Human serum albumin encapsulated gold nanoclusters : effects of cluster synthesis on natural protein characteristics

Russell, B. A. and Jachimska, B. and Kralka, I. and Mulheran, P. A. and Chen, Y. (2016) Human serum albumin encapsulated gold nanoclusters : effects of cluster synthesis on natural protein characteristics. Journal of Materials Chemistry B. ISSN 2050-750X (https://doi.org/10.1039/C6TB01827K)

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Abstract

The differences in physiochemical properties between native Human Serum Albumin (HSA) and HSA encapsulated gold nanoclusters (HSA-AuNCs) are characterised. The molecules light absorbance (UV/Vis), electrophoretic mobility, dynamic viscosity, density, hydrodynamic radius (DLS), absorption (QCM) and chemical bonding (XPS) characteristics were studied. The UV/Vis and DLS data shows the formation of large aggregates for HSA-AuNCs between pH 4-6 which is not observed for native HSA. This observation was further supported by QCM measurements showing a large increase in mass adsorbed at pH 6 between HSA and HSA-AuNCs. The DLS data also reveals a hydrodynamic radius of 12nm for HSA-AuNCs, nearly double that of 7nm for native HSA at pH higher than 6, suggesting the formation of compact HSA-AuNCs dimers. The electrophoretic mobility data for both HSA-AuNCs and HSA were converted to zeta potentials. The zeta potential of HSA-AuNCs was seen to be more negative between pH6-12, suggesting that the protein surface is interacting with unreacted gold salt anions. Measurements of density and viscosity were also found to be in agreement with previous data suggesting HSA-AuNCs forms aggregates. XPS data also suggests that not all reactants are used up during the HSA-AuNCs synthesis and positive side chains play a part in the initial synthesis stages. It was concluded that HSA-AuNCs most likely form dimers at natural and high pH. Between pH 4-6 HSA-AuNCs form very large aggregates limiting their use as a fluorescent probe in this pH range. It was also found that the native characteristics of HSA are altered upon HSA-AuNCs synthesis which needs to be taken into consideration when applying HSA-AuNCs as a fluorescent probe in all fluorescent imaging and sensing.

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