Fluorescence resonance energy transfer in polydiacetylene liposomes

Conjugated polydiacetylene (PDA) possessing stimuli-responsive properties has been intensively investigated for developing efficient sensors. We report here fluorescence resonance energy transfer (FRET) in liposomes synthesized using different molar ratios of dansyl-tagged diacetylene and diacetylene-carboxylic acid monomers. Photopolymerization of diacetylene resulted in cross-linked PDA liposomes. We used steady-state electronic absorption, emission, and fluorescence anisotropy (FA) analysis to characterize the thermal-induced FRET between dansyl fluorophores (donor) and PDA (acceptor). We found that the monomer ratio of acceptor to donor ( R ad) and length of linkers (functional part that connects dansyl fluorophores to the diacetylene group in the monomer) strongly affected FRET. For R ad = 10 000, the acceptor emission intensity was amplified by more than 18 times when the liposome solution was heated from 298 to 338 K. A decrease in R ad resulted in diminished acceptor emission amplification. This was primarily attributed to lower FRET efficiency between donors and acceptors and a higher background signal. We also found that the FRET amplification of PDA emissions after heating the solution was much higher when dansyl was linked to diacetylene through longer and flexible linkers than through shorter linkers. We attributed this to insertion of dansyl in the bilayer of the liposomes, which led to an increased dansyl quantum yield and a higher interaction of multiple acceptors with limited available donors. This was not the case for shorter and more rigid linkers where PDA amplification was much smaller. The present studies aim at enhancing our understanding of FRET between fluorophores and PDA-based conjugated liposomes. Furthermore, receptor tagged onto PDA liposomes can interact with ligands present on proteins, enzymes, and cells, which will produce emission sensing signal. Therefore, using the present approach, there exist opportunities for designing FRET-based highly sensitive and selective chemical and biochemical sensors.     

Bacteriorhodopsin optoelectronic synapses

Synapses are critical components of an artificial neural network. Bacteriorhodopsin thin film can be used to construct compact, finely graded synapses for an optoelectronic neural network, based on its photochromic properties. Measurements show that these photochromic changes are blocked at low temperature. Thermal gating will allow synapses to be written on the film optically and then read without erasure by the same light and also will permit local implementation of an associative learning rule for updating synaptic weights.     

A Full Flexible NH4+ Ion Battery Based on the Concentrated Hydrogel Electrolyte for Enhanced Performance

Non-metal ammonium ( ) ions have recently been explored as effective charge carriers in battery systems due to their abundancy, light weight, small hydration shells in water. The research concerning the use of redox chemistry in batteries, particularly in flexible batteries, is still in its infancy. For the first time, we report a flexible full ion battery (AIB) composed of a concentrated hydrogel electrolyte sandwiched between NH₄V₃O₈ ⋅ 2.9H₂O nanobelts cathode and polyaniline (PANI) anode, for enhanced performance. The hydrogel electrolyte is simply synthesized by using ammonium sulfate, xanthan gum and water. As a reference, the AIB based on the liquid aqueous electrolyte is prepared first, which exhibits a capacity of 121 mAh g⁻¹ and a capacity retention of 95 % after 400 cycles at a specific current of 0.1 A g⁻¹. On the other hand, the simple synthesis of the hydrogel electrolyte allows us to facilely tune and optimize the salt contents in the electrolyte, to maximize the ionic conductivity, transport kinetics, mechanical characteristics, and consequently the battery performance. It is found that the flexible battery based on the hydrogel electrolyte prepared from 3 M ammonium sulfate solution shows the best electrochemical performance, i. e., a capacity of 60 mAh g⁻¹ while maintaining a capacity retention of 88 % after 250 cycles at a specific current of 0.1 A g⁻¹. Moreover, the flexible AIB retains excellent electrochemical performance when bent at different angles, demonstrating remarkable mechanical strength and flexibility. Therefore, this study sheds new light on the utilization of concentrated hydrogel electrolyte in the AIB chemistry, for developments of novel electrochemical energy storage technology with high safety and low cost.     

Tailoring heterogeneous polymer networks through polymerization‐induced phase separation: influence of composition and processing conditions on reaction kinetics and optical properties

Polymerization‐induced phase separation from an all‐monomeric system by direct copolymerization offers the formation of heterogeneous polymeric structures without reliance on polymer blends, block copolymers, or interpenetrating polymer networks. This study examines the potential for the formation of compositional heterogeneity in copolymer networks obtained by free‐radical photopolymerizations of initially homogeneous mixtures of bisphenol A glycidyl dimethacrylate and isodecyl methacrylate as the comonomer ratios and polymerization conditions are varied. Comonomer proportions that control thermodynamic stability prior to (as determined by cloud point measurements) and during [as determined by turbidity measurements coupled with near‐infrared (IR) spectroscopy] polymerization were shown to be a more influential factor on phase separation than irradiance‐imposed kinetic control of the photopolymerization process. Through photorheometry coupled with near‐IR and ultraviolet–visible (UV–Vis), the onset of phase separation was shown to occur at very low conversions and always prior to gelation (as estimated by the crossover of G′/G″). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1796–1806