Showing papers in "Analytical Chemistry in 2000"
1,603 citations
TL;DR: Oligonucleotide surface coverages of hexanethiol 12-mer oligonucleotides on gold nanoparticles were significantly higher than on planar gold thin films, and olig onucleotide spacer sequences improve the hybridization efficiency of oligon nucleotide-modified nanoparticles from approximately 4 to 44%.
Abstract: Using a fluorescence-based method, we have determined the number of thiol-derivatized single-stranded oligonucleotides bound to gold nanoparticles and their extent of hybridization with complementary oligonucleotides in solution. Oligonucleotide surface coverages of hexanethiol 12-mer oligonucleotides on gold nanoparticles (34 ± 1 pmol/cm2) were significantly higher than on planar gold thin films (18 ± 3 pmol/cm2), while the percentage of hybridizable strands on the gold nanoparticles (1.3 ± 0.3 pmol/cm2, 4%) was lower than for gold thin films (6 ± 2 pmol/cm2, 33%). A gradual increase in electrolyte concentration over the course of oligonucleotide deposition significantly increases surface coverage and consequently particle stability. In addition, oligonucleotide spacer sequences improve the hybridization efficiency of oligonucleotide-modified nanoparticles from ∼4 to 44%. The surface coverage of recognition strands can be tailored using coadsorbed diluent oligonucleotides. This provides a means of indire...
1,058 citations
TL;DR: This work describes a new type of mass analyzer which employs trapping in an electrostatic field and demonstrates high-mass resolution up to 150,000 for ions produced by laser ablation, along with high-energy acceptance and wide mass range.
Abstract: This work describes a new type of mass analyzer which employs trapping in an electrostatic field. The potential distribution of the field can be represented as a combination of quadrupole and logarithmic potentials. In the absence of any magnetic or rf fields, ion stability is achieved only due to ions orbiting around an axial electrode. Orbiting ions also perform harmonic oscillations along the electrode with frequency proportional to (m/z)-1/2. These oscillations are detected using image current detection and are transformed into mass spectra using fast FT, similarly to FT ICR. Practical aspects of the trap design are presented. High-mass resolution up to 150 000 for ions produced by laser ablation has been demonstrated, along with high-energy acceptance and wide mass range.
954 citations
TL;DR: For proteins of < 20 kDa, this new radical site dissociation method cleaves different and many more backbone bonds than the conventional MS/MS methods that add energy directly to the even-electron ions.
Abstract: For proteins of <20 kDa, this new radical site dissociation method cleaves different and many more backbone bonds than the conventional MS/MS methods (e.g., collisionally activated dissociation, CAD) that add energy directly to the even-electron ions. A minimum kinetic energy difference between the electron and ion maximizes capture; a 1 eV difference reduces capture by 103. Thus, in an FTMS ion cell with added electron trapping electrodes, capture appears to be achieved best at the boundary between the potential wells that trap the electrons and ions, now providing 80 ± 15% precursor ion conversion efficiency. Capture cross section is dependent on the ionic charge squared (z2), minimizing the secondary dissociation of lower charge fragment ions. Electron capture is postulated to occur initially at a protonated site to release an energetic (∼6 eV) H• atom that is captured at a high-affinity site such as −S−S− or backbone amide to cause nonergodic (before energy randomization) dissociation. Cleavages betwe...
952 citations
TL;DR: Stripping voltammetric measurements of microgram per liter levels of cadmium, lead, thallium, and zinc in nondeaerated solutions yielded well-defined peaks, along with a low background, following short deposition periods, indicating great promise to centralized and decentralized testing of trace metals.
Abstract: Bismuth-coated carbon electrodes display an attractive stripping voltammetric performance which compares favorably with that of common mercury-film electrodes. These bismuth-film electrodes are prepared by adding 400 μg/L (ppb) bismuth(III) directly to the sample solution and simultanously depositing the bismuth and target metals on the glassy-carbon or carbon-fiber substrate. Stripping voltammetric measurements of microgram per liter levels of cadmium, lead, thallium, and zinc in nondeaerated solutions yielded well-defined peaks, along with a low background, following short deposition periods. Detection limit of 1.1 and 0.3 ppb lead are obtained following 2- and 10-min deposition, respectively. Changes in the peak potentials (compared to those observed at mercury electrodes) offer new selectivity dimensions. Scanning electron microscopy sheds useful insights into the different morphologies of the bismuth deposits on the carbon substrates. The in situ bismuth-plated electrodes exhibit a wide accessible po...
