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Poly-3-thienylboronic Acid Nanoparticles: Synthesis, Characterization, and Interaction with Saccharides Studied at the Level of Individual Nanoparticles
Polythiophenboronic acid (PThBA) combines anaffinity for saccharides with the unique properties of conductingpolymers. This polymer was synthesized by enzymatic catalyzedoxidative polymerization, characterized by UV−vis spectroscopy insolvents of different polarity and by 1H NMR. A suspension ofPThBA nanoparticles (PThBA NPs) was prepared by injecting amethanol solution of PThBA into an aqueous electrolyte. PThBANPs were characterized by scanning electron microscopy. Nano-particle tracking analysis and dynamic light scattering were used tostudy the concentration of the particles and the particle sizedistribution. The effect of pH on these properties was analyzed andan increase in nanoparticle size was observed at alkaline pH. Thiseffect was explained by electrostatic swelling of the nanoparticles.Measurements of ζ-potentials in the wide pH range showed the presence of acidic groups with a pKa of 8.6; the value of the surfacecharge at the conditions of maximal deprotonation of these groups was estimated to be ∼70 mC/m2. Changes in the optical spectraof PThBA NPs due to variations in pH and additions of organic solvents indicate transformations between twisted and planarconformations of the polymer backbone. The binding of saccharides by PThBA NPs resulted in a decrease in the size and charge ofthe nanoparticles. Recently developed wide-field surface plasmon resonance microscopy (WF-SPRM) can simultaneously monitorevery single nanoparticle among many thousands adsorbed on a surface. It was used for the first time to study chemosensitivenanoparticles. The described above effects of pH change and saccharide binding described above, monitor were confirmed by usingintegral techniques in monitoring individual nanoparticles, by WF-SPRM. The pH effects were shown to be reversible. An increase inthe affinity of PThBA NPs for saccharides at a more alkaline pH was also observed. A fast recovery of polymer binding sites by a pHdecrease was demonstrated. The synthesized and characterized PThBA NPs can be further used for various purposes includinganalytical assays, chemical sensors, or chemosensitive nanotechnological devices.