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Colloids and Surfaces A: Physicochem. Eng. Aspects 374 (2011) 18

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Colloids and Surfaces A: Physicochemical andEngineering Aspects

journa l homepage: www.e lsev ier .com

Synthe idetheir an

Tamar G nera The Institute o ity, 52b The Mina and ced Mc Racah Institut

a r t i c l

Article history:Received 26 AAccepted 12 OAvailable onlin

Keywords:Zinc oxide nanoparticlesIron oxide nanoparticlesZinc ferrite nanoparticlesAntibacterial activityMagnetism

effebacteowth

ysis of reactive oxygen species (ROS) formation from water and oxygen. Aqueous suspensions of ZnOnanoparticles (ZnO nanouids) are the preferred formulation for using the antibacterial agent in liquidphases and for the incorporation of the nanoparticles in different commercial products. However, ZnOnanoparticles in aqueous media tend to aggregate into large occulates, due to their hydrophobic nature,and thusdonot interactwithmicroorganismseffectively. In this study, zinc oxidewas combinedwith ironoxide to produce magnetic composite nanoparticles with improved colloidal aqueous stability, together

1. Introdu

Antibacttries, e.g.,medicine anfor disinfecthehumanbthat are presons, the inis increasinantibacteriamore stableand some ohuman bod

CorresponE-mail add

0927-7757/$ doi:10.1016/j.with adequate antibacterial activity. For this purpose, the Zn/Fe oxide composite nanoparticles were syn-thesized by basic hydrolysis of Fe2+ and Zn2+ ions in aqueous continuous phase containing gelatin. Theobtained composite nanoparticles were composed of iron oxide, zinc oxide and zinc ferrite phases. Theeffect of the weight ratio [Zn]/[Fe] of the composite nanoparticles on their properties (composition, size,magnetic behavior and colloidal stability) was elucidated. The antibacterial activity of these nanopar-ticles was tested against Staphylococcus aureus and Escherichia coli and was found to be dependent onthe weight ratio [Zn]/[Fe], i.e., the higher the ratio, the higher the antibacterial activity. In addition, theactivity against Staphylococcus aureuswas signicantly higher than that observed against Escherichia coli.

2010 Elsevier B.V. All rights reserved.

ction

erial agents are of great importance in several indus-water disinfection, textiles, packaging, construction,d food [1,2]. The organic compounds traditionally usedtion pose several disadvantages, including toxicity toody and sensitivity tohigh temperatures andpressuressent in many industrial processes [13]. For these rea-terest in inorganic disinfectants such as metal oxidesg [1,35]. These inorganic compounds present strongl activity at low concentrations [6]. They are also muchin extreme conditions [3,4], considered as non-toxic,

f them even contain mineral elements essential to they [79].

ding author. Tel.: +972 3 5318861; fax: +972 3 6355208.ress: [email protected] (S. Margel).

Among metal oxide powders, ZnO demonstrates signicantgrowth inhibition of a broad spectrum of bacteria [10,11]. The sug-gested mechanism for the antibacterial activity of ZnO is basedmainly on catalysis of formation of reactive oxygen species (ROS)from water and oxygen [1,3,5,12,13], that disrupt the integrityof the bacterial membrane, although additional mechanisms havealso been suggested [6,10,1419]. Since the catalysis of radical for-mation occurs on the particle surface [5,20], particles with largersurface area demonstrate stronger antibacterial activity. Therefore,as the size of the ZnO particles decreases their antibacterial activityincreases [1,10,12,21].

