Reagent Injection Research Articles

K-Channel: A Multifunctional Architecture for Dynamically Reconfigurable Sample Processing in Droplet Microfluidics

By rapidly creating libraries of thousands of unique, miniaturized reactors, droplet microfluidics provides a powerful method for automating high-throughput chemical analysis. In order to engineer in-droplet assays, microfluidic devices must add reagents into droplets, remove fluid from droplets, and perform other necessary operations, each typically provided by a unique, specialized geometry. Unfortunately, modifying device performance or changing operations usually requires re-engineering the device among these specialized geometries, a time-consuming and costly process when optimizing in-droplet assays. To address this challenge in implementing droplet chemistry, we have developed the "K-channel," which couples a cross-channel flow to the segmented droplet flow to enable a range of operations on passing droplets. K-channels perform reagent injection (0-100% of droplet volume), fluid extraction (0-50% of droplet volume), and droplet splitting (1:1-1:5 daughter droplet ratio). Instead of modifying device dimensions or channel configuration, adjusting external conditions, such as applied pressure and electric field, selects the K-channel process and tunes its magnitude. Finally, interfacing a device-embedded magnet allows selective capture of 96% of droplet-encapsulated superparamagnetic beads during 1:1 droplet splitting events at ∼400 Hz. Addition of a second K-channel for injection (after the droplet splitting K-channel) enables integrated washing of magnetic beads within rapidly moving droplets. Ultimately, the K-channel provides an exciting opportunity to perform many useful droplet operations across a range of magnitudes without requiring architectural modifications. Therefore, we envision the K-channel as a versatile, easy to use microfluidic component enabling diverse, in-droplet (bio)chemical manipulations.

Automated sugaring-out liquid-liquid extraction based on flow system coupled with HPLC-UV for the determination of procainamide in urine

A fully automated sugaring-out assisted liquid-liquid extraction procedure was suggested. The procedure was based on the separation of the acetonitrile phase, containing a target analyte from the homogeneous sample solution after injection of sugaring-out reagent (glucose) into a mixing chamber of the flow system. Air bubbling was used to promote the extraction process and phase separation. After the fast phase separation in the mixing chamber, the acetonitrile phase containing the target analyte was transferred to an HPLC-UV system. Under the optimal conditions, the detector response of procainamide was linear in the concentration range of 6×10−7–4×10−5molL−1. The limit of detection, calculated from a blank test based on 3σ, was 2×10−7molL−1. The proposed method was successfully applied for the determination of procainamide in human urine samples and the analytical results agreed fairly well with the results obtained by reference CE method.

Fully chip-embedded automation of a multi-step lab-on-a-chip process using a modularized timer circuit.

For highly-integrated microfluidic systems, an actuation system is necessary to control the flow; however, the bulk of actuation devices including pumps or valves has impeded the broad application of integrated microfluidic systems. Here, we suggest a microfluidic process control method based on built-in microfluidic circuits. The circuit is composed of a fluidic timer circuit and a pneumatic logic circuit. The fluidic timer circuit is a serial connection of modularized timer units, which sequentially pass high pressure to the pneumatic logic circuit. The pneumatic logic circuit is a NOR gate array designed to control the liquid-controlling process. By using the timer circuit as a built-in signal generator, multi-step processes could be done totally inside the microchip without any external controller. The timer circuit uses only two valves per unit, and the number of process steps can be extended without limitation by adding timer units. As a demonstration, an automation chip has been designed for a six-step droplet treatment, which entails 1) loading, 2) separation, 3) reagent injection, 4) incubation, 5) clearing and 6) unloading. Each process was successfully performed for a pre-defined step-time without any external control device.

