Enzymes as bionanoreactors: glucose oxidase for the synthesis of catalytic Au nanoparticles and Au nanoparticle-polyaniline nanocomposites

The use of biomaterials such as enzymes for the synthesis of functional materials is important because such biologically guided processes can significantly reduce energy consumption in manufacturing processes. Glucose oxidase (GOx) has been exploited as a reducing as well as a stabilising agent for the green chemical synthesis of Au nanoparticles at pH 7.0 under ambient conditions. The synthesized Au nanoparticle-GOx composite was found to act as a highly-effective catalyst towards the reduction of p-nitrophenol to p-aminophenol in the presence of NaBH4. The catalytic activity of GOx was largely inhibited after its participation in the reduction of metal salt to form nanoparticles. A detailed mechanistic investigation was carried out using fluorescence spectroscopy, Fourier transform infra-red (FTIR) spectroscopy and circular dichroism (CD) to gain insights into the conformational changes in the enzyme structure. The catalytic activity of GOx towards the oxidation of glucose was taken advantage of to form a Au nanoparticle-polyaniline (Au NP-PANI) composite at room temperature. The production of the green emeraldine salt form of polyaniline (PANI) was extremely low in case of Au nanoparticle-GOx composite, where GOx was involved as a reducing agent. However, H2O2 generated during the catalytic reaction of GOx acted as a simultaneous reducing and oxidizing agent, leading to the formation of an Au NP-PANI core-shell composite in a controlled fashion.