Template-Assisted Electrodeposited Copper Nanostructres for Selective Detection of Hydrogen Peroxide.

In this study, we demonstrate the electrodeposition of copper nanoparticles (NPs) on pencil graphite electrodes (PGEs) utilizing sodium dodecyl sulphate (SDS) as a soft template. The utilization of the surfactant had an impact on both the physical arrangement and electrochemical characteristics of the modified electrodes. The prepared Cu-SDS/PGE electrodes had hierarchical dendritic structures of copper NPs, thereby increasing the surface area and electrochemical catalytic activity in comparison with Cu/PGE electrodes. The Cu-SDS/PGE electrode showed excellent catalytic activity in reducing hydrogen peroxide, resulting in the sensitive and selective detection of hydrogen peroxide. The electrode exhibited a good sensitivity of 21.42 µA/µM/cm2, a lower limit of detection 0.35, and a response time of less than 2 s over a wide range spanning 1 µM to 1 mM of hydrogen peroxide concentrations. The electrodes were also highly selective for H2O2 with minimal interference from other analytes even at concentrations higher than that of H2O2. The approach offers the benefit of electrode preparation in just 5 min, followed by analysis in 10 min, and enables for the quantitative determination of hydrogen peroxide within 30 min. This can be achieved utilizing a newly prepared, cost-effective electrode without the need for complex procedures.

Recent Electrochemical Advancements for Liquid-Biopsy Nucleic Acid Detection for Point-of-Care Prostate Cancer Diagnostics and Prognostics.

Current diagnostic and prognostic tests for prostate cancer require specialised laboratories and have low specificity for prostate cancer detection. As such, recent advancements in electrochemical devices for point of care (PoC) prostate cancer detection have seen significant interest. Liquid-biopsy detection of relevant circulating and exosomal nucleic acid markers presents the potential for minimally invasive testing. In combination, electrochemical devices and circulating DNA and RNA detection present an innovative approach for novel prostate cancer diagnostics, potentially directly within the clinic. Recent research in electrochemical impedance spectroscopy, voltammetry, chronoamperometry and potentiometric sensing using field-effect transistors will be discussed. Evaluation of the PoC relevance of these techniques and their fulfilment of the WHO's REASSURED criteria for medical diagnostics is described. Further areas for exploration within electrochemical PoC testing and progression to clinical implementation for prostate cancer are assessed.

A double-conducting polymer nanowire-based electrochemical aptasensor for highly sensitive and low fouling detection of cortisol in saliva.

A cortisol biosensor was developed based on double-conducting polymer nanowires, which exhibits excellent conductivity, resistance to biological contamination, and outstanding sensing performance. The biosensor employs dual-mode electrochemical techniques, namely, differential pulse voltammetry (DPV) and chronoamperometry (CA), for the sensitive and low fouling detection of the glucocorticoid hormone cortisol. Experimental results demonstrated that the linear detection range of the biosensor in DPV mode was 1.0 × 10-14-1.0 × 10-8 M, with a detection limit of 0.131 × 10-14 M. In CA mode, the biosensor exhibited a detection range of 1.0 × 10-13-1.0 × 10-7 M and a detection limit of 0.313 × 10-13 M. The biosensor was successfully utilized for the rapid detection of cortisol in human saliva. The combination of a high-specificity cortisol aptamer and functionalized double-conducting polymer nanowires ensured the exceptional specificity and sensitivity of the biosensor in detecting real biological samples.

Innovative voltammetric techniques for bumadizone analysis in pharmaceutical and biological samples: emphasizing green, white, and blue analytical approaches.

