Electrode Substrate Research Articles

Powder-Based Cu3VS4 Photocathode Prepared by Particle-Transfer Method for Water Splitting Using the Whole Range of Visible Light

Powder-based Cu3VS4 photoelectrode with 1.5–1.6 eV of a band gap that was responsive to whole range of visible light was fabricated by a particle transfer method, aiming at enhancement of the photocathodic performance. The particle-transferred Cu3VS4 photoelectrode with a Au-contacting layer (Cu3VS4/Au) showed much higher photocathodic performance for water reduction to produce H2 under simulated sunlight irradiation (AM-1.5 G) than previously reported Cu3VS4/FTO prepared by a conventional drop-casting method. This drastic enhancement is due to the good contact between photocatalyst particles and the Au-contacting layer of the substrate electrode. Loading of a Pt cocatalyst was effective for further enhancement of the photocathodic performance of the Cu3VS4/Au photoelectrode. Pt(1 nm)-loaded Cu3VS4/Au gave about 4 mA cm−2 of the cathodic photocurrent at −0.41 V vs NHE at pH7 that was four times higher than that without a Pt cocatalyst under simulated sunlight irradiation (AM-1.5 G). When Cu3VS4 particles with a small particle size were prepared by a flux method, better durability was obtained compared with a solid-state reaction. Efficient photoelectrodes based on a powdered metal sulfide utilizing whole range of visible light have successfully been developed by a particle transfer method, loading of a Pt cocatalyst, and a flux method on photoelectrochemical performance.

Microfabricated Solid‐contact Potentiometric Sensor for Determination of Tedizolid Phosphate, Application to Content Uniformity Testing

AbstractSolid contact sensors were designed for determination of the antibiotic prodrug tedizolid phosphate. The sensors are based on; microfabricated copper as cost‐effective electrode substrate and graphene layer as a transducer. The ion sensing PVC polymeric membrane was optimized by proper selection of the anion exchanger. The graphene layer was characterized by scanning electron microscopy, Raman spectroscopy, FT‐IR, besides measuring electrochemical impedance for the fabricated sensors. The potential drift decreased down to 0.133 mV h−1 compared to 6.67 mV h−1 for graphene free sensor. The sensors have been used to determine tedizolid phosphate in its pharmaceutical formulation and content uniformity testing applications.

Manganese sulfide enables the formation of a highly active β-MnOOH electrocatalyst for effective alkaline water oxidation

Inspired by the manganese (Mn)-containing oxygen-evolving complex of photosystem II, large efforts have been made in the last few years to develop efficient artificial Mn-based catalysts for water oxidation but with limited success. Most of such Mn-based electrocatalysts are merely precatalysts and form MnOx structures as active phases under electrocatalytic conditions. The current focus includes the advancement of synthetic methods to produce solid-state MnOx catalysts of controllable shape, size, composition, and electronic structure. We now learned that using the new hexakis(pyridiniumsulfido) MnII complex 1, [Mn(pyHS)6](OTf)2, as a molecular precursor furnishes cubic-shaped manganese sulfide nanostructures under hot-injection conditions. The latter were electrophoretically deposited on different electrode substrates and found to undergo unexpected transformation to crystalline β-MnOOH with surface stabilized MnIII sites under alkaline water oxidation conditions instead of forming previously known active layered birnessite δ-MnO2 phase. This anomalously active β-MnOOH material outperforms recently reported MnOx-based catalysts for water oxidation under identical reaction conditions.

