Prion diseases are a group of fatal neurodegenerative disorders that include  scrapie in sheep , bovine spongiform encephalopathy, Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheineker  diseases in humans . It is suggested that the main reason of these diseases  is asssociated with the  conversion of the  cellular  prion proteins (PrP^C) into their misfolded  pathogenic isoform PrP^Sc. The accumulation of PrP^Sc   in the central nervous system is the common feature of the prion diseases. So far there is no available effective ante mortem test of the presence of PrP^Sc. At the same time, possibility of early diagnosis of prion disease could increase effectivity of the therapy. We therefore focused our work on development biosensors for detection prion proteins. For this purpose we used mass-sensitive affinity sensor based on quartz crystal microbalance (QCM).

Because PrP^Sc is highly infectious compound, we have focused on PrP^C detection. The methods of detection of PrP^SC and PrP^C is, however analogical. The differences consists in using different antibodies. The PrP^C specific antibodies PRI308 that selective bind to 106-126 amino acid residues of recombinat PrP^C (recPrP) have been immobilised on a surface formed by mixture of with covalently attached neutravidin and tightly adsorbed biotinylated protein A. The protein A due to its natural afinity towards the Fc region of antibodies was used for the oriented immobilization of antibodies. We have shown, that QCM biosensor allowing to detect recPrP with detection limit 4.4 nM, which is sufficient for detection PrP^C in blood (physiological concentrations 20 nM). However further effort would be necessary for development more sensitive method that will allow to detect trace concentration of PrP^Sc. These experiments are in progress.Time dependent AFM images performed in solution during interaction of recPrP with the PRI308 suggest that the surface roughness changed during the immobilization process. The integrity of the layer was investigated by cyclic voltammetry at the presence of redox couple Fe(CN)₆^4-/3-. These measurements indicate that the sensitive layer with the PRI 308 is practically impermeable for redox probe species. 

Acknowledgements. This work was financially supported by European Commission under 6 FP program NoE NeuroPrion (Contract No. FOOD-CT-2004-506579), by Agency for Promotion Research and Development under the contract No. APVV-0362-07 and by Slovak Grant Agency (Projects No. 2/7134/27, VVCE-0064-07  and 1/4016/07 to T.H).

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