Aqueous suspensions of ZnO nanoparticles (ZnO nanouids) arethe preferred formulation for using the antibacterial agent in liquidphases and for the incorporation of these nanoparticles in variouscommercial products such as building materials or water desalina-tion systems [3,5,10]. The dispersion of metal oxide nanoparticlesin physiological solutions is also important for biological in vitroand in vivo studies [22]. However, ZnO nanoparticles in aqueousmedia agglomerate into occulates ranging from several hundrednanometers to several microns and thus do not interact with

see front matter 2010 Elsevier B.V. All rights reserved.colsurfa.2010.10.015sis and characterization of zinc/iron oxtibacterial properties

ordona, Benny Perlsteina, Or Houbarab, Israel Felf Nanotechnology and Advanced Materials, Department of Chemistry, Bar Ilan UniversEverard Goodman Faculty of Life Sciences, The Institute of Nanotechnology and Advane of Physics, The Hebrew University, 91904 Jerusalem, Israel

e i n f o

ugust 2010ctober 2010e 29 October 2010

a b s t r a c t

Inorganic metal oxides may serve aschemical stability and efcient antidemonstrates signicant bacterial gr/ locate /co lsur fa

composite nanoparticles and

c, Ehud Baninb, Shlomo Margela,

900 Ramat Gan, Israelaterials, Bar Ilan University, 52900 Ramat Gan, Israel

ctive disinfectants, due to their relatively non-toxic prole,rial activity. Among metal oxide nanoparticles, zinc oxideinhibition on a broad spectrum of bacteria, mainly by catal-

2 T. Gordon et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 374 (2011) 18

microorganisms effectively [12,22,23]. Several research groupshave applied different methods, e.g., ultrasonication, milling anduse of stabilizing agents [3,16,22], in order to avoid nanopar-ticle aggregation, but this appears to have been only partiallysuccessful.

By contnanoparticlbe kept as aperiods of tantibacteriamagnetic nation of H2Oreagent (Feto producethis radicalcles, to enh

In our lathe preparaticles of acontinuousnucleationon gelatin/with magnloidal stabiof the nanoids from exstudy, sevethesizedbyratios on geoxide nanogated.

2. Experim

2.1. Materi

Gelatinchloride anAldrich (Rewater throuLtd., High W

2.2. Preparacomposite n

Magnetidescribed p(10mmol/5containingtion (6mmoraised to 9.dure was reby extensivof the nano

Zn/Fe oxmanner, suof different[Zn]/[Fe] offerent voluwith approHCl). 240the gelatin

ZnOnanFe2+ ions by

2.3. Nanoparticles characterization

Quantitative analysis of Zn and Fe was performed by analyzingsolutions of the nanoparticles in 6N HCl, using inductively coupled

(ICPwas

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nanarticlNaN2 shnanoide nrast, ferrouid (suspensions of magnetic iron oxidees such as Fe3O4) have good colloidal stability, and mayn aqueous suspension without agglomeration for longime. However, they are not known to have signicantl properties, in spite of the recent nding that Fe3O4noparticles possess catalytic activity toward the reduc-2 [24]. The iron oxide nanoparticles act as Fentons

2+/Fe3+ in solutions) that reacts with hydrogen peroxidehydroxyls and peroxide radicals. One may suggest thatformation acts synergistically with the ZnO nanoparti-ance their antibacterial effect.boratory, we have recently developed a newmethod fortion of stable non-toxic iron oxide magnetic nanopar-narrow size distribution dispersed in an aqueousphase [2527]. These nanoparticles are prepared byand then growth of thin magnetic iron oxide layersiron oxide nuclei. Combining the ZnO nanoparticlesetic iron oxide nanoparticles may improve the col-lity of the ZnO nanouid, and provide easier handlingparticles for concentrating and cleaning the nanou-cess reagents by a magnetic column [2527]. In thisral zinc/iron oxide composite nanoparticles were syn-basichydrolysisof Fe2+ andZn2+ ionsofdifferentweightlatin/Zn/Fe nuclei. The stability of the different Zn/Fe

uids and their antibacterial activity were also investi-

ental

als

(from porcine skin), ferric chloride tetrahydrate, zincd sodium nitrate were all purchased from Sigmahovot, Israel). Water was puried by passing deionizedgh an Elgastat Spectrum reverse osmosis system (Elgaycombe, UK).

