Role of dextran in stabilization of polypyrrole nanoparticles for photoacoustic imaging

Polypyrrole with bioinert surface is a prospective contrast agent for photoacoustic imaging. Dextran (Dex) was successfully tested as a steric stabilizer of the dispersion polymerization producing stable polypyrrole nanoparticles (PPy-NPs). Polymerizations were mediated with three different oxidizers: iron (III) chloride, ammonium persulfate and cerium ammonium nitrate. The use of the Dex allowed good control of particle size within the range 60–200 nm through varying concentration of the Dex and polymerization temperature, with the exception of cerium mediated polymerizations, which produced 30 nm particles independently of the reaction conditions. Stabilization effect of the Dex resulted from a reversible adsorption of the Dex on the surface of nanoparticles. Spectral analysis confirmed the complete removal of the Dex from particle surfaces during washing procedure, which indicated no grafting of the Dex to PPy-NPs mediated with a radical process initiated with decay of persulfate or single electron oxidation of the Dex by cerium ammonium nitrate. Photoacoustic measurement proved detectable signals in near infrared regions.