Isotope Labeling:
Techniques for labeling a substance with a stable or radioactive isotope. It is not used for articles involving labeled substances unless the methods of labeling are substantively discussed. Tracers that may be labeled include chemical substances, cells, or microorganisms.
JoVE General
Protease- and Acid-catalyzed Labeling Workflows Employing 18O-enriched Water
Boston Biomedical Research Institute
Stable isotope labeling workflows employing 18O-enriched water (LeO-workflows) are versatile tools for quantitative and qualitative proteomics studies. In protease-assisted (PALeO) workflows, 18O-atoms are introduced by proteolytic cleavage and carboxyl oxygen exchange reactions mediated by proteases. In the acid-catalyzed (ALeO) workflow, 18O-atoms are introduced by carboxyl oxygen exchange at low pH.
JoVE General
Concentration of Metabolites from Low-density Planktonic Communities for Environmental Metabolomics using Nuclear Magnetic Resonance Spectroscopy
1Biosphere Oriented Biology Research Unit, RIKEN Advanced Science Institute, 2Graduate School of Nanobioscience, Yokohama City University, 3Advanced NMR Metabomics Research Team, RIKEN Plant Science Center, 4Graduate School of Bioagricultural Science, Nagoya University
A method for metabolite extraction from microbial planktonic communities is presented. Whole community sampling is achieved by filtration onto specially prepared filters. After lyophilization, aqueous-soluble metabolites are extracted. This approach allows for application of environmental metabolomics to trans-omics investigations of natural or experimental microbial communities.
JoVE General
Stable Isotopic Profiling of Intermediary Metabolic Flux in Developing and Adult Stage Caenorhabditis elegans
1Department of Pediatrics, The Children's Hospital of Philadelphia, 2Department of Pediatrics, University of Pennsylvania
Stable isotopic profiling by gas chromatography mass spectrometric analysis of intermediary metabolic flux is described in the nematode, Caenorhabditis elegans. Methods are detailed for assessing isotopic enrichment in carbon dioxide, organic acids, and amino acids following isotope exposure either during development on agar plates or during adulthood in liquid culture.
JoVE Chemistry
Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies
1Structural Biology Division, The Walter and Eliza Hall Institute of Medical Research, 2The University of Melbourne
Biophysical and biochemical studies of interactions among membrane-embedded protein domains face many technical challenges, the first of which is obtaining appropriate study material. This article describes a protocol for producing and purifying disulfide-stabilized transmembrane peptide complexes that are suitable for structural analysis by solution nuclear magnetic resonance (NMR) and other analytical applications.
JoVE General
Identification of protein complexes with quantitative proteomics in S. cerevisiae
1Department of Cellular and Physiological Sciences, University of British Columbia - UBC, 2Department of Biochemistry and Molecular Biology, University of British Columbia - UBC
Here we describe a new quantitative proteomics technique for identifying protein complexes in Saccharomyces cerevisiae. In this study, we have used the SILAC method together with affinity purification followed by tandem mass spectrometry to identify with high specificity the binding partners of an ER protein, Scs2p.
JoVE Immunology and Infection
Preparation and Use of HIV-1 Infected Primary CD4+ T-Cells as Target Cells in Natural Killer Cell Cytotoxic Assays
Department of Immunology and Microbiology, Rush University Medical Center
Cytotoxicity assays to measure natural killer cell lytic responses to HIV-infected cells is limited by the purity of the target cells. We demonstrate here the isolation of a highly purified population of HIV-1 infected primary T-cell blasts by taking advantage of HIV-1 s ability to down-modulate CD4.
JoVE General
A Protocol for the Identification of Protein-protein Interactions Based on 15N Metabolic Labeling, Immunoprecipitation, Quantitative Mass Spectrometry and Affinity Modulation
1Max Planck Institute of Molecular Plant Physiology, 2University of Kaiserslautern
We present a variation of the QUICK (QUantitative Immunoprecipitation Combined with Knockdown) approach that was introduced previously to distinguish between true and false protein-protein interactions. Our approach is based on 15N metabolic labeling, the modulation of affinities of protein-protein interactions by the presence/absence of ATP, immunoprecipitation, and quantitative mass spectrometry.
