Binding and potential-triggered release of l-glutamate with molecularly imprinted polypyrrole in neutral pH solutions

Molecularly imprinted polymers (MIPs) are interesting for potential-regulated trafficking of molecules. In this study, we investigate the binding properties of l-glutamate (Glu) in molecularly imprinted polypyrrole (MIPPy) in neutral pH solutions. We prepared MIPPy by electrochemically depositing Glu-doped polypyrrole and subsequently overoxidizing the polymer. By means of immunofluorescence microscopy analysis of MIPPy using specific anti-Glu antibodies, we demonstrate binding of Glu in MIPPy. Visual imaging of the samples allows us to easily discern between selective and non-selective interactions. Significant fluorescence is observed from MIPPy incubated in solutions containing Glu, while control MIPPy samples imprinted with Cl− and subsequently exposed to Glu do not yield detectable fluorescence signals. To quantify the binding interactions, we use electrochemical quartz microbalance (EQCM) measurements. Glu uptake by MIPPy occurs in the absence of an applied electrical potential. From the change in mass of MIPPy versus the Glu concentration in solution, we determine a binding free energy of −6.0 ± 0.2 kJ/mol. Based on these results, the binding interactions are discussed in terms of hydrogen bonding combined with electrostatic interactions between the polymer and the neurotransmitter. Glu release from MIPPy is triggered at low potentials (−0.3 V (Ag/AgCl)). These properties make MIPPy interesting for applications such as drug delivery and chemical implants.