1,720,963 research outputs found
The role of surface chemistry in impedimetric aptasensing
No full textSurface chemistry is a key parameter in the choice of proper materials for electrochemical detection. It has been previously shown that the presence of oxygen containing groups (OCGs) on the surface of graphene oxide (GO) can be both effective and detrimental. This poses a question when GO materials are used as electrochemical platforms for biosensing. In this work, we study how the surface chemistry of graphene oxide nanocolloids (GONCs) affects the impedimetric biosensing of ochratoxin A (OTA), in terms of immobilization of biorecognition element and detection step. OCGs on GONCs were tuned by applying increasing reduction potentials from −0.3 V to −1.2 V, resulting in GONC platforms with decreasing amounts of oxygen functionalities. It was discovered that the sensitivity of biosensing is correlated to the residual amount of OCGs on GO surface. For a more detailed investigation, three representative materials, namely unreduced GONCs, as well as GONCs reduced at potentials of −0.8 V and −1.2 V were chosen. Results were compared in terms of calibration sensitivity, selectivity and reproducibility of the impedimetric response. GONCs reduced at −1.2 V have shown the best electroanalytical response for the impedimetric detection of OTA. These findings are anticipated to contribute to the design of novel biosensors, whereby an optimized platform is employed for the immobilization of the biorecognition element
Unravelling the Aptamer‐Analyte Interaction Dynamics through Fluorescence Quenching in Graphene Quantum Dots (GQDs) Based Homogeneous Assays
No full textGraphene quantum dots (GQDs) are used here as a biosensing platform for the recognition of the major food contaminant ochratoxin A (OTA), with a fluorescently labelled DNA aptamer (FAM OTA aptamer) functioning as the biorecognition element. The detection principle lies in the formation of noncovalent interactions between the FAM OTA aptamer and the GQD surface, and the consequent fluorescence quenching. The further change in the fluorescence signal, induced by the formation of the FAM OTA Aptamer/OTA conjugate during the detection step, could then be correlated to the presence and concentration of the target analyte. Upon tuning the concentration of GQDs, a switch in the biorecognition mechanism occurred. Specifically, while a lower GQD concentration (0.060 mg/mL) resulted in a restoration of the fluorescence intensity upon incubation with OTA, a higher GQD concentration (0.150 mg/mL) provided a further quenching of the final fluorescence intensity. Upon further calibration study, it was discovered that the latter mechanism provided a better option in terms of linearity of response, detection limit and selectivity.Nanyang Technological UniversityA. B. acknowledges Nanyang Technological University for the financial support
Electroactive Nanocarbon Can Simultaneously Work as Platform and Signal Generator for Label‐Free Immunosensing
No full textElectroactive nanocarbon can be defined as a carbon nanomaterial that contains electrochemically reducible oxygen functionalities. We show here how an electroactive nanocarbon material can work both as a platform and as a signal generator when developing an immunosensor for the detection of mycotoxins. The suitability of the material for the immobilization of the biorecognition element by the formation of multiple noncovalent interactions, and the concurrent ability to provide a significant reduction peak are combined here in a label-free, single-step immunosensor. The variation in the current intensity, owing to the reduction of the electroactive platform, is correlated to the electrochemical availability of the oxygen functionalities involved in the interaction with the biorecognition element first, and the antibody/antigen conjugate in the detection step. We demonstrated here a direct dependence between the signal generated from the electroactive nanocarbon platform and each step of the biorecognition event, which allows the selective and precise detection of the analyte under investigation
Effect of surface chemistry on bio-conjugation and bio-recognition abilities of 2D germanene materials
No full textThe interest of the scientific community for 2D graphene analogues has been recently focused on 2D-Xene materials from Group 14. Among them, germanene and its derivatives have shown great potential because of their large bandgap and easily tuneable electronic and optical properties. With the latter having been already explored, the use of chemically modified germanenes for optical bio-recognition is yet to be investigated. Herein, we have synthesized two germanene materials with different surface ligands namely hydrogenated germanene (Ge-H) and methylated germanene (Ge-Me) and used them as an optical platform for the label-free biorecognition of Ochratoxin A (OTA), a highly carcinogenic food contaminant. It was discovered that firstly the surface ligands on chemically modified germanenes have strong influence on the intrinsic fluorescence of the material; secondly they also highly affect both the bio-conjugation ability and the bio-recognition efficiency of the material towards the detection of the analyte. An improved calibration sensitivity, together with superior reproducibility and linearity of response, was obtained with a methylated germanene (Ge-Me) material, indicating also the better suitability of the latter for real sample analysis. Such research is highly beneficial for the development and optimization of 2D material based optical platforms for fast and cost-effective bioassays.Ministry of Education (MOE)A.B. gratefully acknowledges Ministry of Education (MOE), AcRF Tier 1 grant (Reference No: RG9/19) for the financial support. J. S. acknowledges the financial support of Grant Agency of the Czech Republic (GACR: 19-17593Y). Z. S. was supported by ERC CZ project LL2003 from the Ministry of Education Youth and Sports (MEYS)
Electroactive nanocarbon materials as signaling tags for electrochemical PCR
