Showing papers in "Analytical Chemistry in 2007"
TL;DR: It is shown that the data produced here can be used to determine both size and concentration of gold nanoparticles directly from UV-vis spectra, and the precision of various methods are discussed.
Abstract: The dependence of the optical properties of spherical gold nanoparticles on particle size and wavelength were analyzed theoretically using multipole scattering theory, where the complex refractive index of gold was corrected for the effect of a reduced mean free path of the conduction electrons in small particles. To compare these theoretical results to experimental data, gold nanoparticles in the size range of 5 to 100 nm were synthesized and characterized with TEM and UV−vis. Excellent agreement was found between theory and experiment. It is shown that the data produced here can be used to determine both size and concentration of gold nanoparticles directly from UV−vis spectra. Equations for this purpose are derived, and the precision of various methods is discussed. The major aim of this work is to provide a simple and fast method to determine size and concentration of nanoparticles.
2,981 citations
TL;DR: Using this device, the first quantitative measurements of the influence of transient stimulation schedules on the proliferation, osteogenic differentiation, and motility of human primary mesenchymal stem cells are performed.
Abstract: There is increasing demand for automated and quantitative cell culture technology, driven both by the intense activity in stem cell biology and by the emergence of systems biology. We built a fully automated cell culture screening system based on a microfluidic chip that creates arbitrary culture media formulations in 96 independent culture chambers and maintains cell viability for weeks. Individual culture conditions are customized in terms of cell seeding density, composition of culture medium, and feeding schedule, and each chamber is imaged with time-lapse microscopy. Using this device, we perform the first quantitative measurements of the influence of transient stimulation schedules on the proliferation, osteogenic differentiation, and motility of human primary mesenchymal stem cells.
640 citations
TL;DR: The results show that free flow acoustophoresis can be used to perform complex separation tasks, thereby offering an alternative to expensive and time-consuming methods currently in use.
Abstract: A novel method, free flow acoustophoresis (FFA), capable of continuous separation of mixed particle suspensions into multiple outlet fractions is presented. Acoustic forces are utilized to separate particles based on their size and density. The method is shown to be suitable for both biological and nonbiological suspended particles. The microfluidic separation chips were fabricated using conventional microfabrication methods. Particle separation was accomplished by combining laminar flow with the axial acoustic primary radiation force in an ultrasonic standing wave field. Dissimilar suspended particles flowing through the 350-μm-wide channel were thereby laterally translated to different regions of the laminar flow profile, which was split into multiple outlets for continuous fraction collection. Using four outlets, a mixture of 2-, 5-, 8-, and 10-μm polystyrene particles was separated with between 62 and 94% of each particle size ending up in separate fractions. Using three outlets and three particle siz...
631 citations
TL;DR: The aptamer-modified CNT-FETs are promising candidates for the development of label-free protein biosensors, according to electrical properties, which provided better results than the ones obtained using IgE-mAb-modified cNT- FETs under similar conditions.
Abstract: We have fabricated label-free protein biosensors based on aptamer-modified carbon nanotube field-effect transistors (CNT-FETs) for the detection of immunoglobulin E (IgE). After the covalent immobilization of 5‘-amino-modified 45-mer aptamers on the CNT channels, the electrical properties of the CNT-FETs were monitored in real time. The introduction of target IgE at various concentrations caused a sharp decrease in the source-drain current, and a gradual saturation was observed at lower concentrations. The amount of the net source-drain current before and after IgE introduction on the aptamer-modified CNT-FETs increased as a function of IgE concentration. The detection limit for IgE was determined as 250 pM. We have also prepared CNT-FET biosensors using a monoclonal antibody against IgE (IgE−mAb). The electrical properties of the aptamer- and antibody-modified CNT-FETs were compared. The performance of aptamer-modified CNT-FETs provided better results than the ones obtained using IgE−mAb-modified CNT-FET...
618 citations
TL;DR: Multiplex sensing was demonstrated by the distinct response of the plasmon spectra of the GNrMPs to binding events of three targets, which can play a key role in developing novel optical biosensors for both in vivo and in vitro detection and single-receptor kinetics.
