Selective Recovery and Detection of Gold with Cucurbit[n]urils (n = 5-7).

Environmentally benign methods for gold recovery and detection are highly desirable for a sustainable future. Herein, we demonstrate a selective recovery and detection strategy of gold with cucurbit[n]urils (Q[n = 5-7]) by means of outer-surface interactions. Tetrachloroaurate anion ([AuCl4]-) is able to be rapidly precipitated with Q[n] in forms of supramolecular adducts. X-ray crystallography of four Q[n = 5-7]·[AuCl4]- complexes reveal that strong outer-surface interactions between Q[n = 5-7] and [AuCl4]- are the major driving force for the formation of Q[n = 5-7]·[AuCl4]- complexes. Impressively, each Q[6] macrocycle is surrounded by 12 [AuCl4]- anions. Each of these 12 [AuCl4]- anions is connected to four adjacent [AuCl4]- anions, leading to the formation of a three-dimensional supramolecular framework with tubular channels. In addition, we found an interesting inclusion complex [Au(OH2)4]3+⊂Q[7] in the Q[7]·[AuCl4]- complex, which is the first example of hydrated metal cation encapsulated inside the cavity of Q[n]. Spectroscopic data suggest that Q[n = 5-7] possess a high affinity and selectivity for [AuCl4]- even in the presence of other transition-metal ions. Q[n] modified electrodes are found to be an effective material for the detection of trace gold in dilute solutions.

Electrogenerated chemiluminescence of ZnO nanorods and its sensitive detection of cytochrome C.

Various kinds of ZnO nanoparticles have been successfully used in gas sensing applications, however, these nanomaterials have been rarely investigated in electrogenerated chemiluminescence (ECL). In the present work, ZnO nanorods (ZnONRs) were synthesized by hydrothermal method, and characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). ECL behaviors of ZnONRs were investigated in neutral aqueous condition in the presence of K2S2O8. Cyclic voltammetry (CV) results revealed that ZnONRs can react with K2S2O8 to generate strong light emission, revealing that K2S2O8 can act as coreactant of ZnONRs ECL. ZnONRs synthesized under different pH conditions exhibited different ECL intensities, and the most intense ECL signal was obtained at pH 7.0. Cytochrome C could compete with ZnONRs to react with K2S2O8, and exhibited apparent inhibiting effect on ZnONRs ECL, which can be sensitively detected in the range of 1.0 × 10-11-5.0 × 10-9molL-1, with a detection limit of 4.7 × 10-12molL-1 (3σ). The present ECL system exhibited high sensitivity and good stability, which is suitable for the fabrication of novel ECL sensors.

A novel aptasensor for lysozyme based on electrogenerated chemiluminescence resonance energy transfer between luminol and silicon quantum dots.

In the present work, electrogenerated chemiluminescence (ECL) of luminol was investigated in neutral condition at a gold electrode in the presence of silicon quantum dots (SiQDs). The results revealed that SiQDs can not only greatly enhance luminol ECL, but also act as energy acceptor to construct a novel ECL resonance energy transfer (ECL-RET) system with luminol. As a result, strong anodic ECL signal was obtained in neutral condition at the bare gold electrode, which is suitable for biosensing application. Lysozyme exhibited apparent inhibiting effect on the ECL-RET system, based on which an ECL aptasensor was fabricated for the sensitive detection of lysozyme. The proposed method showed high sensitivity, good selectivity, and wide linearity for the detection of lysozyme in the range of 5.0×10-14-5.0×10-9gmL-1 with a detection limit of 5.8×10-15gmL-1 (3σ). The results suggested that as-proposed luminol/SiQDs ECL biosensor will be promising in the detection enzyme.

Electrogenerated chemiluminescence of Si quantum dots in neutral aqueous solution and its biosensing application.

