Abstract:
Embodiments of the present invention relate to methods for preparing high optical density solutions of nanoplates, such as silver nanoplates or silver platelet nanoparticles, and to nanoparticles, solutions and substrates prepared by said methods. The process can include the addition of stabilizing agents (e.g., chemical or biological agents bound or otherwise linked to the nanoparticle surface) that stabilize the nanoparticle before, during, and/or after concentration, thereby allowing for the production of a stable, high optical density solution of silver nanoplates. The process can also include increasing the concentration of silver nanoplates within the solution, and thus increasing the solution optical density.

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
       [0001]    This application claims the benefit of priority from U.S. Provisional Application 61/795,149, filed on Oct. 11, 2012, which is incorporated by reference in its entirety. Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    Various embodiments of the invention relate to methods for preparing high optical density solutions of silver platelet nanoparticles (e.g., nanoplates) and to nanoparticles, solutions and substrates prepared by said methods. 
         [0004]    2. Description of the Related Art 
         [0005]    Nanoparticles, including nanospheres, nanorods, nanowires, nanocubes, nanoplates, as well as other shapes can be synthesized from a range of materials. Nanoparticles made from metals including gold and silver have unique optical properties which can be tuned to interact with light throughout the electromagnetic spectrum due to the localized surface plasmon resonance supported by these nanomaterials. Technologies that take advantage of the unique optical properties of silver nanoparticles, (e.g., such as silver nanoplates), include, but are not limited to, diagnostic, photonic, medical, and obscurant technologies. A subset of these technologies including photothermal tumor ablation, hair removal, acne treatment, wound healing, and antimicrobial applications among others, may use solutions of nanoparticles with high optical densities. Silver platelet nanoparticles, which are also known as silver nanoplates or silver nanoprisms, are of particular interest for technologies that utilize nanoparticle optical properties due to their tunable spectral peaks and extremely high optical efficiencies. While methods to fabricate silver platelet nanoparticles via photoconversion (Jin et al. 2001; Jin et al. 2003), pH-controlled photoconversion (Xue 2007), thermal growth (Hao et al. 2004; Hao 2002; He 2008; Metraux 2005), templated growth (Hao et al. 2004; Hao 2002), and seed mediated growth (Aherne 2008; Chen; Carroll 2003; Chen; Carroll 2002, 2004; Chen et al. 2002; He 2008; Le Guevel 2009; Xiong et al. 2007) have been developed, these methods generate relatively dilute solutions with correspondingly low visible and near-infrared optical densities, (e.g., such as optical densities of less than 10 cm −1 , such as 1-9 cm −1 , 5-10 cm −1 ). 
       SUMMARY 
       [0006]    For many silver nanoplate applications, a more concentrated solution of the silver nanoplates is of utility and can be particularly advantageous. In some instances, when the as-fabricated solutions of silver nanoplates are concentrated to yield a higher particle density under previously developed methods, the shape of the particle can undergo a change resulting in a shift in the solution optical properties. In many cases, these changes result in an undesirable degradation of their optical properties. Accordingly, several embodiments of the present invention provide methods for preparing high optical density solutions of silver nanoplates from dilute silver nanoplate solutions that substantially or fully preserve the optical properties of as-fabricated silver nanoplates when the particle concentration is increased. The high optical density solutions of silver nanoplates can be exposed to substrates to generate nanoplate composites with high loading levels. 
         [0007]    Various embodiments of the invention provide a method for preparing high optical density solutions of silver platelet nanoparticles, as well as the nanoparticles and solutions prepared by those methods. In one embodiment, the process comprises the replacement of one or more original components (e.g., chemical or biological agents) bound, or otherwise coupled to, the nanoparticle surface with a stabilizing agent. The stabilizing agent can be a biological or chemical agent that stabilizes the nanoplates before, during, and/or after concentration, thereby allowing for the production of a stable, high optical density solution of silver nanoplates. In one embodiment, the process also comprises a method of increasing the concentration of silver nanoplates within the solution, and thus increasing the solution optical density. In several embodiments, the stability (e.g., the characteristics of the nanoparticles in the solution, such as shape, size, optical properties, peak response, plasmonic properties, etc.) of the high optical density solution is unaffected or substantially unaffected during the process. 
         [0008]    In one embodiment, a high optical density solution comprises silver nanoplates that have been stabilized with stabilizing agents (e.g., surface bound molecules chemical agents, and/or biological agents). In various embodiments, a solution of silver platelet nanoparticles (e.g., silver nanoplates) have been surface functionalized with chemical or biological agents that are physisorbed to the surface, molecularly bound to the surface through specific interactions, or encapsulate each nanoplate on its surface. 
         [0009]    In one embodiment, a high optical density solution of silver nanoplates is associated with a substrate. In one embodiment, a portion of the nanoplates in solution bind to the substrate to create a nanoplate-substrate composite. The high optical density solutions of silver nanoplates can be exposed to substrates to generate nanoplate composites where a substantial portion of the surface area of a substrate is coated with nanoplates. In some embodiments the substrate comprises fibers, cloth, mesh, bandages, socks, wraps, other articles of clothing, sponges, high porosity substrates, particles with edge lengths greater than 1 micron, beads, hair, skin, paper, absorbent polymers, foam, wood, cork, slides, roughened surfaces, biocompatible substrates, filters, and/or medical implants. 
