Biosynthesis of Zinc Oxide Nanoparticles Using Averrhoa Bilimbi Fruit Extract: Deagglomeration and Antibiofilm Activity Measurements

Abstract

Zinc oxide nanoparticle was biosynthesized using Averrhoa bilimbi fruit extract as reducing and capping agent, with a focus on the impact of in-situ deagglomeration method on physical properties and pathogenic inhibition activity against Escherichia coli biofilm. Biosynthesis variables included deagglomeration method (ultrasonication vs. PVA as deagglomerant), temperature (30, 60 °C), and zinc precursor/plant extract volumetric ratio (1:2, 2:1). Upon calcination at 375 °C, crystalline ZnO nanoparticles with high phase purity were obtained. The final product formed soft agglomerates, as indicated by hydrodynamic mean particle diameters of 1.0-3.5 mm compared against mean individual particle diameter of 22 nm. Chemical deagglomeration and lower precursor/extract ratio promoted smaller agglomerates. Interaction between deagglomeration method and biosynthesis temperature implied that physical deagglomeration was more effective at higher temperature while the opposite applied for chemical deagglomeration. Antibiofilm activity of the nanoparticles was indicated by an average E. coli population reduction of 61% at 50 ppm ZnO dose, which increased to 78% at 200 ppm dose. Lower biosynthesis temperature and precursor/extract ratio increased antibiofilm activity, likely due to higher availability of residual plant extract biomolecules in the final ZnO nanoparticle product. Deagglomeration method did not directly impact the activity. However, the combination of chemical deagglomeration and higher ZnO dose produced a synergistic effect in inhibiting the E. coli biofilm growth. Overall, ZnO nanoparticle synthesized using Averrhoa bilimbi fruit extract exhibited promising antimicrobial activity against E. coli.