Dimethylcyclam based fluoroionophore having Hg2+- and Cd2+-selective signaling behaviors

Single-Atom Switching as a General Approach to Designing Colorimetric and Fluorogenic Probes for Mercury Ions

By performing a single-atom replacement within common fluorophores, we have developed a facile and general strategy to prepare a broad-spectrum class of colorimetric and fluorogenic probes for the selective detection of mercury ions in aqueous environments. Thionation of carbonyl groups from existing fluorophore cores results in a great reduction of fluorescence quantum yield and loss of fluorescence emission. The resulting thiocaged probes are efficiently desulfurized to their oxo derivatives in the presence of mercury ions, leading to pronounced changes in chromogenic and fluorogenic signals. Because these probes exhibit high selectivity, excellent sensitivity, good membrane-permeability, and rapid responses towards mercury ions, they are suitable for visualization of mercury in both aqueous and intracellular environments.

Fluorescent sensor based models for the detection of environmentally-related toxic heavy metals

The quest for industrial and biotechnological revolution has been contributed in increasing environmental contamination issues, worldwide. The controlled or uncontrolled release of hazardous pollutants from various industrial sectors is one of the key problems facing humanity. Among them, adverse influences of lead, cadmium, and mercury on human health are well known to cause many disorders like reproductive, neurological, endocrine system, and cardiovascular, etc. Besides their presence at lower concentrations, most of these toxic heavy metals are posing noteworthy toxicological concerns. In this context, notable efforts from various regulatory authorities, the increase in the concentration of these toxic heavy metals in the environment is of serious concern, so real-time monitoring is urgently required. This necessitates the exploration for novel and efficient probes for recognition of these toxic agents. Among various methodologies adopted for tailoring such probes, generally the methodologies, in which changes associated with spectral properties, are preferred for the deceptive ease in the recognition process. Accordingly, a promising modality has emerged in the form of radiometric and colorimetric monitoring of these toxic agents. Herein, we review fluorescent sensor based models and their potentialities to address the detection fate of hazardous pollutants for a cleaner environment. Second, recent advances regarding small molecule and rhodamine-based fluorescent sensors, radiometric and colorimetric probes are discussed. The information is also given on the photoinduced electron transfer (PET) mechanism, chelation enhancement fluorescence (CHEF) effect and spirocyclic ring opening mechanism.

A new quinoline-based fluorescent probe for Cd2+ and Hg2+ with an opposite response in a 100% aqueous environment and live cell imaging

A new quinoline-based dual fluorescent probe L was synthesized for the detection of Cd²⁺ (turn-on) and Hg²⁺ (turn-off) in a 100% aquatic system. Its in vivo sensitivities to Cd²⁺ and Hg²⁺ were demonstrated in the EC9706 cell line.

A fluorescent chemosensor for Hg(2+) and Cd(2+) ions in aqueous medium under physiological pH and its applications in imaging living cells

A new BODIPY derivative with 2,2'-(ethane-1,2-diylbis(oxy))bis(N,N-bis(pyridine-2-ylmethyl)aniline unit as the metal receptor has been designed and synthesized. The dye selectively detects either Cd(2+) or Hg(2+) ions in the presence of hosts of other biologically important and environmentally relevant metal ions in aqueous medium at physiological pH. Binding of metal ions causes a change in the emission behavior of the dye from weakly fluorescent to highly fluorescent. Confocal microscopic experiments validate that the dye can be used to identify changes in either Hg(2+) or Cd(2+) levels in living cells.

A rhodamine-based fluorescent probe for Cu(II) determination in aqueous solution

An 'off-on' rhodamine-based fluorescence probe for the selective detection of Cu(II) has been designed, exploiting the guest-induced structure transform mechanism. This system shows a sharp Cu(II)-selective fluorescence enhancement response in an aqueous system under physiological pH, and possesses high selectivity against a background of environmentally and biologically relevant metal ions. Under optimum conditions, the fluorescence intensity enhancement of this system is linearly proportional to the Cu(II) concentration from 50 nM to 6.0 μM with a detection limit of 29 nM.

