Assay methods and materials

A method of labelling a binding agent having an analyte binding site for an analyte, comprising the steps of:

• forming a complex between said binding agent and a labelling reagent, the labelling reagent comprising a targeting moiety and a reactive group, wherein said complex is formed by binding of said targeting moiety to said binding site;
• causing the reactive group to react with the binding agent;
• and
• causing the targeting moiety to dissociate from the binding agent.

A method of preparing a kit for use in determining an analyte in a sample, comprising

• (a) modifying a binding agent having an analyte binding site capable of binding either said analyte or an analyte analogue, said modification comprising creating a reporter site adapted to interact in a detectable manner with a reporter molecule when the modified binding agent is bound to analyte, but not when the modified binding agent is bound to analyte analogue;
• and
• (b) packaging together
• (i) said modified binding agent;
• (ii) said reporter molecule;
• and
• (iii) said analyte analogue.

A method of determining an analyte in a sample, comprising contacting the sample with

• (i) an antibody having a first antigen binding site capable of binding either said analyte or an analyte analogue, and a second antigen binding site capable of binding a reporter molecule;
• (ii) said analyte analogue;
• and
• (iii) said reporter molecule;
• wherein said second antigen binding site is capable of binding the reporter molecule when the first antigen binding site is bound to analyte, but not when the first antigen binding site is bound to analyte analogue,
• and optionally determining the amount of reporter molecule bound to the second antigen binding site.

A kit for determining an analyte in a sample, comprising

• (i) an analogue of said analyte;
• (ii) a reporter molecule;
• and
• (iii) an antibody having a first antigen binding site capable of binding either said analyte or said analyte analogue and a second antigen binding site capable of binding said reporter molecule;
• wherein said second antigen binding site is capable of binding the reporter molecule when the first antigen binding site is bound to analyte, but not when the first antigen binding site is bound to analyte analogue.