1,720,962 research outputs found
Premio di laurea magistrale in Ingegneria Biomedica
No full textUna larga frazione delle attività di tipo biologico, dal trasporto di sostanze alla trasmissione di segnali, avviene all’interfaccia tra le cellule e l’ambiente circostante: la membrana cellulare, con il suo doppio strato lipidico, costituisce tale interfaccia. La membrana cellulare ospita inoltre un gran numero di proteine, responsabili dell’attività fisiologica (si pensi ad esempio che queste rappresentano circa il 60% dei target farmacologici). Per tale motivo lo studio presentato, svolto in collaborazione tra il Dipartimento di Ingegneria Chimica, Materiali e Ambiente della Sapienza e l’Istituto per la Microelettronica e i Microsistemi del Consiglio Nazionale delle Ricerche di Bologna, ha come scopo ultimo quello di sviluppare dei biosensori che permettano di esaminare il comportamento della membrana cellulare e delle proteine in essa integrate. Le proteine di membrana mantengono la loro funzionalità solo nel loro ambiente nativo, per questo motivo è necessario lo sviluppo di tecniche mimetiche, che si sforzino di simulare il doppio strato lipidico: in questo modo diventerà possibile rilevare l’insieme di processi chimici e fisici a esse associati, d’importanza fondamentale in una vasta gamma di applicazioni biomediche. Uno dei maggiori fattori che influenzano lo sviluppo ed il funzionamento dei biosensori è la comunicazione tra l’elemento sensibile (in questo caso di natura biologica) e l’elemento di trasduzione. Il grafene, uno strato monoatomico di atomi di carbonio, può svolgere un ruolo decisivo, poiché le sue proprietà elettrochimiche, quali ad esempio l’elevata conducibilità, il basso rumore e la bassa resistenza di trasferimento di carica, facilitano lo scambio d’informazioni tra il recettore ed il trasduttore
Design and fabrication of graphene/lipid nanostructured interfaces for applications in membrane protein biosensing
Full text linkPlasma membranes, or cytoplasmatic membranes, are the reaction fields of many biological reactions involved in diseases, and an active barrier for the transportation of information and materials between the inside and outside compartments of cells. Lipid bilayers are the fundamental structure of cell membranes. Examining the functional behavior of lipids and proteins and their ensemble by using artificial lipid bilayers integrated in biosensors is important in order to determine the physical and chemical processes involved in cell membrane reactions, that are relevant in a wide range of biomedical applications. By using supported lipid bilayers (SLBs) on graphene-based substrates, it is possible to develop novel biosensors able to obtain molecular information from membrane proteins embedded in lipid bilayers: the graphene acts as the transducer of the electrical signals and the phospholipidic bilayers with embedded molecular proteins form the receptor layer. The main objectives of this thesis are the design and optimization of the interactions between graphene and lipid bilayers, through the analysis of the fabrication process of graphene, its surface treatments and how these affects the formation of supported lipid membranes. These are essential steps aiming at manufacturing a novel properly designed biosensing platform with integrated membrane proteins. Nanomaterials can play a very significant role in the development of the next generation of biosensors, since they can help to address some of the key issues in the development of biosensors. Graphene is a carbon-based nanomaterial that has recently attracted most interest due to its unique electronic properties, arising from its crystal structure, which result in a extremely low noise level and an increased signal-to-noise ratio. The fabrication of biosensors based on SLBs on graphene requires the study and optimization of the building blocks of the sensor and of the interface between them. The formation of SLBs is strongly influenced by the physical and chemical properties of the underlying substrates. Then, in order to induce the formation of lipid bilayers possessing a sufficient stability for practical biosensing applications, the wetting properties of the supporting layer should be investigated. Since graphene is a hydrophobic material, the introduction of defects on the surface both by heat treatments or functionalization have been investigated
Novel electrochemical biosensors based on a biomimetic graphene-lipid bilayer interface
No full textIn our work we investigate the development of a novel electrochemical biosensor that integrates a graphene layer as the transducer element for the analysis of electroactive membrane proteins. Graphene is used as transducer because of its unique properties (high surface area, electrical conductivity, ultra-high electron mobility, wide electrochemical potential window, low charge-transfer resistance, reduction of overvoltage), all of which are responsible for the enhancement of the direct electron transfer between graphene and the membrane proteins. However, in biosensors for membrane proteins a major problem is the denaturation of such proteins when they are in contact with the electrode solid surface. To avoid this, membrane proteins are normally embedded in a biological system mimicking their native environment, the supported lipid bilayer (SLB). This study is focused on the synthesis of the graphene interface through chemical vapour deposition, on its surface treatments through a mild oxidation to improve its biocompatibility, and on the investigation of the graphene interface with SLBs. The obtained films of graphene are characterized using scanning electron microscopy, Raman spectroscopy and measuring the water contact angles before and after surface treatments. The interaction of the graphene surface with liposomes and the formation of the graphene-supported lipid bilayer are investigated using electrochemical impedance spectroscopy
Synthesis of smooth graphene surfaces by CVD for electrochemical biosensors with supported lipid membranes
No full textIn this work we perform an ab initio study on the design of a novel electrochemical biosensor, in which graphene and membrane proteins would serve as transducer and biological recognition elements, respectively. Graphene is used as transducer because of its unique and intriguing properties, namely surface area, electrical conductivity, ultra high electron mobility, wide electrochemical potential window, low charge-transfer resistance, and reduction of overvoltage. All these properties are responsible for the enhancement of the direct electron transfer between the graphene surface and the membrane proteins. Membrane proteins are the chosen biosensing element for this study since they represent almost 60% of all human protein drug targets. The main problem is that the contact with electrode surface causes the denaturation of membrane proteins, so they need to be embedded in a system mimicking their native environment (i.e. the cell membrane). Supported lipid bilayers (SLBs) are widely used as artificial cell membranes for biophysical studies and nano-biotechnology applications. They are most often generated starting from a liposome solution in which surfaces are incubated for a certain period of time. SLBs form preferentially and are functional on more hydrophilic substrates, whereas graphene surfaces are highly hydrophobic, and so they need to be modified
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
Graphene-lipids interaction. Towards the fabrication of a novel sensor for biomedical uses
No full textIn this work we investigate the use of graphene as transducer in a novel biosensor for biomedical uses, in which electroactive membrane proteins would serve as biological recognition elements. Membrane proteins maintain their functionalities only if embedded in the cell membrane, so it is necessary to develop a system, which mimics their native environment. This study is focused on surface treatments of graphene to improve its biocompatibility and a first investigation of its interaction with liposomes, which rupture and spread to form a Supported Lipid Bilayer under specific surface conditions. The first step involved the characterization of the graphene membranes synthesized by Chemical Vapor Deposition, using several techniques to determine their morphological and structural properties. From these investigations, the CVD-synthesized graphene resulted to be mono- to few-layer. Next, the interaction of graphene with lipids (1,2-dioleoyl-sn-glicero-3-phosphocholine), in particular the formation of a supported lipid bilayer due to the liposome spreading, was investigated via electrochemical impedance spectroscopy. This indicated the presence of a stable insulating lipid layer on the graphene surface after liposome incubation
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
