Capture particles for harvesting analytes from solution and methods for using them are described. The capture particles are made up of a polymeric matrix having pore size that allows for the analytes to enter the capture particles. The pore size of the capture particles may be changeable upon application of a stimulus to the particles, allowing the pore size of the particles to be changed so that analytes of interest remain sequestered inside the particles. The polymeric matrix of the capture particles may be made of co-polymeric materials having a structural monomer and an affinity monomer, the affinity monomer having properties that attract the analyte to the capture particle. The capture particles may be used to isolate and identify analytes present in a mixture. They may also be used to protect analytes which are typically subject to degradation upon harvesting and to concentrate low an analyte in low abundance in a fluid.