There are no documented electroanalytical methods for quantifying the anti-inflammatory drug bumadizone (BUM) in pharmaceutical or biological matrices. So, a new voltammetric method was developed to determine BUM at nano concentrations in pharmaceutical forms, in the presence of its alkaline degradant, and in biological fluids. Five electrodes were tested, including three nano-reduced graphene oxide (nRGO) electrodes (5%, 15%, and 20%), a carbon paste electrode (CPE), and a 10% nRGO-modified CPE. The 10% nRGO-modified electrode showed the best performance, offering high selectivity and low detection limits, with good linearity in the concentration range of 0.9 × 102 to 15 × 102 ng mL-1. Differential pulse voltammetry successfully applied this electrode for BUM determination in various samples, achieving excellent recovery without preliminary separation. The method was validated according to ICH guidelines and compared favorably to the reference method. Its environmental impact was assessed using AGREE and Eco-scale metrics in addition to the RGB algorithm, showing superior greenness and whiteness profiles due to safer solvents and lower energy consumption, along with high practical effectiveness using the BAGI metric.

Novel solution-gated transistor sensor-based SnO2 epitaxial thin films grown by pulsed laser deposition for nitrite detection.

A solution-gate controlled thin-film transistor with SnO2 epitaxial thin films (SnO2-SGTFT) is successfully utilized for highly sensitive detection of nitrite. The SnO2 films are deposited as channel materials on a c-plane sapphire (c-Al2O3) substrate through pulsed laser deposition (PLD), with superior crystal quality and out-of-plane atomic ordering. PtAu NPs/rGO nanocomposites are electrodeposited on a gold electrode to function as a transistor gate to further enhance the nitrite catalytic performance of the device. The change in effective gate voltage due to the electrooxidation of nitrite on the gate electrode is the primary sensing mechanism of the device. Based on the inherent amplification effect of transistors, the superior electrical properties of SnO2, and the high electrocatalytic activity of PtAu NPs/rGO, the SnO2-SGTFT sensor has a low detection limit of 0.1 nM and a wide linear detection range of 0.1 nM ~ 50 mM at VGS = 1.0 V. Furthermore, the sensor has excellent characteristics such as rapid response time, selectivity, and stability. The practicability of the device has been confirmed by the quantitative detection of nitrite in natural lake water. SnO2 epitaxial films grown by PLD provide a simple and efficient way to fabricate nitrite SnO2-SGTFT sensors in environmental monitoring and food safety, among others. It also provides a reference for the construction of other high-performance thin-film transistor sensors.

Efficient selenate removal from impaired waters with TiO2-assisted electrocatalysis.

Aquatic selenium (Se) oxyanions have profound ecosystem and human health impacts, necessitating their conversion and immobilization into elemental Se(0) to mitigate the aquatic Se pollution. While thermodynamically favorable, this transformation encounters kinetic limitations, especially for selenate (SeO42-) or Se(VI). To lower the activation barrier, we investigated the electrocatalytic Se(VI) transformation using five affordable catalysts on graphite cathodes, including TiO2, underpotentially deposited Cu (UPD Cu), underpotentially deposited Cd (UPD Cd), Co, and CuFe. Among these five catalysts, we identified characteristic Se(VI) reduction peaks for TiO2 through cyclic voltammetry. Other catalysts removed less than 5% of 1-mM Se(VI) in 24-h chronoamperometry tests while leaching ppm-level metal cations in the treated water. In contrast, TiO2 as the electrocatalyst could remove more than 80% of 1-mM Se(VI) with negligible catalyst dissolution. Mechanistic investigations revealed a six-electron Se(VI)/Se(0) reduction pathway at -0.30 V (vs. Ag/AgCl), resulting in red Se(0) deposits on the TiO2-coated graphite cathode. Further potential decrease to more negative than -0.45 V led to Se(-II) formation, triggering cathodic Se(0) dissolution and surface regeneration. Electrochemical impedance spectroscopy indicated that Se(VI) reduction was optimal with a moderate TiO2 loading of 0.55 mg cm-2 and acidic environments (pH=1.0∼2.5), achieving an optimized removal of 88.7 ± 2.3% under -0.70 V and an energy input of 3.6 kWh kg-1 Se. These findings lay the foundation for efficient selenate removal from impaired waters. Future efforts should evaluate catalyst performance over time and refine electrode and reactor designs to improve efficiency.

Ultrasensitive detection of H2O2 via electrochemical sensor by graphene synergized with MOF-on-MOF nanozymes.

