Nucant multivalent pseudopeptide labeled with Alexa Fluor 546 (N6L-AF546) and doxorubicin (DOX) were slowly released from magnetic nanoparticles (MNP) in the presence of salts. Release behavior of the electrostatically immobilized molecules was studied by dispersing: a MF66-N6L-AF546, b MF66-DOX, c MF66-DOXN6L-AF546 in water (blue), PBS buffer (pH 7.4) (red) or phenol-red-free complete DMEM (green). Plain lines represent the release of DOX and dashed lines represent the release of N6L-AF546. Samples were incubated at 37°C and at different times supernatants were analyzed by fluorescence (Dox λexc = 495 nm, λem = 600 nm and N6L-AF546 λexc = 555 nm, λem = 575 nm; for MF66-DOXN6L-AF546 each emission signal was corrected for the fluorescence of the other immobilized molecule). Values were compared to a reference sample containing the total amount of the corresponding molecule immobilized on the MNP.