Ratiometric fluorescent sensor for silver ion and its resultant complex for iodide anion in aqueous solution

Synthesis and Properties of Norphthalocyanines Functionalized with a Tetrathiacrown Ether-Tetrathiafulvalene Substituent

To construct novel ion receptors and D-A self-assembly systems for materials with better functions, the annulation of a tetrathiafulvalene donor with a magnesium norphthalocyanine core via a flexible tetrathiacrown ether bridge afforded a new triad 1. The structure of this product was characterized by 1H NMR and infrared spectroscopy, time-of-flight mass spectrometry, and elemental analysis. The optical and electrochemical properties were investigated using UV-vis spectroscopy and cyclic voltammetry. The complex of triad 1 and 2,3,5,6- tetrafluoro-7,7,8,8-tetracyanoquinodimethane produced electron transfer with a radical cationic character, as confirmed by UV-Vis and electron paramagnetic resonance analysis. Furthermore, the target compound presented evident intramolecular charge-transfer interactions in ground states, which were explained using density functional theory. Furthermore, norphthalocyanine 1 was able to coordinate Ag⁺ through the peripheral ligating oxathiaether crown.

New Insights for Exploring the Risks of Bioaccumulation, Molecular Mechanisms, and Cellular Toxicities of AgNPs in Aquatic Ecosystem

Silver nanoparticles (AgNPs) are commonly used in numerous consumer products, including textiles, cosmetics, and health care items. The widespread usage of AgNPs results in their unavoidable discharge into the ecosystem, which pollutes the aquatic, groundwater, sediments, and marine environments. These nanoparticles (NPs) activate the production of free radicals reactive species in aquatic organisms that interrupt the functions of DNA, cause mitochondrial dysfunction, and increase lipid peroxidation, which terminates the development and reproduction both in vivo and in vitro. The life present in the aquatic ecosystem is becoming threatened due to the release and exploitation of AgNPs. Managing the aquatic ecosystem from the AgNP effects in the near future is highly recommended. In this review, we discussed the background of AgNPs, their discharge, and uptake by aquatic organisms, the mechanism of toxicity, different pathways of cytotoxicity, and bioaccumulation, particularly in aquatic organisms. We have also discussed the antimicrobial activities of AgNPs along with acute and chronic toxicity in aquatic groups of organisms.

Fluorenone-Based Fluorescent and Colorimetric Sensors for Selective Detection of I- Ions: Applications in HeLa Cell Imaging and Logic Gate

Fluorenone-based fluorescent and colorimetric sensors 1 and 2 have been developed that displayed selective detection of iodide ions in the presence of interferences. Sensors displayed the fluorescence emission enhancement response toward I- with detection limits of 8.0 and 11.0 nM, respectively, which is accomplished through inhibition of intramolecular charge transfer and C=N isomerization. Excellent sensitivity and unique fluorescence enhancement response of sensors toward I- make them superior because most of the previously reported iodide sensors are based on the fluorescence quenching mechanism and are less sensitive. The sensing potential of sensors toward I- ions was investigated through 1H NMR titration, dynamic light scattering, Job's plots, and density functional theory analysis. Further, sensors displayed reversible behavior by the alternate addition of I- and Cu2+ ions that substantiate their role as recyclable sensors for the on-site detection of I- ions. Advantageously, fluorescence enhancement response of sensors was favorably used for fluorescence imaging of I- in live HeLa cells and the design of the logic gate. These sensors were successfully applied in diversified applications such as the preparation of sensors' coated paper strips and the determination of I- ions in blood serum, food, and real water samples.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Non-porous interpenetrating Co-bpe MOF for colorimetric iodide sensing

MOFs with their accessible voids/channels have been explored immensely for sensing due to their exclusive host-guest chemistry. However, unavailability of pores/voids in interpenetrating non-porous MOFs limits their applications in sensing. We herein report for the first time, hitherto, a non-porous MOF with an interpenetrating ladder structure for iodide sensing. A Co-bpe MOF was synthesized by hydrothermal reaction between cobalt nitrate and 1,2-bis(4-pyridyl)ethylene (bpe) in methanol and tested against colorimetric sensing of halides. The supramolecular structure of the Co-bpe MOF was stabilized through strong hydrogen bonding. We propose a double nucleophilic substitution reaction mechanism for iodide detection, which is one of its own kind. While Co-bpe showed a significant color change from dark maroon to dark green in the presence of iodide, the rest of halides did not display any pronounced colorimetric effect. The limit of detection (LOD) of this material was found to be 2.7 × 10^-7 M. This article focuses on the equal competency of non-porous MOF materials with the porous MOFs in sensing applications.

