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michael somekh

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Papers by michael somekh

Cheap optical transducers (CHOTs) for narrowband ultrasonic applications

Measurement Science and Technology, Feb 5, 2007

We have developed an innovative ultrasonic transducer system (CHOT) which is optically excited by... more We have developed an innovative ultrasonic transducer system (CHOT) which is optically excited by means of lasers. It can be used both for generation and detection of narrowband ultrasound and provides non-contact (or even remote), couplant-free generation and/or detection. It has also the advantage of being inexpensive to manufacture and the simplicity of its concept makes it ideal for industrial applications. In this study we present results where CHOTs have been used both for excitation and detection of surface acoustic waves. An initial theoretical model is also presented which describes the principle of operation.

Label-Free, High Resolution, Multi-Modal Light Microscopy for Discrimination of Live Stem Cell Differentiation Status

Scientific Reports, Jan 15, 2018

A label-free microscopy method for assessing the differentiation status of stem cells is presente... more A label-free microscopy method for assessing the differentiation status of stem cells is presented with potential application for characterization of therapeutic stem cell populations. The microscopy system is capable of characterizing live cells based on the use of evanescent wave microscopy and quantitative phase contrast (QPC) microscopy. The capability of the microscopy system is demonstrated by studying the differentiation of live immortalised neonatal mouse neural stem cells over a 15 day time course. Metrics extracted from microscope images are assessed and images compared with results from endpoint immuno-staining studies to illustrate the system's performance. Results demonstrate the potential of the microscopy system as a valuable tool for cell biologists to readily identify the differentiation status of unlabelled live cells.

Sub-100 nm resolution microscopy based on proximity projection grating scheme

Scientific Reports, Feb 26, 2015

Structured illumination microscopy (SIM) has been widely used in life science imaging application... more Structured illumination microscopy (SIM) has been widely used in life science imaging applications. The maximum resolution improvement of SIM, compared to conventional bright field system is a factor of 2. Here we present an approach to structured illumination microscopy using the proximity projection grating scheme (PPGS), which has the ability to further enhance the SIM resolution without invoking any nonlinearity response from the sample. With the PPGS-based SIM, sub-100 nm resolution has been obtained experimentally and results corresponding to 2.4 times resolution improvement are presented. Furthermore, it will be shown that an improvement of greater than 3 times can be achieved.

$Research paper thumbnail of High Aspect-Ratio Open Grating Fabry-Perot Resonator for High-Sensitivity Refractive Index Sensing$

High Aspect-Ratio Open Grating Fabry-Perot Resonator for High-Sensitivity Refractive Index Sensing

IEEE Sensors Journal

This paper presents a high aspect-ratio open grating Fabry-Perot resonator theoretically and expe... more This paper presents a high aspect-ratio open grating Fabry-Perot resonator theoretically and experimentally for aqueous refractive index sensing with high figure of merit. Transmission line modelling and associated Smith charts are utilized to give a better intuitive understanding of the physical sensing mechanism. The analysis aids understanding of the relative contribution to refractive index changes both within the grating fingers and external to them. Measurements of refractive index are carried out with Kretschmann coupling configuration for both transverse magnetic (TM) and transverse electric (TE) polarization. The results show an improvement of 10-and 44-fold in figure of merit over conventional SPR for TM and TE, respectively. When the designed system is analyzed for sensitivity, 1.874×10 -8 RIU is achieved with a single frame even without a reference channel for noise cancellation. With 794 frames averaging (approximately 1-second acquisition time), the sensitivity of the system can be further improved to 1.609×10 -9 RIU. The simulations and experimental results demonstrate strong potential for biosensing applications, e.g., kinetic molecular binding, ultrasensitive refractive index sensing and photoacoustic detection.

