Patent ID: 8828741

Claim:
A method, comprising: forming a mixture comprising (a) a liquid, (b) a complex comprising an analyte and an optical label and (c) the optical label in an uncomplexed state with respect to the analyte, the optical label in the uncomplexed state having a greater mobility than the complex, with at least some of the mixture positioned between first and second surfaces of a reaction chamber, reducing a distance separating the first and second surfaces and displacing at least some of the mixture from between the first and second surfaces, detecting optical label remaining between the first and second surfaces while the distance separating the first and second surfaces is reduced, and determining the presence of the analyte based on the detected optical label; without removing the mixture from or introducing a liquid free of the first optical label into the reaction chamber at any time between forming a mixture, reducing a distance and detecting the optical label; wherein, during at least a portion of the step of reducing the distance separating the first and second surfaces, the distance separating the surfaces changes as a function of position along the first surface.