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Caffeine is a major component of xanthine alkaloids and commonly consumed in many popular beverages. Due to its occasional side effects, reduction of caffeine in a natural way is of great importance and economic significance. Recent studies reveal that caffeine can be converted into non-stimulatory theacrine in the rare tea plant Camellia assamica var. kucha (Kucha), which involves oxidation at the C8 and methylation at the N9 positions of caffeine. However, the underlying molecular mechanism remains unclear. Here, we identify the theacrine synthase CkTcS from Kucha, which possesses novel N9-methyltransferase activity using 1,3,7-trimethyluric acid but not caffeine as a substrate, confirming that C8 oxidation takes place prior to N9-methylation. The crystal structure of the CkTcS complex reveals the key residues that are required for the N9-methylation, providing insights into how caffeine N-methyltransferases in tea plants have evolved to catalyze regioselective N-methylation through fine tuning of their active sites. These results may guide the future development of decaffeinated drinks.

An electrochemical sensor is described for simultaneous voltammetric determination of dopamine (DA) and uric acid (UA). It is based on the use of a nanomaterial composed of gold nanoparticles and 3-dimensional graphene (Au NP@3D GR). The 3D GR was prepared by chemical vapor deposition using nickel nanoparticles as the template at a temperature of around 900 °C. The surface of 3D GR contains oxygen-functional groups after treatment with acid. Carboxylated Au NP were self-assembled and anchored onto the surface of 3D GR. The nanomaterial was placed on a ITO electrode. The few-layer graphene on the ITO glass has a porous structure and the distribution of Au NP is uniform. The electrode shows a high sensitivity and a low detection limit for DA and UA. Figures of merit include detection limits of 0.1 M for DA and of 0.1 μM for UA, and well separated peaks at potentials of 0.18 and 0.30 V (vs. Ag/AgCl), respectively, at pH 7.0. The electrode has good repeatability and stability. Graphical abstract Carboxylated gold nanoparticles were self-assembled and immobilized on 3-dimensional graphene by chemical vapor deposition for simultaneous determination of dopamine (DA) and uric acid (UA).

A three-dimensional (3D) continuous and interconnected network graphene foam (GF) was synthesized by chemical vapor deposition using nickel foam as a template. The morphologies of the GF were observed by scanning electron microscopy. X-ray diffraction and Raman spectroscopy were used to investigate the structure of GF. The graphene with few layers and defect free was closely coated on the backbone of the 3D nickel foam. After etching nickel, the GF was transferred onto indium tin oxide (ITO) glass, which acted as an electrode to detect uric acid using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The GF/ITO electrode showed a high sensitivity for the detection of uric acid: approximately 9.44 mA mM(-1) in the range of 25 nM-0.1 μM and 1.85 mA mM(-1) in the range of 0.1-60 μM. The limit of detection of GF/ITO electrode for uric acid is 3 nM. The GF/ITO electrode also showed a high selectivity for the detection of uric acid in the presence of ascorbic acid. This electrode will have a wide range of potential application prospects in electrochemical detection., (Copyright © 2015. Published by Elsevier Inc.)

