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The study of graphene-based carbon nanocomposites has remarkably increased in recent years. Functionalized graphene-based nanostructures, including graphene oxide and reduced graphene oxide, have great potential as new innovative electrode materials in the fabrication of novel electrochemical sensors. Electrochemical sensors based on aptamers attracted great attention because of their high sensitivity and selectivity, and simple instrumentation, as well as low production cost. Aptamers as a potent alternative to antibodies are functional nucleic acids with a high tendency to specific analytes. Electrochemical aptasensors show specific recognition ability for a wide range of analytes. Although aptamers are selected in vitro in contrast to antibodies, they are interesting due to advantages like high stability, easy chemical modifications, and the potential to be employed in nanostructured device fabrication or electrochemical sensing devices. Recently, new nanomaterials have shown a significant impact on the production of electrochemical sensors with high efficiency and performance. This review aims to give an outline of electrochemical aptasensors based on the graphene family materials and discuss the detection mechanism in this type of aptasensors. The present review summarizes some of the recent achievements in graphene-based aptasensors and includes their recent electroanalytical applications.

Rapid and accurate bacteria identification, particularly Escherichia coli (E. coli), is essential in the monitoring of health, environment, and food safety. E. coli, a prevalent pathogenic bacterium, serves as a key indicator of food and water contamination. Carbon quantum dots (CQDs) have appeared as promising fluorescent probes because of their small size, ease of synthesis, low toxicity, and tunable fluorescence using different carbon-rich precursors. Advances in both bottom-up and top-down synthesis procedures have enabled precise control over CQD properties and surface functionalities, enhancing their capabilities in biosensing. Among the critical factors influencing CQD performance is the strategic selection of precursors, which determines the surface chemistry and recognition potential of the resulting nanodots. The integration with other nanomaterials and the surface modification of CQDs with specific functional groups or recognition elements further improves their sensitivity and selectivity toward E. coli. This review summarizes recent progress in the modification of CQDs for the fluorescent detection of E. coli, highlighting relevant sensing mechanisms and the influence of different precursors, such as antibiotics and sugars, as well as various functionalization and surface modification strategies. The aim is to provide insight into the rational design of efficient, selective, and cost-effective CQD-based biosensors for bacterial detection.

Advances in materials science have accelerated the development of diagnostic tools with the last decade witnessing the development of enzyme-free sensors, owing to the improved stability, low cost and simple fabrication of component materials. However, the specificity of non-enzymatic sensors for certain analytes still represents a challenging task, for example the determination of cholesterol level in blood is vital due to its medical relevance. In this work, a reagent displacement assay for cholesterol sensing in serum samples was developed. It is based on coating of a glassy carbon electrode with a polymer of intrinsic microporosity (PIM) that forms a host-guest complex with methylene blue (MB). In the presence of cholesterol, the MB electroactive probe was displaced due to the stronger association of cholesterol guest to the PIM host. The decrease in the oxidative current was proportional to the cholesterol concentration achieving a detection limit of approximately 0.1 nM. Moreover, to further assist the experimental studies, comprehensive theoretical calculations are also performed by using density functional theory (DFT) calculations.

Mesoporous SBA-15 silicate with a high surface area was prepared by a hydrothermal method, successively modified by organic melamine ligands and then used for deposition of Pd nanoparticles onto it. The synthesized materials were characterized with infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), nitrogen physisorption, scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR) and inductively coupled plasma (ICP-OES). The catalyst was effectively used in the Mizoroki–Heck coupling reaction of various reactants in the presence of an organic base giving the desired products in a short reaction time and with small catalysts loadings. The reaction parameters such as the base type, amounts of catalyst, solvents, and the temperature were optimized. The catalyst was easily recovered and reused at least seven times without significant activity losses.Graphic Abstract

We present the first results of the holographic beam-mapping program for the Canadian Hydrogen Intensity Mapping Experiment (CHIME). We describe the implementation of a holographic technique as adapted for CHIME, and introduce the processing pipeline which prepares the raw holographic timestreams for analysis of beam features. We use data from six bright sources across the full 400–800 MHz observing band of CHIME to provide measurements of the copolar and cross-polar beam response in both amplitude and phase for all 1024 dual-polarized feeds in the array. In addition, we present comparisons with independent probes of the CHIME beam, which indicate the presence of polarized beam leakage. Holographic measurements of the beam have already been applied in science with CHIME, e.g., in estimating the detection significance of far-sidelobe fast radio bursts, and in validating the beam models used for CHIME’s first detections of 21 cm emission (in cross-correlation with measurements of large-scale structure from galaxy surveys and the Lyα forest). Measurements presented in this paper, and future holographic results, will provide a unique data set to characterize the CHIME beam and improve the experiment’s prospects for a detection of the baryon acoustic oscillation signal.

We report the detection of a new 21 cm absorption system associated with the radio source NVSS J164725 + 375218 at a redshift of z = 2.327, identified through a pilot survey conducted by the Canadian Hydrogen Intensity Mapping Experiment (CHIME). This is the fifth detection of an associated system at z > 2. By analyzing a subset of available data, we conduct a spectrally blind survey for 21 cm absorption systems within the redshift range of 0.78–2.55 along 202 lines of sight toward known sources in the declination range of 35° to 60°. We detect three 21 cm absorbers: two previously known intervening systems and one newly discovered associated system. By fitting the absorption profiles with models containing one to three Gaussian components and selecting the best model using the Bayesian information criterion, we estimate the optical depth, velocity-integrated optical depth, and the ratio between the H i column density and the spin temperature of the absorption systems. These results demonstrate CHIME’s ability to discover new absorbers, even in a small subset of its full dataset.

