Synthesis of blue emitting Aloe-Gold nanoclusters and their molecular Binding, antibacterial and cytotoxicity Profiling

The use of Gold nanoclusters (AuNCs) is snowballing due to their unique optical and biological properties. However, many of these clusters are synthesised using toxic and costly chemicals, which limits their scope of application. Hence, this study proposes a simple and safe microwave-assisted approach to synthesise blue-green emitting AuNCs using Aloe Africana leaf juice extract (Aloe-AuNCs). The study also examines their molecular binding, antibacterial activity and cytotoxicity. The optical properties and morphology were investigated by varying gold salt concentration (0.005, 0.001, 0.05, and 0.01 M), pH (3, 6, and 12), and mixing volume ratio (1:2, 1:1, and 2:1). The results showed that 1:2 mixing ratio, 0.01 M gold salt concentration at the pH of 12 is the optimum conditions for obtaining Aloe-AuNCs with the size of 1.98 ± 0.98 nm, maximum emission at 450 nm and quantum yield of 2.17 %. The structural analysis showed that it contains phenols and carbonyl functional groups. The as-synthesised Aloe-AuNCs were tested for molecular binding using DPPH as the molecular model. The binding constant was found to be 1.47 × 10⁻², showing the potential of Aloe-AuNCs as a carrier for future applications. The emission stability of Aloe-AuNCs was evaluated at 37 ℃, and they were stable for up to 48 h with enhanced emission intensity. Furthermore, The Aloe-AuNCs were tested for antimicrobial properties against S.aureus and E.coli, which showed inhibition at all concentrations. The cell viability against THP-1 revealed that the Aloe-AuNCs were biocompatible with cell viability of up to 90 %, and the RNA electropherogram showed that the patterns for the treated and untreated THP-1 were the same. This study demonstrates that Aloe Africana can be used to synthesise AuNCs, and Aloe-AuNCs have the potential for various biological applications.