Synergistic effects of polyaniline/poly(methyl methacrylate)/carbon nanotubes in nanocomposite polymer substrate electrodes for solar energy applications

Unique polyaniline (PANI)/poly(methyl methacrylate) (PMMA)/multiwalled carbon nanotubes (MWCNTs) nanocomposite polymer substrate electrodes (NPSEs) were prepared using in situ polymerization. PMMA microbeads (10 mm) were also added as fillers inside the NPSEs during polymerization. Different weight percentages of MWCNTs (1, 2, and 5 wt.%) were added to the NPSEs. The surface morphology of the PANI/PMMA/MWCNTs NPSEs was studied by scanning electron microscopy, Fourier transform infrared, and X-ray diffraction. Thermal stability was studied by thermo-gravimetric analyses and differential thermal analysis. Meanwhile, the four-probe analyzer and the solar simulator determined the electrical conductivities and photovoltaic parameters of the NPSEs based solar devices. The synthesized NPSEs with optimized compositions PANI/PMMA (1%)–MWCNTs (5%) showed superior photovoltaic performance along with improved thermal and electrical conductivities. Therefore, these NPSEs possess a future potential for the fabrication of solar devices in the field of solar energy applications.

Poly(safranine T)-deep eutectic solvent/copper oxide nanoparticle-carbon nanotube nanocomposite modified electrode and its application to the simultaneous determination of hydroquinone and catechol

This work presents the combined use of safranine (SF) as a redox polymer and multiwalled carbon nanotubes (MWCNT)-copper oxide nanoparticles (CuO) in the development of a novel sensor for the simultaneous analysis of hydroquinone (HQ) and catechol (CAT). Electropolymerisation of SF was carried out in acid-doped ethaline deep eutectic solvent to prepare poly(safranine) (PSFEthaline) film electrodes with three different nanostructured architectures on pencil graphite electrodes (PGE) as electrode substrate. The polymerisation was done after nanomaterial surface modification to obtain PSFEthaline-HCl/MWCNT/PGE, PSFEthaline-HCl/CuO/PGE, and PSFEthaline-HCl/MWCNT-CuO/PGE. The synthesis, preparation, and characterisation of PSF film-coated electrodes were studied using cyclic voltammetry and electrochemical impedance spectroscopy to investigate the contribution of each nanomaterial on sensor performance. The best result for polymer film growth was obtained with PSF electrodeposited on MWCNT-CuO/PGE in HCl doped-ethaline. The analytical performance of the modified electrode was evaluated for electrochemical sensing of HQ and CAT by differential pulse voltammetry in aqueous Britton-Robinson buffer solution. Due to the combined effect of MWCNT-CuO nanocomposite film and PSF, the modified electrode sensor provided sensitive and selective detection of HQ and CAT with good peak separation. The simultaneousdetermination of HQ and CAT in both tap water and milk samples was successfully carried out to demonstrate the analytical applicability of the sensor. The sensor could be a promising analytical approach for monitoring the amount of HQ and CAT in real samples.

Tuning the Redox Chemistry of Copper Oxide Nanoarchitectures Integrated with rGOP via Facet Engineering: Sensing H2S toward SRB Detection.

The ultrasensitive determination of sulfate reducing bacteria (SRB) is of great significance for their crucial roles in environmental and industrial harms together with the early detection of microbial corrosion. In this work, we report the development of highly efficient electrocatalysts, i.e., Cu2O-CuO extended hexapods (EHPs), which are wrapped on homemade freestanding graphene paper to construct a flexible paper electrode in the electrochemical sensing of the biomarker sulfide for SRB detection. Herein Cu2O-CuO EHPs have been synthesized via a highly controllable and facile approach at room temperature, where the redox centers of copper oxide nanoarchitectures are tuned via facet engineering, and then they are deposited on the graphene paper surface through an electrostatic adsorption to enable homogeneous and highly dense distribution. Owing to the synergistic contribution of high electrocatalytic activity from the Cu mixed oxidation states and abundant catalytically active facets of Cu2O-CuO EHPs and high electrical conductivity of the graphene paper electrode substrate, the resultant nanohybrid paper electrode has exhibited superb electrochemical sensing properties for H2S with a wide linear range up to 352 μM and an extremely low detection limit (LOD) of 0.1 nM with a signal-to-noise ratio of 3 (S/N = 3), as well as high sensitivity, stability, and selectivity. Furthermore, taking advantage of the good biocompatibility and mechanical flexibility, the electrochemical sensing platform based on the proposed electrode has been applied in the sensitive detection of SRB in environmental samples through the sensing of sulfide from SRB, which holds great promise for on-site and online corrosion and environmental monitoring.

