Showing papers in "Analyst in 2007"
TL;DR: These topics are summarized in this review: miniaturization of electronic tongues and hybrid systems for liquid sensing, as well as approaches embracing mass- and optical-sensors, and various pattern recognition systems were proposed.
Abstract: Electronic tongue systems are multisensor devices dedicated to automatic analysis of complicated composition samples and to the recognition of their characteristic properties. Recently, the number of publications covering this topic has significantly increased. Many possible architectures of such devices were proposed: potentiometric, voltammetric, as well as approaches embracing mass- and optical-sensors. For the analysis of sensor array data, various pattern recognition systems were proposed. All of these topics are summarized in this review. Moreover, additional problems are considered: miniaturization of electronic tongues and hybrid systems for liquid sensing.
366 citations
TL;DR: This paper has reviewed the main research studies that have been made of gas sensors that use nanomaterials and made a critical review of the possible advantages and drawbacks of these nanostructured material-based sensors.
Abstract: Gas detection is important for controlling industrial and vehicle emissions, household security and environmental monitoring. In recent decades many devices have been developed for detecting CO2, CO, SO2, O2, O3, H2, Ar, N2, NH3, H2O and several organic vapours. However, the low selectivity or the high operation temperatures required when most gas sensors are used have prompted the study of new materials and the new properties that come about from using traditional materials in a nanostructured mode. In this paper, we have reviewed the main research studies that have been made of gas sensors that use nanomaterials. The main quality characteristics of these new sensing devices have enabled us to make a critical review of the possible advantages and drawbacks of these nanostructured material-based sensors.
360 citations
TL;DR: The orthogonality of separation, which in some cases may obviate chromatographic separation, can be used to differentiate isomers, to reduce background, to resolve isobaric species, and to improve signal-to-noise ratios by selective ion transmission.
Abstract: High-Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS) and Differential Mobility Spectrometry (DMS) harness differences in ion mobility in low and high electric fields to achieve a gas-phase separation of ions at atmospheric pressure. This separation is orthogonal to either chromatographic or mass spectrometric separation, thereby increasing the selectivity and specificity of analysis. The orthogonality of separation, which in some cases may obviate chromatographic separation, can be used to differentiate isomers, to reduce background, to resolve isobaric species, and to improve signal-to-noise ratios by selective ion transmission. This review will focus on the applications of these techniques to the separation of various classes of analytes, including chemical weapons, explosives, biologically active molecules, pharmaceuticals and pollutants. These papers cover the period up to January 2007.
316 citations
TL;DR: The potential of breath analysis for clinical diagnosis and the strengths and weaknesses of the analytical methods used are discussed, and selected ion flow tube mass spectrometry, SIFT-MS, using which on-line real-time analyses of single breath exhalations can be carried out.
Abstract: The potential of breath analysis for clinical diagnosis and the strengths and weaknesses of the analytical methods used are discussed. Special attention is given to selected ion flow tube mass spectrometry, SIFT-MS, using which on-line real-time analyses of single breath exhalations can be carried out. Illustrative data on the concentration distributions of several breath metabolites amongst the healthy population are presented and their relations to disease when elevated above the normal are alluded to.
300 citations
TL;DR: These studies show that nanotube-coated microelectrodes can be used with fast scanning techniques and are advantageous for in vivo measurements of neurotransmitters because of their greater sensitivity and resistance to fouling.
