A glassy carbon electrode modified with a nickel(II) norcorrole complex and carbon nanotubes for simultaneous or individual determination of ascorbic acid, dopamine, and uric acid

Ultrasensitive multiwall carbon nanotube-mesoporous MCM-41 hybrid-based platform for the electrochemical detection of ascorbic acid

An ultrasensitive multiwall carbon nanotube-MCM-41 hybrid-based ascorbic acid sensor for electro-detection in real samples is proposed. The MWCNT–MCM-41 hybrid preparation via dispersion was optimized through an experimental design based on CCD/RSM.

A novel strategy for sensitive and rapid detection of ascorbic acid via the Tyndall effect of cobalt hydroxide nanoflakes

Cobalt oxyhydroxide (CoOOH) nanoflakes, as nanoenzymes and fluorescence quenchers, have been widely used in colorimetric and fluorescent analysis. However, their promising light scattering property—the Tyndall effect (TE)—has never been applied in biosensors and biological analysis to date. Herein, we report for the first time a novel strategy for point-of-care detection of ascorbic acid (AA) with the TE of CoOOH nanoflakes providing colorimetric signaling. In this detection system, CoOOH nanoflakes exhibit a strong red TE signal under the illumination of a hand-held 635 nm laser pointer pen. However, the introduction of AA could induce a significant decrease of the TE because it could reduce CoOOH into Co²⁺ and results in the degradation of the CoOOH nanoflakes. The changes in the TE intensity could be read-out using a smartphone for the portable quantitative analysis of AA. The results showed that this CoOOH nanoflake-based TE-inspired assay (TEA) exhibited a good linear range from 0.25 μM to 40 μM for AA, with a detection limit of 12 nM. It also showed high selectivity toward AA over common potential interfering species. Importantly, this method possessed the advantages of simple operation, low consumption of time and equipment-free analysis and was successfully applied to the detection of AA in vitamin C tablets.

A novel colorimetric nanosensor was initially developed for the equipment-free sensitive detection of ascorbic acid based on the Tyndall effect of cobalt hydroxide nanoflakes.

Friedel–Crafts acylation of antiaromatic norcorroles: electronic and steric modulation of the paratropic current

The first ever Friedel–Crafts acylation of an antiaromatic macrocycle was performed for norcorrolatonickel(ii) reacting with aromatic or aliphatic carboxylic acid chlorides in the presence of AlCl₃.

Selective and simultaneous sensing of ascorbic acid, dopamine and uric acid based on nitrogen-doped mesoporous carbon

Development of novel sensing nanostructures for facile, economical and fast applications has attracted more and more interest. Herein, a nitrogen-doped mesoporous carbon (NMC) was synthesized by pyrolyzing a mixture of melamine and carbon black at a low-temperature (600 °C) and exploited for the simultaneous sensing of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The as-made NMC exhibits a rougher surface and smaller size than carbon black. Such a one-pot method is very versatile, quick and inexpensive, easy to handle (solvent-, catalyst-, and template-free) and scalable. The oxidation potentials of the NMC/GCE negatively shift and the current responses are enhanced greatly towards the oxidation of AA, DA and UA thanks to the large surface area, mesoporous structure and N-doped active sites. The peak to peak potential separations are 258 and 410 mV for AA-DA and AA-UA. The linear ranges of AA, DA and UA are 5-4500 μM, 0.005-35 μM and 0.5-3500 μM, respectively, and their detection limits are 0.15 μM (AA), 1.6 nM (DA) and 0.15 μM (UA). Meanwhile, the NMC/GCE exhibits satisfactory stability and anti-interference ability. These results show that NMC could be a promising candidate material for electrochemical sensor construction.

Aptamer based ratiometric electrochemical sensing of 17β-estradiol using an electrode modified with gold nanoparticles, thionine, and multiwalled carbon nanotubes

Gold nanoparticles (AuNPs) with a size of ~3 nm were placed on a thionine-multiwalled carbon nanotube (Thi-CNTs) conjugate to form a novel AuNP-Thi-CNTs nanocomposite. Its morphology and composition were characterized by transmission electron microscopy, atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The nanocomposite was placed on an electrode and used as a redox-active signaling interface to fabricate a ratiometric electrochemical aptasensor for 17β-estradiol (E2). The potentiostatic insertion method was applied to insert an aptamer against E2 into a thin alkane monolayer to warrant an adequate distance between aptamers. The aptamer against E2 acts as both a collector and separator to specifically bind E2. The electrode displays two peak signals (at +0.50 V vs. SCE for E2; and at -0.32 V for Thi) which increase and decrease, respectively, in the 12 pM to 60 nM E2 concentration range. Therefore, the current ratio can be used to reliably, reproducibly, and sensitively quantify the concentration of E2. Graphical abstract Schematic presentation of a novel AuNP-Thi-CNTs nanocomposite. AuNP-Thi-CNTs showed good electrocatalytic oxidation to E2. AuNP-Thi-CNTs was used as self-redox signal interface to fabricate aptasensor. Dual signals of extrinsic E2 and inner Thi was applied to monitor the concentration of E2.