電界誘起気泡を用いた植物細胞への試薬導入の研究

電界誘起気泡を用いた植物細胞への試薬導入の研究

Micro-mixing measurement by chemical probe in homogeneous and isotropic turbulence

The chemical probe is commonly used to evaluate the performance of chemical reactors. By a localized injection of chemical reagents, it is possible to measure the local micro-mixing, which is readily related to the selectivity of chemical reactions, since mixing at the molecular scale is the limiting factor for a wide range of chemical systems. The raw result of the chemical-probe method is a segregation index that allows comparison of different situations (various locations in the reactor, various Reynolds numbers, various geometries, etc.). Beyond the qualitative assessment provided by this segregation index, it is possible to obtain the intrinsic micro-mixing time by means of a micro-mixing model, describing the temporal evolution of a chemical reaction whose rate is governed by the micro-mixing. Here a key step is the choice of micro-mixing model. Several micro-mixing models available in the literature have been used in some specific cases without evaluating their appropriateness for the problem in hand. The main difficulty in this evaluation is that the real flows often do not fully satisfy the basic model assumptions, in particular the condition of homogeneous and isotropic turbulence (HIT).The present work aims at assessing the validity of a micro-mixing model under “ideal” experimental conditions, i.e. HIT with no mean flow, to avoid the bias due to the flow gradients. The HIT is obtained here by a system of oscillating grids placed in a vessel. The chemical probe measurements carried out by the iodide/iodate reaction system are applied to the two most commonly used phenomenological models in the literature: the IEM (Interaction by Exchange with the Mean) and the EDD (Engulfment, Deformation and Diffusion) models. The benchmark for the micro-mixing models is based on comparison of the local turbulent kinetic energy (TKE) dissipation rate both drawn from the micro-mixing time by the theoretical model of Bałdyga and the reference direct experimental determination by laser Doppler velocimetry measurements. It is shown that the engulfment model EDD seems the more appropriate to analyze the chemical data and provide a quantitative characterization of micro-mixing.

An improved lance design for hot metal de-sulphurisation

Hot metal de-sulphurisation is a dip-lance process involving the pneumatic injection of fine-grained de-sulphurisation reagents into the molten metal. For maximum efficiency the particles must be dispersed in the ladle as widely as possible to increase the total interfacial area which is primarily controlled by the lance design. Seven different lance configurations were modelled and simulated to determine the most efficient design using physical and mathematical modelling approach. A 0.25 scale plexi-glass model of the 100 T hot metal ladle was fabricated for the study. Residence time and mixing time studies were carried out using the electrical conductivity measurement technique through stimulus response of injected saturated salt solution. Mathematical modelling approach using momentum balance was used to simulate fluid flow profile of lance-ladle assembly under operating conditions using computational fluid dynamics package ANSYS-CFX. Based on the studies a new curved port lance has been designed which resulted in uniform and swirling flow profile inside the ladle without rotating the lance. Injection through the new lance increased the residence time of the particles and reduced the dead zones. The new design was fabricated and experimented at de-sulphurisation stations and has resulted in reduced flux consumption and treatment time.

Determination of Organic Partitioning Coefficients in Water-Supercritical CO2 Systems by Simultaneous in Situ UV and Near-Infrared Spectroscopies.

CO2 injected into depleted oil or gas reservoirs for long-term storage has the potential to mobilize organic compounds and distribute them between sediments and reservoir brines. Understanding this process is important when considering health and environmental risks, but little quantitative data currently exists on the partitioning of organics between supercritical CO2 and water. In this work, a high-pressure, in situ measurement capability was developed to assess the distribution of organics between CO2 and water at conditions relevant to deep underground storage of CO2. The apparatus consists of a titanium reactor with quartz windows, near-infrared and UV spectroscopic detectors, and switching valves that facilitate quantitative injection of organic reagents into the pressurized reactor. To demonstrate the utility of the system, partitioning coefficients were determined for benzene in water/supercritical CO2 over the range 35-65 °C and approximately 25-150 bar. Density changes in the CO2 phase with increasing pressure were shown to have dramatic impacts on benzene's partitioning behavior. Our partitioning coefficients were approximately 5-15 times lower than values previously determined by ex situ techniques that are prone to sampling losses. The in situ methodology reported here could be applied to quantify the distribution behavior of a wide range of organic compounds that may be present in geologic CO2 storage scenarios.

