Biosynthesis of silver nanoparticles using supercritical CO 2 mediated phenolic contents extracted from Lagerstroemia speciosa leaf inhibits Klebsiella pneumoniae biofilm formation

A large number of scientists are now working in order to create silver nanoparticles (AgNPs) that can be used as biomedicines against cancerous cell lines and bacteria that are resistant to drugs. In the current study, optimal supercritical fluid extract (SFE) of Lagerstroemia speciosa (LS) leaves at pressure 29.59 MPa, temperature 89.50 ºC and extraction time 53.85 min. was used to extract phenolic compounds for the synthesis of AgNPs. The synthesis was studied for 0–20 hrs. Initially the synthesis was confirmed by observing change in colour phenomenon. UV -spectroscopy confirmed the synthesis of nanoparticles (SFELS-AgNPs) demonstrated a maximum surface plasmon resonance at 430 nm. The crystallite dimension of nanoparticles was determined using XRD (13.47 nm), TEM results confirmed the diameter of the obtained silver nanoparticles between 8–20 nm. The nanoparticles possessed − 25.6 mV electric charge on the surface confirmed using zeta potential analyser. Furthermore, energy-dispersive X-ray analysis (EDAX), was used to analyze the presence of differential elements in generated materials. The developed nanoparticles were evaluated for their potential antimicrobial properties against, two gram-positive viz. Staphylococcus aureus and Bacillus cereus , and three gram-negative bacteria viz. Klebsiella pneumonia , Pseudomonas aeruginosa and Escherichia coli with different concentrations (100–400 µg/mL). The nanoparticle showed a minimum inhibitory concentration (MIC) of 64 µg/ml whereas the minimum bactericidal concentration (MBC) 128 µg/ml against K. pneumonia . They significantly inhibited K. pneumonia biofilm formation confirmed using scanning electron microscopy (SEM). The results were encouraging compared to the standards drug Chloramphenicol and other controls. The generated nanoparticles have highly effective antimicrobial properties against pathogenic bacteria.