Paper published in Journal of the Acoustical Society of America

Our work on acoustic and optical trapping of microbubbles has been published as G. Memoli, C. R. Fury, P. N. Gélat, K. O. Baxter & P. H. Jones.  'Acoustic force measurements on polymer-coated microbubbles in a microfluidic device', Journal of the Acoustical Society of America 141 3346 (2017).

From the abstract:  This work presents an acoustofluidic device for manipulating coated microbubbles, designed for the simultaneous use of optical and acoustical tweezers. A comprehensive characterization of the acoustic pressure in the device is presented, obtained by the synergic use of different techniques in the range of acoustic frequencies where visual observations showed aggregation of microbubbles. In absence of bubbles, the combined use of laser vibrometry and finite element modelling supported a non-invasive measurement of the acoustic pressure and an  enhanced understanding of the system resonances. Calibrated holographic optical tweezers were then used for a direct measurement of the acoustic forces acting on an isolated microbubble at low driving pressures and to confirm the spatial distribution of the acoustic field. This allowed quantitative pressure measurements by particle tracking using polystyrene beads and an evaluation of the related uncertainties. The extension of the tracking technique to polymer-coated microbubbles allowed acoustic force measurements at higher pressures, highlighting four peaks in the acoustic response of the device. Results and methodologies are relevant to acoustofluidic applications requiring a precise characterization of the acoustic field and, in general, to biomedical applications with microbubbles or deformable particles.

SPIE Conference Proceedings: OTOM XI

Proceedings from the SPIE Optics + Photonics 2014 conference have been published.  These include Chris F's paper on optical and acoustic manipulation of microbubbles in a microfluidic device: C. R. Fury, P. H. Jones and G. Memoli.  'Multi-scale manipulation of microbubbles employing simultaneous optical and acoustical trapping', Proc SPIE 9164, Optical Trapping and Optical Micromanipulation XI, 91642Z, doi: 10.1117/12.2061622 (2014).

From the abstract: We present a dual-modality microbubble trapping system that incorporates the fine spatial resolution of optical tweezers, with the long range, high force manipulation of acoustic tweezers, in a single microfluidic system. We demonstrate aggregation of polymer microbubbles in the node of an acoustic field, and subsequent selection and separation of a single microbubble using holographic optical tweezers. We further characterize the optical tweezers by measuring the transverse spring constant, and use the calibrated trap to determine the acoustic force on the bubble for varying parameters of optical trap diameter and power, and acoustic frequency and driving voltage. Further development of the system to include acoustic emission measurement is presented, with the goal of having a multi-purpose mechanical and cavitation detection set-up combined into a single system

SPIE Optics + Photonics Conference

Last week Chris F attended the Optical Trapping and Optical Micromanipulation (OTOM) XI conference, as part of SPIE Optics + Photonics 2014 in San Diego.  Chris presented a poster on "Multi-scale manipulation of microbubbles employing simultaneous optical and acoustical trapping" based on work from the NPL-UCL-Oxford microbubble trapping project.  You can see movies from the experiments described in his poster below:

SPIE Photonics Europe Conference Proceedings

Proceedings from the SPIE Photonics Europe 2014 conference have been published.  These include our paper on the characterization of holographic optical traps for microbubbles as part of the NPL/UCL microbubble project: C. R. Fury, C. J Harfield, P. H. Jones, E. P. J. Stride & G. Memoli.  'Experimental characterisation of holographic optical traps for microbubbles', Proc SPIE 9126 Nanophotonics V, 91263L doi:10.1117/12.2055889 (2014)

From the abstract: In this study microscopic gas bubbles (7-12 μm diameter) suspended in water were optically trapped in a custom-built microfluidic slide using holographically generated Laguerre-Gaussian (‘doughnut’) beam optical tweezers. The optical potential was then characterized as a function of bubble size, trapping laser power and trapping beam diameter (Laguerre-Gaussian beam mode) using the trap spring constant in the plane transverse to the beam propagation direction, obtained from the position fluctuations of the bubble in the trap measured by video microscopy and particle tracking. It was found that microbubbles were held at the equilibrium position of buoyant and optical forces at a distance from the focus of the beam that increased with laser power, and that optical trapping in this configuration was only possible within a specific range of trap and bubble parameters. Furthermore an optimum size of the doughnut beam to microbubble diameter which maximized the transverse spring constant was found . A ray optics model of the optical forces acting on microbubbles in a focused Laguerre-Gaussian beam was used in order to calculate the trap spring constants and equilibrium trapping position as a function of the different parameters, and highlight key physical behaviours.

