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Comparison of protein immobilization methods with covalent bonding on paper for paper-based enzyme-linked immunosorbent assay
Full text linkIn this study, two methods were examined to optimize the immobilization of antibodies on paper when conducting a paper-based enzyme-linked immunosorbent assay (P-ELISA). Human IgG, as a test-capture protein, was immobilized on paper via the formation of Schiff bases. Aldehyde groups were introduced onto the surface of the paper via two methods: NaIO4 and 3-aminopropyltriethoxysilane (APTS) with glutaraldehyde (APTS-glutaraldehyde). In the assay, horseradish peroxidase-conjugated anti-human IgG (HRP-anti-IgG) binds to the immobilized human IgG, and the colorimetric reaction of 3,3′,5,5′-tetramethylbenzyzine (TMB) produces a blue color in the presence of H2O2 and HRP-anti-IgG as a model analyte. The immobilization of human IgG, the enzymatic reaction conditions, and the reduction of the chemical bond between the paper surface and immobilized human IgG all were optimized in order to improve both the analytical performance and the stability. In addition, the thickness of the paper was examined to stabilize the analytical signal. Consequently, the APTS-glutaraldehyde method was superior to the NaIO4 method in terms of sensitivity and reproducibility. Conversely, the reduction of imine to amine with NaBH4 proved to exert only minimal influence on sensitivity and stability, although it tended to degrade reproducibility. We also found that thick paper was preferential when using P-ELISA because a rigid paper substrate prevents distortion of the paper surface that is often caused by repeated washing processes
Comparison of protein immobilization methods with covalent bonding on paper for paper-based enzyme-linked immunosorbent assay
No full textIn this study, two methods were examined to optimize the immobilization of antibodies on paper when conducting a paper-based enzyme-linked immunosorbent assay (P-ELISA). Human IgG, as a test-capture protein, was immobilized on paper via the formation of Schiff bases. Aldehyde groups were introduced onto the surface of the paper via two methods: NaIO4 and 3-aminopropyltriethoxysilane (APTS) with glutaraldehyde (APTS-glutaraldehyde). In the assay, horseradish peroxidase-conjugated anti-human IgG (HRP-anti-IgG) binds to the immobilized human IgG, and the colorimetric reaction of 3,3′,5,5′-tetramethylbenzyzine (TMB) produces a blue color in the presence of H2O2 and HRP-anti-IgG as a model analyte. The immobilization of human IgG, the enzymatic reaction conditions, and the reduction of the chemical bond between the paper surface and immobilized human IgG all were optimized in order to improve both the analytical performance and the stability. In addition, the thickness of the paper was examined to stabilize the analytical signal. Consequently, the APTS-glutaraldehyde method was superior to the NaIO4 method in terms of sensitivity and reproducibility. Conversely, the reduction of imine to amine with NaBH4 proved to exert only minimal influence on sensitivity and stability, although it tended to degrade reproducibility. We also found that thick paper was preferential when using P-ELISA because a rigid paper substrate prevents distortion of the paper surface that is often caused by repeated washing processes
Using a microfluidic paper-based analytical device and solid-phase extraction to determine phosphate concentration
Full text linkPhosphate is an essential nutrient, but in high concentrations it contributes to water pollution. Traditional methods for phosphate measurement, such as absorption spectrophotometry and ion chromatography, require expensive equipment and skilled operators. This study introduces a microfluidic paper-based analytical device (μPAD) that is designed to accomplish field-based, low-concentration phosphate measurements. This μPAD utilizes colorimetric detection based on the molybdenum blue method. Herein, we describe how the conditions were optimized in terms of design and sensitivity by adjusting reagent concentrations, paper thickness, and the time frames for sample introduction, and reaction. The operation consists of simply dipping the μPAD into a sample, capturing images in a home-made photo studio box, and processing the images with ImageJ software to measure RGB intensity. An additional preconcentration step involves solid-phase extraction with an anion exchange resin that achieves a 10-fold enrichment, which enables detection that ranges from 0.05 to 1 mg L−1 with a detection limit of 0.089 mg L−1 and a quantification limit of 0.269 mg L−1. The replicated measurements showed good reproducibility both intraday and interday (five different days) as 4.7 % and 3.0 % of relative standard deviations, respectively. After storage in a refrigerator for as long as 26 days, this μPAD delivered stable and accurate results for real-world samples of natural water, soil, and toothpaste. The results produced using this system correlate well with those produced via spectrophotometry. This μPAD-based method is a cost-effective, portable, rapid, and simple approach that allows relatively unskilled operators to monitor phosphate concentrations in field applications
