Self-assembled metal colloid monolayers

Abstract

A biosensor based on complexes between biomolecule receptors and colloidal Au nanoparticles, and more specifically, colloid layers of receptor/Au complexes that can be used to detect biomolecule analytes through measuring of binding-induced changes in electrical resistance or surface plasmon resonance. Also disclosed is a method for detecting and analysing carrier-borne chemical compounds with Raman spectroscopy using an improved SERS substrate. Further disclosed is an improved method for detecting compounds in solvents using capillary electrophoresis in conjunction with Raman spectroscopy.

What is claimed is:  
     
         1 . A process for detecting and quantifying an amount of a chemical compound in a carrier, said process comprising: 
 placing a sample comprising said chemical compound in said carrier on a surface-enhanced Raman scattering (SERS)-active surface;    subjecting said sample to Raman spectroscopy; and    analyzing data generated by said Raman spectroscopy and determining a concentration of said compound in said sample from said data    wherein said SERS-active surface is prepared by a method comprising the steps of: 
 coating a substrate with a bifunctional organic film to impart to said substrate a functionality that allows for bonding of metal colloid particles; and  
 contacting the organic film coated substrate with a solution of colloid metal particles to bind said particles to functional groups on said organic film thereby forming a monolayer or submonolayer of said particles.  
   
     
     
         2 . The process of  claim 1 , wherein said substrate is selected from the group consisting of glass, quartz, alumina, tin oxides and metals.  
     
     
         3 . The process of  claim 1 , wherein functionality is imparted either by covalent or non-covalent bonding.  
     
     
         4 . The process of  claim 1 , wherein said metal colloid monolayers or submonolayers comprise a colloid of a metal particles selected from the group consisting of silver, gold, mixtures of silver and gold, and silver/gold bimetallic particles.  
     
     
         5 . The process of  claim 1 , wherein the size of said metal particles lies within the range of 3-100 nm.  
     
     
         6 . The process of  claim 1 , wherein said contacting of the organic film with a solution of metal colloid particles is done by immersing the coated substrate into a solution of colloid metal particles causing the particles to bind to functional groups of the organic film coated substrate.  
     
     
         7 . The process of  claim 1 , wherein said bifunctional organic film is an organosilane, poly(allylamine) hydrochloride or a biotin.  
     
     
         8 . The process of  claim 7 , wherein said coating step involves surface-initiated polymerization of a bifunctional alkoxysilane having the formula (RO) 3 Si(CH 2 ) 3 A, wherein pendent functional group A has a high affinity toward metal surfaces.  
     
     
         9 . The process of  claim 3 , wherein said metal particles are coated with a protein.  
     
     
         10 . The process of  claim 9 , wherein said substrate is coated with biotin and then contacted with a colloidal metal derivatized with a protein and streptavidin or avidin, thereby forming a colloid based biocompatible surface held together by non-covalent interactions.  
     
     
         11 . The process of  claim 1 , wherein said chemical compound is selected from the group consisting of pesticides, disinfection-generated pollutants and environmental toxins and said carrier is water.  
     
     
         12 . The process of  claim 11 , wherein said chemical compound is a pesticide, and said pesticide is an organophosphorous pesticide.  
     
     
         13 . The process of  claim 11 , wherein said chemical compound is a disinfection-generated pollutant and said pollutant is a haloacetic acid.  
     
     
         14 . The process of  claim 1 , wherein said compound is a compound having a Raman-active mode, and said carrier is air.  
     
     
         15 . A process for detecting and quantifying an amount of a chemical compound in a carrier, said process comprising: 
 placing a sample comprising said chemical compound in said carrier on a surface-enhanced Raman scattering (SERS)-active surface;    subjecting said sample to Raman spectroscopy; and    analyzing data generated by said Raman spectroscopy and determining a concentration of said compound in said sample from said data    wherein said SERS-active surface is prepared by a method comprising the steps of: 
 coating a substrate selected from the group consisting of glass, quartz, alumina, tin oxides and metals, with a bifunctional organic film selected from the group consisting of organosilanes, poly(allylamine) hydrochloride and biotin, to impart to said substrate a functionality that allows for bonding of metal colloid particles, to form an organic film coated substrate; and  
 immersing the organic film coated substrate in a solution of colloid metal particles to bind said particles to functional groups on said organic film thereby forming a monolayer or submonolayer of said particles,  
   
     
     
         16 . The process of  claim 15 , wherein said colloid metal particles are selected from Au and Ag.  
     
