**4. Applications of antimicrobial activity**

Nowadays, the alternative antimicrobials are highly considered due to the intense growing bacterial resistance towards conventional drugs [30]. In this regard, the development of novel multifunctional materials with antimicrobial properties that meet the requirements of a drug delivery system allowing the minimization of antibiotic concentration is of great interest. The essential characteristics of ferrite nanoparticles such as the high surface-to-volume ratio and nanoscale particle size, improve their reaction with pathogenic microbes. Also, the high surface area, low crystallite size and porosity have a significant role in improving the efficiency of NPs even at low (20 ppm) concentrations [31]. The main drawbacks in the use of these materials are that their antimicrobial properties easily change by varying their size, shape and crystallinity [32].

There are only few studies that investigate the antimicrobial effect of transition metal substituted Co ferrite nanopowders. Zhang et al. reported that the bactericidal effectiveness against gram-negative *E. coli* bacteria of CuxCo1−xFe2O4 (x = 0.0, 0.3, 0.5, 0.7, 1.0) NPs prepared by wet chemical co-precipitation method was enhanced by increasing Cu content [33]. The mechanisms involved in the

**55**

against *S. aureus* [31].

*Progress, Challenges and Opportunities in Divalent Transition Metal-Doped Cobalt Ferrites…*

antibacterial activity of NPs are: (*i*) decomposition of ferrite and formation of reactive oxygen species, (*ii*) electrostatic interaction of nanomaterials with cell membrane and (*iii*) photocatalytic light activation of nanoparticles [34–37]. The particle size, morphology, surface area, increase in oxygen vacancies, chemical molecule diffusion ability and discharge of metal ions also play important roles in the bactericidal activity [38]. Good antibacterial activity against *E. coli* and grampositive *S. aureus* of Cu0.5Co0.5Fe1.9Bi0.1O4 NPs synthetized by combustion technique

The bacterial growth rate inhibition of Zn-substituted Co ferrite (ZnxCo1− xFe2O4, x = 0.0, 0.5, 1.0) nanoparticles (NPs) obtained via sol-gel route was found to be higher for the methicillin-resistant *S. aureus* (MRSA) than for *E. coli* strains [40]. Oppositely, the antibacterial activity of the ZnxCo1−xFe2O4 (x = 0, 0.3, 0.5, 0.7, 1.0) NPs obtained by sol-gel process using citric acid as chelating agent was higher against gram negative bacteria (*E. coli*) than against gram-positive bacteria (*S. aureus*). Generally, the antibacterial capacities increased with increasing Zn content [41]. The *in vitro* antimicrobial activity of Co0.6Zn0.4Fe2O4 prepared by citrate-gel method tested against a wide range of gram-positive (*B. subtilis, S. aureus,* 

*M. luteus*) and gram-negative (*E. coli, P. aeruginosa, K. planticola*) bacteria revealed its efficiency in treatment of plants and trees affected by large microbial cells [42]. Good antibacterial effects of Zn-doped Co ferrite NPs prepared using curd as fuel via combustion method against gram-negative *S. typhi* and gram-positive *S. aureus* was also reported [43]. The obtained result indicated that Zn doped Co ferrite may be used as component in cosmetics, emulsions, creams, powders and lotions for dermatological and biomedical treatments (drug carriers, magnetically directed

The bactericidal activity of Co0.5Fe0.5Fe2O4 and Co0.2Fe0.8Fe2O4 NPs with average particle size of 5.0–6.4 nm, has been studied against gram-negative (*E. coli*), gram-positive (*S. aureus*), bacteria and fungi (*C. parapsilosis* and *C. albicans*), pathogens known to increasing mortality associated with multidrug resistance [5, 44]. Co0.2Fe0.8Fe2O4 NPs exhibited good antibacterial efficiency (21–70%) against all tested microorganisms. The number of colonies decreased considerable with increasing Co

