WO2010132611A2

WO2010132611A2 - Textured metal nanopetals

Info

Publication number: WO2010132611A2
Application number: PCT/US2010/034612
Authority: WO
Inventors: Michelle Khine
Original assignee: The Regents Of The University Of California
Priority date: 2009-05-13
Filing date: 2010-05-12
Publication date: 2010-11-18
Also published as: WO2010132611A3

Abstract

A device is provided that contains a heat-shrunk thermoplastic base having a high-surface area textured metal surface, wherein the textured metal surface has an average height from about 100 nanometers to about 5 micrometers. Methods of making and using the device are also described herein.

Description

TEXTURED METAL NANOPETALS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Application Serial No. 61/177,916, filed May 13, 2009, the disclosure of which is hereby incorporated by reference in its entirety for all purposes.

FIELD OF THE INVENTION

[0002] The invention disclosed herein related to the field of micro fabrication.

SUMMARY OF THE INVENTION

[0003] This invention provides a device comprising, or alternatively consisting essentially of, or yet further consisting of a heat-shrunk thermoplastic base having a high-surface area textured metal surface, wherein the textured metal surface comprises a plurality of cracks and has an average height from about 100 nanometers to about 5 micrometers. For the purpose of illustration only, the textured metal surface comprises, or alternatively consists essentially of, or yet further consists of at least one metal selected from the group consisting of silver, gold and copper. Other molecules can be affixed or conjugated to the metal surface, such as a luminescent molecule, a fluorescent molecule or a catalyst.

[0004] Methods to prepare the devices are also provided. The methods comprise, or alternatively consist essentially of, or yet further consist of: a) depositing a metal onto a heat sensitive thermoplastic receptive material; and b) reducing the material by at least about 60% until cracks form in the metal deposited on the receptive material, thereby preparing a textured metal surface.

[0005] In one aspect, the heat sensitive thermoplastic material is uniaxially biased prior to performing steps a) and b) and/or during step b). By applying layers of metals or by layering with different metals having slightly different stiffness, one can controllably induce cracking of the metal surface to produce petal-like, high surface area substrates. The devices have sharper nanostructures that can be used, inter alia, as higher field enhancements such as field emitters. [0006] In performing the methods, the metal is deposited by sputter coating, evaporation or chemical vapor deposition and is deposited in a thickness from about 2 nanometers to about 100 nanometers. The metal is any suitable metal, for example one or more of the group of silver, gold or copper. During the method, the material is reduced by heating or other suitable method to achieve a surface texture in the range of from about 100 nanometers to about 5 micrometers.

[0007] In a further aspect, the method also requires affixing or conjugating to the metal surface one or more of a luminescent molecule, a fluorescent molecule or a catalyst.

[0008] A device produced by the method and its variations are also provided by this invention. Kits for preparing the devices and methods for use are further provided.

BRIEF DESCRIPTION OF THE FIGURE

[0009] Figures IA to 1C are scanning electron microscope (SEM) images of biaxial (a) and uniaxial (b) nanopetals created by wrinkling bimetallic films (40 nanometer gold on the top of 40 nanometer silver). The Figure IA shows the petals at 20 μm and the inset at 3 μm. Figure IB shows wrinkles at 20 μm and the inset at 3 μm. Figure 1C is a wide-field epiflourescence image and corresponding intensity profile along the lines of dyes on a glass plate (on left) and on uniaxial petals (on right).

DETAILED DESCRIPTION OF THE INVENTION

[0010] Throughout this disclosure, various technical and patent publications are referenced to more fully describe the state of the art to which this invention pertains. These publications are incorporated by reference, in their entirety, into this application.

Definitions

[0011] As used herein, certain terms may have the following defined meanings.

[0012] As used in the specification and claims, the singular form "a," "an" and "the" include plural references unless the context clearly dictates otherwise. [0013] As used herein, the term "comprising" is intended to mean that the compositions and methods include the recited elements, but do not exclude others. "Consisting essentially of when used to define compositions and methods, shall mean excluding other elements of any essential significance to the combination when used for the intended purpose. Thus, a composition consisting essentially of the elements as defined herein would not exclude trace contaminants or inert carriers. "Consisting of shall mean excluding more than trace elements of other ingredients and substantial method steps for preparing the microfluidic device. Embodiments defined by each of these transition terms are within the scope of this invention.

