A novel sensing material based on pyrene doped polyethersulfone worm-like structured thin film is developed using a facile technique for detection of nitroaromatic explosive vapours. The formation of p-p stacking in the thin fluorescent film allows a highly sensitive fluorescence quenching which is detectable by the naked eye in a response time of a few seconds.Nitroaromatic (NA) explosives are the primary constituents of many unexploded land mines worldwide.1,2 Selective, fast and low-cost detection of NA explosives, such as trinitrotoluene (TNT) and dinitrotoluene (DNT), is crucial for military operations, homeland security, and environmental safety. 3 Various analytical and spectroscopic methods have been developed for sensitive detection of NA compounds. [4][5][6][7] These instrumental techniques are mostly expensive and not portable for use in the field. The detection of NA explosives using fluorescent-based sensors has been extensively studied because of their sensitivity, portability, and short response time. [8][9][10][11][12][13] The most important report in this field was published by Swager' group. 14 They used a conjugated polymer scaffold and improved the detection sensitivity. 14 Trogler and co-workers developed a new class of fluorescent films which were fabricated by spin-coating onto suitable solid substrates for detecting NA explosives both in the air and organic solvents. 15 The underlying explosive detection mechanism of the fluorescent polymer is photo-induced electron transfer (PET) from the polymers to the NA explosives. The key feature of this phenomenon is the presence of the p-p-stacking (excimer) between the polymer chains and chromophore groups.This p-stacked formation can significantly enhance the sensing performance of films.14,15In this report, we have fabricated a novel fluorescent thin film based on the pyrene-doped polyethersulfone (Py-PES) polymer for detection of nitro-explosive vapours using a rapid and facile method. The experimental details of the preparation of this sensing film are given in ESI. † To prepare the fluorescent polymer, we chose pyrene (Py) as the fluorescent dye because of its potential to form highly emissive excited dimers, high fluorescence yield, and known fluorescence quenching sensitivity to NA compounds. 16 The driving force for the quenching mechanism of Py-PES thin films is the formation of p-p Scheme 1 Schematic representation of the quenching mechanism for the Py-PES film by TNT based on photo-electron transfer (PET) process. The main driving force for the PET process is the energy gap between the conduction band of Py-PES films and the LUMO of NA explosives. NA explosives accept the electron from exited state of pyrene due to their low LUMO energies and as a result the fluorescent film is quenched 18 (see details in ESI †).a UNAM-National Nanotechnology Research Center, Bilkent University, 06800 Ankara, Turkey. E-mail: birlik@unam.bilkent.edu.tr b Department of Chemistry, Gazi University, Polatli, 06900, Ankara, Turkey c Institute of Materials Sc...
A facile self-assembly method is described to prepare PEGylated silica nanocarriers using hydrophobic mesoporous silica nanoparticles and a pluronic F127 polymer. Pluronic capped nanocarriers revealed excellent dispersibility in biological media with cyto-and blood compatibilities.The high surface area and pore volume, good chemical stability and ease of surface functionalization of mesoporous silica nanoparticles (MSNs) make them promising materials for biological applications as drug carriers and theranostic agents.1,2 In addition silica based materials are generally accepted as biocompatible materials by the U.S. Food and Drug Administration (FDA). However, recent studies demonstrated their potential in vitro and in vivo toxicity, especially when their size is reduced to the nano scale. 3,4 Although the toxicity of silica based nanomaterials depends on several factors including particle size, shape, surface chemistry and porosity, [5][6][7] there is a general consensus that chemical structure of the surface is the predominant factor which determines the interactions with biological systems. 8 The surface of bare silica is covered with negatively charged silanol groups, which can electrostatically interact with positively charged tetraalkylammonium moieties of the cell membrane and can lead to cytotoxicity by membranolysis or inhibition of cellular respiration. 8,9 Also, rapid aggregation of silica based nanoparticles in biological media can result in mechanical obstruction in the capillary vessels of several vital organs, leading to organ failure and even death. 10,11 Therefore, replacing the surface silanol groups with biocompatible molecules is essential to improve the biocompatibility of MSNs. Among numerous polymeric or organosilane surface modification ligands, polyethylene glycol (PEG) is the mostly used one due to its well established biocompatibility, hydrophilicity, and antifouling properties.12 However, the PEGylation process has some limitations;(i) it mostly requires tedious organic synthesis and surface modification 13 and (ii) pores of MSNs may be closed by the long PEG polymer chains, which can hinder the drug loading process. To overcome these limitations, here we report a facile self-assembly method using octyl modified hydrophobic MSNs and an amphiphilic block copolymer (F127). F127, a FDA approved biocompatible pluronic polymer, contains two hydrophilic PEG blocks and a hydrophobic polypropylene oxide (PPO) between the two PEG blocks. 14 When the powder of hydrophobic MSNs is added into the F127 solution they are easily transferred into water by selfassembly of F127 molecules onto the MSN surface through the hydrophobic interaction between the PPO block of F127 and surface octyl groups of the MSNs (Scheme 1). In addition, cargo loaded and PEGylated MSNs can be simply prepared by loading the hydrophobic MSNs before the F127 capping process. The F127 capped particles are dispersible in both water and phosphate buffered saline (PBS), whereas uncapped MSNs are easily aggregated and precipitated...
Since the discovery of dipeptide self-assembly, diphenylalanine (Phe-Phe)-based dipeptides have been widely investigated in a variety of fields. Although various supramolecular Phe-Phe-based structures including tubes, vesicles, fibrils, sheets, necklaces, flakes, ribbons, and wires have been demonstrated by manipulating the external physical or chemical conditions applied, studies of the morphological diversity of dipeptides other than Phe-Phe are still required to understand both how these small molecules respond to external conditions such as the type of solvent and how the peptide sequence affects self-assembly and the corresponding molecular structures. In this work, we investigated the self-assembly of valine-alanine (Val-Ala) and alanine-valine (Ala-Val) dipeptides by varying the solvent medium. It was observed that Val-Ala dipeptide molecules may generate unique self-assembly-based morphologies in response to the solvent medium used. Interestingly, when Ala-Val dipeptides were utilized as a peptide source instead of Val-Ala, we observed distinct differences in the final dipeptide structures. We believe that such manipulation may not only provide us with a better understanding of the fundamentals of the dipeptide self-assembly process but also may enable us to generate novel peptide-based materials for various applications.
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