Mn1−xCoxFe2O4 (x = 0.2, 0.4, 0.6, 0.8) prepared using open-air auto combustion was found to have excellent antifungal activity against *Rhizopus fungi* and its efficiency increase with increasing Co content [7]. Ashour et al. demonstrated the antimicrobial activity of metal (Zn, Mn, Cu) doped Co ferrite nanoparticles against *B. subtilis, S. aureus, E. coli, P. aeruginosa and C. albicans*. The

Zn-substituted Co ferrite NPs, were more active against gram-positive than gramnegative bacteria and had strong antifungal activity against *C. albicans*. Gammairradiated Zn-substituted Co ferrite (150 kGy) was more active against *S. aureus*

The MxCo1−xFe2O4 (M = Zn, Cu, Mn; x = 0.00, 0.25, 0.50, 0.75) NPs synthetized via sol-gel method were investigated as antibacterial agents towards bacteria that commonly diffused on the surfaces of the medical operating room walls (*S. lentus, S. sciuri, S. vitulinus, S. aureus, A. viridians* and *E. columbae*). The antibacterial activity is enhanced in the following order: MnxCo1−xFe2O4 > CuxCo1−xFe2O4 > ZnxCo1− xFe2O4. The most effective ferrite was Zn0.75Co0.25Fe2O4 NPs which exhibited the highest activity towards all investigated pathogenic bacteria. The highest activity of Mn0.75Co0.25Fe2O4 was against *S. vitulinus*, while Cu0.75Co0.25Fe2O4 NPs were effective

The antimicrobial performance of MxCo1−xFe2O4; (M = Zn, Cu, Mn; x = 0, 0.5) NPs prepared using a sol-gel method in the presence of citric acid and ethylene glycol upon pathogenic microorganisms infected urinary tract and blood samples was

and *P. aeruginosa*, as a result of the decreasing crystallite size [35].

was obtained, due to the co-doping of Cu and Bi in Co ferrite [39].

drug delivery, imaging factors and cancer therapy) [35].

content in the investigated NPs [5].

*DOI: http://dx.doi.org/10.5772/intechopen.93298*

*Progress, Challenges and Opportunities in Divalent Transition Metal-Doped Cobalt Ferrites… DOI: http://dx.doi.org/10.5772/intechopen.93298*

antibacterial activity of NPs are: (*i*) decomposition of ferrite and formation of reactive oxygen species, (*ii*) electrostatic interaction of nanomaterials with cell membrane and (*iii*) photocatalytic light activation of nanoparticles [34–37]. The particle size, morphology, surface area, increase in oxygen vacancies, chemical molecule diffusion ability and discharge of metal ions also play important roles in the bactericidal activity [38]. Good antibacterial activity against *E. coli* and grampositive *S. aureus* of Cu0.5Co0.5Fe1.9Bi0.1O4 NPs synthetized by combustion technique was obtained, due to the co-doping of Cu and Bi in Co ferrite [39].

The bacterial growth rate inhibition of Zn-substituted Co ferrite (ZnxCo1− xFe2O4, x = 0.0, 0.5, 1.0) nanoparticles (NPs) obtained via sol-gel route was found to be higher for the methicillin-resistant *S. aureus* (MRSA) than for *E. coli* strains [40]. Oppositely, the antibacterial activity of the ZnxCo1−xFe2O4 (x = 0, 0.3, 0.5, 0.7, 1.0) NPs obtained by sol-gel process using citric acid as chelating agent was higher against gram negative bacteria (*E. coli*) than against gram-positive bacteria (*S. aureus*). Generally, the antibacterial capacities increased with increasing Zn content [41]. The *in vitro* antimicrobial activity of Co0.6Zn0.4Fe2O4 prepared by citrate-gel method tested against a wide range of gram-positive (*B. subtilis, S. aureus, M. luteus*) and gram-negative (*E. coli, P. aeruginosa, K. planticola*) bacteria revealed its efficiency in treatment of plants and trees affected by large microbial cells [42]. Good antibacterial effects of Zn-doped Co ferrite NPs prepared using curd as fuel via combustion method against gram-negative *S. typhi* and gram-positive *S. aureus* was also reported [43]. The obtained result indicated that Zn doped Co ferrite may be used as component in cosmetics, emulsions, creams, powders and lotions for dermatological and biomedical treatments (drug carriers, magnetically directed drug delivery, imaging factors and cancer therapy) [35].

