No abstract

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).

As-deposited sol-gel derived amorphous tungsten oxide films transform into nanostructured films with an interconnected framework of grains and pores and a dominant triclinic crystalline phase upon annealing at 250°C. Transmission electron microscopy and scanning electron microscopy images clearly reveal the annealing-induced microstructural evolution for the film. Subsequent to lithium intercalation, the film annealed at 250°C shows quasi-reversible structural changes, as ascertained by X-ray diffraction and Fourier transform infrared spectral data. Dynamic transmission modulation for film revealed a high optical modulation of 72% ͑ = 650 nm͒ and a coloration efficiency maximum of 132 cm 2 C −1 at 800 nm under a lithium intercalation level of x = 0.20. X-ray photoelectron spectroscopy of the W 4f core levels demonstrated a progressive increase in the W 5+ content at the expense of W 6+ proportion as the insertion coefficient was raised from 0 to 0.25, with 0.20 as the threshold value above which the W 5+ content exceeds the W 6+ proportion. A new W 4+ state also appears which acts to lower the coloration efficiency for x ജ 0.22. The presence of charged oxygen interstitials in the vicinity of electrochemically active tungsten sites is also responsible for the coloration efficiency decline at high ion insertion levels.

Composite thin films of poly(3,4-ethylenedioxythiophene) (PEDOT)-enwrapped functionalized multiwalled carbon nanotubes (MWCNTs) have been synthesized over multiple length scales by electropolymerization of the monomer without the use of any other supporting electrolyte. The functionalized MWCNTs are incorporated into the positively charged polymer deposit as counterions during oxidative electropolymerization. The morphology, electrochemistry, and electrochromism of the PEDOT-MWCNT films have been compared with those of control PEDOT films doped by triflate ions. Such a comparison enabled us to demonstrate the profound effect of MWCNTs as counterions, realized in terms of better electropolymerization rate, higher conductivity, faster color-bleach kinetics, higher charge storage capacity, and substantially amplified coloration efficiency (eta = 414 cm(2) C(-1), lambda(max) = 575 nm, E = -1.5 V) in comparison to the values of eta reported to date for PEDOT. The strong interaction between the polymer and MWCNTs, the interconnected nanotubular structures, and the porous framework of the film allow facile charge transport and larger ion uptake during redox switching. Electrochemical investigations on devices based on PEDOT-MWCNT and control PEDOT films established the practical utility of PEDOT-MWCNT films as they show lower charge-transfer resistance, higher diffusional capacitance, and a much smaller amplitude of impedance as compared to control PEDOT films.

Nanocomposite assemblies of poly(3,4-ethylenedioxythiophene) (PEDOT), embedded with (a) fluoro alkyl phosphate based ionic liquid functionalized graphene (ILFG) and (b) reduced graphene oxide (RGO) prepared from a modified Hummers' method, have been synthesized. Defect free graphene nanosheets within the size of a few nanometers were achieved in the PEDOT-ILFG nanocomposite. In contrast, structures comprising graphene oxide wrinkles interspersed with the amorphous polymer were obtained in the PEDOT-RGO nanocomposite. X-ray photoelectron spectroscopy showed that neat ILFG was considerably less oxidized as compared to the neat RGO, which ratified the superiority of the ionic liquid functionalization strategy over the conventional chemical approach, for exfoliating graphite. Substantially higher electrochemical activity, improved ionic/electronic conductivity, much faster switching rates, and an almost ballistic enhancement in the electrochromic coloration efficiency attained for the PEDOT-ILFG nanocomposite in comparison to PEDOT-RGO film were irrefutable proofs that demonstrated the ability of the ionic liquid to not only fortify the structure of graphene but also facilitate charge transport through the bulk of the film, by providing less impeded pathways. Since PEDOT-ILFG/-RGO nanocomposites of good uniformity have been achieved, this, to some extent, addresses the challenge associated with the processing of graphene based high performance materials for practical applications.