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Sample introduction techniques for microchip electrophoresis: A review
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
James M. Karlinsey
The number of applications of microfluidic analysis systems continues to increase, along with the variety of substrate materials and complexity of the devices themselves. One of the most common features of these devices that has remained relatively unchanged, however, is the introduction of a sample mixture into a separation channel so that individual components can be separated by electrophoresis. Whether a relatively simple mixture of amino acids or a more complex sample of DNA fragments extracted and amplified on-chip, the ability to reliably and reproducibly inject a representative sample is arguably the most significant requirement for an electrophoretic micro total analysis system (μTAS). This review will focus on the different methods reported for sample introduction in microchip electrophoresis, highlighting both pressure-driven and electrokinetic techniques, with an emphasis on the methods employed in μTAS applications.
Source:Analytica Chimica Acta, Volume 725
James M. Karlinsey
The number of applications of microfluidic analysis systems continues to increase, along with the variety of substrate materials and complexity of the devices themselves. One of the most common features of these devices that has remained relatively unchanged, however, is the introduction of a sample mixture into a separation channel so that individual components can be separated by electrophoresis. Whether a relatively simple mixture of amino acids or a more complex sample of DNA fragments extracted and amplified on-chip, the ability to reliably and reproducibly inject a representative sample is arguably the most significant requirement for an electrophoretic micro total analysis system (μTAS). This review will focus on the different methods reported for sample introduction in microchip electrophoresis, highlighting both pressure-driven and electrokinetic techniques, with an emphasis on the methods employed in μTAS applications.
Graphical Abstract
Graphical abstract Highlights
► Pressure injections for microchip electrophoresis are reviewed for the first time. ► Electrokinetic and pressure injections are both presented for comparison. ► Injections for capillary electrophoresis are presented for context.A density-based segmentation for 3D images, an application for X-ray micro-tomography
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
Thanh N. Tran, Thanh T. Nguyen, Tofan A. Willemsz, Gijs van Kessel, Henderik W. Frijlink, Kees van der Voort Maarschalk
Density-based spatial clustering of applications with noise (DBSCAN) is an unsupervised classification algorithm which has been widely used in many areas with its simplicity and its ability to deal with hidden clusters of different sizes and shapes and with noise. However, the computational issue of the distance table and the non-stability in detecting the boundaries of adjacent clusters limit the application of the original algorithm to large datasets such as images. In this paper, the DBSCAN algorithm was revised and improved for image clustering and segmentation. The proposed clustering algorithm presents two major advantages over the original one. Firstly, the revised DBSCAN algorithm made it applicable for large 3D image dataset (often with millions of pixels) by using the coordinate system of the image data. Secondly, the revised algorithm solved the non-stability issue of boundary detection in the original DBSCAN. For broader applications, the image dataset can be ordinary 3D images or in general, it can also be a classification result of other type of image data e.g. a multivariate image.
Source:Analytica Chimica Acta, Volume 725
Thanh N. Tran, Thanh T. Nguyen, Tofan A. Willemsz, Gijs van Kessel, Henderik W. Frijlink, Kees van der Voort Maarschalk
Density-based spatial clustering of applications with noise (DBSCAN) is an unsupervised classification algorithm which has been widely used in many areas with its simplicity and its ability to deal with hidden clusters of different sizes and shapes and with noise. However, the computational issue of the distance table and the non-stability in detecting the boundaries of adjacent clusters limit the application of the original algorithm to large datasets such as images. In this paper, the DBSCAN algorithm was revised and improved for image clustering and segmentation. The proposed clustering algorithm presents two major advantages over the original one. Firstly, the revised DBSCAN algorithm made it applicable for large 3D image dataset (often with millions of pixels) by using the coordinate system of the image data. Secondly, the revised algorithm solved the non-stability issue of boundary detection in the original DBSCAN. For broader applications, the image dataset can be ordinary 3D images or in general, it can also be a classification result of other type of image data e.g. a multivariate image.
Graphical Abstract
Graphical abstract Highlights
► We revised the DBSCAN algorithm for segmentation and clustering of large 3D image dataset and classified multivariate image. ► The algorithm takes into account the coordinate system of the image data to improve the computational performance. ► The algorithm solved the instability problem in boundaries detection of the original DBSCAN. ► The segmentation results were successfully validated with synthetic 3D image and 3D XMT image of a pharmaceutical powder.Evolving chemometric models for predicting dynamic process parameters in viscose production
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
Carlos Cernuda, Edwin Lughofer, Lisbeth Suppan, Thomas Röder, Roman Schmuck, Peter Hintenaus, Wolfgang Märzinger, Jürgen Kasberger
In viscose production, it is important to monitor three process parameters in order to assure a high quality of the final product: the concentrations of H2SO4, Na2SO4 and Z n SO4. During on-line production these process parameters usually show a quite high dynamics depending on the fiber type that is produced. Thus, conventional chemometric models, which are trained based on collected calibration spectra from Fourier transform near infrared (FT-NIR) measurements and kept fixed during the whole life-time of the on-line process, show a quite imprecise and unreliable behavior when predicting the concentrations of new on-line data. In this paper, we are demonstrating evolving chemometric models which are able to adapt automatically to varying process dynamics by updating their inner structures and parameters in a single-pass incremental manner. These models exploit the Takagi–Sugeno fuzzy model architecture, being able to model flexibly different degrees of non-linearities implicitly contained in the mapping between near infrared spectra (NIR) and reference values. Updating the inner structures is achieved by moving the position of already existing local regions and by evolving (increasing non-linearity) or merging (decreasing non-linearity) new local linear predictors on demand, which are guided by distance-based and similarity criteria. Gradual forgetting mechanisms may be integrated in order to out-date older learned relations and to account for more flexibility of the models. The results show that our approach is able to overcome the huge prediction errors produced by various state-of-the-art chemometric models. It achieves a high correlation between observed and predicted target values in the range of [0.95,0.98] over a 3 months period while keeping the relative error below the reference error value of 3%. In contrast, the off-line techniques achieved correlations below 0.5, ten times higher error rates and the more deteriorate, the more time passes by.
