Luminescent optical detection of volatile electron deficient compounds by conjugated polymer nanofibers

Optical detection of volatile electron deficient analytes via fluorescence quenching is demonstrated using ca. 200 nm diameter template-synthesized polyfluorene nanofibers as nanoscale detection elements. Observed trends in analyte quenching effectiveness suggest that, in addition to energetic factors, analyte vapor pressure and polymer/analyte solubility play an important role in the emission quenching process. Individual nanofibers successfully act as luminescent reporters of volatile nitroaromatics at sub-parts per million levels. Geometric factors, relating to the nanocylindrical geometry of the fibers and to low nanofiber substrate coverage, providing a less crowded environment around fibers, appear to play a role in providing access by electron deficient quencher molecules to the excited states within the fibers, thereby facilitating the pronounced fluorescence quenching response

Nonlinear refractive index and three-photon absorption coefficient of poly(9,9-dioctylfluorence)

We investigate the optical Kerr effect and third harmonic generation (THG) arising from chi((3)) of poly(9,9-dioctylfluorence), which is an emerging organic pi-conjugated polymer from the perspective of diverse optoelectronic applications. The measured nonlinear refractive index, obtained with closed-aperture Z-scan, is n(2)=(2.04 +/- 0.10)x10(-12) esu at lambda=1540 nm. Open-aperture Z-scan yields the three-photon absorption coefficient of gamma=(1.88 +/- 0.26)x10(-3) cm(3)/GW(2) at lambda=1064 nm, arising from chi((5)) response. The wavelength-dependent THG indicates that this semiconducting polymer can be a potentially useful polymer system for nonlinear-optics applications involving high-order optical processes in the mid-IR range. (C) 2009 American Institute of Physics. (doi:10.1063/1.3269588

Transparent polymer-based SERS substrates templated by a soda can

This paper demonstrates the reproducible fabrication of transparent Surface Enhanced Raman Scattering (SERS) substrates, fabricated by employing an aluminium soda can to template nanostructures on a flexible thermoplastic polymer surface, followed by deposition of a silver over layer. Electron microscopy and finite element modelling simulations strongly suggested the SERS response arose at regions of high electromagnetic field strength occurring between metallic clusters following illumination by monochromatic radiation. The sensors exhibited rapid, quantitative and high sensitivity, for example, 5 × 10−10 M (204 pg/mL) crystal violet detection in 10 min using a simple drop and dry method. We also show detection of glucose employing a chemically modified silver surface bearing a pre-deposited SAM layer. Furthermore, the transparent substrates permitted back excitation and collection through the substrate with corresponding spectra exhibiting clear and well-defined spectral SERS peaks. Finally, we present the detection of trace amounts of melamine in complex media solution (milk and infant formula). We benchmark the sensor performance using commercial analytical instrumentation (MS-MS) and show comparable sensitivity between the SERS substrates and MS-MS

Elimination of oxygen interference in the electrochemical detection of monochloramine, using in situ pH control at interdigitated electrodes

Disinfection of water systems by chloramination is a method frequently used in North America as an alternative to chlorination. In such a case, monochloramine is used as the primary chlorine source for disinfection. Regular monitoring of the residual concentrations of this species is essential to ensure adequate disinfection. An amperometric sensor for monochloramine would provide fast, reagent-free analysis; however, the presence of dissolved oxygen in water complicates sensor development. In this work, we used in-situ pH control as a method to eliminate oxygen interference by conversion of monochloramine to dichloramine. Unlike monochloramine, the electrochemical reduction of dichloramine occurs outside the oxygen reduction potential window and is therefore not affected by the oxygen concentration. Potential sweep methods were used to investigate the conversion of monochloramine to dichloramine at pH 3. The pH control method was used to calibrate monochloramine concentrations between 1 and 10 ppm, with a detection limit of 0.03 ppm. Tests were carried out in high alkalinity samples, wherein it was found that the sensitivity of this method effectively remained unchanged. Monochloramine was also quantified in the presence of common interferents (copper, phosphate, and iron) which also had no significant impact on the analysis

Removal of dissolved oxygen interference in the amperometric detection of monochloramine using a pH control method

Monochloramine amperometric determination was investigated using a pH control method to eliminate dissolved oxygen as an interferent. This method allowed local pH conditions to become more acidic, causing the production of dichloramine. This species showed an onset of electro-reduction at 450 mV, far outside of the oxygen reduction region. Monochloramine was calibrated using this method and showed good linearity (0.99) and a limit of detection of 0.03 ppm

Redox cycling at interdigitated nanowire electrode arrays: enhanced electrochemical sensing

