Determination of the concentrations of trace and doping elements in GaAs by neutron activation analysis

The concentrations of ten trace and dopant elements in GaAs semiconductor were determined by reactor neutron activation analysis after removal of As by evaporation of AsCl₃. The retentions of the elements of interest were measured using radiotracers. The concentrations of doping elements (Te, Cr and Zn) in commercial GaAs samples were compared to the limit of detection of these elements to analyze the possibility to use NAA for concentration depth profiling measurements. The NAA results were compared with those of electrical measurements and SIMS and the discrepancies found are discussed.     

A colorimetric assay for d-Penicillamine in urine and plasma samples based on the aggregation of gold nanoparticles

We report herein the development of a highly sensitive colorimetric method for detection of d-Penicillamine using citrate-capped gold nanoparticles (AuNPs). This assay relies upon the distance-dependent of gold nanoparticles surface plasmon resonance band of gold nanoparticles. By replacing the thiol-containing chelator drug, d-Penicillamine, with citrate on the gold nanoparticles surface, a new peak appearing at a longer wavelength intensifies and shifts further to the red from the original peak position due to aggregation of gold nanoparticles which depends on ionic strength, gold nanoparticles and d-Penicillamine concentration. During this process, the plasmon band at 521 nm decreases gradually along with the formation of a new red-shifted band at 630 nm. The calibration curve which is derived from the ratio intensities of absorbance at longer wavelength (630 nm) to original wavelength (521 nm) displays a linear relation in the range of 5.0 × 10^?6–3.0 × 10^?4 M d-Penicillamine. Lower limit of detection for d-Penicillamine, at the signal-to-noise ratio of 3 (3σ), was 3.8 × 10^?6 M. The developed methodology was successfully applied for the determination of d-Penicillamine in human urine and plasma.     

Rapid screening and determination of nerve agent metabolites in human urine by LC-MS/MS

Qualitative screening procedures have been developed for the rapid detection and identification of the metabolites of nerve agents in the urine samples and extracts using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The combination of negative electrospray ionization (ESI) using a C₁₈ column and water-methanol mobile phase modified with ammonium formate provides a rapid screening procedure for nerve agent degradation products with limit of detection of 1 ng/mL in the precursor-ion analysis. Also, determination of the alkyl methylphosphonic acids was carried out by the SRM scan mode with the limit of detection of 0.1 ng/mL. These procedures will be applicable to the trace analysis of metabolites of nerve agents in human urine matrices in the Organisation for the Prohibition of Chemical Weapons (OPCW) proficiency test.     

A paper-based lateral flow assay for morphine

Morphine was used as a model analyte to examine the possibility of using cellulose, physically modified by papermaking and converting techniques, as a capillary matrix in a lateral flow type of diagnostic assay. This research was directed toward low-cost, disposable, and portable paper-based diagnostics, with the aim of addressing the analytical performance of paper as a substrate in the analysis for drugs of abuse. Antibody Fab fragments were used as sensing molecules, and gold nanoparticle detection was employed. Inkjet printing was used to pattern sensing biomolecules as detection zones on paper. To validate the usefulness of paper as a diagnostic platform, the principle of a direct sandwich assay, based on immunocomplex formation between morphine and the anti-morphine Fab fragment and detection of the formed immunocomplex by another Fab fragment, was implemented. Results were compared with that achieved by using nitrocellulose as a reference material. Possible interfering from the sample matrix on assay quality was investigated with spiked oral fluid samples. Under optimized conditions, a visually assessed limit of detection for the sandwich assay was 1 ng/mL, indicating that the paper-based test devices developed in this work can perform screening for drugs of abuse and can fulfill the requirement for a sensitive assay in diagnostically relevant ranges. Fig

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Quantitative analysis by high-performance liquid chromatography atmospheric pressure chemical ionization mass spectrometry: The determination of the renin inhibitor CP-80,794 in human serum

A specific method was developed for the quantitative determination of the renin inhibitor CP-BO,794. Serum extracts containing the drug and an internal standard were injected into a standard reverse-phase high-performance liquid chromatography (HPLC) column. The mobile phase, methanol/water (8/2), flowed at 1 ml/min through the column and then via a heated nebulizer interface into a corona discharge atmospheric pressure chemical ionization source. The assay minimum limit of quantification was 50 pg/mL. It exhibits satisfactory accuracy and precision over the range 50 pg/ml, to 10 ng/mL. A minor modification of the HPLC mobile phase was necessary to attain extremely low detection limits. The addition of a structural analogue contributed to enhancing the precision of the assay.     

