ANTIBIOTIC COATED MAGNETITE NANOPARTICLES FOR BIOLOGICAL APPLICATIONS

Transcription

1 ANTIBIOTIC COATED MAGNETITE NANOPARTICLES FOR BIOLOGICAL APPLICATIONS E.L. Foca-nici Ciurlica a, C. Nadejde a, D.E. Creanga a, A. Carlescu a and V. Badescu b a Faculty of Physics, Alexandru Ioan Cuza University of Iasi, 11A Carol I Bd., , Iasi, Romania b National Institute of Research & Development for Technical Physics, 7 Mangeron Bd., Iasi, Romania dorina.creanga@gmail.com Abstract Biomedical uses of magnetic nanoparticles are mostly focused on tumor cells investigation and treatment while in the next we present new antibiotic coated Fe 3 O 4 nanoparticles intended as magnetically controllable pharmaceutical agents for the recovery of bacteria loaded tissues and organs. We described the stable magnetic colloid prepared by an adapted coprecipitation method, with further magnetite stabilization by oleic acid and second layer of biologically active molecule (rifampicin - a broad-spectrum bacteriostatic antibiotic efficient in lung infectious diseases). Physical investigations of the double-layer coated magnetite nanoparticles were carried out by X-ray diffraction (XRD), and Vibrating Sample Magnetometry (VSM) and capillary viscosimetry that evidenced good crystalinity, granularity, magnetic and rheological properties of the submicron magnetic particles. The mean particle size calculated from Fe 3O 4 diffraction peaks according to the Debye Scherrer formula was equal to 11.9 nm while the magnetic core diameter was found equal to 8.5 nm. Ferrophase volume fraction was equal to 2.56 % while viscosity was found equal to Kg /ms. The issues of product efficiency but also of its stability and preservation led to the utilization of chloroform in the step of double coating with rifampicin due to high solubility level, considering further possible lyophylization and resuspension in water prior utilization. Keywords: co-precipitation, magnetite, oleic acid, rifampicin, biocompatibility, stability 1. INTRODUCTION Superparamagnetic nanoparticles have been intensively studied due to their diversified applications, in both technical and biomedical fields. Magnetic nanoparticles can be dispersed in carrier fluids due to specific interactions between the particle surfaces and surfactant shells as well as between the coating shell and the carrier fluid. Complex structure type magnetic core/non-magnetic shell is required for the stability of the nanoparticle dispersions in the carrier liquids (to prevent ferrophase particles agglomerations) for most types of applications. Magnetic nanoparticles intended for biomedical applications are usually biocompatible ferrite powders coated with organic molecular shell able to ensure active pharmaceutical agents grafting on the functionalized surface of magnetic nanoparticles. Iron oxides, such as magnetite (Fe 3 O 4 ) are rather stable against oxidation and display significant magnetization, being preferred in various applications due also to their lack of toxicity [1-3]. Several studies reported various procedures of coating iron oxide nanoparticles either with double layers based on of fatty acids [4] or by capping the magnetic cores with a carboxylic acid shell such as oleic, lauric or myristic acid with further dispersion in a non-polar carriers [5, 6] or in polar media containing biologically active molecules [7] or polymers [8]. One common efficient technique for magnetite nanoparticles synthesis with convenient size distribution is the aqueous co-precipitation method. Based on this type of protocol, we report the preparation routine and physical characterization of submicron-sized magnetite particles, stabilized with oleic acid and further functionalized with antibiotic molecules (rifampicin) dispersed in organic solvent (chloroform)