Ratiometric fluorescent detection of silver nanoparticles in aqueous samples using peptide-based fluorogenic probes with aggregation-induced emission characteristics

The quantification of silver nanoparticles and Ag⁺ contamination in the aquatic ecosystem has attracted considerable interest. Benzoimidazolyl-cyanovinylene (1) was synthesized as an aggregation-induced emission fluorophore, and a fluorescent peptidyl probe (2 and 3) bearing this fluorophore was developed. The fluorescent peptidyl probes coordinated with Ag⁺ selectively among various metal ions, leading to a ratiometric response to Ag⁺ in pure aqueous solutions. Furthermore, an "in situ" protocol was developed to quantify AgNPs using 2 with H₂O₂ as an oxidizing reagent. The fluorescent detection method for Ag⁺ and AgNPs showed promising detection properties such as high selectivity, high sensitivity, fast response, visible light excitation, well-operations in pure aqueous solution, and large fluorescent signal change. The detection limits of Ag⁺ (0.64 ppb) and AgNPs (1.1 ppb) were significantly low. According to the binding mode study, Ag⁺ induced the formation of a 2:1 complex between 2 and Ag⁺ and the chirality of the peptide part of the probe was not critical for this process. The formation of aggregates of the probe triggered by Ag⁺ from AgNPs induced a significant change in fluorescence. Furthermore, the amounts of spiked AgNPs in groundwater and tap water were quantified using the fluorescent detection method with 2.

A chromo-fluorogenic HMT sensor for Ag+ and the resultant HMT-Ag complex turn-off probe for F- in DMSO: experimental and theoretical studies

The photophysical properties of Hexamethylenetetramine (HMT) were investigated through physical methods and spectroscopically in dimethyl sulfoxide (DMSO) at ambient temperature. Evidently, HMT turned out as a sensor, selective and sensitive to silver ion (Ag⁺) only, among other cations, through colorimetric and fluorometric activities (observable by naked eye) and spectrally, both by UV-Vis and fluorescence spectroscopy. The resulting complex pedant (HMT-Ag) is highly responsive to the presence of fluoride ion (F⁻) in aqueous soluble DMSO, evidenced by changes in absorption spectra as well as fluorescence quenching, upon addition of the respective ions. Consequently, spectral changes induced by the addition of these ions, were consistently concomitant with colour changes, from colourless to light brown (HMT-Ag) to dark brown (HMT-Ag-F) in daylight condition, while bright light blue colour (HMT) to dark blue brownish (HMT-Ag) under UV-light conditions. The experimental results were complimented by theoretical studies, which are well within agreement of one another.

Recent Advances in Luminescent Recognition and Chemosensing of Iodide in Water

This Minireview covers the latest developments of chemosensors based on transition-metal receptors and organic fluorophores with specific binding sites for the luminescent detection and recognition of iodide in aqueous media and real samples. In all selected examples within the last decade (made-post 2010), the iodide sensing and recognition is probed by monitoring real-time changes of the fluorescence or phosphorescence properties of the chemosensors. This review highlights effective strategies to iodide sensing from a structural approach where the iodide recognition/sensing process, through supramolecular interactions as coordination bonds, hydrogen bonds, halogen bonds and electrostatic interactions, is transduced into an optical change easily measurable. The selective iodide sensing is an active field of research with global interest due to the importance of iodide in biological, medicinal, industrial, environmental and chemical processes.

Ratiometric DNA sensing with a host-guest FRET pair

A supramolecular host-guest FRET pair based on a carboxyfluorescein-labelled cucurbit[7]uril (CB7-CF, as acceptor) and the fluorescent dye 4',6-diamidino-2-phenylindole (DAPI, as donor) is developed for sensing of DNA. In comparison to the commercial DNA staining dye SYBR Green I, the new chemosensing ensemble offers dual-emission signals, which allows a linear ratiometric response over a wide concentration range.