Aimei Wu,2,* Xinyi Chen,6,7 Xiaoying Meng,2 Qianyun Zhang,2 Zheng Tan,2 Hong Yue,2 Juncang Wu1,21Department of Neurology, Hefei Second People's Hospital Affiliated to Bengbu Medical University, Hefei, Anhui, 230011, People's Republic of China; 2Department of Neurology, Hefei Second People's Hospital, Hefei, Anhui, 230011, People's Republic of China; 3Department of Neurology, The First Affiliated Hospital of Anhui Medical University, Hefei, People's Republic of China; 4Anhui Province Key Laboratory of Cognition and Neuropsychiatric Disorders, Hefei, People's Republic of China; 5Collaborative Innovation Centre of Neuropsychiatric Disorder and Mental Health, Hefei, 230000, People's Republic of China; 6Department of Neurology, Hefei Hospital Affiliated to Anhui Medical University (Hefei Second People's Hospital), Hefei, Anhui, 230011, People's Republic of China; 7The Fifth Clinical School of Medicine, Anhui Medical University, Hefei, Anhui, 230011, People's Republic of China *These authors contributed equally to this work Correspondence: Juncang Wu; Hong Yue, Intersection of Guangde Road and Leshui Road, Hefei, Anhui, 230011, People's Republic of China, Tel/Fax +86 551 13956076148 ; +86 551 18949855780, Email [email protected] ; [email protected] Background and Purpose: The role of serum uric acid (UA) level in patients suffering from stroke remains controversial. Our aim was to investigate the effect of UA level on clinical outcomes in patients with intracerebral hemorrhage (ICH). Methods: In the retrospective cohort study, we analyzed data from 250 patients with intracerebral hemorrhage (85 women and 165 men) to investigate the difference in UA levels between patients with a good prognosis and those with a poor prognosis. Additionally, we analyzed the impact of UA levels on the risk of short-time prognosis of ICH patients. Results: Patients with a good prognosis presented with significantly lower levels of UA (348.71 ± 84.97 μmol/L) than those with poor prognosis (393.06 ± 148.46 μmol/L). Furthermore, multivariate logistic regression model demonstrated that a high UA level was a likely risk factor for worse prognosis among patients suffering in ICH (odds ratio [95% confidence interval], 1.006 [1.0012, 1.0108]; P = 0.015). Additionally, UA has a threshold effect value of 363.9 μmol/L and was presented in levels that were in a nonlinear relationship with incidence rate of short-time prognosis outcome of ICH patients. Conclusion: Our findings indicate that higher UA levels can increase the risk of poor clinical prognosis in patients with ICH and high UA levels are not conductive to the clinical prognosis of patients with ICH. These findings provide a new perspective on the treatment and prevention of ICH. [ABSTRACT FROM AUTHOR]

Nickel foam (NF) was used as sacrificial template to synthesize graphene foam (GF) by chemical vapor deposition (CVD). ZnO NSAs were grown on the GF by hydrothermal synthesis to fabricate ZnO NSA/GF, which was used to detect dopamine in the presence of ascorbic acid and uric acid. The inter-connected ZnO NSAs with the sheet size of ~ 10 μm and thickness of ~ 500 nm uniformly distributed on the GF. The ZnO NSA/GF shows a sensitivity of 0.95 μA μM−1 in the concentration range of 0–80 μM and a measured limit of detection of 1 μM for determination of dopamine. Furthermore, the prepared electrode displays a reliable anti-interference to ascorbic acid and uric acid. It also shows an excellent reproducibility and long-time stability. The ZnO NSA/GF electrode was applied in human urine samples and exhibited satisfied recoveries. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide nanosheet arrays/carbon nanofibers (MoS2 NSA/CNFs) were synthesized by electrospinning and hydrothermal synthesis. Scanning electron microscopy and X-ray diffraction analysis were used to characterize the morphology and structure of the MoS2 NSA/CNFs composite. Using MoS2 NSA/CNFs as a working electrode, the electrochemical properties of the electrode for the detection of levodopa (LD) and uric acid (UA) were determined by cyclic voltammetry and differential pulse voltammetry. The sensitivity of the electrode for the detection of LD and UA is 0.91 and $0.73\,\,\mu \text{A}\cdot \mu \text{M}^{-1}$ in the range of 1–60 $\mu \text{M}$ , respectively, and the electrode exhibits an excellent repeatability and stability. So, MoS2 NSA/CNFs electrode can be used in the electrochemical biosensor for the detection of LD and UA. [ABSTRACT FROM AUTHOR]

Spherical nickel nanoparticles were prepared by an N 2 H 4 -based solution reduction route. Then, graphene was deposited on the template of nickel nanoparticles by chemical vapor deposition (CVD) at a high temperature. After etching nickel, small-sized, porous and free-standing 3D graphene foam (3D GF) was obtained. It was transferred on the indium tin oxide (ITO) glass (3D GF/ITO) for electrochemical determination of levodopa in the presence/absence of uric acid. The results show that the pore size of the 3D GF is ~1 μm. The electrode shows a high sensitivity of 0.24 μA·μM−1 for the detection of levodopa. The electrode also shows a low measured limit of detection, superior selectivity, reproducibility and stability. Meanwhile, it shows a great potential in the clinical application. • Nickel nanoparticles were prepared using a N 2 H 4 -based solution reduction route. • A novel 3D porous graphene foam (GF) was prepared by chemical vapor deposition using the template of nickel nanoparticles. • 3D GF has an interconnected structure with a small pore diameter of ~1 μm. • The 3D GF shows a high sensitivity of 0.24 μA·μM−1 for the determination of levodopa. • The 3D GF also shows a low measured limit of detection, excellent selectivity and stability. [ABSTRACT FROM AUTHOR]

