1,720,959 research outputs found
Laser manufacturing for multi-analyte paper-based diagnostic sensors
No full textWe present here our work on the fabrication of paper-based multiplexed diagnostic sensors, using direct-write laser-based processes (Laser Induced Forward Transfer and photo-polymerisation), for the detection of glucose and proteins (BSA)
Direct-write laser techniques for the manufacture of multiplexed paper-based diagnostic sensors
No full textThe ever-present need for affordable and reliable devices for health monitoring has led to a significant growth over the past few years in the development and applications of paper-based point-of-care diagnostics that operate with minimal reagent volumes, are portable and need no special training or equipment for their use. We present here our work on the fabrication of multiplexed paper-based diagnostic sensors for the detection of glucose and bovine serum albumin (BSA) using lasers-based methods. Our use of lasers for the fabrication of the devices is justified by the versatility, speed of production, and cost, all of which are of critical importance for mass-market applications. A laser direct-write process, Laser-Induced Forward Transfer (LIFT), was used to print the reagents and biological molecules on paper substrates that facilitate the sensing of the specific analytes. A second laser-based process was also implemented to create hydrophobic walls and barriers in paper and membrane substrates, which define the wells and channels that can guide biological and chemical solutions through the paper devices. A pulsed KrF excimer laser operating at 248 nm was used for LIFT and a continuous wave laser at 405 nm was used for patterning of the paper. The small dimensions of the structures produced (~100 µm) and the precise and low-volume (nl) deposition of materials by these processes enable the miniaturisation of these devices ensuring the minimal use of reagents. We have quantified the speed and cost of our laser-based methods and believe they can be up-scaled for mass production
Engineering fluidic delays in paper-based devices using laser direct-writing
No full textWe report the use of a new laser-based direct-write technique that allows programmable and timed fluid delivery in channels within a paper substrate which enables implementation of multi-step analytical assays. The technique is based on laser-induced photo-polymerisation, and through adjustment of the laser writing parameters such as the laser power and scan speed we can control the depth and/or the porosity of hydrophobic barriers which, when fabricated in the fluid path, produce controllable fluid delay. We have patterned these flow delaying barriers at pre-defined locations in the fluidic channels using either a continuous wave laser at 405nm, or a pulsed laser operating at 266nm. Using this delay patterning protocol we generated flow delays spanning from minutes to over an hour. Since the channels and flow delay barriers can be written via a common laser-writing process, this is a distinct improvement over other methods that require specialist operating environments, or custom-designed equipment. This technique can therefore be used for rapid fabrication of paper-based microfluidic devices that can perform single or multistep analytical assays
Laser-polymerised fluidic channels for the manufacture of multiplexed paper-based diagnostic sensors
No full textPaper-based microfluidics is a rapidly progressing inter-disciplinary technology driven by the need for low-cost alternatives to conventional point-of-care diagnostic tools. For transport of reagents/analytes, such devices often consist of interconnected hydrophilic fluid-flow channels that are demarcated by hydrophobic barrier walls that extend through the thickness of the paper. Here, we present a laser-based fabrication procedure that uses laser-induced polymerisation of a photopolymer to produce the required fluidic channels in paper or other porous materials. Experimental results showed that the structures successfully guide the flow of fluids and also allow containment of fluids in wells, and hence the technique is suitable for fabrication of paper-based microfluidic devices.The minimum width for the hydrophobic barriers that successfully prevented fluid leakage was ~120 µm and the minimum width for the fluidic channels that can be formed was ~80 µm, the smallest reported so far for paper-based fluidic patterns. The patterns can be produced rapidly using simple low power c.w. laser sources at a writing speed of order 1 ms-1 and we have successfully demonstrated techniques for controlled delay, forward biased and multiplexed flow of several different fluids. We show our early results for diagnostic paper-based sensors for the detection of glucose and bovine serum albumin (BSA) using colorometric readout, which we believe makes the technique especially useful for mass-market applications, particularly in developing world situations where simplicity, cheapness and ready availability are the key parameters
Laser-direct-write technique for rapid prototyping of multiplexed paper-based diagnostic sensors
No full textThe demand for low-cost alternatives to conventional point-of-care diagnostic tools has led to significant developments in the field of paper-based diagnostics, and several methods, which include photolithography, inkjet printing, wax printing etc., have been reported for the fabrication of fluidic devices in porous materials such as paper. Here, we present a simple, laser-based direct-write procedure, which relies on light-induced photo-polymerisation of a photopolymer previously impregnated in the porous substrates for fabrication of the user-defined fluidic patterns within such substrates. During the subsequent development step, the un-polymerised photopolymer is washed-out; however, the hydrophobic polymerized structures that remain in the substrate, and extend throughout its thickness define the barrier-walls of the hydrophilic fluidic patterns they demarcate. These structures contain and guide liquids without any leakage, thus validating the feasibility of using this technique in the production of microfluidic devices. Our results show that for cellulose paper, the minimum widths the hydrophobic barrier-walls should have to successfully contain fluids is ~ 120 µm, and similarly, the minimum dimensions a fluidic channel can have to guide fluids is ~ 80 µm, both of which are the smallest values reported so far. These patterns can be produced rapidly via scanning of a low power continuous-wave laser at speeds of the order of one meter per second and we have successfully implemented it in patterning a range of porous materials including nitrocellulose membranes, glass fibre filter and polyvinylidene fluoride. To further validate the applicability of these laser-patterned devices as sensors, we have demonstrated their use for a range of colorimetric assays including the detection of glucose, protein and nitrite, and also an enzyme-linked immunosorbent assay for detection of C-reactive protein. Finally, we have quantified the speed and cost of our laser-based method and believe that it is suited to up-scaling for mass production
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
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
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