A device for analyzing a liquid sample, comprising: a first plate and a second plate, wherein: i. the plates are movable relative to each other into different configurations; ii. one or both plates are flexible; iii. each of the plates has, on its respective surface, a sample contact area for contacting a blood sample; iv. one or both of the plates comprise spacers that are fixed with a respective plate, wherein the spacers have a predetermined substantially uniform height and a predetermined constant inter-spacer distance that is in the range of 1 μm to 120 μm and wherein at least one of the spacers is inside the sample contact area; v. one of the plates comprises, on its sample contact area, a storage site that has a predetermined area and comprises a reagent that, upon contacting the sample, dissolves into the sample, diffuses in the sample, and binds to the target entity; wherein one of the configurations is an open configuration, in which: the two plates are separated apart, the spacing between the plates is not regulated by the spacers, and the sample is deposited on one or both of the plates; wherein another of the configurations is a closed configuration; and in the closed configuration: at least part of the sample is compressed by the two plates into a layer of highly uniform thickness, wherein the uniform thickness of the layer is confined by the inner surfaces of the two plates and is regulated by the plates and the spacers and is 250 μm or less, wherein the uniform thickness of the layer is substantially less than a linear dimension of the predetermined area of the storage site on the first plate or second plate; and wherein the thickness of the flexible plate times the Young's modulus of the flexible plate is in the range 60 to 750 GPa-μm. a first plate and a second plate, wherein: i. the plates are movable relative to each other into different configurations; ii. one or both plates are flexible; iii. each of the plates has, on its respective surface, a sample contact area for contacting a blood sample; iv. one or both of the plates comprise spacers that are fixed with a respective plate, wherein the spacers have a predetermined substantially uniform height and a predetermined constant inter-spacer distance that is in the range of 1 μm to 120 μm and wherein at least one of the spacers is inside the sample contact area; v. one of the plates comprises, on its sample contact area, a storage site that has a predetermined area and comprises a reagent that, upon contacting the sample, dissolves into the sample, diffuses in the sample, and binds to the target entity; i. the plates are movable relative to each other into different configurations; ii. one or both plates are flexible; iii. each of the plates has, on its respective surface, a sample contact area for contacting a blood sample; iv. one or both of the plates comprise spacers that are fixed with a respective plate, wherein the spacers have a predetermined substantially uniform height and a predetermined constant inter-spacer distance that is in the range of 1 μm to 120 μm and wherein at least one of the spacers is inside the sample contact area; v. one of the plates comprises, on its sample contact area, a storage site that has a predetermined area and comprises a reagent that, upon contacting the sample, dissolves into the sample, diffuses in the sample, and binds to the target entity; wherein one of the configurations is an open configuration, in which: the two plates are separated apart, the spacing between the plates is not regulated by the spacers, and the sample is deposited on one or both of the plates; wherein another of the configurations is a closed configuration; and in the closed configuration: at least part of the sample is compressed by the two plates into a layer of highly uniform thickness, wherein the uniform thickness of the layer is confined by the inner surfaces of the two plates and is regulated by the plates and the spacers and is 250 μm or less, wherein the uniform thickness of the layer is substantially less than a linear dimension of the predetermined area of the storage site on the first plate or second plate; and wherein the thickness of the flexible plate times the Young's modulus of the flexible plate is in the range 60 to 750 GPa-μm.