Self-assembled metal colloid monolayers

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,

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.

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.

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.

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.

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.

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.