Bare and surface modified polystyrene nanoparticles with an anionic sulfate end group were synthesized by emulsion polymerization for adsorption of a protein (immunoglobulin G, IgG) by passive adsorption and electrostatic attraction for application as a biosensor. Dynamic light scattering (DLS) measurements confirmed the formation of an IgG-polystyrene latex complex, showing increased hydrodynamic diameter (D(h)) of approximately 178 nm (passive adsorption) and approximately 220 nm (electrostatic attraction) after IgG adsorption. An increased Zeta (zeta) potential value from -38.8 mV to -3.84 mV following IgG adsorption by electrostatic attraction also reflected the formation of the IgG-polystyrene latex complex. Solid phase immunodetection results demonstrated the formation of the IgG-polystyrene latex complex by showing fluorescent signals induced by FITC, which conjugated to IgG on the surface of the polystyrene. In addition, immunoassay results showed that adsorbed IgG on the polystyrene latex surface was not desorbed and maintained immunoreactivity after 1 month from the initial IgG-polystyrene latex complex formation.