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Plasmonic and colloidal stability behaviours of Au-acrylic coreshell nanoparticles with thin pH-responsive shells
Shanglin Wu, Mingning Zhu, Dongdong Lu, QIng Lian, Ben Spencer, Daman J Adlam, Judith A Hoyland, Kirsten Volk, Matthias Karg, Brian R Saunders:
Nanoscale, 10, 18565-18575 (2018)
doi: 10.1039/C8NR07440B
accepted: 21.09.2018

The localised surface plasmon resonance (LSPR) of Au nanoparticles (NPs) as well as its interaction with nearby entities provides a wealth of fundamental and practical information at the nanometre scale. A number of studies have investigated core-shell NPs with Au cores and polymer shells that are temperature-responsive. However, there are very few studies of pH-responsive Au-polymer NP shells. Precipitation polymerisation is a scalable method and here we establish such a method to synthesise pH-responsive Au-poly(methyl methacrylate) copolymer core-shell NPs without the need for pre-functionalisation. The comonomers used were methacrylic acid (MAA) or 2-carboxyethyl acrylate (CEA) and the shells were crosslinked with ethylene glycol dimethacrylate. A series of five core-shell systems with collapsed shell thicknesses less than 30 nm are studied. The shell-thicknesses for the CEA-based core-shell NPs are relatively thin (< 5 nm) compared to related Au-polymer core-shell NPs prepared using precipitation polymerisation. The LSPR properties of the core-shell NPs were dependent on the shell thickness and were successfully simulated using finite difference time domain (FDTD) calculations. Two systems are considered further as exemplars. The MAA-based core-shell system with the thickest shell exhibited enhanced colloidal stability to added electrolyte. The CEA-based core-shell dispersion with the thinnest shells displayed reversible pH-triggered aggregation and was cytocompatible for HeLa cells. Proof-of-concept data are presented that demonstrate intracellular pH reporting.

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