From Kiwi Peels’ “End-of-Life” to Gold Nanoparticles: the Upcycling of a Waste

Abstract

Following a green approach, kiwi peels (a waste) were washed in hot water to obtain a water-based polyphenolic extract (KPWW) used to reduce Au3+ (coming from a HAuCl4 water-based solution) for forming gold nanoparticles (AuNPs). Indeed, KPWW, as shown after performing high-performance liquid chromatography-mass spectrometry (HPLC/MS-MS) analysis, is mainly composed by different polyphenols acting as reductant agents, accomplishing a red-ox reaction and decorating the AuNPs-KPWW surface. Spectroscopic and morphologic techniques were used in synergy for investigating the AuNPs-KPWW main features. Polyhedral-shaped plasmonic nanoparticles with a mean size of 30±10 nm and a negative charge of −40 mV were thus obtained. The AuNPs’ stability was assessed under different working conditions, investigating the role of ionic strength, pH, and temperature. The photostability was also assessed by irradiating AuNPs-KPWW with a solar simulator lamp. Both temperature and solar light did not perturb AuNPs-KPWW. Thanks to the presence of polyphenols, the antioxidant and skin-lightening properties were positively demonstrated. Moreover, the protective role of AuNPs in scavenging H2O2 and ·OH was also investigated by inhibiting the oxidation of a biomolecule. The sunscreen ability of AuNPs-KPWW was also estimated, and the theoretical calculation of the sun protection factor (SPF) was determined. Finally, the AuNPs-KPWW biocompatibility was tested on endothelial colony-forming cells and normal dermal fibroblasts as human cell lines, revealing that AuNPs-KPWW did not affect cell viability and did not alter cell morphology, demonstrating their safety and their potential application in nanomedicine.