An Exploratory Study of Physical Therapists From High-Income Countries Practising Outside of Their Scope in Low and Middle-Income Countries.

PURPOSE: To quantify how often physical therapists from high-income countries (HIC) travelling to low- and middle-income countries (LMIC) practise outside their scope of practice, in what circumstances, and their likelihood of doing the same in the future. METHODS: An exploratory descriptive study using a survey. RESULTS: One hundred and twenty-six licensed physical therapists from around the world participated. Physical therapists typically spent less than a month (73.8 per cent) in LMIC; 67.5 per cent believed that physical therapists practise outside of their scope, and 31.7 per cent reported doing so. Reasons were believing that something is better than nothing (47.5 per cent ), a mismatch between the physical therapist's and host's expectations (40.0 per cent ), and preserving their relationship with the host (25.0 per cent ). It was deemed appropriate by 64.5 per cent to practise outside of their scope in some situations and 53.8% considered repeating the activity in the future. Half of the respondent's first experience in LMIC occurred as a student or in their first decade of practice. CONCLUSIONS: Working in LMIC requires a keen understanding of the risks and challenges associated with such experiences. To ensure best practice, a skill set that consists of critical self-reflection, systems thinking, and structural competency combined with clinical competency and accountability is imperative.

Development of a graded index microlens based fiber optical trap and its characterization using principal component analysis.

We demonstrate a miniaturized single beam fiber optical trapping probe based on a high numerical aperture graded index (GRIN) micro-objective lens. This enables optical trapping at a distance of 200µm from the probe tip. The fiber trapping probe is characterized experimentally using power spectral density analysis and an original approach based on principal component analysis for accurate particle tracking. Its use for biomedical microscopy is demonstrated through optically mediated immunological synapse formation.

Biologically enabled sub-diffractive focusing.

Evolution shows that photonic structures are a constituent part of many animals and flora. These elements produce structural color and are useful in predator-prey interactions between animals and in the exploitation of light for photosynthetic organisms. In particular, diatoms have evolved patterned hydrated silica external valves able to confine light with extraordinary efficiency. Their evolution was probably guided by the necessity to survive in harsh conditions of sunlight deprivation. Here, we exploit such diatom valves, in conjunction with structured illumination, to realize a biological super-resolving lens to achieve sub-diffractive focusing in the far field. More precisely, we consider a single diatom valve of Arachnoidiscus genus which shows symmetries and fine features. By characterizing and using the transmission properties of this valve using the optical eigenmode technique, we are able to confine light to a tiny spot with unprecedented precision in terms of resolution limit ratio, corresponding in this case to 0.21λ/NA.

Gold nanorod assisted intracellular optical manipulation of silica microspheres.

We report on the improvement of the infrared optical trapping efficiency of dielectric microspheres by the controlled adhesion of gold nanorods to their surface. When trapping wavelength was equal to the surface plasmon resonance wavelength of the gold nanorods (808 nm), a 7 times improvement in the optical force acting on the microspheres was obtained. Such a gold nanorod assisted enhancement of the optical trapping efficiency enabled the intracellular manipulation of the decorated dielectric microsphere by using a low power (22 mW) infrared optical trap.

GPU accelerated toolbox for real-time beam-shaping in multimode fibres.

We present a GPU accelerated toolbox for shaping the light propagation through multimode fibre using a spatial light modulator (SLM). The light is modulated before being coupled to the proximal end of the fibre in order to achieve arbitrary light patterns at the distal end of the fibre. First, the toolbox optimises the acquisition time of the transformation matrix of the fibre by synchronous operation of CCD and SLM. Second, it uses the acquired transformation matrix retained within the GPU memory to design, in real-time, the desired holographic mask for on-the-fly modulation of the output light field. We demonstrate the functionality of the toolbox by acquiring the transformation matrix at the maximum refresh rate of the SLM - 204 Hz, and using it to display an on-demand oriented cube, at the distal end of the fibre. The user-controlled orientation of the cube and the corresponding holographic mask are obtained in 20 ms intervals. Deleterious interference effects between the neighbouring points are eliminated by incorporating an acousto-optic deflector (AOD) into the system. We remark that the usage of the toolbox is not limited to multimode fibres and can be readily used to acquire transformation matrix and implement beam-shaping in any other linear optical system.

Optical trapping of NaYF4:Er3+,Yb3+ upconverting fluorescent nanoparticles.

