Aqueous synthesis and characterization of bovine hemoglobin-conjugated cadmium sulfide nanocrystals

• CdS nanocrystals were synthesized by biomimetic method in bovine hemoglobin (BHb) solution.
• The study of the interaction between Cd2+/CdS and BHb.
• The optical properties of BHb-conjugated CdS nanocrystals.
• The synthesis process of BHb-conjugated CdS nanocrystals is facile, effective and environment friendly.
• The change of secondary structure of BHb after binding to CdS nanocrystals.

Cadmium sulfide (CdS) nanocrystals with average diameter about 5.5 nm were synthesized in aqueous solution of bovine hemoglobin (BHb) via simple biomimetic method. Powder X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) characterizations were used to determine the structure and morphology of CdS nanocrystals. It was revealed that amount of BHb, chelating of Cd2+ to BHb and reaction temperature were key factors in controlling shape and dispersion of CdS nanocrystals. The binding sites of BHb to CdS nanocrystals and the change of secondary structure of protein have been identified by Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopy. It was found that conjugating of BHb with Cd2+ and CdS could protect nanocrystals from agglomerating. Moreover, the thermostability of BHb enhanced after conjugating with CdS nanocrystals. The interaction mechanism of BHb with Cd2+/CdS was also proposed. The quantum-confined effect of CdS nanocrystals was confirmed by ultraviolet–visible (UV–vis) spectrum. The nanocrystals exhibited a well-defined photoluminescence (PL) emission feature at about 510 nm with narrow full width at half maximum (FWHM).