     
         17 . The process of  claim 15 , wherein the size of said metal particles lies within the range of about 3 to about 100 nm.  
     
     
         18 . The process of  claim 15 , wherein said metal particles are coated with a protein.  
     
     
         19 . The process of  claim 18 , wherein said substrate is coated with biotin and then contacted with a colloid metal coated with a protein and streptavidin thereby forming a colloid based biocompatible surface held together by non-covalent interactions.  
     
     
         20 . The process of  claim 15 , wherein said compound is a pesticide, and said carrier is water.  
     
     
         21  The process of  claim 20 , wherein said pesticide is an organophosphorous pesticide.  
     
     
         22 . The process of  claim 12 , wherein said organophosphorous pesticide is selected from the group consiting of methyl-parathion, diazinon, cyanox, formthion, dimethoate, fonofoxon, chlorfenvinphos, trichlorofon, and mixtures thereof.  
     
     
         23 . The process of  claim 21 , wherein said organophosphorous pesticide is selected from the group consiting of methyl-parathion, diazinon, cyanox, formthion, dimethoate, fonofoxon, chlorfenvinphos, trichlorofon, and mixtures thereof.  
     
     
         24 . The process of  claim 1 , wherein said colloidal metal particles are monodisperse Au particles having a particle size of about 3 to about 100 nm, sufficiently spaced on said substrate to be only weakly SERS enhancing, overcoated with Ag.  
     
     
         25 . The process of  claim 24 , wherein the Ag overcoating is formed using autometallography.  
     
     
         26 . The process of  claim 1  wherein said data derived from said Raman spectroscopy is analyzed to determine a concentration of said compound in said sample.  
     
     
         27 . The process of  claim 15 , wherein said colloidal metal particles are monodisperse Au particles having a particle size of 3-100 nm, sufficiently spaced on said substrate to be only weakly SERS enhancing, overcoated with Ag.  
     
     
         28 . The process of  claim 27 , wherein the Ag overcoating is formed using autometallography.  
     
     
         29  A biosensor for quantifying the presence of a biomolecule analyte, said biosensor comprising a complex of a receptor that binds to said biomolecule analyte and colloidal Au nanoparticles, said complex being surface confined on a substrate to form at least one layer of receptor/colloidal Au nanoparticle complexes on said substrate.  
     
     
         30 . The biosensor of  claim 29 , wherein said nanoparticles have a particle diameter between about 3 nm and about 100 nm.  
     
     
         31 . The biosensor of  claim 30 , wherein said complex is formed by exposing a surface of an Au colloidal monolayer formed on said substrate to said receptor.  
     
     
         32 . The biosensor of  claim 29 , wherein said complex is formed by forming an receptor/Au nanoparticle complex colloid and surface confining said complex on said substrate.  
     
     
         33 . The biosensor of  claim 29 , wherein said Au nanoparticles act as a discontinuous conductor and said receptor functions as an insulator that surrounds the particles of said conductor, wherein swelling of said insulator, caused by a complexing of said receptor with a biomolecule antigen increases insulator volume and decreases conductor volume fraction.  
     
     
         34 . The biosensor of  claim 33 , wherein a coverage of said receptor/Au nanoparticle complex on said substrate is adjusted whereby, when no biomolecule analyte is present, and said swelling does not occur, said conductor concentration is greater than a percolation threshold value, and when said biomolecule analyte is present and said swelling occurs, said conductor concentration is reduced to a value below said percolation threshold value.  
     
     
         35 . The biosensor of  claim 29 , wherein a plurality of analyte/Au nanoparticle complex layers are formed on said substrate.  
     
     
         36 . A device for determining the presence and concentration of a biomolecule analyte, said device comprising; 
 the biosensor of  claim 29;     means for applying a voltage across said biosensor:    means for measuring an electrical characteristic of said biosensor; and    means for converting the measured electrical characteristic to a biomolecule analyte concentration.    
     
