An electrochemical sensor based on electro-polymerization of caffeic acid and Zn/Ni-ZIF-8–800 on glassy carbon electrode for the sensitive detection of acetaminophen

Au nanoparticles anchored carbonized ZIF-8 for enabling real-time and noninvasive glucose monitoring in sweat

Wearable sensors can easily enable real-time and noninvasive glucose (Glu) monitoring, providing vital information for effectively preventing various complications caused by high glucose level. Here, a wearable sensor based on nanozyme-catalyzed cascade reactions is designed for Glu monitoring in sweat. Au nanoparticles (AuNPs) are anchored to the carbonated zeolitic imidazolate framework-8 (ZIF-8-C), endowing the sensor with Glu oxidase (GOx)-like and peroxidase (POD)-like activity. A flexible screen-printed carbon electrode (SPCE) is decorated with the resultant AuNPs@ZIF-8-C, which is further modified with biocompatible and swellable calcium alginate (CA) gels for the preparation of the wearable Glu sensor. The linear range for Glu detection is 10∼300 μM with a limit of detection (LOD) of 4.99 μM, which covers the physiological Glu concentration range in human sweat (10-200 μM). The developed wearable Glu sensor can fit well with the skin tissues due to the flexibility of the SPCE, and thus it can be successfully applied in real-time and noninvasive monitoring of Glu in human sweat. Additionally, the wearable Glu sensor exhibits high antibacterial activity resulted from the generated hydroxyl radicals (·OH), enabling long-term Glu monitoring in sweat.

D-Histidine modulated chiral metal-organic frameworks for discriminating 3,4-Dihydroxyphenylalanine enantiomers based on a chemiluminescence quenching mode

BACKGROUND

Drug enantiomers often display distinguishable or even opposite pharmacological and toxicologic activities. Therefore it is of great necessity to discriminate enantiomers for guaranteeing safetyness and effectiveness of chiral drugs. Facile chiral discrimination has long been a noticeable challenge because of the minimal differences in physicochemical properties of enantiomers. As one of high-performance chirality selection components, chiral metal-organic frameworks (CMOFs) are bringing new opportunities for the establishment of chiral discrimination platform with merits of high enantioselectivity, low cost, and facile operation.

RESULTS

By introducing D-Histidine as a modulator, a CMOFs material termed as D-Histidine-ZIF-8 was prepared on chitosan (CS) with an in-situ growth protocol. The positively charged CMOFs/CS hybrids were adsorbed onto negatively charged polystyrene microplate via electrostatic interaction to form a chiral discrimination interface. This interface can effectively adsorb 3,4-Dihydroxyphenylalanine (DOPA) enantiomers, and the adsorbed molecules can be quantitated based on their quenching behavior on the chemiluminescent (CL) signal of Co2+-catalyzed luminol-H2O2 reaction. The results of contact angle measurements and density functional theory calculations imply that CMOFs/CS have stronger affinity towards D-isomer than L-isomer. Thus the sensitivity for quantifying D-isomer is 2.93 times of that for L-isomer, demonstrating the enantioselectivity of the CMOFs/CS hybrids. The content of D-isomer in nonracemic mixtures of DOPA enantiomers and real samples were assayed with satisfactory results, showing the practicality of this method. The strategy also exhibited discrimination capacity for many other chiral molecules.

SIGNIFICANCE

The CMOFs/CS hybrids prepared with in-situ growth protocol display satisfactory selectivity for discriminating enantiomers. Due to usage of multi-well microplate platform, the method is anticipated to achieve high-throughput assay in the future work. This study paves a pathway for facile chiral discrimination based on a chemiluminescence quenching mode to meet the demand of drug development and manufacture.

Room-temperature fabrication of zeolitic imidazolate framework-8 nanoparticles combined with graphitized and carbonylated carbon nanotubes networks for the ultrasensitive gallic acid electrochemical detection

Gallic acid (GA) has important application value in several fields of foods, medicines, and chemical engineering. However, the excessive intake of GA may cause gastrointestinal discomfort and nerve damage. Herein, an economical room-temperature fabrication strategy was reported for the preparation of zeolitic imidazolate framework-8 (ZIF-8) nanoparticles combined with graphitized and carbonylated carbon nanotubes (GCMCN) networks, which were used to achieve the ultrasensitive electrochemical detection of GA. The GCMCN@ZIF-8 nanocomposite modified electrode realized an accurate and rapid analysis of GA (Linear concentration range: 0.1-20 μM, LOD: 4.77 nM). GCMCN networks with graphitization and carboxylation boosted the electrical conductivity of electrode modification layer and enhanced the electrochemical interface area between sensing electrode and electrolyte. ZIF-8 nanoparticles with more active interaction sites and high porosity possessed high adsorption capacity for GA molecules. The fabricated electrochemical sensing platform exhibited good GA quantitative analysis property in food samples (Recovery: 93.88-106.73 %, RSD: 1.04-3.73).

