Simultaneous Electrochemical Detection of Dopamine and Uric Acid via Au@Cu-Metal Organic Framework.

The incorporation of noble metals with metal-organic frameworks (MOFs) are conducive to the simultaneous electrochemical detection of analytes owing to multiple accessible reaction sites. Herein, Au@Cu-metal organic framework (Au@Cu-MOF) is successfully synthesized and modified as a screen-printed carbon electrode (SPCE), which serves as an excellent electrocatalyst for the oxidation of dopamine (DA) and uric acid (UA). The sensor shows a linear range from 10 µM to 1000 µM, with sensitivity and detection limit of 0.231 µA µM-1 cm-2 and 3.40 µM for DA, and 0.275 µA µM-1 cm-2 and 10.36 µM for UA. Au@Cu-MOF could realize the individual and simultaneous electrochemical sensing of DA and UA, with distinguishable oxidation peak potentials. Moreover, it exhibits reproducibility, repeatability, and stability. Ultimately, the sensor provides an avenue for an ultrasensitive label-free electrochemical detection of DA and UA.

A review of zeolitic imidazolate frameworks (ZIFs) as electrochemical sensors for important small biomolecules in human body fluids.

Small biomolecules play a critical role in the fundamental processes that sustain life and are essential for the proper functioning of the human body. The detection of small biomolecules has garnered significant interest in various fields, including disease diagnosis and medicine. Electrochemical techniques are commonly employed in the detection of critical biomolecules through the principle of redox reactions. It is also a very convenient, cheap, simple, fast, and accurate measurement method in analytical chemistry. Zeolitic imidazolate frameworks (ZIFs) are a unique type of metal-organic framework (MOF) composed of porous crystals with extended three-dimensional structures. These frameworks are made up of metal ions and imidazolate linkers, which form a highly porous and stable structure. In addition to their many advantages in other applications, ZIFs have emerged as promising candidates for electrochemical sensors. Their large surface area, pore diameter, and stability make them ideal for use in sensing applications, particularly in the detection of small molecules and ions. This review summarizes the critical role of small biomolecules in the human body, the standard features of electrochemical analysis, and the utilization of various types of ZIF materials (including carbon composites, metal-based composites, ZIF polymer materials, and ZIF-derived materials) for the detection of important small biomolecules in human body fluids. Lastly, we provide an overview of the current status, challenges, and future outlook for research on ZIF materials.

A copper-based metal-organic framework decorated with electrodeposited Fe2O3 nanoparticles for electrochemical nitrite sensing.

An amperometric nitrite sensor is reported based on a screen-printed carbon electrode (SPCE) modified with copper(II)-benzene-1,4-dicarboxylate (Cu-BDC) frameworks and iron(III) oxide nanoparticles (Fe2O3 NPs). First, copper(I) oxide (Cu2O) nanocubes were synthesized, followed by a solvothermal reaction between Cu2O and H2BDC to form square plate-like Cu-BDC frameworks. Then, Fe2O3 NPs were electrodeposited on Cu-BDC frameworks using a potentiostatic method. The Fe2O3@Cu-BDC nanocomposite benefits from high conductivity and large active surface area, offering excellent electrocatalytic activity for nitrite oxidation. Under optimal amperometric conditions (0.55 V vs. Ag/AgCl), the sensor has a linear range of 1 to 2000 µM with a detection limit of 0.074 µM (S/N = 3) and sensitivity of 220.59 µA mM-1 cm-2. The sensor also provides good selectivity and reproducibility (RSD = 1.91%, n = 5). Furthermore, the sensor exhibits long-term stability, retaining 91.4% of its original current after 4 weeks of storage at room temperature. Finally, assessing nitrite in tap and mineral water samples revealed that the Fe2O3@Cu-BDC/SPCE has a promising prospect in amperometric nitrite detection.

Observation of ionic conductivity on PUA-TBAI-I2 gel polymer electrolyte.