Effect of Different Hot-Pressing Pressure and Temperature on the Performance of Titanium Mesh-Based MEA for DMFC.

The hot-pressing process of the membrane electrode assembly (MEA) is one of the research hotspots in the field of the fuel cell. To obtain suitable titanium mesh-based MEA hot pressing process parameters, titanium mesh was used as electrode substrate material. The anode and cathode of MEA were prepared by the drip-coated method, and the titanium mesh-based MEA was prepared under different hot-pressing pressure and temperature, respectively. The performance of titanium mesh-based MEA was studied by morphological observation, elemental analysis, thickness measurement, single cell test and numerical fitting analysis. The results demonstrated that: with increasing hot-pressing pressure from 0 MPa to 10 MPa, the forming thickness of titanium mesh-based MEA is getting thin gradually, and the peak power density of titanium mesh-based MEA first increased and then gradually decreased; with increasing hot-pressing temperature from 115 °C to 155 °C, the peak power density of titanium mesh-based MEA enhanced at the beginning and then also gradually decreased. Under the premise of a hot-pressing time of 180 s and the optimal operating temperature of DMFC of 60 °C, the appropriate hot-pressing process conditions of titanium mesh-based MEA are a hot-pressing pressure of 5 MPa and a hot-pressing temperature of 135 °C. The results can provide a technological reference for the preparation of titanium mesh MEA for DMFC.

Combined SECM and spectroscopy investigation of the interfacial chemistry of chalcopyrite during anodic oxidation

Hydrometallurgical copper extraction from chalcopyrite (CuFeS2), the most abundant copper-containing resource in the world, is always challenged by its passivation during industrial application, whose mechanisms are still not fully understood. In this study, the interfacial chemistry of chalcopyrite during the anodic oxidation was studied by combined Scanning Electrochemical Microscopy (SECM) and spectroscopic analyzes of Raman spectroscopy and X-ray absorption near-edge spectroscopy (XANES). Ex-situ SECM feedback mode was firstly used to detect and image the formation of passivating films. Then, the in-situ SECM substrate generation-tip collection (SG-TC) experiment by positioning the micro-platinum probe just above the chalcopyrite surface was conducted so that electrochemically active dissolution products can be deposited and monitored. Subsequently, Raman spectroscopy was performed on the SECM tip and the chalcopyrite substrate electrode respectively to identify the products that were released into the solution and then collected on the tip, as well as the ones left behind on the mineral surface. The SECM feedback mode mapping and approach curves demonstrated that under the passive and trans-passive potential regions, low conductive passivation films formed on the chalcopyrite surface, which contributed to the hindered dissolution of chalcopyrite due to the decreased electron transfer rate. In-situ SECM SG-TC results from the anodically oxidized chalcopyrite suggested that soluble sulfur species, most likely thiosulfate ions (S2O32−) were dissolved from the surface during the passivation films formation. The released S2O32− was evidenced by comparing with the pyrite anodic oxidation experiment and sulfur K-edge XANES analysis of the electrolytes collected after chalcopyrite anodic dissolution. In-situ Raman spectra of the oxidized chalcopyrite surface confirmed metal deficient layers were the passivation layers.

