Exploiting the native inspiratory ability of a mass spectrometer to improve analysis efficiency

In this study, a new approach to perform self-aspirating sampling in mass spectrometry (MS) analysis was developed by using the native inspiratory ability of a mass spectrometer. Specifically, the inspiratory channel and sampling inlet of the MS instrument were integrated into a single pathway through a sealed ionization chamber to facilitate analyte delivery and improve sample utilization. Based on this approach, combined with structural simplification and optimization, a versatile electrospray ionization (ESI) source has been constructed and characterized using different mass spectrometers. In addition to the self-aspirating ability, this source configuration can provide sub-ambient pressure (SAP) conditions for ionization, which were conducive to suppressing the background ions generated from some air-involved reactions. Moreover, it can also be used directly for electrospray-driven extraction ionization. With the SAP-ESI source, a conventional mass spectrometer enables rapid analysis of both volatiles and solutions via secondary electrospray ionization and coaxial electrospray ionization, respectively. As the compact gas pathway of the source will promote the efficient transfer and ionization of the sampled substances, the total consumption of the analyte for each analysis can be reduced to subnanogram level and a subppbv limit detection is achieved. Other demonstrated features such as the versatility, easy operation as well as simple assembly will likely contribute to the prevalence of the proposed sampling and ionization strategy.

In this study, a new approach to perform self-aspirating sampling in mass spectrometry (MS) analysis was developed by using the native inspiratory ability of a mass spectrometer.     

Investigation of the electrochemical oxidation of 2,3′-bisindolylmethanes in positive-ion electrospray ionization mass spectrometry

Electrochemical reactions in electrospray may affect the electrospray ionization mass spectrometry (ESI-MS) detection of the analytes. During ESI-MS analysis of 2,3′-bisindolylmethanes in the positive-ion mode, when methanol or acetonitrile was used as the solvent, electrochemical oxidation products as the dehydro and radical cations were observed. Lower sample introduction rates tended to result in a higher oxidation ratio of 2,3′-bisindolylmethanes. The ESI-MS experiments of 2,3′-bisindolylmethanes in different acetonitrile/methanol solvent mixtures indicated that abundant H⁺, Na⁺ or K⁺ would facilitate the adduct formation process, and otherwise electrochemical oxidation dominated the ionization process. Additionally, when dichloromethane was used as the solvent, [M − 3H]⁺, [M − 2H]⁺˙ and [M − 3H + O]⁺ ions are the predominant ions, and the experimental results revealed that the dehydrogenation and oxidative dehydrogenation reactions of 2,3′-bisindolylmethanes in dichloromethane are electrochemical reactions.

The electrochemical oxidation reactions of 2,3′-bisindolylmethanes were affected by the solvent in the positive-ion electrospray ionization mass spectrometry (ESI-MS).     

Microfluidic gradient device for simultaneously preparing four distinct types of microparticles

Preparing monodisperse, reproducible and functionally sophisticated microparticles is challenging but important for biomedical applications. Droplet microfluidics is a microparticle generation method that can precisely control the geometry and composition of microparticles. Droplet microfluidics generally produces only one type of microparticle at a time. Here, we report a simple and controllable method to simultaneously prepare four distinct types of microparticles by combining droplet generation with a gradient generator. The method can be more widely applied and with higher productivity than other microparticle generation methods due to the integration of dispersed phases which paves the way for the application to regenerative medicine. Different sizes, heterogenous and anisotropic microparticles are generated by manipulating the poly(lactic-co-glycolic acid) concentration gradient, the poly(ε-caprolactone)/poly(lactic-co-glycolic acid) ratio gradient, and the dimethyl carbonate/dichloromethane ratio gradient. This straightforward preparation of microparticles will promote their application in drug delivery agents, identifiers for biological assays, microsensors and tissue engineering.

Preparing monodisperse, reproducible and functionally sophisticated microparticles is challenging but important for biomedical applications.     