Abstract: Gold nanorods (GNRs) with different aspect ratios were fabricated through seed-mediated growth and surface activation by alkanethiols for the attachment of antibodies to yield gold nanorod molecular probes (GNrMPs). Multiplex sensing was demonstrated by the distinct response of the plasmon spectra of the GNrMPs to binding events of three targets (goat anti-human IgG1 Fab, rabbit anti-mouse IgG1 Fab, rabbit anti-sheep IgG (H+L)). Plasmonic sensors are highly specific and sensitive and can be used to monitor refractive index changes caused by molecular interactions in their immediate vicinity with potential to achieve single-particle biosensing. This technique can play a key role in developing novel optical biosensors for both in vivo and in vitro detection and single-receptor kinetics.
503 citations
TL;DR: The results suggest that TEX86 analysis by HPLC/APCI-MS is robust and can be determined with analytical errors comparable to those of other temperature proxies.
Abstract: The TEX86 is a recently proposed paleothermometer through which ancient seawater temperatures of up to 120 My ago can be reconstructed. It is based on the relative distribution of glycerol dibiphytanyl glycerol tetraethers as measured by high-performance liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (HPLC/APCI-MS). The aim of this study was to examine and improve several analytical aspects in the determination of this important proxy in environmental matrices. Comparison of TEX86 analysis using single ion mode (SIM) and mass scanning (m/z 950 to 1450) detection, respectively, revealed that SIM is up to 2 orders of magnitude more sensitive and that the TEX86 can be determined with a reproducibility of +/-0.004 or +/-0.3 degrees C using this method. Comparison of TEX86 values obtained with two different HPLC/APCI-MS set-ups revealed no significant differences. In addition, analysis of TEX86 of extracts obtained by Soxhlet, ultrasonic, and accelerated high-pressure extraction techniques also showed no significant differences between the methods. Our results suggest that TEX86 analysis by HPLC/APCI-MS is robust and can be determined with analytical errors comparable to those of other temperature proxies.
490 citations
TL;DR: A new elemental analysis (EA) technique for organic species (CHNO) that allows fast on-line analysis (10 s) and reduces the required sample size to approximately 1 ng, approximately 6 orders of magnitude less than standard techniques.
Abstract: We present a new elemental analysis (EA) technique for organic species (CHNO) that allows fast on-line analysis (10 s) and reduces the required sample size to ∼1 ng, ∼6 orders of magnitude less than standard techniques. The composition of the analyzed samples is approximated by the average elemental composition of the ions from high-resolution electron ionization (EI) mass spectra. EA of organic species can be performed on organic/inorganic mixtures. Elemental ratios for the total organic mass, such as oxygen/carbon (O/C), hydrogen/carbon (H/C), and nitrogen/carbon (N/C), in addition to the organic mass to organic carbon ratio (OM/OC), can be determined. As deviations between the molecular and the ionic composition can appear due to chemical influences on the ion fragmentation processes, the method was evaluated and calibrated using spectra from 20 compounds from the NIST database and from 35 laboratory standards sampled with the high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The a...
460 citations
TL;DR: With this system, a 10-pL droplet, encapsulating less than one copy of viral genomic DNA through Poisson statistics, showed real-time PCR amplification curves with a cycle threshold of approximately 18, 20 cycles earlier than commercial instruments.
Abstract: The first lab-on-chip system for picoliter droplet generation and PCR amplification with real-time fluorescence detection has performed PCR in isolated droplets at volumes 106 smaller than commercial real-time PCR instruments. The system utilized a shearing T-junction in a silicon device to generate a stream of monodisperse picoliter droplets that were isolated from the microfluidic channel walls and each other by the oil-phase carrier. An off-chip valving system stopped the droplets on-chip, allowing them to be thermally cycled through the PCR protocol without droplet motion. With this system, a 10-pL droplet, encapsulating less than one copy of viral genomic DNA through Poisson statistics, showed real-time PCR amplification curves with a cycle threshold of ∼18, 20 cycles earlier than commercial instruments. This combination of the established real-time PCR assay with digital microfluidics is ideal for isolating single-copy nucleic acids in a complex environment.
455 citations
TL;DR: The SiNW array biosensor described here is ultrasensitive, non-radioactive, and more importantly, label-free, and is of particular importance to the development of gene expression profiling tools and point-of-care applications.