Facile Route to Achieve Self-Supported Cu(OH)2/Ni3S2 Composite Electrode on Copper Foam for Enhanced Capacitive Energy Storage Performance

Herein, a Cu(OH)2/Ni3S2 composite was successfully prepared through facile two-step electrodeposition. As the electrode substrate and the only copper source, the copper foam underwent surface oxidation by galvanostatic deposition technology to form Cu(OH)2, and the subsequent coverage of Ni3S2 was achieved by potentiostatic deposition. The Cu(OH)2 acts as a skeleton, providing support for Ni3S2 growth, thus providing more abundant electrochemical active sites. By virtue of the in situ growth strategy and the synergy of different components, the optimized Cu(OH)2/Ni3S2 electrode illustrates significantly enhanced pseudocapacitance performance, with an areal specific capacitance of 11.43 F cm−2 at 2 mA cm−2, good coulombic efficiency of 94.55%, and remarkable cyclic stability (83.33% capacitance retention after 5000 cycles).

TiN nano arrays on nickel foam prepared by multi-arc ion plating for fast-charging supercapacitors

Physical vapor deposition (PVD) technologies have been widely used to produce metal nitride films on planar substrate for electrode of ultrafast charging supercapacitors. However, planar electrode structure greatly limits the energy density of device. This work, for the first time, employs multi-arc ion plating (MAIP) to efficiently prepare titanium nitride (TiN) nano arrays on 3D current collector (i.e., nickel foam). The array morphology, composition, crystal structure, electrical and electrochemical properties of TiN as a function of working pressure are investigated. The optimized electrode exhibits a large specific capacitance of 90.18 F g−1 and a good stability with capacity loss of 11.9% after 10,000 charge-discharge cycles at 1 A g−1. The assembled symmetrical supercapacitor can achieve a high energy density of 4.72 Wh kg−1 with a power density of 800 W kg−1 under current density of 1 A g−1. The general findings open a new and promising strategy in facile and efficient fabrication of electrode materials towards ultrafast charging supercapacitors.

A Flexible Electrochemiluminescence Sensor Equipped With Vertically Ordered Mesoporous Silica Nanochannel Film for Sensitive Detection of Clindamycin.

Fast, convenient, and highly sensitive detection of antibiotic is essential to avoid its overuse and the possible harm. Owing to enrichment effect and antifouling ability of ultrasmall nanochannels, the vertically ordered mesoporous silica nanochannel film (VMSF) has great potential in the development of the facile electrochemiluminescence (ECL) sensor for direct and sensitive analysis of antibiotics in complex samples. In this study, we demonstrated a flexible ECL sensor based on a cost-effective electrode covered with a VMSF for sensitive detection of clindamycin. Polyethylene terephthalate coated with indium tin oxide (PET-ITO) is applied as a flexible electrode to grow VMSF using the electrochemically assisted self-assembly (EASA) method. The negatively charged VMSF nanochannels exhibit significant enrichment toward the commonly used cationic ECL luminophores, tris(2,2-bipyridyl) dichlororuthenium (II) (Ru (bpy)3 2+). Using the enhanced ECL of Ru (bpy)3 2+ by clindamycin, the developed VMSF/PET-ITO sensor can sensitively detect clindamycin. The responses were linear in the concentration range of 10 nM–25 μM and in the concentration range of 25–70 μM. Owing to the nanoscale thickness of the VMSF and the high coupling stability with the electrode substrate, the developed flexible VMSF/PET-ITO sensor exhibits high signal stability during the continuous bending process. Considering high antifouling characteristic of the VMSF, direct analysis of clindamycin in a real biological sample, human serum, is realized.

