Thu 24 Nov 2016 – 3:30 pm (Murdoch University, Postgrad Suite ECL2.031)
Towards frequency-based electronic bio-detection at the nano-scale
Dr Peter Metaxas — School of Physics, University of Western Australia
Magnetic biosensing exploits chemically functionalised magnetic nanoparticles for labelling and subsequent detection of analytes of interest in biological samples, opening routes to new technologies for point-of-care medical diagnostics [1]. Many solid state nanoparticle detection techniques are voltage-level based. For example, in conventional magnetoresistive sensors, the magnetic configuration within the device is modified by the nanoparticles’ stray magnetic fields, generating a change in the device resistance (and thus the voltage across the device). In contrast, electrically probed, field-dependent magnetisation dynamics in magnetic nanostructures offer a route towards intrinsically frequency-based electronic biosensing. This resonance-based approach potentially offers high speed sensing with nano-scale devices [2] which can operate under very large magnetic field ranges [3]. We demonstrate the potential of this approach first using large area, periodically nanostructured ferromagnets (“magnonic crystals”) [3,4]. These systems enable us to probe the effect of nanoparticles on ferromagnetic resonances that are confined to regions in the crystal with lateral dimensions on the order of 100 nm. Secondly we look at nanoparticle sensing exploiting the “gyrotropic” resonance of ferromagnetic vortices. We show how the localized field of a nanoparticle can stiffen the vortex, leading to field sensitivities exceeding those conventionally measured in uniform fields [5]. Finally, we experimentally demonstrate spintronic, frequency-based detection of superparamagnetic beads and discuss future directions of this work (e.g. [5]).
This work would not have been possible without contributions from collaborators at the the Unité Mixte de Physique CNRS/Thales (France), University of Southampton (UK), the National University of Singapore and AIST (Japan).
[1] Gaster et al., Nat. Med., 15, 1327 (2009). [2] Braganca et al., Nanotechnol., 21, 235202 (2010). [3] Sushruth et al., Phys. Rev Appl., 6, 044005 (2016). [4] Metaxas et al., Appl. Phys. Lett. 106, 232406 (2015). [4] Fried and Metaxas, Phys. Rev. B, 93, 064422 (2016). [5] Albert et al., Nanotechnol. 27, 455502 (2016).
A central conclusion of this research is that advances in the study of amorphous structure will involve abandoning the traditional descriptive geometrical approach to structure in favour of regarding structure in terms of the statistical correlations between local structural elements. It is hoped that the description of this exciting open problem will be both accessible to and of interest for mathematicians.
The nucleation of minerals from ions in aqueous solution underpins important processes from biomineralisation to scale formation and carbon sequestration. All this begins with ion pairing, but what happens next is still a matter that is hotly debated for systems such as calcium carbonate, where the classical nature of nucleation has been called into question [1,2,3]. Therefore it is vital to use both experiment and simulation to fill in the missing details as to how crystalline minerals form. In this presentation we will examine the possible pathways by which two common biominerals, calcium carbonate and calcium oxalate, nucleate in order to try to explain how proteins may influence and control this process. Based on simulation results it will be demonstrated that hard rocks and soft matter are perhaps not as different as they might seem during their earlier stages of formation. 
