Biomedical Nanotechnology Lecture 2 PDF

Biomedical Nanotechnology Lecture 2 Inorganic Nanostructures: Properties and Synthesis Duan Hongwei Office: N1.3-B3-12 Office hour: Teams meeting by request 1 The Framework Introduction...

Biomedical Nanotechnology Lecture 2 Inorganic Nanostructures: Properties and Synthesis Duan Hongwei Office: N1.3-B3-12 Office hour: Teams meeting by request 1 The Framework Introduction BioMedical Nanotechnology Characterisation Nanostructure Medical Application Property Synthesis Diagnostics Therapeutics 2 Key Points: 1. Quantum size effect (semiconductor QDs) 2. Optical properties of quantum dots (QDs) 3. Surface plasmon resonance (SPR) & factors controlling the SPR of metal nanostructures 4. Properties of magnetic nanoparticles 5. Wet-chemistry for inorganic nanoparticle synthesis 6. The stabilizing mechanisms of nanoparticles 3 Colors: Visible Light Spectrum Longer wavelength Shorter wavelength Lower energy Higher energy 4 Topic 1 Semiconductor Quantum Dots (QDs) 5 Fluorescence Imaging: A Powerful Tool for Biomedicine http://www.youtube.com/watch_popup?v=DA8DvDE_nZo Traditional fluorophores:  Organic dye  Fluorescent proteins Nanoscale fluorophores:  Semiconductor quantum dots 6 Fluorescence of Organic Dyes Fluorescence is the emission of light by a substance that has absorbed light. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. The first excited Absorption singlet state (excitation): higher energy (shorter wavelength) Fluorescence (emission): lower energy (longer wavelength) Ground state 7 Fluorescence of Organic Dyes Stokes shift Absorption (excitation) Fluorescence (emission)  Stokes shift: the difference between positions of the band maxima of the excitation and emission spectra. 8 Fluorescent Dyes & Proteins Fluorescent Fluorescent Fluorescent Excitation Green Non- laser fluorescent Excitation Fluorescent protein Resource: http://www.osa-opn.org/home/gallery/ 9 Semiconductor Quantum Dots (QDs) Photograph of 10 QDs of different sizes (irradiated by 365nm UV light) Emission wavelength of QDs increases with their sizes (1-10 nm) size increase Fluorescence Spectra Transmission Electron Microscope 10 Quantum Size Effect  When size of the QD is smaller than double the Bohr radius of exciton (electron & hole), energy band gap of the QD exhibits strong quantum size confinement and becomes size- dependent. Electronic Energy Level Energy Level of QDs conduction The band gap of QDs is size-dependent and band electron decreases with increasing sizes. energy gap Smaller band gap corresponds to longer wavelength. valence hole band Small Big QDs Bulk Semiconductor 11 Quantum Size Effect Quantum Dots Space Energy Emission decrease level wavelength increase decreases electron 12 Quantum Size Effect Electronic energy level of QDs conduction band Ex Em energy gap valence band Small Big  Quantum dot emits light when electrons that were excited into the conduction return back to valence band and combine with holes.  Light that can excite smaller QDs also can excite larger QDs.  QD emission color evolves from blue, green to red when its size increases. 13 QD: Optical Properties CdSe QDs Absorption Spectra Emission Spectra Excitation Narrow & symmetrical emission Single wavelength excitation of multi-colored QDs Broad absorption profile Superior photo-stability https://www.youtube.com/watch_popup?v=SVyC8JW-Q3A&vq=medium#t=14 14 QD: Optical Properties 15 QDs: Chemical Composition 16 Organic Dye: Excitation (absorption) and Emission (Fluorescence) Non-excitation Excitation The first excited Emission singlet state Ground state Stokes shift 17 QDs vs Organic Fluorophores Excitation Emission Photo stability Dyes  Broad & unsymmetrical emission  Narrow band excitation Dye  Selective wavelength for excitation of different dyes  Poor photo-stability 18 QD vs. Organic Dye: Photo Stability Comparison of photo-stability of QDs and organic dyes: dye fluorescence quickly decays under irradiation while QD fluorescence remains stable. Nuclei: QD630 Microtubule: Alexa488 Nuclei: Alexa488 Microtubule: QD630  Advantage of QD for immunofluorescence staining: Excellent photo-stability Nat. Biotechnol. 