1,720,977 research outputs found
Quantitative analysis of performance of a hydrogen peroxide-based glucose biosensor
Full text linkA partial glucose biosensor was constructed using a selective internal layer, an enzyme layer and a gold electrode. Both membrane layers are based on cross-linked polyvinyl alcohol (PVA). The performance of the partial glucose biosensor was analyzed particularly with respect to the interfering effects of acetaminophen, a non-ionic molecule. The sensitivity of the immobilized enzyme to glucose was high but it was not high enough to counter acetaminophen interference. The addition of the moderately selective PVA internal layer did not seem to have a significant effect on interference. A mathematical model was then used to analyze the performance of a completed biosensor. A simulated external layer was added to the two layers. The mathematical model predicted that the addition of an external layer with lowered permeability to solutes could improve the performance of the sensor
Production of enzymatic glucose biosensors
Full text linkFor this project, two types of glucose biosensors namely hydrogen peroxide- based glucose biosensor and mediated glucose biosensor have been developed. The performance of a glucose biosensor depends mostly on the immobilization method and support materials that are being used. For hydrogen peroxide-based glucose biosensor, selection of suitable materials for enzyme immobilization was done. Four types of immobilization materials, including chemically-linked PVA, TMOS sol-gel, alumina sol-gel, and freezed-thawed PVA cryogel, were used to immobilize glucose oxidase (GOD) to determine the most appropriate material for GOD immobilization. Generally the membranes had shown good sensitivity except for the chemically cross-linked PVA. However, the main differences with the enzyme immobilization appmethods were enzyme leakage and the values of Km app. Freeze-thawed PVA-GOD was membranes, which showed satisfactory sensitivity and adequate value of Km app chosen as the support material for immobilizing GOD. The enzyme leakage of this type of membrane was improved by reducing enzyme loading. Even though this type of sensor is very simple and easy to construct, it suffers from electrochemical interferences from common electroactive species present in blood such as acetaminophen. Thus, a selective inner layer based on permselectivity was studied. pHEMA, at a cross-linking ratio of 0.043 which resulted in a permselectivity of 10, successfully eliminated acetaminophen interference. Nafion membrane was used as the outer membrane to protect the biosensor. For the mediated based glucose biosensor development, the scopes of work include the preparation of active layer, preparation of external layer and the fabrication of glucose biosensor. Three methods of tethering a mediator to an enzymatic membrane were studied to construct a non-leaking mediated glucose biosensor. The methods were immobilization of glucose oxidase (GOD) and ferrocene redox polymer in cross-linked poly (vinyl alcohol) (CLPVA) with bovine serum albumin (BSA) as a protein stabilizer, immobilization of ferrocene carboxylic acid and glucose oxidase in a sol gel derived silica (SGS) matrix containing cross-linked poly (vinyl alcohol) (CLPVA) and nafion, and lastly multilayered construction of glucose oxidase and redox poly (allylamine) ferrocene utilizing layer-by-layer covalent attachment. After evaluating the biosonser response amperometrically at 0.363V, the first method, which was immobilization of glucose oxidase and ferrocene redox polymer in CLPVA with the addition of BSA was selected for the fabrication of disposable glucose biosensor since this type of sensor provided good responses over a wide range of concentration. Nafion was chosen as the external layer and the works on the fabrication of the glucose biosensor are ongoing
Liposomes: an ideal system for active ingredient delivery
