DNAzyme recognition triggered cascade signal amplification for rapid and highly sensitive visual detection of uranyl ions.

This work presents a rapid and highly sensitive colorimetric assay using bifunctional DNA probe decorated agarose microbeads (MBs) coupled with a cascade signal amplification system, including rolling circle amplification (RCA) and the hemin/G-quadruplex-catalyzed colorimetric reaction, for visualized detection of uranyl ions. The DNA probe integrates the UO22+-specific DNAzyme/substrate as the target recognition unit and a DNA primer as the signal conversion unit. The presence of uranyl ions induces the efficient cleavage of the DNA substrates with the catalysis of DNAzyme. Then the conjugated primers are released from MBs, initiating the RCA reaction (the first amplification). The RCA product consists of repetitive G-quadruplexes that can lead to a second amplification by catalyzing the oxidation of ABTS2- with hemin binding, resulting in a coloration that is visible to the naked eye. The whole assay procedure could be finished within 40 min, including recognition of uranyl and DNA cleavage (5 min), the RCA reaction (30 min) and data readout either by eye or using a UV-vis spectrometer (5 min for each sample). In the optimal conditions, concentrations as low as 5 nM uranyl ions could be distinguished by the naked eye. With UV-vis spectrometric measurement, the visible absorbance had a linear relationship with the concentration of uranyl ions with a dynamic range from 1 nM to 50 nM, and a low detection limit of 0.48 nM (i.e. ∼0.12 ppb) was obtained. Excellent selectivity and anti-interference capability in water samples were also certified. This facile visualized assay could be applied in detecting trace-level uranium for on-site environmental analysis.

Cloud point extraction associated with differential pulse voltammetry: preconcentration and determination of trace uranyl in natural water.

A procedure for the electroanalytical determination of uranyl ions pre-concentrated from natural water by cloud point extraction (CPE) is developed in this study. CPE parameters, such as surfactant concentration, extractant concentration, pH and additive concentration were optimized. After CPE, the solution was diluted for electrochemical determination by differential pulse voltammetry (DPV) with a mercury film electrode (Hg-GCE). The current response of uranyl showed a linear relationship with concentration from 10 nmol L-1 to 1 µmol L-1. The hyphenated method combining CPE and DPV achieved a detection limit of uranyl as low as 0.15 nmol L-1. The presence of some foreign ions interfered greatly with the current response of electrochemical detection. Therefore, the hyphenated technique combining CPE and DPV is important because the CPE step provides selectivity against the co-existing metal ions for electrochemical detection. No interference was seen from the representative foreign metal ions in the CPE-DPV method. The developed method was successfully applied for the determination of uranyl ions in natural water. The average recovery using CPE-DPV in real samples varied from 94.4% to 103.2% and the precision was comparable with that of inductively coupled plasma mass spectrometry (ICP-MS), indicating the good accuracy and precision of the method developed. This hyphenated technique could have greater potential applications for the determination of uranyl ions in aqueous environments.

Graphene Oxide Carburization Enhanced Ionization Efficiency for TIMS Isotope Ratio Analysis of Uranium at Trace Level.

Isotope analysis of trace uranium is important in nuclear safeguards and nuclear forensics, which requires the analytical methodologies with high sensitivity, accuracy, and precision. As one of the most powerful techniques in isotopic measurement, thermal ionization mass spectrometry (TIMS) usually suffers from its relatively low sensitivity in ultratrace measurements. To overcome this limitation, we have developed a new filament carburization technique for TIMS, with graphene oxide (GO) as the ionization enhancer. A high and steady ionization efficiency of ∼0.2% for uranium was achieved in single-filament mode, which was 10× the classical double-filament method. With total evaporation (TE) measurements, this method was validated with certified reference materials (CRMs) at the picogram level, and the relative uncertainties for n(235U)/ n(238U) were as low as the ∼1% level. The enhancement mechanism of GO's promoting effect on uranium ionization was attributed to the uniform microstructure facilitating energy transfer and formation of carbides. This approach provides an alternative simple and rapid method for trace uranium isotope analysis with high sensitivity and excellent repeatability. Filament carburization and uranium loading could be accomplished within 10 min. This technique has great advantage in analysis of trace uranium isotope ratios and can be applied in the researches of environmental analysis and nuclear forensics.

Microfluidic dielectrophoresis device for trapping, counting and detecting Shewanella oneidensis at the cell level.

