Micro-patterns of gold nanoparticles assembled by photovoltaic optoelectronic tweezers: application to plasmonic fluorescence enhancement.

Noble metal nanostructures are well-known for their ability to increase the efficiency of different optical or physical phenomena due to their plasmonic behavior. This work presents a simple strategy to obtain Au plasmonic patterns by optically induced nanoparticle assembly and its application as fluorescence enhancement platforms. This strategy is based on the so-called photovoltaic optoelectronic tweezers (PVOT) being the first time they are used for fabricating Au periodic micro-patterns. Fringe patterns with a sub-structure of aggregates, assembled from individual spherical nanoparticles of 3.5 or 170 nm diameters, are successfully obtained. The spatial distribution of the aggregates is controlled with micrometric accuracy and the patterns can be arranged over large-scale active areas (tens of mm2). The outcome for the ultra-small (3.5 nm) particles is particularly relevant because this diameter is the smallest one manipulated by PVOT so far. Testing experiments of plasmonic fluorescence enhancement show that the 170-nm patterns present a much better plasmonic behavior. For the 170-nm platform they reveal a 10-fold enhancement factor in the fluorescence of Rhodamine-B dye molecules and a 3-fold one for tagged DNA biomolecules. Hence, the results suggest that these latter plasmonic platforms are good candidates for efficient bio-imaging and biosensing techniques, among other applications.

Exploring the Reduction Mechanism of 99Tc(VII) in NaClO4: A Spectro-Electrochemical Approach.

Technetium (Tc) is an environmentally relevant radioactive contaminant whose migration is limited when Tc(VII) is reduced to Tc(IV). However, its reaction mechanisms are not well understood yet. We have combined electrochemistry, spectroscopy, and microscopy (cyclic voltammetry, rotating disk electrode, X-ray photoelectron spectroscopy, and Raman and scanning electron microscopy) to study Tc(VII) reduction in non-complexing media: 0.5 mM KTcO4 in 2 M NaClO4 in the pH from 2.0 to 10.0. At pH 2.0, Tc(VII) first gains 2.3 ± 0.3 electrons, following Tc(V) rapidly receives 1.3 ± 0.3 electrons yielding Tc(IV). At pH 4.0-10.0, Tc(IV) is directly obtained by transfer of 3.2 ± 0.3 electrons. The reduction of Tc(VII) produced always a black solid identified as Tc(IV) by Raman and XPS. Our results narrow a significant gap in the fundamental knowledge of Tc aqueous chemistry and are important to understand Tc speciation. They provide basic steps on the way from non-complexing to complex media.

Optoelectronic manipulation of bio-droplets containing cells or macromolecules by active ferroelectric platforms.

Photovoltaic optoelectronic tweezers are a useful platform with many applications in optical manipulation and nanotechnology. They are based on electrical forces associated with the bulk photovoltaic effect presented by certain ferroelectric crystals, such as Fe doped lithium niobate. This manipulation technique has experienced huge developments in recent years, although its use in biology and biomedicine is still scarce. Recently, a novel strategy has been reported that extends the platform capabilities to the manipulation of polar droplets, such as water and aqueous bio-droplets, promising great potential for biological applications. In this work, we are taking this challenge, addressing the manipulation of cells and macromolecules contained inside the droplets by optoelectronic ferroelectric platforms. On the one hand, experiments of photoelectric induced migration of DNA and sperm droplets have been successfully developed and the corresponding droplet dynamics have been analyzed in depth. From this analysis, parameters of the biomaterial such as its concentration and its electrical charge have been evaluated, showing the sensing capabilities of the platform. In fact, the charge of sperm cells has been demonstrated to be negative, and the relative sperm concentration of the samples determined. On the other hand, experiments on the light-induced merging of two droplets have been carried out. Specifically, sperm droplets are mixed with droplets containing acridine orange, a convenient dye for visualization purposes. The spermatozoa become clearly visible in the final droplet through fluorescence imaging. The results point out the multiple possibilities of application of the optoelectronic ferroelectric platform in biology and biomedicine including the development of "lab on a chip" devices. Hence, these capabilities introduce these platforms as an efficient tool in biotechnology.

