Magnetic colloids for the generic capture of viruses

In molecular biology or in the diagnostic field, a strong interest has been devoted to the use of magnetic nanoparticles as an efficient tool for a fast and easy biomolecule extraction. Various methods allow the synthesis of numerous types of magnetic particles, but very few of them can be adapted to biological protocols. For biological tests based on the final detection of nucleic acids, the major difficulties in the choice of these magnetic beads are their fast magnetic separation, requiring a high magnetic oxide content and overall a good compatibility with enzymes used for nucleic acid amplification. In this study, magnetic colloids were obtained from oil in water (o/w) magnetic emulsion by a two-step polymer immobilization procedure. First, a polycation, poly(ethyleneimine), was adsorbed to ensure charge inversion of the emulsion droplets. Then poly(maleic anhydride-co-methyl vinyl ether) was either chemically grafted or adsorbed if under its hydrolyzed form. The obtained colloids were characterized in terms of colloidal stability, surface charge density, and morphology and were evaluated in a reverse transcription-PCR (RT-PCR) inhibition test. Selected colloids were used for the nonspecific capture of viruses, with RT-PCR being used as a means of detection. Particle size and charge studies allowed us to follow each step of their synthesis, showing the relevance of these methods. The prepared magnetic particles exhibit a good RT-PCR compatibility when used in the range of 5-40 microg in the 50 microl amplification mix. Finally, virus capture tests revealed a capture efficiency of 90% with an average detection sensitivity of 10(3)pfu/ml.