Acidic and basic polymers for molecularly imprinted folic acid sensors—QCM studies with thin films and nanoparticles

Folic acid has been used as a template to generate molecularly imprinted polymers (MIPs), both thin films and nanoparticles. Systematic studies on binding behavior include using two different polymer systems, namely methacrylates and acrylate–vinyl pyrrolidone copolymers. Both yield sensor characteristics with lower limits of detection of 1–30 ppm with QCM (quartz crystal microbalance), whereas the non-imprinted polymers do not generate any signals. For methacrylate-based systems, switching from thin films to MIP nanoparticles increases sensitivity by a factor of 3 and selectivity toward metabolites (leucovorin and anhydroleucovorin) from broadband to specific. In contrast to this, in poly vinyl pyrrolidone based materials going from thin films to MIP nanoparticles does not increase sensitivity, but selectivity: thin films yield selectivity factors of 2–3 between folic acid and its metabolites, whereas nanoparticles do not show any response toward the latter and thus can be regarded specific. Hence, not only the heterocyclic backbone, but also the carboxylic groups of the folic acid molecule play fundamental role in detection. Vinyl pyrrolidone thus is the more suitable monomer than methacrylic acid to ensure these properties.