No full textLiposomes were first described about 40 years ago (Bangham et al., 1965). At first they were used to study biological membranes. The ability of liposomes to encapsulate different materials has given rise to the relatively recent use of liposomes as carriers for the incorporation of active ingredients. These processes, which are known as liposomal delivery systems (LDS), have shown remarkable progress over the years. However, in spite of intense scientific activities all over the world, the first drug based on liposomes was introduced to the market only in 1996 (Lasic, 1996). Liposomes are self-assembled colloidal particles that occur naturally and can be prepared artificially. They are microscopic spherical vesicles formed by phospholipids dispersed in water. When amphiphatic lipid molecules containing polar heads and hydrophobic hydrocarbon tails are suspended in an aqueous medium, they can associate spontaneously to form bilayer vesicles. The basic structure of liposomes is similar to biological cell membranes, thus making them very attractive as delivery vehicles including for topical drug delivery. The resulting vesicles comprise an aqueous compartment surrounded by one or more lipid bilayers, which are relatively impermeable to the entrapped substances (Storm and Crommelin, 1998, Gregoriadis, 1993)
Mathematical modeling of an amperometric glucose sensor: the effect of membrane permeability and selectivity on performance
Full text linkInterference from electro-active chemicals such as ascorbic acid, uric acid and acetaminophen can be a problem for peroxide based glucose biosensors. Most works focused on the employment of a perm-selective membrane sandwiched between the electrode and the active component of the sensor to overcome this problem. In this work, a mathematical model has been developed to study the effect of membrane permeability and selectivity on peroxide based glucose biosensor performance. Digital simulation was carried out using the finite difference method. As expected, membrane selectivity to peroxide played a major role in interference reduction. However, interestingly, the model also suggested that the manipulation of the transport properties of the protective outer layer would also result in acceptable interference reduction
Systematic selection of material for an amperometric glucose biosensor
Full text linkThe internal selective membrane for an amperometric glucose biosensor was selected quantitatively based on its transport properties. A rotating disk electrode was used to obtain the permeability of acetaminophen, a common interferent for peroxide-based glucose biosensor, and hydrogen peroxide through cross-linked poly(vinyl alcohol) (PVA). All diffusion experiments were performed using a gold rotating electrode as platinum electrode exhibited slow electron transfer on its surface during the oxidation of acetaminophen, thus rendering it ineffective for this work. Selectivity of crosslinked PVA to peroxide was based on the permeability of peroxide compared to that acetaminophen. As hydrogen peroxide is small, its permeability was only affected when the mesh size of cross-linked PVA was significantly reduced. The permeability of the bigger acetaminophen, on the other hand, was linearly proportional to the mesh size of the cross-linked PVA. Cross-linked PVA membrane was found to display marginal selectivity towards peroxide
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
Estimation of the surface area of a screen-printed carbon electrode modified with gold nanoparticles and cysteine using electrochemical impedance spectroscopy
Full text linkThis work concerns with the estimation of the surface area of a screen-printed carbon electrode (SPCE) modified with gold nanoparticles (AuNPs) and cysteine, using electrochemical impedance spectroscopy (EIS). Interpretation of EIS results was based on charge-transfer reactions at high frequencies, followed by diffusion through the monolayers at lower frequencies. Estimates of the electrode fractional surface coverage (θ), active site radius (ra), and the distance between two adjacent sites (2rb) were obtained by assuming that charge transfer occurred at the active sites and that there were planar diffusions of redox species to these sites. Using EIS, fractional surface coverage was estimated to be around 0.467 for EC modified SPCE, 0.497 for ETSC modified SPCE, and 0.25 for ETSTSC modified SPCE. For the EC modified SPCE, the ra and 2rb were estimated to be 14.8 µm and 68 µm. For the ETSC modified SPCE, the estimated ra and 2rb were 14.3 µm and 63.6 µm. The estimated ra and 2rb for ETSTSC were 13.42 µm and 85 µm. respectively. The inactive site areas for EC, ETSC and ETSTSC modified SPCEs were 0.0587 m2, 0.0624 m2, and 0.0314 m2. The results obtained during this research work suggest that modifying SPCEs using gold and cysteine through electrodeposition of AuNPs, linking with thiourea, self-assembly of AuNPs and self-assembly of cysteine (ETSC) resulted in an electrode with sufficiently high surface area that has the potential to be used as a biosensor for skin sensitiser detection
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