896 citations
TL;DR: In this article, a method for analyzing a sample of an analyte provided as a sample solution comprising a solvent and a dopant is provided, either separately or as the solvent of the sample solution.
Abstract: There is provided a method of, and apparatus for, analyzing a sample of an analyte provided as a sample solution comprising a solvent and an analyte. A dopant is provided, either separately or as the solvent of the sample solution. The sample solution is formed into a spray, for example in a nebulizer, and the solvent evaporated. The sample stream is irradiated in a region at atmospheric pressure, either in the liquid state prior to formation of a spray, or in the liquid state after formation of a droplet spray, or in the vapour state after evaporation of the sprayed droplets, to ionize the dopant. Then, subsequent collisions between the ionized dopant and the analyte, either directly or indirectly, result in ionization of the analyte. Analyte ions are passed from the atmospheric pressure ionization region into a mass analyzer for mass analysis. This technique has been found to give much enchanced inonization for some substances, as compared to atmospheric pressure chemical ionization.
761 citations
TL;DR: This method can generate topologically complex microfluidic systems and can fabricate a membrane containing a channel that crosses over and under itself, but does not intersect itself and, therefore, can be fabricated in the form of any knot.
Abstract: This paper describes a procedure for making topologically complex three-dimensional microfluidic channel systems in poly(dimethylsiloxane) (PDMS). This procedure is called the “membrane sandwich” method to suggest the structure of the final system: a thin membrane having channel structures molded on each face (and with connections between the faces) sandwiched between two thicker, flat slabs that provide structural support. Two “masters” are fabricated by rapid prototyping using two-level photolithography and replica molding. They are aligned face to face, under pressure, with PDMS prepolymer between them. The PDMS is cured thermally. The masters have complementary alignment tracks, so registration is straightforward. The resulting, thin PDMS membrane can be transferred and sealed to another membrane or slab of PDMS by a sequence of steps in which the two masters are removed one at a time; these steps take place without distortion of the features. This method can fabricate a membrane containing a channel...
745 citations
TL;DR: A detailed recipe to determine correct potentiometric selectivity coefficients unaffected by such biases is presented.
Abstract: Selectivities of solvent polymeric membrane ion-selective electrodes (ISEs) are quantitatively related to equilibria at the interface between the sample and the electrode membrane. However, only correctly determined selectivity coefficients allow accurate predictions of ISE responses to real-world samples. Moreover, they are also required for the optimization of ionophore structures and membrane compositions. Best suited for such purposes are potentiometric selectivity coefficients as defined already in the 1960s. This paper briefly reviews the basic relationships and focuses on possible biases in the determination of selectivity coefficients. The traditional methods to determine selectivity coefficients (separate solution method, fixed interference method) are still the same as those originally proposed by IUPAC in 1976. However, several precautions are needed to obtain meaningful data. For example, errors arise when the response to a weakly interfering ion is also influenced by the primary ion leaching from the membrane. Wrong selectivity coefficients may be also obtained when the interfering agent is highly preferred and the electrode shows counterion interference. Recent advances show how such pitfalls can be avoided. A detailed recipe to determine correct potentiometric selectivity coefficients unaffected by such biases is presented.
733 citations
TL;DR: The protein search engine "ProFound", which employs a Bayesian algorithm to identify proteins from protein databases using mass spectrometric peptide mapping data, consistently identifies the correct protein(s) even when the data quality is relatively low or when the sample consists of a simple mixture of proteins.
Abstract: We describe the protein search engine “ProFound”, which employs a Bayesian algorithm to identify proteins from protein databases using mass spectrometric peptide mapping data The algorithm ranks protein candidates by taking into account individual properties of each protein in the database as well as other information relevant to the peptide mapping experiment The program consistently identifies the correct protein(s) even when the data quality is relatively low or when the sample consists of a simple mixture of proteins Illustrative examples of protein identifications are provided
601 citations
TL;DR: An integrated system for rapid PCR-based analysis on a microchip has been demonstrated and an on-chip DNA concentration technique has been incorporated into the system to further reduce analysis time by decreasing the number of thermal cycles required.