Abstract: Dopamine and serotonin are important neurotransmitters that interact in the brain. While dopamine is easily detected with electrochemical sensors, the detection of serotonin is more difficult because reactive species formed after oxidation can adsorb to the electrode, reducing sensitivity. Carbon nanotube treatments of electrodes have been used to increase the sensitivity, promote electron transfer, and reduce fouling. Most methods have focused on nanotube coatings of large electrodes and slower electrochemical techniques that are not conducive to measurements in vivo. In this study, we investigated carbon-fiber microelectrodes modified with single-walled carbon nanotubes for the co-detection of dopamine and serotonin in vivo. Using fast-scan cyclic voltammetry, S/N ratios for the neurotransmitters increased after nanotube coating. Electrocatalytic effects of nanotubes were not apparent at fast scan rates but faster kinetics were observed with slower scanning. Nanotube-modified microelectrodes showed significantly less fouling after exposure to serotonin than bare electrodes. The nanotube-modified electrodes were used to monitor stimulated dopamine and serotonin changes simultaneously in the striatum of anesthetized rat after administration of a serotonin synthetic precursor. These studies show that nanotube-coated microelectrodes can be used with fast scanning techniques and are advantageous for in vivo measurements of neurotransmitters because of their greater sensitivity and resistance to fouling.
267 citations
TL;DR: The components of electrochemical DNA biosensors and the important issues in their design are described and methods of transducing DNA binding events are discussed.
Abstract: Electrochemical DNA biosensors exploit the affinity of single-stranded DNA for complementary strands of DNA and are used in the detection of specific sequences of DNA with a view towards developing portable analytical devices. Great progress has been made in this field but there are still numerous challenges to overcome. This review for researchers new to the field describes the components of electrochemical DNA biosensors and the important issues in their design. Methods of transducing DNA binding events are discussed along with future directions for DNA biosensors.
242 citations
TL;DR: Results suggest that the solubility of the analyte plays an important role in desorption from the paper surface in DESI-MS, which has advantages over extractive techniques in terms of speed and sample preservation.
Abstract: Desorption electrospray ionization mass spectrometry (DESI-MS) is employed in the forensic analysis of documents. Blue ballpoint pen inks applied to ordinary writing paper are examined under ambient conditions without any prior sample preparation. When coupled to an automated moving stage, two-dimensional molecular images are generated. Proof-of-principle experiments include characterization of a simulated forged number and examination of older written records. This application of DESI has advantages over extractive techniques in terms of speed and sample preservation. The effects of the desorbing solvent composition, in this case a mixture of methanol and water, and of flow rate, are evaluated. Results suggest that the solubility of the analyte (dyes Basic Blue 7, Basic Violet 3 and Solvent Blue 26) plays an important role in desorption from the paper surface.
192 citations
TL;DR: SORS can be used to distinguish non-invasively between calcification types I and II within tissue of up to 10 mm deep, which secures the first step in taking this technique forward for clinical applications seeking to use Raman spectroscopy as an adjunct to mammography for early diagnosis of breast cancer.
Abstract: Breast calcifications are often the only mammographic features indicating the presence of a cancerous lesion. Calcium oxalate (type I) may be found in and around benign lesions, however calcium hydroxyapatite (type II) is usually found within proliferative lesions, which can include both benign and malignant pathologies. However, the composition of type II calcifications has been demonstrated to vary between benign and malignant proliferative lesions, and could be an indicator for the possible disease state. Raman spectroscopy has previously been demonstrated as a powerful tool for non-destructive analysis of tissues, utilising laser light to probe chemical composition. Raman spectroscopy is traditionally a surface technique. However, we have recently developed methods that permit its application for obtaining sample composition to clinically relevant depths of many mm. We report the first demonstration of spatially offset Raman spectroscopy (SORS) for potential in vivo breast analysis. This study evaluates the possibility of utilising SORS for measuring calcification composition through varying thicknesses of tissues (2 to 10 mm), which is about one to two orders of magnitude deeper than has been possible with conventional Raman approaches. SORS can be used to distinguish non-invasively between calcification types I and II (and carbonate substitution of phosphate in calcium hydroxyapatite) within tissue of up to 10 mm deep. This result secures the first step in taking this technique forward for clinical applications seeking to use Raman spectroscopy as an adjunct to mammography for early diagnosis of breast cancer, by utilising both soft tissue and calcification signals. Non-invasive elucidation of calcification composition, and hence type, associated with benign or malignant lesions, could eliminate the requirement for biopsy in many patients.
