Relevance of the dinoflagellate Gonyaulax fragilis in mucilage formations of the Adriatic Sea

Oceanographic cruises were carried out monthly from June 1999 to July 2002 to follow the mucilage formation process in the Northern Adriatic Sea. Results show that in correspondence with these events the dinoflagellate Gonyaulax fragilis (Schütt) Kofoid was observed both in the water column and within mucilage aggregates. In the water column, increasing abundances were observed from May until July, with values never exceeding 8500 cells l(-1). Much higher densities were observed within superficial gelatinous aggregates (22800-3400000 cells l(-1)). In mucilage samples, a large number of decomposing cells were present, together with abundant alive cells, enveloped in exudates. G. fragilis isolated from mucilage samples was cultured in three different culture media; it was characterized by a low growth rate but it produced a high amount of polysaccharides. The highest yield both in terms of cell number and carbohydrate production was observed in the medium having the highest nitrogen and phosphorus content and the lowest N/P ratio. The monomeric composition of G. fragilis carbohydrates, compared with that of mucilage samples, showed that in both natural and cultured samples galactose was the most abundant sugar; in addition, an overall good correlation, especially between the monomeric carbohydrate composition of G. fragilis grown in f/2 medium and that of a mucilage sample in which this species was present in high density, was observed.     

Phytase activity in sourdough lactic acid bacteria: purification and characterization of a phytase from Lactobacillus sanfranciscensis CB1

The phytase activity of 12 species of sourdough lactic acid bacteria was screened. It was intracellular only, largely distributed among the species and strains of Lactobacillus sanfranciscensis possessed the highest levels of activity. A monomeric ca. 50-kDa phytase was purified to homogeneity from L. sanfranciscensis CB1 by three chromatographic steps. L. sanfranciscensis CB1 exhibited the highest hydrolysing activity on Na-phytate after reaching the stationary phase of growth (ca. 12 h). Cells cultivated in the presence of maltose and fructose showed an increase of the phytase activity of ca. 35% with respect to the other carbon sources used. The phytase was optimally active at pH 4.0 and 45 degrees C. The enzyme was strongly inhibited by 2 mM of phenylmethylsulfonyl fluoride (PMSF), and 2 mM Hg(2+) and Fe(2+). It had a pI of ca. 5.0. The substrate specificity was dependent on the type of phosphate ester; a very low activity was detected on alpha-D-glucose-1-phosphate and D-fructose-6- and 1,6-phosphate, while the highest hydrolysis was found towards adenosine-5'-tri-, di- and mono-phosphate. Compared to these substrates, the activity on Na-phytate was also relevant. The enzyme was thermo-stable after exposure to 70 degrees C for 30 min; the D value calculated at 80 degrees C was ca. 10 min. As shown by the Central Composite Design (CCD) applied to study the individual and interactive effects of pH, temperature and NaCl, acidic conditions and elevated temperatures were indispensable for the enzyme adaptation to high NaCl concentrations. L. sanfranciscensis CB1 cells or the correspondent cytoplasmic extract were used to ferment a sourdough for 8 h at 37 degrees C; a marked decreased (64-74%) of the Na-phytate concentration was found compared with the unstarted dough. The sourdough started with L. sanfranciscensis CB1 cells was re-used for several times and the phytase activity was maintained to a considerable level.     

High‐Speed and Low‐Energy Nitride Memristors

High‐performance memristors based on AlN films have been demonstrated, which exhibit ultrafast ON/OFF switching times (≈85 ps for microdevices with waveguide) and relatively low switching current (≈15 μA for 50 nm devices). Physical characterizations are carried out to understand the device switching mechanism, and rationalize speed and energy performance. The formation of an Al‐rich conduction channel through the AlN layer is revealed. The motion of positively charged nitrogen vacancies is likely responsible for the observed switching.     

