Ion recognition by 1,2,3-triazole moieties synthesized via “click chemistry”

1,2,3-Triazole-based ligands obtained through copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) have been exploited in vast array of research domains owing to the stitching of simpler molecules through a needle of Cu(I) catalyst. The numerous reports on ion(s) detection capabilities of synthesized 1,4-disubstituted 1,2,3-triazole ligands using absorption and fluorescence spectroscopy are accessible. This review enlists substituted 1,2,3-triazole-based sensor probes, since 2010, synthesized selectively by CuAAC, having the ability to sense either a single ion or multiple ions under specific set of conditions along with their detection limits. The review also apprehends the different techniques and sensing mechanisms involved in the detection of ions by chemosensor probes.     

Rhodamine-based highly sensitive colorimetric off-on fluorescent chemosensor for Hg2+ in aqueous solution and for live cell imaging

A novel rhodamine-based highly sensitive and selective colorimetric off-on fluorescent chemosensor for Hg(2+) ions is designed and prepared by using the well-known thiospirolactam rhodamine chromophore and furfural hydrazone as signal-reporting groups. The photophysical characterization and Hg(2+)-binding properties of sensor RS1 in neutral N, N-dimethylformamide (DMF) aqueous solution are also investigated. The signal change of the chemosensor is based on a specific metal ion induced reversible ring-opening mechanism of the rhodamine spirolactam. The response of the chemosensor for Hg(2+) ions is instantaneous and reversible. And it successfully exhibits a remarkably "turn on" response toward Hg(2+) over other metal ions (even those that exist in high concentration). Moreover, this sensor is applied for in vivo imaging in Rat Schwann cells to confirm that RS1 can be used as a fluorescent probe for monitoring Hg(2+) in living cells with satisfying results, which further demonstrates its value of practical applications in environmental and biological systems.     

Integration of Metal-Organic Frameworks with Bi-Nanoprobes as Dual-Emissive Ratiometric Sensors for Fast and Highly Sensitive Determination of Food Hazards

Functional nanoprobes which detect specific food hazards quickly and simply are still in high demand in the field of food-safety inspection research. In the present work, a dual-emission metal-organic framework-based ratiometric fluorescence probe was integrated to detect Cu²⁺ and Pb²⁺ with rapidness and ease. Specifically, quantum dots (QDs) and carbon quantum dots (CQDs) were successfully embedded into zeolitic imidazolate framework-67 (ZIF-67) to function as a novel ratiometric fluorescent sensing composite. The ratiometric fluorescence signal of CQDs/QDs@ZIF-67 was significantly aligned with the concentration of metal ions to give an extremely low detection limit of 0.3324 nM. The highly sensitive and selective CQDs/QDs@ZIF-67 composite showed potential for the rapid and cost-effective detection of two metal ions.     

Selective and sensitive optical chemosensor for detection of Ag(I) ions based on 2(4-hydroxy pent-3-en-2-ylideneamine) phenol in aqueous samples

A selective and sensitive chemosensor, based on the 2(4-hydroxy pent-3-en-2-ylideneamine) phenol (HPYAP) as chromophore, has been developed for colorimetric and visual detection of Ag(I) ions. HPYAP shows a considerable chromogenic behavior toward Ag(I) ions by changing the color of the solution from pale-yellow to very chromatic-yellow, which can be easily detected with the naked-eye. The chemosensor exhibited selective absorbance enhancement to Ag(I) ions in water samples over other metal ions at 438 nm, with a linear range of 0.4–500 μM (r² = 0.999) and a limit of detection 0.07 μM of Ag(I) ions with UV–vis spectrophotometer detection. The relative standard deviation (RSD) for 100 μM Ag(I) ions was 2.05% (n = 7). The proposed method was applied for the determination Ag(I) ions in water and waste water samples.     

Pyrene-linked triazole-modified homooxacalix[3]arene: a unique C3 symmetry ratiometric fluorescent chemosensor for Pb2+

A new type of fluorescent chemosensor based on homooxacalix[3]arene was synthesized. The fluorescent sensor was highly selective for Pb(2+) in comparison with other metal ions tested by enhancement of the monomer emission of pyrene. The C(3) symmetric structure of homooxacalix[3]arene has potential application in the development of a new ratiometric fluorescent chemosensor for heavy metal ions.     

A new selective fluorescence chemosensor for Cu(II) in water

A new chemosensor for the Cu(II) ion has been realized by connecting via an amido bond an anthracenyl residue to the all cis 2,4,6-triamino-1,3,5-trihydroxycyclohexane ligand (TACI). This sensor is able to detect micromolar concentrations of Cu(II) ions in water at pH 7 without interference with many other divalent transition metal ions.     