188 citations
TL;DR: This paper evaluated several commercially available technologies and procedures for the isolation of nucleic acid with the extraction of HIV-1 RNA from human plasma as a model system and found that solid-phase extraction with silica or glass in the presence of a chaotropic salt provides the highest extraction efficiency.
Abstract: Currently available nucleic acid testing (NAT)-based assays are complex and time-consuming, and they require expensive instrumentation and dedicated laboratory spaces for sample preparation as well as for amplification and detection of the nucleic acid target Reagents required for these tests are also expensive and must be transported and stored refrigerated or frozen These characteristics have limited the use of such assays for point-of-care (POC) testing, especially in resource-poor settings Efforts to develop simple and rapid NAT-based assays have focused predominantly on the amplification and detection steps, with sample preparation and nucleic acid extraction remaining the bottleneck in the development of NAT systems suitable for POC applications or resource-limited settings A review of NAT platforms and technologies currently under development and validation for rapid field testing revealed that, in addition to requiring expensive and complex instrumentation, many of these systems also require off-line sample preparation and reagent handling In their current format, they are therefore not appropriate for POC testing in resource-limited settings We evaluated several commercially available technologies and procedures for the isolation of nucleic acid with the extraction of HIV-1 RNA from human plasma as a model system Our results indicate that solid-phase extraction with silica or glass in the presence of a chaotropic salt provides the highest extraction efficiency However, none of the existing methods and technologies is readily adaptable to a POC system The integration of sample preparation procedures well suited to NAT-based assays in resource-limited settings therefore remains a challenge
184 citations
TL;DR: The capability and advantages of cell-based sensors over conventional sensing technology are described, followed by a discussion of the influence of cell adhesion, spreading and viability during cell patterning on the subsequent impedance measurements and sensing applications.
Abstract: Cell-based impedance biosensing is an emerging technology that can be used to non-invasively and instantaneously detect and analyze cell responses to chemical and biological agents. This article highlights the fabrication and measurement technologies of cell impedance sensors, and their application in toxin detection and anti-cancer drug screening. We start with an introduction that describes the capability and advantages of cell-based sensors over conventional sensing technology, followed by a discussion of the influence of cell adhesion, spreading and viability during cell patterning on the subsequent impedance measurements and sensing applications. We then present an electronic circuit that models the cell-electrode system, by which the cellular changes can be detected in terms of impedance changes of the circuit. Finally, we discuss the current status on using cell impedance sensors for toxin detection and anti-cancer drug screening.
181 citations
TL;DR: The use of combinations of spectral discrimations along with time-resolved monitoring schemes based on luminescence lifetime or intensity-lifetime ratios enables all-optical real-time multianalyte determination.
Abstract: Multiple optical sensors for chemical species are sensitive, non-toxic and non-invasive and enable spatially and temporally resolved multianalyte detection. Recent advances are highlighted with a focus on fluorescence-based methods and the biologically and clinically important analytes oxygen, pH, carbon dioxide and temperature. Indicator chemistries such as permeation-selective microbeads and nanoparticles allow the production of microscopically homogeneous sensor layers. The use of combinations of spectral discrimations along with time-resolved monitoring schemes based on luminescence lifetime or intensity-lifetime ratios enables all-optical real-time multianalyte determination.
TL;DR: This review summarizes the recent developments of novel technology enabling ultrasensitive protein detection by focusing on two groups of techniques that involve either polymerase amplification of affinity DNA probes or signal amplification by the use of nano-/micro-materials.
