• 한국초전도학회:학술대회논문집
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• v.10
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• pp.7-7
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• 2000

A high $T_c$ SQUID system is developed for the application to biological immunoassay. In this application, magnetic nanoparticles are used as magnetic markers to perform immunoassay, i.e., to detect binding reaction between an antigen and its antibody. The antibody is labeled with ${\gamma}-Fe_2O_3\;(or\;Fe_3O_4)$ nanoparticles, and the binding reaction can be magnetically detected by measuring the magnetic field from the nanoparticles. Design and set up of the system is described. The system consists of (1) SQUID magnetometer or gradiometer made of 30-deg. bicrystal junctions, (2) field and compensation coils to apply the magnetic field of about 1 mT, (3) special Dewar to realize a 2 mm-distance between the SQUID and the sample, (4) two layers of cylindrical shielding to reduce the extemal magnetic noise to about 1/100, and (5) an electric slider to move the sample with a speed of 10 mm/sec. The sensitivity of the system is studied in terms of detectable magnetic flux. For the measurement bandwidth from 0.2 Hz to 10 Hz, minimum-detectable amplitude of the magnetic flux is $0.8\;m\;{\Phi}_o$ and $0.25\;m{\Phi}_o$ for the magnetometer and the gradiometer, respectively, when the magnetic field of 1 mT is applied. The difference between them is due to the residual environmental noise, and the applied magnetic field does not increase the system noise. The corresponding weight of the magnetic markers is 1 ng and 310 pg, respectively. An experiment is also conducted to measure antigen-antibody reaction with the present system. It is shown that the sensitivity of the present system is 10 times better than that of the conventional method using an optical marker. A one order of magnitude improvement of sensitivity will be realized by the sophistication of the present system.

• Clean Technology
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• v.23 no.1
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• pp.27-33
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• 2017

In this study, toxicities of seven metals (Cu, Cd, Cr, As(III), As(V), Zn, Ni) and five metal oxide nanoparticles (NPs: CuO, ZnO, NiO, $TiO_2$, $Fe_2O_3$) were evaluated based on the growth of Chlorella vulgaris. Effect on algae growth was evaluated by integrating the results of absorption, chlorophyll content, and cell count. The toxicity rankings of metals was observed as Cr ($0.7mgL^{-1}$) > Cu ($1.7mgL^{-1}$) > Cd ($3.2mgL^{-1}$) > Zn ($3.9mgL^{-1}$) > Ni ($13.2mgL^{-1}$) > As(III) ($17.8mgL^{-1}$) ${\gg}$ As(V) (> $1000mgL^{-1}$). Slightly different orders and sensitivities of metal toxicity were examined depending on endpoints of algal growth. In case of NPs, regardless of endpoints, similar toxicity rankings of NPs ($TEC_{50}$) were observed, showing ZnO ($2.4mgL^{-1}$) > NiO ($21.1mgL^{-1}$) > CuO ($36.6mgL^{-1}$) > $TiO_2$ ($62.5mgL^{-1}$) > $Fe_2O_3$ ($82.7mgL^{-1}$). These results indicate that an integrating results of endpoints might be an effective strategy for the assessment of contaminants.

• Journal of the Korean Magnetics Society
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• v.18 no.1
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• pp.24-27
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• 2008

We have prepared $MnFe_2O_4$ nanoparticles with polyol method. The crystallographic and magnetic properties were measured by using X-ray diffraction(XRD), vibrating sample magnetometer(VSM) and $M\"{o}ssbauer$ spectroscopy. The high resolution transmission electron microscope(HRTEM) shows uniform nanoparticle-sizes with $6{\sim}8$ nm. The crystal structure is found to be single-phase cubic spinel with space group of Fd3m. The lattice constant of $MnFe_2O_4$ nanparticles is determined to be $8.418{\pm}0.001{\AA}$. $M\"{o}ssbauer$ spectrum of $MnFe_2O_4$ nanparticles at room temperature(RT) shows a superparamagnetic behavior. In VSM analysis, the diagnosis of the superparamagnetic behavior is also shown in hysteresis loop at RT. $M\"{o}ssbauer$ spectrum at 4.2K shows that the well developed two sextets are with different hyperfine field $H_{hfA}=498$(A-site) and $H_{hfB}=521$(B-site) kOe.

• Applied Chemistry for Engineering
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• v.17 no.3
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• pp.274-279
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• 2006

To synthesize ZnO colloidal solution by a sol-gel process, zinc acetate ($C_{4}H_{6}O_{4}Zn{\cdot}2H_{2}O{\cdot}0.2\;mol$) and lithium hydroxide ($LiOH{\cdot}H_{2}O{\cdot}0.14\;mol$) in the ethanol were added to the solution containing a dispersing agent, hydroxypropyl cellulose (HPC). The nanosize and physical shape of the synthesized ZnO particles were determined by HPC acting as the dispersing agent. Nanosized ZnO particles were also obtained by a precipitation method based on zinc-2-ethylhexagonate. The precipitates were characterized by DLS, XRD, FE-SEM, and UV-vis. As the results, the ZnO colloids tend to self-assemble into a well-ordered hexagonal close-packed structure. The ZnO nanoparticles have an average diameter of nearly 40 nm with a narrow size distribution.

• Bulletin of the Korean Chemical Society
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• v.33 no.8
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• pp.2789-2792
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• 2012

• Proceedings of the Korean Magnestics Society Conference
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• 2009.05a
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• pp.75-76
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• 2009

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.250.2-250.2
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• 2008

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.48.2-48.2
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• 2008

• Applied Chemistry for Engineering
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• v.17 no.4
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• pp.420-425
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• 2006

Nano sized mixed metal hexagonal ferrite powders with improved magnetic properties have been prepared by sol-gel method using propylene oxide as a gelation agent. To obtain the desired ferrite, two different metal ions were used. One of the ions has only +2 formal charge. The key step in the processes is that hydrated $Ba^{2+}$ or $Sr^{2+}$ ions are hydrolyzed and condensed at the surface of the previously formed $Fe_{2}O_{3}$ gel. In this processes, all the reaction can be finished within a few minutes. The magnetic properties of the produced powder were improved by heat treatment. The highest values of the magnetic properties were achieved at temperature $150^{\circ}C$ lower than those of the previously published values. The highest observed values of coercivity and the saturation magnetization of Sr-ferrite and Ba-ferrite powder were 6198 Oe, 5155 Oe and 74.4 emu/g, 68.1 emu/g, respectively. The ferrite powder annealed at $700^{\circ}C$ showed spherical particle shapes. The resulting spheres which were formed by the aggregation of nanoparticles with size 3~5 nm have diameter around 50 nm. The powder treated at $800^{\circ}C$ showed hexagonal-shaped grains with crystallite size above 500 nm.

• Journal of the Korean Magnetics Society
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• v.26 no.4
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• pp.129-132
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• 2016

The effect of thermal-nitrification on L1o transfomation in nano-sized FePt particles was studied. As-synthesized FePt nanoparticles by thermal decomposition method have fcc structured phase and their Hc and Ms were 247.34 Oe and 27.308 emu/g, respectively. According to the XRD analysis, phase transformation from fcc (face centered cubic) to fct (face centered tetragonal) structure was revealed by heating under $NH_3+H_2$ mixed-gas atmosphere. Also a slight shift of each (111) peak indicated phase transformation from fcc to fct structure. Hc and Ms of fct FePtN were 1058.2 Oe and 32.718 emu/g, respectively. The nano-sized FePtN magnetic particles synthesized by thermal decomposition method and mixed-gas nitrification are expected for advanced applications such as high density magnetic recording media and biomedical materials.