Gold nanostars coated with neutral and charged polyethylene glycols: A comparative study of in-vitro biocompatibility and of their interaction with SH-SY5Y neuroblastoma cells

• Charged or neutral polyethylene glycol coating makes gold nanostars biocompatible.
• Overcoating negatively nanostars with cationic PAH polymer promotes internalization
• Internalization of PAH-coated gold nanostars results in reduced biocompatibility.
• Two-photon luminescence allows to evidence cell internalization of gold nanostars.

Gold nanostars (GNS) have been coated with four different polyethylene glycols (PEGs) equipped with a –SH function for grafting on the gold surface. These PEGs have different chain lengths with average MW = 2000, 3000, 5000 and average number of –O–CH2–CH2 — units 44, 66, and 111, respectively. Two are neutral and two are terminated with –COOH and –NH2 functions, thus bearing negative and positive charges at physiological pH, thanks to the formation of carboxylate and ammonium groups. The negative charge of the GNS coated with PEG carboxylate has also been exploited to further coat the GNS with the PAH (polyallylamine hydrochloride) cationic polymer. Vitality tests have been carried out on SH-SY5Y cells treated with the five differently coated GNS for 4, 24, and 48 h, at Au concentrations ranging from 1.25 to 100 μg/mL. The same tests have been repeated with the pure PEGs and PAH. Excellent biocompatibility was found for all PEGs, independently on charge and chain length, both for coated GNS and for the pure polymers. On the contrary, poor biocompatibility was found for PAH overcoated GNS and for pure PAH, although the latter only at high concentrations. Exploiting the two-photon luminescence of GNS, we have found by confocal laser scanning microscopy that when GNS are coated with PEGs they do not enter SH-SY5Y cells, while when overcoated with PAH they massively penetrate into the cytoplasm. This causes cell death by dramatically changing cell morphology, as demonstrated also by atomic force microscopy.

SynopsisGold nanostars coated with neutral, negatively or positively charged polyethylene glycols are biocompatible to SH-SY5Y cells and do not enter in the cytoplasm, unless they are further overcoated with the cationic polymer polyallylamine hydrochloride.Figure optionsDownload as PowerPoint slide