Abstract: Proteins are essential components of organisms and are involved in a wide range of biological functions. There are increasing demands for ultra-sensitive protein detection, because many important protein biomarkers are present at ultra-low levels, especially during the early stages of disease. Measuring proteins at low levels is also crucial for investigations of the protein synthesis and functions in biological systems. In this review, we summarize the recent developments of novel technology enabling ultrasensitive protein detection. We focus on two groups of techniques that involve either polymerase amplification of affinity DNA probes or signal amplification by the use of nano-/micro-materials. The polymerase-based amplification of affinity DNA probes indirectly improves the sensitivity of protein detection by increasing the number of detection molecules. The use of nano-/micro-materials conjugated to affinity probes enhances the measurement signals by using the unique electrical, optical, and catalytic properties of these novel materials. This review describes the basic principles, performances, applications, merits, and limitations of these techniques.
TL;DR: Surface enhanced Raman scattering (SERS) has been used to detect bacteria captured by polyclonal antibodies sorbed onto protein-A-modified silver nanoparticles and resulted in an intensity enhancement of over 20-fold.
Abstract: Surface enhanced Raman scattering (SERS) has been used to detect bacteria captured by polyclonal antibodies sorbed onto protein-A-modified silver nanoparticles. The selectivity and discrimination of the technique were assured by using a specific antibody to the model bacterium, Escherichia coli. As the SERS enhancement mechanism depends upon the metal surface proximity, 8 nm was considered as the optimum distance between the bacterium and the nanoparticle surface. Spectral reproducibility was verified using Principal Components Analysis to differentiate the clusters corresponding to the biomolecules and/or bacteria sorbed onto nanoparticles. Compared to the normal Raman spectrum, the SERS technique resulted in an intensity enhancement of over 20-fold.
TL;DR: The various approaches highlighted here illustrate the rich capabilities of electrochemical methods as simple, low-cost, sensitive tools for the determination of these important biological analytes at trace and ultra-trace levels.
Abstract: Electrochemical methods for the detection of amino acids, peptides, and proteins in a variety of media are reviewed. Label-free strategies in which the detection is based on the inherent electrochemical properties of the analyte are discussed. Various processes such as direct or mediated (in solution or immobilised) redox processes and interfacial ion transfers have been employed for the electrochemical detection and determination of the target analytes. The various methods covered encompass voltammetry at uncoated and modified electrodes and at immiscible liquid-liquid interfaces, potentiometry at polymer membrane electrodes and electrochemical impedance spectroscopy. The determination of the target analytes in complex biological matrices is discussed. The various approaches highlighted here illustrate the rich capabilities of electrochemical methods as simple, low-cost, sensitive tools for the determination of these important biological analytes at trace and ultra-trace levels.
TL;DR: The results indicate that, contrary to many other electrodes, the oxidation of phenolic compounds on CILE is highly stable and does not result in electrode fouling.
Abstract: A carbon ionic liquid electrode (CILE) was used for the investigation of the electrochemical oxidation of phenolic compounds in acidic media using cyclic voltammetry, chronoamperometry and square wave voltammetry techniques. The results indicate that, contrary to many other electrodes, the oxidation of phenolic compounds on CILE is highly stable and does not result in electrode fouling. Cyclic voltammetry showed that phenolic compounds such as phenol, 2,4-dichlorophenol and catechol were oxidized at CILE and remained electroactive after multiple cycles and at high concentrations of phenol. The cyclic voltammetric response of the CILE is very stable with more than 99% of the initial activity remaining after 20 s of stirring of a 0.5 mM solution of phenol.
TL;DR: Urine samples obtained from drug abusers were screened for drugs of abuse and their metabolites using DESI-MS and the results obtained were compared to results obtained from GC-MS experiments, indicating that the sensitivity of DESI was more than adequate for this study.