"Naked-eye" colorimetric and "turn-on" fluorometric chemosensors for reversible Hg2+ detection

Two new Hg(2+)-colorimetric and fluorescent sensors based on 2-[3-(2-aminoethylsulfanyl) propylsulfanyl]ethanamine covalently bound to one and two units of rhodamine-6G moieties, 1 and 2, were synthesised, and their sensing behaviors toward metal ions were investigated by UV/Vis and fluorescence spectroscopy. Upon the addition of Hg(2+), the sensors exhibited highly sensitive "turn-on" fluorescence enhancement as well as a color change from colorless to pink, which was readily noticeable for naked eye detection. Especially, 1 exhibited the reversible behavior and revealed a very high selectivity in the presence of competitive ions, particularly Cu(2+), Ag(+), Pb(2+), Ca(2+), Cd(2+), Co(2+), Fe(2+), Mn(2+), Na(+), Ni(2+), K(+), Ba(2+), Li(+) and Zn(2+), with a low detection limit of 1.7 ppb toward Hg(2+).

Turn-on fluorescent InP nanoprobe for detection of cadmium ions with high selectivity and sensitivity

We reported a "turn-on" fluorescent InP nanoprobe for detection of cadmium ions in hydrophobic and hydrophilic media. The method based on the turn-on fluorescence detection of cadmium ions has shown its high selectivity and sensitivity, which are independent of the pH of the tested samples. Also, this approach exhibits an immediate response to cadmium ions, and visualized detection of cadmium ions has further been demonstrated under a UV lamp.

A simple and efficient dual optical signaling chemodosimeter for toxic Hg(II)

10-Methylthioacridone, designated as acrithion, has been employed as an easily accessible chemodosimeter for the optical targeting of toxic Hg(2+) in buffered aqueous DMSO. The Hg(2+)-mediated desulfurization of the probe is translated into selective dual signaling of Hg(2+) by means of color bleaching and fluorescence amplification while several other metal ions, including potentially competing Ag(+), Cu(2+) and Pb(2+), afford no significant interferences even in excess concentrations.

Layer-by-layer immobilization of carbon dots fluorescent nanomaterials on single optical fiber

We report within this paper the development of a fiber-optic based sensor for Hg(II) ions. Fluorescent carbon nanoparticles were synthesized by laser ablation and functionalized with PEG(200) and N-acetyl-L-cysteine so they can be anionic in nature. This characteristic facilitated their deposition by the layer-by-layer assembly method into thin alternating films along with a cationic polyelectrolyte, poly(ethyleneimine). Such films could be immobilized onto the tip of a glass optical fiber, allowing the construction of an optical fluorescence sensor. When immobilized on the fiber-optic tip, the resultant sensor was capable of selectively detecting sub-micromolar concentrations of Hg(II) with an increased sensitivity compared to carbon dot solutions. The fluorescence of the carbon dots was quenched by up to 44% by Hg(II) ions and interference from other metal ions was minimal.

Ultra-sensitive fluorescent sensor for Hg2+ based on a donor-acceptor-donor framework

A new fluoroionophore [E-4,4'-di(N-(2-pyridyl)amino)stilbene, E1] with a donor-acceptor-donor framework, which features a central stilbene (acceptor) fluorophore and two terminal pyridylamino (donor) ionophores, is reported. The probe displays an ultrasensitive fluorescence quenching response toward Hg(2+) in H(2)O/THF. Coordination of Hg(2+) to E1 affords a 2:1 complex, enabling the detection of Hg(2+) at a concentration as low as 4.4 × 10(-14) M. The interactions between the two species have been thoroughly characterized with UV-vis absorption spectroscopy, fluorescence spectroscopy, and nuclear magnetic resonance spectroscopy. Density functional theory calculations provide further insights into the nature of the fluorescence quenching response. In contrast, a fluorescent molecule with the donor-acceptor architecture, E-4-(N-(2-pyridyl)amino)stilbene (E4), exhibits a greatly attenuated fluorescence quenching response toward Hg(2+).

Synthesis of a novel fluorescent sensor bearing dansyl fluorophores for the highly selective detection of mercury (II) ions

A new macromolecule possessing two dansyl moieties and based on 2-[4-(2-aminoethylthio)butylthio]ethanamine was prepared as a fluorescent sensor and its mercury sensing properties toward various transition metal, alkali, and alkali earth ions were investigated. The designed compound exhibited pronounced Hg²⁺-selective ON-OFF type fluorescence switching upon binding. The new compound provided highly selective sensing to Hg²⁺ in acetonitrile-water solvent mixtures with a detection limit of 2.49 x 10^{-7 M or 50 ppb.} The molecular modeling results indicated that ions-recognition of the sensor originated from a self assembly process of the reagent and Hg²⁺ to form a helical wrapping structure with the favorable electrostatic interactions of Hg²⁺coordinated with sulfur, oxygen, nitrogen atoms and aromatic moieties.