Biodegradable composites with improved barrier properties and transparency from the impregnation of PLA to bacterial cellulose membranes

Poly(lactic acid) (PLA) was impregnated in bacterial cellulose (BC) membranes. BC/PLA films were prepared by solvent casting and mechanical, optical and barrier properties, and biodegradation process were investigated. The transparency of processed films was higher than that of neat BC and increased with PLA content. Moreover, the incorporation of PLA to BC enhanced significantly the water vapor barrier properties of the BC membranes. The bionanocomposites contained a high percentage of cellulose due to the impregnation method that leads to the film with a BC content of 94%, which practically maintains the excellent mechanical properties of BC. However, when increasing the PLA content in the bionanocomposites the mechanical properties decreased slightly with respect to BC. Biodegradation under real soil conditions was determined indirectly through the study of the visual degradation and disintegration, demonstrating that the bionanocomposites were degraded faster than the neat PLA. The successful production of BC/PLA bionanocomposites suggested the possible application of them for active food packaging. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43669.     

Super-Resolution Microscopy to Study Interorganelle Contact Sites

Interorganelle membrane contact sites (MCS) are areas of close vicinity between the membranes of two organelles that are maintained by protein tethers. Recently, a significant research effort has been made to study MCS, as they are implicated in a wide range of biological functions, such as organelle biogenesis and division, apoptosis, autophagy, and ion and phospholipid homeostasis. Their composition, characteristics, and dynamics can be studied by different techniques, but in recent years super-resolution fluorescence microscopy (SRFM) has emerged as a powerful tool for studying MCS. In this review, we first explore the main characteristics and biological functions of MCS and summarize the different approaches for studying them. Then, we center on SRFM techniques that have been used to study MCS. For each of the approaches, we summarize their working principle, discuss their advantages and limitations, and explore the main discoveries they have uncovered in the field of MCS.     

Nitrogen-doped graphene with enhanced oxygen reduction activity produced by pyrolysis of graphene functionalized with imidazole derivatives

Nitrogen-doped graphene nanoplatelets (N-GNP) with 1.6–3.3 at.% nitrogen content were synthesized by thermal annealing of GNP functionalized with a series of imidazole-based nitrogen-containing precursors of different nature, charge and nitrogen content. The imidazole derivatives included one ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) and two polymers, a neutral one, poly(vinylimidazole) (PVI) and a poly(ionic liquid), poly(3-butyl-1-vinylimidazolium bromide) (PBVIBr). N-GNP showed enhanced electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline media compared to pristine GNP, with the number of electrons transferred in oxygen-saturated KOH at low overpotentials following the trend: 2.5 (pristine GNP) < 2.9 (N-GNP from PVI–GNP) < 3.3 (N-GNP from BMIBF₄–GNP) < 3.5 (N-GNP from PBVIBr-GNP). Interestingly, ORR catalytic activity did not correlate with total nitrogen content but was more affected by Brunauer–Emmett–Teller (BET) surface area. The most active materials were N-GNP with lowest doping levels and highest surface area resulting from the ionic (imidazolium-based) nitrogen precursors.     

On-chip transduction of nucleic acid hybridization using spatial profiles of immobilized quantum dots and fluorescence resonance energy transfer

The glass surface of a glass-polydimethylsiloxane (PDMS) microfluidic channel was modified to develop a solid-phase assay for quantitative determination of nucleic acids. Electroosmotic flow (EOF) within channels was used to deliver and immobilize semiconductor quantum dots (QDs), and electrophoresis was used to decorate the QDs with oligonucleotide probe sequences. These processes took only minutes to complete. The QDs served as energy donors in fluorescence resonance energy transfer (FRET) for transduction of nucleic acid hybridization. Electrokinetic injection of fluorescent dye (Cy3) labeled oligonucleotide target into a microfluidic channel and subsequent hybridization (within minutes) provided the proximity for FRET, with emission from Cy3 being the analytical signal. The quantification of target concentration was achieved by measurement of the spatial length of coverage by target along a channel. Detection of femtomole quantities of target was possible with a dynamic range spanning an order of magnitude. The assay provided excellent resistance to nonspecific interactions of DNA. Further selectivity of the assay was achieved using 20% formamide, which allowed discrimination between a fully complementary target and a 3 base pair mismatch target at a contrast ratio of 4:1.     

Comparative analysis of the transfer function of closed and open split-ring metamaterial slab lenses

The transfer function of some in-plane periodic split-ring metamaterial slab lenses is analyzed for several configurations across the slab. The transfer function is obtained by means of full-wave electromagnetic computations using the simulation software CST Microwave Studio, and it is compared with the transfer function obtained analytically for a continuous slab of reference. Significant differences are found in the transfer function of the analyzed structures. The closest behavior to the continuous slab lens was found for the partially open structure comprising an integer number of periods across the slab. Experiments are provided which confirms the theoretical results.     

Proteolytic activity at quantum dot-conjugates: kinetic analysis reveals enhanced enzyme activity and localized interfacial "hopping"

Recent studies show that polyvalent, ligand-modified nanoparticles provide significantly enhanced binding characteristics compared to isolated ligands. Here, we assess the ability of substrate-modified nanoparticles to provide enhanced enzymatic activity. Energy transfer assays allowed quantitative, real-time measurement of proteolytic digestion at polyvalent quantum dot-peptide conjugates. Enzymatic progress curves were analyzed using an integrated Michaelis-Menten (MM) formalism, revealing mechanistic details, including deviations from classic MM-behavior. A "hopping" mode of proteolysis at the nanoparticle was identified, confirming enhanced activity.     

Carbon nanotubes/chitin nanowhiskers aerogel achieved by quaternization‐induced gelation

Organic aerogels from polysaccharides such as cellulose and chitin are of particular importance because they utilize renewable feedstocks. In this article, the aerogels were prepared through the self‐assembly of chitin nanowhiskers previously modified. The surface of chitin nanowhiskers was rendered cationic through two reactions. A first reaction between hydroxyl groups of chitin and 2‐chloroethyl isocyanate and a second reaction between the chloride groups of isocyanate anchored to the surface and 1‐methylimidazole. This modification led to stable aqueous suspensions of the chitin nanowhiskers with gelation and rheological properties. Additionally, chitin nanowhiskers aerogels containing modified carbon nanotubes were obtained. The addition of modified carbon nanotubes provoked a change in the morphology of the hydrogels and as a consequence, the rheological properties of the hydrogel are modified as well. In contrast from previous procedures, this method has not required any kind of solvent exchange or high pressure in order to obtain the final materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42547.     

Semiconductor quantum dots in bioanalysis: crossing the valley of death

Colloidal semiconductor quantum dots (QDs) have evolved beyond scientific novelties and are transitioning into bona fide analytical tools. We describe the burgeoning role of QDs in many different fields of bioanalyses and highlight the advantages afforded by their unique physical and optical properties.