Patent ID: 8163154

Claim:
A method, comprising the steps of: (i) providing a fractionation channel comprising a nanoporous membrane about 15 μm to 100 μm in length fixedly attached therein, and an analyte reservoir and a waste reservoir in fluid communication with the fractionation channel, wherein the nanoporous membrane further comprises a cross-linked polymer having a plurality of pores having an average diameter of about 2 nm; (ii) introducing an analyte solution into the analyte reservoir, wherein the analyte solution comprises a plurality of proteins comprising native conformations larger in size than the average diameter of the plurality of pores; (iii) applying a first electric field having a polarity directed toward a first face of the nanoporous membrane, wherein the first electric field electrophoretically transports a quantity of the plurality of proteins to the first face, and wherein the plurality of proteins is initially excluded from entering the nanoporous membrane; (iv) increasing the first applied electric field by a predetermined incremental voltage and maintaining the increased applied electric field for a fixed period of time; (v) repeating step (iv) while increasing the applied electric field by the predetermined incremental voltage with each step until a first fraction of the plurality of proteins is transported a distance into or through the nanoporous membrane; (vi) performing a PAGE separation analysis of remaining protein fractions disposed at the first face; (vii) repeating step (iv) while increasing the applied electric field by the predetermined incremental voltage with each step until an additional fraction of the plurality of proteins is transported a distance into or through the nanoporous membrane or until a predetermined maximum electric field is reached or surpassed; and (viii) repeating step (vi) after each additional fraction of proteins has been transported into or through the nanoporous membrane.