Capillary flow for a heterogenous assay in a micro-channel environment

An apparatus comprising:

• a first channel, wherein a first fluid introduced to the apparatus flows through said first channel, wherein said first channel comprises:
• an upstream region;
• a tagging region downstream of said upstream region, wherein an analyte is tagged when said first fluid flows through said tagging region by interacting with a tagging reagent present in the tagging region;
• a capture region downstream of said tagging region, wherein at least one tagged analyte is captured when said first fluid flows through said capture region by binding to at least one analyte capture reagent immobilized in the capture region;
• a second channel in fluid communication with said first channel intermediate said tagging region and said capture region;
• a trigger channel communicating with said first channel, wherein said first fluid flows through said trigger channel toward said second channel, causing a second fluid to flow through said second channel and subsequently flow into said capture region of said first channel;
• wherein said second channel comprises means for retarding flow rate, whereby first fluid flowing through said tagging region flows into said capture region before said second fluid flows through said second channel into said capture region of said first channel.