Single-Cell Nanoencapsulation: From Passive to Active Shells

Single-cell nanoencapsulation is an emerging field in cell-surface engineering, emphasizing the protection of living cells against external harmful stresses in vitro and in vivo. Inspired by the cryptobiotic state found in nature, cell-in-shell structures are formed, which are called artificial spores and which show suppression or retardation in cell growth and division and enhanced cell survival under harsh conditions. The property requirements of the shells suggested for realization of artificial spores, such as durability, permselectivity, degradability, and functionalizability, are demonstrated with various cytocompatible materials and processes. The first-generation shells in single-cell nanoencapsulation are passive in the operation mode, and do not biochemically regulate the cellular metabolism or activities. Recent advances indicate that the field has shifted further toward the formation of active shells. Such shells are intimately involved in the regulation and manipulation of biological processes. Not only endowing the cells with new properties that they do not possess in their native forms, active shells also regulate cellular metabolism and/or rewire biological pathways. Recent developments in shell formation for microbial and mammalian cells are discussed and an outlook on the field is given.     

Validation of analytical methods for heterocyclic amines in seven food matrices using high-performance liquid chromatography-tandem mass spectrometry

ABSTRACT

Heterocyclic amines (HCAs) are potent mutagens generated by the high temperatures of the cooking process. The purpose of this study was to develop and validate analytical methods for HCAs determination using high-performance liquid chromatography-tandem mass spectrometry in seven food matrices: corn oil, milk, 20% ethanol, pork, flat fish, sea mustard (Undaria pinnatifida), and radish. Six isotopically labelled internal standards were used for quantitation, and Chem Elut and Oasis hydrphilic-liphophilic balance cartridges were applied for sample preparation to remove interferences. Calibration curves showed good linearity (R² > 0.99) in all matrices. The ranges of the method detection limit and method quantitation limit were 0.009–2.35 ng g^?1 and 0.025–7.13 ng g^?1, respectively. The recoveries ranged from 67.5% to 119.6%. The coefficients of variation ranged from 0.3% to 15.1% for intra-day and ranged from 0.8% to 19.1% for inter-day. The methods were applied to 24 total diet study samples for HCAs quantitation. These results indicate that the established methods are reliable for determining HCAs in various foods.     

A Traffic Delay and Bandwidth Based Multipath Scheduling Approach for Optimal Routing in Underwater Optical Network

Wireless Personal Communications - Optical networks are future networks that will support the vast bandwidth demand for communication in diverse domain and service applications scale to worldwide...     

AFM study of the differential inhibitory effects of the green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) against Gram-positive and Gram-negative bacteria

(−)-Epigallocatechin-3-gallate (EGCG), a main constituent of tea catechins, affects Gram-positive and Gram-negative bacteria differently; however, the underlying mechanisms are not clearly understood. Atomic force microscopy (AFM) was used to compare morphological alterations in Gram-positive and Gram-negative bacteria induced by EGCG and by H₂O₂ at sub-minimum inhibitory concentrations (MICs). EGCG initially induced aggregates in the cell envelopes of Staphylococcus aureus and eventually caused cell lysis, which was not observed in cells treated with H₂O₂. It initially induced nanoscale perforations or microscale grooves in the cell envelopes of Escherichia coli O157:H7 which eventually disappeared, similar to E. coli cells treated with H₂O₂. An E. coli O157:H7 tpx mutant, with a defect in thioredoxin-dependent thiol peroxidase (Tpx), was more severely damaged by EGCG when compared with its wild type. Similar differing effects were observed in other Gram-positive and Gram-negative bacteria when exposed to EGCG; it caused aggregated in Streptococcus mutans, while it caused grooves in Pseudomonas aeruginosa. AFM results suggest that the major morphological changes of Gram-negative bacterial cell walls induced by EGCG depend on H₂O₂ release. This is not the case for Gram-positive bacteria. Oxidative stress in Gram-negative bacteria induced by EGCG was confirmed by flow cytometry.     