Microfluidic paper-based analytical devices for antioxidant vitamins C and E in foods
Full text linkIn this study, we developed microfluidic paper-based analytical devices (μPADs) for the determination of antioxidant vitamins. The proposed μPADs utilize the reduction of metal ions by hydrophilic and hydrophobic antioxidant vitamins, which is followed by colorimetric reactions with chelating reagents. Hydrophilic vitamin C reduces Fe(III) to Fe(II) and forms a stable Fe(II)-bathophenanthroline complex in an aqueous solution. By contrast, this complex is unstable in organic solvents, and hydrophobic vitamin E requires Fe(III) and bathophenanthroline to be replaced with Cu(II) and bathocuproine. In these results, the relationship between the logarithm of a vitamin's concentration and its color intensity was linear and ranged from 4.4 to 35 mg L−1 for ascorbic acid and 50–200 mg L−1 for α-tocopherol. The limits of detection, estimated from the standard deviation of blank samples, were 3.1 mg L−1 for ascorbic acid and either 27 mg L−1 (in hexane) or 48 mg L−1 (in ethanol) for α-tocopherol. The proposed method was used to quantify vitamin C in bell peppers, mandarin oranges, kiwifruit, and lemons, as well as vitamin E in almonds, almond milk, and dietary supplements. The results demonstrate the effectiveness of these μPADs for the practical analysis of antioxidant vitamins in food samples
Automated Spectrophotometric Multi-Pumping Flow System for the Determination of Total Iron in Wine
No full text[eng] A new automated system based on a multi-pumping flow system (MPFS) for the spectrophotometric determination of total iron in various wine samples is presented. This analytical protocol is based on the complex formation between Fe (II) and 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP). The addition of ascorbic acid allows the determination of total iron by reducing the Fe (III) present in the samples to Fe (II). Several physical and chemical parameters, including the mixing coil length, the sample volume, the chromogenic reagent concentration, the pH, and the ascorbic acid concentration have been characterized in order to optimize the analytical conditions. The limits of detection and quantification were 34 mg L 1 and 114 mg L 1 respectively. The developed procedure requires minimal sample preparation
A microfluidic paper-based analytical device that uses gelatin film to assay protease activity via time readout
No full textFood processing, detergents, and pharmaceuticals frequently employ proteases, which are enzymes that break the chemical bonds of both proteins and peptides. In this work, we developed a microfluidic paper-based analytical device (µPAD) for protease activity assays via time readout. To accomplish this, we folded the µPAD to form layers, then inserted a water-insoluble gelatin film between the layers of paper to form the device. Lamination helps to maintain the gelatin film between the introduction zone, which is the upper layer, and the detection channel, which is the lower layer. Proteases decompose the gelatin film when it enters the introduction zone, which then allows it to flow into the detection channel. The protease activity in the sample solution determines the time required to dissolve the gelatin film, which leads to a linear relationship between the logarithm of the protease concentration and the time required to flow the solution a specific distance on the detection channel. The µPAD was used to measure proteases in concentrations that ranged from 0.25 to 1 mg L−1 for bromelain, 2.5 to 10 mg L−1 for papain, and 1 to 8 mg L−1 for trypsin. The limits of quantification for bromelain, papain, and trypsin were 0.41, 2.7, and 9.2 mg mL−1, respectively. The relative standard deviations for bromelain were smaller than 2 % for concentrations ranging from 0.5 to 1.0 mg L−1. We compared the µPAD to a commercially available protease activity assay kit, which relies on quenching fluorescein isothiocyanate-labeled casein. Both methods demonstrated the same order of activity: bromelain > papain > trypsin. The proposed device allowed the assay of bromelain in both pineapple pulp and juice, which were stored at room temperature. When first using the proposed device, the bromelain in the pulp gradually lost its activity, while the activity of the bromelain in the juice showed no significant change for five days. The µPAD requires no analytical instruments for quality control and monitoring of the protease activity in food
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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