[0014] A "thermoplastic material" is intended to mean a plastic material which shrinks upon heating. In one aspect, the thermoplastic materials are those which shrink uniformly without distortion. A "Shrinky-Dink" is a commercial thermoplastic which is used a children's toy. The shrinking can be either biaxially (isotropic) or uniaxial (anisotropic). Suitable thermoplastic materials for inclusion in the methods of this invention include, for example, high molecular weight polymers such as acrylonitrile butadiene styrene (ABS), acrylic, celluloid, cellulose acetate, ethylene -vinyl acetate (EVA), ethylene vinyl alcohol (EVAL), fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), ionomers kydex, a trademarked acrylic/PVC alloy, liquid crystal polymer (LCP), polyacetal (POM or Acetal), polyacrylates (Acrylic), polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), Polycyclohexylene Dimethylene Terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone polyethylenechlorinates (PEC), polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), and spectralon.

[0015] A "metal" for use in this invention includes but is not limited to platinum, gold, titanium, silver, copper, a dielectric substance, a paste or any other suitable metal or combination thereof. Examples of suitable dielectric substances include metal oxides, such as aluminum oxide, titanium dioxide, silver oxide and silicon dioxide. Examples of suitable pastes include conductive pastes such as silver pastes.

[0016] The metal can be applied to the thermoplastic material by a variety of methods known to one skilled in the art, such as printing, sputtering and evaporating. The term "evaporating" is intended to mean thermal evaporation, which is a physical vapor deposition method to deposit a thin film of metal on the surface of a substrate. By heating a metal in a vacuum chamber to a hot enough temperature, the vapor pressure of the metal becomes significant and the metal evaporated. It recondenses on the target substrate. As used herein, the term "sputtering" is intended to mean a physical vapor deposition method where atoms in the target material are ejected into the gas phase by high-energy ions and then land on the substrate to create the thin film of metal. Such methods are well known in the art (Bowden et al. (1998) Nature (London) 393: 146-149; Bowden et al. (1999) Appl. Phys. Lett. 75: 2557-2559; Yoo et al. (2002) Adv. Mater. 14: 1383-1387; Huck et al. (2000) Langmuir 16: 3497-3501; Watanabe et al. (2004) J. Polym. Sci. Part B: Polym. Phys. 42: 2460-2466; Volynskϋ et al. (2000) J. Mater. Sci. 35: 547-554; Stafford et al. (2004) Nature Mater. 3: 545-550; Watanabe et al. (2005) J. Polym. Sci. Part B: Polym. Phys. 43: 1532-1537; Lacour, et al. (2003) Appl. Phys. Lett. 82: 2404-2406.)

[0017] In addition, the metal can be applied to the thermoplastic material using "pattern transfer." The term "pattern transfer" refers to the process of contacting an image-forming device, such as a mold or stamp, containing the desired pattern with an image-forming material to the thermoplastic material. After releasing the mold, the pattern is transferred to the thermoplastic material. In general, high aspect ratio pattern and sub-nanometer patterns have been demonstrated. Such methods are well known in the art (Sakurai, et al., US Patent 7,412,926; Peterman, et al., US Patent 7,382,449; Nakamura, et al., US Patent 7,362,524; Tamada, US Patent 6,869,735).

[0018] Another method for applying the image forming material includes, for example "micro-contact printing". The term "micro-contact printing" refers to the use of the relief patterns on a PDMS stamp (also referred to as the thermoplastic material) to form patterns of self-assembled monolayers (SAMs) of an image-forming material on the surface of a thermoplastic material through conformal contact. Micro-contact printing differs from other printing methods, like inkjet printing or 3D printing, in the use of self-assembly (especially, the use of SAMs) to form micro patterns and microstructures of various image-forming materials. Such methods are well known in the art (Cracauer, et al., US Patent 6,981,445; Fujihira, et al., US Patent 6,868,786; Hall, et al., US Patent 6,792,856; Maracas, et al., US Patent 5,937,758).

[0019] A "patterning device" is intended to be broadly interpreted as referring to a device that can be used to convey a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate.

[0020] A "pattern" is intended to mean a mark or design.

[0021] A "crack" intends an interruption of the continuity of a surface.

[0022] All numerical designations, e.g., pH, temperature, time, concentration, and molecular weight, including ranges, are approximations which are varied ( + ) or ( - ) by increments of 0.1. It is to be understood, although not always explicitly stated that all numerical designations are preceded by the term "about". It also is to be understood, although not always explicitly stated, that the reagents described herein are merely exemplary and that equivalents of such are known in the art.

