Catalytic gold nanoparticles immobilized on yeast: From biosorption to bioreduction

• AuNPs can be immobilized on dead yeast cell by reacting Pichia pastoris with HAuCl4.
• NH2 and OH were demonstrated to play a crucial role in the biosorption process.
• Mannocarolose may be responsible for the bioreduction of [AuCl4]−.
• Au/P. pastoris exhibited good catalytic activity for the reduction of 4-NP.
• The catalytic activity is closely related to the interaction between AuNPs and yeast.

In this study, gold nanoparticles (AuNPs) were biologically synthesized and bound to the cell surface of yeast Pichia pastoris (P. pastoris), which exhibited high affinity for Au(III) species in aqueous solution. With the assistance of TEM, FTIR and XRD, the biosynthesis of the AuNPs was investigated by chemical modification of the cell surface, KBr desorption of Au(III) species from the cell surface, and reduction of Au(III) species with mannocarolose extracted from the yeast. Furthermore, the results showed that [AuCl4]− ions were rapidly absorbed and reduced into Au(I) ions by NH2, OH, and other functional groups on the cell surface. Further, the Au(I) ions were reduced into Au(0) to form AuNPs immobilized on the cells. Mannocarolose played an important role in the reduction process. And the catalytic application of AuNPs/P. pastoris to the reduction of 4-nitrophenol was studied. Two other catalysts were prepared by introducing an extraneous reductant to clarify the importance of the AuNPs-yeast involvement in the reduction of 4-nitrophenol. The AuNPs/P. pastoris composites exhibited the best catalytic activity, and their catalytic activity can remain stable even after several rounds of reuse. This work demonstrates the fabrication of a catalyst, through the immobilization of AuNPs onto yeast by extending biosorption to biosynthesis, thus highlighting their potential application as environmentally benign catalysts.

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