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    Many small open ocean animals, such as Antarctic krill, are an important part of marine ecosystems. To discover what will happen to animals such as krill in a changing ocean, experiments are run in aquaria where conditions can be... more
    Many small open ocean animals, such as Antarctic krill, are an important part of marine ecosystems. To discover what will happen to animals such as krill in a changing ocean, experiments are run in aquaria where conditions can be controlled to simulate water characteristics predicted to occur in the future. The response of individual animals to changing water conditions can be hard to observe, and with current observation techniques it is very difficult to follow the progress of an individual animal through its life. Optical coherence tomography (OCT) is an optical imaging technique that allows images at high resolution to be obtained from depths up to a few millimeters inside biological specimens. It is compatible with in vivo imaging and can be used repeatedly on the same specimens. In this work, we show how OCT may be applied to post mortem krill samples and how important physiological data such as shell thickness and estimates of organ volume can be obtained. Using OCT we find an average value for the thickness of krill exoskeleton to be (30±4) µm along a 1 cm length of the animal body. We also show that the technique may be used to provide detailed imagery of the internal structure of a pleopod joint and provide an estimate for the heart volume of (0.73±0.03) mm3.
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    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... more
    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.
    We report the first implementation of the fiber based microfluidic Raman spectroscopic detection scheme, which can be scaled down to micrometre dimensions, allowing it to be combined with other microfluidic functional devices. This novel... more
    We report the first implementation of the fiber based microfluidic Raman spectroscopic detection scheme, which can be scaled down to micrometre dimensions, allowing it to be combined with other microfluidic functional devices. This novel Raman spectroscopic detection scheme, which we termed as Waveguide Confined Raman Spectroscopy (WCRS), is achieved through embedding fibers on-chip in a geometry that confines the Raman excitation and collection region which ensures maximum Raman signal collection. This results in a microfluidic chip with completely alignment-free Raman spectroscopic detection scheme, which does not give any background from the substrate of the chip. These features allow a WCRS based microfluidic chip to be fabricated in polydimethylsiloxane (PDMS) which is a relatively cheap material but has inherent Raman signatures in fingerprint region. The effects of length, collection angle, and fiber core size on the collection efficiency and fluorescence background of WCRS were investigated. The ability of the device to predict the concentration was studied using urea as a model analyte. A major advantage of WCRS is its scalability that allows it to be combined with many existing microfluidic functional devices. The applicability of WCRS is demonstrated through two microfluidic applications: reaction monitoring in a microreactor and detection of analyte in a microdroplet based microfluidic system. The WCRS approach may lead to wider use of Raman spectroscopy based detection in microfluidics, and the development of portable, alignment-free microfluidic devices.
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    Over the last century, optical spectroscopic techniques have played a crucial role in expanding our understanding of the chemistry behind various materials. Amongst all the spectroscopic techniques, Raman spectroscopy possesses a unique... more
    Over the last century, optical spectroscopic techniques have played a crucial role in expanding our understanding of the chemistry behind various materials. Amongst all the spectroscopic techniques, Raman spectroscopy possesses a unique identity due to its specificity, high information content and ease of sampling. Although a weak phenomenon, advancement in detector technologies and efficient spectrometers has driven the wider application of this technique over the last two decades.
    abstract Optical chromatography is a powerful technique, capable of separating micron-sized particles within a fluid flow, based on their intrinsic properties, including size, shape and refractive index. Briefly, particles in a fluid flow... more
    abstract Optical chromatography is a powerful technique, capable of separating micron-sized particles within a fluid flow, based on their intrinsic properties, including size, shape and refractive index. Briefly, particles in a fluid flow are subject to two forces, the Stokes drag force due to the fluid and then an introduced optical force as supplied by a laser beam, acting in opposite but collinear directions.
    Raman microspectroscopy is a label-free and nondestructive technique to measure the intrinsic chemical profile of single cells. The naturally weak Raman signals hampered the application of Raman spectroscopy for high-throughput... more
    Raman microspectroscopy is a label-free and nondestructive technique to measure the intrinsic chemical profile of single cells. The naturally weak Raman signals hampered the application of Raman spectroscopy for high-throughput measurements. Nearly all photosynthetic microorganisms contain carotenoids that are active molecules for resonance Raman at a 532 nm excitation wavelength. Hence, the acquisition time for a single photosynthetic microorganism can be as short as 1 ms. The carotenoid bands in Raman spectra of photosynthetic microorganisms utilizing 13CO2 shifted when compared to the spectra of cells utilizing 12CO2. Here, a mixture of 12C- and 13C-cyanobacterial cells were counted using a microfluidic-device-based Raman-activated cell counting procedure to prove the concept that Raman spectroscopy can be used as a high-throughput method to profile a cell population.
