Fluorescent-based micellar incorporated hydrogel materials for selective determination of long-chain aldehydes.

A highly sensitive micelle-induced sensory has been developed for detection of long-chain aldehydes as potential biomarkers of respiratory cancers. The micelle-like sensor was fabricated through the partial self-assembly of CTAB and S2 surfactants, containing a fluorescent hydrazine-functionalized dye (Naph-NH2). In principle, long-chain aldehydes with amphiphilic character act as the induced-fit surfactants to form well-entrapped micellar particles, as well as react with Naph-NH2 to form hydrazone derivatives resulting in fluorescent enhancement. The limit of detection (LOD) of micellar Naph-NH2/CTAB/S2 platform was calculated to be ∼  64.09-80.98 µM for detection of long-chain aldehydes, which showed fluorescent imaging in lung cancer cells (A549). This micellar sensory probe demonstrated practical applicability for long-chain aldehyde sensing in human blood samples with an accepted percent recovery of ~ 94.02-102.4%. Beyond Naph-NH2/CTAB/S2 sensor, the milcellar hybrid sensor was successfully developed by incorporating a micelle-like platform with supramolecular gel regarding to carboxylate-based gelators (Gel1), which showed a tenfold improvement in sensitivity. Expectedly, the determination of long-chain aldehydes through these sensing platforms holds significant promise for point-of-care cancer diagnosis and therapy.

Molecularly dispersed nickel complexes on N-doped graphene for electrochemical CO2 reduction.

In this work, new hybrid catalysts based on molecularly dispersed nickel complexes on N-doped graphene were developed for electrochemical CO2 reduction (ECR). Nickel(II) complexes (1-Ni, 2-Ni), and a new crystal structure ([2-Ni]Me), featuring N4-Schiff base macrocycles, were synthesized and investigated for their potential in ECR. Cyclic voltammetry (CV) in NBu4PF6/CH3CN solution demonstrated that the nickel complexes bearing N-H groups (1-Ni and 2-Ni) showed a substantial current enhancement in the presence of CO2, while the absence of N-H groups ([2-Ni]Me) resulted in an almost unchanged voltammogram. This indicated the necessity of the N-H functionality towards ECR in aprotic media. All three nickel complexes were successfully immobilized on nitrogen-doped graphene (NG) via non-covalent interactions. All three Ni@NG catalysts exhibited satisfactory CO2-to-CO reduction in aqueous NaHCO3 solution with the faradaic efficiency (FE) of 60-80% at the overpotential of 0.56 V vs. RHE. The ECR activity of [2-Ni]Me@NG also suggested that the N-H moiety from the ligand is less important in the heterogeneous aqueous system owing to viable hydrogen-bond formation and proton donors from water and bicarbonate ions. This finding could pave the way for understanding the effects of modifying the ligand framework at the N-H position toward fine tuning the reactivity of hybrid catalysts through molecular-level modulation.

Stabilisation of copper(i) polypyridyl complexes toward aerobic oxidation by zinc(ii) in combination with acetate anions: a facile approach and its application in ascorbic acid sensing in aqueous solution.

A new and facile approach to stabilise copper(i) complexes in aqueous solution by the addition of zinc(ii) ions in combination with acetate ions (OAc-) was demonstrated. This stability enhancement toward the aerobic oxidation of copper(i) species was investigated by various techniques including UV-vis spectroscopy, 1H-NMR, FT-IR, and ESI-MS. Our experimental results together with DFT calculations led to a proposed structure of [(adpa)Cu-OAc-Zn(OAc)(H2O)2]+/2+. It was also postulated that zinc(ii) with its Lewis acidity may attract electrons from the Cu centre through the bridging ligands (OAc-), resulting in the lower reactivity of Cu(i) with O2. In addition, this strategy was shown to be applicable to ascorbic acid detection by monitoring a change in the redox states of copper complexes using fluorescence spectroscopy. Moreover, it was demonstrated that the method was sensitive and accurate for the quantitative analysis of ascorbic acid in vitamin C tablets.

Tuning the reactivity of copper complexes supported by tridentate ligands leading to two-electron reduction of dioxygen.

