Synthesis of CuO/g-C3N4 composites, and their application to voltammetric sensing of glucose and dopamine

Highly dispersed noble metal nanoparticle composites on biomass-derived carbon-based carriers: synthesis, characterization, and catalytic applications

Precious metal nanoparticles have been widely investigated due to their excellent activity shown in catalysis and sensing. However, how to prepare highly dispersed noble metal nanoparticles to improve the lifetime of catalysts and reduce the cost is still an urgent problem to be solved. In this study, a carbon-based carrier material was prepared by an expansion method and loaded with Pd or Ag nanoparticles on this carbon material to synthesize precious metal nanoparticle composites, which were characterized in detail. The results show that the nanoparticles prepared using this method exhibit superior dispersion. Under the synergistic effect of noble metal nanoparticles and porous carbon carriers, the composites exhibited excellent catalytic degradation of p-nitrophenol and showed excellent sensing performance in the modified hydrogen peroxide sensor electrode. This approach is highly informative for the preparation of nanocomposites in medical and environmental fields.

Common Transition Metal Oxide Nanomaterials in Electrochemical Sensors for the Diagnosis of Monoamine Neurotransmitter‐Related Disorders

Monoamine neurotransmitters are essential for learning, mental alertness, emotions, and blood flow, among other functions. Fatal neurological disorders that signal the imbalance of these biomolecules in the human system include Parkinson's disease, myocardial infarction, Alzheimer's disease, hypoglycemia, Schizophrenia, and a host of other ailments. The diagnosis of these monoamine neurotransmitter‐related conditions revolves around the development of analytical tools with high sensitivity for the four major monoamine neurotransmitters namely dopamine, epinephrine, norepinephrine, and serotonin. The application of electrochemical sensors made from notable metal oxide nanoparticles or composites containing the metal oxide nanoparticles for the detection of these monoamine neurotransmitters was discussed herein. More importantly, the feasibility of the application of the ZnO, CuO, and TiO2 nanoparticle‐based electrochemical sensors for a comprehensive diagnosis of monoamine neurotransmitter‐related conditions was critically investigated in this review.

Nitrogen Defect-Rich Graphitic Carbon Nitride for Highly Sensitive Voltammetric Determination of Tryptophan

Here, a highly sensitive electrochemical sensor for detection of tryptophan (Trp) using a nitrogen defect graphitic carbon nitride-modified glassy carbon electrode (ND-CN/GCE) was introduced. ND-CN/GCE showed a higher oxidation current for Trp than the graphitic carbon nitride-modified glassy carbon electrode (g-CN/GCE) and bare glassy carbon electrode (BGCE). The synthesized nitrogen defect-rich graphitic carbon nitride (ND-CN) was characterized using X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical impedance spectroscopy and cyclic voltammetry were used to further analyze the electrochemical properties of BGCE, g-CN/GCE, and ND-CN/GCE. The oxidation of Trp at ND-CN/GCE is a diffusion-controlled process at pH 3.0. It was calculated that the transfer coefficient, rate constant, and diffusion coefficient of Trp were 0.53, 2.24 × 103 M-1 s-1, and 8.3 × 10-3 cm2 s-1, respectively, at ND-CN/GCE. Trp was detected using square wave voltammetry, which had a linear range from 0.01 to 40 μM at pH 3.0 and a limit of detection of about 0.0034 μM (3σ/m). Analyzing the presence of Trp in a milk and multivitamin tablet sample with a percentage recovery in the range of 97.0-108% satisfactorily demonstrated the practical usability of the electrochemical sensor. The ND-CN/GCE additionally displays good repeatability and reproducibility and satisfactory selectivity.

