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Table 4 Multiple mechanisms of antimicrobial action for various metallic nanoparticles [96]

From: ‘Green’ synthesis of metals and their oxide nanoparticles: applications for environmental remediation

S. no.

Nanoparticles

Multiple mechanisms

1

Nitric oxide-releasing nanoparticles (NO NPs)

NO forms reactive nitrogen oxide intermediates (RNOS) by reacting with superoxide (O2)

(a) RNOS cause direct nitrosative damage to DNA, including causing strand breaks, formation of abasic sites and depleting the Fe in a bacterial cell

(b) RNOS inactivate zinc metalloproteins, which results in inhibition of microbial cellular respiration

(c) RNOS also cause lipid peroxidation

2

Chitosan-containing nanoparticles

(a) Due to its positive charge, chitosan binds with DNA in bacterial and fungal cells, thereby inhibiting transcription of mRNA resulting in protein translation

(c) Chitosan also decreases the activities of metalloproteins

3

Silver-containing nanoparticles (Ag NPs)

The antimicrobial activity of silver (Ag) is due to its Ag+ ions

(a) Ag+ inhibits the electron transport chain of microbes

(b) Ag+ damages DNA and RNA by binding with them

(c) Ag+ also inhibits cell division by inhibiting DNA replication

(d) Ag+ ions form ROS, which are toxic to both bacterial cells and eukaryotic host cells

4

Zinc oxide-containing nanoparticles (ZnO NPs)

(a) ZnO NPs destroy both lipids and the proteins of the membrane, which can cause cell death

(b) ZnO NPs also form Zn2+ ions and ROS, including hydrogen peroxide (H2O2),which damage the bacterial cell

5

Copper-containing nanoparticles

(a) Copper interacts with amine and carboxyl groups, which are present on microbes such as B. subtilis

(b) Higher concentrations of Cu2+ ions can produce ROS

6

Titanium dioxide-containing nanoparticles (TiO2 NPs)

(a) In the photocatalysis process, TiO2 NPs generate ROS, including hydrogen peroxide (H2O2) and hydroxyl radicals (·OH), upon exposure to near-UV and UVA radiation

7

Magnesium-containing nanoparticles

(a) MgX2 NPs also cause lipid peroxidation of the microbial cell envelope by generating ROS

(b) MgF2 NPs can cause lipid peroxidation and a drop in cytoplasmic pH, which raises membrane potential