A series of copper complexes bearing polypyridyl tridentate ligands have been prepared to fine tune their reactivity toward the oxygen reduction reaction (ORR). During the process of preparation of our copper complexes, we successfully obtained two new crystal structures which are [Cu2(µ-Cl)2(adpa)2](ClO4)2 (2b) and [Cu2(addpa)(CH3CN)2(ClO4)2](ClO4)2 (3a) and a new structure [Cu2(addpa)(CH3CN)2(H2O)2](ClO4)4 (3b) captured after the catalytic ORR. Electrochemical studies and stoichiometric chemical reduction of copper(ii) complexes by ascorbic acid indicated that the presence of an anthracene unit helps to facilitate the reduction of Cu(ii) as well as the stabilisation of Cu(i) species. Regarding oxygen activation, the dinuclear Cu(i) complex 3a showed significantly higher ORR activity than its analogous mononuclear complex 2a. Complex 3a was also found to be relatively robust and competent in catalytic O2 reduction. The observed H2O2 product after this catalysis, together with the data obtained from DFT calculations supported that 3a exhibited a 2H+, 2e- catalytic activity towards the ORR as opposed to the expected 4H+, 4e- process usually found in copper complexes with tridentate ligands. The proton (H+) source for this process was expected from ascorbic acid which also serves as a reducing agent in this reaction. This work highlighted an approach for tuning the ORR activity of the copper complexes by the introduction of a conjugated-π moiety to the supporting ligand.

A new formaldehyde sensor from silver nanoclusters modified Tollens' reagent.

A selective colorimetric assay for detecting formaldehyde (FA) was proposed based on silver nanoclusters (AgNCs) templated by polymethacrylic acid (PMAA). The chemodosimeter was easily fabricated by the formation of Tollens' reagent in the presence of AgNCs (AgNCs@Tollens). The detection principle was based on the change in the color caused by the change in the particle size from nanoclusters (no LSPR) to nanoparticles (with LSPR) upon the reduction of Tollens' reagent by FA. In the presence of FA, the intensity of a new absorbance band with a maximum at a wavelength of 430 nm corresponding to the LSPR of the AgNPs linearly increased as a function of the FA concentration, exhibiting a color change that could be observed by the naked eye. This method provided a working range of 30-50 µM with lower detection limit (LOD) of 27.99 µM. The proposed method exhibited excellent selectivity towards FA over other aldehyde-containing compounds.

Cysteamine-capped copper nanoclusters as a highly selective turn-on fluorescent assay for the detection of aluminum ions.

A new type of copper nanoclusters was synthesized by a one-pot reaction using cysteamine as a capping agent and reducing agent (Cys-CuNCs). The synthesized CuNCs exhibited a spherical shape and a monodisperse and strong fluorescent emission characteristic peak at 430nm when exciting at 330nm. The Cys-CuNCs were demonstrated as a fluorescent chemodosimeter for the selective detection of Al3+. In the presence of Al3+, the fluorescent emission of the Cys-CuNCs was considerably enhanced, while other studied metal ions did not show this phenomenon. The fluorescent intensity near 380nm linearly increased with an increasing Al3+ concentration. The proposed method provided a working range of 1-7µM with a low detection limit of 26.7nM and was applied to determine Al3+ in drinking water samples with satisfactory results.

A circular dichroism sensor for selective detection of Cd2+ and S2- based on the in-situ generation of chiral CdS quantum dots.

We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd2+ and S2- based on chiral CdS quantum dots (QDs) generated by a facile in-situ reaction. The chiral quantum dots are generated in solutions composed of Cd2+, S2-, cysteamine (CA) and L-penicillamine (L-PA), with the number of the generated particles limited by either the Cd2+ or S2- concentration. We show that the magnitude of the CD signal produced by the QDs is linearly related to the initial concentration of Cd2+ and S2-, with excellent selectivity over other ions. Our sensor functions over concentration ranges of 65-200µM and 7-125µM with detection limits of 59.7 and 1.6µM for Cd2+ and S2-, respectively. The sensor is applied in real water samples with results comparing favorably with those obtained from ICP-OES (for Cd2+) and HPLC (for S2-).

Self-assembly of Gd3+/SDS/HEPES complex and curcumin entrapment for enhanced stability, fluorescence image in cellular system.