Determination of Platinum-Group Elements and Gold in Silicates by Gamma Activation Autoradiography and Instrumental Gamma Activation Analysis

The potential of the gamma activation determination of platinum-group elements and gold both by instrumental gamma activation analysis (bulk analysis) and by monitoring their distribution using autoradiography (local analysis) is studied. It is shown that platinum-group elements and gold can be determined by direct gamma-ray spectrometry in silicate samples with a detection limit of 10^–3–10^–5%. In contact gamma activation autoradiography, the detection limit for these elements is about 10 ng with a spatial resolution of 10–20 m.     

Radiochemical separation and determination of platinum,gold and palladium in complex matrices employing substoichiometric thermal neutron activation analysis

A radiochemical separation method has been developed for the separation of platinum, gold and palladium from various matrices by thermal neutron activation analysis and employing substoichiometric extractions of Pt and Au with 2-mercaptobenzothiazole and Pd with isonitrosobenzoylacetone. Decontamination factors for the individual elements after separation was also studied and was found to be greater than 10⁵ for most of the elements.     

A fluorogenic heterogeneous immunoassay for cardiac muscle troponin cTnI on a digital microfluidic device

We describe a fluorogenic two-site noncompetitive heterogeneous immunoassay with magnetic beads on a low-voltage digital microfluidic platform using closed electrowetting-on-dielectric (EWOD). All the steps of an enzyme-linked immunosorbent assay (ELISA) were performed on the device using 9H-(1, 3-dichloro-9, 9-dimethylacridin-2-one-7-yl) phosphate as the fluorogenic substrate for the enzyme alkaline phosphatase. The performance of the system was demonstrated with cardiac marker Troponin I (cTnI) as a model analyte in phosphate-buffered saline samples. cTnI was detected within the diagnostically relevant range with a limit of detection of 2.0 ng/mL (CV?=?6.47 %). Washing of magnetic beads was achieved by movement through a narrow region of buffer bridging one drop to another with minimal fluid transfer. More than 90 % of the unbound reagents were removed after five washes. Further experiments testing human blood serum on the same platform demonstrated a sample-to-answer time at ～18.5 min detecting 6.79 ng/mL cTnI.     

Highly selective piezoelectric sensor for lead(II) based on the lead-catalyzed release of gold nanoparticles from a self-assembled nanosurface

A novel quartz crystal microbalance (QCM) sensor has been developed for highly selective and sensitive detection of Pb²⁺ by exploiting the catalytic effect of Pb²⁺ ions on the leaching of gold nanoparticles from the surface of a QCM sensor. The use of self-assembled gold nanoparticles (AuNPs) strongly enlarges the size of the interface and thus amplifies the analytical response resulting from the loss of mass. This results in a very low detection limit for Pb²⁺ (30 nM). The high selectivity is demonstrated by studying the effect of potentially interfering ions both in the absence and presence of Pb²⁺ ions. This simple and well reproducible sensor was applied to the determination of lead in the spiked drinking water. This work provides a novel strategy for fabricating QCM sensors towards Pb²⁺ in real samples. Figure

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The Prognostic Value of Histidine-Rich Glycoprotein RNA in Breast Tissue Using Unmodified Gold Nanoparticles Assay

The aim of is this study is to explore the role of tissue histidine-rich glycoprotein (HRG) RNA as a promising clinically useful biomarker for breast cancer patients prognosis using nanogold assay. Expression of the HRG RNA was assessed by gold nanoparticles and conventional RT-PCR after purification by magnetic nanoparticles in breast tissue samples. The study included 120 patients, 60 of which were histologically proven breast carcinoma cases, 30 had benign breast lesions and 30 were healthy individuals who had undergone reductive plastic surgery. ER, PR and HER2 status were also investigated. The prognostic significance of tissue HRG RNA expression in breast cancer was explored. The magnetic nanoparticles coated with specific thiol modified oligonucleotide probe were used successfully in purification of HRG RNA from breast tissue total RNAs with satisfactory yield. The developed HRG AuNPs assay had a sensitivity and a specificity of 90 %, and a detection limit of 1.5 nmol/l. The concordance rate between the HRG AuNPs assay with RT-PCR after RNA purification using magnetic nanoparticles was 93.3 %. The median follow-up period was 60 months. Among traditional prognostic biomarkers, HRG was a significant independent prognostic marker in relapse-free survival (RFS). HRG RNA is an independent prognostic marker for breast cancer and can be detected using gold NPs assay, which is rapid, sensitive, specific, inexpensive to extend the value for breast cancer prognosis.     

