WO2002028551A1 - Procédé de fabrication de nano-coques - Google Patents

Procédé de fabrication de nano-coques Download PDF

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Publication number
WO2002028551A1
WO2002028551A1 PCT/US2001/030368 US0130368W WO0228551A1 WO 2002028551 A1 WO2002028551 A1 WO 2002028551A1 US 0130368 W US0130368 W US 0130368W WO 0228551 A1 WO0228551 A1 WO 0228551A1
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Prior art keywords
solution
metal
silver
functionalized
nanoshell
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PCT/US2001/030368
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English (en)
Inventor
Nancy J. Halas
Joseph B. Jackson
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Wm. Marsh Rice University
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Priority to AU2001296374A priority Critical patent/AU2001296374A1/en
Publication of WO2002028551A1 publication Critical patent/WO2002028551A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/1601—Process or apparatus
    • C23C18/1633—Process of electroless plating
    • C23C18/1635—Composition of the substrate
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/1601—Process or apparatus
    • C23C18/1633—Process of electroless plating
    • C23C18/1655—Process features
    • C23C18/1658—Process features with two steps starting with metal deposition followed by addition of reducing agent
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/18—Pretreatment of the material to be coated
    • C23C18/1851—Pretreatment of the material to be coated of surfaces of non-metallic or semiconducting in organic material
    • C23C18/1872—Pretreatment of the material to be coated of surfaces of non-metallic or semiconducting in organic material by chemical pretreatment
    • C23C18/1875—Pretreatment of the material to be coated of surfaces of non-metallic or semiconducting in organic material by chemical pretreatment only one step pretreatment
    • C23C18/1879—Use of metal, e.g. activation, sensitisation with noble metals
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/18—Pretreatment of the material to be coated
    • C23C18/20—Pretreatment of the material to be coated of organic surfaces, e.g. resins
    • C23C18/2006—Pretreatment of the material to be coated of organic surfaces, e.g. resins by other methods than those of C23C18/22 - C23C18/30
    • C23C18/2046—Pretreatment of the material to be coated of organic surfaces, e.g. resins by other methods than those of C23C18/22 - C23C18/30 by chemical pretreatment
    • C23C18/2053—Pretreatment of the material to be coated of organic surfaces, e.g. resins by other methods than those of C23C18/22 - C23C18/30 by chemical pretreatment only one step pretreatment
    • C23C18/206—Use of metal other than noble metals and tin, e.g. activation, sensitisation with metals
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/18—Pretreatment of the material to be coated
    • C23C18/20—Pretreatment of the material to be coated of organic surfaces, e.g. resins
    • C23C18/28—Sensitising or activating
    • C23C18/285—Sensitising or activating with tin based compound or composition
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/38—Coating with copper
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/42—Coating with noble metals

Definitions

  • the present invention relates generally to composite particles with sub-micron sizes having a metal coating layer adjacent a dielectric layer or core and methods of making thereof.
  • Particles able to absorb or scatter light of well-defined colors have been used in applications involving detection, absorption, or scattering of light, for example medical diagnostic imaging.
  • Such particles are typically colloidal metal particles.
  • colloidal conventionally refers to the size of the particles, generally denoting particles having a size between about 1 nanometer and about 1 micron.
  • Small particles made from certain metals that are in the size range of colloidal metal particles tend to have a particularly strong interaction with light, termed a resonance, with a maximum at a well-defined wavelength.
  • metals include gold, silver, platinum, and, to a lesser extent, others of the transition metals.
  • Light at the resonance wavelength excites particular collective modes of electrons, termed plasma modes, in the metal. Hence the resonance is termed the plasmon resonance.
  • the metal material of a colloidal particle By selecting the metal material of a colloidal particle, it possible to vary the wavelength of the plasmon resonance.
  • the plasmon resonance involves the absorption of light, this gives a solution of absorbing particles a well-defined color, since color depends on the wavelength of light that is absorbed.
  • Solid gold colloidal particles have a characteristic absorption with a maximum at 500-530 nanometers, giving a solution of these particles a characteristic red color. The small variation in the wavelength results from a particle size dependence of the plasmon resonance.
  • solid silver colloidal particles have a characteristic absorption with a maximum at 390-420 nanometers, giving a solution of these particles a characteristic yellow color.
  • particles can be made that exhibit absorption or scattering of selected characteristic colors across a visible spectrum.
  • a solid metal colloidal particle absorbing in the infrared is not known.
  • Optical extinction, in particular absorption or scattering, in the infrared is desirable for imaging methods that operate in the infrared.
  • optical communications such as long distance phone service that is transmitted over optical fibers, operate in the infrared.
  • the wavelength of the plasmon resonance would depend on the ratio of the thickness of the metal coating to the size, such as diameter of a sphere, of the core. In this manner, the plasmon resonance would be geometrically tunable, such as by varying the thickness of the coating layer.
  • a disadvantage of this approach was its reliance on bulk dielectric properties of the materials. Thus, thin metal coatings, with a thickness less than the mean free path of electrons in the shell, were not described.
  • coated nanoparticles particles with a size between about 1 nanometer and about 5 microns
  • improved agreement with theoretical modeling of the coated nanoparticles resulted from the incorporation in the theory of a non- bulk, size-dependent value of the electron mean free path. That is, improved agreement with theory was achieved by developing an improved theory applicable to thin metal coatings.
  • improved theory a dependence of the width of the plasmon resonance on the thickness of the metal coating was described.
  • Nanoshell structures that exhibit structural tunability of optical resonance's from the visible into the infrared can currently be fabricated.
  • Gold has the advantage of a strong plasmon resonance that can be tuned by varying the thickness of the coating. More generally, the resonance may be tuned by varying either the core thickness or the thickness of the coating, in turn affecting the ratio of the thickness of the coating to the thickness of the core. This ratio determines the wavelength of the plasmon resonance.
  • a further advantage of gold- coated particles is that they have shown promise as materials with advantages in imaging and diagnostics. In particular, they have utility as band-pass optical filters, impeding the photo- oxidation of conjugated polymers, and in conjunction with sensing devices based on surface enhanced Raman substrates.
  • gold is a costly material and it would be desirable to have an alternative.