Electrochemical sensor based on a three dimensional nanostructured MoS2 nanosphere-PANI/reduced graphene oxide composite for simultaneous detection of ascorbic acid, dopamine, and uric acid

A three dimensional (3D) nanostructured composite based on the self-assembly of MoS₂ nanospheres and polyaniline (PANI) loaded on reduced graphene oxide (denoted by 3D MoS₂-PANI/rGO) was prepared via a feasible one-pot hydrothermal process. The 3D MoS₂-PANI/rGO nanocomposite not only exhibits good functionality and bioaffinity but also displays high electrochemical catalytic activity. As such, the developed 3D MoS₂-PANI/rGO nanocomposite can be employed as the sensing platform for simultaneously detecting small biomolecules, i.e., ascorbic acid (AA), dopamine (DA), and uric acid (UA). The peak currents obtained from the differential pulse voltammetry (DPV) measurements depended linearly on the concentrations in the wide range from 50 μM to 8.0 mM, 5.0 to 500 μM, and 1.0 to 500 μM, giving low detection limits of 22.20, 0.70, and 0.36 μM for AA, DA, and UA, respectively. Furthermore, the 3D MoS₂-PANI/rGO-based electrochemical sensor also exhibited high selectivity, good reproducibility and stability toward small molecule detection. The present sensing strategy based on 3D MoS₂-PANI/rGO suggests a good reliability in the trace determination of electroactive biomolecules.

A three dimensional (3D) nanostructured composite based on the self-assembly of MoS₂ nanospheres and polyaniline (PANI) loaded on reduced graphene oxide (denoted by 3D MoS₂-PANI/rGO) was prepared via a feasible one-pot hydrothermal process.

Reaction of antiaromatic porphyrinoid with active methylene compounds

Antiaromatic norcorrolatonickel(ii) reacts regioselectively under basic conditions with active methylene compounds, yielding mono-substituted derivatives in which spectroscopic and redox properties of the starting macrocycle are retained.

Sonication-assisted preparation of a nanocomposite consisting of reduced graphene oxide and CdSe quantum dots, and its application to simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid

Cadmium selenide quantum dots were capped with reduced graphene oxide that was modified with thioglycolic acid. The nanocomposite was prepared by 5-min sonication of a solution of graphene oxide, thioglycolic acid, and cadmium(II) nitrate and selenium powder in the presence of NaBH₄. X-ray diffraction and transmission electron microscopy were used to characterize the nanocomposite. A glassy carbon electrode (GCE) was modified with this nanocomposite and used for simultaneous determination of dopamine (DA), ascorbic acid (A) and uric acid (UA). The modified GCE was characterized by using cyclic voltammetry and differential pulse voltammetry. Simultaneous determination of AA, DA and UA was accomplished at working voltages of -50, +148 and + 280 mV (all vs. Ag/AgCl), respectively. The voltammetric response to DA is linear in the 4.9 to 74.0 μM concentration range, and the detection limit (defined as 3σ of the blank) is 0.11 μM. The respective data are 0.39-1.0 mM and 66 μM for AA, and 9.0 to 120.0 μM and 0.12 μM for UA. The electrode was successfully applied to the determination of the 3 species in spiked urine samples. Graphical abstract Graphical abstract contains poor quality of text in image. Otherwise, please provide replacement figure file.Thank you for your comment. New garaphical abstract was attached. A sonochemical method was applied for synthesizing reduced graphene oxide decorated thioglycolic acid capped cadmium selenide quantum dots. A modified glassy carbon electrode was prepared for simultaneous determination of ascorbic acid, dopamine and uric acid.

Advances in the design of nanomaterial-based electrochemical affinity and enzymatic biosensors for metabolic biomarkers: A review

This review (with 340 refs) focuses on methods for specific and sensitive detection of metabolites for diagnostic purposes, with particular emphasis on electrochemical nanomaterial-based sensors. It also covers novel candidate metabolites as potential biomarkers for diseases such as neurodegenerative diseases, autism spectrum disorder and hepatitis. Following an introduction into the field of metabolic biomarkers, a first major section classifies electrochemical biosensors according to the bioreceptor type (enzymatic, immuno, apta and peptide based sensors). A next section covers applications of nanomaterials in electrochemical biosensing (with subsections on the classification of nanomaterials, electrochemical approaches for signal generation and amplification using nanomaterials, and on nanomaterials as tags). A next large sections treats candidate metabolic biomarkers for diagnosis of diseases (in the context with metabolomics), with subsections on biomarkers for neurodegenerative diseases, autism spectrum disorder and hepatitis. The Conclusion addresses current challenges and future perspectives. Graphical abstract This review focuses on the recent developments in electrochemical biosensors based on the use of nanomaterials for the detection of metabolic biomarkers. It covers the critical metabolites for some diseases such as neurodegenerative diseases, autism spectrum disorder and hepatitis.