Name: novel photoacoustic microscopy and optical coherence tomography dual-modality chorioretinal imaging in living rabbit eyes
Uploaded: 2018-02-08T15:00:00
Description: Watch this Scientific Journal Video about Novel Photoacoustic Microscopy and Optical Coherence Tomography Dual-modality Chorioretinal Imaging in Living Rabbit Eyes at JoVE.com

This work was supported by the generous support of the National Eye Institute 4K12EY022299 (YMP), Fight for Sight-International Retinal Research Foundation FFS GIA16002 (YMP), unrestricted departmental support from Research to Prevent Blindness, and the University of Michigan Department of Ophthalmology and Visual Sciences. This work utilized the Core Center for Vision Research funded by P30 EY007003 from the National Eye Institute.

Rabbits are a United States Department of Agriculture (USDA) covered species. Its use in biomedical research needs to follow strict regulations. All rabbit experiments were performed in accordance with the ARVO (The Association for Research in Vision and Ophthalmology) Statement for the Use of Animals in Ophthalmic and Vision Research, after approval of the laboratory animal protocol by the University Committee on Use and Care of Animals (UCUCA) of the University of Michigan (Protocol PRO00006486, PI Yannis Paulus).
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<ol>
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An intact and regular tear film is essential for high-quality fundus images. An irregular and deteriorated tear films can significantly degrade image quality42. To preserve the integrity of the tear film and prevent corneal superficial punctate keratopathy, it is critical to lubricate the cornea using eyewash very frequently, approximately every two min. If there are any concerns regarding the opacity of the eye, use a slit lamp and fluorescein strips to check the cornea conditions.
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Recent decades have witnessed the explosive development of the field of biomedical photoacoustic imaging1,2,3,4,5,6,7,8. Based on the energy conversion of light into sound, the emerging photoacoustic imaging can visualize biological samples at scales from organelles, cells, tissues, organs to small-animal whole body and can reveal its anatomical, functional, molecular, genetic, and metabolic information1,2,9,10,11,12. Photoacoustic imaging has found unique applications in a range of biomedical fields, such as cell biology13,14, vascular biology15,16, neurology17,18, oncology19,20,21,22, dermatology23, pharmacology24, and hematology25,26. Its application in ophthalmology, that is, photoacoustic ocular imaging, has attracted substantial interests from both scientists and clinicians and is currently under active investigation.
In contrast to routinely used ocular imaging technologies27, such as fluorescein angiography (FA) and indocyanine green angiography (ICGA) (based on fluorescence contrast), optical coherence tomography (OCT) (based on optical scattering contrast), and its derivative OCT angiography (based on motion contrast of red blood cells), photoacoustic ocular imaging uses optical absorption as the contrast mechanism. This is different from conventional ocular imaging technologies and provides a unique tool for studying optical absorption properties of the eye, which are usually associated with the pathophysiological status of ocular tissue28. To date, significant excellent work has been done in photoacoustic ocular imaging29,30,31,32,33,34,35,36,37, but these studies focus on the posterior segment of the eyes of small animals, such as rats and mice. The pioneering studies well demonstrate the feasibility of photoacoustic imaging in ophthalmology but there is still a long way to go towards clinical translation of the technology since eyeball sizes of rats and mice are much smaller (less than one-third) than that of humans. Due to the propagation of ultrasound waves over a significantly longer distances, signal intensity and image quality may greatly suffer when the technique is used for imaging the posterior segment of larger eyes.
Towards this goal, we recently reported the noninvasive, label-free chorioretinal imaging in living rabbits using integrated photoacoustic microscopy (PAM) and spectral-domain OCT (SD-OCT)38. The system has excellent performance and could visualize the retina and choroid of the eyes of larger animals based on endogenous absorption and scattering contrast of ocular tissue. Preliminary results in rabbits show that the PAM could noninvasively distinguish individual retinal and choroidal blood vessels using a laser exposure dose (~80 nJ) significantly below the American National Standards Institute (ANSI) safety limit (160 nJ) at 570 nm39; and the OCT could clearly resolve different retinal layers, the choroid, and the sclera. It is the very first demonstration of posterior segment imaging of larger animals using PAM and might be a major step towards clinical translation of the technology considering that the eyeball size of rabbits (18.1 mm)40 is almost 80% of the axial length of humans (23.9 mm).
In this work, we provide a detailed description of the dual-modality imaging system and experimental protocols used for noninvasive, label-free chorioretinal imaging in living rabbits and demonstrate the system performance through representative retinal and choroidal imaging results.