Electrogenerated chemiluminescence (ECL) of semiconductor quantum dots (QDs) has been considered as a powerful technique in the fabrication of biosensor, however, high-toxicity of heavy metal ion containing in QDs severely limits their further applications, and the search for the alternative benign nanomaterials with high ECL efficiency is urgent. Herein, ECL behavior of eco-friendly silicon quantum dots (SiQDs) was reported in neutral aqueous condition. Stable and intense cathodic ECL emission was obtained in phosphate buffer solution (PBS) with K2S2O8 as coreactant. ECL resonance energy transfer (ECL-RET) system was established with SiQDs ECL as energy donor and gold nanoparticles (AuNPs) as energy acceptor, based on which a novel ECL biosensor was fabricated. AuNPs was connected at the terminal of hairpin DNA to form a signal probe. When the probe was modified on SiQDs, ECL-RET occurred due to the short distance between AuNPs and SiQDs, resulting in the apparent decrease of ECL signal. Target DNA can open the loop of hairpin DNA, and move AuNPs away from the electrode surface. As a result, the ECL-RET process was hampered, and the ECL emission resumed. The increased ECL signals varied linearly with the target DNA concentrations in the range of 0.1fM to 1pM with the detection limit of 0.016fM (3σ). The proposed ECL sensor exhibited highly sensitivity and good selectivity in the detection of target DNA.

Electrogenerated Chemiluminescence Resonance Energy Transfer between Ru(bpy)3(2+) Electrogenerated Chemiluminescence and Gold Nanoparticles/Graphene Oxide Nanocomposites with Graphene Oxide as Coreactant and Its Sensing Application.

In the present work, strong anodic electrogenerated chemiluminescence (ECL) of Ru(bpy)3(2+) was observed at a graphene oxide modified glassy carbon electrode (GO/GCE) in the absence of coreactants. The electrocatalytical effect of GO on the oxidation of Ru(bpy)3(2+) suggested that GO itself can act as the coreactant of Ru(bpy)3(2+) ECL, which can be used to fabricate the ECL biosensor. Thiol group terminated adenosine triphosphate (ATP) aptamer was immobilized on the GO film via DNA hybridization. When gold nanoparticles/graphene oxide (AuNPs/GO) nanocomposites were modified on the aptamer through the S-Au bond to form a sandwich-like structure, the ECL resonance energy transfer (ECL-RET) could occur between Ru(bpy)3(2+) and AuNPs/GO nanocomposites, resulting in an apparent decrease of ECL signal. After the ECL sensor was incubated in ATP solution, the AuNPs/GO nanocomposites were released from the electrode due to the specific interaction between aptamer and ATP, leading to the increased ECL signal. On the basis of these results, an ECL aptasensor was fabricated and could be used in the sensitive and selective detection of ATP in the range of 0.02-200 pM with a detection limit of 6.7 fM (S/N = 3). The proposed ECL aptasensor can be applied in the detection of ATP in real samples with satisfactory results.

Electrochemiluminescent Sensing for Caspase-3 Activity Based on Ru(bpy)3(2+)-Doped Silica Nanoprobe.

Caspase-3 is one of the most frequently activated cysteine proteases during the apoptosis process and has been identified as a well-established cellular marker of apoptosis. In this study, a novel approach for the sensitive determination of caspase-3 activity was proposed using electrochemiluminescence (ECL) of Ru(bpy)3(2+)-doped silica (Ru@SiO2) with tripropylamine (TPA) as coreactant. A nanocomposite containing gold nanoparticles (AuNPs), poly(dimethyldiallyl ammonium chloride) (PDDA), and multiwalled carbon nanotubes (CNTs) was fabricated as an ECL platform. The biotinylated DEVD-peptide (biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Gly-Cys) was immobilized on the nanocomposite surface via the strong bonding interaction between AuNPs and the thiol group. Then the streptavidin-modified Ru(bpy)3(2+)-doped silica (Ru@SiO2-SA) was immobilized on the ECL platform via the specific interaction between biotin and streptavidin to generate ECL signal. Caspase-3 can specifically recognize and cleave the N-terminus of DEVD, leading to the loss of the biotin label and the decrease of ECL intensity to determine the activity of caspase-3. The results revealed a new ECL avenue for the sensitive and specific monitor of caspase-3, and the platform could be utilized to evaluate anticancer drugs.

