One-dimensional (1D) nanostructures based on organic materials are attracting significant research interest owing to the many novel chemical, physical, and electronic properties that may arise in such systems and the possibility of exploiting these properties in a variety of applications. [1,2] In particular, the potential of semiconducting polymer nanowires has already been explored for initial demonstration of nanoscale electronic and photonic devices such as field-effect transistors, [3] field emitters, [4] and sub-wavelength active waveguides, [5] optically pumped lasers, [6] photodetectors [7] and electroluminescent diodes. [8] However, for 1D nanostructures in general, a key challenge is the development of new approaches that will permit controlled anisotropic alignment of nanowires and nanotubes and, preferably, also enable dynamic manipulation of their orientation in real time.In this regard, nematic liquid crystal (LC) materials have long been employed as anisotropic solvents for orientation of non-spherical guests. They are excellent hosts for spectroscopic studies both of the anisotropy of the optical and electronic properties of aligned guest molecules, [9] and of the nature of energy and charge-transfer processes occurring within guests.[10] The anisotropic optical properties of oriented guests may also be combined with the dynamic switchabilty of LCs to realize reconfigurable photonic devices. Electric field switching of the alignment of small organic molecules in LC hosts was proposed as far back as 1968 and 1973 for realization of single layer pleochroic colored [11] and fluorescent [12] displays, respectively. More recently, nematic LCs have been employed to demonstrate optical absorption and photoluminescence (PL) dichroism in oligothiophene [13,14] and poly(phenylene vinylene)-type [15,16] guests. By electric field assisted reorientation of the oligothiophenes in particular, a switchable polarized PL contrast was achieved. [13,14] Alignment of carbon nanotubes in nematic LC hosts has also permitted optical transmission modulation by electric field switching [17] and electrical conductance modulation by either electric [18] or magnetic [19] field switching.In this Communication, we demonstrate the alignment and dynamic manipulation of novel conjugated polymer nanowires in a nematic LC host. A low-molecular-weight, room temperature nematic LC material, E7, is employed as the host matrix. The guest nanowires are composed of poly(9,9-dioctylfluorenyl-2,7-diyl), PFO, a highly efficient blueemitting, semiconducting polymer with good thermal and oxidative stability, and are synthesized using a template method.[20] Initial single wire optical spectroscopic studies yield well-resolved PL spectra characteristic of PFO b-phase, in which polymer chain segments adopt a planarized and extended conformation. Importantly, nanowire PL emission is also found to be axially polarized, consistent with internal alignment of b-phase strands during synthesis. Incorporation of nanowires into the E7 host results in stro...
Quantitative point-of-care (POC) devices are the next generation for serological disease diagnosis. Whilst pathogen serology is typically performed by centralized laboratories using Enzyme-Linked ImmunoSorbent Assay (ELISA), faster on-site diagnosis would infer improved disease management and treatment decisions. Using the model pathogen Bovine Herpes Virus-1 (BHV-1) this study employs an extended-gate field-effect transistor (FET) for direct potentiometric serological diagnosis. BHV-1 is a major viral pathogen of Bovine Respiratory Disease (BRD), the leading cause of economic loss ($2 billion annually in the US only) to the cattle and dairy industry. To demonstrate the sensor capabilities as a diagnostic tool, BHV-1 viral protein gE was expressed and immobilized on the sensor surface to serve as a capture antigen for a BHV-1-specific antibody (anti-gE), produced in cattle in response to viral infection. The gE-coated immunosensor was shown to be highly sensitive and selective to anti-gE present in commercially available anti-BHV-1 antiserum and in real serum samples from cattle with results being in excellent agreement with Surface Plasmon Resonance (SPR) and ELISA. The FET sensor is significantly faster than ELISA (<10 min), a crucial factor for successful disease intervention. This sensor technology is versatile, amenable to multiplexing, easily integrated to POC devices, and has the potential to impact a wide range of human and animal diseases.
Polyfluorene nanotubes are synthesized by solution assisted wetting of porous anodic alumina membranes. Well aligned arrays of close packed (∼109 tubes/cm−2) discrete nanotubes are obtained. Individual tubes have diameters of ∼260 nm and wall thicknesses of ∼50 nm. X-ray diffraction measurements carried out on nanotube arrays embedded in host templates indicate a polymer chain alignment along the long axes of the template pores and, as a result, along the long axes of the nanotubes themselves. Optical spectroscopic studies of mats of nanotubes on glass substrates yield well resolved emission spectra reflecting a narrowed distribution of emitting chain segments with increased effective conjugation lengths. The data indicate intrachain reorientation of the amorphous random poly(9,9-dioctylfluorene-2,7-diyl) molecular conformation to the more planar (low energy) extended 21 helical β-phase conformation within the tubes. Raman spectra acquired for template embedded tubes are also consistent with β-phase formation. Finally, polarization resolved photoluminescence data demonstrate a pronounced axial orientation of the emissive β-phase chains within the tubes.
Residual free-chlorine concentration in water supplies is a key metric studied to ensure disinfection. High residual chlorine concentrations lead to unpleasant odours and tastes, while low concentrations may lead to inadequate disinfection. The concentration is most commonly monitored using colorimetric techniques which require additional reagents. Electrochemical analysis offers the possibility for in-line analysis without the need for additional reagents. Electrochemical-based detection of chlorine is influenced by the solution pH, which defines the particular chlorine ionic species present in solution. As such, controlling the pH is essential to enable electrochemical based detection of residual chlorine in water. To this end, we explore the application of solid state interdigitated electrodes to tailor the in-situ pH of a solution while simultaneously detecting free-chlorine. Finite element simulations and subsequent electrochemical characterization, using gold interdigitated microelectrode arrays, were employed to explore the feasibility of an in-situ pH control approach. In practice, the approach converted residual chlorine from an initial mixture of two species (hypochlorous acid and hypochlorite ion), to one species (hypochlorous acid). Chlorine detection was shown in water samples using this exploratory method, resulting in a twofold increase in signal response, compared to measurements without pH control. Finally, tap water samples were measured using the in-situ pH control method and the results showed excellent correlation (within experimental error) with a commercial instrument, demonstrating the efficacy of the developed technique. This work establishes the possibility of deploying an electrochemical based reagent-free, in-line chlorine sensor required for water distribution networks.
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