$Research paper thumbnail of Analysis of Open Grating-Based Fabry–Pérot Resonance Structures With Potential Applications for Ultrasensitive Refractive Index Sensing$

Analysis of Open Grating-Based Fabry–Pérot Resonance Structures With Potential Applications for Ultrasensitive Refractive Index Sensing

IEEE Sensors Journal, 2021

We report a theoretical framework to explain the characteristics of Fabry-Pérot (FP) resonances e... more We report a theoretical framework to explain the characteristics of Fabry-Pérot (FP) resonances excited in a thin film-based grating consisting of a thin gold layer and a rectangular dielectric grating in the sub-wavelength and near-wavelength grating regimes. The zeroth-order diffraction inside the grating layer forms an FP resonant cavity with effective refractive index arising from an averaging effect between the refractive indices of the grating material and the filling material between the grating grooves. A simplified model based on Fresnel equations and phase matching condition is proposed to predict the FP resonant mode for the grating structure, this is compared with rigorous coupledwave analysis to determine its range of validity. We also compare the performance of the proposed structure with other thin film-based interferometers for refractive index sensing applications, in terms of, sensitivity, full width at half maximum, figure of merit and dynamic range. The proposed structure has a full width at half maximum around 10 times to 60 times narrower than conventional surface plasmon resonance and conventional FP resonators. Thus, the figure of merit is higher than Kretschmann based surface plasmon resonance and FP structures by a factor of 20 and 2 respectively with a wider dynamic range. The total energy stored in the grating resonant cavity is 5 and 20-fold greater than the surface plasmon resonance configuration and the conventional FP structures. Since the resonator discussed here is an open structure, it is far better suited for liquid sensing compared to a closed FP structure.

Label-Free, High Resolution, Multi-Modal Light Microscopy for Discrimination of Live Stem Cell Differentiation Status

Scientific reports, Jan 15, 2018

A label-free microscopy method for assessing the differentiation status of stem cells is presente... more A label-free microscopy method for assessing the differentiation status of stem cells is presented with potential application for characterization of therapeutic stem cell populations. The microscopy system is capable of characterizing live cells based on the use of evanescent wave microscopy and quantitative phase contrast (QPC) microscopy. The capability of the microscopy system is demonstrated by studying the differentiation of live immortalised neonatal mouse neural stem cells over a 15 day time course. Metrics extracted from microscope images are assessed and images compared with results from endpoint immuno-staining studies to illustrate the system's performance. Results demonstrate the potential of the microscopy system as a valuable tool for cell biologists to readily identify the differentiation status of unlabelled live cells.

The effect of elastic anisotropy on contrast in the scanning acoustic microscope

Philosophical Magazine A, 1984

The contrast obtained with polycrystalline specimens in the scanning acoustic microscope is compu... more The contrast obtained with polycrystalline specimens in the scanning acoustic microscope is computed by taking account of the anisotropic stiffness tensor. The resulting variation of signal with defocus is fundamentally different from that which could be obtained with an isotropic material regardless of the values of the elastic properties. In many cases this results largely from the excitation of pseudo-surface waves which effect the response of the microscope in a similar manner to 'leaky' Rayleigh waves. The reasons why some materials fail to give good acoustic images of grain structure are discussed.

Acoustic Microscopy of Ultrasonic Attenuation

Le Journal de Physique Colloques, 1983

L1att6nuation ultrasonique peutgtre imagse 2 l'aide d'un microscope acoustique 2 balayage. La zon... more L1att6nuation ultrasonique peutgtre imagse 2 l'aide d'un microscope acoustique 2 balayage. La zone de plastique situse au niveau d'une craquelure sous contrainte a 6t6 imagge par transmission, le contraste provenant d'un amortissement de dislocation. I1 est aussi montr6 que le contraste en mode &flexion est sensible 2 lktt6nuation ce qui permet de d6tecter et dlimager l'attenuation avec une r6solution spatiale dlenviron 2pm.

Phase sensitive array detection with polarisation modulated differential sensing

Sensors and Actuators B: Chemical, 2006

It has recently been shown that polarisation modulated differential surface plasmon sensing can b... more It has recently been shown that polarisation modulated differential surface plasmon sensing can be used to monitor refractive index changes of approximately 2 × 10 -7 refractive index units. The information for these measurements is carried by a small-modulated light component and a relatively large constant background signal. These measurements have, hitherto, only been carried out as point measurements. In this paper we demonstrate that multipoint measurements can be obtained using a CMOS camera array that directly detects the amplitude and phase of the oscillating component of the light. The effectiveness of the parallel measurement is demonstrated by monitoring the changes in a waveguide mode as the refractive index of the dielectric layer is changed by exposure to ultraviolet radiation. This paper demonstrates the potential of phase sensitive CMOS detection in applications where spatially resolved differential imaging is required, especially in the field of chemical and biological sensing.