Anodic Electrogenerated Chemiluminescence of Ru(bpy)3(2+) with CdSe Quantum Dots as Coreactant and Its Application in Quantitative Detection of DNA.

In the present paper, we report that CdSe quantum dots (QDs) can act as the coreactant of Ru(bpy)3(2+) electrogenerated chemiluminescence (ECL) in neutral condition. Strong anodic ECL signal was observed at ~1.10 V at CdSe QDs modified glassy carbon electrode (CdSe/GCE), which might be mainly attributed to the apparent electrocatalytic effect of QDs on the oxidation of Ru(bpy)3(2+). Ru(bpy)3(2+) can be intercalated into the loop of hairpin DNA through the electrostatic interaction to fabricate a probe. When the probe was bound to the CdSe QDs modified on the GCE, the intense ECL signal was obtained. The more Ru(bpy)3(2+) can be intercalated when DNA loop has larger diameter and the stronger ECL signal can be observed. The loop of hairpin DNA can be opened in the presence of target DNA to release the immobilized Ru(bpy)3(2+), which can result in the decrease of ECL signal. The decreased ECL signal varied linearly with the concentration of target DNA, which showed the ECL biosensor can be used in the sensitive detection of DNA. The proposed ECL biosensor showed an excellent performance with high specificity, wide linear range and low detection limit.

Electrogenerated chemiluminescence resonance energy transfer between luminol and CdSe@ZnS quantum dots and its sensing application in the determination of thrombin.

In this work, electrogenerated chemiluminescence resonance energy transfer (ECL-RET) between luminol as a donor and CdSe@ZnS quantum dots (QDs) as an acceptor was reported in neutral conditions. It was observed that a glassy carbon electrode modified with CdSe@ZnS quantum dots (CdSe@ZnS/GCE) can catalyze the luminol oxidation to promote the anodic luminol ECL without coreactants. The intensity of anodic luminol ECL (0.60 V) at the CdSe@ZnS/GCE was enhanced more than 1 order of magnitude compared with that at the bare GCE. Another stronger anodic ECL peak observed at more positive potential (1.10 V) could be assigned to the ECL-RET between the excited state of luminol and the QDs. A label-free ECL aptasensor for the detection of thrombin was fabricated based on the synergic effect of the electrocatalysis and the ECL-RET. The approach showed high sensitivity, good selectivity, and wide linearity for the detection of thrombin in the range of 10 fM-100 pM with a detection limit of 1.4 fM (S/N = 3). The results suggested that the as-proposed luminol-QDs ECL biosensor will be promising in the detection of protein.

Speciation of inorganic- and methyl-mercury in biological matrixes by electrochemical vapor generation from an L-cysteine modified graphite electrode with atomic fluorescence spectrometry detection.

A novel nonchromatographic speciation technique for ultratrace inorganic mercury (Hg(2+)) and methylmercury (CH(3)Hg(+)) in biological materials is developed and validated by electrolytic vapor generation (EVG) coupled with atomic fluorescence spectrometry (AFS). The studies show that CH(3)Hg(+) and Hg(2+) can be converted to Hg vapor efficiently on an l-cysteine modified graphite cathode, which has never been reported before. We observe that only Hg(2+) can be converted efficiently to Hg vapor at low current mode (0.2 A). While at high current mode (2.2 A), both CH(3)Hg(+) and Hg(2+) can be reduced efficiently. As a result, we successfully establish an exact and sensitive method based on the current control to detect mercury speciation for the first time. The factors of electrolytic conditions have been optimized, and the potential mechanism is discussed. Under the optimal conditions, the detection limits (3s) of Hg(2+) and CH(3)Hg(+) in aqueous solutions are 0.098 and 0.073 µg L(-1), respectively. The relative standard deviations for 6 replicate determinations of 2 µg L(-1) Hg are determined as 3.2% and 4.7% for Hg(2+) and CH(3)Hg(+). The accuracy of the method is verified through the analysis of certified reference materials (CRM, NRC-DORM-2), and the proposed method has been applied satisfactorily to the determination of mercury speciation in several seafood samples by calibration curve mode.

