A water-soluble azobenzene-containing functional monomer 4-[(4-methacryloyloxy)phenylazo] benzenesulfonic acid (MAPASA) was developed for the fabrication of a photoresponsive molecularly imprinted hydrogel material that can function in the biocompatible aqueous media. Cross-linking the functional monomer with various bisacrylamide and bismethacrylamide cross-linkers produced polyacrylamide hydrogels with enough optical transparency in the aqueous media for spectroscopic characterization and measurements. Paracetamol, (N-(4-hydroxyphenyl)acetamide), a common analgesic and antipyretic drug, was adopted as the molecular template for the imprinting. Reorientation of the hydrated sulfonated azobenzene chromophores in the course of their trans−cis photoisomerization was found to be sterically demanding. When incorporated into the relatively confined and rigid hydrogel environment generated by the most commonly adopted polyacrylamide cross-linker, N,N′-methylenebisacrylamide (1-C), these chromophores were not able to undergo photoisomerization. Lengthening the spacers separating the polymerizable acrylamide/methacrylamide functionalities at both ends of the cross-linkers from ethylene (2-C) to octylene (8-C) enhanced the flexibility of the resultant hydrogel matrices and resumed the photoisomerization properties of the chromophores. The rate of photoisomerization gradually increased with spacer length. On the other hand, substrate binding strength of the imprinted receptors dropped with the increasing flexibility of the hydrogels. Balancing these factors, the cross-linker N,N′-hexylenebismethacrylamide (6-C) was subsequently selected as the optimal cross-linker for the fabrication of the photoresponsive imprinted hydrogel. Scatchard analysis revealed the specific and nonspecific binding strength of the resultant imprinted hydrogel to be 1.96 × 105 and 747.0 M−1, respectively. The density of the imprinted receptors in the hydrogel was 0.47 µmol g−1. The affinity of the hydrogel for paracetamol can be photoregulated. Upon irradiation at 353 nm, 83.6% of receptor-bound paracetamol was released from the imprinted hydrogel. Subsequent irradiation at 440 nm caused 94.1% of the released paracetamol to be rebound by the hydrogel again. Such a photoregulated release and uptake process is repeatable. Results of our work demonstrated the potential of stimuli-responsive molecularly imprinted materials as biocompatible smart chemicals and drugs transfer systems.
Flexible and high performance supercapacitors are very critical in modern society. In order to develop the flexible supercapacitors with high power density, free-standing and flexible three-dimensional graphene/carbon nanotubes/MnO2 (3DG/CNTs/MnO2) composite electrodes with interconnected ternary 3D structures were fabricated, and the fast electron and ion transport channels were effectively constructed in the rationally designed electrodes. Consequently, the obtained 3DG/CNTs/MnO2 composite electrodes exhibit superior specific capacitance and rate capability compared to 3DG/MnO2 electrodes. Furthermore, the 3DG/CNTs/MnO2 based asymmetric supercapacitor demonstrates the maximum energy and power densities of 33.71 W h kg(-1) and up to 22,727.3 W kg(-1), respectively. Moreover, the asymmetric supercapacitor exhibits excellent cycling stability with 95.3% of the specific capacitance maintained after 1000 cycle tests. Our proposed synthesis strategy to construct the novel ternary 3D structured electrodes can be efficiently applied to other high performance energy storage/conversion systems.
In this paper, by combination of the specificity of a molecularly imprinted technique, the water solubility of hydrogels and the photoisomerization property of azobenzene chromophores, we report a new and quick detection method for trace melamine in aqueous media based on photo-responsive molecularly imprinted hydrogels (MIHs). The MIHs were fabricated using a water-soluble azobenzenecontaining 4-[(4-methacryloyloxy)phenylazo]benzenesulfonic acid (MAPASA) as the functional monomer, 1,3,5-benzenetriol as a mimic template, and tetramethacryloyl triethylene tetramine (TTT) as the cross-linker. The MIHs show specific affinity to melamine with a binding constant of 3.20 Â 10 4 M À1 in aqueous Tris-HCl buffer at pH 7.0. The density of the melamine-specific receptor sites in the MIHs material is 2.69 mmol g À1 MIHs. Upon alternate irradiation at 365 and 440 nm, the MIHs can quantitatively uptake and release melamine. The photoisomerization rate of MIHs is related to the concentration of melamine in the detecting solution, and therefore, a quick detection method for trace melamine is established. Analytical application of the MIHs to detect the melamine concentration in both milk and milk powder has been accomplished successfully with a simple pre-treatment of the samples.
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