2 aiming lyophylization preservation, in order to develop a stable magnetic fluid based on double-layer coated magnetite nanoparticles, intended for drug delivery toward tissues and organs loaded with bacterial germs. 2. EXPERIMENTAL Ferrous chloride tetrahydrate (FeCl 2 x 4H 2 O), ferric chloride hexahydrate (FeCl 3 x 6H 2 O), sodium hydroxide (NaOH), oleic acid, ethanol and chloroform used in this experimental protocol (all pure reagents) were purchased from Sigma-Aldrich. Distilled deionized water was used throughout the whole experiment to prepare the solutions. Rifampicin pure crystalline powder (C 43 H 58 N 4 O 12 ), provided by Sigma, is a broad-spectrum bactericidal antibiotic of the rifamycin group, typically indicated for the treatment of lung bacterial infections, such as tuberculosis. In this work, we performed the synthesis of magnetite nanoparticles based on chemical precipitation of mixed trivalent and divalent iron ions (2:1 molar ratio) in alkaline medium at relatively high temperature (80ºC) and in atmospheric conditions; the preparation protocol (which is not a complicated process but it seems to be rather difficult to control), is summarized in Figure 1. FIG. 1. Preparation steps of the double-layered magnetite nanoparticles (NP- nanoparticle) Chemical co-precipitation consists of two processes: nucleation (formation of centers of crystallization) and subsequent growth of particles; the co-precipitation process (Massart s procedure [9]), was carried out by dropwise addition of 100 ml NaOH solution 25% into the mixture of the aqueous solutions of iron salts (0.358 g FeCl 3 x 6H 2 O in 100 ml deionized water and g FeCl 2 x 4H 2 O in 100 ml deionized water), brought at the

3 temperature of 80 C, and maintained at this temperature under continuous vigorous magnetic stirring, following the reaction: 8NaOH + 2FeCl 3 + FeCl 2 Fe 3 O NaCl + 4 H 2 O The solution turned from brown to black indicating the formation of magnetite (Fe 3 O 4 ). Nucleation and growth of magnetite particles were allowed to occur for 60 minutes under continuous magnetic stirring. Following the precipitation process, the separation of two phases can be easily observed: solid phase and supernatant liquid. First, the black solid phase was magnetically decanted (while the supernatant was carefully removed) and repeatedly washed with deionized water (in order to ensure the elimination of residual salts); further washing with 2 ml ethanol was needed for water traces removal as well as subsequent heating for five minutes to ensure the ethanol evaporation. Ferrophase was sterically stabilized with 6 ml oleic acid (OA), the mixture being heated up to 80 C on a water bath, under intense stirring for 30 minutes. Excess oleic acid was phase separated by dropwise addition of 4 ml of water, then the OA-coated magnetite was washed twice with 30 ml ethanol [10]. The OA-coated iron oxide nanocrystals were further dispersed in 6 ml of chloroform containing 30 mg rifampicin (RIF), with vigorously magnetic stirring for one hour. The result of this multi-step procedure was 10 ml stable magnetic fluid based on double-layer coated magnetite nanoparticles that could be further transferred into water prior the utilization. The particle size, fluid viscosity, as well as the saturation magnetization, are of great importance for the magnetic fluid behavior. Thus, the main features such as volume fraction of the nanoparticles and the viscosity of the fluid were measured using standard laboratory techniques: the density and volume fraction were assessed by gravimetric method using a PW 254 balance with 10-4 g accuracy, while viscosity was determined by capillary method using an Ubbelohde viscometer. X-ray diffraction (XRD) investigation of the sample was accomplished using a Shimadzu 6000 X-ray diffractometer using Cu-K α radiation at λ = Å. The crystallite size was determined from the full width at half medium of the 311 peak based on Debye-Scherrer formula. The magnetization curves were obtained with a Quantum Design 600 vibrating sample magnetometer (VSM) at room temperature. 3. RESULTS AND DISCUSSION The aqueous magnetic fluid obtained through the dispersion of double layer coated magnetite nanoparticles was characterized by rheological investigation (data presented in Table 1). TABLE 1. The rheological properties of double shell coated magnetite dispersed in chloroform Density Volume fraction Viscosity Fluid type (Kg/m 3 ) (%) ( x 10-3 Kg/ms) Magnetic fluid sample Chloroform The XRD pattern (Fig. 3) of the synthesized magnetite nanoparticles displayed characteristic peaks, having positions and relative intensities consistent with the spinel structure of magnetite crystals.

