0.9 μM using 50 μM probe 1 and in the range of 0.5 μM to 6 μM with a detection limit of 0.3 μM using 10 μM probe 1. More importantly, probe 1 can respond to HSO3- rapidly within 40 s. Furthermore, probe 1 was successfully applied to detect HSO3- in real white wines and the bioimaging of HSO3- in living cells. The superior properties of probe 1 make it of great potential use for studying the effects of HSO3- in other biosystems.

An aggregation-induced emission-based fluorescence turn-on probe for Hg2+ and its application to detect Hg2+ in food samples

In this work, we presented a new tetraphenylethene-derived fluorescent probe TPE-M for Hg²⁺ detection in an aqueous solution. Probe TPE-M is molecularly dissolved in CH₃OH/PBS (20 mM, pH = 7.4) (3 : 7, v/v) mixed solution and is almost non-emissive. Reaction of TPE-M with Hg²⁺ leads to release of an AIE-active precursor 4, and results in a significant fluorescence enhancement. The Hg²⁺ recognition process has some distinct advantages including rapid response, high selectivity and sensitivity, strong anti-interference ability, and a low detection limit (4.16 × 10⁻⁶ M). Moreover, the probe is applicable to detect Hg²⁺ in real food samples such as shrimp, crab and teas, suggesting the practical applicability of TPE-M.

A new AIE-based fluorescent probe TPE-M for Hg²⁺ detection in an aqueous solution has been developed.

A highly selective and reversible fluorescence "OFF-ON-OFF" chemosensor for Hg2+ based on rhodamine-6G dyes derivative and its application as a molecular logic gate

A new rhodamine-6G-based chemosensor X was designed and synthesized for the colorimetric and fluorometric detection of Hg²⁺. The chemosensor X responsed to Hg²⁺ had good sensitivity, high selectivity and excellent reversibility in HEPES buffer (10 mM, pH 7.4)/CH₃CN (40:60, V/V). The recognition mechanism of X toward Hg²⁺ was evaluated by Job's plot, IR and MS. Meanwhile, X-Hg²⁺ fluorescence lifetime was also measured. It was interesting that X displayed favorable reversibility to form an "off-on-off" type signaling behavior with the Hg²⁺-induced emission spectra being quenched by I^-. Furthermore, it could be applied as a molecular logic gate and test strips based on X exhibited a good reversibility selectivity to Hg²⁺.

Photophysics of "Floppy" Dyads as Potential Biomembrane Probes

In the study a dyad (C6 probe), constructed of two dyes with highly different hydrophobicities, was investigated by steady-state and time-resolved spectroscopic techniques in chloroform, methanol, and in phospholipid vesicles, respectively. The dyad was built on two dyes: the lipophilic benzo[a]pyrene (BaP) and the hydrophilic sulforhodamine B (SRB). The dyes were linked via a short, but flexible alkyl chain (six C-atoms). Based on their spectroscopic properties, BaP and SRB showed a very efficient non-radiative resonance energy transfer in solution. Incorporation into a lipid bilayer limited the relative flexibility (degree of freedom) between donor and acceptor and was used for the investigation of fundamental photophysical aspects (especially of FRET) as well as to elucidate the potential of the dyad to probe the interface of vesicles (or cells). The location of the two dyes in vesicles and their respective accessibility for interactions with dye-specific antibodies was investigated. Based on the alteration of the anisotropy, on the rotational correlation time as well as on the diffusion coefficient the incorporation of the C6 probe into the vesicles was evaluated. Especially the limitation in the relative movements of the two dyes was considered and used to differentiate between potential parameters, that influence the energy transfer in the dyad. Transient absorption spectroscopy (TAS) and pulsed-interleave single molecule fluorescence experiments were performed to better understand the intramolecular interactions in the dyad. Finally, in a showcase for a biosensing application of the dyads, the binding of an SRB-specific antibody was investigated when the dyad was incorporated in vesicles. Graphical Abstract.

Fluorescent Probes Based on π-Conjugation Modulation between Hemicyanine and Coumarin Moieties for Ratiometric Detection of pH Changes in Live Cells with Visible and Near-infrared Channels