Novel chemical sensor for detection Ca(II) ions based on ferutinin

A new optical chemical sensor based on medicinal compound, jaeschkeanadiol p-hydroxyben-zoate (Ferutinin), has been designed and utilized for Ca(II) ions detections. This natural optical sensor exhibits immense selectivity including fluorescence and absorption ratiometric for Ca(II) ions within precious physiological pH range. Further, the chelation process of the Ca(II) ions with the medicinal optical sensor ferutinin yields a 1:1 (metal: ligand) complex which is accompanied by fluorescence enhancement of the main emission band centered at 355 nm of the medicinal probe. The fluorescence "turn-on" effect is a clear evidence for the chelation process between ferutinin medicinal probe and Ca(II) ions and this could be simply detected. The new sensor was proposed depending on significant fluorescence mechanism, (MLCT, metal-ligand charge transfer). However, the interaction of the medicinal optical sensor with Ca(II) in presence of other cations was examined without any significant interference. Also, the new developed optical sensor consecutively exhibits low limit of detection (LOD) 1.5 nM for Ca(II) which is detected in very significant physiological pH range (pH = 7.4). Also, the probe provides high binding affinity towards Ca(II) with large binding constant K_b 5.97 × 10⁴ M^-1. As a result, this optical sensor may apply for detection Ca(II) in cell or biological samples.

A Fluorescent Turn-On Carbazole-Rhodanine Based Sensor for Detection of Ag+ Ions and Application in Ag+ Ions Imaging in Cancer Cells

Carbazole - Rhodanine conjugate is an effective fluorescent host for silver ions through fluorometric transformation from green to red color with a hyperchromic emission. An intramolecular charge transfer process derived from carbazole towards rhodanine favors interaction of thiocarbonyl S and carboxylic acid O of the rhodanine moiety towards Ag⁺ ion. Carbazole - rhodanine dyad accomplishes the lowest detection limit of 12.8 × 10^-9 M and high quantum efficiency. A fluorescence reversibility of the probe with I^- ion surges reutilization of sensor molecule as an Ag⁺ ion probe with minimal loss in the fluorescent efficiency. This fluorescent ligand is a biocompatible probe and is also a proficient candidate for fluorescent imaging of Ag⁺ ion in live cells.

A highly selective and sensitive fluorescent chemosensor for distinguishing cadmium(ii) from zinc(ii) based on amide tautomerization

A naphthalimide-derived fluorescent sensor termed L2 was designed and synthesized.

A new BODIPY-derived ratiometric senor with internal charge transfer (ICT) effect: colorimetric/fluorometric sensing of Ag+

BODIPY was modified with α-4-aminostyryl group to form a colorimetric/fluorometric dual mode ratiometric Ag⁺ sensor, and the sensor-doped PVC film enables the naked-eye Ag⁺ detection in totally aqueous solution.

A Tetraphenylethene-Naphthyridine-Based AIEgen TPEN with Dual Mechanochromic and Chemosensing Properties

Synthesis of new tetraphenylethene (TPE) conjugates via an innocuous route led to the revelation of a unique TPE-based aggregation-induced emissive fluorogen 3 (TPEN), which showed an interesting mechanochromic property when the emission was changed from blue to green upon grinding and green to blue upon fuming. The mechanochromic property of TPEN has been explored to prepare ink-free rewritable paper for security documentation. A detailed photophysical investigation of the TPE-naphthyridine scaffold led to the discovery of its high sensitivity to silver ions (Ag⁺) over other metal ions with a detection limit of 0.25 μM in an aqueous system. The stoichiometry of the complex of TPEN and silver ion was established to be 2:1 (TPEN:Ag⁺) on the basis of photophysical studies, mass analysis, and high-resolution mass spectrometry analysis.

