# Comparative Study of Physicochemical Properties and Antibacterial Potential of Cyanobacteria Spirulina platensis-Derived and Chemically Synthesized Silver Nanoparticles

## TL;DR

This study compares silver nanoparticles made from cyanobacteria and chemically, finding the former more stable and effective against bacteria.

## Contribution

Demonstrates the antibacterial efficacy and stability of Spirulina platensis-derived silver nanoparticles compared to chemically synthesized ones.

## Key findings

- Splat-AgNPs are spherical and stable with a zeta-potential of -50.0 mV, while Chem-AgNPs are irregular and larger.
- Splat-AgNPs show stronger bactericidal activity against both Gram-positive and Gram-negative bacteria.
- Splat-AgNPs disrupt bacterial membrane permeability and H+-fluxes via FoF1-ATPase.

## Abstract

The “green
synthesis” of nanoparticles
(NPs) offers
cost-effective and environmentally friendly advantages over chemical
synthesis by utilizing biological sources such as bacteria, algae,
fungi, or plants. In this context, cyanobacteria and their components
are valuable sources to produce various NPs. The present study describes
the comparative analysis of physicochemical and antibacterial properties
of chemically synthesized (Chem-AgNPs) and cyanobacteria Spirulina platensis-derived silver NPs (Splat-AgNPs).
The physicochemical characterization applying complementary dynamic
light scattering and transmission electron microscopy revealed that
Splat-AgNPs have an average hydrodynamic radius of ∼ 28.70
nm and spherical morphology, whereas Chem-AgNPs are irregular-shaped
with an average radius size of ∼ 53.88 nm. The X-ray diffraction
pattern of Splat-AgNPs confirms the formation of face-centered cubic
crystalline AgNPs by “green synthesis”. Energy-dispersive
spectroscopy analysis demonstrated the purity of the Splat-AgNPs.
Fourier transform infrared spectroscopy analysis of Splat-AgNPs demonstrated
the involvement of some functional groups in the formation of NPs.
Additionally, Splat-AgNPs demonstrated high colloidal stability with
a zeta-potential value of (−50.0 ± 8.30) mV and a pronounced
bactericidal activity against selected Gram-positive (Enterococcus hirae and Staphylococcus
aureus) and Gram-negative (Pseudomonas
aeruginosa and Salmonella typhimurium) bacteria compared with Chem-AgNPs. Furthermore, our studies toward
understanding the action mechanism of NPs showed that Splat-AgNPs
alter the permeability of bacterial membranes and the energy-dependent
H+-fluxes via FoF1-ATPase, thus playing
a crucial role in bacterial energetics. The insights gained from this
study show that Spirulina-derived synthesis is a
low-cost, simple approach to producing stable AgNPs for their energy-metabolism-targeted
antibacterial applications in biotechnology and biomedicine.