We report two ratiometric fluorescent probes based on π-conjugation modulation between coumarin and hemicyanine moieties for sensitive ratiometric detection of pH alterations in live cells by monitoring visible and near-infrared fluorescence changes. In a π-conjugation modulation strategy, a coumarin dye was conjugated to a near-infrared hemicyanine dye via a vinyl connection while lysosome-targeting morpholine ligand and o-phenylenediamine residue were introduced to the hemicyanine dye to form closed spirolactam ring structures in probes A and B, respectively. The probes show only visible fluorescence of the coumarin moiety under physiological and basic conditions because the hemicyanine moieties retain their closed spirolactam ring structures. However, decrease of pH to acidic condition causes spirolactam ring opening, and significantly enhances π-conjugation within the probes, thus generating new near-infrared fluorescence peaks of the hemicyanine at 755 nm and 740 nm for probes A and B, respectively. Moreover, the probes display ratiometric fluorescence response to pH with decreases of the coumarin fluorescence and increases of the hemicyanine fluorescence when pH changes from 7.4 to 2.5. The probes are fully capable of imaging pH changes in live cells with good ratiometric responses in visible and near-infrared channels, and effectively avoid fluorescence blind spots under neutral and basic pH conditions - an issue that typical intensity-based pH fluorescent probes run into. The probe design platform reported herein can be easily applied to prepare a variety of ratiometric fluorescent probes for detection of biological thiols, metal ions, reactive oxygen and nitrogen species by introducing appropriate functional groups to hemicyanine moiety.

Ratiometric Near-Infrared Fluorescent Probes Based On Through-Bond Energy Transfer and π-Conjugation Modulation between Tetraphenylethene and Hemicyanine Moieties for Sensitive Detection of pH Changes in Live Cells

In this paper, we present three ratiometric near-infrared fluorescent probes (A-C) for accurate, ratiometric detection of intracellular pH changes in live cells. Probe A consists of a tetraphenylethene (TPE) donor and near-infrared hemicyanine acceptor in a through-bond energy transfer (TBET) strategy, while probes B and C are composed of TPE and hemicyanine moieties through single and double sp2 carbon-carbon bond connections in a π-conjugation modulation strategy. The specific targeting of the probes to lysosomes in live cells was achieved by introducing morpholine residues to the hemicyanine moieties to form closed spirolactam ring structures. Probe A shows aggregation-induced emission (AIE) property at neutral or basic pH, while probes B and C lack AIE properties. At basic or neutral pH, the probes only show fluorescence of TPE moieties with closed spirolactam forms of hemicyanine moieties, and effectively avoid blind fluorescence imaging spots, an issue which typical intensity-based pH fluorescent probes encounter. Three probes show ratiometric fluorescence responses to pH changes from 7.0 to 3.0 with TPE fluorescence decreases and hemicyanine fluorescence increases, because acidic pH makes the spirolactam rings open to enhance π-conjugation of hemicyanine moieties. However, probe A shows much more sensitive ratiometric fluorescence responses to pH changes from 7.0 to 3.0 with remarkable ratio increase of TPE fluorescence to hemicyanine fluorescence up to 238-fold than probes B and C because of its high efficiency of energy transfer from TPE donor to the hemicyanine acceptor in the TBET strategy. The probe offers dual Stokes shifts with a large pseudo-Stokes shift of 361 nm and well-defined dual emissions, and allows for colocalization of the imaging readouts of visible and near-infrared fluorescence channels to achieve more precisely double-checked ratiometric fluorescence imaging. These platforms could be employed to develop a variety of novel ratiometric fluorescent probes for accurate detection of different analytes in applications of chemical and biological sensing, imaging, and diagnostics by introducing appropriate sensing ligands to hemicyanine moieties to form on-off spirolactam switches.

Lanthanide(iii) coordination polymers for luminescence detection of Fe(iii) and picric acid

Two 2D coordination polymers exhibit a sensitive and fast luminescence quenching response to Fe³⁺and picric acid (PA) in water with a high quenching effect constant (K_sv) for PA (>17 000 M⁻¹) and Fe³⁺(>3950 M⁻¹).

Design and application of a fluorogenic receptor for selective sensing of cations, small neutral molecules, and anions

An unprecedented single multi-analyte fluorogenic receptor, a sodium salt of N-(methyl-2-thiophenyl)-tyrosine (NaHTyrthio), is reported for the selective sensing of cations (Cu²⁺), small neutral molecules (nitrobenzene and aniline) and anions (F⁻) by variable spectral responses.

New Six-Membered pH-Insensitive Rhodamine Spirocycle in Selective Sensing of Cu2+ through C-C Bond Cleavage and Its Application in Cell Imaging

A new rhodamine-based chemosensor 1 with a six-membered spirocyclic ring has been synthesized, which exhibits excellent pH stability and shows selective "turn-on" fluorescent detection of Cu²⁺ ions over a series of other metal ions including Cu⁺ ions. The expansion of spirocycle improves the stability and selectivity of the chemosensors in sensing of metal ions. Till today only few rhodamine structures R1-R5 with thiourea-, hydrazine amide-, or pyrrole-decorated six-membered spirocyclic rings are known that exhibit metal-ion sensing via C-N bond cleavage of the spiro ring. In this context, rhodamine compound that responds to the metal ion through C-C bond cleavage of the six-membered spiro ring is completely unknown. The present example is a first-time report that demonstrates selective sensing of Cu²⁺ ions through C-C bond cleavage over the conventional existing systems in the literature. The chemosensor 1 is cell permeable and can detect Cu²⁺ in live cells using confocal microscopy in the biologically relevant pH range with high photostability.

