Brushite nanoparticles based electrochemical sensor for detection of uric acid, xanthine, hypoxanthine and caffeine.

The research in the field of biosensors has recently been focused on the design and development of functional electrode materials that can respond to changes in their biochemical environment. Here, we report the synthesis of dicalcium phosphate dihydrate (DCPD), also known as brushite (CaHPO4·2H2O) by soft chemical method and its application for electrochemical sensing of four different analytes. Phase purity, structure, chemical composition and surface morphology of the synthesized nanoparticles have been investigated using powder XRD, FTIR, SEM, XPS and HRTEM methods. Electrochemical sensor was prepared by modifying GCE with brushite and the modified electrodes were successfully used for either independent or simultaneous determination of uric acid, xanthine, hypoxanthine and caffeine in their mixture. The brushite/GCE exhibited four strong well-defined separate peaks corresponding to the oxidation of UA, XN, HXN and CF in phosphate buffer saline (PBS) at pH 7.4. The fabricated electrode showed low detection limits (S/N = 3) of 0.576, 1.0, 0.076 and 1.26 µM for UA, XN, HXN and CF respectively. Practical application of the fabricated electrode has been demonstrated by determining UA, XN, HXN and CF in human urine and coffee samples by direct method. The brushite offers scope for fabrication of sensor systems for implantable medical applications.

Quantitative Structure-Neurotoxicity Assessment and In Vitro Evaluation of Neuroprotective and MAO-B Inhibitory Activities of Series N'-substituted 3-(1,3,7-trimethyl-xanthin-8-ylthio)propanehydrazides.

The neurotoxic, neuroprotective and MAO-B inhibitory effects of series N'-substituted 3-(1,3,7-trimethyl-xanthin-8-ylthio)propanehydrazides are evaluated. The results indicate compounds N'-(2,3-dimethoxybenzylidene)-3-(1,3,7-trimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-ylthio)propanehydrazide (6k) and N'-(2-hydroxybenzylidene)-3-(1,3,7-trimethyl-2,6-dioxo-2,3,6,7-tetrahydro-1H-purin-8-ylthio)propanehydrazide (6l) as most perspective. The performed QSTR analysis identified that the decreased lipophilicity and smaller dipole moments of the molecules are the structural features ensuring lower neurotoxicity. The obtained results may be used as initial information in the further design of (xanthinyl-8-ylthio)propanhydrazides with potential hMAOB inhibitory effect and pronounced neuroprotection.

Structure-Based Design of Xanthine-Benzimidazole Derivatives as Novel and Potent Tryptophan Hydroxylase Inhibitors.

Tryptophan hydroxylases catalyze the first and rate-limiting step in the synthesis of serotonin. Serotonin is a key neurotransmitter in the central nervous system and, in the periphery, functions as a local hormone with multiple physiological functions. Studies in genetically altered mouse models have shown that dysregulation of peripheral serotonin levels leads to metabolic, inflammatory, and fibrotic diseases. Overproduction of serotonin by tumor cells causes severe symptoms typical for the carcinoid syndrome, and tryptophan hydroxylase inhibitors are already in clinical use for patients suffering from this disease. Here, we describe a novel class of potent tryptophan hydroxylase inhibitors, characterized by spanning all active binding sites important for catalysis, specifically those of the cosubstrate pterin, the substrate tryptophan as well as directly chelating the catalytic iron ion. The inhibitors were designed to efficiently reduce serotonin in the periphery while not passing the blood-brain barrier, thus preserving serotonin levels in the brain.

Initiation of cytosolic plant purine nucleotide catabolism involves a monospecific xanthosine monophosphate phosphatase.

