Ratiometric detection of Cr3+ and Hg2+ by a naphthalimide-rhodamine based fluorescent probe

Simultaneous bioimaging recognition of Al3+ and Cu2+ in living-cell, and further detection of F- and S2- by a simple fluorogenic benzimidazole-based chemosensor

A simple Schiff base (BMSA) prepared from salicylaldehyde and 2-(1H-benzo[d]imidazol-2-yl)aniline was evaluated as an efficient fluorescent chemosensor for the selective recognition of Al³⁺and Cu²⁺ over other common metal ions. This sensor could detect Al3⁺ in CH₃OH/PBS with distinct emission red-shift (the detection limit 0.31μM)and Cu²⁺in CH₃OH/Tris-HCL (the detection limit 0.54μM) with obvious fluorescence quenching. The obtained BMSA-Al³⁺ and BMSA-Cu²⁺ complexes could act as cascade sensors for detecting F^- and S^2-, respectively. The recognizing behavior of BMSA toward Al³⁺and Cu²⁺ has been investigated in detail through Job's Plot, FT-IR NMR, and HRMS analysis. Moreover, this chemosensor was verified to be of low cytotoxicity and good imaging characteristics for the detection of Al³⁺ and Cu²⁺, and further for the recognition of F^- and S^2- in living cells, suggesting that BMSA was proved to be a useful tool for tracking Al3⁺/Cu²⁺and F^-/S^2- ions in vivo.

Nanomolar colorimetric quantitative detection of Fe³⁺ and PPi with high selectivity

A novel rhodamine and 8-hydroxyquinoline-based derivative was synthesized, which is shown to act as a colorimetric chemosensor for Fe(3+) in aqueous solution with high selectivity over various environmentally and biologically relevant metal ions and anions with a distinct color change from colorless to pink in very fast response time (<1 min). Fe(3+) can be detected quantitatively in the concentration range from 6.7 to 16 μM and the detection limit (LOD) on UV-vis response of the sensor can be as low as 15 nM. The 'in situ' prepared Fe(3+) complex (1⋅Fe) showed high selectivity toward PPi against many common anions, and sensitivity (the LOD can be as low as 71 nM). In addition, both the chemosensor and the 'in situ' prepared Fe(3+) complex are reusable for the detection of Fe(3+) and PPi respectively.

5-Hydroxymethylfurfural modified rhodamine B dual-function derivative: Highly sensitive and selective optical detection of pH and Cu(2+)

A dual-function optical chemosensor (RBF) was designed and easily synthesized by condensation reaction of 5-Hydroxymethylfurfural and rhodamine B hydrazide. RBF exhibited highly sensitive, highly selective and quick response to acidic pH. The fluorescence intensity of RBF exhibited a more than 41-fold increase within the pH range from 7.50 to 3.73 with a pKa value of 5.02, which could be successfully applied to monitor intracellular pH in living PC12 cells and HeLa cells. Additionally, the spectroscopy of UV-Vis and EDTA-adding experiments indicated that RBF was a highly selective and reversible colorimetric chemosensor for Cu(2+) in Tris-HCl (10mM, pH=7.2) aqueous buffer solution as well as other metal ions had no obvious interference. Moreover, RBF has been successfully applied to detect Cu(2+) in real water samples.

Dimethyl yellow-based colorimetric chemosensors for “naked eye” detection of Cr3+ in aqueous media via test papers

New dimethyl yellow-based dipodal receptors as colorimetric probes were designed and synthesised for selectively sensing Cr³⁺ in a “naked eye” output manner via test papers.

Highly Hg2+-sensitive and selective fluorescent sensors in aqueous solution and sensors-encapsulated polymeric membrane

The sensors in solutions and sensors encapsulated polymeric membranes exhibited high sensitivity and selectivity for Hg²⁺ detection, with detection limits of 0.2–49 ppb.

A robust fluorescent chemosensor for aluminium ion detection based on a Schiff base ligand with an azo arm and application in a molecular logic gate

A new azo based chemosensor for detection of Al³⁺ ion has been reported. The sensor has been well characterized using different techniques like single crystal X-ray, NMR, IR, UV etc. Detection limit of the chemosensor was found to be 6.93 nM.

Rhodamine-based ratiometric fluorescent probes based on excitation energy transfer mechanisms: construction and applications in ratiometric sensing

Rhodamine is a convenient platform for the construction of “OFF–ON” ratiometric excitation energy transfer fluorescent probes.

