On-Surface Synthesis of Porosity-Controlled Molecularly Imprinted Polymeric Receptors for the Biotinyl Moiety

Controlled on-surface synthesis of polymer films using amide-based, environmentally friendly, nonionic deep eutectic solvents (ni-DESs) has been developed to regulate the porous features of the films. An appropriate combination of acetamide (A), urea (U), and their methyl derivatives (N-methylacetamide (NMA) and N-methylurea (NMU)) was used to prepare ni-DES. Polymer films were electrosynthesized using 4-aminobenzoic acid (4-ABA) and pyrrole as monomers in ni-DESs. We presumed that the flickering-cluster-like complexes and the extended H-bond networks in ni-DESs enhance the porosity of the polymer films, thus improving permeability features, as reflected in sensor performance. Electrosynthesized polymer films, imprinted with biotin templates (MIPs), have been tested as receptors for biotinylated targets. Molecular dynamics simulations of the prepolymerization mixture revealed the formed complexes between 4-ABA and biotin comprising high-frequency H-bonds. X-ray photoelectron spectroscopy (XPS) and reflection absorption infrared spectroscopy (RAIRS) studies revealed the structural integrity in the polymer films irrespective of the medium. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) measurements showed a highly corrugated and porous nature for MIP_A‑U and MIP_NMU‑U when prepared in A-U and NMU-U ni-DESs. Atomic force microscope (AFM) studies support these observations, displaying an enhancement in the surface roughness from 1.44 nm (MIP_aqueous) to 23.6 nm (MIP_NMU‑U). QCM analysis demonstrated a remarkable improvement in sensitivity of MIP_A‑U (17.99 ± 0.72 Hz/mM) and MIP_NMU‑U (18.40 ± 0.81 Hz/mM) films toward the biotin methyl ester (BtOMe, biotin derivative) than the MIP_aqueous film. The chemosensor devised with the above MIP recognition films selectively recognized BtOMe (LOD = 12.5 ng/mL) and biotinylated biomolecules, as shown by the stability constant K_s values (MIP_A‑U = 1442 and MIP_NMU‑U = 1502 M^–1). The porous network generated in the polymer films by the flickering-cluster-like complexes present in the ni-DES facilitates the analyte diffusion and recognition. We propose this ni-DES as an economically advantageous and environmentally friendly alternative to conventional ionic liquids and organic solvents in polymer synthesis and to influence polymer morphology for developing hierarchical materials.