<table border="0" cellpadding="0" cellspacing="0" style="width:824px;" width="822">
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	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Dual-modality imaging system</td>
			<td style="width:279px;"></td>
			<td style="width:157px;"></td>
			<td style="width:159px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">OPO laser</td>
			<td style="width:279px;">Ekspla (Vilnius, Lithuania)</td>
			<td style="width:157px;">NT-242</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Beam attenuator</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">AHWP10M-600</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Motorized rotation stage</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">PRM1/MZ8</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Motorized rotation stage controller</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">TDC001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Focusing lens</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">AC254-250-B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Pinhole</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">P50S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Collimating lens</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">AC127-030-B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Photodiode</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">PDA36A&#160;</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Laser shutter</td>
			<td style="width:279px;">Vincent Associates Inc. (Toronto, Canada)</td>
			<td style="width:157px;">LS6S2T0</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Laser shutter driver</td>
			<td style="width:279px;">Vincent Associates Inc. (Toronto, Canada)</td>
			<td style="width:157px;">VCM-D1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Dichroic mirror</td>
			<td style="width:279px;">Semrock, Inc. (Rochester, NY, USA)</td>
			<td style="width:157px;">Di03-R785-t3-25&#215;36</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Scan lens</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">OCT-LK3-BB</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Ophthalmic lens</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">AC080-010-B-ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Ultrasonic transducer</td>
			<td style="width:279px;">Optosonic Inc. (Arcadia, CA, USA)</td>
			<td style="width:157px;">Custom</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Amplifier</td>
			<td style="width:279px;">L3 Narda-MITEQ (Hauppauge, NY, USA)</td>
			<td style="width:157px;">AU-1647</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Band-pass filter</td>
			<td style="width:279px;">Mini-Circuits (Brooklyn, NY, USA)</td>
			<td style="width:157px;">BLP-30+</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Digitizer</td>
			<td style="width:279px;">DynamicSignals LLC (Lockport, IL, USA)</td>
			<td style="width:157px;">PX1500-4&#160;</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Synchronization electronics</td>
			<td style="width:279px;">National Instruments Corporation (Austin, TX, USA)</td>
			<td style="width:157px;">USB-6353</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">OCT module</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">Ganymede-II-HR</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Dispersion compensation glass</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">LSM03DC</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Illumination LED light</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">MCWHF2&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Power meter</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td style="width:157px;">S121C&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Power meter interface</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td>PM100USB&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Height measurement tool&#160;</td>
			<td style="width:279px;">Thorlabs, Inc. (Newton, NJ, USA)</td>
			<td>BHM1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Fundus camera</td>
			<td style="width:279px;">Topcon Corporation (Tokyo, Japan)&#160;</td>
			<td>TRC 50EX</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Matlab</td>
			<td style="width:279px;">MathWorks (Natick, MA, USA)</td>
			<td style="width:157px;">2017a</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Oscilloscope</td>
			<td style="width:279px;">Teledyne LeCroy (Chestnut Ridge, NY, USA)</td>
			<td style="width:157px;">WaveJet 354T</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:229px;">Animal experiment</td>
			<td style="width:279px;"></td>
			<td style="width:157px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Water-circulating blanket</td>
			<td style="width:279px;">Stryker Corporation (Kalamazoo, MI, USA)</td>
			<td style="width:157px;">TP-700</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Ketamine hydrochloride injection</td>
			<td style="width:279px;">Par pharmaceutical, Inc. (Woodcliff Lake, NJ, USA)</td>
			<td style="width:157px;">NDC code 42023-115-10</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Xylazine hydrochloride</td>
			<td>VetOne (Boise, ID, USA)</td>
			<td style="width:157px;">NDC code 13985-704-10</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Tropicamide ophthalmic</td>
			<td style="width:279px;">Akorn Pharmaceuticals Inc. (Lake Forest, IL, USA)</td>
			<td style="width:157px;">NDC code 17478-102-12</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Phenylephrine hydrochloride ophthalmic</td>
			<td style="width:279px;">Paragon BioTeck, Inc. (Portland, OR, USA)</td>
			<td style="width:157px;">NDC code 42702-102-15</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Eye lubricant</td>
			<td style="width:279px;">Hub Pharmaceuticals LLC (Rancho Cucamonga, CA, USA)</td>
			<td style="width:157px;">NDC code 17238-610-15</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Eyewash</td>
			<td style="width:279px;">Altaire Pharmaceuticals, Inc. (Aquebogue, NY, USA)</td>
			<td style="width:157px;">NDC code 59390-175-18</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Tetracaine hydrochloride ophthalmic solution</td>
			<td style="width:279px;">Bausch &#38; Lomb, Inc. (Rochester, NY, USA)</td>
			<td style="width:157px;">NDC code 24208-920-64</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Flurbiprofen sodium ophthalmic solution</td>
			<td style="width:279px;">Bausch &#38; Lomb, Inc. (Rochester, NY, USA)</td>
			<td style="width:157px;">NDC code 24208-314-25</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:229px;">Neomycin and Polymyxin B Sulfates and Dexamethasone Ophthalmic Ointment</td>
			<td style="width:279px;">Bausch &#38; Lomb, Inc. (Rochester, NY, USA)</td>
			<td style="width:157px;">NDC code 24208-795-35</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:229px;">Meloxicam injection</td>
			<td style="width:279px;">Henry Schein Inc. (Queens, NY, USA)</td>
			<td style="width:157px;">NDC code 11695-6925-1</td>
			<td></td>
		</tr>
	</tbody>
</table>

