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Introduction to Nanoparticles

Silver nanoparticles (AgNPs) are very effective in their antimicrobial abilities. Because of the extremely high surface area to volume ratio, these nanoparticles are very effective in producing Ag+ ions. which are very toxic to living cells. This is because Ag+ ions produce reactive oxygen species (ROS) which disrupt metabolism, and interfere with the ability of DNA to replicate by causing it to condense. 

The silver nanoparticles themselves do not directly effect the bacterium. They release silver ions that damage the cell. However, the nanoparticles can easily enter the cell because it is mistaken for glucose because it is approximately the same size. The ions however must enter through ion transport channels.

Silver Nanoparticles under 50.0k x magnification on a Scanning Electron Microscope

Silver Nanoparticles

There are three types of carbon which elicit antimicrobial properties: carbon nanotubes (CNT), fullerenes, and graphene oxide (GO). 

Carbon nanotubes, especially single-walled carbon nanotubes (SWCNT) display very effective antibacterial properties. CNTs influence cellular membrane integrity, metabolism processes, and morphology of various bacteria, most notably, E. Coli. Scientists believe SWCNTs penetrate cell membranes more effectively than their multi-walled counterpart due to their smaller nanotube diameter. 

Fullerenes are spherical molecules made of carbon atoms. Fullerenes inhibit energy metabolism after entering the bacteria. They do this by releasing molecules which inhibit the respiratory chain and thus limiting energy production. They show antimicrobial activity against different species of bacteria including E. Coli, Salmonella, and Streptococcus spp. 

Graphene oxide (GO) is a monolayer of carbon atoms which is synthesized by splitting carbon nanotubes or oxidizing graphite, a similar carbon-based molecule. GO is a sharp nanosheet which is where its antimicrobial properties stem from. These nanosheets produce stress on the cell membrane when, in direct contact, leads to damage. 

SWCNT (left) and MWCNT (right)

Graphene Oxide (Left) and Fullerene (right)

Carbon Nanoparticles

Gold nanoparticles (AuNP) exhibit antibacterial properties mainly by making changes to protein in the cell wall or in the cytoplasm. AuNPs halt the production of enzymes that aid in the production of ATP which reduces the cell's metabolism. It also reduces the production of a subunit of ribosome which stops the creation of tRNA. This leads to cell destruction because tRNA is necessary in protein production. It also binds to the thiol groups in molecules that are part of the respiratory chain which disrupts it and releases ROS, promptly destroying the cell from the inside. Different sized dosages of AuNPs are needed depending on whether the bacteria is Gram positive or Gram negative. Gram positive bacteria have thicker cell membranes and so a higher dosage of AuNPs is needed to penetrate. AuNPs are much more efficient than gold particles because of their high surface area to volume ratio. This leads to higher reactivity because of more contact area with the bacteria.

Gold Nanoparticles

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