Abstract: Arrays of highly ordered n-type silicon nanowires (SiNW) are fabricated using complementary metal-oxide semiconductor (CMOS) compatible technology, and their applications in biosensors are investigated. Peptide nucleic acid (PNA) capture probe-functionalized SiNW arrays show a concentration-dependent resistance change upon hybridization to complementary target DNA that is linear over a large dynamic range with a detection limit of 10 fM. As with other SiNW biosensing devices, the sensing mechanism can be understood in terms of the change in charge density at the SiNW surface after hybridization, the so-called "field effect". The SiNW array biosensor discriminates satisfactorily against mismatched target DNA. It is also able to monitor directly the DNA hybridization event in situ and in real time. The SiNW array biosensor described here is ultrasensitive, non-radioactive, and more importantly, label-free, and is of particular importance to the development of gene expression profiling tools and point-of-care applications.
448 citations
TL;DR: In this article, a nonoxidative approach to detect dopamine with high sensitivity and selectivity was proposed. But, it is not suitable for the detection of Parkinson's disease, as the products of dopamine oxidation can react with ascorbic acid present in samples and regenerate dopamine again, severely limiting the accuracy of detection.
Abstract: Most of the current techniques for detection of dopamine exploit its ease of oxidation. However, the oxidative approaches suffer from a common problem. The products of dopamine oxidation can react with ascorbic acid present in samples and regenerate dopamine again, which severely limits the accuracy of detection. In this paper, we report a nonoxidative approach to electrochemically detect dopamine with high sensitivity and selectivity. This approach takes advantage of the high performance of our newly developed poly(anilineboronic acid)/carbon nanotube composite and the excellent permselectivity of the ion-exchange polymer Nafion. The binding of dopamine to the boronic acid groups of the polymer with large affinity affects the electrochemical properties of the polyaniline backbone, which act as the transduction mechanism of this nonoxidative dopamine sensor. The unique reduction capability and high conductivity of single-stranded DNA functionalized, single-walled carbon nanotubes greatly improved the electrochemical activity of the polymer in physiological buffer, and the large surface area of the carbon nanotubes largely increased the density of the boronic acid receptors. The high sensitivity along with the improved selectivity of this sensing approach is a significant step forward toward molecular diagnosis of Parkinson's disease.
446 citations
TL;DR: The strategies used here will be highly useful for aptamer selection against complex target samples in order to generate a large number of aptamers in a variety of biomedical and biotechnological applications, paving the way for molecular diagnosis, therapy, and biomarker discovery.
Abstract: In this paper, we describe a new way to generate molecular probes for specific recognition of cancer cells. Molecular medicine will require a large number of probes for molecular recognition and characterization of a variety of diseased cells. Aptamers, single-stranded DNA/RNA probes, are poised to become a chemist's antibody and have the potential to serve as molecular probes for a variety of biomedical applications. By applying newly developed cell-SELEX (cell-based systematic evolution of ligands by exponential enrichment) against whole living cells, panels of aptamers have been evolved from an initial DNA library to characterize target cells at the molecular level. Ramos cells, a B-cell lymphoma cell line, were used as target cells for the generation of effective molecular probes. By taking advantages of the repetitive and broad enrichment strategy, the selected aptamers could bind to target cells and other closely related cell lines in variant patterns with an equilibrium dissociation constant (Kd) i...
TL;DR: A series of fluorophores with single-exponential fluorescence decays in liquid solution at 20 degrees C were measured independently by nine laboratories using single-photon timing and multifrequency phase and modulation fluorometry instruments with lasers as excitation source.
Abstract: A series of fluorophores with single-exponential fluorescence decays in liquid solution at 20 °C were measured independently by nine laboratories using single-photon timing and multifrequency phase and modulation fluorometry instruments with lasers as excitation source. The dyes that can serve as fluorescence lifetime standards for time-domain and frequency-domain measurements are all commercially available, are photostable under the conditions of the measurements, and are soluble in solvents of spectroscopic quality (methanol, cyclohexane, water). These lifetime standards are anthracene, 9-cyanoanthracene, 9,10-diphenylanthracene, N-methylcarbazole, coumarin 153, erythrosin B, N-acetyl-l-tryptophanamide, 1,4-bis(5-phenyloxazol-2-yl)benzene, 2,5-diphenyloxazole, rhodamine B, rubrene, N-(3-sulfopropyl)acridinium, and 1,4-diphenylbenzene. At 20 °C, the fluorescence lifetimes vary from 89 ps to 31.2 ns, depending on fluorescent dye and solvent, which is a useful range for modern pico- and nanosecond time-dom...
