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Quantum dots have unique optical properties that make them useful fluorescent probes for cellular and in vivo imaging. They have broad absorption spectra and narrow, size-dependent emission spectra. Making hydrophobic quantum dots water-soluble involves coating them with bifunctional ligands, encapsulating them in micelles or liposomes, or polymer coating. Quantum dots can be conjugated to biomolecules like avidin and used for multiplexed imaging. They have advantages over organic dyes like greater photostability and brightness. Quantum dots have been used for various cellular imaging applications as well as in vivo imaging of vasculature, receptors, and other targets.
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7 imaging
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- 2. Quantum dots astools for cellular imaging
- 3. What are quantumdots ? • • • • Crystalline fluorophores CdSe semiconductor core ZnS Shell (surface passivation) Hydrophobic crystals
- 4. What are quantumdots • Unique Spectral properties Broad absorption Narrow emission Wavelength depends on size CdSe/ZnS QD samples Annu. Rev. Anal. Chem. 2013. 6:143–62, Michalet , X. et al. Science. 2005, 307 , 538 – 44
- 5. Making hydrophobic quantumdots biocompatible • Various methods for making them watersoluble – Derivatizing surface with bifunctional ligands – Encapsulating in phospholipid micelles or liposomes – Polymer coating Gao , X. et al. Adv.Experim.Med. Biol. 2007, 620,57-73
- 6. Conjugating quantum dotsto biomolecules • Avidin or protein-G with positively charged tail conjugated to negatively charged DHLA coat of quantum dots Goldman E.R. et al.( 2002 ) JACS,124 , 6378 – 82 ; Analytical Chemistry , 74 , 841 – 7 . Avidin protein G
- 7. Quantum dots v/s otherfluorescent probes • Broader excitation spectrum and narrower gaussian emission spectrum • No spectral overlap between dots of different size – better for multiplexing Jaiswal & Simon 2004
- 8. Quantum dots formultiplexing
- 9. Quantum dots formultiplexing benign prostate gland Multiplex Immunostaining gland with a single malignant cell Malignant HRS cells To differentiate Hodgkin’s from non-Hodgkin’s lymphoma B cells T cells Liu J et al. Anal. Chem. 2010, 82, 6237–6243; Am. Chem. Soc. Nano 4:2755–65
- 10. Quantum dots v/sother fluorescent probes Photostability (quantum dots do not photobleach) 3T3 cells Scale bar 10 µm. Red: qdot 605 Conjugate Green: Alexa488 Conjugate Wu et al. Nat. Biotechnol. 2003;21(1):41-62
- 11. Quantum dots v/sother fluorescent probes • Brighter than other fluorophores Quantum dots Fluorescein Larson et al. 2003
- 12. Quantum dots andimaging In vivo visualization of capillaries Quantum dots FITC-Dextran Larson et al. 2003, Science 300:1434-1436
- 13. Quantum dots andimaging anti-α-tubulin antibody anti-Her2 antibody Cancer cell surface marker red & green Microfilaments biotinylated phalloidin Actin filaments Nuclear antigens Wu et al. Nat. Biotechnol. 2003;21(1):41-62
- 14. Quantum dots andimaging Glycine Receptors Diffusion of single Qdot-GlyRs in synaptic boutons Primary antibody ↔ secondary Antibody – biotin ↔ QD Streptavidin Dahan et al. Science. 2003, 302:442-445
- 15. Quantum dots andimaging EGF receptor EGF-QD Live imaging of receptor mediated endocytosis Lidke et al. Nat. Biotechnol. 2004, 22:198
- 16. Quantum dots andimaging 1 µm 200 nm 200 nm Single quantum dot crystals can be observed in electron micrographs
- 17. Quantum dots andimaging: FRET
- 18. Quantum dots andimaging: FRET • Quantum dots have been used in FRET • In conjunction with Texas Red • In conjunction with fluorescent quenchers Willard et al. Nat Materials. 2003, 2:575
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- 20. Advantages • • • • Specific labeling ofcells and tissues Useful for long-term imaging Useful for multi-color multiplexing Suitable for dynamic imaging of subcellular structures • May be used for FRET-based analysis
- 21. Disadvantages • Colloidal polymer-coatedquantum dots can aggregate irreversibly • Toxic in vivo • Quantum dots are bulkier than many organic fluorophores – Accessibility issues – Mobility issues • Cannot diffuse through cell membrane – Use of invasive techniques may change physiology
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- 24. Multifunctional NP forImaging 24
- 25. Imaging techniques andrelated contrast agents X-ray Iodinated contrast materials Au MRI Gadolinium-based Fe-based 19 F-based PET Radioactively labelled agents (11C, 18F)
- 26. X-ray CT CT isubiquitous in the clinical setting as. The increasing use and development of micro-CT and hybrid systems that with PET, MRI. The most investigated NPs in this field are gold NPs, since they have large absorption coefficients against the x-ray source used for CT imaging and may increase the signal-to-noise ratio of the technique. To date, different types of gold NPs have been tested in a preclinical setting as contrast agents for molecular imaging: nanospheres, nanocages, nanorods and nanoshells. Gold NPs formulations as an injectable imaging agent have been utilized to study the distribution in rodent brain ex vivo
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- 28. PET The strategy utilizedis consisting in incorporating PET emitters within the components of the NP, or entrapping them within the core. brain cancer Oku et al (2011), Int. J. Pharm. 403 :170–177
- 29. MRI MRI relies uponthe enhancement of local water proton relaxation in the presence of a contrast agent (CA). CA are compounds that catalytically shorten the relaxation times of bulk water protons. T1 (longitudinal relaxation– in simple terms, the time taken for the protons to realign with the external magnetic field) Positive CA (Gd) T2 (transverse relaxation –in simple terms, the time taken for the protons to exchange energy with other nuclei) Negative CA (Iron oxide agents )
- 30. Gd-based NP several nanotechnologicalapproaches have been devised, based on 2 ideas: -carrying many Gd chelates; -slow down the rotation of the complex Examples include liposomes micelles dendrimers fullerenes. However, this approach has not yet achieved clinical applications.
