Encapsulated dye coated noble metal nanoparticles with increased surface enhanced raman scattering properties as contrast agents

Abstract

The present disclosure provides semiconductor-metal composite nanoparticles with optical properties that are superior to those of pure materials for use as contrast agents. The composites include noble metal nanoparticles having a layer of linker molecules being bound to the surface of the noble metal nanoparticle and a layer of dye molecules bound to the layer of linker molecules. The dye molecules are selected such that they form an ordered structure that exhibits a collective absorption band shift, compared to the individual dye molecule, when bound to the noble metal nanoparticle. This structure is encapsulated in a stabilizing coating layer forming a multi-shell structure with properties suitable for biosensing and other detection applications which exhibit enhanced Raman scattering compared to nanoparticles having dye molecules bound thereto not in the ordered structure.

1 . A method of producing exitonic semiconductor noble metal composite nanoparticles for enhanced Raman scattering, comprising:
 preparing a solution of dye molecules and linker molecules;   adding the solution of dye and linker molecules to a solution of noble metal nanoparticles under conditions selected to induce self-assembly of the linker and dye molecules to produce composite particles having a layer of the linker molecules attached to a surface of the noble metal nanoparticle and a layer of the dye molecules attached to the layer of linker molecules, the dye molecules being selected such that they interact cooperatively with each other and with the surface, when bound to the linker layer, to produce an optical absorption spectrum that is shifted in wavelength relative to an absorption spectrum of a single dye molecule;   encapsulating the composite particles in a stabilizing and fluorescence-reducing coating layer; and   washing the encapsulated composite particles.   
     
     
         2 . The method according to  claim 1  wherein said noble metal nanoparticles are any of gold, silver, copper, nickel, palladium, platinum, ruthenium, rhodium, osmium, iridium, or an alloy of any of the foregoing metals. 
     
     
         3 . The method according to  claim 1  wherein said linker molecules have a length in a range from about 0.1 nm to about 10 nm. 
     
     
         4 . The method according to  claim 1  wherein said linker molecules are separate molecules from said dye molecule and include any one of one or combination of thiocholine, trimethylammonium conjugated alkanethiols, acrylates, NN-trimethyl(alkyl)ammonium, tetrabutylammonium, tetratmethylammonium brominde, cetyltrimethylammonium bromide, citrates, poly methacrylate, ascorbic acid, DNAs, 2-mercaptopropionic acid, 16-mercaptohexadecanoic acid, dodecyl sulfate, amino acids, homocysteine, homocystine, cysteine, cysteine, cysteine, and glutathione and derivatives thereof. 
     
     
         5 . The method according to  claim 1  wherein said linker molecules are a molecular portion of the dye molecule, said molecular portion including a moiety which binds to the surface of the noble metal nanoparticle. 
     
     
         6 . The method according to  claim 5  wherein said dye includes thiolated aggregate-forming dyes containing said molecular agent that adsorb directly on the surface of the nanoparticle. 
     
     
         7 . The method according to  claim 1  wherein said dye includes any one of polymethine dye, where the polymethine dye may be, but not limited to, a cyanine dye, including but not limited to merocyanines, indocyanines, anthrocyanines, phycocyanine, isocyanines, pseudoisocyanines and thiacyanines; squaraines; perylene bisimides; any of the above in combination, e. g., a squaraine and a cyanine conjugated together. 
     
     
         8 . The method according to  claim 1  wherein said dye includes all classes of cyanine dye that form J-aggregates, H-aggregates, aggregates in which a collective absorption of the aggregate is different than that of the monomeric species of that dye. 
     
     
         9 . The method according to  claim 1 , wherein said stabilizing coating is a lipid bilayer, said lipid bilayer being any one of phospholipid alone, sphingolipid alone, phospholipid and sphingolipid, phospholipid and sterol, sphingolipid and sterol, phospholipid and sphingolipid and sterol, wherein said phospholipid is one type or a mixture of phospholipids, said sphingolipid is one type or a mixture of sphingolipids, and said sterol is one type or a mixture of sterols, to form a mixture. 
     
     
         10 . The method according to  claim 9  wherein said phospholipids have one or more hydrocarbon chain(s) being any one or combination of saturated, monounsaturated, and polyunsaturated. 
     
