Présentation PowerPoint

					PhD Course
TOPICS IN (NANO)
BIOTECHNOLOGY
Nanoscale Imaging
and Nanoparticles
    January 15th, 2007
                 Nanoscale Imaging

•   SEM
•   TEM
•   Scanning Probe Microscopy
     •   Scanning tunnelling microscopy
     •   Atomic force microscopy
     •   Others
                     Field Ion Microscope
• First instrument providing images of atoms.

• Principle of operation is field ionisation (closely
  related to field emission).

• An imaging gas is introduced, these gas atoms
  approach the emitter, hop about until they are
  accommodated to the emitter temperature and are
  then ionised in the high-field regions above
  protruding atoms.

• These ionised atoms then fly along the field
  lines and produce spots on the fluorescent screen
  corresponding to the protruding emitter atom.
                        Field Ion Microscope




FEM & FIM are only useful for samples which can be formed into
very sharp tips.
Electron Source (Themionic GUN)
http://idol.union.edu/~malekis/ESC24/Seyffie's%20Pages/I
maging/Imaging.htm
Transmission Electron Microscope
  • Specimens for examination under the transmission
    electron microscope (TEM) must be specially
    prepared to a thickness that permits the passage of
    electrons (50-500 nm). As the wavelength of
    electrons is much smaller than that of light, the
    resolution attainable in TEM images is many orders
    of magnitude better than that of a light microscope.
    Transmission electron microscopes can reveal the
    finest internal details of a cell.

  • For biological samples, cell structure and morphology
    is commonly determined whilst the localisation of
    antigens or other specific components within cells is
    readily undertaken using specialised preparative
    techniques.

  • Atomic resolution possible
Transmission Electron Microscope
Transmission Electron Microscopy
             Paramyxovirus                  Flu Virus




                             Herpes Virus
          Collagen Fibres
  Scanning Electron Microscope
• By scanning an electron beam across a
  specimen and collecting electrons emitted
  from the irradiated spot we can obtain
  topographical and chemical information on
  materials from the macroscopic scale to very
  high magnifications with great depth of field in
  focus.
• Resolution ~1 nm.
Scanning Electron Microscope
SEM vs TEM
  Scanning Electron Microscopy
                              Hibiscus Pollen



                                                Beetles Skin


Holm Oak Leaf




                            Penicillin Spores




        Mosquito Antennae
Scanning Probe Microscopy
• Scanning Tunnelling Microscopy
• Atomic Force Microscopy
• Others
     Scanning Probe Microscopes
• SPMs are a family
  of instruments
  used for studying
  properties of
  materials from the
  atomic to the
  micron level.
Scanning Tunnelling Microscopy
• Invented 1981 (Binnig & Rohrer)
• Use sharpened, conducting tip with a bias voltage
  applied between the tip and the sample.
• Within ~1 nm of the sample, electrons tunnel
  between the tip and the sample (direction depending
  on the sign of the bias voltage).

• This tunnelling current varies exponentially with the
  tip-to-sample spacing.

• Tip and sample must be conductors or
  semiconductors (cannot image insulating materials).

• Measures a surface of constant tunnelling probability
  (not the physical topography!)
Scanning Tunnelling Microscopy




http://www.iap.tuwien.ac.at/www/surface/STM_Gallery/stm_
animated.gif
Scanning Tunnelling Microscopy




                    Sub-angstrom
                    vertical &
                    atomic lateral
                    resolution.
Scanning Tunnelling Microscopy
 Imaging Modes

 • Constant Height
    – Fast
    – Only useful for smooth
      surfaces


 • Constant Current
    – Slower
    – Good for irregular
      surfaces
Scanning Tunnelling Microscopy
STM Images
       Atomic Force Microscopy
• An AFM probes the surface of a sample with a sharp tip.
  Tip located at the free end of cantilever that is 100-200
  m long.

• Forces between the tip and cantilever cause the
  cantilever to bend and/or twist.

• This deflection is measured as the tip is scanned over
  the surface, providing a map of the surface topography.

• AFMs can be used to study insulators and conductors.

