Calotropis procera flower extracts: a green approach to zinc oxide with a pineapple-like nanoleaf morphology for biological applications

Abstract

Water contamination can trigger Escherichia coli (E. coli) infections, which are extremely harmful to humans. Healthy individuals typically recover within a week from symptoms such as severe abdominal pain, diarrhea, and vomiting. However, children and elderly individuals are at a higher risk of developing kidney dysfunction. To kill these life-threatening bacteria, reactive oxygen species (ROS) generating zinc oxide (ZnO) nanomaterials were synthesized via a sustainable green approach using medicinally rich Calotropis procera (C. procera) flower extract. The functional groups and wurtzite crystalline structure of the synthesized ZnO were revealed by Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (PXRD) analysis, respectively. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) demonstrated the formation of pineapple-like nanoleaves (PNLs), with sizes ranging from 61 to 122 nm, along with well-defined lattice fringes, confirming their nanoscale dimensions and high crystallinity. Energy-dispersive X-ray (EDX) spectroscopy further confirmed the elemental composition (1 : 1 ratio of Zn and O in ZnO) and purity of the ZnO nanomaterials. Antioxidant activity was measured using the standard 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay at different concentrations. Lipid peroxidation (LPO) exhibited strong ROS-generating capability, leading to membrane protein damage and ultimately cell death. Minimum inhibitory concentration (MIC) analysis revealed selective antimicrobial activity against Gram-negative E. coli, while polymerase chain reaction (PCR) confirmed DNA fragmentation, supporting bacterial cell cleavage. The ZnO PNLs exerted excellent cytotoxic effect against A431 skin cancer cells, with an IC₅₀ value of 70.41 μM. Increased intracellular ROS levels induced apoptotic morphological changes in A431 cells. Confocal scanning microscopy revealed enhanced fluorescence in A431 human epidermal cells treated with ZnO PNLs, indicating concentration-dependent ROS generation and cellular internalization. Inverse molecular docking analysis was further performed to identify favorable binding affinity scores against 11 skin cancer-associated protein targets at the molecular level. Overall, ZnO PNLs synthesized using the C. procera flower extract exhibited excellent biocompatibility and potent antibacterial and anticancer activities against E. coli and A431 skin cancer cells.