TL;DR: The proposed work demonstrates that the high specificity of aptamers together with the use of magnetic beads are the key features for aptamer-based analysis in complex matrixes, opening the possibility of a real application to diagnostics or medical investigation.
Abstract: The DNA thrombin aptamer has been extensively investigated, and the coupling of this aptamer to different transduction principles has demonstrated the wide applicability of aptamers as bioreceptors in bioanalytical assays. The goal of this work was to design an aptamer-based sandwich assay with electrochemical detection for thrombin analysis in complex matrixes, using a simple target capturing step by aptamer-functionalized magnetic beads. The conditions for the aptamer immobilization and for the protein binding have been first optimized by surface plasmon resonance, and then transferred to the electrochemical-based assay performed onto screen-printed electrodes. The assay was then applied to the analysis of thrombin in buffer, spiked serum, and plasma and high sensitivity and specificity were found. Moreover, thrombin was generated in situ in plasma by the conversion of its precursor prothrombin, and the formation of thrombin was followed at different times. The concentrations detected by the electrochemical assay were in agreement with a simulation software that mimics the formation of thrombin over time (thrombogram). The proposed work demonstrates that the high specificity of aptamers together with the use of magnetic beads are the key features for aptamer-based analysis in complex matrixes, opening the possibility of a real application to diagnostics or medical investigation.
TL;DR: The homologous series approach is extended toward a building block approach that can be applied as a new exclusion criterion for incorrect formula assignments and new techniques are proposed, suitable to be implemented in automated evaluation software.
Abstract: Ultrahigh-resolution mass spectrometry via the Fourier transform ion cyclotron resonance technique (FT-ICR-MS) allows the identification of thousands of different molecular formulas in natural organic matter and petroleum samples. Molecular formula assignment from mass data is most critical and time-consuming for these samples, and in many cases, several formulas can be determined for the same molecular mass. Therefore, automated procedures are required for an efficient exploitation of the extensive data sets. Here, we revise statements in a recent publication,1 which might result in a misleading impression about our approach of formula assignment in a previous work. We also summarize and categorize existing procedures for formula assignment. In addition, we propose new techniques, which are suitable to be implemented in automated evaluation software. The homologous series approach is extended toward a building block approach that can be applied as a new exclusion criterion for incorrect formula assignments. The examination of stable isotope ratios of individual molecules in natural organic matter can be applied as an additional and intrinsic evaluation for calculated molecular formulas.
TL;DR: The assembly of poly(ethylene glycol) (PEG) and mixed peptide/PEG monolayers on gold nanoparticle surfaces is described to provide useful cues in the assembly of stable peptides/gold nanoparticle bioconjugates capable of being internalized into cells.
Abstract: Gold nanoparticles have shown great promise as therapeutics, therapeutic delivery vectors, and intracellular imaging agents. For many biomedical applications, selective cell and nuclear targeting are desirable, and these remain a significant practical challenge in the use of nanoparticles in vivo. This challenge is being addressed by the incorporation of cell-targeting peptides or antibodies onto the nanoparticle surface, modifications that frequently compromise nanoparticle stability in high ionic strength biological media. We describe herein the assembly of poly(ethylene glycol) (PEG) and mixed peptide/PEG monolayers on gold nanoparticle surfaces. The stability of the resulting bioconjugates in high ionic strength media was characterized as a function of nanoparticle size, PEG length, and monolayer composition. In total, three different thiol-modified PEGs (average molecular weight (MW), 900, 1500, and 5000 g mol-1), four particle diameters (10, 20, 30, and 60 nm), and two cell-targeting peptides were e...
TL;DR: Differences in gender, diurnal variation, and age in a human population are explored and targeted profiling produces robust models, generates accurate metabolite concentration data, and provides data that can be used to help understand metabolic differences in a healthy population.