Sealing Method of Thermoplastics Mediated By Surface Chemical Modification

Thermoplastics are optically transparent, lightweight, mechanically hard, and highly cost-effective material, making them suitable for fabricating integrated physical, chemical, or biological sensors. Thermoplastics are easily moldable mainly via stamping or engraving method. Stamping utilizes hard material having positive structures as a stamp to print patterns repeatedly on a substrate one example of which is imprint molding, while engraving carves the pattern using sharp object one example of which is a computer numerical control (CNC) micromilling. After pattern formation, thermoplastics need to be sealed. Many thermoplastics adopt sealing method known as "thermal bonding" which is realized by applying high pressure and temperature, closer to the glass transition temperature of the thermoplastic used. However, due to high heat and pressure applied, patterns tend to deform or collapse, sacrificing surface morphology. Moreover, thermal bonding is restricted to sealing two homogeneous substrates. For this reason, alternative sealing methods have been reported such as solvent-assisted bonding, adhesive layer bonding, and microwave welding, to name a few, to obtain high fidelity in pattern morphology and realize sealing between heterogeneous substrates. In this study, the innate properties of thermoplastics were employed to graft chemical functionalities to tune the wettability of original thermoplastics. The core idea is to make surface flexible to become highly wetting after surface oxidation of thermoplastics. In general, thermoplastics are not easily hydroxylated by means of plasma treatment, UV exposure, or UV/ozone treatment. However, it was reported that carbonate or carbonyl backbone can undergo aminolysis, which opens a possibility that chemical functionalities can be grafted onto thermoplastics without having to go through hydroxylation. In specific, addition of amine functionality causes scission of the carbonate or carbonyl backbone by the donation of the lone pair of electrons to the carbonyl group, opening the double bond between carbon and oxygen. This results in the formation of robust urethane linkage between amine-bearing chemicals and a thermoplastic which contains carbonate or carbonyl backbone as its component. Among many choices of chemicals, silane coupling agents were widely adopted. Silane coupling agents are synthetic hybrid inorganic-organic compounds widely used for bridging silicon with non-silicon compounds. In this study, silane coupling agent bearing amine functional group as its organic moiety is used to graft it onto thermoplastics bearing carbonate or carbonyl backbone. After the grafting, the dangling inorganic moiety at the terminal surface of the thermoplastic, in this case alkoxysilane, makes the substrate feasible for surface hydroxylation, which is not readily realized with plasma treatment, UV exposure, or UV/ozone treatment. Two hydroxylated surfaces then form robust siloxane bond (Si–O–Si) at the interface, facilitating thermoplastic sealing. After realizing the sealing, the chemically modified surfaces were further tuned freely into hydrophilic or hydrophobic by subsequent reaction with silane coupling agents bearing versatile organic moieties. In particular, after thermoplastic sealing, microchannel structure engraved on thermoplastic was selectively modified into hydrophobic to realize sequential injection of multiple reagents for solid-phase-based nucleic acid purification, without the need for precise valve control. Besides realizing sealing between two hard thermoplastics, we extend the concept for sealing thermoplastics with another widely adopted material, poly(dimethylsiloxane) (PDMS). PDMS is a transparent elastomer, widely utilized for the fabrication of microfluidic devices owing to high transparency, simple replica molding, easy surface oxidation, low cost, and low material toxicity. Sealing between hard thermoplastic and soft PDMS poses numerous advantages particularly offering construction of microvalves or micropumps where flexible components become necessary. Besides, these heterogeneous assemblies can provide desirable environment for performing cell-based research because PDMS is gas permeable. It is experimentally proven that heating the contacted substrates after surface oxidation of both PDMS and thermoplastics does not realize sealing. In this study, simple and room temperature processes for realizing sealing between PDMS and thermoplastics were introduced employing variety of silane coupling agents. First, we introduce the formation of amine-epoxy bond employing two silane coupling agents. Later, we simplify the process by adopting only one silane coupling agent in two different ways. One method is mediated by the formation of urethane linkage followed by robust siloxane bond formation, and another method is mediated by instantaneous chemical reaction between nucleophiles and electrophiles followed by siloxane bond formation. Permanent sealing was readily realized at room temperature condition on a large area homogeneously, making these sealing method highly feasible particularly when thermally fragile microstructures or heat-sensitive biomolecules must be integrated onto or incorporated into the PDMS-thermoplastic microdevice prior to sealing.