2003, 21, 41 19 QDs vs Dyes QDs Dyes Narrow & symmetrical emission Broad & unsymmetrical emission Broad absorption profile Narrow band excitation Single wavelength excitation of Selective wavelength for excitation multi-colored QDs of different dyes Superior photo-stability Poor photo-stability 20 Size Exclusion Chromatography (SEC) Separation of different sized QDs by SEC SEC chromatogram Fluorescence spectra Elution time  Bigger QDs that emits longer wavelength fluorescence have shorter elution time than smaller QDs. 23 Quantum Dot's Learning Adventure https://www.youtube.com/watch_popup?v=6JGL7ffsBvE 24 Topic 2 Metal Nanostructures 25 The “Color” of Gold Gold coin Gold nanoparticle Gold nanorod 26 Metal Nanostructures Dietary “No adverse side-effect” Supplements “maintain a robust immune system” From brochure Antioxidant source of metal elements Resource: http://www.purestcolloids.com/ 27 Metallic Bonding & Free Electrons The free electron model is a simple model for the behavior of valence electrons in a crystal structure of a metallic solid. It is also valid for metal nanoparticles. Metallic bonding: The electron are donated to the entire structure, forming a cloud of electrons that are mobile and surround a core of cations. Metal nanoparticles consist of ion matrix and free electrons. 28 Surface Plasmon Resonance  Localized surface plasmon resonance (LSPR) is collective electron charge oscillations in metallic nanoparticles that are excited by light. J. Phys. Chem. B 2003, 107, 668 29 Surface Plasmon Resonance  When the resonance is coherent with that of the external optical field, nanoparticles exhibit strong absorption at this wavelength of the external field. Absorption is transferred into heat. 14 nm Au nanoparticles 520 nm UV-vis spectrum 30 Why are Gold Nanoparticle Dispersion RED? Au nanoparticles White 14 nm Au Light nanoparticles Red light pass 520 nm through! 31  Surface Plasmon Resonance: Size Dependence Au nanoparticles  Surface plasmon resonance of metal nanoparticles red-shifts with increasing nanoparticle sizes. Extinction (a.u.)  Uneven excitation of free electrons for bigger nanoparticles leads to the retardation effect and correspondingly the red-shift (move to longer wavelength) of the SPR. Wavelength (nm) “retardation effect” Int. Rev. Phys. Chem. 2000, 19, 409 32  Surface Plasmon Resonance: “Shape effect” Au nanorods Extinction (a.u.) Wavelength (nm)  Au nanorods exhibit both transverse and longitudinal surface plasmon resonances (along their two axes).  Their longitudinal peaks are very sensitive to their aspect ratio (L/W ratio) (larger ratio leads to longer wavelength) and can cover a wide spectral range. Acc. Chem. Res. 2008, 12, 1578 33 Surface Plasmon Resonance: Aggregation State  Surface plasmon band red-shifts upon aggregation of nanoparticles due to interparticle coupling. For 14 nm Au nanoparticles, the dispersion color experiences red-to-blue transition during aggregation, which is widely used in Au nanoparticle-based colorimetric biosensors. Single Au nanoparticles Aggregated Au nanoparticles Color 34 Topic 3 Magnetic Nanostructures 37 Permanent magnetic bar has many magnetic domains that are directing the similar direction 38 Magnetic Nanoparticles  Size-dependent magnetic property: due to surface effect (surface atoms are less ordered than the atom inside the nanoparticles), bigger nanoparticles (less surface atoms) exhibit stronger magnetic property. Magnetization Size (nm) Nat. Med. 2007, 13, 95-99. 39 Magnetic Nanoparticles  Polymerization around the aligned magnetic nanoparticles in external magnetic field leads to structural fixation of the nanoparticles to form nanochains. Magnet Chem. Mater. 2015, 3071 40 Magnetic Nanochains Random nanochain Aligned nanochain Rotating field Directional field 42 Magnetic Nanoparticles: Heating Magnetic nanoparticles generate heat under a high-frequency oscillating magnetic field (OMF) as a result of magnetic relaxation. During the OMF exposure (gray area), the nanoparticle has a much higher heating rate than the bulk solution and the temperature gradient grows with time. After the exposure, the nanoparticle temperature quickly decreases while the bulk solution slightly increased to equilibrate with the nanoparticles. ACS Nano 2014, 5199 43 Topic 4 Synthesis of Nanoparticles 44 Synthesis of Nanoparticles Synthesis Nanoparticles Surface Engineering Bio-functionalization 45 Nanoparticles & Surface coating Ligands Gold Nanoparticles Size Surface atom (%) Bulk 2 32 Surface 4 17 Nanocrystal 6 11 10 7 20 4  Nanoparticles have a significant portion of atoms on their surfaces  Chemical bonding of the surface atoms is different from bulk ones, leading to high surface energy  Surface coating ligand to direct the growth of nanoparticles and stabilize the structures through chemical bonding 46 Gold Nanoparticle Synthesis: Citrate Reduction Water-based gold nanoparticles 20nm Citrate: reducing agent & coating ligand  Citrate reduction leads to controlled synthesis of gold nanoparticles of 5-100 nm in size ( facile chemistry & excellent reproducibility) Frens, G. "Controlled nucleation for the regulation of the particle size in monodisperse gold suspensions", Nature (London), Phys. Sci. 1973, 241, 20-22. 