•Cellulose nanowhiskers, silver nanoparticles and electrospun nanofibers were combined to produce ternary nanocomposites.•E-tongue sensing units were designed using ternary nanomposites.•Feature ...selection procedure using e-tongue data allowed the discrimination of distinct heavy metal solutions.•Aqueous solutions containing lead could be classified down to nanomolar concentration.
Contamination of water resources with heavy metal ions raises concerns because of their capability to accumulate in living organisms and cause serious health problems. As a consequence, the development of sensitive and reliable sensors capable to provide fast and accessible analysis of water quality regarding heavy metals is highly keen. Nanomaterials advancements have provided considerable improvements in these sensors, enabling efficient detection of different water pollutants even at extremely low concentration. In this work, we evaluated the performance of ternary nanocomposites based on electrospun nanofibers, cellulose nanowhiskers (CNW) and silver nanoparticles as sensing layers used in the electrical detection of heavy metals. These three materials were distinctly combined, resulting in six different sensors, which were arranged to compose an impedimetric electronic tongue. The synergism between the components could be verified by the enhancement of bulk conductance ability when CNW:Ag was combined with electrospun nanofibers. Adjustments of sensors and frequencies enabled efficient discrimination of distinct heavy metal ions. Moreover, the sensor array could distinguish pure water from aqueous solution contaminated with Pb2+ at concentrations as low as of 10 nmol L−1.
Reliable gas sensors operating at room temperature are in demand for monitoring the environment for hazardous pollutants, such as ammonia (NH3) gas that may become toxic to humans and animals above a ...threshold concentration. In this paper we report on the combination of three materials, namely polyaniline (PANI), graphene oxide (GO) and zinc oxide (ZnO), to produce hybrid layer-by-layer (LbL) films used for sensing NH3 with impedance spectroscopy measurements. The deposition of tetralayered PANI/GO/PANI/ZnO LbL films was confirmed with UV–vis. absorption and Raman spectroscopies, while atomic force microscopy (AFM) served to investigate film morphology. Exposure of these LbL films to NH3 caused film roughness to vary, in an effect that depended on the number of tetralayers. Because of synergy in the materials properties, the films with 3 tetralayers were found to be the most adequate for detecting NH3 in the range from 25ppm to 500ppm with a response time of 30s. These figures of merit are adequate for monitoring working environments regarding gas exposure, and highlight the usefulness of the control of film architecture provided by the LbL technique.
In recent decades, the climate in North and Northeast Brazil has undergone significant changes, which indicate potential risks for water and food security due to increasing temperatures, changing ...precipitation patterns, and greater frequency of some extreme events. For example, there is evidence of changes in the strength of the hydrological cycles on North and Northeast Brazil river basins, but the magnitude and extension of the precipitation changes are highly dependent on the precipitation dataset under consideration and the methodology. Here, we analyze the precipitation trends in North and Northeast Brazil hydrological basins and the possible associated mechanisms and present the rainfall climatological cycles in these basins using multi-datasets. The results showed that, in most river basins, there is a clear distinction between the rainy and dry seasons, with a contrast between the basins of the North (which receive a higher amount of rainfall) and the Northeast Brazil (with low rainfall volume, especially in the Parnaíba and Eastern Northeast Atlantic basins). Moreover, the annual rainfall has undergone an increasing trend in western Brazil river basins and a decreasing trend in the eastern. This east–west dipole is associated with the strengthening (weakening) of the Walker and Hadley circulations in western (eastern) Brazil in recent decades. A multidecadal variability is seen to modulate the precipitation changes, which is in phase with the AMO cycle. CMIP6 detection and attribution experiments showed that both natural and anthropogenic factors can play a role in the recent changes observed in northern Brazil river basins.
The South American Monsoon System (SAMS) is a major climatic feature of South America, and its domain extends from Amazon to La Plata basin. The SAMS region is vulnerable to variations of climate and ...precipitation patterns, which could impact economic activities and lead to potential societal consequences. In the face of a warming future scenario, the importance of the study of the past climate with numerical simulations is to evaluate the climate models and to assure the reliability of future projections. Here we investigate the Mid-Holocene SAMS, evaluating changes in strength, life cycle and associated dynamical mechanisms in ten Earth System Models simulations. Our results show that the SAMS was weaker in the Mid-Holocene than in the pre-industrial climate in December–January–February (DJF), but stronger in September–October–November (SON). This is probably a consequence of insolation variations in the Mid-Holocene, which contributed to changes in the moisture flux from the Atlantic Ocean to the continent, the strength of the upper-level atmospheric circulation, and the amount of precipitation over the SAMS region. Moreover, we suggest that the life cycle of the SAMS was altered during the Mid-Holocene, with an earlier onset and demise. Our results also indicate that Mid-Holocene SAMS changes are connected to precipitation variations near Northeast Brazil, in a dipole configuration of precipitation between western Amazon and Northeast Brazil, due to the influence of the Walker cell. Finally, this study highlights a need for improvement of the numerical models to better simulate the amount of precipitation over South America and the upper-level circulation over western Amazon in SON, which are crucial factors for a more realistic representation of the SAMS.
The NV centers in a diamond were successfully created by the femtosecond laser single pulse. We also investigated the effect on the diamond lattice induced by the different laser pulse widths from ...both experimental and theoretical perspectives. Interestingly, in spite of the high thermal conductivity of a diamond, we found that there is a suitable pulse repetition rate of several tens kHz for the formation of NV center ensembles by the femtosecond laser pulse irradiation.
