Iron oxide nanoparticles are magnetic single crystals and can be used as magnetic resonance imaging contrast reagents for in-vivo imaging , drug delivery vehicle, hyperthermia genertor for therapy, adjuvant for vaccine, and magnetic sensing probe for in-vitro diagnostics. These amine terminated iron oxide nanocrystals of various diameters (10 nm-30 nm) are now available in an easy-to-use kit format to enable researchers to conjugate proteins/ligands of their own choice to these iron oxide nanoparticles. The kit is used to specifically conjugate iron oxide nanoparticles and thiol containing ligands with low non-specific binding. It contains sufficient reagents & components for performing 5 conjugation reactions using 1 mg iron oxide nanoparticles per reaction. The iron oxide nanoparticles are activated using SMCC (succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate) followed by conjugation to thiol groups that are present on the target protein/ligands such as bovine serum albumin, streptavidin and immunoglobulin.