A nonionic surfactant-decorated liquid crystal sensor for sensitive and selective detection of proteins

Proteins are responsible for most biochemical events in human body. It is essential to develop sensitive and selective methods for the detection of proteins. In this study, liquid crystal (LC)-based sensor for highly selective and sensitive detection of lysozyme, concanavalin A (Con A), and bovine serum albumin (BSA) was constructed by utilizing the LC interface decorated with a nonionic surfactant, dodecyl beta-Dglucopyranoside. A change of the LC optical images from bright to dark appearance was observed after transferring dodecyl beta-D-glucopyranoside onto the aqueous/LC interface due to the formation of stable self-assembled surfactant monolayer, regardless of pH and ion concentrations studied in a wide range. The optical images turned back from dark to bright appearance after addition of lysozyme, Con A and BSA, respectively. Noteworthy is that these proteins can be further distinguished by adding enzyme inhibitors and controlling incubation temperature of the protein solutions based on three different interaction mechanisms between proteins and dodecyl beta-D-glucopyranoside, viz. enzymatic hydrolysis, specific saccharide binding, and physical absorption. The LC-based sensor decorated with dodecyl beta-Dglucopyranoside shows high sensitivity for protein detection. The limit of detection (LOD) for lysozyme, Con A and BSA reaches around 0.1 mg/mL, 0.01 mg/mL and 0.001 mg/mL, respectively. These results might provide new insights into increasing selectivity and sensitivity of LC-based sensors for the detection of proteins. (C) 2016 Elsevier B.V. All rights reserved

Experimental and DFT studies on aggregation behavior of dodecylsulfonate-based surface active ionic liquids in water and ethylammonium nitrate

The present work aims to systematically study the aggregation behavior of one halogen-free surface active ionic liquid (SAIL), i.e., 1-butyl-3-methylimidazolum dodecylsulfonate ([C(4)mim][C12H25SO3]), in water and ethylammonium nitrate (EAN), respectively. Multiple-state ordered aggregates, viz. lyotropic liquid crystals (LLCs) (normal hexagonal and laminar lyotropic liquid phases, i.e. H-1 and L-alpha phases) and lamellar gels, were facilely tuned only by the concentration of SAIL or solvent type. Furthermore, it is particularly interesting that LLC phases were constructed in H2O while lamellar gels were obtained in the EAN media environment, which were characterized by polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS). According to the investigative SAXS patterns, some structural parameters were calculated, suggesting that a higher concentration of SAIL results in a denser arrangement whereas an opposite trend generates because of a higher temperature. FT-IR spectra and density functional theory (DFT) calculations reveal that both strong H-bonding and electrostatic interactions between EAN and the headgroups of [C(4)mim][C12H25SO3] facilitate gelation. For the self-assembled lamellar gels formed by [C(4)mim][C12H25SO3] in EAN, a thermally reversible sol-gel transition was observed by differential scanning calorimetry (DSC). The rheological results show that the H1 phase formed by [C(4)mim][C12H25SO3] in water exhibits a viscoelastic gel-like behavior among the whole frequency region while L-alpha phase displays a viscous behavior at lower frequencies and an elastic behavior at higher frequencies. This work is expected to set a basis for application of the eco-friendly halogen-free SAIL in some fields, e.g. electrochemistry, supramolecular chemistry and drug delivery. (c) 2016 Elsevier B.V. All rights reserved

Rational design of photo-responsive supramolecular nanostructures based on an azobenzene-derived surfactant-encapsulated polyoxometalate complex

Using an ionic self-assembly (ISA) approach, photo-responsive surfactant-encapsulated polyoxometalate complexes (SECs) were fabricated in water from an original Keggin-type polyoxometalate (POM) and a cationic surfactant containing an azobenzene group, viz. phosphotungstic acid (H-3[PW12O40]) and 4-ethyl-4'-(trimethylaminohexyloxy) azobenzene bromide (ETAB). The driving forces and self-assembly mechanism of the ETAB-POM supramolecular hybrids were investigated by NMR, Fourier transform infrared (FTIR), UV/vis and small angle X-ray scattering (SAXS) characterization methods. Of particular interest is the complex solution which shows an obvious variation upon UV light irradiation. On a macroscale, its turbidity increases obviously, from a clear solution before UV irradiation to a turbid state. The microcosmic structures of the complex change from coral-like structures to dispersive nanospheres. These phenomena can be ascribed to the transformation of ETAB from trans-to cis-isomers after exposure to UV light. Beyond that, a cyclic voltammetric (CV) method was employed to observe the electrochemical properties of SECs. The results obtained in this work will shed light of the SECs' applications in phase separation, heterogeneous catalysis reactions, the detection of environmental pollutants, etc