We report on the first experimental observation of stable optical trapping of dielectric NaYF4:Er(3+),Yb(3+) upconverting fluorescent nanoparticles (~26 nm in diameter) using a continuous wave 980 nm single-beam laser. The laser serves both to optically trap and to excite visible luminescence from the nanoparticles. Sequential loading of individual nanoparticles into the trap is observed from the analysis of the emitted luminescence. We demonstrate that the trapping strength and the number of individual nanoparticles trapped are dictated by both the laser power and nanoparticle density. The possible contribution of thermal effects has been investigated by performing trapping experiment in both heavy water and into distilled water. For the case of heavy water, thermal gradients are negligible and optical forces dominate the trap loading behaviour. The results provide a promising path towards real three dimensional manipulation of single NaYF4:Er(3+),Yb(3+) nanoparticles for precise fluorescence sensing in biophotonics experiments.

Modal characterization using principal component analysis: application to Bessel, higher-order Gaussian beams and their superposition.

The modal characterization of various families of beams is a topic of current interest. We recently reported a new method for the simultaneous determination of both the azimuthal and radial mode indices for light fields possessing orbital angular momentum. The method is based upon probing the far-field diffraction pattern from a random aperture and using the recorded data as a 'training set'. We then transform the observed data into uncorrelated variables using the principal component analysis (PCA) algorithm. Here, we show the generic nature of this approach for the simultaneous determination of the modal parameters of Hermite-Gaussian and Bessel beams. This reinforces the widespread applicability of this method for applications including information processing, spectroscopy and manipulation. Additionally, preliminary results demonstrate reliable decomposition of superpositions of Laguerre-Gaussians, yielding the intensities and relative phases of each constituent mode. Thus, this approach represents a powerful method for characterizing the optical multi-dimensional Hilbert space.

Bidirectional optical sorting of gold nanoparticles.

We present a generic technique allowing size-based all-optical sorting of gold nanoparticles. Optical forces acting on metallic nanoparticles are substantially enhanced when they are illuminated at a wavelength near the plasmon resonance, as determined by the particle's geometry. Exploiting these resonances, we realize sorting in a system of two counter-propagating evanescent waves, each at different wavelengths that selectively guide nanoparticles of different sizes in opposite directions. We validate this concept by demonstrating bidirectional sorting of gold nanoparticles of either 150 or 130 nm in diameter from those of 100 nm in diameter within a mixture.

Dynamics of primary and secondary microbubbles created by laser-induced breakdown of an optically trapped nanoparticle.

Laser-induced breakdown of an optically trapped nanoparticle is a unique system for studying cavitation dynamics. It offers additional degrees of freedom, namely the nanoparticle material, its size, and the relative position between the laser focus and the center of the optically trapped nanoparticle. We quantify the spatial and temporal dynamics of the cavitation and secondary bubbles created in this system and use hydrodynamic modeling to quantify the observed dynamic shear stress of the expanding bubble. In the final stage of bubble collapse, we visualize the formation of multiple submicrometer secondary bubbles around the toroidal bubble on the substrate. We show that the pattern of the secondary bubbles typically has its circular symmetry broken along an axis whose unique angle rotates over time. This is a result of vorticity along the jet towards the boundary upon bubble collapse near solid boundaries.

Willin/FRMD6 expression activates the Hippo signaling pathway kinases in mammals and antagonizes oncogenic YAP.

The Salvador/Warts/Hippo (Hippo) signaling pathway defines a novel signaling cascade regulating cell contact inhibition, organ size control, cell growth, proliferation, apoptosis and cancer development in mammals. The Drosophila melanogaster protein Expanded acts in the Hippo signaling pathway to control organ size. Previously, willin/FRMD6 has been proposed as the human orthologue of Expanded. Willin lacks C-terminal sequences that are present in Expanded and, to date, little is known about the functional role of willin in mammalian cells. When willin is expressed in D. melanogaster epithelial tissues, it has the same subcellular localization as Expanded, but cannot rescue growth defects associated with expanded deficiency. However, we show that ectopic willin expression causes an increase in phosphorylation of the core Hippo signaling pathway components MST1/2, LATS1 and YAP, an effect that can be antagonized by ezrin. In MCF10A cells, loss of willin expression displays epithelial-to-mesenchymal transition features and willin overexpression antagonizes YAP activity via the N-terminal FERM domain of willin. Therefore, in mammalian cells willin influences Hippo signaling activity by activating the core Hippo pathway kinase cassette.

