Bidirectional lateral flow test strip and method

A test strip adapted to receive a sample within a predetermined volume range and detect an analyte therein, the test strip comprising:

• a sample addition zone to which a sample may be added;
• an absorbent zone proximal to the sample addition zone;
• one or more test zones distal to the sample addition zone, at least one of the test zones including a first analyte binding agent immobilized therein which is capable of binding to the analyte to be detected;
• a terminal sample flow zone distal to the one or more test zones, the absorbent zone being positioned relative to the sample addition zone and having an absorption capacity relative to the other zones of the test strip such that a distal diffusion front of a sample added to the sample addition zone within the predetermined volume range diffuses from the sample addition zone to a distal diffusion point within the terminal sample flow zone and then diffuses proximal relative to the one or more test zones;
• and
• a conjugate buffer addition zone distal to the terminal sample flow zone to which a conjugate buffer may be added.

A method for detecting an analyte in a sample comprising:

• delivering a sample to a test strip which causes a distal diffusion front of the sample to (a) diffuse in a distal direction to one or more test zones, at least one of the test zones including a first analyte binding agent immobilized therein which binds to analyte in the sample, (b) diffuse to a terminal sample flow zone distal to the one or more test zones, and (c) diffuse to a position proximal to the one or more test zones;
• delivering a conjugate buffer to the test strip at a position distal to the terminal sample flow zone, delivery of the conjugate buffer causing a second analyte binding agent to diffuse proximally past the terminal sample flow zone to the one or more test zones after the distal diffusion front of the sample diffuses proximal to the one or more test zones, the second analyte binding agent binding to analyte immobilized in the test zones;
• and
• detecting the second analyte binding agent immobilized in the test zones.