Wednesday, 8 December 2010

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.

AbstractOptical 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.

Friday, 3 December 2010

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.

Wednesday, 10 November 2010

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.

Tuesday, 9 November 2010

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.

Monday, 8 November 2010

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.

Monday, 1 November 2010

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.

Sunday, 24 October 2010

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

Friday, 1 October 2010

Bubble Ultrasound Group Meeting

The next Bubble Ultrasound Group meeting is being held at Imperial College on Friday 1 October. This is a regular series of meetings that brings together researchers working in microbubble technology and usually consists of a number of short talks on current research with time for discussion on future directions. The programme for the 1 October meeting is:

2:00 Welcome & Introduction
2:05 Jean-Pierre O'Brien
2:35 Mehrdad Azmin
3:05 David Thomas
3:35 John Casey
4:05 Veronique Mahue
4:35 General discussion

Monday, 27 September 2010

New group members

Agata Pawlikowska is joining the group for a PhD.  Agata studied at Wroclaw University of Technology and at Imperial College where she worked on holographic optical traping and gained an MSc in Optics and Photonics.  She is working for a PhD on the UCL/NPL optical and acoustical microbubble trapping project.  

Also, Radhika Patel is returning to the group.  Radhika worked in our lab over the summer as a Nuffield Foundation Bursary Student, and will be spending the rest of the year with us working on her MSci project.

Friday, 24 September 2010

Nanophotonics meets quantum optics and NOIs meeting

This week Susan and Marios have been attending the 'Nanophotonics meets quantum optics' Physics School in Physikzentrum Bad Honnef, Germany, where they also presented a poster on some of our most recent work on nanofibre trapping.

On the last day of the Physics School the annual project meeting of our European project 'Nanofibre Optical Interfaces for Ions, Atoms and Molecules (NOIs)' was held, with progress reports from participants based in Cork, Moscow, London, Innsbruck and Mainz.

Tuesday, 21 September 2010

Visit to NanoSoft Lab, IPCF-CNR (Messina)

Phil spent the week of 13-18 September visiting Onofrio Marago and colleagues at the NanoSoft Lab, IPCF-CNR (Messina).  The visit was part of our International Joint Project on Photonic Force Microscopy funded by the Royal Society.  Among the highlights of the week was a half-day meeting on graphene with talks by Onofrio, Giuseppe Angilella (Catania) and Prof Norman March (former holder of the Coulson Chair in Theoretical Chemisty, Oxford).

Friday, 20 August 2010

Radial Polarization Movie

We have been working on an interferometric method for high-efficiency synthesis of cylindrical vector beams.

These are the class of laser beams that are linearly polarized in a cylindrical basis, the most common examples being beams where the polarization is purely radial or purely azimuthal. 

The latest movie from this experiment is here and on our YouTube channel. In this movie you can see the characteristic 'donut' shape of the beam and the intensity transmission pattern through a polaroid which demonstrates the radial and azimuthal polarization states.  These beams have many applications in, for example, high-resolution miroscopy and optical  trapping.

Monday, 16 August 2010

Photonic Force Microscopy Book Chapter

Our book chapter on 'Photonic Force Microscopy: from femtonewton force sensing to ultra-sensitive spectroscopy' in the volume 'Scanning Probe Microscopy in Nanoscience and Nanotechnology' is published by Springer, and can be viewed on Google Books

Monday, 9 August 2010

Nuffield Bursary Update (3)

Throughout the course of her Nuffield Foundation project this summer Radhika Patel will be making updates of her progress on our blog.  Her third instalment is below. 

Radhika writes: We wanted to improve the optical tweezers setup I have been working on so this week we partly dismantled the microscope was in order to get a better look at what was inside. Having made some adjustments, Susan and I have returned to aligning the beams, trapping particles and calibrating the trap again. In addition to this, we have started the process of integrating some optical fibres into the setup. Part of the last week was spent learning how to cut and prepare the fibres for use in the setup and actually connectorising some of the fibres.

Phil, Marios and I attended Richard Berry's lecture on Single-molecule observations of turnover, co-operativity and mechanochemistry in a macromolecular complex. As this was the first talk I had attended related to optical tweezing, it was interesting to hear about some of its applications.

Thursday, 5 August 2010

Optical Binding Movie

We have been working on an experiment to demonstrate evanescent wave optical binding of microparticles.

The latest movie from this experiment is here and on our YouTube channel. In this movie you can see 1 micron diameter silica microparticles suspended in water above the surface of a glass prism.  The microparticles organise into 1D chains when exposed to the evanescent field of a laser beam reflected from the surface below.

Monday, 2 August 2010

UCL Optical Tweezers on YouTube

The UCL Optical Tweezers Group now has a YouTube channel at

We will be publishing movies from our experiments like the one shown here of an optically trapped microbubble, together with references to the relevant papers. You can subscribe to the channel by using the button below:
Subscribe to me on YouTube

Friday, 23 July 2010

Nuffield Bursary Update (2)

Throughout the course of her Nuffield Foundation project this summer Radhika Patel will be making updates of her progress on our blog.  Her second instalment is below.