The bactericidal activity of Co0.5Fe0.5Fe2O4 and Co0.2Fe0.8Fe2O4 NPs with average particle size of 5.0–6.4 nm, has been studied against gram-negative (*E. coli*), gram-positive (*S. aureus*), bacteria and fungi (*C. parapsilosis* and *C. albicans*), pathogens known to increasing mortality associated with multidrug resistance [5, 44]. Co0.2Fe0.8Fe2O4 NPs exhibited good antibacterial efficiency (21–70%) against all tested microorganisms. The number of colonies decreased considerable with increasing Co content in the investigated NPs [5].

Mn1−xCoxFe2O4 (x = 0.2, 0.4, 0.6, 0.8) prepared using open-air auto combustion was found to have excellent antifungal activity against *Rhizopus fungi* and its efficiency increase with increasing Co content [7]. Ashour et al. demonstrated the antimicrobial activity of metal (Zn, Mn, Cu) doped Co ferrite nanoparticles against *B. subtilis, S. aureus, E. coli, P. aeruginosa and C. albicans*. The Zn-substituted Co ferrite NPs, were more active against gram-positive than gramnegative bacteria and had strong antifungal activity against *C. albicans*. Gammairradiated Zn-substituted Co ferrite (150 kGy) was more active against *S. aureus* and *P. aeruginosa*, as a result of the decreasing crystallite size [35].

The MxCo1−xFe2O4 (M = Zn, Cu, Mn; x = 0.00, 0.25, 0.50, 0.75) NPs synthetized via sol-gel method were investigated as antibacterial agents towards bacteria that commonly diffused on the surfaces of the medical operating room walls (*S. lentus, S. sciuri, S. vitulinus, S. aureus, A. viridians* and *E. columbae*). The antibacterial activity is enhanced in the following order: MnxCo1−xFe2O4 > CuxCo1−xFe2O4 > ZnxCo1− xFe2O4. The most effective ferrite was Zn0.75Co0.25Fe2O4 NPs which exhibited the highest activity towards all investigated pathogenic bacteria. The highest activity of Mn0.75Co0.25Fe2O4 was against *S. vitulinus*, while Cu0.75Co0.25Fe2O4 NPs were effective against *S. aureus* [31].

The antimicrobial performance of MxCo1−xFe2O4; (M = Zn, Cu, Mn; x = 0, 0.5) NPs prepared using a sol-gel method in the presence of citric acid and ethylene glycol upon pathogenic microorganisms infected urinary tract and blood samples was

*Advanced Functional Materials*

magnetic resonance imaging and gas sensors [23].

auto-combustion the ferrite structure [7].

**4. Applications of antimicrobial activity**

varying their size, shape and crystallinity [32].

The magnetic properties of Co1−x−ySrxZnyFe2O4 (x = 0.0, 0.01, 0.05, 0.3 and y = 0.0, 0.05, 0.1, 0.4, 0.5, 0.7) NPs synthetized by spontaneous gel autocombustion (Pechini) technique were strongly influenced by the presence of both dopant ions, resulting in a superparamagnetic behavior [23]. The decrease of *MS* values with increasing dopant ions content and decreasing particle size is due to the surface anisotropy of nanoferrites, while the decrease of *HC* values is the result of some structural defects, such as dislocations, grain boundaries and anisotropy. The obtained results recommended the Zn-Sr co-doped Co ferrite as excellent candidate for various applications such as information storage devices, contrast agents in

