1 NANOPARTICLES: Definition and Significance Synthesis and Characterization Stabilization Ordering Optical Properties Magnetic Properties Catalysis Other Applications Acknowledgements: M. D. Porter

2 Definitions* Nanoparticle- Particle with 1 dimension in the 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. *These definitions are constructed from a compilation of literature, and represent the most commonly used verbiage over a span of years

3 Metallic Nanoparticle Synthesis M = Au, Pt, Ag, Pd, Co, Fe, etc. Reductant = Citrate, Borohydride, Alcohols Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1,

4 Control Factors Average Size Reductant Concentration Stirring Rate Temperature Size Distribution Rate of Reductant Addition Stirring Rate Fresh Filtered Solutions Stabilization Solution Composition Hayat, M. A., Ed., Colloidal Gold: Principles, Methods, and Applications; Academic Press: San Diego, 1989; Vol 1.

5 Functionalized Reductions Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1,

6 Bimetallic Nanoparticle Core-Shell Mixed Alloy M1M1 M1M1 M2M2 + M Reductant M1M1 M ReductantM M Reductant Toshima, N.; Yonezawa, T. New Journal of Chemistry 1998,

7 Semiconductor Nanoparticles (Q-dots) R R NC Se Cd Se CN R R TOP/TOPO 200ºC PO CdSeOP PO OP Pickett et al. The Chemical Record 2001, 1,

8 Semiconductor Nanoparticles Mix Intermicelle exchange Cd 2+ S 2- Cd 2+ S 2- CdS Thiol capping Micelle disruption CdS Functionalized particles can be isolated by centrifugation or by precipitation Shipway et al. Chemphyschem 2000, 1, CdCl 2 Na 2 S

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10 Characterization TechniqueInformation TEM/SEM Size/Shape/Size Distribution UV/vis absorbanceSize/Size Distribution AFM Size/Shape/Size Distribution X-rayComposition IRFunctionality

11 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 Figure adapted from: Ottewill, R. H. In Emulsion Polymerization; Piirma, I., Ed.; Academic Press: New York, 1982, pp Low [electrolyte] Strong repulsion Order Intermediate [electrolyte] Repulsive contacts Disorder High [electrolyte] Stable Aggregated Coagulated Flocculated

12 Forces 1.Electrostatic- Charged surfaces and stabilizers 2.Steric- Geometric effects/solvation effects 3.van der Waals- Attraction of hydrocarbon chains towards each other Y YY Y Y Y Y Y Y Y X, Y = Cationic, Anionic, or Nonionic Functional Groups Ottewill, R. H. In Emulsion Polymerization; Piirma, I., Ed.; Academic Press: New York, 1982, pp 1-49.

13 Ionic Groups Stabilizer Neutralization of surface charge causes aggregation Tails bind via hydrophobic attraction- enhanced stability OR Hydrophobic attraction binds tails, leading to an excess of positive charge Stabilization More Stabilizer + + +

14 Nonionic Groups Hydrophobic interactions bind the tail group to the NP, while the polar head groups extend into solution Polar head groups are hydrated, providing a steric barrier to prevent aggregation

15 Surface Charges Where: Verwey, E. J. W.; Overbeek, J. T. G. Theory and Stability of Lyophobic Colloids: The Interaction of Sol Particles Having an Electrical Double Layer; Elsevier, Inc.: New York, New York,  r = Potential at distance r from NP surface  s = Potential at NP surface a = radius of NP r = distance from NP surface e = elementary charge N A = Avogadro’s number  = Permittivity of free space k = Boltzmann’s constant T = Temperature I = Ionic Strength

16 Effect of Electrolyte Concentration on Potential Profiles C 1 > C 2 C1C1 C2C2 Low C High C

17 Interaction Energy V t = V r + V a Where V r = Potential energy of electrostatic interactions (may include contribution from steric interactions) V a = Potential energy of van der Waals interactions V r Double layer term (DLVO theory) surface charge & environment (electrolyte & solvent); thickness and density of adsorbed layer and interaction with solvent V a Material nature (dispersion frequency, static polarizability, density)- Hamaker constants* Derjaguin, B. V., Landau, L., Acta Physicochim. USSR, 1941, 14, 633 Verwey, E. J. W.; Overbeek, J. T. G. Theory and Stability of Lyophobic Colloids: The Interaction of Sol Particles Having an Electrical Double Layer; Elsevier, Inc.: New York, New York, Hamaker, H. C., Physica, 1937, 4, *An estimate of the Hamaker constant may be determined from AFM measurements: Argento, C.; French, R. H. Journal of Applied Physics 1996, 80,