- 31. Magnetic Nanoparticles magnetic NPs(MNPs) are of considerable interest because they may behave either as contrast agents or carriers for drug delivery. Among these, the most promising and developed NP system is represented by superparamagnetic iron oxide agents 31
- 32. Types of Magnets • Ferromagneticmaterials: the magnetic moments of neighboring atoms align resulting in a net magnetic moment. • Paramagnetic materials are randomly oriented due to Brownian motion, except in the presence of external magnetic field . • Superparamagnetic Combination of paramagnetic and ferromagnetic properties. Made of nano-sized ferrous magnetic particles, but affected by Brownian Motion. They will align in the presence of an external magnetic field. B 32
- 33. The most promisingand developed NP system is represented by superparamagnetic iron oxide agents, consisting of a magnetite (Fe3O4) and/or maghemite (Fe2O3) crystalline core surrounded by a low molecular weight carbohydrate (usually dextran or carboxydextran) or polymer coat. Iron oxide NPs can be classified according to their core structure, such as Monocrystalline (MION; 10–30 nm diameter), or according to their size as ultra-small superparamagnetic (USPIO) (20–50 nm diameter), superparamagnetic (SPIO) (60–250 nm).
- 34. J Lodhia etal. Biomed Imaging Interv J 2010; 6(2):e12
- 35. Polymer Coated MagnetiteNanoparticles Dextran, silane, poly-lactic acid, PEG, dextran, chitosan, gelatin, ethylcellulose…
- 36. Formation of Nanoparticles •Solution of Dextran, FeCl3.6H2O and FeCl2.4H2O (acidic solution) – Less Dextran Larger Particles • Drip in Ammonium hydroxide (basic) at ~2oC • Stirred at 75oC for 75 min. • Purified by washing and ultra-centrifugation • Resulting Size ~ 10-20 nm • Plasma half-life: 200 min 36
- 37. Variation of Formation •Change Coating Material • Crosslinking coating material – Increases plasma half-life – Same Particle Size Lee H et al. J. AM. CHEM. SOC. 2007,129, 1273-12745
- 38. Magnetite Cationic Liposomes(MCL) Fe3O4 • Why Cationic? – Interaction between + liposome and – cell – membrane results in 10x uptake.
- 39. Formation of MCL •magnetite NP dispersed in distilled water • N-(α-trimethyl-amminoacetyl)-didodecyl-D-glutamate chloride (TMAG) Dilauroylphosphatidylcholine (DLPC) Dioleoylphosphatidyl-ethanolamine (DOPE) added to dispersion at ratio of 1:2:2 • Stirred and sonicated for 15 min • pH raised to 7.4 by NaCl and Na phosphate buffered and then sonicated DLPC DOPE
- 40. Uses of NanoMagnets • Hyperthermia – An oscillating magnetic field on nanomagnets result in local heating by (1) hysteresis, (2) frictional losses (3) Neel or Brown relaxation
- 42. Cancer Treatment • Heatingdue to magnetic field results in two possibilities Death due to overheating Increase in heat shock proteins result in anti-cancer immunity. Ito A., Honda H., Kobayashi T. Cancer Immunol Immunother Res 2006 55; 320-328 42
- 43. Delivery Magnetic nanoparticles •Magnetite nanoparticles encapsulated in liposomes – (1) Antibody conjugated (AML) – (2) Positive Surface Charge (MCL) • Sprague-Dawley rats injected with two human tumors. – Liposomes injected into 1 tumor (black) and applied Alternating Magnetic Field Ito A., Honda H., Kobayashi T. Cancer Immunol Immunother Res 2006 55; 320-328 43
- 44. Effect of Hyperthermia Treated Tumor BeforeTreatment Untreated Tumor Rectum antitumor immune response After Treatment
- 45. Uses of NanoMagnets • External Magnetic field for nanoparticle delivery – Magnetic nanoparticles loaded with drug can be directed to diseased site for Drug Delivery or MRI imaging.
