A glucose/oxygen enzymatic fuel cell based on gold nanoparticles modified graphene screen-printed electrode: Proof-of-concept in human saliva

This paper presents a new direct electron transfer based-miniaturized glucose/oxygen enzymatic fuel cell (EFC) whose operating ability has been tested in real saliva samples. The bioanode and biocathode are a graphene working electrode and a graphite counter electrode localized on the same screen printed electrode (SPE) modified with poly(vinyl alcohol) N-methyl-4(4′-formylstyryl)pyridinium methosulfate acetal (PVA-SbQ)/cellobiose dehydrogenase from Corynascus Thermophilus (CtCDH) C291Y/AuNPs and with Trametes Hirsuta laccase (ThLac)/AuNPs, respectively.

In order to optimize the bioanode, several CDH immobilization procedures were adopted, such as drop-casting, use of Nafion membrane or PVA-SbQ photopolymer. The photopolymer showed the best performance in terms of stability and reliability. As biocathode a partially optimized laccase electrode was employed with the variant that the used nanomaterials allowed to reduce the overpotential of O₂/H₂O redox reaction catalyzed by Trametes Hirsuta Laccase (ThLac), drop-casted onto the gold nanoparticles (AuNPs) modified SPE.

The performances of bioanode and biocathode were tested separately, initially immobilizing the two enzymes onto separated graphene SPEs. An efficient direct electron transfer was achieved for both elements, obtaining an apparent heterogeneous electron transfer rate constant (ks) of 0.99 ± 0.05 s⁻¹ for CtCDH C291Y and 5.60 ± 0.05 s⁻¹ for ThLac. Both electrodes were then assembled in a two compartment EFC obtaining a maximal power output of 5.16 ± 0.15 µW cm−2 at a cell voltage of 0.58 V and an open circuit voltage (OCV) of 0.74 V. Successively, the bioanode and biocathode were assembled in a non-compartmentalized EFC and a remarkable 50% decrease of the maximum power output at the value of 2.15 ± 0.12 µW cm⁻² at cell voltage of 0.48 V and an OCV of 0.62 V at pH 6.5 was registered. In order to reduce the cell dimensions in view of its possible integration in biomedical devices, the bioanode and biocaythode were realized by immobilization of both enzymes onto the same SPE. The so miniaturized EFC delivered a maximal power output of 1.57 ± 0.07 µW cm² and 1.10 ± 0.12 µW cm⁻² with an OCV of 0.58 V and 0.41 V in a 100 µM glucose solution and in human saliva, respectively.