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19 Nanoparticle Films

20 Ligand Directed Assembly Bifunctional ligand nanoparticle substrate + + Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1,

21 Natan, M. J.; et. al. Chem. Materials 2000, 12, Tapping mode AFM (1  m x 1  m) of HSCH 2 CH 2 OH linked Au colloid multilayers: (A) monolayer; (B) 3 Au treatments; (C) 5 Au treatments; (D) 7 Au treatments; (E) 11 Au treatments. Monolayer formed by adsorption of Au particles on 3- mercaptopropyltrimethoxysilane derivatized SiO 2 surface Multilayers constructed by immersion in a 5 mM solution of 2- mercaptoethanol for 10 min. followed by immersion in Au particle solution for 40 – 60 min.

22 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,

23 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,

24 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,

25 AFM of Microcontact Patterned Nanoparticle Array Natan, M. J.; et al. Chem. Mater. 2000, 12, AFM scan (10  m x 10  m) of microcontact printed Au surfaces. HOOC(CH 2 ) 15 SH is initially stamped on substrate. The surface is then exposed to 1.0 mM 2-mercaptoethylamine followed by exposure to a 17 nM solution of 12 nm Au nanoparticles.

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27 Optical Properties and Applications of Nanoparticles Plasmon Absorbance Surface-Enhanced Raman Spectroscopy (SERS) Fluorescence Spectroscopy

28 Plasmon Absorbance - Background 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 EM radiation of SP at a particular energy

29 Plasmon Absorbance - Factors Surface functionality, temperature, and the solvent Particle concentration and particle size S. Link et al. J. Phys. Chem. B 1999, 103,

30 GOLD QUANTUM DOTS VARIOUS DIAMETERS

31 Plasmon Absorbance - Applications Coupled – Plasmon Absorbances Storhoff et al. J. Am. Chem. Soc., 120 (9), ,

32 Plasmon Absorbance – Applications (continued) Storhoff et al. J. Am. Chem. Soc., 120 (9), , ABS of DNA

33 Surface Enhanced Raman Spectroscopy SERS 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 Creighton et al. J. Chem. Soc. Faraday Trans , 75, Aggregated nanoparticles have additional plasmon resonances associated with interparticle plasmon coupling

34 SERS - Factors Particle size Nie et al. J. Am. Chem. Soc. 1998, 120,

35 SERS - Applications Au nanoparticle with Raman label and antibody Antibody Antigen (analyte) Linker molecule Raman signal to detector Laser Raman Reporter molecule 0.8 cm Porter group

36 Application - Analysis of Prostate Specific Antigen (PSA) 1000 ng/mL 100 ng/mL 10 ng/mL 0 ng/mL AntibodyAnti-PSA (prostate specific antigen) AntigenPSA Raman label DSNB Integration time 60 seconds PSA -Prostate cancer marker -Different forms -Analysis of composition change gives information of the malignancy

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38 Binds w/o Mg 2+ Binds & cuts w Mg 2+

39 Fluorescence – Applications Nie et al. Anal. Chem., 72 (9), , 2000.

40 Dye added to DNA Nanoparticle fluor. Random binding via histones

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42 POTENTIAL APPLICATIONS RAPID GENE MAPPING FUND. STUDY OF PROTEIN – DNA INTERACTIONS -HOW DOES PROTEIN FIND SPECIFIC BINDING SITE AMONG MANY NONSPECIFIC SITES? -HOW DOES RNA POLYMERASE MOVE DURING TRANSCRIPTION? ALL ON SINGLE-MOLECULE BASIS INTEGRATE  AVG. PROPS. OF ENSEMBLE OF MOLECULES

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49 PARTIAL FILLING TIC RIC for nortriptyline Analytes 10 ppm 1 = nortriptyline 2 = salbutamol 3 = diphenhydramine

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52 AC 2004, 362A

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54 MICROPARTICLES HOST CODING ELEMENTS -ORG. SOLVENT, POLYMER PARTICLES SWELL OPEN CODING ELEMENTS ENTER IN WATER, PARTICLES CLOSE, TRAPPED -CODING ELEMENTS BOUND TO PARTICLE SURFACE ALSO CONTAIN CAPTURE REAGENTS CODING ELEMENTS (COLORED) -FLUORESCENT ORGANIC DYES (Δλ = 50 to 200 nm) -FLOUR. SEMICON NANOCRYSTALS (Δλ = 10 to 20 nm) -IR, RAMAN REPORTERS

55 Au Ag GaAs GaP Al stripes on Si Photolith. & etching

56 Particles coated with antihuman IgG + flourescein tagged human IgG Particles coated with anti-rabbit IgG + Texas red tagged rabbit IgG IMMUNOASSAY Was ist los?

