A highly sensitive immunoassay, the immunomagnetic reduction, is used to measure several biomarkers for plasma that is related to Alzheimer's disease (AD). These biomarkers include Aβ-40, Aβ-42, and tau proteins. The samples are composed of four groups: healthy controls (n = 66), mild cognitive impairment (MCI, n = 22), very mild dementia (n = 23), and mild-toserve dementia, all due to AD (n = 22). It is found that the concentrations of both Aβ-42 and tau protein for the healthy controls are significantly lower than those of all of the other groups. The sensitivity and the specificity of plasma Aβ-42 and tau protein in differentiating MCI from AD are all around 0.9 (0.88−0.97). However, neither plasma Aβ-42 nor tau-protein concentration is an adequate parameter to distinguish MCI from AD. A parameter is proposed, which is the product of plasma Aβ-42 and tau-protein levels, to differentiate MCI from AD. The sensitivity and specificity are found to be 0.80 and 0.82, respectively. It is concluded that the use of combined plasma biomarkers not only allows the differentiation of the healthy controls and patients with AD in both the prodromal phase and the dementia phase, but it also allows AD in the prodromal phase to be distinguished from that in the dementia phase.

In addition to synthesizing biofunctionalized magnetic nanopaticles for the purpose of magnetically labeling biomolecules, a system to measure the ac magnetic susceptibility of the labeled sample was developed. When a targeted biomolecule was mixed with magnetic fluid possessing biofunctionalized magnetic nanoparticles, portions of magnetic nanoparticles agglomerated to form clusters due to the association with the targeted biomolecule. Due to the formation of magnetic clusters, the measured ac magnetic susceptibility reduced. The relationship between the mixed-frequency ac magnetic susceptibility reduction and the amount of the detected biomolecule was established.

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Articles you may be interested inMagnetic field role on the structure and optical response of photonic crystals based on ferrofluids containing Co0.25Zn0.75Fe2O4 nanoparticles Magnetic field dependant backscattering of light in water based ferrofluid containing polymer covered Fe3O4 nanoparticles J. Appl. Phys. 113, 054902 (2013); 10.1063/1.4789970 Particle blocking and carrier fluid freezing effects on the magnetic properties of Fe 3 O 4 -based ferrofluids J. Appl. Phys. 105, 07B511 (2009); 10.1063/1.3068461 X-ray diffraction and Mössbauer studies of structural changes and L1 0 ordering kinetics during annealing of polycrystalline Fe 51 Pt 49 thin filmsThe patterns of kerosene-based ferrofluid films in applied parallel and perpendicular magnetic fields were studied. The time dependence of quasiperiodic chains in a parallel magnetic field, the perfect hexagonal crystal structure in a weaker perpendicular field, and the labyrinthine pattern in a stronger perpendicular field were observed. The Fe 3 O 4 kerosene-based ferrofluids that we used in this study were synthesized by the coprecipitation method. As the parallel external magnetic field was applied to a ferrofluid film, the ordered quasiperiodic chains were obtained. On the other hand, the initial nonequilibrium disordered quantum columns were formed in an applied perpendicular magnetic field, and an equilibrium hexagonal structure with columns occupying its vortices was formed after two hours. The distance between these columns decreases as the strength of the applied magnetic field increases, and hence, the patterns change gradually from the hexagonal structure to a labyrinthine pattern with the strength of the perpendicular field above a critical value. Thus, a phase transition exists in the ferrofluid film system as the field strength increases.

Magnetic nanoparticles biofunctionalized with antibodies against β-amyloid-40 (Aβ-40) and Aβ-42, which are promising biomarkers related to Alzheimer's disease (AD), were synthesized. We characterized the size distribution, saturated magnetizations, and stability of the magnetic nanoparticles conjugated with anti-Aβ antibody. In combination with immunomagnetic reduction technology, it is demonstrated such biofunctionalized magnetic nanoparticles are able to label Aβs specifically. The ultralow-detection limits of assaying Aβs in vitro using the magnetic nanoparticles via immunomagnetic reduction are determined to a concentration of ∼10 ppt (10 pg/mL). Further, immunomagnetic reduction signals of Aβ-40 and Aβ-42 in human plasma from normal samples and AD patients were analyzed, and the results showed a significant difference between these two groups. These results show the feasibility of using magnetic nanoparticles with Aβs as reagents for assaying low-concentration Aβs through immunomagnetic reduction, and also provide a promising new method for early diagnosis of Alzheimer's disease from human blood plasma.