Interdigitated nanowire arrays can be used to perform generator collector type electrochemical measurements. For this set up, one comb of nanowire arrays are used to perform a standard voltammetric technique while the other comb is biased at a constant potential. This technique gives rise to multiple benefits, most notably enhancement of electrochemical signals due to redox cycling, and reduced diffusional overlap in the electrode arrays. Simulations have been used to optimize the electrode designs and to help understand the processes that occur at the electrode surfaces under these conditions. The combination of experimental and simulation data has led to the optimization of a generator collector system with significant collection efficiencies at a variety of conditions

Nanoimprint lithography-based fabrication of plasmonic array of elliptical nanoholes for dual-wavelength, dual-polarisation refractive index sensing

We report on the novel fabrication and characterisation of plasmonic arrays of elliptical nanohole, and their use for refractive index based sensing. The substrates were fabricated using nanoimprint lithography into a chromium hard mask followed by transfer of the patterns into the underlying gold layer by dry etching—a combination of processes amendable to mass manufacturing. 3D-FDTD simulations were undertaken and showed the transmission spectrum was dependant upon the polarisation of the incident light, with a series of minima that can be attributed to plasmonic effects on the gold/water or gold/substrate interfaces. Each polarisation showed two peaks on the gold/water interface, one in the visible and one in the near-infrared part of the spectrum. Simulated electric field profiles showed that the electric field in the infrared propagates deep in the bulk while the one in the visible was more tightly bound to the surface. Experimental transmission spectra of the fabricated samples showed good agreement with the simulated ones. Bulk refractive index experiments were carried out and sensitivities of 293 nm/RIU and 414 nm/RIU were obtained for the two spectral features of interest when the polarisation was along the long axis of the elliptical nanohole for the visible and infrared features, respectively, and 293 nm/RIU and 323 nm/RIU measured when the polarisation was along the short axis of the nanohole

Diffusion profile simulations and enhanced iron sensing in generator-collector mode at interdigitated nanowire electrode arrays

Gold interdigitated nanowire electrode arrays (INEAs) (∼100 nm wide, ∼50 nm high, ∼45 μm long and ∼500 nm spacing) on a Si/SiO2 chip substrate were fabricated and characterised. Arrays were employed in both non-generator-collector (non-GC) mode (one array electrically connected) and in generator-collector (GC) mode (both arrays electrically connected). In non-GC mode, the individual arrays were confirmed to behave as microelectrodes arising from linear diffusion to the total area of the array. By contrast, in GC-mode, arrays displayed steady-state electrochemical behaviour arising from enhanced diffusion to the nanowires and redox cycling (RC) between adjacent electrodes. Finite element simulations were investigated to explore the effect of altering connected and non-connected electrodes on the diffusional behaviour of the arrays with 500 nm separations. They correlated well with the experimental observations for the influence of the collector electrode potential on redox reactions taking place at the generator for a range of scan rates. The suitability of the gold INEAs towards iron sensing in water is also reported. A calibration curve is obtained for 0.5–40 μM (28–2234 μg L−1) Fe2+ with a limit of detection (LOD) of 0.01 μM (0.6 μg L−1) well below the permitted level in drinking water. Finally, iron determination in tap water using a standard addition technique is presented

Interlaboratory comparison study of the Colony Forming Efficiency assay for assessing cytotoxicity of nanomaterials

Nanotechnology has gained importance in the past years as it provides opportunities for industrial growth and innovation. However, the increasing use of manufactured nanomaterials (NMs) in a number of commercial applications and consumer products raises also safety concerns and questions regarding potential unintended risks to humans and the environment. Since several years the European Commission’s Joint Research Centre (JRC) is putting effort in the development, optimisation and harmonisation of in vitro test methods suitable for screening and hazard assessment of NMs. Work is done in collaboration with international partners, in particular the Organisation for Economic Co-operation and Development (OECD). This report presents the results from an interlaboratory comparison study of the in vitro Colony Forming Efficiency (CFE) cytotoxicity assay performed in the frame of OECD's Working Party of Manufactured Nanomaterials (WPMN). Twelve laboratories from European Commission, France, Italy, Japan, Poland, Republic of Korea, South Africa and Switzerland participated in the study coordinated by JRC. The results show that the CFE assay is a suitable and robust in vitro method to assess cytotoxicity of NMs. The assay protocol is well defined and is easily and reliably transferable to other laboratories. The results obtained show good intra and interlaboratory reproducibility of the assay for both the positive control and the tested nanomaterials. In conclusion the CFE assay can be recommended as a building block of an in vitro testing battery for NMs toxicity assessment. It could be used as a first choice method to define dose-effect relationships for other in vitro assays.JRC.I.4-Nanobioscience