Direct electrochemistry and electrocatalysis of hemoglobin on a glassy carbon electrode modified with poly(ethylene glycol diglycidyl ether) and gold nanoparticles on a quaternized cellulose support. A sensor for hydrogen peroxide and nitric oxide

A glassy carbon electrode was modified with gold nanoparticles (Au-NPs) on a quaternized cellulose support in a film composed of poly(ethylene glycol diglycidyl ether) (PEGDGE), and Hb was immobilized on the Au-NPs. The sensor film was characterized by UV–vis spectra, scanning electron microscopy, and electrochemical impedance spectroscopy. Cyclic voltammetry of the Hb in the Au@Qc/PEGDGE film revealed a pair of well-defined and quasi reversible peaks for the protein heme Fe(III)/Fe(II) redox couple at about ?0.333 V (vs. SCE). The sensor film also exhibited good electrocatalytic activity for the reduction of nitric oxide and hydrogen peroxide. The amperometric response of the biosensor depends linearly on the concentration of nitric oxide in the 0.9 to 160 μM range, and the detection limit is as low as 12 nM (at 3σ). The response to hydrogen peroxide is linear in the 59 nM to 4.6 μM concentration range, and the detection limit is 16 nM (at 3σ). This biosensor is sensitive, reproducible, and long-term stable. Figure

An electrochemical biosensor based on the immobilization of hemoglobin in Au@Qc NPs /Poly ethylene glycol diglycidyl ether composite film is developed.     

Determination of cyanide using a chemiluminescence system composed of permanganate,rhodamine B,and gold nanoparticles

We describe a new chemiluminescence (CL) system based on the oxidation of rhodamine B (RhoB) with alkaline potassium permanganate in the presence of gold nanoparticles (Au-NPs) and anionic detergent sodium dodecyl sulfate. Free RhoB is weakly chemiluminescent when oxidized with permanganate at alkaline pH values. However, a remarkably strong enhancement of CL is observed in the presence of Au-NPs, probably due to a strong interaction between RhoB and the NPs. The possible mechanism was studied via recording the CL emission. It is also found that the intensity of CL gradually decreases in the presence of cyanide due to its interaction with the Au-NPs. The relation between the decreased CL intensity and cyanide concentration was exploited to develop a method for the determination of cyanide in the 0.01–0.5 μM concentration range, with a detection limit of 2.8 nM. The method was used to determine cyanide in spiked water, urine, and serum. Figure

Alkaline permanganate-rhodamine B-SDS CL reaction is dramatically enhanced by gold nanoparticles. Based on the inhibiting effect of cyanide on this system, a sensitive CL method was developed for its determination     

Use of hydroxylapatite composite membranes for analysis of bisphenol A

This study evaluates solid-phase micro-extraction (SPME) coupled with gas chromatography–mass spectrometry (GC–MS) to determine trace levels of bis-phenol A in water and leached from plastic containers. In our study, we used very thin composite membranes prepared in the laboratory. The extraction using headspace post-derivatization with bis(trimethylsilyl) trifluoroacetamide (BSTFA), containing 1 % trimethylchlorosilane (TMCS) vapor, following SPME was compared with extraction without derivatization. The SPME experimental procedures to extract bis-phenol A in water were optimized with a relatively polar polyacrylate (PA)-coated fiber, an extraction time of 50 min, and desorption at 300 °C for 2 min. Headspace derivatization following SPME was performed using 7 μL of BSTFA with 1 % TMCS at 65 °C for 30 s. The precision was 5.2 % without derivatization and 9.0 % headspace derivatization. The detection limit was determined to be at the nanogram per liter level. When SPME was used following headspace derivatization, the detection limit was one order of magnitude better than that achieved without derivatization. The results of this study reveal the adequacy of the SPME–GC–MS method for analyzing bisphenol A leached from plastic containers. The concentrations of bisphenol A leached from plastic containers into water ranged from 0.7 to 78.5 μg L^?1.     