Jatropha oil-based polyurethane acylate gel polymer electrolyte was mixed with different concentrations of tetrabutylammonium iodide salt (TBAI). The temperature dependences of ionic conductivity, dielectric modulus and relaxation time were studied in the range of 298 to 393 K. The highest ionic conductivity of (1.88 ± 0.020) × 10-4 Scm-1 at 298 K was achieved when the gel contained 30 wt% of TBAI and 2.06 wt% of I2. Furthermore, the study found that conductivity-temperature dependence followed the Vogel-Tammann Fulcher equation. From that, it could be clearly observed that 30 wt% TBAI indicated the lowest activation energy of 6.947 kJ mol-1. By using the fitting method on the Nyquist plot, the number density, mobility and diffusion coefficient of the charge carrier were determined. The charge properties were analysed using the dielectric permittivity, modulus and dissipation factor. Apart from this, the stoke drag and capacitance were determined.

Author Correction: Electrochemical Performance of Supercapacitor with Stacked Copper Foils Coated with Graphene Nanoplatelets.

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Electrochemical Performance of Supercapacitor with Stacked Copper Foils Coated with Graphene Nanoplatelets.

The energy density of conventional supercapacitors is in the range of 6-10 Wh kg-1, which has restricted them from many applications that require devices with long durations. Herein, we report a method for enhancing the energy density of a device through the parallel stacking of five copper foils coated on each side with graphene nanoplatelets. Microporous papers immersed in 2 M aqueous sodium sulphate were used as separators. With a low contact resistance of 0.05 Ω, the supercapacitor yielded an optimum specific energy density and a specific power density of 24.64 Wh kg-1 and 402 W kg-1 at 0.8 V, respectively. The working potential was increased to 2.4 V when three of the supercapacitors were connected in series, forming a tandem device. Its potential for real applications was manifested by the ability to light up a light-emitting diode for 40 s after charging for 60 s.

Modified plastic optical fiber with CNT and graphene oxide nanostructured coatings for ethanol liquid sensing.

A high sensitivity and simple ethanol sensor based on an un-cladded multimode plastic optical fiber (UCPOF) coated with carbon nanotubes (CNTs) for the detection of different concentrations of ethanol in de-ionized water is developed and demonstrated. The UCPOF probe is fabricated by chemically removing the fiber cladding and integrated with CNT as a sensing layer. The effect of surface morphology on the sensor performance is investigated by characterizing another UCPOF coated with GO nanomaterial. The developed fibers are coated with CNTs and GO using drop casting technique. Energy dispersive X-ray spectroscopy (EDX), atomic-force microscopy (AFM) and scanning electron microscope (SEM) are used to investigate the element and morphology of the synthesized nanomaterials. The experimental results indicated that the absorbance spectrum of the CNT-based UCPOF sensor increases linearly with a higher sensitivity of 0.68/vol% and magnitude change of 95.4% as compared to 0.19/vol% and 56.3%, respectively, for the GO-based sensor. The UCPOF coated with CNT exhibits faster response and recovery than that of GO. The sensor shows high selectivity to ethanol amongst a range of diluted organic VOCs. The superior sensing performance of the developed fiber sensor indicates its high efficiency for ethanol detection in various industrial applications.

Horseradish peroxidase-labeled silver/reduced graphene oxide thin film-modified screen-printed electrode for detection of carcinoembryonic antigen.

In this study, a disposable and simple electrochemical immunosensor was fabricated for the detection of carcinoembryonic antigen. In this method, silver nanoparticles (AgNPs) were mixed with reduced graphene oxide (rGO) to modify the surface of screen-printed carbon electrode (SPE). Initially, AgNPs-rGO modified-SPEs were fabricated by using simple electrochemical deposition method. Then the carcinoembryonic antigen (CEA) was immobilized between the primary antibody and horseradish peroxidase (HRP)-conjugated secondary antibody onto AgNPs-rGO modified-SPEs to fabricate a sandwich-type electrochemical immunosensor. The proposed method could detect the CEA with a linear range of 0.05-0.50µgmL-1 and a detection limit down to 0.035µgmL-1 as compared to its non-sandwich counterpart, which yielded a linear range of 0.05-0.40µgmL-1, with a detection limit of 0.042µgmL-1. The immunosensor showed good performance in the detection of carcinoembryonic antigen, exhibiting a simple, rapid and low-cost. The immunosensor showed a higher sensitivity than an enzymeless sensor.