Efficacy of vitrectomy and inner limiting membrane peeling in age-related macular degeneration resistant to anti-vascular endothelial growth factor therapy, with vitreomacular traction or epiretinal membrane.

We assessed the efficacy of vitrectomy and inner limiting membrane (ILM) peeling, followed by anti-vascular endothelial growth factor (VEGF) therapy, anti-VEGF-resistant age-related macular degeneration (AMD) due to vitreomacular traction (VMT) or epiretinal membrane (ERM). We identified six patients with anti-VEGF-resistant AMD due to VMT or ERM amongst a total of 588 patients with AMD (821 eyes) referred to Okayama University Hospital between February 2012 and May 2014. These patients underwent vitrectomy to release the VMT (4 cases) or remove the ERM (2 cases), along with ILM peeling. The regimen used for intravitreal injections of anti-VEGF reagents after surgery was based on the severity of exudative changes in each patient. Preoperative and postoperative best-corrected visual acuity (BCVA) and central retinal thickness (CRT) measurements were compared. After vitrectomy and ILM peeling, all six patients responded to anti-VEGF therapy, which was then able to maintain dry retinas. Mean BCVA did not improve significantly (0.49 ± 0.28 before vs. 0.43 ± 0.38 after surgery, P = 0.538). However, mean CR was significantly decreased after surgery, from 423 ± 83.5μm to 257 ± 75.8μm (P = 0.0078). Vitrectomy and ILM peeling followed by anti-VEGF therapy may be a useful therapeutic option for anti-VEGF-resistant AMD with VMT or ERM.

A one-step strategy for ultra-fast and low-cost mass production of plastic membrane microfluidic chips.

An ultra-fast, extremely cost-effective, and environmentally friendly method was developed for fabricating flexible microfluidic chips with plastic membranes. With this method, we could fabricate plastic microfluidic chips rapidly (within 12 seconds per piece) at an extremely low cost (less than $0.02 per piece). We used a heated perfluoropolymer perfluoroalkoxy (often called Teflon PFA) solid stamp to press a pile of two pieces of plastic membranes, low density polyethylene (LDPE) and polyethylene terephthalate (PET) coated with an ethylene-vinyl acetate copolymer (EVA). During the short period of contact with the heated PFA stamp, the pressed area of the membranes permanently bonded, while the LDPE membrane spontaneously rose up at the area not pressed, forming microchannels automatically. These two regions were clearly distinguishable even at the micrometer scale so we were able to fabricate microchannels with widths down to 50 microns. This method combines the two steps in the conventional strategy for microchannel fabrication, generating microchannels and sealing channels, into a single step. The production is a green process without using any solvent or generating any waste. Also, the chips showed good resistance against the absorption of Rhodamine 6G, oligonucleotides, and green fluorescent protein (GFP). We demonstrated some typical microfluidic manipulations with the flexible plastic membrane chips, including droplet formation, on-chip capillary electrophoresis, and peristaltic pumping for quantitative injection of samples and reagents. In addition, we demonstrated convenient on-chip detection of lead ions in water samples by a peristaltic-pumping design, as an example of the application of the plastic membrane chips in a resource-limited environment. Due to the high speed and low cost of the fabrication process, this single-step method will facilitate the mass production of microfluidic chips and commercialization of microfluidic technologies.

Novel technique for visualizing primordial germ cells in sturgeons (Acipenser ruthenus, A. gueldenstaedtii, A. baerii, and Huso huso).