[0023] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non- limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," "greater than," "less than," and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. MODES FOR CARRYING OUT THE INVENTION

Methods for Preparing the Textured Nanopetals

[0024] The preparation of the textured nanopetal surface comprises, or alternatively consists essentially of, or yet further consists of the steps of: a) depositing a metal onto a thermoplastic material; and b) reducing the surface area of the receptive material by at least about 60% until the metal on the material cracks, thereby forming the textured metal nanopetals.

[0025] Steps a) and b) prepare a metal nanopetal surface on the thermoplastic material. Methods for preparing a metal wrinkled surface can be found in PCT Patent Application No. PCT/US08/083283, which is incorporated by reference in its entirety. Metal petals are formed by using layers of metals or different metals and reducing the thermoplastic material until the metal surface cracks open, thereby producing a "petaled" surface.

[0026] In some embodiments, step a) can be repeated before step b) and each time the metal can be the same or different.

[0027] In one embodiment, the thermoplastic material is a heat sensitive thermoplastic receptive material which in one aspect is to be uniaxially or biaxially stressed upon heating or alternatively, uniaxially or biaxially pre-stressed prior to heating. In certain embodiments, the depositing of the metal onto heat sensitive thermoplastic receptive material is by evaporating, which is a physical vapor deposition method to deposit a thin film of metal on the surface of a substrate. By heating a metal in a vacuum chamber to a hot enough temperature, the vapor pressure of the metal becomes significant and the metal evaporated. It recondenses on the target substrate. The height of the metal is dependent on length of processing time. The thermoplastic substrate must be far enough from the source such that the plastic does not heat up during deposition.

[0028] After the metal is deposited on the thermoplastic, it is placed in an oven, or similar device, to be heated, and upon heating, because of the stiffness incompatibility between the metal and the shrinking thermoplastic, petals form. The spacing between the metal petals can be controlled by the amount of heating, and hence shrinkage. [0029] Petal height can be controlled by adjusting the metal film thickness. In the context of metal wrinkles, Figure 17 of the PCT application PCT/US08/083283 shows a plot of the maximum average metal height as a function of metal layer thickness. Therefore, one can easily predict the spacing between and height of the metal petals by adjusting the thickness of metal deposited onto the thermoplastic material and the time the thermoplastic material is heated. The thickness of metal deposited onto the thermoplastic material can be easily controlled using the metal deposition methods disclosed herein by adjusting parameters such as time, temperature, and the like. Such methods are well known to one of skill in the art.

[0030] In addition, the metals can be the same or different or and/or alternatively deposited in multiple layers in a thickness from about 0.1 nm, or alternatively about 0.2 nm, or alternatively about 0.25 nm, or alternatively about 0.3 nm, or alternatively about 0.35 nm, or alternatively about 0.4 nm, or alternatively about 0.45 nm, or alternatively about 0.5 nm, or alternatively about 0.55 nm, or alternatively about 0.6, or alternatively about 0.7 nm, or alternatively about 75 nm, or alternatively about 0.8 nm, or alternatively about 0.85 nm, or alternatively about 0.9 nm, or alternatively about 1 nm, or alternatively about 2 nm, or alternatively about 3 nm or alternatively about 4 nm, or alternatively about 5 nm, or alternatively about 7.5 nm, or alternatively about 8, or alternatively about 10 nm, or alternatively about 15 nm, or alternatively about 20 nm, or alternatively about 25 nm, or alternatively about 30 nm, or alternatively about 35 nm, or alternatively about 40 nm, or alternatively about 45 nm, or alternatively about 50 nm, or alternatively about 55 nm, or alternatively about 60 nm, or alternatively about 65 nm, or alternatively about 70 nm or alternatively about 75 nm, or alternatively about 85 nm, or alternatively about 90 nm, or alternatively about 95 nm, or alternatively about 100 nm, or alternatively about 105 nm, or alternatively about 110 nm or alternatively about 120 nm, or alternatively about 125 nm, or alternatively about 130 nm, or alternatively about 135 nm, or alternatively about 140 nm, or alternatively about 145 nm, or alternatively about 150 nm, or alternatively about 155 nm, or thicker. Therefore, one can easily predict the spacing between and height of the metal petals by adjusting the thickness of metal deposited onto the thermoplastic material and the time the thermoplastic material is heated. The thickness of metal deposited onto the thermoplastic material can be easily controlled using the metal deposition methods disclosed herein by adjusting parameters such as time, temperature, and the like. Such methods are well known to one of skill in the art.