tion of the Fe3O4, the ZnO and the Zn/Fe oxideanoparticles

c iron oxide (Fe3O4) nanoparticles were prepared asreviously [25,26]. Briey, 240l FeCl24H2O solutionml 0.01N HCl) were added to 80ml aqueous solution240mg porcine gelatin, followed by 86l NaNO3 solu-l/5ml H2O). After a reaction time of 10min, the pH was5 by adding NaOH aqueous solution (1N). This proce-peated four more times. Excess reagents were removede dialysis against water, which also neutralized the pHparticle dispersions.ide composite nanoparticles were prepared in a similarbstituting the Fe2+ ions for a mixture of Fe2+ and Zn2+

weight ratios. The mixtures containing weight ratio1:9, 3:7, 1:1, 8:2 and 9:1 were prepared by mixing dif-mes of FeCl24H2O solution (10mmol/5ml 0.01N HCl)priate volumes of ZnCl2 solution (10mmol/5ml 0.01Nl of each of the [Zn]/[Fe] mixtures were then added tosolution.oparticleswere alsoprepared similarly, substituting theZn2+ ions and eliminating the NaNO3 oxidation step.

plasmaZnO

ray difradiati

Moxideature (50mCianalyzne eare rel

Thecles w(TechnLaB6),Systembutionwere mElectro

Mausing ainterfe

2.4. An

Thetested(Gram105 cellight w37 C.serial dcolony

3. Res

Ironsized bthin nucleachelatiboxylato appwater-Gelatinous sothe genuclea

Zn/substitweightcles ofwere ppositeadded.

ZnOnanoping the

Fig.ferentiron ox) spectrometer Ultima-2 (Jobin Yvon Horiba).identied by X-ray diffraction (XRD) spectroscopy (X-

ometer, model D8 Advance, Bruker AXS, with Cu K

er studies (MS) of the iron oxide and the various Zn/Feosite nanoparticles were performed at room temper-using a conventional constant acceleration drive and:Rh sources. The experimental magnetic spectra werea least square t procedure, where a magnetic hyper-

Heff) distribution was used. The 57Fe isomer shifts (I.S.)to -Fe, measured at RT.diameter and size distribution of the various nanoparti-easured by transmission electron microscopes (TEM)2 BIO TWIN operating at 120kV and JEOL-JEM2100

g image analysis software AnalySIS Auto (Soft ImagingbH, Germany). The hydrodynamic size and size distri-e nanoparticles dispersed in aqueous continuous phaseured by a submicron particle analyzer (N4MD, CoulterLtd., Hialeah, FL, USA).c measurements were performed at room temperature,mercial (Quantum Design) superconducting quantum

e device (SQUID) magnetometer.

crobial studies

imicrobial activity of the various nanoparticles wasg two common bacterial pathogens: Escherichia colitive) and Staphylococcus aureus (Grampositive). Briey,l in LuriaBertani broth (LB) were shaken (250 rpm) inthe various nanoparticles mixtures (0.3%) for 24h atnumber of viable bacteria was determined by platingons on LB agar plates and determining the number ofing units (CFU) [28].

and discussion

enanoparticles of 17.34.6nmdiameterwere synthe-cleation, followed by controlled growth of iron oxidento gelatin/iron oxide nuclei, as shown in Fig. 1. Thestep is based on the complexation of Fe2+ ions withtes of the gelatin (probably primary amines and/or car-followed by partial oxidation with sodium nitrate (upately 50%) of the chelated Fe2+ to Fe3+, so that thele gelatin contains both Fe2+ and Fe3+ chelated ions.oxide nuclei were then formed by adding NaOH aque-

n up to pH 9.5. The growth of the iron oxide lms onto/iron oxide nuclei was accomplished by repeating thestep four more times.ide composite nanoparticles were prepared similarly,the Fe2+ ions by a mixture of Fe2+ and Zn2+ of different

os. In this study ve Zn/Fe oxide composite nanoparti-rent [Zn]/[Fe] weight ratios (1:9, 3:7, 1:1, 8:2 and 9:1)red. The [Zn]/[Fe] weight ratios of the produced com-particles were similar to the [Zn]/[Fe] ratios initially

oparticleswere also prepared similarly to the iron oxidees, substituting the Fe2+ ions by Zn2+ ions and eliminat-O3 oxidation step.

