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...

Nanocrystalline films of Au, Ag, and Cu have been prepared at the toluene-water interface by the interaction of metal-triphenylphosphine complexes in the organic layer with partially hydrolyzed tetrakishydroxymethylphosphonium chloride in the aqueous layer. The nanocrystals have been characterized by a host of microscopic and spectroscopic techniques. The free-standing films could be transferred from the interface onto solid supports. Furthermore, films could be dissolved to yield either a hydrosol or an organosol with the help of appropriate surfactants.

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There is a growing demand to integrate biosensors with microfluidics to provide miniaturized platforms with many favorable properties, such as reduced sample volume, decreased processing time, low cost analysis and low reagent consumption. These microfluidics-integrated biosensors would also have numerous advantages such as laminar flow, minimal handling of hazardous materials, multiple sample detection in parallel, portability and versatility in design. Microfluidics involves the science and technology of manipulation of fluids at the micro- to nano-liter level. It is predicted that combining biosensors with microfluidic chips will yield enhanced analytical capability, and widen the possibilities for applications in clinical diagnostics. The recent developments in microfluidics have helped researchers working in industries and educational institutes to adopt some of these platforms for point-of-care (POC) diagnostics. This review focuses on the latest advancements in the fields of microfluidic biosensing technologies, and on the challenges and possible solutions for translation of this technology for POC diagnostic applications. We also discuss the fabrication techniques required for developing microfluidic-integrated biosensors, recently reported biomarkers, and the prospects of POC diagnostics in the medical industry.

ABSTRACT:The surface modified and aligned mesoporous anatase titania nanofiber mats (TiO 2 −NF) have been fabricated by electrospinning for esterified cholesterol detection by electrochemical technique. The electrospinning and porosity of mesoporous TiO 2 −NF were controlled by use of polyvinylpyrrolidone (PVP) as a sacrificial carrier polymer in the titanium isopropoxide precursor. The mesoporous TiO 2 − NF of diameters ranging from 30 to 60 nm were obtained by calcination at 470°C and partially aligned on a rotating drum collector. The functional groups such as −COOH, −CHO etc. were introduced on TiO 2 −NF surface via oxygen plasma treatment making the surface hydrophilic. Cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) were covalently immobilized on the plasma treated surface of NF (cTiO 2 −NF) via N-ethyl-N0-(3-dimethylaminopropyl carbodiimide) and N-hydroxysuccinimide (EDC-NHS) chemistry. The high mesoporosity (∼61%) of the fibrous film allowed enhanced loading of the enzyme molecules in the TiO 2 −NF mat. The ChEt-ChOx/cTiO 2 −NF-based bioelectrode was used to detect esterified cholesterol using electrochemical technique. The high aspect ratio, surface area of aligned TiO 2 −NF showed excellent voltammetric and catalytic response resulting in improved detection limit (0.49 mM). The results of response studies of this biosensor show excellent sensitivity (181.6 μA/mg dL −1 /cm 2 ) and rapid detection (20 s). This proposed strategy of biomolecule detection is thus a promising platform for the development of miniaturized device for biosensing applications.

Ionic liquids (ILs) are important for their antimicrobial activity and are found to be toxic to some microorganisms. To shed light on the mechanism of their activities, the interaction of an imidazolium-based IL 1-butyl-3-methylimidazolium tetrfluoroborate ([BMIM][BF]) with E. coli bacteria and cell-membrane-mimicking lipid mono- and bilayers has been studied. The survival of the bacteria and corresponding growth inhibition are observed to be functions of the concentration of the IL. The IL alters the pressure-area isotherm of the monolayer formed at an air-water interface by the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid. The in-plane elasticity of the lipid layer is reduced as a consequence of the insertion of this IL. The X-ray reflectivity study from a polymer-supported lipid bilayer shows strong perturbation in the self-assembled structure of the bilayer due to the interaction. As a consequence, there is a considerable decrease in bilayer thickness and a corresponding increase in electron density. These results, however, depend on the chain configurations of the lipid molecules.

Ultrathin nanocrystalline films of gold formed at different temperatures at the organic-aqueous interface have been investigated by X-ray diffraction, electron microscopy, atomic force microscopy, and electronic spectroscopy. The films are smooth and continuous over relatively large length scales and are generally approximately 100 nm thick. The size of the nanocrystals is sensitive to the reaction temperature, which also determines whether the film is metallic or an activated conductor. The surface plasmon band of gold is highly red-shifted in the films. Alkanethiols perturb the structure of the films, with the magnitude of the effect depending on the chain length. Accordingly, the position of the plasmon band and the electrical resistance of the films are affected by interaction with alkanethiols; the plasmon band approaches that of isolated nanocrystals in the presence of long-chain thiols.

The behavior of mixed-ligand-coated gold nanoparticles at a liquid-liquid interface during compression has been investigated. The system was characterized by measuring pressure-area isotherms and by simultaneously performing in situ X-ray studies. Additionally, Monte Carlo (MC) simulations were carried out in order to interpret the experimental findings. With this dual approach it was possible to characterize and identify the different stages of compression and understand what happens microscopically: first, a compression purely in-plane, and, second, the formation of a second layer when the in-plane pressure pushes the particles out of the plane. The first stage is accompanied by the emergence of an in-plane correlation peak in the scattering signal and a strong increase of the pressure in the isotherm. The second stage is characterized by the weakening of the correlation peak and a slower increase in pressure.