An electrochemical sensor was developed for the detection of hydrogen peroxide (H2O2), utilizing the synergistic effects of graphene (Gr) and MOF-on-MOF nanozymes (FeCu-NZs). Initially, Fe-MOF with peroxide-like activity is synthesized using a solvothermal method. Subsequently, the organic ligand on its surface binds Cu2+, enhancing the enzyme-like activity further. The resulting FeCu-NZs exhibit a distinctive electrochemical signal in response to H2O2. Moreover, integrating FeCu-NZs with Gr significantly amplifies the electrochemical signal and effectively reduces the sensor's detection limit. The developed sensor exhibited linear ranges of 0.1-3800 µM, with a limit of detection (LOD) of 0.06 µM. Additionally, FeCu-NZs catalyze H2O2 to generate abundant •OH radicals, and colorimetric detection of H2O2 is facilitated using the color rendering principle of 3,3',5,5'-tetramethylbenzidine (TMB). Notably, this detection method was applied to determine  H2O2 concentrations in real samples, achieving a recovery exceeding 95.7%. In summary, this research provides a practical platform for the construction of traditional nanozymes and the integration of electrochemical systems, which have broad applications in food analysis, environmental monitoring, and medical diagnosis.

Four polyoxomolybdated-based 3D compounds as supercapacitors and amperometric sensors.

Four polyoxomolybdated compounds based on Tetp (Tetp = 4-[4-(2-Thiophen-2-yl-ethyl)-4H-[1, 2, 4]triazole-3-yl]-pyridine), namely [Zn(Tetp)2(H2O)2][(ß-Mo8O26)0.5] (Zn-Mo8), [Co(Tetp)2(H2O)2][(ß-Mo8O26)0.5] (Co-Mo8), [Cu4(Tetp)6(H2O)2]{H3[K(H2O)3](θ-Mo8O26)(Mo12O40)}·8H2O (Cu-Mo20) and [Cu3(Tetp)3][PMo12O40]·H2O (Cu-PMo12) are synthesized by hydrothermal methods and are used as electrode materials for supercapacitors(SCs) and electrochemical sensors. Inserting polyoxometalates (POMs) with redox active sites into transition metal compounds (TMCs) can improve the internal ion/electron transfer rate, thus effectively enhancing the electrochemical performance. Compared with the parent POMs, four compounds exhibit excellent electrochemical properties. In particular, Cu-PMo12 shows an excellent specific capacitance (812.3 F g-1 at 1 A g-1) and stability (94.42%), as well as a wide detection range (0.05 to 1250 µM) and a low detection limit (0.057 µM) for NO2- sensing.

Copper-doped titanium dioxide nanoparticles decorated on 2D-hexagonal boron nitride nanosheets for susceptible electrochemical detection of an anti-cancer drug in environmental and biological samples.

Chlorambucil (CML) cures chronic lymphatic leukemia (white blood cell cancer). A high dose of CML can cause several side effects like bone marrow suppression, anemia, peripheral neuropathy, and infertility in the human body. In this research, we have synthesized a nanocomposite based on copper-doped titanium dioxide (CuTiO2) adorned with 2D hexagonal boron nitride (CuTiO2@BN) for the efficient electrochemical detection of CML. A series of characterization techniques FT-IR, XRD, Raman spectroscopy, SEM, TEM, EDAX XPS, and electrochemical characterization were used to analyze the CuTiO2@BN nanocomposite structural and morphological compositions. The sensing performance of the CuTiO2@BN modified GCE for CML detection has been assessed using voltammetry methods. The chronoamperometry technique analyzed the kinetics of the electrochemical oxidation of CML at CuTiO2@BN/GCE. The CuTiO2@BN-based glassy carbon electrode (GCE) has a synergetic electro-catalytic effect on CML oxidation due to its many active sites, enhanced surface area, fast charge transfer, and numerous defects. For the detection of CML, the suggested electrochemical sensor exhibits excellent selectivity, low limit of detection (LOD) as found 5.0 nM, wide linear ranges (0.02-8000 µM), and quick reaction times.