     
         37 . The device of  claim 36 , wherein said electrical characteristic is resistance.  
     
     
         38 . A process for detecting and quantifying an amount of a biomolecule analyte, in a carrier, said process comprising forming a biosensor comprising a complex of a receptor that binds to said biomolecule analyte and colloidal Au nanoparticles, said complex being surface confined on a substrate to form at least one layer of a receptor/colloidal Au nanoparticle complex on said substrate; wherein 
 said Au nanoparticles act as a discontinuous conductor and said receptor functions as an insulator that surrounds the particles of said conductor, wherein swelling of said insulator, caused by a complexing of said receptor with a biomolecule analyte increases insulator volume and decreases conductor concentration, a coverage of said receptor/Au nanoparticle complex on said substrate being adjusted whereby, when no biomolecule analyte is present, and said swelling does not occur, said conductor concentration is greater than a percolation threshold value, and when said biomolecule analyte is present and said swelling occurs, said conductor concentration is reduced to a value below said percolation threshold value;    exposing said biosensor to said carrier containing said biomolecule analyte;    applying a voltage across said biosensor;    measuring an electrical characteristic of said biosensor; and    converting the measured electrical characteristic to a biomolecule analyte concentration.    
     
     
         39 . A process for detecting and quantifying an amount of a biomolecule analyte, in a carrier, said process comprising forming a biosensor comprising a layer of a receptor/colloidal Au nanoparticle complex surface confined on a substrate, said layer having an initial thickness insufficient to achieve surface plasmon resonance upon application of a voltage across said biosensor; 
 first exposing said biosensor to said carrier containing said biomolecule analyte, and;    subsequently exposing said biosensor to an additional amount of said receptor/colloidal Au nanoparticle complex, whereby,    when analyte biomolecules are present in said carrier, said analyte biomolecules in said carrier bind to said receptor of said complex surface confined to said substrate upon exposure to said biosensor and to said receptor of said additonal amount of said complex upon subsequent exposure of said biosensor to said additional amount of said receptor/colloidal Au nanoparticle complex, increasing the thickness of said layer whereby said layer has a final thickness sufficient to achieve surface plasmon resonance upon application of a voltage across said biosensor, said method further comprising; 
 applying a voltage across said biosensor;  
 measuring an electrical characteristic of said biosensor; and  
 converting the measured electrical characteristic to a biomolecule analyte concentration.  
   
     
     
         40 . The process of  claim 39 , wherein said electrical characteristic is resistance.  
     
     
         41  An improved method for detecting low concentrations of at least one compound in a solvent using capillary electrophoresis, said method comprising: 
 providing a surface enhanced Raman scattering (SERS)-active surface on a substrate;  
 placing a first end of a capillary tube in a solvent reservoir containing said solvent and placing a second end of said capillary tube on said SERS-active surface:  
 applying an electric current between said solvent reservoir and said SERS-active surface to cause said solvent to elute through said capillary tube onto said SERS-active surface;  
 moving said second end of said capillary tube across said SERS-active surface whereby different compounds in said solvent are deposited at different positions on said SERS-active surface;  
 subjecting said different compounds to Raman spectroscopy; and  
 analyzing data generated by said Raman spectroscopy and determining a composition of said different compounds in said solvent;  
 wherein said SERS-active surface is prepared by a method comprising the steps of: 
 coating a substrate with a bifunctional organic film to impart to said substrate a functionality that allows for bonding of metal colloid particles; and  
 contacting the organic film coated substrate with a solution of colloid metal particles to bind said particles to functional groups on said organic film thereby forming a monolayer or submonolayer of said particles.  
 
 
     
     
         42 . The method of  claim 41 , wherein said substrate is electrically conductive and said electric current is applied between said solvent reservoir and said substrate.  
     
     
         43 . The method of  claim 41 , wherein said second end of said capillary is metallized and said electric current is applied between said solvent reservoir and said second end of said capillary.  
     
     
         44 . The method of  claim 41 , wherein said SERS-active surface on which said compounds are eluted is analyzed by rastering said surface across a focused laser and recording a resulting Raman spectra.  
     