  • Silver is an example of an alternative metal that would be advantageous to coat onto a dielectric core. Silver is less expensive and has a stronger plasmon resonance than gold. Further, the plasmon resonance of a solid silver nanosphere occurs at shorter wavelengths than the corresponding gold plasmon resonance, so the nanoshell geometry will allow for the shifting of the silver plasmon resonance across more of the visible spectral range. Still further, silver could be used as an alternative in many of the same applications as gold. Thus, a method of making silver nanoshells is desirable.
  • the Raman effect is an inelastic scattering of light as a result of its interaction with matter.
  • the incident light is scattered inelastically by the vibrational states of the molecule.
  • Raman spectroscopy is the measurement of the wavelength and intensity of the inelastically scattered light. It will be understood that for a molecular vibration to be Raman active, the vibration must be accompanied by a change in polarizability (but not a change in dipole moment) of the molecule.
  • SERS Surface enhanced Raman scattering
  • the incident light stimulates the electromagnetic fields on the surface of the metal, which in turn interacts with the molecule, enhancing the Raman signal.
  • the emitted spectrum is the collected Raman spectrum and the metal surface is known as the surface enhanced Raman substrate.
  • Macroscopic roughened metal substrates have been known to increase the surface enhanced Raman cross section by a factor of 10 6 or larger. Although chemical interactions can contribute to this effect, this enhancement is primarily due to the strong electric fields at the surface of the substrate upon illumination.
  • Most SERS substrates are based on roughened metal electrodes, aggregated nanoparticles, or isolated nanoparticles on planar surfaces.
  • nanoshells are excellent Raman enhancers.
  • the tunable plasmon resonance of nanoshells provides a degree of control over the local fields and enables the absorption of the substrate to be tuned to the resonance of the laser.
  • An advantage of the nanoshell geometry is the increased control and precision of the Raman enhancement. This contrasts with the known SERS enhancement associated with a fractal network of aggregated colloid in solution. This enhancement depends on a more complicated geometry and is harder to achieve reliably. Due to the tunability of the plasmon resonance and the greater strength of the plasmon resonance for silver, makes silver nanoshells highly desirable for the application of SERS in the infrared.
  • silver is known to have rapid nucleation kinetics. This means that it is difficult to prevent the preferential formation of solid silver colloids in solution instead of a coating of silver on a dielectric core. Further, heretofore methods that have been used for formation of gold nanoshells have not been sufficiently successful in making silver nanoshells.
  • Typical methods of trying to improve the coating of silver on dielectric cores involve slowing down the kinetics in order to control the deposition rate.
  • the addition of a base or a surfactant to a solution of the cores and silver ions before the addition of reducing agent slows down the formation of silver colloid, but these methods have not been shown to form complete silver coatings.
  • the metal does coat on a dielectric core, it typically does so as a bumpy layer of particles, rather than as a smooth complete coating. To date, no method has been available for forming a smooth uniform coating of silver on a dielectric core to form a particle.
  • small metal-coated particles with other advantages, such magnetism arising from the metal coating.
  • Small magnetic particles have many applications. Such articles are used as toner in xerography, in ferrofluid vacuum seals, in nuclear magnetic resonance imaging as contrast agents, and in magnetic data storage. These magnetic particles are typically micron-sized in diameter or larger. The large size of these particles renders them less than satisfactory for several specialized applications.
  • the magnetic particles were smaller, cost reduction by reducing the number of processing steps would be achieved in xerographic applications.
  • the enhanced solubility due to carbon coating provided by smaller particles may be advantageous.
  • high density may be enhanced by using smaller particles.
  • the carbon coating and ability to disperse the nanoparticles in aqueous solutions may provide advantages for wetting and coating. Consequently, there is a potential need for sub-micron-sized metal, alloy, or metal carbide particles and a method for producing bulk amounts of these particles in a high yield process.
  • the present invention features a method of making a nanoshell that includes providing a solution that includes a functionalized dielectric substrate, a plurality of metal ions, and a reducing agent. Further, the method includes raising the pH of the solution effective to coat the substrate with the metal.
  • the solution may be provided by providing a functionalized dielectric substrate, and mixing the functionalized substrate with a plurality of metal ions in solution in the presence of a reducing agent.
  • the metal may be selected from among silver, nickel, and copper.
  • the present invention features a method of making a nanoshell that includes providing a functionalized dielectric substrate, combining the functionalized substrate with a solution containing metal ions, mixing a reducing agent comprising formaldehyde, with the solution, and mixing a base selected from the group consisting of ammonium hydroxide and sodium hydroxide with the solution to provide a rapid rise in pH such that the metal ions reduce onto the functionalized core to form the nanoshell, where the metal is selected from the group consisting of silver, nickel, and copper.
  • the present invention features a method of making a nanoshell that includes providing a functionalized dielectric layer, contacting the layer with a solution containing metal ions, mixing a reducing agent with the solution, mixing a base with the solution so as to create a rapid rise in pH such that the metal ions reduce onto the functionalized layer to form the metal layer.
  • the pH preferably rises to at least 11, more preferably at least 12, still more preferably at least 13.
  • the rise in pH preferably occurs in an interval of time between about 0 and about 1.5 seconds, more preferably between about 0 and about 1 seconds, most preferably between about 0 and about 0.5 seconds.
  • the functionalized substrate may be provided by providing a solution of gold colloid aged between about 5 and about 50 days, more preferably between about 14 and about 40 days, and mixing a dielectric substrate having a plurality of linker molecules attached thereto with the solution.
  • the functionalized substrate may be provided by providing a dielectric substrate, attaching a linker molecule to the substrate, and attaching gold colloid to the linker molecule.
  • the nanoshell may have a plasmon resonance with a maximum at a wavelength between about 400 nanometers and about 2000 nanometers, more preferably between about 500 nanometers and about 1500 nanometers, still more preferably between about 500 nanometers and about 1100 nanometers.
  • the method may further include attaching at least one Raman active molecule to the nanoshell.
  • the nanoshell may enhance scattering of light by the Raman active molecule by an enhancement factor of at least about 50,000, more preferably at least about 1,000,000, still more preferably at least about 10 12 .
  • the nanoshell may be magnetic.
  • Embodiments of the present invention have the advantage of providing complete shells.