JoVE General
Metabolic Pathway Confirmation and Discovery Through 13C-labeling of Proteinogenic Amino Acids
1Department of Energy, Environmental and Chemical Engineering, Washington University, 2Department of Biology, Washington University, 3Department of Energy, Environmental and Chemical Engineering and Department of Biology, Washington University
13C-isotope labeling is a useful technique for determining the cell central metabolism for various types of microorganisms. After cells have been cultured with a specific labeled substrate, GC-MS measurement can reveal functional metabolic pathways based on unique labeling patterns in proteinogenic amino acids.
JoVE General
Biochemical and High Throughput Microscopic Assessment of Fat Mass in Caenorhabditis Elegans
1Center for Human Genetic Research and Department of Medicine, Massachusetts General Hospital and Harvard Medical School, 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology
We present robust biochemical and microscopic methods for studying Caenorhabditis elegans lipid stores. A rapid, simple, fixing-staining procedure for fluorescent lipid droplet imaging leverages the spectral properties of the lipophilic dye Nile red. We then present biochemical measurement of triglycerides and phospholipids using solid phase extraction and gas chromatography-mass spectrometry.
JoVE General
Genome-wide Screen for miRNA Targets Using the MISSION Target ID Library
The Target ID Library is a plasmid-based, genome-wide collection of cloned cDNA used to identify miRNA targets. Here we demonstrate its use and application.
JoVE General
Linking Predation Risk, Herbivore Physiological Stress and Microbial Decomposition of Plant Litter
1School of Forestry and Environmental Studies, Yale University, 2Department of Biological Sciences, Virginia Tech, 3Department of Ecology, Evolution and Behavior, The Hebrew University of Jerusalem
We present methods to evaluate how predation risk can alter the chemical quality of herbivore prey by inducing dietary changes to meet demands of heightened stress, and how the decomposition of carcasses from these stressed herbivores slows subsequent plant litter decomposition by soil microbes.
JoVE General
Profiling Thiol Redox Proteome Using Isotope Tagging Mass Spectrometry
1Plant Molecular and Cellular Biology Program, University of Florida, 2Department of Biology, University of Florida, 3Interdisciplinary Center for Biotechnology Research, University of Florida, 4Genetics Institute, University of Florida
Reactive oxygen species level is elevated when cells encounter stress conditions. Here we show the example of 3'-3' diaminobenzidine staining as well as cysTMT labeling and mass spectrometry to profile the redox proteome in Pseudomonas syringae treated tomato leaves.
JoVE General
Isolation of Translating Ribosomes Containing Peptidyl-tRNAs for Functional and Structural Analyses
1Department of Biological Sciences, University of Alabama Huntsville, 2Department of Biology, Stanford University
A major impediment to biochemical analyses of ribosomes containing nascent peptidyl-tRNAs has been the presence of other ribosomes in the same samples, ribosomes not involved in the translation of the specific mRNA sequence being analyzed. We developed a simple methodology to purify, exclusively, the ribosomes containing the nascent peptidyl-tRNA of interest.
JoVE General
Quantification of Proteins Using Peptide Immunoaffinity Enrichment Coupled with Mass Spectrometry
1Clinical Research Division, Fred Hutchinson Cancer Research Center - FHCRC, 2Department of Biochemistry and Microbiology, University of Victoria, 3Broad Institute of MIT and Harvard, 4Genome BC Proteomics Centre, University of Victoria, 5Plasma Proteome Institute
Stable Isotope Standards and Capture by Anti-Peptide Antibodies (SISCAPA) couples affinity enrichment of peptides with stable isotope dilution mass spectrometry (MRM-MS) to provide quantitative measurement of peptides as surrogates for their respective proteins. Here we describe the protocol using magnetic particles in a partially automated format.
JoVE General
GC-based Detection of Aldononitrile Acetate Derivatized Glucosamine and Muramic Acid for Microbial Residue Determination in Soil
1DOE-Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, 2Department of Soil Science, University of Wisconsin, Madison, 3Department of Soil and Water Science, University of Florida
We describe a method protocol for the GC-based analysis of the aldonitrile acetate derivatives of glucosamine and muramic acid extracted from soil. For elucidation of the chemical mechanism, we also present a strategy to confirm the structure of the derivative and the ion fragments formed upon electron ionization.