Abstract: Urine samples obtained from drug abusers were screened for drugs of abuse and their metabolites using DESI-MS and the results obtained were compared to results obtained from GC–MS experiments. The detected analyte classes included amphetamines, opiates, cannabinoids and benzodiazepines. The compounds detected were codeine, morphine, oxymorphone, 11-nor-9-carboxy-Δ9-tetrahydrocannabinol, Δ9-tetrahydrocannabinol, alprazolam, temazepam, oxazepam, N-desmethyldiazepam (nordiazepam) and hydroxytemazepam. Identities of all the analytes were confirmed by tandem mass spectrometry, matching MS/MS spectra with authentic standard compounds. The concentrations of the analytes in the samples were obtained from semi-quantitative GC–MS studies and were in the range of 270–22 000 ng mL−1. The analytes could be detected by DESI even after a hundred-fold dilution indicating that the sensitivity of DESI was more than adequate for this study. Selectivity in the DESI-MS measurements for different kinds of analytes could be increased further by optimizing the spray solvent composition: the use of an entirely aqueous solvent enhanced the signal of polar analytes, such as the benzodiazepines, whereas the use of a spray solvent with a high organic content increased the signal of less polar analytes, such as codeine and morphine.
TL;DR: The results of this study suggest that DCDR spectroscopy could be a simple, fast, near-patient technique capable of assisting the diagnosis of ocular infection.
Abstract: The technique of drop coating deposition Raman (DCDR) spectroscopy has been shown to be a highly reproducible and sensitive method of obtaining Raman spectra from low concentration protein solutions. This study assesses the ability of DCDR to analyse changes in the relative protein concentrations of aqueous tertiary protein mixtures, with protein levels similar to that found in human tear fluid. The three proteins used to make the mixtures were lysozyme, lactoferrin and albumin. The combination of DCDR spectroscopy and principal components analysis is found to be sensitive enough to detect small changes in the relative protein concentrations, from very small sample volumes (1.5 µl). With certain mixtures it was found that the deposition of proteins was not homogeneous across the width of the ring, but averaging spectra taken at different positions could compensate for this. Principal components regression was able to predict the protein concentrations of test solutions with a good degree of accuracy (root-mean-square errors of prediction of 0.083, 0.112, and 0.082 mg ml−1 or 8.3, 11.2 and 8.2% of the mean concentration value, for lysozyme, lactoferrin and albumin concentrations respectively). The results of this study suggest that DCDR spectroscopy could be a simple, fast, near-patient technique capable of assisting the diagnosis of ocular infection.
TL;DR: The first extensive study of yeast metabolite GC x GC-TOFMS data from cells grown under fermenting, R, and respiring, DR, conditions is reported.
Abstract: The first extensive study of yeast metabolite GC x GC-TOFMS data from cells grown under fermenting, R, and respiring, DR, conditions is reported. In this study, recently developed chemometric software for use with three-dimensional instrumentation data was implemented, using a statistically-based Fisher ratio method. The Fisher ratio method is fully automated and will rapidly reduce the data to pinpoint two-dimensional chromatographic peaks differentiating sample types while utilizing all the mass channels. The effect of lowering the Fisher ratio threshold on peak identification was studied. At the lowest threshold (just above the noise level), 73 metabolite peaks were identified, nearly three-fold greater than the number of previously reported metabolite peaks identified (26). In addition to the 73 identified metabolites, 81 unknown metabolites were also located. A Parallel Factor Analysis graphical user interface (PARAFAC GUI) was applied to selected mass channels to obtain a concentration ratio, for each metabolite under the two growth conditions. Of the 73 known metabolites identified by the Fisher ratio method, 54 were statistically changing to the 95% confidence limit between the DR and R conditions according to the rigorous Student's t-test. PARAFAC determined the concentration ratio and provided a fully-deconvoluted (i.e. mathematically resolved) mass spectrum for each of the metabolites. The combination of the Fisher ratio method with the PARAFAC GUI provides high-throughput software for discovery-based metabolomics research, and is novel for GC x GC-TOFMS data due to the use of the entire data set in the analysis (640 MB x 70 runs, double precision floating point).
