Preparation, Characterization, and Evaluation of Zinc Oxide Nanoparticles Suspension as an Antimicrobial Media for Daily Use Soft Contact Lenses

Purpose: Infection and inflammation during wearing contact lenses are the problems for the users of daily soft contact lenses. All Gram-positive bacteria, Gram-negative bacteria, and fungi play a role in this problem. In past decades, nanoparticles have largely been studied and shown good antimicrobial activity against various microorganisms. The present study aimed to prepare, characterize, and evaluate zinc oxide nanoparticles (ZNPs) as antimicrobial agents against different microorganisms. Materials and Methods: The ZNPs were synthesized in a special structure using the sol-gel process and characterized by XRD, TEM, and EDX. Antimicrobial properties of ZNPs suspension were investigated against different microorganisms (i.e., Staphylococcus aureus, Staphylococcus epidermidis, Listeria monocytogenes, Bacillus subtilis, Pseudomonas aeruginosa, Salmonella typhi, Escherichia coli, and Candida albicans) by the Scanning Electron Microscopy of lens surfaces and pour plate method of immersed lens suspension for microbial enumeration. Results: The XRD, TEM, and EDX spectrum showed hexagonal structure and no impurity in the nanoparticles with a size of about 20 to 40 nanometers. Sterilized suspension of ZNPs was applied against bacterial species, and the results indicated 4 logarithms (CFU/mL) microbial growth reduction for most Gram-positive and Gram-negative species, except for Pseudomonas aeruginosa that showed 3.5 logarithms (CFU/mL) growth reduction. Furthermore, 1 and 1.7 logarithms (CFU/mL) growth reduction were observed for Candida albicans, applying 250 and 500 ppm ZNPs suspension, respectively, which is an acceptable result for fungal growth inhibition. Findings of this study indicated that the suspensions of ZNPs with 250 and 500 ppm showed acceptable bacteriostatic and bactericidal effects. Conclusions: In vitro antimicrobial activity showed that the suspension of ZNPs with 250 ppm concentration could effectively cause a proper reduction and inhibition in the growth of both Gram-positive and Gram-negative microorganisms. Therefore, the results revealed the efficacy of the antibacterial properties of synthesized ZNPs suspension in aqueous media.