A sensitive enzyme-free electrochemical sensor based on ZnWO4@co-MNPC@MIP for specific recognition and determination of chloramphenicol in milk sample.

We have carefully built a new chloramphenicol (CAP) electrochemical sensor, which takes the zinc tungstate @ cobalt magnetic nanoporous carbon @ molecularly imprinted polymer (ZnWO4@Co-MNPC@MIP) as the core. First, we successfully prepared Co-MNPC nanomaterials using an efficient one-step hydrothermal method and a direct carbonization method. Next, we recombined ZnWO4 with Co-MNPC and synthesized the completely new ZnWO4@Co-MNPC complex by using the hydrothermal method. To further improve its performance, we combined ZnWO4@Co-MNPC with a molecular imprinted polymer and coated a molecular imprinted (MIP) shell on the surface of ZnWO4@Co-MNPC by precipitation polymerization. This shell not only gives the sensor a new performance but also gives it a stronger peak current, resulting in a more accurate detection of CAP. Under optimal conditions, the ZnWO4@Co-MNPC@MIP (MMIP) electrode has a stronger CAP detection peak current than the one-component electrode, with a fairly wide linear range: 0.007-200 µM and 200-1400 µM. Even more surprisingly, the detection limit is as low as 0.0027 µM, which allows the sensor to maintain excellent selectivity and stability in the face of various interferences, making it an excellent electrochemically modified electrode. Compared to magnetic non-molecular imprint sensors (MNIPs), MMIP sensors have higher detection efficiency. After practical application, we found that the ZnWO4@Co-MNPC@MIP modified electrode was satisfactory in milk samples.

A sensitive and selective voltammetric method for the detection of pyrogallol in tomato and water samples using platinum electrode modified with alizarin red S film.

In contrast to the hyperactive platinum electrode, ARS modified platinum electrode presents a remarkable inertness toward adsorption and surface processes and lends it for further voltammetric applications. Measuring pyrogallol levels in samples is significant for assessing their antioxidant activity, which is crucial for understanding their potential health benefits and ability to combat oxidative stress. In addition, the excess consumption of pyrogallol can have significant negative effects on human health. A voltammetric sensor has been developed for the determination of pyrogallol using ARS modified platinum electrode. The electrode was prepared by electrodeposition of alizarin red S on a platinum electrode using cyclic voltammetry with a potential scan range of - 0.4 to 1.2 V against an Ag/AgCl quasi reference electrode for 60 cycles as optimum number of cycles. The modified electrode was characterized by CV and SEM techniques. This modified alizarin red S platinum electrode showed remarkable electrocatalytic performance and stability, resulting in a significant increase in pyrogallol oxidation current by 11.05% compared to the pyrogallol oxidative current at the unmodified platinum electrode. A well-defined oxidation peak was observed at ~ 0.40 V. The sensor exhibited a low limit of detection (LOD) of 0.28 µM and a linear standard curve covering the ranges of 1.0-40 µM and 0.01-10.0 mM pyrogallol. Extensive studies were performed to evaluate possible interferences from various organic and inorganic compounds and yielded satisfactory results that confirm the selectivity of the developed sensor for pyrogallol determination. In addition, the ARS-Pt electrode provided consistently reliable results for the accurate detection of pyrogallol in water and tomato samples.

Electrodialysis desalination: The impact of solution flowrate (or Reynolds number) on fluid dynamics throughout membrane spacers.

