Effects of storage conditions on the stability of blood-based markers for the diagnosis of Alzheimer's disease.

OBJECTIVES: Alzheimer's disease (AD) is considered the most common cause of dementia in older people. Recently, blood-based markers (BBM) Aß1-42, Aß1-40, and phospho Tau181 (p-Tau181) have demonstrated the potential to transform the diagnosis and prognostic assessment of AD. Our aim was to investigate the effect of different storage conditions on the quantification of these BBM and to evaluate the interchangeability of plasma and serum samples. METHODS: Forty-two individuals with some degree of cognitive impairment were studied. Thirty further patients were retrospectively selected. Aß1-42, Aß1-40, and p-Tau181 were quantified using the LUMIPULSE-G600II automated platform. To assess interchangeability between conditions, correction factors for magnitudes that showed strong correlations were calculated, followed by classification consistency studies. RESULTS: Storing samples at 4 °C for 8-9 days was associated with a decrease in Aß fractions but not when stored for 1-2 days. Using the ratio partially attenuated the pre-analytical effects. For p-Tau181, samples stored at 4 °C presented lower concentrations, whereas frozen samples presented higher ones. Concerning classification consistency in comparisons that revealed strong correlations (p-Tau181), the percentage of total agreement was greater than 90 % in a large number of the tested cut-offs values. CONCLUSIONS: Our findings provide relevant information for the standardization of sample collection and storage in the analysis of AD BBM in an automated platform. This knowledge is crucial to ensure their introduction into clinical settings.

Engineering Aspects for the Design of a Bicarbonate Zero-Gap Flow Electrolyzer for the Conversion of CO2 to Formate.

CO2 electrolyzers require gaseous CO2 or saturated CO2 solutions to achieve high energy efficiency (EE) in flow reactors. However, CO2 capture and delivery to electrolyzers are in most cases responsible for the inefficiency of the technology. Recently, bicarbonate zero-gap flow electrolyzers have proven to convert CO2 directly from bicarbonate solutions, thus mimicking a CO2 capture medium, obtaining high Faradaic efficiency (FE) and partial current density (CD) toward carbon products. However, since bicarbonate electrolyzers use a bipolar membrane (BPM) as a separator, the cell voltage (VCell) is high, and the system becomes less efficient compared to analogous CO2 electrolyzers. Due to the role of the bicarbonate both as a carbon donor and proton donor (in contrast to gas-fed CO2 electrolyzers), optimization by using know-how from conventional gas-fed CO2 electrolyzers is not valid. In this study, we have investigated how different engineering aspects, widely studied for upscaling gas-fed CO2 electrolyzers, influence the performance of bicarbonate zero-gap flow electrolyzers when converting CO2 to formate. The temperature, flow rate, and concentration of the electrolyte are evaluated in terms of FE, productivity, VCell, and EE in a broad range of current densities (10-400 mA cm-2). A CD of 50 mA cm-2, room temperature, high flow rate (5 mL cm-2) of the electrolyte, and high carbon load (KHCO3 3 M) are proposed as potentially optimal parameters to benchmark a design to achieve the highest EE (27% is obtained this way), one of the most important criteria when upscaling and evaluating carbon capture and conversion technologies. On the other hand, at high CD (>300 mA cm-2), low flow rate (0.5 mL cm-2) has the highest interest for downstream processing (>40 g L-1 formate is obtained this way) at the cost of a low EE (<10%).

Importance of cerebrospinal fluid storage conditions for the Alzheimer's disease diagnostics on an automated platform.

OBJECTIVES: Alzheimer's disease (AD) is considered the most common cause of dementia in older people. Cerebrospinal fluid (CSF) Aß1-42, Aß1-40, total Tau (t-Tau), and phospho Tau (p-Tau) are important biomarkers for the diagnosis, however, they are highly dependent on the pre-analytical conditions. Our aim was to investigate the potential influence of different storage conditions on the simultaneous quantification of these biomarkers in a fully-automated platform to accommodate easier pre-analytical conditions for laboratories. METHODS: CSF samples were obtained from 11 consecutive patients. Aß1-42, Aß1-40, p-Tau, and t-Tau were quantified using the LUMIPULSE G600II automated platform. RESULTS: Temperature and storage days significantly influenced Aß1-42 and Aß1-40 with concentrations decreasing with days spent at 4 °C. The use of the Aß1-42/Aß1-40 ratio could partly compensate it. P-Tau and t-Tau were not affected by any of the tested storage conditions. For conditions involving storage at 4 °C, a correction factor of 1.081 can be applied. Diagnostic agreement was almost perfect in all conditions. CONCLUSIONS: Cutoffs calculated in samples stored at -80 °C can be safely used in samples stored at -20 °C for 15-16 days or up to two days at RT and subsequent freezing at -80 °C. For samples stored at 4 °C, cutoffs would require applying a correction factor, allowing to work with the certainty of reaching the same clinical diagnosis.

