Optimization and Purification of Cadmium Sulfide Quantum Dots Biosynthesized by the Fungus Fusarium Oxysporum
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Cadmium sulfide (CdS) quantum dots have been synthesized extracellularly by the fungus Fusarium oxysporum when treated with CdSO4 in aqueous conditions. The quantum dots produce an emission range primarily between 450 and 550 nm. Optimization into the production system reveals that quantum dots are more efficiently synthesized when F. oxysporum cultures are grown to stationary phase and exposed to 20% mycelial biomass per volume, a pH of 9, a salt stress concentration of 0.25 M, along with the addition of 15 mM of 3-MPA and 25 mM of NaBH4. Synthesis of quantum dots reached a maximum after approximately 5 days of reaction time (120 h). Investigations into the secondary stress metabolism of F.oxysporum suggest that triggering this pathway leads to a higher output of CdS quantum dots. A water and acetone purification technique shows that CdS quantum dots can be extracted successfully from biologically synthesized quantum dot samples and different ratios of water to acetone show purification of different sized quantum dots. The possible mechanisms for CdS quantum dot formation are discussed.