Solution processed nanostructured hybrid materials based on PbS quantum dots and reduced graphene oxide with tunable optoelectronic properties.

Nanostructured hybrid materials (NHMs) are promising candidates to improve the performance of several materials in different applications. In the case of optoelectronic technologies, the ability to tune the optical absorption of such NHMs is an appealing feature. Along with the capacity to transform the absorbed light into charge carriers (CC), and their consequently efficient transport to the different electrodes. In this regard, NHM based on graphene-like structures and semiconductor QDs are appealing candidates, assuming the NHMs retain the light absorption and CC photogeneration properties of semiconductor QDs, and the excellent CC transport properties displayed by graphene-like materials. In the current work a solution-processed NHM using PbS quantum dots (QDs) and graphene oxide (GO) was fabricated in a layer-by-layer configuration by dip-coating. Afterwards, these NHMs were reduced by thermal or chemical methods. Reduction process had a direct impact on the final optoelectronic properties displayed by the NHMs. All reduced samples displayed a decrement in their resistivity, particularly the sample chemically reduced, displaying a 107 fold decrease; mainly attributed to N-doping in the reduced graphene oxide (rGO). The optical absorption coefficients also showed a dependence on the rGO's reduction degree, with reduced samples displaying higher values, and sample thermally reduced at 300 °C showing the highest absorption coefficient, due to the combined absorption of unaltered PbS QDs and the appearance of sp2 regions within rGO. The photogenerated current increased in most reduced samples, displaying the highest photocurrent the sample reduced at 400 °C, presenting a 2500-fold increment compared to the NHM before reduction, attributed to an enhanced CC transfer from PbS QDs to rGO, as a consequence of an improved band alignment between them. These results show clear evidence on how the optoelectronic properties of NHMs based on semiconductor nanoparticles and rGO, can be tuned based on their configuration and the reduction process parameters.

Tuning the optoelectronic properties of PEDOT:PSS-PVP core-shell electrospun nanofibers by solvent-quantum dot doping and phase inversion.

In the present study core-shell PEDOT:PSS-polyvinylpirrolidone nanofibers were synthesized by coaxial electrospinning. These fibers were doped with different solvents (dimethylsulphoxide, dimethyl sulfoxide (DMSO), isopropyl alcohol (IPA), and ethylene glycol), and PbS nanoparticles at different concentrations; additionally, the coaxial electrospinning setup process was inverted in order to exchange the phases comprising the core-shell morphology. Experimental results showed that DMSO and IPA solvents produced a change in the PEDOT:PSS phase from its benzoid structure to a more conjugated (quinoid) one. The synthesized samples displayed an increment in the conductance of the composite nanofibers, based on a more conjugated structure of the PEDOT:PSS phase, and a better dispersion of the PbS nanoparticles within the nanofibers; this increment was, under certain synthesis conditions, up to three orders of magnitude higher than in the case of the nanofibers with no solvent, nor nanoparticles, added. Photoresponse also showed a clear increment in the value of the photogenerated current as the concentration of the nanoparticles increased. Inverting the arrangement of the core-shell phases in the nanofibers increased the conductance and the photogenerated current in the cases analyzed. These results show novel evidence on the capability of tuning the conductance and photoresponse of composite core-shell nanofibers, based on the doping of the PEDOT:PSS phase with different solvents and PbS nanoparticles, and the arrangement of the core-shell phases. Tailoring the optoelectronic properties of conductive, flexible nanofibers is a desirable competence in technological areas such as transparent flexible conductors, biosensors and tissue engineering.

[Cerebral hydatidosis. Analysis of a series of 23 cases]. / Hidatidosis cerebral. Análisis de una serie de 23 casos.

BACKGROUND: The aim of the present study was to contribute to the knowledge of cerebral hydatidosis so as to improve the prognosis of a benign condition with a malignant behavior, as it has a high relapse rate with a high morbidity. METHODS: A retrospective study of cerebral hydatidosis has been carried out in 23 patients, seen at the University Hospital Virgen del Rocío during the last 20 years. The following variables were recorded: 1) Sex and age at presentation; 2) epidemiological data; 3) number, size, localization and rate of growth of cysts; 4) latency period; 5) clinical features; 6) yield of imaging procedures; 7) surgical approaches and medical therapy; and 8) relapses and sequelae. A comparative study was made of patients aged 14 years or less and those above this age. RESULTS: The mean age of the patients was 15.1 +/- 10.3 years (65% were younger than 14 years). 24% were males. 65% came from Extremadura and 74% had a rural background. The latency period was 7.9 +/- 9.2 months (range 15 days-36 months), and it was shorter in children (4.2 +/- 3.8 vs 12.6 +/- 12.7 months) (p less than 0.05). 74% had a single cyst. The cyst size was greater in children (91 +/- 46 vs 67 +/- 35 mm), as it was the rate of growth, particularly in patients younger than 10 years (13.5 +/- 7 vs 9.2 +/- 2 mm/year) (p less than 0.001). 48% had intraparenchymal localization and 70% were in the right hemisphere. In two cases the localization was intraventricular and it was cerebellar in one. Cranial computed tomography was the imaging procedure with the highest yield. The diagnosis was confirmed with pathological examination. In 6 patients (26%) the Dowling and Orlando technique (hydatid delivery) was carried out without subsequent relapses. In 7 cases (30%), and owing to surgical technique difficulties or accidents, puncture and aspiration were carried out, with 4 relapses (57%). In 10 cases cyst rupture occurred, with 6 relapses (60%). The growth rate of the relapses was 9.4 +/- 6.5 mm/month. 87% had severe sequelae, associated with relapses and multiplicity, two patients died (9%). CONCLUSIONS: 1) Cerebral hydatidosis predominates in children and young adult males of a rural background; 2) usually there is a long latency period, which is shorter in children; 3) the size and the growth rate of the cysts is greater in children; 4) computed tomography is the imaging technique with the highest yield; 5) Dowling and Orlando technique is the most effective surgical procedure; 6) the incidence of relapses is high, depending on the type of surgical approach.

The optoelectronic behaviour of carbon nanoparticles: evidence of the importance of the outer carbon shell.

The particular properties of carbon nanoparticles (CNPs) have generated great interest in biomedicine, bioanalysis and optoelectronics. However, an association between the CNPs' physicochemical properties with their molecular and morphological characteristics is, even today, a topic of discussion. In this work, we use a simple method of synthesis with the ultimate aim of elucidating the structural nature of the obtained CNPs and its relationship with their well-known fluorescent properties. The sample is studied by high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS), nuclear magnetic resonance (NMR), UV-visible and IR spectroscopy, electrochemistry and electrogenerated chemiluminescence (ECL). The results showed that the nanoparticles are constituted by a graphitic core surrounded by an amorphous layer, which seems to be significant in the determination of the optical and electronic properties observed in the system under study.