Current Detection Limits Research Articles

Bloch surface waves biosensing in the ultraviolet wavelength range – Bragg structure design for investigating protein adsorption by in situ Kretschmann-Raether ellipsometry

We designed a Bragg mirror structure with an SiO2 top layer to create a resonance in the ultraviolet wavelength range, near the absorption peak position of various proteins. We demonstrate that the wavelength of enhanced sensitivity can be adjusted by proper design of the 1D photonic structure. The possibility to design the wavelength of enhanced sensitivity supports measurements of better selectivity, optimized for the absorption of the target material. Since the width of the resonant peak in the reflectance spectra can be sharper than those of plasmonics, and they can be positioned at more favourable regions of the instrument and material (e.g., in terms of intensity or selectivity), the sensitivity can exceed those of plasmon-enhanced measurements. In this study we demonstrate the main features of the concept at the example of in situ spectroscopic ellipsometry of fibrinogen adsorption in the Kretschmann-Raether configuration. We realized a resonant peak with a full width at half maximum of 3 nm near the wavelength of 280 nm, which coincides with the absorption maximum of fibrinogen. The influence of depolarization and surface roughness on the measurements, and the potential for improving the current experimental detection limit of 45 pg/mm2 is also discussed.

A comprehensive assessment of two-decade radioactivity monitoring around the Channel Islands

The Channel Islands are located in the Normand-Breton Gulf (NBG), in the mid-part of the English Channel (France, Normandy). In the northern part, off Cap La Hague, controlled amounts of radioactive liquid waste are discharged by the ORANO La Hague nuclear fuel reprocessing plant (RP). Radionuclides were monitored in the NBG to assess the dispersion of radioactive discharges from the RP in the marine environment. The temporal and spatial distribution of the data are consistent with the history of the discharges, with most gamma emitter radionuclide environmental levels being close to or below the current limits of detection. A clear fingerprint of H-3, C-14 and I-129 radionuclides discharged from the RP is measured. The hydrodynamics in the NBG do not yield a simple gradient with linear distance from the outfall of the RP. Modelling tools were used to understand how radioactive discharges spread from the source of input. Dispersion patterns clearly illustrate the different behaviours of soluble and non-soluble radionuclides. The study indicated that the footprint of radioactive liquid discharges by French nuclear facilities was still measurable in species collected from the NBG for the mostly dissolved radionuclides. The less conservative ones, with a high affinity for suspended matter, are potentially influenced by old releases. These pathways could be investigated by dedicated hydrodynamic dispersion models. Overall, in the Channel Islands the levels are low and consistent with the general decrease in liquid radionuclide discharges by the RP since the 1990s.

Nanoelectromechanical Position-Sensitive Detector with Picometer Resolution.

Subnanometer displacement detection lays the solid foundation for critical applications in modern metrology. In-plane displacement sensing, however, is mainly dominated by the detection of differential photocurrent signals from photodiodes, with resolution in the nanometer range. Here, we present an integrated nanoelectromechanical in-plane displacement sensor based on a nanoelectromechanical trampoline resonator. With a position resolution of 4 pm/ for a low laser power of 85 μW and a repeatability of 2 nm after five cycles of operation as well as good long-term stability, this new detection principle provides a reliable alternative for overcoming the current position detection limit in a wide variety of research and application fields.

Bound detergent molecules in bacterial reaction centers facilitate detection of tetryl explosive.

Bacterial reaction centers (BRC) from Rhodobacter sphaeroides were found to accelerate, about 100-fold, the reaction between tetryl (2,4,6-trinitrophenylmethylnitramine) explosive and n-lauryl-N-N-dimethylamine-N-oxide (LDAO) that results in the formation of picric acid-like product with characteristic UV-VIS absorption spectrum with peaks at 345 and 415nm. Moreover, this product also affects the spectra of BRC cofactors in the NIR spectral region and stabilizes the conformational changes associated with slow charge recombination. The evolution of the NIR absorption changes correlated with the kinetics of the product formation. Comparison between the wild-type and the R26 carotenoid-less strain indicates that tetryl-LDAO reaction is roughly five times faster for R26, which allows for identifying the carotenoid binding site as the optimal reaction site. Another, less-defined reaction site is located in the BRC's hydrophobic cavity. These effects are highly selective for tetryl and not observed for several other widespread nitric explosives; slowed-down charge recombination allows for distinguishing between tetryl and QB-site herbicides. The current limit of detection is in the ppb range or ~ 100nM. Details of the molecular mechanisms of the reactions and perspectives of using these effects in bioassays or biosensors for explosives detection are also discussed.

