Method for detecting the presence of a protease enzyme in a sample

A method of detecting the presence of a protease in a sample comprising the steps of:

• i) contacting the sample with a first reactant, the reactant being a peptide capable of being cleaved by the protease and producing a reaction product in the presence of the protease, wherein said reaction product is detectable as a consequence of cleavage by the protease;
• ii) separating at least some of the components in the sample which are smaller than a threshold size into a visualisation zone, the reaction product being smaller than the threshold size;
• wherein said separating comprises using a selective membrane interposed between the reaction zone and visualization zone to separate components in the sample, the membrane preventing passage from the reaction zone to the visualization zone of components having a greater size than the threshold size;
• and
• iii) detecting the presence of the reaction product in the visualisation zone in order to indicate the presence of the protease in the sample.