ows a picture of a similar concentration (0.4%) of the dif-particles dispersed in anaqueous continuousphase. Theanoparticles and the Zn/Fe oxide composite nanopar-

T. Gordon et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 374 (2011) 18 3

ticles contablack coloryellow withaqueous susdetected intion of thetranslucentpension, whillustrated l

Mssbau[Zn]/[Fe] oxdemonstratwithout anyindicates thFig. 1. A scheme describing the formation of the magnetic

ining a relatively high percentage of iron have a typical, which changes to lighter shades of brown and then

increasing percentage of Zn. The ZnO nanoparticlepension has a typical white color. No precipitation wasthe suspensions for at least 2 weeks after the comple-synthesis. All nanoparticles aqueous suspensions weredue to their small particle size, except for the ZnO sus-ich already contains agglomerated particles as will beater.er spectra of the iron oxide nanoparticles and theide composite nanoparticles of the weight ratio 1:9emagnetismat RT and smeared broadmagnetic sextetsdistinct peaks. The distance between the extreme lines

at theblocking temperature (TB) of these samples iswell

above RT. T455 (4) kO515 and 49ues are 491that the smand [Zn]/[Fwhicharemcussed latedetected, an

The RTZn/Fe oxidedoublet onsplitting (1interpretatiiron oxide nanoparticles.

he t of both spectra indicates a maximum Heff value ofe. The RTHeff values forFe2O3 and Fe2O3 are around5kOe, respectively, whereas for Fe3O4 the two Heff val-and 453kOe [29]. These results, therefore,may indicateearedmagnetic spectra of these two samples (iron oxidee] of weight ratio of 1:9) correspond to nano-size Fe3O4agneticallyorderedatRT. TheZnphase (ZnFe2O4 asdis-

r) in the 1:9 [Zn]/[Fe] oxide nanoparticles could not bed probably was hidden within the smeared spectrum.

Mssbauer spectra obtained for the remainder of thesamples are very similar to each other and show one

ly with an I.S. of 0.340.36mm/s and a quadrupole/2e2Qq) in the range of 0.560.64mm/s. Therefore, ouron is that the Mssbauer spectra of these Zn/Fe oxide


Fig. 2. A pictu composite nanoparticles dispersed in an aqueous continuous phase (0.4%),from iron oxid

nanoparticllower thanthe [Zn]/[Feture at 14Oobvious thaperatures.ZnFe2O4 paquadrupoletionmade ananoparticl

XRD stuof the varioof Fe3O4 anHowever, frposite nanoand 9:1, cona hexagonaies of the Znsame wurtzspectra of t3:7and1:1,limit) and/o

The fastTEM (HRTEfor the concTypical anaticles and trespectivelycrystalline oter of the imThedistancmatching thture of Fe3representsof the imagtion patternexperimentcan readily065-3107, aBecause thdistinguishing techniqnanoparticltioned oxidagreementbility of therepresentslined by thefringes are

erplanar spacings d220, d311 and d131 in the cubic FCC struc-Fe3O4 or that of ZnFe2O4. This is sufcient proof that the]/[Fe] oxide composite nanoparticles contains Fe3O4 and/or4.4 represents a HRTEM micrograph of the ZnO nanopar-

displaying typical lattice-fringe contrast of closely-packedanoparticles (5nm diameter). Fourier analysis of the lat-ages was readily available to provide identication of thenO nanoparticles. The Fourier transform pattern taken fromage is illustrated in the inset in Fig. 4. Analysis of this pat-vealed ring pattern like reections that can be referreddexed in terms of the hexagonal structure describing ZnOarameters: a=3.25 A, c=5.21 A, PDF 01-089-1397). Fromeections the following distances were calculated: 0.28nm,m ad000dry

compess tide n17.3re showing the visibility of the iron oxide, the zinc oxide and the various Zn/Fe oxidee only (left) to zinc oxide only (right).