A novel "turn-on" thiooxofluorescein-based colorimetric and fluorescent sensor for Hg2+ and its application in living cells

A novel water-soluble fluorescent probe FLS2 based on the thiooxofluorescein derivative has been firstly designed and synthesized. UV-vis absorption and fluorescence spectra studies showed that the FLS2 as a colorimetric and ratiometric fluorescent probe exhibited high selectivity and sensitivity towards Hg²⁺, which was mainly attributed to the special binding with the receptor unit accompanied with the spirolactam ring-opening progress. In addition, the probe FLS2 could be used as a naked-eye indicator for Hg²⁺ with reversible response. It displayed approximate 37-fold fluorescent enhancement at 529nm in the presence of only 2.0 equiv. Hg²⁺ and the detection limit was calculated at about 39nM. What's more, cellular imaging experiment revealed that the sensor had excellent biocompatibility and low cytotoxicity that could be utilized for monitoring Hg²⁺ in living cells.

A new 2-(2'-hydroxyphenyl)quinazolin-4(3H)-one derived acylhydrazone for fluorescence recognition of Al3

A new 2-(2'-hydroxyphenyl)quinazolin-4(3H)-one derived acylhydrazone (QP) was designed and synthesized as a fluorescent sensor. In Tris∙HCl buffer (10mM, pH7.4)/ethanol (1/9, v/v) solution, QP exhibits a highly selective fluorescence response to Al³⁺ over other metal ions with a significant blue-shifted and enhanced emission at 473nm. QP interacts with Al³⁺ reversibly through a 1:2 binding ratio with a detection limit of 4.79×10^-8M. Potential applicability of QP for Al³⁺ detection in tap and lake water samples were also examined by 'proof-of-concept' experiments.

Rhodamine Diaminomaleonitrile Conjugate as a Novel Colorimetric Fluorescent Sensor for Recognition of Cd2+ Ion

Rhodamine diaminomaleonitrile linked probe (RD-1) shows highly sensitive colorimetric and selective turn-on fluorescent response to Cd²⁺ over other metal ions. The fluorescence intensity and absorbance of the probe RD-1 showed a good linearity, with very low detection limits of 18.5 nm. The probe RD-1 was preliminarily applied to the determination of Cd²⁺ ion in water samples from river and tap water with satisfying results. The live cell image confocal microscopy, HeLa cell demonstrated that RD-1 had low cytotoxicity with good membrane permeable property is successfully applied to fluorescence microscopic imaging for the detection of Cd²⁺ ions.

Design, properties and application of a facile fluorescence switch for Cu(II)

A facile fluorescence switch based on Schiff base 2,2'-[1,3-phenylenbis- (methylidynenitrilo)]bis[benzenethiol] (PMBB) has been developed and used to sensing metal ions. UV-vis absorption and fluorescence emission spectra show that the PMBB receptor has high selectivity and sensitivity for Cu(II) ions. Based on the photoinduced electron transfer (PET) and chelation enhanced fluorescence (CHEF) mechanisms, the receptor exhibits an fluorescence "turn-on" switch signal for Cu(II). The 1:1 binding mode of PMBB and Cu (II) ions can be obtained by the Job-plot and ESI-Mass spectra data. Noticeably, the color changes (from colorless to yellow) of PMBB solutions for Cu(II) sensing can be observed by naked eyes in the sunlight. The detection limit of the receptor for Cu(II) may reach 10(-7)mol/L with a good linear relation in the lower concentrations of Cu(II). To develop the practical application, the Cu(II) ions in swimming pool water samples were detected. Results show that PMBB receptor as a fluorescent probe can use to detect the trace level of Cu(II) in the environmental samples. This work contributes to providing a facile strategy for designing efficient probes and developing their practical application value.

New sensitive and selective calixarene-based fluorescent sensors for the detection of Cs+ in an organoaqueous medium

A calixarene-based fluorescent sensor has been designed for the detection of Cs⁺ in the micromolar range.

FRET based selective and ratiometric detection of Al(iii) with live-cell imaging

A cell permeable FRET based platform for dual mode ‘naked-eye’in vitroandin vivodetection of Al³⁺over other common ions (including trivalent ions).