Nonenzymatic glucose sensor based on poly(3,4-ethylene dioxythiophene)/electroreduced graphene oxide modified gold electrode

In this study, a nonenzymatic glucose sensor based on a Au electrode was modified using layered poly(3,4-ethylene dioxythiophene) (PEDOT) and electroreduced graphene oxide (ERGO). The modified electrode was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The electrochemical performance of the electrode material was evaluated to assess its use in glucose sensor applications. In addition, the effect of layer numbers of the layered composite on glucose activity was investigated. The monolayer PEDOT–ERGO nanocomposite exhibited high current density, high sensitivity, and low detection limit of approximately 5 mA cm−2, 696.9 μA mM−1 cm−2, and 0.12 μM, respectively. Moreover, an electrode interference test was conducted in the presence of various interfering species such as ascorbic acid, uric acid, dopamine, and H2O2, revealing excellent selectivity of the nonenzymatic glucose sensor. Thus, the PEDOT–ERGO modified Au electrode could be utilized as a promising nonenzymatic glucose biosensor.

Modelling the broadband emission from the white dwarf binary system AR Scorpii

AR Scorpii is a compact binary system which consists of a magnetic white dwarf and an M-type main sequence cool star. This binary system was discovered as a source of pulsating radiation in radio, infrared, optical, ultraviolet and X-ray wavebands. In this work, we have analyzed the γ-ray data in the energy range 100 MeV to 500 GeV from the Fermi-Large Area Telescope (LAT) observations for the period August 4, 2008 to March 31, 2019. The γ-ray emission from AR Scorpii over the last decade is not statistically significant and therefore 2σ upper limit on the integral flux above 100 MeV has been estimated. We reproduce the non-thermal broadband spectral energy distribution of AR Scorpii using an emission model having two synchrotron components due to the relativistic electrons in very high magnetic fields. The first component (Synchrotron-1) broadly describes the emissions at radio to high energy X-rays through the synchrotron radiation originating from a spherical region of radius ~ 1.8 × 1010 cm and a magnetic field strength of ~ 103 Gauss. The second component (Synchrotron-2) which reproduces the X-ray emission at lower energies and predicts the γ-ray emission, originates from another spherical region with radius ~ 1.4 × 1010 cm and a magnetic field strength of ~ 106 Gauss. The relativistic electron populations in both the emission regions are described by a smooth broken power law energy distribution. The γ-ray emission predicted by the Synchrotron-2 model is below the broadband sensitivity of the Fermi-LAT and is also consistent with the 95% confidence level upper limit on the integral flux above 100 MeV derived from more than 10 years of observations. According to our model, the binary system AR Scorpii could be a γ-ray source, although its emission level must be below the current detection limit of the Fermi-LAT.

Optimization of impedance-measured reflux events in GORD utilizing acid exposure time

BackgroundCombining impedance with pH monitoring improves the detection and characterization of gastro-oesophageal reflux (GOR), yet the two modalities frequently differ in GOR quantification. Ambulatory 24-h pH-impedance monitoring often reveals more significant oesophageal acid exposure than impedance-measured reflux activity in patients with symptomatic gastro-oesophageal reflux disease (GORD). The purpose of this study is to elucidate the discrepancies between these modalities by assessing the predictive accuracy of impedance compared to acid exposure standards.MethodsA single-institution, retrospective review of sequential 24-h pH-impedance results of 72 patients with symptomatic GOR off anti-secretory therapy was conducted. Reflux events measured by impedance were stratified by patient position and compared to oesophageal acid exposure time (AET). Oesophageal AET limits for GORD detection were utilized as gold standards to generate serial receiver operator characteristics (ROC) curves to assess the sensitivity and specificity of current impedance GORD detection limits and identify optimized impedance standards based on area under the curve (AUC) analysis.ResultsMean total AET time was 10.5% (± 9.9%), and 63.8% of patients had elevated AET. By impedance, median GOR frequency was 43 (IQR 21–68), and 22.2% exceeded conventional GOR frequency limits of normal. ROC curve analysis revealed the current impedance standard of > 73 GOR events has a sensitivity of 32.6% and specificity of 96.5% (AUC 0.74) for GORD detection. By AUC analysis, an impedance threshold of > 41 GOR events is optimal for GORD detection (sensitivity 69.6%, specificity 80.7%, AUC 0.83).ConclusionConventional impedance standards for abnormal GOR frequency are weakly sensitive for the detection of GORD, providing a possible explanation to discrepancies in AET and impedance interpretation. Lowering impedance-measured GOR frequency limits to > 41 optimizes sensitivity and specificity while increasing congruence between pH and impedance metrics.