In plants, guanosine monophosphate (GMP) is synthesized from adenosine monophosphate via inosine monophosphate and xanthosine monophosphate (XMP) in the cytosol. It has been shown recently that the catabolic route for adenylate-derived nucleotides bifurcates at XMP from this biosynthetic route. Dephosphorylation of XMP and GMP by as yet unknown phosphatases can initiate cytosolic purine nucleotide catabolism. Here we show that Arabidopsis thaliana possesses a highly XMP-specific phosphatase (XMPP) which is conserved in vascular plants. We demonstrate that XMPP catalyzes the irreversible entry reaction of adenylate-derived nucleotides into purine nucleotide catabolism in vivo, whereas the guanylates enter catabolism via an unidentified GMP phosphatase and guanosine deaminase which are important to maintain purine nucleotide homeostasis. We also present a crystal structure and mutational analysis of XMPP providing a rationale for its exceptionally high substrate specificity, which is likely required for the efficient catalysis of the very small XMP pool in vivo.

Xanthine Derivatives Reveal an Allosteric Binding Site in Methylenetetrahydrofolate Dehydrogenase 2 (MTHFD2).

Methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) plays an important role in one-carbon metabolism. The MTHFD2 gene is upregulated in various cancers but very low or undetectable in normal proliferating cells, and therefore a potential target for cancer treatment. In this study, we present the structure of MTHFD2 in complex with xanthine derivative 15, which allosterically binds to MTHFD2 and coexists with the substrate analogue. A kinetic study demonstrated the uncompetitive inhibition of MTHFD2 by 15. Allosteric inhibitors often provide good selectivity and, indeed, xanthine derivatives are highly selective for MTHFD2. Moreover, several conformational changes were observed upon the binding of 15, which impeded the binding of the cofactor and phosphate to MTHFD2. To the best of our knowledge, this is the first study to identify allosteric inhibitors targeting the MTHFD family and our results would provide insights on the inhibition mechanism of MTHFD proteins and the development of novel inhibitors.

Plumbagin can potently enhance the activity of xanthine oxidase: in vitro, in vivo and in silico studies.

BACKGROUND: Abnormally elevated xanthine oxidase (XO) activity has been verified to cause various pathological processes, such as gout, oxidative stress injury and metabolic syndrome. Thus, XO activators may exhibit above potential toxicological properties. Plumbagin (PLB) is an important active compound in traditional Chinese medicine (TCM), while its obvious toxic effects have been reported, including diarrhea, skin rashes and hepatic toxicity. However, the potential toxicity associated with enhancement of XO activity has not been fully illuminated so far. METHODS: The present study investigated the effect of PLB on XO activity by culturing mouse liver S9 (MLS9), human liver S9 (HLS9), XO monoenzyme system with PLB and xanthine. Then, the molecular docking and biolayer interferometry analysis were adopted to study the binding properties between PLB and XO. Finally, the in vivo acceleration effect also investigated by injected intraperitoneally PLB to KM mice for 3 days. RESULTS: PLB could obviously accelerate xanthine oxidation in the above three incubation systems. Both the Vmax values and intrinsic clearance values (CLint, Vmax/Km) of XO in the three incubation systems increased along with elevated PLB concentration. In addition, the molecular docking study and label-free biolayer interferometry assay displayed that PLB was well bound to XO. In addition, the in vivo results showed that PLB (2 and 10 mg/kg) significantly increased serum uric acid levels and enhanced serum XO activity in mice. CONCLUSION: In summary, this study outlines a potential source of toxicity for PLB due to the powerful enhancement of XO activity, which may provide the crucial reminding for the PLB-containing preparation development and clinical application.

Insights into xanthine riboswitch structure and metal ion-mediated ligand recognition.

Riboswitches are conserved functional domains in mRNA that mostly exist in bacteria. They regulate gene expression in response to varying concentrations of metabolites or metal ions. Recently, the NMT1 RNA motif has been identified to selectively bind xanthine and uric acid, respectively, both are involved in the metabolic pathway of purine degradation. Here, we report a crystal structure of this RNA bound to xanthine. Overall, the riboswitch exhibits a rod-like, continuously stacked fold composed of three stems and two internal junctions. The binding-pocket is determined by the highly conserved junctional sequence J1 between stem P1 and P2a, and engages a long-distance Watson-Crick base pair to junction J2. Xanthine inserts between a G-U pair from the major groove side and is sandwiched between base triples. Strikingly, a Mg2+ ion is inner-sphere coordinated to O6 of xanthine and a non-bridging oxygen of a backbone phosphate. Two further hydrated Mg2+ ions participate in extensive interactions between xanthine and the pocket. Our structure model is verified by ligand binding analysis to selected riboswitch mutants using isothermal titration calorimetry, and by fluorescence spectroscopic analysis of RNA folding using 2-aminopurine-modified variants. Together, our study highlights the principles of metal ion-mediated ligand recognition by the xanthine riboswitch.