Controllable Heteroatom Doping Effects of CrxCo2-xP Nanoparticles: a Robust Electrocatalyst for Overall Water Splitting in Alkaline Solutions.

The effect of doping Cr on the electrocatalytic activity of Co2P supported on carbon black (CrxCo2-xP/CB) for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution was investigated. A beneficial improvement in the performance of Co2P toward HER and OER was discovered. For the HER at -200 mV overpotential, the turnover frequency (TOF) increases almost 6-fold from 0.26 to 1.52 electron siteCo-1 s-1 when Co2P/CB has a small amount of Cr added to form Cr0.2Co1.8P/CB. Similarly, we estimate an increase from 0.205 to 0.585 electron siteCo-1 s-1 for the OER at 1.6 V for the same change in composition. With 10 atom % Cr doping, the Cr0.2Co1.8P/CB catalyst needed 226 mV overpotential to produce a cathodic current density of -100 A gCo-1 and 380 mV overpotential to produce an anodic current density of 100 A gCo-1. Based on both experimental results and theoretical calculations, the activity improvement results from optimization of the electronic properties of Co2P after Cr doping.

Optoelectronic generation of bio-aqueous femto-droplets based on the bulk photovoltaic effect.

The generation and manipulation of small aqueous droplets is an important issue for nano- and biotechnology, particularly, when using microfluidic devices. The production of very small droplets has been frequently carried out by applying intense local electric fields to the fluid, which requires power supplies and metallic electrodes. This procedure complicates the device and reduces its versatility. In this work, we present a novel and flexible, to the best of our knowledge, electrodeless optoelectronic method for the production of tiny droplets of biologically friendly aqueous fluids. Our method takes advantage of the photoinduced electric fields generated by the bulk photovoltaic effect in iron-doped lithium niobate crystals. Two substrate configurations, presenting the polar ferroelectric axis either parallel or perpendicular to the active surface, have been successfully tested. In both crystal geometries, small droplets on the femtoliter scale have been obtained, although with a different spatial distributions correlated with the symmetry of the photovoltaic fields. The overall results demonstrate the effectiveness of the optoelectronic method to produce femtoliter droplets, both with pure water and with aqueous solutions containing biological material.

Mielopatías no traumáticas: experiencia del servicio de Neurología / Nontraumatic myelopathies: experience of neurology service

Material y métodos. Se estudiaron, de marzo de 1996 al mismo mes de 1998, 22 pacientes (14 mujeres, 63.3 por ciento, y 8 hombres, 18.2 por ciento) hospitalizados en el Servicio de neurología con diagnóstico de mielopatía no traumática (MNT). Se les realizó una evaluación Neurológica completa, un estudio del líquido cefalorraquídeo (LCR) e imagen por resonancia magnética (IRM) o tomografía axial computada (TAC). Se evaluaron las causas de MNT, la evolución funcional al egreso y cada tres meses hasta completar un año. Resultados: el rango de edad fue de 17 a 78 años (media: 46.5 ñ 16.15); nueve pacientes (40.5 por ciento) tenían antecedentes de proceso infeccioso. El inicio de los síntomas varió de 3 a 330 h; en 91 por ciento fue torácica, 4.5 por ciento cervical y 4.5 por ciento lumbar; 59 por ciento tuvieron síndrome de sección medular y 86.4 por ciento afección de esfínteres. Se efectuó el estudio del LCR a 19 pacientes: 78.9 por ciento fue anormal, destacando pleocitosis e hiperproteinorraquia, BAAR en 3 y en uno se observaron amibas de vida libre: La IRM fue anormal en 90.4 por ciento. La evolución funcional tuvo tendencia hacia la mejoría, p< 0.001: los diagnósticos fueron: 50 por ciento mielitis transversa, 13.6 por ciento tuberculosis, 13.6 por ciento tumores, 13.6 por ciento esclerosis múltiple, 4.5 por ciento enfermedad vascular y 4.5 por ciento amibas de vida libre