novel photoacoustic microscopy and optical coherence tomography dual-modality chorioretinal imaging in living rabbit eyes

Photoacoustic ocular imaging is an emerging ophthalmic imaging technology that can noninvasively visualize ocular tissue by converting light energy into sound waves and is currently under intensive investigation. However, most reported work to date is focused on the imaging of the posterior segment of the eyes of small animals, such as rats and mice, which poses challenges for clinical human translation due to small eyeball sizes. This manuscript describes a novel photoacoustic microscopy (PAM) and optical coherence tomography (OCT) dual-modality system for posterior segment imaging of the eyes of larger animals, such as rabbits. The system configuration, system alignment, animal preparation, and dual-modality experimental protocols for in vivo, noninvasive, label-free chorioretinal imaging in rabbits are detailed. The effectiveness of the method is demonstrated through representative experimental results, including retinal and choroidal vasculature obtained by the PAM and OCT. This manuscript provides a practical guide to reproducing the imaging results in rabbits and advancing photoacoustic ocular imaging in larger animals.

The dual-modality imaging system and experimental protocol have been successfully tested in the authors&#39; laboratory using four New Zealand White rabbits. The following showcases some representative results.
Figure 1&#160;shows the schematic of the PAM and SD-OCT dual-modality imaging system. It is composed of the following modules: photoacoustic light source, variable laser attenuator, beam coll...

Watch this Scientific Journal Video about Novel Photoacoustic Microscopy and Optical Coherence Tomography Dual-modality Chorioretinal Imaging in Living Rabbit Eyes at JoVE.com

Novel Photoacoustic Microscopy and Optical Coherence Tomography Dual-modality Chorioretinal Imaging in Living Rabbit Eyes

This manuscript describes the novel setup and operating procedure of a photoacoustic microscopy and optical coherence tomography dual-modality system for noninvasive, label-free chorioretinal imaging of larger animals, such as rabbits.

Photoacoustic ocular imaging is an emerging ophthalmic imaging technology that can noninvasively visualize ocular tissue by converting light energy into ...

