The synthesis and characterization of monodispersed chitosan-coated Fe3O4 nanoparticles via a facile one-step solvothermal process for adsorption of bovine serum albumin
© Shen et al.; licensee Springer. 2014
Received: 24 February 2014
Accepted: 30 May 2014
Published: 11 June 2014
Preparation of magnetic nanoparticles coated with chitosan (CS-coated Fe3O4 NPs) in one step by the solvothermal method in the presence of different amounts of added chitosan is reported here. The magnetic property of the obtained magnetic composite nanoparticles was confirmed by X-ray diffraction (XRD) and magnetic measurements (VSM). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) allowed the identification of spherical nanoparticles with about 150 nm in average diameter. Characterization of the products by Fourier transform infrared spectroscopy (FTIR) demonstrated that CS-coated Fe3O4 NPs were obtained. Chitosan content in the obtained nanocomposites was estimated by thermogravimetric analysis (TGA). The adsorption properties of the CS-coated Fe3O4 NPs for bovine serum albumin (BSA) were investigated under different concentrations of BSA. Compared with naked Fe3O4 nanoparticles, the CS-coated Fe3O4 NPs showed a higher BSA adsorption capacity (96.5 mg/g) and a fast adsorption rate (45 min) in aqueous solutions. This work demonstrates that the prepared magnetic nanoparticles have promising applications in enzyme and protein immobilization.
In the past several decades, magnetic nanomaterials of iron oxides (Fe3O4 NPs) have attracted much research interest due to their potential applications in magnetic storage, catalysis, electrochemistry, drug delivery, medical diagnostics, and therapeutics based on their unique magnetic, physiochemical, and optical properties [1–5]. Among the various methods for the preparation of Fe3O4 NPs, the solvothermal approach is one of great significance [6–9]. Under the solvothermal conditions, Fe3O4 NPs were usually composed of multiple single-domain magnetic nanocrystals. To date, the solvothermal method was developed for the preparation of magnetite spheres with strong magnetization through the hydrolysis and reduction of iron chloride in ethylene glycol at high temperatures. However, producing Fe3O4 NPs with specific functional groups on the surface and acceptable size distribution without particle aggregation has consistently been a problem. Thus, a variety of modifiers were added to the reaction mixtures to control the size of Fe3O4 NPs and improve the colloidal stability and biocompatibility, such as poly(acrylic acid) (PAA) , polyethyleneimine (PEI) [11, 12], polyethylene glycol (PEG) , and other biocompatible polymers [14, 15]. These modifiers are usually polymers bearing carboxylate or other charged groups. During the formation process of Fe3O4 NPs, these charged groups can coordinate with iron cations in solution, and affect the nucleation and aggregation of the nanocrystals, resulting in the formation of Fe3O4 NPs with controllable grain size and self-assembled structures. Compared with the types of polymers mentioned above, chitosan has been intensively studied as a base material for magnetic carriers because of its significant biological and chemical properties. The conventional method for preparing Fe3O4 NPs coated with chitosan is the coprecipitation method that involves obtaining the magnetic nanoparticles, followed by chitosan coating. Several research teams have tried to simplify the procedure to obtain Fe3O4 NPs coated with chitosan in one step [16–20]. However, there are very few reports on the synthesis of magnetic nanoparticles coated with chitosan (CS-coated Fe3O4 NPs) by a one-step solvothermal process.
In this paper, we report the preparation of monodispersed CS-coated Fe3O4 NPs in the presence of different amounts of added chitosan via a facile one-step solvothermal process. A detailed characterization of the products was carried out to demonstrate the feasibility of this method for obtaining CS-coated Fe3O4 NPs. Bovine serum albumin (BSA) isolation experiments were used to demonstrate the potential of the materials for adsorption.
Ferric chloride hexahydrate (FeCl3 · 6H2O, >99%), anhydrous sodium acetate (NaOAc), ethylene glycol (EG), polyvinylpyrrolidone (PVP), bovine serum albumin (BSA), and chitosan (low molecular weight, Brookfield viscosity 20 cps) were purchased from Aldrich (St. Louis, MO, USA). The pure water was obtained from a Milli-Q synthesis system (Millipore, Billerica, MA, USA).