Abstract: Metabolomics may have the capacity to revolutionize disease diagnosis through the identification of scores of metabolites that vary during environmental, pathogenic, or toxicological insult. NMR spectroscopy has become one of the main tools for measuring these changes since an NMR spectrum can accurately identify metabolites and their concentrations. The predominant approach in analyzing NMR data has been through the technique of spectral binning. However, identification of spectral areas in an NMR spectrum is insufficient for diagnostic evaluation, since it is unknown whether areas of interest are strictly caused by metabolic changes or are simply artifacts. In this paper, we explore differences in gender, diurnal variation, and age in a human population. We use the example of gender differences to compare traditional spectral binning techniques (NMR spectral areas) to novel targeted profiling techniques (metabolites and their concentrations). We show that targeted profiling produces robust models, gener...
TL;DR: Comparison of metabolite levels in the culture supernatant and the cell interior revealed that the common assumption of whole broth quenching protocols attributing the metabolites found exclusively to the intracellular pools may not be valid in many cases.
Abstract: In the present work we investigated the most commonly applied methods used for sampling of microorganisms in the field of metabolomics in order to unravel potential sources of error previously ignored but of utmost importance for accurate metabolome analysis. To broaden the significance of our study, we investigated different Gram-negative and Gram-positive bacteria, i.e., Bacillus subtilis, Corynebacterium glutamicum, Escherichia coli, Gluconobacter oxydans, Pseudomonas putida, and Zymononas mobilis, and analyzed metabolites from different catabolic and anabolic intracellular pathways. Quenching of cells with cold methanol prior to cell separation and extraction led to drastic loss (>60%) of all metabolites tested due to unspecific leakage. Using fast filtration, Gram-negative bacteria also revealed a significant loss (>80%) when inappropriate washing solutions with low ionic strength were applied. Adapting the ionic strength of the washing solution to that of the cultivation medium could almost completely avoid this problem. Gram-positive strains did not show significant leakage independent of the washing solution. Fast filtration with sampling times of several seconds prior to extraction appears to be a suitable approach for metabolites with relatively high intracellular level and low turnover such as amino acids or TCA cycle intermediates. Comparison of metabolite levels in the culture supernatant and the cell interior revealed that the common assumption of whole broth quenching protocols attributing the metabolites found exclusively to the intracellular pools may not be valid in many cases. In such cases a differential approach correcting for medium-contained metabolites is required.
TL;DR: The developed label and method is versatile, offers enhanced performances, and can be easily extended to other protein detection schemes as well as in DNA analysis.
Abstract: A novel double-codified nanolabel (DC-AuNP) based on gold nanoparticle (AuNP) modified with anti-human IgG peroxidase (HRP)-conjugated antibody is reported. It represents a simple assay that allows enhanced spectrophotometric and electrochemical detection of antigen human IgG as a model protein. The method takes advantage of two properties of the DC-AuNP label: first, the HRP label activity toward the OPD chromogen that can be related to the analyte concentration and measured spectrophotometrically; second, the intrinsic electrochemical properties of the gold nanoparticle labels that being proportional to the protein concentration can be directly quantified by stripping voltammetry. Beside these two main direct determinations of human IgG, a secondary indirect detection was also applicable to this system, exploiting the high molar absorptivity of gold colloids, by which, the color intensity of their solution was proportional to the concentration of the antigen used in the assay. Paramagnetic beads were used as supporting material to immobilize the sandwich-type immunocomplexes resulting in incubation and washing times shorter than those typically needed in classical ELISA tests by means of a rapid magnetic separation of the unbound components. A built-in magnet graphite-epoxy-composite electrode allowed a sensibly enhanced adsorption and electrochemical quantification of the specifically captured AuNPs. The used DC-AuNP label showed an excellent specificity/selectivity, as a matter of fact using a different antigen (goat IgG) a minimal nonspecific electrochemical or spectrophotometric signal was measured. The detection limits for this novel double-codified nanoparticle-based assay were 52 and 260 pg of human IgG/mL for the spectrophotometric (HRP-based) and electrochemical (AuNP-based) detections, respectively, much lower than those typically achieved by ELISA tests. The developed label and method is versatile, offers enhanced performances, and can be easily extended to other protein detection schemes as well as in DNA analysis.
TL;DR: A supplemental collisional activation (CAD) method that targets the nondissociated (intact) electron-transfer (ET) product species ([M + 2H]+*) to improve ETD efficiency for doubly protonated peptides (ETcaD).