Biosynthesis of 15N-labeled cylindrospermopsin and its application as internal standard in stable isotope dilution analysis

Cylindrospermopsin (CYN) is a cyanobacterial toxin associated with human and animal poisonings. Due to its toxicity in combination with its widespread occurrence, the development of reliable methods for selective, sensitive detection and accurate quantification is mandatory. Liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis using stable isotope dilution analysis (SIDA) represents an ideal tool for this purpose. U-[¹⁵N₅]-CYN was synthesized by culturing Aphanizomenon flos-aquae in Na¹⁵NO₃-containing cyanobacteria growth medium followed by a cleanup using graphitized carbon black columns and mass spectrometric characterization. Subsequently, a SIDA-LC-MS/MS method for the quantification of CYN in freshwater and Brassica matrices was developed showing satisfactory performance data. The recovery ranged between 98 and 103 %; the limit of quantification was 15 ng/L in freshwater and 50 μg/kg dry weight in Brassica samples. The novel SIDA was applied for CYN determination in real freshwater samples as well as in kale and in vegetable mustard exposed to toxin-containing irrigation water. Two of the freshwater samples taken from German lakes were found to be CYN-contaminated above limit of quantification (17.9 and 60.8 ng/L). CYN is systemically available to the examined vegetable species after exposure of the rootstock leading to CYN mass fractions in kale and vegetable mustard leaves of 15.0 μg/kg fresh weight and 23.9 μg/kg fresh weight, respectively. CYN measurements in both matrices are exemplary for the versatile applicability of the developed method in environmental analysis.      

Polypyrrole–gold nanostructured composite,active and durable electrocatalytic material

The consequences of treatment of gold nanocrystals present in polypyrrole–gold composites and electrodeposited gold nanocrystals (PPY–Au and Au NPs) with OH radicals generated in Fenton’s reaction were investigated. Particularly, the changes in the morphology and the electrochemical properties of those materials are shown. For both materials, the etching effect was noticed. Contrary to significantly reduced catalytic activity, the changes observed in size and shape of gold nanostructures were less pronounced. In the case of PPY–Au composite material, the etching effects were less intense. Even after a 60-min radical treatment of the PPY–Au composite material, the gold–nanocrystal catalytic activity remained high. The limited dissolution of the gold nanocrystals in the PPY–Au composites, compared to bare Au NPs, can be explained by the presence of the polymer which served as a kind of protective barrier against the oxidizing agent. A decrease in the electrocatalytic properties vs. the electrooxidation of ethanol of both forms of gold nanocrystals were observed after the treatment with hydroxyl radicals.     

Sensitive determination of nitric oxide using an electrochemical sensor based on MWCNTs decorated with spherical Au nanoparticles

This paper describes the synthesis, characterisation and application of a very sensitive electrochemical sensor based on a glassy carbon electrode modified with multiwalled carbon nanotubes (MWCNTs) decorated with homogeneously distributed spherical gold nanoparticles (AuNPs). These AuNPs presented diameters ranging from 2 to 10 nm. The AuNPs were prepared directly on the MWCNTs’ surface via a synthesis using HAuCl₄ and citric acid as the reducing agent. The resulting material (Au/MWCNTs) was characterised by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and Raman spectroscopy. The developed Au/MWCNTs sensor was used in the determination of nitric oxide (NO) in phosphate buffer solution at pH 4.4 by differential pulse voltammetry. In the potential window between 0.5 and 0.65 V, a well-defined oxidation peak was observed, whose height was proportional to the NO concentration in the solution. The Au/MWCNTs-modified electrode exhibited high sensitivity for the determination of nitric oxide, with the limit of detection being 0.21 nmol L^?1 (S/N?=?3). No significant interference was detected for nitrite and CO₂ in the NO detection. Our study demonstrated that the resultant Au/MWCNT-modified electrode can be used for nitric oxide detection in the presence of ascorbic acid, dopamine and uric acid, being potentially useful for determinations of NO in real samples. Figure

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A label-free electrochemical biosensor for microRNA detection based on apoferritin-encapsulated Cu nanoparticles

MicroRNAs (miRNAs), a class of small endogenous nonprotein-coding RNAs, regulate a wide range of biological processes, and their abnormal expressions are related to the growth and development of plants. Thus, a simple, rapid, and highly sensitive assay for miRNA detection is of great significance. In this work, a label-free and ultrasensitive assay for miRNA detection using protein cage nanoparticles has been developed. Apoferritin-encapsulated Cu nanoparticles (Cu-apoferritin) could be immobilized on the electrode through special reaction between amino and carboxyl. Hybridization event between the probe DNA and the target miRNA-159a is confirmed by electrochemical oxidation signal after Cu released into the detection buffer by adjusting the pH. This assay is highly selective and sensitive with a low detection limit of 3.5 fM. Moreover, the developed method can even discriminate single-base mismatched strand between the complementary targets. The effect of abscisic acid on the expression level of miRNA-159a in Arabidopsis thaliana seeds was also investigated.     