No full textElectrochemical polymerase chain reaction (PCR) represents a valid alternative to the optical-based PCR due to reduced costs of signaling labels, use of simpler instrumentation, and possibility of miniaturization and portability of the systems, which can facilitate decentralized detection. The high intrinsic electroactivity and strong linear relationship between the material concentration and its redox signal suggest a possible use of oxidized nanocarbon materials as electroactive tags for PCR. Herein, we compared three different nanographene oxide materials namely nGO-1, nGO-2 and nGO-3 as signaling tags for the detection of genetically modified organisms (GMO) by electrochemical PCR. The three materials differ in size, chemical composition as well as type and amount of oxygen functionalities verified by extensive characterization with X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM) and electrochemical methods. A sense primer sequence belonging to the Cauliflower Mosaic Virus 35S promoter (a common genetic marker for GMO screening) was used to conjugate to the nanocarbon materials by carbodiimide chemistry before PCR amplification with a biotinylated antisense strand. Finally, the amplified electroactive PCR product was detected, where the reduction signal derived from the electrochemically reducible oxygenated functionalities on the nanocarbon material surface was directly correlated to the presence of GMO. Overall, we were able to correlate the different material characteristics with their performance as electroactive labels and identify the nanocarbon material that exhibits the highest potential to be used as innovative electroactive label for PCR in the amplification and detection of the selected target sequence.Ministry of Education (MOE)A.B. acknowledges Ministry of Education (MOE) Singapore, AcRF Tier 1 grant (Reference No: RG88/20) for the financial support. A.A. acknowledges the support of the Double-Hundred Program for Foreign Experts of Shandong Province (WST2019011). Z.S. was supported by Czech Science Foundation (GACR No. 20-16124J)
Rapid electrochemical detection of COVID-19 genomic sequence with dual-function graphene nanocolloids based biosensor
Full text linkDiscovered in December 2019, the Severe Acute Respiratory Syndrome Coronavirus 2 (aka SARS-CoV-2 or 2019-nCoV) has attracted worldwide attention and concerns due to its high transmissibility and the severe health consequences experienced upon its infection, particularly by elderly people. Over 329 million people have been infected till date and over 5.5 million people could not survive the respiratory illness known as COVID-19 syndrome. Rapid and low-cost detection methods are of utmost importance to monitor the diffusion of the virus and to aid in the global fight against the pandemic. We propose here the use of graphene oxide nanocolloids (GONC) as an electroactive nanocarbon material that can act simultaneously as a transducing platform as well as the electroactive label for the detection of 2019-nCoV genomic sequences. The ability of GONC to provide an intrinsic electrochemical signal arising from the reduction of the electrochemically reducible oxygen functionalities present on its surface, allows GONC to be used as a simple and sensitive biosensing platform. Different intrinsic electroactivity of the material was obtained at each step of the genosensing process, starting from the immobilization of a short-stranded DNA probe and followed by the incubation with different concentrations of the target 2019-nCoV DNA strand. Monitoring such variations enabled the quantification of the target analyte over a wide dynamic range between 10−10 and 10−5 M. All in all, this proof-of-concept system serves as a stepping stone for the development of a rapid, sensitive and selective analytical tool for the detection of 2019-nCoV as well as other similar viral vectors. The use of cost-effective electrochemical detection methods coupled with the vast availability and suitability of carbon-based nanomaterials make this sensing system a valid candidate for low-cost and point-of-care analysis.Ministry of Education (MOE)A.B. acknowledges Ministry of Education (MOE), AcRF Tier 1 grant (Reference No: RG88/20) for the financial support. A.A. acknowledges the support of the Double-Hundred Program for Foreign Experts of Shandong Province (WST2019011)
Electrochemical polymerase chain reaction using electroactive graphene oxide nanoparticles as detection labels
No full textElectroactive nanocarbon tags are used in this work to label the DNA primers for the polymerase chain reaction (PCR) amplification of Cauliflower Mosaic Virus 35S promoter sequence, one of the most common markers for the detection of genetically modified organisms (GMOs). The PCR product carrying the electrochemical label can be directly detected on miniaturized electrodes, with the working signal being correlated to the reduction of oxygen-containing groups on the nanocarbon surface. A linear relationship was first established between the electrochemical signal and the nanomaterial concentration, both for the unconjugated electroactive nanocarbon and the conjugates with single-stranded and double-stranded DNA. After which, PCR amplification using a modified sense-primer was performed, and discrimination between amplified products from positive samples (GMO maize) and negative controls (non-GMO maize) was achieved successfully. After the optimization of PCR experimental conditions using the electroactive nanocarbon label, the electrochemical signal recorded as a function of PCR cycle number showed an exponential increase, very similar to that obtained in optical-based real-time PCR. From that, the extrapolated cycle threshold value showed a linear relationship with the initial number of copies of target DNA. Through the findings, electroactive nanocarbon material demonstrated high potential as electrochemical label for PCR, with the electrochemical signals produced directly correlated to the amount of PCR product. This work will serve as a stepping stone for the development of a robust, efficient, and portable electrochemical PCR system, with a reduced cost considering the wide availability and suitability of carbon nanomaterials for mass production, and the cost-effective electrochemical detection.Ministry of Education (MOE)A.B. gratefully acknowledges Ministry of Education (MOE), AcRF Tier 1 grant (Reference No: RG18/17) and Nanyang Technological University for the funding of this research
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
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