Experimentally and Theoretically Revealing the Co-Doping Effects of Ce-Sr in Gd2Zr2O7.

To safely dispose radioactive waste (including, e.g., thorium and radiostrontium), Ce4+ and Sr2+ were chosen as simulated surrogates of α and ß waste and were introduced into the Gd3+ site in Gd2Zr2O7 to maintain the average cationic radius and to compensate for charge. A series of Gd2-xSrx/2Cex/2Zr2O7 (0.00 ≤ x ≤ 0.25) compounds were examined by experimental and theoretical calculations to investigate the co-doping effects of α and ß waste in a Gd2Zr2O7-based matrix. The effects of Ce4+ and Sr2+ content on the phase, unit cell parameters, active modes, mechanical property, and microstructure were studied systematically. Moreover, the limit of incorporation of Ce4+ and Sr2+ in Gd2Zr2O7 pyrochlore and the lattice parameters were also calculated through virtual crystal approximation theory, and the results were found to well agree with experimental results.

Metal-enhanced fluorescence of graphene oxide sheets.

Graphene oxide (GO) is an excellent chemical tunable optical platform for imaging and sensing. The photoluminescence (PL) quantum yield of GO is relatively low, which limited the application of the intrinsic and tunable fluorescence from GO. Here, we report the first case of metal-enhanced fluorescence (MEF) of GO. A significant enhancement (~10-fold) in fluorescence intensity is observed from GO on the Ag substrate as compared to that on the glass. FL, Raman, and SEM images are used to investigate the MEF behavior and are coincident with each other. The influence of the metal particle size of Ag substrate is investigated. The fluorescence is also found to be responsive when adding different metal ions into GO solution. GO contacting directly with metal substrate exhibits strong MEF without quenching, which makes it possible to use GO sheets for three-dimension optical imaging and sensing.

Single-strand DNA-scaffolded copper nanoclusters for the determination of inorganic pyrophosphatase activity and screening of its inhibitor.

A fluorescence method for the determination of inorganic pyrophosphatase (PPase) activity has been established based on copper nanoclusters (CuNCs). The polythymine of 40 mer (T40) acts as a template for the reduction reaction from Cu2+ to Cu0 by ascorbic acid (AA). This reaction leads to the formation of fluorescent CuNCs with excitation/emission peaks at 340/640 nm. However, the higher binding affinity between inorganic pyrophosphate (PPi) and Cu2+ hinders the effective formation of CuNCs. This shows low fluorescence intensity. PPase catalyzes the hydrolysis of PPi into Pi during which free Cu2+ ions are produced. This facilitates the formation of fluorescent CuNCs. Thus, the fluorescence intensity was restored. The fluorescence enhancement of the system has a linear relationship with PPase activity in the range 0.3 to 20 mU·mL-1, and the detection limit is0.2 mU·mL-1. The relative intensity (I/I0) at 640 nm for the analytical solution versus system is also employed to screen the inhibitor for PPase with high efficiency. Graphical abstract Schematic representation of a fluorescent assay for the determination of inorganic pyrophosphatase activity and screening its inhibitor based on single-strand polythymine-scaffolded copper nanoclusters.

Quantitative Analysis of Surface Sites on Carbon Dots and Their Interaction with Metal Ions by a Potentiometric Titration Method.

Carbon dots (CDs) possess abundant functional groups on their surface which are related to their application in various fields such as sensing, imaging, and catalysis. Understanding the amount and properties of these functional groups and their interaction with metal ions is essential but has posed longstanding challenges because of the diverse and complex structures of CDs. In this work, potentiometric titration is demonstrated as an effective method to figure out the categories and amounts of functional groups. Surface complexation modeling with the FITEQL program was applied to the quantification of the surface sites on CDs with the titration data. Then with the obtained molar concentrations of the surface sites, the pKas of these surface sites were calculated with the Hyperquad program. Finally, titration experiments of CDs with and without Fe(III) were carried out and the stability constants of Fe(III) and ArgCDs were simulated on the Hyperquad program. By utilizing the stability constants, the distribution of Fe(III) species at different pHs and the concentrations of Fe(III) and CDs were also investigated. This potential method might be used for characterizing the surface sites on other CDs or even other soluble nanoparticles as well as for investigating the interactions of the surface sites with different metal ions.

