posted on 2024-01-08, 10:03authored bySubramanian Suriyanarayanan, Gustaf D. Olsson, Ian A. Nicholls
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 MIPA‑U and MIPNMU‑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 (MIPaqueous) to 23.6
nm (MIPNMU‑U). QCM analysis demonstrated a remarkable
improvement in sensitivity of MIPA‑U (17.99 ±
0.72 Hz/mM) and MIPNMU‑U (18.40 ± 0.81 Hz/mM)
films toward the biotin methyl ester (BtOMe, biotin derivative) than
the MIPaqueous 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 Ks values (MIPA‑U = 1442 and
MIPNMU‑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.