Mechanical properties of an interpenetrating network poly(vinyl alcohol)/alginate hydrogel with hierarchical fibrous structures

Bioinspired hierarchical fibrous structures were constructed in an interpenetrating poly(vinyl alcohol, PVA)/alginate hydrogel network to improve its mechanical properties. The interpenetrating hydrogel network with hierarchical fibrous structures was prepared by combining the confined drying method and freeze–thaw method. First, Ca²⁺ cross-linked alginate formed a nano–micro hierarchical fibrous structure via the confined drying method. Then, PVA that was uniformly distributed among the Ca²⁺–alginate chains was cross-linked by hydrogen bonding via the freeze–thaw method, further dividing the hierarchical fibers into finer fibers. The results of a tensile test demonstrated that both the tensile stress and fracture energy improved by more than double after the introduction of 2 wt% PVA, achieving a combination of high strength (∼12.9 MPa), high toughness (∼13.2 MJ m⁻³) and large strain (∼161.4%). Cyclic tensile tests showed that a hysteresis loop existed on the loading–unloading curves of the hydrogel along the fibrous directions, and a good self-recovery property emerged after resting for a period of time. The hydrogel with hierarchical fibrous structures constructed by alginate and PVA can be employed in biomedical applications in the future.

The mechanical properties both along and perpendicular to the fibrous directions were improved more than double after the construction of hierarchically arranged fibrous structures in the interpenetrating network PVA/alginate hydrogel.     

One-pot analysis of enantiomeric excess of free amino acids by electrospray ionization mass spectrometry

An electrospray ionization mass spectrometric method for the simultaneous analysis of the enantiomeric excess of free amino acids, without chromatographic separation, was demonstrated using a quasi-racemic mixture of deuterium-labelled and unlabelled chiral copper(ii) complexes. This convenient method enables the simultaneous high-sensitivity determination of the enantiomeric excess of 12 amino acids.

A mass spectrometric method for the simultaneous analysis of the enantiomeric excess of free amino acids, without chromatographic separation, was demonstrated using a quasi-racemic mixture of deuterium-labelled and unlabelled chiral Cu(ii) complexes.     

Synthesis and the growth mechanism of ultrafine silver nanowires by using 5-chloro-2-thienylmagnesium bromide as the additive

Synthesis of silver nanowires (Ag NWs) has been studied for decades. However, Ag NWs with diameters below 20 nm synthesised by simple and robust approaches are still rarely reported. In this work, Ag NWs with an average diameter of ∼15 nm and an aspect ratio of over 1000 have been prepared by using a Grignard reagent 5-chloro-2-thienylmagnesium bromide as an assistant additive. In particular, the presence of 5-chloro-2-thienylmagnesium bromide is proven to be beneficial for the in situ formation of smaller AgBr and AgCl particles step by step in comparison with traditional inorganic halide ions, and then promote the final growth of ultrafine Ag NWs.

The presence of 5-chloro-2-thienylmagnesium bromide is beneficial for the in situ formation of smaller AgBr and AgCl particles step by step and the final growth of ultrafine Ag NWs with an average diameter of ∼15 nm and an aspect ratio of over 1000.     

Biomimetic enzyme barrier for preventing intestine-derived LPS induced diseases

Biomimetic enzyme barrier (BEB) encapsulated microcapsules with alginate shells were in situ fabricated with a microfluidic electrospray approach for preventing intestine-derived LPS induced diseases. As the alginate shells could protect the contents in gastric juice and release them in the intestine, the inner BEB could form a consecutive immune barrier on the surface of the intestine during the release. Through combining BEB with alkaline phosphatase, the immune barrier could degrade and prevent the permeation of lipopolysaccharide, which enhanced the intestinal barrier function. Thus, the BEB microcapsules were imparted with outstanding ability in preventing intestine-derived LPS induced diseases. Based on an in vivo study, we demonstrated that this BEB microcapsule could effectively protect organ function, restore intestinal barrier integrity, prevent the permeation of LPS and alleviate inflammation. Therefore, the generated microcapsules have potential for clinical applications.

Biomimetic enzyme barrier (BEB) encapsulated microcapsules could prevent intestine-derived LPS induced diseases.     