Synthesis,spectroscopic characterization and biological evaluation of a novel chemosensor with different metal ions

A novel chemosensor, namely 3‐(4‐chlorophenyl)‐1‐(pyridin‐2‐yl)prop‐2‐en‐1‐one, CPPEO, and its metal complexes have been synthesized and characterized by using sets of chemical and spectroscopic techniques, such as elemental analysis, mass, Fourier transform‐infrared and UV–Vis spectral analysis. The thermal properties of the metal complexes have been investigated by thermogravimetric techniques. The decomposition mechanism of the titled complexes was suggested. The results showed that the Co²⁺ and Mn²⁺ complexes have an octahedral geometry, while Zn²⁺ and Cd²⁺ complexes have tetrahedral geometry. The kinetic and thermodynamic parameters of the thermal decomposition stages have been evaluated using the Coats–Redfern method. The optical sensing response of the investigated chemosensor to the different metal ions was investigated. It responds well to the tested metal ions as reflected from the significant change in both absorption and emission spectra upon adding different concentrations of the metal salts, confirming the intramolecular charge transfer of the chemosensor upon effective coordination with the used metal ions. This leads to enhancing ICT interaction, causing a significant shift in the presence of strongly complexing metal ions. This was fully reversible, where the solution of dye‐metal ion complex was decomplexed by adding an EDTA solution to revert the original spectrum of the dye. The stability constants, K, for the complexes of the investigated chemosensor with the mentioned metal ions were calculated, indicating that Co²⁺ is the most effectively detected, and the potential of the novel dye was highly efficient switchers for Co²⁺ ions. Additionally, the molecular modeling was carried out for the chemosensor and its metal complexes. Finally, the solid complexes have been tested for their in vitro antimicrobial activities against some bacterial strains (Gram +ve and Gram ?ve bacteria), as well as antifungal strains.     

Hybrid supraparticles of carbon dots/porphyrin for multifunctional tongue-mimic sensors

Supraparticles（SPs）, such as assembly of inorganic components with organic, have made tremendous attention in biochemical analysis, which represents a novel but challenging research orientation. Herein, a single-SPs multifunctional fluorescent sensor array has been developed for high-throughput detection of heavy metal ions in biofluids, which is based on an inorganic/organic hybrid SPs consisting of carbon dots（CDs） and an easily available porphyrin [5,10,15,20-tetra（4-carboxyphenyl）porphyrin（T...     

Carbon Quantum Dots from Pomelo Peel as Fluorescence Probes for “Turn-Off–On” High-Sensitivity Detection of Fe3+ and L-Cysteine

This study designed a “turn-off–on” fluorescence analysis method based on carbon quantum dots (CQDs) to detect metal ions and amino acids in real sample systems. CQDs were derived from green pomelo peel via a one-step hydrothermal process. The co-doped CQDs with N and S atoms imparted excellent optical properties (quantum yield = 17.31%). The prepared CQDs could be used as fluorescent “turn-off” probes to detect Fe³⁺ with a limit of detection of 0.086 µM, a linear detection range of 0.1–160 µM, and recovery of 83.47–106.53% in water samples. The quenched CQD fluorescence could be turned on after adding L-cysteine (L-Cys), which allowed detection of L-Cys with a detection limit of 0.34 µM and linear range of 0.4–85 µM. Recovery of L-Cys in amino acid beverage was 87.08–122.74%. Visual paper-based testing strips and cellulose/CQDs composite hydrogels could be also used to detect Fe³⁺ and L-Cys.     

Thiacalix[4]arene based fluorescent probe for sensing and imaging of Fe3+ ions

A thiacalix[4]arene based fluorescent chemosensor 3 in the cone conformation has been synthesized and its recognition behaviour is evaluated toward various metal ions in mixed aqueous media. The chemosensor 3 showed high selectivity towards Fe(3+) ions by fluorescence quenching of excimer emission. Further, evaluation of the 3·Fe(3+) complex prepared in situ demonstrated great promise for the detection of the Fe(3+) ion in the presence of amino acids, blood serum and bovine serum albumin (BSA) solution. The compound 3 has suitable permeability into the PC3 cells and can be utilized as a Fe(3+) selective sensor in living cells (PC3 cells).     

A colorimetric indicator-displacement assay array for selective detection and identification of biological thiols

A simple, inexpensive yet highly selective colorimetric indicator-displacement assay array for the simultaneous detection and identification of three important biothiols at micromolar concentrations under physiological conditions and in real samples has been developed in this work. With use of an array composed of metal indicators and metal ions, clear differentiation among cysteine, homocysteine and glutathione was achieved. On the basis of the colour change of the array, quantification of each analyte was accomplished easily, and different biothiols were identified readily using standard chemometric approaches (hierarchical clustering analysis). Moreover, the colorimetric sensor array was not responsive to changes with 19 other natural amino acids, and it showed excellent reproducibility. Importantly, the sensor array developed was successfully applied to the determination and identification of the three biothiols in a real biological sample.

