Graphene is a single-atom-thick two-dimensional carbon nanosheet with outstanding chemical, electrical, material, optical, and physical properties due to its large surface area, high electron mobility, thermal conductivity, and stability. These extraordinary features of graphene make it a key component for different applications in the biosensing and imaging arena. However, the use of graphene alone is correlated with certain limitations, such as irreversible self-agglomerations, less colloidal stability, poor reliability/repeatability, and non-specificity. The addition of gold nanostructures (AuNS) with graphene produces the graphene–AuNS hybrid nanocomposite which minimizes the limitations as well as providing additional synergistic properties, that is, higher effective surface area, catalytic activity, electrical conductivity, water solubility, and biocompatibility. This review focuses on the fundamental features of graphene, the multidimensional synthesis, and multipurpose applications of graphene–Au nanocomposites. The paper highlights the graphene–gold nanoparticle (AuNP) as the platform substrate for the fabrication of electrochemical and surface-enhanced Raman scattering (SERS)-based biosensors in diverse applications as well as SERS-directed bio-imaging, which is considered as an emerging sector for monitoring stem cell differentiation, and detection and treatment of cancer.

Antioxidants interact with free radicals, terminating the adverse chain reactions and converting them to harmless products. Antioxidants thus minimize the oxidative stress and play a crucial role in the treatment of free radicals-induced diseases. However, the effectiveness of natural and/or synthetic antioxidants is limited due to their poor absorption, difficulties to cross the cell membranes, and degradation during delivery, hence contributing to their limited bioavailability. To address these issues, antioxidants covalently linked with nanoparticles, entrapped in nanogel, hollow particles, or encapsulated into nanoparticles of diverse origin have been used to provide better stability, gradual and sustained release, biocompatibility, and targeted delivery of the antioxidants with superior antioxidant profiles. This review aims to critically evaluate the recent scientific evaluations of nanoparticles as the antioxidant delivery vehicles, as well as their contribution in efficient and enhanced antioxidant activities.

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steel substrates via closed field unbalanced magnetron sputtering technology. These were investigated using XRD, SEM, XPS, UV-Vis, FTIR and nanoindentation techniques. Analysis of the optical properties showed the solar absorptance, in the visible range, of the Ti x M 1ÀxÀy N y films improved significantly from 51% to 81% with AlSi-doping and an increase of solar absorptance of up to 66% was recorded from films doped with Al. Moreover, the Al doping can reduce the thermal emittance in the infrared range from 6.06% to 5.11%, whereas doping with AlSi reduces the emittance to ca. 3.58%. The highest solar selectivity of 22.63 was achieved with TiAlSiN films. Mechanical studies showed enhanced hardness by $32%; enhanced yield strength by $16% and enhanced plastic deformation by $110% of Al and AlSi doped TiN matrix. IntroductionA spectrally selective surface is, generally, used to improve the photothermal conversion performance and, as such, it possesses two characteristics: high absorptance, a in the visible region of solar spectrum (0.3 to 2.5 mm) and low emittance, 3, (i.e., high reection) in the infra-red (IR) region ($2.5 mm) at operating temperatures. An excellent selective surface maximises the absorption of incoming photons in the visible region and minimises photon emission through thermal radiation in the IR energy region. Such a surface can be designed by an absorber-reector assembly. In such an approach, the reector is coated with a highly absorbing layer over the visible solar spectrum, while the infrared region is made transparent. Various types of metal nitrides based selective solar surfaces such as TiN, ZrN, HfN, TiAlN, TiAlON, NbAlN, NbAlON, MoAlN, and WAlN have been investigated by numerous groups.1-11 Over the past few years, transition metal nitride based thin lms have attracted signicant research interest as selective solar surfaces in solar thermal conversion devices. Generally, the energy conversion performance of a selective solar surface depends on the lm materials, lm design and fabrication technique used. A multi-layer lm stack with mixture of metal nitride, metal oxide and metal oxynitride lms e.g., TiAlN/AlON, and TiAl/ TiAlN/TiAlON/TiAlO has been explored for the potential commercial development of selective solar surfaces.3,12 TiAlN/ TiAlON/Si 3 N 4 selective absorbers have been produced on various substrates such as copper, nickel, stainless steel, glass and nimonic alloys.13 However, these materials are yet to be commercialized for solar energy conversion applications. View Article OnlineView Journal | View Issue solar selective surface applications, transition metal oxides based thin lms also received signicant research interests. 15-19Various synthesis methods such as evaporation, electrodeposition, chemical conversion, chemical vapour deposition and magnetron sputtering have been employed in manufacturing selective solar surfaces. Owing to its advantages in large area deposition, dry, clean and environment friendly, magnetron sputtering technique is widely used for syn...

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