Mesoscopic 3D Charge Transport in Solution-Processed Graphene-Based Thin Films: A Multiscale Analysis

Graphene and related 2D material (GRM) thin films consist of 3D assembly of billions of 2D nanosheets randomly distributed and interacting via van der Waals forces. Their complexity and the multiscale nature yield a wide variety of electrical characteristics ranging from doped semiconductor to glassy metals depending on the crystalline quality of the nanosheets, their specific structural organization ant the operating temperature. Here, the charge transport (CT) mechanisms are studied that are occurring in GRM thin films near the metal-insulator transition (MIT) highlighting the role of defect density and local arrangement of the nanosheets. Two prototypical nanosheet types are compared, i.e., 2D reduced graphene oxide and few-layer-thick electrochemically exfoliated graphene flakes, forming thin films with comparable composition, morphology and room temperature conductivity, but different defect density and crystallinity. By investigating their structure, morphology, and the dependence of their electrical conductivity on temperature, noise and magnetic-field, a general model is developed describing the multiscale nature of CT in GRM thin films in terms of hopping among mesoscopic bricks, i.e., grains. The results suggest a general approach to describe disordered van der Waals thin films.

Multiscale Charge Transport in van der Waals Thin Films: Reduced Graphene Oxide as a Case Study

Large area van der Waals (vdW) thin films are assembled materials consisting of a network of randomly stacked nanosheets. The multiscale structure and the two-dimensional (2D) nature of the building block mean that interfaces naturally play a crucial role in the charge transport of such thin films. While single or few stacked nanosheets (i.e., vdW heterostructures) have been the subject of intensive works, little is known about how charges travel through multilayered, more disordered networks. Here, we report a comprehensive study of a prototypical system given by networks of randomly stacked reduced graphene oxide 2D nanosheets, whose chemical and geometrical properties can be controlled independently, permitting to explore percolated networks ranging from a single nanosheet to some billions with room-temperature resistivity spanning from 10^-5 to 10^-1 Ω·m. We systematically observe a clear transition between two different regimes at a critical temperature T*: Efros-Shklovskii variable-range hopping (ES-VRH) below T* and power law behavior above. First, we demonstrate that the two regimes are strongly correlated with each other, both depending on the charge localization length ξ, calculated by the ES-VRH model, which corresponds to the characteristic size of overlapping sp² domains belonging to different nanosheets. Thus, we propose a microscopic model describing the charge transport as a geometrical phase transition, given by the metal-insulator transition associated with the percolation of quasi-one-dimensional nanofillers with length ξ, showing that the charge transport behavior of the networks is valid for all geometries and defects of the nanosheets, ultimately suggesting a generalized description on vdW and disordered thin films.

The conquest of middle-earth: combining top-down and bottom-up nanofabrication for constructing nanoparticle based devices

The development of top-down nanofabrication techniques has opened many possibilities for the design and realization of complex devices based on single molecule phenomena such as e.g. single molecule electronic devices. These impressive achievements have been complemented by the fundamental understanding of self-assembly phenomena, leading to bottom-up strategies to obtain hybrid nanomaterials that can be used as building blocks for more complex structures. In this feature article we highlight some relevant published work as well as present new experimental results, illustrating the versatility of self-assembly methods combined with top-down fabrication techniques for solving relevant challenges in modern nanotechnology. We present recent developments on the use of hierarchical self-assembly methods to bridge the gap between sub-nanometer and micrometer length scales. By the use of non-covalent self-assembly methods, we show that we are able to control the positioning of nanoparticles on surfaces, and to address the deterministic assembly of nano-devices with potential applications in plasmonic sensing and single-molecule electronics experiments.

Antigen-specific suppression of cultured lymphocytes from patients with neurocysticercosis

The biological parasite-host interactions involved in neurocysticercosis (NC) are of a complex nature. A lymphoproliferation assay was performed using mononuclear cells from 11 patients with NC, who were classified according to the alterations obtained by imaging examinations. Antigen extracts from the membrane and/or scolex of Taenia solium and from the vesicular fluid of Taenia crassiceps were used. Mononuclear cells from patients with NC showed antigen-specific suppression when compared with a control group. The patients presenting calcified cysts showed higher suppression when compared with patients in the active phase of disease. The antigen in the vesicular fluid of T. crassiceps seems to play a suppressor role in vitro, completely inhibiting cell proliferation induced by the mitogens phytohaemagglutinin, concanavalin A and pokeweed mitogen.

Measles vaccine coverage and immune response in children of Caiabi and Metuktire Indian tribes living in malarial endemic area: Parque indígena do Xingu, Central Brazil

Measles vaccination efficiency was evaluated in children from two Indian tribes - Caiabi and Metuktire - living in the Amazon region, in the Parque Indigena do Xingu (PIX). The population sample, selected at random, made up 37 Caiabi and 28 Metuktire children, aged from 20-75 months (40%). For operational and epidemiological reasons, measles vaccine is given from 6 months of age. The average age of children when they received the vaccine was 11.5 months for the first dose and 20 months for the second. The search for IgG antibodies against measles virus and Plasmodium falciparum was made through immunofluorescence assay (IFA). Measles vaccine coverage has reached 60% at 12 months of age and 92% at 18 months, whereas post-vaccine serum conversion was 95% in Caiabi children (geometric mean of titres (GMT) 126) and 89% in Metuktire (GMT 109). The difference in GMT is not statistically significant. Seventy-three per cent of Caiabi children (GMT 101) and 100% of Metuktire children (GMT135) were plasmodium antibody positive, showing they had been exposed to malarial infection. Despite the differences detected, the immune response to measles vaccine was satisfactory in both groups, with a positive percentage consistent with that achieved in non-malarial areas in Americas. The results show the efficiency of a vaccination programme in an indigenous area despite the difficulties in reaching the villages and maintaining the cold chain, and also despite the malaria endemicity.