Cadmium Sulphide-Reduced Graphene Oxide-Modified Photoelectrode-Based Photoelectrochemical Sensing Platform for Copper(II) Ions.

A photoelectrochemical (PEC) sensor with excellent sensitivity and detection toward copper (II) ions (Cu2+) was developed using a cadmium sulphide-reduced graphene oxide (CdS-rGO) nanocomposite on an indium tin oxide (ITO) surface, with triethanolamine (TEA) used as the sacrificial electron donor. The CdS nanoparticles were initially synthesized via the aerosol-assisted chemical vapor deposition (AACVD) method using cadmium acetate and thiourea as the precursors to Cd2+ and S2-, respectively. Graphene oxide (GO) was then dip-coated onto the CdS electrode and sintered under an argon gas flow (50 mL/min) for the reduction process. The nanostructured CdS was adhered securely to the ITO by a continuous network of rGO that also acted as an avenue to intensify the transfer of electrons from the conduction band of CdS. The photoelectrochemical results indicated that the ITO/CdS-rGO photoelectrode could facilitate broad UV-visible light absorption, which would lead to a higher and steady-state photocurrent response in the presence of TEA in 0.1 M KCl. The photocurrent decreased with an increase in the concentration of Cu2+ ions. The photoelectrode response for Cu2+ ion detection had a linear range of 0.5-120 µM, with a limit of detection (LoD) of 16 nM. The proposed PEC sensor displayed ultra-sensitivity and good selectivity toward Cu2+ ion detection.

Utilization of reduced graphene oxide/cadmium sulfide-modified carbon cloth for visible-light-prompt photoelectrochemical sensor for copper (II) ions.

A newly developed CdS/rGO/CC electrode was prepared based on a flexible carbon cloth (CC) substrate with cadmium sulfide (CdS) nanoparticles and reduced graphene oxide (rGO). The CdS was synthesized using an aerosol-assisted chemical vapor deposition (AACVD) method, and the graphene oxide was thermally reduced on the modified electrode surface. The existence of rGO in the CdS-modified electrode increased the photocurrent intensity of the CdS/rGO/CC-modified electrode by three orders of magnitude, compared to that of the CdS/ITO electrode and two orders of magnitude higher than the CdS/CC electrode. A new visible-light-prompt photoelectrochemical sensor was developed based on the competitive binding reaction of Cu(2+) and CdS on the electrode surface. The results showed that the effect of the Cu(2+) on the photocurrent response was concentration-dependent over the linear ranges of 0.1-1.0 µM and 1.0-40.0 µM with a detection limit of 0.05 µM. The results of a selectivity test showed that this modified electrode has a high response toward Cu(2+) compared to other heavy metal ions. The proposed CdS/rGO/CC electrode provided a significantly high potential current compared to other reported values, and could be a practical tool for the fast, sensitive, and selective determination of Cu(2+).

Fabrication of graphene/gold-modified screen-printed electrode for detection of carcinoembryonic antigen.

Immunosensors based on gold nanoparticles and reduced graphene oxide (AuNPs/rGO)-modified screen-printed electrodes (SPEs) were successfully synthesized using an electrochemical deposition method. The modified SPEs were characterized using a field emission scanning electron microscope (FESEM) and Raman spectroscopy to analyze the morphology and composition of AuNPs and rGO. Both the FESEM and Raman spectroscopy revealed that the AuNPs were successfully anchored on the thin film of rGO deposited on the surface of the SPEs. Characterization with a ferri-ferrocyanide couple [Fe(CN)6(3-/4-)] showed that the electron transfer kinetic between the analyte and electrode was enhanced after the modification with the AuNPs/rGO composite on the electrode surface, in addition to increasing the effective surface area of the electrode. The modified SPE was immobilized with a sandwich type immunosensor to mimic the ELISA (enzyme-linked immunosorbent assay) immunoassay. The modified SPE that was fortified with the sandwich type immunosensor exhibited double electrochemical responses in the detection of carcinoembryonic antigen (CEA), with linear ranges of 0.5-50 ng/mL and 250-2000 ng/mL and limits of detection of 0.28 ng/mL and 181.5 ng/mL, respectively.