Abstract: Electron-transfer dissociation (ETD) delivers the unique attributes of electron capture dissociation to mass spectrometers that utilize radio frequency trapping-type devices (eg, quadrupole ion traps) The method has generated significant interest because of its compatibility with chromatography and its ability to: (1) preserve traditionally labile post-translational modifications (PTMs) and (2) randomly cleave the backbone bonds of highly charged peptide and protein precursor ions ETD, however, has shown limited applicability to doubly protonated peptide precursors, [M + 2H]2+, the charge and type of peptide most frequently encountered in "bottom-up" proteomics Here we describe a supplemental collisional activation (CAD) method that targets the nondissociated (intact) electron-transfer (ET) product species ([M + 2H]+*) to improve ETD efficiency for doubly protonated peptides (ETcaD) A systematic study of supplementary activation conditions revealed that low-energy CAD of the ET product population leads to the near-exclusive generation of c- and z-type fragment ions with relatively high efficiency (77 +/- 8%) Compared to those formed directly via ETD, the fragment ions were found to comprise increased relative amounts of the odd-electron c-type ions (c+*) and the even-electron z-type ions (z+) A large-scale analysis of 755 doubly charged tryptic peptides was conducted to compare the method (ETcaD) to ion trap CAD and ETD ETcaD produced a median sequence coverage of 89%-a significant improvement over ETD (63%) and ion trap CAD (77%)
TL;DR: An electrochemical, aptamer-based (E-AB) sensor for the detection of platelet-derived growth factor (PDGF) directly in blood serum that employs alternating current voltammetry to monitor target-induced folding in a methylene blue-modified, PDGF-binding aptamer.
Abstract: We report an electrochemical, aptamer-based (E-AB) sensor for the detection of platelet-derived growth factor (PDGF) directly in blood serum. The E-AB approach employs alternating current voltammetry to monitor target-induced folding in a methylene blue-modified, PDGF-binding aptamer. The sensor is sensitive, highly selective, and essentially reagentless: we readily detect the BB variant of PDGF at 1 nM directly in undiluted, unmodified blood serum and at 50 pM (1.25 ng/mL) in serum-diluted 2-fold with aqueous buffer. The sensitivity and selectivity achieved by this sensor match or significantly exceed those of the best analogous optical approaches. For example, the detection limit attained in 50% serum is achieved against a >25 million-fold excess of contaminating blood proteins and represents a 4 order of magnitude improvement over the most sensitive optical PDGF aptasensor reported to date. Moreover, the E-AB sensor combines these promising attributes in a platform that is reusable, label-free, and electronic. Given these advantages, E-AB sensors appear well suited for implementation in portable microdevices directed at the direct detection of proteins and small molecules in complex, largely unprocessed clinical samples.
TL;DR: The use the aptamer-conjugated nanoparticles for the collection and detection of multiple cancer cells and the wide applicability of this methodology for medical diagnostics and cell enrichment and separation is extended.
Abstract: We have extended the use the aptamer-conjugated nanoparticles for the collection and detection of multiple cancer cells. The aptamers were selected using a cell-based SELEX strategy in our laboratory for cancer cells that, when utilized in this method, allow for the selective recognition of the cells from complex mixtures including fetal bovine serum samples. Aptamer-conjugated magnetic nanoparticles were used for the selective targeting cell extraction, and aptamer-conjugated fluorescent nanoparticles were employed for sensitive cellular detection. Employing both types of nanoparticles allows for selective and sensitive detection not possible by using the particles separately. Fluorescent nanoparticles amplify the signal intensity versus a single fluorophore label resulting in improved sensitivity. In addition, aptamer-conjugated magnetic nanoparticles allow for extraction and enrichment of target cells not possible with other separation methods. Fluorescent imaging and a microplate reader were used for ...
TL;DR: Chlorine residuals in drinking water can react with some antibiotics, but ascorbic acid was found to be an effective chlorine quenching agent without affecting the analysis and stability of the antibiotics in water.
Abstract: A multirun analytical method has been developed and validated for trace determination of 24 antibiotics including 7 sulfonamides, 3 macrolides, 7 quinolones, 6 tetracyclines, and trimethoprim in chlorine-disinfected drinking water using a single solid-phase extraction method coupled to liquid chromatography with positive electrospray tandem mass spectrometry detection. The analytes were extracted by a hydrophilic-lipophilic balanced resin and eluted with acidified methanol (0.1% formic acid), resulting in analyte recoveries generally above 90%. The limits of quantitation were mostly below 10 ng/L in drinking water. Since the concentrated sample matrix typically caused ion suppression during electrospray ionization, the method of standard addition was used for quantitation. Chlorine residuals in drinking water can react with some antibiotics, but ascorbic acid was found to be an effective chlorine quenching agent without affecting the analysis and stability of the antibiotics in water. A preliminary occurrence study using this method revealed the presence of some antibiotics in drinking waters, including sulfamethoxazole (3.0-3.4 ng/L), macrolides (1.4-4.9 ng/L), and quinolones (1.2-4.0 ng/L).