Willow catkin template synthesis of NiS@NSC hollow tubes for highly sensitive dual-function electrochemical detection of acetaminophen and Cu2

Public health and environmental well-being have become increasingly threatened by the contamination of pharmaceuticals and heavy metal ions. This study focuses on addressing this critical issue by developing a novel electrochemical sensor for the dual-functional detection of acetaminophen (AP) and Cu2+. Utilizing willow catkins as a biomass template, a hollow tubular NiS@NSC composite was prepared by simple nickel salt impregnation combined with calcination and sulfurization. A highly sensitive dual-functional electrochemical sensor was thus constructed that can detect both acetaminophen (AP) and Cu2+. By examining its electrochemical properties, the sensor achieves an impressive detection limit of 1.33 pM for AP, with a linear range of 4.00 pM ~ 0.15 mM. The sensor can also detect Cu2+, with a detection limit of 1.04 µM, and a linear range of 3.13 µM ~ 0.66 mM. The sensor also exhibits strong resistance to interference, and good repeatability and stability. In addition, the sensor has demonstrated good performance in actual sample analysis, including the detection of AP in serum and Cu2+ in wastewater. This excellent electrochemical sensing performance is mainly attributed to the synergistic effect of its unique tubular structure and highly conductive N, S co-doped carbon. This results in the sensor exhibiting minimal charge transfer resistance, an extensive electrochemically active surface area, and a high density of active sites.

Advanced Electrochemical Monitoring of Carbendazim Fungicide in Foods Using Interfacial Superassembly of NRPC/NiMn Frameworks

A simple, sensitive and reliable sensing system based on nitrogen-rich porous carbon (NRPC) and transition metals, NRPC/Ni, NRPC/Mn and NRPC/NiMn was developed and successfully applied as electrode materials for the quantitative determination of carbendazim (CBZ). The synergistic effect of NRPC and bimetals with acceptable pore structure together with flower-like morphology resulted in producing a highly conductive and interconnected network in NRPC/NiMn@GCE, which significantly enhanced the detection performance of CBZ. The electrochemical behavior investigated by cyclic voltammetry (CV) showed improved CBZ detection for NRPC/NiMn, due to the controlled adsorption/diffusion process of CBZ by the NRPC/NiMn@GCE electrode. The influences of various factors such as pH, NRPC/NiMn concentration, CBZ concentration and scan rate were studied. Under optimal conditions, 0.1 M phosphate-buffered saline (PBS) with a pH of 7.0 containing 30 µg/mL NRPC/NiMn, a favourable linear range detection of CBZ from 5 to 50 µM was obtained. Moreover, a chronoamperometric analysis showed excellent repeatability, reproducibility and anti-interfering ability of the fabricated NRPC/NiMn@GCE sensor. Furthermore, the sensor showed satisfactory results for CBZ detection in real samples with acceptable recoveries of 96.40-104.98% and low RSD values of 0.25-3.45%.

Construction of functionalized carbon nanotube@metal oxide nanocomposite for high-performance electrochemical measurement of antipyretic drug in water samples

Acetaminophen (AP) acts as supportive clinical therapy for fever and dysmenorrhea. An overdose of AP may result in severe adverse diseases, such as liver dysfunction. In addition, AP is a key-listed environmental pollutant, which is difficult to degrade in the environment and has serious effects on living bodies. Therefore, the simple and quantitative determination of AP is highly relevant today. In this work, tin dioxide (SnO2) nanoparticles with functionalized multi-walled carbon nanotube (f-MWCNT) as a hybrid composite were prepared by hydrothermal-assisted synthesis. The composite material was characterized by various spectral, morphological, and electrochemical tests. Electrochemical investigations were conducted using a SnO2@f-MWCNT-reinforced electrode for the detection of AP. The composite electrode exhibited better functional properties, which facilitated electron transfer and enhanced electrical conductivity. The calculated low detection limit (LOD) of 0.36 nM is with a wide linear range of concentration from 0.001 to 673 µM. Additionally, the SnO2@f-MWCNT-modified electrode exhibited good anti-interference capability, repeatability, reproducibility, storage, and operational stability. The developed SnO2@f-MWCNT-modified electrode was applied to practical analysis in diverse water matrices (river, drinking, and pond) with acceptable recovery percentages. A synthesized nanoscale metal oxide electrocatalyst is of great interest and an active research area that serves as a foundation for the development of new, cost-effective electrochemical antibiotic drug sensors.