     
         11 . The method according to  claim 9  wherein said phospholipids and sphingolipids have headgroups selected from the group consisting of phosphatidyl choline (PC), phosphatidyl ethanolamine (PA), phosphatidyl inositol (PI), and phosphatidyl glycerol (PG). 
     
     
         12 . The method according to  claim 9  wherein said phospholipids, sphingolipids and sterols have headgroups can be positively charged, negatively charged, zwitterionic, or neutral. 
     
     
         13 . The method according to  claim 9  wherein said phospholipids, sphingolipids and sterols include chemically modified tail groups and/or chemically modified headgroups. 
     
     
         14 . The method according to  claim 9  wherein said phospholipids are any one or combination of naturally occurring or synthetic, and wherein said sphingolipids are any one or combination of naturally occurring or synthetic, and wherein said sterols are any one or combination of naturally occurring or synthetic. 
     
     
         15 . The method according to  claim 9  wherein the encapsulating step comprises adding detergent molecules in a suspension of lipids into which the nanoparticles are immersed to form the lipid bilayer around said nanoparticles. 
     
     
         16 . The method according to  claim 9  including controlling a distribution of charged lipids in said lipid bilayer by addition of acids and/or salts in a suspension of lipids into which the nanoparticles are immersed to form the lipid bilayer around said nanoparticles. 
     
     
         17 . The method according to  claim 9  wherein lipid encapsulated dye aggregate coated noble metal nanoparticles are separated from unbound phospholipids and organic dye molecules by centrifugation. 
     
     
         18 . The method according to  claim 9  wherein said dye aggregate coated noble metal nanoparticles are capped by positively or negatively charged ligands with lipids. 
     
     
         19 . The method according to  claim 1 , wherein the stabilizing coating encapsulating a nanoparticle has a ligand covalently linked thereto wherein the ligand is an antibody, an antibody fragment, or other targeting ligands to selectively target cell surface receptors and sub-cellular markers. 
     
     
         20 . The method according to  claim 19 , wherein said other targeting ligands includes any one or combination of antibody fragments, peptides, DNA, RNA, proteins, affibodies, monobodies, drugs, cell surface markers, and sub-cellular markers. 
     
     
         21 . The method according to  claim 1  wherein said encapsulated dye aggregate coated noble metal nanoparticles are conjugated to monoclonal antibodies and other targeting ligands using one or both of physical and chemical means of associating these with either the gold particle core, or the phospholipid encapsulating said gold nanoparticles. 
     
     
         22 . The method according to  claim 1 , where the stabilizing coating is a lipid bilayer, where the dye is housed within the bilayer structure itself, on either surface of the bilayer, or the use of an ordered structure -forming dye modified so as to be conjugated physically to a lipid component. 
     
     
         23 . The method according to  claim 1  wherein said composite has a dielectric constant having wavelength dependent real and imaginary parts value which are
 approximately equal and 
 approach zero at a given wavelength, 
 and wherein excitation of said composite by a laser excitation source having a wavelength near the given wavelength results in an enhanced SERS signal compared to excitation of the same nanoparticle in which the dye does not form an ordered structure with a shifted absorption spectrum. 
 
     
     
         24 . The method according to  claim 1  wherein the stabilization coating has a thickness in a range from about 0.1 nm to about 100 nm. 
     
     
         25 . The method according to  claim 1  wherein said stabilizing coating is an inorganic oxide selected from semiconductor oxide and transition metal. 
     
     
         26 . The method according to  claim 1 , wherein said stabilizing coating is an oxide of any one of silicon, titanium and mixtures thereof. 
     
     
         27 . A method of producing enhanced Raman scattering with exitonic semiconductor noble metal composite nanoparticles produced according to the method of  claim 1 , comprising:
 identifying the optimal excitation wavelengths for field enhancement through a theoretical simulation that includes the complex dielectric constants of the metal and the molecular aggregate, wherein a wavelength near where the plasmon is observed is matched with the excitation wavelength (or stokes shifted wavelength) and a wavelength near where the real and imaginary components of ϵ jagg  are approximately equal and approach zero is matched with the Stokes shift (or excitation wavelength) and identifying the plasmon through a combination of theoretical simulation and experimental measurement, and depends on the size, shape, composition and environment of the metal nanoparticle.   demonstrating the field enhancement by measuring Raman scattering strength with excitation at different wavelengths.