Development and Application of Subtype-Selective Fluorescent Antagonists for the Study of the Human Adenosine A1 Receptor in Living Cells.

The adenosine A1 receptor (A1AR) is a G-protein-coupled receptor (GPCR) that provides important therapeutic opportunities for a number of conditions including congestive heart failure, tachycardia, and neuropathic pain. The development of A1AR-selective fluorescent ligands will enhance our understanding of the subcellular mechanisms underlying A1AR pharmacology facilitating the development of more efficacious and selective therapies. Herein, we report the design, synthesis, and application of a novel series of A1AR-selective fluorescent probes based on 8-functionalized bicyclo[2.2.2]octylxanthine and 3-functionalized 8-(adamant-1-yl) xanthine scaffolds. These fluorescent conjugates allowed quantification of kinetic and equilibrium ligand binding parameters using NanoBRET and visualization of specific receptor distribution patterns in living cells by confocal imaging and total internal reflection fluorescence (TIRF) microscopy. As such, the novel A1AR-selective fluorescent antagonists described herein can be applied in conjunction with a series of fluorescence-based techniques to foster understanding of A1AR molecular pharmacology and signaling in living cells.

Convenient synthesis of three-dimensional hierarchical CuS@Pd core-shell cauliflowers decorated on nitrogen-doped reduced graphene oxide for non-enzymatic electrochemical sensing of xanthine.

A novel hybrid with three-dimensional (3D) hierarchical CuS@Pd core-shell cauliflowers decorated on nitrogen-doped reduced graphene oxide (CuS@Pd/N-RGO) has been prepared by a facile wet-chemical route without utilizing any template molecules and surfactants. The characterization results reveal that the 3D flower-like structure of CuS "core" is composed of interconnecting nanoplates, which is conductive to the loading of Pd nanoparticles' "shell" and results in the robust interaction between the core and shell for the formation of CuS@Pd cauliflowers. Anchoring such appealing CuS@Pd cauliflowers on the two-dimensional N-RGO can efficaciously inhibit the aggregation of CuS@Pd cauliflowers and accelerate the kinetics of xanthine oxidation. Benefiting from the multi-functional properties and unique morphology, the sensor constructed by CuS@Pd/N-RGO exhibits excellent performance for non-enzymatic detection of xanthine including a wide detection range of 0.7-200.0 µM (0.94 V vs. SCE), a low detection limit of 28 nM (S/N = 3), high reproducibility (relative standard deviation (RSD) = 4.1%), and commendable stability (retained 90% of the initial electrochemical responses after storage for 30 days), which is amongst the best of various electrochemical sensors reported for xanthine assays till date. Reliable and satisfying recoveries (95-105%, RSD ≤ 4.1%) are achieved for xanthine detection in real samples. The inspiring results make the uniquely structural CuS@Pd/N-RGO greatly promising in non-enzymatic electrochemical sensing applications. Graphical abstract A high-performance non-enzymatic xanthine sensor has been constructed by the three-dimensional hierarchical CuS@Pd core-shell cauliflowers decorated on nitrogen-doped reduced graphene oxide.

Monodispersed gold nanoparticles entrapped in ordered mesoporous carbon/silica nanocomposites as xanthine oxidase mimic for electrochemical sensing of xanthine.