     
         45 . A metal colloid monolayer comprising a plurality of colloidal Ag clad Au nanoparticles surface confined on a substrate, said monolayer having a gradient of nanoparticle density in a first direction, and a gradient in particle size in a second direction perpendicular to said first direction.  
     
     
         46 . The metal colloid monolayer of  claim 45 , wherein said nanoparticles are bound to said substrate by bonding with functional groups of a bifunctional organic film.  
     
     
         47 . The metal colloid monolayer of  claim 46 , wherein said bifunctional organic film is selected from the group consisting of an organosilane, poly(allylamine) hydrochloride and biotin.  
     
     
         48 . The metal colloid monolayer of  claim 45 , wherein said substrate is selected from the group consisting of glass, quartz, alumina, tin oxides and metals.  
     
     
         49 . The metal colloid monolayer of  claim 45 , wherein said nanoparticles have a size of about 3 nm to about 100 nm.  
     
     
         50 . A metal colloid monolayer comprising a plurality of colloidal Ag clad Au nanoparticles surface confined on a substrate, said monolayer having a gradient of nanoparticle density in a first direction, and a gradient in particle size in a second direction perpendicular to said first direction formed by: 
 coating a substrate with a bifunctional organic film;    immersing the coated substrate into a colloidal Au solution such that a first leading edge of said substrate is immersed in said colloidal Au solution for a longer period of time relative to a first trailing edge to provide a monolayer of Au nanoparticles having a decreasing level of coverage from said first leading edge to said first trailing edge;    withdrawing said substrate from said colloidal Au solution;    rotating said substrate through an angle of about 90°;    immersing the substrate provided with the monolayer of Au nanoparticles in an Ag +  solution such that a second leading edge of said substrate is immersed in said Ag +  solution for a longer period of time relative to a second trailing edge to provide a monolayer of Au nanoparticles having a decreasing level of Ag cladding thickness from said second leading edge to said second trailing edge; and    withdrawing said substrate from said Ag +  solution.    
     
     
         51 . The metal colloid monolayer of  claim 50 , wherein said nanoparticles are bound to said substrate by bonding with functional groups of a bifunctional organic film.  
     
     
         52 . The metal colloid monolayer of  claim 51 . wherein said bifunctional organic film is selected from the group consisting of an organosilane, poly(allylamine) hydrochloride and biotin.  
     
     
         53 . The metal colloid monolayer of  claim 50 , wherein said substrate is selected from the group consisting of glass, quartz, alumina, tin oxides and metals.  
     
     
         54 . The metal colloid monolayer of  claim 50 , wherein said Au nanoparticles, prior to cladding, have a uniform size of about 3 nm to about 10 nm.  
     
     
         55 . A method of determining optimal surface characteristics of a metal colloid monolayer comprising a plurality of colloidal Ag clad Au nanoparticles surface confined on a substrate for use in an analytical procedure, said method comprising: 
 coating a substrate with a bifunctional organic film;    immersing the coated substrate into a colloidal Au solution such that a first leading edge of said substrate is immersed in said colloidal Au solution for a longer period of time relative to a first trailing edge to provide a monolayer of Au nanoparticles having a decreasing level of coverage from said first leading edge to said first trailing edge;    withdrawing said substrate from said colloidal Au solution;    rotating said substrate through an angle of about 90°;    immersing the substrate provided with the monolayer of Au nanoparticles in an Ag +  solution such that a second leading edge of said substrate is immersed in said Ag +  solution for a longer period of time relative to a second trailing edge to provide a monolayer of Au nanoparticles having a decreasing level of Ag cladding thickness from said second leading edge to said second trailing edge;    withdrawing said substrate from said Ag +  to form a monolayer having a gradient of nanoparticle density in one direction, and a gradient in particle size in another direction;    using the gradated monolayer for an analytical procedure; and    analyzing the results achieved at different regions of said gradated monolayer to determine a nanoparticle coverage and particle size that provides an optimal result.    
     
     
         56 . The method of  claim 55 , wherein said monolayer is a surface enhanced Raman scattering response substrate.  
     
     
         57 . The method of  claim 55 , wherein said monolayer is a biosensor for detecting the presence of a biological ligand.