Paper in J Phys: Conf Ser

A paper on laser vibrometer characterization of the ultrasonic coupling into the microfluidic chips used in the NPL/UCL microbubble trapping project as presented at the 12th Anglo-French Physical Acoustics Conference (AFPAC2013) 16-18 Jan 2013, has been published as C. Fury et al, Laser vibrometry characterisation of a microfluidic lab-on-a-chip device: a preliminary investigation J Phys: Conf Ser 498 012002 (2014).

From the abstract: Since their original inception as ultrasound contrast agents, potential applications of microbubbles have evolved to encompass molecular imaging and targeted drug delivery. As these areas develop, so does the need to understand the mechanisms behind the interaction of microbubbles both with biological tissue and with other microbubbles. There is therefore a metrological requirement to develop a controlled environment in which to study these processes. Presented here is the design and characterisation of such a system, which consists of a microfluidic chip, specifically developed for manipulating microbubbles using both optical and acoustic trapping. A laser vibrometer is used to observe the coupling of acoustic energy into the chip from a piezoelectric transducer bonded to the surface. Measurement of the velocity of surface waves on the chip is investigated as a potential method for inferring the nature of the acoustic fields excited within the liquid medium of the device. Comparison of measured surface wavelengths with wave types suggests the observation of anti-symmetric Lamb or Love-Kirchhoff waves. Further visual confirmation of the acoustic fields through bubble aggregation highlights differences between the model and experimental results in predicting the position of acoustic pressure nodes in relation to excitation frequency.

Theoretical Characterisation of Microbubbles Paper

As part of the NPL/UCL/Oxford microbubble trapping collaborative project a paper Theoretical characterisation of the radial and translational motion of coated microbubbles under acoustic excitation has been published as C. J. Harfield et al, J. Phys.: Conf. Ser 457 012001 (2013).

From the abstract: Ultrasound contrast agents, in the form of coated microbubbles, are a powerful tool in current diagnostic imaging. Given their sensitive dynamic response they also have the potential to be used for quantitative measurements of the properties of the surrounding tissue (e.g. percentage perfusion or blood pressure). For this potential to be realised, however, the theoretical descriptions of bubble behaviour, in particular the constitutive equations for the microbubble shell, need to be improved and a method needs to be developed for the accurate characterisation of individual bubbles. In this paper the first steps are taken towards deriving a complete model for the coupled radial and translational motion of a coated bubble. It is then shown that with this model the bubble can be characterised by a unique set of parameters describing the bubble shell corresponding to its viscous and elastic response. This uniqueness will enable the model to be used to interpret experimental data and quantify these parameters for which accurate values are currently lacking but which are critical to predicting bubble response and hence enabling advanced diagnostic applications.

Big Bang Science Fair

POP! The Sound of Bubbles was at the Big Bang Science Fair in the ExCeL Centre in Docklands 14 - 17 March.  Members of the NPL/UCL/Oxford microbubble project together with colleagues from NPL, Glasgow University and King's College demonstrated bubble science to over 63,000 visitors in four days.
Among the visitors to our stand was the Secretary of State for Business, Innovation and Skills, Vince Cable, here being shown our Kundt Tube demonstration of acoustic resonance by Ian Butterwoth of the NPL.

Susan Skelton PhD viva

Congratulations to Optical Tweezers PhD student Susan Skelton who has successfully defended her PhD thesis on Applications of cylindrical vector beams for optical micromanipulation.  Susan will be leaving the group to start a postdoc at the University of Osaka, Japan, in the Laboratory for Scientific Instrumentation and Engineering (LaSIE) under the supervision of Prof Satoshi Kawata.  Many thanks to Dr Stephen Hogan (UCL) and Dr David McGloin (Dundee University) for acting as examiners.