Abstract: An integrated system for rapid PCR-based analysis on a microchip has been demonstrated. The system couples a compact thermal cycling assembly based on dual Peltier thermoelectric elements with a microchip gel electrophoresis platform. This configuration allows fast (∼1 min/cycle) and efficient DNA amplification on-chip followed by electrophoretic sizing and detection on the same chip. An on-chip DNA concentration technique has been incorporated into the system to further reduce analysis time by decreasing the number of thermal cycles required. The concentration injection scheme enables detection of PCR products after performing as few as 10 thermal cycles, with a total analysis time of less than 20 min. The starting template copy number was less than 15 per injection volume.
573 citations
TL;DR: More than 15 uncommon plant metabolites were identified, some of which are novel in Arabidopsis, such as tartronate semialdehyde, citramalic acid, allothreonine, or glycolic amide.
Abstract: Unknown compounds in polar fractions of Arabidopsis thaliana crude leaf extracts were identified on the basis of calculations of elemental compositions obtained from gas chromatography/low-resolution quadrupole mass spectrometric data. Plant metabolites were methoximated and silylated prior to analysis. All known peaks were used as internal references to construct polynomial recalibration curves of from raw mass spectrometric data. Mass accuracies of 0.005 ± 0.003 amu and isotope ratio errors of 0.5 ± 0.3% (A + 1/A), respectively, 0.3 ± 0.2% (A + 2/A), could be achieved. Both masses and isotope ratios were combined when the elemental compositions of unknown peaks were calculated. After calculation, compound identities were elucidated by searching metabolic databases, interpreting spectra, and, finally, by comparison with reference compounds. Sum formulas of more than 70 peaks were determined throughout single GC/MS chromatograms. Exact masses were confirmed by high-resolution mass spectrometric data. More...
TL;DR: The capabilities of surface-enhanced Raman spectroscopy to detect the chemical vapor signature emanating from buried TNT-based landmines are demonstrated and it is shown that SERS can be a significant improvement over current landmine detection methods.
Abstract: Time, cost, and casualties associated with demining efforts underscore the need for improved detection techniques. Reduction in the number of false positives by directly detecting the explosive material, rather than casing material, is desirable. The desired field sensor must, at a minimum, demonstrate reproducibility, the necessary level of sensitivity, portability, instrumental stability, and fast system response times. Ideally, vibrational spectroscopic techniques have the potential to remove false positives, since every chemical has a unique bond structure. Herein, we demonstrate the capabilities of surface-enhanced Raman spectroscopy to detect the chemical vapor signature emanating from buried TNT-based landmines. We present reproducible results obtained from blind tests controlled by the Defense Advanced Research Projects Agency (DARPA) that demonstrate vapor detection of 2,4-dinitrotoluene at concentration levels of 5 ppb or less. The results presented used acquisition times of 30 s on a fieldable ...
TL;DR: A new matrix-assisted laser desorption/ionization (MALDI) time-of-flight/time- of-flight (TOF/TOF) high-resolution tandem mass spectrometer is described for sequencing peptides.
Abstract: A new matrix-assisted laser desorption/ionization (MALDI) time-of-flight/time-of-flight (TOF/TOF) high-resolution tandem mass spectrometer is described for sequencing peptides. This instrument combines the advantages of high sensitivity for peptide analysis associated with MALDI and comprehensive fragmentation information provided by high-energy collision-induced dissociation (CID). Unlike the postsource decay technique that is widely used with MALDI-TOF instruments and typically combines as many as 10 separate spectra of different mass regions, this instrument allows complete fragment ion spectra to be obtained in a single acquisition at a fixed reflectron voltage. To achieve optimum resolution and focusing over the whole mass range, it may be desirable to acquire and combine three separate sections. Different combinations of MALDI matrix and collision gas determine the amount of internal energy deposited by the MALDI process and the CID process, which provide control over the extent and nature of the fr...
TL;DR: A look at some of the basic concepts and novel components used to construct prototype devices in the construction of prototype devices.
Abstract: A look at some of the basic concepts and novel components used to construct prototype devices.
TL;DR: This method is simple, rapid, and selective compared with conventional techniques and could be readily applied to the analysis of free amino acids in soy sauce.
