Polymer‐Modulated Fructose Dehydrogenase Bioelectrocatalysis on Highly Porous Gold Electrodes for Direct Electron Transfer Fructose Sensing in Fermentation Broth

Herein, an amperometric fructose biosensor is developed by immobilizing fructose dehydrogenase (FDH) on highly porous gold (h‐PG) electrodes modified with polymeric interlayers. Poly(acrylic acid) (PAA), poly(vinyl alcohol) (PVA), and poly(diallyldimethylammonium chloride) (PDDA) are used to tune the enzyme–electrode interface, generating h‐PG/PAA/FDH, h‐PG/PVA/FDH, and h‐PG/PDDA/FDH bioelectrodes. The h‐PG layer, prepared by hydrogen‐bubble‐assisted electrodeposition, exhibits 18–46 µm pores, nanocoral‐like Au features, and an electroactive area of 26 ± 3 cm 2 , about 300 times larger than bare Au. SEM, cyclic voltammetry, and XPS confirm the porous morphology and polymer deposition. The polymer interface controls FDH bioelectrocatalysis. h‐PG/PAA/FDH shows the lowest fructose oxidation onset potential, −0.063 ± 0.005 V, and the highest catalytic current, 32 ± 4 µA at +0.205 V with 10 mM D‐fructose. Amperometry provides a 0.02–1 mM linear range, K M app = 6.4 ± 0.8 mM, sensitivity of 6.4 ± 0.2 µA mM −1 , and LOD of 5 µM. h‐PG/PAA/FDH retains 95% of its initial response after 180 days in fermentation broth and enables fructose monitoring during Gluconobacter oxydans cultivation. These results identify PAA as the most effective interlayer among those investigated for FDH stabilization, direct electron transfer, and lower onset potential ( E onset ) for fructose sensing in complex fermentation broth matrices.