Facile green extracellular biosynthesis of CdS quantum dots by white rot fungus Phanerochaete chrysosporium

This study details a novel method for the extracellular microbial synthesis of cadmium sulfide (CdS) quantum dots (QDs) by the white rot fungus Phanerochaete chrysosporium. P. chrysosporium was incubated in a solution containing cadmium nitrate tetrahydrate, which became yellow from 12 h onwards, indicating the formation of CdS nanocrystals. The purified solution showed a maximum absorbance peak between 296 and 298 nm due to CdS particles in the quantum size regime. The fluorescence emission at 458 nm showed the blue fluorescence of the nanoparticles. X-ray analysis of the nanoparticles confirmed the production of CdS with a face-centered cubic (fcc) crystal structure. The average grain size of the nanoparticles was approximately 2.56 nm, as determined from the full width at half-maximum (FWHM) measurement of the most intense peak using Schererʹs equation. Transmission electron microscopic analysis showed the nanoparticles to be of a uniform size with good crystallinity. The changes to the functional groups on the biomass surface were investigated through Fourier transform infrared spectroscopy. Furthermore, the secretion of cysteine and proteins was found to play an important role in the formation and stabilization of CdS QDs. In conclusion, our study outlines a chemical process for the molecular synthesis of CdS nanoparticles.