Public thesis defense of Margo HAUWAERT - ICTEAM
sst |
Exploring relevant properties of superparamagnetic nanoferrites towards inductive sensing
Wednesday June 10th, 2026 - 4:15pm - Auditorium BARB92 - Place Sainte-Barbe 1, 1348 Louvain-la-Neuve
Lateral flow assays (LFA) provide rapid point-of-care diagnostics, but their standard colourimetric readout with gold nanoparticle labels is only semi-quantitative. Replacing these labels with superparamagnetic nanoferrites (SPNF) and reading the strip with magnetic sensors enables quantification which is insensitive to the optical and electrochemical variability of biological matrices. Leveraging these advantages requires understanding how SPNF composition, size, coating, substrate and measurement conditions jointly determine the effective magnetic properties. This thesis investigates Fe3O4, MnFe2O4, CoFe2O4 nanoparticles from synthesis to inductive detection. Their magnetic properties are characterised from DC to GHz range, and from 2 K to 300 K. Studied configurations are compacted powder, cellulose membranes and aqueous suspensions. A combined Debye fitting procedure applied simultaneously to mobile and immobilised suspensions separates the Néel and Brownian relaxation contributions, resolving the effective anisotropy-diameter degeneracy that limits single-configuration analysis. Inductive detection is demonstrated with affordable and portable sensors.
Four main findings emerge. First, SPNF dispersed in membranes exhibit initial susceptibilities three to four times higher than in powder, attributed to reduced interactions; characterisation in a configuration representative of the final application is therefore necessary to avoid underestimating the available signal. Second, manganese ferrite consistently yields higher susceptibility than iron oxide across all methods and configurations, a consequence of its lower magnetocrystalline anisotropy. Third, drying nanoparticle-loaded membranes under a 500 mT static field improves the inductive signal by 8 to 16 %, by pre-aligning the easy axes of the nanoparticles with the sensing field before immobilisation upon evaporation; the effect requires no modification to the SPNF or the sensor electronics. Fourth, inductive sensor reproduces the susceptibility hierarchy from laboratory instruments, but its lowest sensed mass (7 micrograms for MnFe2O4) remains at least two orders of magnitude above levels relevant for low-abundance biomarker detection on lateral flow assays.
Jury members
Prof. Jean-Pierre Raskin (UCLouvain), Supervisor
Prof. Laurent Francis (UCLouvain), Chairperson
Prof. Denis Flandre (UCLouvain), Secretary
Prof. Sophie Hermans (UCLouvain)
Dr. Simo Spassov (IRM-KMI)
Prof. Luc Dupré (UGent)
Prof. Montserrat Rivas (Universidad de Oviedo, Spain)