Evolution of graphene oxide (GO)-based nanohybrid materials with diverse compositions: an overview.

The discovery of the 2D nanostructure of graphene was in fact the beginning of a new generation of materials. Graphene itself, its oxidized form graphene oxide (GO), the reduced form of GO (RGO) and their numerous composites are associates of this generation. Out of this spectrum of materials, the development of GO and related hybrid materials has been reviewed in the present article. GO can be functionalized with metals (Ag and Mg) and metal oxides (CuO, MgO, Fe2O3, Ag2O, etc.) nanoparticles (NPs), organic ligands (chitosan and EDTA) and can also be dispersed in different polymeric matrices (PVA, PMMA, PPy, and PAn). All these combinations give rise to nanohybrid materials with improved functionality. An updated report on the chronological development of such nanohybrid materials of diverse nature has been delivered in the present context. Modifications in synthesis methodologies as well as performances and applications of individual materials are addressed accordingly. The functional properties of GO were synergistically modified by photoactive semiconductor NPs; as a result, the GO-MO hybrids acquired excellent photocatalytic ability and were able to degrade a large variety of organic dyes (MB, RhB, MO, MR, etc.) and pathogens. The large surface area of GO was successfully complemented by the NPs so that high and selective adsorption capacity towards metal ions and organic molecules as well as improved charge separation properties could be achieved. As a result, GO-MO hybrids have been considered effective materials in water purification, energy storage and antibacterial applications. GO-MO hybrids with magnetic particles have exhibited selective destruction of cancerous cells and controlled drug release properties, extremely important in the pharmaceutical field. Chitosan and EDTA-modified GO could form 3D network-like structures with strong efficiency in removing heavy metal ions and organic pollutants. GO as a filler enhanced the strength, flexibility and functional properties of common polymers, such as PVA and PVC, to a large extent while, GO-CP composites with polyaniline and polypyrrole are considered suitable for the fabrication of biosensors, supercapacitors, and MEMS as well as efficient photothermal therapy agents. In summary, GO-based hybrids with inorganic and organic counterparts have been designed, the unique properties of which are exploited in versatile fields of applications.

Controlling distance, size and concentration of nanoconjugates for optimized LSPR based biosensors.

In this report, we have examined the distance- and size-dependent localized surface plasmon resonance (LSPR) between fluorescent quantum dots (QDs) and adjacent gold nanoparticles (AuNPs) to provide a comprehensive evaluation, aiming for practical application in biosensing platform. A series of peptides with different chain lengths, connected between QDs and AuNPs is initially applied to prepare various CdSe QDs-peptide-AuNP systems to optimize LSPR signal. Separation distance between two nanoparticles of these systems before and after conjugation is also confirmed by quantum mechanical modeling and corroborated with their LSPR influenced fluorescence variations. After detailed optimizations, it can be noted that larger sized AuNPs make strong quenching of QDs, which gradually shows enhancement of fluorescence with the increment of distance and the smaller sized AuNPs. Depending on the requirement, it is possible to tune the optimized structure of the CdSe QD-peptide-AuNP nanostructures for the application. In this work, two different structural designs with different peptide chain length are chosen to construct two biosensor systems, observing their fluorescence enhancement and quenching effects, respectively. Using different structural orientation of these biosensors, two nanoconjugates has applied for detection of norovirus and influenza virus, respectively to confirm their application in sensing.

Exploring properties of polyaniline-SDS dispersion: a rheological approach.

The paper describes steady and dynamic rheological characterization of a system in which polyaniline (PAn) is dispersed in aqueous medium by the effect of a surfactant sodium dodecyl sulphate (SDS). During polymerization of aniline in SDS medium, large and agglomerated micelle-polymer structures are formed (supported by TEM and DLS) resulting in high viscosity of the medium. On application of steady shear micellar entanglements are ruptured and the system exhibits yield properties followed by shear thinning. From the frequency dependence of storage and loss modulii (G' and G'') it seems that the system behaves more like a viscous fluid rather than an elastic liquid. Carrying out the same experiments on another dispersion in which PAn is stabilized by dodecyl benzenesulphonic acid (DBSA), very different viscoelastic response was received. DBSA molecules become counter-ions to PAn chains and this way large and interconnected PAn-DBSA structures are formed by mutual sharing of DBSA anions and PAn chains. This system therefore, exhibits gel like properties and encounters a gel to sol transition at larger deformation. Detailed studies have established that PAn-SDS is a stabilized dispersion that resembles entangled polymeric solutions to some extent while PAn-DBSA is a partially flocculated system. Therefore, rheological response of the system is mainly governed by the mutual orientation of PAn with respect to the micelles rather than the individual properties of the components. None of these systems, however, follow the established Maxwell's model and a single relaxation time is not obtained. Rather, Rouse model of multiple relaxation times is partially applicable to PAn-SDS dispersion.