Anthraquinone/activated carbon electrochemical sensor and its application in acetaminophen analysis

Acetaminophen (AC) can inhibit the synthesis of prostaglandins in the body, and has antipyretic and analgesic effects. In this paper, a two-step microwave impregnation method was used to prepare anthraquinone (AQ)-doped carbon composite, which were applied to the surface modification of glassy carbon electrodes (GCE) for the determination of acetaminophen (AC) using differential pulse voltammetry (DPV). The composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and Fourier infrared spectroscopy (FT-IR). The results showed that anthraquinone was successfully modified on the surface of activated carbon. The peak current of AC increased with its concentration in the range of 0.1 μM to 700 μM (R2 = 0.998) and a detection limit of 0.05 μM was obtained with 20%AQ doped carbon electrochemical sensor (20%AQ-C/GCE). Electrochemical Impedance Spectroscopy (EIS) test results indicated that the charge transfer resistance (Rct) of 20%AQ-C/GCE is only the one-fourth of that of bare GCE. The proposed 20%AQ-C/GCE sensor has good stability, reproducibility and selectivity for the detection of AC. The sensor is also suitable for the detection of real samples, indicating its good practicality.

Photocatalytic Degradation of Acetaminophen in Aqueous Environments: A Mini Review

Over the past few decades, acetaminophen (ACT), a typical nonsteroidal anti-inflammatory drug (NSAID), has gained global usage, positioning itself as one of the most extensively consumed medications. However, the incomplete metabolism of ACT leads to a substantial discharge into the environment, classifying it as an environmental contaminant with detrimental effects on non-target organisms. Various wastewater treatment technologies have been developed for ACT removal to mitigate its potential environmental risk. Particularly, photocatalytic technology has garnered significant attention as it exhibits high efficiency in oxidizing and degrading a wide range of organic pollutants. This comprehensive review aims to systematically examine and discuss the application of photocatalytic technology for the removal of ACT from aqueous environments. Additionally, the study provides a detailed overview of the limitations associated with the photocatalytic degradation of ACT in practical applications, along with effective strategies to address these challenges.

Enhanced Acetaminophen Electrochemical Sensing Based on Nitrogen-Doped Graphene

Because of the widespread acetaminophen usage and the danger of harmful overdosing effects, developing appropriate procedures for its quantitative and qualitative assay has always been an intriguing and fascinating problem. A quick, inexpensive, and environmentally friendly approach based on direct voltage anodic graphite rod exfoliation in the presence of inorganic salt aqueous solution ((NH4)2SO4-0.3 M) has been established for the preparation of nitrogen-doped graphene (exf-NGr). The XRD analysis shows that the working material appears as a mixture of few (76.43%) and multi-layers (23.57%) of N-doped graphenes. From XPS, the C/O ratio was calculated to be 0.39, indicating a significant number of structural defects and the existence of multiple oxygen-containing groups at the surface of graphene sheets caused by heteroatom doping. Furthermore, the electrochemical performances of glassy carbon electrodes (GCEs) modified with exf-NGr for acetaminophen (AMP) detection and quantification have been assessed. The exf-NGr/GCE-modified electrode shows excellent reproducibility, stability, and anti-interfering characteristics with improved electrocatalytic activity over a wide detection range (0.1-100 µM), with a low limit for AMP detection (LOD = 3.03 nM). In addition, the developed sensor has been successfully applied in real sample analysis for the AMP quantification from different commercially available pharmaceutical formulations.