Responsivity of the differential-intensity surface plasmon resonance instrument

Sensors and Actuators B: Chemical, 2016

Surface plasmon resonance is used for the sensitive measurement of minute concentrations of bioan... more Surface plasmon resonance is used for the sensitive measurement of minute concentrations of bioanalytes and probing of electrochemical processes. Typical refractive index sensitivity, for the intensity approach, is around 10 -6 refractive index units (RIUs). A better sensitivity has been suggested by developing a differential-intensity detection method. This method relies on the excitation of surface plasmons using a weakly focused beam with the average angle of incidence equal to the resonance angle, while the reflected light is detected using a bi-cell photodiode. The Bi-cell signal is processed by calculating the difference between its two units, normalized to their sum. This ratio estimates the shift in the resonance angle using a model that represents the resonance curve with a quadratic function. However, this model does not explain the effects of parameters such as the angular width of the excitation beam and the specifications of the sensing structure on the system's response. This paper presents a detailed evaluation of the responsivity using experimental and theoretical approaches, which can predict the effect of the different parameters, paving the way towards the investigation of a better sensitivity and the optimization of the system's design for different applications.

Live Imaging of Cellular Internalization of Single Colloidal Particle by Combined Label-Free and Fluorescence Total Internal Reflection Microscopy

Molecular Pharmaceutics, 2015

In this work we utilise the combination of label-free total internal reflection microscopy and to... more In this work we utilise the combination of label-free total internal reflection microscopy and total internal reflectance fluorescence (TIRM/TIRF) microscopy to achieve a simultaneous, live imaging of single, label-free colloidal particle endocytosis by individual cells. The TIRM arm of the microscope enables label free imaging of the colloid and cell membrane features, while the TIRF arm images the dynamics of fluorescent-labelled clathrin (protein involved in endocytosis via clathrin pathway), expressed in transfected 3T3 fibroblasts cells. Using a model polymeric colloid and cells with a fluorescently-tagged clathrin endocytosis pathway, we demonstrate that wide field TIRM/TIRF co-imaging enables live visualization of the process of colloidal particle interaction with the labelled cell structure, which is valuable for discerning the membrane events and route of colloid internalization by the cell. We further show that 500 nm diameter model polystyrene colloid associates with clathrin, prior to and during its cellular internalisation. This association is not apparent with larger, 1 µm diameter colloids, indicating an upper particle diameter limit for clathrin-mediated endocytosis.

Shedding light on life

Physics World, 2008

Since the discovery of X-rays in 1895, curiosity as well as clinical need has produced huge advan... more Since the discovery of X-rays in 1895, curiosity as well as clinical need has produced huge advances in our ability to visualize structures inside the human body. X-ray radiographic imaging led the way, followed in 1957 by the use of gamma-ray cameras, and then ultrasound imaging, magnetic resonance imaging (MRI), and positron emission tomography (PET). Together, these tools, in which physics plays a key part, underpin modern clinical-imaging practice. The length scales that these techniques interrogate, however, leave much to be desired if one is interested in the very small. Clinical MRI, for example, can only resolve structures down to 100 µm. While some living cells are more than 80 µm across, interesting and important cellular processes -such as signalling between cells -may take place over length scales of much less than 1 µm. Living cells are essentially defined by their complex spatial structures -for example the doughnut shape of red blood cells and the elongated projections (known as axons) of neuronal cells are key to their functions. Underlying these broad morphological characteristics, however, are much finer-scale molecular assemblies, such as the cytoskeleton (a protein "scaffolding" that stabilizes the larger-scale intracellular structures) and microdomains within cell membranes, which are the locii of many molecular signalling events. Any technique to study the properties of biological molecules and their many interactions should ideally provide spatial information, because researchers increasingly need to integrate information about the interactions that underlie a biological effect with data Visualizing and understanding complex biological systems at the cellular level is an endeavour that requires the best efforts of both biologists and physicists, explain

