Aplicaciones fotónicas y biomédicas de silicio poroso nanoestructurado

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid. Facultad de Ciencias, Departamento de Física Aplicada. Fecha de lectura: 13-06-201

Nanoporous silicon-based surface patterns fabricated by UV laser interference techniques for biological applications

The fabrication of selectively functionalized micropatterns based on nanostructured porous silicon (nanoPS) by phase mask ultraviolet laser interference is presented here. This single-step process constitutes a flexible method for the fabrication of surface patterns with tailored properties. These surface patterns consist of alternate regions of almost untransformed nanoPS and areas where nanoPS is transformed into Si nanoparticles (Si NPs) as a result of the laser irradiation process. The size of the transformed areas as well as the diameter of the Si NPs can be straightforwardly tailored by controlling the main fabrications parameters including the porosity of the nanoPS layers, the laser interference period areas, and laser fluence. The surface patterns have been found to be appropriate candidates for the development of selectively-functionalized surfaces for biological applications mainly due to the biocompatibility of the untransformed nanoPS regions.Postprint (author's final draft

Nanostructured porous silicon photonic crystal for applications in the infrared

In the last decades great interest has been devoted to photonic crystals aiming at the creation of novel devices which can control light propagation. In the present work, two-dimensional (2D) and three-dimensional (3D) devices based on nanostructured porous silicon have been fabricated. 2D devices consist of a square mesh of 2 μm wide porous silicon veins, leaving 5x5 μm square air holes. 3D structures share the same design although multilayer porous silicon veins are used instead, providing an additional degree of modulation. These devices are fabricated from porous silicon single layers (for 2D structures) or multilayers (for 3D structures), opening air holes in them by means of 1KeV argon ion bombardment through the appropriate copper grids. For 2D structures, a complete photonic band gap for TE polarization is found in the thermal infrared range. For 3D structures, there are no complete band gaps, although several new partial gaps do exist in different high-symmetry directions. The simulation results suggest that these structures are very promising candidates for the development of low-cost photonic devices for their use in the thermal infrared rangeThe authors also gratefully acknowledge funding from Comunidad de Madrid (Spain) under project “Microseres” and Ministerio de Economía y Competitividad (Spain) under Research Project MAT2011-28345-C02-0

Generation of a protocol for the synthesis of chitosan nanoparticles loaded with florfenicol through the ionic gelation method

La formación de nanopartículas de quitosano mediante el método de gelación iónica tiene un alto potencial para la carga, transporte y liberación controlada de moléculas. Es un método sencillo y las nanopartículas presentan buena absorción, estabilidad, biocompatibilidad y baja toxicidad. El florfenicol es uno de los antibióticos más utilizados en la industria acuícola y es administrado mezclado con el alimento en altas concentraciones, lo cual genera problemas de dosis efectivas y de residuos no deseados. De esta manera, la síntesis de nanopartículas de quitosano (Q) cargadas con florfenicol podría otorgar ventajas a la hora de proteger, transportar y liberar de forma controlada el fármaco en peces de interés económico. En el presente estudio se sintetizaron nanopartículas de quitosano y tripolifosfato de sodio (TPP) con y sin florfenicol para evaluar su carga efectiva y liberación. Los resultados obtenidos con espectrometría FTIR corroboran la formación de las nanopartículas de Q-TPP con los cambios observados en los patrones de espectros infrarojo entre el quitosano matriz y las nanopartículas sintetizadas. Las nanopartículas de Q-TPP pueden cargar entre 48 y 50% de florfenicol en su interior. El ensayo de liberación in vitro del antibiótico mostró una liberación controlada y estable en el tiempo en condiciones de pH ácido y temperatura controlada de 15° C de hasta 10 días. Finalmente, se muestra que las nanopartículas de Q-TPP tienen potencial para atrapar y liberar de forma controlada el fármaco evaluadoThe formation of nanoparticles of chitosan by the ionic gelation method has a high potential for loading, transport and controlled release of molecules. It is a simple method and the nanoparticles have good absorption, stability, biocompatibility and low toxicity. Florfenicol is one of the most used antibiotics in the aquaculture industry and is administered mixed with the feed in high concentrations, which generates problems of effective doses and unwanted residues. In this way, the synthesis of chitosan (Q) nanoparticles loaded with florfenicol could provide advantages when it comes to protecting, transporting and releasing the drug in fish of economic interest in a controlled manner. In the present study, nanoparticles of chitosan and sodium tripolyphosphate (TPP) with and without florfenicol were synthesized to evaluate their effective loading and release. The results obtained with FTIR spectrometry corroborate the formation of the Q-TPP nanoparticles with the changes observed in the infrared spectra patterns between the matrix chitosan and the synthesized nanoparticles. Q-TPP nanoparticles can carry between 48 and 50% of florfenicol inside. The in vitro release assay of the antibiotic showed a controlled and stable release over time under conditions of acid pH and controlled temperature of 15 degrees C for up to 10 days. Finally, it is shown that the Q-TPP nanoparticles have the potential to trap and release the evaluated drug in a controlled manne

