Glutaraldehyde fixation promotes palladium and gold nanoparticles formation in yeast and enhances their catalytic activity in 4-nitrophenol reduction

When observing biosynthesized metal nanoparticles in microorganisms, glutaraldehyde is commonly used as a fixative to prepare TEM ultra-thin sections. However, as a chemical reagent with aldehyde groups, its reduction potential on metal ions has yet to be studied elaborately. Herein, we explored the influences of glutaraldehyde on yeast-synthesized gold nanoparticles (AuNPs), palladium nanoparticles (PdNPs) and their catalytic performance. A modified method for ultra-thin section preparation without glutaraldehyde fixation was developed to exclude its influence on AuNPs/PdNPs observation. It was confirmed that glutaraldehyde could promote the biosynthesis of AuNPs and PdNPs extra- and intracellularly, without altering their crystal structure and chemical state. The adsorption and reduction of Au(III)/Pd(II) were attributed to the different components of the yeast cell. Specifically, the amines and carboxyl groups in proteins and polysaccharides were involved in adsorption, while the reducing sugars hydrolyzed from polysaccharides were responsible for Au(III)/Pd(II) reduction. After glutaraldehyde fixation, the catalytic activities of Au/Pd-loaded yeast in 4-nitrophenol reduction were enhanced as well. Therefore, the influence of chemical fixatives in biosynthesized metal nanoparticles should be taken into consideration in regard to SEM, TEM observation and catalytic performance.