Mixing apparatus & method for an optical agglutination assay device

Apparatus for use in determining the presence of a target analyte in an unknown sample, comprising:

• a) an assay card including i) an entry port for receiving said sample, ii) a plurality of reservoirs each containing a reagent for detection of the target analyte and being of the type which reduces in volume when positive pressure is applied to expel the contents thereof and will return toward its original volume when said applied pressure is reversed, iii) a fluid conveying track fluidly connecting said reservoirs with said entry port and extending downstream thereof, and iv) a viewing area positioned for viewing and analyzing the fluid contents of a downstream portion of said track;
• b) actuator means for applying pressure to said reservoirs to expel the contents thereof into said track to mix them together and with said sample in said entry port;
• c) detector means operable to provide an output signal indicative of the presence of the mixed reagents at said viewing area;
• and
• d) control means operable in response to said output signal to cause said actuator means to reverse the applied pressure at least once, to reverse the direction of fluid flow in said track and to thereafter again apply positive pressure, whereby the reversal of fluid flow further agitates and mixes said reagents and sample.