A method is provided herein, the method includes: applying a sample comprising target nucleic acids to a sample application zone of a substrate; applying an aqueous buffer to the sample application zone of the substrate to washes away one or more inhibitors present on the sample application zone; and applying an isothermal nucleic acid amplification reaction mixture to the sample application zone to amplify the target nucleic acid to form a nucleic acid amplification product. The target nucleic acid having a first molecular weight is substantially immobilized at the sample application zone and wherein the amplification product having a second molecular weight.