  • a complete shell includes shell metal completely surrounding the substrate particle. Further, when the nanoshell has a plasmon resonance and the shell layer is complete, the particles' extinction maximum is related to its geometry, specifically, to the ratio of the thickness of an inner nonconducting layer to the thickness of an outer conducting layer.
  • the present invention comprises a combination of features and advantages which enable it to overcome various problems of prior methods.
  • the various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.
  • Figure 1 is a TEM image of a gold functionalized particle and b) schematic illustration of a gold functionalized particle made by the process of Examples 1-4;
  • Figure 2 is a) a TEM image of a particle before (left) and b) another TEM image after the rapid pH change in the silver deposition process of Example 5 (right);
  • Figure 3 is a plot of UV/Nis (dashed) and Mie scattering theory (solid) of spectra for various core and shell sizes grown by the method of Example 5, where the theoretical and experimental dimensions of the nanoshell samples to which these spectra correspond are displayed in Table 1;
  • Figure 4 is a TEM image of a particle after the rapid pH change in the nickel deposition process of Example 6;
  • Figure 5 is a plot of the extinction spectrum calculated from Mie scattering theory of various metal nanoshells, where the geometry is a core radius of 50 nm with a 10 nm shell;
  • Figure 6 is a plot of the extinction spectrum calculated from Mie scattering theory for various metal nanoshells where the geometry is a core radius of 100 nm with a 10 nm shell;
  • Figure 7 is (a) TEM image of hydroquinone-deposited silver onto 120nm diameter silica particle according to the method of Example 10 and (b) a plot of UV/Nis spectra of increasing deposited silver, where spectra 1 through 4 represent increasing amounts of silver deposition;
  • Figure 8 is (a) a plot of UV/Nis spectra of silica particle as more silver is deposited using ⁇ PG as the reducing agent according to the method of Example 11 and (b) TEM images corresponding to the silver silica particles in solution;
  • Figure 9 is a plot of a Raman spectrum of 100 mM solution of p-MA in ethanol with the ethanol background subtracted, where the peak at 1598 cm “1 correlates with the asymmetric stretching of the carbon ring, the peak at 1085 cm “1 is thought to be an aromatic ring vibration having some C-S stretching character, and the 380 cm "1 peak is currently unidentified (see text);
  • Figure 10 is a plot of typical Raman spectra of pMA solution with silver nanoshells (red) and a silver nanoshell background (blue), where the nanoshells have an 79 nm silica core and ⁇ 13nm silver shell, and the three Stokes modes, 390 cm -1 , 1077 cm ⁇ ⁇ and 1590 cm -1 , all correspond to- Raman active bending and stretching modes of the benzene ring of the pMA adsorbate molecule.
  • Figure 11 is a plot of an average Raman spectra where the blue line represents the NPG silver/silica substrate solution and the red line represents substrate solution with p-MA;
  • Figure 12 is a plot of a comparison of the calculated
  • Figure 13 is a TEM image of a tin functionalized particle obtained according to Example 17.
  • Figure 14 is a plot of a Uv/Visible spectrum of a silver-coated particle obtained according to Example 18.
  • the present invention includes a process for reducing silver to produce silver nanoshells.
  • Silver nanoshells are made by creating the silica core, functionalizing it with gold particles, and then reducing silver onto these particles. More particularly, the fabrication of silver nanoshells is achieved by growing a silica core, prefunctionalizing its surface, attaching ultrasmall gold colloid, then reducing silver onto this seed structure until a shell of the desired thickness is formed.
  • Monodisperse silica cores are preferably grown using the Stober method, described in Werner Stober, Arthur Fink, and Ernst Bohn, J. Colloid and Interface Science 26, 62-69 (1968), entitled Controlled Growth of Monodisperse Silica Spheres in the Micron Size Range, hereby incorporated herein by reference.
  • Stober particles tetraethylorthosilicate (TEOS), ammonium hydroxide (NFL t OH), and water are added to a glass beaker containing ethanol, and the mixture is stirred overnight.
  • the size of the particles that result herein termed Stober particles, is dependent on the relative concentrations of the reactants.
  • the cores are preferably spherical particles between about 1 nanometers to about 5 microns in diameter, more preferably between about 1 nanometers and about 4 microns in diameter.
  • a plurality of cores, for example in solution, is preferably monodisperse.
  • Monodisperse particles are defined herein as particles that have a small variation in the distribution of particle sizes. For spherical particles the size is given by the particle diameter. The small variation is preferably quantified as the standard deviation.
  • core particles are characterized by a distribution of diameters with a standard deviation of up to about 20%, more preferably about 10%.
  • core particles are initially functionalized with 3-aminopropyltrimethoxysilane (APTMS).
  • APTMS 3-aminopropyltrimethoxysilane
  • the silane group attaches to the silica surface, and the amine group is exposed for further functionalization.
  • APTMS is preferably added to a solution containing silica core particles.
  • the solvent for the core particles is preferably ethanol.
  • the solution is preferably centrifuged to separate the particles from solution and thus remove byproducts.
  • the particles are then preferably resuspended in ethanol. Centrifugation and resuspension is preferably repeated, preferably for a total of between 2 to 3 cycles of centrifugation and resuspension.
  • ultrasmall gold colloid (l-3nm) is synthesized using a solution of 45mL of water, 1.5mL of 29.7mM HAuC14, 300uL of IM NaOH and ImL (1.2mL aqueous solution diluted to lOOmL with water) of tetrakis(hydroxymethyl)phosphonium chloride (THPC).
  • the gold colloid thus formed is preferably aged under refrigeration for between about 5 and about 50 days, more preferably for between about 14 and about 40 days.
  • this gold is then added to the initially functionalized silica particles.
  • An aqueous solution of gold colloid is preferably added to an ethanol solution of the silica particles.
  • the volume ratio of the gold colloid solution to the silica particle solution is preferably 10:1.
  • the combined solution is preferably allowed to react overnight.
  • the gold colloid covalently bonds to the arnine- terminated silica particles which provide nucleation sites for the chemical deposition of a metallic shell, forming functionalized particles.
  • the functionalized silica particle solution is preferably centrifuged to separate the particles from solution and thus remove byproducts and any excess gold colloid.
  • the functionalized particles are then preferably resuspended in water.
  • the solvent is preferably water.