ZnO nanoflowers (ZnO NFs) were prepared by hydrothermal synthesis and graphene oxide nanosheets (GO NSs) were synthesized by the Hummer's method. Then, ZnO NFs were dispersed in GO dispersion and sprayed onto ITO-coated glass. Finally, the ZnO NFs-GO NSs/ITO was annealed to form the ZnO NFs-rGO NSs/ITO, acting as the electrode for the determination of levodopa (LD) under the interference of uric acid (UA). The results reveal that the ZnO NFs are made up of nanorods with the diameter of ∼ 150 nm and the length of ∼ 2 µm and ZnO NFs are covered by rGO NSs. The ZnO NFs-rGO NSs/ITO electrode exhibits an enhanced electrochemical response due to its excellent redox activity, which shows a high sensitivity (0.66 µA µM−1), low measured detection limit (1 µM) and excellent selectivity for determination of LD. The electrode was used to detect the LD in the actual sample of human serum for practical application, revealing satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract An electrochemical dopamine (DA) sensor was developed based on WS 2 nanospheres-carbon nanofibers (WS 2 NSs-CNFs) electrode. Carbon nanofibers (CNFs) were synthesized by electrospinning and then WS 2 nanospheres (WS 2 NSs) were grown on the CNFs by a hydrothermal process. The WS 2 NSs-CNFs composite was used for electrochemical detection of DA in the presence/absence of uric acid. The results show that sugar-gourd shaped WS 2 NSs are grown dispersedly on the surface of CNFs. The sensitivity of WS 2 NSs-CNFs electrode for DA is 5.36 μA·μM−1·cm−2 in the concentration range of 0.5–60 μM and the limit of detection (LOD) is 0.01 μM. Moreover, the electrode also exhibits good selectivity, reproducibility and stability. The WS 2 NSs-CNFs electrode was also employed for analysis of the biomolecular content in human urine, exhibiting desirable results. Graphical abstract Unlabelled Image Highlights • The CNFs were prepared by electrospinning. • WS 2 nanospheres-carbon nanofibers (WS 2 NSs-CNFs) were prepared by a facile hydrothermal process. • The WS 2 NSs-CNFs demonstrates a high sensitivity (5.36 μA·μM−1·cm−2) and a low limit of detection (0.01 μM) for dopamine (DA). • The WS 2 NSs-CNFs can selectively and accurately detect DA in the presence of UA. [ABSTRACT FROM AUTHOR]

ZnO nanoflowers (ZnONFs) were synthesized by a simple hydrothermal method. Then, ZnONFs suspension was sprayed onto the indium tin oxide coated glass. Finally, graphene was deposited on the surface of ZnONFs (graphene/ZnONFs) by chemical vapor deposition, which is used to electrochemically determine levodopa in the presence of uric acid. The results show that the length and diameter of ZnONFs are ∼ 2.5 µm and 50 nm, respectively. Graphene with multi-layers and some defects are deposited on the surface of ZnONFs. The sensitivity and measured limit of detection of the graphene/ZnONFs for levodopa are 0.32 µA µM−1 and 1 µM in the range of 1-60 µM, respectively. The graphene/ZnONFs also show good selectivity, repeatability and stability for the determination of levodopa. The proposed electrode is also successfully used to determine levodopa in human urine samples and it is potential for use in clinical research. [ABSTRACT FROM AUTHOR]

Nickel nanoparticles (Ni-NPs) were synthesized by the reduction reaction of NiCl2·6H2O, N2H4·H2O and NaOH, and then the graphene layers were coated on the surface of Ni-NPs by the carbide cladding method while triethylene glycol was used as carbon source. After etching Ni, the obtained 3D hollow graphene balls (HGBs) were sprayed onto the ITO coated glass to fabricate 3D HGBs/ITO electrode, which acted as a working electrode for determining dopamine and uric acid simultaneously. The results indicate that the multi-layered 3D HGBs maintain the original size of Ni-NPs (the diameter of ~ 100 nm) and have few defects. The 3D HGBs/ITO electrode exhibits a high sensitivity of 1.16 and 0.94 μA μM− 1 for detecting dopamine and uric acid, respectively. Also, it shows a low measured limit of detection, excellent selectivity, reproducibility and stability. It is potential for use in clinical research. [ABSTRACT FROM AUTHOR]