es belong to nano-size Fe3O4 particles with TB valuesRT. Indeed, typical study of the magnetic behavior of] sample of weight ratio 3:7 as a function of tempera-e indicates clearly that its TB is around 100K. It is quitet for lower Fe concentrations TB should be at lower tem-Alternatively, Mssbauer measurements of nano-sizerticles performed recently at RT [30], also exhibit a puresplitting of about 0.42 (2)mm/s. Thus, the determina-bove is not conclusive, and these Zn/Fe oxide compositees may contain ZnFe2O4 phase and/or Fe3O4 phase.dies were performed in order to identify the ZnO phaseus nanoparticles. Due to the similarity in the structured ZnFe2O4 the two phases are indistinguishable by XRD.om the XRD spectra it can be concluded that the com-particleswith the higher [Zn]/[Fe]weight ratios, i.e., 8:2tain, in addition to the iron oxide or zinc ferrite phases,l phase of wurtzite ZnO (PDF 01-089-1397). XRD stud-O nanoparticles exhibit that they are composed of theite ZnO phase. ZnO phase was not identied in the XRDhe composite samples of [Zn]/[Fe] of weight ratios 1:9,eitherdue to its lowconcentration (belowthedetectionr low crystallinity, or because of its absence.Fourier transform (FFT) analysis of the high resolutionM) images of the nanoparticles provides further supportlusionsmade regarding the identication of eachphase.lyses of the 3:7 [Zn]/[Fe] oxide composite nanopar-he ZnO nanoparticles are presented in Figs. 3 and 4,. The micrograph shown in Fig. 3 illustrates a singlef the 3:7 [Zn]/[Fe] oxide composite nanoparticle (cen-age). The nanoparticle displays lattice-fringe contrast.

esmeasured between these lattice fringes are 0.298nm,e interplanar spacing d022 of both the cubic FCC struc-

O4 and ZnFe2O4. The inset at the top right corner (A)the computed Fourier transform pattern of the portione marked by the white square and looks like a diffrac-identical to one that would be recorded in a diffraction

the intture of3:7 [ZnZnFe2O

Fig.ticles,ZnO ntice imsmall Zthe imtern reand in(cell pthese r0.266nd1010,

Theoxideto be liron oxoxide:. Analysis of this pattern reveals sets of reections thatbe referred to the FCC structure of both Fe3O4 (PDF 03-=8.39 A) and ZnFe2O4 (PDF 01-082-1042, a=8.44 A).

ese oxides are structurally similar they could not beed in the high resolution image. But this image analyz-ue suggests that these 3:7 [Zn]/[Fe] oxide compositees might be composed of one or both of the above men-es (Fe3O4 or ZnFe2O4). This observation is also in goodwith the Mssbauer ndings that also show the possi-se two oxides. The inset in the left top corner of Fig. 3(B)the ltered and magnied portion of the image out-white square. The distances measured between lattice0.29nm, 0.26nm and 0.26nm matching respectively,

Fig. 3. High roxide composthe image). Thsured betweend022 of both thFourier transfotions correspois the processthe lattice frinspacings.nd 0.248nm, corresponding to the interplanar spacing2 and d1011 planes, respectively.diameter of the iron oxide, the zinc oxide and the Zn/Feosite nanoparticles, as measured by TEM, was found

han 20nm. Table 1 shows that the dry diameter of theanoparticles is signicantly larger than that of the zinc4.6 and 3.90.5, respectively. In addition, the particleesolution electron micrograph (FFT processed) of the 3:7 [Zn]/[Fe]ite nanoparticle showing a single crystalline nanoparticle (center ofe nanoparticle displays lattice-fringe contrast. The distances mea-these lattice fringes are 0.298nm, matching the interplanar spacing

e cubic FCC structure of Fe3O4 and ZnFe2O4. Inset (A) is the computedrmtaken fromthemarkedarea (white square), showing sets of reec-nding to the interplanar spacing, d220, d311 and d131 planes. Insert (B)ed and magnied image of the marked area (white square) showingges of the d220, d311 and d131 planes with the marked interplanar