  • the solvent is ethanol. Centrifugation and resuspension are preferably repeated for a total number of cycles of preferably between 2 and 4.
  • the gold-functionalized silica particles are mixed with 0.15mM solution of fresh silver nitrate and stirred vigorously. A small amount (typically 25-50 micro-liters) of 37% formaldehyde is added to begin the reduction of the silver ions onto the gold particles on the surface of the silica. This step is followed by the addition of 50 micro-liters of doubly distilled ammonium hydroxide. The “amounts” or “relative amounts” of gold-functionalized silica and silver nitrate dictate the core to shell ratio and hence the absorbance.
  • the nanoshell solution is preferably centrifuged to separate the nanoshells from solution and thus remove byproducts and any solid silver colloid that formed.
  • the nanoshells are preferably resuspended in a solvent.
  • the solvent is preferably water. Alternatively, the solvent is ethanol. Centrifugation and resuspension may be repeated for a total number of cycles of preferably between 1 and 2.
  • the substrate particles are not limited to core particles.
  • a substrate particle generally is any particle that includes at least an outer surface of silica or other substrate material.
  • substrate particles may have shapes other than spherical.
  • the core is spherical in shape, the core may have other shapes such as cubical, cylindrical, hemispherical, elliptical, and the like.
  • alternative substrate materials may be used.
  • the substrate material preferably is characterized by a smaller permittivity than the metal that is to be coated on it.
  • Suitable materials include dielectric materials and semiconducting materials. Many dielectric materials are also semiconducting.
  • suitable subtrate materials include silicon dioxide, titanium dioxide, polymethyl methacrylate, polystyrene, gold sulfide cadmium sulfide, cadmium sulfide, gallium arsenide, and the like.
  • suitable substrate materials include dendrimers.
  • linker molecules may be used.
  • the linker molecule preferably is attachable to the core and has an atomic site that has an affinity for a metal.
  • the atomic site may be selected from among sulfur, nitrogen, phosphorous, and the like.
  • the linker molecule may include an amino acid that has a terminal group that includes an active atomic site.
  • the linker molecule is preferably a silane that hydrolyzes in water to form hydroxyl groups that are bondable to the active hydroxyl groups on the core.
  • Suitable silanes include APTMS, 3- aminopropyltriethoxysilane, diaminopropyl-diethoxy silane, 4-aminobutyldimethylmethoxy silane, mercaptopropyltrimethoxy silane, diphenyltriethoxy silane reacted with tetrahydrothiophene, and the like.
  • the linker molecule is preferably a non-metallic material. Suitable non-metallic materials include CdS and CdSe.
  • a linker molecule may be cross-linked to another linker molecule. Cross-linking may be achieved, for example, by a thermal or a photo-induced chemical crosslinking process.
  • alternative metal colloids may be used in place of gold colloids in attaching to a linker molecules.
  • Alternative metals include silver, platinum, tin, and nickel.
  • Crosscurrent filtration conventionally includes a plurality of inner membranes contained within an outer wall.
  • the inner membranes are preferably tubular, as is the outer wall.
  • the inner membranes are preferably arranged in a bundle within the outer wall.
  • the inner membranes include pores in their sides. Liquid contained between the outer wall and the inner membranes is maintained at a different pressure than liquid within the membranes. Thus there is a pressure differential across the pores.
  • the solution to be separated in fed into adjacent ends of the inner membranes.
  • a pump propels the solution into the ends.
  • the solution flows through the inner tubular members filtrate passes though the pores.
  • the filtrate contains the solvent and byproducts.
  • the retentate passes through the inner membranes to their opposite ends where it is collected.
  • the retentate includes the particles.
  • cross-current filtration is used to achieve separation of nanoshells from solution the retentate includes the nanoshells.
  • cross-current filtration is used to achieve separation of nanoshell intermediates, such as APTMS-bearing particles or gold-functionalized particles, the retentate includes the nanshell intermediate.
  • cross-current filtration has been observed to be successful for separating silver nanshells from solution and intermediates thereof.
  • the pH preferably rises to a value of at least about 11, more preferably at least about 12, most preferably at least about 13.
  • the pH of the solution is preferably about 6.
  • the rise in pH is preferably accomplished with a time interval between about 0 and about 1.5 seconds, more preferably between about 0 and about 1 seconds, most preferably between about 0 and about 0.5 seconds.
  • the reduction of silver in this method is novel.
  • the addition of NH 4 OH causes a rapid increase in the pH of the solution, resulting in the reduction of Ag+ ions and their deposition onto the nanoparticle surface, forming a silver shell.
  • formaldehyde alone a technique that is capable of forming gold nanoshells, did not form silver nanoshells.
  • the present inventors made the surprising discovery that, on a lab bench experimental scale, a rapid squirt of ammonium hydroxide resulting in formation of silver nanoshells. This is contrary to most reduction techniques. Most reduction techniques slow the reaction down in order to control the deposition rate.
  • the present inventors believe that prior to this, there has not been a controlled reduction of silver ions in solution in a uniform manner of less than ⁇ 30nm.
  • the addition of base speeds up the kinetics.
  • a rapid rise in pH is achieved by rapid mixing of a base with a solution containing metal ions, a reducing agent, and a functionalized substrate.
  • Rapid mixing on a lab bench experimental scale was achieved in the examples described below by a rapid squirt of ammonium hydroxide from a pipet into a solution containing silver nitrate, formaldehyde, and gold-functionalized silica cores. The solution was stirred as the ammonium hydroxide was added. It is contemplated that rapid mixing on a commercial scale may be achieved by any suitable conventional method.
  • Tin functionalization may be used to functionalize a substrate for receipt of metal on the surface of the substrate.
  • functionalization with gold colloid attached to a linker molecule attached to a substrate may be replaced by tin functionalization, as described below.
  • nanoshells each having a layer of a shell metal may be made by mixing tin ions and substrate particles in solution to form functionalized particles, followed by reduction of the shell metal onto the functionalized particles.
  • spherical silica particles are made using the Stober method, as described above. After separation from a reactant solution, such as by centrifugation, the Stober particles are redispersed in a first solvent and submerged in a solution of SnCl 2 in a second solvent.
  • the first solvent may be water.
  • the solvent is a methanol/water mixture, preferably 50% by volume methanol.
  • the second solvent may be water.