Enhancing electrochemical properties of a two-dimensional zeolitic imidazole framework by incorporating a conductive polymer for dopamine detection

The zeolitic imidazole framework with a leaf-shaped morphology (ZIF-L) has a wide range of promising applications in gas storage, battery materials, catalytic reactions, and optoelectronic devices due to its planar leaf-like structure and large surface area. However, the low conductivity, weak catalytic activity, and poor stability in the water dielectric medium of ZIF-L limit its further practical application. To solve these problems, we added the conductive polymer heterocyclic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to ZIF-L for the sensitive detection of dopamine (DA). The synthesized composite ZIF-L/PEDOT:PSS (ZIF-L/PEDOT) not only retained the surface morphology of ZIF-L but also exhibited excellent electrochemical properties. The higher electrical conductivity of ZIF-L/PEDOT than that of ZIF-L was due to the enhanced electron transfer at the interface between ZIF-L and PEDOT:PSS. As a result, we developed an electrochemical biosensor based on the ZIF-L/PEDOT composite, which has a limit of detection of 7 nM for DA and a wide linear range from 25 nM to 500 μM. Furthermore, the current drop was negligible after 28 days, proving that the biosensor has excellent stability. Based on the above-mentioned outstanding performance, the ZIF-L/PEDOT-based biosensor was successfully used to detect DA in human serum samples. These results demonstrated that ZIF-L/PEDOT is expected to play an essential role in disease detection.

Codoping g-C3N4 with boron and graphene quantum dots: Enhancement of charge transfer for ultrasensitive and selective photoelectrochemical detection of dopamine

The development of superior photoelectrochemical (PEC) sensors for biosensing has become a major objective of PEC research. However, conventional PEC-active materials are typically constrained by a weak photocurrent response owing to their limited surface-active sites and high electron-hole recombination rate. Here, a boron and graphene quantum dots codoped g-C₃N₄ (named GBCN) as PEC sensor for highly sensitive dopamine (DA) detection was fabricated. GBCN exhibited the greatest photocurrent response and PEC activity compared to free g-C₃N₄ and g-C₃N₄ doped with boron. The proposed PEC sensor for DA determination exhibited a broad linear range (0.001-800 μM) and a low detection limit (0.96 nM). In particular, a sensitivity up to 10.3771 μA/μM/cm² was seen in the case of GBCN. The high PEC activity can be attributed to the following factors: (1) the boron and graphene quantum dots co-doping significantly increased the specific surface area of g-C₃N₄, providing more adsorption sites for DA; (2) the dopants extended the absorption intensity of g-C₃N₄, red-shifting the absorption from 470 to 540 nm; and (3) the synergism of boron and graphene quantum dots efficiently boosted the photogenerated electrons migration from the conduction band of g-C₃N₄ to graphene quantum dots, facilitating charge separation. In addition, GBCN also exhibited good anti-interference ability and stability. This research may shed light on the creation of a highly sensitive and selective PEC platform for detecting biomolecules.

Simultaneous Determination of Dopamine and Uric Acid in Real Samples Using a Voltammetric Nanosensor Based on Co-MOF, Graphene Oxide, and 1-Methyl-3-butylimidazolium Bromide

A chemically modified carbon paste electrode, based on a CoMOF-graphene oxide (GO) and an ionic liquid of 1-methyl-3-butylimidazolium bromide (CoMOF-GO/1-M,3-BB/CPE), was fabricated for the simultaneous determination of dopamine (DA) and uric acid (UA). The prepared CoMOF/GO nanocomposite was characterized by field emission-scanning electron microscopy (FE-SEM), the X-ray diffraction (XRD) method, a N₂ adsorption-desorption isotherm, and an energy dispersive spectrometer (EDS). The electrochemical sensor clearly illustrated catalytic activity towards the redox reaction of dopamine (DA), which can be authenticated by comparing the increased oxidation peak current with the bare carbon paste electrode. The CoMOF-GO/1-M,3-BB/CPE exhibits a wide linear response for DA in the concentration range of 0.1 to 300.0 µM, with a detection limit of 0.04 µM. The oxidation peaks' potential for DA and uric acid (UA) were separated well in the mixture containing the two compounds. This study demonstrated a simple and effective method for detecting DA and UA in real samples.