At present, strategies to disperse hydrophobic molecules in water without altering their chemical structures include conventional surfactant-based micellar and vesicular systems, encapsulation into water dispersible polymeric nanoparticles, and loading onto the surface of various metal nanoparticles. Here, we report a simple and low cost platform to incorporate hydrophobic molecules into a stable water dispersible nanostructure that can significantly increase the stability of the encapsulated materials. The platform is based on the incorporation of hydrophobic molecules into the self-assembled complex of gadolinium ion (Gd3+), sodium dodecyl sulfate (SDS), and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) called GdSH. After being incorporated, the two model hydrophobic dyes, curcumin and curcumin borondifluoride show approximately 50% and 30% improved stability, respectively. Investigation of the self-assembled 10-14 multilayered 60nm spheres with inter-layer distances of 4.25nm indicates coordination of SDS and HEPES with Gd3+. Incorporation of the hydrophobic molecules into the multilayered spheres results in reduction of the interlayer distance of the multilayer spheres to 4.17nm, suggesting enhanced packing of the hydrophobic chain of SDS and HEPES around the Gd3+. The incorporation of the two curcuminoids into the self-assembled complex also causes an increase in fluorescence quantum yield of the two dyes, thus suggesting spatial confinement of the packed dye molecules. The better cellular uptake of the nanoparticles is responsible for the expected enhancement in fluorescence image of the encapsulated materials.

Cysteamine capped CdS quantum dots as a fluorescence sensor for the determination of copper ion exploiting fluorescence enhancement and long-wave spectral shifts.

We described a turn-on fluorescence sensor for the determination of Cu(2+) ions, utilizing the quantum confinement effect of cadmium sulfide quantum dots capped with cysteamine (Cys-CdS QDs). The fluorescence intensity of the Cys-CdS QDs was both enhanced and red shifted (from blue-green to yellow) in the presence of Cu(2+). Fluorescence enhancement was linearly proportional to the concentration of Cu(2+) in the concentration range 2 to 10µM. Other cations at the same concentration level did not significantly change the intensity and spectral maxima of Cys-CdS QDs, except Ag(+). The limit of detection was 1.5µM. The sensor was applied to the determination of Cu(2+) in (spiked) real water samples and gave satisfactory results, with recoveries ranging from 96.7 to 108.2%, and with RSDs ranging from 0.3 to 2.6%.

Circular dichroism sensor based on cadmium sulfide quantum dots for chiral identification and detection of penicillamine.

A new chemical sensor based on the measuring of circular dichroism signal (CD) was fabricated from cysteamine capped cadmium sulfide quantum dots (Cys-CdS QDs). The chiral-thiol molecules, d-penicillamine (DPA) and l-penicillamine (LPA), were used to evaluate potentials of this sensor. Basically, DPA and LPA provide very low CD signals. However, the CD signals of DPA and LPA can be enhanced in the presence of Cys-CdS QDs. The CD spectra of DPA and LPA exhibited a mirror image profile. Parameters affecting the determination of DPA and LPA were thoroughly investigated in details. Under the optimized condition, the CD signals of DPA and LPA displayed a linear relationship with the concentrations of both enantiomers, ranging from 1 to 35 µM. Detection limits of this sensor were 0.49 and 0.74 µM for DPA and LPA, respectively. To demonstrate a potential application of this sensor, the proposed sensor was used to determine DPA and LPA in real urine samples. It was confirmed that the proposed detection technique was reliable and could be utilized in a broad range of applications.

A circular dichroism sensor for Ni(2+) and Co(2+) based on L-cysteine capped cadmium sulfide quantum dots.

A new circular dichroism sensor for detecting Ni(2+) and Co(2+) was proposed for the first time using chiral chelating quantum dots. The detection principle was based on changing of circular dichroism signals of the chiral quantum dots when forming a chiral complex with Ni(2+) or Co(2+). L-Cysteine capped cadmium sulfide quantum dots (L-Cyst-CdS QDs) were proposed as a chiral probe. The CD spectrum of L-Cyst-CdS QDs was significantly changed in the presence of Ni(2+) and Co(2+). On the other hand, other studied cations did not alter the original CD spectrum. Moreover, when increasing the concentration of Ni(2+) or Co(2+), the intensity of the CD spectrum linearly increased as a function of concentration and could be useful for the quantitative analysis. The proposed CD sensor showed linear working concentration ranges of 10-60 µM and 4-80 µM with low detection limits of 7.33 µÐœ and 1.13 µM for the detection of Ni(2+) and Co(2+), respectively. Parameters possibly affected the detection sensitivity such as solution pH and incubation time were studied and optimized. The proposed sensor was applied to detect Ni(2+) and Co(2+) in real water samples, and the results agreed well with the analysis using the standard ICP-OES.