JoVE Bioengineering
Mass Cytometry: Protocol for Daily Tuning and Running Cell Samples on a CyTOF Mass Cytometer
The steps necessary for daily tuning and optimization of the performance of a CyTOF mass cytometer are described. Comments on optimal sample preparation and flow rate are discussed
JoVE Clinical and Translational Medicine
Assessment of Gastric Emptying in Non-obese Diabetic Mice Using a [13C]-octanoic Acid Breath Test
Enteric Neuroscience Program, Department of Physiology and Biomedical Engineering, Mayo Clinic
Determination of gastric emptying with a non-invasive [13C]-octanoic acid breath test for tracking gastroparesis in female NOD LtJ mice.
JoVE General
Mechanical Stimulation of Chondrocyte-agarose Hydrogels
1Department of Mechanical and Materials Engineering, Queen's University, 2Department of Chemical Engineering, Queen's University
The biosynthesis of cartilaginous extracellular matrix by chondrocytes can be affected by application of mechanical stimuli. This method describes the technique of applying dynamic compressive strains to chondrocytes encapsulated in 3D constructs and the evaluation of induced changes in chondrocyte metabolism.
JoVE General
DNA Stable-Isotope Probing (DNA-SIP)
Department of Biology, University of Waterloo
DNA stable-isotope probing is a cultivation-independent method to identify and characterize active communities of microorganisms that are capable of utilizing specific substrates. Assimilation of substrate enriched in heavy isotope leads to incorporation of labelled atoms into microbial biomass. Density gradient ultracentrifugation retrieves labelled DNA for downstream molecular analyses.
JoVE Chemistry
Large Scale Non-targeted Metabolomic Profiling of Serum by Ultra Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS)
Proteomics and Metabolomics Facility, Colorado State University
Non-targeted metabolite profiling by ultra performance liquid chromatography coupled with mass spectrometry (UPLC-MS) is a powerful technique to investigate metabolism. This article outlines a typical workflow utilized for non-targeted metabolite profiling of serum including sample organization and preparation, data acquisition, data analysis, quality control, and metabolite identification.
JoVE General
A High-throughput Method for Measurement of Glomerular Filtration Rate in Conscious Mice
1Division of Nephrology-Hypertension, Department of Medicine, University of California, San Diego, 2San Diego VA Healthcare System
Measurement of glomerular filtration rate (GFR) is the gold standard for kidney function assessment. Here we describe a high-throughput method which allows the determination of GFR in conscious mice by using a single bolus injection, determination of fluorescein isothiocyanate (FITC)-inulin in plasma and calculation of GFR by a two-phase exponential decay model.
JoVE General
Preparation, Purification, and Characterization of Lanthanide Complexes for Use as Contrast Agents for Magnetic Resonance Imaging
Department of Chemistry, Wayne State University
We demonstrate the metalation, purification, and characterization of lanthanide complexes. The complexes described here can be conjugated to macromolecules to enable tracking of these molecules using magnetic resonance imaging.
JoVE Applied Physics
Atom Probe Tomography Studies on the Cu(In,Ga)Se2 Grain Boundaries
1Department of Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, 2Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg ( ZSW )
In this work, we describe the use of the atom-probe tomography technique for studying the grain boundaries of the absorber layer in a CIGS solar cell. A novel approach to prepare the atom probe tips containing the desired grain boundary with a known structure is also presented here.
JoVE General
Induction and Monitoring of Adoptive Delayed-Type Hypersensitivity in Rats
Department of Physiology and Biophysics, University of California, Irvine (UCI)
Delayed type hypersensitivity (DTH) is an inflammatory reaction mediated by CCR7- effector memory T (TEM) lymphocytes. Here we demonstrate how to activate antigen-specific TEM cells, induce adoptive DTH in Lewis rats and monitor the inflammatory response.