Fast Identification Method of Total Normal Surface Absorptances Using Inverse Techniques

This paper proposes a simple and fast method to identify the normal absorptance of various surfaces submitted to a radiation source, using inverse techniques. The method consists of imposing during a lap of a few seconds a radiative flux on the front face of a sample whose absorptance is to be identified. The time-dependent temperature on the rear face is measured, and the procedure of inversion is implemented to give a time function of absorbed flux. Only one time–temperature function is measured using a current type K thermocouple. The normal absorptance of the front face is obtained by comparing the time heat flux function of the source and the identified absorbed heat flux function. This method can be quickly and efficiently adopted for many practical applications without the need to use optical devices, which give accurate measurement but at substantial cost. The inverse technique using a conjugate gradient method of minimization with adjoint problem is implemented to estimate the absorbed heat flux. In order to achieve good values of radiative absorptances, reliable knowledge of thermal diffusivities and adequately manufactured samples are required.     

Vegetable oil aided hydrothermal synthesis of cerium oxide nanocrystals

Hydrothermal synthesis of cerium oxide nanocrystals was performed with in-situ surface modification using soybean oil and palm oil as capping agents. The synthesized nanocrystals were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). TEM results showed single crystalline nature with stable dispersion. FT-IR spectra and TGA plots further confirmed the adsorption of fatty acid molecules onto cerium oxide surface. Our findings have the advantages of reduced materials costs compared to using single component surfactants and the production of valuable by-product glycerol.     

Influence of Thiol Self‐Assembled Monolayer Processing on Bottom‐Contact Thin‐Film Transistors Based on n‐Type Organic Semiconductors

The performance of bottom‐contact thin‐film transistor (TFT) structures lags behind that of top‐contact structures owing to the far greater contact resistance. The major sources of the contact resistance in bottom‐contact TFTs are believed to reflect a combination of non‐optimal semiconductor growth morphology on the metallic contact surface and the limited available charge injection area versus top‐contact geometries. As a part of an effort to understand the sources of high charge injection barriers in n‐channel TFTs, the influence of thiol metal contact treatment on the molecular‐level structures of such interfaces is investigated using hexamethyldisilazane (HMDS)‐treated SiO₂ gate dielectrics. The focus is on the self‐assembled monolayer (SAM) contact surface treatment methods for bottom‐contact TFTs based on two archetypical n‐type semiconductors, α,ω‐diperfluorohexylquarterthiophene (DFH‐4T) and N,N′bis(n‐octyl)‐dicyanoperylene‐3,4:9,10‐bis(dicarboximide) (PDI‐8CN₂). TFT performance can be greatly enhanced, to the level of the top contact device performance in terms of mobility, on/off ratio, and contact resistance. To analyze the molecular‐level film structural changes arising from the contact surface treatment, surface morphologies are characterized by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The high‐resolution STM images show that the growth orientation of the semiconductor molecules at the gold/SAM/semiconductor interface preserves the molecular long axis orientation along the substrate normal. As a result, the film microstructure is well‐organized for charge transport in the interfacial region.     

Non‐Covalent Self‐Assembly and Covalent Polymerization Co‐Contribute to Polydopamine Formation

Polydopamine is the first adhesive polymer that can functionalize surfaces made of virtually all material chemistries. The material‐independent surface modification properties of polydopamine allow the functionalization of various types of medical and energy devices. However, the mechanism of dopamine polymerization has not yet been clearly demonstrated. Covalent oxidative polymerization via 5,6‐dihydroxyindole (DHI), which is similar to the mechanism for synthetic melanin synthesis, has been the clue. Here, it is reported that a physical, self‐assembled trimer of (dopamine)₂/DHI exists in polydopamine, which has been known to be formed only by covalent polymerization. It is also found that the trimeric complex is tightly entrapped within polydopamine and barely escapes from the polydopamine complex. The result explains the previously reported in vitro and in vivo biocompatibility. The study reveals a different perspective of polydopamine formation, where it forms in part by the self‐assembly of dopamine and DHI, providing a new clue toward understanding the structures of catecholamines such as melanin.     

Light Extraction of Organic Light Emitting Diodes by Defective Hexagonal‐Close‐Packed Array

Defective silica sphere arrays having locally hexagonal‐closed‐packed structure but lack of long range ordering were incorporated into organic light emitting diodes as grating to extract the waveguided light trapped in the indium tin oxide/organic layers and the glass substrate. Using these defective hexagonal‐closed‐packed gratings for light extraction, broad band lambertian emitters are obtained due to the periodicity broadening and the random orientation in the gratings, resulting in enhancements in current and power efficiencies by a factor of 1.7 and 1.9, respectively.