87,592 research outputs found
Nanostructure-Based Fluorescent Biosensors
No full textNanostructure-Based Fluorescent Biosensors
Shivaram K. a, Gunnella R. a, Giuliodori A. M.b, Spurio R.b, Fabbretti A. b, Perrozzi F.c
Ottaviano L.c
aSchool of Science and Technology, Physics Division, University of Camerino, Via Madonna delle Carceri 9, 62032 Camerino; e-mail: [email protected]
bSchool of Biosciences and Veterinary Medicine, Biology Division, University of Camerino, Via Gentile III da Varano, 62032 Camerino
cDipartimento di Scienze Fisiche e Chimiche, Universita' dell'Aquila Via Vetoio, 67100 L'Aquila
We have investigated a fluorescent biosensor based on graphene oxide (GO) for the measurement of interaction between a fluorophore FAM (Carboxyfluorescein)-labeled single-stranded DNA with its complementary single-stranded DNA oligonucleotide (target). The graphene oxide adsorbs the FAM-labeled single stranded DNA (probe) and quenches its fluorescence. Upon addition of the complementary single stranded DNA oligonucleotide, the probe hybridizes to its target [1] thus producing a double- stranded DNA, which detaches from the GO. The release of the double helix leads to the recovery of dye fluorescence that can be monitored by fluorimetric techniques. Pristine GO [2,3] flakes were prepared using a modified Hummers method and dispersed in water with a concentration of 0.5 mg/mL. The samples were prepared by drop casting, the GO and DNA with buffered solution [1] on 300 nm SiO2 /Si(100) at room temperature. AFM image of the GO flakes,) shows the typical AFM image of the DNA-GO complex, where the bright areas on the GO surface might be due to the adsorption of DNA. In this complex the thickness is about 3 nm.This observation indicates that GO can strongly adsorb ssDNA and can efficiently quench its fluorescence. The fluorescently labeled ssDNA-GO complex displayed significant fluorescence enhancement upon addition of complementary target DNA oligonucleotide (Figure 1b). This recovery of fluorescence increases with increasing concentration of the target DNA added to the mixture.
References
1. Lu, C.-H., Angew. Chem. Int. Ed. 48: 4785–4787 (2009). doi: 10.1002/anie.200901479.
2. Nan-Fu Chiu et al. M. Aliofkhazraei (Ed.), ISBN: 978-953-51-1182-5, InTech (2013). DOI: 10.5772/56221.
3. F. Perrozzi et al., J. Phys.: Condens. Matter 27, 013002 (2015) doi:10.1088/0953-8984/27/1/013002 Graphene oxide: from fundamentals to applications
XPS study of graphene oxide reduction induced by (100) and (111)-oriented Si substrates
No full textThe reduction of graphene oxide (GO) has been extensively studied in literature in order to let GO partially recover the properties of graphene. Most of the techniques proposed to reduce GO are based on high temperature annealing or chemical reduction. A new procedure, based on the direct reduction of GO by etched Si substrate, was recently proposed in literature. In the present work, we accurately investigated the Si-GO interaction with x-ray photoelectron spectroscopy. In order to avoid external substrate oxidation factors we used EtOH as the GO solvent instead of water, and thermal annealing was carried out in UHV. We investigated the effect of Si(100), Si(111) and Au substrates on GO, to probe the role played by both the substrate composition and substrate orientation during the reduction process. A similar degree of GO reduction was observed for all samples but only after thermal annealing, ruling out the direct reduction effect of the substrate
Tunable sulfur desorption in exfoliated MoS2 by means of thermal annealing in ultra-high vacuum
No full textThe effects of thermal annealing in ultra-high vacuum on the electronic structures of bulk and liquid
exfoliated MoS2 have been studied by core level and valence band X-ray photoemission spectroscopy.
A quantitative analysis of core level spectra demonstrates, in the case of exfoliated MoS2, that, upon
annealing above 200 C, defect formation occurs in the form of sulfur single and double vacancies. Sulfur
vacancies introduce surface states in the band gap (determined by the analysis of the valence band spectra).
This determines a rigid shift of the core levels to lower binding energies, as a consequence of an
upward band bending
Tunable sulfur desorption in exfoliated MoS2 by means of thermal annealing in ultra-high vacuum
No full textThe effects of thermal annealing in ultra-high vacuum on the electronic structures of bulk and liquid exfoliated MoS2 have been studied by core level and valence band X-ray photoemission spectroscopy. A quantitative analysis of core level spectra demonstrates, in the case of exfoliated MoS2, that, upon annealing above 200 C, defect formation occurs in the form of sulfur single and double vacancies. Sulfur vacancies introduce surface states in the band gap (determined by the analysis of the valence band spectra). This determines a rigid shift of the core levels to lower binding energies, as a consequence of an upward band bending
Few layered MoS2 lithography with an AFM tip: description of the technique and nanospectroscopy investigations
No full textA novel technique to lithograph the MoS2 surface is described here. Mechanically exfoliated MoS2 flakes have been patterned with an atomic force microscope tip. After the patterning process, the lithographed areas have been removed by selective chemical etching. The electronic properties of the MoS2 flakes have been analyzed with spatially resolved photoelectron spectroscopy, with tunable incident photon energy, provided by a synchrotron light source. Tens of meV core level shifts can be recorded in relation to the flakes edges, coming from both the exfoliation and from the lithography
Unravelling the Role of the Central Metal Ion in the Electronic Structure of Tris-(8-Hydroxyquinoline) Metal Chelates: Photoemission Spectroscopy and Hybrid Functional Calculations
No full textResponse to NO2 and other gases of resistive chemically exfoliated MoS2-based gas sensors
No full textResponse to NO<inf>2</inf> and other gases of resistive chemically exfoliated MoS<inf>2</inf>-based gas sensors
No full textWe report on the fabrication, the morphological, structural, and chemical characterization, and the study of the electrical response to NO2 and other gases of resistive type gas sensors based on liquid chemically exfoliated (in N-methyl pyrrolidone, NMP) MoS2 flakes annealed in air either at 150 °C or at 250 °C. The active material has been analyzed by scanning electron microscopy (SEM), and micro Raman and X-ray core level photoemission spectroscopies. SEM shows that MoS2 exfoliated flakes are interconnected between electrodes of the sensing device to form percolation paths. Raman spectroscopy of the flakes before annealing demonstrates that the flakes are constituted by crystalline MoS2, while, annealing at 250 °C, does not introduce a detectable bulk contamination in the expected form of MoO3. The sensor obtained by thermal annealing in air at 150 °C exhibits a peculiar p-type response under exposure to NO2. In line with core level spectroscopy evidences, this behavior is potentially ascribed to nitrogen substitutional doping of S vacancies in the MoS2 surface (nitrogen atoms being likely provided by the intercalated NMP). Thermal annealing the MoS2 flakes in air at 250 °C irreversibly sets an n-type behavior of the gas sensing device, with a NO2 detection limit of 20 ppb. This behavior is assigned, in line with core level spectroscopy data, to a significant presence of S vacancies in the MoS2 annealed flakes and to the surface co-existence of MoO3 arising from the partial oxidation of the flakes surface. Both p- and n-type sensors have been demonstrated to be sensitive also to relative humidity. The n-type sensor shows good electrical response under H2 exposure
Variations on the Author
No full text“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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