Source:Analytica Chimica Acta, Volume 725
Carlos Cernuda, Edwin Lughofer, Lisbeth Suppan, Thomas Röder, Roman Schmuck, Peter Hintenaus, Wolfgang Märzinger, Jürgen Kasberger
In viscose production, it is important to monitor three process parameters in order to assure a high quality of the final product: the concentrations of H2SO4, Na2SO4 and Z n SO4. During on-line production these process parameters usually show a quite high dynamics depending on the fiber type that is produced. Thus, conventional chemometric models, which are trained based on collected calibration spectra from Fourier transform near infrared (FT-NIR) measurements and kept fixed during the whole life-time of the on-line process, show a quite imprecise and unreliable behavior when predicting the concentrations of new on-line data. In this paper, we are demonstrating evolving chemometric models which are able to adapt automatically to varying process dynamics by updating their inner structures and parameters in a single-pass incremental manner. These models exploit the Takagi–Sugeno fuzzy model architecture, being able to model flexibly different degrees of non-linearities implicitly contained in the mapping between near infrared spectra (NIR) and reference values. Updating the inner structures is achieved by moving the position of already existing local regions and by evolving (increasing non-linearity) or merging (decreasing non-linearity) new local linear predictors on demand, which are guided by distance-based and similarity criteria. Gradual forgetting mechanisms may be integrated in order to out-date older learned relations and to account for more flexibility of the models. The results show that our approach is able to overcome the huge prediction errors produced by various state-of-the-art chemometric models. It achieves a high correlation between observed and predicted target values in the range of [0.95,0.98] over a 3 months period while keeping the relative error below the reference error value of 3%. In contrast, the off-line techniques achieved correlations below 0.5, ten times higher error rates and the more deteriorate, the more time passes by.
Graphical Abstract
Graphical abstract Highlights
► Quality assurance of process parameters in viscose production. ► Automatic prediction of spin-bath concentrations based on FTNIR spectra. ► Evolving chemometric models for efficiently handling changing system dynamics over time (no time-intensive re-calibration needed). ► Significant reduction of huge errors produced by statistical state-of-the-art calibration methods. ► Sufficient flexibility achieved by gradual forgetting mechanisms.Ultrasensitive aptamer-based bio bar code immunomagnetic separation and electrochemiluminescence method for the detection of protein
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
Debin Zhu, Xiaoming Zhou, Da Xing
An ultrasensitive aptamer-based bio bar code immunomagnetic separation and electrochemiluminescence (IM-ECL) method for the detection of protein is developed. The target protein is captured by biotin-labeled aptamer (biotin probe) and [Ru(bpy)3]2+ (TBR)-Au bio bar code-labeled aptamer (ECL nanoprobe), to form a double aptamer–protein sandwich complex. The complex is then immobilized on the streptavidin microbeads through biotin–streptavidin linkage and detected by ECL assay. The ECL signal of the target protein is amplified by the TBR-bio bar code DNAs. As an example, platelet-derived growth factor B-chain homodimer (PDGF-BB) was detected by the method. Experimental results show that the detection limit of the assay is 1pM of PDGF-BB. A calibration curve with a linearity range from 1pM to 10nM is established, thus, make quantitative analysis possible. The method has been used to detect PDGF-BB in fetal calf serum with minimum background interference. Due to the wide availability of aptamer for numerous proteins, this aptamer-based bio bar code IM-ECL method holds great promise in protein detection.
Source:Analytica Chimica Acta, Volume 725
Debin Zhu, Xiaoming Zhou, Da Xing
An ultrasensitive aptamer-based bio bar code immunomagnetic separation and electrochemiluminescence (IM-ECL) method for the detection of protein is developed. The target protein is captured by biotin-labeled aptamer (biotin probe) and [Ru(bpy)3]2+ (TBR)-Au bio bar code-labeled aptamer (ECL nanoprobe), to form a double aptamer–protein sandwich complex. The complex is then immobilized on the streptavidin microbeads through biotin–streptavidin linkage and detected by ECL assay. The ECL signal of the target protein is amplified by the TBR-bio bar code DNAs. As an example, platelet-derived growth factor B-chain homodimer (PDGF-BB) was detected by the method. Experimental results show that the detection limit of the assay is 1pM of PDGF-BB. A calibration curve with a linearity range from 1pM to 10nM is established, thus, make quantitative analysis possible. The method has been used to detect PDGF-BB in fetal calf serum with minimum background interference. Due to the wide availability of aptamer for numerous proteins, this aptamer-based bio bar code IM-ECL method holds great promise in protein detection.
Graphical Abstract
Graphical abstract Highlights
► The ECL nanoprobe was synthesized by bifunctioning AuNPs with the capture aptamer and the TBR-bio bar code DNAs with a ratio of 1:100. ► The ECL nanoprobe and the biotin-labeled aptamer were incubated with the target protein to form a double aptamer–protein sandwich complex. ► The sandwich complex was captured by the streptavidin microbeads through biotin–streptavidin linkage and detected by ECL assay.Separation and electrochemical detection of paracetamol and 4-aminophenol in a paper-based microfluidic device
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
Leandro Yoshio Shiroma, Murilo Santhiago, Angelo L. Gobbi, Lauro T. Kubota
The present work describes the construction and application of a simple, low cost and sensitive microfluidic paper-based device with electrochemical detection for the detection of paracetamol and 4-aminophenol. The separation channels of a width of 2.0mm were created on paper using a wax printing process to define the regions of the device. A baseline separation level of the analytes can be obtained in 0.1molL−1 acetate buffer solution at pH 4.5 and by injecting 500nL of the standard solutions at 12mm from the working electrode. The electrochemical detection system was created at the end of the channels through a process known as sputtering. The previously separated analytes were detected at the end of the hydrophilic separation channel by applying a potential of 400mV vs. pseudo Au on the working electrode. Experimental variables such as type of paper (cation exchanger and n1), pH, sample volume, applied potential and distance of sample injection were evaluated and, under the conditions of higher response, it was possible to obtain detection limits of 25.0 and 10.0μmolL−1 for paracetamol and 4-aminophenol, respectively.