A dual-signal output electrochemical aptasensor for glypican-3 ultrasensitive detection based on reduced graphene oxide-cuprous oxide nanozyme catalytic amplification strategy.

Glypican-3 (GPC3) is an essential reference target for hepatocellular carcinoma detection, follow-up and prediction. Herein, a dual-signal electrochemical aptasensor based on reduced graphene oxide-cuprous oxide (RGO-Cu2O) nanozyme was developed for GPC3 detection. The RGO-Cu2O nanoenzyme displayed excellent electron transport effect, large specific surface area and outstanding peroxidase-like ability. The differential pulse voltammetry (DPV) signal of Cu2O oxidation fraction and the chronoamperometry (i-t) signal of H2O2 decomposition catalyzed by RGO-Cu2O nanozyme were used as dual-signal detection. Under optimal conditions, the log-linear response ranges were 0.1 to 500.0 ng/mL with the limit of detection 0.064 ng/mL for DPV technique, and 0.1-50.0 ng/mL for i-t technique (detection limit of 0.0177 ng/mL). The electrochemical aptasensor has remarkably analytical performance with wide response range, low detection limit, excellent repeatability and specificity, good recovery in human serum samples. The two output signals of one sample achieve self-calibration of the results, effectively avoiding the occurrence of possible leakage and misdiagnosis of a single detection signal, suggesting that it will be a promising method in the early biomarker detection.

Harnessing Graphene-Modified Electrode Sensitivity for Enhanced Ciprofloxacin Detection.

Increased evidence has documented a direct association between Ciprofloxacin (CFX) intake and significant disruption to the normal functions of connective tissues, leading to severe health conditions (such as tendonitis, tendon rupture and retinal detachment). Additionally, CFX is recognized as a potential emerging pollutant, as it seems to impact both animal and human food chains, resulting in severe health implications. Consequently, there is a compelling need for the precise, swift and selective detection of this fluoroquinolone-class antibiotic. Herein, we present a novel graphene-based electrochemical sensor designed for Ciprofloxacin (CFX) detection and discuss its practical utility. The graphene material was synthesized using a relatively straightforward and cost-effective approach involving the electrochemical exfoliation of graphite, through a pulsing current, in 0.05 M sodium sulphate (Na2SO4), 0.05 M boric acid (H3BO3) and 0.05 M sodium chloride (NaCl) solution. The resulting material underwent systematic characterization using scanning electron microscopy/energy dispersive X-ray analysis, X-ray powder diffraction and Raman spectroscopy. Subsequently, it was employed in the fabrication of modified glassy carbon surfaces (EGr/GC). Linear Sweep Voltammetry studies revealed that CFX experiences an irreversible oxidation process on the sensor surface at approximately 1.05 V. Under optimal conditions, the limit of quantification was found to be 0.33 × 10-8 M, with a corresponding limit of detection of 0.1 × 10-8 M. Additionally, the developed sensor's practical suitability was assessed using commercially available pharmaceutical products.

Chronoamperometric interrogation of an electrochemical aptamer-based sensor with tetrahedral DNA nanostructure pendulums for continuous biomarker measurements.

Tetrahedral DNA nanostructure (TDN) is highly promising in developing electrochemical aptamer-based (E-AB) sensors for biomolecular detection, owing to its inherit programmability, spatial orientation and structural robustness. However, current interrogation strategies applied for TDN-based E-AB sensors, including enzyme-based amperometry, voltammetry, and electrochemical impedance spectroscopy, either require complicated probe design or suffer from limited applicability or selectivity. In this study, a TDN pendulum-empowered E-AB sensor interrogated by chronoamperometry for reagent-free and continuous monitoring of a blood clotting enzyme, thrombin, was developed. TDN pendulums with extended aptamer sequences at three vertices were immobilized on a gold electrode via a thiolated double-stranded DNA (dsDNA) at the fourth vertex, and their motion is modulated by the bonding of target thrombin to aptamers. We observed a significantly amplified signalling output on our sensor based on the TDN pendulum compared to E-AB sensors modified with linear pendulums. Moreover, our sensor achieved highly selective and rapidly responsive measurement of thrombin in both PBS and artificial urine, with a wide dynamic range from 1 pM to 10 nM. This study shows chronoamperometry-enabled continuous biomarker monitoring on a sub-second timescale with a drift-free baseline, demonstrating a novel approach to accurately detect molecular dynamics in real time.

