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) 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. To optimize the bioanode, several CDH immobilization procedures were adopted. The photopolymer showed the best performance in terms of stability and reliability. The bioanode and biocathode performances 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. Then, 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. To reduce the cell dimensions given its possible integration in biomedical devices, the bioanode and biocaythode were realized by immobilizing 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.