         [0010]    In several embodiments, a process for increasing the optical density of a solution of stable, silver nanoplates comprises the following: (i) providing a solution comprising silver nanoplates having a plate shape, a first extinction spectra, and a first peak optical density between 0.1-10 cm −1 ; (ii) adding a concentration stabilizing chemical agent to the solution of silver nanoplates; and (iii) increasing the concentration of silver nanoplates using tangential flow filtration, thereby increasing the optical density of the solution to a second peak optical density greater than 10 cm −1 , wherein the silver nanoplates comprise the plate shape and the first extinction spectra at the optical density greater than 10 cm −1 . 
         [0011]    In various embodiments, the stabilizing agent comprises or consists essentially of at least one of the group consisting of polyvinyl pyrollidone, polyvinyl alcohol, polyethylene glycol, and dextran. In various embodiments, the stabilizing agent comprises or consists essentially of at least one of the group consisting of polysulphonates, ethylene oxides, phenols, and carbohydrates. In one embodiment, the concentration stabilizing chemical agent is a water soluble polymer. In one embodiment, the concentration stabilizing chemical agent is a metal or metalloid oxide. In one embodiment, the stabilizing chemical agent is a silicon dioxide shell. In various embodiment, the silicon dioxide shell ranges in thickness from 1 nm to 100 nm. In one embodiment, the stabilizing chemical agent is a titanium dioxide shell. In various embodiments, a combination of stabilizing agents are used. 
         [0012]    In various embodiments, the process further comprises adding any of the group selected from an acid, a base, and a buffering agent to the solution. In one embodiment, the silver nanoplates have an aspect ratio of between 1.5 and 25. In one embodiment, the nanoplate has an edge length between 10 nm and 250 nm. In some embodiments, the solution of silver nanoplates is formed using a seed mediated growth method. In one embodiment, the concentration of silver nanoplates is washed with between 1 and 5 wash volumes after increasing the concentration using tangential flow filtration. In one embodiment, the solution of silver nanoplates is incubated with a substrate. 
         [0013]    In various embodiments, a process for generating a solution of silver nanoplates with high optical density comprises the following: (i) providing a solution of silver nanoplates with a first peak optical density between 0.1-10 cm −1 , (ii) adding a concentration stabilizing chemical agent to the solution of silver nanoplates; (iii) adding a buffer to the solution of silver nanoplates; and (iv) increasing the concentration of the silver nanoplates to increase the optical density of the solution greater than 10 cm −1 . 
         [0014]    In one embodiment, the concentration stabilizing chemical agent comprises a derivative of a vinyl polymer. In one embodiment, the polymer is polyvinyl alcohol (PVA). In one embodiment, the polymer is polyvinyl pyrrolidone (PVP). In one embodiment, the process further comprises adding one of the group consisting of sodium bicarbonate and sodium borate to the solution. 
         [0015]    In several embodiments, a process for generating a solution of silver nanoplates with extremely high optical density comprises the following: (i) adding a concentration stabilizing chemical agent to a solution of silver nanoplates or precursor reagents and (ii) increasing the concentration of silver nanoplates to increase the optical density of the solution. 
         [0016]    In various embodiments, the silver nanoplates have an aspect ratio of between 1.5 and 25 (e.g., 1.5-10, 25-50); and/or the nanoplate has an edge length between about 10 nm and 250 nm (e.g., 50-250, 65-100 nm); and/or the nanoplate is triangular in cross section; and/or the nanoplate is circular in cross section. In one embodiment, the perimeter of the nanoplate cross section has between 4 and 8 edges (e.g., 4, 5, 6, 7, 8). In various embodiments, the solution of silver nanoplates is formed using one or more of a photoconversion method, a pH-controlled photoconversion method, a thermal growth method, a seed mediated growth method, and/or a solution comprising a shape stabilizing agent or agents and a silver source. In various embodiments, chemical or biological agents, and/or electromagnetic radiation, and/or heat, or a combination thereof are used to reduce the silver source. In one embodiment, the solution of silver nanoplates is formed from some combination of a reducing agent, a shape stabilizing agent, a light source, a heat source, and a silver source. 
         [0017]    In one embodiment, an acid, base, or buffering agent is added to change the solution pH. In various embodiments, the concentration stabilizing chemical agent is added prior to, during, and/or after the formation of the silver nanoplates. In one embodiment, the concentration stabilizing chemical agent acts as a shape stabilizing agent. In one embodiment, the concentration stabilizing chemical agent acts as a reducing agent. In one embodiment, the concentration stabilizing chemical agent acts as an agent to change the solution pH. 
         [0018]    In one embodiment, the concentration stabilizing chemical agent is a water soluble polymer. In various embodiments, the polymer is any one or more of a derivative of polysulfonate, sodium polystyrene sulfonate, a derivative of a vinyl polymer, and a polyvinyl alcohol (PVA). In various embodiments, the PVA has a molecular weight of less than about 80,000 Dalton (e.g., 1,000-50,000, 25,000-75,000 Dalton), between about 80,000 Dalton and 120,000 Dalton (e.g., 85,000-95,000, 100,000-110,000 Dalton), and/or more than about 120,000 Dalton (e.g., 150,000-300,000 Dalton). In one embodiment, the polymer is polyvinylpyrrolidone (PVP). In various embodiments, the PVP has a molecular weight of less than about 20,000 Dalton (e.g., 2,000-12,000 Dalton), more than about 20,000 Dalton (e.g., 35,000-400,000 Dalton), between about 20,000 Dalton and 60,000 Dalton (e.g., 40,000-55,000 Dalton), and/or more than about 60,000 Dalton (e.g., 70-100,000, 90-150,000 Dalton). In one embodiment, the polymer is an ethylene oxide derivative. 
         [0019]    In one embodiment, the polymer is a polyethylene glycol (PEG). In various embodiments, the PEG has a molecular weight of less than about 5,000 Dalton (e.g., 200-3,000, 1,000-4,500 Dalton), between about 5,000 Dalton and 10,000 Dalton (e.g., 7,000-8,000, 6,000-7,500 Dalton), and/or more than about 10,000 Dalton (e.g., 12,000-35,000, 18,000-45,000 Dalton). In one embodiment, the PEG contains a single functional group. In one embodiment, the PEG contains more than one functional group (e.g., two, three, or more functional groups). In one embodiment, the functional group or groups comprise any of an amine, thiol, acrylate, alkyne, maleimide, silane, azide, hydroxyl, lipid, disulfide, fluorescent molecule, and/or biotin. In one embodiment, the functional group or groups can be any one or more of an amine, thiol, acrylate, alkyne, maleimide, silane, azide, hydroxyl, lipid, disulfide, fluorescent molecule, and/or biotin. In one embodiment, the concentration stabilizing agent is a carbohydrate derivative. In various embodiments, the polymer is a monosaccharide, a disaccharide, an oligosaccharide, a polysaccharide, and/or dextran. In various embodiments, the dextran has a molecular weight that is less than about 2,000 Dalton (e.g., 200-1,400, 1,000-1,900 Dalton), between about 2,000 Dalton and 5,000 Dalton (e.g., 3,000-3,500, 2,000-4,000 Dalton), and/or more than about 5,000 Dalton (e.g., 6,000-8,000, 7,000-13,000 Dalton). 
         [0020]    In various embodiments, the concentration stabilizing chemical agent is any one or more of a phenol, a monomeric phenol, a dimeric phenol, a trimeric phenol, a polyphenol, a tannic acid, is gum Arabic, a biological molecule, a protein, a bovine serum albumin, streptavidin, biotin, a peptide, an oligonucleotide, a naturally occurring oligonucleotide, a synthetic oligonucleotide, a metal or metalloid oxide, and/or a silicon dioxide shell. In one embodiment, a silicon dioxide shell has ranges in thickness from about less than 1 nm to about 100 nm (e.g., 10-70, 30-90, 40-60 nm). In one embodiment, a combination of stabilizing agents are used. In various embodiments, the solvent can be one or more of water, an alcohol, ethanol, isopropyl alcohol, t-butanol, a mixture of a water and an alcohol. 
         [0021]    In one embodiment, the concentration of silver nanoplates is increased using tangential flow filtration. In one embodiment, the tangential flow filtration is performed using a tangential flow filter membrane. In one embodiment, the tangential flow membrane is made from a cellulose ester or mix of cellulose esters. In various embodiments, the tangential flow membrane is made from one or more of polyetheresulfone and/or polysulfone. In various embodiments, the tangential flow membrane has a molecular weight cut off of less than about 10 kD (e.g., 1-5, 8 kD), of between about 10 kD and 500 kD (e.g., 50-250, 300-400 kD), of more than about 500 kD (e.g., 750, 1000, 5000 kD or more), of less than about 0.05 μm, of between about 0.05 μm and 0.5 μm (e.g., 0.01, 0.03 μm), and/or of more than about 0.5 μm (e.g., 1.0, 2, 5, 10, 100 μm). 
         [0022]    In various embodiments, the silver nanoplate solution is concentrated to produce a solution with an optical density of greater than about 10 cm −1  (e.g., 15-45 cm −1 , 30-150 cm −1 , or more), greater than about 50 cm −1  (e.g., 80-150 cm −1 , 60-120 cm −1 , 100 cm −1  or more), greater than about 75 cm −1  (e.g., 80-110 cm −1 , 200-400 cm −1 , 1000 cm −1  or more), greater than about 100 cm −1  (e.g., 150-350 cm −1 , 200-400 cm −1  or more), and/or greater than about 500 cm −1 (e.g., 600-1500 cm −1 , 1000 cm −1  or more). 
         [0023]    In one embodiment, the solvent of the concentrated solution is exchanged using tangential flow filtration. In one embodiment, the concentrated solution is processed to remove residual chemicals using tangential flow filtration. 
         [0024]    In various embodiments, a solution of nanoparticles comprising silver nanoparticles is coated with a polymer with an optical density greater than 100 cm −1 (e.g., 160-550 cm −1 , 900-1100 cm −1 , 100 cm −1 , 1000 cm −1  or more). 
         [0025]    In one embodiment, the solution of silver nanoplates is incubated with a substrate (e.g., fibers, cloth, mesh, bandages, socks, wraps, other articles of clothing, sponges, high porosity substrates, particles with edge lengths greater than  1  micron, beads, hair, skin, paper, absorbent polymers, foam, wood, cork, slides, roughened surfaces, biocompatible substrates, filters, and/or medical implants). In one embodiment, the substrate is removed from the solution of silver nanoplates and dried. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention, in which the following is a description of the drawings. The drawings are examples, and should not be used to limit the embodiments. Moreover, recitation of embodiments having stated features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the stated features. Further, features in one embodiment (such as in one figure) may be combined with descriptions (and figures) of other embodiments. 
           [0027]      FIG. 1  illustrates the optical spectrum of a silver nanoplate solution as fabricated using a photoconversion method according to one embodiment of the present invention. In one embodiment, a silver nanoplate solution is fabricated using a photoconversion method identified as [DSS1099, alternative spectrum ARS1134]—as fabricated, these silver nanoplates have an optical density of less than 1 cm −1 . 
           [0028]      FIG. 2  illustrates a transmission electron micrograph of silver nanoplates fabricated using a photoconversion method according to one embodiment of the present invention. Scale bar is 50 nm. 
           [0029]      FIG. 3  illustrates one embodiment of plates concentrated in the absence of a concentration stabilizing agent with normalized (bottom) and unnormalized (top) extinction spectra of as-fabricated silver nanoplates before and after tangential flow filtration concentration. After concentration the plates have a significantly changed peak shape as demonstrated by the normalized plot, and a spectral peak at 400 nm that demonstrates that a large number of silver nanoplates have turned into silver nanospheres. In one embodiment, plates are concentrated with the identification [MGM1201 and 1195E]. 
           [0030]      FIG. 4  illustrates one embodiment of plates concentrated in the presence of a concentration stabilizing agent with normalized (bottom) and unnormalized (top) extinction spectra of as-fabricated silver nanoplates before and after tangential flow filtration concentration using a concentration stabilizing agent. After being concentrated the plates retain their spectral peak shape with no increase in the spectral peak at 400 nm. In one embodiment, plates are concentrated with the identification [MGM1282 and 1279A]. 
           [0031]      FIG. 5  illustrates extinction spectra of high optical density nanoplate solutions processed using the methods described in various embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]    Several embodiments of the present invention comprise processes for making solutions of plasmonic nanoparticle including silver nanoplates that are suitable for performing treatment of a target body region (e.g., such as for tumor ablation, hair removal, acne treatment, wound healing, and antimicrobial applications). Optical Density (O.D.) is the logarithmic ratio of the radiation incident on a material to the radiation transmitted through the material (O.D.=−log 10 (I 1 /I 0 ) where I 1  is the intensity of transmitted light and I 0  is the intensity of the incident light). For solutions, the optical density is a function of the path length through the liquid sample is expressed in units of cm −1 . In some instances, optical density is expressed without the unit cm −1 —such as in instances in which a standard path length of 1 cm is used. 
       Silver Nanoplate Physical Description 
       [0033]    In one embodiment, silver nanoplates are characterized by lengths along the three principle axes wherein: the axial length of two of the principle axes is at least two times greater than the axial length of the shortest principle axis and the shortest principal axial length is less than about 500 nm. 
         [0034]    The ratio of the average of the two longer principle axes to the shorter principle axes is referred to as the aspect ratio. In one embodiment the average aspect ratio of the silver plates is greater than 1.5, 2, 3, 4, 5, 7, 10, 20, 30, or 50, or any range therein (e.g., greater than 8, 9, 11, 12, 13, 14, 15, 25, 35, 40, 45). In various embodiments the average aspect ratio of the silver plates is between 1.5 and 25, 2 and 25, 1.5 and 50, 2 and 50, 3 and 25, or 3 and 50 (e.g., 5 and 20, 10 and 15, 5 and 40, 5 and 30, 5 and 20, 10 and 50, 20 and 50, 30 and 50, 40 and 50, 10 and 20, 20 and 30, 30 and 40, 40 and 50, and any values between 1.5 and 50, inclusive). 
         [0035]    In one embodiment the nanoplate has edge lengths less than 500 nm, 250 nm, 200 nm, 150 nm, 100 nm, 80 nm, 60 nm or 50 nm (e.g., 400 nm, 300 nm, 225 nm, 175 nm, 125 nm, 90 nm, 70 nm, 55 nm, and any values between 500 and 50 nm, inclusive). In one embodiment the nanoplate has edge lengths greater than 5 nm, 10 nm, 20 nm, 30 nm, 50 nm or 100 nm, or any value therein or more (e.g., 15, 25, 40, 60, 70 75, 80, 90, 5-100, 20-80, 30-50, 45-95 nm, and/or 30 nm to 100 nm, 20 nm to 150 nm, 10 nm to 200 nm, 10 nm to 300 nm). In one embodiment the nanoplate has a thickness (third principle axis) that is less than 500 nm, 300 nm, 200 nm, 100 nm, 80 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, or 10 nm, or any value therein (e.g., 400 nm, 250 nm, 150 nm, 75 nm, 5 nm to 20 nm, 5 nm to 30 nm, 10 nm to 30 nm, 10 nm to 50 nm, 10 nm to 100 nm). 
         [0036]    Silver nanoplates have a variety of different cross sectional shapes including circular, triangular, or shapes that have any number of discrete edges. In one embodiment the nanoplates have less than 20, 15, 10, 8, 6, 5, or 4 edges (e.g., 18, 12, 11, 9, 2, 1). In one embodiment the nanoplates have more than 2, 3, 4, or 5 edges (e.g., 6, 7, 10, 15, 20 or more). In some embodiments the silver nanoplates have sharp corners and in other embodiments the corners are rounded. In some embodiments of silver nanoplates, there are a variety of different cross sectional shapes within the same sample. In other embodiments of silver nanoplate solutions greater than 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the number of particles in solution are silver nanoplates with the other particles having different shapes including but not limited to spherical, cubic, and irregular. In one embodiment the nanoplates have one or two flat sides. In another embodiment the nanoplates are pyramidal. 
       Silver Nanoplate Fabrication 
       [0037]    The silver nanoplates utilized in various embodiments of this invention may be fabricated using photoconversion (Jin et al. 2001; Jin et al. 2003), pH controlled photoconversion (Xue 2007), thermal growth (Hao et al. 2004; Hao 2002; He 2008; Metraux 2005), templated growth (Hao et al. 2004; Hao 2002), seed mediated growth (Aherne 2008; Chen; Carroll 2003; Chen; Carroll 2002, 2004; Chen et al. 2002; He 2008; Le Guevel 2009; Xiong et al. 2007), or alternative methods. Alternative methods include methods in which the silver nanoplates are formed from a solution comprising a shape stabilizing agent or agents and a silver source, and in which chemical agents, biological agents, electromagnetic radiation, or heat are used to reduce the silver source. 
         [0038]      FIG. 1  illustrates the optical spectrum of a silver nanoplate solution as fabricated using a photoconversion method according to one embodiment of the present invention. In one embodiment, a silver nanoplate solution is fabricated using a photoconversion method identified as [DSS1099, alternative spectrum ARS1134]—as fabricated, these silver nanoplates have an optical density of less than 1 cm −1 . 
         [0039]      FIG. 2  illustrates a transmission electron micrograph of silver nanoplates fabricated using a photoconversion method according to one embodiment of the present invention. In  FIG. 2 , the scale bar is 50 nm. 
         [0040]      FIG. 3  illustrates one embodiment of plates concentrated in the absence of a concentration stabilizing agent with normalized (bottom) and unnormalized (top) optical extinction spectra of as-fabricated silver nanoplates before and after tangential flow filtration concentration. After concentration the plates have a significantly changed peak shape as demonstrated by the normalized plot, and a spectral peak at 400 nm that demonstrates that a large number of silver nanoplates have turned into silver nanospheres. In one embodiment, plates are concentrated with the identification [MGM1201 and 1195E]. 
         [0041]      FIG. 4  illustrates one embodiment of plates concentrated in the presence of a concentration stabilizing agent with normalized (bottom) and unnormalized (top) optical extinction spectra of as-fabricated silver nanoplates before and after tangential flow filtration concentration using a concentration stabilizing agent. After being concentrated the plates retain their spectral peak shape with no increase in the spectral peak at 400 nm. In one embodiment, plates are concentrated with the identification [MGM1282 and 1279A]. 
         [0042]      FIG. 5  illustrates optical extinction spectra of high optical density nanoplate solutions processed using the methods described in various embodiments of the invention. 
       Silver Nanoplate Coating 
       [0043]    In one embodiment, silver nanoplates have molecules that are adsorbed or otherwise bound to the particle surface. The molecules on the surface are the reactants or reactant by-products of the synthesis. One object of one embodiment of this invention is to partially or fully exchange the molecules that are bound to the surface of the silver nanoplates with other molecules that more fully protect the particles from changing shape during concentration. Another object of one embodiment of the invention is to use a stabilizing agent during fabrication that generates plate shapes and also stabilizes the nanoplates during subsequent concentration. 
         [0044]    In various embodiments, stabilizing agent variants that may be utilized include chemical or biological agents that are physisorbed to the surface, molecularly bound to the surface through specific interactions (e.g. thiol or amine), or encapsulate the surface (i.e. a metal oxide or metalloid oxide shell). In various embodiments, specific chemical agents of interest include polymers such as polysulphonates, vinyl polymers, carbohydrates, ethylene oxides, phenols, and carbohydrates. In various embodiments, specific examples of these polymers include poly(sodium) styrene sulfonate, polyvinyl alcohol, polyvinyl pyrrolidone, tannic acid, dextran, and polyethylene glycol (PEG) including PEG molecules which contain one or more chemical groups (e.g. amine, thiol, acrylate, alkyne, maleimide, silane, azide, hydroxyl, lipid, disulfide, fluorescent molecule, or biomolecule moieties). In various embodiments, specific biomolecules of interest include proteins, peptides, and oligonucleotides, including biotin, bovine serum albumin, streptavidin, neutravidin, wheat germ agglutinin, naturally occurring and synthetic oligonucleotides and peptides, including synthetic oligonucleotides which have one or more chemical functionalities (e.g. amine, thiol, dithiol, acrylic phosphoramidite, azide, digoxigenin, alkynes, or biomolecule moieties). Specific encapsulating chemical agents of interest include metal oxide shells such as SiO 2  and TiO 2 . Stabilizing agents may be added prior to the formation of silver nanoplates, during the formation of silver nanoplates, or after the formation of silver nanoplates. An additional chemical agent of interest is gum arabic. 
       Carrier Solutions 
       [0045]    In one embodiment of this invention the silver nanoplates are fabricated in aqueous solutions. In other embodiments the silver nanoplates are fabricated in other solutions that can include ethanol, isopropanol, or organic solvents such as heptane, toluene, or butanol. 
         [0046]    In one embodiment an acid, base or buffering agent (e.g., a buffer) is added to change the solution pH either before, during, or after the addition of a stabilant. In various embodiments, the nanoplates are suspended in a sodium bicarbonate buffer or a sodium borate buffer. 
       Surface Stabilization 
       [0047]    In various embodiments, stabilizing agents can be solid or liquid formulations that are added to the silver plate solution. The stabilizing agents have an affinity for the surface of the silver nanoplates and will associate with the plate surface. In some embodiments, the bound molecules on the silver nanoplates will be displaced by the added stabilizing agents. In some embodiments the stabilants are added to the as-fabricated silver nanoplate solution. In other embodiments, the solution of nanoplates is washed, or the residual reactants are otherwise removed. In other embodiments, the suspending solution is exchanged with a different suspending media which includes ethanol, isopropanol, or other polar or non-polar liquids before the stabilizing agents are added. 
         [0048]    Once the stabilizing agent is added, the mixture of the stabilant and the silver nanoplates can undergo a number of different processes including heating, boiling, boiling under reflux, rotoevaporation, vacuum, stirring, stirring with magnetic stir bars, stirring with overhead mixers, stirring with homogenizers, shaking, microfluidization, refrigeration, and freezing. 
       Washing and Concentrating 
       [0049]    In one embodiment, after the stabilization step is complete, the silver nanoplates can be washed to remove residual reactants or to exchange the solution with another solution. In various embodiments, the exchange of solution can be accomplished using dialysis, centrifugation, filtration, or tangential flow filtration. One embodiment of the invention is where the number of wash volumes exchanged within the sample is 1, 2, 3, 4, 5, between 1 and 5, between 5 to 10, between 10 to 20, or more than 20 wash volumes. 
         [0050]    High optical density solutions of the nanoparticles can be fabricated using centrifugation, evaporation, filtration, dialysis or tangential flow filtration. One embodiment of this invention utilizes tangential flow filtration as the process of concentrating the silver nanoplate solution. The filter membrane utilized may be formed from a variety of materials. Specific filter membrane materials of interest include cellulose esters, polysulfone, and polyetheresulfone. The filter membrane utilized may have pores with a molecular weight cutoff of less than about 10 kD, between 10 kD to 500 kD, or more than about 500 kD (e.g., between 10 kD, to 100 kD, 10 kD to 500 kD, 20 kD to 500 kD, 20 kD to 250 kD), and/or pore sizes of less than about 0.05 between 0.05 μm and 0.5 or larger than about 0.5 μm (e.g., between 0.02 μm and 0.1 μm, 0.05 μm and 0.2 μm, 0.05 μm and 0.5 μm, 0.10 μm and 0.2 μm, 0.1 μm and 0.5 μm). Tangential flow filtration can also be utilized to change the solvent in which the silver nanoplates are dispersed. Specific solvents of interest include water and alcohols (e.g. t-butanol, ethanol, and isopropyl alcohol), as well as other polar or non-polar solvents. Additionally, tangential flow filtration can be utilized to remove residual chemicals. 
         [0051]    This invention includes embodiments in which the silver nanoplate solution concentration is increased to produce a final solution with optical densities of greater than about 5 cm −1 , greater than about 10 cm −1 , greater than about 50 cm −1 , greater than about 75 cm − , greater than about 100 cm −1 , greater than about 500 cm −1 , or greater than about 1000 cm −1  (e.g., between 10 cm −1  to 100 cm −1 , 30 cm −1  to 300 cm −1 , 50 cm −1  to 500 cm −1 , 100 cm −1  to 1000 cm −1 , 300 cm −1  to 3000 cm −1 , or 500 cm −1  to 5000 cm −1 ) One embodiment of the invention is where the silver nanoplate solution concentration is increased to above 10 6 , 10 7 , 10 8 , 10 9 , 10 10 , 10 11 , 10 12 , 10 13  particles per milliliter. 
       Storage 
       [0052]    One embodiment of the invention is where the concentrated particles are stored at temperatures below −10, 0, 4, 6, 10, or 20 degrees C. 
         [0053]    One embodiment of the invention is where the particles are frozen and dried under vacuum. One embodiment is where the particles are freeze dried. One embodiment is where the particles are supercritically dried. Another embodiment is where an additional stabilant or other cryoprotectant is added to the solution before the particles are heat dried or freeze dried. 
       Composites 
       [0054]    In one embodiment of the invention, high optical density solutions of silver nanoplates are associated with a substrate. Examples of substrates include fibers, cloth, mesh, bandages, socks, wraps, other articles of clothing, sponges, high porosity substrates, particles with diameters greater than  1  micron, beads, hair, skin, paper, absorbent polymers, foam, wood, cork, slides, roughened surfaces, biocompatible substrates, filters, or medical implants. In one embodiment, the high optical density solutions of silver nanoplates at a concentration of at least 1 mg/mL, 10 mg/mL, 100 mg/mL (e.g., 1 to 10, 3 to 30, 5 to 50, 10 to 20, 5 to 50, 3 to 50, 1 to 100 mg/mL, 10 to 100, 20 to 100, 30 to 100 mg/mL) are incubated with the substrate. In another embodiment, the high optical density solutions of silver nanoplates at a concentration of at least 1 mg/mL, 10 mg/mL, or 100 mg/mL (e.g., 1 to 10, 3 to 30, 5 to 50, 10 to 20, 5 to 50, 3 to 50, 1 to 100 mg/mL, 10 to 100, 20 to 100, 30 to 100 mg/mL) are incubated with the substrate. In another embodiment the silver nanoplates are prepared at an optical density of at least 10, 100, 300, 500, 1000, or 2000 cm −1  (e.g., between 10-100, 20-200, 30-300, 50-500, 100-1000, 200-1000, 300-1000, 500-1000, or 200-2000 cm −1 ) before incubating with the substrate. In another embodiment the substrate is chemically treated to increase the binding of the nanoplates to the substrate. For example, the substrate could be functionalized with a molecule that yielded a positively or negatively charged surface. In another embodiment, the pH of the incubating solution is selected in order to optimize binding. In another embodiment, the silver nanoplates cover at least 5%, 10%, 20%, 30%, 50% or 75% of the substrate (e.g., 5% to 10%, 10% to 100%, 10% to 50%, 50% to 100%, 30% to 100%, 30% to 70%, 40% to 80%, 50% to 90%, 60% to 100%, 70% to 100%, 80% to 100%, 90% to 100%, 0% to 5%, 1% to 10%, 2% to 20%, 5% to 30%, and/or 1% to 50% of the substrate). In another embodiment, other solvents or chemicals are added to the incubation solution. In another embodiment a biological linker (e.g. antibodies, peptides, DNA) is used to bind the high optical density silver nanoplates to the surface of the substrate. In one embodiment, the incubation is for less than 1 minute, 5 minutes, 20 minutes, 60 minutes, or 120 minutes (e.g., 0 to 1 minute, 1 minute to 120 minutes, 5 minutes to 120 minutes, 20 minutes to 120 minutes, 60 minutes to 120 minutes, 5 minutes to 60 minutes, 10 minutes to 60 minutes, 20 minutes to 60 minutes, 0 minutes to 10 minutes, 0 minutes to 20 minutes, or 0 minutes to 5 minutes). 
         [0055]    In one embodiment, the substrate is separated from the incubating solution and dried. The substrate can be dried using air drying, heat drying, freeze drying, or supercritical drying. In another embodiment the dried substrate can be further processed by soaking the substrate in another material, painting the substrate with another material, or exposing the substrate to another material that is in the vapor phase. 
         [0056]    Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as disclosing certain embodiments of the invention only, with a true scope and spirit of the invention being indicated by the following claims. 
         [0057]    The subject matter described herein may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting. While embodiments are susceptible to various modifications, and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms or methods disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the various embodiments described and the appended claims. Any methods disclosed herein need not be performed in the order recited. 
         [0058]    The methods disclosed herein include certain actions taken by a practitioner; however, they can also include any third-party instruction of those actions, either expressly or by implication. For example, actions such as “identifying a target region of skin tissue” include “instructing the identification of a target region of skin tissue.” 
         [0059]    The ranges disclosed herein also encompass any and all overlap, sub-ranges, and combinations thereof. Language such as “up to,” “at least,” “greater than,” “less than,” “between,” and the like includes the number recited. Numbers preceded by a term such as “about” or “approximately” or “substantially” include the recited numbers. For example, “about 3 mm” includes “3 mm.” The terms “approximately”, “about” and/or “substantially” as used herein represent an amount or characteristic close to the stated amount or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of the stated amount or characteristic. 
       EXAMPLES  
       [0060]    Modern nanoparticle synthesis techniques have enabled the development of materials with unique optical properties for a wide range of applications including diagnostic, obscurant, and therapeutic applications. When as-fabricated nanoplates are concentrated using tangential flow filtration, the shape many of the plates shift to nanospheres, reducing the formulation efficacy, as evidenced by the increased peak height at 400 nm. By exchanging the surface capping agent of as-fabricated silver nanoplates with an agent that provides stability before, during, and/or after concentration, the silver nanoplates can be concentrated to increase the solution optical density without destabilizing the plates and degrading the beneficial optical properties. 
         [0061]    The description of specific examples below are intended for purposes of illustration only and are not intended to limit the scope of the invention disclosed herein. 
       Example 1 
       [0062]    15 L of silver nanoplates with a peak optical density of about 5 cm −1  were mixed with 3.5 g of polyvinylalcohol (PVA), and concentrated using tangential flow filtration using a 500 kD polysulfone tangential flow membrane with 3100 cm 2  of surface area. The solution was concentrated for approximately 90 minutes, and the final solution volume was reduced from 15 L to 0.5 L. The increase of the silver nanoplate solution optical density was from 5 to about 150 cm −1 . Thus, according to one embodiment, a method for increasing a silver nanoplate solution from 5 cm −1  to 150 cm −1  (e.g., an increase of roughly 30 times the optical density) comprises the steps of adding PVA to silver nanoplates, and concentrating the solution with tangential flow filtration. 
       Example 2 
       [0063]    1.2 L of silver nanoplates with a peak optical density of about 4 cm −1  were mixed with 4 L of anhydrous ethanol and about 49 mL of ammonium hydroxide solution. 0.6 mL of a dilute aminopropyltriethoxysilane (APTES) was added to the solution. After 15 minutes of incubation, 6.5 mL of tetraethylorthosilicate (TEOS) solution was added. After 24 hours 1 L of the solution was concentrated using a 500 kD polysulfone tangential flow membrane with 1050 cm 2  of surface area. The final solution volume was decreased to 150 mL, increasing the silver nanoparticle solution optical density to about 40 cm −1 . Thus, according to one embodiment, a method for increasing a silver nanoplate solution from 4 cm −1  to 40 cm −1  (e.g., an increase of roughly 10 times the optical density) comprises the steps of adding anhydrous ethanol, ammonium hydroxide solution, aminopropyltriethoxysilane (APTES), and tetraethylorthosilicate (TEOS) to the silver nanoplates, and concentrating the solution with tangential flow filtration. 
       Example 3 
       [0064]    A 40 mL solution of 40 O.D. solution of concentrated silver nanoplates was spun at 3000 RCF for 30 minutes. This processed was used to concentrate the silver nanoplates to an optical density of 1000 O.D. 
       Example 4 
       [0065]    A 5 mL solution of 1000 OD silver nanoplates was added to a 3″×3″ section of absorbant cloth (Absorber Synthetic Drying Chamois, Clean Tools). After addition, the substrate was allowed to air dry. Once dried, the silver nanoplates were bound to the surface of the absorbant cloth and were not released when the cloth was subsequently wet and water removed by applying pressure. 
       REFERENCES  
       [0066]    Aherne, D. L., D. M.; Gara, M.; Kelly, J. M., 2008: Optical Properties and Growth Aspects of Silver Nanoprisms Produced by Highly Reproducible and Rapid Synthesis at Room Temperature.  Advanced Materials,  18, 2005-2016. 
         [0067]    Chen, S., and D. L. Carroll, 2003: Controlling 2-dimensional growth of silver nanoplates.  Self - Assembled Nanostructured Materials Symposium  ( Mater. Res. Soc. Symposium Proceedings  Vol. 775), 343-348|xiii+394. 
         [0068]    Chen, S. H., and D. L. Carroll, 2002: Synthesis and characterization of truncated triangular silver nanoplates.  Nano Letters,  2, 1003-1007. 
         [0069]    Chen, S. H., and D. L. Carroll, 2004: Silver nanoplates: Size control in two dimensions and formation mechanisms.  Journal of Physical Chemistry B,  108, 5500-5506. 
         [0070]    Chen, S. H., Z. Y. Fan, and D. L. Carroll, 2002: Silver nanodisks: Synthesis, characterization, and self-assembly.  Journal of Physical Chemistry B,  106, 10777-10781. 
         [0071]    Hao, E., G. C. Schatz, and J. T. Hupp, 2004: Synthesis and optical properties of anisotropic metal nanoparticles.  Journal of Fluorescence,  14, 331-341. 
         [0072]    Hao, E. K., K. L.; Hupp, J. T.; Schatz, G. C., 2002: Synthesis of Silver Nanodisks using Polystyrene Mesospheres as Templates.  J Am Chem Soc,  124, 15182-15183. 
         [0073]    He, X. Z., X.; Chen, Y.; Feng, J., 2008: The evidence for synthesis of truncated silver nanoplates in the presence of CTAB.  Materials Characterization,  59, 380-384. 
         [0074]    Jin, R., Y. Cao, C. A. Mirkin, K. L. Kelly, G. C. Schatz, and J. G. Zheng, 2001: Photoinduced Conversion of Silver Nanospheres to Nanoprisms.  Science,  294, 1901-1903. 
         [0075]    Jin, R., Y. C. Cao, E. Hao, G. S. Metraux, G. C. Schatz, and C. A. Mirkin, 2003: Controlling anisotropic nanoparticle growth through plasmon excitation.  Nature,  425, 487. 
         [0076]    Le Guevel, X. W., F. Y.; Stranik, O.; Nooney, R.; Gubala, V.; McDonagh, C.; MacCraith, B. D., 2009: Synthesis, Stabilization, and Functionalization of Silver Nanoplates for Biosensor Applications.  J Phys Chem C,  113, 16380-16386. 
         [0077]    Metraux, G. S. M., C. A; 2005: Rapid Thermal Synthesis of Silver Nanoprisms with Chemically Tailorable Thickness.  Advanced Materials,  17, 412-415. 
         [0078]    Xiong, Y. J., A. R. Siekkinen, J. G. Wang, Y. D. Yin, M. J. Kim, and Y. N. Xia, 2007: Synthesis of silver nanoplates at high yields by slowing down the polyol reduction of silver nitrate with polyacrylamide.  Journal of Materials Chemistry,  17, 2600-2602. 
         [0079]    Xue, C. M., C. A., 2007: pH-Switchable Silver Nanoprism Growth Pathways.  Angew Chem Int Ed,  46, 2036-2038. 
         [0080]    Each of the references listed above is incorporated by reference in its entirety.