Synthesis and characterization of CuO@S-doped g-C3N4 based nanocomposites for binder-free sensor applications

This study presents the simultaneous exfoliation and modification of heterostructured copper oxide incorporated sulfur doped graphitic carbon nitride (CuO@S-doped g-C₃N₄) nanocomposites (NCs) synthesized via chemical precipitation and pyrolysis techniques. The results revealed that the approach is feasible and highly efficient in producing 2-dimensional CuO@S-doped g-C₃N₄ NCs. The findings also showed a promising technique for enhancing the optical and electrical properties of bulk g-C₃N₄ by combining CuO nanoparticles (NPs) with S-doped g-C₃N₄. The crystallite and the average size of the NCs were validated using X-ray diffraction (XRD) studies. Incorporation of the cubical structured CuO on flower shaped S-doped-g-C₃N₄ was visualized and characterized through XRD, HR-SEM/EDS/SED, FT-IR, BET, UV-Vis/DRS, PL, XPS and impedance spectroscopy. The agglomerated NCs had various pore sizes, shapes and nanosized crystals, while being photo-active in the UV-vis range. The synergistic effect of CuO and S-doped g-C₃N₄ as co-modifiers greatly facilitates the electron transfer process between the electrolyte and the bare glassy carbon electrode. Specific surface areas of the NCs clearly revealed modification of bulk S-doped g-C₃N₄ when CuO NPs are incorporated with S-doped g-C₃N₄, providing a suitable environment for the binder-free decorated electrode with sensing behavior for hazardous pollutants. This was tested for the preparation of a 4-nitrophenol sensor.

Metal vs. Metal-Free Catalysts for Oxidation of 5-Hydroxymethylfurfural and Levoglucosenone to Biosourced Chemicals

Lignocellulosic feedstocks, such as forestry biomass and agricultural crop residues, can be utilized to generate biofuels and biochemicals. Converting these organic waste materials into biochemicals is widely regarded as a remedial approach to develop a sustainable, clean, and green energy source. Nevertheless, are these methods sustainable and clean? Prior studies have shown that most such conversions use metals - including heavy metals or noble metals - as catalysts. In addition to the fact that many metals (e. g., aluminum, cobalt, titanium, platinum) have been listed as critical minerals, these methods suffer from high cost, deactivation, and leakage problems and the release of toxic wastes. This Review summarizes catalytic methods using metal and metal-free catalysts for the oxidation of the platform molecules 5-hydroxymethylfurfural and levoglucosenone and demonstrates the potential and effectiveness of metal-free catalysts.

Recent Trends and Future Perspectives of Emergent Analytical Techniques for Mercury Sensing in Aquatic Environments

Environmental emissions of mercury from industrial waste and natural sources, even in trace amounts, are toxic to organisms and ecosystems. However, industrial-scale mercury detection is limited by the high cost, low sensitivity/specificity, and poor selectivity of the available analytical tools. This review summarizes the key sensors for mercury detection in aqueous environments: colorimetric-, electrochemical-, fluorescence-, and surface-enhanced Raman spectroscopy-based sensors reported between 2014-2021. It then compares the performances of these sensors in the determination of inorganic mercury (Hg²⁺ ) and methyl mercury (CH₃ Hg⁺ ) species in aqueous samples. Mercury sensors for aquatic applications still face serious challenges in terms of difficult deployment in remote areas and low robustness, reliability, and selectivity in harsh environments. We provide future perspectives on the selective detection of organomercury species, which are especially toxic and reactive in aquatic environments. This review is intended as a valuable resource for scientists in the field of mercury sensing.