Design of multichannel potentiostat for remote and longtime monitoring of glucose concentration during yeast fermentation.

This paper presents the design of a wireless portable and multichannel potentiostat for remote monitoring in enclosed environments for long-time applications. In this paper, the proposed potentiostat is tested for monitoring the glucose concentration during the fermentation of yeast in real time for more than 24 h. The potentiostat is powered by a USB-connected battery and operated through a Bluetooth using a LabVIEW designed data monitoring and control panel. The potentiostat is capable of performing cyclic voltammetry or chronoamperometry on six biosensors simultaneously and gives the real-time response using Bluetooth connection. The potentiostat has a common counter electrode and reference electrode connection to all biosensors and independent working electrodes for all biosensors. The potentiostat was tested and validated by comparing the results obtained by a commercial potentiostat. The tests performed for monitoring the glucose concentration during the fermentation process showed a current detection limit of 180 nA and reported a standard deviation of ±2% for anodic and cathodic current peaks for cyclic voltammetry measurements when compared with the commercially available device. This study enables the novel method of monitoring the fermentation process wirelessly for days.

Digital Sensing and Molecular Computation by an Enzyme-Free DNA Circuit.

DNA circuits form the basis of programmable molecular systems capable of signal transduction and algorithmic computation. Some classes of molecular programs, such as catalyzed hairpin assembly, enable isothermal, enzyme-free signal amplification. However, current detection limits in DNA amplification circuits are modest, as sensitivity is inhibited by signal leakage resulting from noncatalyzed background reactions inherent to the noncovalent system. Here, we overcome this challenge by optimizing a catalyzed hairpin assembly for single-molecule sensing in a digital droplet assay. Furthermore, we demonstrate digital reporting of DNA computation at the single-molecule level by employing ddCHA as a signal transducer for simple DNA logic gates. By facilitating signal transduction of molecular computation at pM concentration, our approach can improve processing density by a factor of 104 relative to conventional DNA logic gates. More broadly, we believe that digital molecular computing will broaden the scope and efficacy of isothermal amplification circuits within DNA computing, biosensing, and signal amplification in general.

Complex scalar dark matter in the gauged two-Higgs-doublet model

The complex scalar dark matter (DM) candidate in the gauged two Higgs doublet model (G2HDM), stabilized by a peculiar hidden parity ($h$-parity), is studied in detail. We explore the parameter space for the DM candidate by taking into account the most recent DM constraints from various experiments, in particular, the PLANCK relic density measurement and the current DM direct detection limit from XENON1T. We separate our analysis in three possible compositions for the mixing of the complex scalar. We first constrain our parameter space with the vacuum stability and perturbative unitarity conditions for the scalar potential, LHC Higgs measurements, plus Drell-Yan and electroweak precision test constraints on the gauge sector. We find that DM dominated by composition of the inert doublet scalar is completely excluded by further combining the previous constraints with both the latest results from PLANCK and XENON1T. We also demonstrate that the remaining parameter space with two other DM compositions can be further tested by indirect detection like the future CTA gamma-ray telescope.

Imaging unlabeled proteins on DNA with super-resolution.

Fluorescence microscopy is invaluable to a range of biomolecular analysis approaches. The required labeling of proteins of interest, however, can be challenging and potentially perturb biomolecular functionality as well as cause imaging artefacts and photo bleaching issues. Here, we introduce inverse (super-resolution) imaging of unlabeled proteins bound to DNA. In this new method, we use DNA-binding fluorophores that transiently label bare DNA but not protein-bound DNA. In addition to demonstrating diffraction-limited inverse imaging, we show that inverse Binding-Activated Localization Microscopy or ‘iBALM’ can resolve biomolecular features smaller than the diffraction limit. The current detection limit is estimated to lie at features between 5 and 15 nm in size. Although the current image-acquisition times preclude super-resolving fast dynamics, we show that diffraction-limited inverse imaging can reveal molecular mobility at ∼0.2 s temporal resolution and that the method works both with DNA-intercalating and non-intercalating dyes. Our experiments show that such inverse imaging approaches are valuable additions to the single-molecule toolkit that relieve potential limitations posed by labeling.