4 (a) (b) FIG. 2. (a) The XRD patterns (b) The magnetization curves of the magnetite nanoparticles with OA-RIF shell The mean particle size calculated from Fe 3 O 4 diffraction peaks according to the Debye Scherrer formula (equation 1) was equal to 12 nm (Table 2): Kλ D XRD = (1) β cosθ where K is the shape factor (K = 0.9), the X-ray wavelength, λ = 1.54 Å, β is the line broadening at half the maximum intensity (FWHM) in radians and θ is the Bragg angle. The magnetic properties of the resulted magnetite nanoparticles were estimated from their magnetization and susceptibility curves (Fig. 4). The double-layered nanoparticles exhibit superparamagnetic behavior, the saturation magnetization being as high as ka/m. Using magnetization data, the average size of magnetic diameter (d M ) and the concentration of the coated nanoparticles in the sample was calculated using Langevin s equation (Table 2): 3 18k d M = πµ M 0 B T dm S M dh B S H 0 (2) n 6 M s 3 d M M B = π (3) In the above relations, d M is the magnetic particle diameter, n is the concentration of magnetic nanoparticles in the fluid, k B is Boltzmann s constant (k B = Nm/K), T the absolute temperature, µ 0 vacuum magnetic permeability (µ 0 = N/A 2 ), M S saturation magnetization of the sample and M B saturation magnetization of the bulk magnetite (M B = 0.92 x 10 6 A/m). TABLE 2. The dimensional analysis data of the investigated magnetic fluid samples D XRD (nm) d M (nm) n ( x /m 3 )

5 Experimental investigations, including XRD and magnetometry studies, suggested that the relatively low saturation magnetization of coated nanoparticles is possibly due to their surface characteristics, in our case being most likely attributed to the existence of surfactants non-magnetic coatings. Further improvement of the experimental procedure is intended to enhance magnetic control possibilities in the antibiotic coated magnetic nanoparticles toward the bacterial loaded organs where classical treatments failed. 4. CONCLUSIONS Following the investigation of the nano-sized magnetite particles, we assume that the resulted magnetic fluid based on double-layer coated nanoparticles obtained by co-precipitation method, could be used for biological applications. Manufacturing such type of nanomaterials, could be also useful in cell therapies by targeting celldelivery systems loaded with magnetite nanoparticles in the presence of uniform magnetic fields. The use of chloroform as carrier liquid was motivated by the ability of this solvent to dissolve biodegradable molecules forming an organic phase that can be emulsified in an aqueous solution followed by organic solvent evaporation. Thus, the resulted magnetic nanoparticles can be resuspended in deionized water, and further used in various biomedical applications. ACKNOWLEDGMENTS The authors acknowledge The National Council of the Higher Education's Scientific Research (CNCSIS), which financially supported the present study, through the grant PN II IDEI_2021 no. 474/2009. REFERENCESS [1.] GUSTAFSSON, S., et al., Evolution of Structural and Magnetic Properties of Magnetite Nanoparticles for Biomedical Applications, Cryst. Growth Des., year 2010, nr. 10 (5), page [2.] KIPP, J.E., The role of solid nanoparticle technology in the parenteral delivery of poorly watersoluble drugs, Int. J. Pharm., year 2004, nr. 284, page 109. [3.] TOURINHO, F.A., et al., Electric double layered magnetic fluids based on spinel ferrite nanostructures, Braz. J. Phys., year 1998, nr. 28 (4), page 345. [4.] BICA, D.,et al., Sterically stabilized water based magnetic fluids: syntheissi, structure and properties, J. Magn. Magn. Mat., year 2007, nr. 311, page 17. [5.] VEKAS, L., BICA, D., and AVDEEV, M., Magnetic nanoparticles and concentrated magnetic nanofluids: synthesis, properties and some applications, China Particuology, year 2007, nr. 5, page 43. [6.] XU, H., et al., Preparation of hydrophilic magnetic nanospheres with high saturation magnetization, J. Magn. Magn. Mat., year 2007, nr. 311, page125. [7.] ZABLOTSKAYA, A., et al, Synthesis and characterization of nanoparticles with an iron oxide magnetic core and a biologically active trialkylsilylated aliphatic alkanolamine shell, J. Magn. Magn. Mat., year 2007, nr. 311, page 135. [8.] KALELE, S., NARANI, R. and KRISHNAN, K.M., Probing temperature-sensitive behavior of pnipaam-coated iron oxide nanoparticles using frequency-dependent magnetic measurements, J. Magn. Magn. Mat., year 2009, nr. 321, page 1377.

6 [9.] MASSART, R., Preparation of aqueous magnetic liquids in alkaline and acidic media, IEEE Transactions on Magnetics, year 1981, nr. 17, page [10.] POLYAK, N., et al., High field gradient targeting of magnetic nanoparticle-loaded endothelial cells to the surfaces of steel stents, Proc. Natl. Acad. Sci. U S A., year 2008, nr. 105 (2), page 698.