Ligand-controlled growth and stabilization of doped ZnO2 nanoparticles for dual antibacterial and enzyme inhibition

Maintaining structural stability in multifunctional nanoparticles (NPs) remain a challenge in nanomedicine. To address this limitation, organic ligand-capped pristine and doped zinc peroxide (ZnO₂) NPs were synthesized via co-precipitation method for enhanced antibacterial efficacy against Gram-positive bacteria (methicillin-resistant Staphylococcus aureus (MRSA) and Bacillus cereus (BC)), and inhibition of the acetylcholinesterase enzyme (AChE). The synthesized samples were characterized using complementary characterization techniques. In-situ studies confirmed citrate (cit) molecules slow down the nucleation kinetics, while manganese (Mn) and cobalt (Co) doping reduces the optical bandgap from 3.07 eV to 2.89 eV, and 2.79 eV, respectively. Critically, ligand engineering and doping substantially improved bioactivity. ZnO₂ NPs exhibited dose-dependent antimicrobial activities, with 7.7 ± 0.9 mm and 8.6 ± 0.9 mm zones of inhibition (ZOIs) at 1000 µg/ml concentration against MRSA and BC, respectively. Incorporation of 3% Mn into the ZnO₂ lattice improved the ZOIs to 8.9 ± 1.7 mm against MRSA and 11 ± 1.9 mm against BC at 1000 µg/ml concentration. Notably, 5% Co-doped with cit capping exhibits the ZOIs of 12.5 ± 2.0 mm against MRSA and 6.4 ± 1.5 mm BC at 1000 µg/ml. 3% Mn-doped ZnO₂ NPs with dmlt as capping agent showed ZOIs of 10.3 ± 1.7 mm against MRSA and 12.3 ± 1.9 mm against BC at 1000 µg/ml concentration. Furthermore, the anti-acetylcholinesterase enzyme (AChE) activities of the synthesized NPs were assessed. At 125 µg/ml concentration, cit-capped ZnO₂ NPs inhibits 75.5 ± 0.1% of AChE activity. 3% Mn-doped ZnO₂ NPs show the inhibition of 73.2 ± 0.2% AChE, enhancing to 82 ± 0.3% upon pent capping. In contrast, 3% Co-doped ZnO₂ NPs and dmlt-capped 5% Co-doped ZnO₂ NPs exhibit modest AChE inhibition, with values of 62.4 ± 0.3% and 54.5 ± 0.2%, respectively. Molecular docking studies suggested moderate interaction of ZnO₂ NPs with phenol-soluble modulins alpha2 (PSMα2), strong interaction with Phospholipase C Regulator (PlcR), and moderate interaction with 1EEA (acetylcholinesterase from Electrophorus electricus (electric eel)). This study introduced a novel approach utilizing highly stabilized ZnO₂ NPs as potent antimicrobial agents and acetylcholinesterase inhibitors.