Provided herein are methods for the collection and amplification of circulating nucleic acids from a non-cellular fraction of a biological sample. Circulating nucleic acids are extracted from the non-cellular fraction and are circularized to generate single-stranded nucleic acid circles, which are then subsequently amplified by rolling circular amplification using random primers to produce an amplified library. Devices for the collection of a non-cellular fraction from a biological sample are also provided. The device includes a filtration membrane and a dry solid matrix, which is in direct contact with the filtration membrane.