Solid-phase microextraction/gas chromatography–mass spectrometry method optimization for characterization of surface adsorption forces of nanoparticles

A complete characterization of the different physico-chemical properties of nanoparticles (NPs) is necessary for the evaluation of their impact on health and environment. Among these properties, the surface characterization of the nanomaterial is the least developed and in many cases limited to the measurement of surface composition and zetapotential. The biological surface adsorption index approach (BSAI) for characterization of surface adsorption properties of NPs has recently been introduced (Xia et al. Nat Nanotechnol 5:671–675, 2010; Xia et al. ACS Nano 5(11):9074–9081, 2011). The BSAI approach offers in principle the possibility to characterize the different interaction forces exerted between a NP's surface and an organic—and by extension biological—entity. The present work further develops the BSAI approach and optimizes a solid-phase microextraction gas chromatography–mass spectrometry (SPME/GC-MS) method which, as an outcome, gives a better-defined quantification of the adsorption properties on NPs. We investigated the various aspects of the SPME/GC-MS method, including kinetics of adsorption of probe compounds on SPME fiber, kinetic of adsorption of probe compounds on NP's surface, and optimization of NP's concentration. The optimized conditions were then tested on 33 probe compounds and on Au NPs (15 nm) and SiO₂ NPs (50 nm). The procedure allowed the identification of three compounds adsorbed by silica NPs and nine compounds by Au NPs, with equilibrium times which varied between 30 min and 12 h. Adsorption coefficients of 4.66?±?0.23 and 4.44?±?0.26 were calculated for 1-methylnaphtalene and biphenyl, compared to literature values of 4.89 and 5.18, respectively. The results demonstrated that the detailed optimization of the SPME/GC-MS method under various conditions is a critical factor and a prerequisite to the application of the BSAI approach as a tool to characterize surface adsorption properties of NPs and therefore to draw any further conclusions on their potential impact on health. Graphical Abstract

The basic principle of SPME/GC-MS method for characterization of nanoparticles surface adsorption forces     

Melt miscibility of HDPE/UHMWPE,LDPE/UHMWPE,and LLDPE/UHMWPE blends detected by dynamic rheometer

The dynamic rheological behavior of high density polyethylene (HDPE)/ultrahigh molecular weight polyethylene (UHMWPE) blends, low density polyethylene (LDPE)/UHMWPE blends and linear low density polyethylene (LLDPE)/ UHMWPE blends was measured in parallel plate rheometer at 200°C. The analysis of log-additivity rule, Cole-Cole plots and Han curves of the three series blends indicated that the LDPE/UHMWPE blends were miscible in the melt, while the HDPE/UHMWPE blends and LLDPE/UHMWPE blends showed phase separation. The DSC results of LLDPE/UHMWPE blends and HDPE/UHMWPE blends were consistent with the rheological properties, while for the thermal properties of LDPE/UHMWPE blends, results revealed three endothermic peaks, which indicated a liquid-solid phase separation in LDPE/UHMWPE blends.     

Kinetics and possible mechanism of hydrogen chloride oxidation over supported copper-containing salt catalysts: II. Kinetics of HCl oxidation in the deacon and methane oxychlorination reactions over the CuCl2-KCl-LaCl3 catalyst

The kinetics of HCl oxidation at 350–425°C over the supported CuCl₂-KCl-LaCl₃ catalyst has been investigated using a gradientless technique. The HCl oxidation kinetics in the Deacon and methane oxychlorination reactions has been studied in order to substantially extend the \(Cl_2 \left( {P_{Cl_2 } } \right)\) partial pressure variation range. When the reaction rate is independent of P _HCl, HCl oxidation on the copper-potassium catalysts is described by the same rate equation, irrespective of whether the catalyst contains lanthanum or not. The introduction of lanthanum chloride increases the HCl oxidation rate by one order of magnitude. The rate equation obtained has significant advantages over the equation corresponding to the Kenney-Slama equation. The kinetic features of HCl oxidation over the lanthanum-containing catalyst, whether the process depends on P _HCl or not, can be explained in terms of the superposition of the Kenney-Slama dissociative mechanism and the catalytic mechanism suggested here. The role of lanthanum chloride in both HCl oxidation pathways is considered.     