A fully integrated fast scan cyclic voltammetry electrochemical method: Improvements in reaction kinetics and signal stability for specific Ag(I) and Hg(II) analysis

• A fully integrated FSCV electrochemical method is developed. • This proposed method is to improve reaction kinetics and signal stability. • TdT-yielded DNAs can be used to construct electrode substrate favorably. • The platform is suited for Ag(I) and Hg(II) analysis well. • The method is conducive to the development of the real-time detection device. Inspired by the urgent need to detect trace heavy metal ions in various real samples, we construct a unique electrochemical biosensing method for heavy metal ions Ag(I) and Hg(II) analysis in this work. The biosensor is constructed by using terminal deoxynucleotidyl transferase (TdT) to catalyze the addition of dCTP and dTTP in 3′-OH end of original DNAs, thus producing enough long DNAs. This unique DNAs have a strong affinity to Ag(I) and Hg(II), and C-Ag(I)-C and T-Hg(II)-T structures occurs at the electrode surface. Meanwhile, the introduction of fast-scanning cyclic voltammetry (FSCV) can achieve the stable signal output all the while, where the reaction kinetics are superior to the diffusion kinetics, resulting in a significant improvement on reaction kinetics and signal stability. Based on it, simple detection of Ag(I) or Hg(II) is demonstrated powerfully with good detection limit (3 × 10 −14 M or 3 × 10 −15 M, S/N = 3); additionally, simultaneous detection of Ag(I) and Hg(II) is achieved with negligible interference. Furthermore, the proposed method has been also applied for some DNA electronic computing logic gates by designing simple or multiple inputs and output favorably. Based on these, the FSCV method has potential applications for the monitoring of heavy metal ions in real sample analysis.

Catalytic hairpin assembly assisted target-dependent DNAzyme nanosystem coupled with AgPt@Thi for the detection of lead ion

An ultrasensitive electrochemical biosensor for detection of lead ions (Pb2+) is proposed based on catalytic hairpin assembly and target-induced DNAzyme signal amplification strategy. Polyethyleneimine-reduced graphene oxide (PEI-rGO) combined with gold@silver nanosheets (Au@Ag NSs) are used as electrode substrate modification materials, which not only increase the specific surface area but also exhibit stronger conductivity than pure PEI-rGO or Au@Ag NSs. Hairpin chain 1 (HP1) is immobilized on the surface of modified electrode by Au–S. Then trigger (Tr) DNA can induce the opening of the HP1 hairpin, thus exposing the binding sequence to hybridize with Hairpin chain 2 (HP2) and catalyzing the opening and binding of the hairpin HP2. The process is cyclic and will produce abundant HP1-HP2 duplex strands. When Pb2+ is present, it can catalyze DNAzyme (Pb2+-HP2) to specifically cut the substrate chain HP1, and only a partial sequence of HP1 remains on the surface of the electrode. Finally, the signal probe (AgPt@Thi-CP) can be hybridized with the part of the HP1 sequence after being cut to generate a significant electrical signal. Under optimal conditions, the Pb2+ concentration measured by prepared electrochemical biosensor has a good linear relationship in the range of 0.05 pM–5 nM, and the detection limit is 0.028 pM. This method can be used for the trace detection of Pb2+ in tap water samples, and it also provides a platform for the detection of other targets.

CB/PDMS electrodes for dielectric elastomer generator with low energy loss, high energy density and long life

Dielectric elastomer generator (DEG), consisting of highly deformable dielectric elastomer (DE) film sandwiched between compliant electrodes, can convert mechanical energy into electrical energy. The widely used carbon grease (CG) electrode has short service life. The conductive rubber electrode is the most promising electrode, but its properties still need to be improved to obtain DEG with high energy density and long life. In this study, thin electrode film of superconducting carbon black (CB)/Polydimethylsiloxane (PDMS) composite with smooth surface, uniform thickness and good dispersion of CB in PDMS matrix was prepared by using solution blending combined with ultrasonication followed by freeze drying and mask scraping technique. The strong interfacial bonding between the electrode and DE substrate was obtained by optimizing CB content and mask scraping technique and by using PDMS in both electrode and DE substrate. High elongation at break, good compliance, high electrical conductivity (EC) and high stability of EC were successfully obtained. Compared with DEG using CG electrode, the energy loss at the same conditions of DEG using the electrodes with 6 wt% CB is reduced by 40.3%, and the harvested energy density (up to 20.5 mJ/cm3) increases by 32%. More importantly, CB/PDMS electrode can withstand 60,000 cycles of stretching under 200% strain, much higher than that reported in previous studies.