  • the second solvent is a methanol/water mixture, preferably 50 % by volume methanol.
  • a solution of tin chloride in a methanol/water solvent preferably includes a surfactant, such as CF 3 COOH.
  • the tin-functionalized silica particles are separated from solution and redispersed in water.
  • the separation from solution is achieved on the lab bench scale by centrifugation. Centrifugation has the advantage of removing any excess tin and preparing the tin-coated nanoparticles for further metal reduction.
  • the pH tends to be about 3.
  • the pH is preferably modified to at least 9. Modification of the pH has the advantage of achieving reaction conditions favorable for reduction of a shell metal, such as silver.
  • preparation of nanoshells by reduction of a silver preferably proceeds as described above.
  • excess solid silver nanoparticles are produced during the reaction they are preferably separated from the silver nanoshells, for example by centrifugation.
  • Tin is preferably used in excess of the amount needed to form a complete monolayer on a substrate particle. That is, tin is preferably added in an amount so that there are more tin ions that hydroxyl groups on the surface. This is believed to have the advantage of providing larger nucleation sites onto which the silver is reduced.
  • the coverage of tin is preferably uniform. It has been observed that when water is used as the solvent for tin functionalization the tin tends to form small uniformly distributed clusters. Alternatively, it has been observed that when a methanol/water mixture is used the tin tends not to form clusters. If parts of the Stober surface have more dense coverage of tin, then silver tends to reduce faster onto those areas and compromises the uniformity of the shell thickness.
  • An advantage of tin functionalization is the elimination of the use of a linker molecule, as well as the use of gold in the functionalization process of silica in order to grow nanoshells.
  • the elimination of the use of gold in functionalizing a substrate reduces the cost of materials used in forming a nanoshell from the substrate.
  • the elimination of the use of gold colloid also provides a less complex, faster method for producing metal nanoshells, as preparation of a gold colloid solution preferably includes an aging period of at least two weeks, whereas preparation of a tin ion solution preferably proceeds in the amount of time needed to dissolve tin chloride in solution.
  • a further advantage of functionalization of substrates, such as Stober particles, with tin is the creation of an improved catalytic surface for the reduction of metal salts.
  • a substrate functionalized with tin has more catalytic sites for metal ions to reduce than a substrate functionalized with gold attached to a linker molecule.
  • alternative metals to tin are used to functionalize a substrate particle.
  • titanium has similar reduction properties to tin.
  • titanium could be used in replacement of tin for this process.
  • the above-described embodiments of the present method of making silver nanoshells may be used to form nanoshells of any metal that has similarly rapid nucleation kinetics as silver.
  • this method may be used to form nickel nanoshells simply by substituting a nickel salt (e.g. nickel chloride) for the silver salt (e.g. silver nitrate).
  • nickel salt e.g. nickel chloride
  • silver salt e.g. silver nitrate
  • other metals may have alternative useful properties to a strong plasmon resonance.
  • nickel is magnetic.
  • Magnetic nanoparticles are potentially useful in such applications as disclosed above, including magnetic recording media,' magnetic imaging, and the like.
  • this method may be used to form nanoshells of other materials for which a similar method that does not include the rapid rise in pH. Such methods are used to make gold nanoshell.
  • the present inventors have found that such a method of reduction when applied to copper, adding formaldehyde to a solution containing a functionalized substrate and copper ions, excluding a rapid rise in pH resulting from rapid addition and mixing of ammonium hydroxide fails to form copper nanoshells.
  • the present method is contemplated for the formation of copper nanoshells.
  • alternative shell metals to silver are reduced onto a tin-functionalized substrate particle.
  • Alternative metals include nickel and copper.
  • a method of making a nanoshell may further include attaching at least one Raman active molecule to the nanoshell.
  • the nanoshell may enhance scattering of light by the Raman active molecule by an enhancement factor of at least about 50,000, more preferably at least about 1,000,000, still more preferably at least about 10 12 .
  • SERS surface enhanced Raman scattering
  • Monodisperse silica cores were grown using the Stober method, described in Stober, W.; Fink, A.; Bohn, E. J. Colloid Interface Sci. 1968, 26, 62, hereby incorporated herein by reference.
  • This method is known to yield solutions of mondisperse silica particles in the size range of 80-500 nm, where the particle size is dependent on relative reactant concentrations.
  • TEOS tetraethylorthosilicate
  • ⁇ H4OH ammonium hydroxide
  • water were added to a glass beaker containing ethanol, and the mixture was stirred overnight.
  • the size of the Stober particles was dependent on the relative concentrations of the reactants.
  • a solution of 1.5 ml TEOS, 3.5 ml NH4OH (29%) and 45mL ethanol typically yielded particles with a mean diameter of 210 nm.
  • the solution was centrifuged and the nanoparticles were redispersed several times in ethanol to remove any residual reactants.
  • silica nanoparticles that were made by the method of Example 1 were functionalized with 3-aminopropyltrimethoxysilane (APTMS).
  • ATMS 3-aminopropyltrimethoxysilane
  • This reaction provided an amine-moiety coating for the exterior of the silica nanoparticles.
  • the number and surface area of nanoparticles in solution was estimated using the amount of TEOS added, the density of Stober particles (2.0 g/cm.3), and the size of the particles as determined by transmission electron microscopy (TEM). This information was used to determine how much of a silane, 3- aminopropyltrimethoxysilane (APTMS) would be required to coat the nanoparticle surface with several monolayers, assuming 0.4 nm 2 per silane molecule.
  • TEM transmission electron microscopy
  • Ultrasmall gold colloid (l-3nm) was synthesized using a recipe disclosed in D. G. Duff and A. Baiker, Langmuir 9, 2301 (1993), hereby incorporated herein by reference. This entailed a solution of 45mL of water, 1.5mL of 29.7mM HAuC14, 300uL of IM NaOH and ImL (1.2mL aqueous solution diluted to lOOmL with water) of tetrakishydroxymethylphosphoniumchloride (THPC). This solution was then aged for about 14 days under refrigeration. After this time the gold solution was concentrated to 2ml using a rotovap.
  • THPC tetrakishydroxymethylphosphoniumchloride
  • the amine-functionalized silica particles obtained as in Example 2 were added to a solution of ultrasmall gold colloid (1-3 nm) obtained as in Example 3.