Shewanella oneidensis, a model organism for electrochemical activity bacteria, has been widely studied at the biofilm level. However, to obtain more information regarding this species, it is essential to develop an approach to trap and detect S. oneidensis at the cell level. In this study, we report a rapid and label-free microfluidic platform for trapping, counting and detecting S. oneidensis cells. A microfluidic chip was integrated with a modified dielectrophoresis (DEP) trapping technique and hole arrays of different hole sizes. By numerical simulation and an elaborate electric field distribution design, S. oneidensis cells were successfully trapped and positioned in the hole arrays. Real time fluorescence imaging was also used to observe the trapping process. With the aid of a homemade image program, the trapped bacteria were accurately counted, and the results demonstrated that the amount of bacteria correlated with the hole sizes. As one of the significant applications of the device, Raman identification and detection of countable S. oneidensis cells was accomplished in two kinds of holes. The microfluidic platform provides a quantitative sample preparation and analysis method at the cell level that could be widely applied in the environmental and energy fields.

Significant enhanced uranyl ions extraction efficiency with phosphoramidate-functionalized ionic liquids via synergistic effect of coordination and hydrogen bond.

The influence of the linking group between the phosphoryl and bridging moieties in phosphoryl-containing task-specific ionic liquids (TSILs) on the extraction of uranyl ions was experimentally and theoretically investigated. A novel phosphoramidate-based TSIL with an amine group as the linking moiety resulted in a higher uranyl ion extraction efficiency compared with that of other phosphoryl-based TSILs. A distribution ratio of 4999 ± 51 can be achieved for uranyl ions. The uranyl ions (76.7 ± 1.5%) were stripped from the loaded ionic liquid phase in a single stage using 0.05 M diethylenetriamine pentaacetic acid in a 1.0 M guanidine carbonate solution. The extraction stoichiometry of the uranyl ions was determined by a slope analysis of the extraction data. Furthermore, the fundamental nature of the interaction between the phosphoramidate-based TSIL and uranyl ions was theoretically studied for the first time. The theoretical calculations demonstrated that the synergistic effect of the complexation interaction and H-bond formation between the phosphoramidate-functional ionic liquid and uranyl nitrate led to the higher extraction efficiency. These results provide a basis for rational design, synthesis and potential applications of novel TSILs for uranyl extraction.

A New Method of Fixing High-Aspect-Ratio Microstructures by Gel.

In the microfabrication processes, it is necessary to examine the quality of the structures to ensure the whole process runs smoothly. However, the examination process of pattern defects is interrupted during the fabrication of high-aspect-ratio microstructures. The inevitable pattern defects arise from capillary forces which occur during the liquid drying process. In this paper, a new method that enables us to fix the microstructures with gel to restrict deformations before the rinsed liquid drying process has been proposed. It is effective to avoid the capillary forces by preventing the formation of the liquid level. The process parameters, types of gel, gel time and observation time were discussed and the flatness and thickness of the gel layer could be controlled. A series of high-aspect-ratio microstructures were fixed in good condition by gel.

Microstructure-Enhanced Liquid⁻Liquid Extraction in a Real-Time Fluorescence Detection Microfluidic Chip.

Microfluidic system is widely employed in the detection of environmental contaminants and biological specimens. One of the critical issues which limits the applications of microfluidic chips is the limit of detection of trace specimens. Liquid⁻liquid extraction is of great importance in the preprocessing in microfluidic devices. In this paper, we developed a real-time fluorescence detection microfluidic chip combined with a microstructure-enhanced liquid⁻liquid laminar extraction technique, which concentrated the trace compound and realized real-time monitoring. Auxiliary microstructures integrated in the microfluidic chip were applied to increase the extraction efficiency, which was proved by the FEM (finite element method) simulation as well. A common fluorescence probe, Rhodamine 6G (Rh6g), was used in the experiment to demonstrate the performance of the microfluidic system. It revealed that the liquid⁻liquid laminar extraction combined with auxiliary microstructures of a cross shape was an effective method for enrichment. The efficiency of microstructure-enhanced liquid⁻liquid extraction was increased by 350% compared to the traditional laminar flow extraction.

Ultralong focal length microlens array fabricated based on SU-8 photoresist.

In this paper, a novel method to fabricate ultralong focal length microlens arrays has been proposed. The microlens arrays were fabricated based on surface tension when heating temperature is over a glass transition temperature of SU-8 photoresist. An ultralong focal length was achieved by the large radius of curvature of a photoresist surface. Microlenses of widths from 30 to 210 µm were successfully fabricated. The longest focal length was up to 4.4 mm from the microlens of 210 µm width. The formation mechanism was also studied and validated by simulation based on the finite element method.

Highly sensitive surface-enhanced Raman scattering based on multi-dimensional plasmonic coupling in Au-graphene-Ag hybrids.

We report an efficient surface-enhanced Raman scattering (SERS) substrate by utilizing the multi-dimensional plasmonic coupling in Au nanoparticle (NP)-graphene-Ag NP hybrid structures. An ultrasensitive SERS detection with a limit of down to 10(-13) M has been achieved when the sandwiched hybrid film is fabricated on an Ag substrate.