Ultrahigh nanostructured drug payloads from degradable mesoporous silicon aerocrystals

Porous silicon has found increased attention as a drug delivery system due to its unique features such as high drug payloads, surface area and biodegradation. In this study supercritical fluid (SCF) assisted drying of ultrahigh porosity (>90%) silicon particles and flakes was shown to result in much higher mesopore volumes (~4.66 cm³/g) and surface areas (~680 m²/g) than with air-drying. The loading and physical state of the model drug (S)-(+)-Ibuprofen in SCF dried matrices was quantified and assessed using thermogravimetric analysis, differential scanning calorimetry, UV-Vis spectrophotometry, gravimetric analysis, gas adsorption and electron microscopy. Internal drug payloads of up to 72% were achieved which was substantially higher than values published for both conventionally dried porous silicon (17-51%) and other mesoporous materials (7-45%). In-vitro degradability kinetics of SCF-dried matrices in simulated media was also found to be faster than air-dried controls. The in-vitro release studies provided improved but sustained drug dissolution at both pH 2.0 and pH 7.4.

Enhancement of Peroxidase Stability Against Oxidative Self-Inactivation by Co-immobilization with a Redox-Active Protein in Mesoporous Silicon and Silica Microparticles

The study of the stability enhancement of a peroxidase immobilized onto mesoporous silicon/silica microparticles is presented. Peroxidases tend to get inactivated in the presence of hydrogen peroxide, their essential co-substrate, following an auto-inactivation mechanism. In order to minimize this inactivation, a second protein was co-immobilized to act as an electron acceptor and thus increase the stability against self-oxidation of peroxidase. Two heme proteins were immobilized into the microparticles: a fungal commercial peroxidase and cytochrome c from equine heart. Two types of biocatalysts were prepared: one with only covalently immobilized peroxidase (one-protein system) and another based on covalent co-immobilization of peroxidase and cytochrome c (two-protein system), both immobilized by using carbodiimide chemistry. The amount of immobilized protein was estimated spectrophotometrically, and the characterization of the biocatalyst support matrix was performed using Brunauer-Emmett-Teller (BET), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), and Fourier transform infrared (FTIR) analyses. Stability studies show that co-immobilization with the two-protein system enhances the oxidative stability of peroxidase almost four times with respect to the one-protein system. Thermal stability analysis shows that the immobilization of peroxidase in derivatized porous silicon microparticles does not protect the protein from thermal denaturation, whereas biogenic silica microparticles confer significant thermal stabilization.

First field records of Pachycrepoideus vindemiae as a parasitoid of Drosophila suzukii in European and Oregon small fruit production areas

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a destructive crop pest native to Southeast Asia that recently invaded countries in Europe and North America, severely impacting commercial fruit production in its new host range. Here we report the results of a survey aimed at determining the presence of indigenous D. suzukii parasitoid populations carried out from May to October 2012 in two areas negatively affected by this fruit pest: Trento Province, Northern Italy, and Oregon in the Pacific Northwest of the USA. We conducted field and laboratory studies in order to determine the status of biological control agents utilizing D. suzukii as a host. Our study sites included a range of commercial soft fruits and natural non-commercial habitats. In each site, sentinel traps were baited with either D. suzukii or Drosophila melanogaster Meigen (Diptera: Drosophilidae) larvae in different food substrates. The generalist parasitoid, Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae), was collected from both D. suzukii and D. melanogaster pupae in traps deployed in a selection of these sites. This report of P. vindemiae in 2012 represents the first identification of D. suzukii parasitoids in Europe. A successive parasitism efficacy test was set up under controlled laboratory conditions confirming the ability of P. vindemiae to attack D. suzukii pupae. In addition, an historical digression with analysis of the original documents in the Italian archives has been provided in order to unravel the correct species name. We finally discuss the possible practical implications of this finding for the biological control of D. suzukii.

In-Vivo Assessment of Tissue Compatibility and Calcification of Bulk and Porous Silicon

The compatibility of both bulk and porous silicon at the subcutaneous site has been assessed for the first time, following ISO standard procedures. The in-vivo responses to implantation were monitored in the guinea pig and histopathological reactions evaluated at 1, 4, 12 and 26 weeks. Attention is focused here on the histological assessment protocols used, and the results demonstrating in-vivo evidence for good tissue compatibility, and porous Si bioactivity with regards calcification.

Silicon as an Active Biomaterial

The response of a range of porous Si and poly Si films to storage in acellular simulated body fluids is summarised and its implications discussed. It is suggested that the combination of VLSI technology, micromachining and surface microstructuring achievable with silicon, could establish this prominent semiconductor as a very useful biomaterial by the next century. The ‘biocompatibility’ of a variety of silicon microstructures, and even bulk silicon has received surprisingly little study, but now warrants detailed in-vitro and in-vivo assessment.

A Study of the Factors Which Determine the Modulation Speed of a Shallow PN Junction Porous Silicon Led

The effect of the chemical thinning of the porous silicon structure on the speed and efficiency of electroluminescent devices, produced by the anodisation of a pn junction in bulk silicon is investigated. Thinning of the silicon wires results in an increase in the efficiency but at the expense of a reduction in operating speed. It is demonstrated that the operating speed is limited by the photoluminescence lifetime for small signal excitation. However, for large signals, the electroluminescence can be turned off more than 5 times faster than the photoluminescence lifetime, indicating that this need not necessarily limit device operating speed.

Proton-exchanged LiNbO(3) waveguides: relevance of atmospheric environment during annealing

The relevance of the type of atmosphere used during the annealing of proton-exchanged LiNbO(3) planar waveguides is discussed. The experimental evidence, based on a comparison of the refractive-index profiles of waveguides annealed under wet O(2), dry O(2), or ambient atmospheres, with various gas flow rates, suggests that the atmosphere type does not influence the properties of the resulting waveguide.