Kit and Method

A method of determining the presence or absence in a sample of biomarker. The method comprising the steps of; providing a porous substrate which carries an antigen; contacting the substrate with the sample; contacting the substrate with a composition comprising a secondary antibody; and observing the substrate. Preferably, the secondary antibody is conjugated to colloidal gold particles and the antigen is selected from mycolic acids or derivatives. The mycolic acid derived antigens being selected from one or more of the following classes; natural mycolic acids, synthetic mycolic acids, salts of mycolic acids, esters of mycolic acids, sulphur-containg mycolic acid compounds and/or salts or esters thereof, structural analogues of mycolic acids and/or salts or esters thereof, and mycolic acid wax esters and/or salts or esters thereof. The antigen is preferably; a trehalose monomycolate antigen, a trehalose dimycolate antigen, a mycolic acid wax ester antigen, a glucose monomycolate antigen, or a combination thereof. Also disclosed are kits comprising a substrate which carries an antigen; and a composition comprising a secondary antibody or a device comprising a housing and a substrate; wherein the substrate carries and antigen and is located within the housing; and wherein the antigen is a mycolic acid or derivative.