Current perspectives on supercharging reagents in electrospray ionization mass spectrometry

In electrospray ionization mass spectrometry (ESI-MS), analytes are introduced into the mass spectrometer in typically aqueous-organic solvent mixtures, including pH modifiers. One mechanism for improving the signal intensity and simultaneously increasing the generation of higher charge-state ions is the inclusion of small amounts (approx. <0.5% v/v mobile phase solution) of charge-inducing or supercharging reagents, such as m-nitrobenzyl alcohol, o-nitrobenzyl alcohol, m-nitrobenzonitrile, m-(trifluoromethyl)-benzyl alcohol and sulfolane. We explore the direct and indirect (colligative properties) that have been proposed as responsible for their modes of action during ESI. Of the many theorized mechanisms of ESI, we re-visit the three most popular and highlight how they are impacted by supercharging observations on small ions to large molecules including proteins. We then provide a comprehensive list of 34 supercharging reagents that have been demonstrated in ESI experiments. We include an additional 19 potential candidate isomers as supercharging reagents and comment on their broad physico-chemical properties. It is becoming increasingly obvious that advances in technology and improved ion source design, analyzers e.g. the use of ion mobility, ion trap, circular dichroism (CD) spectroscopy, together with computer modeling are increasing the knowledge base and, together with the untested isomers and yet-to-be unearthed ones, offer opportunities for further research and application in other areas of polymer research.

A simple illustration of the positive electrospray ionization (ESI) environment.     

Complex calcium carbonate/polymer microparticles as carriers for aminoglycoside antibiotics

Composite microparticles of CaCO₃ and two pectin samples (which differ by the functional group ratio) or corresponding nonstoichiometric polyelectrolyte complexes with different molar ratios (0.5, 0.9 and 1.2) are obtained, characterized and tested for loading and release of streptomycin and kanamycin sulphate. The synthesized carriers were characterized before and after drug loading in terms of morphology (by SEM using secondary electron and energy selective backscattered electron detectors), porosity (by water sorption isotherms) and elemental composition (by elemental mapping using energy dispersive X-ray and FTIR spectroscopy). The kinetics of the release mechanism from the microparticles was investigated using Higuchi and Korsmeyer–Peppas mathematical models.

Self-assembled microparticles of CaCO₃ and pectin/polyelectrolyte complexes as carriers for streptomycin and kanamycin sulfates by transformation into calcium phosphates.     

Synergetic treatment of dye contaminated wastewater using microparticles functionalized with carbon nanotubes/titanium dioxide nanocomposites

The highly efficient treatment of azo dye contaminated wastewater from the textile industry is an important but challenging problem. Herein, polydimethylsiloxane (PDMS) microparticles, incorporating multiple-walled carbon nanotubes/titanium dioxide (MWCNTs/TiO₂) nanocomposites, were successfully synthesized to treat wastewater containing Rhodamine B (RhB) dyes in a synergetic approach, by combining sorption and photocatalytic degradation. The surfactant wrapping sol–gel method was applied to synthesize MWCNTs/TiO₂ nanocomposites with TiO₂ nanoparticles evenly distributed on the surface of the MWCNTs. The PDMS microparticles were fabricated with an oil-in-water (O/W) single emulsion template, using needle-based microfluidic devices. MWCNTs/TiO₂ nanocomposites (at a weight ratio of 1%, and 2%, respectively) were mixed with the PDMS precursor as the dispersed phase, and an aqueous solution of polyvinyl alcohol (PVA) was used as the continuous phase. Highly monodispersed microparticles, with average diameters of 692.7 μm (Coefficient of Variation, CV = 0.74%) and 678.3 μm (CV = 1.04%), were formed at an applied flow rate of the dispersed and continuous phase of 30 and 200 μL min⁻¹, respectively. The fabricated hybrid microparticles were employed for the treatment of RhB, involving a dark equilibrium for 5 hours and UV irradiation for 3 hours. The experimental conditions of applied PDMS type, mass loading amount, treatment duration, photodegradation kinetics, initial concentration of pollutants and environmental pH values were investigated in this work. The PDMS microparticles with 2 wt% MWCNTs/TiO₂ nanocomposites can exhibit a removal efficiency of 85%. Remarkably, an efficiency of 70% can be retained after the microparticles have been recycled and reused for 3 cycles. The PDMS–MWCNTs/TiO₂ microparticles possess a superior performance over conventional treatment approaches for dye contaminated wastewater, especially in recyclability and the prevention of secondary pollution. This work provides a feasible and eco-friendly route for developing an efficient and low-cost microfluidic method for treating complicated water environmental systems.

PDMS–MWCNTs/TiO₂ microparticles made by microfluidics can achieve 85% removal efficiency of RhB pollutant in wastewater via synergetic treatment.     