Source:Analytica Chimica Acta, Volume 725
Leandro Yoshio Shiroma, Murilo Santhiago, Angelo L. Gobbi, Lauro T. Kubota
The present work describes the construction and application of a simple, low cost and sensitive microfluidic paper-based device with electrochemical detection for the detection of paracetamol and 4-aminophenol. The separation channels of a width of 2.0mm were created on paper using a wax printing process to define the regions of the device. A baseline separation level of the analytes can be obtained in 0.1molL−1 acetate buffer solution at pH 4.5 and by injecting 500nL of the standard solutions at 12mm from the working electrode. The electrochemical detection system was created at the end of the channels through a process known as sputtering. The previously separated analytes were detected at the end of the hydrophilic separation channel by applying a potential of 400mV vs. pseudo Au on the working electrode. Experimental variables such as type of paper (cation exchanger and n1), pH, sample volume, applied potential and distance of sample injection were evaluated and, under the conditions of higher response, it was possible to obtain detection limits of 25.0 and 10.0μmolL−1 for paracetamol and 4-aminophenol, respectively.
Graphical Abstract
Graphical abstract Highlights
► Low cost and simple paper-based microfluidic device with electrochemical detection. ► Only two steps are necessary for the construction of the device, construction of the hydrophobic walls and gold sputtering. ► The substrate works as a separation platform and makes the separation of paracetamol and 4-aminophenol. ► Paper works as a filter and no sample pre treatment is necessary to perform the analysis. ► Baseline separation of the analytes can be achieved by injecting the sample at 12mm from the working electrode.Electromembrane extraction combined with gas chromatography for quantification of tricyclic antidepressants in human body fluids
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
Saied Saeed Hosseiny Davarani, Amin Morteza Najarian, Saeed Nojavan, Mohammad-Ali Tabatabaei
Recent advances in electromembrane extraction (EME) methodology calls for effective and accessible detection methods. Using imipramine and clomipramine as model therapeutics, this proof-of-principle work combines EME with gas chromatography analysis employing a flame ionization detector (FID). The drugs were extracted from acidic aqueous sample solutions, through a supported liquid membrane (SLM) consisting of 2-nitrophenyl octyl ether (NPOE) impregnated on the walls of the hollow fiber. EME parameters, such as SLM composition, type of ion carrier, pH and the composition of donor and acceptor solutions, agitation speed, extraction voltage, and extraction time were studied in detail. Under optimized conditions, the therapeutics were effectively extracted from different matrices with recoveries ranging from 90 to 95%. The samples were preconcentrated 270–280 times prior to GC analysis. Reliable linearity was also achieved for calibration curves with a regression coefficient of at least 0.995. Detection limits and intra-day precision (n =3) were less than 0.7ngmL−1 and 8.5%, respectively. Finally, method was applied to determination and quantification of drugs in human plasma and urine samples and satisfactory results were achieved.
Source:Analytica Chimica Acta, Volume 725
Saied Saeed Hosseiny Davarani, Amin Morteza Najarian, Saeed Nojavan, Mohammad-Ali Tabatabaei
Recent advances in electromembrane extraction (EME) methodology calls for effective and accessible detection methods. Using imipramine and clomipramine as model therapeutics, this proof-of-principle work combines EME with gas chromatography analysis employing a flame ionization detector (FID). The drugs were extracted from acidic aqueous sample solutions, through a supported liquid membrane (SLM) consisting of 2-nitrophenyl octyl ether (NPOE) impregnated on the walls of the hollow fiber. EME parameters, such as SLM composition, type of ion carrier, pH and the composition of donor and acceptor solutions, agitation speed, extraction voltage, and extraction time were studied in detail. Under optimized conditions, the therapeutics were effectively extracted from different matrices with recoveries ranging from 90 to 95%. The samples were preconcentrated 270–280 times prior to GC analysis. Reliable linearity was also achieved for calibration curves with a regression coefficient of at least 0.995. Detection limits and intra-day precision (n =3) were less than 0.7ngmL−1 and 8.5%, respectively. Finally, method was applied to determination and quantification of drugs in human plasma and urine samples and satisfactory results were achieved.
Graphical Abstract
Graphical abstract Highlights
In this study electromembrane extraction (EME) procedure was combined with GC-FID for quantification of tricyclic antidepressants (TCADs) in human body fluids. ► Electromembrane extraction of tricyclic anti-depressants (TCADs). ► Combine EME with GC-FID detection. ► Direct water injection to GC capillary column. ► Extraction of TCADs from human body fluids. ► Enrichment factor higher than 215 with 2mL sample solution.Quantification of retinoid concentrations in human serum and brain tumor tissues
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
Ramadan Ali, Benito Campos, Gerhard Dyckhoff, Walter E. Haefeli, Christel Herold-Mende, Jürgen Burhenne
Retinoic acid signaling is essential for central nervous system (CNS) differentiation and appears to be impaired in tumors. Thus far, there are no established methods to quantify relevant retinoids (all-trans-retinoic acid, 9-cis-retinoic acid, 13-cis retinoic acid, and retinol) in human brain tumors. We developed a single step extraction and quantification procedure for polar and apolar retinoids in normal tissue, lipid-rich brain tumor tissues, and serum. This quantification procedure is based on high performance liquid chromatography (HPLC) with diode-array detection (DAD) using all-trans-acitretin as an internal standard and extraction by liquid–liquid partition with ethyl acetate and borate buffer at pH 9. Recovery with this extraction procedure was higher than earlier (two-step) liquid–liquid extraction procedures based on hexane, NaOH, and HCl. The overall quantification procedure was validated according to Food and Drug Administration (FDA) guidelines and fulfilled all criteria of accuracy, precision, selectivity, recovery, and stability. The overall method accuracy varied between −5.6% and +5.4% for serum and −3.8% and +6.2% for tissues, and overall precision ranged from 3.1% to 6.9% for serum and 2.1% to 8.3% for tissues (%CV batch-to-batch). The lower limit of quantification for all compounds in tumor tissue (and serum) was 3.9ngg−1 (ngmL−1). Using this assay, photodegradation of the retinoids was evaluated and endogenous polar and apolar retinoids were quantified in sera and brain tumor tissues of patients and compared with serum and tonsil tissue concentrations of controls. It may thus serve as a suitable method for the characterization of retinoid uptake and metabolism in the respective compartments.