[0031] Various heights or the metal nanopetals can be achieved from about 0.1 nanometers to about 100 nanometers. In a particular embodiment, the height of the metal is about 2 nanometers. In an alternative embodiment, the height of the metal is about 5 nanometers, or alternatively, about 10 nanometers, or alternatively, about 20 nanometers, or alternatively, about 30 nanometers, or alternatively, about 40 nanometers, or alternatively, about 50 nanometers, or alternatively, about 60 nanometers, or alternatively, about 70 nanometers, or alternatively, about 80 nanometers, or alternatively, about 90 nanometers, or alternatively, about 100 nanometers.

[0032] In some embodiments, petal heights can be achieved from about 100 nanometers to about 5 micrometers. In an particular embodiment, the height of the metal is about 200 nanometers. In an alternative embodiment, the height of the metal is about 200 nanometers, or alternatively, about 300 nanometers, or alternatively, about 500 nanometers, or alternatively, about 700 nanometers, or alternatively, about 1 micrometer, or alternatively, about 2 micrometers, or alternatively, about 3 micrometers, or alternatively, about 4 micrometers, or alternatively, less than about 5 micrometers.

[0033] In addition, the directionality of the petals is controlled by grooving the substrate prior to metal deposition. Alternatively, the directionality of the petals can be controlled by monodirectional shrinking using a uniaxially biasing thermoplastic receptive material. In one embodiment, the method to prepare a textured metal surface further comprises first heating a heat sensitive thermoplastic receptive material under conditions that reduce the size of the thermoplastic receptive material biaxially by at least about 60%, followed by uniaxially biasing the thermoplastic receptive material to shrink along one axis or dimension prior to depositing a metal onto a heat sensitive thermoplastic receptive material, and reducing the material by at least about 60%, thereby preparing a textured metal surface.

[0034] It is contemplated that any metal can be deposited onto the thermoplastic receptive material to fabricate the metal petals disclosed herein. In some embodiments, the metal is at least one of platinum, gold, titanium, silver, copper, a dielectric substance, a paste or any other suitable metal or combination thereof. Examples of suitable dielectric substances include metal oxides, such as aluminum oxide, titanium dioxide, silver oxide and silicon dioxide. Examples of suitable pastes include conductive pastes such as silver pastes. Depending on the intended use of the metal surface, it may be desired that the metal be deposited in a given pattern or design. For example, the metal can be deposited to only a desired area of the thermoplastic receptive material to form isolated metal sections or 'islands' on the thermoplastic receptive material. Methods for the controlled deposition of metals are well known in the art.

[0035] The periodicity of the petals as the wavelength of the petals scale according to the thickness to the 3/4th power. Therefore, tighter petals are achieved by changing the thickness, or height of the metal layer.

[0036] In some embodiments, the metal is deposited by one or more of sputtering, evaporation or chemical vapor deposition. Sputtering is a physical vapor deposition method where atoms in the target material are ejected into the gas phase by high-energy ions and then land on the substrate to create the thin film of metal.

[0037] In some embodiments, the metal is deposited in a desired pattern.

[0038] It is contemplated that any thermoplastic material can be used in the methods disclosed herein. In one aspect of the disclosed invention, the thermoplastic materials are those which shrink uniformly without substantial distortion. Suitable thermoplastic materials for inclusion in the methods of this invention include, for example, high molecular weight polymers such as acrylonitrile butadiene styrene (ABS), acrylic, celluloid, cellulose acetate, ethylene-vinyl acetate (EVA), ethylene vinyl alcohol (EVAL), fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), ionomers kydex, a trademarked acrylic/PVC alloy, liquid crystal polymer (LCP), polyacetal (POM or Acetal), polyacrylates (Acrylic), polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or Nylon), polyamide- imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), Polycyclohexylene Dimethylene Terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone polyethylenechlorinates (PEC), polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and spectralon. In one embodiment, the thermoplastic material is polystyrene.

[0039] Heat can be used to reduce the size of the thermoplastic receptive material 5 by at least 65%, or alternatively, at least 70%, or alternatively, at least 75%, or alternatively, at least 80%, or alternatively, at least 85%, or alternatively, at least 90%.

[0040] In some embodiments, the thermoplastic material is reduced to achieve a surface texture having a periodicity in the range of from about 10 nanometers to about 5 micrometers.

[0041] In some embodiments, the thermoplastic material is reduced to achieve a surface texture having a periodicity in the range of from about 10 nanometers to about 600 nanometers. In one aspect, the pre-stressed thermoplastic material is reduced to achieve a surface texture having a periodicity in the range of from about 15 nanometers to about 100 nanometers. In yet another aspect, the pre-stressed thermoplastic material is reduced to achieve a surface texture having a periodicity selected from the group consisting of about 15 nanometers, about 30 nanometers, about 60 nanometers, and about 600 nanometers.

[0042] In some embodiments, the heat sensitive thermoplastic material is reduced by heating. In some embodiments, the temperature used to heat and reduce the size of the thermoplastic material is from about 100⁰C to about 250⁰C, or alternatively from about 120⁰C to about 220⁰C, or alternatively from about 150⁰C to about 200⁰C, or alternatively from about 180⁰C to about 190⁰C, or alternatively about 185°C.

Devices

[0043] The methods disclosed herein are capable of fabricating various devices to be used in applications such as molecular detection, optical devices, filters and sorters, high-surface area conductors and actuators, molecular detection, optical devices, filters and sorters, high- surface area conductors and actuators, metrology, surface-enhanced Raman scattering (SERS), metal-enhanced fluorescence (MEF), and extraordinary light transmission. Exploitation of these and other plasmon-induced effects have benefited numerous applications, including near-field optical microscopy, sub-wavelength photonics, biochemical sensing and solar energy harvesting.

[0044] Thus, this invention also provides a device comprising a heat-shrunk thermoplastic base having a textured metal surface, wherein the texture has an average height from about 100 nanometers to about 0.1 micrometers. In one embodiment, the texture has an average height of about 100 nanometers, or alternatively, about 100 nanometers, or alternatively, about 300 nanometers, or alternatively, about 500 nanometers, or alternatively, about 700 nanometers, or alternatively, about 1 micrometer, or alternatively, about 2 micrometers, or alternatively, about 3 micrometers, or alternatively, about 4 micrometers, or alternatively, less than about 5 micrometers, as low as 0.1 nanometers, as described above.

[0045] Petal height can be controlled by adjusting the metal film thickness. Therefore, one can easily predict the spacing between and height of the metal petals by adjusting the thickness of metal deposited onto the thermoplastic material and the time the thermoplastic material is heated. The thickness of metal deposited onto the thermoplastic material can be easily controlled using the metal deposition methods disclosed herein by adjusting parameters such as time, temperature, and the like. Such methods are well known to one of skill in the art.

Industrial Applicability

[0046] This invention provides substrates of nanopetals which means of manufacture is considerably faster and significantly less expensive and more robust than other means of achieving such metal nano-structures (including self-assembly method, focus ion beam lithography and e-beam lithography) (Lakowicz, J.R. (2008) Analyst 133:1308-1346). The sharp edges of petals enable the applicants to concentrate and localize electromagnetic field.

Thus, the nanopetals are promising materials for surface plasmon-based sensing applications, such as metal enhanced fluorescence (MEF) and surface enhanced Ramon spectroscopy (SERS) (Lakowicz (2008) supra, Ko, H. et al. (2008). For MEF applications, previous studies show that bimetallic films can extend the penetration depth of surface plasmon to increase the amount of molecules in the enhanced region. (Ong, B. H. et al.

(2007) Lab on a Chip 7(4):506-512. This technique utilizes metallic nanostructures in which the plasmons resonate with the fluorophores to increase their fluorescence emission intensities. A typical ~10-fold enhancement has been applied to improve detection of DNA hybridization and immunoassay. (Malicka J. et al. (2003) Biochem. And Biophysical Res. Comm. 306(l):213-218 and Asian, K. et al. (2005) 16(1): 55-62. The inventors first results show that after deposited dyes on the petals, a 7- fold enhancement on fluorescence intensity can be achieved (Fig. 1C). The strong plasmons on the surface of nanopetals can resonance well with fluorophors. Such huge enhancement makes nanopetals as good substrates for single molecules detection. For SERS applications, the strong localized electromagnetic filed on the sharp edges would enhance Ramon signals of molecules for label-free bimolecular detection. (Lakowicz, J. R. et al. (2008), supra.).

[0047] Nanoparticles are the typical materials for nanocatalysis due to their large surface area. (Xu, W. et al. (2008) Nature Materials 7(12):992-996 and Chen, M.S. et al. (2006) Accounts of Chemical Res. 39(10):739-746). They have been applied on catalyzing many chemical reactions to improve synthesis efficiency, pollutant removal and et al. However, after catalysis, it is not easy to remove nanoparticles to get pure productions. Here, these nanopetals, immobilized on the substrates, are free of this problem. The large surface area of petals would be suitable materials for catalysis, such as active for CO oxidation. (Chen, M.S. et al. (2006), supra.)

[0048] Moreover, all these applications can be easily integrated into Shrinky-Dinks based microfluidic devices, disclosed in PCT/US08/083283 which were developed by the inventors. A significant plasmon effect and large surface area, together with the high throughput of lab-on-chip technique, makes the nanopetals promising low-cost substrates for ultra-sensitive and -fast detection for biomedical applications.

[0049] Metallic thin films and nanostructures exhibit remarkable optical properties which originate in their ability to support coherent electronic oscillations at their interfaces with surrounding dielectric media (Maier, S. A., et al. (2005) J Appl Phys 98: 1-10). These supported plasmons can be spatially confined (Localized Surface Plasmon Resonance, LSPR) or free to propagate along the interface boundary (Surface Plasmon Polaritons, SPP). The enhanced electromagnetic fields associated with these modes form the basis of many observed optical phenomena arising from highly enhanced absorption and scattering cross- sections when incident radiation couples to the plasmonic oscillations. These include surface-enhanced Raman scattering (SERS), metal-enhanced fluorescence (MEF), and extraordinary light transmission (Xu, H., et al. (1999) Phys. Rev. Lett. 83: 4357 - 4360, Shuming N., et al. (1997) Science 275: 1102-1106, Song, J.-H., et al. (2005) Nano Lett. 5: 1557-1561). Exploitation of these and other plasmon-induced effects have benefited numerous applications, including near-field optical microscopy, sub-wavelength photonics, biochemical sensing and solar energy harvesting (Okamoto, K., et al. (2006) J. Opt. Soc. Am. B 23: 1674-1678, Ebbesen, T. W., et al. (1998) Nature 391 : 667-669, Barnes, W. L., et al. (2004) Phys. Rev. Lett. 92: 107401-4). In addition to these, SPPs allow directional flow of energy when combined with suitably designed metallic nanostructures to mediate radiative energy transfer over distances of 10^"4 -10^"7 m (Jeffrey N., et al. (2008) Nature Mater 7: 442-453, Anthony J., et al. (2008) Appl. Phys. Lett. 92: 013504/1-3).

[0050] A wide variety of platforms have been used for fabrication of structures capable of supporting plasmonic modes, with the most popular approach being deposition of Au or Ag thin films or nanoparticles (1 and 2D arrays) on inert substrates (Joseph R., et al. (2006) Appl. Phys. Lett. 89: 153120/1-3, Anton Kuzyk, et. al., (2007) Optics Express 15: 9908- 9917, Andrew, P., et al. (2004) Science 306: 1002-1005). The techniques used, however, are typically labor intensive nanofabrication and expensive methods such as electron beam lithography and ion beam milling. While there are some effective bottom-up manufacturing approaches using pre-patterned substrates for nanoparticle deposition, such as rippled silicon or faceted alumina, it is believed that there has been no approach as cost-effective and amenable to large-scale production as the one disclosed herein (H. Raether, "Surface Plasmons on Smooth and Rough Surfaces and on Gratings", Springer, Berlin, (1988), Murray, W. A., et al. (2004) Phys. Rev. B 69: 165407/1-7).

[0051] Disclosed herein is a simple and ultra-rapid technique to controllably create complex nano- to micro- scale nanopetal patterns on a receptive thermoplastic material, such as printable pre-stressed polystyrene (PS) sheets. Because thermoplastic materials contract to a fraction of their size when heated, the mismatch in stiffness between a metal film such as a gold thin film and the carrier thermoplastic material substrate is leveraged. As the thermoplastic material retracts, it carries the stiffer thin metal layer with it, causing the stiffer, non-shrinkable film to buckle or petal. The methods disclosed herein has been informed by theoretical work that addresses the scaling relationship between the length scales of the petals (wavelengths and amplitudes) and the thickness of the metal film, material properties of the film and substrate and the overall shrinking strain produced (Cerda, E., et al, (2002) Nature, 419: 579-598, Huang, Z., et al, (2004) Phys. Rev. E, 70: 030601). The petal length scales arise from a competition between the elastic bending energy of the film and the elastic energy of deformation of the substrate. By this method, plasmon-active petals are created with a large range of wavelengths (> 30x) and periodicity, directionality and aspect ratios, and even patterns. While there have been several demonstrations of metal wrinkles on polymers, all have reported considerably larger wrinkle wavelengths (Yoo P.J., et al., (2002) Adv. Mater., 18:1383-1387, Bowden N, et al., (1999) Appl. Phys. Lett. 75: 2557-2559, Huck W.T.S., et al., (2000) Langmuir 16: 3497- 3501 Watanabe M., et al., (2004) J. Polym. Sci. Part B: Polym. Phys. 42: 2460-2466 (2004), Watanabe M., (2005) J. Polym. Sci. Part B: Polym. Phys; 43: 1532-1537, Volynskii A.L., et al., (2000) J. Mater. Sci. 35: 547-554). Using the methods disclosed herein, petals from less than 100 nanometers to greater than 5 microns can be created.

