Bio/chemical assay devices and methods for simplified steps, small samples, accelerated speed, and ease-of-use

A method for locally releasing a reagent into a portion of a liquid sample, comprising:

• (a) obtaining a sample;
• (b) obtaining a first and second plates that are movable relative to each other into different configurations, wherein:
• (i) one or both of the plates comprise spacers that are fixed to a respective plate;
• (ii) one or both of the plates is flexible;
• (iii) the spacers have a pillar shape, a substantially flat top surface, a predetermined substantially uniform height and a predetermined constant inter-spacer distance that is at least about 2 times larger than the size of an analyte, and wherein the Young's modulus of the spacers times the filling factor of the spacers is equal or larger than 2 MPa;
• and
• (iv) the first plate comprises, on its surface, a storage site that has a predetermined area and comprises a reagent that, upon contacting the sample, dissolves into the sample and diffuses in the sample;
• (c) depositing the sample on one or both of the plates when the plates are configured in an open configuration, wherein the open configuration is a configuration in which the two plates are either partially or completely separated apart and the spacing between the plates is not regulated by the spacers;
• (d) after (c), compressing the sample by bringing the two plates into a closed configuration, wherein the closed configuration is a configuration in which at least part of the sample is compressed into a layer of uniform thickness that is confined by the inner surfaces of the two plates and that covers the storage site, wherein the uniform thickness of the layer is regulated by the spacers and the plates, is less than 250 um, and is substantially less than the linear dimension of the predetermined area of the storage site;
• (e) after (d) and while the plates are in the closed configuration, incubating the sample for a relevant time length and then stopping the incubation, wherein the relevant time length is:
• (i) about equal to or longer than the time that it takes for the target entity to diffuse across the thickness of the uniform thickness layer at the closed configuration;
• and
• (ii) shorter than the time that it takes the target entity to laterally diffuse across the linear dimension of the predetermined area of the binding site;
• whereby, after the incubation, the majority of the reagent that is initially on the storage site is in the relevant volume of the sample,
• wherein the incubation is a process to allow the reagent to bind or mix with the sample, and wherein the relevant volume is a portion of the sample that is above the binding site at the closed configuration.