Diverse Role of\nBuffer Mediums and Protein Concentrations\nto Mediate the Multimodal Interaction of Phenylalanine-Functionalized\nGold Nanoparticle and Lysozyme Protein at Same Nominal pH

Recently, buffer molecules have been known to affect\nintermolecular\nprotein–protein interactions at physiological pH. However,\nthe roles of buffer molecules and different monolayer protein concentrations\nremain elusive in controlling the interaction of gold nanoparticles\n(Au NPs) with protein molecules. Herein, for the first time taking\nphenylalanine functionalized gold nanoparticles (Au-Phe NPs) and lysozyme\n(Lyz) protein as model systems, we report that buffer molecules of\ndifferent charges (at a particular pH) play diverse roles in protein-Au\nNPs interaction, particularly in protein induced Au NPs aggregation.\nAmong different buffers, negatively charged buffer (citrate and phosphate)\ninduces aggregation of both Au-Phe NPs and Lyz protein, whereas zwitterionic\nand positive buffer (HEPES, MOPS, and Tris) only cause the Au NPs\naggregation. Taking the diverse role of buffer into account, we propose\nmultimodal models for stability and protein induced aggregation mechanism\nof NPs at different monolayer (sub-, near-, and excess) concentrations\nof Lyz in different medium.