Recognizing and quantifying specific biomolecules in aqueous samples are constantly needed in research and diagnostic laboratories. As the typical detection procedures are rather lengthy and involve the use of labeled secondary antibodies or other agents to provide a signal, efforts have been made over the last 10 y to develop alternative label-free methods that enable direct detection. We propose and demonstrate an extremely simple, lowcost, label-free biodetector based on measuring the intensity of light reflected by the interface between a fluid sample and an amorphous fluoropolymer substrate having a refractive index very close to that of water and hosting various antibodies immobilized in spots. Under these index-matching conditions, the amount of light reflected by the interface allows straightforward quantification of the amount of antigen binding to each spot. Using antibodies targeting heterologous immunoglobulins and antigens commonly used as markers for diagnoses of hepatitis B and HIV, we demonstrate the limit of detection of a few picograms per square millimeter of surface-bound molecules. We also show that direct and real-time access to the amount of binding molecules allows the precise extrapolation of adhesion rates, from which the concentrations of antigens in solution can be estimated down to fractions of nanograms per milliliter.immunoassay | optical biosensor | protein microarray | biomolecular detection | reflective phantom interface
A series of segmented polyurethanes obtained from perfluoropolyether (PFPE) and isophorone diisocyanate (IPDI) were studied by using quantitative thermal analysis. The glass transition behavior of the segregated phases of the segmented copolymers, compared to the corresponding amorphous homopolymers, was characterized in order to determine the dependence of the phase separation on the composition. The glass transition was observed to shift and broaden for both the hydrogenated and the fluorinated phase, reducing the corresponding content in the polymer, and the measured ∆cp on the segregated phases deviates from the expected ones according to the homopolymer values. To investigate the effects of the size of the separated domains and of the interfacial constraints on the glass transition behavior, heat capacity measurements were carried out on PFPE models with perfluorinated or methilolic chain ends absorbed on amorphous silica. The chain mobility reduction associated with a nanoscopic confinement is responsible for the effects on the glass transition measured by DSC. This phenomenon seems to rule the observed similar behavior within the polyurethane series investigated in the present work.
Ten model coatings, selected and obtained from a family of fluorinated resins synthesized by the reaction of perfluoroether oligomeric diols of different molecular weights with polyisocyanurates of hexamethylenediisocyanate (HDI) and isophoronediisocyanate (IPDI), were characterized with differential scanning calorimetry, mechanical testing, and electrochemical impedance spectroscopy measurements. The electrochemical and chemico-physical measurements show that the glass-transition temperature of the starting isocyanate trimers greatly influences the properties of the final urethane coatings; the IPDI trimer gives harder coatings with lower water permeabilities than the corresponding HDI-based materials. Moreover, for each class of materials (from IPDI or HDI), the fluorine content plays a relevant role: the higher the fluorine percentage, the lower the water absorption into the coatings. Furthermore, the chain length of the polyols used for the synthesis of the prepolymers is a variable that exhibits great influence on the coating properties: coatings containing shorter perfluoropolyether segments show better barrier properties. orinated polyether to the cyclic trimers (polyisocyanurates) of hexamethylenediisocyanate (HDI) or isophoronediisocyanate (IPDI). The prepolymers can be self-cured by exposure to atmospheric moisture [monocomponent (MC), moisture-curing formulations] or crosslinked by the addition of stoichiometric amounts of ZDOL polyethers [BC (bicomponent) formulations]. Several properties of this new class of materials have been recently described, 1 including electrochemical impedance for TiO 2 -pigmented coatings. 2 PFPE coatings are characterized by high durability and peculiar surface properties and so are very interesting candidates for developing new anticorrosive protective systems for steel, concrete, and other engineering materials. As a matter of fact, the water permeability and barrier behavior of coating systems containing PFPE may depend
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