TL;DR: It is demonstrated that the HA-AuNP fabrication can be easily achieved in a wide range of pH (2 to 12) and the background SERS spectra of HA is relatively weak in absolute intensity, allowing the detection of the enhanced Raman signal from trace amount of contaminants.
Abstract: Humic acid (HA) solutions provide an unexpected medium for direct fabrication of gold nanoparticles (HA–AuNP) and a clear window for surface-enhanced Raman scattering (SERS) with many potential applications in the ultrasensitive chemical analysis of environmental pollutants. It is demonstrated that the HA–AuNP fabrication can be easily achieved in a wide range of pH (2 to 12). The background SERS spectra of HA is relatively weak in absolute intensity, allowing the detection of the enhanced Raman signal from trace amount of contaminants. An in-situ approach is illustrated where the HA–AuNP fabrication is carried out with a HA solution containing the target pollutant. The technique may allow for the direct detection of organic pollutants present in the humic fraction of soil.
TL;DR: The 5- HT oxidation current increased in the presence of the serotonin transporter (SERT) inhibitor, fluoxetine (1 microM), providing evidence that the oxidation current was associated with 5-HT.
Abstract: A diamond microelectrode was used to sensitively, reproducibly and stably record overflow of 5-hydroxytryptamine (5-HT, serotonin) from enterochromaffin cells (EC) of the intenstinal mucosal layer. 5-HT is an important neurotransmitter and paracrine signalling molecule in the gastrointestinal tract. The diamond microelectrode was formed by overcoating a sharpened 76 µm diameter Pt wire with a thin layer of conducting diamond. After insulation with polypropylene, the conically-shaped microelectrode had a diameter of about 10 µm at the tip and 80 µm at the cylindrical portion. The exposed length was 100–200 µm. Continuous amperometry with the microelectrode poised at a detection potential of 700 mV vs. Ag|AgCl was used to measure 5-HT overflow as an oxidation current. 5-HT overflow was elicited by both mechanical and electrical stimulation. Some minor electrode fouling, a common problem with the oxidative detection of 5-HT, was seen for diamond but the response stabilized enabling recording in vitro. Both 5-HT and the paracrine hormone, melatonin, were detected in the extracellular solution. The 5-HT oxidation current increased in the presence of the serotonin transporter (SERT) inhibitor, fluoxetine (1 µM), providing evidence that the oxidation current was associated with 5-HT.
TL;DR: Some practical aspects and implications of framing food legislation in terms of metal species are presented and the role of speciation data should be considered.
Abstract: As a safeguard for human health, guidelines and regulations stipulating maximum permissible concentrations (MPCs) of metals in foods have been set to limit our dietary exposure to toxic metals. It is now well accepted, however, that the chemical form of the metal must be considered when assessing the possible human health consequences of exposure, and this in turn has led to discussion on the incorporation of speciation data in the setting of MPCs for metals in foods. Some practical aspects and implications of framing food legislation in terms of metal species are presented.
TL;DR: Platinum electrodes with widths of 2 and 4 microm and spacing of 2 microm gave redox cycling efficiencies of 9 and 4 respectively, which gave a dopamine/K(4)[Fe(CN)(6)] selectivity of 2 could be obtained.
Abstract: A pair of interdigitated ultramicroelectrodes (UMEs) is used to electrochemically detect a weak reductor ( dopamine) in the presence of a stronger one (K-4[ Fe(CN)(6)]). In the mixture of both reductors, one of the two interdigitated electrodes ( the generator electrode) is used to oxidize both species at 700 mV vs. Ag/AgCl, followed by subsequent ( selective) reduction of the oxidized dopamine at 400 mV. A regenerated dopamine molecule can thus be oxidized several times ( redox cycling) and enable selective detection even in the presence of the stronger reductor. In order to obtain high redox cycling efficiency, we designed and realized platinum electrodes with widths of 2 and 4 mu m and spacing of 2 mu m, which gave redox cycling efficiencies of 9 and 4 respectively. Using this electrode design, a dopamine/K-4[Fe(CN)(6)] selectivity of 2 could be obtained.
