Characteristics and useful effects for human health of antioxidant carbon nanodots contained in microwave-assisted Opuntia humifusa extract (MA-OHE(CD)) were investigated in this work. MA-OHE(CD) was characterized using transmission electron microscopy, dynamic light scattering analysis, X-ray diffraction, UV–vis spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform-infrared spectroscopy. Besides, total phenolic content and antioxidant activity of MA-OHE(CD) were measured. It was revealed that the MA-OHE(CD) increases aquaporin-3 expression in human epidermal keratinocytes cell with hydrophilic characteristics. Moreover, the bio-active compound extraction efficacy and antioxidant activity of microwave-assisted extraction were great when compared to maceration.

Carbon nanodots (CNDs) are 0D quasi-spherical nanoparticles that are less than 10 nm in size. CNDs that possess surface functional groups such as hydroxyl, amino, and carboxyl groups have been demonstrated to scavenge free radicals efficiently and effectively, resulting in them being beneficial for cosmetic and cosmeceutical applications. In this study, we successfully prepared novel CNDs, namely black VC, using vitamin C (VC) as a promising precursor. Black VC was prepared by a facile one-step method based on short-time microwave irradiation. The properties of black VC were characterized by transmission electron microscopy (TEM) analysis, X-ray diffraction (XRD), high-resolution X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and UV–vis spectrophotometry. Radical scavenging, cell viability, and anti-pollution activity assays were also conducted to demonstrate the functionalities of black VC. The developed black VC exhibited lower cytotoxicity and better antioxidant, metal chelating ability, and anti-pollution activities than its precursor. These results provide a new approach for developing advanced antioxidants for innovative cosmetic formulations using a simple microwave treatment method. However, black VC retained some problems of its precursor in the form of low stability, which is likely to be a challenge for its cosmeceutical application.