We describe methods for synthesis and formulations of stable elastomeric negative acoustic contrast particles with controllable compressibility and density. These elastomeric negative acoustic contrast particles have a density/compressibility ratio that is less than that of water and therefore exhibit negative acoustic contrast under acoustic radiation exposure. This negative acoustic contrast allows our elastomeric negative acoustic contrast particles to be acoustically manipulated (e.g. separated) differently from other components (e.g. cells) within an aqueous solution. This disclosure also describes methods for biofunctionalization of the elastomeric negative acoustic contrast particles and as an example their use as platforms for bioassays. Potential applications of these elastomeric negative acoustic contrast particles include sensitive bioassays based on acoustic flow cytometry and other types of techniques that utilize acoustic fields, including ultrasound imaging and ultrasound triggered drug delivery.