- 46. Magnetic Drug DeliverySystem • Using Magnetic Nanoparticles for Drug Delivery • Widder & others developed method in late 1970s • Drug loaded magnetic nanoparticles introduced through IV or IA injection and directed with External Magnets • Requires smaller dosage because of targeting, resulting in fewer side effects 46
- 47. Magnetic Nanoparticles/Carriers M • MagnetiteCore • Starch Polymer Coating M M M • Bioavailable • Phosphate in coating for functionalization • Chemo Drug attached to Coating M Magnetite Core Starch Polymer M M • Mitoxantrone • Drug Delivered to Rabbit with Carcinoma 47
- 48. Results of DrugDelivery • External magnetic field (dark) • deliver more nanoparticles to tumor • No magnetic field (white) • most nanoparticles in non tumor regions Alexiou C et al ANTICANCER RES 27: 2019-2022 (2007) 48
- 49. Magnetic nanoparticles inmedicine They consist of a metal or metallic oxide core, encapsulated in an inorganic or a polymeric coating, that renders the particles biocompatible, stable, and may serve as a support for biomolecules. • Drug or therapeutic radionuclide is bound to a magnetic NP, introduced in the body, and then concentrated in the target area by means of a magnetic field. • Depending on the application, the particles release the drug or give rise to a local effect (hyperthermia). • Drug release can proceed by simple diffusion or take place through mechanisms requiring enzymatic activity or changes in physiological conditions (pH, osmolality, temperature, etc…).
- 50. Multifunctional Magnetic Nanoparticles • • • • Magneticnanocrystals as ultrasensitive MR contrast agents: MnFe2O4 Anticancer drugs as chemotherapeutic agents: doxorubicin, DOX Amphiphilic block copolymers as stabilizers: PLGA-PEG Antibodies to target cancer cells: anti-HER antibody (HER, herceptin) conjugated by carboxyl group on the surface of the MMPNs 50 Yang, etal. Angew. Chem. 2007, 119, 8992 –8995.
- 51. Magnetic nanoparticles The applicationof magnetic nanoparticles in cancer therapy is one of the most successful biomedical exploitations of nanotechnology. The efficacy of the particles in the treatment depends upon the specific targeting capacity of the nanoparticles to the cancer cells. Efficient, surface-engineered magnetic nanoparticles open up new possibilities for their therapeutic potential. … effective conjugation of folic acid on the surface of superparamagnetic iron oxide nanoparticles (SPION) enables their high intracellular uptake by cancer cells. Such magnetic-folate conjugate nanoparticles are stable for a long time over a wide biological pH range: additionally, such particles show remarkably low phagocytosis as verified with peritoneal macrophages.
- 52. Conclusions • Nanomagnets canbe made bioavailable by liposomal encapsulation with targeting • Nanoparticles smaller than 20 nm can be useful for local heat generation • Intracellular hyperthermia kills the cancer cell and releases heat shock proteins. These are used to target and kill other cancer cells. • Results in reduction in growth of tumor size • Nanomagnets can be used for MR Imaging in 52 vivo
- 53. MICROBUBBLES • Used withultrasound echocardiography and magnetic resonance imaging (MRI) • Diagnostic imaging - Traces blood flow and outlines images • Drug Delivery and Cancer Therapy
- 54. MICROBUBBLES • Small (1-7µm) bubbles of air (CO2, Helium) or high molecular weight gases (perfluorocarbon). • Enveloped by a shell (proteins, fatty acid esters). • Exist - For a limited time only! 4 minutes-24 hours; gases diffuse into liquid medium after use. • Size varies according to Ideal Gas Law (PV=nRT) and thickness of shell.