JoVE General
A Lectin HPLC Method to Enrich Selectively-glycosylated Peptides from Complex Biological Samples
1Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco - UCSF, 2Buck Institute for Age Research, 3Department of Chemistry, Purdue University
Lectin-conjugated POROS beads were employed for HPLC. Glycopeptide standards served as positive and negative controls. MARS-14 depleted, trypsin-digested human plasma was chromatographed and flow-through (FT) and bound fractions collected for ESI-LC-MS/MS analyses. Glycopeptides were enriched in the bound fraction as compared to FT.
JoVE General
Quantitative Phosphoproteomics in Fatty Acid Stimulated Saccharomyces cerevisiae
Description of a quantitative phosphorylation procedure using cryolysis, urea solubilziation, HILIC fractionation and IMAC enrichment of phosphorylated peptides.
JoVE General
One-step Metabolomics: Carbohydrates, Organic and Amino Acids Quantified in a Single Procedure
The urease method of sample preparation for GC/MS analysis of intermediary metabolites is presented by its inventor. The method allows one-step follow-up of newborn screening for inborn errors by tandem mass spectrometry by quantifying carbohydrates, organic and amino acids all in a single process.
JoVE Clinical and Translational Medicine
Assessment of Cardiac Function and Energetics in Isolated Mouse Hearts Using 31P NMR Spectroscopy
Department of Anesthesiology & Pain Medicine, University of Washington School of Medicine
Langendorff-mode isolated heart perfusion, in conjunction with 31P NMR spectroscopy, combines the fields of biochemistry and physiology into one experiment. The protocol allows for the dynamic measurement of high energy phosphate content and turnover in the heart while concurrently monitoring physiologic function. When performed correctly, this is a valuable technique in the assessment of cardiac energetics.
JoVE General
Synthesis of Nine-atom Deltahedral Zintl Ions of Germanium and their Functionalization with Organic Groups
Department of Chemistry and Biochemistry, University of Notre Dame
We present the high-temperature synthesis of intermetallic precursors K4Ge9, their dissolution in ethylenediamine to form Ge94- deltahedral Zintl ions, and the reaction of the clusters with alkynes to form organo-Zintl ions. The latter are characterized by electrospray mass spectrometry in solutions and by single-crystal X-ray diffraction in the solid state.
JoVE General
Assaying the Kinase Activity of LRRK2 in vitro
Department of Molecular Neuroscience, UCL Institute of Neurology
Leucine Rich Repeat Kinase 2 is a large multidomain kinase, mutations in which are the most common genetic cause of Parkinson's disease. Analysis of the kinase activity of this protein has proven to be a crucial tool in understanding the biology and dysfunction of this protein. In this paper, in vitro assaying of the kinase activity of LRRK2 and a selection of its mutants is described, providing an experimental system to examine phosphorylation of putative substrates and potential dysfunction of LRRK2 in disease.
JoVE General
Application of MassSQUIRM for Quantitative Measurements of Lysine Demethylase Activity
Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences
We present a method for using MALDI mass spectrometry and reductive methylation chemistry to quantify changes in lysine methylation.
JoVE General
Functional Imaging of Brown Fat in Mice with 18F-FDG micro-PET/CT
1Department of Translational Imaging, The Methodist Hospital Research Institute, Houston, 2Diabetes Research Center, The Methodist Hospital Research Institute, Houston
A method of functional imaging of mouse brown adipose tissue (BAT) is described in which cold-stimulated uptake of 18F-Fluorodeoxyglucose (FDG) in BAT is non-invasively assessed with a standardized micro-PET/CT protocol. This method is robust and sensitive to detect differences in BAT activities in mouse models.
JoVE Clinical and Translational Medicine
Hyperinsulinemic-Euglycemic Clamp in the Conscious Rat
1Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Calgary, 2Faculty of Kinesiology, University of Calgary
The hyperinsulinemic-euglycemic clamp is the "gold standard" for the assessment of insulin action. Insulin is infused at a constant rate stimulating glucose uptake. The amount of exogenous glucose infused to counter this drop is indicative of insulin sensitivity. Here the procedure is performed on a conscious, unrestrained rat.