Monodispersed Au nanoparticles in ordered mesoporous carbon/silica (Au/OMCS) nanocomposites were prepared by the solvent evaporation induced self-assembly. Au/OMCS nanocomposites were characterized through XRD, BET, and TEM. The obtained nanocomposites exhibit uniform mesopores with the size of 18 ± 2 nm. And ultrafine Au nanoparticles with the size of 3~7 nm are well dispersed in the cavities. An ultrasensitive nanoenzyme sensor was fabricated based on a Au/OMCS-modified electrode. The Au/OMCS-modified electrode displays high xanthine oxidase-like catalytic activity evaluated through cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The DPV response currents are linearly dependent on concentrations of xanthine (Xa) in the range 0.10-20 µM, along with a high sensitivity of 6.84 µA µM-1 cm-2 and very low detection limit of 0.006 µM (S/N = 3) under the optimal working potential of 0.64 V vs. SCE. Interference experiments show that the nanoenzyme sensor has no obvious responses to most potentially interfering species at a potential of 0.64 V. The fabricated sensor has been applied to the determination of Xa in spiked urine samples with recoveries ranging from 98.26 to 101.4%. Graphical abstract.

Inhibition of Xanthine Oxidase-Catalyzed Xanthine and 6-Mercaptopurine Oxidation by Flavonoid Aglycones and Some of Their Conjugates.

Flavonoids are natural phenolic compounds, which are the active ingredients in several dietary supplements. It is well-known that some flavonoid aglycones are potent inhibitors of the xanthine oxidase (XO)-catalyzed uric acid formation in vitro. However, the effects of conjugated flavonoid metabolites are poorly characterized. Furthermore, the inhibition of XO-catalyzed 6-mercaptopurine oxidation is an important reaction in the pharmacokinetics of this antitumor drug. The inhibitory effects of some compounds on xanthine vs. 6-mercaptopurine oxidation showed large differences. Nevertheless, we have only limited information regarding the impact of flavonoids on 6-mercaptopurine oxidation. In this study, we examined the interactions of flavonoid aglycones and some of their conjugates with XO-catalyzed xanthine and 6-mercaptopurine oxidation in vitro. Diosmetin was the strongest inhibitor of uric acid formation, while apigenin showed the highest effect on 6-thiouric acid production. Kaempferol, fisetin, geraldol, luteolin, diosmetin, and chrysoeriol proved to be similarly strong inhibitors of xanthine and 6-mercaptopurine oxidation. While apigenin, chrysin, and chrysin-7-sulfate were more potent inhibitors of 6-mercaptopurine than xanthine oxidation. Many flavonoids showed similar or stronger (even 5- to 40-fold) inhibition of XO than the positive control allopurinol. Based on these observations, the extremely high intake of flavonoids may interfere with the elimination of 6-mercaptopurine.

Honey as Source of Nitrogen Compounds: Aromatic Amino Acids, Free Nucleosides and Their Derivatives.

The content of selected major nitrogen compounds including nucleosides and their derivatives was evaluated in 75 samples of seven varieties of honey (heather, buckwheat, black locust, goldenrod, canola, fir, linden) by targeted ultra-high performance liquid chromatography-diode array detector - high-resolution quadrupole time-of-flight mass spectrometry (UHPLC-DAD-QqTOF-MS) and determined by UHPLC-DAD. The honey samples contained nucleosides, nucleobases and their derivatives (adenine: 8.9 to 18.4 mg/kg, xanthine: 1.2 to 3.3 mg/kg, uridine: 17.5 to 51.2 mg/kg, guanosine: 2.0 to 4.1 mg/kg; mean amounts), aromatic amino acids (tyrosine: 7.8 to 263.9 mg/kg, phenylalanine: 9.5 to 64.1 mg/kg; mean amounts). The amounts of compounds significantly differed between some honey types. For example, canola honey contained a much lower amount of uridine (17.5 ± 3.9 mg/kg) than black locust where it was most abundant (51.2 ± 7.8 mg/kg). The presence of free nucleosides and nucleobases in different honey varieties is reported first time and supports previous findings on medicinal activities of honey reported in the literature as well as traditional therapy and may contribute for their explanation. This applies, e.g., to the topical application of honey in herpes infections, as well as its beneficial activity on cognitive functions as nootropic and neuroprotective, in neuralgia and is also important for the understanding of nutritional values of honey.