- 55. ultrasound • Ultrasound useshigh frequency sound waves to image internal structures • The wave reflects off different density liquids and tissues at different rates and magnitudes • It is harmless, but not very accurate
- 56. Ultrasound and Microbubbles •Air in microbubbles in the blood stream have almost 0 density and have a distinct reflection in ultrasound • The bubbles must be able to fit through all capillaries and remain stable Soft Matter, 2008, 4, 2350–2359
- 57. Shell Air or HighMolecular Weight Gases 1-7µm
- 58. Preparation of microbubbles -Homogeneization - Sonication - microfluidic T-devices
- 59. O2 microbubbles coatedwith PAAs Cationic PAA Diameter = 549.5 ± 94.7 nm PZ = 8.54±1.21 pH = 3.28 PAA-cholesterol Diameter = 491.4 ± 38.2 nm PZ = 6.22±1.17 pH = 6.50
- 60. Application of microbubbletechnology for ultrasound imaging of the heart
Editor's Notes
- #4 Shell:protects the core from oxidation, prevents the leaching of highly toxic Cd 2+ions, improves the quantum yield and the fluorescence efficiency.
- #13 (A) Fluorescent capillaries containing 1 M QDs were clearly visible through the skin at the base of the dermis (100 m deep). Excitation at 900 nm was delivered through a 20 0.95 NA water-immersion objective lens (40 mW out of the objective, average power at the focal plane unknown); the skin was stabilized by a dorsal skin clamp. Blue pseudocolor is collagen imaged via its second harmonic signal at 450 nm. Dashed line indicates position of line scan shown in (D).
- #15 Primary antibody secondary Antibody – biotin QD Streptavidin
- #36 uspio COATING: it reduces the aggregation tendency of the uncoated particles, thus improving their dispersibility and colloidal stability; protects their surface from oxidation; provides a surface for conjugation of drug molecules and targeting ligands; increases the blood circulation time by avoiding clearance by the reticuloendothelial system; makes the particles biocompatible and minimizes nonspecific interactions, thus reducing toxicity; Without coating, opsonin proteins deposit on Magnetite and mark them for removal by RES
- #37 Fe+2Fe2+3O4 = Fe3O4
- #39 DDS techniques to develop antibody-conjugated liposomes (immunoliposomes) containing magnetite nanoparticles (antibody-conjugated magnetoliposomes, AMLs). The targeting ability of AMLs mainly depends on the specificity of the antibody and the quantity and quality (including homogenous antigen expression) of the antigen on the tumor cell surface. enhanced by conferring a positive surface charge to liposomes. We have developed ‘‘magnetite cationic liposomes’’ (MCLs) with improved adsorption and accumulation properties.
- #41 Unless tumor specific, damage can be done to all cells. Intracellular hyperthermia is based on the principle that a magnetic particle can generate heat by hysteresis loss under an alternating magnetic field (AMF). In 1979, Gordon et al. A causa del fenomeno dell’isteresi magnetica, l’energia fornita al nucleo durante la fase di magnetizzazione non viene interamente restituita durante quella di smagnetizzazione, ma, ad ogni ciclo, rimane immagazzinata nel nucleo. Poi si dissipa in calore Schematic representation of Néel relaxation of nanoparticles, where the magnetic moment rotates within each particle and Brownian relaxation, where the particle rotates as a whole.
- #47 Widder and others developed magnetic micro- and nanoparticles to which cytotoxic drugs could be attached in late 1970s (1978). The drug/carrier complex is then injected into the subject either via intravenous or intra-arterial injection. High-gradient, external magnetic fields generated by rare earth permanent magnets (generally NdFeB, neodymium magnet, Neodymium, Iron & Boron) are used to guide and concentrate the drugs at target site (ie: tumor locations). Once the magnetic carrier is concentrated at the tumor or other target in vivo, the therapeutic agent is then released from the magnetic carrier, either via enzymatic activity or through changes in physiological conditions such as pH, osmolality, or temperature, leading to increased uptake of the drug by the tumor cells at the target sites.
- #48 Core-shell structure: Core = magnetic iron oxide (usually magnetite – [Fe3O4] or maghemite [gamma-Fe2O3]) Shell = generally a polymer such as silica, dextran, or PVA, or metals such as gold to which functional groups can be attached vis cross-linkers Can be synthesized using both ionic and non-ionic surfactant techniques or encapsulated within a structure such as carbon cage or ferritin protein Functionalized by attaching carboxyl groups, amines, biotin, streptavidin, antibodies, and others. A number of groups have developed techniques for the synthesis of magnetoliposomes. Core = magnetic iron oxide Shell = artificial liposome Generally used for magnetic hyperthermia (JAMES), but may be useful in drug delivery More recently, gold/cobalt nanoparticles with core-shell structure and tailorable morphology have been synthesized in the size range of 5-25 nm Produced via the rapid decomposition of organometallic precursors in the presence of surfactants that control the size and shape of the particles. Major advantage = cobalt has a magnetic moment nearly twice that of magnetite or maghemite. Another strategy for synthesis involves the precipitation of magnetic iron oxide nanoparticles within a porous polymer micro- or nanoparticle scaffold. Advantage = possible to produce particles with a relatively tight size distribution and well-defined, spherical morphology.