TL;DR: It is demonstrated for the first time that Kerr-gated Raman spectroscopy is capable of non-destructive probing of sufficient biochemical information from calcifications buried within tissue, and this information can potentially be used as a first step in identifying the type of lesion.
Abstract: Breast calcifications are found in both benign and malignant lesions and their composition can indicate the disease state. Calcium oxalate (dihydrate) (COD) is associated with benign lesions, however calcium hydroxyapatite (HAP) is found mainly in proliferative lesions including carcinoma. The diagnostic practices of mammography and histopathology examine the morphology of the specimen. They can not reliably distinguish between the two types of calcification, which may indicate the presence of a cancerous lesion during mammography. We demonstrate for the first time that Kerr-gated Raman spectroscopy is capable of non-destructive probing of sufficient biochemical information from calcifications buried within tissue, and this information can potentially be used as a first step in identifying the type of lesion. The method uses a picosecond pulsed laser combined with fast temporal gating of Raman scattered light to enable spectra to be collected from a specific depth within scattering media by collecting signals emerging from the sample at a given time delay following the laser pulse. Spectra characteristic of both HAP and COD were obtained at depths of up to 0.96 mm, in both chicken breast and fatty tissue; and normal and cancerous human breast by utilising different time delays. This presents great potential for the use of Raman spectroscopy as an adjunct to mammography in the early diagnosis of breast cancer.
TL;DR: Two sets of technologies are described which comply with the constraints of the POC environment and illustrate a possible route for the development of microfluidic devices, which could fulfil the needs of clinicians for disease staging and monitoring.
Abstract: Microfluidic devices have been long advertised as a key candidate to revolutionize point-of-care (POC) diagnostics. Recent advances in this field have addressed some of the most important issues, which limited the deployment of microfluidic devices outside of clinical laboratories. This contribution discusses important technical and economic constraints that microfluidic products must overcome to be adopted by healthcare systems. Two sets of technologies are described which comply with the constraints of the POC environment. As such, these technologies illustrate a possible route for the development of microfluidic devices, which could fulfil the needs of clinicians for disease staging and monitoring.
TL;DR: It is demonstrated with transmission electron microscopy and X-ray photoelectron spectroscopy that single-walled carbon nanotubes contain significant amounts of iron in the form of Fe(3)O(4), which even after acid washing, is not removed.
Abstract: We demonstrate with transmission electron microscopy and X-ray photoelectron spectroscopy that single-walled carbon nanotubes contain significant amounts of iron in the form of Fe3O4, which even after acid washing, is not removed.
TL;DR: The fabrication, evaluation and attractive performance of multiwall carbon nanotube(MWCNT)/polysulfone biocomposite membrane modified thick-film screen-printed electrochemical biosensors are reported and the comparison of graphite with MWCNT as conductor material is described.
Abstract: The fabrication, evaluation and attractive performance of multiwall carbon nanotube(MWCNT)/polysulfone biocomposite membrane modified thick-film screen-printed electrochemical biosensors are reported. The fabricated carbon nanotube/polysulfone (CNT/PS) strips combine the attractive advantages of carbon nanotube materials, polysulfone matrix and disposable screen-printed electrodes. Such thick-film carbon nanotubes/polysulfone sensors have a well defined performance, are mechanically stable, and exhibit high electrochemical activity. Furthermore, biocompatibility of CNT/PS composite allows easy incorporation of biological functional moiety of horseradish peroxidase by phase inversion technique. The comparison of graphite with MWCNT as conductor material is described in this paper. The proposed H2O2 biosensor exhibited a linear range (applied potential, −0.2 V) from 0.02 to 0.5 mM and a KMapp of 0.71 mM.