A Large-scale 12CO, 13CO, and C18O Molecular Cloud Survey in the Outer Galactic Plane over I = [129.°75, 140.°25] and b = [−5.°25, +5.°25

Abstract We present the data of an unbiased J = 1–0 12CO/13CO/C18O survey of molecular clouds in the Galactic plane over l = [129.°75, 140.°25] and b = [−5.°25, +5.°25]. For the full 10.°5 × 10.°5 region sampled at 30″, there are 1,590,120 spectra for each isotopologue. The high sensitivity and large spatial dynamic range of the maps provide valuable insights into the structure, physical properties, and kinematics of the molecular gas. The new data successfully trace the most distant spiral arm, as well as the internal subfeatures of the nearby spiral arms. The combined data set of 12CO, 13CO, and C18O allows us to make a more accurate inventory of gas column density and mass for molecular gas within this Galactic interval than hitherto attempted. A statistical analysis reveals that a large fraction of the observed molecular gas is emitted from regions with low excitation conditions. As expected, a considerable amount of H2 mass is found to be confined to the spiral arms. Moreover, we find that the C18O emission is exclusively seen along spiral arms at current detection limits. The physical properties of molecular gas vary considerably in different spiral arms and inter-arms. We find that the column density probability density functions and the amount of relatively denser gas (traced by 13CO or C18O) appear to be closely related to the level of massive star formation activity within the molecular gas. The high-quality data also reveal that the warp and flare of the Galactic plane become obvious beyond the Perseus arm in this Galactic longitude range.

Establishing Meaningful Limits of Detection for Ion-Selective Electrodes and Other Nonlinear Sensors.

Although IUPAC has recommended a probabilistic approach to determining limit of detection (LOD) based on false-positive and false-negative rates for more than 20 years, the LOD definition for ion-selective electrodes (ISEs) long predates these recommendations and conflicts substantively with them. Although it is well known that the ISE LOD definition does not follow best practice, it continues to be used due to simplicity and a lack of available methods for estimating LOD for nonlinear sensors. Here, we use ISEs as a model system for estimation of LOD for nonlinear sensors that is consistent with broad IUPAC recommendations and justified using statistical theory. Using freely available software, the new approach and updated definition is demonstrated through theory, simulation, and an environmental application. The results show that the current LOD definition for ISEs performs substantially worse than the proposed definition when assessed against IUPAC recommendations, including ignoring sensor noise and LOD uncertainty, leading to bias of an order of magnitude or more. Further, the environmental application shows that the new definition, which includes estimates of LOD uncertainty, allows more objective assessment of sensor response and fitness for purpose. The growing demand for ultrasensitive sensors that operate in complex matrices has pushed the boundaries of traditional calibration approaches. These sensors often operate near their limit of detection (LOD), with additional challenges created if their response is nonlinear. These challenges are amplified when assessing new sensors, since they may be less reproducible and noisier than benchmark techniques.

An Updated Visual Orbit of the Directly Imaged Exoplanet 51 Eridani b and Prospects for a Dynamical Mass Measurement with Gaia

Abstract We present a revision to the visual orbit of the young, directly imaged exoplanet 51 Eridani b using four years of observations with the Gemini Planet Imager. The relative astrometry is consistent with an eccentric ( ) orbit at an intermediate inclination ( °), although circular orbits cannot be excluded due to the complex shape of the multidimensional posterior distribution. We find a semimajor axis of au and a period of yr, assuming a mass of 1.75 for the host star. We find consistent values with a recent analysis of VLT/SPHERE data covering a similar baseline. We investigate the potential of using the absolute astrometry of the host star to obtain a dynamical mass constraint for the planet. The astrometric acceleration of 51 Eri derived from a comparison of the Hipparcos and Gaia catalogs was found to be inconsistent at the 2σ–3σ level with the predicted reflex motion induced by the orbiting planet. Potential sources of this inconsistency include a combination of random and systematic errors between the two astrometric catalogs and the signature of an additional companion within the system interior to current detection limits. We also explored the potential of using Gaia astrometry alone for a dynamical mass measurement of the planet by simulating Gaia measurements of the motion of the photocenter of the system over the course of the extended 8 yr mission. We find that such a measurement is only possible (>98% probability) given the most optimistic predictions for the Gaia scan astrometric uncertainties for bright stars and a high mass for the planet (≳3.6 M Jup).

Extending the Detection Limit in Fragment Screening of Proteins Using Reverse Micelle Encapsulation.