Iodide-assisted silver nanoplates for colorimetric determination of chromium(III) and copper(II) via an aggregation/fusion/oxidation etching strategy.

The authors have studied the role of different ligands on the surfaces of silver nanoplates for regulating their analytical applications. Citrate-capped silver nanoplates are applied for the detection of chromium ions (Cr3+) based on aggregation of silver nanoplates. Cr3+ can cause aggregation through high affinity between Cr3+ and carboxylate groups of citrates, resulting in a color change from dark yellow to purple and at last colorless. The detection limit is 8.0 nM. This system shows excellent selectivity in the presence of a variety of other metal ions. Further, silver nanoplates coupled with iodide ions are employed for the colorimetric determination of copper ions (Cu2+) based on a new strategy of fusion/oxidation etching nanoplates. When Cu2+ is introduced into this silver nanoplate system, Cu2+ can oxidize I- to iodine (I2), which can further oxidize silver to form silver iodide (AgI). Simultaneously, the solution color changes from dark yellow to colorless. The lower limit detection is 0.27 µM. This assay exhibits excellent selectivity for Cu2+ over other environmental metal ions. It is perceived that this design concept will open up a fresh insight of simple, rapid and reliable detection of other heavy metal ions in drinking water and environmental samples. Graphical abstract Iodide-assisted silver nanoplates can be used for the colorimetric and visual ldetermination of Cr3+ and Cu2+ based on an aggregation/fusion/oxidation etching mechanism. These systems allows selective and sensitive determination of the ions in real samples.

DNA-scaffold copper nanoclusters integrated into a cerium(III)-triggered Fenton-like reaction for the fluorometric and colorimetric enzymatic determination of glucose.

A fluorometric and colorimetric method are described for the determination of hydrogen peroxide and glucose by integrating copper nanoclusters (CuNCs) into a Fenton-like reaction. The mechanism mainly depends on the fast formation of long-strand DNA-templated CuNCs with strong red fluorescence (with excitation/emission maxima at 340/640 nm) in the absence of H2O2. The DNA can be cleaved into short-oligonucleotide fragments by hydroxy radicals as formed in the Ce(III)-triggered Fenton-like reaction in the presence of H2O2. As a result, short-strand DNA loses the ability as a template for the formation of CuNCs. This leads to a decrease of fluorescence. The colorimetric assay, in turn, is based on the oxidation of colorless Ce(III) ions to the distinctly yellow Ce(IV) ions (with an absorption maximum at 400 nm) by H2O2. Compared with those assays based on the use of enzyme mimics, this method does not require any chromogenic substrates such as ABTS and TMB. Based on the dual-signal readout platform, we successfully achieved the detection of H2O2 and glucose. LODs are as low as 0.266 µM and 2.92 µM. The methods were applied to the sensitive determination of glucose by using glucose oxidase (GOx) which catalyzes the oxidization of glucose to produce H2O2. The practical application was demonstrated by determination of glucose in human serum, with apparent recoveries of 98.4-101.9% and 99.1-105.6%, respectively. The concentration of glucose ranges from 1 to 500 µM and 50 to 600 µM based on the dual-signal readout platform, respectively. This fluorometric and colorimetric dual-mode strategy will pave a new avenue for constructing effective assays for H2O2-related analytes in biochemical and clinical applications. Graphical abstractSchematic representation of a fluorometric and colorimetric dual-readout strategy for the sensitive determination of hydrogen peroxide and glucose. The assay has been designed by integrating copper nanoclusters into a Ce(III)-triggered Fenton-like reaction.

DNA-templated copper nanoclusters as a fluorescent probe for fluoride by using aluminum ions as a bridge.

A selective fluorescent on-off-on probe has have designed for the detection of fluoride (F-) ions based on DNA-templated copper nanocluster (CuNCs) and by using aluminum(III) ions as a bridge. A 40-mer polythymine acts as a template for the reduction of Cu(II) to Cu(0) by ascorbic acid. This result is the formation of red fluorescent CuNCs, with excitation/emission peaks at 340/640 nm. After addition of Al3+ ions, the fluorescence of CuNCs is quenched because the interaction of Al3+ and DNA disturbs the formation of DNA-templated CuNCs. Fluorescence is restored on addition of fluoride to the system. This is due to the desorption of Al3+ from the DNA and the formation of the Al(OH)3F- complex. This system displays a fast fluorometric response to fluoride, with high selectivity over other anions. Fluorescence increases linearly in the 2 to 150 µM F- concentration range, and the detection limit is 1.0 µM. This probe has been successfully used for the detection of F- ions in four brands of toothpaste. The method is rapid, cost-effective, selective, and does not require toxic solvents and reagents. Graphical abstract Schematic presentation of a method for fluorometric determination of fluoride by using DNA-templated copper nanoclusters (CuNCs) and using aluminum(III) as a bridge. The red fluorescence of the CuNCs is quenched in the presence of Al(III) ions but restored after addition of fluoride.

Localized Surface Plasmon Resonance Meets Controlled/Living Radical Polymerization: An Adaptable Strategy for Broadband Light-Regulated Macromolecular Synthesis.

The photophysical process of localized surface plasmon resonance (LSPR) is, for the first time, exploited for broadband photon harvesting in photo-regulated controlled/living radical polymerization. Efficient macromolecular synthesis was achieved under illumination with light wavelengths extending from the visible to the near-infrared regions. Plasmonic Ag nanostructures were in situ generated on Ag3 PO4 photocatalysts in a reversible addition-fragmentation chain transfer (RAFT) system, thereby promoting polymerization of various monomers following a LSPR-mediated electron transfer mechanism. Owing to the LSPR-enhanced broadband photon harvesting, high monomer conversion (>99 %) was achieved under natural sunlight within 0.8 h. The deep penetration of NIR light enabled successful polymerization with reaction vessels screened by opaque barriers. Moreover, by trapping active oxygen species generated in the photocatalytic process, polymerization could be implemented without pre-deoxygenation.

Microplasma Anode Meeting Molten Salt Electrochemistry: Charge Transfer and Atomic Emission Spectral Analysis.

Molten salt electrolysis is normally conducted with solid anode, such as noble metal or graphite, which has defects such as high cost or emission of carbon oxide. Herein, we report that a microplasma based on atmospheric-pressure glow discharge could act as a kind of gaseous anode for electrolysis in molten salt. When the Ag/Ag+ redox couple was chosen as the research object, the microplasma anode could initiate charge-transfer reactions in the molten salt and Ag could be electrodeposited with current efficiency of above 90%. The microplasma anode has also shown excellent anticorrosive performance in both chloride and carbonate molten salt. Furthermore, the microplasma anode could potentially serve as an excitation source of atomic emission spectrometry (AES), making it possible to determine the concentration of Ag ions in the molten salt in situ and in real-time. With properties such as being carbon-free and having corrosion resistance and extensive utilization for analysis, the microplasma anode has opened a new direction for molten salt electrochemistry.

Dispersion-aggregation-dispersion colorimetric detection for mercury ions based on an assembly of gold nanoparticles and carbon nanodots.

