Metal ion determination by sandwich aggregation assay

A method for determining the amount of a polyvalent metal ion in a matrix using a sandwich aggregation assay, comprising:

• (a) contacting the polyvalent metal ion with a reagent comprising a conjugate of a ligand and a chelating agent capable of forming at least a 2:1 stoichiometric ratio complex of chelating agent to polyvalent metal ion,
• (b) contacting the complexed chelating agent with a carrier in the liquid matrix, said carrier being linked to a specific binding partner for said ligand, whereby a plurality of said carriers bind to the complexed chelating agent through the interaction of the ligand and the binding partner and aggregate in liquid matrix, thereby causing an increase in light absorbance which is proportional to the concentration of the polyvalent metal ions in the liquid matrix;
• and
• (c) measuring the resulting aggregation in the liquid matrix as a function of the amount of the polyvalent metal ion present in the liquid matrix.

A method for determining the amount of lead ions in a liquid matrix using a sandwich aggregation assay, comprising:

• (a) contacting the lead ions with a reagent comprising a chelating agent, wherein the chelating agent is capable of forming at least a 2:1 stoichiometric ratio complex of chelating agent to lead ions;
• (b) linking the chelating agent to a carrier in the liquid matrix wherein a plurality of carriers linked to complexed chelating agents aggregate, thereby causing an increase in light absorbance which is proportional to the concentration of the lead ions in the liquid matrix;
• and
• (c) measuring the resulting aggregation in the liquid matrix as a function of the amount of the lead ions present in the liquid matrix.

A test composition for determining the amount of a polyvalent metal ion in a liquid matrix using a sandwich aggregation assay, consisting essentially of:

• (1) a chelating agent capable of forming at least a 2:1 stoichiometric ratio complex of chelating agent to polyvalent metal ion, and
• (2) carriers for the chelating agent, wherein said chelating agent:
• (a) is linked to said carriers, or
• (b) is in the form of a conjugate with a ligand, and a specific binding partner for said ligand is linked to said carriers;
• wherein, upon complexation of the chelating agent with the polyvalent metal ion, the carriers linked to the complexed chelating agents are characterized by the ability to aggregate, thereby causing an increase in light absorbance which is proportional to the concentration of the polyvalent metal ion in the liquid matrix.