The optimization of xanthine derivatives leading to HBK001 hydrochloride as a potent dual ligand targeting DPP-IV and GPR119.

A series of xanthine compounds derived from the previous hit 20i with modification on the terminal side chain was discovered through ring formation strategy. Systematic optimization of the compounds with rigid heterocycles in the hydrophobic side chain led to the new lead compound HBK001 (21h) with the improved DPP-IV inhibition and moderate GPR119 agonism activity in vitro. As a continuing work to further study the PK and PD profiles, 21h and its hydrochloride (22) were synthesized on grams scale and evaluated on the ADME/T and oral glucose tolerance test (OGTT) in ICR mice. Compound 22 showed the improved bioavailability and blood glucose-lowering effect in vivo compared to its free base 21h probably attributed to its improved solubility and permeability. The preliminary toxicity studies on compound 22 exhibited that the result of mini-Ames was negative and the preliminary acute toxicity LD50 in mice was above 1.5 g/kg, while it showed moderate inhibition on hERG channel with IC50 4.9 µM maybe due to its high lipophilicity. These findings will be useful for the future drug design for more potent and safer dual ligand targeting DPP-IV and GPR119 for the treatment of diabetes.

XANTHINE NEPHROLITHIASIS IN JUVENILE CAPTIVE GIANT OTTERS (PTERONURA BRASILIENSIS).

Nephrolithiasis has been reported in several aquatic mammals including bottlenose dolphins (Tursiops truncatus), small clawed otters (Amblonyx cinereus), European river otters (Lutra lutra), North American river otters (Lontra canadensis), northern elephant seals (Mirounga angustirostris), Florida manatees (Trichechus manatus latirostris), and California sea lions (Zalophus californianus). Compositions of calculi in previous cases were predominantly calcium oxalate or ammonium acid urate. Xanthine urolithiasis is rare in veterinary medicine. Primary cases (without exposure to xanthine dehydrogenase inhibitors) occur as a consequence of hereditary xanthinuria, although the causal mutation has only been discovered in a subset of cases. Five captive juvenile giant otters (Pteronura brasiliensis) from two facilities were diagnosed with nephrolithiasis: three siblings from one set of parents and two siblings from another pair. Serum analyte assays revealed renal compromise in affected individuals. Computed tomography (CT) confirmed the presence of nephrolithiasis in one individual. Postmortem evaluation identified extensive bilateral nephrolithiasis on gross necropsy in four of five cases. Calculus analyses identified 100% xanthine composition. Histologic examination revealed marked nephrolithiasis with associated tubular necrosis and gastric mineralization. Nutrient composition of the diet including mineral and purine content was assessed. No association between diet and nephroliths was found in this study. This is the first report of xanthine nephrolithiasis in aquatic mammals. The potential role of diet and genetics in xanthine nephrolithiasis in the small inbred population of giant otters under human care needs further investigation to assess the implications of this disease process for the long-term captive management of this species.

Efficacy of chalcone and xanthine derivatives on lipase inhibition: A systematic review.

Losing weight has significant impact on chronic disease management. Orlistat, a lipase inhibitor, has alternative effect for weight controlling. To find more candidates, we conducted a review of chalcone and xanthine derivatives regarding their anti-lipase activity. Eight databases were searched including PubMed, Scopus, Web of Science (ISI), Virtual Health Library (VHL), System for Information on Grey Literature in Europe (SIGLE), Global Health Library (GHL), EMBASE, and Google Scholar in August 2018. We found chalcone scaffold was more effective on lipase inhibition than xanthine scaffold. Among 19 investigated chalcones, only isoliquiritigenin and licuroside demonstrated an effect on preventing weight gain and increase in the total cholesterol and total triglycerides aside apart from their high activity on inhibiting lipase. Effect and type of inhibition of individual chalcones differed depending on their structure. In addition, very few studies investigated xanthine compounds and their activities were inconsistent. We suggest more studies investigate the ability of chalcones and modifying their structure to find out other compounds with higher efficacy.

Independent association of plasma xanthine oxidoreductase activity with serum uric acid level based on stable isotope-labeled xanthine and liquid chromatography/triple quadrupole mass spectrometry: MedCity21 health examination registry.

Background We developed a novel high-sensitive assay for plasma xanthine oxidoreductase (XOR) activity that is not affected by the original serum uric acid level. However, the association of plasma XOR activity with that level has not been fully examined. Methods This cross-sectional study included 191 subjects (91 males, 100 females) registered in the MedCity21 health examination registry. Plasma XOR activity was determined using our assay for plasma XOR activity with [13C2,15N2] xanthine and liquid chromatography/triple quadrupole mass spectrometry. Serum levels of uric acid and adiponectin, and visceral fat area (VFA) obtained by computed tomography were measured, and insulin resistance was determined based on the homeostasis model assessment (HOMA-IR) index. Results The median values for uric acid and plasma XOR activity were 333 µmol/L and 26.1 pmol/h/mL, respectively. Multivariable linear regression analysis showed a significant and positive association of serum uric acid level (coefficient: 26.503; 95% confidence interval: 2.06, 50.945; p = 0.035) with plasma XOR activity independent of VFA and HOMA-IR, and also age, gender, alcohol drinking habit, systolic blood pressure, estimated glomerular filtration rate (eGFR), glycated hemoglobin A1c, triglyceride, and adiponectin levels. The "gender*XOR activity" interaction was not significant (p = 0.91), providing no evidence that gender modifies the relationship between plasma XOR activity and serum uric acid level. Conclusions Plasma XOR activity was found to be positively associated with serum uric acid level independent of other known confounding factors affecting that level, including gender difference, eGFR, adiponectin level, VFA, and HOMA-IR.

Influence of binding affinity and blood plasma level on cerebral pharmacokinetics and PET imaging characteristics of two novel xanthine PET radioligands for the A1 adenosine receptor.

INTRODUCTION: The suitability of novel positron emission tomography (PET) radioligands for quantitative in vivo imaging is affected by various physicochemical and pharmacological parameters. In this study, the combined effect of binding affinity, lipophilicity, protein binding and blood plasma level on cerebral pharmacokinetics and PET imaging characteristics of three xanthine-derived A1 adenosine receptor (A1AR) radioligands was investigated in rats. METHODS: A comparative evaluation of two novel cyclobutyl-substituted xanthine derivatives, 8-cyclobutyl-3-(3-[18F]fluoropropyl)-1-propylxanthine ([18F]CBX) and 3-(3-[18F]fluoropropyl)-8-(1-methylcyclobutyl)-1-propylxanthine ([18F]MCBX), with the reference A1AR radioligand 8-cyclopentyl-3-(3-[18F]fluoropropyl)-1-propylxanthine ([18F]CPFPX) was conducted. This evaluation included in vitro competition binding assays, in vitro autoradiography and in vivo PET imaging. Differences in cerebral pharmacokinetics and minimal scan duration required for quantification of cerebral distribution volume (VT) were assessed. RESULTS: Measured Ki values of non-labeled CBX, MCBX and CPFPX were 10.0 ± 0.52 nM, 3.3 ± 0.30 nM and 1.4 ± 0.15 nM, respectively (n = 3-4). In vitro autoradiographic binding patterns in rat brain were comparable between the radioligands, as well as the fraction of non-specific binding (1.0-1.9%). In vivo cerebral pharmacokinetics of the novel cyclobutyl-substituted xanthines differed considerably from that of [18F]CPFPX. Brain uptake and VT of [18F]CBX were substantially lower despite the higher concentration of radiotracer in plasma. [18F]MCBX showed comparable uptake and VT, but faster cerebral kinetics than [18F]CPFPX. However, the faster kinetics of [18F]MCBX did not enable the quantification of cerebral VT in a shorter scan time. CONCLUSIONS: The combined effect of individual physicochemical and pharmacological properties of a radiotracer on its PET imaging characteristics cannot be readily predicted. In vivo performance of the xanthine A1AR radioligands was mainly influenced by binding affinity; plasma concentrations and cerebral kinetics were of secondary importance.