Simultaneous Determination of Caffeic Acid and Ferulic Acid Using a Carbon Nanofiber-Based Screen-Printed Sensor

This work aims to achieve the simultaneous qualitative and quantitative determination of two hydroxycinnamic acids (ferulic acid and caffeic acid) from standard solutions and from a phyto-homeopathic product using a carbon nanofiber-based screen-printed sensor (CNF/SPE). The two compounds are mentioned in the manufacturer's specifications but without indicating their concentrations. The stability and reproducibility of the CNF/SPE were found to be effective and the sensitivity was high for both caffeic acid-CA (limit of detection 2.39 × 10^-7 M) and ferrulic acid-FA (limit of detection 2.33 × 10^-7 M). The antioxidant capacity of the compounds in the analyzed product was also determined by the DPPH (2,2-diphenyl-1-picrylhydrazyl) method. The electrochemical method was efficient and less expensive than other analytical methods; therefore, its use can be extended for the detection of these phenolic compounds in various dietary supplements or pharmaceutical products.

Transition metal copper composite ionic liquid self-built ratiometric sensor for the detection of paracetamol

In this paper, a MOF derivative Cu-PF₆-MOF composed of transition metal copper and ionic liquid [BMIM] PF₆ was used to construct a ratiometric electrochemical sensor for paracetamol detection. Cu-PF₆-MOF was synthesized by chemical bath method and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), X-ray Photoelectron Spectroscopy (XPS) and X-ray powder diffraction (XRD). Owing to the introduction of ionic liquid [BMIM] PF₆ and the synthetic effect on transition metal copper and ionic liquid [BMIM] PF₆, Cu-PF₆-MOF has the higher conductivity, larger electroactive surface area and better intrinsic catalytic properties of the skeletal transition metal, exhibiting enhanced electrocatalytic response to the reduction of paracetamol. The stable reduction peak at -104 mV was used as the ratiometric signal for analytical paracetamol detection using differential pulse voltammetry (DPV), with a linear range of 0.1-100 μM and a detection limit of 0.03 μM (S/N = 3). In addition, the constructed sensor showed good reproducibility, stability and interference resistance, as well as ideal recoveries (98.20%-104.40%) for the analysis of paracetamol in water samples.

Electrochemical immunosensor based on AuNPs/Zn/Ni-ZIF-8-800@graphene for rapid detection of aflatoxin B1 in peanut oil

Peanut oil is a basic food raw material in life. However, aflatoxin contamination in peanut oil is considered to be one of the most serious food safety problems in the world. Based on AuNPs/Zn/Ni-ZIF-8-800@graphene composite, a simple, efficient and sensitive electrochemical immunosensor was developed to detect aflatoxin B1 (AFB1) in peanut oil. The bare glassy carbon electrode was modified by graphene, bimetallic organic framework material (Zn/Ni-ZIF-8-800), chitosan and gold nanoparticles. The electrochemical immunosensor was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) and cyclic voltammetry (CV), and the electrochemical signal changes after antibody and AFB1 binding were investigated in detail. Under the optimal conditions, the linear range of the electrochemical immunosensor was 0.18-100 ng/mL, and the detection limit was 0.18 ng/mL. In addition, the prepared sensor has high selectivity and long-term stability, which lays a foundation for the simple, rapid and sensitive detection of AFB1 in peanut oil.

Reversible inhibition of the oxidase-like activity of Fe single-atom nanozymes for drug detection

Mechanism research of nanozymes has always been of great interest since their emergence as outstanding mimics of friable natural enzymes. An important but rarely mentioned issue in mechanism research of nanozymology is the inhibitory effect of nanozymes. And conventional nanozymes with various active sites hinder the mechanism research, while single-atom Fe-N-C nanozymes with similar active sites to natural enzymes exhibit structural advantages. Herein, we synthesized Fe single-atom nanozymes (Fe-SANs) with ultrahigh oxidase-like activity and found that a common analgesic-antipyretic drug 4-acetamidophenol (AMP) had inhibitory effects for the oxidase-like activity of Fe-SANs. We investigated the inhibitory effects in detail and demonstrated that the inhibition type was reversible mixed-inhibition with inhibition constants (K i and ) of 0.431 mM and 0.279 mM, respectively. Furthermore, we put forward a colorimetric method for AMP detection based on nanozyme inhibition. The research on the inhibitory effects of small molecules on nanozymes expands the scope of analysis based on nanozymes and the inhibition mechanism study may offer some insight into investigating the interaction between nanozymes and inhibitors.