Rhodamine B-based ordered mesoporous organosilicas for the selective detection and adsorption of Al(iii)

A novel “Off–On” solid chemosensor for Al³⁺ was constructed by combining ordered mesoporous silica with a rhodamine B derivative.

A new visible-light-excitable ICT-CHEF-mediated fluorescence 'turn-on' probe for the selective detection of Cd(2+) in a mixed aqueous system with live-cell imaging

A new quinoline based sensor was developed and applied for the selective detection of Cd(2+) both in vitro and in vivo. The designed probe displays a straightforward approach for the selective detection of Cd(2+) with a prominent fluorescence enhancement along with a large red shift (∼38 nm), which may be because of the CHEF (chelation-enhanced fluorescence) and ICT (internal charge transfer) processes after interaction with Cd(2+). The interference from other biologically important competing metal ions, particularly Zn(2+), has not been observed. The visible-light excitability of the probe merits in the viewpoint of its biological application. The probe enables the detection of intracellular Cd(2+) with non-cytotoxic effects, which was demonstrated with the live RAW cells. The experimentally observed change in the structure and electronic properties of the sensor after the addition of Cd(2+) were modelled by the density functional theory (DFT) and time-dependent density functional theory (TDDFT) computational calculations, respectively. Moreover, the test strip experiment with this sensor exhibits both absorption and fluorescence color changes when exposed to Cd(2+) in a mixed aqueous solution, which also makes the probe more useful. The minimum limit of detection of Cd(2+) by the probe was in the range of 9.9 × 10(-8) M level.

Synthesis of new colori/fluorimetric chemosensor for selective sensing of biologically important Fe³⁺, Cu²⁺ and Zn²⁺ metal ions

New Schiff base chemosensors (1 and 2) based on aryl ether amine were synthesized and demonstrated positional isomer and functional group dependent colori/fluorimetric sensing of Fe(3+), Cu(2+) and Zn(2+) at ppm level. Methoxy salicylaldehyde based chemosensor 1 exhibited selective colorimetric sensing of Fe(3+) whereas 2-hydroxy naphthaldehyde based chemosensor 2 showed selective disappearance of yellow color for Cu(2+) ions. Interestingly, both 1 and 2 exhibited a highly selective strong turn-on fluorescence for Zn(2+). The significance of COOH group in 1 and 2 for Zn(2+) turn-on fluorescence sensing has been confirmed by structure-property studies. Concentration dependent studies of 1 and 2 indicate that Fe(3+), Cu(2+) and Zn(2+) can be detected up to 10 μM. The formation of 1:1 Zn(2+) and chemosensor (1 and 2) confirmed by NMR studies. High selectivity of 1 and 2 was demonstrated by interference studies in presence of different metal ions.

Morphology-directing synthesis of rhodamine-based fluorophore microstructures and application toward extra- and intracellular detection of Hg(2+)

A new, easily synthesizable rhodamine-based chemosensor with potential N2O2 donor atoms, L(3), has been characterized by single-crystal X-ray diffraction together with (1)H NMR and high-resolution mass spectrometry (HRMS) studies. L(3) was found to bind selectively and reversibly to the highly toxic Hg(2+) ion. The binding stoichiometry and formation constant of the sensor toward Hg(2+) were determined by various techniques, including UV-vis, fluorescence, and Job's studies, and substantiated by HRMS methods. None of the biologically relevant and toxic heavy metal ions interfered with the detection of Hg(2+) ion. The limit of detection of Hg(2+)calculated by the 3σ method was 1.62 nM. The biocompatibility of L(3) with respect to its good solubility in mixed organic/aqueous media (MeCN/H2O) and cell permeability with no or negligible cytotoxicity provides good opportunities for in vitro/in vivo cell imaging studies. As the probe is poorly soluble in pure water, an attempt was made to frame nano/microstructures in the absence and in the presence of sodium dodecyl sulfate (SDS) as a soft template, which was found to be very useful in synthesizing morphologically interesting L(3) microcrystals. In pure water, micro-organization of L(3) indeed occurred with block-shaped morphology very similar to that in the presence of SDS as a template. However, when we added Hg(2+) to the solution of L(3) under the above two conditions, the morphologies of the microstructures were slightly different; in the first case, a flowerlike structure was observed, and in second case, a simple well-defined spherical microstructure was obtained. Optical microscopy revealed a dotlike microstructure for L(3)-SDS assemblies, which changed to a panicle microstructure in the presence of Hg(2+). UV-vis absorption and steady-state and time-resolved fluorescence studies were also carried out in the absence and presence of Hg(2+), and also the SDS concentration was varied at fixed concentrations of the receptor and guest. The results revealed that the fluorescence intensity increased steadily with [SDS] until it became saturated at ∼7 mM SDS, indicating that the extent of perturbation to the emissive species increases with the increase in [SDS] until it becomes thermodynamically stable. There was also an increase in anisotropy with increasing SDS concentration, which clearly manifests the restriction of movement of the probe in the presence of SDS.

