New Fluorescent Chemosensor Based on Exciplex Signaling Mechanism

Real scenario of metal ion sensor: is conjugated polymer helpful to detect hazardous metal ion

Metal ions from natural and anthropogenic sources cause pollution to society and the environment is major concern in the present scenario. The deposition and contamination of metal ions in soil and water affect the biogeochemical cycles. Thus, it threatens the everyday life of living and non-living organisms. Reviews on the detection of metal ions through several techniques (Analytical methods, electrochemical techniques, and sensors) and materials (Nanoparticles, carbon dots (quantum dots), polymers, chiral molecules, metal-organic framework, carbon nanotubes, etc.) are addressed separately in the present literature. This review reveals the advantages and disadvantages of the techniques and materials for metal ion sensing with crucial factors. Furthermore, it focus on the capability of conjugated polymers (CPs) as metal ion sensors able to detect/sense hazardous metal ions from environmental samples. Six different routes can synthesize this type of CPs to get specific properties and better metal ion detecting capability in vast research areas. The metal ion detection by CP is time-independent, simple, and low cost compared to other materials/techniques. This review outlines recent literature on the conjugated polymer for cation, anion, and dual ion sensors. Over the last half decades published articles on the conjugated polymer are discussed and compared.

Covalent organic frameworks as multifunctional materials for chemical detection

Sensitive and selective detection of chemical and biological analytes is critical in various scientific and technological fields. As an emerging class of multifunctional materials, covalent organic frameworks (COFs) with their unique properties of chemical modularity, large surface area, high stability, low density, and tunable pore sizes and functionalities, which together define their programmable properties, show promise in advancing chemical detection. This review demonstrates the recent progress in chemical detection where COFs constitute an integral component of the achieved function. This review highlights how the unique properties of COFs can be harnessed to develop different types of chemical detection systems based on the principles of chromism, luminescence, electrical transduction, chromatography, spectrometry, and others to achieve highly sensitive and selective detection of various analytes, ranging from gases, volatiles, ions, to biomolecules. The key parameters of detection performance for target analytes are summarized, compared, and analyzed from the perspective of the detection mechanism and structure-property-performance correlations of COFs. Conclusions summarize the current accomplishments and analyze the challenges and limitations that exist for chemical detection under different mechanisms. Perspectives on how future directions of research can advance the COF-based chemical detection through innovation in novel COF design and synthesis, progress in device fabrication, and exploration of novel modes of detection are also discussed.

A highly sensitive and selective fluorescent turn-on chemosensor bearing a 7-diethylaminocoumarin moiety for the detection of cyanide in organic and aqueous solutions

Novel 7-diethylaminocoumarin based dyes showed high sensitivity and selectivity to cyanide anions in both organic and aqueous solutions, which was observed by a drastic increment in the emission intensity.

Recent advances in the synthesis and synthetic applications of Betti base (aminoalkylnaphthol) and bis-Betti base derivatives

The multicomponent reaction between 2-naphthol, arylaldehydes and ammonia yields aminobenzylnaphthols in a process known as the Betti reaction, which was first uncovered at the beginning of the 20th century. Various methods have been reported for the synthesis of aminobenzylnaphthol (Betti base) and bis-Betti base derivatives using various types of naphthols, aromatic amines, heteroaromatic amines, and aliphatic and cyclic amines instead of ammonia or diamines and aliphatic and aromatic aldehydes or dialdehyde compounds under various conditions in recent years. The Betti reaction produces racemic and non-racemic aminobenzylnaphthol ligands. It is also clear that the most important area of application of the non-racemic aminonaphthols prepared in this manner is their use in asymmetric synthesis, either as chiral ligands or as chiral auxiliaries. The functional groups in these Mannich products offer many ring closure possibilities. Some of these products or the starting bifunctional compounds possess biological activity. Herein, we present a selection of the relevant studies on this topic.