Preparation of Cu (II)/PEI–QPEI/SiO2 nanopowder as antibacterial material

The silica nanoparticles were prepared by the sol–gel process, and then twice modified and grafted by polyethylenimine (PEI) on their surface. After quaternary ammonium reaction and chelated copper reaction, the PEI/SiO₂, QPEI/SiO₂, PEI–QPEI/SiO₂ and Cu (II)/PEI–QPEI/SiO₂ nanopowders were obtained in turn. The morphology and structure of the products were characterized through SEM, EDX, HRTEM, FTIR and element analysis. At the same time, the antibacterial activity of the products to E. coli and Candida were evaluated through quantification and qualitative ways, e.g. microcalorimetric method and culture dish method. The results suggested that the Cu (II)/PEI–QPEI/SiO₂, a novel three-component functional nanopowder, presented the best antibacterial activity to both E. coli and Candida duo to the synergistic sterilization capability of the ammonium salt and copper ions, compared with other products. It indicated that the Cu (II)/PEI–QPEI/SiO₂ nanopowder could be a novel antibacterial nanomaterial to widely application in preventing and minimizing bacteria of the organism and environment in future.     

Thermally stimulated discharge current (TSDC) characteristics in β-phase PVDF–BaTiO3 nanocomposites

β-phase polyvinylidene fluoride (PVDF)–BaTiO₃ nanocomposite samples have been prepared by solution mixing method. XRD data represent that the crystallinity of PVDF decreases with increase in loading level of BaTiO₃ nanoparticles. DSC curve represents that the melting point of PVDF is lightly affected by loading concentration of BaTiO₃. The morphology and microstructure of PVDF and PVDF embedded by BaTiO₃ nanofillers were investigated by using inverted contrast microscopy (ICM) and scanning electron microscopy (SEM). FTIR interferrometry is proven that PVDF and BaTiO₃ are not chemically interacting; therefore, interaction of BaTiO₃ is van der Waals type of interaction. The thermally stimulated discharge current (TSDC) of PVDF and PVDF–BaTiO₃ nanocomposites sample was characterized by single peak. The observed TSDC peak is discussed on the basis of dipolar and interfacial polarization.     

A sensor based on incorporating Ni2+ into ZnO nanoparticles-multi wall carbon nanotubes-poly methyl metacrylat nanocomposite film modified carbon paste electrode for determination of carbohydrates

The ZnO nanoparticles (ZnONPs) were synthesized with gelatin as stabilizer via the sol-gel method and were characterized by transmission electron microscope (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). An electrochemical sensor based on ZnO nanoparticles-multi wall carbon nanotubes-poly methyl metacrylat (ZnONPs-MWCNT-PMMA) composite film was developed by incorporating Ni²⁺ into the ZnONPs-MWCNT-PMMA film modified carbon paste electrode (Ni²⁺/ZnONPs-MWCNT-PMMA/CPE). The electrochemical activity of Ni²⁺/ZnONPs-MWCNT-PMMA/CPE was illustrated in 0.10 M NaOH using cyclic voltammetry. The Ni²⁺/ZnONPs-MWCNT-PMMA/CPE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple. Ni²⁺/ZnONPs-MWCNT-PMMA/CPE also show good electrocatalytic activity toward the oxidation of carbohydrates (glucose, fructose and sorbitol). The Ni²⁺/ZnONPs-MWCNT-PMMA/CPE gives a good linear range with a detection limit of 8, 6, and 9 μM towards the determination of glucose, fructose and sorbitol, respectively by amperometry. Furthermore, the modified sensor was successfully applied to the sensitive determination of carbohydrates in real samples.     

Spin-trapped Radicals: Determination by LC-TSP-MS and LC-ESI-MS

The 4-POBN[α-(4-pyridyl-l-oxide)-N-tert-butyl-nitrone] radical adducts of ethyl and pentyl radicals were determined by a combination of high performance liquid chromatography (HPLC) combined with electron paramagnetic resonance (EPR) with HPLC-electrospray (ESI)-mass spectrometry and HPLC-thermospray (TSP)-MS. The identifIcation of the peak corresponding to the spin-trapped radical was done by performing HPLC-EPR under the same chromatographic conditions as the HPLC-MS. The radical adducts could be determined by both techniques, even though for ESI only 12 μL/min of the total 1 mL/min HPLC flow rate could be directed into the ion source.     