A pyrenyl-appended triazole-based calix[4]arene as a fluorescent sensor for Cd2+ and Zn2+

The synthesis and evaluation of a novel calix[4]arene-based fluorescent chemosensor 8 for the detection of Cd(2+) and Zn(2+) is described. The fluorescent spectra changes observed upon addition of various metal ions show that 8 is highly selective for Cd(2+) and Zn(2+) over other metal ions. Addition of Cd(2+) and Zn(2+) to the solution of 8 results in ratiometric measurement.     

Synthesis of porphyrin-appended terpyridine as a chemosensor for cadmium based on fluorescent enhancement

The design and synthesis of a porphyrin-appended terpyridine, 5-(4-([2,2′:6′,2″]-terpyridin-4-yl-carboxyamidyl)phenyl)-10,15,20-triphenylporphyrin (H₂TPPTPy) and its application as potential fluoroionophore for recognition of metal ions are reported. For preparation of the fluoroionophore, a novel simple strategy with improved total yield has been applied for the synthesis of 2,2′:6′,2″-terpyridine-4′-carboxylic acid as a ligand. H₂TPPTPy shows chelation-enhanced fluorescence effect with cadmium ion via the interruption of photoinduced electron transfer (PET) process, which has been utilized as the basis of the fabrication of the Cd(II)-sensitive fluorescent chemosensor. The analytical performance characteristics of the proposed Cd(II)-sensitive chemosensor were investigated. It shows a linear response toward Cd(II) in the concentration range of 3.2 × 10⁻⁶ to 3.2 × 10⁻⁴ M with a limit of detection of 1.2 × 10⁻⁶ M. The chemosensor shows good selectivity for Cd(II) over a large number of cations, such as alkali, alkali earth and transitional metal ions except Cu(II) and Zn(II). The sensor has been used for determination of Cd(II) in water samples with satisfactory recoveries.     

Selective sensing of Fe3+ based on fluorescence quenching by 2,6-bis(benzoxazolyl)pyridine with beta-cyclodextrin in neutral aqueous solution

A selective and sensitive fluorescent chemosensor (BBOZP-CD) for Fe(3+) was composed of water-soluble beta-cyclodextrins and 2,6-bis(benzoxazolyl)pyridine which was synthesized through the reaction of 2,6-pyridinedicarboxylic acid and o-aminophenol catalyzed by polyphosphoric acid under microwave irradiation. The chemosensor BBOZP-CD for metal ions were carefully investigated by fluorescent quenching in present of metal ions. The result showed BBOZP-CD chemosensor was remarkable fluorescence quenching and a highly selectivity and sensitivity for Fe(3+) in neutral aqueous solution, and the other common metal ions did not notably disturb the detection of Fe(3+). Additionally, the effect of pH to the chemosensor for Fe(3+) was also studied. The result indicated the respond signals of BBOZP-CD to Fe(3+) was stable and hardly influenced while the pH value was greater than 3.6.     

A quinoline-based selective ‘turn on’ chemosensor for zinc(II) via quad-core complex,and its application in live cell imaging

An efficient quinoline-based fluorescent chemosensor (QLNPY) was successfully developed for the detection of zinc ions (Zn²⁺). This novel chemosensor displayed higher sensitivity and selectivity toward Zn²⁺ over other competitive metal ions accompanying with obvious fluorescence enhancement. The QLNPY-Zn²⁺ complex can be further used as a new fluorescent “turn-off” sensor for pyrophosphate (PPi) and sulfur ion (S^2?) via a Zn²⁺ displacement approach. The limits of detection were calculated to be 3.8 × 10^?8 M for Zn²⁺, 3.7 × 10^?7 M for PPi and 4.9 × 10^?7 M for S^2?. The binding mechanism of QLNPY and Zn²⁺ was investigated through NMR, HR-MS analysis and further studied by crystallographic analysis. Additionally, further application of QLNPY for sequential bioimaging of Zn²⁺ and PPi was studied in HepG2 cells, suggesting that the quinoline-based chemosensor possesses great potential applications for the detection of intracellular Zn²⁺ and PPi in vivo.     

