Green synthesis of zinc oxide nanoparticles using Lippia citriodora extract: Naproxen loading and interaction studies with human serum albumin

In this paper, zinc oxide nanoparticles (ZnONPs) were synthesized via a green method using Lippia citriodora (Also known as Aloysia citrodora Paláu and Lemon verbena) extract as a reducing and stabilizing agent. The green synthesized ZnONPs were subsequently loaded with Naproxen (Nap) to obtain a novel nano-drug formulation. Structural and morphological characterizations were performed using Ultraviolet-Visible Spectroscopy (UV-Vis), Fourier Transform Infrared Spectroscopy (FT-IR), Field Emission Scanning Electron Microscopy (FE-SEM), and Atomic Force Microscopy (AFM) techniques. FE-SEM analysis and particle size distribution histograms showed that the average size of ZnONPs was approximately 29 nm, which increased to about 35 nm after Nap loading. UV–Vis and fluorescence spectroscopy were used to study the interactions with Human Serum Albumin (HSA). The fluorescence quenching mechanism indicated a static quenching process, with Stern–Volmer quenching constants (K sv ) in the range of 6.38 × 10⁴ to 1.64 × 10⁵ L.mol⁻¹ as the temperature increased from 288.15 to 310.15 K. The calculated bimolecular quenching rate constants (K q ) were in the range of 10 ¹ ² to10 ¹ ³ L.mol⁻¹ .s⁻¹ , exceeding the maximum diffusion-controlled limit and further confirming static quenching, overall suggesting binding between the synthesized nano-drug and HSA. Thermodynamic parameters showed negative Gibbs free energy values, demonstrating a spontaneous binding process mainly governed by hydrophobic interactions. These results demonstrate that green-synthesized ZnONPs using Lippia citriodora extract provide a stable and biocompatible carrier for Nap with favorable protein-binding features, highlighting their potential in drug delivery and biomedical applications. • Green synthesis of ZnONPs using Lippia citriodora extract. • Efficient loading of naproxen onto green-synthesized ZnONPs. • HSA binding studies reveal static quenching via hydrophobic interactions. • Plant-based ZnONPs show strong potential as biocompatible drug carriers.