Microfluidic preparation,shrinkage, and surface modification of monodispersed alginate microbeads for 3D cell culture

Functionalized alginate microbeads (MB) have been widely used for three-dimensional (3D) culture of cells and creating biomimetic tissue models. However, conventional methods for preparing these MB suffer from poor polydispersity, due to coalescence of droplets during the gelation process and post-aggregation. It remains an immense challenge to prepare alginate MB with narrow size distribution and uniform shape, especially when their diameters are similar to the size of cells. In this work, we developed a simple method to produce monodispersed, cell-size alginate MB through microfluidic emulsification, followed by a controlled shrinkage process and gelation in mineral oil with low concentration of calcium ion (Ca²⁺). During the gelation process caused by the diffusion of Ca²⁺ from the oil to water phase, a large amount of satellite droplets with sub-micrometer sizes was formed at the water/oil interface. As a result, each original droplet was transformed to one shrunken-MB with much smaller size and numerous submicron-size satellites. To explore the feasibility of the shrunken-MB for culturing with cells, we have successfully modified a variety of polymer nanofilms on MB surfaces using a layer-by-layer assembly approach. Finally, the nanofilm-modified MB was applied to a 3D culture of GFP-expressing fibroblast cells and demonstrated good biocompatibility.

Cell-size alginate microbeads for 3D cell culture were prepared by microfluidic emulsification and controlled shrinkage, followed by nanofilm modification.     

Synthesis and properties of porous CLEAs lipase by the calcium carbonate template method and its application in biodiesel production

In this work, porous cross-linked enzyme aggregates (p-CLEAs) were synthesized by the in situ co-precipitation method using CaCO₃ microparticles as templates. The preparation procedure involved the immobilization of crude lipase as CLEAs via precipitation with ammonium sulfate and entrapping these lipase molecules into the CaCO₃ templates, followed by DTT (dithiothreitol)-induced assembly of lipase molecules to form lipase microparticles (lipase molecules were assembled into microparticles internally using disulfide bonds within the lipase molecules as the molecular linkers and stimulated by dithiothreitol); finally, the removal of CaCO₃ templates was performed by EDTA to form pores in CLEAs. The scanning electron microscopy analysis of p-CLEAs showed a porous structure. p-CLEAs showed obvious improvement in thermal stability (after incubation at 65 °C, p-CLEAs lipase retained 86% relative activity, while free lipase retained only 33.67%) and pH stability (p-CLEAs relative activity was over 90% while for free lipase, the relative activity ranged from 72% to 89% from pH 6 to 9) than free lipase and could hold relatively high activity retention without activity loss at 4 °C for more than six months. The application of p-CLEAs in producing biodiesel showed a higher degree of conversion. The conversion of fatty acid methyl ester (FAME) was 89.7%; this value was higher by approximately 7.4% compared to that of the conventional CLEAs under the optimized conditions of a methanol–oil molar ratio of 6 : 1, with a p-CLEAs lipase dose of 20% and water content of 3% at 45 °C for 24 h. The FAME conversion remained greater than 70% even after reusing the p-CLEAs lipase for 8 reactions. The results demonstrated that the p-CLEAs lipase is suitable for applications in the preparation of biodiesel.

Porous cross-linked enzyme aggregates (p-CLEAs) were synthesized. This p-CLEAs presented a complete structure with abundant channels, large specific surface and more efficient catalytic effect compared with conventional CLEAs.     

Close-packed silane nanodot arrays by capillary nanostamping coupled with heterocyclic silane ring opening

We report the parallel generation of close-packed ordered silane nanodot arrays with nanodot diameters of few 100 nm and nearest-neighbor distances in the one-micron range. Capillary nanostamping of heterocyclic silanes coupled with ring-opening triggered by hydroxyl groups at the substrate surfaces yields nanodots consisting of silane monolayers with exposed terminal functional groups. Using spongy mesoporous silica stamps with methyl-terminated mesopore walls inert towards the heterocyclic silanes, we could manually perform multiple successive stamping cycles under ambient conditions without interruptions for ink refilling. Further functionalizations include the synthesis of polymer nanobrushes on the silane nanodots by surface-initiated atom-transfer radical polymerization. Proteins-of-interest fused to the HaloTag were site-specifically captured to silane nanodots functionalized by copper-free reactions with azide derivatives. Thus, bioorthogonal functionalization for bioanalytics with a spatial resolution in the one-micron range may be realized on solid supports compatible with fluorescence-based optical microscopy. The feature sizes of the silane nanodot arrays match well the length scales characteristic of a variety of biomolecular submicroscopic organizations in living cells, thus representing a compromise between miniaturization and the resolution limit of optical microscopy for sensitive high-throughput bioanalytics.