A liquid crystal-based sensor for the simple and sensitive detection of cellulase and cysteine

A liquid crystal (LC)-based sensor, which is capable of monitoring enzymatic activity at the aqueous/LC interface and detecting cellulase and cysteine (Cys), was herein reported. When functionalized with a surfactant, dodecyl beta-D-glucopyranosicie, the 4-cyano-4'-pentylbiphenyl (5CB) displays a dark-to-bright transition in the optical appearance for cellulase. We attribute this change to the orientational transition of LCs, as a result of enzymatic hydrolysis between cellulase and surfactant. Furthermore, by adding cellulase and Cu2+, our surfactant-LCs system performs an interesting ability to detect Cys, even though Cys could not interact with surfactant or LC directly. Alternatively, through the strong binding between Cys and Cu2+, cellulase was able to hydrolyze surfactant in the presence of Cu2+, leading to the transition of LCs from dark to bright. The detection limit of the LC sensor was around 1 x 10(-5) mg/mL and 82.5 mu M for cellulase and Cys, respectively. The LC-based sensor may contribute to the development of low-cost, expedient, and label-free detection for cellulase and Cys and the design strategy may also provide a novel way for detecting multiple analytes. (C) 2016 Elsevier B.V. All rights reserved

A polyoxometalate-based supramolecular chemosensor for rapid detection of hydrogen sulfide with dual signals

Hydrogen sulfide (H2S) has been verified as an important biological mediator in human physiological activities, but its rapid and accurate detection is remaining a challenge. Based on our early work, Eu-containing polyoxometalate/ionic liquid-type gemini surfactant hybrid nanoparticles fabricated by EuW10O36.32H(2)O (Eu-POM) and 1,2-bis(3-hexadecylimidazolium-1-yl) ethane bromide ([C-16-2-C(16)im]Br-2) via ionic self-assembly (ISA) strategy, we modified the hybrids with copper (II) ion and used them as a novel turn-off supramolecular fluorescence probe for H2S immediate response. Although copper (II) ions can cause decrease of the fluorescence intensity, the probe with moderate amount of copper (II) still has a high performance in emission property. The copper (II) ion-modified supramolecular sensor (CSS) shows dual signals in the fluorescence intensity and absorbance for H2S detection, and the detection limit is about 1.25 mu M. Furthermore, CSS displays high selectivity for H2S in the presence of other anions and species (e.g. Cl-, Br-, I-, SO42-, SO32-, S2O32-, AC(-), H2O2, HCO3-, L-cysteine, homocysteine and L-glutathione), and also have potential for preferential imaging in vivo. Besides, the fluorescence quenching mechanism of CSS in the presence of H2S was explored. CuS generated by the reaction between Cu2+ and H2S was testified to act as a quencher, and the nonradiative resonance energy transfer mechanism was speculated to be responsible for fluorescence quenching. It is anticipated that the as-prepared CSS will be used as an efficient chemosensor for the rapid detection of H2S, which is critical for the diagnosis of some diseases, e.g. Alzhermer's disease, Down's syndrome, and diabetes, etc. (C) 2016 Elsevier Inc. All rights reserved

Bottom-up preparation of gold nanoparticle-mesoporous silica composite nanotubes as a catalyst for the reduction of 4-nitrophenol

Gold (Au) nanoparticle (NP)-mesoporous silica (SiO2) composite nanotubes were prepared by a bottom-up approach, in which Au NPs were anchored to the inner wall of mesoporous SiO2 tubular shells. In this composite, the agglomeration, exfoliation, and grain growth of Au NPs were restricted, and the loading and size of the catalyst NPs were easily tuned. The mesoporous shell, open ends, and one-dimensional passage of the SiO2 nanotubes all promote the diffusion of reactants, which enhanced the catalytic efficiency of this composite in the reduction of 4-nitrophenol, The Au NP-mesoporous SiO2 composite nanotubes also demonstrated good reusability, and no leaching or agglomeration of the Au NPs was observed during the catalytic reaction. (C) 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved