Electrochemical biosensing of L-phenylalanine and bioelectrosynthesis of phenylpyruvate based on an efficient cofactor regeneration electrode

This study presents a hybrid system combining MIP-202 (Zr⁴⁺-Asp-coordinated framework) immobilized L-phenylalanine dehydrogenase with polymerized methylene blue (PMB) based electrodes. MIP-202 acted as a biocompatible framework that preserved enzymatic activity. PMB modulated the oxidation of the enzyme cofactor NADH into NAD + via proton-coupled electron transfer (PCET), reducing overpotentials. Such a biohybrid, operated at a relatively low potential of +0.15 V vs. SCE, enables proof-of-concept electrochemical biosensing of L-phenylalanine (L-Phe) and bioelectrosynthesis of phenylpyruvate (PPA). Both applications are of great significance, as L-Phe is an important biomarker for the diagnostics of phenylketonuria, while PPA is a common α-keto acid. It demonstrated a limit of detection (LOD) of 17.03 μM for L-phe and a ca. two-fold increase in PPA production compared to the enzyme-only system without cofactor regeneration.