The expression and dissemination of beta-lactamase enzymes is the most frequently used antibiotic resistance mechanism in bacteria. The synthesis and characterization of a new nanocomposite particle was performed to inhibit serine beta-lactamase activities. The nanostructure based on an ultra-small iron oxide (Fe3O4) nanocore, is in-situ coated with a hydrophilic and biodegradable compound of N-phosphonomethyl iminodiacetic acid (PMIDA). Through amidation reaction, a tetra-dentate molecule such as (S)-N-(5-Amino-1-carboxypentyl) iminodiacetic acid (NTA) was covalently conjugated to the acid-terminated Fe-PMIDA nanoparticles. The re-sulted Fe-PMIDA-NTA nanostructure was further coordinated with Co2+ ions. Once the nanoparticles loaded with the cobalt ions, the positively charged nanocomposite particles were found effective toward class C beta-lactamase having 66% inhibition of enzyme activity with an IC50 of 45.68 mu g/mL. A significant level of synergism was also observed by co-administration of Fe-PMIDA-NTA-Co2+ NPs and cephalexin as our model of beta-lactam antibiotic against Escherichia coli bacteria. (C) 2021 Published by Elsevier B.V.