Abstract: A method for the determination of underivatized amino acids based on capillary electrophoresis coupled to electrospray ionization mass spectrometry (CE-ESI-MS) is described. To analyze free amino acids simultaneously a low acidic pH condition was used to confer positive charge on whole amino acids. The choice of the electrolyte and its concentration influenced resolution and peak shape of the amino acids, and 1 M formic acid was selected as the optimal electrolyte. Meanwhile, the sheath liquid composition had a significant effect on sensitivity and the highest sensitivity was obtained when 5 mM ammonium acetate in 50% (v/v) methanol-water was used. Protonated amino acids were roughly separated by CE and selectively detected by a quadrupole mass spectrometer with a sheath flow electrospray ionization interface. Under the optimized conditions, 19 free amino acids normally found in proteins and several physiological amino acids were well determined in less than 17 min. The detection limits for basic amino acids were between 0.3 and 1.1 mumol/L and for acidic and low molecular weight amino acids were less than 6.0 mumol/L with pressure injection of 50 mbar for 3 s (3 nL) at a signal-to-noise ratio of 3. This method is simple, rapid, and selective compared with conventional techniques and could be readily applied to the analysis of free amino acids in soy sauce.
TL;DR: Volatile compounds emanated from human skin were studied by gas chromatography/mass spectrometry to identify compounds that may be human-produced kairomones which are used for host location by the mosquito, Aedes aegypti (L.).
Abstract: Volatile compounds emanated from human skin were studied by gas chromatography/mass spectrometry (GC/MS). The purpose of this study was to identify compounds that may be human-produced kairomones which are used for host location by the mosquito, Aedes aegypti (L.). The procedure used to collect volatiles was chosen because of prior knowledge that attractive substances can be transferred from skin to glass by handling. Laboratory bioassays have shown that the residuum on the glass remains attractive to mosquitoes until the compounds of importance evaporate. The sampling and analytical procedures modeled the above-cited process as closely as possible except that the evaporation of compounds from the glass surface was accomplished by thermal desorption from glass beads in a heated GC injection port. This made possible the solventless injection of volatiles onto the column. The compounds were cryofocused on the head of the column with liquid nitrogen prior to GC separation. A single stage of mass spectrometry...
TL;DR: Dielectrophoretic field-flow-fractionation was applied to several clinically relevant cell separation problems, including the purging of human breast cancer cells from normal T-lymphocytes and from CD34+ hematopoietic stem cells, the separation of the major leukocyte subpopulations, and the enrichment of leukocytes from blood.
Abstract: Dielectrophoretic field-flow-fractionation (DEP-FFF) was applied to several clinically relevant cell separation problems, including the purging of human breast cancer cells from normal T-lymphocytes and from CD34+ hematopoietic stem cells, the separation of the major leukocyte subpopulations, and the enrichment of leukocytes from blood. Cell separations were achieved in a thin chamber equipped with a microfabricated, interdigitated electrode array on its bottom wall that was energized with AC electric signals. Cells were levitated by the balance between DEP and sedimentation forces to different equilibrium heights and were transported at differing velocities and thereby separated when a velocity profile was established in the chamber. This bulk-separation technique adds cell intrinsic dielectric properties to the catalog of physical characteristics that can be applied to cell discrimination. The separation process and performance can be controlled through electronic means. Cell labeling is unnecessary, an...
TL;DR: Capillary electrochromatography was conducted using an electroosmotically pumped microfluidic system and BODIPY and fluorescein were loaded onto a 200-micron-long chromatographic bed and then separated in an isocratic CEC run with an acetonitrile/buffer mobile phase.
Abstract: A 330-pL chromatographic bed was fabricated on a glass substrate as part of an electroosmotically pumped microfluidic system. Two weirs within a sample channel formed a cavity in which octadecylsilane (ODS) coated silica beads (1.5−4 μm diameter) were trapped. ODS beads were mobilized into and out of the cavity using electroosmotic flow through a bead-introduction channel which accessed the cavity. This procedure allowed the beads in the cavity to be repeatedly exchanged. A 1 nM solution of a nonpolar analyte (BODIPY 493/ 503) in buffer was loaded onto the beads for different lengths of time using an electroosmotic flow of 1.2 nL/s. The material retained on the ODS phase was then eluted by electroosmotic flow of acetonitrile with a concentration enhancement of up to 500 times. Capillary electrochromatography was conducted using a similar device. BODIPY and fluorescein were loaded onto a 200-μm-long chromatographic bed and then separated in an isocratic CEC run with an acetonitrile/buffer mobile phase. Com...
TL;DR: The attractive performance characteristics of the glutamate biosensor illustrate the advantages of Prussian Blue-based "artificial peroxidase" as transducer for hydrogen peroxide detection.
