Optical properties of silver nanoparticles upon exposure to bacteria

The overuse of antibiotics has led to bacteria becoming increasingly resistant to drug therapy. The need to develop antibiotics with broad, nonspecific mechanism of action is essential for overcoming multidrug resistance. Silver nanoparticles are one such antibiotic treatment that has been an active area of research for decades.

Normani et al. summarizes studies related to how the optical properties of silver nanoparticles — in particular, the localized surface plasmon resonance (LSPR) — change in the presence of bacteria.

“Briefly, we noticed that although the silver bactericidal effect has been studied for several decades, the modulation of its optical properties upon interaction with bacteria has been largely overlooked,” said author Giuseppe Maria Paternò. “This is a pity, since investigations of these effects can be used to gain more insight into the biophysics underpinning their interaction.”

The main antibacterial agent of silver nanoparticles is identified as positively charged silver ions released during an oxidative dissolution reaction. The uptake of silver ions causes cell membrane degradation and generation of reactive oxygen species — a known cause of apoptosis.

Previous studies have explored the role of oxidative dissolution in influencing the optical properties of silver nanoparticles although not in the context of bacterial interaction. Other research has investigated how the LSPR changes in the presence of biological macromolecules like DNA. Work by Normani et al. demonstrates the spectral position of the LSPR undergoes a blue shift upon exposure to bacteria.

“Such bacteria-induced changes in optical features can be practically exploited to build bacterial sensors and drug-screening platforms — for instance, to evaluate the activity of bacteria against selected drugs and antibiotics,” said Paternò.

Source: “Bringing the interaction of silver nanoparticles with bacteria to light,” by Simone Normani, Nicholas Dalla Vedova, Guglielmo Lanzani, Francesco Scotognella, and Giuseppe Maria Paternò, Biophysics Reviews (2021). The article can be accessed at http://doi.org/10.1063/5.0048725 .