High Resolution Imaging of TGFβ3 Treated Human Keratinocyte via a Newly Developed Widefield Surface Plasmon Resonance Microscope

IFMBE Proceedings, 2007

In this study high resolution imaging of human adult (HaCaTs) Keratinocytes cells using the newly... more In this study high resolution imaging of human adult (HaCaTs) Keratinocytes cells using the newly developed Widefield Surface Plasmon Resonance (WSPR) system will be discussed. Surface Plasmon Resonance (SPR) occurs at the interface between a dielectric and a thin conducting layer when p-polarized light strikes at a specific angle thus excites free electrons and generates surface plasmon electromagnetic wave. The SPR excitation angle can be changed by the binding of bio-molecular species to the metallised layer, and is directly proportional to the refractive index and thickness of that molecular species. Our WSPR system provide high lateral resolution imaging close to 500 nanometers [1] and was used to investigate cell surface interactions under two different culture conditions: HaCaTs cultured on SPR substrate with Transforming Growth Factor β3 (TGFβ3) (50ng/ml) [2] and without TGFβ3. In less than 24 hours, HaCaTs cultured in the presence of TGFβ3 showed enhanced division and motility along with decreased cell attachment as compared with cells maintained in TGFβ3 free media. It is to be noted that cellular signaling by TGFβ3 is very important for enhancing tissue development in wound repair and that this study for the first time enabled optical interrogation of cell surface interface without the need for Immunostaining.

Widefield Surface Plasmon Resonance Microscope: A Novel Biosensor Study of Cell Attachment to Micropatterned Substrates

3rd Kuala Lumpur International Conference on Biomedical Engineering 2006, 2007

In this study, Human adult, low Ca2+, high Temperature (HaCaTs) Keratinocytes were cultured on mi... more In this study, Human adult, low Ca2+, high Temperature (HaCaTs) Keratinocytes were cultured on microcontact printed fibronectin repeat gratings of 1.8, 3.8, 5, 12.5 and 25µm for 24 hours. The cells were then fixed with 0.1% Glutaraldehyde and dehydrated in serial alcohol . The alignment of the cells were then measured, where 0º represents 100% alignment to the pattern, in order to identify those features that promoted the highest degree of cell alignment. From the quantitative analysis it became clear that HaCaTs cells align most readily to the 12.5µm pattern. A 12.5µm stamp was therefore used to stamp pattern fibronectin on to prefabricated Au/Cr/glass surface plasmon substrates. HaCaTs cells were cultured on the substrates for 24 hours and imaged with the "Widefield Surface Plasmon Resonance" (WSPR) microscope [1]. The WSPR system enables the examination of nanometric interfacial interactions of HaCaTs on patterned and un-patterned surface at lateral resolution down to 500nm. Our preliminary results demonstrate that the WSPR microscope is capable of imaging the cell surface interface and as such will prove to be a very useful tool in understanding the processes involved in cell guidance and wound repair.

Sub-100 nm resolution microscopy based on proximity projection grating scheme

Scientific Reports, 2015

Structured illumination microscopy (SIM) has been widely used in life science imaging application... more Structured illumination microscopy (SIM) has been widely used in life science imaging applications. The maximum resolution improvement of SIM, compared to conventional bright field system is a factor of 2. Here we present an approach to structured illumination microscopy using the proximity projection grating scheme (PPGS), which has the ability to further enhance the SIM resolution without invoking any nonlinearity response from the sample. With the PPGS-based SIM, sub-100 nm resolution has been obtained experimentally and results corresponding to 2.4 times resolution improvement are presented. Furthermore, it will be shown that an improvement of greater than 3 times can be achieved.