57 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

58 Magnetic Cell Sorting MP Modify MP by attaching an effector Roger, Pons, Massart, et al. Eur. Phys. J. AP 5, (1999)

59 Bind to Specific Cells MP + Cell MP Cell MP Cell

60 Uses for magnetically labeled cells A: Cell sorting B: Magnetic Fluid Hyperthermia Jordan, A. et al. J Magn Mater, 201 (1999) Roger, J.; et. al. Eur Phys. J. AP 5, (1999)

61 Drug Targeting Gene Transfection 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 (mag. fluid hyperthermia) Scherer, F; et al. Gene Therapy, 9 p (2002)

62 Other Possible Uses for Magnetic Nanoparticles MRI Contrast Enhancement a GMR Detection Methods b Magnetocaloric Refrigeration c a: Ahrens, E. T; et al. Proc. Natl. Acad. Sci. USA: 95 p (1998) b: Tondra, M; Porter, M; Lipert R; J. Vac. Sci. Tech. A: 18 p (2000) c: McMichael, R. D.; et al. J. Magn. Magn. Mater. 111 p (1992)

63 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)

64 Animal Test Results Jordan, A. et. al. J. Magn Magn Mater, 201 (1999)

65 Magnetic Recording Media Can be manufactured through a 6 step process Todorovic, M. Schultz, S. Wong, J. Scherer, A. App. Phys. Lett (74) Left: synthesis scheme. Right: SEM image of substrate. a)before step (f). b)same array filled with nickel c) MFM (12  m x 12  m) image of array.

66 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

67 Magnetic Recording Media Current methods of recording are proprietary (i.e. very little information about how they work is available) Theoretical density limit for data storage is on the order of 100 Gbits/in 2 Theoretical density limit for reliable data storage is only on the order of 40 Gbits/in 2

68 Nanomotors/Generators using Ferrofluids Zahn, M. J. Nano. Rsrch, 3: 73-78, 2001

69 Nanomotors/Generators using Ferrofluids Currently, 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

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71 Catalysis Au nanoparticles supported on TiO 2 substrates show high activity for oxidation of CO at room temperature and below. TiO 2 Support Oxygen Adsorption (on TiO 2 ) CO adsorption (on Au) Haruta, M.; Date, M. Applied Catalysis A: General 2001, 222, Reaction proceeds at corner, step, and edge sites of Au 2-3 Atoms high 12 Atoms in length 3.5 nm Au nanoparticle

72 Bimetallic Catalysis Figure taken from: Toshima, N.; Yonezawa, T. New Journal of Chemistry 1998, and references therein. Geometric effects lead to higher activity and selectivity for certain reactions. CH 2 =CH-CN + H 2 OCH 2 =CH-CONH 2 Reaction proceeds most favorably with Pd-Cu particles, and is 100% selective when using a 3:1 Cu:Pd ratio. CH3-CH-CN OH

73 Effect of Composition Catalytic activity as a function of nanoparticle composition for the hydrogenation of 1,3-Cyclooctadiene Figure taken from: Toshima, N.; Yonezawa, T. New Journal of Chemistry 1998, Interaction of the two metals: PdPt e - density C=C bond prefers e - deficient sites (donor acceptor interactions); leads to selective hydrogenation

74 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.

75 CVs of methylviologen in 0.1 M Na 2 SO 4 at (a) EC roughened electrode, and (b) NP array electrode Surface Properties Couple 1: V & 0.72 V;  E p = 60 mV Couple 2: V & V;  E p = 60 mV (a) (b) No adsorption of MV! No active sites for adsorption of MV on nanoparticle array Zheng, J.; Li, X.; Gu, R.; Lu, T. Journal of Physical Chemistry B 2002, 106,

76 Surface Comparison SEM images of (A) EC roughened electrode and (B) NP array electrode Ag Electrode polished, then roughened by potential steps in 0.1 M KCl NP array made by dipping an Indium-Tin Oxide (ITO) electrode in poly- L -lysine for two hours, then into a colloidal silver solution overnight 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,

77 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

78 Drying of Paint

79 Rings… Stone, H. A.; Shmuylovich, L.; Shen, A. Q. Langmuir 2002, 18, Rings form as the contact line between the liquid and dry substrate undergoes pinning and de-pinning cycles, while mass transport occurs toward the boundary (rate of evaporation highest at edge). Particles build-up at the interface during each pinning cycle so that rings are left when the liquid dries.