Corrosion Behavior of As-Cast and Heat-Treated Al-Co Alloys in 3.5 wt% NaCl.

The present work evaluates the effect of Co content on the microstructure and corrosion performance of Al-Co alloys of various compositions (2-32 wt% Co), fabricated by flux-assisted stir casting. A preliminary investigation on the effect of heat treatment (600 °C, up to 72 h) on the microstructure and corrosion behavior of Al-20 wt% Co and Al-32 wt% Co was also conducted. The Al- (2-10) wt% Co alloys were composed of acicular Al9Co2 particles uniformly dispersed in an Al matrix. The Al-20 wt% Co and Al-32 wt% Co alloys additionally contained Al13Co4 blades enveloped in Al9Co2 wedges. Heat treatment of Al-20 wt% Co and Al-32 wt% Co led to a significant reduction in the volume fraction of Al13Co4 and a decrease in hardness. Al-Co alloys with high Co content (10-32 wt% Co) exhibited greater resistance to localized corrosion in 3.5 wt% NaCl, but lower resistance to general corrosion compared to the (0-5 wt% Co) alloys. Heat treatment led to a slight increase in the corrosion resistance of the Al-Co alloys. The microstructure of the produced alloys was analyzed and correlated with the corrosion performance. Finally, corrosion mechanisms were formulated.

Flow-Through Amperometric Biosensor System Based on Functionalized Aryl Derivative of Phenothiazine and PAMAM-Calix-Dendrimers for the Determination of Uric Acid.

A flow-through biosensor system for the determination of uric acid was developed on the platform of flow-through electrochemical cell manufactured by 3D printing from poly(lactic acid) and equipped with a modified screen-printed graphite electrode (SPE). Uricase was immobilized to the inner surface of a replaceable reactor chamber. Its working volume was reduced to 10 µL against a previously reported similar cell. SPE was modified independently of the enzyme reactor with carbon black, pillar[5]arene, poly(amidoamine) dendrimers based on the p-tert-butylthiacalix[4]arene (PAMAM-calix-dendrimers) platform and electropolymerized 3,7-bis(4-aminophenylamino) phenothiazin-5-ium chloride. Introduction of the PAMAM-calix-dendrimers into the electrode coating led to a fivefold increase in the redox currents of the electroactive polymer. It was found that higher generations of the PAMAM-calix-dendrimers led to a greater increase in the currents measured. Coatings consisted of products of the electropolymerization of the phenothiazine with implemented pillar[5]arene and PAMAM-calix-dendrimers showing high efficiency in the electrochemical reduction of hydrogen peroxide that was formed in the enzymatic oxidation of uric acid. The presence of PAMAM-calix-dendrimer G2 in the coating increased the redox signal related to the uric acid assay by more than 1.5 times. The biosensor system was successfully applied for the enzymatic determination of uric acid in chronoamperometric mode. The following optimal parameters for the chronoamperometric determination of uric acid in flow-through conditions were established: pH 8.0, flow rate 0.2 mL·min-1, 5 U of uricase per reactor. Under these conditions, the biosensor system made it possible to determine from 10 nM to 20 µM of uric acid with the limit of detection (LOD) of 4 nM. Glucose (up to 1 mM), dopamine (up to 0.5 mM), and ascorbic acid (up to 50 µM) did not affect the signal of the biosensor toward uric acid. The biosensor was tested on spiked artificial urine samples, and showed 101% recovery for tenfold diluted samples. The ease of assembly of the flow cell and the low cost of the replacement parts make for a promising future application of the biosensor system in routine clinical analyses.

