Single mode fiber optic evanescent wave refractometer

A refractive index measurement device comprising in combination:

• a sample fiber optic coupler having a sample fusion joint;
• a reference fiber optic coupler having a reference fusion joint;
• a light splitter;
• a light input member positioned to input light into said light splitter;
• said light splitter inputting a first predetermined portion of said light into said sample fiber optic coupler, whereby an evanescent field is produced surrounding said sample fusion joint, and
• a second predetermined portion of said light into said reference fiber optic coupler;
• a light detector member for detecting light output from said sample fiber optic coupler and from said reference fiber optic couplery;
• a difference determination member for processing the detected light from said sample fiber optic coupler and from said reference fiber optic coupler;
• whereby the value derived from said detected light from said sample fiber optic coupler is independent of variations in light from said light input member.

A method of immunoassay measurement of a target component comprising the steps of:

• forming a sample coupler fusion joint from a plurality of single mode fiber-optic fibers;
• forming a reference coupler fusion joint from at least one single mode fiber optic fiber;
• coating the fusion-joint of said sample coupler with a first immunoassay component for specifically binding to the target component;
• surrounding the coated fusion joint with the target component;
• inserting light into a light splitter;
• transmitting light from a first split portion of light from said light splitter into one of said sample coupler optic fibers after coating the, fusion joint;
• transmitting light from a second split portion of light from said light splitter into said reference coupler at least one optic fiber;
• measuring light output from two or more of the sample coupler optic fibers before and after surrounding the fusion joint with the target component;
• measuring light from one or more of said reference coupler at least one optic fiber and establishing a light reference value;
• determining the presence or concentration of the target component by measuring changes in the output of light from said two or more sampler coupler optic fibers due to the specific binding of the target component to the first immunoassay component as compared to said light reference value.

A method of assay measurement of a target component in a fluid, using a device having

• a target single mode fiber optic coupler, said coupler having a fusion joint of at least two single mode optical fibers;
• a light splitter, and
• a reference single mode fiber optic coupler, said coupler having a fusion joint of at least one single mode optical fiber, which fusion joint is in a medium of stable index of refraction;
• said method comprising the steps of:
• surrounding the fusion joint of said target optic coupler with the target component;
• inserting light into said light splitter;
• inserting light from said light splitter into one of said target coupler optical fibers;
• inserting light from said light splitter into said reference coupler at least one optical fiber;
• measuring and summing the output of light from two or more of the target coupler optical fibers and from said reference coupler at least one optical fiber, before and after surrounding the target coupler with the target component;
• and
• determining the presence or concentration of the target component in the fluid by comparing changes in the light output levels of said two or more optical fibers due to the target component relative to said, reference coupler light output levels.

An immunoassay method for determining a target analyte in a fluid sample, which method does not use labeled reagents and is based upon measuring changes in refractive index in an evanescent field surrounding a fiber optic coupler, said coupler having a plurality of optical fibers which are first coupled and then drawn to a single mode diameter, comprising:

• immobilizing an antibody or antigen for specifically binding to the target analyte on the fiber optic coupler;
• illuminating at least one of the plurality of optical fibers to provide the surrounding evanescent field with a first portion of light from a light splitter;
• obtaining a first refractive index of the surrounding evanescent field by measuring a first ratio of coupled power as a percentage of the total power in the optical fibers of the fiber optic coupler;
• contacting the fluid sample to the fiber optic coupler such that any target analyte in the fluid sample specifically binds to the immobilized antibody or antigen;
• obtaining a second refractive index of the surrounding field by measuring a second ratio of coupled power as a percentage of the total power in the optical fibers of the fiber optic coupler being in contact with the fluid sample;
• and
• illuminating at least one optical fiber of a reference coupler with a second portion of light from a light splitter, said reference coupler having at least one optical fiber that is drawn to a single mode diameter, said reference coupler being within a medium of stable refractive index, thereby determining an illumination reference level by measuring light output from said reference coupler.