Polymer modified paper - reducing sensitivity losses in paper-based analytical devices

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The fibrous structure of paper allows for the transport of aqueous solutions through capillary action. Thus, paper makes the generation of microfluidic devices possible, which do not re-quire any pumps for fluid movement. However, despite huge efforts, as of today only rather simple diagnostic devices based on paperstrips have been realized. A main reason for this is that for paperbased diagostics even today a large number of very fundamental problems re-main unsolved and strong losses of the sensitivity are observed when standard immunodiag-nostic processes are transferred to paper-based devices These sensitivity losses are mainly caused by light scattering during optical detection and unspecific adsorption of analytes to the highly polar paper fibers. To address these problems it is proposed in this research project to modify the paper fibers with polymers, which are covalently attached to the fiber surface by C,H-insertion reactions. This enables on the one hand generation of hydrophobic barriers for the fluidic layout, on the other hand allows coating of the paper fibers with protein repellent polymer. This would minimize the non-specific adsorption and accordingly retention of an ana-lyte (e.g. protein) transported through the channel by capillary action. Ideally, the non-specific adsorption would be totally suppressed. The investigation of the retention will be carried out in situ using microscopy techniques. Finally, it is planned that a third class of polymers will be deposited in selected areas of the channel. These molecules will be covalently attached to the fibers during a hot stamping step. These polymers will allow a spatially controlled modification of the paper with probe molecules, which will be studied subsequently in model reactions by means of immunological methods. Due to the fact that the immobilization reaction occurs close to the surface and the modification of the fibers will be carried out the an (almost) isore-fractive material, light scattering will be strongly attenuated and the sensitivity of the sensor will be correspondingly enhanced compared to read-out of standard paper-based analytical processes.