Magnetite nanoparticles (MNPs) are quite preferable material for different bioassays because of their quite low toxicity both for cells and for mammals and big variety of their surface functionalization approaches. We have synthesized MNPs via simple and convenient co-precipitation method with preliminary filtration of FeCl₂ and FeCl₃ solution, under argon atmosphere and non-magnetic stirring. MNPs were citrate-stabilized and then modified stage-by-stage with tetraethoxysilane (TEOS), (3-Aminopropyl)triethoxysilane (APTES) and acylated with succinic anhydride resulting in carboxylated MNPs. Carboxylated MNPs were covalently bounded with folic acid antibody (FA-1) via 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). MNP-EDC-FA-1 were passed through test-stripe with the line containing folic acid-gelatin conjugate. The conjugation of MNP-EDC-FA-1 with folic acid was observed visually, and the magnetic signal distribution was scanned through the test-stripe with magnetic particle quantification technique (MPQ) developed earlier. Visually, the line with folic acid-gelatin conjugate on the test-stripe has turned dark, with color intensity strongly depending on MNP-EDC-FA-1 concentration. MPQ has shown that the great majority of MNP-EDC-FA-1 was bounded with acid-gelatin conjugate. MPQ technique allowed quantifying down to 5 ng of MNP-EDC-FA-1 in this experiment with MNPs synthesized, with strong peak at the acid-gelatin conjugate line.