The addition of surfactants assures the control of the crystal nucleation and growth, due to their capability to act as a protective coating for NPs, reduces coalescence and enhances the crystallite size, porosity and specific surface. All these parameters further allow the control of the magnetic properties. In this regard, Co0.5Zn0.5Fe2O4 NPs prepared by co-precipitation method with ethanol as a surfactant show good *MS* and large *HC* [13]. When Co2+ ion with higher magnetic moment replaced Ni2+ ion with lower magnetic moment at B-sites, the *HC* and *MR* of CoxNi1−xFe2O4, (x = 0.0–0.4) [26] and NixCo1−xFe2O4 (x = 0, 0.25, 0.5, 0.75, 1.0) [27] increased, while *MS* changed randomly. This increase is the result of cations distribution at the octahedral (B) and tetrahedral (A) sites in lattice structure, in spin canting and spin disorder [26, 27]. The Ni1−xCoxFe2O4 (x = 0.0, 0.15, 0.3, 0.45, 0.6, 0.75, 0.9, 1.0) synthesized by Pechini's sol-gel method showed an increase of *MS*, *HC* and *TC* by Co2+ doping. Also, the number of magnetic domains increases and

domain wall movement is facilitated by increasing particle size [28].

The magnetic properties of Co ferrite are also modified by incorporating Mn2+ ions. In case of MnxCo1−xFe2O4 (x = 0.2, 0.4, 0.6, 0.8) synthesized by sol-gel precipitation method, the *MS* increases (up to x = 0.4) and then decreases (up to x = 0.8) with increasing Mn2+ content, due to the surface disorders resulted from the distortion of the magnetic moments at the surface and to the antiferromagnetic nature of the Mn2+ ions. The *K* decreased with increasing Mn2+ content, indicating the interaction between grains [29]. The *MS* and magnetic moment increase with increasing Co2+ content in Mn1−xCoxFe2O4 (x = 0.2, 0.4, 0.6, 0.8) obtained by

Nowadays, the alternative antimicrobials are highly considered due to the intense growing bacterial resistance towards conventional drugs [30]. In this regard, the development of novel multifunctional materials with antimicrobial properties that meet the requirements of a drug delivery system allowing the minimization of antibiotic concentration is of great interest. The essential characteristics of ferrite nanoparticles such as the high surface-to-volume ratio and nanoscale particle size, improve their reaction with pathogenic microbes. Also, the high surface area, low crystallite size and porosity have a significant role in improving the efficiency of NPs even at low (20 ppm) concentrations [31]. The main drawbacks in the use of these materials are that their antimicrobial properties easily change by

There are only few studies that investigate the antimicrobial effect of transition metal substituted Co ferrite nanopowders. Zhang et al. reported that the bactericidal effectiveness against gram-negative *E. coli* bacteria of CuxCo1−xFe2O4 (x = 0.0, 0.3, 0.5, 0.7, 1.0) NPs prepared by wet chemical co-precipitation method was enhanced by increasing Cu content [33]. The mechanisms involved in the

**54**

investigated by Maksoud et al. The tested pathogens were gram-positive bacteria (*S. epidermidis, S. aureus, MRSA and E. faecalis, B. subtilis*), gram-negative bacteria (*A. baumannii, E. cloacae, E. coli, K. pneumoniae, P. aeruginosa*) and uni-cellular fungi (*C. albicans*). Zn-Co ferrite NPs displayed a maximum growth inhibition against *K. pneumoniae*, *P. aeruginosa* and *C. albicans* [30].

The antimicrobial activity of co-doped Co0.5M0.5Fe2O4 NPs (M = Cu, Zn, Mn, Ni) obtained by the sol-gel process using citric acid as the chelating agent tested against *E. coli* and *S. aureus* revealed that substituted Co ferrite NPs exhibited the most effective biocidal property, while the substitution of Zn and Cu in Co ferrite NPs considerably enhanced the antibacterial activity [45].