Source:Analytica Chimica Acta, Volume 725
Ramadan Ali, Benito Campos, Gerhard Dyckhoff, Walter E. Haefeli, Christel Herold-Mende, Jürgen Burhenne
Retinoic acid signaling is essential for central nervous system (CNS) differentiation and appears to be impaired in tumors. Thus far, there are no established methods to quantify relevant retinoids (all-trans-retinoic acid, 9-cis-retinoic acid, 13-cis retinoic acid, and retinol) in human brain tumors. We developed a single step extraction and quantification procedure for polar and apolar retinoids in normal tissue, lipid-rich brain tumor tissues, and serum. This quantification procedure is based on high performance liquid chromatography (HPLC) with diode-array detection (DAD) using all-trans-acitretin as an internal standard and extraction by liquid–liquid partition with ethyl acetate and borate buffer at pH 9. Recovery with this extraction procedure was higher than earlier (two-step) liquid–liquid extraction procedures based on hexane, NaOH, and HCl. The overall quantification procedure was validated according to Food and Drug Administration (FDA) guidelines and fulfilled all criteria of accuracy, precision, selectivity, recovery, and stability. The overall method accuracy varied between −5.6% and +5.4% for serum and −3.8% and +6.2% for tissues, and overall precision ranged from 3.1% to 6.9% for serum and 2.1% to 8.3% for tissues (%CV batch-to-batch). The lower limit of quantification for all compounds in tumor tissue (and serum) was 3.9ngg−1 (ngmL−1). Using this assay, photodegradation of the retinoids was evaluated and endogenous polar and apolar retinoids were quantified in sera and brain tumor tissues of patients and compared with serum and tonsil tissue concentrations of controls. It may thus serve as a suitable method for the characterization of retinoid uptake and metabolism in the respective compartments.
Graphical Abstract
Graphical abstract Highlights
► It is the first sensitive assay for the quantification of retinoids in lipid-rich tissue (brain). ► We report the relationship between gender and age for retinoids other than retinol. ► This is the first report assessing the light sensitivity of different retinoids in biological matrix. ► This is the first report analyzing serum:tissue ratios of retinoid concentrations in normal tissue (tonsils). ► We report the relationship of retinoid serum:tissue ratios in tumors and confirm substantial accumulation in tissue.Fluorescence-quenching-based homogeneous caspase-3 activity assay using photon upconversion
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
Johanna Vuojola, Terhi Riuttamäki, Essi Kulta, Riikka Arppe, Tero Soukka
Caspase proteases are key mediators in apoptosis and thus of great interest in pharmaceutical industry. Enzyme-activity assays are commonly employed in the screening of protease inhibitors that are potential drug candidates. Conventional homogeneous fluorescence-based assays are susceptible to autofluorescence originating from biological material. This background autofluorescence can be eliminated by using upconverting phosphors (UCPs) that emit visible light upon excitation at near-infrared. In the assay energy was transferred from a UCP-donor to a conventional fluorophore acceptor that resided at one end of a caspase-3-specific substrate peptide. Attached to the other end was a quencher molecule that was used to attenuate the acceptor emission through intramolecular energy transfer in an intact peptide. In non-inhibitory conditions the enzyme reaction separated the fluorophore from the quencher and the emission of the fluorophore was recovered. The method was applied for the detection and characterization of a known caspase-3 inhibitor Z-DEVD-FMK, and the assay gave IC50 values of approximately 13nM for this inhibitor. We have demonstrated the applicability of UCPs on a fluorescence-quenching-based homogeneous enzyme-activity assay for the detection of caspase-3 inhibitors. The use of near-infrared excitable UCPs enables inexpensive instrumentation and total elimination of autofluorescence, while the use of an internally quenched substrate molecule diminishes the background resulting from radiatively excited acceptor molecules. The reduction of autofluorescence and radiative background result in high signal-to-background ratios (ratios of approximately 100 were obtained). By further utilizing assay miniaturization and signal enhancement in a white microtitration plate, a significant reduction in the reagent consumption can be achieved rendering the assay applicable for high-throughput screening.
Source:Analytica Chimica Acta, Volume 725
Johanna Vuojola, Terhi Riuttamäki, Essi Kulta, Riikka Arppe, Tero Soukka
Caspase proteases are key mediators in apoptosis and thus of great interest in pharmaceutical industry. Enzyme-activity assays are commonly employed in the screening of protease inhibitors that are potential drug candidates. Conventional homogeneous fluorescence-based assays are susceptible to autofluorescence originating from biological material. This background autofluorescence can be eliminated by using upconverting phosphors (UCPs) that emit visible light upon excitation at near-infrared. In the assay energy was transferred from a UCP-donor to a conventional fluorophore acceptor that resided at one end of a caspase-3-specific substrate peptide. Attached to the other end was a quencher molecule that was used to attenuate the acceptor emission through intramolecular energy transfer in an intact peptide. In non-inhibitory conditions the enzyme reaction separated the fluorophore from the quencher and the emission of the fluorophore was recovered. The method was applied for the detection and characterization of a known caspase-3 inhibitor Z-DEVD-FMK, and the assay gave IC50 values of approximately 13nM for this inhibitor. We have demonstrated the applicability of UCPs on a fluorescence-quenching-based homogeneous enzyme-activity assay for the detection of caspase-3 inhibitors. The use of near-infrared excitable UCPs enables inexpensive instrumentation and total elimination of autofluorescence, while the use of an internally quenched substrate molecule diminishes the background resulting from radiatively excited acceptor molecules. The reduction of autofluorescence and radiative background result in high signal-to-background ratios (ratios of approximately 100 were obtained). By further utilizing assay miniaturization and signal enhancement in a white microtitration plate, a significant reduction in the reagent consumption can be achieved rendering the assay applicable for high-throughput screening.
