Proteins and nanoparticles (NPs) provide a promising platform for supramolecular interaction. We are currently exploring both fundamental and applied aspects of this interaction. On the fundamental side, we have fabricated a series of water-soluble anionic and cationic NPs to interact with cationic and anionic proteins respectively. A Varity of studies such as, activity assay, fluorescence titration, isothermal titration calorimetry etc. were carried out to quantify the binding properties of these functional NPs with those proteins. Those studies reveal the prospect of tuning the affinity between the nanoparticles and proteins by the surface modification. On the application side, we have used this protein-nanoparticle interaction in protein refolding where we successfully refolded the thermally denatured proteins toward its native structure. We have also applied this particle-protein recognition to create a biocompatible protein sensor using a protein-NP conjugate. Green fluorescent protein and a series of cationic NPs were used for a protein sensor for the identification of protein analytes through displacement process. We have extended this application even in sensing the proteins in human serum.