Cysteamine CdS quantum dots decorated with Fe3+ as a fluorescence sensor for the detection of PPi.

A new sensitive and selective fluorescence sensor for the detection of pyrophosphate (PPi) in aqueous media based on the Fe(3+) decorated cysteamine CdS QDs ([Cys-CdS QDs]-Fe(3+)) was proposed. The presence of PPi can induce the fluorescence quenching of [Cys-CdS QDs]-Fe(3+) due to the high formation constants between the phosphate group and Fe(3+). Because the complex between Fe(3+) and PPi acts as an efficient quencher, the concentration of PPi can be evaluated by tracking the degree of fluorescence quenching. The fabricated sensor was optimized to obtain the best sensor selectivity and sensitivity. Under optimal conditions, a linear relationship between the fluorescence response and the concentration of PPi was established in the range of 0.5-10 µM. The limits of detection and quantitation for PPi were found to be 0.11 and 2.78 µM, respectively. Furthermore, the proposed sensor exhibited high selectivity toward PPi relative to other common anions. The proposed sensor was successfully applied to the detection of PPi in urine samples with satisfactory results.

Selective turn-on fluorescence sensor for Ag+ using cysteamine capped CdS quantum dots: determination of free Ag+ in silver nanoparticles solution.

Cadmium sulfide quantum dots capped with cysteamine (Cys-CdS QDs) were demonstrated as a selective fluorescence probe for sensing of free trace silver ions. The fluorescence intensity of the Cys-CdS QDs can be enhanced only in the presence of free Ag(+) and the fluorescence spectrum was slightly red shift from the original spectra. In addition, the fluorescence intensities were linearly increased upon increasing Ag(+) concentration. At the optimized condition for Ag(+) detection, when adding other metal ions to the Cys-CdS QDs solution, fluorescence spectra of Cys-CdS QDs did not change significantly revealing good selectivity of the sensors towards Ag(+). The working linear concentration range was found to be 0.1-1.5 µM with LOD of 68 nM. The proposed sensor was then applied to detect free Ag(+) in the silver nanoparticles solution. The results showed that the proposed sensor can be efficiently used with good accuracy and precision providing the simple method for detection of free Ag(+) in silver nanoparticles of quality control products.

A highly selective turn-on ATP fluorescence sensor based on unmodified cysteamine capped CdS quantum dots.

Unmodified cysteamine capped nanocrystalline cadmium sulfide quantum dots (Cys-CdS QDs) were demonstrated as a selective turn-on fluorescence sensor for sensing adenosine-5'-triphosphate (ATP) in aqueous solution for the first time. The fluorescence intensity of the Cys-CdS QDs was significantly enhanced in the presence of ATP. In addition, the fluorescence intensity of the Cys-CdS QDs increased when increasing ATP concentrations. On the other hand, other phosphate metabolites and other tested common anions did not significantly alter the fluorescence intensity of the Cys-CdS QDs. In addition, this sensor showed excellent discrimination of pyrophosphate (PPi) from ATP detection. The proposed sensor could efficiently be used for ATP sensing at very low concentration with LOD of 17 µM with the linear working concentration range of 20-80 µM. The feasibility of the proposed sensor for determining ATP in urine samples was also studied, and satisfactory results were obtained.

Cu2+-modulated cysteamine-capped CdS quantum dots as a turn-on fluorescence sensor for cyanide recognition.