Facile formation of stimuli-responsive,fluorescent and magnetic nanoparticles based on cellulose stearoyl ester via nanoprecipitation

In comparison to stimuli-responsive, multi-functional nanoparticles (NPs) from synthetic polymers, such NPs based on sustainable, naturally occurring polysaccharides are still scarce. In the present study, stable stimuli-responsive, fluorescent and magnetic NPs were fabricated using cellulose stearoyl esters (CSEs) consisting of cellulose and stearoyl groups. The multifunctional NPs with the average diameters between 80 and 250 nm were obtained after facile nanoprecipitation using CSE solutions containing Fe₃O₄-NPs. Using the aqueous solution of fluorescent rhodamine B as precipitant, NPs with rhodamine B on NP surface were obtained. Rhodamine B could be released depending on the temperature. In comparison, stearoylaminoethyl rhodamine B can be encapsulated in CSE-NPs, which renders obtained NPs reversible fluorescence in response to UV illumination and heat treatment.     

A wide range optical pH sensor for living cells using Au@Ag nanoparticles functionalized carbon nanotubes based on SERS signals

p-Aminothiophenol (pATP) functionalized multi-walled carbon nanotubes (MWCNTs) have been demonstrated as an efficient pH sensor for living cells. The proposed sensor employs gold/silver core-shell nanoparticles (Au@Ag NPs) functionalized MWCNTs hybrid structure as the surface-enhanced Raman scattering (SERS) substrate and pATP molecules as the SERS reporters, which possess a pH-dependent SERS performance. By using MWCNTs as the substrate to be in a state of aggregation, the pH sensing range could be extended to pH 3.0～14.0, which is much wider than that using unaggregated Au@Ag NPs without MWCNTs. Furthermore, the pH-sensitive performance was well retained in living cells with a low cytotoxicity. The developed SERS-active MWCNTs-based nanocomposite is expected to be an efficient intracellular pH sensor for bio-applications.     

Gel-assisted synthesis of anatase TiO2 nanoparticles and application for electrochemical determination of L-tryptophan

Anatase titanium dioxide nanoparticles (TiO₂-NPs) were synthesized with and without gelatin via the sol-gel method. The TiO₂-NPs were characterized by a number of techniques, such as thermogravimetric analysis (TGA), X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR) and ultraviolet visible spectroscopy (UV-Vis). The particle sizes of the TiO₂-NPs prepared with and without gelatin were ～13 and ～17 nm, respectively. The main advantage of using gelatin as a stabilizing agent is that it provides long-term stability for nanoparticles by preventing particles agglomeration. The results indicated that gelatin was a reliable green stabilizer, which can be used as a polymerization agent in the sol-gel method for synthesis of tiny size TiO₂-NPs. Moreover, the composite film was prepared by synthesized TiO₂-NPs nanoparticles and multi wall carbon nanotube (MWNT) on glassy carbon electrode (TiO₂-MWNT/GCE). The TiO₂-MWNT/GCE responded linearly to L-tryptophan (L-Trp) in the concentration of 1.0 × 10^?6 to 1.5 × 10^?4 M with detection limit of 5.2 × 10^?7 M at 3 using amperometry. The studied sensor exhibited good reproducibility and long-term stability.     

Production of Pt nanoparticles-supported chelating group-modified graphene for direct methanol fuel cells

In this study, Pt nanoparticles (NPs) were supported on reduced graphene oxide with the aid of disodium ethylenediamine-tetraacetate, where the Pt iona were initially attached to EDTA-functionalized graphene oxide (EDTA-GO) sheets and then the metal ion and the graphene oxide were reduced simultaneously by ethylene glycol. Electrochemical properties of the catalysts were studied by measuring cyclic voltammetries, and functional groups of the synthesized materials were investigated by Fourier transform infrared spectrometry. Average sizes and lattice parameters were measured by scanning electron microscopy, transmission electron microscopy images, and X-ray diffraction. The results showed that Pt NPs were successfully deposited on the EDTA-GO with the crystallite size of about 2.3 nm. The prepared catalysts demonstrated an enhanced tolerance towards CO poisoning, when EDTA-GO was used as supports. This suggests that EDTA plays a crucial role in the dispersion and electrocatalytic activity of the metal nanoparticles.     