Abstract: The specially deposited Prussian Blue denoted as “artificial peroxidase” was used as a transducer for hydrogen peroxide. The electrocatalyst was stable, highly active, and selective to hydrogen peroxide reduction in the presence of oxygen, which allowed sensing of H2O2 around 0.0 V (Ag/AgCl). Glutamate oxidase was immobilized on the surface of the Prussian Blue-modified electrode in a Nafion layer using a nonaqueous enzymology approach. The calibration range for glutamate in flow injection system was 1 × 10-7−1 × 10-4 M. The lowest concentration of glutamate detected (1 × 10-7 M) and the highest sensitivity in the linear range of 0.21 A M-1 cm-2 were achieved. The influence of reductants was practically avoided using the low potential of an indicator electrode (0.0 V Ag/AgCl). The attractive performance characteristics of the glutamate biosensor illustrate the advantages of Prussian Blue-based “artificial peroxidase” as transducer for hydrogen peroxide detection.
TL;DR: A novel ionization source for biological mass spectrometry that combines atmospheric pressure (AP) ionization and matrix-assisted laser desorption/ionization (MALDI) and the transfer of the ions from the atmospheric pressure ionization region to the high vacuum is pneumatically assisted (PA) by a stream of nitrogen, hence the acronym PA-AP MALDI.
Abstract: A novel ionization source for biological mass spectrometry is described that combines atmospheric pressure (AP) ionization and matrix-assisted laser desorption/ionization (MALDI). The transfer of the ions from the atmospheric pressure ionization region to the high vacuum is pneumatically assisted (PA) by a stream of nitrogen, hence the acronym PA-AP MALDI. PA-AP MALDI is readily interchangeable with electrospray ionization on an orthogonal acceleration time-of-flight (oaTOF) mass spectrometer. Sample preparation is identical to that for conventional vacuum MALDI and uses the same matrix compounds, such as α-cyano-4-hydroxycinnamic acid. The performance of this ion source on the oaTOF mass spectrometer is compared with that of conventional vacuum MALDI-TOF for the analysis of peptides. PA-AP MALDI can detect low femtomole amounts of peptides in mixtures with good signal-to-noise ratio and with less discrimination for the detection of individual peptides in a protein digest. Peptide ions produced by this me...
TL;DR: P perturbations of electroosmotic flow in open capillaries that are due to induced pressure gradients resulting from axial variations in the wall zeta-potential are investigated.
Abstract: The present work is an analytical and experimental study of electroosmotic flow (EOF) in cylindrical capillaries with nonuniform wall surface charge (ζ-potential) distributions. In particular, this study investigates perturbations of electroosmotic flow in open capillaries that are due to induced pressure gradients resulting from axial variations in the wall ζ-potential. The experimental inquiry focuses on electroosmotic flow under a uniform applied field in capillaries with an EOF-suppressing polymer adsorbed onto various fractions of the total capillary length. This fractional EOF suppression was achieved by coupling capillaries with substantially different ζ-potentials. The resulting flow fields were imaged with a nonintrusive, caged-fluorescence imaging technique. Simple analytical models for the velocity field and rate of sample dispersion in capillaries with axial ζ-potential variations are presented. The resulting induced pressure gradients and the associated band-broadening effects are of particul...
TL;DR: The results showed that the direct oxidation of TPrA played an important role in the ECL processes, and the enhancement of the T PrA oxidation current might lead to an increase in theECL intensity.
Abstract: We describe the electrogenerated chemiluminescence (ECL) processes of the Ru(bpy)32+ (bpy = 2,2‘-bipyridyl)/tripropylamine (TPrA) system at glassy carbon, platinum, and gold electrodes. The electrochemical behavior of TPrA on different electrode materials and its influence on the ECL process are demonstrated. At glassy carbon electrodes, the direct oxidation of TPrA began at ∼0.6 V vs SCE and exhibited a broad irreversible anodic peak. Two ECL waves were observed, one in the potential region more negative than 1.0 V vs SCE and one at more positive potentials. The first ECL process apparently occurs without the electrogeneration of Ru(bpy)33+, in contrast to that of the second ECL wave. At Pt and Au electrodes, however, the formation of surface oxides significantly blocked the direct oxidation of TPrA. An ECL wave below 1.0 V did not appear at Pt and was very weak at gold. The ECL peaks at potentials of 1.1−1.2 V were also much weaker than those observed at the glassy carbon electrode. These results showed...
