Our work has just been published in PNAS

Magnetic control of graphitic microparticles in aqueous solutions, Johnny Nguyen, Dario Valter Conca, Johannes Stein, Laura Bovo, Chris A. Howard, and Isabel Llorente Garcia,

Significance. This paper presents the first ever magnetic transport of diamagnetic graphite microparticles in water solutions. Given the dominance of viscous drag forces at the microscale, moving a microparticle that is submerged in liquid is comparably as hard as moving a macroparticle within dense honey. While diamagnetism is a weak magnetic property, for graphite it can be exploited to generate useful transport in liquid. The contactless magnetic control of biocompatible micrographite, together with graphite’s unique physical properties, opens up new possibilities for applications in sensing, analysis, synthesis, and diagnosis in chemistry, biology, medicine, and physics.

Abstract. Graphite is an inexpensive material with useful electrical, magnetic, thermal, and optical properties. It is also biocompatible and used universally as a substrate. Micrometer-sized graphitic particles in solution are therefore ideal candidates for novel lab-on-a-chip and remote manipulation applications in biomedicine, biophysics, chemistry, and condensed-matter physics. However, submerged graphite is not known to be amenable to magnetic manipulation, the optimal manipulation method for such applications. Here, we exploit the diamagnetism of graphite and demonstrate contactless magnetic positioning control of graphitic microflakes in diamagnetic aqueous solutions for the first time. We develop a theoretical model for magnetic manipulation of graphite microflakes and demonstrate experimentally magnetic transport of such particles over distances 200μm with peak velocities 15μm/s in inhomogeneous magnetic fields. We achieve fully biocompatible transport for lipid-coated graphite in NaCl aqueous solution, paving the way for previously undiscovered biomedical applications. Our results prove that micrometer-sized graphite can be magnetically manipulated in liquid media.

See UCL’s Press Release here: https://www.ucl.ac.uk/news/2019/feb/moving-graphite-particles-liquid-using-magnetism

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We welcome PhD student Riccardo Tognato

Riccardo Tognato joined our group at the start of August 2018. Riccardo will be carrying out his PhD research project on the biophysics of virus entry into living cells. The aim of his project is to investigate the molecular interactions relevant to virus entry by means of precision force spectroscopy with optical tweezers and light-sheet fluorescence microscopy experiments at the single molecule level.

We welcome summer student Yahel Houston

Yahel Houston (graduated in Physics by UCL) has joined our lab on July 9th 2018 to carry out a summer research project. Yahel secured a summer scholarship from the Institute for the Physics of Living Systems (IPLS) for his stay. We will be working with us for 8 weeks on a project entitled Single-molecule light-sheet fluorescence microscopy for imaging receptor proteins on the surface of living cells.

Read our new paper:

Orienting lipid-coated graphitic micro-particles in solution using AC electric fields: A new theoretical dual-ellipsoid Laplace model for electro-orientation, J.Nguyen, Jonathan G. Underwood and I.Llorente García. Colloids and Surfaces A: Physicochemical and Engineering Aspects 549, 237-251 (2018). Link to published paperLink to free accepted manuscript in Arxiv.

Abstract

Graphitic micro-particles coated with thin layers in solution are technologically interesting as they can be manipulated with electric fields. Modeling the electrical manipulation of submerged layered micro-particles analytically or numerically is not straightforward. In particular, the generation of reliable quantitative torque predictions for electro-orientation experiments has been elusive. The traditional Laplace model approximates the coated particle by an ellipsoid with a confocal ellipsoidal layer and solves Laplace’s equation to produce convenient analytical predictions. However, due to the non-uniformity of the layer thickness around the ellipsoid, this method can lead to incorrect torque predictions. Here we present a new theoretical dual-ellipsoid Laplace model that corrects the effect of the non-uniform layer thickness by calculating two layered ellipsoids, each accounting for the correct layer thickness along each relevant direction for the torque. Our model describes the electro-orientation of submerged lipid-coated graphitic micro-particles in the presence of an alternating current (AC) electric field and is valid for ellipsoids with moderate aspect ratios and coated with thin shells. It is one of the first models to generate correct quantitative electric torque predictions. We present model results for the torque versus frequency and compare them to our measurements for lipid-coated highly ordered pyrolytic graphite (HOPG) micro-flakes in aqueous NaCl solution at MHz frequencies. The results show how the lipid shell changes the overall electrical properties of the micro-flakes so that the torque is low at low frequencies and increases at higher frequencies into the MHz regime. The torque depends critically on the lipid-shell thickness, the solution conductivity and the shape of the particle, all of which can be used as handles to control the response of the particles.

 

Today we showed our lab to Physics undergraduates attending the Conference of Astronomy and Physics Students (CAPS’17) at UCL

On 29-June-2017, we have had four groups of undergraduate students touring our lab and learning about our Biophysics research. Approx. 20 Physics undergraduate and masters students attending the annual Conference of Astronomy and Physics Students (CAPS’17) at UCL passed by and PhD students Johnny Nguyen and Dario Conca, together with project student Basile Khatir, explained their experiments to them:

We welcome project student Basile Khatir

On May 22nd 2017 we welcomed Basile Khatir, a student from the Institut d’Optique Graduate School in Paris, France.

Basile is joining us for three months to work on a project entitled “Whispering-gallery-mode biosensors for early diagnosis of disease“. For this project, our lab collaborates with Prof. Peter Barker and Dr. Lia Li at UCL Physics.

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