Engineering of Electron Affinity and Interfacial Charge Transfer of Graphene for Self-Powered Nonenzymatic Biosensor Applications

Abstract

Facile electron transport and intimate electronic contact at the catalyst–electrode interface are critical for the ideal performance of electrochemical devices such as glucose biofuel cells and biosensors. Here, through a comprehensive experimental–theoretical exploration, we demonstrate that engineering of interfacial properties, including interfacial electron dynamics, electron affinity, electrode–catalyst–adsorbate electrical synergy, and electrocatalytically active surface area, can lead to highly efficient graphene-based electrochemical devices. We selected two closely related but electronically and surface chemically different functionalized graphene analoguesgraphene acid (GA) and reduced graphene oxide (rGO)as the model graphenic platforms. Our studies reveal that compared to rGO, GA is a superior bifunctional catalyst with high oxygen reduction reaction (an onset potential of 0.8 V) and good glucose oxidation activities. Spectroscopic and electrochemical analysis of GA and rGO indicated that the higher carboxylic acid content on GA increases its overall electron affinity and coupled with improved conductivity and band alignment, which leads to GA’s better electrochemical performance. The formulation of a heterostructure between GA and samarium oxide (Sm2O3) nanoparticles led to augmented conductivity (lower charge-transfer resistance) and glucose binding affinity, resulting in a further enhanced glucose oxidation activity. The interdimensional Sm2O3/GA heterostructure, leveraging their enhanced glucose oxidation capacity, exhibited excellent nonenzymatic amperometric glucose sensing performance, with a detection limit of 107 nM and a sensitivity of 20.8 μA/μM. Further, a nonenzymatic, membrane-free glucose biofuel cell (with Sm2O3/GA heterostructure as anode and GA as biocathode) produced a power density of 3.2 μW·cm–2 (in PBS spiked with 3 mM glucose), which can function as self-powered glucose sensors with 70 nM limit of detection. The study establishes the potential of interfacial engineering of GA to engage it as a highly tunable substrate for a broad range of electrochemical applications, especially in future self-powered biosensors.

Graphene Acid: A Versatile 2D Platform for Catalysis

“…Sanad and coworkers deposited Sm 2 O 3 particles (see Figure 11a) on GA, and explored its electrocatalytic performance for glucose oxidation (Figure 11b) and ORR compared to an analogous Sm 2 O 3 /rGO sample. [16] Sm 2 O 3 /GA presented a good electrocatalytic behaviour developing a glucose oxidation current of 0.62 mA and an ORR activity with an onset potential of 0.8 V and a half-wave potential of 0.75 V vs RHE. From the comparison between Sm 2 O 3 /rGO and Sm 2 O 3 /GA the authors concluded that the faster electron transfer in the latter is attributable to the already mentioned higher electronic conductivity of GA.…”

“…Very recently, Sanad and coworkers took advantage of the catalytic potential and good electron conduction of GA to develop an electrocatalyst able to carry out the non‐enzymatic glucose oxidation reaction and the oxygen reduction reaction (ORR), achieving improved performance compared to rGO [16] . These authors concluded that the increased number of COOH groups on GA compared to rGO resulted in a significantly higher ORR activity with an onset potential of 0.8 V, the highest reported for graphenic materials.…”

“…Sanad and coworkers deposited Sm 2 O 3 particles (see Figure 11a) on GA, and explored its electrocatalytic performance for glucose oxidation (Figure 11b) and ORR compared to an analogous Sm 2 O 3 /rGO sample [16] . Sm 2 O 3 /GA presented a good electrocatalytic behaviour developing a glucose oxidation current of 0.62 mA and an ORR activity with an onset potential of 0.8 V and a half‐wave potential of 0.75 V vs RHE.…”

“…In addition, these authors elucidated the active sites for the glucose oxidation activity by a combination of experiments and calculations (Figure 11c), and concluded that the Sm 2 O 3 /GA has a lower charge‐transfer resistance, better HOMO‐LUMO alignment, reduced charge‐transfer resistance and substrate (glucose or oxygen) binding affinity. In the same paper the authors explored the use of the Sm 2 O 3 /GA as a sensor of glucose in different environments [16] . Hence, the same electrode containing the Sm 2 O 3 /GA was tested in artificial and saliva samples for the detection of glucose.…”

“…(b) Glucose oxidation on Sm 2 O 3 /GA. (c) Catalytic cycle for glucose oxidation on Sm 2 O 3 /GA [16] …”