Ultraviolet laser patterning of porous silicon

This work reports on the fabrication of 1D fringed patterns on nanostructured porous silicon (nanoPS) layers (563, 372, and 290nm thick). The patterns are fabricated by phase-mask laser interference using single pulses of an UV excimer laser (193nm, 20ns pulse duration). The method is a single-step and flexible approach to produce a large variety of patterns formed by alternate regions of almost untransformed nanoPS and regions where its surface has melted and transformed into Si nanoparticles (NPs). The role of laser fluence (5-80mJcm-2), and pattern period (6.3-16µm) on pattern features and surface structuring are discussed. The results show that the diameter of Si NPs increases with fluence up to a saturation value of 75nm for a fluence ˜40mJcm-2. In addition, the percentage of transformed to non-transformed region normalized to the pattern period follows similar fluence dependence regardless the period and thus becomes an excellent control parameter. This dependence is fitted within a thermal model that allows for predicting the in-depth profile of the pattern. The model assumes that transformation occurs whenever the laser-induced temperature increase reaches the melting temperature of nanoPS that has been found to be 0.7 of that of crystalline silicon for a porosity of around 79%. The role of thermal gradients across the pattern is discussed in the light of the experimental results and the calculated temperature profiles, and shows that the contribution of lateral thermal flow to melting is not significant for pattern periods =6.3µm.Postprint (published version

Silicon-based photonic crystals fabricated using proton beam writing combined with electrochemical etching method

A method for fabrication of three-dimensional (3D) silicon nanostructures based on selective formation of porous silicon using ion beam irradiation of bulk p-type silicon followed by electrochemical etching is shown. It opens a route towards the fabrication of two-dimensional (2D) and 3D silicon-based photonic crystals with high flexibility and industrial compatibility. In this work, we present the fabrication of 2D photonic lattice and photonic slab structures and propose a process for the fabrication of 3D woodpile photonic crystals based on this approach. Simulated results of photonic band structures for the fabricated 2D photonic crystals show the presence of TE or TM gap in mid-infrared rang

Phonon structure, infra-red and raman spectra of Li2MnO3 by first-principles calculations

The layer-structured monoclinic Li2MnO3 is a key material, mainly due to its role in Li-ion batteries and as a precursor for adsorbent used in lithium recovery from aqueous solutions. In the present work, we used first-principles calculations based on density functional theory (DFT) to study the crystal structure, optical phonon frequencies, infra-red (IR), and Raman active modes and compared the results with experimental data. First, Li2MnO3 powder was synthesized by the hydrothermal method and successively characterized by XRD, TEM, FTIR, and Raman spectroscopy. Secondly, by using Local Density Approximation (LDA), we carried out a DFT study of the crystal structure and electronic properties of Li2MnO3. Finally, we calculated the vibrational properties using Density Functional Perturbation Theory (DFPT). Our results show that simulated IR and Raman spectra agree well with the observed phonon structure. Additionally, the IR and Raman theoretical spectra show similar features compared to the experimental ones. This research is useful in investigations involving the physicochemical characterization of Li2MnO3 materia

