Sensitive immunoassays using coated nanoparticles

A method for determining the presence or absence of an analyte in a liquid sample, comprising:

• a) providing a test device comprising;
• (i) a sample receiving member;
• (ii) a carrier in fluid communication with the sample receiving member;
• (iii) a labeled reagent which is mobile in the carrier in the presence of the liquid sample, the labeled reagent comprising a ligand that binds to the analyte and a coated nanoparticle comprising a core and a shell that increases the reflectance of the nanoparticle having the ligand attached thereto, wherein the coated nanoparticle does not include a Raman-active molecule;
• and
• (iv) a binding reagent effective to capture the analyte, when present, immobilized in a defined detection zone of the carrier;
• wherein the liquid sample applied to the sample receiving member mobilizes the labeled reagent such that the sample and labeled reagent are transported along the length of the carrier to pass into the detection zone, and wherein detection of the labeled reagent in the detection zone is indicative of the presence of analyte in the liquid sample;
• b) contacting the liquid sample with the sample receiving member of the test device;
• c) allowing the liquid sample applied to the sample receiving member to mobilize said labeled reagent such that the liquid sample and labeled reagent move along the length of the carrier to pass into the detection zone;
• d) detecting the presence of the labeled reagent in the detection zone by measuring reflectance, wherein detection of the labeled reagent in the detection zone is indicative of the presence of analyte in the liquid sample, and failure to detect the presence of the labeled reagent in the detection zone is indicative of the absence of the analyte in the liquid sample.

A method for determining the presence or absence of an analyte in a liquid sample, comprising:

• a) providing a test device comprising:
• (i) a sample receiving member;
• (ii) a carrier in fluid communication with the sample receiving member;
• and
• (iii) a binding reagent effective to capture the analyte, when present, immobilized in a defined detection zone of the carrier;
• b) mixing the liquid sample with a labeled reagent comprising a ligand that binds to the analyte and a coated nanoparticle comprising a core and a shell that increases the reflectance of the nanoparticle having the ligand attached thereto, wherein the coated nanoparticle does not include a Raman-active molecule;
• c) contacting the mixture of b) with the sample receiving member of the test device;
• d) allowing the mixture of b) applied to the sample receiving member to move along the length of the carrier to pass into the detection zone;
• e) detecting the presence of the labeled reagent in the detection zone by measuring reflectance, wherein detection of the labeled reagent in the detection zone is indicative of the presence of analyte in the liquid sample, and failure to detect the presence of the labeled reagent in the detection zone is indicative of the absence of the analyte in the liquid sample.

A test device for determining the presence or absence of an analyte in a liquid sample, comprising:

• (a) a sample receiving member;
• (b) a carrier in fluid communication with the sample receiving member;
• (c) a labeled reagent which is mobile in the carrier in the presence of the liquid sample, the labeled reagent comprising a ligand that binds to the analyte and a coated nanoparticle consisting essentially of a core and a shell that increases the reflectance of the nanoparticle having the ligand attached thereto, wherein said ligand is bound to the surface of the shell;
• and
• (d) a binding reagent effective to capture the analyte, when present, immobilized in a defined detection zone of the carrier;
• wherein the liquid sample applied to the sample receiving member mobilizes the labeled reagent such that the sample and labeled reagent are transported along the length of the carrier to pass into the detection zone, and wherein detection of labeled reagent in the detection zone is indicative of the presence of analyte in the liquid sample.

A method for determining the presence or absence of analyte in a liquid sample, comprising:

• a) providing a test device comprising;
• (i) a sample receiving member;
• (ii) a carrier in fluid communication with the sample receiving member;
• (iii) a labeled reagent which is mobile in the carrier in the presence of the liquid sample, the labeled reagent comprising a ligand that binds to the analyte and a coated nanoparticle consisting essentially of a core and a shell that increases the reflectance of the nanoparticle having the ligand attached thereto, wherein said ligand is bound to the surface of the shell;
• and
• (iv) a binding reagent effective to capture the analyte, when present, immobilized in a defined detection zone of the carrier;
• wherein the liquid sample applied to the sample receiving member mobilizes the labeled reagent such that the sample and labeled reagent are transported along the length of the carrier to pass into the detection zone, and wherein detection of labeled reagent in the detection zone is indicative of the presence of analyte in the liquid sample;
• b) contacting the liquid sample with the sample receiving member of the test device;
• c) allowing the liquid sample applied to the sample receiving member to mobilize the labeled reagent such that the liquid sample and labeled reagent move along the length of the carrier to pass into the detection zone;
• d) detecting the presence of the labeled reagent in the detection zone by measuring reflectance, wherein detection of the labeled reagent in the detection zone is indicative of the presence of analyte in the liquid sample, and failure to detect the presence of the labeled reagent in the detection zone is indicative of the absence of the analyte in the liquid sample.