We report the parallel generation of close-packed ordered silane nanodot arrays with nanodot diameters of few 100 nm and nearest-neighbor distances in the one-micron range.     

Effects of the aspect ratio of the conductive agent on the kinetic properties of lithium ion batteries

We fabricated lithium-ion batteries (LIBs) using the Super P and carbon nanotubes (CNTs) as conductive agents to investigate the effect of the aspect ratio of conductive agent on the kinetic properties of LIB. The electrode fabricated with CNTs, which have a high aspect ratio (length: 200 μm), exhibited outstanding rate capability at 30C despite of their low concentration, while the electrode fabricated with the carbon black showed poor rate capability. These results indicate that the aspect ratio of conductive agent influence the diffusion coefficient of lithium ions, which is calculated from the galvanostatic intermittent titration technique analysis, and that conductive agent should have high aspect ratio to improve the kinetic properties of LIBs. This study provides insights that are useful for designing high-performance LIBs by reducing the amount of conductive agent, leading to increased loading of active material.

We fabricated lithium-ion batteries (LIBs) using the Super P and carbon nanotubes (CNTs) as conductive agents to investigate the effect of the aspect ratio of conductive agent on the kinetic properties of LIB.     

Preparation of Ni micropillar arrays with high aspect ratios using anodic porous alumina template and their application to molds for imprinting

Anodic porous alumina templates with controlled microscale geometrical structures were prepared by a process combining mask formation and subsequent selective etching of the alumina layer. In this process, the anisotropic etching of anodic porous alumina allows the preparation of anodic porous alumina with microhole array patterns having high aspect ratios. The electrodeposition of Ni using the obtained alumina templates generated an array of Ni micropillars with high aspect ratios. The height of Ni micropillars could also be controlled by adjusting the thickness of the anodic porous alumina. The obtained Ni micropillar array with a high aspect ratio was applied as a mold for imprinting. The ordered microstructures of TiO₂ with high aspect ratios were prepared by imprinting using the Ni mold.

Ni micropillar array with high aspect ratio prepared using anodic porous alumina.     

Electrospray ionization of native membrane proteins proceeds via a charge equilibration step

Electrospray ionization mass spectrometry is increasingly applied to study the structures and interactions of membrane protein complexes. However, the charging mechanism is complicated by the presence of detergent micelles during ionization. Here, we show that the final charge of membrane proteins can be predicted by their molecular weight when released from the non-charge reducing saccharide detergents. Our data indicate that PEG detergents lower the charge depending on the number of detergent molecules in the surrounding micelle, whereas fos-choline detergents may additionally participate in ion–ion reactions after desolvation. The supercharging reagent sulfolane, on the other hand, has no discernible effect on the charge of detergent-free membrane proteins. Taking our observations into the context of protein-detergent interactions in the gas phase, we propose a charge equilibration model for the generation of native-like membrane protein ions. During ionization of the protein-detergent complex, the ESI charges are distributed between detergent and protein according to proton affinity of the detergent, number of detergent molecules, and surface area of the protein. Charge equilibration influenced by detergents determines the final charge state of membrane proteins. This process likely contributes to maintaining a native-like fold after detergent release and can be harnessed to stabilize particularly labile membrane protein complexes in the gas phase.

The electrospray ionization mechanism contributes to preserving the structures and interactions of membrane protein complexes in native mass spectrometry.     