Effects of Benzyl-Functionalized Cationic Surfactants on the Inhibition of the Hydrogen Evolution Reaction in CO2 Reduction Systems.

Cationic surfactants, mainly hexadecyl cetrimonium bromide (CTAB), are widely used in electrocatalysis to affect the selectivity of the reaction, specifically to inhibit the hydrogen evolution reaction (HER) in CO2 reduction (CO2R) systems. However, little research has been done on the modification of the functional groups present in such surfactants in order to promote this HER-inhibiting effect. In this work, the effectiveness of CTAB was promoted by substituting a methyl group of the quaternary amine for a benzyl group. This cationic surfactant, cetalkonium chloride (CKC), increased the hydrophobicity of the surface of the electrode, promoting the HER inhibition and the CO2R when HCO3- is used as a carbon source, which allows combining capture and conversion in one and the same medium, making it industrially highly attractive. By performing a detailed electrochemical characterization, we proved that the benzyl group formed an enhanced hydrophobic layer on the surface of the electrode in addition to the alkyl chain of the surfactant, showing higher effectiveness compared to CTAB. In fact, the Faradaic efficiency of the CO2R increased from 39 to 66% in saturated HCO3- electrolytes by using CKC instead of CTAB as the HER inhibitor. This opens up a wide range of avenues for research on the application of surfactants in the field of electrocatalysis, because, as proven, a selective modification of it can tune the selectivity of the reaction, adding a new variable in the design of an efficient carbon capture and utilization system.

Increased flexibility in methadone take-home scheduling during the COVID-19 pandemic: Should this practice be incorporated into routine clinical care?

In the context of the COVID-19 pandemic and the state of emergency that the government of Spain declared, the rapid adaptation of health services is of paramount importance to preserve access to and continuity of service delivery. This research note underscores the importance of ensuring a sufficient quantity of methadone take-home doses for patients on methadone maintenance treatment (MMT) to maximize their adherence to government-imposed lockdown restrictions and social distancing measures designed to curtail the spread of SARS-CoV-2. We evaluate the impact of COVID-19 on take-home medication (number of days provided) in a methadone clinic in Barcelona (Catalonia, Spain). This work conveys that we should consider maintaining the take-home practices that we adopted in response to the pandemic, even after the pandemic has abated.

Optospintronics in Graphene via Proximity Coupling.

The observation of micrometer size spin relaxation makes graphene a promising material for applications in spintronics requiring long-distance spin communication. However, spin dependent scatterings at the contact/graphene interfaces affect the spin injection efficiencies and hence prevent the material from achieving its full potential. While this major issue could be eliminated by nondestructive direct optical spin injection schemes, graphene's intrinsically low spin-orbit coupling strength and optical absorption place an obstacle in their realization. We overcome this challenge by creating sharp artificial interfaces between graphene and WSe2 monolayers. Application of circularly polarized light activates the spin-polarized charge carriers in the WSe2 layer due to its spin-coupled valley-selective absorption. These carriers diffuse into the superjacent graphene layer, transport over a 3.5 µm distance, and are finally detected electrically using Co/h-BN contacts in a nonlocal geometry. Polarization-dependent measurements confirm the spin origin of the nonlocal signal. We also demonstrate that such signal is absent if graphene is contacted to bilayer WSe2 where the inversion symmetry is restored.

Highly Oriented Atomically Thin Ambipolar MoSe2 Grown by Molecular Beam Epitaxy.

Transition metal dichalcogenides (TMDCs), together with other two-dimensional (2D) materials, have attracted great interest due to the unique optical and electrical properties of atomically thin layers. In order to fulfill their potential, developing large-area growth and understanding the properties of TMDCs have become crucial. Here, we have used molecular beam epitaxy (MBE) to grow atomically thin MoSe2 on GaAs(111)B. No intermediate compounds were detected at the interface of as-grown films. Careful optimization of the growth temperature can result in the growth of highly aligned films with only two possible crystalline orientations due to broken inversion symmetry. As-grown films can be transferred onto insulating substrates, allowing their optical and electrical properties to be probed. By using polymer electrolyte gating, we have achieved ambipolar transport in MBE-grown MoSe2. The temperature-dependent transport characteristics can be explained by the 2D variable-range hopping (2D-VRH) model, indicating that the transport is strongly limited by the disorder in the film.