Primordial germ cells (PGCs) are the origin of all germ cells in developing embryos. In the sturgeon embryo, PGCs develop from the vegetal hemisphere, which mainly acts as an extraembryonic source of nutrition. Current methods for studying sturgeon PGCs require either killing the fish or using costly and time-consuming histological procedures. Here, we demonstrate that visualization of sterlet (Acipenser ruthenus>) PGCs in vivo is feasible by simply labeling the vegetal hemisphere with fluorescein isothiocyanate (FITC)-dextran. We injected FITC-dextrans, with molecular weights varying between 10 000 and 2 000 000, into the vegetal pole of 1- to 4-cell stage embryos. At the neurula to tail-bud developmental stages, FITC-positive PGC-like cells appeared ventrally around the developing tail bud in the experimental group that received a high-molecular-weight FITC-dextran. The highest average number of FITC-positive PGC-like cells was observed in embryos injected with FITC-dextran having a molecular weight of 500 000 (FD-500). The pattern of migration of the labeled cells was identical to that of PGCs, clearly indicating that the FITC-positive PGC-like cells were PGCs. Labeled vegetal cells, except for the PGCs, were digested and excreted before the embryos starting feeding. FITC-labeled PGCs were observed in the developing gonads of fish for at least 3 mo after injection. We also found that FD-500 could be used to visualize PGCs in other sturgeon species. To the best of our knowledge, this report is the first to demonstrate in any animal species that PGCs can be visualized in vivo for a long period by the injection of a simple reagent.

장수풍뎅이 유충의 간보호 효능 및 항암활성

Beetle larvae have been used as a traditional medicine to treat various human liver diseases. To prove the liver protective function of Allomyrina dichotoma larvae (ADL), we induced liver damage by the intraperitoneal injection of a hepatotoxic reagent, diethylnitrosamine (DEN), to C3H/HeN male mice and orally administered freeze-dried ADL powder. ADL powder lessened DEN-induced hepatotoxicity considering the reduced signs of acute and chronic hepatotoxicities, such as the ALP level in the blood serum, TUNEL-positive hepatocytes, ductural reactions, steatotic hepatocytes, and collagen deposition of the Masson’s trichrome staining. In addition to hepatoprotection, the anti-cancer activity of ADL has been examined. The ADL powder was extracted with ethanol and then fractionated with hexane, ethyl acetate, and water by a solvent partition technique. The ethyl acetate fraction showed cytotoxicity to various cancer cells through induction of apoptosis and necrosis, as well as the perturbed metabolism of the cancer cell to trigger autophagy. Collectively, ADL contains bioactive substances that can protect hepatocytes from toxic chemicals and trigger cell death in cancer cells. Thus, further purification and analyses of ADL fractions could lead to the identification of novel bioactive compounds.

An Investigation of the Pressure Pulsing Reagent Delivery Approach

Pressure pulsing technology is an innovative method that has been developed with the aim of overcoming preferred flow paths associated with remediation techniques that rely on the injection of reagents. Numerical and field experiments were conducted to assess how pressure pulsing affects groundwater flow and solute transport during reagent injection. A series of field experiments were performed at two field sites where a monitoring network designed to capture the breakthrough of solutes delivered from an injection well was installed. Pressure pulsing and conventional injection methods were used at each site. One site was comprised of fine sand with low heterogeneity, while the other was moderately heterogeneous with discrete layers varying from fine sand to silt. The data suggest that breakthrough was more uniform for the pressure pulsing injections; however, this difference was minor and complicated by sorption of some of the tracers employed. The groundwater flow and solute transport modeling exercise simulated the rapid boundary pressure modulation that occurs in association with pressure pulsing. Two-dimensional (2D) simulations revealed that repeated sudden onset of injection cessation produces brief periods of gradient reversal and the development of a mixing zone near the injection well. The spatial extents of this mixing zone were found to be highly dependent upon the hydraulic diffusivity of the medium, with medium heterogeneity and pulsing frequency playing secondary roles. Three-dimensional (3D) numerical simulations were used to benchmark the observations from one of the field sites. The results from the modeling effort showed that solute breakthrough from a pressure pulsing injection is more dispersed relative to a conventional injection as a result of the mixing zone phenomenon; however, we were unable to directly observe this mixing zone using the instrumentation deployed at the two field sites.

Localization of Core Planar Cell Polarity Proteins, PRICKLEs, in Ameloblasts of Rat Incisors: Possible Regulation of Enamel Rod Decussation.

