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.

Marigold carotenoids: Much more than lutein esters.

Carotenoids constitute a large group of lipophilic pigments whose health-promoting benefits have been widely recognized. Hydroxy-containing carotenoids can be found in both free form or esterified with fatty acids in several plant matrices, but the native carotenoid profile is overall poorly explored due to the difficulty of analyzing carotenoid esters. One of the main natural sources of carotenoids is the marigold flower, which has been extensively used by the industry for the production of food colorants or supplements, both often manufactured with no saponification process. Although lutein esters are well established as the major compounds naturally found in marigold petals and their products, carotenoid esters other than the lutein ones have not been extensively examined. We carried out a comprehensive identification of carotenoids and carotenoid esters from marigold petals by LC-DAD-(APCI+)MS/MS. Whereas 18 carotenoids were identified in the saponified extract, 56 were identified when no saponification procedure was carried out: 6 free carotenoids, 20 monoesters and 30 diesters. This is the first time that esters of zeaxanthin, violaxanthin, auroxanthin, zeinoxanthin and ß-cryptoxanthin are identified in marigold. The structural information obtained through characteristic fragmentation patterns and diagnostic fragments in MS and MS/MS spectra (APCI+) sustained the differentiation between carotenoid esters with similar characteristics. Therefore, the separation of carotenoids by reversed-phase liquid chromatography using C30 columns in combination with DAD and APCI-MS/MS detection allowed high sensitivity and selectivity for carotenoid ester analysis.

Simultaneous detection of ATP metabolites in human plasma and urine based on palladium nanoparticle and poly(bromocresol green) composite sensor.

A sensitive voltammetric sensor based on palladium nanoparticles (PdNPs) and poly-bromocresol green (pBG) composite layer immobilized on amide functionalized single-walled carbon nanotubes (AmSWCNTs) modified pyrolytic graphite (PdNPs:pBG/AmSWCNTs/PG) has been prepared for the simultaneous determination of adenosine triphosphate (ATP) catabolites, inosine (INO), hypoxanthine (HX), xanthine (XT), and uric acid (UA). The modified PdNPs:pBG/AmSWCNTs/PG was characterized by electrochemical experiments and surface analysis, which exhibited exceptional electrocatalytic effects towards the oxidation of INO, HX, XT, and UA with a significant enhanced peak current and well resolved peaks separation for all the analytes. The linear calibration curves were obtained in the concentration range of 0.001-175 µM, 0.001-200 µM, 0.001-150 µM, and 0.001-200 µM and limits of detection were found as 0.95 nM, 1.04 nM, 1.07 nM, and 0.43 nM corresponding to INO, HX, XT, and UA, respectively. The common metabolites present in the biological fluids did not interfere in the determination. The applicability of the proposed sensor was successfully demonstrated by determining INO, HX, XT, and UA in the human plasma and urine and the obtained results were validated by using HPLC.

Xanthine oxidase functionalized Ta2O5 nanostructures as a novel scaffold for highly sensitive SPR based fiber optic xanthine sensor.

Fabrication and characterization of a surface plasmon resonance based fiber optic xanthine sensor using entrapment of xanthine oxidase (XO) enzyme in several nanostructures of tantalum (v) oxide (Ta2O5) have been reported. Chemical route was adopted for synthesizing Ta2O5 nanoparticles, nanorods, nanotubes and nanowires while Ta2O5 nanofibers were prepared by electrospinning technique. The synthesized Ta2O5 nanostructures were characterized by photoluminescence, scanning electron microscopy, UV-Visible spectra and X-ray diffraction pattern. The probes were fabricated by coating an unclad core of the fiber with silver layer followed by the deposition of XO entrapped Ta2O5 nanostructures. The crux of sensing mechanism relies on the modification of dielectric function of sensing layer upon exposure to xanthine solution of diverse concentrations, reflected in terms of shift in resonance wavelength. The sensing probe coated with XO entrapped Ta2O5 nanofibers has been turned out to possess maximum sensitivity amongst the synthesized nanostructures. The probe was optimized in terms of pH of the sample and the concentration of XO entrapped in Ta2O5 nanofibers. The optimized sensing probe possesses a remarkably good sensitivity of 26.2nm/µM in addition to linear range from 0 to 3µM with an invincible LOD value of 0.0127µM together with a response time of 1min. Furthermore, probe selectivity with real sample analysis ensure the usage of the sensor for practical scenario. The results reported open a novel perspective towards a sensitive, rapid, reliable and selective detection of xanthine.

Ratiometric sensing of metabolites using dual-emitting ZnS:Mn2+ quantum dots as sole luminophore via surface chemistry design.

We herein present an effective and versatile platform for ratiometric sensing of metabolites using intrinsically dual-emitting ZnS:Mn2+ quantum dots (QDs) as sole reporter. To avoid notoriously non-specific interactions, a special triple-layer "filter screen" around the inorganic QD core is rationally constructed, which is made of oleic acid, cetyltrimethyl ammonium bromide and bio-enzymes. In the presence of the analytes, the in-situ enzymatic H2O2 molecules diffuse and pass through the "filter screen" along the molecule interspace, which then reacts with the inorganic core and leads to more dramatically quenching of the Mn2+ emission. The ratiometric signal readout is so distinct that can be observed by naked eyes (from orange to violet). In contrast, various coexisting bio-molecules, due to larger size, are well prevented from penetrating the filter screen by steric hindrance effect. So, various potential interfering substances do not disturb the assay. Under optimal conditions, five kinds of the corresponding substrates, namely glucose, cholesterol, lactate, xanthine and uric acid are well quantified by the emission intensity ratio of I470/I615, and the linear ranges are 0.1-200µM, 0.1-200µM, 1-200µM, 1-200µM and 1-200µM, respectively. The detection limits can even reach quasi-picomole levels. Because of favorable analytical performances (excellent selectivity, appropriate sensitivity and broad linear range), the proposed system can direct assay the analytes in blood without any sample pre-treatment.