The overall goal of this novel imaging setup and operating procedure is to perform photoacoustic microscopy and optical coherence tomography dual-modality for non-invasive, label-free chorioretinal imaging of the eyes of larger mammals, such as rabbits. This method can help answer key questions in ophthalmic imaging about the imaging depth, resolution, and clinical translation required to discern oxygen saturation, blood distribution, and melanin in larger animals. The main advantage of this technique is that it allows noninvasive visualization of ocular tissue for the acquisition of photoacoustic microscopy`and optical coherence tomography dual-modality images.To begin, select an optical parametric oscillator laser pumped by a diode pump solid state laser as the light source for the photoacoustic microscope and use a beam splitter to divide the column aided beam with a split ratio of 19 reflection to 10 transmission. Successively deflect the reflected portion by the M3 mirror and dichroic mirror and use a two-dimensional galvanometer to raster scan the reflection. Deliver the scanned beam through a telescope composed of a scanned lens with a focal length of 36 millimeters and an ophthalmic lens with a focal length of 10 millimeters and focus the beam on the fundus by the rabbit eye optics.Before beginning the imaging procedure, please a water circulating heating blanket on the body support and set the temperature of the circulating water to 38 degree Celsius. Record the pre procedure vitals and confirm the appropriate level of sedation by the rabbit's heart and respiratory rates. Dilate the rabbit pupils with one drop each of tropicamide 1%ophthalmic and phenylephrine hydrochloride 2.5%ophthalmic.Use an ultrasonic amplifier to amplify the signal and filter the signal by a low pass filter. Place a power meter above the rabbit eye and measure the laser pulse energy on the rabbit cornea to keep it below the American National Standards Institute safety limit. To enable the optical coherence tomography or OCT system to image the posterior segment of the rabbit eye, add an ophthalmic lens after the scan lens.Use a zooming housing tube to adjust the length of the reference arm to confirm its match with the optical path length of the sample arm. For spectral domain OCT imaging, place the rabbit on to the imaging platform of a clinical fundus camera and obtain 50 degree fundus red free and autofluoroscence images. Next, transfer the animal to the platform of the OCT system with one eye under the ophthalmic lens.Illuminate the eye using the LED light and open the OCT software. Check the CCD camera image of the fundus and draw a straight line in the software to represent the OCT B scan of interest. Begin scanning adjusting the reference arm length to visualize the OCT image and to optimize the dispersion compensation factor in the OCT software to get the sharpest images.Then set data, the appropriate data acquisition parameters and save the images. For photoacoustic microscope imaging, turn on the optical parametric oscillator laser. Start the photoacoustic microscope control software and tune the lase wavelength to one of the absorption peaks of the targeted chromaforce.Initialize the position of the galvanometer and monitor the laser energy before the rabbit cornea to confirm that it is below the American National Standard Institute Safety Limit. Map the ultrasonic transducer on a three dimensional translation stage, and place the transducer tip in contact with the rabbit conjunctiva so that the tip is pointing to the fundus. Use a drop of eye lubricant to better couple the transducer tip in the rabbit conjunctiva and turn on the LED illumination light.Visualize the rabbit fundus through the MatLab software and set the scanning region of interest including the center and the physical size of the region. Open the laser shutter and start B scan of the beam observing the detected photoacoustic signal on the oscilloscope and finally tuning the transducer position to maximize the signal intensity along the entire B scan as necessary. Then set the data acquisition parameters process the raw data and visualize the photoacoustic microscope image in two dimensions.At the end of the imaging session transfer the rabbit back to the fundus camera to examine the fundus for any post imaging morphological changes and rinse the rabbit cornea with eye wash. Apply flurbiprofen ophthalmic, neomycin and polymyxin b sulfates and dexamethasone ophthalmic ointment to the cornea and close the eye. Then transfer the rabbit and the water circulating blanket into a recovery chamber with monitoring until full recovery.In this representative fundus photograph, the choroidal vessels are spread over most parts of the rabbit funds, while the retinal vessels are confined within the medullary ray. Here a typical photoacoustic microscopy image of the choroidal vasculature within the fundus is shown with the choroidal vessels blood vessels delineated at high lateral resolution. In this OCT B scan image, the retina, choroid, and sclera are visualized with a high axial resolution with the choroidal vessels observed below the retinal pigment epithelium layer.Using the dual-modality imaging system 2D maximum intensity projection and 3D volumetric rendering of retinal vessels can be obtained by photoacoustic imaging. Orthogonal slices of the 3D image demonstrate how photoacoustic microscopy can also be used to visualize individual retinal vessels which lie above the retinal pigment epithelium layer and to confirm the different depths at which the retinal and choroidal vessels are located. Here an OCT B scan image shows individual retinal vessels.And the nerve fiber layer confirming the photoacoustic microscopy imaging results. Once mastered, this technique can be completed in approximately one hour if it is performed properly via to remember to set the laser irradiance at low ANLI setting limits to revive lubricants once eye rinse to avoid dehydration and to monitor the rabbit condition every 15 minutes. Following the procedure, automated slide immunohistochemistry can be performed to answer additional question about confirming choroidal neovascularization development and to amplify the volume of the neovascularization in rabbit.After its development this technique paved the way for researchers in the field of ophthalmology to explore choroidal diseases in rabbit bearing disease models including choroidal neovascularization models. After watching this video, you should have a good understanding of how to detect single chorioretinal blood vessels in rabbit eyes using a novel multimodal molecular imaging system for early stage diagnosis of wet age related macular degeneration. Don't forget this.Working with glass fall laser and animal can be extremely hazardous and that precaution such as wearing goggle and lab coats should always be taken while performing this procedure.