To confirm the possible involvement of planar cell polarity proteins in odontogenesis, one group of core proteins, PRICKLE1, PRICKLE2, PRICKLE3, and PRICKLE4, was examined in enamel epithelial cells and ameloblasts by immunofluorescence microscopy. PRICKLE1 and PRICKLE2 showed similar localization in the proliferation and secretory zones of the incisor. Immunoreactive dots and short rods in ameloblasts and stratum intermedium cells were evident in the proliferation to differentiation zone, but in the secretion zone, cytoplasmic dots decreased and the distal terminal web was positive for PRICKLE1 and PRICKLE2. PRICKLE3 and PRICKLE4 showed cytoplasmic labeling in ameloblasts and other enamel epithelial cells. Double labeling of PRICKLE2 with VANGL1, which is another planar cell polarity protein, showed partial co-localization. To examine the transport route of PRICKLE proteins, PRICKLE1 localization was examined after injection of a microtubule-disrupting reagent, colchicine, and was compared with CX43, which is a membrane protein transported as vesicles via microtubules. The results confirmed the retention of immunoreactive dots for PRICKLE1 in the cytoplasm of secretory ameloblasts of colchicine-injected animals, but fewer dots were observed in control animals. These results suggest that PRICKLE1 and PRICKLE2 are transported as vesicles to the junctional area, and are involved in pattern formation of distal junctional complexes and terminal webs of ameloblasts, further implying a role in the formed enamel rod arrangement.

A CFD-based evaluation of selective non-catalytic reduction of nitric oxide in iron ore grate-kiln plants

The overall goal of this study is to explore the function of selective non–catalytic reduction of nitric oxide (NO) in iron ore grate–kiln plants. Computational fluid dynamics is used to model the flow and the injection of urea and cyanuric acid reagents. Temperature, residence time and inlet NO content are varied, and the effects on the reduction of NO are studied. The simulations show that the use of urea results in a higher reduction of NO within the temperature window investigated as compared to cyanuric acid; however, urea cannot be used for NO reduction over the entire range of applicable temperatures. Cyanuric acid is usable within the entire temperature range for high NO content (i.e., 300 ppm) in the flue gas, but it is not effective for low NO concentration (i.e., 150 ppm). Moreover, the simulations indicate that temperature has a larger influence on the NO reduction than the residence time.

Structure and Size-selective Permeability of the Synovial Membrane of the Temporomandibular Joint of the Mouse Measured by MR Imaging at 7T.

We analyzed the anatomical structure of the temporomandibular joint (TMJ) and molecular weight dependency of synovial membrane permeability in mice using 7-tesla magnetic resonance (MR) imaging. We obtained 3-dimensional (3D) T1-weighted gradient echo (3D-T1W) and 3D T2-weighted rapid acquisition with relaxation enhancement (3D-T2W RARE) MR images of the TMJ of male C57BL6 mice with voxel resolution of 65 µm. Two-dimensional (2D) T1w images were measured every 45 s before and after bolus intravenous (IV) injection of contrast reagents: gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA; 0.5 kDa); oligomer-based contrast agent (CH3-DTPA-Gd; 2.1 kDa); gadolinium-labeled polylysine (Gd-polylysine; 10 kDa); and gadolinium-labeled albumin (Gd-albumin; 74 kDa). T1W images depicted the temporal bone and mandibular condyle as regions with lower signal intensity and the disc as a region of intermediate intensity. In the Gd-DTPA-enhanced T1W and T2W images, the articular disc could be identified as a region with lower signal intensity than that of the upper and lower joint cavities. After IV injection of Gd-DTPA or CH3-DTPA-Gd, the signal intensity of the joint cavities increased within 10 min, but this increase was not shown with Gd-polylysine and Gd-albumin. The structural findings obtained by MR imaging agreed with those obtained by hematoxylin-eosin staining under light microscopy. Contrast-enhanced MR imaging suggested that smaller (<2.1 kDa) but not larger (>10 kDa) molecules can permeate the synovial membrane. Our results suggest the utility of MR imaging for analyzing the structure of the TMJ as well as permeability of the synovial membrane.