MoS2 nanoflakes were prepared by exfoliating commercial MoS2 powders with the assistance of ultrasound and graphene foam was synthesized by chemical vapor deposition using nickel foam as the template. MoS2-graphene hybrid nanosheets were developed through the combination of MoS2 nanoflakes and graphene nanosheets by ultrasonic dispersion. The hybrid nanosheets were sprayed onto the ITO coated glass, which acts as an electrode for the simultaneously electrochemical determination of levodopa and uric acid. The MoS2-graphene hybrid nanosheets were characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The results show that the hybrid nanosheets are composed of MoS2 and graphene with a sheet-like morphology. The sensitivity of the electrode for levodopa and uric acid is 0.36 μA μM−1 and 0.39 μA μM−1, respectively. The electrode also shows low limit of detection, good selectivity, reproducibility and stability. And it is potential for use in clinical research. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) graphene foam (GF) was prepared by chemical vapor deposition (CVD) using nickel foam as the template. ZnO nanowire arrays (ZnO NWAs) were vertically grown on the 3D GF by hydrothermal synthesis to prepare ZnO NWAs/GF. This hybrid combines the properties of ZnO NWAs and 3D GF, which has favorable electrocatalysis and outstanding electrical conductivity. The vertically aligned ZnO NWAs grown on the GF enlarged the electroactive surface area, which was investigated from the Fe ( CN ) 6 3 - 4 + redox kinetic study. The ZnO NWAs/GF was used as an electrochemical electrode for the determination of Levodopa (LD) in the presence of uric acid (UA). The electrochemical responses of the ZnO NWAs/GF electrode were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results show that the sensitivity of the electrode for LD is 3.15 μA μM −1 in the concentration range of 0.05–20 μM and the measured detection limit of the electrode for LD is 50 nM. The electrode also shows good selectivity, reproducibility and stability. The proposed electrode is succsefully used to determine LD in human plasma samples and it is potential for use in clinical research. [ABSTRACT FROM AUTHOR]

Based on the Au nanoparticles-ZnO nanocone arrays/graphene foam electrode, a novel dopamine biosensor was successfully developed. Graphene foam was synthesized by chemical vapor deposition, ZnO nanocone arrays were grown on its surface by a hydrothermal method and Au nanoparticles with carboxyl groups were self-assembled onto the ZnO nanocone arrays to obtain Au nanoparticles-ZnO nanocone arrays/graphene foam electrode. The result indicates that the prepared electrode has a high sensitivity (4.36 μA μM−1) and low limit of detection (0.04 μM, S/N = 3) for the detection of dopamine. The prepared electrode also exhibits an excellent selectivity under the interference of uric acid, good repeatability and stability. The prepared sensor has been successfully applied in real samples and has a great potential to be used in the field of medical and health. Unlabelled Image • A highly sensitive and selective dopamine biosensor based on the Au-ZnO NCAs/GF electrode. • The optimal pH value of PBS solution for detection of DA is 7.5. • The Au-ZnO NCAs/GF electrode shows a high sensitivity of 4.36 μA•μM-1 and lower LOD of 0.04 μM for detection of DA. • The Au-ZnO NCAs/GF electrode also shows an excellent selectivity, reproducibility and stability. [ABSTRACT FROM AUTHOR]

Levodopa and uric acid are important neurotransmitters associated with many neurological diseases. Abnormal concentrations of levodopa and uric acid in biological fluids can be used for the evaluation of such diseases. In this work, three-dimensional graphene foam (3D GF) was prepared by chemical vapor deposition. ZnS nanoparticles were in-situ grown on the surface of 3D GF (ZnS NPs/3D GF) using a simple hydrothermal method, which was used to simultaneously determinate levodopa and uric acid. The results show that a porous mesh film made up of ZnS NPs with the diameter of 200 nm is evenly covered on the surface of 3D GF. The ZnS NPs/3D GF electrode exhibits a high sensitivity of 2.34 and 2.39 μA·μM−1·cm−2 for the detection of levodopa and uric acid, respectively. Also, it shows a low limit of detection, excellent selectivity, good anti-interference ability and stability. Moreover, the electrode was successfully used in human plasma samples. Unlabelled Image • A porous mesh film made up of ZnS nanoparticles is grown on the GF (ZnS NPs/3D GF) by a hydrothermal process. • The ZnS NPs/3D GF demonstrates a high sensitivity and low detection limits for simultaneous detection of levodopa and uric acid. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]