Abstract: Devices and methods are provided for immobilizing a diagnostic target (e.g., indicative of a disease) from a solution (e.g., a biological fluid). The diagnostic target is first bound to a capture conjugate that includes a reversibly-associative polymer moieties attached to a first binding moiety that binds to the diagnostic target. Once the diagnostic target is bound to the capture conjugate, the solution is subjected to a change in heat and/or pH to cause the reversibly-associative polymer moieties to aggregate. The aggregates are then immobilized (e.g., via filtration).