Nowadays, fuel cells (FCs) attracted a great deal of attention due to their many applications and advantages: Higher efficiency than diesel or gas engines, less pollution than fossil fuels, no using fuels such as oil and gas and reducing economic dependence on fossil fuel producing countries and easy maintenance are the advantages of FCs. However, the obstacles encountered FCs commercialization’s are mainly expensive electrocatalyst materials such as platinum (Pt), it’s poisoning by intermediates like as CO and sluggish electrooxidation kinetics of fuels. For this reasons, in order to minimize the amount of Pt and accordingly total cost of FCs and also decreasing the poisoning effects, Pt particles are deposited on/in different conductive supports. Herein we investigated the effect of carbon nanoparticles (CNPs) and reduced graphene oxide (RGO) nanosheets on the carbon-ceramic electrode (CCE) as support for Pt nanoparticles (PtNPs) toward formic acid electro-oxidation. PtNPs were successfully deposited on the CNPs and RGO with electrochemical method. The fabricated nanocomposites were characterized by the field emission scanning electron microscopy, energy-dispersive X-ray and X-ray powder diffraction spectroscopy. The electrocatalytic activities of the prepared electrocatalysts for oxidation of formic acid were investigated in 0.1 M H 2 SO 4 solution by electrochemical techniques including cyclic voltammetry (CV) and chronoamperometry (CA). The results of the experiments revealed that the PtNPs on the CNPs, PtNPs/CNPs/CCE, shows more electrocatalytic activity than the RGO nanosheets support. This high electrocatalytic efficiency of the PtNPs/CNPs/CCE can be attributed to large specific surface area and unique structure of CNPs that is being used as support. The influence of some experimental agents on the electrocatalytic activity of the PtNPs/CNPs/CCE was investigated and the optimal conditions were suggested. The present investigation reveals that the PtNPs/CNPs/CCE is a promising electrocatalyst for the formic acid electro-oxidation reaction in FCs. Graphic Abstract Preparation and electrocatalytic performance of carbon support and alone PtNPs toward oxidation of formic acid.

In this paper, multivariate curve resolution-alternating least squares (MCR-ALS) was applied for simultaneous determination of phenylephrine (PHE) and dextromethorphan (DEX) at the surface of bare carbon paste electrode (CPE). PHE and DEX are present in most the cold pharmaceuticals, and their voltammetric peaks have a high overlap that makes difficult or impossible their simultaneous electrochemical determinations without further experiments like modification of electrode, applying analytical techniques other than differential pulse voltammetry (DPV), or cyclic voltammetry. In this study, DEX and PHE were quantified on the surface of CPE without any further purification or modification. After recording DPV signals from thirty-three samples from these drugs and correcting potential shifts, MCR-ALS was applied to resolve overlapped peaks of these pharmaceuticals and quantitative determination of them in mixtures. Equality constraint was applied as a constraint during optimization and led to unique results from MCR-ALS. This study is the first report of using equality constraint in the analysis of first-order electrochemical data. The detection limit was determined, which was 1.79 μM for DEX and 1.93 μM for PHE, respectively. The main advantages of this method are its simplicity, low cost, and its speed since there is no need to modify electrode.

Multivariate analysis is one of the most interesting analytical methods in the analysis of many electrochemical data from pharmaceutical and biological analytes. However, there are some challenges in the electrochemical analysis including potential shifts from sample to sample and alterations in the baselines. To minimise the effect of these alterations in baselines and potentials, one tries to do all experiments in one day. However, this is impossible when there are many samples. Calibration transfer is one of the most interesting methods to transfer calibration model between two conditions or two instruments. In this study, a calibration transfer strategy was used to transfer the multivariate calibration model of DPV data from a mixture of ascorbic acid (AA) and uric acid (UA) in the same experimental condition but two different times. The data were recorded from the unmodified electrode and the voltammetric peaks of target compounds are overlapped with each other, making it impossible to be estimated by conventional univariate electrochemical methods. In this study, it was shown that before calibration transfer the prediction results are not accurate and the per cent of relative error in predicted concentration from slave data was comparable to the per cent of relative error in a predicted concentration of UA and AA in the master data.Graphical abstractSynopsis: For the first time, calibration transfer strategy was applied to reuse the multivariate calibration model of DPV data for prediction of samples which acquired after one month. Reusing the calibration model is economic and time saving approach for prediction of data which are acquired in different time with the same experimental condition.

The current review summarized the progress that has been made over the years for the colorimetric determination of corticosteroids using chromophore reagents. Following an introduction to the subject and the fundamentals of colorimetric detection of corticosteroids, the chromophoric reagents were described in detail, and a perspective on the future of these materials was proposed. Different chromophores and various colorimetric reactions used for the detection of corticosteroids in real samples were reviewed. The key point of this review is to investigate and collect the colorimetric methods to improve the sensors based on image analysis, wearable sensors, and smartphones for corticosteroids in the future.