Narrowly size-distributed functionalized magnetic emulsions with diameters between 200 and 300 nm bearing reactive amine or carboxylic groups were prepared respectively via single adsorption or layer-by-layer adsorption process. The colloidal stability of the functionalized magnetic emulsion was related to the polymer adsorbed amount and to the adsorption methodology. The single adsorption of poly(ethyleneimine) onto negatively charged magnetic emulsion led to amino-containing magnetic nanodroplets for nucleic acid extraction, concentration and amplification. The enzymatic amplification of adsorbed nucleic acid molecules (i.e. RNA) was found to be related to both initial nucleic acid concentration and the used magnetic particles in the amplification step. The undesirable inhibition phenomena observed in the enzymatic amplification (i.e. RT-PCR) process was eliminated by the addition of appropriate negatively charged polyelectrolyte before the amplification step. The encapsulation of magnetic emulsion via layer-by-layer polyelectrolytes adsorption process was used to elaborate functionalized core-shell magnetic colloids. The characterized final magnetic dispersions were evaluated in specific nucleic acids capture and detection, and in proteins immobilization process.