Chemiluminescence of a cyclometallated iridium(III) complex and its application in the detection of cysteine.

Chemiluminescence (CL) of a cyclometallated iridium (III) complex {tris[1-(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine]iridium(III)} in the presence of potassium permanganate and oxalic acid is reported for the first time. Cysteine exhibits sufficient enhancing effect on the CL generated from the cyclometallated iridium(III) complex, which make it possible for the sensitive detection of cysteine using a flow-injection-chemiluminescence (FI-CL) method. The optimum conditions for the chemiluminescence emission were investigated. Under the optimal condition, the linear range for the determination of cysteine was 1.0 × 10(-9) -5.0 × 10(-6) mol/L with a detection limit of 6.9 × 10(-10) mol/L. A relative standard deviation of 1.6% was obtained for eight replicate determinations. The mechanisms of CL are proposed and the emitting species was identified as the metal-to-ligand charge-transfer (MLCT) excited states of the iridium complex.

Enhancing and inhibiting effects of benzenediols on chemiluminescence of a novel cyclometallated iridium(III) complex.

A novel chemiluminescence (CL) system, including the cyclometallated iridium(III) complex {tris[1-(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine]iridium}, potassium permanganate and oxalic acid, is proposed for the determination of benzenediols. This method is based on the fact that hydroquinone and catechol exhibited an inhibiting effect, while resorcinol exhibited an enhancing effect on CL intensity. The optimum conditions for CL emission were investigated. Under optimal conditions, the detection limits of hydroquinone, catechol and resorcinol were 6.4 × 10(-8), 2.7 × 10(-9) and 8.1 × 10(-7) mol/L, respectively. The method has been successfully applied to the determination of benzenediols in different types of water sample. The luminophors of the CL systems were all identified as the metal-ligand charge-transfer (MLCT) excited state of the iridium complex.

Synthesis, characterization, and electrochemiluminescence of luminol-reduced gold nanoparticles and their application in a hydrogen peroxide sensor.

It was found that chloroauric acid (HAuCl(4)) could be directly reduced by the luminescent reagent luminol in aqueous solution to form gold nanoparticles (AuNPs), the size of which depended on the amount of luminol. The morphology and surface state of as-prepared AuNPs were characterized by transmission electron microscopy, UV/visible spectroscopy, X-ray photoelectron spectroscopy, FTIR spectroscopy, and thermogravimetric analysis. All results indicated that residual luminol and its oxidation product 3-aminophthalate coexisted on the surface of AuNPs through the weak covalent interaction between gold and nitrogen atoms in their amino groups. Subsequently, a luminol-capped AuNP-modified electrode was fabricated by the immobilization of AuNPs on a gold electrode by virtue of cysteine molecules and then immersion in a luminol solution. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The as-prepared modified electrode exhibited an electrochemiluminescence (ECL) response in alkaline aqueous solution under a double-step potential. H2O2 was found to enhance the ECL. On this basis, an ECL sensor for the detection of H2O2 was developed. The method is simple, fast, and reagent free. It is applicable to the determination of H2O2 in the range of 3x10(-7)-1x10(-3) mol L(-1) with a detection limit of 1x10(-7) mol L(-1) (S/N=3).

Comparative studies on electrogenerated chemiluminescence of luminol on gold nanoparticle modified electrodes.