Well done Dr Skelton, and good luck in Japan!

SPIE Conference Proceedings

Our contributions to the Optical Trapping and Optical Micromanipulation IX meeting at SPIE Optics + Photonics 2012 are now published in the conference proceedings as:

S. E. Skelton, M. Sergides, M. G. Donato, S. Vasi, R. Sayed, P. G. Gucciardi, R. Saija, M. A. Iatì, O. M. Maragò and P. H. Jones.  'Shaping the trapping volume in optical tweezers using cylindrical vector beams', Proc. SPIE 8458, Optical Trapping and Optical Micromanipulation IX, 84582Z, doi: 10.1117/12.929927 (2012)

S. E. Skelton, M. Sergides, G. Memoli, O. M. Maragò and P. H. Jones.  'Optical squeezing of microbubbles: Ray optics and Mie scattering calculations', Proc. SPIE 8458, Optical Trapping and Optical Micromanipulation IX, 84581F, doi: 10.1117/12.929900 (2012)

M. Sergides, S. E. Skelton, E. Karczewska, K. Thorneycroft, O. M. Maragò and P. H. Jones.  'Optically bound particle structures in evanescent wave traps', Proc. SPIE 8458, Optical Trapping and Optical Micromanipulation IX, 84583C, doi: 10.1117/12.929612 (2012)

SPIE Optics + Photonics Conference

Marios and Susan are attending the Optical Trapping and Optical Micromanipulation IX conference, part of SPIE Optics + Photonics, in San Diego, CA, 12 - 16 August.  Susan will be giving a talk 'Optical squeezing of microbubbles: Ray optics and Mie scattering calculations' (Paper 8458-51) on Wed 16 Aug (Session 10: Combining optical traps with acoustics) and presenting a poster on 'Shaping of the trapping volume in optical tweezers using cylindrical vector beams' (Paper 8458-110).  Marios will be presenting a poster 'Optically bound particle structures in evanescent wave traps' (Paper 8458-124).

Royal Society Summer Exhibition

This week we have been at the Royal Society Summer Exhibition 2012 with a display titled POP! The sound of bubbles.  Opposite you can see members of the team explaining the science of bubbles to guests at the soiree on Thu 05 Jul.

The exhibition and our display also featured on the BBC news, and in BBC R4's Material World programme on 05 July. The podcast of this show will be available to download for the next few weeks. 

Trapping and deformation of microbubbles in a dual-beam fibre-optic trap

  

Our paper Trapping and deformation of microbubbles in a dual-beam fibre-optic trap has been published as S E Skelton et al, Journal of Optics 14 075706 (2012).

From the abstract:  We present results of numerical calculations to evaluate the performance of a dual-beam fibre-optic trap for low refractive index particles such as ultrasound contrast agent microbubbles. Using a geometrical optics approach, we determine the range of parameters of microbubble size and beam dimensions over which the optical trap is stable and evaluate the trapping forces and spring constants. Additionally, we calculate the optically induced stress profile over the surface of the microbubble and evaluate the resulting deformation of the microbubble using elastic membrane theory. Our results suggest that such an experiment could be a useful tool for quantifying the mechanical properties (elastic modulus) of the shell material of an ultrasound contrast agent microbubble.

This paper has been included in the IoPscience collection of featured articles "chosen for their quality and recency".

New Group Members

Chris Fury has joined the UCL Optical Tweezers Group from April 2012 to study for a PhD.  Chris gained a degree in Physics from Exeter University, followed by an MSc in Fusion Energy from York University, which included a research project at the Central Laser Facility at the Rutherford Appleton Lab.

Chris joins the group to work at the National Physical Laboratory on the NPL/UCL optical and acoustic microbubble trapping project.