Reagentless electrochemical biosensors through incorporation of unnatural amino acids on the protein structure

Typical protein biosensors employ chemical or genetic labeling of the protein, thus introducing an extraneous molecule to the wild-type parent protein, often changing the overall structure and properties of the protein. While these labeling methods have proven successful in many cases, they also have a series of disadvantages associated with their preparation and function. An alternative route for labeling proteins is the incorporation of unnatural amino acid (UAA) analogues, capable of acting as a label, into the structure of a protein. Such an approach, while changing the local microenvironment, poses less of a burden on the overall structure of the protein. L-DOPA is an analog of phenylalanine and contains a catechol moiety that participates in a quasi-reversible, two-electron redox process, thus making it suitable as an electrochemical label/reporter. The periplasmic glucose/galactose binding protein (GBP) was chosen to demonstrate this detection principle. Upon glucose binding, GBP undergoes a significant conformational change that is manifested as a change in the electrochemistry of L-DOPA. The electroactive GBP was immobilized onto gold nanoparticle-modified, polymerized caffeic acid, screen-printed carbon electrodes (GBP-LDOPA/AuNP/PCA/SPCE) for the purpose of direct measurement of glucose levels and serves as a proof-of-concept of the use of electrochemically-active unnatural amino acids as the label. The resulting reagentless GBP biosensors exhibited a highly selective and sensitive binding affinity for glucose in the micromolar range, laying the foundation for a new biosensing methodology based on global incorporation of an electroactive amino acid into the protein's primary sequence for highly selective electrochemical detection of compounds of interest.

Embedded ionic liquid modified ZIF-8 in CaMgAl hydrotalcites for bio-glycerol transesterification

Novel modified MOF intercalated hydrotalcites was synthesized for catalyzing the conversion of glycerol into high value-added glycerol carbonate in this paper. [APmim]OH/ZIF-8 was prepared by encapsulating aminopropyl hydroxide imidazole ionic liquid in ZIF-8 and inserted in Ca-Mg-Al hydrotalcites with layered structures to prepare [APmim]OH/ZIF-8/LDH with strong basicity and high specific surface area. ZIF-8, [APmim]OH/ZIF-8 and [APmim]OH/ZIF-8/LDH were characterized by XRD, FT-IR, SEM and nitrogen adsorption-desorption. The results showed that the conversion rate of glycerol can reach 98.6% and the glycerol carbonate yield was 96.5% in the transesterification of glycerol with dimethyl carbonate catalyzed by [APmim]OH/ZIF-8/LDH when the molar ratio of DMC and glycerol was 3 : 1, the catalyst dosage was 3 wt%, the reaction temperature was 75 °C and the reaction time was 80 minutes. The glycerol conversion rate can still reach more than 90% after five reaction cycles.

Simultaneous detection of acetaminophen, catechol and hydroquinone using a graphene-assisted electrochemical sensor

Simple, rapid and sensitive analysis of drug-derived pollutants is critically valuable for environmental monitoring. Here, taking acetaminophen, hydroquinone and catechol as a study example, a sensor based on an ITO/APTES/r-GO@Au electrode was developed for separate and simultaneous determination of phenolic pollutants. ITO electrodes that are modified with 3-aminopropyltriethoxysilane (APTES), graphene (GO) and Au nanoparticles (Au NPs) can significantly enhance the electronic transport of phenolic pollutants at the electrode surface. The redox mechanisms of phenolic pollutants include the electron transfer with the enhancement of r-GO@Au. The modified ITO electrode exhibits excellent electrical properties to phenolic pollutants and a good linear relationship between ECL intensity and the concentration of phenolic pollutants, with a limit of detection of 0.82, 1.41 and 1.95 μM, respectively. The separate and simultaneous determination of AP, CC and HQ is feasible with the ITO/APTES/r-GO@Au electrode. The sensor shows great promise as a low-lost, sensitive, and rapid method for simultaneous determination of drug-derived pollutants.

Simple, rapid and sensitive analysis of drug-derived pollutants is critically valuable for environmental monitoring.