Comparative studies on the electrogenerated chemiluminescence (ECL) behavior of luminol on various electrodes modified with gold nanoparticles of different size were carried out in neutral solution by conventional cyclic voltammetry (CV). The results demonstrated that the gold nanoparticle modified electrodes could generate strong luminol ECL in neutral pH conditions. The catalytic performance of gold nanoparticle modified electrodes on luminol ECL depended not only on the gold nanoparticles but also on the substrate. Gold electrode and glassy carbon electrode were the most suitable substrates for the self-assembly of gold nanoparticles. Moreover, the gold nanoparticle modified gold and glassy carbon electrode had satisfying stability and reproducibility and did not need tedious pretreatment of electrode surface before each measurement. It was also found that luminol ECL behavior depended on the size of gold nanoparticles. The most intense ECL signals were obtained on a 16-nm-diameter gold nanoparticle modified electrode. The modified electrode prepared by the self-assembly method exhibited much better catalytic effect on luminol ECL than that prepared by the electrically deposited method. The ECL behavior of luminol on a gold nanoparticle self-assembled gold electrode was also investigated by other transient-state electrochemical techniques, such as chronoamperometry, differential pulse voltammetry, normal pulse voltammetry, and square wave voltammetry. The strongest ECL intensity was obtained under square wave voltammetric condition.

[The enhancement and inhibition of lucigenin chemiluminescence by phenol and aniline derivatives].

The effect of phenol and aniline derivatives on the lucigenin-H2O2-Co2+ chemiluminescence (CL) at different pH was studied. In NaHCO-Na2CO3 medium, some compounds enhanced the lucigenin CL while others inhibited the lucigenin CL. In NaOH medium, all tested compounds inhibited the lucigenin CL. It was found that the magnitude of enhancement and inhibition by tested compounds was related to their molecular structures, media, and pH. The fluorescence spectra of the system after the CL reaction and the CL spectra of the lucigenin system were studied. The possible mechanisms for CL enhancement and inhibition have been proposed. On the one hand, the competition of phenol and aniline derivatives with lucegenin for H2O2/HO2(-) led to the inhibition. On the other hand, the nucleophilic adducts of lucigenin formed by the reactions of some phenol and aniline derivatives with lucegin reacted with lucigenin to give rise to lucigenin radicals, followed by the reactions with the dissolved oxygen to give CL, resulting in the enhancement. The competition of these two routes led to the CL enhancement or inhibition under different conditions.

Electrogenerated chemiluminescence of luminol on a gold-nanorod-modified gold electrode.

Electrogenerated chemiluminescence (ECL) of luminol on a gold-nanorod-modified gold electrode was studied, and five ECL peaks were obtained under conventional cyclic voltammetry in both neutral and alkaline solutions. Among them, four ECL peaks (ECL-1-4) were also observed on a gold-nanosphere-modified gold electrode, but the intensities of these ECL peaks were enhanced about 2-10-fold on a gold-nanorod-modified gold electrode in neutral solution. One new strong ECL peak (ECL-5) was obtained at -0.28 V (vs SCE) on a gold-nanorod-modified gold electrode in both neutral and alkaline solutions and enhanced with an increase in pH. In strong alkaline solutions, ECL-1 and ECL-2 on a gold-nanosphere-modified electrode were much stronger than those on a gold-nanorod-modified gold electrode, while ECL-3-5 appeared to only happen on a gold-nanorod-modified gold electrode. The emitter of all the ECL peaks was identified as 3-aminophthalate. The ECL peaks were found to depend on the scan direction, the electrolytes, the pH, and the presence of O(2) and N(2). The reaction pathways for ECL-4 have been further elucidated, and the mechanism of the new ECL peak (ECL-5) has been proposed. The results indicate that a gold-nanorod-modified gold electrode has a catalytic effect on luminol ECL different from that of a gold-nanosphere-modified gold electrode, revealing that the shape of the metal nanoparticles has an important effect on the luminol ECL behavior. The strong ECL of luminol in neutral solution obtained on a gold-nanorod-modified electrode may be used for the sensitive detection of biologically important compounds in physiological conditions.