JoVE Bioengineering
Cellular Lipid Extraction for Targeted Stable Isotope Dilution Liquid Chromatography-Mass Spectrometry Analysis
1Centers for Cancer Pharmacology and Excellence in Environmental Toxicology, University of Pennsylvania, 2Department of Pharmacology, University of Pennsylvania
This protocol will demonstrate the extraction and analysis of free and esterified bioactive fatty acids from cells. Fatty acids are accurately quantified using stable isotope dilution, chiral liquid chromatography, electron capture atmospheric chemical ionization multiple reaction monitoring mass spectrometry (SID-LC-ECAPCI-MRM/MS).
JoVE General
Bacterial Gene Expression Analysis Using Microarrays
Department of Environmental Toxicology, University of California Santa Cruz - UCSC
JoVE Bioengineering
Biomolecular Detection employing the Interferometric Reflectance Imaging Sensor (IRIS)
1Department of Electrical and Computer Engineering, Boston University, 2Department of Biomedical Engineering, Boston University, 3Center for Advanced Genomics Technology, Boston University, 4Department of Medicine, Section of Infectious Diseases, Boston University School of Medicine, 5Department of Microbiology, Boston University School of Medicine, 6CNR (National Research Council), Istituto di Chimica del Riconoscimento Molecolare
Quantitative, high-throughput, real-time, and label-free biomolecular detection (DNA, protein, etc.) on SiO2 surfaces can be achieved using a simple interferometric technique which relies on LED illumination, minimal optical components, and a camera. The Interferometric Reflectance Imaging Sensor (IRIS) is inexpensive, simple to use, and amenable to microarray formats.
JoVE General
Microwave-assisted One-pot Synthesis of N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB)
1Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California at Los Angeles, 2Crump Institute for Molecular Imaging, David Geffen School of Medicine, University of California at Los Angeles, 3California NanoSystems Institute, University of California at Los Angeles, 4Nuclear Medicine, PET Center, Shanghai Medical Collegea, Fudan University, 5Electronics and Information Engineering, College of Electronics and Information Engineering, Wuhan Textile University
A facile, one-pot synthesis of N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) was developed based on a non-aqueous, three-step radiochemical process. Using microwave heating, the entire procedure can be completed in less than 30 min, or 60 min with further purification by preparative HPLC. The decay-corrected radiochemical yields (RCYs) were 35-5% (n > 30).
JoVE Clinical and Translational Medicine
Labeling Stem Cells with Ferumoxytol, an FDA-Approved Iron Oxide Nanoparticle
1Department of Radiology, Molecular Imaging Program at Stanford (MIPS), 2Stanford School of Medicine, Stanford University
We describe a technique for labeling and tracking stem cells with FDA-approved, superparamagnetic iron oxide (SPIO), ferumoxytol (Feraheme). This cellular imaging technique that utilizes magnetic resonance (MR) imaging for visualization, is readily accessible for long-term monitoring and diagnosis of successful or unsuccessful stem cell engraftments in patients.
JoVE General
Selective Labelling of Cell-surface Proteins using CyDye DIGE Fluor Minimal Dyes
Research and Development, GE Healthcare Bio-Sciences AB
A simple and specific method was demonstrated for fluorescent labeling and enhanced detection of cell surface proteins without a fractionation step. Differential abundance in cell surface proteins was analyzed using two-dimensional (2-D) electrophoresis and Ettan™ DIGE technology.
JoVE General
Performing Custom MicroRNA Microarray Experiments
1Department of Pharmacology, University of Minnesota, 2Masonic Cancer Center, University of Minnesota
A simple procedure of performing custom microRNA microarray experiments is described. The steps include isolating RNA, labeling RNA and reference DNA, hybridizing the samples to microarrays, scanning the microarrays, quantifying and analyzing hybridization signals.
JoVE General
Purification of Progenitors from Skeletal Muscle
The Biomedical Research Centre, University of British Columbia
Method for the enzymatic dissociation, surface labeling and purification by flow cytometry of fibro/adipogenic and myogenic progenitors from murine skeletal muscle.
JoVE General
Combining QD-FRET and Microfluidics to Monitor DNA Nanocomplex Self-Assembly in Real-Time
1Mechanical Engineering, Johns Hopkins University, 2Biomedical Engineering, Duke University, 3Biomedical Engineering, Johns Hopkins University
We present a novel and powerful integration of nanophotonics (QD-FRET) and microfluidics to investigate the formation of polyelectrolyte polyplexes, which is expected to provide better control and synthesis of uniform and customizable polyplexes for future nucleic acid-based therapeutics.