Application of polypyrrole multi-walled carbon nanotube composite layer for detection of mercury, lead and iron ions using surface plasmon resonance technique.

Polypyrrole multi-walled carbon nanotube composite layers were used to modify the gold layer to measure heavy metal ions using the surface plasmon resonance technique. The new sensor was fabricated to detect trace amounts of mercury (Hg), lead (Pb), and iron (Fe) ions. In the present research, the sensitivity of a polypyrrole multi-walled carbon nanotube composite layer and a polypyrrole layer were compared. The application of polypyrrole multi-walled carbon nanotubes enhanced the sensitivity and accuracy of the sensor for detecting ions in an aqueous solution due to the binding of mercury, lead, and iron ions to the sensing layer. The Hg ion bonded to the sensing layer more strongly than did the Pb and Fe ions. The limitation of the sensor was calculated to be about 0.1 ppm, which produced an angle shift in the region of 0.3° to 0.6°.

Fabrication and characterization of graphene hydrogel via hydrothermal approach as a scaffold for preliminary study of cell growth.

BACKGROUND: Three-dimensional assembly of graphene hydrogel is rapidly attracting the interest of researchers because of its wide range of applications in energy storage, electronics, electrochemistry, and waste water treatment. Information on the use of graphene hydrogel for biological purposes is lacking, so we conducted a preliminary study to determine the suitability of graphene hydrogel as a substrate for cell growth, which could potentially be used as building blocks for biomolecules and tissue engineering applications. METHODS: A three-dimensional structure of graphene hydrogel was prepared via a simple hydrothermal method using two-dimensional large-area graphene oxide nanosheets as a precursor. RESULTS: The concentration and lateral size of the graphene oxide nanosheets influenced the structure of the hydrogel. With larger-area graphene oxide nanosheets, the graphene hydrogel could be formed at a lower concentration. X-ray diffraction patterns revealed that the oxide functional groups on the graphene oxide nanosheets were reduced after hydrothermal treatment. The three-dimensional graphene hydrogel matrix was used as a scaffold for proliferation of a MG63 cell line. CONCLUSION: Guided filopodia protrusions of MG63 on the hydrogel were observed on the third day of cell culture, demonstrating compatibility of the graphene hydrogel structure for bioapplications.

Simple room-temperature preparation of high-yield large-area graphene oxide.

Graphene has attracted much attention from researchers due to its interesting mechanical, electrochemical, and electronic properties. It has many potential applications such as polymer filler, sensor, energy conversion, and energy storage devices. Graphene-based nanocomposites are under an intense spotlight amongst researchers. A large amount of graphene is required for preparation of such samples. Lately, graphene-based materials have been the target for fundamental life science investigations. Despite graphene being a much sought-after raw material, the drawbacks in the preparation of graphene are that it is a challenge amongst researchers to produce this material in a scalable quantity and that there is a concern about its safety. Thus, a simple and efficient method for the preparation of graphene oxide (GO) is greatly desired to address these problems. In this work, one-pot chemical oxidation of graphite was carried out at room temperature for the preparation of large-area GO with ~100% conversion. This high-conversion preparation of large-area GO was achieved using a simplified Hummer's method from large graphite flakes (an average flake size of 500 µm). It was found that a high degree of oxidation of graphite could be realized by stirring graphite in a mixture of acids and potassium permanganate, resulting in GO with large lateral dimension and area, which could reach up to 120 µm and ~8000 µm(2), respectively. The simplified Hummer's method provides a facile approach for the preparation of large-area GO.

Developmental aspects of androgen action.

