Enantioselective electrochemical L-phenylalanine sensor based on molecularly imprinted polymer embedded with redox probes

Phenylketonuria (PKU) patients require rapid and decentralized monitoring of their phenylalanine (Phe) level to manage high levels of L-phenylalanine (L-Phe). However, affinity-based detection of L-Phe is still challenging due to its small size compared to traditional receptors as well as the necessity of enantiomeric selectivity against D-Phe. In this study, nanoscale electrochemistry was utilized for affinity-based enantioselective detection of L-Phe by utilizing the electrochemical signal of redox probes within artificial receptors upon selective binding. We prepared a molecularly imprinted polymer composite (MIPC) for L-Phe with nanoscale thickness through electrochemical copolymerization of redox-active methylene blue (MB) and β-cyclodextrin (β-CD), achieving self-reporting detection of L-Phe with high enantioselectivity. Using the differential pulse voltammetry (DPV), the MIPC-based enantioselective sensor can detect L-Phe in the range of 1.00 × 10⁻⁸ M–1.00 × 10⁻⁴ M with a detection limit of 6.83 × 10⁻⁹ M (S/N = 3). Additionally, the MIPC-based L-Phe sensor demonstrated the ability to perform repetitive L-Phe measurements after a simple regeneration step. The detection of L-Phe in human serum was conducted with the present sensor, and the results were validated using enzyme-linked immunosorbent assay (ELISA) analysis. The present nanoscale MIPC-based L-Phe sensor offers excellent chiral selectivity and reusability in human serum samples, paving the way for advancements in enantioselective point-of-care diagnostics.