Fig. 4. High resolution electron micrograph of ZnO nanoparticles showing closelypacked agglomerate-like ZnO crystalline nanoparticles (5nm). The inset is thecomputed Fourier transform pattern of the image showing sets of reections corre-sponding to the interplanar spacing d1010, d0002 and d1011 planes.

Table 1Mean diameter of the iron oxide, the zinc oxide and the zinc/iron oxide compositenanoparticles.

[Zn]/[Fe] (w/w) Particle diameter [nm]

Dry Hydrodynamic

Iron oxide 17.3 4.6 100 361:9 14.9 4.0 111 343:7 11.3 2.5 125 591:1 4.2 0.5 138 628:2 3.5 0.5 138 379:1 3.4 0.7 161 48Zinc oxide 3.9 0.5 296 47

size decreases as the weight ratio of [Zn]/[Fe] increases, as demon-strated in Table 1 and in the TEM (Fig. 5) and the HRTEM imagesshown in Figs. 3 and 4. Table 1 also demonstrates that the hydrody-namic diameter of the different oxide nanoparticles, as measuredby light scattering, is signicantlyhigher than that of thedrydiame-ter, e.g., thehydrodynamicdiameterof the ironoxidenanoparticles,the 3:7 [Zn]/[Fe] oxide composite nanoparticles and the zinc oxidenanoparticles are 10036, 12559 and 29647nm, respec-tively while that of the dry diameter are 17.34.6, 11.32.5 and3.90.5nm, respectively. Themain reason for this difference is dueto the fact that the hydrodynamic diameter measurements are per-formed in aqueous continuous phase and also include the water

Fig. 5. TEM images of the iron oxide nanoparticles (A), the 3:7 [Zn]/[Fe] composite nanoparticles (B), the(D).8:2 [Zn]/[Fe] composite nanoparticles (C) and the ZnO nanoparticles


Fig. 6. Magne[Zn]/[Fe] oxidenetic hysteres

molecules aalso exhibitdynamic dithe smallesthe ZnO nancontrary tofor the ironrelatively hmay be dueto their relthat the ironanoparticlwhile the Zpacked agg

MagnetiZnO and theFig. 6. Ferronanoparticlweight ratiloop at roooxide nanonetite and tnanoparticlZn/Fe oxideof the latterFor the [Zn]the temperaat 14Oe ind100K).Howat RT showsa ferromagn

eansd forus Znnanoptization curves at room temperature of the iron oxide, ZnO andcomposite nanoparticles of weight ratio 3:7, 1:1 and 8:2: ferromag-

is loop curves (A) paramagnetic and diamagnetic curves (B).

Fig. 7. Mincubatethe variowithoutdsorbed on the surface of these nanoparticles. Table 1s that the ZnO nanoparticles possess the highest hydro-ameter, whereas the iron oxide nanoparticles showt hydrodynamic diameterabout 3 times smaller thanoparticles (10036nm vs. 29647nm, respectively),the dry diameter ratio of those nanoparticles (17.34.6oxide and 3.90.5nm for the ZnO nanoparticles). Thisigh hydrodynamic diameter of the ZnO nanoparticlesto partial agglomeration of these nanoparticles, due

atively hydrophobic nature. Indeed, Fig. 5 illustratesn oxide nanoparticles and the Zn/Fe oxide compositees are composed of single non-agglomerated particles,nO nanoparticles (Fig. 5D) are composed of closely

