The authors have no acknowledgements.

1. Mica and&#160;Slides&#160;Preparation
<ol>
	<li>Place No. 1&#189; (0.17 mm) coverslips into staining rack.</li>
	<li>Sonicate for 30 min in 2% detergent at 60 &#176;C.</li>
	<li>Wash 20 times with deionized water.</li>
	<li>Remove slides using forceps and blow dry using compressed air or nitrogen.</li>
	<li>Cut mica sheet into 10 x 10 mm square pieces using scissors or razor blade.</li>
	<li>Cut each mica piece into 2-3 thinner leaflets using razor blade. 
	NOTE: This step requires use of sharp blade.</li>
</ol>
2. Mica Assembly and Chamber Mounting
<ol>
	<li>Clean microscopic glass slide with ethanol.</li>
	<li>Glue leaflet of mica cut in step 1.6 to glass slide using optical adhesive. Low viscosity adhesive is advised to better spread the drop and glue the mica.</li>
	<li>Cure under UV lamp, 10 min. 
	NOTE: Adhesive is cured by UV light with maximum absorption in the range of 350 to 380nm and the recommended energy required for full cure is 4.5 J/cm2. However, different light sources can be used for this step (see materials provided by adhesive supplier).</li>
	<li>Expose a clean mica surface by removing the first few layers with Scotch tape.</li>
	<li>Place small drop (~20 &#956;m) of optical adhesive onto the mica surface. 
	NOTE: At this step, high viscosity adhesive with low autofluorescence level is advised. Our experience showed that using combination of low (step 2.2) and high viscosity adhesives increases significantly effectiveness of mica splitting (step 2.7).</li>
	<li>Gently place freshly cleaned coverslip onto the drop of adhesive, avoiding air bubbles, let settle for 1 min.</li>
	<li>Cure under UV lamp, 10 min. 
	NOTE: after this step, the sandwich of glass slide, mica and coverslip can be stored for a relatively long period of time (up to few weeks). Proceed to the next step just before the actual SLB preparation, to make sure the mica surface is fresh. 
	NOTE: Adhesive is cured by UV light with maximum absorption in the range of 350 to 380nm and the recommended energy required for full cure is 4.5J/cm2. However, different light sources can be used for this step (see materials provided by adhesive supplier).</li>
	<li>Using an exacto knife, gently dismount the coverslip from side glass slide as shown in the video. In most cases, a thin and flat layer of mica will remain attached to the coverslip. Mica attached to glass slide can be reused (repeat from step 2.4).</li>
	<li>Check the surface quality by naked eye or under a dissecting microscope, to make sure that mica layer is still glued to the coverslip and was not removed completely during splitting in step 2.8. Making a small scratch with a forceps or dissecting needle will help to distinguish between the adhesive which has a detectably different consistency from mica.</li>
	<li>Remove rubber seal from a 1.5 ml vial cap and glue the cap upside down to the surface using optical adhesive or nail polish, and cure with UV lamp, or let air dry 10 min, respectively. 
	NOTE: If the sample is prepared for simultaneous optical (TIRFM or confocal) with AFM imaging, a 1.5 ml vial cap might be too small to mount the AFM head on the microscope stage. In that case, the cap might be substituted by any plastic O-ring with a bigger diameter, suitable for AFM head mounting. In case when the experiment requires removing the cap without damaging the mica surface, silicone grease can be used instead of glue or nail polish.</li>
</ol>
3. Supported Lipid Bilayer (SLB) Formation
<ol>
	<li>Place freshly prepared liposome solution into chamber with surface. The minimum volume required for SLB formation is ~30 &#956;l. 
	NOTE: For more details on the liposome and SLB formation, refer to published protocols, such as such as Bag et&#160;al., 201415.</li>
	<li>Proceed with SLB formation using desired protocol. During incubation and imaging, the chamber can be placed in a heat-block or heated microscope stage to maintain temperature required to keep the lipids being used above their melting temperature.</li>
</ol>

<ol>
	<li>Giocondi, M. -. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+topography+of+membrane+domains.">Surface topography of membrane domains.</a> Biochimica et Biophysica Acta (BBA) - Biomembranes. 1798, 703-718 (2010).</li><li>Garcia-Saez, A. J., Schwille, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+analysis+of+membrane+dynamics.">Surface analysis of membrane dynamics.</a> Biochim Biophys Acta. 1798, 766-776 (2010).</li><li>Plochberger, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cholesterol+slows+down+the+lateral+mobility+of+an+oxidized+phospholipid+in+a+supported+lipid+bilayer.">Cholesterol slows down the lateral mobility of an oxidized phospholipid in a supported lipid bilayer.</a> Langmuir. 26, 17322-17329 (2010).</li><li>El Kirat, K., Morandat, S., Dufr&#234;ne, Y. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoscale+analysis+of+supported+lipid+bilayers+using+atomic+force+microscopy.">Nanoscale analysis of supported lipid bilayers using atomic force microscopy.</a> Biochimica et Biophysica Acta (BBA) - Biomembranes. 1798, 750-765 (2010).</li><li>Szmodis, A. W., Blanchette, C. D., Longo, M. L., Orme, C. A., Parikh, A. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermally+induced+phase+separation+in+supported+bilayers+of+glycosphingolipid+and+phospholipid+mixtures.">Thermally induced phase separation in supported bilayers of glycosphingolipid and phospholipid mixtures.</a> Biointerphases. 5, 120-130 (2010).</li><li>Strulson, M. K., Maurer, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microcontact+printing+for+creation+of+patterned+lipid+bilayers+on+tetraethylene+glycol+self-assembled+monolayers.">Microcontact printing for creation of patterned lipid bilayers on tetraethylene glycol self-assembled monolayers.</a> Langmuir. 27, 12052-12057 (2011).</li><li>Satriano, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasma+oxidized+polyhydroxymethylsiloxane--a+new+smooth+surface+for+supported+lipid+bilayer+formation.">Plasma oxidized polyhydroxymethylsiloxane--a new smooth surface for supported lipid bilayer formation.</a> Langmuir. 26, 5715-5725 (2010).</li><li>Bag, N., Sankaran, J., Paul, A., Kraut, R. S., Wohland, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calibration+and+limits+of+camera-based+fluorescence+correlation+spectroscopy:+a+supported+lipid+bilayer+study.">Calibration and limits of camera-based fluorescence correlation spectroscopy: a supported lipid bilayer study.</a> Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry. 13, 2784-2794 (2012).</li><li>Singh, S., Keller, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atomic+force+microscopy+of+supported+planar+membrane+bilayers.">Atomic force microscopy of supported planar membrane bilayers.</a> Biophysical Journal. 60, 1401-1410 (1991).</li><li>Przybylo, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lipid+Diffusion+in+Giant+Unilamellar+Vesicles+Is+More+than+2+Times+Faster+than+in+Supported+Phospholipid+Bilayers+under+Identical+Conditions.">Lipid Diffusion in Giant Unilamellar Vesicles Is More than 2 Times Faster than in Supported Phospholipid Bilayers under Identical Conditions.</a> Langmuir. 22, 9096-9099 (2006).</li><li>Scomparin, C., Lecuyer, S., Ferreira, M., Charitat, T., Tinland, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diffusion+in+supported+lipid+bilayers:+influence+of+substrate+and+preparation+technique+on+the+internal+dynamics.">Diffusion in supported lipid bilayers: influence of substrate and preparation technique on the internal dynamics.</a> Eur Phys J E Soft Matter. 28, 211-220 (2009).</li><li>Oreopoulos, J., Yip, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combined+scanning+probe+and+total+internal+reflection+fluorescence+microscopy.">Combined scanning probe and total internal reflection fluorescence microscopy.</a> Methods. 46, 2-10 (2008).</li><li>Shaw, J. E., Slade, A., Yip, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+in+situ+total+internal+reflectance+fluorescence/atomic+force+microscopy+studies+of+DPPC/dPOPC+microdomains+in+supported+planar+lipid+bilayers.">Simultaneous in situ total internal reflectance fluorescence/atomic force microscopy studies of DPPC/dPOPC microdomains in supported planar lipid bilayers.</a> J Am Chem Soc. 125, 11838-11839 (2003).</li><li>Skaug, M. J., Faller, R., Longo, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlating+anomalous+diffusion+with+lipid+bilayer+membrane+structure+using+single+molecule+tracking+and+atomic+force+microscopy.">Correlating anomalous diffusion with lipid bilayer membrane structure using single molecule tracking and atomic force microscopy.</a> J Chem Phys. 134, (2011).</li><li>Bag, N., Yap, D. H., Wohland, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temperature+dependence+of+diffusion+in+model+and+live+cell+membranes+characterized+by+imaging+fluorescence+correlation+spectroscopy.">Temperature dependence of diffusion in model and live cell membranes characterized by imaging fluorescence correlation spectroscopy.</a> Biochimica et Biophysica Acta. , (2013).</li><li>Sbalzarini, I. F., Koumoutsakos, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Feature+point+tracking+and+trajectory+analysis+for+video+imaging+in+cell+biology.">Feature point tracking and trajectory analysis for video imaging in cell biology.</a> J Struct Biol. 151, 182-195 (2005).</li><li>Linkert, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metadata+matters:+access+to+image+data+in+the+real+world.">Metadata matters: access to image data in the real world.</a> J Cell Biol. 189, 777-782 (2010).</li><li>Schutz, G. J., Schindler, H., Schmidt, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-molecule+microscopy+on+model+membranes+reveals+anomalous+diffusion.">Single-molecule microscopy on model membranes reveals anomalous diffusion.</a> Biophys J. 73, 1073-1080 (1997).</li><li>Matysik, A., Kraut, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TrackArt:+the+user+friendly+interface+for+single+molecule+tracking+data+analysis+and+simulation+applied+to+complex+diffusion+in+mica+supported+lipid+bilayers.">TrackArt: the user friendly interface for single molecule tracking data analysis and simulation applied to complex diffusion in mica supported lipid bilayers.</a> BMC Research Notes. 7, (2014).</li></ol>

The authors have nothing to disclose.

This protocol describes a method for preparing smooth and thin mica surfaces for lipid bilayer deposition and high resolution imaging. The technique requires minimal manual skills, limited mostly to the careful disassembly of the glass-mica-glass sandwich (step 2.8), which is critical for obtaining a high quality mica surface. Inspection of the freshly cleaved mica is always required at this point, since it is possible for the mica to detach from the optical adhesive without cleaving, leaving exposed areas of optical adh...

The overall goal of the present protocol is to show a method for preparing mica surfaces for high resolution imaging of mica supported lipid bilayers (SLBs) using optical total internal reflection fluorescence microscopy (TIRFM) or confocal microscopy, which could also be combined with atomic force microscopy (AFM).
SLBs are a widely used model for numerous studies of lipid clustering, phase separation, dynamics of bilayer components or their interactions with peptides, proteins or other compounds1-5. Different substrates might be used for SLB formation (i.e. glass, mica, silicon dioxide, polymers) depending on the nature of the study4,6-8. Typical membrane studies rely on microscopy-based imaging techniques, such as TIRFM and AFM. Thus, for TIRFM imaging, a glass surface is a typical choice because glass is transparent. Preparation of glass is relatively easy, and the quality of the results is primarily determined by thorough surface cleaning prior to deposition of lipid vesicles. AFM due to its high axial resolution requires mica surfaces. Mica is a silicate mineral, with close to perfect basal cleavage. Thus, the freshly cleaved mica is atomically flat, allowing observation of membrane height differences even at the sub-nanometer scale9.
Diffusion studies using methods such as fluorescence correlation spectroscopy (FCS), single molecule tracking (SMT), and fluorescence recovery after photobleaching (FRAP) showed however, that lipid membrane dynamics depend heavily on the type of surface onto which they are deposited, whereby glass and mica can give widely varying results10,11. These differences include not only the diffusion coefficients of the membrane probes, but also the detection of separate populations of particles diffusing with different rates, and possibly switching between different states.
Thus, the direct comparison of results obtained using TIRFM and AFM techniques is often problematic, unless the same surface (in this case mica) is used. Although there are some studies where TIRFM and AFM bilayer imaging was conducted on the same mica surface12,13, mica is rarely used for optical microscopy, mostly because of handling problems. Mica preparation requires cutting by hand into thin leaflets, which are then glued to the coverslip using optical adhesive12. This method however requires some practice to achieve satisfactory results. Moreover, the surfaces obtained are often wavy and thick, making them difficult to use with low working distance, high numerical aperture lenses.
Mica surfaces prepared as described in this protocol are very thin (~220 &#956;m, including the coverslip thickness of 170 &#956;m) and extremely flat, avoiding &#8220;waviness&#8221;, which is critical for successful high resolution imaging. They can be used for TIRFM or confocal setups. Moreover, the same samples can be transferred to AFM, and even imaged simultaneously with TIRFM/confocal and AFM. Combining these two techniques allows direct correlation of diffusion behavior with bilayer membrane structure14. Because mica surfaces are freshly cleaved, they are clean and do not require time consuming, poorly reproducible, and potentially dangerous cleaning procedures (glass cleaning protocols usually include chemicals such as Piranha solution, sulfuric acid, sodium/potassium hydroxide). Mounting of a small chamber, also described in the protocol, reduces the volume of vesicles required for effective bilayer formation to less than 50 &#956;l. Finally, the whole process of surface assembly is not time consuming (preparation takes less than 30 min), and does not require a high degree of manual skill, as does conventional mica cleavage and gluing.

<table border="0" cellpadding="0" cellspacing="0" width="710">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Name of Material/ Equipment</td>
			<td style="width:135px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:167px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Bath Sonicator</td>
			<td style="width:135px;">Fisher Scientific</td>
			<td style="width:119px;">FB15051</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Coverslips 24 x 50mm - No H1.5</td>
			<td style="width:135px;">Marienfeld</td>
			<td style="width:119px;">102222</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">DOPC</td>
			<td style="width:135px;">Avanti Polar Lipids</td>
			<td style="width:119px;">850357</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Hellmanex III (detergent)</td>
			<td style="width:135px;">Hellma Analytics</td>
			<td style="width:119px;">320.003</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Mica V-1 Grade</td>
			<td style="width:135px;">SPI Suppliers</td>
			<td style="width:119px;">1872-CA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Optical Adhesive (high viscosity)</td>
			<td style="width:135px;">Norland Products</td>
			<td style="width:119px;">NOA63</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Optical Adhesive (low viscosity)</td>
			<td style="width:135px;">Norland Products</td>
			<td style="width:119px;">NOA60</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sphingomyelin-ATTO647N</td>
			<td style="width:135px;">AttoTec</td>
			<td>AD 647N-171</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">UV lamp</td>
			<td style="width:135px;">Synoptics Ltd.</td>
			<td style="width:119px;">GelVue GVM20</td>
			<td>The lamp was set to 100% power</td>
		</tr>
	</tbody>
</table>

preparation of mica supported lipid bilayers for high resolution optical microscopy imaging

Supported lipid bilayers (SLBs) are widely used as a model for studying membrane properties (phase separation, clustering, dynamics) and its interaction with other compounds, such as drugs or peptides. However SLB characteristics differ depending on the support used. 
Commonly used techniques for SLB imaging and measurements are single molecule fluorescence microscopy, FCS and atomic force microscopy (AFM). Because most optical imaging studies are carried out on a glass support, while AFM requires an extremely flat surface (generally mica), results from these techniques cannot be compared directly, since the charge and smoothness properties of these materials strongly influence diffusion. Unfortunately, the high level of manual dexterity required for the cutting and gluing thin slices of mica to the glass slide presents a hurdle to routine use of mica for SLB preparation. Although this would be the method of choice, such prepared mica surfaces often end up being uneven (wavy) and difficult to image, especially with small working distance, high numerical aperture lenses. Here we present a simple and reproducible method for preparing thin, flat mica surfaces for lipid vesicle deposition and SLB preparation. Additionally, our custom made chamber requires only very small volumes of vesicles for SLB formation. The overall procedure results in the efficient, simple and inexpensive production of high quality lipid bilayer surfaces that are directly comparable to those used in AFM studies.

The diffusion behavior of fluorescent lipid probes in SLBs is different depending on the substrate. TIRFM combined with the SMT technique is a valuable method for visualizing particle movements and extracting their diffusion coefficients. Single molecule signals of a Sphingomyelin-ATTO647N probe diffusing in a DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) bilayer supported on glass and mica are shown on the attached animated figure. The mica surface was prepared according to the protocol presented here. To est...

Watch this Scientific Journal Video about Preparation of Mica Supported Lipid Bilayers for High Resolution Optical Microscopy Imaging at JoVE.com

Preparation of Mica Supported Lipid Bilayers for High Resolution Optical Microscopy Imaging

We present a method of preparing mica supported lipid bilayers for high resolution microscopy. Mica is transparent and flat on an atomic scale, but rarely used in imaging because of handling difficulties; our preparation results in even deposition of the mica sheet, and reduces the material used in bilayer preparation.

Supported lipid bilayers (SLBs) are widely used as a model for studying membrane properties (phase separation, clustering, dynamics) and its interaction ...

preparation-mica-supported-lipid-bilayers-for-high-resolution-optical

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Bioengineering

13.3K Views.  Nanyang Technological University. We present a method of preparing mica supported lipid bilayers for high resolution microscopy. Mica is transparent and flat on an atomic scale, but rarely used in imaging because of handling difficulties; our preparation results in even deposition of the mica sheet, and reduces the material used in bilayer preparation.

Video: Preparation of Mica Supported Lipid Bilayers for High Resolution Optical Microscopy Imaging

High-resolution Fiber-optic Microendoscopy for in situ Cellular Imaging

Many biological and clinical studies require the longitudinal study and analysis of morphology and function with cellular level resolution. Traditionally, multiple experiments are run in parallel, with individual samples removed from the study at sequential time points for evaluation by light microscopy. Several intravital techniques have been developed, with confocal, multiphoton, and second harmonic microscopy all demonstrating their ability to be used for imaging in situ 1. With these systems, however, the required infrastructure is complex and expensive, involving scanning laser systems and complex light sources. Here we present a protocol for the design and assembly of a high-resolution microendoscope which can be built in a day using off-the-shelf components for under US$5,000. The platform offers flexibility in terms of image resolution, field-of-view, and operating wavelength, and we describe how these parameters can be easily modified to meet the specific needs of the end user.
We and others have explored the use of the high-resolution microendoscope (HRME) in in vitro cell culture 2-5, in excised 6 and living animal tissues 2,5, and in human tissues in vivo 2,7. Users have reported the use of several different fluorescent contrast agents, including proflavine 2-4, benzoporphyrin-derivative monoacid ring A (BPD-MA) 5, and fluoroscein 6,7, all of which have received full, or investigational approval from the FDA for use in human subjects. High-resolution microendoscopy, in the form described here, may appeal to a wide range of researchers working in the basic and clinical sciences. The technique offers an effective and economical approach which complements traditional benchtop microscopy, by enabling the user to perform high-resolution, longitudinal imaging in situ.

High-resolution Fiber-optic Microendoscopy for in situ Cellular Imaging

In many biological and clinical situations it is advantageous to study cellular processes as they evolve in their native microenvironment. Here we describe the assembly and use of a low-cost fiber-optic microscope which can provide real time imaging in cell culture, animal studies, and clinical patient studies.

Many biological and clinical studies require the longitudinal study and analysis of morphology and function with cellular level resolution.  ...

Three-dimensional Optical-resolution Photoacoustic Microscopy

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As the mainstays of in vivo three-dimensional (3-D) optical microscopy, single-/multi-photon fluorescence microscopy and optical coherence tomography (OCT) have demonstrated their extraordinary sensitivities to fluorescence and optical scattering contrasts, respectively. However, the optical absorption contrast of biological tissues, which encodes essential physiological/pathological information, has not yet been assessable. 
The emergence of biomedical photoacoustics has led to a new branch of optical microscopy optical-resolution photoacoustic microscopy (OR-PAM)1, where the optical irradiation is focused to the diffraction limit to achieve cellular1 or even subcellular2 level lateral resolution. As a valuable complement to existing optical microscopy technologies, OR-PAM brings in at least two novelties. First and most importantly, OR-PAM detects optical absorption contrasts with extraordinary sensitivity (i.e., 100%). Combining OR-PAM with fluorescence microscopy3 or with optical-scattering-based OCT4 (or with both) provides comprehensive optical properties of biological tissues. Second, OR-PAM encodes optical absorption into acoustic waves, in contrast to the pure optical processes in fluorescence microscopy and OCT, and provides background-free detection. The acoustic detection in OR-PAM mitigates the impacts of optical scattering on signal degradation and naturally eliminates possible interferences (i.e., crosstalks) between excitation and detection, which is a common problem in fluorescence microscopy due to the overlap between the excitation and fluorescence spectra. 
Unique for optical absorption imaging, OR-PAM has demonstrated broad biomedical applications since its invention, including, but not limited to, neurology5, 6, ophthalmology7, 8, vascular biology9, and dermatology10. In this video, we teach the system configuration and alignment of OR-PAM as well as the experimental procedures for in vivo functional microvascular imaging.

Optical-resolution photoacoustic microscopy (OR-PAM) is an emerging technology capable of imaging optical absorption contrasts in vivo with cellular resolution and sensitivity. Here, we provide a visualized instruction on the experimental protocols of OR-PAM, including system configuration, system alignment, typical in vivo experimental procedures, and functional imaging schemes.

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As ...

Wideband Optical Detector of Ultrasound for Medical Imaging Applications

Optical sensors of ultrasound are a promising alternative to piezoelectric techniques, as has been recently demonstrated in the field of optoacoustic imaging. In medical applications, one of the major limitations of optical sensing technology is its susceptibility to environmental conditions, e.g. changes in pressure and temperature, which may saturate the detection. Additionally, the clinical environment often imposes stringent limits on the size and robustness of the sensor. In this work, the combination of pulse interferometry and fiber-based optical sensing is demonstrated for ultrasound detection. Pulse interferometry enables robust performance of the readout system in the presence of rapid variations in the environmental conditions, whereas the use of all-fiber technology leads to a mechanically flexible sensing element compatible with highly demanding medical applications such as intravascular imaging. In order to achieve a short sensor length, a pi-phase-shifted fiber Bragg grating is used, which acts as a resonator trapping light over an effective length of 350 &#181;m. To enable high bandwidth, the sensor is used for sideway detection of ultrasound, which is highly beneficial in circumferential imaging geometries such as intravascular imaging. An optoacoustic imaging setup is used to determine the response of the sensor for acoustic point sources at different positions.

Optical detection of ultrasound is impractical in many imaging scenarios because it often requires stable environmental conditions. We demonstrate an optical technique for ultrasound sensing in volatile environments with miniaturization and sensitivity levels appropriate for optoacoustic imaging in restrictive scenarios, e.g. intravascular applications.

Optical sensors of ultrasound are a promising alternative to piezoelectric techniques, as has been recently demonstrated in the field of optoacoustic ...

High-resolution Spatiotemporal Analysis of Receptor Dynamics by Single-molecule Fluorescence Microscopy

Single-molecule microscopy is emerging as a powerful approach to analyze the behavior of signaling molecules, in particular concerning those aspect (e.g., kinetics, coexistence of different states and populations, transient interactions), which are typically hidden in ensemble measurements, such as those obtained with standard biochemical or microscopy methods. Thus, dynamic events, such as receptor-receptor interactions, can be followed in real time in a living cell with high spatiotemporal resolution. This protocol describes a method based on labeling with small and bright organic fluorophores and total internal reflection fluorescence (TIRF) microscopy to directly visualize single receptors on the surface of living cells. This approach allows one to precisely localize receptors, measure the size of receptor complexes, and capture dynamic events such as transient receptor-receptor interactions. The protocol provides a detailed description of how to perform a single-molecule experiment, including sample preparation, image acquisition and image analysis. As an example, the application of this method to analyze two G-protein-coupled receptors, i.e., &#946;2-adrenergic and &#947;-aminobutyric acid type B (GABAB) receptor, is reported. The protocol can be adapted to other membrane proteins and different cell models, transfection methods and labeling strategies.

This protocol describes how to use total internal reflection fluorescence microscopy to visualize and track single receptors on the surface of living cells and thereby analyze receptor lateral mobility, size of receptor complexes as well as to visualize transient receptor-receptor interactions. This protocol can be extended to other membrane proteins.

Single-molecule microscopy is emerging as a powerful approach to analyze the behavior of signaling molecules, in particular concerning those aspect (e.g., ...

Fluorescence-quenching of a Liposomal-encapsulated Near-infrared Fluorophore as a Tool for In Vivo Optical Imaging

Optical imaging offers a wide range of diagnostic modalities and has attracted a lot of interest as a tool for biomedical imaging. Despite the enormous number of imaging techniques currently available and the progress in instrumentation, there is still a need for highly sensitive probes that are suitable for in vivo imaging. One typical problem of available preclinical fluorescent probes is their rapid clearance in vivo, which reduces their imaging sensitivity. To circumvent rapid clearance, increase number of dye molecules at the target site, and thereby reduce background autofluorescence, encapsulation of the near-infrared fluorescent dye, DY-676-COOH in liposomes and verification of its potential for in vivo imaging of inflammation was done. DY-676 is known for its ability to self-quench at high concentrations. We first determined the concentration suitable for self-quenching, and then encapsulated this quenching concentration into the aqueous interior of PEGylated liposomes. To substantiate the quenching and activation potential of the liposomes we use a harsh freezing method which leads to damage of liposomal membranes without affecting the encapsulated dye. The liposomes characterized by a high level of fluorescence quenching were termed Lip-Q. We show by experiments with different cell lines that uptake of Lip-Q is predominantly by phagocytosis which in turn enabled the characterization of its potential as a tool for in vivo imaging of inflammation in mice models. Furthermore, we use a zymosan-induced edema model in mice to substantiate the potential of Lip-Q in optical imaging of inflammation in vivo. Considering possible uptake due to inflammation-induced enhanced permeability and retention (EPR) effect, an always-on liposome formulation with low, non-quenched concentration of DY-676-COOH (termed Lip-dQ) and the free DY-676-COOH were compared with Lip-Q in animal trials.

Fluorescence-quenching of a Liposomal-encapsulated Near-infrared Fluorophore as a Tool for In Vivo Optical Imaging

The use of fluorophores for in vivo imaging can be greatly limited by opsonization, rapid clearance, low detection sensitivity and cytotoxic effects on the host. Encapsulation of fluorophores in liposomes by film hydration and extrusion leads to fluorescence quenching and protection which enables in vivo imaging with high detection sensitivity.

Optical imaging offers a wide range of diagnostic modalities and has attracted a lot of interest as a tool for biomedical imaging. Despite the enormous ...

Atomic Force Microscopy Imaging and Force Spectroscopy of Supported Lipid Bilayers

Atomic force microscopy (AFM) is a versatile, high-resolution imaging technique that allows visualization of biological membranes. It has sufficient magnification to examine membrane substructures and even individual molecules. AFM can act as a force probe to measure interactions and mechanical properties of membranes. Supported lipid bilayers are conventionally used as membrane models in AFM studies. In this protocol, we demonstrate how to prepare supported bilayers and characterize their structure and mechanical properties using AFM. These include bilayer thickness and breakthrough force. 
The information provided by AFM imaging and force spectroscopy help define mechanical and chemical properties of membranes. These properties play an important role in cellular processes such as maintaining cell hemostasis from environmental stress, bringing membrane proteins together, and stabilizing protein complexes.

We describe a protocol for preparation of supported lipid bilayers and its characterization using atomic force microscopy and force spectroscopy.

Atomic force microscopy (AFM) is a versatile, high-resolution imaging technique that allows visualization of biological membranes. It has sufficient ...

Single Molecule Fluorescence Microscopy on Planar Supported Bilayers

In the course of a single decade single molecule microscopy has changed from being a secluded domain shared merely by physicists with a strong background in optics and laser physics to a discipline that is now enjoying vivid attention by life-scientists of all venues 1. This is because single molecule imaging has the unique potential to reveal protein behavior in situ in living cells and uncover cellular organization with unprecedented resolution below the diffraction limit of visible light 2. Glass-supported planar lipid bilayers (SLBs) are a powerful tool to bring cells otherwise growing in suspension in close enough proximity to the glass slide so that they can be readily imaged in noise-reduced Total Internal Reflection illumination mode 3,4. They are very useful to study the protein dynamics in plasma membrane-associated events as diverse as cell-cell contact formation, endocytosis, exocytosis and immune recognition. Simple procedures are presented how to generate highly mobile protein-functionalized SLBs in a reproducible manner, how to determine protein mobility within and how to measure protein densities with the use of single molecule detection. It is shown how to construct a cost-efficient single molecule microscopy system with TIRF illumination capabilities and how to operate it in the experiment.

Preparation of protein-functionalized planar glass-supported lipid bilayers, determination of protein mobility within and measurement of protein densities is shown here. A roadmap to building a noise-reduced Total Internal Reflection microscope is outlined, which allows visualizing single bilayer-resident fluorochromes with high spatiotemporal resolution.

In the course of a single decade single molecule microscopy has changed from being a secluded domain shared merely by physicists with a strong background ...