We report on a bimetallic, bifunctional electrode where a platinum (Pt) surface was patterned with nanostructured gold (Au) fingers with different film thicknesses, which was functionalized with ...glucose oxidase (GOx) to yield a highly sensitive glucose biosensor. This was achieved by using selective adsorption of a self-assembled monolayer (SAM) onto Au fingers, which allowed GOx immobilization only onto the Au-SAM surface. This modified electrode was termed bifunctional because it allowed to simultaneously immobilize the biomolecule (GOx) on gold to catalyze glucose, and detect hydrogen peroxide on Pt sites. Optimized electrocatalytic activity was reached for the architecture Pt/Au-SAM/GOx with 50nm thickness of Au, where synergy between Pt and Au allowed for detection of hydrogen peroxide (H2O2) at a low applied potential (0V vs. Ag/AgCl). Detection was performed for H2O2 in the range between 4.7 and 102.7 nmol L–1, with detection limit of 3.4×10−9 mol L−1 (3.4 nmol L−1) and an apparent Michaelis-Menten rate constant of 3.2×10−6molL−1, which is considerably smaller than similar devices with monometallic electrodes. The methodology was validated by measuring glucose in artificial saliva, including in the presence of interferents. The synergy between Pt and Au was confirmed in electrochemical impedance spectroscopy measurements with an increased electron transfer, compared to bare Pt and Au electrodes. The approach for fabricating the reproducible bimetallic Pt/Au electrodes is entirely generic and may be explored for other types of biosensors and biodevices where advantage can be taken of the combination of the two metals.
•Controlled synthesis of Gold Nanostructures by photolithography on platinum surface•Hybrid surface (bimetallic) with better features compared to their monometallic counterparts•For the first time we propose a methodology for selective immobilization of SAM only on the Au and platinum free•Bifunctional Nanostructured surface for glucose biosensing in artificial saliva.
► A novel single-ion conducting polymer electrolyte, lithium polyvinyl alcohol oxalate borate (LiPVAOB), was prepared. ► It is from the reaction of poly(vinyl alcohol) with boric acid, lithium ...hydroxide and oxalic acid. ► The prepared materials act as single-ion polymer electrolytes. ► Their electrochemical window can be stable up to 7V (vs. Li+/Li). ► They are of great attraction for high voltage lithium ion batteries with high energy density.
In this study, a novel single-ion conducting polymer electrolyte, lithium polyvinyl alcohol oxalate borate (LiPVAOB), from the reaction of poly(vinyl alcohol) (PVA) with different molar ratio of boric acid, oxalic acid and lithium carbonate was prepared. The prepared materials were characterized by Fourier transformation infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), differential thermal analysis (DTA), electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry. Ionic conductivity of these polymer electrolytes from adding an assistant (about 20wt.% propylene carbonate) is dependent on molar ratio of the reactants and can up to 6.11×10−6Scm−1 at ambient temperature. Their electrochemical window can be stable up to 7V (vs. Li+/Li), which is of great attraction for high voltage lithium ion batteries with high energy density.
Recent data have linked hypoxia, a classic feature of the tumor microenvironment, to the function of specific microRNAs (miRNAs); however, whether hypoxia affects other types of noncoding transcripts ...is currently unknown. Starting from a genome-wide expression profiling, we demonstrate for the first time a functional link between oxygen deprivation and the modulation of long noncoding transcripts from ultraconserved regions, termed transcribed-ultraconserved regions (T-UCRs). Interestingly, several hypoxia-upregulated T-UCRs, henceforth named 'hypoxia-induced noncoding ultraconserved transcripts' (HINCUTs), are also overexpressed in clinical samples from colon cancer patients. We show that these T-UCRs are predominantly nuclear and that the hypoxia-inducible factor (HIF) is at least partly responsible for the induction of several members of this group. One specific HINCUT, uc.475 (or HINCUT-1) is part of a retained intron of the host protein-coding gene, O-linked N-acetylglucosamine transferase, which is overexpressed in epithelial cancer types. Consistent with the hypothesis that T-UCRs have important function in tumor formation, HINCUT-1 supports cell proliferation specifically under hypoxic conditions and may be critical for optimal O-GlcNAcylation of proteins when oxygen tension is limiting. Our data gives a first glimpse of a novel functional hypoxic network comprising protein-coding transcripts and noncoding RNAs (ncRNAs) from the T-UCRs category.
Incorporating electronic tongues into microfluidic devices brings benefits as dealing with small amounts of sample/discharge. Nonetheless, such measurements may be time-consuming in some applications ...once they require several operational steps. Here, we designed four collinear electrodes on a single printed circuit board, further comprised inside a straight microchannel, culminating in a robust e-tongue device for faster data acquisition. An analog multiplexing circuit automated the signal’s routing from each of the four sensing units to an impedance analyzer. Both instruments and a syringe pump are controlled by dedicated software. The automated e-tongue was tested with four Brazilian brands of liquid sucralose-based sweeteners under 20 different flow rates, aiming to systematically evaluate the influence of the flow rate in the discrimination among sweet tastes sold as the same food product. All four brands were successfully distinguished using principal component analysis of the raw data, and despite the nearly identical sucralose-based taste in all samples, all brands’ significant distinction is attributed to small differences in the ingredients and manufacturing processes to deliver the final food product. The increasing flow rate improves the analyte’s discrimination, as the silhouette coefficient reaches a plateau at ~3 mL/h. We used an equivalent circuit model to evaluate the raw data, finding a decrease in the double-layer capacitance proportional to improvements in the samples’ discrimination. In other words, the flow rate increase mitigates the formation of the double-layer, resulting in faster stabilization and better repeatability in the sensor response.
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