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J Phys Condens Matter ; 33(3): 035001, 2020 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-33078711


Technological applications involving 2D MoS2 require transfer of chemical vapor deposition (CVD) grown material from its original substrate and subsequent lithographic processes. Inevitably, those steps contaminate the surface of the 2D material with polymeric residues affecting the electronic and optical properties of the MoS2. Annealing in forming gas is considered an efficient treatment to partially remove such residues. However, hydrogen also interacts with MoS2 creating or saturating sulfur vacancies. Sulfur vacancies are known to be at the origin of n-doping evident in the majority of as-grown MoS2 samples. In this context, investigating the impact of thermal annealing in forming gas on the electronic and optical properties of MoS2 monolayer is technologically important. In order to address this topic, we have systematically studied the evolution of CVD grown MoS2 monolayer using Raman spectroscopy, photoluminescence, x-ray photoelectron spectroscopy and transport measurements through a series of thermal annealing in forming gas at temperatures up to 500 °C. Efficient removal of the polymeric residues is demonstrated at temperatures as low as 200 °C. Above this value, carrier density modulation is identified by photoluminescence, x-ray photoelectron spectroscopy and electrical characterization and is correlated to the creation of sulfur vacancies. Finally, the degradation of the MoS2 single layer is verified with annealing at or above 350 °C through Raman and photocurrent measurements.

Sci Rep ; 10(1): 7898, 2020 05 12.
Artigo em Inglês | MEDLINE | ID: mdl-32398716


Aggression plays a crucial role in survival all across the animal kingdom. In this study, we investigate the aggressive behaviour of Drosophila suzukii, a known agricultural pest. Bioassays were performed between same sex pairs and the effect of environmental (food deprivation, sex, age and photophase) and social factors (non-social and social). Initially the inter-male and inter-female aggression was determined ethologically consisting of several behaviour patterns. Two hours starvation period increase locomotor activity of flies, promoting increased aggressive behaviour. Most of the behavioural patterns were common between males and females with a few sex-selective. Number of male encounters was higher in flies held in isolation than in those that had been reared with siblings whereas in case of females, only those that were isolated exhibited increased aggression. Females and males D. suzukii that were 4-day-old were more aggressive. In addition it is found that on the 3rd hour after the beginning of photophase, regardless of age, both males and females rise to high intensity aggression patterns.

Agressão/fisiologia , Drosophila/fisiologia , Meio Ambiente , Comportamento Social , Fatores Etários , Animais , Feminino , Privação de Alimentos/fisiologia , Masculino , Atividade Motora/fisiologia
Talanta ; 165: 458-465, 2017 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-28153283


An immunosensor for fast and accurate determination of C-reactive protein (CRP) in human serum samples based on an array of all-silicon broad-band Mach-Zehnder interferometers (BB-MZIs) is demonstrated. The detection was based on monitoring the spectral shifts during the binding of CRP on the antibody molecules that have been immobilized on the sensing arms of the BB-MZIs. By employing the reaction rate as the analytical signal the assay time was compressed to few minutes. The detection limit was 2.1ng/mL, the quantification limit was 4.2ng/mL and the linear dynamic range extended up to 100ng/mL. The measurements performed in human serum samples with the developed immunosensor were characterized by high repeatability and accuracy as it was demonstrated by dilution linearity and recovery experiments. In addition, the concentration values determined were in excellent agreement with those determined for the same samples by a standard clinical laboratory method. The compact size of the chip makes the proposed immunosensor attractive for incorporation into miniaturized devices for the determination of clinical analytes at the point-of-need.

Técnicas Biossensoriais/métodos , Proteína C-Reativa/análise , Desenho de Equipamento , Interferometria/instrumentação , Interferometria/métodos , Silício/química , Humanos , Limite de Detecção
Langmuir ; 30(31): 9599-606, 2014 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-25019927


The electrochemical behavior of colloidal solutions of graphene oxide (GO) is described here in detail. The GO reduction is shown to exhibit near-reversible electron transfer on Pt electrodes, based on E1/2 and ΔEp values. The observed peak current is found to depend linearly on the concentration of the GO and the square root of the scan rate, suggesting that the response is diffusion-limited. The difference between the experimental and diffusion-only limited theoretical current values suggests that migration may be hindering mass transport to the electrode surface. Varying the type and concentration of the supporting electrolyte showed that mass transport is weakly influenced by the presence of negative charges on the graphene particles. The effect of pH on GO was also investigated, and it was found that the reduction peak heights were directly related to proton concentration in acidic solutions. On the basis of the results presented here, we propose that the observed response of GO on Pt electrodes is a result of the reduction of protons from the colloidal double layer. This difference is observed only because the Pt electrode surface can efficiently catalyze proton reduction.

PLoS One ; 7(11): e49037, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-23145057


Hydrogen is a highly promising energy source with important social and economic implications. The ability of green algae to produce photosynthetic hydrogen under anaerobic conditions has been known for years. However, until today the yield of production has been very low, limiting an industrial scale use. In the present paper, 73 years after the first report on H(2)-production from green algae, we present a combinational biological system where the biodegradation procedure of one meta-substituted dichlorophenol (m-dcp) is the key element for maintaining continuous and high rate H(2)-production (>100 times higher than previously reported) in chloroplasts and mitochondria of the green alga Scenedesmus obliquus. In particular, we report that reduced m-dcps (biodegradation intermediates) mimic endogenous electron and proton carriers in chloroplasts and mitochondria, inhibit Photosystem II (PSII) activity (and therefore O(2) production) and enhance Photosystem I (PSI) and hydrogenase activity. In addition, we show that there are some indications for hydrogen production from sources other than chloroplasts in Scenedesmus obliquus. The regulation of these multistage and highly evolved redox pathways leads to high yields of hydrogen production and paves the way for an efficient application to industrial scale use, utilizing simple energy sources and one meta-substituted dichlorophenol as regulating elements.

Clorófitas/metabolismo , Cloroplastos/metabolismo , Hidrogênio/metabolismo , Fenol/metabolismo , Scenedesmus/metabolismo , Biodegradação Ambiental , Complexo de Proteínas da Cadeia de Transporte de Elétrons/metabolismo , Elétrons , Hidrogenase/metabolismo , Mitocôndrias/metabolismo , Oxirredução , Fotossíntese , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Prótons