Sulfidogenic Bioreactor-Mediated Formation of ZnS Nanoparticles with Antimicrobial and Photocatalytic Activity

The use of sulfidogenic bioreactors is a biotechnology trend to recover valuable metals such as copper and zinc as sulfide biominerals from mine-impacted waters. In the present work, ZnS nanoparticles were produced using “green” H2S gas generated by a sulfidogenic bioreactor. ZnS nanoparticles were physico-chemically characterized by UV-vis and fluorescence spectroscopy, TEM, XRD and XPS. The experimental results showed spherical-like shape nanoparticles with principal zinc-blende crystalline structure, a semiconductor character with an optical band gap around 3.73 eV, and fluorescence emission in the UV-visible range. In addition, the photocatalytic activity on the degradation of organic dyes in water, as well as bactericidal properties against several bacterial strains, were studied. ZnS nanoparticles were able to degrade methylene blue and rhodamine in water under UV radiation, and also showed high antibacterial activity against different bacterial strains including Escherichia coli and Staphylococcus aureus. The results open the way to obtain valorous ZnS nanoparticles from the use of dissimilatory reduction of sulfate using a sulfidogenic bioreacto

Antibacterial films of silver nanoparticles embedded into carboxymethylcellulose/chitosan multilayers on nanoporous silicon: A layer-by-layer assembly approach comparing dip and spin coating

The design and engineering of antibacterial materials are key for preventing bacterial adherence and proliferation in biomedical and household instruments. Silver nanoparticles (AgNPs) and chitosan (CHI) are broad-spectrum antibacterial materials with different properties whose combined application is currently under optimization. This study proposes the formation of antibacterial films with AgNPs embedded in carboxymethylcellulose/chitosan multilayers by the layer-by-layer (LbL) method. The films were deposited onto nanoporous silicon (nPSi), an ideal platform for bioengineering applications due to its biocompatibility, biodegradability, and bioresorbability. We focused on two alternative multilayer deposition processes: cyclic dip coating (CDC) and cyclic spin coating (CSC). The physicochemical properties of the films were the subject of microscopic, microstructural, and surface–interface analyses. The antibacterial activity of each film was investigated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria strains as model microorganisms. According to the findings, the CDC technique produced multilayer films with higher antibacterial activity for both bacteria compared to the CSC method. Bacteria adhesion inhibition was observed from only three cycles. The developed AgNPs–multilayer composite film offers advantageous antibacterial properties for biomedical applicationsPID2020-112770RB-C2

Effect of including a dietary supplement of raisins, a food rich in polyphenols, on cognitive function in healthy older adults; a study protocol for a randomized clinical trial

Background Polyphenols have been shown to be effective against many chronic diseases, including neurodegenerative diseases. Specifically, the consumption of raisins, being a food rich in polyphenols, has been attributed with neuroprotective benefits. Therefore, our main objective is to evaluate the effect of including 50 g of raisins in the diet daily for 6 months, on the improvement of cognitive performance, cardiovascular risk factors and markers of inflammation in a population of older adults without cognitive impairment. Methods Design and intervention: This study will be a randomized controlled clinical trial of two parallel groups. Each subject included in the study will be randomly assigned to one of two study groups: control group (no supplement), intervention group (50 g of raisins daily during 6 months). Study population: The participants will be selected by consecutive sampling in the Primary Care consultations of urban health centers in Salamanca and Zamora (Spain), taking into account the selection criteria. Study variables: Two visits will be made, baseline and at 6 months. Cognitive performance will be evaluated (MiniMental State Examination test, Rey Auditory Verbal Learning Test, verbal fluency and montreal cognitive assessmentm(Moca)). It will also be analyzed the level of physical activity, quality of life, activities of daily living, energy and nutritional composition of the diet, body composition, blood pressure, heart rate, markers of inflammation and othermlaboratory tests of clinical relevance (glycaemia, total cholesterol, HDL cholesterol, LDL cholesterol and triglycerides). In addition, sociodemographic data, personal and family history, medication use and alcohol and tobacco consumption will be collected. Discussion In this project, it is intended to contribute to minimize the problems derived from cognitive deterioration in older people