A rhodamine-benzothiazole conjugated sensor for colorimetric, ratiometric and sequential recognition of copper(II) and sulfide in aqueous media

A new rhodamine-benzothiazole conjugated colorimetric sensor 1 that exhibits sequential recognition to Cu(2+) and S(2-) in CH3CN/HEPES buffer (v/v=1:1, HEPES 10mM, pH=7.0) solution has been developed. Sensor 1 displays highly selective and sensitive recognition to Cu(2+) with a ratiometric behavior, and the resultant 1-Cu(2+) complex can act as a highly selective S(2-) sensor via Cu(2+) displacement approach. The Cu(2+) and S(2-) recognition processes are rapid and reversible, and the Cu(2+) and S(2-) inputs can result in an INHIBIT logic gate.

A new FRET ratiometric fluorescent chemosensor for Hg²⁺ and its application in living EC 109 cells

On the basis of fluorescent resonance energy transfer, a new fluorophore dyad (L) bearing rhodamine B and naphthalimide was developed as fluorescent ratiometric chemosensor for Hg(2+) in aqueous solution. L exhibited high selectivity and excellent sensitivity towards Hg(2+) with a broad pH span (1.0-8.0) and the detection limit of L was 2.11×10(-8) M. Sensor L for the detection of Hg(2+) was rapid and the recognizing event could complete in 2.5 min. A significant change in the color could be used for naked-eye detection. The selective fluorescence response of L to Hg(2+) is due to the Hg(2+)-promoted ring opening of spirolactam of rhodamine moiety, leading to a cyclization reaction of thiourea moiety. In addition, fluorescence imaging experiments of Hg(2+) in living EC 109 cells demonstrated its value of practical applications in biological systems.

Physiology and methodology of chromium toxicity using alga Scenedesmus quadricauda as model object

Physiological responses of Scenedesmus quadricauda to Cr(VI) and Cr(III) excess were studied in buffer with circumneutral pH (6.5). Total Cr content was similar in low (1 μM of both oxidation states) but higher in 10 μM Cr(VI) treatment and high accumulation potential was detected (80-82% and 41-65% in 1 and 10 μM treatments, respectively). Specific fluorescence indicator (6-((anthracen-9-yl) methyleneamino)-2H-chromen-2-one) confirmed partial reduction of Cr(VI) to Cr(III) under exposure conditions. Viability and chlorophyll autofluorescence were more depleted by Cr(VI) while Cr(III) stimulated increase in ROS and lipid peroxidation. Antioxidative enzyme activities showed significantly higher values in 10 μM treatments of both Cr oxidation states. Depletion of mitochondrial proteins was not reflected in alteration of total soluble proteins indicating sensitivity of this organelle to Cr and TTC test showed no clear oxidation state-related effect. In this view, "Cr(VI) is not more toxic than Cr(III)" at least for some parameters. Subsequent study with the application of 10 μM Cr(VI) confirmed that HEPES buffer is more suitable exposure solution for toxicological studied than water or inorganic salts (higher chlorophyll autofluorescence was observed) and pH 6.5 is more suitable than low or high pH (4.5 or 8.5) in terms of Cr uptake. Another known Cr(III) fluorescence indicator (naphthalimide-rhodamine) also confirmed partial reduction of Cr(VI) to Cr(III) at acidic pH but only traces were seen at alkaline pH.

Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species

In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu²⁺, Fe²⁺/Fe³⁺, Zn²⁺and Hg²⁺.

Fluorescent and colorimetric sensors for environmental mercury detection

The development of fluorescent and colorimetric sensing strategies for environmental mercury is described.

FRET versus PET: ratiometric chemosensors assembled from naphthalimide dyes and crown ethers

Crown-containing naphthalimide dyads exhibited a ratiometric fluorescence response in the presence of metal cations and protons resulting from the competition between PET and FRET processes.