lomerated nanoparticles.zation curves at room temperature of the iron oxide, theZn/Fe oxide composite nanoparticles are illustrated inmagnetic behavior was found only for the iron oxidees and the [Zn]/[Fe] oxide composite nanoparticles ofos 1:9 and 3:7. Fig. 6A exhibits the typical hysteresism temperature of the iron oxide and the 3:7 [Zn]/[Fe]particles. The ferromagnetism is attributed to the mag-o the zinc ferrite phases [31]. As expected, themagnetitees show a higher magnetic saturation moment than thecomposite nanoparticles, due to the lower Fe quantity(the values are stated in units of emu/g nanoparticles)./[Fe] oxide composite nanoparticles of 3:7 weight ratio,ture dependence of themagnetization curvemeasuredicates that its TB is below room temperature (aroundever, isothermal elddependenceof themagnetizationa ferromagnetic-like behavior, whichmay be related toetic residue at RT. Fig. 6B exhibits that the Zn/Fe oxide

compositeshow paramnanoparticlticles demo

The antithe variousined on twbacteriumresults are

The ZnOand complecomposite nOverall it iszinc/iron oxa bactericida [Zn]/[Fe]8:2, 9:1 andcaused onlyteriostatic athe [Zn]/[Feaffect on E.ous reportto ZnO thanobserved inpolarity of tthat the S.E. coli. Thischarged freoxide ions,concentratiand standard errors of CFU per ml of E. coli (A) and S. aureus (B)24h in LB media in the presence of the iron oxide, the zinc oxide and/Fe oxide composites (0.3%). The control refers to bacteria incubatedarticles. *No CFU count.nanoparticles with [Zn]/[Fe] weight ratio of 1:1 and 8:2agnetic behavior, whereas zinc/iron oxide composite

es with [Zn]/[Fe] weight ratio of 9:1 and ZnO nanopar-nstrate diamagnetic behavior [32].microbial activity of the iron oxide, the zinc oxide andZn/Fe oxide composite nanoparticles has been exam-o common bacterial pathogens: the Gram negativeE. coli and the Gram positive bacterium S. aureus. Thesummarized in Fig. 7.nanoparticles exhibit the highest bactericidal activitytely eradicated both bacterial species. The Zn/Fe oxideanoparticles show variable activity on the two species.clear that the S. aureus is more sensitive to some of theide composite nanoparticles than E. coli. For example,al affect against S. aureus is evident in all particles withweight ratio higher than 1:1 (i.e., [Zn]/[Fe] weight ratioZnOnanoparticles),while complete killing of E. coliwasby particles containing only ZnO. Furthermore, a bac-ffect on S. aureus is evident in nanoparticles in which] weight ratio was 1:1, whereas those particles had nocoli. These ndings are in good agreement with a previ-that also demonstrated that S. aureus is more sensitiveE. coli [28]. One explanation for the higher resistanceE. coli compared to S. aureus is due to differences in theheir cell membrane. Sonohara et al. [33] have reportedaureus membrane has a smaller negative charge thanwould allow a higher level of penetration of negativelye radicals such as superoxide radical anions and per-causing damage and cell death to S. aureus at lowerons than those required to damage E. coli [21,28,33].


The ability of ZnO to inhibit bacterial growth by generation ofradical oxygen species is well documented [1,3,5,12,13]. ZnO is asemiconductor with a wide band gap. As with other semiconduc-tors, radiation of ZnO with higher photon energy than its band gapcauses movconductionthe formatiin the valenthe surfacegroups andence of oxya superoxidso forth. De[5]. It couldwould act iof free radicnanoparticlweight ratioproperties,activity. It cof the zinc/istudy are msis, iron oxi[Zn]/[Fe] wlimited antiour XRD meactivity in t

4. Conclus

The presoxide, zincranging betgrowth of Ziron oxide nite nanopar1:1 are comdetected). T8:2 and9:1magnetite pnetite and/nanoparticltion: the loeffect, and talso exhibitthe antibacStaphylococsitive. AlthE. coli wasposite nanohave shownand to a lenanoparticlas antibact(as ZnO nanIn the futuand the Zn/include othticles forwapollutants w

Acknowled

This stu(Microscalethank to Dr

References

[1] O. Yamamoto, Inuence of particle size on the antibacterial activity of zincoxide, International Journal of Inorganic Materials 3 (2001) 643646.