Valley Polarization by Spin Injection in a Light-Emitting van der Waals Heterojunction.

The band structure of transition metal dichalcogenides (TMDCs) with valence band edges at different locations in the momentum space could be harnessed to build devices that operate relying on the valley degree of freedom. To realize such valleytronic devices, it is necessary to control and manipulate the charge density in these valleys, resulting in valley polarization. While this has been demonstrated using optical excitation, generation of valley polarization in electronic devices without optical excitation remains difficult. Here, we demonstrate spin injection from a ferromagnetic electrode into a heterojunction based on monolayers of WSe2 and MoS2 and lateral transport of spin-polarized holes within the WSe2 layer. The resulting valley polarization leads to circularly polarized light emission that can be tuned using an external magnetic field. This demonstration of spin injection and magnetoelectronic control over valley polarization provides a new opportunity for realizing combined spin and valleytronic devices based on spin-valley locking in semiconducting TMDCs.

Large-Area Epitaxial Monolayer MoS2.

Two-dimensional semiconductors such as MoS2 are an emerging material family with wide-ranging potential applications in electronics, optoelectronics, and energy harvesting. Large-area growth methods are needed to open the way to applications. Control over lattice orientation during growth remains a challenge. This is needed to minimize or even avoid the formation of grain boundaries, detrimental to electrical, optical, and mechanical properties of MoS2 and other 2D semiconductors. Here, we report on the growth of high-quality monolayer MoS2 with control over lattice orientation. We show that the monolayer film is composed of coalescing single islands with limited numbers of lattice orientation due to an epitaxial growth mechanism. Optical absorbance spectra acquired over large areas show significant absorbance in the high-energy part of the spectrum, indicating that MoS2 could also be interesting for harvesting this region of the solar spectrum and fabrication of UV-sensitive photodetectors. Even though the interaction between the growth substrate and MoS2 is strong enough to induce lattice alignment via van der Waals interaction, we can easily transfer the grown material and fabricate devices. Local potential mapping along channels in field-effect transistors shows that the single-crystal MoS2 grains in our film are well connected, with interfaces that do not degrade the electrical conductivity. This is also confirmed by the relatively large and length-independent mobility in devices with a channel length reaching 80 µm.

Light generation and harvesting in a van der Waals heterostructure.

Two-dimensional (2D) materials are a new type of materials under intense study because of their interesting physical properties and wide range of potential applications from nanoelectronics to sensing and photonics. Monolayers of semiconducting transition metal dichalcogenides MoS2 or WSe2 have been proposed as promising channel materials for field-effect transistors. Their high mechanical flexibility, stability, and quality coupled with potentially inexpensive production methods offer potential advantages compared to organic and crystalline bulk semiconductors. Due to quantum mechanical confinement, the band gap in monolayer MoS2 is direct in nature, leading to a strong interaction with light that can be exploited for building phototransistors and ultrasensitive photodetectors. Here, we report on the realization of light-emitting diodes based on vertical heterojunctions composed of n-type monolayer MoS2 and p-type silicon. Careful interface engineering allows us to realize diodes showing rectification and light emission from the entire surface of the heterojunction. Electroluminescence spectra show clear signs of direct excitons related to the optical transitions between the conduction and valence bands. Our p-n diodes can also operate as solar cells, with typical external quantum efficiency exceeding 4%. Our work opens up the way to more sophisticated optoelectronic devices such as lasers and heterostructure solar cells based on hybrids of 2D semiconductors and silicon.

Ultrasensitive photodetectors based on monolayer MoS2.

Two-dimensional materials are an emerging class of new materials with a wide range of electrical properties and potential practical applications. Although graphene is the most well-studied two-dimensional material, single layers of other materials, such as insulating BN (ref. 2) and semiconducting MoS2 (refs 3, 4) or WSe2 (refs 5, 6), are gaining increasing attention as promising gate insulators and channel materials for field-effect transistors. Because monolayer MoS2 is a direct-bandgap semiconductor due to quantum-mechanical confinement, it could be suitable for applications in optoelectronic devices where the direct bandgap would allow a high absorption coefficient and efficient electron-hole pair generation under photoexcitation. Here, we demonstrate ultrasensitive monolayer MoS2 phototransistors with improved device mobility and ON current. Our devices show a maximum external photoresponsivity of 880 A W(-1) at a wavelength of 561 nm and a photoresponse in the 400-680 nm range. With recent developments in large-scale production techniques such as liquid-scale exfoliation and chemical vapour deposition-like growth, MoS2 shows important potential for applications in MoS2-based integrated optoelectronic circuits, light sensing, biomedical imaging, video recording and spectroscopy.