*3.5. Disc-Diffusion Method*

The synthesized poly(*o*-anisidine)/BaSO4 nanocomposites were evaluated for their antibacterial activity against different strains of bacteria using the disc-diffusion technique. It was found that poly(*o*-anisidine)/BaSO4 nanocomposites are effective for inhibiting the bacterial strains. The composites showed significant efficacy against *Pseudomonas aeruginosa* (Gram-negative) and *Staphylococcus aureus* (Gram-positive). The antibacterial activity of the BaSO4 nanocomposites is noteworthy and reported in Table 3.


**Table 3.** Inhibition zone of antibacterial test of the BaSO4 nanocomposite.

The POA/BaSO4 nanocomposite that inhibited *Pseudomonas aeruginosa* growth was found to be optimal at 7% (Table 3 and Figure 6). Similarly, *Staphylococcus aureus* growth was

inhibited by the POA/BaSO4 nanocomposites. The maximum inhibition was associated with 10% of the POA/BaSO4 nanocomposites against Gram-positive bacteria (*Staphylococcus aureus*). Nanoparticles have a small size, a larger surface area than bulky particles, and better penetration; therefore, they have a greater bactericidal effect. The specific process by which nanoparticles enter bacteria is unclear; however, studies have shown that treating bacterial cultures with nanoparticles alters the shape of the membranes and significantly increases membrane permeability, impairing normal transport through the plasma membrane. Bacterial cells die when they are unable to manage the transport across the plasma membrane. It was believed that due to their small size, barium-sulphate nanoparticles enter the bacterial cell membrane and link to functional groups of proteins, causing denaturation. They are also hypothesized to cause bacterial cell death by interacting with phosphorus and sulphur compounds, such as DNA. Total bacterial inhibition was proportional to BaSO4-nanoparticle concentrations [30]. It was found that the BaSO4 nanoparticles have a significant antibacterial activity, which may be utilized for practical uses.
