Nonenzymatic Saliva-Range Glucose Sensing Using Electrodeposited Cuprous Oxide Nanocubes on a Graphene Strip

Abstract

Cuprous oxide (Cu2O) nanomaterials provide a versatile platform for building nonenzymatic glucose sensors. In particular, Cu2O nanocubes with controllable sizes and distributions can be deposited electrochemically on a conductive graphene strip as a soft substrate under different conditions, including overpotential, temperature, copper-ion electrolyte concentration, and deposition time. Graphene provides a promising substrate for sensing because of its high conductivity, high specific surface area, and unique thermal and mechanical properties. A more negative overpotential is found to produce smaller nanocubes with a large number density, while the deposition temperature could affect the morphology of nanocubes. The size of the nanocubes increases with increasing copper-ion concentration and deposition time. Using an optimal condition of −1.0 V vs Ag/AgCl, 1 mM [Cu2+], and 100 s deposition time at room temperature, we obtain a near-homogeneous monolayer of Cu2O-shell Cu-core nanocubes, ∼50 nm in size, on a graphene strip substrate. The Cu2O nanocubes/graphene system is used as a high-performance sensor with a wide detection range of 0.002–17.1 mM and a high sensitivity appropriate for saliva-range glucose sensing. It has also been used to test glucose in the real saliva sample with 95% accuracy. This nonenzymatic glucose sensor is considerably better in performance than other nonenzymatic sensors, including those based on bare graphene, and graphene sputter-coated with a Cu film, and conventional enzymatic sensors such as glucose oxidase immobilized on graphene (with and without Nafion). In addition to being an excellent catalyst, Cu2O nanocubes have a large specific surface area and a large amount of active sites. These nanomaterial properties, along with the use of a high-conductivity substrate like graphene, make the Cu2O nanocubes/graphene sensor among the best saliva-range glucose sensors reported to date.

Recent Advancement in Biofluid-Based Glucose Sensors Using Invasive, Minimally Invasive, and Non-Invasive Technologies: A Review

“…The device is capable of detecting glucose within a 0.002–17.1 mM range with 95% accuracy and the highest sensitivity of 36.40 μA mM −1 cm −2 when tested with real saliva samples. The reported device is also air-stable and can remain functional even after 6 months [ 17 ].…”

“…(Reproduced with permission from Gao et al, ACS Appl. Nano Mater., May 2021 [ 17 ]. Copyright 2021, authors under open access licenses.)…”

“…During the reaction, the enzyme is converted to GOx (FADH2) from GOx (FAD), resulting in the generation of current or voltage changes, which are then measured by the electrodes. The typical reaction scheme is GOx (FAD) + glucose → gluconolactone + GOx (FADH2) ( Figure 2 b) [ 17 ].…”

A Concise and Systematic Review on Non-Invasive Glucose Monitoring for Potential Diabetes Management

“…Sometimes morphological changes in nanomaterials have been introduced to offer an enhanced diagnosis approach. Very recently, non-enzymatic and highly sensitive glucose sensors based on composite nanosystems like cuprous oxide nanocubes embedded on graphene have been adopted for a systematic probing of salivary glucose levels [ 124 ]. Several other enzyme-free electrochemical-based salivary glucose sensors developed in the recent past based on composite structures include Au nanoparticles on CuO nanorods (∼2009 A mM ), IrO @NiO core–shell nanowires (1439.4 A mM cm ), CuBr@CuO nanoparticles (3096 A mM cm ), Cu-Pt nanoparticles on glassy carbon electrode (2209 A mM cm ), and many more [ 112 , 125 , 126 , 127 ].…”

Sandwich-Type Electrochemical Sensor for Mucin-1 Detection Based on a Cysteine–Histidine–Cu@Cuprous Oxide Nanozyme

“…As is well known, the signal molecules usually influence the property of electrochemical sensors . A nanozyme, one type of mimic enzyme with the unique properties of nanomaterials and the functions of catalysts, has been widely used as the signal molecules of electrochemical sensors. − Specifically, copper-based nanoparticles including metallic Cu, cupric oxide (CuO), cuprous oxide (Cu 2 O), and their composite oxides are studied as nanozymes and exhibit similar properties of catalase, peroxidase, oxidase, or superoxide dismutase. − Among them, Cu 2 O nanozymes have gained much attention owing to their economic, suitable redox potentials, and high electrochemical activities. , For example, CuO@Cu 2 O, Ag@Cu 2 O, Ag 3 PO 4 @Cu 2 O, ZnO-Au@Cu 2 O, Mn­(OH) 2 @Cu 2 O, TiO 2 @Cu 2 O, and CoO@Cu 2 O have been used as electrocatalysts or photoelectrocatalysts to build electrochemical sensors. The postsynthetic modification method was applied to the abovementioned Cu 2 O nanozyme to develop its catalytic activities and applicable scopes.…”