Antitumoral and MMP-2 inhibition activity of raloxifene or tamoxifen loaded nanoparticles containing dimethyl-β-cyclodextrin

A new nanoparticle formulation has been developed by using dimethyl-β-cyclodextrin (DM-β-CD) with raloxifene HCl or tamoxifene citrate. Both drugs are insoluble in water and represent as low bioavailibilities when given orally. Tamoxifen has an FDA approval for breast cancer prevention and the treatment. Raloxifene is approved for osteoprosis treatment. Both drugs were selected as a model drug antitumoural activity and MMP-2 inhibition studies were evaluated on breast cancer cell lines MCF-7 and MDA-MB 231. MMP-2 is known to be responsible for tumour invasion and initation the of angiogenesis. DM-β-CD and sodium taurocholate (NaTC) have been used as absorption enhancers to increase penetration effect of raloxifene/tamoxifen on the tumour cells and aimed to provide high antitumoral activity and MMP-2 inhibition results by developed nanoparticle formulations. The effects of two absorption enhancers were compared. The highest antitumoral activity was observed for DM-β-CD—raloxifene HCl nanoparticle formulation and also MMP-2 enzyme inhibit effectively.     

TiO2 and TiO2/SiO2 nanoparticles obtained by sol–gel method and applied on dye sensitized solar cells

In this work we show the synthesis and characterization of TiO₂ and TiO₂/SiO₂ nanoparticles synthesized by sol–gel method using HF and HCl as catalysts. The obtained nanoparticles were analyzed by N₂ adsorption–desorption isotherms, transmission electronic microscopy, Ultraviolet–visible spectroscopy and X-ray diffractometry. Mesoporous, homogeneously polycondensed TiO₂/SiO₂ materials, containing nanocrystalline anatase phase with band gap similar to pure titania were obtained. Films of the powdered oxides were applied to assemble dye sensitized solar cells that presented electrical parameters, Fill Factor and efficiencies similar to devices obtained by only TiO₂. The sol–gel route arises as an alternative way to prepare TiO₂/SiO₂ materials for solar cells.     

Impact of PS/SiO2 morphologies on the SERS activity of PS/SiO2/Ag nanocomposite particles

To understand the relationship between the morphology of carboxyl-functionalized polystyrene/silica (PS/SiO₂) nanocomposite microspheres and the surface-enhanced Raman scattering (SERS) performance of PS/SiO₂/Ag nanocomposite particles, core-shell and raspberry-like PS/SiO₂ composite microspheres were used as templates to prepare PS/SiO₂/Ag nanocomposite particles. The core-shell and raspberry-like structured PS/SiO₂ templates were prepared via in situ sol-gel reaction by hydrolysis tetraethyl orthosilicate (TEOS) in alkali solution. Silver nanoparticles (10–50 nm) were loaded on the PS/SiO₂ templates’ surface by chemical reduction. The morphology and structure of the PS/SiO₂/Ag particles were characterized by TEM, SEM, X-ray diffraction (XRD), and ultraviolet-visible (UV-vis) spectroscopy. Rhodamine 6G (R6G) was selected as a model chemical to study the enhancement performance of substrate constructed by PS/SiO₂/Ag nanocomposite. Results indicated that the PS/SiO₂/Ag nanocomposite prepared based on the core-shell templates showed higher SERS activity. The beneficial effect was associated with a lower specific area of core-shell structure and the larger average diameter of nanosilvers than that of the raspberry-like templates.     