Biotinylated Photopolymers for 3D‐Printed Unibody Lab‐on‐a‐Chip Optical Platforms

The present work reports the first demonstration of straightforward fabrication of monolithic unibody lab‐on‐a‐chip (ULOCs) integrating bioactive micrometric 3D scaffolds by means of multimaterial stereolithography (SL). To this end, a novel biotin‐conjugated photopolymer is successfully synthesized and optimally formulated to achieve high‐performance SL‐printing resolution, as demonstrated by the SL‐fabrication of biotinylated structures smaller than 100 µm. By optimizing a multimaterial single‐run SL‐based 3D‐printing process, such biotinylated microstructures are incorporated within perfusion microchambers whose excellent optical transparency enables real‐time optical microscopy analyses. Standard biotin‐binding assays confirm the existence of biotin‐heads on the surfaces of the embedded 3D microstructures and allow to demonstrate that the biofunctionality of biotin is not altered during the SL‐printing, thus making it exploitable for further conjugation with other biomolecules. As a step forward, an in‐line optical detection system is designed, prototyped via SL‐printing and serially connected to the perfusion microchambers through customized world‐to‐chip connectors. Such detection system is successfully employed to optically analyze the solution flowing out of the microchambers, thus enabling indirect quantification of the concentration of target interacting biomolecules. The successful application of this novel biofunctional photopolymer as SL‐material enables to greatly extend the versatility of SL to directly fabricate ULOCs with intrinsic biofunctionality.     

Integrin-targeting with peptide-bioconjugated semiconductor-magnetic nanocrystalline heterostructures

Binary asymmetric nanocrystals (BNCs), composed of a photoactive TiO₂ nanorod joined with a superparamagnetic γ-Fe₂O₃ spherical domain, were embedded in polyethylene glycol modified phospholipid micelle and successfully bioconjugated to a suitably designed peptide containing an RGD motif. BNCs represent a relevant multifunctional nanomaterial, owing to the coexistence of two distinct domains in one particle, characterized by high photoactivity and magnetic properties, that is particularly suited for use as a phototherapy and hyperthermia agent as well as a magnetic probe in biological imaging. We selected the RGD motif in order to target integrin expressed on activated endothelial cells and several types of cancer cells. The prepared RGD-peptide/BNC conjugates, comprehensively monitored by using complementary optical and structural techniques, demonstrated a high stability and uniform dispersibility in biological media. The cytotoxicity of the RGD-peptide/BNC conjugates was studied in vitro. The cellular uptake of RGD-peptide conjugates in the cells, assessed by means of two distinct approaches, namely confocal microscopy analysis and emission spectroscopy determination in cell lysates, displayed selectivity of the RGD-peptide-BNC conjugate for the αvβ3 integrin. These RGD-peptide-BNC conjugates have a high potential for theranostic treatment of cancer.

Open image in new window

     

Filament-Free Bulk Resistive Memory Enables Deterministic Analogue Switching

Digital computing is nearing its physical limits as computing needs and energy consumption rapidly increase. Analogue-memory-based neuromorphic computing can be orders of magnitude more energy efficient at data-intensive tasks like deep neural networks, but has been limited by the inaccurate and unpredictable switching of analogue resistive memory. Filamentary resistive random access memory (RRAM) suffers from stochastic switching due to the random kinetic motion of discrete defects in the nanometer-sized filament. In this work, this stochasticity is overcome by incorporating a solid electrolyte interlayer, in this case, yttria-stabilized zirconia (YSZ), toward eliminating filaments. Filament-free, bulk-RRAM cells instead store analogue states using the bulk point defect concentration, yielding predictable switching because the statistical ensemble behavior of oxygen vacancy defects is deterministic even when individual defects are stochastic. Both experiments and modeling show bulk-RRAM devices using TiO_2-X switching layers and YSZ electrolytes yield deterministic and linear analogue switching for efficient inference and training. Bulk-RRAM solves many outstanding issues with memristor unpredictability that have inhibited commercialization, and can, therefore, enable unprecedented new applications for energy-efficient neuromorphic computing. Beyond RRAM, this work shows how harnessing bulk point defects in ionic materials can be used to engineer deterministic nanoelectronic materials and devices.     

