Construction of orthogonal synchronized bi-directional field to enhance heating efficiency of magnetic nanoparticles.

Magnetic hyperthermia using magnetic nanoparticles (MNPs) has attracted considerable attention as one of the promising tumor therapy. The study has been developed under single magnetic field. Recently, we found that the immobile MNP may generate more heat under two synchronous ac magnetic fields than traditional single and circular polarized fields based on model simulation result. According to this finding we constructed an orthogonal synchronized bi-directional field (OSB field). The system contained two LC resonant inverters (L: inductor, C: capacitor) and both vertical and transverse ac magnetic fields were generated by two Helmholtz coils. To reduce the interference, the axis directional of two coils were arranged orthogonally. The experiments showed that the heating ability of aggregated MNPs is greatly enhanced under this newly designed OSB field without increasing the strength of magnetic field. The OSB field system provides a promising way for future clinical hyperthermia.

Purification of recombinant enhanced green fluorescent protein expressed in Escherichia coli with new immobilized metal ion affinity magnetic absorbents.

A new immobilized metal ion affinity (IMA) adsorbent containing superparamagnetic nanoparticles and coated with hydrophilic resins are proposed here to improve the purification of His-tagged proteins. The magnetic chelating resin was prepared by radical polymerization of magnetite (Fe3O4), styrene, divinyl benzene (DVB) and glycidyl methacrylate-iminodiacetic acid (GMA-IDA) in ethanol/water medium. IDA is immobilized on magnetite as a ligand and pre-charged Cu2+, Zn2+ and Ni2+ as metal ions. To identify the GMA-IDA magnetic particles easily, we named these particles MPGI. The MPGI adsorbent was used to test their suitability for the direct recovery of an intracellular, polyhistidine-tagged protein, enhanced green fluorescent protein [EGFP-(His)(6)], from Escherichia coli lysates in a single step. Parameters influencing the purification efficiencies such as pH, ionic strength and imidazole concentration were optimized to achieve improved separation. The optimal selectively was observed in binding buffer (0.2M NaCl, 0.02M imidazole), washing buffer (0.4M NaCl, 0.03 M imidazole) and elution buffer (0.50M imidazole). The Cu2+-charged MPGI adsorbent had the highest yield and purification factor at 70.4% and 12.3, respectively. The calculated isotherm parameters (Q(m)=53.5 mg/g, K(d)=5.84 mg/mL and Q(m)/K(d)=9.2 mL/g) indicated that the MPGI adsorbent could be used as a suitable adsorbent for EGFP from an aqueous solution.

Application of superparamagnetic nanoparticles in purification of plasmid DNA from bacterial cells.

The aim of this study was to develop a simple and rapid method for purification of ultrapure supercoiled plasmid DNA with high yields from bacterial cultures. Nanosized superparamagnetic nanoparticles (Fe3O4) were prepared by chemical precipitation method using Fe2+, Fe3+ salt, and ammonium hydroxide under a nitrogen atmosphere. The surface of Fe3O4 nanoparticles was modified by coating with the multivalent cationic agent, polyethylenimine (PEI). The nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, Fourier transformation infrared spectroscopy and superconducting quantum interference device magnetometer. The PEI-modified magnetic nanobeads were employed to simplify the purification of plasmid DNA from bacterial cells. We demonstrated a useful plasmid, pRSETB-EGFP, encoding the green fluorescent protein with T7 promoter, was amplified in DE3 strain of Escherichia coli. The loaded nanobeads are recovered by magnetically driven separation and regenerated by exposure to the elution buffer with optimal ionic strength (1.25 M) and pH (9.0). Up to approximately 35 microg of high-purity (A260/A280 ratio=1.87) plasmid DNA was isolated from 3ml of overnight bacterial culture. EGFP expression was detected by fluorescent microscopy in the transformed E. coli cells, indicating the biological activities of DNA fragments were retained after purified from magnetic nanobeads. The protocol, starting from the preparation of bacterial lysate and ending with purified plasmids takes less than 10 min. Thus, the separation and purification qualities of PEI-modified magnetic nanobeads as well as its ease of use surpass those of conventional anion-exchange resins.

Controlled Growth of Gold Nanoparticles in AOT/C(12)E(4)/Isooctane Mixed Reverse Micelles.

Stable anisotropic gold nanoparticles were prepared by the reduction of a relatively high concentration of tetrachloroauric acid with hydrazine in mixed reverse micelles formed with anionic surfactant AOT and nonionic surfactant tetraethylene glycol dodecyl ether (C(12)E(4)) in isooctane. It was found that the C(12)E(4) serves not only as a structure modifier but also as a stabilizer for Au particles, to prevent their further growth and precipitation. By the analyses of a high-resolution electron microscope, electron diffraction patterns, and energy-dispersive X-ray analysis (EDX), the resultant particles have been found to be pure gold of face-centered cubic structure. In the presence of C(12)E(4), the Au particle size is larger than that in the absence of C(12)E(4), while the particle size decreases with increases in the concentration of C(12)E(4). The molar ratio of hydrazine to HAuCl(4) was found to be an important parameter in the control of size and shape for the production of gold nanoparticles. A decrease in the molar ratio of hydrazine to HAuCl(4) resulted in larger Au particles with significantly more polydispersity. When the HAuCl(4) was injected directly into the mixed reversed micelles containing hydrazine, anisotropic gold nanoparticles, such as cylinders and trigons, were obtained at the molar ratio of hydrazine to HAuCl(4) of less than 0.5. Copyright 2001 Academic Press.