A 2D/2D NiCo-MOF/Ti3C2 heterostructure for the simultaneous detection of acetaminophen, dopamine and uric acid by differential pulse voltammetry

A 2D/2D NiCo-MOF/Ti₃C₂ heterojunction is constructed as a non-enzymatic biosensor for the simultaneous electrochemical detection of acetaminophen (AP), dopamine (DA), and uric acid (UA) via differential pulse voltammetry. Benefiting from the synergistic effects of the high electrocatalytic activity of NiCo-MOF, the outstanding conductivity of Ti₃C₂, and the improved specific surface area of NiCo-MOF/Ti₃C₂, NiCo-MOF/Ti₃C₂ displays high sensing performance toward AP (0.01-400 μM), DA (0.01-300 μM), and UA (0.01-350 μM) in 0.1 M phosphate buffer (PB, pH 7.4) at working potentials of 0.346 V vs. SCE for AP, 0.138 V vs. SCE for DA, and 0.266 V vs. SCE for UA. Furthermore, the well-separated oxidation peak potentials allow for the simultaneous detection of the analytes, with detection limits of 0.008, 0.004, and 0.006 μM (S/N = 3), respectively. As a result of its considerable reproducibility and anti-interference and anti-fouling properties, NiCo-MOF/Ti₃C₂ was also developed into a practical sensing platform to detect AP, DA, and UA in serum and urine, presenting excellent recoveries of 98.1-102.2 %.

A simple strategy for the detection of Pb(II) and Cu(II) by an electrochemical sensor based on Zn/Ni-ZIF-8/XC-72/Nafion hybrid materials

In this study, a novel electrochemical sensor for simultaneous detection of Pb(II) and Cu(II) was constructed by using Zn/Ni-ZIF-8/XC-72/Nafion hybrid material as electrode surface modifier. XRD, FT-IR, XPS and SEM were used to study the crystal structure, functional groups, element types and morphologies of the prepared materials. The electrochemical performance of the Zn/Ni-ZIF-8/XC-72/Nafion/GCE sensor were investigated by CV, EIS and DPV. In addition, the effects of various conditions including pH, the type of buffer and the ratio of Zn/Ni-ZIF-8 to XC-72 were also explored for the determination of Pb(II) and Cu(II). Under the optimum conditions, the constructed sensor exhibited outstanding linear response of Pb(II) (0.794-39.6 ppm) and Cu(II) (0.397-19.9 ppm) with detection limits of 0.0150 and 0.0096 ppm, respectively. Finally, the fabricated sensor was further used to detect Pb(II) and Cu(II) in real samples, and the satisfactory recovery was obtained.

Metal-organic framework precursors derived Ni-doping porous carbon spheres for sensitive electrochemical detection of acetaminophen

The sensitive and selective determination of acetaminophen (AP) in the human body is highly desirable to ensure human health. In this work, nickel-doping nanoporous carbon (Ni/C) was fabricated by directly calcining Ni based metal-organic framework (Ni-MOF). The Ni/C based electrochemical sensor was developed for sensitive and selective determination of AP in human blood serum and urine samples. The prepared Ni/C composite possess plentiful catalytic active sites, ordered mesoporous structure and large specific surface area, which endow the constructed Ni/C sensor with a prominent performance for acetaminophen sensing. Under the optimal conditions, the developed method offered good linearity in the range of 0.20-53.75 μM with a low detection limit (S/N = 3) of 4.04 × 10^-2 μM. The electrocatalytic performance of the sensor towards AP was further measured by differential pulse voltammetry and cyclic voltammetry. The results demonstrated that the Ni/C sensor can be feasibly employed for the determination of AP in human blood serum and urine samples with excellent anti-interference stability and good reproducibility. The research reveals a great promising of the Ni/C electrochemical sensor for clinical applications and paves a way for the construction of high-performance electrochemical sensors for AP determination.

Influence of hollow sphere surface heterogeneity and geometry of N-doped carbon on sensitive monitoring of acetaminophen in human fluids and pharmaceutical products

A sensitive and selective acetaminophen sensor assay was designed based on N-HCCS. The surface morphology, and composition of open hollow conjugated spheres of N-HCCS resulted in facile AC diffusion/loading and electrocatalytic oxidation.

Electrochemical sensing platform for naphthol isomers based on in situ growth of ZIF-8 on reduced graphene oxide by a reaction-diffusion technique