Mucilage microcosms

In the summers of 2000, 2001 and 2002, large amounts of sticky mucilaginous material aggregated to form masses of impressive dimensions over large areas of the Adriatic Sea, particularly in its northern part. Aggregates differing in size were sampled by SCUBA divers and submitted to chemical (nutrient and organic matter concentrations) and biological analysis (virus, bacteria and phytoplankton abundances and bacterial metabolism). Suspended and sinking mucilaginous aggregates were biota-rich environments where the abundance of planktonic organisms and the concentration of nutrients were orders of magnitude higher than in the surrounding seawater. The embedded phytoplankton was mostly composed of diatoms, but the dinoflagellate Gonyaulax fragilis, previously reported in association with the aggregates, was also present. A variety of processes occurred within the mucilaginous aggregates which resulted in the transformation of the organic matter composition and lability and contributed to a partial degradation of mucilage. For an efficient degradation of mucilage, several conditions are necessary: high bacterial abundance and activity and an efficient recycling of nutrients within the aggregates. Most of these conditions, appear to change depending on the type and age of the aggregate. During the first phase of aggregation (cobwebs and ribbons), bacterial activities addressed the degradation of organic matter, particularly that of the nitrogen fraction. The degradation products were rapidly taken up by bacteria, supporting an increase in their abundance and production. In aged mucilage (clouds), the degradation processes decreased and the bacterial metabolism suggested the presence of new organic labile compounds probably due to phytoplankton production. On the basis of our results, stringers, generally considered the first step of the aggregation process, seemed to be the result of a mechanical disruption of other types of aggregates.     

Design of Gelatin-Capped Plasmonic-Diatomite Nanoparticles with Enhanced Galunisertib Loading Capacity for Drug Delivery Applications

Inorganic diatomite nanoparticles (DNPs) have gained increasing interest as drug delivery systems due to their porous structure, long half-life, thermal and chemical stability. Gold nanoparticles (AuNPs) provide DNPs with intriguing optical features that can be engineered and optimized for sensing and drug delivery applications. In this work, we combine DNPs with gelatin stabilized AuNPs for the development of an optical platform for Galunisertib delivery. To improve the DNP loading capacity, the hybrid platform is capped with gelatin shells of increasing thicknesses. Here, for the first time, full optical modeling of the hybrid system is proposed to monitor both the gelatin generation, degradation, and consequent Galunisertib release by simple spectroscopic measurements. Indeed, the shell thickness is optically estimated as a function of the polymer concentration by exploiting the localized surface plasmon resonance shifts of AuNPs. We simultaneously prove the enhancement of the drug loading capacity of DNPs and that the theoretical modeling represents an efficient predictive tool to design polymer-coated nanocarriers.     

Novel high-durability luminescent solar concentrators based on fluoropolymer coatings

Fluorescent polymeric coatings can find interesting applications in the field of solar energy as thin-film luminescent solar concentrators (LSCs). At present, polymers such as polycarbonate (PC) or poly(methyl-methacrylate) (PMMA) are commonly used as dye-doped host matrix materials in LSCs. However, LSC devices based on these polymers still present limited lifetimes resulting from the intrinsic poor photostability of the polymeric carrier. In the attempt to achieve high-durability LSC devices, a series of new crosslinked fluoropolymeric systems is presented in this work as potential alternative host matrix coating materials for LSC applications. The chemical, physical and morphological modifications occurring to the crosslinked fluorinated coatings when subjected to long-term UV–vis light exposure (over 1000 h of accelerated weathering) are found to correlate well with the photovoltaic response over long-term operation of functioning LSC devices. In particular, better operational stability compared to reference PMMA-based devices can be obtained with the new crosslinked fluorinated coatings by appropriate selection of crosslinking agent. In addition, the effect of radical scavengers on LSC device operational stability is also investigated and it is found that in the long-term light exposure regime (>600 h) these additives may lead to improvements in LSC device lifetime. The results of this study allow a greater understanding of structure–property relationships in crosslinked fluorinated coatings subjected to long-term weathering and provide useful guidelines for the design of high durability fluorescent coatings for light management and photovoltaics.