• AFMs can be operated in air, vacuum, and in liquids.
  Biological measurements, in particular, are often carried
  out in vitro in biological fluids.
         Atomic Force Microscopy
 Common detection schemes

 • Optical lever
 • Optical interference
 • Piezoelectric effect
 •…




0.1 mm
                Atomic Force Microscopy
          Interaction Forces
          • Van der Waals
          • Contact mode
              – Close
              – Repulsive
          • Non-contact mode
              – 1’s – 10’s of nm tip
                - sample
                separation
              – Attractive


http://www.cookandka
ye.co.uk/products/cfm.
                                  F = 0 @ ~0.2nm (length of chemical bond)
html
 Contact (Repulsive) Mode AFM
• AFM tip makes soft physical contact with
  the sample.

• Contact force causes the cantilever to
  bend to accommodate changes in
  topography.

• Cantilever spring constant less than
  effective spring constant holding atoms
  together in sample.

• F ~ 10-7 – 10-6 N
    Non-Contact (Attractive) Mode
• Vibrating stiff cantilever (100 – 400 Hz)
• Amplitude 1’s – 10’s nm
• Spacing 1’s – 10’s nm
• Total force ~10-12 N
• Detect changes in frequency or amplitude of the
  cantilever caused by changes in the force
  gradient (slope of force-distance curve).
• Height resolution better than 0.1nm
• Good for soft and/or elastic samples
• No contamination of sample by tip
  Contact vs Non-Contact Mode
Comparison
• Non-Contact
  – Low damage
  – Less sensitive to fine
    topographical detail

• Contact
  – Can damage soft samples
    through lateral forces
    (dragging material)
Contact Mode AFM Images




                  300 nm



    150150 m2
                       Tapping Mode AFM
• Similar to non-contact
  mode, but at bottom of
  travel the tip just ‘taps’ the
  sample surface

• Oscillation amplitude is
  monitored

• Eliminates lateral forces
  (friction /drag)

• Excellent for soft samples
  (e.g. biological samples, LB
  films, etc.)

• Tapping Mode overcomes
  problems associated with
  friction, adhesion, and
  electrostatic forces
         AFM in the Life Sciences
• Fundamental Challenges of Microscopy in
  Biology:
   – to preserve the specimen accurately in the native state
   – to achieve sufficient resolution to learn something
     useful about the structure/function of the specimen

• AFM is a breakthrough technology that allows
  three-dimensional imaging and measurement of
  unstained and uncoated structures in air or fluid
  from molecular to micron scales
   – scanners can now be immersed in liquids without
     damage, allowing direct examination of samples in
     biological fluids, water, or fixation media such as
     glutaraldehyde or ethanol
          AFM in the Life Sciences
• In addition to topographic imaging, the AFM can be
  used simultaneously to measure forces on active
  biological specimens, offering insight into cellular
  and even molecular dynamics.

   – Countless biological processes - muscle contraction, cell
     motility, DNA replication, protein synthesis, drug-receptor
     interactions, and many others - are largely governed by
     intermolecular forces. And with its sensitivity at the
     piconewton-level, the AFM is an excellent tool for probing
     such interactions.

• There is increasing use of AFM probes that have
  been chemically tailored to sense a specific
  biological reaction or interaction (e.g. binding forces
  between individual ligand-receptor pairs, cell
  adhesion, antibody or DNA-based assays).
Tapping Mode AFM in Biology
  E-coli




           erythrocyles
      Tapping Mode AFM in Biology




       Successive tapping mode images under liquid of living
             endothelial cells (scan size 70 microns)




Collagen fibres      Human Bone                           Dynamics of Protein Adsorption
      (collagen fibers & hydroxyapatite crystals)   (lysozyme on a new contact lens over time)



http://virtual.itg.uiuc.edu/training/AFM_tutorial/
      Lateral Force Microscopy
• LFM measures the lateral deflections
  (twisting) of the cantilever parallel to the
  plane of the sample surface
• Useful for imaging e.g. composition
  variations not associated with topography,
  and for separating topographic and
  composition variations.
• Also sensitive to changes in the surface
  slope.
• Usually collect both AFM and LFM images
  simultaneously.
Lateral Force Microscopy
                           LFM Images
 scan direction                 scan direction




