Evanescent hemolysis detection

A method for detecting analytes in whole blood without red blood cell separation from the whole blood, the method comprising:

• receiving a whole blood sample in a channel, wherein an optically transmissive medium adjacent to the channel includes a first surface abutting the channel, the first surface defining an optical interface between the optically transmissive medium, wherein the optically transmissive medium is glass and the blood sample when the whole blood sample is received in the channel;
• directing a first light source through the optically transmissive medium to the optical interface at an angle of incidence greater than or equal to a critical angle relative to a normal of the optical interface, wherein the angle of incidence creates total internal reflection of light from the first light source and creates an evanescent field extending into the channel, wherein the evanescent field extends into a plasma layer of the blood sample adjacent to the optical interface and decays to substantially zero before reaching a portion of the channel containing blood cells;
• aiming a first light detector to receive the light from the first light source that has been reflected through the optically transmissive medium from the optical interface;
• measuring absorption of the light from the first light source by an analyte in only a plasma layer of the whole blood sample within range of the evanescent field;
• and
• directing a second light source through optically transmissive medium to the optical interface, wherein light from the second light source has a wavelength that differs from a wavelength of the light from the first light source and wherein the light from the second light source is incident at the optical interface at second an angle of incidence greater than or equal to the critical angle relative to the normal of the optical interface, wherein the second angle of incidence creates total internal reflection of the light from the second light source and creates a second evanescent field extending into the flowing blood sample, wherein the second evanescent field extends into the plasma layer of the flowing whole blood sample adjacent to the optical interface and decays to substantially zero before reaching a portion of the flowing whole blood sample containing blood cells;
• and
• measuring absorption of the light from second light source by the analyte in only the plasma layer of the flowing whole blood sample within the second evanescent field.

An apparatus for determining an analyte content in blood, the apparatus comprising:

• a channel for receiving the flowing blood sample;
• an optical interface between a flowing blood sample and an optically transmissive media, wherein the optically transmissive media is glass, wherein the optically transmissive medium includes a first surface abutting the channel, the first surface defining an optical interface between the optically transmissive medium and the following blood sample;
• a first light source directed through the optically transmissive medium to the optical interface at an angle of incidence greater than or equal to a critical angle relative to a normal of the interface, wherein the angle of incidence creates total internal reflection of light from the first light source and creates the evanescent field extending into the channel, wherein the evanescent field extends into a plasma layer of the flowing blood sample adjacent to the optical interface and decays to substantially zero before reaching a portion of the channel containing blood cells;
• a first light detector configured to detect absorption of light from the first light source in the evanescent field at a first wavelength corresponding to an absorption wavelength of the analyte;
• a second light source directed through optically transmissive medium to the optical interface, wherein light from the second light source has a second wavelength that differs from a first wavelength of the light from the first light source and wherein the light from the second light source is incident at the optical interface at a second an angle of incidence greater than or equal to the critical angle relative to the normal of the optical interface, wherein the second angle of incidence creates total internal reflection of the light from the second light source and creates a second evanescent field extending into the flowing blood sample, wherein the second evanescent field extends into the plasma layer of the flowing whole blood sample adjacent to the optical interface and decays to substantially zero before reaching a portion of the flowing whole blood sample containing blood cells;
• and
• a second light detector configured to detect absorption of light from the second light source in the evanescent field at the second wavelength corresponding to the absorption wavelength of the analyte.