The use of nanometer-sized gold particles as templates for the synthesis of hollow poly(pyrrole), poly(N-methylpyrrole), and poly(3-methylthiophene) is described in this paper. Diffusion coefficients of small molecules through the capsule shell were found to vary by almost 3 orders of magnitude depending on the polymer, polymer oxidation state, and counteranion incorporated during polymer synthesis. A small molecule (anthraquinone) and an enzyme (horseradish peroxidase) were trapped inside hollow capsules by attaching them to the template particle prior to polymerization and particle etching. A thin poly(pyrrole) shell protected the enzyme 2 times longer in neat toluene compared to unencapsulated enzyme. Finally, the potential for using conductive polymer nanoparticles for intracellular delivery or diagnostics was examined by administering partice suspensions to 3T3 murine fibroblasts. Particles ranging in size from 25 to 100 nm were engulfed by fibroblasts without compromising cell viability.