β-Cyclodextrin functionalized 3D reduced graphene oxide composite-based electrochemical sensor for the sensitive detection of dopamine

A three-dimensional reduced graphene oxide nanomaterial with β-cyclodextrin modified glassy carbon electrode (3D-rGO/β-CD/GCE) was constructed and used to detect the electrochemical behavior of dopamine (DA). The nanocomposite materials were characterized by scanning electron microscopy (SEM), infrared spectrometry (FT-IR), Raman spectrogram and thermogravimetric analysis (TGA), which showed that β-CD was well modified on 3D graphene with a porous structure. The electrochemical properties of different modified electrodes were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), proving the highest electron transfer rate of the 3D-rGO/β-CD modified electrode. The experimental conditions such as scan rate, pH, enrichment time and layer thickness were optimized. Under the best experimental conditions, DA was detected by differential pulse voltammetry (DPV) by 3D-rGO/β-CD/GCE with excellent electrocatalytic ability and satisfactory recognition ability, resulting in a wide linear range of 0.5-100 μM and a low detection limit (LOD) of 0.013 μM. The modified electrode based on 3D-rGO/β-CD nanocomposites is promising in the field of electrochemical sensors due to its high sensitivity and other excellent properties.

Copper oxide integrated perylene diimide self-assembled graphitic pencil for robust non-enzymatic dopamine detection

Exploring a robust, extremely sensitive, cost-effective and reliable assay platform for the precise analysis of dopamine (DA) has become a big challenge predominantly at the clinical level. To participate in this quest, herein, we fabricated a perylene diimide (PDI) self-assembled graphitic surface of the graphitic pencil electrode (GPE) anchored copper oxide (CuO). The self-assembled N-rich PDI led to the fast movement of ions by decreasing the bandgap and improved the electron transport kinetics with more exposed catalytic active sites, thus resulting in the robust electrochemical sensing of DA. The designed sensor exhibited good sensitivity (4 μM-1 cm-2), high structural stability, repeatability and excellent reproducibility with an RSD value of 2.9%. Moreover, the developed system showed a wide linear range (5 μM to 500 μM) and reliable selectivity even in the presence of co-existing interferants, such as ascorbic acid and uric acid. The fabricated nanohybrid was eventually employed to analyze DA in spiked physiological fluids and provided satisfactory recoveries. The designed PDI-CuO based interface also showed a very low detection limit of 6 nM (S/N = 3), consequently confirming its suitability for clinical and biological applications.

Metal-Oxide Based Nanomaterials: Synthesis, Characterization and Their Applications in Electrical and Electrochemical Sensors

Pure, mixed and doped metal oxides (MOX) have attracted great interest for the development of electrical and electrochemical sensors since they are cheaper, faster, easier to operate and capable of online analysis and real-time identification. This review focuses on highly sensitive chemoresistive type sensors based on doped-SnO₂, RhO, ZnO-Ca, Sm_x-CoFe_2−xO₄ semiconductors used to detect toxic gases (H₂, CO, NO₂) and volatile organic compounds (VOCs) (e.g., acetone, ethanol) in monitoring of gaseous markers in the breath of patients with specific pathologies and for environmental pollution control. Interesting results about the monitoring of biochemical substances as dopamine, epinephrine, serotonin and glucose have been also reported using electrochemical sensors based on hybrid MOX nanocomposite modified glassy carbon and screen-printed carbon electrodes. The fundamental sensing mechanisms and commercial limitations of the MOX-based electrical and electrochemical sensors are discussed providing research directions to bridge the existing gap between new sensing concepts and real-world analytical applications.

An Improved Synthesis of Water-Soluble Dual Fluorescence Emission Carbon Dots from Holly Leaves for Accurate Detection of Mercury Ions in Living Cells

Background

Carbon dots (CDs) emitting near-infrared fluorescence were recently synthesized from green leaves. However, the Hg²⁺ detection of CDs was limited because of the insufficient water solubility, low fluorescence and poor stability.

Methods

Dual fluorescence emission water-soluble CD (Dual-CD) was prepared through a solvothermal method from holly leaves and low toxic PEI_1.8k. PEG was further grafted onto the surface to improve the water solubility and stability.