novel-photoacoustic-microscopy-optical-coherence-tomography-dual

Research

JoVE Journal

Engineering

Fabricating Metamaterials Using the Fiber Drawing Method

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves 2. This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks 3, negative refractive index materials 4, and lenses that resolve objects below the diffraction limit 5. However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano- and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size 6-7. Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response 8. We combine the stack-and-draw technique used to produce microstructured polymer optical fiber 9 with the Taylor-wire process 10, using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 &deg;C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro- and nano- scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

Metamaterials at terahertz frequencies offer unique opportunities, but are challenging to fabricate in bulk. We adapt the fabrication procedure for microstructured polymer optical fibers to inexpensively fabricate metamaterials potentially on an industrial scale. We produce polymethylmethacrylate fibers containing ~10 &mu;m diameter indium wires separated by ~100 &mu;m, which exhibit a terahertz plasmonic response.

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe ...

Measurement of Coherence Decay in GaMnAs Using Femtosecond Four-wave Mixing

The application of femtosecond four-wave mixing to the study of fundamental properties of diluted magnetic semiconductors ((s,p)-d hybridization, spin-flip scattering) is described, using experiments on GaMnAs as a prototype III-Mn-V system.&#160; Spectrally-resolved and time-resolved experimental configurations are described, including the use of zero-background autocorrelation techniques for pulse optimization.&#160; The etching process used to prepare GaMnAs samples for four-wave mixing experiments is also highlighted.&#160; The high temporal resolution of this technique, afforded by the use of short (20 fsec) optical pulses, permits the rapid spin-flip scattering process in this system to be studied directly in the time domain, providing new insight into the strong exchange coupling responsible for carrier-mediated ferromagnetism.&#160; We also show that spectral resolution of the four-wave mixing signal allows one to extract clear signatures of (s,p)-d hybridization in this system, unlike linear spectroscopy techniques.&#160;&#160; This increased sensitivity is due to the nonlinearity of the technique, which suppresses defect-related contributions to the optical response. This method may be used to measure the time scale for coherence decay (tied to the fastest scattering processes) in a wide variety of semiconductor systems of interest for next generation electronics and optoelectronics.

The technique of femtosecond four-wave mixing is described, including spectrally-resolved and time-resolved configurations. We illustrate the utility of this technique for the investigation of crucial physical properties in the III-V diluted magnetic semiconductors, afforded by its nonlinearity and high temporal resolution.

The application of femtosecond four-wave mixing to the study of fundamental properties of diluted magnetic semiconductors ((s,p)-d hybridization, ...

Coherent anti-Stokes Raman Scattering (CARS) Microscopy Visualizes Pharmaceutical Tablets During Dissolution

Traditional pharmaceutical dissolution tests determine the amount of drug dissolved over time by measuring drug content in the dissolution medium. This method provides little direct information about what is happening on the surface of the dissolving tablet. As the tablet surface composition and structure can change during dissolution, it is essential to monitor it during dissolution testing. In this work coherent anti-Stokes Raman scattering microscopy is used to image the surface of tablets during dissolution while UV absorption spectroscopy is simultaneously providing inline analysis of dissolved drug concentration for tablets containing a 50% mixture of theophylline anhydrate and ethyl cellulose. The measurements showed that in situ CARS microscopy is capable of imaging selectively theophylline in the presence of ethyl cellulose. Additionally, the theophylline anhydrate converted to theophylline monohydrate during dissolution, with needle-shaped crystals growing on the tablet surface during dissolution. The conversion of theophylline anhydrate to monohydrate, combined with reduced exposure of the drug to the flowing dissolution medium resulted in decreased dissolution rates. Our results show that in situ CARS microscopy combined with inline UV absorption spectroscopy is capable of monitoring pharmaceutical tablet dissolution and correlating surface changes with changes in dissolution rate.