A new fluorescence sensor for detection of cyanide ions (CN(-)) in aqueous media based on the recovered fluorescence of cysteamine capped CdS quantum dots [Cys-CdS QDs]-Cu(2+) system was proposed. The fluorescence intensity of Cys-CdS QDs was quenched by Cu(2+) due to the binding of Cu(2+) to cysteamine on the surface of the QDs. The degree of fluorescence quenching was proportional to the concentration of Cu(2+). However, in the presence of CN(-), the fluorescence intensity of Cys-CdS QDs was found to be efficiently recovered. Experimental results showed that the pH of the buffer solution and the concentration of Cu(2+) affected the fluorescence intensity upon adding CN(-). Under the optimal condition, the recovered fluorescence intensity was linearly proportional to the increasing CN(-) concentration in the range 2.5-20 µM. The limit of detection and the limit of quantification were found to be 1.13 µM and 3.23 µM, respectively. In addition, among the tested ions, only CN(-) could turn on the fluorescence intensity suggesting that the [Cys-CdS QDs]-Cu(2+) system was a highly selective sensor for CN(-). Moreover, this proposed sensor was demonstrated to detect CN(-) in drinking water with satisfactory results.

Optical and electrochemical properties of heteroditopic ion receptors derived from crown ether-based calix[4]arene with amido-anthraquinone pendants.

Two heteroditopic receptors based on a calix[4]arene crown ether containing amidoanthraquinone pendants in cone and 1,3-alternate conformations (1 and 2, respectively) were synthesized. Photophysical properties of 1 and 2 were studied by UV-vis and fluorescence spectrophotometry in dried CH(3)CN. Both 1 and 2 showed the highest sensitivity towards F(-) through the appearance of a new charge transfer band at 500 nm and the enhancement of the emission spectra at λ(em) = 542 nm and 528 nm respectively. Interestingly, in the presence of K(+), the fluorescence intensity of 1 at 542 nm increased around 2 fold compared to that in the absence of K(+) upon addition of F(-), while this phenomenon was not observed in the case of receptor 2. Cyclic voltammograms of receptors 1 and 2 showed two consecutive one-electron reversible waves in 40% v/v CH(3)CN in CH(2)Cl(2), corresponding to two single-electron reductions to give mono- and dianions species at E(1/2)I = -1.21 V and E(1/2)II = -1.66 V as well as E(1/2)I = -1.25 V and E(1/2)II = -1.71 V, respectively. H(2)PO(4)(-) gave remarkable potential shifts (ca. 200 mV) of the second reduction waves (E(1/2)II) of both free 1 and 2. In the presence of K(+), only receptor 1 gave remarkable potential shifts in its redox wave II upon adding F(-) and AcO(-). Therefore, receptors 1 and 2 exhibited dual sensing modes by fluorescence spectrophotometry and cyclic voltammetry. The topology of ligands also played an important role in cooperative binding properties of heteroditopic receptor 1 possessing a closer distance between a cation and an anion binding. On the other hand, the two ion binding sites of receptor 2 were separated by a longer distance and did not support the cooperative binding. This resulted in the abstraction of K(+) from receptor 2 upon addition of anions.

Self-assembled coordination nanoparticles from nucleotides and lanthanide ions with doped-boronic acid-fluorescein for detection of cyanide in the presence of Cu2+ in water.

The sensor molecule, F-oBOH, containing boronic acid-linked hydrazide and fluorescein moieties was synthesized. For anion sensing applications, F-oBOH was studied in aqueous media. Unfortunately, F-oBOH was found to be hydrolyzed in water. Therefore, a new strategy was developed to prevent the hydrolysis of F-oBOH by applying self-assembly coordination nanoparticles network (F-oBOH-AMP/Gd(3+) CNPs). Interestingly, the nanoparticles network displayed the enhancement of fluorescent signal after adding Cu(2+) following by CN(-). The network, therefore, possessed a high selectivity for detection of CN(-) compared to other competitive anions in the presence of Cu(2+). Cyanide ion could promote the Cu(2+) binding to F-oBOH incorporated in AMP/Gd(3+) CNPs to give the opened-ring form of spirolactam resulting in the fourfold of fluorescence enhancement compared to Cu(2+) complexation without CN(-). Additionally, the log K value of F-oBOH-AMP/Gd(3+) CNPs⊂Cu(2+) toward CN(-) was 3.97 and the detection limits obtained from naked-eye and spectrofluorometry detections were 20µM and 4.03µM, respectively. The proposed method was demonstrated to detect CN(-) in drinking water with high accuracy.

New polymeric membrane cadmium(II)-selective electrodes using tripodal amine based ionophores.