Results

The Dual-CD solution can emit 487 nm and 676 nm fluorescence under single excitation and exhibit high quantum yield of 16.8%. The fluorescence at 678 nm decreased remarkably while the emission at 470 nm was slightly affected by the addition of Hg²⁺. The ratiometric Hg²⁺ detection had a wide linear range of 0–100 μM and low detection limit of 14.0 nM. In A549 cells, there was a good linear relation between F₄₈₇/F₆₇₆ and the concentration of Hg²⁺ in the range of 0–60 μM; the detection limit was 477 nM. Furthermore, Dual-CD showed visual fluorescence change under Hg²⁺.

Conclusion

Dual-CD has ratiometric responsiveness to Hg²⁺ and can be applied for quantitative Hg²⁺ detection in living cells.

Polydopamine/graphene/MnO2 composite-based electrochemical sensor for in situ determination of free tryptophan in plants

The in vivo detection of small active molecules in plant tissues is essential for the development of precision agriculture. Tryptophan (Trp) is an important precursor material for auxin biosynthesis in plants, and the detection of Trp levels in plants is critical for regulating the plant growth process. In this study, an electrochemical plant sensor was fabricated by electrochemically depositing a polydopamine (PDA)/reduced graphene oxide (RGO)-MnO₂ nanocomposite onto a glassy carbon electrode (GCE). PDA/RGO-MnO₂/GCE exhibited high electrocatalytic activity for the oxidation of Trp owing to the combined selectivity of PDA and catalytic activity of RGO-MnO₂. To address the pH variability of plants, a reliable Trp detection program was proposed for selecting an appropriate quantitative detection model for the pH of the plant or plant tissue of interest. Therefore, a series of linear regression curves was constructed in the pH range of 4.0-7.0 using the PDA/RGO-MnO₂/GCE-based sensor. In this pH range, the linear detection range of Trp was 1-300 μM, the sensitivity was 0.39-1.66 μA μM^-1, and the detection limit was 0.22-0.39 μM. Moreover, the practical applicability of the PDA/RGO-MnO₂/GCE-based sensor was successfully demonstrated by determining Trp in tomato fruit and juice. This sensor stably and reliably detected Trp levels in tomatoes in vitro and in vivo, demonstrating the feasibility of this research strategy for the development of electrochemical sensors for measurements in various plant tissues.

Graphitic Carbon Nitride: A Highly Electroactive Nanomaterial for Environmental and Clinical Sensing

Graphitic carbon nitride (g-C3N4) is a two-dimensional conjugated polymer that has attracted the interest of researchers and industrial communities owing to its outstanding analytical merits such as low-cost synthesis, high stability, unique electronic properties, catalytic ability, high quantum yield, nontoxicity, metal-free, low bandgap energy, and electron-rich properties. Notably, graphitic carbon nitride (g-C3N4) is the most stable allotrope of carbon nitrides. It has been explored in various analytical fields due to its excellent biocompatibility properties, including ease of surface functionalization and hydrogen-bonding. Graphitic carbon nitride (g-C3N4) acts as a nanomediator and serves as an immobilization layer to detect various biomolecules. Numerous reports have been presented in the literature on applying graphitic carbon nitride (g-C3N4) for the construction of electrochemical sensors and biosensors. Different electrochemical techniques such as cyclic voltammetry, electrochemiluminescence, electrochemical impedance spectroscopy, square wave anodic stripping voltammetry, and amperometry techniques have been extensively used for the detection of biologic molecules and heavy metals, with high sensitivity and good selectivity. For this reason, the leading drive of this review is to stress the importance of employing graphitic carbon nitride (g-C3N4) for the fabrication of electrochemical sensors and biosensors.

