Protein G Iron Oxide Nanoparticles IPG is a group of water soluble iron oxide nanoparticles with amphiphilic polymer coating conjugated to protein G. Their functional group is protein G. The zeta potential of SHS is from -20mV to -40mV. Their organic layers consist of a monolayer of oleic acid and a monolayer of amphiphilic polymer. The thickness of the total organic layers is about 4 nm. The hydrodynamic size of the nanoparticles is about 8-10 nm larger than their inorganic core size measured by TEM. The protein G molecules are covalently linked to the polymer. IPG is very stable in most buffer solutions. IPG can bind to the Fc region of IgG thus present Ab in a directional manner for enhanced signal-to-noise ratio and reproducibility.