Paola Borri Visit and Seminar

Paola Borri (Cardiff University) is visiting today and giving the AMOPP/BioP seminar on Novel Multiphoton Microscopy Techniques for Cell Imaging:  CARS Microscopy and Resonant Four-Wave Mixing.

Abstract:  Optical microscopy is an indispensable tool that is driving progress in cell biology, and is still the only practical means of obtaining spatial and temporal resolution within living cells and tissues. Much effort is being devoted recently to achieve intrinsic three-dimensional (3D) spatial resolution by exploiting optical nonlinear effects which can only take place in the small focal volume where high photon densities are reached. One of the most utilised multiphoton (ie nonlinear) microscopy techniques is two-photon fluorescence where the biomolecules of interest are labelled with fluorophores, which are optically excited via simultaneous absorption of two photons. However, these modified biomolecules raise questions if their behaviour is real or artefactual. Furthermore, all organic fluorophores are prone to photo-bleaching which severely limits time-course observations and is accompanied by toxicity effects and consequent cell damage.
Coherent Antistokes Raman Scattering (CARS) microscopy has recently emerged as a new multiphoton microscopy technique which overcomes the need of fluorescent labelling and yet retains biomolecular specificity and intrinsic 3D resolution. We have developed in our laboratory a fully home-built CARS microscope featuring innovative CARS excitation/detection schemes. In particular, we have demonstrated differential-CARS (D-CARS) and single-laser CARS utilising femtosecond laser pulses linearly chirped by glass dispersion. Furthermore we have invented and demonstrated a novel imaging modality, based on the resonant Four-Wave Mixing (FWM) of colloidal nanoparticles. Results on this work showed that nanoparticles, both semiconductor and metallic, can be used as alternative labels beyond fluorescence by exploiting their resonant FWM, to achieve a novel coherent multiphoton microscopy modality free from background and with a spatial resolution significantly surpassing the one-photon diffraction limit. I will present our latest progress with both techniques and their applications to cell imaging.

Brownian Motion of Graphene paper

Our paper 'Brownian Motion of Graphene' has been published online in ACS Nano.  

From the abstract:

Brownian motion is a manifestation of the fluctuation-dissipation theorem of statistical mechanics. It regulates systems in physics, biology, chemistry, and finance. We use graphene as prototype material to unravel the consequences of the fluctuation-dissipation theorem in two dimensions, by studying the Brownian motion of optically trapped graphene flakes. These orient orthogonal to the light polarization, due to the optical constants anisotropy. We explain the flake dynamics in the optical trap and measure force and torque constants from the correlation functions of the tracking signals, as well as comparing experiments with a full electromagnetic theory of optical trapping. The understanding of optical trapping of two-dimensional nanostructures gained through our Brownian motion analysis paves the way to light-controlled manipulation and all-optical sorting of biological membranes and anisotropic macromolecules.

UCL Science Article

A short article on optical trapping called 'Light Forces' written by Susan and Phil is published in the 2010 issue of UCL Science for Schools magazine.

UCL Science is mailed to Schools and Colleges on the UCAS mailing list.  For extra copies contact the editor.

SPIE Conference Proceedings

Conference proceedings 'Plasmon-enhanced optical trapping of metal nanoparticles: force calculations and light-driven rotations of nanoaggregates' published as O. M. Maragò et al Proc. SPIE Vol. 7762, 77622Z (2010). 

Abstract:  We investigate experimentally and theoretically plasmon-enhanced optical trapping of metal nanoparticles. We calculate the optical forces on gold and silver nanospheres through a procedure based on the Maxwell stress tensor in the transition T-matrix formalism. We compare our calculations with experimental results finding excellent agreement. We also demonstrate how light-driven rotations can be generated and detected in non-symmetric nanorods aggregates. Analyzing the motion correlations of the trapped nanostructures, we measure with high accuracy both the optical trapping parameters, and the rotation frequency induced by the radiation pressure.

The paper included some work done with our Royal Society IJP was presented at  the conference Optical Trapping and Optical Micromanipulation VII by Onofrio Maragò.

Visit by Onofrio Marago

Onofrio Marago (NanoSoft Lab, IPCF-CNR, Messina) is visiting the group this week.  Onofrio has a long-running collaboration with the Optical Tweezers Group and exchange visits between UCL and NanoSoft Lab are presently funded by our Royal Society International Joint Project.

New Group Members

Muhammad Abdul Khudus has joined the group for his MSc project.  Muhammad gained his first degree from Imperial College and will be working on a project on nano-optics.

Nobel Laureate at UCL

2010 Physics Nobel Laureate Prof Andre Geim is giving the annual Bragg Lecture at UCL on Wednesday 27 October.  The Bragg Lecture is the premier lecture in condensed-matter and materials physics at UCL.  It is given annually by a distinguished scientist working in the field.

Graphene: Magic of Flat Carbon

Graphene - single atomic plane pulled out of graphite - is a wonder material. It has many superlatives to its name. It is the thinnest material one can imagine and the strongest one ever measured. Its charge carriers have zero effective mass and can travel micron distances without scattering under ambient conditions. Graphene can sustain current densities million times higher than copper, shows record thermal conductivity and stiffness, is impermeable to gases or liquids. It reconciles such conflicting qualities as brittleness and ductility. Electrons in graphene behave in such a way that this allows the investigation of relativistic quantum phenomena in a bench-top experiment. I will overview fascinating properties of graphene and outline some applications.

Location: Christopher Ingold Chemistry Auditorium, UCL

Time: 4.30pm, Wed 27 Oct