Molecularly imprinted polymer-based piezoelectric sensor for enantio-selective analysis of malic acid isomers

A quartz crystal microbalance sensor, having enantio-selective ability to analyze malic acid enantiomers with high sensitivity, was fabricated using a biomimetic ultra-thin film of molecularly imprinted polymer. Such material could be termed as ‘glyco-molecularly imprinted polymer’ since it was synthesized using sugar moiety, adopting non-covalent self-assembly process and subsequent photo-polymerization. The piezoelectric sensor modification via “surface-grafting from” was found to be superior to response better than the physical entrapment of imprinted particles. The glyco-imprinted polymer sensor demonstrated exclusive specificity for l-malic acid, concomitantly present with d-malic acid and respective analogs. The rational design of malic acid/glyco-monomer complex, with composition 1:2, was predicted on the basis of theoretical modeling. The detection limit of l-malic acid was realized as 0.18–0.21 ng mL−1 (S/N = 3, confidence level 95%) for l-malic acid and the linearity was observed within its concentration range 20–210 ng mL−1, at pH 7.0, in aqueous and real samples. The proposed sensor demonstrated a fast, reliable, enantio-selective and quantitative response to malic acid isomers, in real samples.