Porous Transition of Polyelectrolyte Film through Reaction-Induced Phase Separation Caused by Interaction with Specific Metal Ions

We describe a novel method for the simple and eco-friendly fabrication of porous polyelectrolyte films. A polyelectrolyte with many amine groups undergoes structural transformation from a dense to a porous structure upon immersion in a specific metal ion solution. The porous transition was the result of a reaction-induced phase separation, which was caused by the formation of new bonds between the polyelectrolyte and metal ions. This method enables control of the pore size of the porous structure in the nanoscale (54 nm) to microscale (1.63 μm) range through variation of the concentration or type of metal ions in the solution. To the best of our knowledge, this is the first report illustrating wide-range control of the pore size of a porous polyelectrolyte structure achieved by metal ions. These porous polyelectrolyte films with adjustable pore size and metastable metal ions can be employed in applications such as adsorption and catalysis.

Oxaazamacrocycles incorporating the quinoline moiety: synthesis and the study of their binding properties towards metal cations

Nitrogen- and oxygen-containing macrocycles with an endocyclic quinoline moiety synthesized via Pd(0)-catalyzed amination were found to be prospective fluorescent chemosensors for Cu(ii).

Ratiometric fluorophore for quantification of iodide under physiological conditions: applications in urine analysis and live cell imaging

The ratio of fluorescence intensity of fluorophoreI_{395 nm}/I_{475 nm}vs.log [I⁻] undergoes linear change over a broad iodide concentration range of 10⁻⁹to 10⁻⁵M and finds application in urine analysis and live cell imaging.

A ratiometric and selective fluorescent chemosensor for Ca(ii) ions based on a novel water-soluble ionic Schiff-base

A new, simple and water-soluble chemosensor, based on the ionic Schiff-base (ISB), 1-(4-hydroxy-3-((2-mercaptophenylimino)methyl)-5-methoxybenzyl)-4-methoxypyridiniumchloride (3), was synthesized and applied to fluorescently sense Ca(ii) ions.

Novel Zn(ii)-thiazolone-based solid fluorescent chemosensors: naked-eye detection for acid/base and toluene

Three zinc complexes with diverse ligand's substituents show interesting fluorescence switching properties induced by acid/base vapour or toluene.

A rhodamine-based sensor for Hg2+ and resultant complex as a fluorescence sensor for I−

A rhodamine-based sensor displays a quick response for Hg²⁺. The resulting complex can act as a reversible fluorescence sensor for I⁻.

A simple chalcone-based ratiometric chemosensor for silver ion

Herein, we report the selective binding of Ag(+) ion by the anthracene-based chalcone receptor 1. Receptor 1 behaves as a selective and sensitive chemosensor for the recognition of Ag(+) over other heavy and transition metal ions without any interference and is capable of detecting the metal ion down to 0.15 × 10(-6) M. Receptor 1 on binding with Ag(+) ions exhibits a ratiometric fluorescence enhancement, which is due to the inhibition of photoinduced electron transfer along with the intramolecular charge transfer mechanism.

A turn-on fluorescence probe for imaging iodide in living cells based on an elimination reaction

Based on a unique elimination reaction prompted by the iodide, a turn-on fluorescent probe (HCy-OMe-Br) without containing heavy metal has been developed for the first time. The probe can monitor iodide with excellent selectivity and sensitivity and was successfully applied to visualize iodide in living cells.

A simple highly sensitive and selective TURN-ON fluorescent chemosensor for the detection of cadmium ions in physiological conditions

A very simple fluorophore was synthesized and applied as a chemosensor for Cd²⁺ion detection.

A thiacalix[4]crown based chemosensor for Zn2+ and H2PO4−: sequential logic operations at the molecular level

A thiacalix[4]crown based di topic receptor 3 has been synthesized which shows negative allosteric behaviour between Zn²⁺/K⁺ ions. Further, 3-Zn²⁺ complex has been used for detection of H₂PO⁴⁻.

Fluorescence sensing systems for gold and silver species

Here, we provide an overview of the reported fluorescent detection systems for gold and silver species, and discuss their sensing properties with promising features.

N-Unsubstituted-1,2,3-triazole-tethered, AIEE type conjugated polymer as a ratiometric fluorescence probe for silver ions

Selective fluorescence ratiometric detection of Ag⁺ was achieved by a N-unsubstituted-1,2,3-triazole decorated, aggregation-induced emission enhancement (AIEE) type conjugated polymer.

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(-).