TL;DR: The sensitivity of DNA detection was improved to 10 zmol by reducing the amount of immobilized DNA probe and protecting the uncovered surface of the electrode with 2-mercaptoethanol, and dA20 and the yeast choline transport gene were quantitated at the subpicomole level.
Abstract: Naphthalene diimide derivative 1 carrying ferrocenyl moieties at the termini of imide substituents binds intact calf thymus DNA 4 times more strongly than the denatured DNA, and its complex with the intact DNA dissociates 80 times more slowly than that with the denatured DNA. On the basis of these observations, ligand 1 was applied to a probe of electrochemical DNA sensing. A thiol-linked single-stranded DNA probe was immobilized through the S−Au bonding to 20−30 pmol/mm2 on a gold electrode. Following hybridization with the complementary DNA, the electrode was soaked in a solution containing 1 (intercalation step) and then washed with buffer for 5 s. The cyclic voltammogram and differential pulse voltammogram for this electrode gave an electrochemical signal due to the redox reaction of 1 that was bound to the double-stranded DNA on the electrode. Thus, dA20 and the yeast choline transport gene were quantitated at the subpicomole level. The sensitivity of DNA detection was improved to 10 zmol by reducing...
TL;DR: The cyclic voltammetric and kinetic data presented can serve as a benchmark for research groups evaluating the electrochemical properties of semimetallic (i.e., conductive), hydrogen-terminated, polycrystalline diamond.
Abstract: Standard electrochemical data for high-quality, boron-doped diamond thin-film electrodes are presented. Films from two different sources were compared (NRL and USU) and both were highly conductive, hydrogen-terminated, and polycrystalline. The films are acid washed and hydrogen plasma treated prior to use to remove nondiamond carbon impurity phases and to hydrogen terminate the surface. The boron-doping level of the NRL film was estimated to be in the mid 1019 B/cm3 range, and the boron-doping level of the USU films was ∼5 × 1020 B/cm-3 based on boron nuclear reaction analysis. The electrochemical response was evaluated using Fe(CN)63-/4-, Ru(NH3)63+/2+, IrCl62-/3-, methyl viologen, dopamine, ascorbic acid, Fe3+/2+, and chlorpromazine. Comparisons are made between the apparent heterogeneous electron-transfer rate constants, koapp, observed at these high-quality diamond films and the rate constants reported in the literature for freshly activated glassy carbon. Ru(NH3)63+/2+, IrCl62-/3-, methyl viologen, a...
TL;DR: The integration cut the time necessary for the antigen-antibody reaction by 1/90, thus shortening the overall analysis time from 24 h to less than 1 h, and troublesome operations required for conventional immunosorbent assays could be replaced by simple operations.
Abstract: An immunosorbent assay system was integrated into a glass microchip. Polystyrene beads were introduced into a microchannel, and then human secretory immunoglobulin A (s-IgA) adsorbed on the bead surface was reacted with colloidal gold conjugated anti-s-IgA antibody and detected by a thermal lens microscope. The scale merits of liquid microspace on the molecular behavior remarkably contributed to reduced assay time. The integration cut the time necessary for the antigen-antibody reaction by 1/90, thus shortening the overall analysis time from 24 h to less than 1 h. Moreover, troublesome operations required for conventional immunosorbent assays could be replaced by simple operations.
TL;DR: A combined scanning electrochemical microscope (SECM)-atomic force microscope (AFM) is described, which permits the first simultaneous topographical and electrochemical measurements at surfaces, under fluid, with high spatial resolution.
Abstract: A combined scanning electrochemical microscope (SECM)−atomic force microscope (AFM) is described. The instrument permits the first simultaneous topographical and electrochemical measurements at surfaces, under fluid, with high spatial resolution. Simple probe tips suitable for SECM−AFM, have been fabricated by coating flattened and etched Pt microwires with insulating, electrophoretically deposited paint. The flattened portion of the probe provides a flexible cantilever (force sensor), while the coating insulates the probe such that only the tip end (electrode) is exposed to the solution. The SECM−AFM technique is illustrated with simultaneous electrochemical-probe deflection approach curves, simultaneous topographical and electrochemical imaging studies of track-etched polycarbonate ultrafiltration membranes, and etching studies of crystal surfaces.
TL;DR: A novel, sensitive electrochemical immunoassay has been developed using a colloidal gold label that, after oxidative gold metal dissolution in an acidic solution, was indirectly determined by anodic stripping voltammetry (ASV) at a single-use carbon-based screen-printed electrode (SPE).