Preparation of CS-coated Fe3O4 NPs
Functionalized magnetite nanoparticles were synthesized via a versatile solvothermal reaction reported by Li with a slight modification . Typically, FeCl3 · 6H2O (1.50 g), chitosan (with various chitosan/Fe weight ratios: 0, 1/3, 1/2, 2/3, 5/6, 1), NaOAc (3.6 g), and PVP (1.0 g) were added to 70 mL of ethylene glycol to give a transparent solution via vigorous stirring. This mixture was then transferred to a Teflon-lined autoclave (80 mL) for treatment at 200°C for 8 h. The composite nanoparticles were denoted MFCS-0 (naked Fe3O4), MFCS-1/3, MFCS-1/2, MFCS-2/3, MFCS-5/6, and MFCS-1. The products were obtained with the help of a magnet and washed with 0.5% dilute acetic acid and demonized water. Finally, the products were collected with a magnet and dried in a vacuum oven at 60°C for further use.
Transmission electron microscopy (TEM) images were obtained with a JEM-2100 transmission electron microscope (Jeol Ltd., Tokyo, Japan). X-ray diffraction (XRD) analysis was performed using a Dmax-2500 (Rigaku Corporation, Tokyo, Japan). Magnetic measurements (VSM) were studied using a vibrating sample magnetometer (Lake Shore Company, Westerville, OH, USA) at room temperature. Scanning electron microscopy (SEM) images were carried out on a Philips XL30 microscope (Amsterdam, The Netherlands). The zeta potential of these particles was measured by dynamic light scattering (DLS) with a Delsa™ NanoC Particle Size Analyzer (Beckman Coulter, Fullerton, CA, USA). Thermogravimetric analysis (TGA) of the nanocomposite and chitosan was performed in a TGA Q500 from TA Instruments (New Castle, DE, USA). Analyzed samples were heated from 100°C to 800°C at a heating rate of 10°C/min under a nitrogen flow of 50 mL/min. Fourier transform infrared spectroscopy (FTIR) of the nanocomposite and chitosan was performed by Nicolet 5700 (Thermo Nicolet, Waltham, MA, USA). The adsorption of BSA on CS-coated Fe3O4 NPs was measured using a UV-2501PC spectrometer (Shimadzu Corporation, Tokyo, Japan).
Adsorption procedures of BSA
Adsorption of BSA on the CS-coated Fe3O4 NPs was carried out by mixing 10 mg of dried CS-coated Fe3O4 NPs and 10 mL of BSA solution (0.1, 0.2, 0.3, and 0.4 mg/L, pH = 6.0, 0.05 mol/L of Tris-HCl). The mixture was left in a shaker operating at 200 rpm for 10 to 240 min to reach equilibrium. After reaching adsorption equilibrium, the supernatant and the solid were separated by using a permanent magnet. BSA concentrations were measured by a UV-2501PC spectrophotometer at 595 nm. The amounts of BSA adsorbed on the magnetic adsorbents were calculated from mass balance. The standard curve of BSA is Y = 0.867X + 0.033(R2 = 0.9975).
Results and discussion
Average hydrodynamic sizes of CS-coated Fe 3 O 4 NPs dispersed in different media
208.7 ± 12.6
214.2 ± 10.1
217.7 ± 9.5
224.4 ± 10.6
227.8 ± 13.4
PBS plus 10% (v/v) FBS
254.5 ± 5.7
260.1 ± 4.5
279.6 ± 7.7
288.9 ± 10.2
302.5 ± 9.8
286.6 ± 18.5
310.6 ± 35.8
347.0 ± 37.4
369.6 ± 41.2
404.4 ± 25.9
1.0 mol/L NaCl
542.7 ± 50.4
784.1 ± 45.7
1,009.2 ± 66.3
1,445.4 ± 57.1
1,667.8 ± 87.0
In summary, a facile one-step solvothermal method was developed to prepare CS-coated Fe3O4 NPs with tunable magnetism, sizes, suspension stability, and surface charge. The size of the nanoparticles was about 150 nm, and chitosan made up 40% to 48.0% of the weight of the modified Fe3O4 NPs. Compared with Fe3O4 nanoparticles, the CS-coated Fe3O4 NPs showed a higher BSA adsorption capacity. This work revealed a promising method for the recovery of slaughtered animal blood by using magnetic separation technology.
The authors gratefully acknowledge the support for this research from the Youth Foundation of Taizhou University under grant no. 2013QN17.
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