Abstract The binding of 5′-end biotinylated DNA fragments was compared between streptavidin (SA)-coated commercial. M-280 magnetic latex particles with a diameter of 2.8 μm and adsorption-coated polystyrene (PS) latex standard particles whose diameter is 0.272 μm. Amino acid analysis showed the protein content of the commercial particles to correspond to 4× monolayer coverage, while the adsorption-coated PS particles displayed monolayer coverage, or 8 pmol/cm 2. A fluorescence-based method was developed to quantify the adsorption of FITC-labeled SA, biotin, and biotinylated DNA. The validity of the method was substantiated for the labeled protein by both amino acid analysis and a colorimetric protein assay. While the specific binding of biotin was 0.38 mol per mole of SA on the adsorption-coated 0.272-μm particles and slightly higher (0.6 mol per mole SA) on the 2.8-μm particles, the specific binding of the bulky biotinylated 300-bp DNA was more favorable on the smaller particle (0.12 mol per mole SA for 0.272 μm versus 0.04 mol per mole SA for 2.8 μm).