Enhancing the dispersibility and conductivity is an effective solution to develop the application zeolitic imidazole frameworks (ZIF) in the electrochemical field. This work thus employs a novel reaction-diffusion framework (RDF) technique for the in situ growth of ZIF-8 crystals on graphene oxide (GO@ZIF-8) matrixes. In detail, the outer electrolyte of 2-methyl imidazole naturally diffuses into the inner agar gel matrix containing Zn²⁺ cations and GO nanosheets. The long reaction-diffusion makes the growth of ZIF-8 crystals controllable in a vertical gradient. After thermal treatment, the title product of ZIF-8 in situ grown on reduced graphene oxide (rGO@ZIF-8) is obtained and thus exhibits good dispersibility, high conductivity, large surface area, and more catalytic sites. The glassy carbon electrode (GCE) was modified by casting the rGO@ZIF-8 suspension. The obtained rGO@ZIF-8/GCE displays excellent catalytic activity toward naphthol (NAP) isomers. Under the optimal conditions, the amperometric currents of 1-NAP and 2-NAP demonstrate the good linear relationship in wide ranges of 0.05-12 μM and 0.02-15 μM, respectively. Their limits of detection are as low as 15 and 17 nM, respectively. The fabricated modified electrode exhibits excellent selectivity, stability, and reproducibility. The sensor is also utilized to detect NAP molecules in real water samples and indicates good accuracy and reliability.

Enhancing electrochemical sensing for catechol by biomimetic oxidase covalently functionalized graphene oxide

Catechol level is an important indicator for evaluating the quality of tea. Therefore, the exploration of a simple and efficient quantitative detection method for catechol has an important significance. In this study, functionalized graphene oxide was synthesized by chemically modifying the surface of graphene oxide. The prepared carrier was covalently combined with biomimetic oxidase iron porphyrin (FePP, the active center of horseradish peroxidase). Ionic liquid as covalent coupling agents was designed as electronic bridge between biomimetic oxidase and graphene oxide. The novel biomimetic biosensor provided a detection range of 50.0-1600.0 μmol/L by modulating under the optimal conditions of the reaction system (FePP concentration is 1.5 × 10^-3 mol/L, pH 3.0, Nafion solution dosage 1% and temperature 25 °C), the detection limit is 0.09 μmol/L. The biosensor has excellent stability, repeatability and reproducibility, and is expected to be applied to the rapid detection of catechol in actual tea sample..

Layered nanocomposite of zinc sulfide covered reduced graphene oxide and their implications for electrocatalytic applications

Herein, we have synthesized zinc sulfide nanospheres (ZnS NPs) encapsulated on reduced graphene oxide (RGO) hybrid by an ultrasonic bath (50 kHz/60 W). The physical and structural properties of ZnS NPs@RGO hybrid were analyzed by TEM, XRD, EIS and EDS. As-prepared ZnS NPs@RGO hybrid was applied towards the electrochemical determination of caffeic acid (CA) in various food samples. The ZnS NPs@RGO hybrid modified electrode (GCE) exhibited an excellent electrocatalytic performance towards caffeic acid detection and determination, when compared to other modified electrodes. Therefore, the electrochemical sensing performance of the fabricated and nanocomposite modified electrode was significantly improved owing to the synergistic effect of ZnS NPs and RGO catalyst. Furthermore, the hybrid materials provide highly active electro-sites as well as rapid electron transport pathways. The proposed electrochemical caffeic acid sensor produces a wide linear range of 0.015-671.7 µM with a nanomolar level detection limit (3.29 nM). In addition, the real sample analysis of the proposed sensor has applied to the determination of caffeic acid in various food samples.

Synthesis of novel ternary heterogeneous anatase-TiO2 (B) biphase nanowires/Bi4O5I2 composite photocatalysts for the highly efficient degradation of acetaminophen under visible light irradiation

Bi₄O₅I₂ loaded anatase-TiO₂ (B) biphase nanowires composite photocatalysts were fabricated by an in situ calcination method and exhibited outstanding photocatalytic activity. The microstructure, optical performance and band structure of the composite photocatalysts were investigated by relevant characterizations. The results demonstrated the successful formation of heterojunction between anatase-TiO₂ (B) biphase nanowires and Bi₄O₅I₂, which integrated the advantages of homojunction and heterojunction. Therefore, it definitely improved separation efficiency of photo-induced electron-holes because of the formation of multi-junctions. In order to test the enhanced photocatalytic activity, acetaminophen was chosen as target pollutant. The sample with 67% Bi₄O₅I₂ (TiO₂-Bi₄O₅I₂-3) presented the highest photocatalytic activity on the degradation of acetaminophen and its reaction apparent rate constant was 10 and 25 times as that of Bi₄O₅I₂ and TiO₂ biphase nanowires, respectively. Through trapping experiments and LC-MS/MS analysis, OH was proved to be the key active specie during the photocatalytic process of acetaminophen degradation. Meanwhile a possible degradation pathway was proposed based on the detected intermediate products.