Radhika writes: Since working on the optical tweezers setup with Susan Skelton, I have helped install and refine a “particle tracking system” which tracks the particle’s Brownian motion in the trap using the backscattered light from a 'probe' laser beam. We can use this method to measure the spring constant of the optical trap, and calibrate the detector sensitivity so that we can make measurements of the particle’s displacement and the absolute force applied.

We have been visited by Maria Grazia Donato from IPCF-CNR (Messina) and Gianluca Memoli from NPL this week also. Having worked with optics for many years, they have helped improve the experiment as well as my understanding of ray optics and optical tweezers.

Monday, 19 July 2010

Richard Berry Seminar

Richard Berry (Oxford) will be giving the CoMPLEX seminar on Tuesday 27 July on Single-molecule observations of turnover, co-operativity and mechanochemistry in a macromolecular complex.

Abstract: The bacterial flagellar motor has long been a canonical macromolecular complex because of the relative ease with which its output, rotation of the extracellular flagellar filament, can be observed.  In vivo imaging of GFP-labelled components of the motor has revealed that the motor is not a static structure, but that individual proteins are constantly replaced at rates on the order of 1/minute.  Localization at nanometre precision of labels attached to the motor, at frame rates of several to many kilohertz, has also allowed observations of the mechanism of co-operative directional switching in the motor and of its mechanochemical cycle.

Monday, 12 July 2010

Visit by Maria Grazia Donato

Maria Grazia Donato of the Istituto Processi Chimico-Fisici (IPCF-CNR) in Messina is be visiting the group this week.  Maria studied at the University of Messina, and recently joined the CNR where she works on Raman and photoluminescence spectroscopy of both amorphous and crystalline material, and steady-state and time-resolved fluorescence anisotropy of molecular aggregates.  She will be contributing to the work of our Royal Society International Joint Project with Dr Onofrio Marago.

Friday, 9 July 2010

Nuffield Bursary Update

Throughout the course of her Nuffield Foundation project this summer Radhika Patel will be making updates of her progress on our blog.  The first instalment is below.

Radhika writes:
  Having joined the UCL Optical Tweezers Group at the end of June, I have been trapping micron sized particles using a diode laser and measuring the spring constant of the optical trap.  The objective was to familiarise myself with the apparatus and theory of optical trapping, and learn about different methods for calibration. Alongside this I have been learning about the experiment that Susan Skelton (PhD student) is working on which is an inverted optical tweezers.  We have been calibrating the optical tweezers for use in Photonic Force Microscopy (PFM) which is the project put forward to the Nuffield Foundation for the Undergraduate Research Bursary I was granted this summer.

Monday, 5 July 2010

Optical Binding

In a new experiment at UCL we have realised evanescent wave optical binding of microscopic spheres.  A drop of liquid containing a suspension of microspheres is placed on top of a prism and a laser beam focused onto the prism surface from below.  When the beam is incident on the glass-water interface at just greater than the critical angle for total internal reflection an evanescent field penetrates a short distance into the water.  Under these conditions we see the microparticles drawn together into short optically bound chains.

Part (a) of the diagram represents out set-up.  The beam is retro-reflected and re-focused by the concave mirror in order to balance the radiation pressure in each direction.  Part (b) shows a photograph of optically bound chains of 2 micron diameter microspheres.

Friday, 25 June 2010

Nuffield Foundation Research Bursary

Radhika Patel is joining the UCL Optical Tweezers Group this summer with a Nuffield Foundation Undergraduate Research Bursary. This scheme allows UK undergraduates to gain research experience by providing funding for up to eight weeks to complete a research project during the summer vacation. We have hosted two previous Nuffield Foundation students: Muddassar Rashid (2008) who contributed to two publications on the properties of polarisation vortex beams as a result of his project, and Alex Dunning (2009) who performed calculations on the properties of optical nanofibres and will be starting a PhD at Southampton University in October.

Radhika was a pupil at Haberdashers' Aske's School for Girls in Elstree and has just completed the third year of an MSci degree in Physics at UCL. She will be working on a project titled 'Photonic Force Microscopy' which aims to use optically trapped particles for sensitive force measurements and imaging.  We will be reporting on her progress on this blog.

Monday, 21 June 2010

Exam congratulations

Congratulations to our MSci project students Soliman Edris, Caroline Harfield and Shazia Khan on their exam results.

Shazia is thinking of changing subject and studying for an MSc in Economics next year, while Soliman is taking time off to visit family in Egypt. Caroline will be returning to UCL to study for a PhD in the Mechanical Engineering Department supervised by Dr Eleanor Stride. She will be working on modelling of acoustic and optical trapping of microbubbles as part of the NPL / UCL microbubbles as microsensors project.

We still have MSci projects available for next year (2010-11). See or
contact Dr Phil Jones for more details.

Friday, 18 June 2010

Bubble Ultrasound Group Meeting

The next Bubble Ultrasound Group meeting is being held at Imperial College on Friday 18 June. This is a regular series of meetings that brings together researchers working in microbubble technology and usually consists of a number of short talks on current research with time for discussion on future directions. The programme for the 18 June meeting is:

2:00 Welcome & Introduction
2:15 Anna Tokarczyk (ICR, Sutton)
2:40 Helen Mulvana (Imperial)
3:05 Jean-Pierre O'Brien (UCL)
3:30 Eleanor Stride (UCL)