Methods of preparing a polymeric latex composition and water-insoluble biological reagent

A polymeric latex composition having a hydrophobe incorporated therein can be prepared using a novel latex "loading" method. This method includes providing a loadable latex, providing a hydrophobe dissolved in a water-miscible organic solvent, heating the loadable latex to about 30 DEG to about 90 DEG C. and gradually adding the hydrophobe solution to the heated loadable latex under conditions to keep the hydrophobe in solution and to "load" it into the latex particles. In preferred embodiments, the latex is surfactant-free and has particles which have outer reactive groups which are capable of reacting with free amine or sulfhydryl groups of a biological compound. Such latices can be used to prepare water-insoluble biological reagents having a biological compound attached to the particles.