[2] Q.L. Li, S. Mahendra, D.Y. Lyon, L. Brunet, M.V. Liga, D. Li, P.J.J. Alvarez,imicrl: pot146hang,aviouopart

awai,dersMetheven,infecti

andmistrraynelogicaopart. Sandrnal o. PrasaRosellturedtritionones,e suspters 27. Adam2, andAppleanke

reased852amamracteriu, L.c oxidrobio. Tam.C. Leurothe. Huan. Hao,(2008kiyamchme(1998atsunof m

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biomearatioerlstevectioMRI. Reddof zinsics Lement of electrons from the valence band (vb) to theband (cb) of the particle. The result of this process ison of a positive area that can be described as a hole (h+)ce band and a free electron in the conduction band. Onof the ZnO particles, these holes react with hydroxylabsorb water to create a hydroxyl radical. In the pres-gen, the lone electron in the conduction band createse ion, which can also become a hydroxyl radical, andrivatives of this active oxygen damage the bacterial cellbe hypothesized that zinc ferrite, also a semiconductor,n a similar manner, and would catalyze the formationals [34]. This, however, is not the case. The compositees containing zinc ferrite (i.e., those with the [Zn]/[Fe]of 1:9 and 3:7) did not show signicant antibacterial

proving that zinc ferrite has no signicant antibacterialan therefore be assumed, that the antibacterial activityron oxide composite nanoparticles characterized in ourediated by the ZnO phase. In support of this hypothe-de nanoparticles and composite nanoparticles with theeight ratio of 1:9 and 3:7, that show either zero or verymicrobial activity, did not contain any ZnO according toasurements. This may explain the lack of antibacterialhose particles.

ions

ent study demonstrates the unique synthesis of ironoxide and Zn/Fe oxide composite nanoparticles of sizesween3 and17nm, by nucleation followedby controlledn/Fe oxide lms onto gelatin/Zn/Fe oxide nuclei. Theanoparticles are composed of magnetite. The compos-ticles with the [Zn]/[Fe] weight ratios of 1:9, 3:7 andposed of magnetite and zinc ferrite (ZnO phase was nothe composite nanoparticles with the [Zn]/[Fe] ratios ofare composedof zincoxideandeither zinc ferrite and/orhases. This study illustrates that the integrationofmag-or zinc ferrite phases into the Zn/Fe oxide compositees stabilizes these nanoparticles against agglomera-wer the [Zn]/[Fe] ratio, the higher the stabilizationhus the magnetization of the nanoparticles. This studys that the higher the [Zn]/[Fe] weight ratio the higherterial activity of the nanoparticles against E. coli andcus aureus, while the latter was found to be more sen-ough the most efcient antibacterial activity againstdemonstrated for ZnO particles, the Zn/Fe oxide com-particles with [Zn]/[Fe] weight ratio higher than 1:1good bacteriostatic activity on Staphylococcus aureus,

sser extent against E. coli. Therefore, these compositees, applied at higher concentrations, may also be usederial agents, when good colloidal stability is requiredoparticles agglomerate immediately after synthesis).

re, the study of the antibacterial activity of the ZnOFe oxide composite nanoparticles will be extended toer bacterial strains, and the utilization of these nanopar-ter purication fromorganicwaste aswell asmicrobialill also be investigated.

gements

dy was partially supported by a Minerva Grant& Nanoscale Particles and Films). The authors also

. Judith Grinblat for her help in the HRTEM analysis.

Anttro459

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Synthesis and characterization of zinc/iron oxide composite nanoparticles and their antibacterial propertiesIntroductionExperimentalMaterialsPreparation of the Fe3O4, the ZnO and the Zn/Fe oxide composite nanoparticlesNanoparticles characterizationAntimicrobial studies

Results and discussionConclusionsAcknowledgementsReferences

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