Surfactant concentration modulates the motion and placement of microparticles in an inhomogeneous electric field

This study examined the effects of surfactants on the motion and positioning of microparticles in an inhomogeneous electric field. The microparticles were suspended in oil with a surfactant and the electric field was generated using sawtooth-patterned electrodes. The microparticles were trapped, oscillating, or attached to the electrodes. The proportion of microparticles in each state was defined by the concentration of surfactant and the voltage applied to the electrodes. Based on the trajectory of the microparticles in the electric field, we developed a new physical model in which the surfactant adsorbed on the microparticles allowed the microparticles to be charged by contact with the electrodes, with either positive or negative charges, while the non-adsorbed surfactant micellizing in the oil contributed to charge relaxation. A simulation based on this model showed that the charging and charge relaxation, as modulated by the surfactant concentration, can explain the trajectories and proportion of the trapped, oscillating, and attached microparticles. These results will be useful for the development of novel self-assembly and transport technologies and colloids sensitive to electricity.

This study revealed that surfactant micelles played two roles for microparticle motions in an inhomogeneous electric field (trapping, oscillating, or attachment to electrodes): particle charging and charge relaxation, depending on its concentration.     

Development of a bio-electrospray system for cell and non-viral gene delivery

Bio-electrospray technology is a very attractive tool for preparing scaffolds and depositing desired solutions on various targets by electric force. In this study, we focused on the application of a bio-electrospray (BES) technique to spray cells on the target and to simultaneously deliver genetic constructs into the cells, called non-viral gene delivery-based bio-electrospray (NVG-BES). Using this method, we tried to harvest the electric charge produced during electrospray for the cellular internalization of cationic polymer/DNA nanoparticles as well as the delivery of living cells on the desired substrate. Furthermore, we optimized the voltage, culture medium and polymeric cationic charges for high transfection efficiency and cell viability during NVG-BES. As a result, the solutions used during the NVG-BES process played an important role in improving transfection efficiency. We determined that a voltage of 10 kV with PBS as the spraying solution showed high transfection efficiency, probably due to the facilitation of cationic polymer/DNA nanocomplexes in cellular internalization and their subsequent expression. In conclusion, NVG-BES, as a novel method, is expected to deliver genes to cells and simultaneously deliver transfected cells to any substrate or scaffold.

The NVG-BES system facilitated to introduce DNA to cells and delivered cells to a target simultaneously. In this method, a cationic polymer was used as non-viral carrier with electric force by bio-electrospray (BES) system to electrospray living cells onto a target.     

Facile and scaleable transformation of Cu nanoparticles into high aspect ratio Cu oxide nanowires in methanol

In this work, a facile synthetic route for the preparation of high aspect ratio Cu oxide nanowires is reported. The preparation of the Cu oxide nanowires begins with the generation of pure Cu nanoparticles by inert gas condensation (IGC) method, follows by dispersing the obtained nanoparticles in methanol with the aid of ultrasonication. The mixture is stored at different temperature for the transformation from Cu nanoparticle to Cu oxide nanowires. The influences of the kind of solution, the ratio of methanol to Cu nanoparticle, dispersion time and temperature towards the generation of Cu oxide nanowires are studied in detail. Scanning electron microscopy studies indicate that high aspect ratio Cu oxide nanowires with diameter of a few tens of nanometers and length up to several tens of micrometers could be obtained under proper conditions. The mechanism for the transformation of Cu nanoparticles to Cu oxide nanowires is also investigated.

We proposed a facile synthetic route to Cu oxide nanowires with a high aspect ratio. The approach shown in this work is suitable for scale-up synthesis.     

Advances in mass spectrometry-based metabolomics for investigation of metabolites

Metabolomics is the systematic study of all the metabolites present within a biological system, which consists of a mass of molecules, having a variety of physical and chemical properties and existing over an extensive dynamic range in biological samples. Diverse analytical techniques are needed to achieve higher coverage of metabolites. The application of mass spectrometry (MS) in metabolomics has increased exponentially since the discovery and development of electrospray ionization and matrix-assisted laser desorption ionization techniques. Significant advances have also occurred in separation-based MS techniques (gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, capillary electrophoresis-mass spectrometry, and ion mobility-mass spectrometry), as well as separation-free MS techniques (direct infusion-mass spectrometry, matrix-assisted laser desorption ionization-mass spectrometry, mass spectrometry imaging, and direct analysis in real time mass spectrometry) in the past decades. This review presents a brief overview of the recent advanced MS techniques and their latest applications in metabolomics. The software/websites for MS result analyses are also reviewed.

Metabolomics is the systematic study of all the metabolites present within a biological system, supply functional information and has received extensive attention in the field of life sciences.