Mercury is a common heavy metal element in natural systems and is highly toxic to the human body. Herein, a novel colorimetric detection of Hg2+ ions is proposed based on the aggregation of gold nanoparticles (AuNPs) induced by carbon quantum dots (CDs) with the assistance of glutathione (GSH). In this sensing system, the AuNP/CDs composite forms through Au-N bonds. Simultaneously, the color of the solution turns from wine red to blue. The well-dispersed AuNPs can be restored after the addition of GSH, because GSH competes with CDs to bind onto the surface of AuNPs and protect AuNPs from aggregation. In the presence of Hg2+ ions, GSH can chelate with Hg2+ to form a complex, which subsequently enables CDs to facilitate the aggregation of the AuNPs again. Therefore, according to the red-to-blue color change, a colorimetric sensor is established for the sensitive and selective detection of Hg2+ with a detection limit of 7.5 nM. Moreover, this sensor is successfully used to detect Hg2+ spiked in environmental water. This very simple and cost-effective strategy will promote the development of a colorimetric sensor for the determination of other metal ions in biological and environmental fields.

On-off-on luminescent pyrophosphate probe based on the use of Mn-doped ZnS quantum dots and using Eu(III) as a mediator.

A selective phosphorescent on-off-on probe with long decay lifetime has been designed for the detection of pyrophosphate ions (PPi). The detection scheme is based on the use of europium(III)-modulated Mn(II)-doped ZnS quantum dots capped with N-acetyl-L-cysteine. Both the aggregation of quantum dots and electron transfer induced by Eu(III) ions cause phosphorescence to be quenched ("off" state). Phosphorescence is, however, restored on addition of PPi to the system ("on" state). The effect is attributed to the removal of Eu(III) from the carboxy groups on the surface of the quantum dots owing to the stronger interaction between PPi and Eu(III). A linear relationship exists between phosphorescence intensity (best measured at excitation/emission wavelengths of 316/594 nm) and PPi concentration in the 400 nM to 6000 nM with a detection limit of 145 nM. An additional attractive feature is provided by the long-lived phosphorescence (1920 µs) of the quantum dots. It can be used to eliminate interference by short-lived fluorescence in biological samples by performing time resolved measurements. The probe was applied to the determination of PPi in spiked in urine samples and gave recoveries in the range from 98 to 105% with RSDs of <2.0%. Graphical abstract Schematic of a long-lived phosphorescent on-off-on probe for the sensitive and selective detection of pyrophosphate ions (PPi). It is based on the use of Eu(III)-modulated Mn(II)-doped ZnS quantum dots (QDs). Phosphorescence is quenched of QDs after the addition of Eu3+but restored after the addition of PPi.

Time-resolved determination of Fe(II) ions using cysteine-bridged Mn-doped ZnS quantum dots as a phosphorimetric probe.

A time-resolved phosphorescence (TRP) is applied to the highly sensitive determination of Fe(II) ions. The method is based on the use of a phosphorescent probe consisting of cysteine-bridged Mn-doped ZnS quantum dots (Mn/ZnS QDs). The presence of cysteine enhances the phosphorescence of the QDs and also increases the efficiency of quenching caused by Fe(II) ions. This results in strongly improved selectivity for Fe(II). The linear response is obtained in the concentration range of 50-1000 nM with a 19 nM detection limit. Phosphorescence is recorded at excitation/emission peaks of 301/602 nm. The interference of short-lived fluorescent and scattering background from the biological fluids is eliminated by using the TRP mode with a delay time of 200 µs. The determination of Fe(II) in human serum samples spiked at a 150 nM level gave a 92.4% recovery when using the TRP mode, but only 52.4% when using steady-state phosphorescence. This demonstrates that this probe along with TRP detection enables highly sensitive and accurate determination of Fe(II) in serum. Graphical abstract Schematic of a novel phosphorescent method for the detection of Fe2+ ions based on cysteine-bridged Mn-doped ZnS quantum dots. The sensitivity of this assay greatly increases due to the addition of cysteine. Interferences by short-lived auto-fluorescence and the scattering light from the biological fluids is eliminated by using time-resolved phosphorescence mode.

Bare eye detection of Hg(II) ions based on enzyme inhibition and using mercaptoethanol as a reagent to improve selectivity.