Graphical Abstract
Graphical abstract Highlights
► We demonstrate the use of photon upconversion in a caspase-3 activity assay. ► The separation-free assay uses an internally quenched substrate peptide. ► UCPs enable simple instrumentation and total elimination of autofluorescence. ► A sensitive assay with high signal-to-background ratios was achieved. ► Suitable for high-throughput screening through miniaturization and white plates.Development of an electrochemical membrane-based nanobiosensor for ultrasensitive detection of dengue virus
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
Ming Soon Cheng, Jia Shin Ho, Cheong Huat Tan, Jeslyn Pei Sze Wong, Lee Ching Ng, Chee-Seng Toh
A sensitive membrane-based electrochemical nanobiosensor is developed for the detection of dengue type 2 virus (DENV-2) using nanoporous alumina-modified platinum electrode. Its sensing mechanism relies on the monitoring of electrode's Faradaic current response toward redox probe, ferrocenemethanol, which is sensitive toward the formation of immune complexes within the alumina nanochannels. Anti-DENV-2 monoclonal antibody (clone 3H5, isotype IgG) is used as the biorecognition element in this work. The stepwise additions of antibody, bovine serum albumin (BSA) and DENV-2 are characterized by differential pulse voltammetry (DPV). A low detection limit of 1pfumL−1 with linear range from 1 to 103 pfumL−1 (R 2 =0.98) can be achieved by the nanobiosensor. The nanobiosensor is selective toward DENV-2 with insignificant cross reaction with non-specific viruses, Chikungunya virus, West Nile virus and dengue type 3 virus (DENV-3). Relative standard deviation (RSD) for triplicate analysis of 5.9% indicates an acceptable level of reproducibility. The first direct quantitation of DENV-2 concentration in whole mosquito vector is demonstrated using this electrochemical nanobiosensor.
Source:Analytica Chimica Acta, Volume 725
Ming Soon Cheng, Jia Shin Ho, Cheong Huat Tan, Jeslyn Pei Sze Wong, Lee Ching Ng, Chee-Seng Toh
A sensitive membrane-based electrochemical nanobiosensor is developed for the detection of dengue type 2 virus (DENV-2) using nanoporous alumina-modified platinum electrode. Its sensing mechanism relies on the monitoring of electrode's Faradaic current response toward redox probe, ferrocenemethanol, which is sensitive toward the formation of immune complexes within the alumina nanochannels. Anti-DENV-2 monoclonal antibody (clone 3H5, isotype IgG) is used as the biorecognition element in this work. The stepwise additions of antibody, bovine serum albumin (BSA) and DENV-2 are characterized by differential pulse voltammetry (DPV). A low detection limit of 1pfumL−1 with linear range from 1 to 103 pfumL−1 (R 2 =0.98) can be achieved by the nanobiosensor. The nanobiosensor is selective toward DENV-2 with insignificant cross reaction with non-specific viruses, Chikungunya virus, West Nile virus and dengue type 3 virus (DENV-3). Relative standard deviation (RSD) for triplicate analysis of 5.9% indicates an acceptable level of reproducibility. The first direct quantitation of DENV-2 concentration in whole mosquito vector is demonstrated using this electrochemical nanobiosensor.
Graphical Abstract
Graphical abstract Highlights
► Label-free nanobiosensor using virus capture method. ► Direct virus particles detection with specific virus identification. ► Detection range of virus from 1 to 1000pfumL−1 with less than 1h analysis time.Modified mesoporous silica materials for on-line separation and preconcentration of hexavalent chromium using a microcolumn coupled with flame atomic absorption spectrometry
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
Zheng Wang, Dong-Mei Fang, Qing Li, Ling-Xia Zhang, Rong Qian, Yan Zhu, Hai-Yun Qu, Yi-Ping Du
A modified SBA-15 mesoporous silica material NH2-SBA-15 was synthesized successfully by grafting γ-aminopropyl-triethoxysilane. The material was characterized using transmission electron microscopy (TEM) and Fourier transform infrared/Raman (FT-IR/Raman) spectroscopy, and used for the first time in a flow injection on-line solid phase extraction (SPE) coupled with flame atomic absorption spectrometry (FAAS) to detect trace Cr (VI). Effective sorption of Cr (VI) was achieved at pH 2.0 with no interference from Cr (III) and other ions and 0.5molL−1 NH3·H2O solution was found optimal for the complete elution of Cr (VI). An enrichment factor of 44 and was achieved under optimized experimental conditions at a sample loading of 2.0mLmin−1 sample loading (300s) and an elution flow rate of 2.0mLmin−1 (24s). The precision of the 11 replicate Cr (VI) measurements was 2.1% at the 100μgL−1 level with a detection limit of 0.2μgL−1 (3s, n =10) using the FAAS. The developed method was successfully applied to trace chromium determination in waste water. The accuracy was validated using a certified reference material of riverine water (GBW08607).