Protein-gold nanoclusters for identification of amino acids by metal ions modulated ratiometric fluorescence

Here we report that the dual fluorescence emissions from protein-gold (Au) nanoclusters can greatly be modulated by metal ions and the resultant fluorescence ratiometric responses provide a novel sensory method for the identification of amino acids. The protein-gold (Au) nanoclusters were simply synthesized by the reduction of chloroauric acid with bovine serum albumin (BSA), which exhibit dual emissions: the blue at 425 nm from the oxides of BSA, and the red at 635 nm from Au nanoclusters. It has been demonstrated that different metal ions react with BSA-Au nanoclusters and thus greatly affect the two emissions in different ways by fluorescence enhancement or quenching. Interestingly, the addition of amino acids leads to fluorescence ratiometric changes through the interactions with the bound metal ions. When BSA-Au nanocluster probes modulated by four different metal ions were used together to construct a sensor array, different amino acids were clearly discriminated by the distinctive patterns of four ratiometric fluorescence responses. Results and methods reported here provide a unique strategy for the determination of amino acids.     

Rare earth ions-enhanced gold nanoclusters as fluorescent sensor array for the detection and discrimination of phosphate anions

The discrimination and detection of phosphate anions have attracted extensive attention due to their important roles in various biological processes. Compared with sensors to detect one individual phosphate at a time, sensor arrays are able to discriminate multiple phosphates simultaneously. In this study, we developed a rare earth ions enhanced AuNCs-based sensor array to achieve facile and rapid identification of phosphate anions (PPi, ADP and ATP). The rare earth ions (i. e., Ce³⁺, Gd³⁺, Tm³⁺ and Yb³⁺) can significantly enhance the fluorescence of AuNCs through aggregation-induced emission effect. And the subsequent addition of phosphate anions can recover the fluorescence of the AuNCs-rare earth ions assembly. Thanks to the different numbers of phosphate group and different steric hindrance effects of phosphate anions, the recovery fluorescence of AuNCs-rare earth ions assembly induced by PPi, ADP or ATP are respectively distinct. Thus the sensor array composed of AuNCs and different rare earth ions is able to distinguish those phosphate anions. Finally, the sensor array was successfully demonstrated to identify the phosphates in blind samples.     

Single-step multiplex detection of toxic metal ions by Au nanowires-on-chip sensor using reporter elimination

We have developed a Au nanowires (NWs)-on-chip surface-enhanced Raman scattering (SERS) multiplex sensor that can sensitively detect multiple toxic metal ions. Most importantly, the reporter elimination method simplified the detection procedure to a single step, which has been much desired for remote environmental monitoring. This sensor has several notable features. First, it shows high reproducibility based on well-defined single-crystalline Au NWs. Second, single-NW-sensors that can detect a specific metal ion are combined for multiplex sensing of metal ions. Third, when a sample solution is put onto the NWs-on-chip sensor, a decrease in the SERS signal of a specific NW-sensor identifies the target metal ion. Simple, rapid, sensitive and quantitative detection of metal ions becomes possible through the measurement of the SERS signals. We successfully detected ions of mercury (Hg(2+)), silver (Ag(+)), and lead (Pb(2+)) coexisting in the same solution by using this sensor.     

Highly Sensitive and Selective Chemosensor for Cu2+ Based on a Schiff Base

A new chemosensor based on a Schiff base has been designed and synthesized. Its sensing behavior toward various metal ions was investigated by fluorescence and UV-Vis spectroscopic methods. The fluorescence of the sensor was quenched and the color rapidly changed from canary yellow to brown after the addition of Cu²⁺, while no changes occurred after the addition of other metal ions, which contributes to the detection of Cu²⁺ with naked eyes. The fluorescence quantum yield of the ligand was calculated to be 0.52. The corresponding detection limit of Cu²⁺ was 5.721×10^-7 mol/L, and the 1:1 binding mode of the sensor with Cu²⁺ was revealed by Job's plot.     

A fluorescence chemosensor based on peptidase for detecting nickel(II) with high selectivity and high sensitivity

We report herein a new class of metal ion chemosensors and give the first example of a metal-dependent peptidase chemosensor for metal ions. The chemosensor contains the basic specific Ni(II)-dependent peptide bond hydrolysis sequence (Gly-Ala-Ser-Arg-His-Trp-Lys-Phe-Lys). The substrate was labeled with a fluorophore at the N-terminal and a quencher at the C-terminal Lys side chain. Initially, the MOCAc ((7-methoxycoumarin-4-yl)acetyl-) emission was quenched by the nearby quencher. In the presence of Ni(II), the substrate was irreversibly cleaved at the cleavage site, leading to a 20-fold increase in fluorescence intensity. The chemosensor combines the high selectivity of a peptidase (at least greater than tenfold for Ni(II) over other metal ions) with the high sensitivity of fluorescence detection limit of 50 nM and can be applied for the quantitative detection of Ni(II) over a concentration range of three orders of magnitude. Given this degree of selectivity and sensitivity, our molecular engineering design may prove useful in the future development of other peptidase-based probes for different metal ions in toxicological and environmental monitoring.