Precipitating Substrate for Bio-Layer Interferometry

A method for detecting an analyte in a sample comprising:

• providing an optical assembly, said assembly comprising an optical element adapted for coupling to a light source via a fiber, said optical element comprising a transparent material, a first reflective surface and a second reflecting surface separated from said first surface by a distance, d, wherein said first reflective surface comprises a first analyte-binding molecule capable of specifically binding an analyte;
• exposing said optical element to a sample comprising said analyte;
• exposing said optical element to a second analyte binding molecule capable of specifically binding said analyte, and comprising a portion capable of specifically binding to an enzyme-carrying binding molecule, wherein said enzyme catalyzes a reaction to produce a precipitated substrate;
• exposing said optical element to said enzyme-carrying binding molecule
• exposing said optical element to a precipitating substrate, wherein upon binding of said precipitating substrate to said enzyme, said precipitated substrate is produced;
• and
• detecting a change in a thickness at said first reflective surface arising from said precipitated substrate, thereby detecting said analyte in said sample.

An optical assembly, said assembly comprising an optical element adapted for coupling to a light source via a fiber, said optical element comprising a transparent material, a first reflective surface and a second reflecting surface separated from said first surface by a distance, d, wherein said first reflective surface comprises:

• a first analyte-binding molecule capable of specifically binding an analyte;
• said analyte;
• a second analyte binding molecule capable of specifically binding said analyte;
• and
• a precipitated substrate.

A kit comprising:

• providing an optical assembly, said assembly comprising an optical element adapted for coupling to a light source via a fiber, said optical element comprising a transparent material, a first reflective surface and a second reflecting surface separated from said first surface by a distance, d, wherein said first reflective surface comprises a first member of a first binding pair;
• a first portion of a second member of said first binding pair;
• a second portion of a first member of a second binding pair;
• a third portion of a second member of said second binding pair wherein said second member of said second binding pair carries an enzyme wherein said enzyme catalyzes a reaction to produce a precipitated substrate upon binding with a precipitating substrate;
• packaging;
• and
• instructions for use.