         1 m                          1m



step



  22 m2         0.40.4 m2          0.40.4 m2
   NANOPARTICLES AND
NANOPARTICLE APPLICATIONS
                                Overview
• Definition and Significance
• Synthesis and Characterization
• Stabilization
• Ordering
• Optical Properties
• Magnetic Properties
• Catalysis
                                          Definitions
Nanoparticle - Particle with 1 dimension in the 10-100 nm size
range.
Colloid - Particle with dimensions in the 1 nm – 1 mm size
range.
Quantum Dot - Particle with all 3 dimensions in the 1-10 nm
size range.
Latex - Aqueous suspension of polymer particles.
Natural - Contains Protein Impurities; May Cause Allergies
Synthetic - Made via Emulsion Polymerization



                  Significance
   The size of Nanoparticles leads to unique characteristics.
Metallic Nanoparticle Synthesis
M+      +            Reductant                           Nanoparticle


            M+            M+
      M+         +        +    +       ne-
              M       M                                        M

                     M+



        M = Au, Pt, Ag, Pd, Co, Fe, etc.
        Reductant = Citrate, Borohydride,
        Alcohols

     Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM.
                                   Control Factors
Average Size
      Reductant Concentration
      Stirring Rate
      Temperature
Size Distribution
      Rate of Reductant Addition
      Stirring Rate
      Fresh Filtered Solutions
Stabilization
      Solution Composition
        Functionalized Reductions
   M+                                                                       Functionalized
                    +   Reductant
Surfactant                                                                  Nanoparticle
                                            X
                        X




                X
                                                                X




                                Y       Y
                                                    Y
                        Y                                               X
        X                                               Y
                        Y
                                                        Y
                            Y
                                                Y
                                    Y

                                                                    X
            X




                                                            X



                                    X


    Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.
                    Bimetallic Nanoparticle
Core-Shell

              M1+ +                                 M1
              Reductant

  M1      +   M2+ +                                  M1           M2
              Reductant

Mixed Alloy

       M1 + + M 2 + +
       Reductant

       Toshima, N.; Yonezawa, T. New Journal of Chemistry 1998,
       1179-1201.
Alloyed Metal Nano Particles



• Solid-solution alloyed metallic
nano particles can be attained
through simultaneous thermal
decomposition

• Core-shell alloyed nano particles
are produced by a stepwise
reduction process where each
successive step uses larger
diameter water droplet to yield the
alloyed core-shell particles
          Semiconductor nanoparticles
                            (Q-dots)
R         Se       Se       R
  N    C              C
R C Se d           Se N     R
                    200º        TOP/TOP
                      C         O




                                 O
                                 P
                                    CdSe O
                                         P
                                         P
                                     OP
                                         O



    Nigel L. Pickett et al. The Chemical Record 2001, 1, 467-479
Micellar Encapsulation
       Synthesis of Single Metal MNP
        The Reduction of Metal Salts

• Size control: conducting
the reaction in a confined
reactor
• Nano confined reactor
such as water-in-oil or oil-
in-water micro-emulsion
system
• Size of confined space
can be defined by varying
amount of both surfactant
and solvent
• Successful examples
included Fe, Ni and Co
particles
                          Organic Nanoparticles

                                          Dieter Horn et al.
                                          Angew. Chem. Int.
                                          Ed
Organic compound       Water +
                                          2001, 40, 4330-
+ Lipophilic solvent Stabilizer
                                          4361


      Emulsification                    Hydrosol of organic
                                        compound



                           Separation
                           of solvent
Organic Nanoparticles
              Polymer Nanoparticle Synthesis
                      X       X
                                  X       X   X
                                                      X
                                                              Micelle
              X
                                                          X   formed from
          X                                                   emulsifier
                                                                  X

      X

                                                                          X
  X

  X                                                                       X


  X                           Monomer                                         X


      X                                                                       X
                                                                                    Polymer
                                                                          X
      X

                                                                      X           Stability Sphere
          X                                                   X
              X                                           X

                  X                               X
                                          X
                          X   X       X




Initiator
             Synthesis of Single Metal MNP
                                   Thermal Decomposition
• Thermal Decomposition of
organo-metallic complexes can
produce highly mono-disperse
nano particles.
• Size and dispersity control is
attained through high reaction
temperature
• Capping ligands (e.g. Oleic
Acid) can also mediate the
particle growth by forming a
monolayer of nano particles
• Most common precursors:
Metal Carbonyl complexes.
• Morphology can also be
controlled through various
capping ligands

