Gas response behaviour and photochemistry of borondiketonate in acrylic polymer matrices for sensing applications.

The fluorescent spectra in combination with gas response behavior of acrylic polymers doped with dibenzoyl(methanato)boron difluoride (DBMBF2) were studied by fluorescence spectroscopy and time-resolved fluorescence lifetime. The role of acrylic matrix polarity upon the fluorescence spectra and fluorescence lifetime was analyzed. Changes in emission of the dye doped polymers under exposure to toluene, n-hexane and ethanol were monitored. The fluorescence lifetimes were measured for the singlet excited state as well as the exciplex formed between DBMBF2 and toluene. A reduction of the transition energy to the first singlet-excited state in the four polymers was observed, compared to solution. Reversible exciplex formation, viz. a red shifted fluorescence emission was perceived when exposing the polymers to toluene, while for hexane and ethanol only reversible reduction of the fluorescence occurred. Longer singlet and shorter exciplex lifetimes were observed for non-polar matrixes. The latter mechanism is explained in function of the lower charge transfer character of the exciplex in non-polar matrixes. Additionally, the quantum yield of the dye in the polymer matrix increased almost seventh-fold compared to values for solution.

Flexible biochips for detection of biomolecules.

Miniaturization of biosensors is envisaged by the development of biochips consisting of parallel microarray patterns of binding sites on rigid substrates, such as glass or silicon. Thin plastic substrates are promising flexible alternatives because of the possibility for large-area roll-to-roll manufacturing of disposable chips at lower costs. Mature optical lithography technology faces many challenges when used to pattern flexible foils as a result of the substrate instabilities, especially at higher temperatures. In this work, flexible biochips with gold electrode patterns were fabricated on thin polyethylene naphthalate (PEN) foils using photolithography. The gold electrode structures of the chips were manufactured by direct metal patterning and by lift-off processing. Both methodologies resulted in well-defined electrode patterns as concluded from optical microscopy and scanning electron microscopy (SEM) characterization and resistance measurements. The biochips were successfully employed for the electrical and optical detection of DNA molecules. The DNA detection was based on the immobilization of capture DNA between electrode gaps, hybridization with biotin-labeled target DNA, and enzymatic silver enhancement.

Large area liquid crystal monodomain field-effect transistors.

Butyl, hexyl, and decyl derivatives of the liquid-crystalline organic semiconductor 5,5' '-bis(5-alkyl-2-thienylethynyl)-2,2':5',2' '-terthiophene were synthesized and studied with respect to their structural, optical, and electrical properties. By means of an optimized thermal annealing scheme the hexyl and decyl compounds could be processed into self-assembled monodomain films of up to 150 mm in diameter. These were investigated with X-ray diffractometry, which revealed a clearly single-crystalline monoclinic morphology with lamellae parallel to the substrate. Within the lamellae the molecules were found to arrange with a tilt of about 50 degrees with the rubbing direction of the polyimide alignment layer. The resulting, close side-to-side packing was confirmed by measurements of the UV/vis absorption, which showed a dichroic ratio of 19 and indicated H-aggregation. AFM analyses revealed self-affinity in the surface roughness of the monodomain. The compounds showed bipolar charge transport in TOF measurements, with hole mobilities reaching up to 0.02 cm(2)/Vs and maximum electron mobilities around 0.002 cm(2)/Vs. The hexyl derivative was processed into large-area monodomain top-gate field-effect transistors, which were stable for months and showed anisotropic hole mobilities of up to 0.02 cm(2)/Vs. Compared to multidomain bottom-gate transistors the monodomain formation allowed for a mobility increase by 1 order of magnitude.