TY  - JOUR
A1  - Pourshahidi, Ali Mohammad
A1  - Engelmann, Ulrich M.
A1  - Offenhäusser, Andreas
A1  - Krause, Hans-Joachim
T1  - Resolving ambiguities in core size determination of magnetic nanoparticles from magnetic frequency mixing data
JF  - Journal of Magnetism and Magnetic Materials
N2  - Frequency mixing magnetic detection (FMMD) has been widely utilized as a measurement technique in magnetic immunoassays. It can also be used for the characterization and distinction (also known as “colourization”) of different types of magnetic nanoparticles (MNPs) based on their core sizes. In a previous work, it was shown that the large particles contribute most of the FMMD signal. This leads to ambiguities in core size determination from fitting since the contribution of the small-sized particles is almost undetectable among the strong responses from the large ones. In this work, we report on how this ambiguity can be overcome by modelling the signal intensity using the Langevin model in thermodynamic equilibrium including a lognormal core size distribution fL(dc,d0,σ) fitted to experimentally measured FMMD data of immobilized MNPs. For each given median diameter d0, an ambiguous amount of best-fitting pairs of parameters distribution width σ and number of particles Np with R2 > 0.99 are extracted. By determining the samples’ total iron mass, mFe, with inductively coupled plasma optical emission spectrometry (ICP-OES), we are then able to identify the one specific best-fitting pair (σ, Np) one uniquely. With this additional externally measured parameter, we resolved the ambiguity in core size distribution and determined the parameters (d0, σ, Np) directly from FMMD measurements, allowing precise MNPs sample characterization.
Y1  - 2022
U6  - http://dx.doi.org/10.1016/j.jmmm.2022.169969
SN  - 0304-8853
VL  - 563
IS  - In progress, Art. No. 169969
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Engelmann, Ulrich M.
A1  - Pourshahidi, Mohammad Ali
A1  - Shalaby, Ahmed
A1  - Krause, Hans-Joachim
T1  - Probing particle size dependency of frequency mixing magnetic detection with dynamic relaxation simulation
JF  - Journal of Magnetism and Magnetic Materials
N2  - Biomedical applications of magnetic nanoparticles (MNP) fundamentally rely on the particles’ magnetic relaxation as a response to an alternating magnetic field. The magnetic relaxation complexly depends on the interplay of MNP magnetic and physical properties with the applied field parameters. It is commonly accepted that particle core size is a major contributor to signal generation in all the above applications, however, most MNP samples comprise broad distribution spanning  nm and more. Therefore, precise knowledge of the exact contribution of individual core sizes to signal generation is desired for optimal MNP design generally for each application. Specifically, we present a magnetic relaxation simulation-driven analysis of experimental frequency mixing magnetic detection (FMMD) for biosensing to quantify the contributions of individual core size fractions towards signal generation. Applying our method to two different experimental MNP systems, we found the most dominant contributions from approx. 20 nm sized particles in the two independent MNP systems. Additional comparison between freely suspended and immobilized MNP also reveals insight in the MNP microstructure, allowing to use FMMD for MNP characterization, as well as to further fine-tune its applicability in biosensing.
Y1  - 2022
U6  - http://dx.doi.org/10.1016/j.jmmm.2022.169965
SN  - 0304-8853
VL  - 563
IS  - In progress, Art. No. 169965
PB  - Elsevier
CY  - Amsterdam
ER  -