[0052] Because this petaled surface demonstrates tunable LSPR resonance, it holds potential as a low cost and robust substrate for surface enhanced sensing and spectroscopy. In addition, because the petals exhibit hierarchical self-assembly, broad band response can be achieved. Moreover, the unidirectional features allow the possibility of energy harvesting and radiative transfer on the same device by SPP.

[0053] Devices that have a high surface area formed by shrinking substrate have been disclosed in, for example, U.S. Patent Nos: 6,376,619, 6,548,607, 6,573,338, 6,841,258,

7,189,842, 6,395,483, 6,593,089, 6,664,060, 6,482,638, 6,783,838, 6,881,538, 6,913,931 and 7,033,667 and PCT Application Publication No: WO 2009/064816. The nanopetals provided in the present disclosure are distinguished from those devices by provided a greater or enhanced surface area due to the exposure of surfaces of the metal which are originally in contact with the thermoplastic base. Further, applicants' data show a 7- fold enhancement on fluorescence intensity can be achieved from deposited dyes on the nanopetals (Fig. 1C). Further, several thousand folds of increase in intensity at the edges or

"hotspots" of both uniaxial and biaxial nanopetals have been observed. This indicates that the strong plasmons on the surface of nanopetals can resonance well with fluorophors. Such enhancement makes nanopetals desirable substrates even for single molecule detection. Kits

[0054] This invention further provides a kit comprising, or alternatively consisting essentially of, or yet further consisting of the materials necessary to perform the method described above. In one aspect, the kit comprises, or alternatively consists essentially of, or yet further consists of a thermoplastic material and instructions for making the device. In one aspect, the kit further comprises one or more metals for forming the nanopetals. The kit provides instructions for making and using the apparatus described above and incorporated herein by reference.

[0055] In another aspect, this invention provides a method for assaying or screening for new materials and methods having the same function of the inventions as described herein. In this aspect, the new materials and/or methods are used in the methods as described herein and compared to the performance of the devices of this invention.

Experimental

[0056] As shown in Figure 1 , for biaxial nanopetals, 40-nm-thick silver and subsequent 40- nm-thick gold are deposited on a Shrinky-Dink sheet (or KSF50-C; Grafix , 2cm x 1 cm ) using a sputter (SEM coating system; Polaron). To avoid preheating of the substrate, this step is separated to 4 cycles and each cycle (including 10 seconds of sputtering and 20 seconds of cooling) deposits 2.5 nm of gold. After deposition, heating at 160⁰C for 6 minutes in an oven induces retraction of the substrate and causes the non-shrinkable gold film to form biaxial wrinkles. Wrinkling induced cracks make it possible to create nanopetals (Fig. IA). For uniaxial nanopetals, before heating two short-edges of a gold- coated sheet are clamped by clips (2" binder clips; OfficeMax) to ensure it can only retract in the other direction (Fig. IB).

[0057] With the methods of the present technology that includes a second deposition of metal, bimetallic structures on the surface of memory polymers are also attained in order to achieve sharp bi-layered uniaxial and biaxial nanopetals. The sharp edges of the nanopetals exhibit remarkable increase of emission intensity of fluorescent molecules. Several thousand fold increase in intensity at the edges or "hotspots" of both uniaxial and biaxial nanopetals have been observed. The fluorescence intensities observed at the hotspots are brief bursts of intensity as the molecules diffuse through the structures. These bursts are below the resolution limit of our optics and possibly be due to single molecular emission. The intensity of the bursts increases non-linearly with increase laser intensity suggesting that the events may be attributable to stimulated emission, excited-state absorption, or saturation intensity dependent 2-photon emission cross-section. A decrease is also seen in the excited-state lifetime of the fluorescence particles, fluorescein, revealing strong plasmonic interactions. These findings reveal an ultra-sensitive and novel technique using bimetallic nanopetals to enhance fluorescence detection.