    The detection and analysis of bio-chemical analytes are important in the fields of personal healthcare, drug development, and environmental science, among others. The field of microfluidics aims to realize portable devices which can... more
    The detection and analysis of bio-chemical analytes are important in the fields of personal healthcare, drug development, and environmental science, among others. The field of microfluidics aims to realize portable devices which can perform fast and sensitive bioanalyte detection with minimal sample preparation. Raman spectroscopy is a powerful tool for analyte detection owing to its high specificity and its ability for multi-component detection in an analyte. Combining microfluidics with Raman spectroscopy would help achieve miniaturized analytical devices that may provide rich information about a given analyte. However, the low cross-section of Raman process demands special geometries to achieve such a convergence. The majority of the previous embodiments were restricted to free-space geometry, limiting portability. However, in recent studies, fiber-based Raman detection system incorporated in microfluidics offers the opportunity to develop portable optofluidic bioanalyte detection devices. Here, we review various approaches used for using Raman spectroscopy in microfluidics for analyte detection, and various analytical approaches that could be used to enhance the detection sensitivity of Raman spectroscopy-based detection. This is followed by a detailed discussion about the fiber-based optofluidic Raman detection systems.
    We describe the exciting advances of using optical trapping in the field of analytical biotechnology. This technique has opened up opportunities to manipulate biological particles at the single cell or even at subcellular levels which has... more
    We describe the exciting advances of using optical trapping in the field of analytical biotechnology. This technique has opened up opportunities to manipulate biological particles at the single cell or even at subcellular levels which has allowed an insight into the physical and chemical mechanisms of many biological processes. The ability of this technique to manipulate microparticles and measure pico-Newton forces has found several applications such as understanding the dynamics of biological macromolecules, cell–cell interactions and the micro-rheology of both cells and fluids. Furthermore we may probe and analyse the biological world when combining trapping with analytical techniques such as Raman spectroscopy and imaging.
    Waveguide confined Raman spectroscopy (WCRS) incorporates a fibre based Raman detection system in a microfluidic platform enabling the spectroscopic detection of analyte. It offers the possibility to develop portable, alignment free... more
    Waveguide confined Raman spectroscopy (WCRS) incorporates a fibre based Raman detection system in a microfluidic platform enabling the spectroscopic detection of analyte. It offers the possibility to develop portable, alignment free devices for bio-analyte sensing with minimal sample preparation. Ultimate sensitivity is limited by the fibre auto-fluorescence background. Here we report enhanced bio-analyte detection sensitivity by combining WCRS with continuous wavelength modulation technique. We used urea as a model analyte and the modulation parameters have been optimized to maximize the sensitivity of the device.
    We demonstrate a microfluidics-based fluorescence detection device where the filters, source, detector, and electronically controlled valves are embedded into a Polydimethylsiloxane (PDMS)-based microfluidic chip. The device reported here... more
    We demonstrate a microfluidics-based fluorescence detection device where the filters, source, detector, and electronically controlled valves are embedded into a Polydimethylsiloxane (PDMS)-based microfluidic chip. The device reported here has been specifically designed for chlorophyll a fluorescence sensing in autonomous systems, such as oceanic applications. In contrast to a monolithic approach, the modular approach made the fabrication of this device simpler and cheaper. For fluorescence detection, an InGaN/GaN LED is used as the excitation source to specifically excite chlorophyll a; a metal-dielectric Fabry–Perot filter was used to extinguish out-of-band excitation. A simple Si photodiode is used as detector and provided with a thermally evaporated CdS emission filter to block the excitation source. This filter combination provides an excellent solution to the difficult problem of combining high-rejection excitation and emission filters in an integrated thin-film format. Furthermore, the metal-dielectric filter provides a much broader angular response than a comparable multilayer Bragg mirror, which is a key advantage in the integrated format. We use a novel paraffin wax-based valve design affords low power single-use actuation, between 0.5 and 1 J per actuation and withstands 0.6 bar differential pressure, which provides better performance than its previously reported counterparts. The remote valve-controlled operation of the fluorescence detection system is demonstrated, illustrating the measurement of a chlorophyll a solution, with a detection limit of 340 μM and subsequent valve-controlled flushing of the measurement reservoir.