The authors describe a colorimetric method for the determination of Hg2+ ions based on the inhibition of the activity of the enzyme urease. The pH value of solution increases when urease hydrolyzes urea, which can be visualized by adding a pH indicator such as Phenol Red (PhR). Mercaptoethanol as a typical thiol is added to the system to improve selectivity because it binds metal ions and then - unlike the Hg2+ mercaptoethanol complex - does not inhibit urease. Hence, the color of the pH indicator PhR turns from yellow to pink as the solution becomes alkaline. The Hg2+ mercaptoethanol complex, in contrast, strongly inhibits urease and the color of the solution remains yellow. The findings were used to design a photometric assay based on the measurement of the ratio of absorptions of PhR at 558 nm and 430 nm. It has a linear response over the 25 to 40 nM Hg2+ concentration range and a 5 nM detection limit. This is well below the guideline values of Hg2+ specified by the US Environmental Protection Agency and the World Health Organization for drinking water (10 nM and 30 nM, respectively). The method was employed to the determination of Hg2+ in water samples spiked with 10 nM levels of Hg2+ where color changes still can be observed visually. Graphical Abstract Schematic presentation of a colorimetric method for the ultrasensitive detection of Hg2+ based on the inhibition of urease activity. Mercaptoethanol is used to improve the selectivity. Even at Hg2+ concentrations as low as 5 nM, the color change still can be easily observed by bare eyes.

Heteroatom-Doped Carbon Dots (CDs) as a Class of Metal-Free Photocatalysts for PET-RAFT Polymerization under Visible Light and Sunlight.

A key challenge of photoregulated living radical polymerization is developing efficient and robust photocatalysts. Now carbon dots (CDs) have been exploited for the first time as metal-free photocatalysts for visible-light-regulated reversible addition-fragmentation chain-transfer (RAFT) polymerization. Screening of diverse heteroatom-doped CDs suggested that the P- and S-doped CDs were effective photocatalysts for RAFT polymerization under mild visible light following a photoinduced electron transfer (PET) involved oxidative quenching mechanism. PET-RAFT polymerization of various monomers with temporal control, narrow dispersity (D≈1.04), and chain-end fidelity was achieved. Besides, it was demonstrated that the CD-catalyzed PET-RAFT polymerization was effectively performed under natural solar irradiation.

Pinpoint the Positions of Single Nucleotide Polymorphisms by a Nanocluster Dimer.

Single nucleotide polymorphisms (SNPs) are the most fundamental internal causes for many genetic diseases. However, the location information on SNPs in a specific DNA sequence is not well acquired through current SNPs detection methods, except for accurate DNA sequencing. Here we report a fluorescence enhancement phenomenon in the process of two silver nanoclusters (AgNCs) approaching closely to form a nanocluster dimer (NCD). The fluorescence intensity is sensitive to the distance between two AgNCs; therefore, the NCD lights into different fluorescence intensities upon binding SNPs targets with mismatched bases at different positions. Interestingly, the fluorescence intensities of the NCD decrease linearly when the position of single mismatched base moves gradually from the middle point to the end of the target DNA. The NCD is a single probe acting as a universal platform to pinpoint various SNP positions. With this single probe, we cannot only identify the existence of SNPs but also pinpoint the location of a specific single mismatched base in the adjacent positions. This strategy is feasible to detect specific gene point mutations in clinical samples.

Nano Endoscopy with Plasmon-Enhanced Fluorescence for Sensitive Sensing Inside Ultrasmall Volume Samples.

Plasmon-enhanced fluorescence (PEF) generally requires the samples settled on a metal substrate and the effective enhancement distance is less than 100 nm, which limit its application in intracellular sensing. Herein, we report a nano endoscopy with PEF effect for sensing analytes inside the extremely small volume samples. The nano endoscopy was fabricated by assembling single nanoporous gold nanowire (PGNW) on the tip of a tungsten needle. It was accurately manipulated to insert into a micro droplet, and an effective sensing was realized at micrometre scale with submicrometer resolution. By taking lysozyme as a model sensing target, a 23-fold improvement of sensitivity was obtained, comparing with that of smooth gold nanowire (SGNW). These results indicated that the nano endoscopy can realize a high spatial resolution sensing, showing its potential application in intracellular sensing.

