Electrospinning SA@PVDF-HFP Core-Shell Nanofibers Based on a Visual Light Transmission Response to Alcohol for Intelligent Packaging.

A naked-eye detector based on a rapid transmittance response to alcohol was designed to offer real-time and reusable detection of fruit freshness. To ensure the hydrophobicity of the fibrous membrane and high light transmission response to alcohol, fluorine-rich poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with a low refractive index was selected as the shell layer, while sodium alginate (SA) and polyvinyl alcohol (PVA) were selected as the core layer for coaxial electrospinning. The core-shell fibrous detector was obtained by treatment with CaCl2 to form a stable hydrogel and by water flushing to remove PVA. The interior structure of the fiber and its evolution were investigated with increasing SA concentration, which changed from a nonconcentric structure to a core-shell structure. Without SA, nonconcentric structured fibers were obtained due to high flowability and incompatibility between the organic solvent phase of PVDF-HFP and the aqueous phase of PVA. As the SA concentration increased, the enhanced viscosity and surface tension decreased the asymmetric mobility significantly, which competed with the charge attractive forces from the Taylor cone surface, leading to a core-shell structure. The as-spun membranes were opaque due to light scattering at the interface between air and fiber and became light transparent after immersion in a rotten fruit-containing alcohol and acetic acid due to a decreased light loss. The rapidly responsive, reusable fibrous membranes with over 90% light transparency developed here have high potential for application in visual intelligent packaging to monitor the freshness of fruits and vegetables.

Preparation and Applications of Electrospun Optically Transparent Fibrous Membrane.

The optically transparent electrospun fibrous membrane has been widely used in many fields due to its simple operation, flexible design, controllable structure, high specific surface area, high porosity, and unique excellent optical properties. This paper comprehensively summarizes the preparation methods and applications of an electrospun optically transparent fibrous membrane in view of the selection of raw materials and structure modulation during preparation. We start by the factors that affect transmittance among different materials and explain the light transmission mechanism of the fibrous membrane. This paper also provides an overview of the methods to fabricate a transparent nanofibrous membrane based on the electrospinning technology including direct electrospinning, solution treatment after electrospinning, heat treatment after electrospinning, and surface modification after electrospinning. It further summarizes the differences in the processes and mechanisms between different transparent fibrous membranes prepared by different methods. Additionally, we study the utilization of transparent as-spun membranes as flexible functional materials, namely alcohol dipstick, air purification, self-cleaning materials, biomedicine, sensors, energy and optoelectronics, oil-water separation, food packaging, anti-icing coating, and anti-corrosion materials. It demonstrates the high transparency of the nanofibers' effects on the applications as well as upgrades the product performance.

Flavin-Based Fluorescent Protein EcFbFP Auto-Guided Surface Display of Methyl Parathion Hydrolase in Escherichia coli.

Methyl parathion hydrolase (MPH) plays an important role in degrading a range of organophosphorus compounds. In order to display MPH on the cell surface of Escherichia coli strain RosettaBlue™, the Flavin-based fluorescent protein EcFbFP was severed as an auto-anchoring matrix. With net negative charges of EcFbFP supplying the driving forces, fusion protein MPH-EcFbFP through a two-step auto-surface display process was finally verified by (a) inner membrane translocation and (b) anchoring at outer membrane. Cells with surface-displayed MPH obtained activity of 0.12 U/OD600 against substrate methyl parathion. MPH when fused with engineered EcFbFP containing 20 net negative charges exhibited fivefold higher anchoring efficiency and tenfold higher enzymatic catalytic activity of 1.10 U/OD600. The above result showed that MPH was successfully displayed on cell surface and can be used for biodegradation of methyl parathion.

Non-peptide guided auto-secretion of recombinant proteins by super-folder green fluorescent protein in Escherichia coli.

Protein secretion in Escherichia coli is usually led by a signal peptide that targets the protein to specific secretory pathways. In this study, we demonstrated that the superfolder green fluorescent protein (sfGFP) could be served as a non-signal peptide to guide protein auto-secretion in E. coli. This auto-secretion was characterized as a three-step process through the sub-cellular localization analysis: inner membrane trans-location followed by anchoring at outer membrane, and then being released into culture media. We further determined that the beta-barrel structure and net negative charges of sfGFP played important roles in its auto-extracellular secretion property. Using sfGFP as a carrier, heterologous proteins ranging from peptide to complex protein, including antibacterial peptide PG4, endo-beta-N-acethylglucosamindase H (Endo H), human arginase-1 (ARG1), and glutamate decarboxylase (GAD) were all successfully expressed and secreted extracellularly when fused to the carboxyl end of sfGFP. Besides facilitating the extracellular secretion, sfGFP fusion proteins can also be correctly folded and formed the active complex protein structure, including the trimetric human ARG1 and homo-hexametric GAD. This is the first report that sfGFP can guide the secretion of recombinant proteins out of the cells from cytoplasm in E. coli without affecting their conformation and function.