Electrochemical determination of lead(II) and copper(II) by using phytic acid and polypyrrole functionalized metal-organic frameworks

A glassy carbon electrode (GCE) was modified with a composite prepared from phytic acid, polypyrrole and a ZIF type metal-organic framework (PA/PPy)/ZIF-8@ZIF-67). The nanocomposite was prepared by in-situ chemical polymerization in the presence of ferric chloride and subsequently functionalized with PA to form PA/PPy/ZIF-8@ZIF-67. The materials were characterized by XRD, FT-IR, BET, XPS, SEM and TEM. The modified GCE was applied to individual and simultaneous detection of Pb(II) and Cu(II), with peak voltages of -0.6 and - 0.1 V, respectively (vs. SCE). The amount of PPy, the ZIF-8@ZIF-67 concentration, polymerization potential, polymerization time and pH value were optimized. Under optimized conditions, the calibration plots have two linear ranges. These are from 0.02 to 200 μM and from 200 to 600 μM for Pb(II), and from 0.2 to 200 μM and 200 to 600 μM for Cu(II). The detection limits are 2.9 nM and 14.8 nM, respectively. Simultaneous detection of Pb(II) and Cu(II) is also demonstrated. The good performance of the electrode is attributed to the large surface area of ZIF-8@ZIF-67, the good electrical conductivity of PPy, and the metal complexation power of PA. The modified GCE was successfully applied to the determination of Pb(II) and Cu(II) in real samples and gave satisfactory recoveries. Graphical abstractSchematic presentation of the construction process of PA/PPy/ZIF-8@ZIF-67/GCE sensor, and the mechanism of Pb(II) and Cu(II) at the prepared sensor.

Recent Advances of Porous Graphene: Synthesis, Functionalization, and Electrochemical Applications

Graphene is a 2D sheet of sp² bonded carbon atoms and tends to aggregate together, due to the strong π-π stacking and van der Waals attraction between different layers. Its unique properties such as a high specific surface area and a fast mass transport rate are severely blocked. To address these issues, various kinds of 2D holey graphene and 3D porous graphene are either self-assembled from graphene layers or fabricated using graphene related materials such as graphene oxide and reduced graphene oxide. Porous graphene not only possesses unique pore structures, but also introduces abundant exposed edges and accelerates mass transfer. The properties and applications of these porous graphenes and their composites/hybrids have been extensively studied in recent years. Herein, recent progress and achievements in synthesis and functionalization of various 2D holey graphene and 3D porous graphene are reviewed. Of special interest, electrochemical applications of porous graphene and its hybrids in the fields of electrochemical sensing, electrocatalysis, and electrochemical energy storage, are highlighted. As the closing remarks, the challenges and opportunities for the future research of porous graphene and its composites are discussed and outlined.

A novel enzyme-free electrochemical biosensor for rapid detection of Pseudomonas aeruginosa based on high catalytic Cu-ZrMOF and conductive Super P

Pseudomonas aeruginosa (P. aeruginosa) is one of the most intractable multidrug-resistant bacteria of nosocomial infections. The conventional detection methods for P. aeruginosa are time-consuming or low detection sensitivity. Here, a novel enzyme-free electrochemical biosensor was constructed to detect P. aeruginosa rapidly and sensitively. Firstly, the ZrMOF with large surface area was synthesized, which offers excellent adsorption. Further, it was connected with a specific amount of Cu²⁺ to synthesize Cu-ZrMOF with high catalytic activity. Then the Cu-ZrMOF@Aptamer@DNA nanocomposite was composed and served as the signal probe to catalyse the decomposition of H₂O₂. Moreover, high conductive Super P was introduced to increase the electron transfer for satisfactory detection sensitivity. The proposed biosensor was constructed and used to quantify P. aeruginosa with a wide linearity range of 10-10⁶ CFU mL^-1 and a low limit of detection of 2 CFU mL^-1 (S/N = 3). Compared with conventional methods, the new method of present biosensor is more sensitive, and less time-consuming (only within 120 min). The analytical performance evaluation indicated that the biosensor exhibits good reproducibility and specificity. Finally, the biosensor was successfully applied to quantify P. aeruginosa in spiked urine samples. These results show that the proposed electrochemical biosensor might be a potential laboratory tool for detecting P. aeruginosa in the clinic.