Acquiring multiple signals along with the reaction time: improving recognition capability of a multidimensional colorimetric sensor array for sensitive protein detection.

The development of sensitive and cheap sensor arrays for identification of proteins plays an important role in many bioanalytical and clinical investigations. Here, we introduce a multidimensional colorimetric sensor array for the detection of multiple proteins based on acquiring multiple signals along with the reaction time to enhance the discrimination ability. In a single experiment, the unique fingerprint for each protein against the sensor array is generated from a response absorbance signal at three reaction time points (at 10 min, 15 min, and 20 min). Our colorimetric sensing system is able to identify ten proteins not only in aqueous solution at 10 nM but also in human urine at the 50 nM level with an accuracy of 100%. Moreover, the identification of HSA in urine at the nanomolar level within a linear range of 0.05-1.0 µM is achieved. Our sensing array system is sufficiently sensitive for the discrimination of pure HSA, binary mixtures of HSA and Lys at a total concentration of 50 nM in urine. This study indicates that the application of the real-time resolved response signals enables the enhancement of the discrimination ability for protein recognition.

A smartphone readable colorimetric sensing platform for rapid multiple protein detection.

A simple, visible and smartphone readable strategy has been proposed for the sensitive detection and discrimination of multiple proteins. By employing five different concentrations of NaCl salt, AuNP exhibited different aggregation behavior for different proteins because of differential ion strength, leading to diverse color changes. The sensing system could not only discriminate twelve proteins at the concentration of 50 nM in aqueous solution, but it could also discriminate these proteins at 200 nM in the presence of human urine with an accuracy of 100%. More importantly, based on the theory of chromatics, we could directly read out the color value using a smartphone to distinguish twelve proteins, pure Lys and HSA at various concentrations, and the mixture of these two proteins in the presence of human urine with no confusion after a hierarchical clustering analysis (HCA). The inexpensive and convenient colorimetric sensor array using the ubiquitous smartphone for signal readout has great potential for the point-of-care diagnosis without additional devices.

Performance and Mechanism of Uranium Adsorption from Seawater to Poly(dopamine)-Inspired Sorbents.

Developing facile and robust technologies for effective enrichment of uranium from seawater is of great significance for resource sustainability and environmental safety. By exploiting mussel-inspired polydopamine (PDA) chemistry, diverse types of PDA-functionalized sorbents including magnetic nanoparticle (MNP), ordered mesoporous carbon (OMC), and glass fiber carpet (GFC) were synthesized. The PDA functional layers with abundant catechol and amine/imine groups provided an excellent platform for binding to uranium. Due to the distinctive structure of PDA, the sorbents exhibited multistage kinetics which was simultaneously controlled by chemisorption and intralayer diffusion. Applying the diverse PDA-modified sorbents for enrichment of low concentration (parts per billion) uranium in laboratory-prepared solutions and unpurified seawater was fully evaluated under different scenarios: that is, by batch adsorption for MNP and OMC and by selective filtration for GFC. Moreover, high-resolution X-ray photoelectron spectroscopic and extended X-ray absorption fine structure studies were performed for probing the underlying coordination mechanism between PDA and U(VI). The catechol hydroxyls of PDA were identified as the main bidentate ligands to coordinate U(VI) at the equatorial plane. This study assessed the potential of versatile PDA chemistry for development of efficient uranium sorbents and provided new insights into the interaction mechanism between PDA and uranium.

A nanoplasmonic probe as a triple channel colorimetric sensor array for protein discrimination.

The salt-induced aggregation, nanoparticle regrowth and self-assembly behaviors of gold nanoparticles (AuNPs) and DNA conjugates could be changed after interaction with different proteins, generating various color changes and a unique fingerprint pattern for each protein. The triple-channel colorimetric signals have been employed for protein discrimination with the naked eye.