Self-adhesive and printable tannin–graphene supramolecular aggregates for wearable potentiometric pH sensing

The pH of sweat is the most common biochemical parameter monitored by integrated wearable devices. A crucial factor in sensing materials for wearable applications is strong contact both with the skin and with the electrode substrate. Currently, the deposition of many sensitive materials on a substrate relies on mixing a small amount of binder, which raises the issue of biocompatibility and the risk of detachment. Herein, we report self-adhesive tannin–graphene supramolecular aggregates for use in wearable potentiometric pH sensors. The abundant phenolic hydroxyl groups in tannin (TA) result in strong adhesion and are also the pH response sites. The graphene (reduced graphene oxide, RGO) induces the supramolecular formation of TA and promotes electron transfer based on the π-π conjugation interaction. The pH sensor has a reversible and Nernstian response, and is not affected by potentially interfering ions. Owing to the strong adhesion of TA–RGO, a wearable pH device was directly fabricated using a dispensing printing technique. The sensor has been shown to be successful in monitoring the pH of sweat in real time. This work emphasizes the importance of the adhesion of sensing materials for use in wearable electrochemical sensors.

Fabrication and Seamless Integration of Insensitive-Bending Fully Printed All-in-One Fabric-Based Supercapacitors Based on Cost-Effective MWCNT Electrodes.

All-in-one supercapacitors are considered to be promising due to their advantages of flexibility and structure stability. However, the sophisticated and precise manufacturing processes and difficulty of series/parallel integration hinder their application and development. Herein, cost-effective all-in-one fabric-based supercapacitors (all-in-one FSCs) are fabricated by utilizing the facile screen-printing technique and multiwalled carbon nanotube (MWCNT) electrodes. The MWCNT electrodes are constructed on the gel-electrolyte-soaked fabric that simultaneously serves as separator and electrode substrates. The as-prepared all-in-one FSC exhibits better capacitive behavior and rate capability and lower internal resistance than traditional sandwiched fabric-based supercapacitors (sandwiched FSCs). Moreover, due to the simplified structure and interface interaction, the all-in-one FSC shows excellent flexibility and stability even under dynamic bending cycles with a relatively high strain rate of 20% s-1. This work also demonstrates the seamless series/parallel integration scheme of all-in-one supercapacitors by designing the screen-printing patterns instead of using metal wires. The proposed fabrication process and series/parallel integration scheme definitely improve the portability of integrated supercapacitors and potentially contribute to the large-scale production and application on wearable electronics.

Research Progress on the Flexibility of an Implantable Neural Microelectrode.

Neural microelectrode is the important bridge of information exchange between the human body and machines. By recording and transmitting nerve signals with electrodes, people can control the external machines. At the same time, using electrodes to electrically stimulate nerve tissue, people with long-term brain diseases will be safely and reliably treated. Young’s modulus of the traditional rigid electrode probe is not matched well with that of biological tissue, and tissue immune rejection is easy to generate, resulting in the electrode not being able to achieve long-term safety and reliable working. In recent years, the choice of flexible materials and design of electrode structures can achieve modulus matching between electrode and biological tissue, and tissue damage is decreased. This review discusses nerve microelectrodes based on flexible electrode materials and substrate materials. Simultaneously, different structural designs of neural microelectrodes are reviewed. However, flexible electrode probes are difficult to implant into the brain. Only with the aid of certain auxiliary devices, can the implant be safe and reliable. The implantation method of the nerve microelectrode is also reviewed.