Immune responses to multiple antigen peptides containing T and B epitopes from Plasmodium falciparum circumsporozoite protein of Brazilian individuals naturally exposed to malaria

We have evaluated the immune responses of individuals living in a malaria endemic area of Brazil to the (T1B)4, a multiple antigen peptide (MAP) from Plasmodium falciparum circumsporozoite (CS) protein and the related monoepitope MAPs, B4 and (T1)4, and the linear peptides, T1B and B. The highest antibody frequencies were against MAPs containing the B cell epitope sequence (T1B)4 (42.2%) and B4 (28.8%), while the highest lymphoproliferative response frequencies were against the MAPs containing the T cell epitope sequence (T1)4 (47%) and (T1B)4 (36.4%). We analysed individual responses considering lymphoproliferative response to (T1)4 MAP and IgG antibody titre to (T1B)4 as patterns of ideal cellular and humoral responses, respectively. The frequency of responders, cellular and/or humoral was 66.6%, significantly higher than non responders (P = 0.003). We also determined the HLA class II haplotype of each individual but no association between these and immune response patterns to the MAPs was observed. The results showed that individuals primed against P. falciparum in their natural habitat, present a very diverse array of responses against the same peptide antigens, varying from no response in one-third of the individuals to cognate B and T cell responses. Our study underlines the importance of previous studies of vaccine candidates to guarantee that the immunization will be capable of reverting inefficient or absent responses to malaria epitopes.

Standardization of procedures of Plasmodium falciparum antigen preparation for serologic tests

The objective of the present study is to standardize the technical variables for preparation and storage of Plasmodium falciparum and of antigen components extracted with the amphoteric detergent Zwittergent. P. falciparum obtained from in vitro culture was stored at different temperatures and for different periods of time. For each variable, antigen components of the parasite were extracted in the presence or absence of protease inhibitors and submitted or not to later dialysis. Products were stored for 15, 30 and 60 days at different temperatures and immunological activity of each extract was determined by SDS-PAGE and ELISA using positive or negative standard sera for the presence of IgG directed to blood stage antigens of P. falciparum. Antigen extracts obtained from parasites stored at -20 degrees C up to 10 days or at -70 degrees C for 2 months presented the best results, showing well-defined bands on SDS-PAGE and Western blots and presenting absorbance values in ELISA that permitted safe differentiation between positive and negative sera.

Malaria diagnosis: a review

Malaria is the most prevalent endemic disease in large parts of the world and is subject to control by health authorities. Today, the goal of malaria control is to prevent mortality and reduce morbidity and socioeconomic losses through the progressive improvement and strengthening of local and national capabilities. The World Health Organization considers early diagnosis as the first basic element of the strategy to control the disease. Traditionally, laboratory diagnosis has been made using the thick blood film, which continues to be the gold standard test. However, this test has disadvantages such as the manner in which the film is prepared, the level of training of the observer, the adequacy of maintenance of materials and equipment and its only fair sensitivity. Thus, many research laboratories have concentrated their efforts on the development of alternative methods for malaria diagnosis. These include methods for the detection of Plasmodia within erythrocytes (fluorescent microscopy, Quantitative Buffy Coat (QBC), dark field microscopy, nucleic acid probes and immunofluorescence), methods for the detection of plasmodial antigens in body fluids (radioimmunoassay, enzyme immunoassay) and methods for the detection of anti-plasmodial antibodies in serum (indirect immunofluorescence, enzyme immunoassay, Western blotting). Here, we critically review the various methods for malaria diagnosis based on the world's literature and our experience with most of them, with emphasis on recent advances.

Evaluation of different methods for Plasmodia detection, in well defined population groups in an endemic area of Brazil (1)

In Brazil, more than 500,000 new cases of malaria were notified in 1992. Plasmodium falciparum and P. vivax are the responsible species for 99.3% of the cases. For adequate treatment, precoce diagnosis is necessary. In this work, we present the results of the traditional Plasmodia detection method, thick blood film (TBF), and the results of alternative methods: Immunofluorescence assay (IFA) with polyclonal antibody and Quantitative Buffy Coat method (QBC) in a well defined population groups. The analysis were done in relation to the presence or absence of malaria clinical symptoms. Also different classes of immunoglobulins anti-P.falciparum were quantified for the global analysis of the results, mainly in the discrepant results. We concluded that alternative methods are more sensitive than TBF and that the association of epidemiological, clinical and laboratory findings is necessary to define the presence of malaria.