  • a gold colloid monolayer on the silane terminated substrates covered ⁇ 30% of the exposed surface area (as determined by TEM).
  • the total surface area of the APTMS functionalized Stober nanoparticles was calculated to ensure this amount of coverage and the functionalized Stober nanoparticles are added to the THPC gold.
  • the solution was then shaken and allowed to sit for at least 8 hours. After the gold colloid attachment the solution was then centrifuged and redispersed in water. This resulted in the gold colloids coating the silica nanoparticles with a surface coverage of nominally 25 percent.
  • Small gold colloid was chosen instead of silver because of the simplicity and reliability of synthesis of gold colloid in this size regime.
  • FIG. 1 A TEM image of the nanoparticle at this stage of growth and a schematic of a gold- functionalized Stober particle are shown in Figure 1.
  • the gold colloid covalently bonded to the amine-terminated surface provides nucleation sites for the chemical deposition of a metallic shell.
  • Gold-functionalized silica particles obtained as in Example 4 were mixed with 0.15mM solution of fresh silver nitrate (AgNO 3 ) and stirred vigorously. A small amount (50 ⁇ L) (Please fill in the actual amount(s) for the experiments producing the data shown in Figures 2 and 3) of
  • FIG. 2 A TEM image of a nanoparticle before and after this rapid pH change is shown in Figure 2. This method produces smooth, complete silver nanoshells and allows for tunability of the plasmon resonance through the visible and into the infrared wavelengths. UV/Visible extinction spectra for a few representative core/shell ratios are shown as broken lines in Figure 3.
  • the plasmon-derived extinction spectra of silver nanoshells obtained as in Example 5 was compared to far field extinction spectra calculated using Mie scattering theory, represented by the solid lines in Figure 3.
  • Mie solved the problem of light scattering from a solid sphere, as described in Mie, G. Ann. Phys. 1908, 24, 377, hereby incorporated herein by reference.
  • Aden and Kerker expanded this solution for the case of a core-shell particle, as disclosed in Aden, A. L.; Kerker, M. J. App. Phys. 1951, 22, 1242, hereby incorporated herein by reference.
  • the calculated spectra shown here follow a series solution developed by Sarkar, as described in Sarkar, D.; Halas, N. J. Phys. Rev.
  • the core and shell dimensions for silver nanoshells corresponding to four different sizes obtained experimentally from the TEM images of those nanostructures are compared to the dimensions used in the theoretical spectra, and are shown in Table 1. In the calculations, the core size and shell thickness variations were assumed to be Gaussian.
  • Gold-functionalized silica particles obtained as in Example 4 were mixed with 8 ml of a 0.541 M solution of fresh nickel chloride (NiCl 2 -6H 2 O) and stirred vigorously. 50 ⁇ L of 37% formaldehyde was added to begin the reduction of the silver onto the gold particles on the surface of the silica particle. At this point the solution was colorless. This step was followed by the addition of 50 ⁇ L doubly distilled concentrated ammonium hydroxide (NH 4 OH). The NH OH causes a rapid increase in the pH of the solution resulting in the reduction of Ni 2+ ions and their deposition onto the nanoparticle surface forming a silver shell. The solution, upon centrifugation, was a very pale light blue.
  • Silver and gold are optically the most active of these metals; however, Mie scattering theory can still be used to predict the optical absorption of other metal nanoshells.
  • the optical extinctions are calculated for these other metals for a core size of radius 50nm and 100 nm with a 10 nm shell.
  • the plasmon-derived resonance of silver nanoshells is only slightly stronger (-10%) than the corresponding gold nanoshell resonance, and that the silver nanoshell resonance appears at a shorter wavelength (-100 nm in this example) than that of the analogous gold nanostructure.
  • the plasmon peaks for metals other than gold and silver are not as favorable for optical applications, each of these metals have other properties which could make these particles worth studying.
  • the conductivity, electron transport properties, magnetism, catalytic properties, and reactivity may all be dependent on the core/shell geometry. The calculations were based on the following method.
  • Each term in the series was related to a physical oscillation mode of the electrons in the nanoshell.
  • the first term in the series represents the dipole oscillation, the second term represents the quadrupole, and so on.
  • the calculated spectrums were computed to an accurate degree by taking in the first five terms in the series.
  • Rs is the total radius of the particle
  • Re is the radius of the core particle
  • ⁇ s, ⁇ m, and ⁇ c are the dielectric of the shell, medium, and core, respectively.
  • the core/shell dependence is apparent in the Rc/Rs terms in the polarizability.
  • the first is size distributions in the cores and shells.
  • the second is related to the mean free path of the electrons.
  • the mean free path of electrons is greater than the thickness of the shell.
  • the mean free path of electrons in bulk silver is 54 nm. This shows itself as a broadening mechanism that must be taken into account. This is done by modifying the dielectric function of the metal in the following way:
  • ⁇ ( ⁇ )exp is the experimental dielectric function
  • ⁇ p is the bulk plasma frequency
  • ⁇ bulk is the bulk collisional frequency
  • T is the modified bulk collisional frequency given by
  • VF is the Fermi velocity of the electrons in the metal
  • a is the reduced electron mean free path, or in this case the shell thickness.
  • the parameter A was calculated by a number of different methods to be of the order of unity and was set to one for these calculations.
  • the bulk collisional frequency embodies a number of physical processes such as electron-electron, electron-phonon, . and electron-impurity interactions. Additional scattering mechanisms due to the microstructure of the metallic shell may also contribute to the homogeneous broadening but were not taken into account in this model.
  • the Drude theory of electrons was used to calculate the bulk collisional and plasma frequencies and Fermi velocities for the various metals. The Drude theory of metals is described in, for example, N. W. Ashcroft and N. Mermin, Solid State Physics (Harcourt, Fort Worth, 1976).
  • Varying amounts of gold-functionalized silica, obtained as in Example 4, were added to 1.2mL Acacia (500mg/L) with a 0.2mL buffer solution (1.5M citric acid, 0.5M sodium citrate, pH 3.5) and 0.3mL silver lactate (37mM in water). Then 0.3mL hydroquinone (0.52M in water) was added while stirring vigorously. Hydroquinone was used as the reducing agent, while the citrate solution and the Acacia as used to stabilize the silver ions and slow down the kinetics of the silver reduction.
