An
assay device for determining an
analyte in an aqueous sample comprises: (i) an elongate flow matrix (6) allowing lateral transport of fluid therethrough by
capillary action, wherein the matrix comprises a liquid application zone (3) and downstream thereof, a detection zone (8) having an immobilized capture agent capable of directly or indirectly binding to said
analyte, (ii) a wicking member (13) placed at the downstream end of the flow matrix and having an upstream end and a downstream end, and (iii) a time indicator (14) placed downstream of the detection zone (8) for indicating when liquid applied to the liquid application zone has reached the time indicator. The time indicator comprises an indicator substance or substance combination which is capable of exhibiting a visible color change when hydrated by the aqueous sample. The
assay device is characterized in that the time indicator (14) is arranged in contact with the wicking member (13) at a variable position between the upstream and downstream ends thereof to thereby permit variation of the time elapsing from the application of the liquid until the indicator substance changes color. A method of performing an
assay for determining an
analyte in a sample, comprises the steps of flowing sample and assay liquid(s) through the flow matrix of the device such that they reach the detection zone in a predetermined sequence, and when the time indicator has changed color, reading the result of the assay in the detection zone.