Near infrared spectroscopic analysis of single malt Scotch whisky on an optofluidic chip.

Standardization and quality monitoring of alcoholic beverages is an important issue in the liquor production industry. Various spectroscopic techniques have proved useful for tackling this problem. An ideal sensing device for alcoholic beverages should be able to detect the quality of alcohol with a small amount of sample at a low acquisition time using a portable and easy to use device. We propose the use of near infra-red spectroscopy on an optofluidic chip for quality monitoring of single malt Scotch whisky. This is chip upon which we have previously realized waveguide confined Raman spectroscopy. Analysis on this alignment-free, portable chip may be performed in only 2 seconds with a sample volume of only 20 µl. Using a partial least square (PLS) calibration, we demonstrate that the alcohol content in the beverage may be predicted to within a 1% prediction error. Principal component analysis (PCA) was employed for successful classification of whiskies based upon their age, type and cask. The prospect of implementing an optofluidic analogue of a conventional fiber based spectroscopic probe allows a rapid analysis of alcoholic beverages with dramatically reduced sample volumes.

Numerical investigation of passive optical sorting of plasmon nanoparticles.

We explore the passive optical sorting of plasmon nanoparticles and investigate the optimal wavelength and optimal beam shape of incident field. The condition for optimal wavelength is found by maximising the nanoparticle separation whilst minimising the temperature increase in the system. We then use the force optical eigenmode (FOEi) method to find the beam shape of incident electromagnetic field, maximising the force difference between plasmon nanoparticles. The maximum force difference is found with respect to the whole sorting region. The combination of wavelength and beam shape study is demonstrated for a specific case of gold nanoparticles of radius 40 nm and 50 nm respectively. The optimum wavelength for this particular situation is found to be above 700 nm. The optimum beam shape depends upon the size of sorting region and ranges from plane-wave illumination for infinite sorting region to a field maximising gradient force difference in a single point.

Visualization of the birth of an optical vortex using diffraction from a triangular aperture.

The study and application of optical vortices have gained significant prominence over the last two decades. An interesting challenge remains the determination of the azimuthal index (topological charge) ℓ of an optical vortex beam for a range of applications. We explore the diffraction of such beams from a triangular aperture and observe that the form of the resultant diffraction pattern is dependent upon both the magnitude and sign of the azimuthal index and this is valid for both monochromatic and broadband light fields. For the first time we demonstrate that this behavior is related not only to the azimuthal index but crucially the Gouy phase component of the incident beam. In particular, we explore the far field diffraction pattern for incident fields incident upon a triangular aperture possessing non-integer values of the azimuthal index ℓ. Such fields have a complex vortex structure. We are able to infer the birth of a vortex which occurs at half-integer values of ℓ and explore its evolution by observations of the diffraction pattern. These results demonstrate the extended versatility of a triangular aperture for the study of optical vortices.

Optical eigenmodes; exploiting the quadratic nature of the energy flux and of scattering interactions.

We report a mathematically rigorous technique which facilitates the optimization of various optical properties of electromagnetic fields in free space and including scattering interactions. The technique exploits the linearity of electromagnetic fields along with the quadratic nature of the intensity to define specific Optical Eigenmodes (OEi) that are pertinent to the interaction considered. Key applications include the optimization of the size of a focused spot, the transmission through sub-wavelength apertures, and of the optical force acting on microparticles. We verify experimentally the OEi approach by minimising the size of a focused optical field using a superposition of Bessel beams.

Experimental and theoretical determination of optical binding forces.

We present an experimental and theoretical study of long distance optical binding effects acting upon micro-particles placed in a standing wave optical field. In particular we present for the first time quantitatively the binding forces between individual particles for varying inter-particle separations, polarizations and incident angles of the binding beam. Our quantitative experimental data and numerical simulations show that these effects are essentially enhanced due to the presence of a reflective surface in a sample chamber. They also reveal conditions to form stable optically bound clusters of two and three particles in this geometry. We also show that the inter-particle separation in the formed clusters can be controlled by altering the angle of the beam incident upon the sample plane. This demonstrates new perspectives for the generation and control of optically bound soft matter and may be useful to understand various inter-particle effects in the presence of reflective surfaces.

