Hybridization of 5-nitroisatin and silver nanoparticles for boosting the antimicrobial performance of poly(lactic acid)/nanocellulose nanocomposite films

This study aims to produce poly(lactic acid) (PLA)/corn cob nanocellulose (CCNC) with enhanced antimicrobial properties. Silver (Ag) is a good antimicrobial agent, but it will cause adverse effects upon the human cells in high exposure concentrations of silver ions. Hence, the objective of this study is to assess the viability of partial substitution of silver nanoparticles (AgNP) using 5-nitroisatin (NI) as an antimicrobial agent for the PLA/CCNC. The antimicrobial efficiency of PLA films was measured using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The agar disc diffusion assay and antimicrobial activity on the plastic surfaces showed that hybridization of the NI and AgNP can give a synergistic antimicrobial effect on the PLA/CCNC nanocomposite. The inhibition zone of PLA/CCNC-5/Ag/NI is larger compared to PLA/CCNC-5/Ag and PLA/CCNC-5/NI. The PLA/ CCNC-5/Ag/NI recorded > 4 log reduction, which indicates 99.999% of growth inhibitory. The silver ion migration from the PLA nanocomposite films was assessed using an inductively coupled plasma-optical emission spectrometer (ICP-OES). It was found that the silver migration from the PLA/CCNC-5/Ag/NI nanocomposite after one week exposure to acetic acid food simulant is still below the European Food Safety Authority regulated level. We can observe that the PLA/CCNC-5/Ag/NI demonstrated lower silver migration (0.037 mg/L) and a higher antibacterial inhibition zone compared to PLA/CCNC-5/Ag. 5-nitroisatin not only partial replacement of AgNP (reduce the dose of AgNP), but it gives a boosting on the antimicrobial performance for the PLA/CCNC-5 nanocomposites.

Automated summary

This study aimed to enhance the antimicrobial properties of PLA/CCNC by partially substituting silver nanoparticles with 5-nitroisatin as an antimicrobial agent. The hybridization of NI and AgNP demonstrated a synergistic antimicrobial effect, resulting in a larger inhibition zone and high growth inhibitory rate in the PLA/CCNC nanocomposite. The migration of silver ions from the PLA nanocomposite films remained below regulated levels, indicating that the PLA/CCNC-5/Ag/NI exhibited lower silver migration and higher antibacterial efficiency compared to PLA/CCNC-5/Ag.