Indicator-free impedimetric detection of BCR/ABL fusion gene based on ordered FePt nanoparticle-decorated electrochemically reduced graphene oxide

A novel indicator-free DNA hybridization biosensor with a graphene-based nanocomposite as the enhanced sensing platform was developed for the detection of the BCR/ABL fusion gene in chronic myelogenous leukemia. The platform was constructed by homogenously distributing ordered FePt nanoparticles (NPs) onto the electrochemically reduced graphene oxide (ERGNO). The surface structure and electrochemical performance of the FePt/ERGNO nanocomposite were systematically investigated. Owing to the synergistic effects of FePt NPs and ERGNO with a large surface area and excellent electron transfer ability, the obtained nanocomposite greatly facilitated the sensing behavior for DNA detection, resulting in excellent sensitivity and selectivity. A remarkable change has been observed in the impedance spectra before and after hybridization of the probe single-stranded DNA (ssDNA) with the target DNA. Under the optimized conditions, the complementary target genes could be quantified in a wide range of 1.0?×?10^?14 to 1.0?×?10^?9 mol/L with a detection limit of 2.6?×?10^?15 mol/L. The approach does not need an oligonucleotide probe or target to be labeled previously, which makes it advantageous in terms of simplicity and noninvasiveness.     

Relating surface-enhanced Raman scattering signals of cells to gold nanoparticle aggregation as determined by LA-ICP-MS micromapping

The cellular response to nanoparticle exposure is essential in various contexts, especially in nanotoxicity and nanomedicine. Here, 14-nm gold nanoparticles in 3T3 fibroblast cells are investigated in a series of pulse-chase experiments with a 30-min incubation pulse and chase times ranging from 15 min to 48 h. The gold nanoparticles and their aggregates are quantified inside the cellular ultrastructure by laser ablation inductively coupled plasma mass spectrometry micromapping and evaluated regarding the surface-enhanced Raman scattering (SERS) signals. In this way, both information about their localization at the micrometre scale and their molecular nanoenvironment, respectively, is obtained and can be related. Thus, the nanoparticle pathway from endocytotic uptake, intracellular processing, to cell division can be followed. It is shown that the ability of the intracellular nanoparticles and their accumulations and aggregates to support high SERS signals is neither directly related to nanoparticle amount nor to high local nanoparticle densities. The SERS data indicate that aggregate geometry and interparticle distances in the cell must change in the course of endosomal maturation and play a critical role for a specific gold nanoparticle type in order to act as efficient SERS nanoprobe. This finding is supported by TEM images, showing only a minor portion of aggregates that present small interparticle spacing. The SERS spectra obtained after different chase times show a changing composition and/or structure of the biomolecule corona of the gold nanoparticles as a consequence of endosomal processing.     

Analysis of citrate-capped gold and silver nanoparticles by thiol ligand exchange capillary electrophoresis

We report on the capillary electrophoretic behavior of citrate-capped gold and silver nanoparticles in aqueous medium when applying a ligand-exchange surface reaction with thiols. Gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) of similar size (39?±?6 and 41?±?7 nm, respectively) and shape were synthesized, covered with a citrate shell, and characterized by microscopic and spectroscopic techniques. The analysis of these NPs by CE was accomplished by using a buffer solution (pH 9.7; 40 mM SDS, 10 mM CAPS; 0.1 % methanol) containing the anions of thioctic acid or thiomalic acid. These are capable of differently interacting with the surface of the AuNPs and AgNPs and thus introducing additional negative charges. This results in different migration times due to the formation of differently charged nanoparticles. Figure

Capillary electrophoretic behavior of citrate-capped gold and silver nanoparticles (NPs) in aqueous medium when applying a ligand-exchange surface reaction with thiols (thioctic and thiomalic acids), which introduces additional negative charges, has been studied