Ferri-Magnetic Sorbents of Heavy Metals and Radionuclides on Base of Humates, Isolated from Oxidized Coals

The results of synthesis and researches of hybrid gumic-magnetic composites are presented in the article. The possibility of regulation of quantitative speciation of composites (containing of Fe) is established at the variation of proportions Fe (II), Fe (III)/HA and the way of reagents injection in a reaction mixture. The possibility of designing of sorbents on the basis of humic acids and chemically connected particles of iron oxides as magnetic-active components for fixation and extraction of heavy metals ions and radionuclides from natural objects by means of magnetic separation is shown. The adsorption degree stands at 95% in an optimal mode.

Artificial permeable redox barriers for purification of soil and ground water: A review of publications

Artificial permeable barriers are used for purification of soil- and groundwater from organic (Cl-containing hydrocarbons and Cl-pesticides) and inorganic (heavy metals and nitrates) pollutants. Most of the created redox barriers are based on introducing electron donors—both inorganic (most often, Fe0 and Fe(II)) and organic. By their construction type, they are subdivided into one-time filled barriers arranged in trenches and multiple-time filled barriers that use boreholes for reagent injection. Fe0 barriers operate not only as reducers but also as sources of newly formed Fe(III) colloids adsorbing elements with permanent and variable valence. Iron sulfides are also used as a reagent, while Fe(II) and S(-I, -II) serve as reducers. Biochemical redox barriers are also applied, in which the activity of natural anaerobic metal-reducing bacteria is stimulated by adding an available organic substance.

Electrical detection of cellular penetration during microinjection with carbon nanopipettes

The carbon nanopipette (CNP) is comprised of a pulled-glass pipette terminating with a nanoscale (tens to hundreds of nm) diameter carbon pipe. The entire inner glass surface of the CNP is coated with a carbon film, providing an electrically conductive path from the carbon tip to the distal, macroscopic end of the pipette. The CNP can double as a nanoelectrode, enabling electrical measurements through its carbon lining, and as a nanoinjector, facilitating reagent injection through its hollow bore. With the aid of a lock-in amplifier, we measured, in real time and with millisecond resolution, variations in impedance and interfacial capacitance as the CNP penetrated into the cytoplasm and nucleus of adherent human osteosarcoma (U20S) cells during microinjection. The capacitance change associated with nucleus penetration was, on average, 1.5 times greater than the one associated with cell membrane penetration. The experimental data was compared and favorably agreed with theoretical predictions based on a simple electrical network model. As a proof of concept, the cytoplasm and nucleus were transfected with fluorescent tRNA, enabling real-time monitoring of tRNA trafficking across the nuclear membrane. The CNP provides a robust and reliable means to detect cell and nucleus penetration, and trigger injection, thereby enabling the automation of cell injection.

A modified method for on-line determination of trace ammonium in seawater with a long-path liquid waveguide capillary cell and spectrophotometric detection

An automated colorimetric method for the on-line determination of trace ammonium in seawater was established using a flow injection technique coupled with a 2.5-m liquid waveguide capillary cell. Using low ammonium seawater as a carrier, a sample was injected into the carrier and mixed with reagents to form indophenol blue dye, which was monitored at a wavelength of 690nm. Different strategies of reagent injection were investigated to obtain a lower reagent blank and a higher detection sensitivity. Experimental parameters were optimized using a univariate experimental design, and the matrix effect of seawater was preliminarily investigated. The proposed method had high sensitivity with a detection limit of 3.6nmol·L−1. The linearity was 10 to 500nmol·L−1 and the upper limit could be extended to 30μmol·L−1 by choosing a less sensitive detection wavelength or lower reaction temperature. The recoveries were between 95.0 and 104.3% and the relative standard deviation was 4.4% (n=7) for an aged seawater sample spiked with 50nmol·L−1 ammonium. The sample throughput was 22h−1. The analytical results obtained with the proposed method showed good agreement with those using reference fluorescence methods. Compared with the normal indophenol blue (off-line) method, the proposed method was superior due to its lower reagent consumption, greater convenience, higher sample throughput, wider linear range (10nmol·L−1 to 30μmol·L−1), as well as higher sensitivity. The method was applied in-field in Wuyuan Bay for 24h on-line monitoring of ammonium concentrations in the surface seawater. In addition, it was also used to analyze surface seawater samples collected from the South China Sea for the study of ammonium distribution.