Optical path clearing and enhanced transmission through colloidal suspensions.

We utilize advanced laser fields to clear a path through a dynamic turbid medium, a concept termed "Optical path clearing (OPC)." Particles are evacuated from a volume of the medium using the gradient and/or scattering forces due to an applied laser field with a suitably tailored spatial profile. Our studies encompass both an analytical model and proof-of-principle experiments where paths are cleared in dense bulk colloidal suspensions. Based on our results we suggest that high-performance and high efficiency OPC will be achieved by multiple-step clearing using dynamic laser fields based on Airy or inverted axicon beams.

Fiber probe based microfluidic raman spectroscopy.

We report a novel fiber probe based Raman detection system on a microfluidic platform where a split Raman probe is directly embedded into a polydimethylsiloxane (PDMS) chip. In contrast to previous Raman detection schemes in microfluidics, probe based detection offers reduced background and portability. Compared to conventional backscattering probe designs, the split fiber probe we used in this system, results in a reduced size and offers flexibility to modify the collection geometry to minimize the background generated by the fibers. Also our microfluidic chip design enables us to obtain an alignment free system. As a proof of concept we demonstrate the sensitivity of the device for urea detection at relevant human physiological levels with a low acquisition time. The development of this system on a microfluidic platform means portable, lab on a chip devices for biological analyte detection and environmental sensing using Raman spectroscopy are now within reach.

Optical chromatography using a photonic crystal fiber with on-chip fluorescence excitation.

We describe the realization of integrated optical chromatography, in conjunction with on-chip fluorescence excitation, in a monolithically fabricated poly-dimethylsiloxane (PDMS) microfluidic chip. The unique endlessly-single-mode guiding property of the Photonic Crystal Fiber (PCF) facilitates simultaneous on-chip delivery of beams to perform optical sorting in conjunction with fluorescence excitation. We use soft lithography to define the chip and insert the specially capped PCF into it through a predefined fiber channel that is intrinsically aligned with the sorting channel. We compare the performance of the system to a standard ray optics model and use the system to demonstrate both size-driven and refractive index-driven separations of colloids. Finally we demonstrate a new technique of enhanced optofluidic separation of biological particles, by sorting of human kidney embryonic cells (HEK-293), internally tagged with fluorescing microspheres through phagocytocis, from those without microspheres and the separation purity is monitored using fluorescence imaging.

Integrated optical transfection system using a microlens fiber combined with microfluidic gene delivery.

Optical transfection is a promising technique for the delivery of foreign genetic material into cells by transiently changing the permeability of the cell membrane. Of the different optical light sources that have been used, femtosecond laser based transfection has been one of the most effective methods for optical transfection which is generally implemented using a free space bulk optical setup. In conventional optical transfection methods the foreign genetic material to be transfected is homogenously mixed in the medium. Here we report the first realization of an integrated optical transfection system which can achieve transfection along with localized drug delivery by combining a microlens fiber based optical transfection system with a micro-capillary based microfluidic system. A fiber based illumination system is also incorporated in the system in order to achieve visual identification of the cell boundaries during transfection. A novel fabrication method is devised to obtain easy and inexpensive fabrication of microlensed fibers, which can be used for femtosecond optical transfection. This fabrication method offers the flexibility to fabricate a microlens which can focus ultra-short laser pulses at a near infrared wavelength to a small focal spot (~3 µm) whilst keeping a relatively large working distance (~20 µm). The transfection efficiency of the integrated system with localized plasmid DNA delivery, is approximately 50%, and is therefore comparable to that of a standard free space transfection system. Also the use of integrated system for localized gene delivery resulted in a reduction of the required amount of DNA for transfection. The miniaturized, integrated design opens a range of exciting experimental possibilities, including the dosing of tissue slices, targeted drug delivery, and targeted gene therapy in vivo.

Propagation characteristics of Airy beams: dependence upon spatial coherence and wavelength.

We generate a broadband "white light" Airy beam and characterize the dependence of the beam properties on wavelength. Experimental results are presented showing that the beam's deflection coefficient and its characteristic length are wavelength dependent. In contrast the aperture coefficient is not wavelength dependent. However, this coefficient depends on the spatial coherence of the beam. We model this behaviour theoretically by extending the Gaussian-Schell model to describe the effect of spatial coherence on the propagation of Airy beams. The experimental results are compared to the model and good agreement is observed.