Abstract
Recent advances in flexible fiber-based microelectrodes have opened a new horizon for sensitive real-time near-cell and even intracellular measurements. In this work, we develop a new type of hierarchical nanohybrid microelectrode based on three-dimensional (3D) porous graphene-wrapped activated carbon fiber (ACF) via a facile and effective electrodeposition of graphene oxide (GO) nanosheets on ACF using a green ionic liquid (IL) as the electrolyte. This technique enables the simultaneous electrodeposition and electrochemical reduction of GO nanosheets on ACF to form 3D porous IL functionalized electrochemically reduced GO (ERGO)-wrapped ACF (IL–ERGO/ACF). The adsorbed IL molecules on the ERGO surface provide sufficient active sites and act as the template for the in situ electrodeposition of highly dense and well-dispersed bimetal PtAu nanoflowers on the 3D IL–ERGO scaffold. By virtue of the unique array of structural and chemical properties of bimetal PtAu nanocatalysts and 3D porous IL–ERGO on ACF, the resultant PtAu nanoflowers-decorated IL–ERGO/ACF (PtAu/IL–ERGO/ACF) microelectrode demonstrates a variety of excellent sensing performances, including high sensitivity, a wide linear range and good selectivity in the electrochemical detection of a newly emerged cancer biomarker, hydrogen peroxide (H2O2). When used for the real-time tracking of H2O2 secreted from female cancer cells, such as breast cancer cells and gynecological cancer cells, the electrochemical sensor based on the PtAu/IL–ERGO/ACF microelectrode provides important information for distinguishing between different cancer cells and normal cells and for evaluating the therapeutic activity of antitumor drugs towards live cancer cells, which are of great clinical significance for cancer diagnosis and management. Super-tough fibres, thinner than human hair, can sense the biomarkers emitted by cancer cells thanks to a nanostructured coating. Carbon-fibre microelectrodes offer the ability to measure tiny amounts of bodily fluids non-invasively. Fei Xiao from Huazhong University of Science and Technology in China and co-workers now report a way to tune the sensitivity of fibre sensors to hydrogen peroxide — a small-molecule metabolite commonly emitted by breast cancers. Three-dimensional, micron-thick graphene coatings, achieved by immersing acid-activated carbon fibres and nanosheet precursors in an ionic liquid, enabled the team to boost electrode sensitivity to levels needed for in vitro studies. The ionic liquids also helped attach platinum–gold catalysts with unique ‘nanoflower’ shapes to the graphene wrapping. The catalyst-enhanced microelectrode proved accurate at distinguishing different lines of cancer cells and evaluating antitumour medications. We develop a new type of flexible nanohybrid microelectrode by decorating high dense PtAu alloy nanoflowers on 3D porous ionic liquid functionalized graphene wrapped activated carbon fiber. In virtue of the unique array of structural and chemical properties, the resultant hierarchical nanohybrid microelectrode exhibits a collection of good sensing performances, and can be used in near-cell sensitive detection of cancer biomarker secreted from different female cancer cells in normal state and treated by antitumor drug, which provides important information in distinguishing different cancer cells and normal cells and evaluating the therapeutic activity of antitumor drug towards the live cancer cells.
Highlights
The development of flexible fiber-based electrodes in micro/nanoscale dimensions has attracted tremendous research interest due to the high spatial resolution derived from the reduced geometric area for threedimensionally (3D) addressable local detection in a small volume.[1,2,3]In addition, the high temporal resolution for fast electron/mass transfer due to nonplanar diffusion[4,5,6] and the intrinsic mechanical and deformational characteristics enable such electrodes to be rolled up and incorporated into compact electrochemical sensor systems
The smooth surface of activated carbon fiber (ACF) becomes relatively rough after electrochemical activation (Figure 2a inset, Supplementary Figures S1c and S1d), which facilitates the electrodeposition of graphene oxide (GO) nanosheets on the surface
The formation mechanism of the 3D graphene network on ACF during the electrochemical reduction process can be ascribed to the following factors: under a negative applied potential, the electrochemical reduction of GO starts from the surface of the ACF electrode, and the GO nanosheets lose their oxygenated groups and become more hydrophobic; they are deposited onto the electrode substrate due to the strong π–π stacking interactions and weak electrostatic repulsion.[29,30,31]
Summary
The development of flexible fiber-based electrodes in micro/nanoscale dimensions has attracted tremendous research interest due to the high spatial resolution derived from the reduced geometric area for threedimensionally (3D) addressable local detection in a small volume.[1,2,3]In addition, the high temporal resolution for fast electron/mass transfer due to nonplanar diffusion[4,5,6] and the intrinsic mechanical and deformational characteristics enable such electrodes to be rolled up and incorporated into compact electrochemical sensor systems. Owing to the synergistic effect at the interface of the bimetal PtAu nanocatalysts, IL molecules and 3D porous ERGO on ACF, the electrochemical H2O2 sensor based on the PtAu/IL–ERGO/ACF microelectrode exhibits a NPG Asia Materials variety of outstanding features, including a high sensitivity of 118 μAcm− 2 mM− 1, a wide linear range from 1.0 μM to 19.94 mM, a low detection limit of 1.0 μM (a signal-to-noise ratio S/N = 3) and good selectivity.
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