A mong the various types of nanomaterials that have been developed, nanostructured metal oxides (NMOs) have recently aroused much interest as immobilizing matrices for biosensor development ( Figure 1) [1][2][3][4][5][6][7][8][9]. Nanostructured oxides of metals such as zinc, iron, cerium, tin, zirconium, titanium, metal and magnesium have been found to exhibit interesting nanomorphological, functional biocompatible, non-toxic and catalytic properties. Th ese materials also exhibit enhanced electron-transfer kinetics and strong adsorption capability, providing suitable microenvironments for the immobilization of biomolecules and resulting in enhanced electron transfer and improved biosensing characteristics. Various morphologies of NMOs have been obtained using a variety of methods, including soft templating for the preparation of nanorods and nanofi bers [10], sol-gel methods for the production of three-dimensional (3D) ordered rough nanostructures [6,11], radiofrequency sputtering for rough nanostructures [4] and hydrothermal deposition for nanoparticles with controlled shape [12]. All of these NMOs have been reported to have potential applications in biosensors. Recently, the optical, electrical and magnetic properties of NMOs have been reported to be enhanced through the incorporation of nanoparticles of conducting or semiconducting materials such as carbon nanotubes, graphene, gold and silver, as well as quantum dots of various semiconductors, with advantages for improved biosensor characteristics [13][14][15][16]. It is expected that the judicious application of an NMO may lead to the fabrication of novel biosensing devices with enhanced signal amplifi cation and coding strategies for bioaffi nity assays and effi cient electrical communication with redox biomolecules/ enzymes that may address future diagnostic needs.Th e unique properties of NMOs off er excellent prospects for interfacing biological recognition events with electronic signal transduction and for designing a new generation of bioelectronics devices that may exhibit novel functions. Th e controlled preparation of an NMO is considered to play a signifi cant role in the development of biosensors. Eff orts are being made to explore the prospects and future challenges of NMOs for the development of biosensing devices and the evolution of new strategies for bioaffi nity assays and effi cient electrical communication. In this review, we focus on developments over the past fi ve years in NMO-based biosensors for clinical and non-clinical applications (Figure 2). Fundamentals of nanostructured metal oxides for biosensingAmong the various immobilizing matrices that have been developed, NMOs have exceptional optical and electrical properties due to electron and phonon confi nement, high surface-to-volume ratios, modifi ed surface work function, high surface reaction activity, high catalytic effi ciency and strong adsorption ability. For these reasons, NMOs have been utilized to increase the loading of biomolecules per Nanostructured metal oxide-based b...

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Reduced graphene oxide (RGO) due to its excellent electrochemical properties and large surface area, has recently aroused much interest for electrochemical biosensing application. Here, the chemically active RGO has been synthesized and deposited onto an indium tin oxide (ITO) coated glass substrate by the electrophoretic deposition technique. This novel platform has been utilized for covalent attachment of the monoclonal antibodies of aflatoxin B1 (anti-AFB1) for food toxin (AFB1) detection. The electron microscopy, X-ray diffraction, and UV-visible studies reveal successful synthesis of reduced graphene oxide while the XPS and FTIR studies suggest its carboxylic functionalized nature. The electrochemical sensing results of the anti-AFB1/RGO/ITO based immunoelectrode obtained as a function of aflatoxin concentration show high sensitivity (68 μA ng(-1) mL cm(-2)) and improved detection limit (0.12 ng mL(-1)). The association constant (ka) for antigen-antibody interaction obtained as 5 × 10(-4) ng mL(-1) indicates high affinity of antibodies toward the antigen (AFB1).

L-Cysteine functionalized magnetite nanoparticles (L-Cyst-Fe3O4 NPs) were synthesized by chemical co-precipitation using Fe2+ and Fe3+ as iron precursors, sodium hydroxide as a base and L-Cysteine as functionalized agent. The structural and morphological studies were carried out using X-ray powder diffraction, transmission electron microscopy, dynamic light scattering, scanning electron microscopy and energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and UV-Vis spectrophotometric techniques. The zeta potential of bare Fe3O4 and functionalized L-Cyst-Fe3O4 NPs were +28 mV and −30.2 mV (pH 7.0), respectively. The positive surface charge changes to negative imply the presence of L-Cyst monolayer at particle interface. Band gap energy of 2.12 eV [bare Fe3O4NPs] and 1.4 eV [L-Cyst-Fe3O4 NPs] were obtained. Lead and chromium removal were investigated at different initial pHs, contact time, temperatures and adsorbate-adsorbent concentrations. Maximum Cr6+ and Pb2+ removal occurred at pH 2.0 and 6.0, respectively. Sorption dynamics data were best described by pseudo-second order rate equation. Pb2+ and Cr6+ sorption equilibrium data were best fitted to Langmuir equation. Langmuir adsorption capacities of 18.8 mg/g (Pb2+) and 34.5 mg/g (Cr6+) at 45 °C were obtained. Regeneration of exhausted L-Cyst-Fe3O4 NPs and recovery of Pb2+/Cr6+ were demonstrated using 0.01 M HNO3 and NaOH. L-Cyst-Fe3O4 NPs stability and reusability were also demonstrated.

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