A method of detecting at least one substance of interest in a liquid sample, said method comprising: providing a liquid sample comprising or suspected of comprising the substance(s) of interest; applying the liquid sample to a porous material in a sufficient amount to at least partially wet the porous material, bringing the porous material and a porous membrane into physical contact over a contact zone, the porous membrane comprising at least one specific binding pair member that is capable of binding, either directly or indirectly, the substance(s) of interest, wherein one or more of the specific binding pair member(s) is an antibody, maintaining the wetted porous material and the porous membrane in contact for a sufficient amount of time for the porous membrane to become wetted at least in the area comprising the specific binding pair member(s) and for liquid present in the porous material to diffuse upwards into the porous membrane comprising the specific binding pair member(s), wherein the porous material is in physical contact with a bottom side of the porous membrane, the specific binding pair member(s) being located above the porous material to which the liquid sample was applied, the porous membrane being in direct contact with the porous material at a site where the specific binding pair member(s) are located, the liquid sample being applied to an area of the porous material other than the contact zone, wherein diffusion of the liquid into the porous membrane results in the substance(s) of interest, if present, to be bound, either directly or indirectly, to the specific binding pair member(s); and detecting the presence or absence of a complex comprising the specific binding pair member(s) and the substance(s) of interest, wherein the presence of at least one complex indicates the presence of at least one of the substances of interest in the liquid sample. providing a liquid sample comprising or suspected of comprising the substance(s) of interest; applying the liquid sample to a porous material in a sufficient amount to at least partially wet the porous material, bringing the porous material and a porous membrane into physical contact over a contact zone, the porous membrane comprising at least one specific binding pair member that is capable of binding, either directly or indirectly, the substance(s) of interest, wherein one or more of the specific binding pair member(s) is an antibody, maintaining the wetted porous material and the porous membrane in contact for a sufficient amount of time for the porous membrane to become wetted at least in the area comprising the specific binding pair member(s) and for liquid present in the porous material to diffuse upwards into the porous membrane comprising the specific binding pair member(s), wherein the porous material is in physical contact with a bottom side of the porous membrane, the specific binding pair member(s) being located above the porous material to which the liquid sample was applied, the porous membrane being in direct contact with the porous material at a site where the specific binding pair member(s) are located, the liquid sample being applied to an area of the porous material other than the contact zone, wherein diffusion of the liquid into the porous membrane results in the substance(s) of interest, if present, to be bound, either directly or indirectly, to the specific binding pair member(s); and detecting the presence or absence of a complex comprising the specific binding pair member(s) and the substance(s) of interest, wherein the presence of at least one complex indicates the presence of at least one of the substances of interest in the liquid sample.