Source:Analytica Chimica Acta, Volume 725
Zheng Wang, Dong-Mei Fang, Qing Li, Ling-Xia Zhang, Rong Qian, Yan Zhu, Hai-Yun Qu, Yi-Ping Du
A modified SBA-15 mesoporous silica material NH2-SBA-15 was synthesized successfully by grafting γ-aminopropyl-triethoxysilane. The material was characterized using transmission electron microscopy (TEM) and Fourier transform infrared/Raman (FT-IR/Raman) spectroscopy, and used for the first time in a flow injection on-line solid phase extraction (SPE) coupled with flame atomic absorption spectrometry (FAAS) to detect trace Cr (VI). Effective sorption of Cr (VI) was achieved at pH 2.0 with no interference from Cr (III) and other ions and 0.5molL−1 NH3·H2O solution was found optimal for the complete elution of Cr (VI). An enrichment factor of 44 and was achieved under optimized experimental conditions at a sample loading of 2.0mLmin−1 sample loading (300s) and an elution flow rate of 2.0mLmin−1 (24s). The precision of the 11 replicate Cr (VI) measurements was 2.1% at the 100μgL−1 level with a detection limit of 0.2μgL−1 (3s, n =10) using the FAAS. The developed method was successfully applied to trace chromium determination in waste water. The accuracy was validated using a certified reference material of riverine water (GBW08607).
Graphical Abstract
Graphical abstract Highlights
► A modified SBA-15 mesoporous silica material (NH2-SBA-15) was synthesized as sorbent. ► The material was used for the first time in a flow injection on-line solid phase extraction (SPE) coupled with flame atomic absorption spectrometry (FAAS) to detect trace Cr (VI). ► The NH2-SBA-15 enables retain Cr (VI) with an enrichment factor of 44. ► The micro-column of NH2-SBA-15 underwent more than 100 adsorption/desorption cycles.Effect of temperature and solvent composition on acid dissociation equilibria, I: Sequenced pssKa determination of compounds commonly used as buffers in high performance liquid chromatography coupled to mass spectroscopy detection
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 725
Juan M. Padró, Agustín Acquaviva, Marcos Tascon, Leonardo G. Gagliardi, Cecilia B. Castells
A new automated and rapid potentiometric method for determining the effect of organic-solvent composition on pK a has been developed. It is based on the measurements of pH values of buffer solutions of variable solvent compositions using a combined glass electrode. Additions of small volumes of one precisely thermostated solution into another, both containing exactly the same analytical concentrations of the buffer components, can produce continuous changes in the solvent composition. Two sequences of potential measurements, one of increasing and the other of decreasing solvent content, are sufficient to obtain the pK a values of the acidic compound within the complete solvent-composition range in about 2h. The experimental design, procedures, and calculations needed to convert the measured pH into the thermodynamic pK a values are thoroughly discussed. This rapid and automated method allows the systematic study of the effect of solvent compositions and temperatures on the pK a. It has been applied to study the dissociation constants of two monoprotic acids: formic acid and triethylamine:HCl in acetonitrile/water mixtures within the range from 0 to 90% (v/v) at temperatures between 20°C and 60°C. These volatile compounds are frequently used to control the pH of the mobile phase in HPLC, especially in methods coupled to mass-spectrometry detection. The obtained pK a values are in excellent agreement with those previously reported. The results were fitted to empirical functions between pK a and temperature and composition. These equations, which can be used to estimate the pK a of these substances at any composition and temperature, would be highly useful in practical work during chromatographic method development.
Source:Analytica Chimica Acta, Volume 725
Juan M. Padró, Agustín Acquaviva, Marcos Tascon, Leonardo G. Gagliardi, Cecilia B. Castells
A new automated and rapid potentiometric method for determining the effect of organic-solvent composition on pK a has been developed. It is based on the measurements of pH values of buffer solutions of variable solvent compositions using a combined glass electrode. Additions of small volumes of one precisely thermostated solution into another, both containing exactly the same analytical concentrations of the buffer components, can produce continuous changes in the solvent composition. Two sequences of potential measurements, one of increasing and the other of decreasing solvent content, are sufficient to obtain the pK a values of the acidic compound within the complete solvent-composition range in about 2h. The experimental design, procedures, and calculations needed to convert the measured pH into the thermodynamic pK a values are thoroughly discussed. This rapid and automated method allows the systematic study of the effect of solvent compositions and temperatures on the pK a. It has been applied to study the dissociation constants of two monoprotic acids: formic acid and triethylamine:HCl in acetonitrile/water mixtures within the range from 0 to 90% (v/v) at temperatures between 20°C and 60°C. These volatile compounds are frequently used to control the pH of the mobile phase in HPLC, especially in methods coupled to mass-spectrometry detection. The obtained pK a values are in excellent agreement with those previously reported. The results were fitted to empirical functions between pK a and temperature and composition. These equations, which can be used to estimate the pK a of these substances at any composition and temperature, would be highly useful in practical work during chromatographic method development.
Graphical Abstract
Graphical abstract Highlights
► We developed a rapid potentiometric method for sequential pK a determinations. ► We measured pK a of buffers from 0 to 90% (v/v) acetonitrile/water and from 20 to 60°C. ► Sequences of 42 pK a-data spanned over a wide solvent composition range needed 2h. ► We measured pK a of formic acid and triethylamine/HCl in up to 90% (v/v) acetonitrile. ► The high-throughput method was applied to obtain pK a of two common buffers in LC/MS.
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 724
Juan M. Bosque-Sendra, Luis Cuadros-Rodríguez, Cristina Ruiz-Samblás, A. Paulina de la Mata
The characterization and authentication of fats and oils is a subject of great importance for market and health aspects. Identification and quantification of triacylglycerols in fats and oils can be excellent tools for detecting changes in their composition due to the mixtures of these products. Most of the triacylglycerol species present in either fats or oils could be analyzed and identified by chromatographic methods. However, the natural variability of these samples and the possible presence of adulterants require the application of chemometric pattern recognition methods to facilitate the interpretation of the obtained data. In view of the growing interest in this topic, this paper reviews the literature of the application of exploratory and unsupervised/supervised chemometric methods on chromatographic data, using triacylglycerol composition for the characterization and authentication of several foodstuffs such as olive oil, vegetable oils, animal fats, fish oils, milk and dairy products, cocoa and coffee.
