Green synthesis of carbon dots nanoparticles from edible swiftlet nest and evaluation of their antioxidant activity

Abstract

Edible swiftlet nest (ESN) confers various health benefits to humans, including immune system enhancement, anti-inflammatory properties, bone strengthening, and antioxidative effect. ESN is notably rich in protein and minerals, with its proteins serving as non-enzymatic antioxidants capable of binding free radicals. However, the antioxidant capacity of ESN is comparatively lower than that of other free radical scavengers, such as carbon dots nanoparticles (CNPs). CNPs features charged ligands on their surface that act as electron donors for free radical binding. The presence of the carbon chain forming proteins in ESN suggests their potential as the primary source for CNPs formation. The enhancement of hydroxyl groups and delocalized electrons is imperative for enhancing the antioxidant activity of ESN. This study aims to enhance the antioxidant activity of ESN by converting it into CNPs nanoparticles. The results demonstrated the effective synthesis of CNPs from the ESN solution using microwave methods. This was evidenced by XRD patterns indicating CNPs formation, and an average particle size of 4.86 nm as indicated by TEM analysis. The optimal microwave heating duration of 30 min yielded CNPs with a prominent emission spectrum peak at 425 nm and significantly high intensity. Absorbance data revealed the presence of C=C bonds, consistent with aromatic CNPs bonds observed in FTIR studies. CNPs possessed hydroxyl and carboxyl linkages, suggesting their potential as antioxidants. The percent inhibition results indicated that CNPs exhibited a substantial percentage (62.5%) at a concentration of 50 mg ml−1. The free radical scavenging activity of the CNPs significantly elevated compared to ESN.