TOPO: Trioctylphosphine Oxide
Plasma Vaporisation
          Semiconductor Compound Nano
                              Particles
High Temperature Organo-Metallic Methods are still the
most popular for both III-V and II-VI compound.
• Thermal decomposition
• Rapid injection of organometallic precursor means fast
nucleation.
• The following growth can be controlled and terminated
by adjusting temperature
                          Other Techniques
                   Laser Ablationa
                 Electrochemistryb
            Hydrothermal Synthesisc
             (Supercritical water)
                        Sol-Geld

a: Neddersen, J; et. al. Appl. Spec. 47 p. 1959-1964 (1993)
b: Lu, D; Tanaka, K. J. Phys. Chem. 100 p. 1833-1837 (1996)
c: Cabanas, A; Poliakoff, M. J. Mater. Chem. 11 p. 1408-1416 (2001)
d: Moreno, E; et. al. Langmuir 18 p. 4972-4978 (2002)
            Characterization
Technique           Information

TEM/SEM       Size/Shape/Size Distribution

 UV/vis        Size/Size Distribution

  AFM         Size/Shape/Size Distribution

  X-ray             Composition

Zetasizer      Size/Size Distribution
 Stabilization of Polymer Nanoparticles
•Stable Dispersion- All particles exist as single entities; order or
disorder
•Aggregation- General term for unstable states
   •Flocculation- Disorder, with weak attraction
   •Coagulation- Disorder, with strong attraction Coagulated

   Low [electrolyte]
                                     Aggregated
   Strong repulsion
   Order
            Intermediate                              Flocculated
            [electrolyte]
Stable
            Repulsive contacts                High
            Disorder                          [electrolyte]
                                                                Forces to Consider
1. Electrostatic- Charged surfaces and stabilizers
2. Steric- Geometric effects/Solvation effects
3. van der Waals- Attraction of polymer chains
   towards each other
                                    X           X   X
                    X       X                               X

                                                                X
            X



    X
        X                                                               X
                                                                                        X, Y = Cationic,
X
                                                                                X
                                                                                        Anionic, or Nonionic
X

                             Y
                                 Y          Y
                                                Y
                                                                                X
                                                                                        Functional Groups
                            Y
X                                                                                   X
                                                Y
                            Y
                                            Y
    X                           Y       Y                                           X

                                                                                X
    X

                                                                            X

        X                                                           X
            X                                                   X

                X                                       X
                                                X
                        X   X           X
                                     Interaction Energy
Vt = Vr + Va                    Where
                                Vr = Potential energy of electrostatic
                                interactions (may include contribution from
                                steric interactions
                                Va = Potential energy of van der Waals
                                interactions
Vr Double layer term (DLVO theory) surface
charge & environment (electrolyte & solvent);
thickness and density of adsorbed layer and
interaction with solvent
Va Material nature (dispersion frequency, static
polarizability, density)- Hamaker constants*
*An estimate of the Hamaker constant may be determined from AFM
measurements: Argento, C.; French, R. H. Journal of Applied Physics
1996, 80, 6081-6090.
                            DLVO Theory


Repulsion




Vr + Va
     0


Attraction




          0   Separation Distance (nm) 200
Nanoparticle Films
            Ligand Directed Assembly

                           nanoparticle
substrate   +
            Bifunctional
               ligand


            +
         Ligand Directed Assembly
                                     • Monolayer formed by
                                     adsorption of Au particles on 3-
                                     mercaptopropyltrimethoxysilane
                                     derivatized SiO2 surface


                                     • Multilayers constructed by
                                     immersion in a 5mM solution of
                                     2-mercaptoethanol for 10 min.
                                     followed by immersion in Au
                                     particle solution for 40 – 60
                                     min.
Tapping mode AFM (1mm x 1mm) of HSCH2CH2OH linked Au colloid
multilayers: (A) monolayer; (B) 3 Au treatments; (C) 5 Au treatments;
(D) 7 Au treatments; (E) 11 Au treatments.
           Natan, M. J.; et. al. Chem. Mater. 2000, 12, 2869-2881
                    Electrostatic Assembly
                          -- - + - --
                        +              +
                                   + -
                       -- -- --
                         - --
•   Polycationic polymer
•   Very stable in most solvents
•   Control inter-layer spacing
•   Conductive, semiconductive, or insulating

      Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.
                Convective Self Assembly
• Definition: Particles are allowed to freely
  diffuse. As the solvent evaporates, particles
  crystallize in a hexagonally close-packed array.
• Optimize: Particle concentration
                 Particle/Substrate charge
                Evaporation


                                 Top
                                 View

      Colvin, V.L.; et. al. J. Am. Chem. Soc. 1999, 121, 11630-11637.
      Photolithography Patterning
• Typically pattern the capture monolayer followed by
  particle adsorption
• Few examples of patterning after nanoparticle
  deposition
                            SEM images showing lithographically
                                defined patterned nanoparticle films
                                with combination of spin-coating
                                driven self-assembly of nanoparticles,
                                interferometric lithography (IL) and
                                reactive ion etching (RIE):

                            (a)   photoresist pattern above blanket
                                  nanoparticle layer;
                            (b) nanoparticle pattern after etching and
                                  photoresist removal;
                            (c) photoresist pattern;
                            (d) nanoparticle pattern after etching and
                                  photoresist removal;
                            (e)-(f) 2D isolated discs.
Photolithography Patterned Nanoparticles




  SEM image of Au
  nanoparticles adsorbed
  onto a patterned (3-     AFM image (80 mm x 80
  mercaptopropyl)-         mm) of a three-layer
  trimethoxysilane         coating of nanoparticles
  monolayer on SiO2        followed by
  coated Silicon wafer.    photopatterning.
     Electron Beam Lithography
• Typically:
  – coat substrate with polymer film
  – write pattern with e- beam
  – dissolve exposed polymer
  – evaporate metal into “holes”




        Somorjai, G. A.; et. al. J. Chem. Phys. 2000, 113(13), 5432-5438.
Images of Nanoparticle Arrays formed
   by Electron Beam Lithography
                       Spin-coat PMMA on Si(100)
                       wafer with 5nm thick SiO2 on
                       surface.
                       Beam current: 600pA
                       Accelerating Voltage: 100dV
                       Beam diameter: 8nm
                       Exposure time: 0.6s at each
                       site
                       Pt deposition: 15 nm by e-
                       beam evaporation
AFM and SEM of Pt nanoparticle array. Particles are
40nm in diameter and spaced 150nm apart.
    Nanosphere Lithography

                 (A) Representation of a single-layer
                     nanopshere mask formed by
                     convective self assembly.
                 (B) Illustration of the exposed sites on
                     the substrate with single-layer mask
                 (C) AFM image (1.7mm x 1.7mm) of Ag
                     deposited on mica with a mask of
                     264nm diameter nanoparticles.
              Mask preparation: Spin coat 267 nm polystyrene
              nanoparticles at 3600 rpm.
              Deposition: Ag vapor deposition
              Mask removal: sonicate 1-4 min. in CH2Cl2

Hulteen, J.C.; Van Duyne, R.P. J. Vac. Sci. Technol. A 1995,
                    13(3), 1553-1558.
                     Microcontact Printing
• PDMS stamp to “ink” a capture monolayer on a
  substrate followed by nanoparticle adsorption
• PDMS stamp to “ink” the nanoparticles directly
  onto the substrate


                                                              Side
                                                              View
                                                              Top
                                                              View

          Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM.
                             2000, 1, 18-52.
  AFM of Microcontact Patterned
       Nanoparticle Array



                        AFM scan (10m x 10m) of
                        microcontact printed Au
                        surfaces. HOOC(CH2)15SH is
                        initially stamped on substrate.
                        The surface is then exposed to
                        1.0 mM 2-mercaptoethylamie
                        followed by exposure to a
                        17nM solution of 12nm Au
                        nanoparticles.