Fabrication of PVC membrane electrodes incorporating selective neutral carriers for Cd(2+) was reported. The ionophores were designed to have different topologies, donor atoms and lipophilicity by attaching tripodal amine (TPA) units to the lipophilic anthracene (ionophore I) and p-tert-butylcalix[4]arene (ionophores II, III and IV). The synthesized ionophores were incorporated to the plasticized PVC membranes to prepare Cd(II) ion selective electrodes (ISEs). The membrane electrodes were optimized by changing types and amounts of ionic sites and plasticizers. The selectivity of the membranes fabricated from the synthesized ionophores was evaluated, the relationship between structures of ionophores and membrane characteristics were explored. The ionophore IV which composed of two opposites TPA units on the calix[4]arene compartment showed the best selectivity toward Cd(2+). The best membrane electrode was fabricated from ionophore IV (10.2 mmol kg(-1)) with KTpClPB (50.1 mol% related to the ionophore) as an ion exchanger incorporated in the DOS plasticized PVC membrane (1:2; PVC:DOS). The Cd-ISE fabricated from ionophore IV exhibited good properties with a Nernstian response of 29.4±0.6 mV decade(-1) of activity for Cd(2+) ions and a working concentration range of 1.6×10(-6)-1.0×10(-2)M. The sensor has a fast response time of 10s and can be used for at least 1 week without any divergence in potential. The electrode can be used in the pH range of 6.0-9.0. The proposed electrodes using ionophores III and IV were employed as a probe for determining Cd(2+) from the oxidation of CdS QDs solution and the real treatment waste water sample with excellent results.

Enhancement of the fluorescence quenching efficiency of DPPH(•) on colloidal nanocrystalline quantum dots in aqueous micelles.

Luminescent CdS quantum dots capped with thioglycolic acid (CdS-TGA QDs) were demonstrated to serve as a fluorescence probe for a model organic radical, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH(•)), employing the quenching of the CdS-TGA QDs emission signal by the radical. Under the optimum conditions, the quenching efficiency of DPPH(•) on CdS-TGA QDs was proportional to the concentration of DPPH(•), following Stern-Volmer relationship. Different types of surfactants (cationic, anionic and neutral surfactants) were introduced to CdS-TGA QDs in order to increase the detection sensitivity. The fluorescence intensity of CdS-TGA QDs was greatly enhanced by cationic and neutral surfactants. Moreover, the quenching efficiency of DPPH(•) on the QDs in the presence of micelles was remarkably ca. 13 times higher than that in the system without micelles. Effects of pH and concentration of surfactants on the fluorescence quenching of CdS-TGA QDs were investigated. Electron spin resonance (ESR) spectroscopy was also used to monitor the DPPH radical species in CdS-TGA QDs mixtures with and without micelles. Fluorescence quenching mechanisms of CdS-TGA QDs by DPPH(•) in the presence and in the absence of CTAB were proposed.

Singlet Oxygen and the Production of Sulfur Oxygenates of Nickel(II) and Palladium(II) Thiolates.

The metal dithiolate [1,5-bis(2-mercaptoethyl)-1,5-diazacyclooctane]nickel(II) (Ni-1), a sterically hindered analogue (Ni-1), and the palladium analogue Pd-1 react with (1)Delta O(2) to yield a variety of stable and isolable metallosulfones (MS(O(2))R) and metallosulfoxides (MS(O)R). Singlet oxygen was generated both photochemically with the sensitizer Rose Bengal and thermally by decomposition of the 1,4-endoperoxide of 1,4-dimethylnaphthalene. Increased rates and oxygenation yields are observed upon excitation of O(2) from its ground state, (3)Sigma, to the excited state, (1)Delta. The reactions are both solvent and concentration dependent, with sulfones generally favored in acetonitrile and sulfoxides favored in methanol. There is also a ligand and metal effect. The proposed mechanistic pathways involving a persulfoxide precursor to single sulfur site O(2) addition (producing metallosulfones) and adjacent sulfur site O(2) addition (producing metallosulfoxides) are consistent with product distribution, comparison to the much studied oxygenation of organic sulfides, and previous isotopic labeling experiments (J. Am. Chem. Soc. 1996, 118, 1791; 1992, 114, 4601; Inorg. Chem. 1993, 32, 4171).