A modified Prussian blue biosensor with improved stability based on the use of self-assembled monolayers and polydopamine for quantitative L-glutamate detection.

A miniature L-glutamate (L-Glu) biosensor is described based on Prussian blue (PB) modification with improved stability by using self-assembled monolayers (SAMs) technology and polydopamine (PDA). A gold microelectrode (AuME) was immersed in NH2(CH2)6SH-ethanol solution, forming well-defined SAMs via thiol-gold bonding chemistry which increased the number of deposited Prussian blue nanoparticles (PBNPs) and confined them tightly on the AuME surface. Then, dopamine solution was dropped onto the PBNPs surface and self-polymerized into PDA to protect the PB structure from destruction. The PDA/PB/SAMs/AuME showed improved stability through CV measurements in comparison with PB/AuME, PB/SAMs/AuME, and PDA/PB/AuME. The constructed biosensor achieved a high sensitivity of 70.683 nA µM-1 cm-2 in the concentration range 1-476 µM L-Glu with a low LOD of 0.329 µM and performed well in terms of selectivity, reproducibility, and stability. In addition, the developed biosensor was successfully applied to the determination of L-Glu in tomato juice, and the results were in good agreement with that of high-performance liquid chromatography (HPLC). Due to its excellent sensitivity, improved stability, and miniature volume, the developed biosensor not only has a promising potential for application in food sample analysis but also provides a good candidate for monitoring L-Glu level in food production.

A direct electrochemical sensor based on covalent organic frameworks/platinum nanoparticles for the detection of ofloxacin in water.

A direct electrochemical sensor based on covalent organic frameworks (COFs)/platinum nanoparticles (PtNPs) composite was fabricated for the detection of ofloxacin (OFX) in water. Firstly, the COF material was synthesized via the condensation reaction of 1,3,5-tris(4-aminophenyl)benzene (TAPB) with terephthalaldehyde (TPA) and integrated with PtNPs by in situ reduction. Then, TAPB-TPA-COFs/PtNPs composite was loaded onto the surface of the glassy carbon electrode (GCE) by drip coating to construct the working electrode (TAPB-TPA-COFs/PtNPs/GCE). The electrochemical performance of TAPB-TPA-COFs/PtNPs/GCE showed a significant improvement compared with that of TAPB-TPA-COFs/GCE, leading to a 3.2-fold increase in the electrochemical signal for 0.01 mM OFX. Under optimal conditions, the TAPB-TPA-COFs/PtNPs/GCE exhibited a wide linear range of 9.901 × 10-3-1.406 µM and 2.024-15.19 µM with a detection limit of 2.184 × 10-3 µM. The TAPB-TPA-COFs/PtNPs/GCE-based electrochemical sensor with excellent performance provides great potential for the rapid and trace detection of residual OFX.

Polydopamine-immobilized yeast cells for portable electrochemical biosensors applied in environmental copper sensing.

The coupling of biological organisms with electrodes enables the development of sustainable, low cost, and potentially self-sustained biosensors. A critical aspect is to obtain portable bioelectrodes where the biological material is immobilized on the electrode surface to be utilized on demand. Herein, we developed an approach for the rapid entrapment and immobilization of metabolically active yeast cells in a biocompatible polydopamine layer, which does not require a separate and time-consuming synthesis. The reported approach allows obtaining the "electrical wire" of intact and active yeast cells with resulting current generation from glucose oxidation. Additionally, the electrochemical performance of the biohybrid yeast-based system has been characterized in the presence of CuSO4, a widely used pesticide, in the environmentally relevant concentration range of 20-100 µM. The system enabled the rapid preliminary monitoring of the contaminant based on variations in current generation, with a limit of detection of 12.5 µM CuSO4. The present approach for the facile preparation of portable yeast-based electrochemical biosensors paves the way for the future development of sustainable systems for environmental monitoring.

Electrochemical and biosensor techniques to monitor neurotransmitter changes with depression.