Polarization control scheme for surface plasmon and optical guided mode control detection

Sensors and Actuators, B: Chemical, 2004

A technique based on what is known as polarizer-compensator-sample-analyzer (PCSA) scheme in elli... more A technique based on what is known as polarizer-compensator-sample-analyzer (PCSA) scheme in ellipsometry, combined with the Kretschmann configuration to excite plasmon and waveguided modes is described. The system allows the control of the polarization state of the reflected light and is shown to have higher sensitivity than the measurement of only the amplitude of the reflected light. We show the response of the system to variations in temperature and small changes in the refractive index of a liquid.

Orientation Characterisation of Aerospace Materials by Spatially Resolved Acoustic Spectroscopy

Journal of Physics: Conference Series, 2014

Material characteristics such as strength, stiffness and fracture resistance are strongly related... more Material characteristics such as strength, stiffness and fracture resistance are strongly related to the underlying microstructure. In order to predict the mechanical behaviour of materials relevant to the aerospace sector such as titanium, nickel and their alloys, detailed knowledge about their texture is required. A robust measurement tool is introduced which can be used to determine the crystallographic orientation of a material. This is achieved by using a laser ultrasonic technique -spatially resolved acoustic spectroscopy (SRAS) combined with a numerical surface acoustic wave (SAW) velocity model. SRAS is used to measure the SAW velocity of a material in a number of different propagation directions. The model predicts the SAW velocity from the material's elastic constants; a search algorithm termed the overlap function is used to compare the SRAS data to the model to determine the crystallographic orientation. We examined a range of materials commonly used for aircraft components. Comparisons between SRAS and electron backscattered diffraction are presented. This is an innovative and all-purpose NDT technique for aerospace materials manufacture monitoring and quality control.

Optically excited nanoscale ultrasonic transducers

The Journal of the Acoustical Society of America, 2015

In order to work at higher ultrasonic frequencies, for instance, to increase the resolution, it i... more In order to work at higher ultrasonic frequencies, for instance, to increase the resolution, it is necessary to fabricate smaller and higher frequency transducers. This paper presents an ultrasonic transducer capable of being made at a very small size and operated at GHz frequencies. The transducers are activated and read optically using pulsed lasers and without physical contact between the instrumentation and the transducer. This removes some of the practical impediments of traditional piezoelectric architectures (such as wiring) and allows the devices to be placed immediately on or within samples, reducing the significant effect of attenuation which is very strong at frequencies above 1 GHz. The transducers presented in this paper exploit simultaneous optical and mechanical resonances to couple the optical input into ultrasonic waves and vice versa. This paper discusses the mechanical and optical design of the devices at a modest scale (a few μm) and explores the scaling of the t...

Double-grating-structured light microscopy using plasmonic nanoparticle arrays

Optics Letters, 2009

Structured illumination increases the spatial bandwidth of optical microscopes. We demonstrate ba... more Structured illumination increases the spatial bandwidth of optical microscopes. We demonstrate bandwidth extension using a physical grating placed close to the sample. This comprises an array of elongated nanoparticles, whose localized surface plasmon resonance is polarization dependent. By arranging the particle orientation to vary with position the grating can be moved by changing the input polarization. A projected optical grating provides an additional independent mechanism for bandwidth extension. Experimental results showing bandwidth improvement in one direction are presented, and the measures necessary to extend the technique for routine imaging are discussed.

Non-contact acoustic microscopy

Measurement Science and Technology, 2000

We demonstrate a fast all-optical surface acoustic wave (SAW) microscope. This acoustic microscop... more We demonstrate a fast all-optical surface acoustic wave (SAW) microscope. This acoustic microscope may be thought of as a non-contact (hence non-perturbing) surface acoustic microscope. The key to producing a sufficiently high SAW amplitude for imaging without producing surface damage is to tailor the generating optical distribution. This can be used to spread the optical power on the sample surface (preventing damage) and to focus the acoustic waves (increasing the amplitude). This paper discusses the general and specific design features of our microscope and important new developments in the general design of such instruments. Our microscope based on this technology is capable of producing high quality, quantitative images of SAW amplitude and phase (velocity) on many materials; this and new, unique, forms of acoustic contrast are demonstrated and discussed.