Natan, M. J.; et. al. Chem. Mater. 2000, 12,
                  2869-2881
    Optical Properties and
 Applications of Nanoparticles
            Plasmon Absorbance
Surface-Enhanced Raman Spectroscopy (SERS)
         Fluorescence Spectroscopy
                     Plasmon Absorbance

• Surface Plasmon (SP): Coherent oscillation in e-
  density at the metal and dielectric interface when e-
  field (of incident light) forces loosely held conduction
  electrons to move with the field
• Plasmon absorbance : absorption of e-magnetic
  radiation of SP at a particular energy
Plasmon Absorbance - Factors
• Surface functionality, temperature, and the
  solvent
• Particle concentration and particle size
Plasmon absorbance - Applications
• Coupled – Plasmon   1
  Absorbances




                      2
   Plasmon absorbance – Applications




James J. Storhoff et al. J. Am. Chem. Soc., 120 (9), 1959 -1964,
                   SERS - Background
• Enhanced e-magnetic field as a consequence of SP
  and the appearance of new electronic states in the
  absorbate as a consequence of absorption

• Enhancement occurs when the exciting radiation is
  coincident with the plasmon absorbance of the
  nanoparticles

• Aggregated nanoparticles have additional plasmon
  resonances associated with interparticle plasmon
  coupling
                              SERS - Factors
• Particles size




    Shuming Nie et al. J. Am. Chem. Soc. 1998, 120,
                    SERS - Applications
Laser
                           Raman
                           signal to
                           detector



                           Au nanoparticle
                           with Raman
                           label and
                           antibody

        Antibody         Linker molecule
        Antigen          Raman Reporter
        (analyte)        molecule
Application - Analysis of Prostate Specific
              Antigen (PSA)
                          Raman spectra of PSA assay

               35000

               30000
                           1000 ng/mL
               25000
                           100 ng/mL
   intensity




               20000
                           10 ng/mL
               15000
                           0 ng/mL
               10000

               5000

                   0
                    200 400 600 800 1000 1200 1400 1600 1800 2000
                                     Raman shift (cm-1)


PSA: Prostate cancer marker. Different forms. Analysis of
composition change gives information of the malignancy
           Fluorescence - Applications

Bioconjugated
fluorescent
nanoparticles –
Probing specific DNA
sequences




  Shuming Nie et al. Anal. Chem., 72 (9), 1979 -1986, 2000.
       Fluorescence – Applications




Shuming Nie et al. Anal. Chem., 72 (9), 1979 -1986, 2000.
           Magnetic Nanoparticles
• Small size implies superparamagnetism
• Ferrofluids: a colloidal mixture of
  magnetic nanoparticles
• Generally made through a reduction
  reaction, however, other methods have
  been used
  – Hydrothermal Synthesis
  – Laser Ablation
                   Magnetic Cell Sorting
Modify MP by attaching an effector




  MP                                        MP




 Roger, Pons, Massart, et. al. Eur. Phys. J. AP 5,
 321-325 (1999)
                            Bind to Specific Cells



 MP             MP
                         Cell          Cell

      MP                                             MP

MP                   +                        MP


           MP
                                              Cell   MP

                         Cell
                                        MP
                                               MP
Uses for magnetically labeled cells

A: Cell sorting                             B: Magnetic Fluid
                                              Hyperthermia




                                     Jordan, A. et. al. J Magn Magn Mater, 201 (1999) 4

Roger, J.; et. al. Eur. Phys. J. AP 5, 321-325
(1999)
Magnetic Fluid Hyperthermia (MFH)
  • Also known as magnetocytolysis
  • Inject fluid containing MP’s into patient
  • Use constant magnetic field to
    maneuver particles to desired location
    (tumor, for example)
  • Expose area to oscillating magnetic field
    to cause extremely localized heating
  • Prototype unit being built in Germany

       Jordan, A. et. al. J Magn Magn Mater, 201 (1999) 413-419
       Magnetic Recording Media
Can be manufactured through a 6 step process

              Left: synthesis
              scheme.


