A method produces polymer nanoparticles. Polymer solution is sprayed through a nozzle toward a collector. An electric field is created at the nozzle, such as by a voltage is applied to the nozzle to create the electric field. The voltage applied to the nozzle is from ˜10 (Kilovolt) to ˜30 (Kilovolt), distance from nozzle tip to collector is from ˜1 (centimeter) to ˜10 (centimeter) and the polymer concentration from ˜0.01% to ˜0.5% w/w. Preferably a grounded liquid collectors is used. The invention provides biocompatible monodisperse polymer nanoparticles having a size of less than ˜300 nm, preferably less than ˜150 nm. Payloads can be associated, and maintain efficacy, including more than one payload such as therapeutic agents and diagnostic agents on the same particles. Preferred particles are poly(methyl methacrylate) (PMMA-COOH) or acrylate analogues.