Ultrasensitive Optical Chemosensor for Cu(II) Detection

Herein, the main objective of this research is to design and synthesize a novel optical chemosensor, 2,6-Bis(4-dimethylaminophenyl)-4-(dicyanomethylene)-cyclohexane-1,1-dicarbo-nitrile (BDC), for detection of one of the most significant metal ions Cu(II). This novel fluorescent chemosensor exhibits unique optical properties with large Stokes shift (about 170 nm) approximately. The fluorescence and UV–vis absorption performance among the BDC probe and Cu(II) ions were examined in 1:9 (v/v) methanol–HEPES buffer (pH = 7.2) solution. Also, BDC displays high selectivity for Cu(II) concerning other cations. Moreover, this probe provides high selectivity and sensitivity based on their fluorescence properties and recognition abilities within a detection limit of the Cu(II) contents (LOD 2.3 x 10⁻⁷ M). The suggested mechanism of BDC sensor is attributed to the chelation process with Cu(II), to establish a 1:1 metal-ligand ratio complex with a binding constant (K_bind = 7.16 x 10⁴ M⁻¹). The detection process is accompanied by quenching the main emission peak of the BDC at 571 nm. All the experimental data were collected to investigate the effects of several important parameters such as reversibility and the concentration limits. Besides, we study the interference of various metal ions on selectivity and detection capacity of this significant Cu (II) ion. This novel chemosensor shows ultrasensitive, fast tracing of Cu(II) in the physiological pH range (pH 7.2) and therefore may propose a novel promising method for the investigation of the biological functions of Cu(II) in living cells.

New phenazine based AIE probes for selective detection of aluminium(iii) ions in presence of other trivalent metal ions in living cells

Phenazine fluorophore based imidazole derivatives (S1 and S2) were synthesized and sensor studies were carried out with various cations. Aggregation induced emission (AIE) was observed selectively for Al³⁺ among other cations under study in case of both sensors. ¹H NMR titration supported the aggregation induced emission of S2 with Al³⁺. ESI mass spectra successfully confirmed the aggregate formation. SEM images clearly showed the aggregation of receptor induced by Al³⁺ in a flower-like fashion. AIE probe was successfully applied for bio-imaging of RAW264.7 cells.

Polynuclear ampyrone based 3d coordination clusters

The use of a monoanionic Schiff base ligand in transition (Co, Ni and Cu) coordination chemistry yields mono-, tetra- and pentanuclear coordination clusters with different structural motifs.

Fluorescence turn-on of salicylaldimine ligands by co-ordination with magnesium and amines

A novel and easily available fluorescent chemosensor that showed highly selective recognition toward magnesium and amines in ethanol is established.

A highly selective fluorescence turn-on chemosensor for Zn2+, and its application in live cell imaging, and as a colorimetric sensor for Co2+: experimental and TD-DFT calculations

A highly sensitive quinoline based “dual” chemosensor used for fluorometric detection of Zn²⁺, live-cell imaging, and colorimetric detection of Co²⁺.

Recent Advances in Macrocyclic Fluorescent Probes for Ion Sensing

Small-molecule fluorescent probes play a myriad of important roles in chemical sensing. Many such systems incorporating a receptor component designed to recognise and bind a specific analyte, and a reporter or transducer component which signals the binding event with a change in fluorescence output have been developed. Fluorescent probes use a variety of mechanisms to transmit the binding event to the reporter unit, including photoinduced electron transfer (PET), charge transfer (CT), Förster resonance energy transfer (FRET), excimer formation, and aggregation induced emission (AIE) or aggregation caused quenching (ACQ). These systems respond to a wide array of potential analytes including protons, metal cations, anions, carbohydrates, and other biomolecules. This review surveys important new fluorescence-based probes for these and other analytes that have been reported over the past five years, focusing on the most widely exploited macrocyclic recognition components, those based on cyclam, calixarenes, cyclodextrins and crown ethers; other macrocyclic and non-macrocyclic receptors are also discussed.

A fluorescence turn-on chemosensor for hydrogen sulfate anion based on quinoline and naphthalimide

A new fluorescence turn-on chemosensor 1 based on quinoline and naphthalimide was prepared and its anion sensing toward various anions behavior was explored in this paper. Sensor 1 exhibited a highly selective fluorescent response toward HSO4(-) with an 8-fold fluorescence intensity enhancement in the presence of 10equiv. of HSO4(-) in DMSO-H2O (1/1, v/v) solution. The sensor also displayed high sensitivity to hydrogen sulfate and the detection limit was calculated to be 7.79×10(-7)M. The sensing mechanism has been suggested to proceed via a hydrolysis process of the Schiff base group. The hydrolysis product has been isolated and further identified by (1)H NMR and MS.