47 Gold Nanoparticle Synthesis: Citrate Reduction 48 Nanocrystal Synthesis Chemical Process Atom Nuclei Nanocrystal  A precursor compound is either decomposed or reduced to generate zerovalent atoms (the building blocks of a metal nanocrystal).  The concentration of metal atoms increases with time as the precursor is decomposed. Once the concentration of atoms reaches the minimum nucleation concentration, the atoms start to aggregate into nuclei via self-nucleation.  The nuclei will grow into nanocrystals of increasingly larger size until an equilibrium state is reached between the atoms on the surface of the nanocrystal and the atoms in the solution. 49 Quantum Dots Synthesis Ar Monodisperse high-quality QDs Thermo Cd Precursor Couple Trioctylphosphine oxide Coordinating ligands containing Se precursor Liquid surfactant, Stirring and at http://www.youtube.com/watch_popup?v=MLJJkztIWfg&NR=1 “high T.” 250-300 J. Am. Chem. Soc. 1993, 115, 8706 degree celsius 50 Size-Controlled Synthesis of Nanocrystals  Control the number of nuclei to control the final size of nanocrystals: for a given amount of precursor, more nuclei give rise to smaller nanocrystals; less nuclei lead to bigger nanocrystals 51 CoPt3 Nanocrystal Synthesis  Temperature controlled nucleation: higher temperature leads to faster nucleation and thus more nuclei (smaller particles) 3.7nm (220 °C) 6.3nm (170 °C) 4.9nm (200 °C) 9.3nm (145 °C) J. Am. Chem. Soc. 2003, 125, 9090 52 Shape-Controlled Synthesis of Nanocrystals Angew. Chem. Int. Ed. 2006, 45, 3414 53 Gold Nanorods: the Seed Growth Method Shape controlled synthesis CTAB: Cetyl TrimethylAmmonium Bromide Preferential ligand binding directed anisotropic growth These 1-D nanostructures have end surfaces being terminated by {110} facets; the side surfaces are enclosed by {111} facets. Strong CTAB binding to the {111} faces can then prevent Au deposition to the {111} faces, resulting in anisotropic growth from the {110} facets. J. Phys. Chem. B 2001, 105, 4065; Adv. Mater. 2001, 13, 1389. 54 Topic 5 Surface Engineering 55 Why Surface Engineering? Water-solubility Colloidal stability Surface-functionality Nanoparticle-cell interaction Biodistribution and pharmacokinetics 56 Stabilizing Mechanisms for Nanoparticles in Aqueous Medium Surface Charge Polymer coating -SH binds to nanoparticle surface Key features of successful surface coatings: highly stable at high-salt medium, resistant to non-specific protein bindings, and easy bioconjugation schemes. 57 Charge-stabilized Nanoparticles Electrical double layer refers to two parallel layers of charge surrounding the object. The first layer, the surface charge (either positive or negative), comprises ions adsorbed directly onto the object due to a host of chemical interactions. The second layer is composed of ions attracted to the surface charge via the coulomb force, electrically screening the first layer. 58 Charge-stabilized Nanoparticles  Repulsion of surface charges on nanoparticle surface prevents the nanoparticles to aggregate  Increase of salt concentration leads to a thinner electrical double layer and thus reduced electrostatic repulsion (poorer colloidal stability). 59 Polymer ligands: Steric Stabilization Polymer coated nanoparticles  As the distance of separation between the particles decreases in the coagulation step, the polymer coatings begin to overlap, which is entropically unfavorable, and thus push the nanoparticles away from each other. Ultimately, it is the crowding of the polymer chains within this overlap volume that produces the steric stabilizing effect.  Polymer ligands should have good solubility in aqueous medium.  Higher graft density of polymer ligands leads to better stabilization (stronger steric stabilizing effect). 60 Surface Modification by Ligand Exchange Reaction Functionalities to be considered  Metal Nanocrystal: thiol (-SH), disulfide (-S-S-), amine (-NH2), Au-S bond is a reasonably strong one-a homolytic Au-S bond strength on the order of ca. -50 kcal/mol  Quantum Dot: thiol (-SH), amine (-NH2), phosphine (-POH),  Oxide Nanoparticles: carboxylic acid (-COOH), amine (-NH2), Ligand Exchange Reaction: The incoming ligand needs to have higher affinity with nanoparticle surface or much higher concentration. 