Use of a device comprising a porous material embedded with components of an aqueous two-phase system (ATPS) for purifying and concentrating a target biomarker for accurate diagnosis of a disease, wherein the target biomarker is cell-free DNA, wherein the device is used in a method comprising the steps of: (a) providing a sample solution comprising the target biomarker of said disease, wherein the sample is a liquid biopsy of a plasma sample that has been taken from a subject; (b) dehydrating components of an aqueous two-phase system (ATPS) on the porous material, wherein said ATPS components are 20% (w/w) PEG 4600, 2% (w/w) SDS, 16% (w/w) Triton-X114, and 18.5% (w/w) Na 2 SO 4, wherein said components form two phase solutions when an aqueous solution travels through said porous material so that one phase solution travels faster than the other phase solution; (c) adding a PEG solution in deionized water to an end of the porous material; (d) adding a Tris-buffered solution containing 2% bovine serum albumin, 0.1% Tween-20, and 0.1% PEG, 20mM Tris pH7.5 to the porous material adjacent to the PEG solution; (e) drying the porous material embedded with said ATPS components; (f) allowing said porous material to wick said sample solution, wherein the target biomarker in the sample solution partitions into the faster moving phase solution and becomes concentrated at the front of the faster moving phase solution; (g) collecting the target biomarker from the front of the faster moving phase solution; and (h) subjecting said final solution to a diagnostic assay for detection or quantification of said target biomarker; wherein the porous material is selected from the group consisting of fiber-glass paper, cotton-based paper, single-layer matrix paper and polyolefin foam pad. (a) providing a sample solution comprising the target biomarker of said disease, wherein the sample is a liquid biopsy of a plasma sample that has been taken from a subject; (b) dehydrating components of an aqueous two-phase system (ATPS) on the porous material, wherein said ATPS components are 20% (w/w) PEG 4600, 2% (w/w) SDS, 16% (w/w) Triton-X114, and 18.5% (w/w) Na 2 SO 4, wherein said components form two phase solutions when an aqueous solution travels through said porous material so that one phase solution travels faster than the other phase solution; (c) adding a PEG solution in deionized water to an end of the porous material; (d) adding a Tris-buffered solution containing 2% bovine serum albumin, 0.1% Tween-20, and 0.1% PEG, 20mM Tris pH7.5 to the porous material adjacent to the PEG solution; (e) drying the porous material embedded with said ATPS components; (f) allowing said porous material to wick said sample solution, wherein the target biomarker in the sample solution partitions into the faster moving phase solution and becomes concentrated at the front of the faster moving phase solution; (g) collecting the target biomarker from the front of the faster moving phase solution; and (h) subjecting said final solution to a diagnostic assay for detection or quantification of said target biomarker; wherein the porous material is selected from the group consisting of fiber-glass paper, cotton-based paper, single-layer matrix paper and polyolefin foam pad.