Facile synthesis of copper ferrite nanoparticles with chitosan composite for high-performance electrochemical sensor

Herein, the synthesis of copper ferrite nanoparticles (CuFe₂O₄ NPs)/chitosan have been prepared by sonochemical route under ultrasonic irradiation bath at 40 kHz and 50 W. A high sensitive and stable modified electrochemical sensor was developed using a composition of copper ferrite nanoparticles coordinated with biopolymer through a facile ultrasound approach. Besides, power and frequency parameters are highly important for sonochemical synthesis and specifically structure, and size of the nanomaterials development during the ultrasonic irradiation time. In this work, ultrasonic bath was used to synthesis of CuFe₂O₄ nanomaterial at 40 kHz with 1 h. CuFe₂O₄/chitosan was characterized by FESEM, EDX, XRD and electrochemical methods. Furthermore, 8-hydroxyguanine is one of biomarker by oxidative stress. The concentrations of 8-hydroxyguanine within a cell are a measurement of oxidative stress in human body. Consequently, the measurement of 8-hydroxyguanine in blood serum samples with high specificity is of greatest importance. The CuFe₂O₄/chitosan modified electrode is displayed a low detection limit of 8.6 nM and long linear range (0.025-697.175 µM).

A feasible sonochemical approach to synthesize CuO@CeO2 nanomaterial and their enhanced non-enzymatic sensor performance towards neurotransmitter

A nanostructured and high conductive cupric oxide (CuO NPs) with hierarchical CeO₂ sheets-like structure was synthesized by a facile sonochemical approach. Furthermore, CuO/CeO₂ nanostructure is synthesized by high-intensity ultrasonic probe (Ti-horn, 50 kHz and 100 W) at ambient air. Moreover, the synthesized CuO/CeO₂ material was characterized by various analytical techniques including FESEM, EDX, XRD and electrochemical methods. Then, the synthesized CuO/CeO₂ composite was applied for the electrocatalytic detection of dopamine using CV and DPV techniques. In addition, the CuO/CeO₂ modified electrode has good electrocatalytic performance with high linear range from 0.025 to 98.5 µM towards the determination of dopamine drug and high sensitivity of the CuO/CeO₂ modified drug sensor was calculated as 16.34 nM and 4.823 μA·µM^-1·cm^-2, respectively. Moreover, a repeatability, reproducibility and stability of the CuO@CeO₂ mixture modified electrode were analyzed towards the determination of dopamine biomolecule. Interestingly, the real time application of CuO@CeO₂ modified electrode was established in different serum and drug samples.

Photoelectrochemical assay for DNA hydroxymethylation determination based on the inhibited photoactivity of black TiO2 nanosphere by ZnO

A photoelectrochemical method was proposed for DNA hydroxymethylation determination using black TiO₂ (B-TiO₂) nanosphere as photoactive material and ZnO as photoactivity inhibitor. After hydroxymethylated DNA (5hmC-DNA) was captured on the probe modified B-TiO₂/ITO electrode surface through hybridization, a glycosyl can be then transferred from uridine diphosphoglucose to 5hmC-DNA and formed a covalent structure with -CH₂OH in the presence of T4 β-glucosyltransferase (β-GT). Afterwards, based on a series of covalent reaction, amino functionalized ZnO nanoparticles are further immobilized to the surface of the electrode. Due to the capacity to expend the irradiation light and the photogenerated electron of electron donor, the modified ZnO nanoparticles can result in a decreased photocurrent. The developed method shows wide linear ranges from 0.05-200 nM for hydroxymethylated DNA and 1-220 unit·mL^-1 for T4-β-glucosyltransferase. The corresponding determination limits were 0.013 nM and 0.24 unit·mL^-1, respectively. The enzyme activity inhibited by 4-phenylimidazole was evaluated. This photoelectrochemical method shows high specificity for 5hmC-DNA (compared to 5fC, 5mC, m6A, control) and β-GT (compared to β-AGT, UGT2B7), and shows excellent stability for testing 5hmC (RSD = 2.75%). Graphical abstractSchematic representation of photoelectrochemical method for DNA hydroxymethylation and β-glucosyltransferase detection based on the glycosylation reaction of -CH₂OH in 5-hydroxymethylcytosine and the inhibition activity of ZnO to the photoactivity of black TiO₂ nanospheres.