Synthesis, characterization and Cu(2+) triggered selective fluorescence quenching of Bis-calix[4]arene tetra-triazole macrocycle

A novel fluorescent bis-calix[4]arene macrocycle 9 incorporating metal-binding pockets was successfully prepared. The structure of macrocycle 9 and its precursors were characterized via EI-MS, MALDI-TOF-MS, ESI-MS, (1)H NMR, (13)CNMR, 2D NMR, and X-ray crystallography. The macrocycle 9 displayed selective fluorescence quenching after interacting with Cu(2+) in the presence competing metal cations including Mg(2+), Ca(2+), Ba(2+), Ag(+), Zn(2+), Ti(4+),Cd(2+), Hg(2+), Pb(2+), In(3+), La(3+), Cr(3+), Ni(2+), Sb(3+), V(5+), Fe(3+), Co(2+), Sn(2+), Sn(2+), and Tl(+). The Cu(2+) limit of detection was found to be 40 nM much lower than its threshold level (∼ 20 μM) in drinking water permitted by the U.S Environmental Protection Agency (EPA). Furthermore, drinking water samples from Karachi University (Pakistan) spiked with Cu(2+) were analysed with the sensing system and the results showed an excellent agreement with the fluorescence quenching phenomenon of macrocycle 9 examined in deionized water. Importantly, the chemosensor 9 could be used to detect Cu(2+) in living cells.

Curcumin based chemosensor for selective detection of fluoride and cyanide anions in aqueous media

The conjugate N,N-dimethyl curcumin analogue fluorophore dye 1 has been synthesized and its performance as a sensor was demonstrated.

ESIPT blocked CHEF based differential dual sensor for Zn2+ and Al3+in a pseudo-aqueous medium with intracellular bio-imaging applications and computational studies

A novel H3SAL-NH probe exhibits ESIPT from the phenolic OH group to the azomethine N atom in the excited state. This is blocked in the presence of Zn²⁺ and Al³⁺ giving turn on fluorescence which is useful for imaging in live HepG2 cells.

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.

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.

A study on fluoride detection and assembly of hydroxyaromatic aldoximes caused by tetrabutylammonium fluoride

Different assemblies formed by the interactions of tetrabutylammonium fluoride with hydroxy-aromatic oximes show characteristic optical properties.

Synthesis and characterization of monometallic rhenium(i) complexes and their application as selective sensors for copper(ii) ions

Monometallic Re(i) complexes, selective and sensitive sensor of Cu(ii) ion, show substantial enhancement in the emission intensity, quantum yield, and lifetime due to the restriction of CN isomerization.

Colorimetric and ratiometric fluorescent chemosensor for fluoride ions based on phenanthroimidazole (PI): spectroscopic, NMR and density functional studies

Phenanthro-imidazole conjugate of biscarbanohyrazone, probe PI was designed, synthesized and characterized for selective detection of fluoride ion.

Study on divalent copper, nickel and zinc model complexes for fluoride ion detection

A series of mononuclear hydroxyaromatic oxime metal complexes were synthesized for detection of fluoride ion and shown that the spectral signals of such complexes depend on the electronic configuration of the metal ion.

A novel chemosensor with visible light excitability for sensing Zn2+in physiological medium and in HeLa cells

A highly sensitive, fluorescent, non-cytotoxic turn-on chemosensor with visible light excitability for the detection of intracellular Zn²⁺ions.

Selective sensing of Hg²⁺ using rhodamine-thiophene conjugate: red light emission and visual detection of intracellular Hg²⁺ at nanomolar level

Rhodamine-thiophene conjugate (L) has been synthesized and characterized by (1)H NMR, FTIR and mass spectra. L shows a large enhancement in emission intensity in presence of Hg(2+). Moreover, naked eye color of L becomes intense red in presence of Hg(2+). The lowest detection limit for Hg(2+) is 1 × 10(-9)M in HEPES buffer (0.1M in EtOH/water, 1/1, v/v, pH 7.4). Hg(2+) induced chelation enhanced fluorescence (CHEF) is associated with spirolacram ring opening of the rhodamine unit. Trace level intracellular Hg(2+) is visualized under fluorescence microscope.

Fluoride anion sensing mechanism of 2-ureido-4[1H]-pyrimidinone quadruple hydrogen-bonded supramolecular assembly: photoinduced electron transfer and partial configuration change

The fluoride anion sensing mechanism of 6-methyl-5-(9-methylene-anthracene)-(2-butylureido-4[1H]-pyrimidinone) (AnUP) has been investigated using the DFT/TDDFT method. The theoretical results indicate that the proton of the N3-H3 group in pyrimidine moiety is captured by the added fluoride anion and then deprotonated. The calculated vertical excitation energies of AnUP-dimer and its deprotonated form agree well with the experimental results. The molecular orbital analysis demonstrates that the first excited state (S1) of AnUP-dimer is a local excited state with a π-π* transition, whereas for the deprotonated form, S1 is a completely charge-separation state and is responsible for the photoinduced electron transfer (PET) process. The PET process from anthracene to the pyrimidine moiety leads to the fluorescence quenching.