Real-time measurement of Brownian relaxation of magnetic nanoparticles by a mixing-frequency method

Abstract

A detection scheme for real-time Brownian relaxation of magnetic nanoparticles ͑MNPs͒ is demonstrated by a mixing-frequency method in this paper. MNPs are driven into the saturation region by a low frequency sinusoidal magnetic field. A high frequency sinusoidal magnetic field is then applied to generate mixing-frequency signals that are highly specific to the magnetization of MNPs. These highly sensitive mixing-frequency signals from MNPs are picked up by a pair of balanced built-in detection coils. The phase delays of the mixing-frequency signals behind the applied field are derived, and are experimentally verified. Commercial iron oxide MNPs with the core diameter of 35 nm are used for the measurement of Brownian relaxation. The results are fitted well with Debye model. Then a real-time measurement of the binding process between protein G and its antibody is demonstrated using MNPs as labels. This study provides a volume-based magnetic sensing scheme for the detection of binding kinetics and interaction affinities between biomolecules in real time.

Suitability of magnetic single- and multi-core nanoparticles to detect protein binding with dynamic magnetic measurement techniques

“…In order to avoid the time-consuming frequency sweep, the so-called susceptibility reduction technique was introduced [8,9]. Another experimental refinement to eliminate dia-or paramagnetic signals from the matrix was the application of the frequency mixing technique, utilizing the nonlinear magnetization-vs.-field curve of superparamagnetic nanoparticles [10][11][12]. In the comparably new rotating magnetic field technique (RMF), the MNPs are exposed to a rotating magnetic field and the phase lag between the rotating field and the sample magnetization is recorded [13,14].…”

Highly stable monodisperse PEGylated iron oxide nanoparticle aqueous suspensions: a nontoxic tracer for homogeneous magnetic bioassays

“…alternating and rotating) has recently become a potent tool for detection of proteins and molecules bound to the NPs. [1][2][3][4][5][6] To conduct a successful homogeneous magnetic bioassay, particularly in a rotating magnetic field (RMF), the iron oxide NP aqueous suspensions relaxing via the Brownian mechanism (d core > 24 nm) are required.…”

“…In the last two decades, there has been a growing trend to employ high temperature decomposition of various iron precursors, such as iron acetylacetonate Fe(acac) 3 , 7 iron-oleate, 8 iron pentacarbonyl Fe(CO) 5 , 9 and hydrated iron(III) oxide FeO(OH) 10 to fabricate iron oxide NPs. By having a precise control over the synthesis parameters, these methods offer crystallized monodisperse particles with appropriate magnetic properties but, solely dispersible in non-polar solvents.…”

Colorize magnetic nanoparticles using a search coil based testing method

“…Biochemically modified MNPs are able to bind with specific kind of antibodies, which is called specific binding process. Many research groups have succeed in detecting the molecular binding process in real-time [1] and distinguishing different concentrations of antibodies by using a MNPs and search-coils integrated detection system [2]. But the detection scheme in the field is limited by detecting only one kind of antibody in each test.…”