Coherent anti-Stokes Raman Scattering CARS Microscopy Visualizes Pharmaceutical Tablets During Dissolution

Coherent anti-Stokes Raman scattering (CARS) microscopy is combined with an intrinsic flow-through dissolution setup to allow in situ and real-time visualization of the surface of pharmaceutical tablets undergoing dissolution. Using this custom-built setup, it is possible to correlate CARS videos with drug dissolution profiles recorded using inline UV absorption spectroscopy.

Traditional pharmaceutical dissolution tests determine the amount of drug dissolved over time by measuring drug content in the dissolution medium. This ...

Writing Bragg Gratings in Multicore Fibers

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers.

We describe a technique for inscribing identical fiber Bragg gratings into each core of a multicore fiber. This is achieved by introducing an additional surface into the optical path to mitigate lensing by the curved surface of the fiber cladding.

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong ...

Dynamic Pore-scale Reservoir-condition Imaging of Reaction in Carbonates Using Synchrotron Fast Tomography

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve geologic seals and allow CO2 to escape. However, the dissolution processes at reservoir conditions are poorly understood. Thus, time-resolved experiments are needed to observe and predict the nature and rate of dissolution at the pore scale. Synchrotron fast tomography is a method of taking high-resolution time-resolved images of complex pore structures much more quickly than traditional &#181;-CT. The Diamond Lightsource Pink Beam was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 hours. The images were segmented and the porosity and permeability were measured using image analysis and network extraction. Porosity increased uniformly along the length of the sample; however, the rate of increase of both porosity and permeability slowed at later times.

Synchrotron fast tomography was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 h.

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve ...

In Depth Analyses of LEDs by a Combination of X-ray Computed Tomography (CT) and Light Microscopy (LM) Correlated with Scanning Electron Microscopy (SEM)

In failure analysis, device characterization and reverse engineering of light emitting diodes (LEDs), and similar electronic components of micro-characterization, plays an important role. Commonly, different techniques like X-ray computed tomography (CT), light microscopy (LM) and scanning electron microscopy (SEM) are used separately. Similarly, the results have to be treated for each technique independently. Here a comprehensive study is shown which demonstrates the potentials leveraged by linking CT, LM and SEM. In depth characterization is performed on a white emitting LED, which can be operated throughout all characterization steps. Major advantages are: planned preparation of defined cross sections, correlation of optical properties to structural and compositional information, as well as reliable identification of different functional regions. This results from the breadth of information available from identical regions of interest (ROIs): polarization contrast, bright and dark-field LM images, as well as optical images of the LED cross section in operation. This is supplemented by SEM imaging techniques and micro-analysis using energy dispersive X-ray spectroscopy.

In Depth Analyses of LEDs by a Combination of X-ray Computed Tomography CT and Light Microscopy LM Correlated with Scanning Electron Microscopy SEM

A workflow for comprehensive micro-characterization of active optical devices is outlined. It contains structural as well as functional investigations by means of CT, LM and SEM. The method is demonstrated for a white LED which can be still be operated during characterization.

In failure analysis, device characterization and reverse engineering of light emitting diodes (LEDs), and similar electronic components of ...