Royal Society Summer Exhibition 2012

The UCL/NPL microbubble trapping project will have a stand at the Royal Society Summer Exhibition 2012, called 'Pop! The sound of bubbles'.  This stand will be run by many of the scientists involved in the project including Gianluca Memoli, Eleanor Stride, Caroline Harfield & Louise Wright.  The exhibition runs from 03-08 July 2012 at the Royal Society.
Our display will feature the science of microbubble trapping as well as many other everyday applications of microbubble technology (including some that might surprise you!).
You can follow the sound of bubbles blog for the latest updates on our project, or the Summer Science 2012 twitter @summerscience for more about the exhibition.

PhD studentship available

A PhD studentship is available as part of a joint project between the National Physical Laboratory, University College London (UCL) and the University of Oxford, aimed at the trapping and manipulation of microbubbles in optical and acoustical fields, to transform them into micro-sensors. The project already employs a PhD student for the theoretical part: we are currently recruiting a student for the experimental side of the project.

The work will be mainly conducted at NPL under the direction of Dr Gianluca Memoli, and the student will be registered for a PhD with Dr Philip Jones, at the Department of Physics & Astronomy, University College London.

The studentship is available for three years, starting in early 2012 and will pay a stipend and fees at a rate applicable for UK and EU students.

Candidates should have a degree in Physics or Engineering and previous experimental experience (with lasers or ultrasound or microfluidics) would be a clear advantage.

The National Physical Laboratory (NPL) is one of the UK's leading science facilities and research centres. It is a world-leading centre of excellence in developing and applying the most accurate standards, science and technology available.

NPL occupies a unique position as the UK's National Measurement Institute and sits at the intersection between scientific discovery and real world application. Its expertise and original research have underpinned quality of life, innovation and competitiveness for UK citizens and business for more than a century.

NPL is based in a unique research environment which is located in pleasant surroundings on the edge of Bushy Park in south-west London. We have a host of onsite facilities including a subsidised crèche, restaurant, and a sports and social club.

NPL Management Limited is committed to supporting their people to develop both personally and professionally and is committed to equal opportunities.

To apply for this position, please send your CV and any other relevant information to:

Dr Gianluca Memoli
Tel: +44 20 8943 6062
Email: gianluca.memoli@npl.co.uk

The cosing date for aplications is 31 December 2011.

Microbubble User Group Meeting

The latest Microbubble User Group (microBUG) meeting is being held on Wed 16 November at Imperial College.  The programme of talks for the day is:

David (single bubble characterisation)
Susan (optical trapping of bubbles)
Terence (acousto-optic bubble characterisation)
Virginie (bubble formation in decompression sickness)
Jonathan (charactertization of adherent microbubbles)
Grace (stability of gold coated bubbles)
IEEE meeting highlights

The meetings are held in the Royal School of Mines, and hosted by Mengxing Tang.

NPL Annual Review

The NPL-UCL Microbubble Project is featured in the latest NPL Annual Review, 110 Years of Impact.

Measuring with microbubbles

NPL is working with University College London on a fascinating project which investigates the dynamics of microbubbles, to see if they can be used as highly sensitive sensors in medical an industrial applications.

Microbubbles are specially-coated bubbles which are designed primarily to enhance ultrasound pulse-echo imagaing.  Their use significantly enhances sound echoes, thereby improving detection accuracy, and therefore diagnosis of 'difficult' cancers (e.g. liver, prostate).

Microbubbles (and specially designed ultrasonic fields) are being studied worldwide as possible vehicles for drug and gene delivery.  They promise to play a crucial role in fighting Alzheimer's disease, or cancers in which the use of chemotherapy is deemed too risky to the patient, and thus a targeted therapy is more effective.

NPL's work in this area is developing the measurement building blocks, to exploit the sensitivity of microbubbles to local changes in their environment, so extending their effectiveness in medical applications and beyond.

For more information about this project contact Phil Jones at UCL, or Gianluca Memoli at NPL.

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

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.

UCL Optical Tweezers on YouTube

The UCL Optical Tweezers Group now has a YouTube channel at www.youtube.com/user/uclopticaltweezers. 

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: