Name: fluorescence-quenching of a liposomal-encapsulated near-infrared fluorophore as a tool for in vivo optical imaging
Uploaded: 2015-01-05T15:00:00.000+00:00
Duration: 10 min 55 s
Description: Watch this Scientific Journal Video about Fluorescence-quenching of a Liposomal-encapsulated Near-infrared Fluorophore as a Tool for In Vivo Optical Imaging at JoVE.com

This work was supported by the Deutsche Forschungsgemeinschaft grants HI-698/10-1 and RU-1652/1-1. We thank Doreen May for excellent technical assistance and the company DYOMICS GmbH, Jena for their kind support.

NOTE: All procedures are approved by the regional animal committee and in accordance with international guidelines on the ethical use of animals.
1. Preparation of Materials and Instruments
<ol>
	<li>Preparation of spontaneously formed vesicle dispersion (SFV)
	<ol>
		<li>Dissolve and prepare stock solutions of the following phospholipids: 214 mg/ml egg phosphatidylcholine (EPC), 134 mg/ml cholesterol, 122 mg/ml 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (ammonium salt) (mPEG2000-DSPE) and 2 mg/ml 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) (ammonium salt) (NBD-DOPE) in chloroform and store in glass vials.</li>
		<li>Furnish approximately 3 ml chloroform in a round bottom flask and transfer the appropriate volume of phospholipid stock solution into the round bottom flask to prepare liposomes composed of EPC:Chol:mPEG2000-DSPE at a molar ratio of 6.5:3:0.5. For double fluorescence labeling of liposomes add 0.3 mol% NBD-DOPE to the lipid solution.</li>
		<li>Evaporate the chloroform from the organic phospholipid solution under reduced pressure (300 mbar) at 55 &#176;C using a rotary evaporator.</li>
		<li>After a homogeneous phospholipid film is formed, reduce the pressure to 10 mbar for 1-2 hr to remove residual chloroform deposit.</li>
		<li>While the chloroform is evaporating, dissolve DY-676-COOH (6.181 &#181;M) in 10 mM Tris buffer pH 7.4 and fill a Dewar vessel with liquid nitrogen. Switch on an ultrasonic bath and set at 50 &#176;C.</li>
		<li>Transfer an appropriate volume (0.5&#8211;1 ml) of DY-676-COOH (6.181 &#181;M) solution to the round bottom flask to hydrate the dry phospholipid film and vortex vigorously until a spontaneously formed vesicle (SFV) dispersion forms. Make sure that all of the phospholipids are dispersed to avoid lipid loss.</li>
		<li>Carefully transfer the round bottom flask containing the SFV dispersion into liquid nitrogen and freeze the dispersion for 3&#8211;5 min. Place the round bottom flask into an ultrasonic bath at 50 &#176;C to thaw the dispersion then vortex the dispersion vigorously for 1&#8211;2 min. Repeat this procedure six times, making a total of seven freeze and thaw cycles.</li>
	</ol>
	</li>
	<li>Extrusion of SFV to form homogeneous liposome vesicles
	<ol>
		<li>Transfer the SFV dispersion into a 1 ml syringe (syringe-a) and extrude the dispersion through a 100 nm polycarbonate membrane using a LiposoFast-Basic extruder into syringe-b.</li>
		<li>Extrude the dispersion from syringe-b, back into syringe-a, then repeat the cycle ten times. Due to extrusion, the solution in the syringe changes from a hazy appearance to a clear dispersion with time. After ten cycles (twenty single extrusion steps) remove syringe-b from the device and extrude the dispersion for the last time from syringe-a directly into a sterile 1.5 ml reaction tube.</li>
	</ol>
	</li>
	<li>Purification of liposomal encapsulated DY-676-COOH from free dye
	<ol>
		<li>Prepare a gel chromatography column using G25 beads soaked in 10 mM Tris buffer pH 7.4 (column length 28 cm, diameter 0.8 cm).</li>
		<li>Transfer 0.5 ml of extruded vesicle dispersion onto the gel bed and let the sample drain into the gel matrix.</li>
		<li>Elute the liposomes with 10 mM Tris buffer pH 7.4 (Figure 1A) and wash the column until the free dye drains completely out of the column. If need be, collect and recycle the free dye by desalting and dehydration according to the manufacturer&#8217;s instructions.</li>
		<li>Concentrate the eluted liposomes by ultracentrifugation (200,000 x g, 2 hr at 8 &#176;C) then disperse them in adequate volume of sterile 10 mM Tris buffer pH, 7.4.</li>
	</ol>
	</li>
	<li>Quantification of encapsulated DY-676-COOH concentration
	<ol>
		<li>Prepare a calibration curve by dissolving DY-676-COOH (0, 82, 124, 247, 494, 988 nM) in 10 mM Tris buffer, pH 7.4 containing 0.1% Triton X100.</li>
		<li>Dissolve 2 &#181;l (100 nmol final lipid of a 50 mmol/L stock) of the liposomes for 5 min at room temperature in 100 &#181;l Tris buffer containing 1% Triton X100 to destroy the vesicles and release the encapsulated dye. Then dilute samples with 10 mM Tris buffer, pH 7.4 to a final Triton-X100 concentration of 0.1% (v/v) making a total volume of 1 ml. Prepare all samples in duplicate.</li>
		<li>Measure the absorption and emission of all samples (free DY-676-COOH and Triton-X100 treated liposomes) at an excitation &#955;=645 nm and an emission &#955; = 700 nm. Establish and use a calibration curve of the free dye to determine the concentration of encapsulated dye.</li>
	</ol>
	</li>
	<li>Liposome characterization
	<ol>
		<li>Determine the sizes and zeta potential of liposomes by dynamic light scattering. Dilute the liposomal samples with filter sterilized (0.2 &#181;m) 10 mM Tris buffer pH 7.4 to a concentration of 100&#8211;300 &#181;M (lipid). Transfer the diluted samples into a low volume disposable cuvette and measure the sample according to the manufacturer&#8217;s instructions.</li>
		<li>Characterize the liposomes by electron microscopy to substantiate the size, integrity and homogeneity of liposomal vesicles according to standard protocols.</li>
	</ol>
	</li>
</ol>
2. Validation of Fluorescence-quenching and Activation of Prepared Liposomes
<ol>
	<li>Physicochemical analysis of fluorescence quenching and activation
	<ol>
		<li>Prepare two 1.5 ml tubes for the Lip-Q and 2 tubes for the free DY-676-COOH. Transfer 100 nmol total lipids (2.38 &#181;l of a 42 mmol/L Lip-Q stock solution, containing 138 &#181;g/ml of the encapsulated DY-676-COOH) into the corresponding tubes. Transfer free DY-676-COOH equivalent to the dye content of Lip-Q (0.38 &#181;g which results for example from 138 &#181;g/1,000 &#181;l x 2.38 &#181;l Lip-Q used). Incubate one tube of each probe at 4 &#176;C and freeze the second tube at -80 &#176;C overnight (16 hr).</li>
		<li>Heat up a heating block to 30 &#176;C. Fill a cooling box with crushed ice and equilibrate an aliquot of 10 mM Tris buffer pH 7.4 to room temperature.</li>
		<li>Remove probes from 4 &#176;C and equilibrate at room temperature (wrapped in aluminum foil to protect from light) and quickly thaw probes from -80 &#176;C at 30 &#176;C for 5 min. Chill the thawed probes on ice for 1 min before transferring them to room temperature (also wrapped in aluminum foil to protect from light).</li>
		<li>Add 10 mM Tris buffer (pH 7.4) to each of the probes to 100 &#181;l final volume and equilibrate all probes at RT for 10 min.</li>
		<li>Pipette 80 &#181;l of each probe into a low volume glass cuvette and measure the absorption of each probe from 400&#8211;900 nm on a spectrometer. Return the probe to their corresponding tubes.</li>
		<li>Transfer 80 &#181;l of each probe into a suitable glass cuvette and measure the fluorescence emission on a spectrofluorometer by exciting the probes at 674 nm and measuring the fluorescence from 694&#8211;800 nm.</li>
	</ol>
	</li>
	<li>Cellular uptake and fluorescence activation
	<ol>
		<li>Get and culture the following cell lines in their corresponding culture media according to standard conditions (37 &#176;C, 5% CO2 and 95% humidified atmosphere). Here, use the murine macrophage cell line J774A.1 (Dulbecco&#8217;s modified Eagle&#8217;s medium supplemented with 10% (v/v) fetal calf serum), the human glioblastoma cell line, U-118MG (MEM containing essential vitamins and 10% (v/v) fetal calf serum) and the human fibrosarcoma cell line, HT-1080 (RPMI with 5% FCS).</li>
		<li>Coat 8-well chamber slides with poly-L-lysine (add 100 &#181;l 0.001% poly-L-lysine to each well and incubate at 37 &#176;C for 10 min. Aspirate solution and let the chamber slides to dry up for at least 4 hr at RT on a sterile workbench. Rinse the chamber slides 3 times with 200 &#181;l Hank&#8217;s buffered saline solution then seal them with paraffin and aluminum foil and store at 4 &#176;C till needed.</li>
		<li>While the chamber slides are drying up, filter-sterilize the liposomes and dye solution and store at 4 &#176;C till needed.</li>
		<li>For probe uptake analysis with the whole body in vivo NIR fluorescence imaging system, prepare 5 small culture flasks for each of the 3 test cell lines (15 flasks in total). Seed 2 x 106 J774A.1, U-118MG and HT-1080 cells per culture flask with 5 ml of the respective culture medium (in quintuples) and grow for 16-24 hr. Parallel to the culture flasks, seed 30,000 cells of each cell line (J774A.1 and HT-1080) or 20,000 cells (U-118MG) to 2 wells of the chamber slide respectively and grow in 500 &#181;l culture medium for 16-24 hr.</li>
		<li>On the next day, add 100 nmol (final lipid amount) of Lip-Q to 2 flasks per cell line and to one well of each cell line on the chamber slide. Immediately transfer 1 flask per cell line to 4 &#176;C and the second flask back to the incubator. 
		NOTE: The volume of the probes added to the flasks and the chamber slides are the same, making the concentration on chamber slides 10-fold higher (5 ml is to 500 &#181;l culture medium). This is necessary because microscopic detection is less sensitive than the NIR fluorescence imaging system where cell pellets from the flasks are imaged.</li>
		<li>Add the free DY-676-COOH at a concentration equivalent to the dye content of Lip-Q to the cells in 2 flasks per cell line and to one well of each cell line on the chamber slide, then immediately transfer 1 flask per cell line to 4 &#176;C (energy depletion) and the other flask together with the chamber slide back to the incubator. Incubate all the cells for 24 hr at the corresponding conditions. The cells in the flask without probe serve as untreated control.</li>
	</ol>
	</li>
	<li>NIRF imaging and semi-quantitative analysis
	<ol>
		<li>After 24 hr incubation duration, harvest the cells in flasks by washing cells 2 times with Hanks buffered salt solution (HBSS) then scrape cells in 500 &#181;l HBSS and pellet by centrifugation (5 min at 200 x g) in 500 &#181;l tubes.</li>
		<li>Place the tubes with the cell pellets (and HBSS) in a NIRF imager and image using filters for excitation (615&#8211;665 nm) and emission (cut in &#62;700 nm).</li>
		<li>Deduct autofluorescence and evaluate the intensity of target versus autofluorescence according to manufacturer instructions. This will give the semi-quantitative levels of fluorescence intensity as average signal (scaled counts/sec), which represents count levels after scaling for exposure time, camera gain, binning and bit depth, so that the measurements are comparable among each other.</li>
	</ol>
	</li>
	<li>Confocal microscopic analysis
	<ol>
		<li>After 24 hr incubation, harvest the cells on chamber slides by washing 2 times with 500 &#181;l HBSS.</li>
		<li>Fix the cells with 200 &#181;l HBSS containing 3.7% (v/v) formaldehyde for 30 min at RT.</li>
		<li>While fixation is going on, dilute the DNA stain, Hoechst-33258 1:50 with mounting solution.</li>
		<li>After fixation, wash the cells 2 times with HBSS then separate the chambers from the glass slides. Add 50 &#181;l mounting solution containing the DNA-stain on each spot corresponding to the wells of the chamber slides. Cover the cells with glass coverslips, seal edges with transparent nail polish and air-dry for 10 min at RT (dark).</li>
		<li>Image cells on a suitable fluorescence microscope or confocal microscope. Use the following excitation and emission settings for visualization of the corresponding components: nuclei (Hoechst-33258: excitation 405 nm, emission 420&#8211;480 nm). NBD-DOPE (liposomal lipid: excitation 488 nm, emission 530 nm). DY-676-COOH (NIR fluorescent dye: excitation 633&#8211;645 nm, emission 650&#8211;700 nm). 
		NOTE: Make sure that the fluorescence microscope available is equipped with suitable filters which permit excitation and emission of wavelengths higher than 630 nm.</li>
	</ol>
	</li>
</ol>

3. Liposome-based In Vivo Fluorescence Imaging of Inflammation
<ol>
	<li>Preparation of animals and materials
	<ol>
		<li>House 8&#8211;12 week-old male NMRI mice weighing approximately 36 g under standard conditions with food and water ad libitum.</li>
		<li>Seven days prior to the start of experiments, give all mice a low pheophorbide diet in order to reduce tissue autofluorescence.</li>
		<li>Twenty-four&#160;hours before the start of each experiment, shave mice at the desired area (e.g., whole back area if imaging of hind leg edema is desired).</li>
		<li>Weigh the animals and calculate the amount of probe to be injected per mouse (Lip-Q and Lip-dQ at 10 &#181;mol (lipid concentration) per kg weight and free DY-676-COOH (equivalent to dye content of Lip-Q used).</li>
		<li>Image the animals in a whole body NIR Fluorescence imager with the same settings used for the cell pellets. This measurement provides autofluorescence of the animals.</li>
		<li>Dissolve 10 mg zymosan-A in 1 ml isotonic saline solution and store overnight at 4 &#176;C.</li>
	</ol>
	</li>
	<li>Induction of inflammation and in vivo NIRF imaging
	<ol>
		<li>Prepare 3 syringes per mouse containing the following solutions. Fill one syringe with 50 &#181;l zymosan-A solution (10 mg/ml) and the second syringe with 50 &#181;l isotonic saline solution. Fill the third syringe with the probes, whereby Lip-Q and Lip-dQ (10 &#181;mol/kg weight (lipid)) are designated for test animals and free DY-676-COOH (concentration as in Lip-Q) for control animals. Make sure the probes are diluted with sterile HBSS to 150 &#181;l final volume.</li>
		<li>Apply eye cream on the eyes of animals to avoid dryness and anesthetize animals with 2% isoflurane till they are deeply asleep and do not react when touched on the paws (this takes about 2 min).</li>
		<li>Place the mouse on a warm mat (still under anesthesia) and inject the zymosan-A solution subcutaneously on the right hind leg and the saline solution on the left hind leg. Immediately inject the probe intravenously and image the animal thereafter then record time of injection/measurement (as t = 0 hr). Save the resulting images as image cubes and repeat the above steps for all other animals and respective probes.</li>
		<li>Image the animals every 2 hr for 10 hr post injection and then at 24 hr post injection, making sure that the stage of the measuring chamber is warm (for example, by placing a warm mat underneath), in order to avoid hypothermia. After each measurement, place the animals in a cage with food and water ad libitum and place the cage in a temperate animal chamber.&#160; Euthanize the animals by first anesthetizing with 2% isoflurane till the animals no longer react to touch, then euthanize with carbon dioxide for 5-10 min, making sure that the animals stop breathing completely and rigor mortis occurs.&#160;</li>
		<li>Dissect the mice according to standard protocols which can be assessed online (http://www.freebookez.com/mouse-dissection-lab-report/) and image the organs.</li>
		<li>Evaluate the measurement results according to manufacturer&#8217;s instructions by first deducting the overall fluorescence of the animals (unmixing) then assigning regions of interest for autofluorescence (left hind leg with saline) and target fluorescence of inflamed area (right hind leg with zymosan-A).</li>
	</ol>
	</li>
</ol>

The authors have nothing to disclose.

Since liposomes can also serve as delivery systems for fluorescent dyes, they enable imaging of target diseases. The encapsulation of high concentrations of fluorescent dyes such as the NIRF dye, DY676-COOH used here, leads to a high level of fluorescence quenching of the entrapped dye. Fluorescence quenching, a phenomenon seen with many fluorophores at high concentration can be exploited in several in vivo imaging applications, where a high sensitivity and reliable detection of the target area is demanded. The ...

Liposomes have been intensively investigated and serve as one of the most biocompatible biomedical drug delivery systems for clinical applications1,2. They are mainly composed of phospholipids and cholesterol, both of which are biocompatible compounds mimicking parts of natural cell membranes. Whereas hydrophilic substances can be entrapped in the aqueous interior, lipophilic agents can be incorporated within the liposomal phospholipid bilayer3. Encapsulation of substances within the aqueous interior of liposomes grants protection against degradation in vivo and also prevents the host system from toxic effects of cytotoxic drugs used for the therapy of diseases, for example chemotherapeutics aimed at destroying tumor cells. The modification of the liposomal surface with polymers like polyethylenglycol (PEGylation) further extends the liposomal blood circulation time in vivo due to sterical stabilization4. Moreover, liposomes can sequester high concentrations of several substances such as proteins5,6, hydrophilic substances7,8 and enzymes9. They therefore serve as reliable clinical therapeutic and diagnostic tools which merit their approval for delivery of cytotoxic drugs such as doxorubicin for cancer therapy4. Due to their flexibility, liposomes can also be loaded with fluorochromes for diagnostic and image-guided surgical purposes.
Fluorescence imaging provides a cost-effective and non-invasive in vivo diagnostic tool which however, demands some basic requirements. It could be demonstrated that fluorochromes which suit best for in vivo imaging have characteristic absorption and emission maxima in the range where light dispersion and scattering as well as tissue autofluorescence originating from water and hemoglobin is low. Thus, such probes have their abs/em maxima between 650 and 900 nm10. Besides this, the stability of fluorochromes both in vitro and in vivo is critical, as opsonization and rapid clearance can greatly limit their application for in vivo imaging11. Other effects such as poor stability and low sensitivity or cytotoxic effects on target organs as seen with indocyanine green (ICG)12-16, are unwanted and must be taken into consideration when designing probes for in vivo imaging. These observations have led to the active development of several preclinical NIR fluorochromes, nanoparticles as well as new techniques for the in vivo imaging of inflammatory processes, cancer and for image-guided surgery17-20. Despite the stability of most preclinical NIRF (near-infrared fluorescence) dyes in vitro, their rapid perfusion and clearance through the liver and kidney impede their use in the in vivo optical imaging of diseases and inflammatory processes.
We therefore present a protocol for the encapsulation of fluorochromes such as the well characterized near-infrared fluorescent dye DY-676-COOH, known for its tendency to self-quench at relatively high concentrations21 in liposomes. At high concentrations H-dimer formation and/or pi-stacking interactions between fluorophore molecules located within each other&#8217;s F&#246;rster radius result in F&#246;rster resonance energy transfer (FRET) between the fluorochrome molecules. At low concentration the space between the fluorophore molecules increases, thereby preventing pi-stacking interaction and H-dimer formation and resulting in high fluorescence emission. The switch between high and low concentration and the accompanying fluorescence quenching and activation is a promising strategy that can be exploited for optical imaging22. In this respect, encapsulation of high concentrations of the NIRF dye DY-676-COOH in the aqueous interior of liposomes is more favorable for in vivo imaging than the free dye. The challenge of the method lies first of all in the correct encapsulation and secondly, in the validation of the benefits resulting from encapsulating high concentrations of the dye. Comparing the imaging properties of quenched liposomes with that of the free dye and also with a non-quenched liposome formulation with low concentrations of the dye is indispensable. We show by a simple, but highly effective film hydration and extrusion protocol combined with alternate freeze and thaw cycles that encapsulation of quenching concentrations of DY-676-COOH in liposomes is feasible. Other methods used to prepare liposomes such as the reversed phase evaporation method23 as well as the ethanol injection method24 enable liposome preparation with high encapsulation efficiencies for many hydrophilic substances. However, the nature of the substance to be encapsulated can influence the encapsulation efficiency. In effect, the film hydration and extrusion protocol presented here revealed the highest efficiency for encapsulation of DY-676-COOH. To illustrate the benefits of liposomal encapsulation of DY-676-COOH, a zymosan-induced edema model, which permits the study of inflammatory processes within a few hours, was used. Here, it is demonstrated that liposomes with high concentrations of the encapsulated DY-676-COOH are more suitable for whole body in vivo optical imaging of inflammatory processes than the free dye or the non-quenched liposomal formulation with low dye concentrations. Thus the underlying protocol provides a simple and fast method to produce quenched fluorescent liposomes and the validation of their activation and imaging potential both in vitro and in vivo.

<table><tbody><tr><td colspan="4">&lt;strong&gt;Materials and equipments for preparation of liposomes&lt;/strong&gt;</td></tr><tr><td>egg phospahtidylcholine</td><td>Avanti Polar Lipids</td><td>840051P</td><td>Dissolve in chloroform and store in glass vials (214 mg/ml)</td></tr><tr><td>cholesterol</td><td>Sigma</td><td>C8667</td><td>Dissolve in chloroform and store in glass vials (134 mg/ml)</td></tr><tr><td>1,2-distearoyl-&lt;em&gt;sn&lt;/em&gt;-glycero-3-phosphoethanolamine-&lt;em&gt;N&lt;/em&gt;-[methoxy(polyethylene glycol)-2000] (ammonium salt)</td><td>Avanti Polar Lipids</td><td>880120P</td><td>Dissolve in chloroform and store in glass vials (122 mg/ml)</td></tr><tr><td>1,2-dioleoyl-&lt;em&gt;sn&lt;/em&gt;-glycero-3-phosphoethanolamine-&lt;em&gt;N&lt;/em&gt;-(7-nitro-2-1,3-benzoxadiazol-4-yl) (ammonium salt)</td><td>Avanti Polar Lipids</td><td>810145P</td><td>Dissolve in chloroform and store in glass vials (2 mg/ml)</td></tr><tr><td>Sartorius MC1 (d = 0.01 mg)</td><td>Sartorius AG</td><td>Research RC 210 P</td><td>used for weighing the phospholipids</td></tr><tr><td>Rotavapor</td><td>B&amp;uuml;chi Labortechnik AG</td><td>R-114</td><td>used for hydration of phospholipid film</td></tr><tr><td>Waterbath</td><td>B&amp;uuml;chi Labortechnik AG</td><td>R-481</td><td>used for hydration of phospholipid film</td></tr><tr><td>Vacuum Controller</td><td>B&amp;uuml;chi Labortechnik AG</td><td>B-720</td><td>used for hydration of phospholipid film</td></tr><tr><td>Vacobox</td><td>B&amp;uuml;chi Labortechnik AG</td><td>B-177</td><td>used for hydration of phospholipid film</td></tr><tr><td>Circulation Chiller</td><td>LAUDA DR. R. WOBSER&lt;br/&gt; GMBH &amp;amp; CO. KG</td><td>WKL 230</td><td>used for hydration of phospholipid film</td></tr><tr><td>DY-676-COOH</td><td>Dyomics GmbH</td><td>676-00</td><td>Dissolve in 10 mM Tris and store stock at -20&amp;deg;C</td></tr><tr><td>Tris-(Hydroxymethyl)-aminomethan</td><td>Applichem</td><td>A1086</td><td>buffer 10 mM, pH 7.4</td></tr><tr><td>Trichlormethan</td><td>Carl Roth GmbH + Co. KG</td><td>Y015.2</td><td>used for liposome preparation</td></tr><tr><td>Sonicator</td><td>Merck Eurolab GmbH</td><td>USR 170 H</td><td>used for liposome preparation</td></tr><tr><td>Vortex Genie 2 (Pop-off Cup, No. 146-3011-00)</td><td>Scientific Industries Inc.</td><td>SI-0256</td><td>used for liposome preparation</td></tr><tr><td>Sephadex G25 medium&amp;nbsp;</td><td>GE Healthcare Europe GmbH</td><td>17-0033-01</td><td>used for liposome purification</td></tr><tr><td>Triton X100</td><td>Ferak Berlin GmbH</td><td>505002</td><td>used to destruct liposomes&amp;nbsp; for dye quantification</td></tr><tr><td>LiposoFast-Basic</td><td>Avestin Inc.</td><td></td><td>used for the extrusion of liposomes</td></tr><tr><td>Polycarbonate filter membrane, 100 nm (Whatman Nucleopore Trans Etch Membrane, NUCLEPR PC 19 MM, 0.1 U)</td><td>VWR</td><td></td><td>used for the extrusion of liposomes via LiposoFast-Basic</td></tr><tr><td>Fluostar Optima</td><td>BMG Labtech</td><td></td><td>used for dye quantification</td></tr><tr><td>Zetasizer Nano ZS</td><td>Malvern</td><td></td><td>used for the determination of liposome size and zetapotential</td></tr><tr><td>Ultracentrifuge&amp;nbsp;</td><td>Beckmann Coulter GmbH</td><td>XL 80</td><td>used for concentration of the samples</td></tr><tr><td>Rotor</td><td>Beckmann Coulter GmbH</td><td>SW 55 TI</td><td>used for concentration of the samples</td></tr><tr><td colspan="4">&lt;strong&gt;Materials and equipments for the evaluation of liposome and optical imaging&lt;/strong&gt;</td></tr><tr><td>Zymosan-A from Saccharomyces cereviciae</td><td>Sigma</td><td>Z4250-250MG</td><td>used for induction of inflammation</td></tr><tr><td>Isotonic Saline (0.9%)</td><td>Fresenius GmbH</td><td>PZN-2159621</td><td>used for the dilution of Zymosan-A</td></tr><tr><td>Isoflurane vaporizer</td><td>Ohmeda Isotec 4</td><td></td><td>used for anesthesizing animals</td></tr><tr><td>Isoflurane</td><td>Actavis GmbH&amp;nbsp;</td><td>PZN-7253744</td><td>anesthesia</td></tr><tr><td>Thermo Mat Pro 20 W</td><td>Lucky Reptile</td><td>61202-HTP-20</td><td>used to keep animals warm during anesthesia</td></tr><tr><td>Omnican-F (1 ml injection)&amp;nbsp;</td><td>Braun</td><td>PZN-3115465</td><td>used for subcutaneous and intravenous application of probes</td></tr><tr><td>Panthenol eye cream</td><td>Jenapharm</td><td>PZN-3524531</td><td>used to prevent dryness of the eyes of animals during anesthesia</td></tr><tr><td>Hanks buffered saline solution</td><td>PAA Laboratories /Biochrom AG</td><td>L2045</td><td>w/o Mg2+, Ca2+ and phenol red. For dilution of probes and for washing of cells</td></tr><tr><td>8-Well chamber slides</td><td>BD Biosciences</td><td>354108</td><td>used for cell culture followed by microscopy&amp;nbsp;</td></tr><tr><td>Cell culture flasks</td><td>Greiner BioOne</td><td></td><td></td></tr><tr><td>Cell culture media</td><td>Gibco (life technologies GmbH)</td><td></td><td></td></tr><tr><td>Fetal calf serum&amp;nbsp;</td><td>Invitrogen</td><td></td><td></td></tr><tr><td>Poly-L-Lysine solution (0.01%, 50&amp;nbsp;ml)</td><td>Sigma</td><td>P4832</td><td>used to coat cell culture chamber slides</td></tr><tr><td>Mountant Permafluor</td><td>ThermoScientific&amp;nbsp;</td><td>S21022-3</td><td>Mounting solution for microscopy</td></tr><tr><td>Hoechst-33258</td><td>AppliChem</td><td></td><td>DNA stain for microscopy</td></tr><tr><td>Hera-Safe</td><td>Heraeus Instruments</td><td></td><td>sterile work bench used for cell culture</td></tr><tr><td>HERA cell</td><td>Heraeus Instruments</td><td></td><td>Incubator used for cell culture</td></tr><tr><td>LSM510-Meta</td><td>Zeiss</td><td></td><td>used for confocal microscopy</td></tr><tr><td>Maestro-TM in vivo fluorescence imaging system</td><td>CRi, Woburn</td><td></td><td>used for whole body fluorescence imaging of small animals</td></tr><tr><td>Spectrophotometer (Ultrospec 4300 pro UV)</td><td>GE Healthcare</td><td></td><td>used for measurement of absorption</td></tr><tr><td>Spectrofluorometer (Jasco FP-6200)</td><td>Jasco</td><td></td><td>used for measurement of fluorescence emission</td></tr><tr><td colspan="4">&lt;strong&gt;Animals&lt;/strong&gt;</td></tr><tr><td>NMRI mice (8-12 weeks old, male)</td><td>Elevage Janvier, France</td><td></td><td>used for inflammation trials</td></tr></tbody></table>

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.

The encapsulation of high concentrations of fluorescent dyes such as the NIRF dye DY676-COOH used here in the aqueous interior of liposomes leads to a high level of fluorescence quenching. Fluorescence quenching, a phenomenon seen with many fluorophores at high concentration, can be exploited in several in vivo imaging applications where a high sensitivity and reliable detection of the target area are demanded. The use of liposomes also provides protection of the dye which is indispensable for in vivo a...

Watch this Scientific Journal Video about Fluorescence-quenching of a Liposomal-encapsulated Near-infrared Fluorophore as a Tool for In Vivo Optical Imaging at JoVE.com

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.

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 ...

fluorescence-quenching-liposomal-encapsulated-near-infrared

Research

JoVE Journal

Bioengineering

16.2K Views.  Jena University Hospital. 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. 

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

Non-invasive Optical Imaging of the Lymphatic Vasculature of a Mouse

The lymphatic vascular system is an important component of the circulatory system that maintains fluid homeostasis, provides immune surveillance, and mediates fat absorption in the gut. Yet despite its critical function, there is comparatively little understanding of how the lymphatic system adapts to serve these functions in health and disease1. Recently, we have demonstrated the ability to dynamically image lymphatic architecture and lymph "pumping" action in normal human subjects as well as in persons suffering lymphatic dysfunction using trace administration of a near-infrared fluorescent (NIRF) dye and a custom, Gen III-intensified imaging system2-4. NIRF imaging showed dramatic changes in lymphatic architecture and function with human disease. It remains unclear how these changes occur and new animal models are being developed to elucidate their genetic and molecular basis. In this protocol, we present NIRF lymphatic, small animal imaging5,6 using indocyanine green (ICG), a dye that has been used for 50 years in humans7, and a NIRF dye-labeled cyclic albumin binding domain (cABD-IRDye800) peptide that preferentially binds mouse and human albumin8. Approximately 5.5 times brighter than ICG, cABD-IRDye800 has a similar lymphatic clearance profile and can be injected in smaller doses than ICG to achieve sufficient NIRF signals for imaging8. Because both cABD-IRDye800 and ICG bind to albumin in the interstitial space8, they both may depict active protein transport into and within the lymphatics. Intradermal (ID) injections (5-50 &mu;l) of ICG (645 &mu;M) or cABD-IRDye800 (200 &mu;M) in saline are administered to the dorsal aspect of each hind paw and/or the left and right side of the base of the tail of an isoflurane-anesthetized mouse. The resulting dye concentration in the animal is 83-1,250 &mu;g/kg for ICG or 113-1,700 &mu;g/kg for cABD-IRDye800. Immediately following injections, functional lymphatic imaging is conducted for up to 1 hr using a customized, small animal NIRF imaging system. Whole animal spatial resolution can depict fluorescent lymphatic vessels of 100 microns or less, and images of structures up to 3 cm in depth can be acquired9. Images are acquired using V++ software and analyzed using ImageJ or MATLAB software. During analysis, consecutive regions of interest (ROIs) encompassing the entire vessel diameter are drawn along a given lymph vessel. The dimensions for each ROI are kept constant for a given vessel and NIRF intensity is measured for each ROI to quantitatively assess "packets" of lymph moving through vessels.

Recently developed imaging techniques using near-infrared fluorescence (NIRF) may help elucidate the role the lymphatic system plays in cancer metastasis, immune response, wound repair, and other lymphatic-associated diseases.

The lymphatic  vascular system is an important component of the circulatory system that  maintains fluid homeostasis, provides immune surveillance, and ...

Immunology and Infection

A Step Beyond BRET: Fluorescence by Unbound Excitation from Luminescence (FUEL)

Fluorescence by Unbound Excitation from Luminescence (FUEL) is a radiative excitation-emission process that produces increased signal and contrast enhancement in vitro and in vivo. FUEL shares many of the same underlying principles as Bioluminescence Resonance Energy Transfer (BRET), yet greatly differs in the acceptable working distances between the luminescent source and the fluorescent entity. While BRET is effectively limited to a maximum of 2 times the F&ouml;rster radius, commonly less than 14 nm, FUEL can occur at distances up to &micro;m or even cm in the absence of an optical absorber. Here we expand upon the foundation and applicability of FUEL by reviewing the relevant principles behind the phenomenon and demonstrate its compatibility with a wide variety of fluorophores and fluorescent nanoparticles. Further, the utility of antibody-targeted FUEL is explored. The examples shown here provide evidence that FUEL can be utilized for applications where BRET is not possible, filling the spatial void that exists between BRET and traditional whole animal imaging.

A Step Beyond BRET: Fluorescence by Unbound Excitation from Luminescence FUEL

Expanding the foundation and applicability of Fluorescence by Unbound Excitation from Luminescence (FUEL) by surveying the relevant principles and demonstrating its compatibility with a multitude of fluorophores and antibody-targeted conditions.

Fluorescence by Unbound Excitation from Luminescence (FUEL) is a radiative excitation-emission process that produces increased signal and contrast ...

Multiplexing Focused Ultrasound Stimulation with Fluorescence Microscopy

By focusing low-intensity ultrasound pulses that penetrate soft tissues, LIPUS represents a promising biomedical technology to remotely and safely manipulate neural firing, hormonal secretion and genetically-reprogrammed cells. However, the translation of this technology for medical applications is currently hampered by a lack of biophysical mechanisms by which targeted tissues sense and respond to LIPUS. A suitable approach to identify these mechanisms would be to use optical biosensors in combination with LIPUS to determine underlying signaling pathways. However, implementing LIPUS to a fluorescence microscope may introduce undesired mechanical artefacts due to the presence of physical interfaces that reflect, absorb and refract acoustic waves. This article presents a step-by-step procedure to incorporate LIPUS to commercially-available upright epi-fluorescence microscopes while minimizing the influence of physical interfaces along the acoustic path. A simple procedure is described to operate a single-element ultrasound transducer and to bring the focal zone of the transducer into the objective focal point. The use of LIPUS is illustrated with an example of LIPUS-induced calcium transients in cultured human glioblastoma cells measured using calcium imaging.

Low-Intensity Pulsed Ultrasound Stimulation (LIPUS) is a modality for non-invasive mechanical stimulation of endogenous or engineered cells with high spatial and temporal resolution. This article describes how to implement LIPUS to an epi-fluorescence microscope and how to minimize acoustic impedance mismatch along the ultrasound path to prevent unwanted mechanical artefacts.

By focusing low-intensity ultrasound pulses that penetrate soft tissues, LIPUS represents a promising biomedical technology to remotely and safely ...

Engineering

In Vivo Optical Imaging of Brain Tumors and Arthritis Using Fluorescent SapC-DOPS Nanovesicles

We describe a multi-angle rotational optical imaging (MAROI) system for in vivo monitoring of physiopathological processes labeled with a fluorescent marker. Mouse models (brain tumor and arthritis) were used to evaluate the usefulness of this method. Saposin C (SapC)-dioleoylphosphatidylserine (DOPS) nanovesicles tagged with CellVue Maroon (CVM) fluorophore were administered intravenously. Animals were then placed in the rotational holder (MARS) of the in vivo imaging system. Images were acquired in 10&#176; steps over 380&#176;. A rectangular&#160;region of interest (ROI) was placed across the full image width at the model disease site. Within the ROI, and for every image, mean fluorescence intensity was computed after background subtraction. In the mouse models studied, the labeled nanovesicles were taken up in both the orthotopic and transgenic brain tumors, and in the arthritic sites (toes and ankles). Curve analysis of the multi angle image ROIs determined the angle with the highest signal. Thus, the optimal angle for imaging each disease site was characterized. The MAROI method applied to imaging of fluorescent compounds is a noninvasive, economical, and precise tool for in vivo quantitative analysis of the disease states in the described mouse models.

In Vivo Optical Imaging of Brain Tumors and Arthritis Using Fluorescent SapC-DOPS Nanovesicles

We describe a multi-angle rotational optical imaging (MAROI) system for in vivo quantitation of a fluorescent marker delivered by saposin C (SapC)-dioleoylphosphatidylserine (DOPS) nanovesicles. Employing mouse models of cancer and arthritis, we demonstrate how the MAROI signal curve analysis can be used for the precise mapping and biological characterization of disease processes.

We describe a multi-angle rotational optical imaging (MAROI) system for in vivo monitoring of physiopathological processes labeled with a fluorescent ...

Medicine

Non-invasive In Vivo Fluorescence Optical Imaging of Inflammatory MMP Activity Using an Activatable Fluorescent Imaging Agent

This paper describes a non-invasive method for imaging matrix metalloproteinases (MMP)-activity by an activatable fluorescent probe, via in vivo fluorescence optical imaging (OI), in two different mouse models of inflammation: a rheumatoid arthritis (RA) and a contact hypersensitivity reaction (CHR) model. Light with a wavelength in the near infrared (NIR) window (650 - 950 nm) allows a deeper tissue penetration and minimal signal absorption compared to wavelengths below 650 nm. The major advantages using fluorescence OI is that it is cheap, fast and easy to implement in different animal models.
Activatable fluorescent probes are optically silent in their inactivated states, but become highly fluorescent when activated by a protease. Activated MMPs lead to tissue destruction and play an important role for disease progression in delayed-type hypersensitivity reactions (DTHRs) such as RA and CHR. Furthermore, MMPs are the key proteases for cartilage and bone degradation and are induced by macrophages, fibroblasts and chondrocytes in response to pro-inflammatory cytokines. Here we use a probe that is activated by the key MMPs like MMP-2, -3, -9 and -13 and describe an imaging protocol for near infrared fluorescence OI of MMP activity in RA and control mice 6 days after disease induction as well as in mice with acute (1x challenge) and chronic (5x challenge) CHR on the right ear compared to healthy ears.

Non-invasive In Vivo Fluorescence Optical Imaging of Inflammatory MMP Activity Using an Activatable Fluorescent Imaging Agent

This paper explains the application of fluorescent imaging using an activatable optical imaging probe to visualize the in vivo activity of key matrix metalloproteinases in two different experimental models of inflammation.

This paper describes a non-invasive method for imaging matrix metalloproteinases (MMP)-activity by an activatable fluorescent probe, via in vivo ...

Dual-Color End-Labeling and Vesicle Encapsulation of RNAs for smFRET-TIRF Studies

Fluorescent End-Labeling and Encapsulation of Long RNAs for Single-Molecule FRET-TIRF Microscopy

Single-molecule F&#246;rster Resonance Energy Transfer (smFRET) excels in studying dynamic biomolecules by allowing precise observation of their conformational changes over time. To monitor RNA dynamics with smFRET, we developed a method to covalently label RNAs at their termini with a FRET pair of fluorophores. This direct end-labeling strategy targets the 5&#39;-phosphate by carbodiimide (EDC)/N-hydroxysuccinimide (NHS) activation and the 3&#39;-ribose by periodate oxidation, which can be adapted to other RNAs regardless of their size and sequence to study them independently of artificial modifications. Furthermore, the 5&#39;-EDC/NHS activation is of general interest to all nucleic acids with a 5&#39;-phosphate. The use of commercially available chemicals eliminates the need to synthesize RNA-specific probes.
Total Internal Reflection Fluorescence (TIRF) microscopy requires the surface-immobilized molecules of interest to be within the evanescent field to be illuminated. A sophisticated way of keeping the RNA molecules within the evanescent field is to encapsulate them in phospholipid vesicles. Encapsulation benefits from the best of both worlds, tethering the molecule to the surface while enabling free diffusion of the molecule. We ensure that each vesicle contains only a single RNA molecule, enabling single-molecule imaging. Upon dual-end labeling and encapsulation of the RNA of interest, smFRET measurements offer a dynamic and detailed view of RNA behavior.

This article describes the dual-color labeling of long RNAs at termini positions and their surface immobilization via encapsulation in phospholipid vesicles for single-molecule FRET TIRF microscopy applications. Combining these techniques enables precise visualization and analysis of RNA dynamics at the single-molecule level.

Single-molecule F&#246;rster Resonance Energy Transfer (smFRET) excels in studying dynamic biomolecules by allowing precise observation of their ...

Biochemistry

Spatio-Temporal In Vivo Imaging of Ocular Drug Delivery Systems using Fiberoptic Confocal Laser Microendoscopy

Subconjunctival injection is an attractive route to administer ocular drugs due to easy trans-scleral access that bypasses anterior ocular barriers, such as the cornea and conjunctiva. While therapeutic effects and pharmacokinetics of the drugs upon subconjunctival injection have been described in some studies, very few assess the ocular distribution of drugs or drug delivery systems (DDS). The latter is critical for the optimization of intraocular DDS design and drug bioavailability to achieve the desired ocular localization and duration of action (e.g., acute versus. prolonged). This study establishes the use of fiberoptic confocal laser microendoscopy (CLM) to qualitatively study the ocular distribution of fluorescent liposomes in real-time in live mice after sub-conjunctival injection. Being designed for in vivo visual inspection of tissues at the microscopic level, this is also the first full description of the CLM imaging method to study spatio-temporal distribution of injectables in the eye after subconjunctival injection.

Spatio-Temporal In Vivo Imaging of Ocular Drug Delivery Systems using Fiberoptic Confocal Laser Microendoscopy

We present a protocol for the use of fiberoptic confocal laser microendoscopy (CLM) to non-invasively study the spatio-temporal distribution of liposomes in the eye after subconjunctival injection.

Subconjunctival injection is an attractive route to administer ocular drugs due to easy trans-scleral access that bypasses anterior ocular barriers, such ...

Utilizing pHluorin-tagged Receptors to Monitor Subcellular Localization and Trafficking

Understanding membrane protein trafficking, assembly, and expression requires an approach that differentiates between those residing in intracellular organelles and those localized on the plasma membrane. Traditional fluorescence-based measurements lack the capability to distinguish membrane proteins residing in different organelles. Cutting edge methodologies transcend traditional methods by coupling pH-sensitive fluorophores with total internal reflection fluorescence microscopy (TIRFM). TIRF illumination excites the sample up to approximately 150 nm from the glass-sample interface, thus decreasing background, increasing the signal to noise ratio, and enhancing resolution. The excitation volume in TIRFM encompasses the plasma membrane and nearby organelles such as the peripheral ER. Superecliptic pHluorin (SEP) is a pH sensitive version of GFP. Genetically encoding SEP into the extracellular domain of a membrane protein of interest positions the fluorophore on the luminal side of the ER and in the extracellular region of the cell. SEP is fluorescent when the pH is greater than 6, but remains in an off state at lower pH values. Therefore, receptors tagged with SEP fluoresce when residing in the endoplasmic reticulum (ER) or upon insertion in the plasma membrane (PM) but not when confined to a trafficking vesicle or other organelles such as the Golgi. The extracellular pH can be adjusted to dictate the fluorescence of receptors on the plasma membrane. The difference in fluorescence between TIRF images at neutral and acidic extracellular pH for the same cell corresponds to a relative number of receptors on the plasma membrane. This allows a simultaneous measurement of intracellular and plasma membrane resident receptors. Single vesicle insertion events can also be measured when the extracellular pH is neutral, corresponding to a low pH trafficking vesicle fusing with the plasma membrane and transitioning into a fluorescent state. This versatile technique can be exploited to study localization, expression, and trafficking of membrane proteins.

Labeling the extracellular domain of a membrane protein with a pH sensitive fluorophore, superecliptic pHluorin (SEP), allows subcellular localization, expression, and trafficking to be determined. Imaging SEP-labeled proteins with total internal reflection fluorescence microscopy (TIRFM) enables the quantification of protein levels in the peripheral ER and plasma membrane.

Understanding membrane protein trafficking, assembly, and expression requires an approach that differentiates between those residing in intracellular ...

Biology

A Bright NIR-II Fluorescence Probe for Vascular and Tumor Imaging

As an emerging imaging technology, near-infrared II (NIR-II, 1000-1700 nm) fluorescence imaging has significant potential in the biomedical field, owing to its high sensitivity, deep tissue penetration, and superior imaging with spatial and temporal resolution. However, the method to facilitate the implementation of NIR-II fluorescence imaging for some urgently needed fields, such as medical science and pharmacy, has puzzled relevant researchers. This protocol describes in detail the construction and bioimaging applications of a NIR-II fluorescence molecular probe, HLY1, with a D-A-D (donor-acceptor-donor) skeleton. HLY1 showed good optical properties and biocompatibility. Furthermore, NIR-II vascular and tumor imaging in mice was performed using a NIR-II optics imaging device. Real-time high-resolution NIR-II fluorescence images were acquired to guide the detection of tumors and vascular diseases. From probe preparation to data acquisition, the imaging quality is greatly improved, and the authenticity of the NIR-II molecular probes for data recording in intravital imaging is ensured.

The present protocol describes a detailed, real-time NIR-II fluorescence imaging operation of a mouse using a NIR-II optics imaging device.

As an emerging imaging technology, near-infrared II (NIR-II, 1000-1700 nm) fluorescence imaging has significant potential in the biomedical field, owing ...

Fluorescence Lifetime Macro Imager for Biomedical Applications

This paper presents a new photoluminescence lifetime imager designed to map the molecular oxygen (O2) concentration in different phosphorescent samples ranging from solid-state, O2-sensitive coatings to live animal tissue samples stained with soluble O2-sensitive probes. In particular, the nanoparticle-based near-infrared probe NanO2-IR, which is excitable with a 625 nm light-emitting diode (LED) and emits at 760 nm, was used. The imaging system is based on the Timepix3 camera (Tpx3Cam) and the opto-mechanical adaptor, which also houses an image intensifier. O2 phosphorescence lifetime imaging microscopy (PLIM) is commonly required for various studies, but current platforms have limitations in their accuracy, general flexibility, and usability.
The system presented here is a fast and highly sensitive imager, which is built on an integrated optical sensor and readout chip module, Tpx3Cam. It is shown to produce high-intensity phosphorescence signals and stable lifetime values from surface-stained intestinal tissue samples or intraluminally stained fragments of the large intestine and allows the detailed mapping of tissue O2 levels in about 20 s or less. Initial experiments on the imaging of hypoxia in grafted tumors in unconscious animals are also presented. We also describe how the imager can be re-configured for use with O2-sensitive materials based on Pt-porphyrin dyes using a 390 nm LED for the excitation and a bandpass 650 nm filter for emission. Overall, the PLIM imager was found to produce accurate quantitative measurements of lifetime values for the probes used and respective two-dimensional maps of the O2 concentration. It is also useful for the metabolic imaging of ex vivo tissue models and live animals.

This paper describes the use of a new, fast optical imager for the macroscopic photoluminescence lifetime imaging of long decay emitting samples. The integration, image acquisition, and analysis procedures are described, along with the preparation and characterization of the sensor materials for the imaging and the application of the imager in studying biological samples.

This paper presents a new photoluminescence lifetime imager designed to map the molecular oxygen (O2) concentration in different phosphorescent samples ...

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

Summary

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Chapters in this video

Non-invasive Optical Imaging of the Lymphatic Vasculature of a Mouse

A Step Beyond BRET: Fluorescence by Unbound Excitation from Luminescence (FUEL)

Multiplexing Focused Ultrasound Stimulation with Fluorescence Microscopy

In Vivo Optical Imaging of Brain Tumors and Arthritis Using Fluorescent SapC-DOPS Nanovesicles

Non-invasive In Vivo Fluorescence Optical Imaging of Inflammatory MMP Activity Using an Activatable Fluorescent Imaging Agent

Fluorescent End-Labeling and Encapsulation of Long RNAs for Single-Molecule FRET-TIRF Microscopy

Spatio-Temporal In Vivo Imaging of Ocular Drug Delivery Systems using Fiberoptic Confocal Laser Microendoscopy

Utilizing pHluorin-tagged Receptors to Monitor Subcellular Localization and Trafficking

A Bright NIR-II Fluorescence Probe for Vascular and Tumor Imaging

Fluorescence Lifetime Macro Imager for Biomedical Applications