Detection of very weak (Kd > 10 mM) interactions of proteins with small molecules has been elusive. This is particularly important for fragment-based drug discovery, where it is suspected that the majority of potentially useful fragments will be invisible to current screening methodologies. We describe an NMR approach that permits detection of protein-fragment interactions in the very low affinity range and extends the current detection limit of ∼10 mM up to ∼200 mM and beyond. Reverse micelle encapsulation is leveraged to effectively reach very high fragment and protein concentrations, a principle that is validated by binding model fragments to E. coli dihydrofolate reductase. The method is illustrated by target-detected screening of a small polar fragment library against interleukin-1β, which lacks a known ligand-binding pocket. Evaluation of binding by titration and structural context allows for validation of observed hits using rigorous structural and statistical criteria. The 21 curated hit molecules represent a remarkable hit rate of nearly 10% of the library. Analysis shows that fragment binding involves residues comprising two-thirds of the protein's surface. Current fragment screening methods rely on detection of relatively tight binding to ligand binding pockets. The method presented here illustrates a potential to faithfully discover starting points for development of small molecules that bind to a desired region of the protein, even if the targeted region is defined by a relatively flat surface.

Mutagenicity assessment of food contact material migrates with the Ames MPF assay

ABSTRACTA major challenge in the safety assessment of food contact materials (FCM) is the evaluation of unknown non-intentionally added substances (NIAS). Even though consumer exposure levels may be quantitatively low, these substances are considered to be of high toxicological concern if they act as DNA reactive mutagens. From a safety assessment perspective, it is therefore important to detect their presence in FCM migrates. The present study applied the Ames MPF assay to assess the mutagenicity of migrates obtained from 30 food contact material samples out of 3 categories: plastics, composite materials and coatings. As a food simulant, 95% ethanol (EtOH) had a superior performance to less volatile simulants when evaluating recovery rates of representative model substances in different volatility categories. To monitor possible interference of the FCM matrix with Ames MPF results, migrates were spiked with reference substances and recovery rates were established. Out of 30 samples tested, two caused significant inhibition of revertant formation in the presence of the spiking control. Overall detection limits of the applied test method were estimated by determination of the lowest effective concentrations (LEC) for 10 Ames-positive substances. Even though the current limits of detection are not sufficient to entirely fulfil regulatory and safety requirements, three out of 30 FCMs showed evidence of dose-dependent effects in the Ames MPF assay. Overall, the data obtained supported the relevance of testing FCM migrates for DNA reactive contaminants and showed the value of the Ames MPF assay for the safety assessment of FCMs.

Label-Free Optical Detection of Multiple Biomarkers in Sweat, Plasma, Urine, and Saliva.

We report a novel label-free quantitative detection of human performance "stress" biomarkers in different body fluids based on optical absorbance of the biomarkers in the ultraviolet (UV) region. Stress biomarker (hormones and neurotransmitters) concentrations in bodily fluids (blood, sweat, urine, saliva) predict the physical and mental state of the individual. The stress biomarkers primarily focused on in this manuscript are cortisol, serotonin, dopamine, norepinephrine, and neuropeptide Y. UV spectroscopy of stress biomarkers performed in the 190-400 nm range has revealed primary and secondary absorption peaks at near-UV wavelengths depending on their molecular structure. UV characterization of individual and multiple biomarkers is reported in various biofluids. A microfluidic/optoelectronic platform for biomarker detection is reported, with a prime focus toward cortisol evaluation. The current limit of detection of cortisol in sweat is ∼200 ng/mL (∼0.5 μM), which is in the normal (healthy) range. Plasma samples containing both serotonin and cortisol resulted in readily detectable absorption peaks at 203 (serotonin) and 247 (cortisol) nm, confirming feasibility of simultaneous detection of multiple biomarkers in biofluid samples. UV spectroscopy performed on various stress biomarkers shows a similar increasing absorption trend with concentration. The detection mechanism is label free, applicable to a variety of biomarker types, and able to detect multiple biomarkers simultaneously in various biofluids. A microfluidic flow cell has been fabricated on a polymer substrate to enable point-of-use/care UV measurement of target biomarkers. The overall sensor combines sample dispensing and fluid transport to the detection location with optical absorption measurements with a UV light emitting diode (LED) and photodiode. The biomarker concentration is indicated as a function of photocurrent generated at the target wavelength.

