The feasibility of the mercaptopropyl acid modified CdTe nanoparticles synthesized in aqueous solution to the labeling of biomoleculespapain via electrostatic interaction was studied in this paper. The absorption spectrum of CdTe papain solution became more flat than that of CdTe nanoparticles in the wavelength range from 400 to 600 nm. While the emission peak of CdTe papain solution underwent a red shift, the intrinsic emission band width was unchanged. The TEM images of monodisperse mercaptopropyl acid stabilized CdTe nanoparticles and CdTe papain solution were compared and the effect of pH of buffer solution was studied. It was proved that the red shift of the emission peak was the result of the electrostatic interaction between CdTe nanoparticles and papain.