Bi-functional Ag-CuxO/g-C3N4 hybrid catalysts for the reduction of 4-nitrophenol and the electrochemical detection of dopamine

The immense need to build highly efficient catalysts has always been at the forefront of environmental remediation research. Herein, we have synthesized dual-phase copper oxide containing Cu2O and CuO originating from the same reaction using hexamethyltetramine (HMT). Simultaneously, we coupled it with g-C3N4 (g-CN), constructing a triple synergetic heterojunction, which is reported significantly less often in the literature. Hydrothermal reactions led to the formation of various catalysts, namely, Ag-Cu2O-CuO-gCN (ACCG), Ag-CuO-gCN (ACG), Ag-Cu2O-CuO (ACC) and Ag-CuO (AC), which were thoroughly characterized via XRD and FESEM to gain structural, crystallographic and morphological insights. We clearly observed the pure phase formation of the catalysts and the development of sheet-like CuO and truncated octahedrons of Cu2O fused together within the g-CN framework. Also, XPS studies revealed the presence of copper in two different oxidation states, namely, Cu2+ and Cu+. BET analysis was performed to analyze the surface area and pore volume of the catalysts, which play very significant roles in catalytic reduction. The catalytic efficiencies of the catalysts were evaluated via the reduction of 100 ppm 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) without using any light irradiation. The most efficient catalyst was ACCG, revealing the reduction of 4-NP in 4 minutes. Both Cu2O and g-CN played significant roles in reduction, following zero-order kinetics, unlike that which is often reported in the literature. We also evaluated the catalytic reduction with different concentrations of 4-NP and tuning the catalyst amount as well. A mechanism was postulated based on the XRD results of the post-catalytic reduction catalyst. The ACCG catalyst was also successfully tested as an effective dopamine sensor. The GC/ACCG electrode exhibited oxidation peak current density of 0.28 mA cm-2, which was much higher than those of the other catalysts. This unique combination of pure phase materials to form a composite as an effective catalyst as well as a sensor is an exclusive effort towards environmental remediation.

A nickel-cobalt bimetallic phosphide nanocage as an efficient electrocatalyst for nonenzymatic sensing of glucose

The authors describe Ni-Co bimetal phosphide (NiCoP) nanocages that exhibit enhanced electrocatalytic performance toward glucose oxidation. The nanocages offer an appealing architecture, large specific area, and good accessibility for the analyte glucose. When placed on a glassy carbon electrode, the sensor exhibits attractive figures of merit for sensing glucose in 0.1 M NaOH solution including (a) a wide linear range (0.005-7 mM), (b) a low determination limit (0.36 μM), (c) high sensitivity (6115 μA•μM^-1•cm^-2), (d) a relatively low working potential (0.50 V vs. Ag/AgCl), and (e) good selectivity, reproducibility, and stability. The sensor is successfully applied to the determination of glucose in human serum samples. Graphical abstractSchematic representation of a glassy carbon electrode modified with Ni-Co bimetal phosphide (NiCoP) nanocage. NiCoP nanocage exhibits excellent electrocatalytic activity toward glucose oxidation. NiCoP nanocage is applied in a sensitive non-enzymatic glucose sensor.

Macro-/meso-porous NiCo2O4 synthesized by template-free solution combustion to enhance the performance of a nonenzymatic amperometric glucose sensor

A sensitive nonenzymatic amperometric glucose sensor is described that relies on a glassy carbon electrode modified with a macro-/meso-porous NiCo₂O₄. NiCo₂O₄ with spinel structure has been prepared via a one-step solution combustion method. The material was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen absorption/desorption. An electrode was coated with the porous material and then displayed excellent electrocatalytic activity towards the direct oxidation of glucose in 0.15 M NaOH solution by cyclic voltammetry. Amperometric I-t curve demonstrated a sensitivity of 2100 μA·mM^-1·cm^-2 at an applied potential of 0.45 V (vs Hg/HgCl). The sensor has a linear response in the 0.001 to 1.0 mΜ glucose concentration range, a fast response time (3.9 s) and a low detection limit (0.38 μΜ). Graphical abstract.