              Right: SEM image of
              substrate. a)before
              step (f). b)same array
              filled with nickel c)
              MFM (12mm x 12 mm)
              image of array.
      Magnetic Recording Media
Each nickel “column” has dimensions on the
order of 170 nm diameter, 200 nm high and
2 m apart. This leads to a particle density
below that of today’s hard drives (by
approximately a factor of 10), however, it
demonstrates that other methods for data
storage are feasible. This method can be
used with current read/write heads
Nanomotors/generators using
       Ferrofluids




     Zahn, M. J. Nano. Rsrch, 3: 73-78, 2001
Nanomotors/generators using
       Ferrofluids
• Currently, it appears that very few
  applications explored (mostly theoretical)
• Paradoxical results
  – below a critical magnetic field strength,
    ferrofluids move opposite an AC field.
  – Fluid viscosity is dependent on the field
    strength (zero viscosity fluid reported)



    Ref’s in review: Zahn, M. J. Nano. Rsrch. 3: 73-78, 2001
       Drug Targeting/Gene
       Transfection Studies
Both are methods of delivery using magnetic
fields.
Magnetic Particles with the appropriate ligands
attached are injected into the body and
manipulated to the positions where they will be
activated using magnetic fields.
At this point, the gene/drug will be taken up by
the cell and act as it is supposed to (depending
on the application)
Often used in conjunction with MFH
     Scherer, F; et. Al. Gene Therapy, 9 p. 102-109 (2002)
Other Possible Uses for Magnetic
         Nanoparticles

 • MRI Contrast Enhancementa
 • GMR detection methods   b

 • Magnetocaloric refrigerationc

a: Ahrens, E. T; et al. Proc. Natl. Acad. Sci. USA: 95 p. 8443-8448
(1998)
b: Tondra, M; Porter, M; Lipert R; J. Vac. Sci. Tech. A: 18 p. 1125-1129
(2000)
c: McMichael, R. D.; et al. J. Magn. Magn. Mater. 111 p. 29-33 (1992)
                                                             Catalysis
Au nanoparticles supported on TiO2 substrates show high
activity for oxidation of CO at room temperature and
below.
Reaction proceeds at corner,
step, and edge sites of Au
                 CO adsorption
                                               3.5 nm Au nanoparticle
                 (on Au)
                                    12 Atoms in length
         Oxygen
         Adsorption                                                    2-3 Atoms
         (on TiO2)                                                     high


                             TiO2 Support



           Haruta, M.; Date, M. Applied Catalysis A: General 2001, 222, 427-437.
                       Bimetallic Catalysis
                       CH2=CH-CN +            CH2=CH-
                       H2O                    CONH2

                                                CH3-CH-
                                                CN O
                                                   H
                          Reaction proceeds most
                          favorably with Pd-Cu particles,
                          and is 100% selective when
Geometric effects lead to using a 3:1 Cu:Pd ratio.
higher activity and
selectivity for certain
reactions.
                 Effect of Composition
                            Interaction of the two metals:
                                    e-
                                    density
                                   Pd       Pt


 Catalytic activity as a
function of nanoparticle
  composition for the
 hydrogenation of 1,3-     C=C bond prefers e- deficient
    Cyclooctadiene         sites (donor acceptor
                           interactions); leads to
                           selective hydrogenation
         Electrochemical Reactions
• Electrochemistry using a roughened silver
electrode has been compared to that using an array
of silver nanoparticles on a support.
• Different molecules adsorb differently on the two
surfaces; i.e. there are different types of active sites.




                             CVs of methylviologen in 0.1 M
                             Na2SO4 at
                             (a) EC roughened electrode,
                             and
                             (b) NP array electrode
                                  Surface Comparison
                                                 Ag Electrode polished,
                        SEM                      then roughened by
                                                 potential steps in 0.1 M
                        images of                KCl
                        (A) EC                   NP array made by dipping
                        roughened                an Indium-Tin Oxide
                        electrode                (ITO) electrode in poly-L-
                                                 lysine for two hours, then
                        and (B) NP               into a colloidal silver
                        array                    solution overnight
                        electrode
                        Defect sites on the EC roughened electrode
                        must be active for MV adsorption.
Zheng, J.; Li, X.; Gu, R.; Lu, T. Journal of Physical Chemistry B 2002, 106, 1019-1023.
         Applications of Latex Particles
•Butadiene
    •Tires, Belts, Cables, Shoes, etc.
    •Oil-resistant Products
•Styrene
    •Linoleum, Plastics, Coatings
•Vinyl Acetate
    •Adhesives and Paints
•Acrylate
    •Adhesives, Paints, Primers, and Leather Finishing
•Chloroprene
    •Belts, Hoses, Cables, etc.
•Natural Rubber Latex
    •Gloves
    •Condoms
Drying of Paint

				
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