Source:Analytica Chimica Acta, Volume 724
Juan M. Bosque-Sendra, Luis Cuadros-Rodríguez, Cristina Ruiz-Samblás, A. Paulina de la Mata
The characterization and authentication of fats and oils is a subject of great importance for market and health aspects. Identification and quantification of triacylglycerols in fats and oils can be excellent tools for detecting changes in their composition due to the mixtures of these products. Most of the triacylglycerol species present in either fats or oils could be analyzed and identified by chromatographic methods. However, the natural variability of these samples and the possible presence of adulterants require the application of chemometric pattern recognition methods to facilitate the interpretation of the obtained data. In view of the growing interest in this topic, this paper reviews the literature of the application of exploratory and unsupervised/supervised chemometric methods on chromatographic data, using triacylglycerol composition for the characterization and authentication of several foodstuffs such as olive oil, vegetable oils, animal fats, fish oils, milk and dairy products, cocoa and coffee.
Graphical Abstract
Graphical abstract Highlights
► Relationships between chemometric and chromatography. ► Use of triglyceride profiles and triglyceride chromatographic fingerprints for the characterization of fat and oils. ► Chemometric tools applied to authenticate fat and oils.Locally linear embedding method for dimensionality reduction of tissue sections of endometrial carcinoma by near infrared spectroscopy
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 724
Na Qi, Zhuoyong Zhang, Yuhong Xiang, Peter de B. Harrington
Locally linear embedding (LLE) is introduced here as a nonlinear compression method for near infrared reflectance spectra of endometrial tissue sections. The LLE has been evaluated by using support vector machine (SVM) classifiers and the projected difference resolution (PDR) method. Synthetic data sets devised to resemble near-infrared spectra of tissue samples were used to characterize the performance of the LLE. The LLE was compared using principal component compression (PCC) method to evaluate nonlinear and linear compression. For a set of real tissue samples, if the compressed data were not range-scaled prior to SVM classification, the principal component compressed data gave an average prediction rate of 39±2% while the LLE 94±2%; if range-scaled after compression, the LLE and PCC performed evenly, with maximum average prediction values of 94±2% and 93±2%, respectively. The SVM without compression yielded a classification rate of 92±2%. The prediction accuracy was consistent with PDR results. Without the second derivative preprocessing, the classification rates were 90±3%, 89±2%, and 78±2% for the LLE compressed, the PCC, and no compression classifications by the SVM, respectively.
Source:Analytica Chimica Acta, Volume 724
Na Qi, Zhuoyong Zhang, Yuhong Xiang, Peter de B. Harrington
Locally linear embedding (LLE) is introduced here as a nonlinear compression method for near infrared reflectance spectra of endometrial tissue sections. The LLE has been evaluated by using support vector machine (SVM) classifiers and the projected difference resolution (PDR) method. Synthetic data sets devised to resemble near-infrared spectra of tissue samples were used to characterize the performance of the LLE. The LLE was compared using principal component compression (PCC) method to evaluate nonlinear and linear compression. For a set of real tissue samples, if the compressed data were not range-scaled prior to SVM classification, the principal component compressed data gave an average prediction rate of 39±2% while the LLE 94±2%; if range-scaled after compression, the LLE and PCC performed evenly, with maximum average prediction values of 94±2% and 93±2%, respectively. The SVM without compression yielded a classification rate of 92±2%. The prediction accuracy was consistent with PDR results. Without the second derivative preprocessing, the classification rates were 90±3%, 89±2%, and 78±2% for the LLE compressed, the PCC, and no compression classifications by the SVM, respectively.
Graphical Abstract
Graphical abstract Highlights
► Locally linear embedding (LLE) is introduced first time to the field of spectroscopy as a dimensionality reduction method for feature extraction of near infrared spectra from reflectance measurements of endometrial tissue sections. ► LLE was evaluated and compared with principal component compression (PCC) by using support vector machine (SVM) classifiers. ► The projected difference resolution (PDR) method was used to evaluate the LLE method. ► Some exemplary synthetic data sets were created and NIR spectral data of real tissue samples were collected to verify LLE coupled to SVM for classification. ► LLE combined with the SVM gave better predictions and can effectively extract more discriminating features compared to PCC without scaling.Estimation of measurement uncertainty of pesticides, polychlorinated biphenyls and polyaromatic hydrocarbons in sediments by using gas chromatography–mass spectrometry
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 724
Óscar Pindado Jiménez, Rosa Mª Pérez Pastor
The evaluation of the uncertainty associated to analytical methods is essential in order to demonstrate quality of a result. However, there is often lack of information about uncertainty of methods to estimate persistent organic pollutants concentration in complex matrix. Current work has thoroughly evaluated uncertainty associated to quantification of several organochloride pesticides, PCBs and PAHs in sediments. A discussion of the main contributions to the overall uncertainty is reported, allowing authors to establish the accuracy of results and plan future improvements. Combined uncertainties ranged between 5–9% (pesticides), 4–7% (PCBs) and 5–10% (PAHs), being uncertainty derived of calibration the main contribution. Also, the analytical procedure was validated analysing a standard reference material (IAEA-408).
Source:Analytica Chimica Acta, Volume 724
Óscar Pindado Jiménez, Rosa Mª Pérez Pastor
The evaluation of the uncertainty associated to analytical methods is essential in order to demonstrate quality of a result. However, there is often lack of information about uncertainty of methods to estimate persistent organic pollutants concentration in complex matrix. Current work has thoroughly evaluated uncertainty associated to quantification of several organochloride pesticides, PCBs and PAHs in sediments. A discussion of the main contributions to the overall uncertainty is reported, allowing authors to establish the accuracy of results and plan future improvements. Combined uncertainties ranged between 5–9% (pesticides), 4–7% (PCBs) and 5–10% (PAHs), being uncertainty derived of calibration the main contribution. Also, the analytical procedure was validated analysing a standard reference material (IAEA-408).
