Abstract: The need for more advanced, accurate and lower cost sensor platforms is constantly growing. However, for certain applications the already existing sensing systems based on biological recognition elements have sometimes restrictions, which limit their use. As a result, sensors with synthetic recognition elements, such as molecular imprinted polymers (MIPs), can be interesting alternatives. Molecular imprinting leads to the formation of inert polymer particles with nanocavities, which can exhibit similar selectivity and specificity to target molecules as' antibodies or enzymes. It is demonstrated that MIPs can be readily incorporated into two different sensor platforms for the detection of histamine in aqueous media. The first platform is based on electrochemical impedance spectroscopy and allows for the accurate detection of histamine in the nanomolar range. The second sensing technique is based on microgravimetry and allows for the detection of histamine in the micromolar range. Using the analogous molecule histidine, it is demonstrated that both sensor platforms are specific for the detection of histamine. (C) 2010 Elsevier B.V. All rights reserved.
Abstract: A new impedeance spectroscopy unit is developed fully customized to become a vital part of label free biosensor arrays with possible applications in DNA and protein sensing Test measurements are conducted to expolre the accuracy and specificity of the system, both under electronic lab conditions as well as under wet cell conditions with synthetic-diamond based sensor electrodes. The impedance of seven resistors was monitored for 17h and a maximum error <0.02% was found, Furthermore the impedance of PBS at different concentrations was monitored for 60 min per concentration and a different impedance for each concentration on was detected. The impedance is also monitored for NaOH, PBs and nuclease free water at different temperatures with a total duration of 60 min per fluid. Systematically different impedances for each temperature per fluid were found and the temperature coefficients were determined. All test measurements lead to results well with in specification.(C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Abstract: In search for a better way to monitor the hybridization and denaturation of DNA onto a diamond based sensor, precise knowledge about the conditions of the immediate surroundings is very critical. One of the factors that have a great influence on the stability of the measurements is the temperature of the liquid environment in which these measurements take place. With this as a focal point, the design of a precise temperature regulator based on a boron doped diamond thin film is a key factor to achieve accurate measurements on a standalone basis. In this work temperature control is achieved making use of a thin boron doped nanocrystalline diamond (B-NCD) film, which, in combination with a proportional-integral-derivative-control (PID), is able to maintain a stable temperature with an accuracy better than 0.1 degrees C. By letting the B-NCD-layer act as a resistor together with the appropriate control it is possible to maintain a stable temperature in a range going from room temperature till 70 degrees C, with an accuracy exceeding a temperature variation 0.1 degrees C. The first prototype makes use of a reference temperature sensor, to verify the accuracy of the results. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Abstract: Mimicking the selectivity and sensitivity of biological systems for sensor devices is of increasing interest in biomedical, environmental and chemical analysis. Synthetic materials with imprinted nanocavities, acting as highly selective artificial receptors, are a tailor-made solution in obtaining such a sensor. Incorporation of such molecularly imprinted polymers (MIPs) in a platform suitable for electrochemical measurements, can offer high sensitivity together with device miniaturization and an electronic read-out. As a proof of principle, a MIP-based sensor for L-nicotine has been developed. To this end, the molecular structure of L-nicotine was imprinted in a polymer matrix of polymethacrylic acid (PMAA). Subsequently, microparticles of the imprinted polymer were immobilized on thin films of the conjugated polymer OC1C10-PPV These films were incorporated in an impedimetric sensing device. Using electrochemical impedance spectroscopy, the real part of the impedance was monitored for various concentrations. This setup allows for the detection of L-nicotine from 1 to 10 nM and is insensitive for the resembling molecule L-cotinine. (C) 2007 Elsevier B.V. All rights reserved.
Abstract: In the work reported here, we investigated the interaction between the semiconducting polymer MDMO-PPV and antibodies against the fluorescent dyes fluorescein isothiocyanate (FITC) and Cy5. The antibodies are adsorbed physically onto thin polymer films on gold electrodes, as seen in AFM images of these films. By tuning the antibody concentration, the contact angle of distilled water with the film can be made to vary between 95 degrees and 50 degrees, showing that different surface densities of antibody can be obtained. That these biosensor films specifically bind their antigenic fluorescent molecules from PBS buffer solution is demonstrated by confocal fluorescence microscopy. Specific antigen-antibody recognition is demonstrated by lack of cross-sensitivity between the two antibodies and their antigens. In a biosensor prototype based on differential impedance spectroscopy, these polymer films show a clear response to 1 ppb antigen solution, with a time constant of 2-3 min. (c) 2004 Elsevier B.V. All rights reserved.
Abstract: We studied the stability of metal/polymer interfaces by measuring the diffusion of calcium into a polymer (OC1C10 PPV) layer during and after deposition of the metal using low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). During deposition the calcium diffusion depth in the PPV was found to be comparable for untreated samples and samples prepared in oxygen ambient (10(-7) mbar). In both cases diffusion depths up to similar to7 nm were observed. For PPV layers treated with atomic oxygen, the diffusion depth during deposition was slightly smaller. After deposition, it was observed that calcium diffusion in OC1C10 PPV continues for several hours. When oxygen was present during calcium deposition or during the spin coating of the PPV, the diffusion coefficient for calcium in PPV was decreased considerably. In these cases accumulation of oxygen (adsorbed in the PPV during deposition or spin coating) at the calcium/PPV interface continued for several hours after deposition. Treatment of the PPV with atomic oxygen before calcium deposition resulted in a strong decrease of the calcium diffusion coefficient after deposition. From XPS measurements it was observed that calcium interacts with the chemically bonded oxygen in the PPV and also with the oxygen absorbed in the PPV layer. It can be concluded that oxygen, either chemically bonded to the PPV chain or adsorbed in the film, reduces the calcium diffusion coefficient. The initial performance of PLEDs with atomic oxygen treated PPV layers and PLEDs with calcium deposited in oxygen ambient was worse than the performance of untreated devices, but the stability in the life-test was better. (C) 2004 Elsevier B.V. All rights reserved.
