In the era of nanotechnology, nanoparticles (NPs) of metals and metal oxides/chalcogenides are widely been used in medical applications where antibiotic-resistant microorganisms become a serious threat to the human health. Cobalt ferrite (CoFe 2 O 4 ) NPs, synthesized by a simple and cost-effective sol-gel auto-combustion method are envisaged for in vitro antimicrobial activities against Gram-positive bacteria (Bacillus subtilis; Staphylococcus aureus) and Gram-negative bacteria (Escherichia

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... i; Pseudomonas aeruginosa). The structure, morphology, elemental analyses and surface area of CoFe 2 O 4 NPs are initially screened. The antimicrobial efficiency of CoFe 2 O 4 NPs is found to be optimum against the Gram-negative bacteria Escherichia coli (15 mm). In addition, membrane leakage assays performed to evaluate the intracellular cytoplasmic leakage with CoFe 2 O 4 NPs demonstrate the ability to destroy the bacterial membrane integrity, confirming their antimicrobial potential. Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.