Ligand Nano-cluster Arrays in a Supported Lipid Bilayer

Currently there is considerable interest in creating ordered arrays of adhesive protein islands in a sea of passivated surface for cell biological studies. In the past years, it has become increasingly clear that living cells respond, not only to the biochemical nature of the molecules presented to them but also to the way these molecules are presented. Creating protein micro-patterns is therefore now standard in many biology laboratories; nano-patterns are also more accessible. However, in the context of cell-cell interactions, there is a need to pattern not only proteins but also lipid bilayers. Such dual proteo-lipidic patterning has so far not been easily accessible. We offer a facile technique to create protein nano-dots supported on glass and propose a method to backfill the inter-dot space with a supported lipid bilayer (SLB). From photo-bleaching of tracer fluorescent lipids included in the SLB, we demonstrate that the bilayer exhibits considerable in-plane fluidity. Functionalizing the protein dots with fluorescent groups allows us to image them and to show that they are ordered in a regular hexagonal lattice. The typical dot size is about 800 nm and the spacing demonstrated here is 2 microns. These substrates are expected to serve as useful platforms for cell adhesion, migration and mechano-sensing studies.

We present a protocol to functionalize glass with nanometric protein patches surrounded by a fluid lipid bilayer. These substrates are compatible with advanced optical microscopy and are expected to serve as platform for cell adhesion and migration studies.

Currently there is considerable interest in creating ordered arrays of adhesive protein islands in a sea of passivated surface for cell biological ...

Switchable Acoustic and Optical Resolution Photoacoustic Microscopy for In Vivo Small-animal Blood Vasculature Imaging

Photoacoustic microscopy (PAM) is a fast-growing invivo imaging modality that combines both optics and ultrasound, providing penetration beyond the optical mean free path (~1 mm in skin) with high resolution. By combining optical absorption contrast with the high spatial resolution of ultrasound in a single modality, this technique can penetrate deep tissues. Photoacoustic microscopy systems can have either a low acoustic resolution and probe deeply or a high optical resolution and probe shallowly. It is challenging to achieve high spatial resolution and large depth penetration with a single system. This work presents an AR-OR-PAM system capable of both high-resolution imaging at shallow depths and low-resolution deep-tissue imaging of the same sample in vivo. A lateral resolution of 4 &#181;m with 1.4 mm imaging depth using optical focusing and a lateral resolution of 45 &#181;m with 7.8 mm imaging depth using acoustic focusing were successfully demonstrated using the combined system. Here,&#160;in vivo&#160;small-animal blood vasculature imaging is performed to demonstrate its biological imaging capability.

Switchable Acoustic and Optical Resolution Photoacoustic Microscopy for In Vivo Small-animal Blood Vasculature Imaging

Here a switchable acoustic resolution (AR) and optical resolution (OR) photoacoustic microscopy (AR-OR-PAM) system capable of both high resolution imaging at shallow depth and low resolution deep tissue imaging on the same sample in vivo is demonstrated.

Photoacoustic microscopy (PAM) is a fast-growing invivo imaging modality that combines both optics and ultrasound, providing penetration beyond the ...

High Resolution 3D Imaging of the Human Pancreas Neuro-insular Network

Using traditional histological methods, researchers are hampered in their ability to image whole tissues or organs in large-scale 3D. Histological sections are generally limited to &#60;20 &#181;m as formalin fixed paraffin section on glass slides or &#60;500 &#181;m for free-floating fixed sections. Therefore, extensive efforts are required for serial sectioning and large-scale image reconstruction methods to recreate 3D for samples &#62;500 &#181;m using traditional methods. In addition, light scatters from macromolecules within tissues, particularly lipids, prevents imaging to a depth &#62;150 &#181;m with most confocal microscopes. To reduce light scatter and to allow for deep tissue imaging using simple confocal microscopy, various optical clearing methods have been developed that are relevant for rodent and human tissue samples fixed by immersion. Several methods are related and use protein crosslinking with acrylamide and tissue clearing with sodium dodecyl sulfate (SDS). Other optical clearing techniques used various solvents though each modification had various advantages and disadvantages. Here, an optimized passive optical clearing method is described for studies of the human pancreas innervation and specifically for interrogation of the innervation of human islets.

Here, we present a protocol to image human pancreas sections in three dimensions (3D) using optimized passive clearing methods. This manuscript demonstrates these procedures for passive optical clearing followed by multiple immunofluorescence staining to identify key elements of the autonomic and sensory neural networks innervating human islets.