  • FIG. 7(a) A TEM image of a representative particle produced by this process is shown in Figure 7(a). It can be seen that the used of this method results in the growth of needle-like silver "spikes" onto the silica nanoparticle surface, in addition to a deposition of Ag that coats the surface in a non-uniform manner.
  • Figure 8 shows spectral evidence of the formation of larger silver colloid ( ⁇ 10nm diameter) present in solution in the form of a shoulder located around 380nm, also evident in the TEM images of the products of this reaction (not shown).
  • the density of the larger silver colloid formed in this reaction was similar enough to the silver/silica nanoparticles formed that separation by centrifugation proved exceedingly difficult.
  • Gold-functionalized silica particles obtained as in Example 4 were mixed with 0.15mM solution of fresh silver nitrate (AgNO 3 ) and stirred vigorously. A small amount of a reducing agent and an optional surfactant were added to the solution.
  • the reducing agent was selected from among Sodium Borohydride, n-propyl gallate, hydroxylamine hydrochloride, UV light, and oleic acid.
  • the surfactant was selected from among polyvinyl alcohol, Acacia (commercial), polyvinyl propanol, Brij 92, Brij 97 (commercial), sodium citrate, potassium carbonate, and tributal phosphate. This method was repeated, using various of the reducing agents and surfactants. In each case, silver shells did not formed, as evidenced by TEM measurements and UN- visible spectra.
  • EXAMPLES 13-15 Surface Enhanced Raman Scattering
  • p-mercaptoaniline (p-MA or 1,4-aminothiolphenol) was chosen as the analyte.
  • the major peak at 1598 cm-1 can be correlated with the asymmetric stretching of the carbon ring.
  • the peak at 1085 cm-1 corresponds to an aromatic ring vibration having some C-S stretching character.
  • the 380 cm-1 peak is currently unidentifiable, peaks in this region typically correspond to wagging modes in aromatic rings.
  • the sulfur bond attaches to the surface leaving the amine group free to interact with other molecules of interest. This could be used as a baseline to scale SERS contribution from an absorbate linked to the surface via the amine group.
  • Examples 13-14 described below silvering techniques were used to grow silver shells and chemically deposit silver onto gold-functionalized Stober particles. Molecules of p- MA were absorbed onto the surface of these particles for the purpose of surface enhanced Raman scattering. The resultant enhancement gives rise to factors on the order of 1.0x106 and 400,000 in Examples 13 and 14, respectively. The surface roughness of the Raman substrate contributes dramatically to the Raman enhancement as shown by classical electromagnetic enhancement theory, as described in Example 15.
  • a 1.0 ⁇ M solution of p-MA in ethanol was added to a solution of silver nanoshells, obtained as in Example 5, with a core radius of 84 nm and 23 nm thick shell.
  • the concentration of shells was approximately 9.88x108 particles per mL.
  • An average result is shown in Figure 10.
  • the enhancement factor was on the order of 10 6 (compared to lOOmM solution of p-MA).
  • the incident excitation wavelength was 1.06 microns (1064 nm).
  • a 10 ⁇ M solution of p-MA in ethanol was added to a silver/silica substrate solution, obtained as in Example 11, with a core radius of 128 nm coated with -14 nm silver particles.
  • the concentration of Raman active particles in this solution was approximately 8.83x109 particles per mL.
  • the Raman enhancement is shown in Figure 11. Because the surface roughness varies from particle to particle, enhancements ranged from 200,000 to 600,000 (compared to lOOmM solution of p-MA). This graph gives a typical Raman enhancement factor of -400,000.
  • Nanoshells with silica cores and silver shells were fabricated.
  • Silver was used as the shell metal because highly reproducible saturation coverages of the paramercaptoaniline adsorbate molecule were obtainable.
  • a series of silica core-silver shell nanoparticles were constructed using 65 nm and 79 nm cores, upon which silver layers ranging from 5 nm to 20 nm were deposited by an electroless plating method. Following fabrication, UV-Vis spectroscopy and Transmission Electron Microscopy measurements were performed and correlated with Mie scattering theory for each nanoshell sample, to verify core and shell thickness. Comparison with theory showed that deviations in the shell thicknesses of 1-2 nm were present in all nanoshell samples fabricated.
  • Concentrations of the nanoshell solutions were determined by comparing the measured UV-Nis spectra to cross sections calculated from Mie scattering theory and accounting for absorption due to the other nanoshells in solution using Beer's law. Using the total particle radius from the Mie scattering calculations and the calculated concentrations all solutions were normalized to 5.5e 13 nm 2 /mL surface area per volume, where e is ln(l). Saturation coverage of paramercaptoaniline onto the Nanoshell samples was obtained consistently when 10 ⁇ L of a 10 ⁇ M solution of pMA was added to 180 ⁇ L of nanoshell solution normalized with respect to nanoparticle surface area.
  • Raman spectra were obtained with a Nicolet 560 FTIR/FT-Raman Spectrophotometer with a 1.0 6 ⁇ m Nd:YAG laser source.
  • An example of a typical Raman spectrum of pMA-adsorbed onto nanoshells in aqueous solution is shown in Figure 2.
  • the three predominant Stokes modes seen in this emission spectrum (390cm “1 , 1077cm “1 , and 1590cm “1 ) all arise from Raman active bending and stretching modes of the benzene ring of the pMA molecule.
  • Anti-Stokes spectra were also obtained for pMA, which consistently showed Boltzmann-type behavior, indicating that optical pumping of the adsorbate by the local field was not occurring. No nanoshell aggregation or flocculation was observed to occur during the experiment.
  • the enhanced Raman response of the adsorbate molecules due to the presence of the local electromagnetic field at a nanoshell surface was determined.
  • the field exciting the molecule, E p was taken as the sum of the incident plane wave and the local electromagnetic field on the nanoshell surface as calculated by Mie scattering theory:
  • the position of the molecule on the nanoshell surface is r', the position of the observer is r, and the vector between r and r' is ⁇ .
  • the incident frequency is ⁇ 0 and the Stokes shifted frequency is ⁇ .
  • E p was taken at the position of the molecule (r') and at the incident frequency ( ⁇ 0 ).
  • the molecular polarizabihty was taken as unity.