Nucleobase synthesis in interstellar ices.

The synthesis of nucleobases in natural environments, especially in interstellar molecular clouds, is the focus of a long-standing debate regarding prebiotic chemical evolution. Here we report the simultaneous detection of all three pyrimidine (cytosine, uracil and thymine) and three purine nucleobases (adenine, xanthine and hypoxanthine) in interstellar ice analogues composed of simple molecules including H2O, CO, NH3 and CH3OH after exposure to ultraviolet photons followed by thermal processes, that is, in conditions that simulate the chemical processes accompanying star formation from molecular clouds. Photolysis of primitive gas molecules at 10 K might be one of the key steps in the production of nucleobases. The present results strongly suggest that the evolution from molecular clouds to stars and planets provides a suitable environment for nucleobase synthesis in space.

In-situ reduction of Ag+ on black phosphorene and its NH2-MWCNT nanohybrid with high stability and dispersibility as nanozyme sensor for three ATP metabolites.

The environmental stability, water-processibility and life-span of black phosphorene (BP) severely limit the application of its electronic devices in aqueous system containing oxygen. We reported the controllable preparation of in-situ reduction and deposition of silver nanoparticles on the BP surface and its amino-functionalized multi-walled carbon nanotubes (NH2-MWCNT) nanocomposite. With the addition of both NH2-MWCNT and Ag+, the BP-based nanocomposite was prepared by ultrasonic-assisted liquid-phase exfoliation and was dispersed in carboxymethyl cellulose sodium (CMC) aqueous solution. The morphology, microstructure, and electrochemical properties of the nanohybrid were characterized. NH2-MWCNT-BP-AgNPs showed high environmental stability, good water-processibility, satisfactory life-spans, superior electrocatalytic capacity with enzyme-like kinetic characteristics. The nanohybrid was applied as electrochemical sensors for single/simultaneous analysis of uric acid (UA), xanthine (XT) and hypoxanthine (HX). Excellent voltammetric responses for simultaneous determination in linear ranges of 0.1-800 µM with a limit of detection (LOD) of 0.052 µM for UA, 0.5-680 µM with a LOD of 0.021 µM for XT, and 0.7-320 µM with a LOD of 0.025 µM for HX under optimal conditions. Besides, the developed nanozyme sensor was employed for simultaneous voltammetric analysis of UA, XT and HX in real samples with acceptable recoveries. This work will provide theoretical guidance and experimental support for the preparation and application of two-dimensional materials, nanozymes and sensing devices.

ATMP-induced three-dimensional conductive polymer hydrogel scaffold for a novel enhanced solid-state electrochemiluminescence biosensor.

Reliable and sensitive detection of xanthine has important medical and biological significance. In this work, a novel three-dimensional (3D) conductive polymer hydrogel of polyaniline (PAni) was feasibly prepared using aniline (Ani), amino trimethylene phosphonic acid (ATMP) and ammonium persulfate ((NH4)2S2O8) as monomer, gelatinizing agent and oxidizing agent, respectively. Protonation of aniline can be achieved by ATMP, inducing good conductivity of the obtained hydrogel. ATMP remained the chelating abilities in the conductive hydrogel, enabling further immobilization with silver nanoparticles (AgNPs) functionalized by a luminol derivative, N-(aminobutyl)-N-(ethylisoluminol) (ABEI). ABEI-Ag@PAni-ATMP exhibited an enhanced performance of solid-state electrochemiluminescence (ECL). Integrated with xanthine oxidase (XOD), the proposed biosensor can be applied in the detection of xanthine via in-situ generated hydrogen peroxide (H2O2), and present a low detection limit of 9.6 nM, a wide linear range (from 0.01 to 200 µM) and excellent stability.