80 Pinning and De-pinning Stone, H. A.; Shmuylovich, L.; Shen, A. Q. Langmuir 2002, 18, Where a particle adheres to the surface a pinning event takes place. Mass transfer builds-up particles at this pinning site until there are no more particles in the vicinity of the edge. At this point, the contact line becomes de-pinned, and will move back until there is another adhered particle. This mechanism leads to the formation of rings when a polymer nanoparticle is left to dry on a glass slide.

81 Ordering in Rings Stone, H. A.; Shmuylovich, L.; Shen, A. Q. Langmuir 2002, 18, Mass transfer during a pinning event drives ordering in ring-forming systems such that a closest-packed layer of particles forms.

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86 Organic Nanoparticles Organic compound + Lipophilic solvent Water + Stabilizer Emulsification Separation of solvent Hydrosol of organic compound Horn et al. Angew. Chem. Int. Ed 2001, 40,

Polymer Nanoparticle Synthesis Initiator Monomer Micelle formed from emulsifier Polymer Stability Sphere Colloid Science, Kruyt, H. R., Ed.; Elsevier: New York, New York, 1952; Vol. 1 Mysels, K. J. Introduction to Colloid Chemistry; Interscience: New York, 1959 Irja Piirma, Ed., Emulsion Polymerization; Academic Press: New York, 1982 Eliseeva, V. I.; Ivanchev, S. S.; Kuckanov, S. I.; Lebedev, A. V. Emulsion Polymerization and its Applications in Industry; Plenum: New York, 1981 Bovey, F. A.; Kolthoff, I. M.; Medalia, A. I.; Meehan, E. J. In High Polymers; Mark, H., Melville, H. W., Marvel, C. S., Whitby, G. S., Eds.; Interscience: New York, 1955; Vol. IX

88 Other Techniques Laser Ablation a Electrochemistry b Hydrothermal Synthesis c (Supercritical water) Sol-Gel d a: Neddersen, J; et al. Appl. Spec. 47 p (1993) b: Lu, D; Tanaka, K. J. Phys. Chem. 100 p (1996) c: Cabanas, A; Poliakoff, M. J. Mater. Chem. 11 p (2001) d: Moreno, E; et al. Langmuir 18 p (2002)

89 DLVO Theory Ottewill, R. H. In Emulsion Polymerization; Piirma, I., Ed.; Academic Press: New York, 1982, pp See also DLVO theory : Derjaguin, B. V., Landau, L., Acta Physicochim. URSS, 1941, 14, 633, and Verwey, E. J. W.; Overbeek, J. T. G. Theory and Stability of Lyophobic Colloids: The Interaction of Sol Particles Having an Electrical Double Layer; Elsevier, Inc.: New York, New York, V r + V a 0 Separation Distance (nm) 0200 Repulsion Attraction

90 Photolithography Patterning Typically pattern the capture monolayer followed by particle adsorption Few examples of patterning after nanoparticle deposition

91 Photolithography Patterned Nanoparticles SEM image of Au nanoparticles adsorbed onto a patterned (3- mercaptopropyl)-trimethoxysilane monolayer on SiO 2 coated silicon wafer. AFM image (80  m x 80  m) of a three-layer coating of nanoparticles followed by photopatterning. Chen, D.; et al. Thin Solid Films, 1998, , Pris, A.D.; Porter, M. D. Nano Lett. 2002, 2(10),

92 Electron Beam Lithography 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),

93 Images of Nanoparticle Arrays Formed by Electron Beam Lithography AFM and SEM of Pt nanoparticle array. Particles are 40 nm in diameter and spaced 150 nm apart. Somorjai, G. A.; et al. J. Chem. Phys. 2000, 113(13), Spin-coat PMMA on Si (100) wafer with 5 nm thick SiO 2 on surface. Beam current: 600 pA Accelerating Voltage: 100 dV (100 kV?) Beam diameter: 8 nm Exposure time: 0.6  s at each site Pt deposition: 15 nm by e - beam evaporation

94 Nanosphere Lithography Hulteen, J.C.; Van Duyne, R.P. J. Vac. Sci. Technol. A 1995, 13(3), (A)Representation of a single-layer nanosphere mask formed by convective self assembly. (B)Illustration of the exposed sites on the substrate with single-layer mask (C)AFM image (1.7  m x 1.7  m) of Ag deposited on mica with a mask of 264 nm diameter nanoparticles. Mask preparation: Spin coat 267 nm polystyrene nanoparticles at 3600 rpm. Deposition: Ag vapor deposition Mask removal: sonicate 1-4 min. in CH 2 Cl 2