Depression is a common mental illness. However, its current treatments, like selective serotonin reuptake inhibitors (SSRIs) and micro-dosing ketamine, are extremely variable between patients and not well understood. Three neurotransmitters: serotonin, histamine, and glutamate, have been proposed to be key mediators of depression. This review focuses on analytical methods to quantify these neurotransmitters to better understand neurological mechanisms of depression and how they are altered during treatment. To quantitatively measure serotonin and histamine, electrochemical techniques such as chronoamperometry and fast-scan cyclic voltammetry (FSCV) have been improved to study how specific molecular targets, like transporters and receptors, change with antidepressants and inflammation. Specifically, these studies show that different SSRIs have unique effects on serotonin reuptake and release. Histamine is normally elevated during stress, and a new inflammation hypothesis of depression links histamine and cytokine release. Electrochemical measurements revealed that stress increases histamine, decreases serotonin, and leads to changes in cytokines, like interleukin-6. Biosensors can also measure non-electroactive neurotransmitters, including glutamate and cytokines. In particular, new genetic sensors have shown how glutamate changes with chronic stress, as well as with ketamine treatment. These techniques have been used to characterize how ketamine changes glutamate and serotonin, and to understand how it is different from SSRIs. This review briefly outlines how these electrochemical techniques work, but primarily highlights how they have been used to understand the mechanisms of depression. Future studies should explore multiplexing techniques and personalized medicine using biomarkers in order to investigate multi-analyte changes to antidepressants.

Rod-Shaped Spinel Co3O4 and Carbon Nitride Heterostructure-Modified Fluorine-Doped Tin Oxide Electrode as an Electrochemical Transducer for Efficient Sensing of Hydrazine.

Engineering low-cost and efficient materials for sensing hydrazine (HA) is critical given the adverse effects of high concentrations on humans. We report an efficient electrode made up of rod-shaped Co3O4/g-C3N4 (Co3O4/graphitic carbon nitride (GCN))-coated fluorine-doped tin oxide as a desirable electrode for the detection of HA. GCN is synthesized by the thermal decomposition of melamine, Co3O4, and the heterostructure is grown by a hydrothermal process. The as-prepared materials were characterized by using spectroscopic and microscopic techniques. The voltammetric studies showed that HA can be oxidized at a lower onset potential of 0.24 V vs reference Ag/AgCl, and the composite yielded a significantly enhanced oxidation peak current than the pure components because of the high electrocatalytic activity and the synergy between Co3O4 and GCN. By employing chronoamperometry, the proposed sensor can detect HA in a wide range with a high sensitivity of 819.52 µA mM-1 cm-2 and a detection limit of 3.14 µM. The high conductivity of Co3O4, enhanced electroactive surface area, the rich redox couples of Co2+/Co3+, and the additional catalytic sites from GCN are responsible for the high performance of the heterostructure.

FeNC nanozyme-based electrochemical immunoassay for sensitive detection of human epidermal growth factor receptor 2.

The proof-of-concept of sensitive electrochemical immunoassay for the quantitative monitoring of human epidermal growth factor receptor 2 (HER2) is reported. The assay is carried out on iron nitrogen-doped carbon (FeNC) nanozyme-modified screen-printed carbon electrode using chronoamperometry. Introduction of target HER2 can induce the sandwiched immunoreaction between anti-HER2 monoclonal antibody-coated microplate and biotinylated anti-HER2 polyclonal antibody. Thereafter, streptavidin-glucose oxidase (GOx) conjugate is bonded to the detection antibody. Upon addition of glucose, 3,3',5,5'-tetramethylbenzidine (TMB) is oxidized through the produced H2O2 with the assistance of GOx and FeNC nanozyme. The oxidized TMB is determined via chronoamperometry. Experimental results revealed that electrochemical immunosensing system exhibited good amperometric response, and allowed the detection of target HER2 as low as 4.5 pg/mL. High specificity and long-term stability are acquired with FeNC nanozyme-based sensing strategy. Importantly, our system provides a new opportunity for protein diagnostics.