Background
Silver
nanoparticles (AgNPs) are known for their antibacterial
characteristics. The green synthesis method, in which plant extracts are
used for AgNP preparation, has attracted attention recently since it
provides an eco-friendly approach. However, there are many operating
conditions for this green synthesis method, and a correlation between
the antibacterial efficiency and AgNP characteristics is needed to
maximize the bactericidal efficacy.
Methods
AgNPs
were synthesized via green synthesis methods from green tea leaf (GT)
and Cassia seed (CS) extracts at 9:1, 1:1, and 1:9 precursor-to-extract
v/v ratios. The resulting AgNPs were tested for antibacterial activity
against S. aureus and the antioxidant level.
Significant findings
This study revealed a robust quantitative correlation between antibacterial activity and AgNP size, with an R2 value of 0.92. Green-synthesized AgNPs with an average particle size of
25 nm (GT) and 12 nm (CS) had a minimum inhibitory concentration (MIC)
of 25 µg mL−1 and 5 µg mL−1, respectively. The
enhanced antibacterial activity of AgCS is attributed to its smaller
particle size. Additionally, we propose the use of a silver precursor to
extract-dry-weight ratio (in mole g−1) to represent an
operating parameter for the green synthesis method. The resulting AgNP
sizes showed a weak negative relationship with this ratio.