Graphical Abstract
Graphical abstract Highlights
► We report an evaluation of uncertainty associated to analysis of POPs in sediments. ► We give useful and easy to follow guidance to calculate uncertainty. ► Evaluation of uncertainty is essential in environmental analysis. ► Uncertainty derived of calibration is the main contribution. ► We present strategies for diminish uncertainty.Recognition of chemical compounds in contaminated water using time-dependent multiple dose cellular responses
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 724
T.H. Pan, B. Huang, J.Z. Xing, W.P. Zhang, S. Gabos, J. Chen
An early determination of toxicant compounds of water contaminations can gain critical time to protect citizens’ health and save substantial amounts of medical costs. To determine toxins in real time, a multi-dose classification algorithm using cellular state variable identification (CSVID) is developed in this paper. First, the dynamic cytotoxicity response profiles of living cells are measured using a real-time cell electronic sensing (RT-CES) system. Changes in cell number expressed as cell index (CI) are recorded on-line as time series. Then CSVID, which reflects the cell killing, cell lysis and certain cellular pathological changes, is extracted from those dynamic cellular responses. Finally, a support vector machine (SVM) algorithm based on CSVID is employed to classify chemical compounds and determine their analogous cellular response pathway. In order to increase the classification accuracy, a majority vote of the class labels is also proposed. Several validation studies demonstrate that CSVID-based classification algorithm has great potential in distinguishing the cytotoxicity response of the cells in the presence of toxins.
Source:Analytica Chimica Acta, Volume 724
T.H. Pan, B. Huang, J.Z. Xing, W.P. Zhang, S. Gabos, J. Chen
An early determination of toxicant compounds of water contaminations can gain critical time to protect citizens’ health and save substantial amounts of medical costs. To determine toxins in real time, a multi-dose classification algorithm using cellular state variable identification (CSVID) is developed in this paper. First, the dynamic cytotoxicity response profiles of living cells are measured using a real-time cell electronic sensing (RT-CES) system. Changes in cell number expressed as cell index (CI) are recorded on-line as time series. Then CSVID, which reflects the cell killing, cell lysis and certain cellular pathological changes, is extracted from those dynamic cellular responses. Finally, a support vector machine (SVM) algorithm based on CSVID is employed to classify chemical compounds and determine their analogous cellular response pathway. In order to increase the classification accuracy, a majority vote of the class labels is also proposed. Several validation studies demonstrate that CSVID-based classification algorithm has great potential in distinguishing the cytotoxicity response of the cells in the presence of toxins.
Graphical Abstract
Graphical abstract Highlights
► Dose- and time-dependent cellular responses are used to evaluate the cytotoxicity. ► The CI can reflect the cell number, cell viability, morphological change, etc. ► The CSVID can capture the dynamic information after cells exposed to toxins. ► The multi-class classification can distinguish the compounds using multi-doses. ► The majority vote strategy (fingerprint) can improve the classification accuracy.Study on the application of reduced graphene oxide and multiwall carbon nanotubes hybrid materials for simultaneous determination of catechol, hydroquinone, p-cresol and nitrite
24 April 2012,
09:30:42
Publication year:
2012
Source:Analytica Chimica Acta, Volume 724
Fangxin Hu, Shihong Chen, Chengyan Wang, Ruo Yuan, Dehua Yuan, Cun Wang
In this paper, the reduced graphene oxide and multiwall carbon nanotubes hybrid materials (RGO–MWNTs) were prepared and a strategy for detecting environmental contaminations was proposed on the basis of RGO–MWNTs modified electrode. The hybrid materials were characterized by the scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and N2 sorption–desorption isotherms. Due to the excellent catalytic activity, enhanced electrical conductivity and high surface area of the RGO–MWNTs, the simultaneous measurement of hydroquinone (HQ), catechol (CC), p-cresol (PC) and nitrite (NO2 −) with four well-separate peaks was achieved at the RGO–MWNTs modified electrode. The linear response ranges for HQ, CC, PC and NO2 − were 8.0–391.0μM, 5.5–540.0μM, 5.0–430.0μM and 75.0–6060.0μM, correspondingly, and the detection limits (S/N=3) were 2.6μM, 1.8μM, 1.6μM and 25.0μM, respectively. The outstanding film forming ability of RGO–MWNTs hybrid materials endowed the modified electrode enhanced stability. Furthermore, the fabricated sensor was applied for the simultaneous determination of HQ, CC, PC and NO2 − in the river water sample.
Source:Analytica Chimica Acta, Volume 724
Fangxin Hu, Shihong Chen, Chengyan Wang, Ruo Yuan, Dehua Yuan, Cun Wang
In this paper, the reduced graphene oxide and multiwall carbon nanotubes hybrid materials (RGO–MWNTs) were prepared and a strategy for detecting environmental contaminations was proposed on the basis of RGO–MWNTs modified electrode. The hybrid materials were characterized by the scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and N2 sorption–desorption isotherms. Due to the excellent catalytic activity, enhanced electrical conductivity and high surface area of the RGO–MWNTs, the simultaneous measurement of hydroquinone (HQ), catechol (CC), p-cresol (PC) and nitrite (NO2 −) with four well-separate peaks was achieved at the RGO–MWNTs modified electrode. The linear response ranges for HQ, CC, PC and NO2 − were 8.0–391.0μM, 5.5–540.0μM, 5.0–430.0μM and 75.0–6060.0μM, correspondingly, and the detection limits (S/N=3) were 2.6μM, 1.8μM, 1.6μM and 25.0μM, respectively. The outstanding film forming ability of RGO–MWNTs hybrid materials endowed the modified electrode enhanced stability. Furthermore, the fabricated sensor was applied for the simultaneous determination of HQ, CC, PC and NO2 − in the river water sample.
Graphical Abstract
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