TL;DR: A novel label-free ECL biosensor for the detection of low-density lipoprotein (LDL) has been developed by using self-assembly and gold nanoparticle amplification techniques and exhibited high sensitivity, good reproducibility, rapid response, and long-term stability.
Abstract: Mercaptoacetic acid (RSH)-capped CdS nanocrystals (NCs) was demonstrated to be electrochemically reduced during potential scan and react with the coreactant S2O82- to generate strong electrochemiluminescence (ECL) in aqueous solution. Based on the ECL of CdS NCs, a novel label-free ECL biosensor for the detection of low-density lipoprotein (LDL) has been developed by using self-assembly and gold nanoparticle amplification techniques. The biosensor was prepared as follows: The gold nanoparticles were first assembled onto a cysteamine monolayer on the gold electrode surface. This gold nanoparticle-covered electrode was next treated with cysteine and then reacted with CdS NCs to afford a CdS NC-electrode. Finally, apoB-100 (ligand of LDL receptor) was covalently conjugated to the CdS NC-electrode. The modification procedure was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy, respectively. The resulting modified electrode was tested as ECL biosensor f...
TL;DR: Experiments involving isotopic tracers revealed that the improved triph phosphate yields in the acidic acetonitrile were in part due to reduced triphosphate decomposition, which is a major problem when extracting with other solvent systems such as methanol/water.
Abstract: Cellular metabolome analysis by chromatography-mass spectrometry (MS) requires prior metabolite extraction. We examined a diversity of solvent systems for extraction of water-soluble metabolites from Escherichia coli. Quantitative yields of approximately 100 different metabolites were measured by liquid chromatography-tandem MS and displayed in clustered heat map format. Many metabolites, including most amino acids and components of central carbon metabolism, were adequately extracted by a broad spectrum of solvent mixtures. For nucleotide triphosphates, however, mixtures of acidic (0.1 M formic acid-containing) acetonitrile/water (80:20) or acetonitrile/methanol/water (40:40:20) gave superior triphosphate yields. Experiments involving isotopic tracers revealed that the improved triphosphate yields in the acidic acetonitrile were in part due to reduced triphosphate decomposition, which is a major problem when extracting with other solvent systems such as methanol/water. We recommend acidic solvent mixtures containing acetonitrile for extraction of the E. coli metabolome.
TL;DR: The developed analytical technique allows the quantitative imaging of selenium together with selected metals in thin sections of biological tissue with limits of detection at the submicrogram per gram range.
Abstract: Quantitative imaging analysis of endogenous an exogenous elements throughout entire organisms is required for studies of bioavailability, transport processes, distribution, contamination and to monitor environmental risks using indicator organisms. An imaging mass spectrometric technique using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) was developed to analyze selenium and metal distributions in longitudinal sections (thickness, 100 μm) of entire slugs (genus arion). Slugs were fed with either a placebo or solutions containing 1000 μg mL-1 Se. Samples (raster area, 25 mm × 45 mm) were scanned together with synthetic matrix-matched standards with a focused beam of a Nd:YAG laser (wavelength, 266 nm; diameter of laser crater, 50 μm; laser power density, 3 × 109 W cm-2) in a large laser ablation chamber. The ablated material was transported with argon as carrier gas to the ICP ion source at a double focusing sector field ICPMS. Ion intensities of selenium (78Se+, 82Se+) were measu...
TL;DR: The fabrication of a label-free, chip-based biosensor based on the localized surface plasmon resonance (LSPR) of gold nanorods is described, which has the significantly lower detection limit and the internal self-reference that the signal of the nanorod sensor providesbased on the measurement of peak wavelength shift.