Characterization of Volatile Organic Metabolites in Lung Cancer Pleural Effusions by SPME–GC/MS Combined with an Untargeted Metabolomic Method

Headspace solid-phase microextraction and gas chromatography/mass spectrometry (HS-SPME–GC/MS) method combined with XCMS Online was tentatively applied to characterize the dysregulated volatile organic metabolites (VOMs) in benign and malignant pleural effusions. A total of 9 dysregulated feature groups were isolated from metabolic features in 35 pleural effusion samples (20 benign effusions and 15 malignant ones from lung cancer patients). Principle component analysis, partial least squares discriminant analysis (PLS-DA) and orthogonal PLS-DA were built to separate benign from malignant pleural effusion groups and to find dysregulated metabolites in significantly different amounts between the two groups. Four dysregulated VOMs such as 2-ethyl-1-hexanol, cyclohexanone, 1,2,4,5-tetramethylbenzene and naphthalene were selected according to the variable influence on the projection value. The concentration of the four dysregulated VOMs in benign and malignant effusions were further determined by external standard method. The median concentrations of 4 VOMs in malignant effusion samples were from 4.7 to 91,121.9 nM, whereas their median levels were only 1.9–318.3 nM in benign ones. The results show that the proposed SPME–GC/MS-based metabolomic approach combined with XCMS Online data processing is a simple, rapid and available method for the characterization of dysregulated VOMs in malignant and benign pleural effusions.     

DNA methylation ratio variability may impede clinical application of cancer diagnostic markers

Hypermethylation at promoter regions of tumour suppressor genes is diagnostic for many cancers. Many genomic regions that may be the targets for clinical diagnostic assays have been identified through use of measuring systems reliant on bisulphite conversion, but few of these promising markers are in clinical use. The comparability of a widely used DNA methylation measuring system involving bisulphite conversion was evaluated by supplying three experienced centres with methylated DNA reference material mixtures that were independently prepared and characterised by mass spectrometry and high-pressure liquid chromatography. A replication scheme was designed to evaluate reproducibility of key analytical steps within and between laboratories by regression analysis. In general, methylation was underestimated and methylation ratio values were highly variable. The difference in methylation ratio between CpG sites was the key contributor to variable results. The CpG site effect followed a similar pattern at all centres and at all methylation levels examined indicating that sequence context had a major effect on methylation ratio measurement using the bisulphite conversion process. The magnitude of underestimation combined with the variability of measurements between CpG sites compromises the concept of measuring genomic regional methylation by averaging the methylation ratios of many CpG sites. There were no significant differences in replicate bisulphite conversions or sample work-up and instrument analysis at each centre thus making this technique suitable for comparative intralaboratory investigations. However, it may not be suitable for a routine diagnostic assay without extensive standardisation efforts.     

Heat of reaction and curing of epoxy resin

The heat of reaction and kinetics of curing of diglycidyl ether of bisphenol-A (DGEBA) type of epoxy resin with catalytic amounts of ethylmethylimidazole (EMI) have been studied by differential power-compensated calorimetry as a part of the program for the study of process monitoring for composite materials. The results were compared with those from 1∶1 and 1∶2 molar mixtures of DGEBA and EMI. A method of determination of heat of reaction from dynamic thermoanalytical instruments was given according to basic thermodynamic principles. The complicated mechanism, possibly involving initial ionic formation, has also been observed in other measurements, such as by time-domain dielectric spectroscopy. The behavior of commercially available DGEBA resin versus purified monomeric DGEBA were compared. The melting point of purified monomeric DGEBA crystals is 41.4 °C with a heat of fusion of 81 J/g. The melt of DGEBA is difficult to crystallize upon cooling. The glass transition of purified DGEBA monomer occurs around ?22 °C with aΔC _p of 0.60 J/K/g.     

Synthesis and preparation of nanoparticles composed of amphiphilic poly(γ-glutamic acid) with different hydrophobic side chains and their potential of membrane disruptive activity

In the development of nanoparticle-based vaccine adjuvants, the interaction between nanoparticles (NPs) and the cells is a key factor. To control them, we focused on the relationship between the hydrophobicity of the side chains and the cell membrane. In this study, amphiphilic poly(γ-glutamic acid) (γ-PGA), using various types of hydrophobic side chains, was synthesized and used to prepare NPs for evaluating the membrane disruptive activity. When leucine ethyl ester (Leu), methionine ethyl ester (Met), or tryptophan ethyl ester (Trp) was grafted, each polymer formed monodispersed NPs at physiological conditions. Significantly, NPs composed of Leu and Trp showed a membrane disruptive activity at the endosomal environment (pH 5–6.5), while NPs composed of Met did not show. This might be due to the weak hydrophobicity of Met compared to that of Leu and Trp, which demonstrated that the interaction between NPs and cells could be controlled by designing the polymer compositions.