Dipstick immunoassay with capture zone comprising immobilised hapten

An immunoassay for a hapten analyte comprises permeable materials 1, 2 having i) a first zone 3 comprising a region of labelled (e.g. gold) antibody 5 specific for the hapten and a region of binding material 6 comprising hapten immobilised by a synthetic hydrophilic material (e.g. PEG) having a molecular mass of over 2000 and ii) a second zone 4 comprising a locating means (e.g. a secondary antibody) having affinity only for the labelled antibody-hapten conjugate. In use a sample comprising aqueous hapten contacts the permeable material at 7 and permeates through the first zone 3 wherein the labelled antibody 5 binds hapten before any unbound labelled antibody is bound by immobilised hapten 6 such that only labelled antibody bound to hapten analyte is permeated to the second zone 4 for detection. Preferably the hapten analyte is cocaine, amphetamine, methamphetamine, aldicarb, paraquat, chlorpyraphos or mycotoxin.