Naked-eye and fluorescence detection of basic pH and F−with a 1,8-naphthalimide-based multifunctional probe

A novel multifunctional colorimetric and fluorescent 1,8-naphthalimide-based probe toward basic pH and F⁻has been developed.

Cyclic aromatic imides as a potential class of molecules for supramolecular interactions

Prospects of stacking interactions of imides beneficial to generation of new soft materials are projected by analysing examples of primary building blocks that provide a basis for understanding at the molecular level.

A fast-response, fluorescent ‘turn-on’ chemosensor for selective detection of Cr3+

A highly selective and sensitive chemosensor 3 for Cr³⁺ detection was designed and synthesized, which showed a fast turn-on fluorescence response under physiological conditions.

A mechanosynthesized, sequential, cyclic fluorescent probe for mercury and iodide ions in aqueous solutions

A fluorescent Hg(2+)-selective chemosensor, 2,5-dimethoxybenzaldehyde thiosemicarbazone (1), was quantitatively prepared by grinding 2,5-dimethoxybenzaldehyde and thiosemicarbazide together in a ball mill for 15min. The excitation and emission maxima of compound 1 are 347 and 450nm, respectively. The reaction of this ligand with Hg(2+) was investigated by FT-IR, (1)H NMR, and fluorescence titration. Results show that the composition of the resulting Hg complex 1-Hg is 2:1 1:Hg, and that the S and imino N atoms serve as the binding sites of the ligand to the Hg(2+) ions. Coordination-assisted fluorescence quenching results show that compound 1 exhibits a highly selective fluorescence response to trace amounts of Hg(2+) in water. More importantly, the resulting complex 1-Hg can be used as a turn-on fluorescence probe for I(-) at a detection limit of 8.4×10(-8)M. Thus, compound 1 is a relatively stable, sequential, cyclic fluorescent probe for Hg(2+) and I(-).

Fluorescent, MRI, and colorimetric chemical sensors for the first-row d-block metal ions

Transition metals (d-blocks) are recognized as playing critical roles in biology, and they most often act as cofactors in diverse enzymes; however, improper regulation of transition metal stores is also connected to serious disorders. Therefore, the monitoring and imaging of transition metals are significant for biological research as well as clinical diagnosis. In this article, efforts have been made to review the chemical sensors that have been developed for the detection of the first-row d-block metals (except Cu and Zn): Cr, Mn, Fe, Co, and Ni. We focus on the development of fluorescent sensors (fall into three classes: "turn-off", "turn-on", and ratiometric), colorimetric sensors, and responsive MRI contrast agents for these transition metals (242 references). Future work will be likely to fill in the blanks: (1) sensors for Sc, Ti, and V; (2) MRI sensors for Cr, Mn, Co, Ni; (3) ratiometric fluorescent sensors for Cr(6+), Mn(2+), and Ni(2+), explore new ways of sensing Fe(3+) or Cr(3+) without the proton interference, as well as extend applications of MRI sensors to living systems.

A ratiometric fluorescent probe with unexpected high selectivity for ATP and its application in cell imaging

Naphthalimide-rhodamine compound (NR) is developed as a ratiometric fluorescent probe for ATP detection based on the FRET mechanism. It shows an unexpected high selectivity for ATP over other anions, especially organic phosphate anions, due to simultaneous interactions of two recognition sites, which benefits fluorescence imaging in living cells.

Rhodamine-Appended Bipyridine: XOR and OR Logic Operations Integrated in an Example of Controlled Metal Migration

A new bipyridyl derivative 1 bearing rhodamine B as visible fluorophore was designed, synthesized and characterized as a fluorescent and colorimetric sensor for metal ions. Interaction with Cu(2+), Zn(2+), Cd(2+), Hg(+), and Hg(2+) ions was followed by UV/Vis and emission spectroscopy. Upon addition of these metal ions, different colorimetric and fluorescent responses were observed. "Off-on-off" (Cu(2+), Zn(2+), and Hg(2+)) and "off-on" (Hg(+) and Cd(2+)) systems were obtained. Probe 1 was explored to mimic XOR and OR logic operations for the simultaneous detection of Hg(+)-Cu(2+) and Hg(+)-Zn(2+) pairs, respectively. DFT calculations were also performed to gain insight into the lowest-energy gas-phase conformation of free receptor 1 as well as the atomistic details of the coordination modes of the various metal ions.