Microfluidic Imaging Flow Cytometry by Asymmetric-detection Time-stretch Optical Microscopy (ATOM)

Scaling the number of measurable parameters, which allows for multidimensional data analysis and thus higher-confidence statistical results, has been the main trend in the advanced development of flow cytometry. Notably, adding high-resolution imaging capabilities allows for the complex morphological analysis of cellular/sub-cellular structures. This is not possible with standard flow cytometers. However, it is valuable for advancing our knowledge of cellular functions and can benefit life science research, clinical diagnostics, and environmental monitoring. Incorporating imaging capabilities into flow cytometry compromises the assay throughput, primarily due to the limitations on speed and sensitivity in the camera technologies. To overcome this speed or throughput challenge facing imaging flow cytometry while preserving the image quality, asymmetric-detection time-stretch optical microscopy (ATOM) has been demonstrated to enable high-contrast, single-cell imaging with sub-cellular resolution, at an imaging throughput as high as 100,000 cells/s. Based on the imaging concept of conventional time-stretch imaging, which relies on all-optical image encoding and retrieval through the use of ultrafast broadband laser pulses, ATOM further advances imaging performance by enhancing the image contrast of unlabeled/unstained cells. This is achieved by accessing the phase-gradient information of the cells, which is spectrally encoded into single-shot broadband pulses. Hence, ATOM is particularly advantageous in high-throughput measurements of single-cell morphology and texture &#8211; information indicative of cell types, states, and even functions. Ultimately, this could become a powerful imaging flow cytometry platform for the biophysical phenotyping of cells, complementing the current state-of-the-art biochemical-marker-based cellular assay. This work describes a protocol to establish the key modules of an ATOM system (from optical frontend to data processing and visualization backend), as well as the workflow of imaging flow cytometry based on ATOM, using human cells and micro-algae as the examples.

Microfluidic Imaging Flow Cytometry by Asymmetric-detection Time-stretch Optical Microscopy ATOM

This protocol describes the implementation of an asymmetric-detection time-stretch optical microscopy system for single-cell imaging in ultrafast microfluidic flow and its applications in imaging flow cytometry.

Scaling the number of measurable parameters, which allows for multidimensional data analysis and thus higher-confidence statistical results, has been the ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, ...

Label-Free Imaging of Single Proteins Secreted from Living Cells via iSCAT Microscopy

We demonstrate interferometric scattering (iSCAT) microscopy, a method capable of detecting single unlabeled proteins secreted from individual living cells in real time. In this protocol, we cover the fundamental steps to realize an iSCAT microscope and complement it with additional imaging channels to monitor the viability of a cell under study. Following this, we use the method for real-time detection of single proteins as they are secreted from a living cell which we demonstrate with an immortalized B-cell line (Laz388). Necessary steps concerning the preparation of microscope and sample as well as the analysis of the recorded data are discussed. The video protocol demonstrates that iSCAT microscopy offers a straightforward method to study secretion at the single-molecule level.

We present a protocol for the real-time optical detection of single unlabeled proteins as they are secreted from living cells. This is based on interferometric scattering (iSCAT) microscopy, which can be applied to a variety of different biological systems and configurations.

We demonstrate interferometric scattering (iSCAT) microscopy, a method capable of detecting single unlabeled proteins secreted from individual living ...

Surgery and Sample Processing for Correlative Imaging of the Murine Pulmonary Valve

The underlying causes of heart valve related-disease (HVD) are elusive. Murine animal models provide an excellent tool for studying HVD, however, the surgical and instrumental expertise required to accurately quantify the structure and organization across multiple length scales have stunted its advancement. This work provides a detailed description of the murine dissection, en bloc staining, sample processing, and correlative imaging procedures for depicting the heart valve at different length scales. Hydrostatic transvalvular pressure was used to control the temporal heterogeneity by chemically fixing the heart valve conformation. Micro-computed tomography (&#181;CT) was used to confirm the geometry of the heart valve and provide a reference for the downstream sample processing needed for the serial block face scanning electron microscopy (SBF-SEM). High-resolution serial SEM images of the extracellular matrix (ECM) were taken and reconstructed to provide a local 3D representation of its organization. &#181;CT and SBF-SEM imaging methods were then correlated to overcome the spatial variation across the pulmonary valve. Though the work presented is exclusively on the pulmonary valve, this methodology could be adopted for describing the hierarchical organization in biological systems and is pivotal for the structural characterization across multiple length scales.

Here, we describe a correlative workflow for the excision, pressurization, fixation, and imaging of the murine pulmonary valve to determine the gross conformation and local extracellular matrix structures.

The underlying causes of heart valve related-disease (HVD) are elusive. Murine animal models provide an excellent tool for studying HVD, however, the ...