A general guide for adsorption of cadmium sulfide (CdS) quantum dots by successive ionic layer adsorption and reaction (SILAR) for efficient CdS-sensitized photoelectrochemical cells

Using CdS quantum dots grown on the surface of mesoscopic TiO2 film through SILAR deposition as a model semiconductor-sensitizer, common but not well understood parameters in the deposition process such as precursor compound & its concentration, solvent, and dipping time of the substrate electrode are systematically checked for suggesting a general guideline to make efficient CdS-sensitized mesoporous TiO2 electrode for photovoltaic and photocatalytic applications. Among many variables, the electrostatic interaction between intrinsic (+)-charge of metal cation (Cd2+) and induced (−)-charge of TiO2 surface, which is generated by the degree of solution’s pH above the point of zero charge (pzc) of TiO2, is observed to be the most critical for controlling the extent of CdS adsorption by taking absorbance and TEM images after a defined SILAR process. The acetate salt is the best one for faster and more adsorption of as-grown CdS due to its role of increasing the pH value in solution as a weak base. The highest pH of ∼ 9.5 obtained by adding a weak base, triethanolamine (TEA) to any Cd2+-dissolved solution induces the most adsorption of CdS within the least cycle optimized for better photovoltaic conversions efficiency and photoelectrochemical H2 evolution than those from any other conditions.

Structural design of flexible interdigital capacitor based upon 3D printing and spraying process

Traditional substrates of metallic interdigital electrodes (IEs) are rigid and undeformable, flexible interdigital capacitors are therefore appealing as strain sensors. In this study, interdigital capacitors were parametrically designed by 3D printing and encapsulated by spraying process. The interdigital circuits of the structure were printed with conductive silicone rubber filled with silver-coated glass fiber and carbon fiber, and the circuits were encapsulated with polydimethylsiloxane. Herein, the interdigital-flexible structures were parametrically designed and firstly served as capacitive sensor, namely flexible interdigital capacitive sensors (FICSs). The spaces between IEs, are extremely sensitive to strain, therefore provide the capacitors with excellent electromechanical behaviors. The optimized FICS benefited for a wide working range of strain (0%∼45%), high sensitivity (gauge factor = 2.7) to a tiny strain of 0.3%, stable working duration at different stretching speeds (18 mm min−1, 36 mm min−1 and 72 mm min−1), prolonged service life (>800 cycles), as well as excellent capability to detect human movement (bulging, grasping and bending). Response mechanism of the FICS was modeled based upon its microstructure evolution, including the distances between IEs and the fillers migration. The printed FICSs with optimized structure provide a comprehensive thought in the design of electronics, further would inspire the branch of 3D printed electronics.

Controlled, partially exfoliated, self-supported functionalized flexible graphitic carbon foil for ultrasensitive detection of SARS-CoV-2 spike protein

This paper reports on an ultrasensitive and label-free electrochemical immunosensor for monitoring the SARS-CoV-2 spike protein (SARS-CoV-2 SP). A self-supported electrode, which can simultaneously serve as an antibody immobilization matrix and electron transport channel, was initially fabricated by a controlled partial exfoliation of a flexible graphitic carbon foil (GCF). Mild acidic treatment enabled the partial oxidation and exfoliation (down to a few layers) of the flexible GCF; this also provided a high percentage of oxygen functionality and an enhanced surface roughness. The substrate electrode was further functionalized with ethylenediamine (EDA) to provide a suitable platform with even a higher surface roughness, for the covalent immobilization of an anti-SARS-CoV-2 antibody. The change in the current response for the [Fe(CN)6]3−/4− redox couple, induced by the binding of SARS-CoV-2 SP to the antibody immobilized on the electrode surface, was used to determine the SARS-CoV-2 SP concentration. The immunosensor thus prepared could detect SARS-CoV-2 SP within 30 min with high reproducibility and specificity over a wide concentration range (0.2–100 ng/mL). Detection limits of 25 pg/mL and 27 pg/mL were found in a phosphate buffer solution (pH 7.4), and diluted blood plasma, respectively. The immunosensor was also employed to detect SARS-CoV-2 SP in artificial human saliva.