A polymer monolith composed of a perovskite and cucurbit[6]uril hybrid for highly selective enrichment of phosphopeptides prior to mass spectrometric analysis

A hybrid monolith was prepared from perovskite and cucurbit[6]uril [poly(hydroxyethyl methacrylate-pentaerythritol triacrylate) monolith] for the enrichment of phosphopeptides. By coupling with mass spectrometry, three goals were simultaneously realized, viz. (a) selective enrichment of phosphopeptides from non-phosphopeptides, (b) identification of mono- and multi-phosphopeptides, and (c) recognition of tyrosine phosphopeptides. The perovskite introduced into the monolith warrants high selectivity for phosphopeptides even at a high (10,000:1) ratio of non-phosphopeptides to phosphopeptides, and and enables identification of eight mono- and multi-phosphopeptides from standard β-casein tryptic digests. Tyrosine phosphopeptides were specifically detected via the recognition capability of cucurbit[6]uril integrated into the monolith. The method has remarkably specific enrichment capacity for phosphopeptides from samples including human serum, nonfat milk, and human acute myelocytic leukemia cell lysate. Graphical abstractSchematic representation of a monolith integrated with perovskite and cucurbit[6]uril. The monolithic column was coupled with mass spectrometry and applied to the enrichment of phosphopeptides. The method has remarkably specific enrichment capacity for phosphopeptides from complex biological samples.

Golf ball-like MoS2 nanosheet arrays anchored onto carbon nanofibers for electrochemical detection of dopamine

Arrays of molybdenum(IV) disulfide nanosheets resembling the shape of golf balls (MoS₂ NSBs) were deposited on carbon nanofibers (CNFs), which are shown to enable superior electrochemical detection of dopamine without any interference by uric acid. The MoS₂ NSBs have a diameter of ∼ 2 μm and are made up of numerous bent nanosheets. MoS₂ NSBs are connected by the CNFs through the center of the balls. Figures of merit for the resulting electrode include (a) a sensitivity of 6.24 μA·μM^-1·cm^-2, (b) a low working voltage (+0.17 V vs. Ag/AgCl), and (c) a low limit of detection (36 nM at S/N = 3). The electrode is selective over uric acid, reproducible and stable. It was applied to the determination of dopamine in spiked urine samples. The recoveries at levels of 10, 20 and 40 μM of DA are 101.6, 99.8 and 107.8%. Graphical abstract Schematic presentation of the golf ball-like MoS₂ nanosheet balls/carbon nanofibers (MoS₂ NSB/CNFs) by electrospining and hydrothermal process to detect dopamine (DA).

Bimetallic ZrHf-based metal-organic framework embedded with carbon dots: Ultra-sensitive platform for early diagnosis of HER2 and HER2-overexpressed living cancer cells

We report here a new bimetallic ZrHf metal-organic framework (ZrHf-MOF) embedded with abundant carbon dots (CDs) (denoted as CDs@ZrHf-MOF), which exhibits strong fluorescence and rich-amino-functionalization. The CDs@ZrHf-MOF can be applied as the scaffold for anchoring aptamer strands to determine human epidermal growth factor receptor-2 (HER2) and living HER2-overexpressed MCF-7 cells. The basic characterizations reveal that the CDs are embedded within the interior cavities of ZrHf-MOF without varying the nanostructure, leading to good biocompatibility, strong fluorescence, and high electrochemical activity of CDs@ZrHf-MOF. As compared with the pristine ZrHf-MOF, the CDs@ZrHf-MOF-based electrochemical aptasensor displays better sensing performances toward both HER-2 and MCF-7 cells, giving an extremely low detection limit of 19 fg mL^-1 (HER2 concentration range: 0.001-10 ng mL^-1) and 23 cell mL^-1 (cell concentration range: 1 × 10²~1 × 10⁵ cell mL^-1), with good selectivity, stability, reproducibility, and acceptable applicability. The proposed strategy for developing CDs@ZrHf-MOF-based aptasensor is promising for the early and sensitive detection of cancer markers and living cancer cells.