Selective in-situ derivatization of intrinsic nickel to nickel hexacyanoferrate on carbon nanotube and its application for electrochemical sensing of hydrazine

Herein we report a simple and selective open-circuit potential-time (OCPT) based preparation of nickel hexacyanoferrate (NiHCF) on nickel and iron impurity containing carbon nanotube (CNT*, *=intrinsic metal impurity) modified glassy carbon electrode (GCE/CNT*NiHCF) using pH2 ferricyanide solution. Unlike potentiodyanamic cycling, OCPT allowed the selective preparation of NiHCF with a distinct redox features at an equilibrium potential=0.38V in pH7 phosphate buffer solution (PBS). Kinetic parameters such as transfer coefficient and rate constant of GCE/CNT*NiHCF were calculated from cyclic voltammetry (CV) studies of the redox peak. Characterization of CNT* and CNT*NiHCF by XRD, TEM, FTIR and Raman spectroscopy techniques revealed the presence of iron and nickel impurities in CNT* and confirmed the formation of CNT*NiHCF and CNT*Fe-NiHCF (Fe-NiHCF=FeHCF+NiHCF) by OCPT and potentiodynamic cycling, respectively. Furthermore, electrocatalytic activity of CNT*NiHCF modified electrode was explored with a model analyte, hydrazine (Hz) in pH7 PBS. Likewise, electron number involved during the rate determining step, complete electrocatalytic reaction and its heterogeneous rate constant values were calculated using CV technique. At optimal amperometric i-t conditions, GCE/CNT*NiHCF showed a linear calibration plot with a current linearity on a range of 20–200μM with current sensitivity and detection limit (signal-to-noise=3) values of 1217.39nAμM−1cm−2 and 0.8μM respectively. It also displayed zero interference from oxalic acid, uric acid, ascorbic acid, sulphate, nitrite, nitrite, magnesium and sodium displaying feasibility to Hz detection in polluted water bodies.

Multiphase circumgalactic medium probed with MUSE and ALMA

Galaxy halos appear to be missing a large fraction of their baryons, most probably hiding in the circumgalactic medium (CGM), a diffuse component within the dark matter halo that extends far from the inner regions of the galaxies. A powerful tool to study the CGM gas is offered by absorption lines in the spectra of background quasars. Here, we present optical (MUSE) and mm (ALMA) observations of the field of the quasar Q1130-1449 which includes a log [N(H I)/cm^-2]=21.71+/-0.07 absorber at z=0.313. Ground-based VLT/MUSE 3D spectroscopy shows 11 galaxies at the redshift of the absorber down to a limiting SFR>0.01 M_sun yr^-1 (covering emission lines of [OII], Hbeta, [OIII], [NII] and Halpha), 7 of which are new discoveries. In particular, we report a new emitter with a smaller impact parameter to the quasar line-of-sight (b=10.6 kpc) than the galaxies detected so far. Three of the objects are also detected in CO(1-0) in our ALMA observations indicating long depletion timescales for the molecular gas and kinematics consistent with the ionised gas. We infer from dedicated numerical cosmological RAMSES zoom-in simulations that the physical properties of these objects qualitatively resemble a small group environment, possibly part of a filamentary structure. Based on metallicity and velocity arguments, we conclude that the neutral gas traced in absorption is only partly related to these emitting galaxies while a larger fraction is likely the signature of gas with surface brightness almost four orders of magnitude fainter that current detection limits. Together, these findings challenge a picture where strong-HI quasar absorbers are associated with a single bright galaxy and favour a scenario where the HI gas probed in absorption is related to far more complex galaxy structures.

Enzymatic sensor for phenols based on titanium dioxide generating surface confined ROS after treatment with H2O2

Titanium dioxide (TiO2) is a popular material as host matrix for enzymes. We now evidence that TiO2 can accumulate and retain reactive oxygen species after treatment by hydrogen peroxide (H2O2) and support redox cycling of a phenolic analyte between horseradish peroxidase (HRP) and an electrode. The proposed detection scheme is identical to that of second generation biosensors, but the measuring solution requires no dissolved H2O2. This significantly simplifies the analysis and overcomes issues related to H2O2 being present (or generated) in the solution. The modified electrodes showed rapid stabilization of the baseline, a low noise level, fast realization of a steady-state current response, and, in addition, improved sensitivity and limit of detection compared to the conventional approach, i.e. in the presence of H2O2 in the measuring solution. Hydroquinone, 4-aminophenol, and other phenolic compounds were successfully detected at sub-μM concentrations. Particularly, a linear response in the concentration range between 0.025 and 2 μM and LOD of 24 nM was demonstrated for 4-aminophenol. The proposed sensor design goes beyond the traditional concept with three sensors’ generations offering a new possibility for the development of enzymatic sensors based on peroxidases and the formation of ROS on titania after treatment with H2O2.