Abstract: We describe the fabrication of a label-free, chip-based biosensor based on the localized surface plasmon resonance (LSPR) of gold nanorods. Gold nanorods were chemisorbed onto a mercaptosilane-modified glass substrate, followed by conjugation of biotin to the nanorods. Streptavidin binding to biotin was monitored by the wavelength shift of the LSPR peak in the UV−vis extinction spectrum of the immobilized gold nanorods due to the change in local refractive index at the gold nanorod surface induced by streptavidin binding. The limit of detection of the sensor is 0.005 μg/mL (94 pM) in PBS and 1 μg/mL (19 nM) in serum, and the dynamic range spans 94 pM to 0.19 μM. The advantages of the nanorod-based sensor over an LSPR sensor that we had previously fabricated from gold nanospheres (Nath, N.; Chilkoti, A. Anal. Chem. 2002, 74, 504−509; J. Fluoresc. 2004, 14, 377−389; Anal. Chem. 2004, 76, 5370−5378) are the significantly lower detection limit and the internal self-reference that the signal of the nanorod sen...
TL;DR: Only CySH2+ (H3A+) and CyS- (HA-) are the electroactive substances and should be responsible for the electrooxidation of CySH, and for the first time, the exact and systemic mechanisms based on the electro active species to explain CySH oxidation at different pH values are established.
Abstract: In this paper, the electrochemical behavior of l-cysteine (CySH) was investigated thoroughly at an ordered mesoporous carbon-modified glassy carbon (OMC/GC) electrode. The voltammetric studies showed there were three anodic peaks for the electrooxidation of CySH in the pH range of 2.00−5.00; however, one peak disappeared above pH 5.00. This behavior has never been reported before. Through the studies of the effect of pH on the distribution fractions (δ) of the four chemical species of CySH, we conclude only CySH2+ (H3A+) and CyS- (HA-) are the electroactive substances and should be responsible for the electrooxidation of CySH. And for the first time, we successfully established the exact and systemic mechanisms based on the electroactive species to explain CySH oxidation at different pH values. On the other hand, a sensitive CySH sensor was developed based on an OMC/GC electrode, which shows a large determination range (18−2500 μmol L-1), a high sensitivity (23.6 μA mmol L-1), and a remarkably low detecti...
TL;DR: An enhanced liquid chromatography-mass spectrometry strategy for the analysis of a selected group of 56 organic pollutants in wastewater, which comprises 38 pharmaceuticals and 10 of their most frequent metabolites, 6 pesticides, and 2 disinfectants is described.
Abstract: This paper describes an enhanced liquid chromatography−mass spectrometry (LC−MS) strategy for the analysis of a selected group of 56 organic pollutants in wastewater. This group comprises 38 pharmaceuticals and 10 of their most frequent metabolites, 6 pesticides, and 2 disinfectants. The LC−MS methodology applied is based in the use of a hybrid triple-quadrupole linear ion trap mass spectrometer (QTRAP) in combination with time-of-flight mass spectrometry (TOF-MS). The join application of both techniques provided very good results in terms of accurate quantification and unequivocal confirmation. Quantification was performed by LC-QTRAP-MS operating under selected reaction monitoring (SRM) mode in both positive and negative electrospray ionization. Unequivocal identification was provided by the acquisition of three SRM transitions per compound in most of the cases and by LC-TOF-MS analysis, which allows obtaining accurate mass measurements of the identified compounds with errors lower than 2 ppm. Additiona...
TL;DR: This system will provide a useful tool to separate colloids and particles for various analytical and preparative applications and may hold potential for separation of cells or development of diagnostic tools requiring point-of-care sample preparation or testing.
Abstract: This paper describes a simple microfluidic sorting system that can perform size profiling and continuous mass-dependent separation of particles through combined use of gravity (1 g) and hydrodynamic flows capable of rapidly amplifying sedimentation-based separation between particles. Operation of the device relies on two microfluidic transport processes: (i) initial hydrodynamic focusing of particles in a microchannel oriented parallel to gravity and (ii) subsequent sample separation where positional difference between particles with different mass generated by sedimentation is further amplified by hydrodynamic flows whose streamlines gradually widen out due to the geometry of a widening microchannel oriented perpendicular to gravity. The microfluidic sorting device was fabricated in poly(dimethylsiloxane), and hydrodynamic flows in microchannels were driven by gravity without using external pumps. We conducted theoretical and experimental studies on fluid dynamic characteristics of laminar flows in wide...