61 Self-Assembled Monolayer Attachment group forms covalent bond with substrate – thiol is used for metal nanoparticles because of the strong metal-S bond. Assembly group - van der Waals forces help to stabilize structure - need long hydrocarbon chain (H and C). Functional head group - interacts with environment and, in this case, will allow for attachment of protein, so would either have –NH2 or -COOH for covalent attachment of protein through amine or carboxyl group. Ordered SAM 62 Surface Modification by Ligand Exchange Reaction Au nanoparticles PNIPAM Citrate gold Ligand Poly(N-isopropyl acrylamide) exchange (PNIPAM) T> LCST T< LCST  Coating of thermosensitive polymer ligands leads to thermo-responsive gold Lower critical solution temperature (LCST) nanoparticles (temperature-controlled is the critical temperature above which the reversible aggregation). solute becomes non-soluble in solution. J. Am. Chem. Soc. 2004, 126, 2656 PNIPAM has a LCST of about 32 °C. 63 Protein Corona on Nanoparticles: Non-specific Binding Nanoparticles, when exposed to biological fluids, become coated with proteins and other biomolecules to form a ‘protein corona’.  The non-specific binding of human serum albumin forms a monolayer on nanoparticle surfaces and has micromolar affinity, and this non-specific binding can be detrimental to the built-in molecular recognition in the nanoparticles. Nat. Nanotechnol. 2009, 4, 577 64 PEGylation: One Way to Reduce Non-specific Binding PEGylation: the process by which poly(ethylene glycol) chains are attached to carriers. Poly(ethylene glycol) (PEG) The ability of PEG to reduce non-specific protein binding is believed to result from the preferred (polar) gauche conformation of PEG in water, which offers two hydrogen bond acceptors in ideal distance for hydrogen bonding with water. This conformation leads to extensive hydration in aqueous environments which, along with good conformational flexibility and high chain mobility, causes a steric exclusion effect that prevents the adsorption of proteins. Nat. Rev. Drug Disc. 2003, 2, 214 65 Topic 6 Carbon Nanomaterials 68 Carbon Nanomaterials zero-dimensional: buckyball (C60) one-dimensional: carbon nanotube (CNT) Carbon Nanomaterials two-dimensional: graphene three-dimensional: graphite Graphene as the basic building block of carbon materials Nanotube Click the play button to view the animation. 69 Buckyball Buckyball (C60) was discovered in 1985 by Robert Curl, Harold Kroto and Richard Smalley. Using laser evaporation of graphite, they found Cn clusters (where n>20 and even more) of which the most common were C60 and C70. Harold Kroto Richard Smalley For the discovery of C60, they were awarded the 1996 Noble Prize in Chemistry. Buckyball (C60) has a cage-like fused-ring structure (truncated icosahedron), which resembles a soccer ball. https://www.youtube.com/watch_popup?v=040Jwg1jHpc 70 Carbon Nanotube  In 1991, Sumio Iijima discovered carbon nanotubes at NEC Fundamental Research Laboratories in Tsukuba, Japan.  Iijima’s high-resolution multi-walled carbon nanotube (MWNT) electron micrographs illustrated that the new carbon species with rounded end caps were fullerene cousins. Sumio Iijima MWNT SWNT The single-walled carbon nanotubes (SWNTs) were discovered in 1993, simultaneously by Iijima and Toshinari Ichihashi at NEC in Japan and Donald S. Bethune and others at IBM Almaden Research Center in San Jose, California. 72 Synthesis of CNTs: Chemical vapor deposition (CVD) During CVD, a substrate is prepared with a layer of metal catalyst particles, most commonly nickel, cobalt, or a combination. The diameters of the nanotubes that are to be grown are related to the size of the metal particles. Nanotubes grow at the sites of the metal catalyst; the carbon-containing gas is broken apart at the surface of the catalyst particle, and the carbon is transported to the edges of the particle, where it forms the nanotubes. The catalyst particles can stay at the tips of the growing nanotubes during the growth process, or remain at the nanotube base, depending on the adhesion between the catalyst particle and the substrate. Entangled, randomly orientated CNTs Vertically aligned CNTs Dense “dandelion-like” CNT Carbon, 2012, 50, 325 http://www.youtube.com/watch_popup?v=19nzPt62UPg&vq=medium 73 Synthesis of CNTs: Chemical vapor deposition (CVD) http://www.youtube.com/watch_popup?v=19nzPt62UPg&vq=medium 74 Graphene The Nobel Prize in Physics for 2010 In 2004, physicists at the University of Manchester and the institute for Microelectronics Technology, Chernogolovka, Russia, first isolated individual graphene planes by using adhesive tape. Graphene is one-atom-thick planar sheets of sp2-bonded Andre Geim Novoselov carbon atoms that are densely packed in a honeycomb crystal lattice. http://www.youtube.com/watch_popup?v= WEnO6AJeP7k&vq=medium#t=13 75