Background: The identification of protein-protein interactions is of great challenge. Therefore, we conducted this study to fabricate a gold surface biochip with activated sophorolipids in combination with 16-amino-1-hexadecanethiol hydrochloride. Methods: We designed a direct on-chip immunological assay strategy for measuring ligand-receptor interactions in a forward or reverse manner, that is, a ligand was immobilized on the biochip surface and allowed to interact with its specific free receptor in the liquid phase and vice versa. The specificity of molecular interactions on the biochip was evaluated using an immunological blocking assay and a chemiluminescent immunoassay. To test the potential utilization of biochip, we used the serum of hemophagocytic lymphohistiocytosis (HLH) patients as an experimental entity. Results: The receptor CD25-based IL-2 and ligand IL-2-based CD25 assays revealed that the detection limits on the biochip were as low as 156pg/mL and 78pg/mL, respectively. Meanwhile, using the receptor- or ligand-based platforms, we found that the positive rates of free IL-2 and soluble CD25 (sCD25) monomers in the sera of HLH patients were 14.3% and 71.4%, respectively, like our previous specific-antibody-based biochip investigation. Also, the biochip shared a good compatibility with CLIA assay in the measurement of sCD25(r=0.77, P<0.01). Conclusions: The biochip platform can be expanded to protein-specific serological diagnosis as a potential substitute for immunoprecipitation and ELISA to understand the interactions between proteins, ligands and receptors, and enzymes and substrates.