TL;DR: The application of the magnetoelastic sensor for the detection of OP pesticides is described by measuring the changes in viscoelasticity caused by the swelling/shrinking of the pH-responsive polymer when exposed to the pesticides.
Abstract: An organophosphorus (OP) pesticide sensor was fabricated by applying a pH-sensitive polymer coating and organophosphorus hydrolase (OPH) enzyme onto the surface of a magnetoelastic sensor, the magnetic analogue of the better-known surface acoustic wave sensor. Organophosphorus hydrolase catalyses the hydrolysis of a wide range of organophosphorus compounds, which changes the pH in the hydrogel. This article describes the application of the magnetoelastic sensor for the detection of OP pesticides by measuring the changes in viscoelasticity caused by the swelling/shrinking of the pH-responsive polymer when exposed to the pesticides. The sensor was successfully used to detect paraoxon and parathion down to a concentration of 1 × 10−7 and 8.5 × 10−7 M respectively.
TL;DR: It is reported the unambiguous detection of a sequence of Hepatitis C Virus at concentrations down to the fractional pM range using Single Wall Carbon Nanotube (SWNT) Field Effect Transistor (FET) devices functionalized with Peptide Nucleic Acid (PNA).
Abstract: We report the unambiguous detection of a sequence of Hepatitis C Virus (HCV) at concentrations down to the fractional pM range using Single Wall Carbon Nanotube (SWNT) Field Effect Transistor (FET) devices functionalized with Peptide Nucleic Acid (PNA).
TL;DR: The role of a cross-linker appears to be more significant for this system than previously anticipated and an effective imprint is achieved, despite the presence of only one site on the template which provides for the formation of effective electrostatic interactions with the functional monomer used, 4-vinylpyridine.
Abstract: The correlation of the recognition properties of a molecularly imprinted polymer (MIP) with the recognition events in pre-polymerisation mixtures is of central importance to our understanding of the molecular imprinting technique. Using the NSAID naproxen as a model template, we have applied parallel theoretical (molecular dynamics) and practical ( 1 H-NMR, X-ray crystallography, HPLC, radioligand binding) methods to examine the nature of template-functional monomer complexation. An effective imprint is achieved, despite the presence of only one site on the template which provides for the formation of effective electrostatic interactions with the functional monomer used, 4-vinylpyridine. This is attributed to the creation of a well-defined receptor site for the acidic terminus of the molecule and complementary van der Waals interactions, as described in preliminary simulations of the pre-polymerisation system, and as confirmed for the resultant MIP by HPLC data. Qualitative agreement is also observed between simulation and proton NMR data examining monomer self-association in the presence and absence of the template. On the basis of the data obtained, the role of a cross-linker appears to be more significant for this system than previously anticipated.
TL;DR: The results indicate the importance of the community size in cell networks used in the stable cell-based screening model for drug screening and indicate the advantage of using direct cell- based measurements in which the amount of drug administered and the time course over which it is administered are strictly controlled for evaluating the quantitative chemical effects of drugs on cells.
Abstract: We investigate the effect of haloperidol on a four-cell and nine-cell cardiomyocyte network on an agarose microchamber array chip to evaluate a cell-based model for drug screening. Using a network of cardiomyocytes whose beating intervals were stable and relatively uniform (they only fluctuated 10% from the mean beating interval), we easily observed the effect of haloperidol on the cell network beating interval 5 min after administering it. We also observed the beating interval returned to its original state 10 min after the haloperidol was washed out of the chip. Although the four-cell network showed the unstable recovery of its beating rhythm after washout of haloperidol, the nine-cell network recovered completely to the stable original beating rhythm even after a second administration of haloperidol. The results indicate the importance of the community size in cell networks used in the stable cell-based screening model. Moreover, they indicate the advantage of using direct cell-based measurements in which the amount of drug administered and the time course over which it is administered are strictly controlled for evaluating the quantitative chemical effects of drugs on cells.