The blocking temperature measurements via variable temperature AC susceptometer – Application on the biofunctionalized magnetic nanoparticles conjugated with biotargets.
Tien-Wei Yang1*, Chih-Yi Wang1, Li-Min Wang1, Shu-Hsien Liao2, Jen-JieChieh2, Herng-ErHorng2, Hong-Chang Yang2
1Department of Physics/Graduate Institute of Applied Physics, National Taiwan University, Taipei, Taiwan
2Institute of Electro-Optical Science and Technology, National Taiwan Normal University, Taipei, Taiwan
* presenting author:Tien-Wei Yang,
An assay of alpha-fetoprotein (AFP) via the measurements of blocking temperature (TB) is reported. The biofunctionalized magnetic nanoparticles (BMNs) are anti-alpha-fetoprotein (antiAFP) coated onto dextran-coated magnetic nanoparticles composed of Fe3O4, labeled as Fe3O4-antiAFP, and then conjugated with AFP biotargets. In Néel relaxation theory, the particles exhibit single-domain ferromagnetic behavior below the TB, and are superparamagnetic above TB. The corresponding blocking temperature can be defined as TB = U/kBln(tm/t0), where kB is the Boltzmann constant, U is the energy barrier to moment reversal, and t0 is a characteristic time, and tm is the measurement time. A platform developed for assaying bio-molecules by using single frequency and variable temperature-field ac susceptometer. If the signal frequency of excitation coil is higher, it means that the measurement time tm will be much less and hence the TB will increase. The measurement time is typically 1-100 sec for DC measurements, and is the inverse of the measurement frequency for AC measurements. The platform was successful to improve the TB from 68 K (DC measurements) to about 250 K (AC measurem).
This provides an indicator for assaying a wide variety of targets including viruses, proteins, tumor markers, etc.

Keywords: blocking temperature, AC susceptometer, magnetic nanoparticles