The present invention is a disposable element for assaying food samples and a method for using the element. The disposable element includes a container having first, second, and third ports, a prefilter disposed in the container, an immuno-sorbent layer having antibodies to a target microbe affixed thereto, the immuno-sorbent layer also being disposed in the container, and an electrode in contact with the immuno-sorbent layer. The prefilter and immuno-sorbent layers are positioned in the container such that a sample introduced into the first port passes through the prefilter and the immuno-sorbent layer when a pressure differential is created between the first and third ports. In addition, liquid entering the second port passes through the immuno-sorbent layer, but not the prefilter, when a pressure differential is created between the second and third ports. The prefilter preferably has a pore size between 10 and 30 microns. The disposable element may be used to measure the level of microbiological contamination in a solid sample caused by a predetermined microbe. The sample is pretreated by mixing the sample with a buffer solution and blending buffer and sample. An aliquot of the blended sample is introduced into the disposable element and is filtered through the prefilter and then passes through the immuno-sorbent layer. A solution having labeled antibodies to the microbe is passed through the immuno-sorbent layer via the second port and the amount of label bound to the immuno-sorbent is measured.