Abstract: A novel, sensitive electrochemical immunoassay has been developed using a colloidal gold label that, after oxidative gold metal dissolution in an acidic solution, was indirectly determined by anodic stripping voltammetry (ASV) at a single-use carbon-based screen-printed electrode (SPE). The use of disposable electrodes allows for simplified measurement in 35 μL of solution. The method was evaluated for a noncompetitive heterogeneous immunoassay of an immunoglobulin G (IgG) and a concentration as low as 3 × 10-12 M was determined, which is competitive with colorimetric ELISA or with immunoassays based on fluorescent europium chelate labels. The high performance of the method is related to the sensitive ASV determination of gold(III) at a SPE (detection limit of 5 × 10-9 M) and to the release of a large number of gold(III) ions from each gold particle anchored on the immunocomplex (e.g., 1.7 × 105 gold atoms are theoretically contained in a 18-nm spherical gold particle).
TL;DR: A high-throughput, robust, sensitive, accurate, and precise assay for simultaneous measurement of trace levels of eight phthalate metabolites in human urine by HPLC-MS/MS to help elucidate potential associations (if any) between human exposure to phthalates and adverse health effects.
Abstract: Because of the ubiquity of phthalates and their potential role in increasing risk for cancer and reproductive dysfunction, the need for human exposure assessment studies is urgent. In response to this need, we developed a high-throughput, robust, sensitive, accurate, and precise assay for simultaneous measurement of trace levels of eight phthalate metabolites in human urine by HPLC−MS/MS. Human urine samples were processed using enzymatic deconjugation of the glucuronides followed by solid-phase extraction. The eluate was concentrated, and the phthalate metabolites were chromatographically resolved by reversed-phase HPLC, detected by APCI-tandem mass spectrometry, and quantified by isotope dilution. This selective analytical method permits rapid detection (7.7 min total run time) of eight urinary metabolites of the most commonly used phthalates with detection limits in the low nanagram per milliliter range. Assay precision was improved by incorporating 13C4-labeled internal standards for each of the eight...
TL;DR: High-repetition fast-scan cyclic voltammetry and chronoamperometry were used to quantify and characterize the kinetics of dopamine and dopamine-o-quinone adsorption and desorption at carbon-fiber microelectrodes, and voltammetrically measured uptake kinetics in the caudate are faster using 2,000 V/s and 240 Hz measurements.
Abstract: High-repetition fast-scan cyclic voltammetry and chronoamperometry were used to quantify and characterize the kinetics of dopamine and dopamine-o-quinone adsorption and desorption at carbon-fiber microelectrodes. A flow injection analysis system was used for the precise introduction and removal of a bolus of electroactive substance on a sub-second time scale to the disk-shaped surface of a microelectrode that was fabricated from a single carbon fiber (Thornel type T650 or P55). Pretreatment of the electrode surfaces consisted of soaking them in purified isopropyl alcohol for a minimum of 10 min, which resulted in S/N increasing by 200−400% for dopamine above that for those that were soaked in reagent grade solvent. Because of adsorption, high scan rates (2000 V/s) are shown to exhibit equivalent S/N ratios as compared to slower, more traditional scan rates. In addition, the steady-state response to a concentration bolus is shown to occur more rapidly when cyclic voltammetric scans are repeated at short in...
TL;DR: Prestructured MALDI-MS sample supports have been developed that simplify high-throughput analysis of biomolecules and improve the detection sensitivity.
Abstract: Prestructured MALDI-MS sample supports have been developed that simplify high-throughput analysis of biomolecules and improve the detection sensitivity. The mass spectrometric sample support is coated with a thin layer of hydrophobic Teflon that carries an array of 200-μm gold spots, which provide hydrophilic sample anchors. Each transferred sample droplet contacts one anchor, on top of which, after solvent evaporation, the sample is exclusively deposited due to the strongly water repellent nature of the Teflon surface. The initial matrix concentration is kept low, enabling sample up-concentration by more than 2 orders of magnitudes before crystallization commences. As a result, the detection sensitivity is improved as documented by mass spectra recorded from 100 amol of various peptides, 1 fmol of a DNA 20 mer, and 5 fmol of a 130 bp PCR product. Size and spacing of the hydrophilic anchors are optimized for MALDI-MS performance (sample spot size ≈ laser irradiation spot size), for short analysis times (p...