The formation of a testis from the indifferent gonad is the prelude to sequential steps in male sex differentiation orchestrated by time-dependent androgen biosynthesis and action. Information about the cellular and molecular mechanisms of androgen action can be obtained by the study of disorders of sex differentiation in males. The pivotal role of the androgen receptor as a ligand-induced transcription factor is emphasised and preliminary studies are described which attempt to identify developmentally regulated androgen-responsive genes. That androgen action can be modulated by gene polymorphisms is illustrated by the influence of an androgen receptor polyglutamine repeat in the multi-factorial causation of less severe forms of male under-masculinization.

Clinical and molecular evidence for the role of androgens and WT1 in testis descent.

Testicular maldescent is a common congenital disorder associated with testicular cancer and infertility. In this study, testis position was assessed in subjects with genital abnormalities due to AR mutations, Denys-Drash and WAGR syndromes or an unknown aetiology. Subjects with completely female genitalia and an AR mutation or an unknown aetiology had a greater proportion of maldescended testes (intra-abdominal and inguinal) than those with less severe abnormalities (P=0.00027 and P<0.000001, respectively). Whereas subjects with severe, moderate or mild abnormalities and an unknown aetiology, had similar testis positions. The Denys-Drash and WAGR syndrome group had a greater proportion of maldescended testes than the AR mutation (P=0.013) and unknown aetiology groups (P=0.00019). Androgen production and AR binding were normal in three subjects with Denys-Drash and WAGR syndromes. These findings indicate that the relationship between testis descent and genital abnormalities is a multi-factorial process with greater complexity than previously proposed.

Evidence that longer androgen receptor polyglutamine repeats are a causal factor for genital abnormalities.

Moderate to severe undermasculinized genitalia was recently shown to be associated with longer polyglutamine repeats within the androgen receptor [AR(Gln)n]. However, it was unknown whether this was because longer AR(Gln)n contributed to the: 1) etiology; 2) severity; and/or 3) testicular maldescent. Therefore, AR(Gln)n length in 175 males with abnormal genitalia were analyzed according to etiology (known or unknown), severity (complete, severe, and moderate), or testis position (abdominal, inguinal, or scrotal). Etiology (P = 0.01) and severity (P = 0.02) but not testis position (P = 0.52) were associated with AR(Gln)n length. The association between the severity of the genital abnormalities and AR(Gln)n length was due to the close association of severity with the etiology (P < 0.0001). A highly selected group with moderate to severe genital abnormalities and multiple criteria to exclude known etiological factors had a greater AR(Gln)n length (mean, 25.33) than all other samples (mean, 23.11; P = 0.0004). The results suggest that AR(Gln)n length does not influence the severity of undermasculinization or testis descent but instead contributes to the causation of genital abnormalities in a subset of patients. These findings, together with a demonstrated relationship between severity and multifactorial etiology, are incorporated into a proposed model for the involvement of AR(Gln)n length in genital abnormalities.

Genetic analysis of the INSL3 gene in patients with maldescent of the testis.

OBJECTIVE: Testicular maldescent is important because it is a common congenital disorder that is associated with an increased risk of infertility and testicular cancer. Murine studies indicate that testicular maldescent can result from disruption of insulin-like factor 3 (INSL3) activity and that it may be more severe when there is concurrent undermasculinisation. Therefore, the INSL3 gene was screened for mutations and polymorphisms that may contribute to testicular maldescent in patients with undermasculinisation as well as those with isolated testicular maldescent. METHODS AND RESULTS: The patient groups consisted of individuals with isolated testicular maldescent (n=28) and patients with undermasculinised genitalia and intra-abdominal (n=24) or inguinal gonads (n=33). The three control groups were: normal males (n=15), males with undermasculinised genitalia and scrotal gonads (n=29) and females (n=82). SSCP/HA mutation screening detected eight variants, five of which were predicted to alter the protein sequence (A-1G, V19L, P25S, A36T, R78H). Three of the amino acid changes (A-1G, V19L, R78H) each occurred in a single control sample and one was identified in a male with undermasculinised genitalia and intra-abdominal testes (P25S). The A36T amino acid polymorphism was found in both patient and control groups at a similar frequency. CONCLUSIONS: The evidence suggests that INSL3 mutations and polymorphisms are not a major cause of testicular maldescent with or without associated undermasculinisation.