Chromatographic resolution of closely related species: drug metabolites and analogs.

In this study, we investigate the separation of a variety of mixtures of drugs, metabolites, and related analogs including representatives of the carbamazepine, methylated xanthine, steroid hormone, nicotine, and morphine families using several automated chromatographic method development screening systems including ultra high performance liquid chromatography, core-shell HPLC, achiral supercritical fluid chromatography (SFC), and chiral SFC. Of the 138 column and mobile phase combinations examined for each mixture, a few chromatographic conditions afford the best overall performance, with a single achiral SFC method (4.6 × 250 mm, 3.0 µm GreenSep Ethyl Pyridine, 25 mM isobutylamine in methanol/CO2) affording good separation for all samples. Four of these mixtures were also resolved by achiral SFC on the Luna HILIC and chiral SFC Chiralpak IB columns using methanol or ethanol with 25 mM isobutylamine as polar modifiers. Modifications of standard chromatography screening conditions afforded fast separation methods (from 1 to 5 min) for baseline resolution of all components of each of these challenging sets of closely related compounds.

Xanthine biosensor based on the direct oxidation of xanthine at an electrogenerated oligomer film.

Poly(o-aminophenol-co-pyrogallol) (PAP) was first synthesized via the electrochemical copolymerization of o-aminophenol and pyrogallol in the acidic solution, using a reduced graphene oxide/glassy carbon (RGO/GC) electrode as a working electrode. Reduced graphene oxide played an important role in increasing PAP amount deposited on the RGO/GC electrode compared to that on the bare GC electrode, which is due to that RGO has the large specific surface area. The results from the spectra of IR, (1)H NMR and ESR and the measurement of molecular weight demonstrated that PAP is an oligomer with the free radicals and exhibited good redox activity in a wide pH range from pH<1-9.0 and can effectively catalyze xanthine oxidation due to the presence of the free radicals and the reversible redox groups in the copolymer chain. On the basis of the direct oxidation of xanthine on PAP, the PAP/RGO/GC electrode was used as a xanthine biosensor. The biosensor showed a linear range from 1.0 to 120µM xanthine at pH 6.0 with a correction coefficient of 0.9965 and fast response to xanthine oxidation. The peak potential of xanthine oxidation shifted from 0.814 to 0.668V as pH increased from 5.0 to 7.5.

Simultaneous analysis of fluoroquinolones and xanthine derivatives in serum by molecularly imprinted matrix solid-phase dispersion coupled with liquid chromatography.

A new molecularly imprinted polymer was synthesized using ofloxacin and theophylline as template and methacryclic acid as function monomer and it was employed as a special dispersant of matrix solid-phase dispersion for selective extraction of fluoroquinolones (ofloxacin, ciprofloxacin and enrofloxacin) and xanthine (caffeine and theophylline) from human serum samples. To eliminate the influences of template leaking on quantitative analysis, acetonitrile-trifluoracetic acid (99:1, v/v) was used as the template removing solution. By using water and acetonitrile-trifluoracetic acid (99.5:0.5, v/v) as the washing and elution solvent, respectively, satisfactory recoveries and clean enough chromatogram could obtained. Good linearity of all the analytes was observed in a range of 0.35-150 µg g(-1) with the correlation coefficient (r(2))≥0.9991. The recoveries of spiked human serum samples were in a range of 89.5-104.0% for fluoroquinolones and xanthine derivatives with RSD less than of 5.0%.

[Identification of 5 constituents of the aqueous extract of Isatis indigotica by HPLC-MS2].

OBJECTIVE: To identify five constituents in the aqueous extract of Isatis indigotica Fort. METHODS: After separation of the aqueous extract of Isatis indigotica Fort. by HPLC, the eluates of five peaks were collected separatively and analysed by MS2. UV spectra and MS2 were compared with those of reference standards of cytidine, uridine, guanosine xanthine and hypoxanthine. RESULTS: Each HPLC elute of the aqueous extract had same retention time, UV spectra and fragment pattern in the MS2 spectrum as the corresponding standards. CONCLUSION: Five constituents of the aqueous extract of Isatis indigotica Fort. are identified as cytidine, hypoxanthine, uridine, xanthine and guanosine.

Absence of carotenes and presence of a tertiary methoxy group in a carotenoid from a thermophilic filamentous photosynthetic bacterium Roseiflexus castenholzii.

We identified pigments in a thermophilic filamentous photosynthetic bacterium Roseiflexus castenholzii strain HL08. We detected neither bacteriochlorophyll (BChl) c nor carotenes in this bacterium cultured under the aerobic dark and the anaerobic light conditions, which may correspond to its lack of chlorosomes. In the cells cultured under the aerobic dark conditions, the carotenoids were derivatives of keto-gamma-carotene, and the major ones were methoxy-keto-myxocoxanthin and keto-myxocoxanthin glucoside fatty acid ester. Although the tertiary methoxy group at C-1' and the double bond at C-3',4' in the psi end group of carotenoid, such as spirilloxanthin, have only been found in purple bacteria, this was the first such report in other bacterial groups. The fatty acid moiety was composed of iso fatty acids, which were rare in the cellular lipids. In the cells cultured under the anaerobic light conditions, in addition to these keto-carotenoids, we also found non-oxidized carotenoids (derivatives of gamma-carotene). Concerning the esterifying alcohol of BChl a, we found a substantial amount of geranylgeraniol, although the major component was phytol. The existence of these pigments makes this bacterium unique among the known species in CHLOROFLEXACEAE.