    In this paper we discuss optical aberrations within a multiplexed optical trapping system. We analyze two of the most powerful methods for optical trap multiplexing: time-shared beam steering and holographic beam shaping in a tandem... more
    In this paper we discuss optical aberrations within a multiplexed optical trapping system. We analyze two of the most powerful methods for optical trap multiplexing: time-shared beam steering and holographic beam shaping in a tandem system with an acousto-optic deflector and spatial light modulator. We show how to isolate and correct for the aberrations introduced by these individual optical components using the spatial light modulator and demonstrate the enhancement this provides to optical trapping.
    In this paper, we utilize the incoherent superposition of nonzero order light modes. We show that this approach brings an additional degree of freedom to the generation of optical fields and notably the formation of superpositions that... more
    In this paper, we utilize the incoherent superposition of nonzero order light modes. We show that this approach brings an additional degree of freedom to the generation of optical fields and notably the formation of superpositions that are otherwise unattainable through the use of refractive or diffractive optical elements and coherent or incoherent light sources. We employ this technique in two exemplary cases: first to create a field with tunable orbital angular momentum whose spatial intensity distribution remains unchanged and second to form an unusual type of “nondiffracting” light beam.
    We report the results of a comparative study of Fourier domain analysis (FDA) and Texture Analysis (TA) of optical coherence tomography (OCT) images of resected human breast tissues for binary classification between normal-abnormal... more
    We report the results of a comparative study of Fourier domain analysis (FDA) and Texture Analysis (TA) of optical coherence tomography (OCT) images of resected human breast tissues for binary classification between normal-abnormal classes and benign-malignant classes. With the incorporation of Fisher linear discriminant analysis (FLDA) in TA for feature extraction, the TA based algorithm provided improved diagnostic performance as compared to the FDA based algorithm in discriminating OCT images corresponding to breast tissues with three different pathologies. The specificity and sensitivity values obtained for normal-abnormal classification were both 100% whereas they were 90% and 85% respectively for benign-malignant classification.
    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... more
    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.
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    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... more
    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.
    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... more
    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.
    Abstract. The instantaneous assessment of high-priced liquor products with minimal sample volume and no special preparation is an important task for quality monitoring and fraud detection. In this contribution the automated classification... more
    Abstract. The instantaneous assessment of high-priced liquor products with minimal sample volume and no special preparation is an important task for quality monitoring and fraud detection. In this contribution the automated classification of Raman spectra acquired with a special optofluidic chip is performed with the use of a number of Artificial Neural Networks. A standard Radial Basis Function Network is adopted to incorporate relevance learning and showed robust classification performance across classification tasks.
    Advancement in technology has influenced the teaching learning process of education, especially in the field of science and technology. This has created a paradigm shift in the whole concept of teaching and learning mechanism. In... more
    Advancement in technology has influenced the teaching learning process of education, especially in the field of science and technology. This has created a paradigm shift in the whole concept of teaching and learning mechanism. In developing countries like India, the pedagogy of science education is “believe what text book says”. ISP(The International School of Photonics)- SPIE (International Society for Optical Engineering) student chapter came up with ‘Optics kit’ developed using locally available components to supplement the teaching of optics in school level so that the optics can be taught through the new paradigm of technology enabled teaching and learning employing ‘Optics kit’,
    Optics Fair 2007 was organized by the ISP-SPIE Student Chapter on 17-18 October 2007. The program was a big success with more than 1300 school students participating in the two day event. The feedback we received was overwhelming. The... more
    Optics Fair 2007 was organized by the ISP-SPIE Student Chapter on 17-18 October 2007. The program was a big success with more than 1300 school students participating in the two day event. The feedback we received was overwhelming. The enthusiastic and motivated faces of the school students told us directly of the success of the program. The Optics Fair was the largest event conducted by the chapter in its three year history.
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    Abstract. We present a simple method applicable to common-path Fourier domain optical coherence tomography (OCT) in which the tissue surface is used as the reference arm. We propose using aluminium hydroxide powder as a potential tissue... more
    Abstract. We present a simple method applicable to common-path Fourier domain optical coherence tomography (OCT) in which the tissue surface is used as the reference arm. We propose using aluminium hydroxide powder as a potential tissue surface diffuser to allow wider application of this method. This technique allows one to avoid placing a reference arm reflective element, such as glass plate, on tissue, and intrinsically avoids both coherent and complex conjugate mirror artifacts associated with glass plates.
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