A method for aqueous phase nucleic acid isolation from a sample, comprising a step of nucleic acid adsorption on a particulate substrate, is disclosed. The method comprises an adsorption reagent preparation step (a) providing an adsorption reagent that includes a sol consisting of an aqueous continuous phase and a dispersed particulate substrate phase including a functionalised particulate polymer prepared by polymerising (1) a first water-soluble acrylamide or acrylamide derivative monomer, (2) at least one cross-linking agent and (3) at least one second water-soluble, cationic and functional monomer, said polymer having a predetermined lower critical solubility temperature (LCST) of 25-45 DEG C; a contact step (b) wherein the adsorption reagent is contacted with the sample containing the nucleic acid; an adsorption step (c) wherein, to carry out the contact step (b), at least one parameter is selected for the reaction medium, said parameters being a pH no higher than 7, an ionic strength no higher than 10<-2> M, and a temperature lower than the polymer LCST; a separation step (d) wherein the dispersed phase is separated from the continuous phase, optionally after it has been observed that adsorption has occurred; and a desorption step (e) wherein the nucleic acid is desorbed from the particulate substrate by increasing the ionic strength until an ionic strength higher than 10<-2> M is achieved.