[0058] While the present invention is exemplified and illustrated by the use of polystyrene sheets to fabricate channel structures and molds, it would be obvious to those of skill in the art that any thermoplastic receptive material that can be patterned to control the dimensions of the channel defining walls and thereby their size, can be used to fabricate the devices disclosed and claimed herein. In addition, although several other embodiments of the invention are described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.

Claims

What is Claimed is:

1. A device comprising a heat-shrunk thermoplastic base having a high-surface area textured metal surface, wherein the textured metal surface comprises a plurality of cracks and has an average height from about 100 nanometers to about 5 micrometers.

2. The device of claim 1, wherein the textured metal surface comprises at least one metal selected from silicon dioxide, silver, gold and copper.

3. The device of claim 1, wherein the textured metal surface comprises two or more metals selected from silicon dioxide, silver, gold and copper.

4. The device of any of claims 1 to 3, further comprising a luminescent molecule.

5. The device of any of claims 1 to 3, further comprising a catalyst.

6. The device of any of claims 1 to 5, wherein the base comprises a plurality of grooves.

7. The device of any of claims 1 to 6, wherein thermoplastic base comprises one or more high molecular weight polymer selected from the group of acrylonitrile butadiene styrene (ABS), acrylic, celluloid, cellulose acetate, ethyl ene-vinyl acetate (EVA), ethylene vinyl alcohol (EVAL), fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), ionomers kydex, a trademarked acrylic/PVC alloy, liquid crystal polymer (LCP), polyacetal (POM or Acetal), polyacrylates (Acrylic), polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), Polycyclohexylene Dimethylene Terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone polyethylenechlorinates (PEC), polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and spectralon.

8. A method to prepare a high-surface area textured metal surface, comprising the steps of: a) depositing a metal onto a heat sensitive thermoplastic receptive material; and b) reducing the material by at least about 60% until cracks form in the metal deposited on the receptive material, thereby preparing a textured metal surface.

9. The method of claim 7, wherein the heat sensitive thermoplastic material is uniaxially biased prior to performing steps a) and b) and/or during step b).

10. The method of claim 8 or 9, further comprising grooving the heat sensitive thermoplastic material prior to step a).

11. The method of any of claims 8 to 10, further comprising depositing a second metal onto the heat sensitive thermoplastic material prior to step b) wherein the second metal is the same or is different from the metal.

12. The method of any of claims 8 to 11, wherein the metal and the second metal each is deposited by sputter coating, evaporation or chemical vapor deposition.

13. The method of any of claims 8 to 12, wherein the metal and the second metal each is deposited in a thickness from about 2 nanometers to about 100 nanometers.

14. The method of any of claims 8 to 13, wherein the metal and the second metal each comprises one or more of the group of silver, gold or copper.

15. The method of any of claims 8 to 14, wherein heat sensitive thermoplastic material is one or more high molecular weight polymer selected from the group of acrylonitrile butadiene styrene (ABS), acrylic, celluloid, cellulose acetate, ethylene-vinyl acetate (EVA), ethylene vinyl alcohol (EVAL), fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), ionomers kydex, a trademarked acrylic/PVC alloy, liquid crystal polymer (LCP), polyacetal (POM or Acetal), polyacrylates (Acrylic), polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), Polycyclohexylene Dimethylene Terephthalate

(PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyester polyethylene (PE), polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone polyethylenechlorinates (PEC), polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and spectralon.

16. The method of any of claims 8 to 15, wherein the material is reduced to achieve a surface texture in the range of from about 100 nanometers to about 5 micrometers.

17. The method of any of claims 8 to 16, wherein the thermoplastic material is polystyrene.

18. The method of any of claims 8 to 17, wherein the metal and the second metal each is deposited in a desired pattern.

19. The method of any of claims 8 to 18, wherein the heat sensitive thermoplastic material is reduced by heating.

20. The method of any of claims 8 to 19, further comprising:

c) depositing a luminescent molecule onto the metal.

21. The method of any of claims 8 to 19, further comprising:

c) depositing a catalyst onto the metal.

22. A device produced by the method of any of claims 8 to 21.