JoVE Neuroscience
DiOLISTIC Labeling of Neurons from Rodent and Non-human Primate Brain Slices
1Section on Neuronal Structure, Laboratory for Integrative Neuroscience, NIAAA, NIH, 2Department Physiology and Pharmacology, Wake Forest University Health Sciences, 3Oregon National Primate Research Center, Division of Neuroscience, Oregon Health and Science University
We demonstrate the use of the gene gun to introduce fluorescent dyes, such as DiI, into neurons in brain slices from rodents and non-human primates of different ages. In this particular case, we use adult mice (3-6 months old) and adult cynomologus monkeys (9-15 years old). This technique, originally described by the laboratory of Dr. Lichtman (Gan et al., 2000), is well suited for the study of dendritic branching and dendritic spine morphology and can be combined with traditional immunostaining, if detergents are kept at a low concentration.
JoVE General
ReAsH/FlAsH Labeling and Image Analysis of Tetracysteine Sensor Proteins in Cells
The biarsenical dyes FlAsH and ReAsH bind specifically to tetracysteine motifs in proteins and can selectively label proteins in live cells. Recently this labeling strategy has been used to develop sensors for different protein conformations or oligomeric states. We describe the labeling approach and methods to quantitatively analyze binding.
JoVE General
Direct Analysis of Single Cells by Mass Spectrometry at Atmospheric Pressure
Department of Chemistry, George Washington University
Single cell analysis is performed by mass spectrometry on plant and animal cells at atmospheric pressure by using a sharpened optical fiber to sample the cells for laser ablation electrospray ionization (LAESI) mass spectrometry.
JoVE General
Amide Hydrogen/Deuterium Exchange & MALDI-TOF Mass Spectrometry Analysis of Pak2 Activation
1Department of Chemistry, Tunghai University, 2Department of Biochemistry, University of California, Riverside
MALDI-TOF mass spectrometry was successfully utilized to monitor the amide hydrogen/deuterium exchange in protein kinase Pak2 activation.
JoVE General
Measuring Cation Transport by Na,K- and H,K-ATPase in Xenopus Oocytes by Atomic Absorption Spectrophotometry: An Alternative to Radioisotope Assays
1Institute of Chemistry, Technical University of Berlin, 2The Vollum Institute, Oregon Health & Science University
We describe a method to quantify the activity of K+-countertransporting P-type ATPases by heterologous expression of the enzymes in Xenopus oocytes and measuring Rb+ or Li+ uptake into individual cells by atomic absorption spectrophotometry. The method is a sensitive and safe alternative to radioisotope flux experiments facilitating complex kinetic studies.
JoVE Bioengineering
Monitoring the Reductive and Oxidative Half-Reactions of a Flavin-Dependent Monooxygenase using Stopped-Flow Spectrophotometry
Department of Biochemistry, Virginia Polytechnic Institute and State University
We describe the use of a stopped-flow instrument to investigate both the reductive and oxidative half-reactions of Aspergillus fumigatus siderophore A (SidA), a flavin-dependent monooxygenase. We then show the spectra corresponding to the species in the reaction of SidA and we calculate the rate constants for their formation.
JoVE General
In vitro Labeling of Human Embryonic Stem Cells for Magnetic Resonance Imaging
Division of Cardiovascular Medicine, Stanford University
In this video, we are showing how to label human embryonic stem cells (hESC) with manganese chloride (MnCl2) which can enter cells via voltage-gated calcium channels when the cells are biologically active. Additionally, we show the use of MnCl2 as cellular MRI contrast agent to determine the in vitro viability of hESC.
JoVE General
Labeling hESCs and hMSCs with Iron Oxide Nanoparticles for Non-Invasive in vivo Tracking with MR Imaging
For the evaluation of new stem cell therapies it is important to non-invasively track the injected cells in vivo. This video will show you how to label human mesenchymal and embryonic stem cells with iron oxide based contrast agents in vivo for subsequent MR imaging in vivo.
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