  • the total Raman electromagnetic field at r was the sum of the electromagnetic field of the molecule and the shell response at the Stokes shifted frequency ⁇ :
  • the electromagnetic field, ERaman is then calculated for r' on the nanoshell surface, assuming a monolayer of a molecule covering the surface of the nanoshell and allowing for a coverage of
  • the experimentally measured Raman enhancement matches the theoretical enhancement in a quantitative manner,
  • the magnitude of the signal which is due to concentration of adsorbate molecules, orientation with respect to normal at the nanoshell surface, and magnitude of their induced dipole moment, is the only adjustable parameter of this experiment. Error was assessed by (in x) structural uncertainty in shell thickness of 1-2 nm described earlier, and (in y) the standard deviation in the peak magnitudes of the data across five independent data runs. The excellent agreement observed here between experiment and classical theory indicates that, for this system, contributions from addition electromagnetic of chemical effects, such as localized plasmons or resonant enhancement of the adsorbate molecules, is not contributing to the SERS response.
  • EXAMPLE 16 The Raman enhancement factor of silver nanoshells was obtained by using a method analogous to Beer's law.
  • Power ABS Power m exv ⁇ - p sE n pMA d + ⁇ shell ( ⁇ s )n shell d ⁇
  • Silica cores were made as described in Example 1. They were centrifuged and resuspended in water. The solution of cores was mixed with tin chloride. A TEM image of one of the functionalized particles is shown in Figure 13.
  • Stober particles were dispersed in a 50/50 methanol and water mixture that is -1% silica by volume.
  • CF 3 COOH (0.504mL) and SnCl 2 (0.22g) were added to 40mL of a 50/50 mixture of water and methanol. This made a 0.072M and 0.029M solution of CF 3 COOH and SnCl 2 , respectively.
  • ImL of silica solution is added to 9mL of Sn solution and allowed to react for at least 45 minutes.
  • This solution was then centrifuged (at least twice) and redispersed in water. This served as a new seed solution.
  • 75 ⁇ L of this seed solution with 8mL of 0.206mM solution of AgNO 3 and 50 ⁇ L of 30% formaldehyde was allowed to stir in a beaker for ⁇ lmin.
  • 100 ⁇ L of ammonium hydroxide was quickly added to the solution.
  • a Uv/Visible spectrum of the resultant nanoshell is shown as the black line in Figure 15.
  • the red line is the Mie Theory calculated fit of a 105 nm radius silica core with a 13nm silver shell.

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Abstract

Cette invention a trait un procédé d'enduction d'une couche métallique complète sur une particule substrat fonctionnalisée afin de constituer une nano-coque. Cette dernière a une résonance de plasmon dont le point maximal est à une longueur d'onde comprise entre 400 nanomètres et 2 micromètres environ. Ce procédé consiste à former une particule substrat fonctionnalisée et à mélanger rapidement une solution contenant la particule, des ions du métal et un agent réducteur, avec une base propre à revêtir de métal la particule substrat fonctionnalisée. Le métal est, de préférence, choisi dans le groupe constitué par de l'argent, du nickel et du cuivre. La particule substrat fonctionnalisée comporte, de préférence, une surface de silice et un revêtement précurseur à base d'étain. Dans une variante, la particule substrat fonctionnalisée peut comporter une surface de silice, des molécules de silane liées à la particule noyau et des particules colloïdales d'or liées aux molécules de silane.
PCT/US2001/030368 2000-09-27 2001-09-27 Procédé de fabrication de nano-coques WO2002028551A1 (fr)

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CN1331598C (zh) * 2004-05-17 2007-08-15 中国科学院大连化学物理研究所 一种在硅基材料上原位组装高分散纳米银粒子的方法
WO2014002093A1 (fr) * 2012-06-26 2014-01-03 Zdf Ltd. Fibres optiques revêtues présentant des caractéristiques améliorées
WO2021074360A1 (fr) 2019-10-17 2021-04-22 Basf Coatings Gmbh Revêtements de diffusion de lumière dans le proche ir (nir) et compositions pour les préparer

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IL156626A (en) 2003-06-24 2009-12-24 Yeda Res & Dev System for selective cell destruction
EP1831424B1 (fr) 2004-12-30 2009-04-08 LG Electronics Inc. Procede de fabrication d'un nano-film a base de ti-o-c
US10994992B2 (en) 2011-01-20 2021-05-04 Technion Research & Development Foundation Limited Method and system for manipulating a cell
JP5649150B1 (ja) * 2014-07-17 2015-01-07 日本エレクトロプレイテイング・エンジニヤース株式会社 無電解メッキ用前処理液および無電解メッキ方法
CN112525878B (zh) * 2020-10-14 2023-05-16 辽宁石油化工大学 一种具有过滤功能sers基底的制备方法及应用

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US3011920A (en) * 1959-06-08 1961-12-05 Shipley Co Method of electroless deposition on a substrate and catalyst solution therefor
US4944985A (en) * 1988-04-11 1990-07-31 Leach & Garner Method for electroless plating of ultrafine or colloidal particles and products produced thereby
US5149566A (en) * 1988-09-27 1992-09-22 Courtaulds Coatings Limited Metal plating process
US5814370A (en) * 1996-06-11 1998-09-29 Sandia Corporation Encapsulation of nanoclusters in dried gel materials via an inverse micelle/sol gel synthesis
US6277489B1 (en) * 1998-12-04 2001-08-21 The Regents Of The University Of California Support for high performance affinity chromatography and other uses

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1331598C (zh) * 2004-05-17 2007-08-15 中国科学院大连化学物理研究所 一种在硅基材料上原位组装高分散纳米银粒子的方法
WO2014002093A1 (fr) * 2012-06-26 2014-01-03 Zdf Ltd. Fibres optiques revêtues présentant des caractéristiques améliorées
US10185083B2 (en) 2012-06-26 2019-01-22 Zdf Ltd. Coated optical fibres having improved features
WO2021074360A1 (fr) 2019-10-17 2021-04-22 Basf Coatings Gmbh Revêtements de diffusion de lumière dans le proche ir (nir) et compositions pour les préparer

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AU2001296374A1 (en) 2002-04-15
WO2002028552A1 (fr) 2002-04-11

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