The incorporation of a spacer among membranes has a major influence on fluid dynamics and performance metrics. Spacers create feed channels and operate as turbulence promoters to increase mixing and reduce concentration/temperature polarization effects. However, spacer geometry remains unoptimized, and studies continue to investigate a wide range of commercial and custom-made spacer designs. The in-depth discussion of the present systematic review seeks to discover the influence of Reynolds number or solution flowrate on flow hydrodynamics throughout a spacer-filled channel. A fast-flowing solution sweeping one membrane's surface first, then the neighboring membrane's surface produces good mixing action, which does not happen commonly at laminar solution flowrates. A sufficient flowrate can suppress the polarization layer, which may normally require the utilization of a simple feed channel rather than complex spacer configurations. When a recirculation eddy occurs, it disrupts the continuous flow and effectively curves the linear fluid courses. The higher the flowrate, the better the membrane performance, the higher the critical flux (or recovery rate), and the lower the inherent limitations of spacer design, spacer shadow effect, poor channel hydrodynamics, and high concentration polarization. In fact, critical flow achieves an acceptable balance between improving flow dynamics and reducing the related trade-offs, such as pressure losses and the occurrence of concentration polarization throughout the cell. If the necessary technical flowrate is not used, the real concentration potential for transport is relatively limited at low velocities than would be predicted based on bulk concentrations. Electrodialysis stack therefore may suffer from the dissociation of water molecules. Next studies should consider that applying a higher flowrate results in greater process efficiency, increased mass transfer potential at the membrane interface, and reduced stack thermal and electrical resistance, where pressure drop should always be indicated as a consequence of the spacer and circumstances used, rather than a problem.

Electrochemical immunosensing of low-density lipoprotein based on sol-gel encapsulation

Abstract Lipoprotein monitoring is desirable in the management of medical conditions such as atherosclerotic cardiovascular disease and coronary artery disease, in which controlling the concentration of these chylomicrons is crucial. Current clinical methods are complex and present poor reproducibility between laboratories. For these reasons, recent guidelines discard the assessment of low-density lipoprotein cholesterol (LDL-C) as a routine analysis during lipid-lowering therapies. Concerning the importance of monitoring this parameter, the authors present an electrochemical immunosensor constructed from a simple and easy-to-reproduce platform that allows detecting and quantifying LDL nanoparticles directly from human serum samples. The performance of the biosensor was studied by scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The biosensing platform displays good stability and linearity between 30 mg dL-1 and 135 mg dL-1 with a detection limit of 20 mg dL-1. The proposed biosensor can be easily employed for monitoring LDL concentration in clinical treatments.

Electrochemically Driven Photosynthetic Electron Transport in Cyanobacteria Lacking Photosystem II.

Light-activated photosystem II (PSII) carries out the critical step of splitting water in photosynthesis. However, PSII is susceptible to light-induced damage. Here, results are presented from a novel microbial electro-photosynthetic system (MEPS) that uses redox mediators in conjunction with an electrode to drive electron transport in live Synechocystis (ΔpsbB) cells lacking PSII. MEPS-generated, light-dependent current increased with light intensity up to 2050 µmol photons m-2 s-1, which yielded a delivery rate of 113 µmol electrons h-1 mg-chl-1 and an average current density of 150 A m-2 s-1 mg-chl-1. P700+ re-reduction kinetics demonstrated that initial rates exceeded wildtype PSII-driven electron delivery. The electron delivery occurs ahead of the cytochrome b6f complex to enable both NADPH and ATP production. This work demonstrates an electrochemical system that can drive photosynthetic electron transport, provides a platform for photosynthetic foundational studies, and has the potential for improving photosynthetic performance at high light intensities.

Neurotransmitter Release of Reprogrammed Cells Using Electrochemical Detection Methods.

The detection of neurotransmitter release from reprogrammed human cell is an important demonstration of their functionality. Electrochemistry has the distinct advantages over alternative methods that it allows for the measuring of the analyte of interest at a high temporal resolution. This is necessary for fast events, such as neurotransmitter release and reuptake, which happen in the order of milliseconds to seconds. The precise description of these kinetic events can lead to insights into the function of cells in health and disease and allows for the exploration of events that might be missed using methods that look at absolute concentration values or methods that have a slower sampling rate. In the present chapter, we describe the use of constant potential amperometry and enzyme-coated multielectrode arrays for the detection of glutamate in vitro. These biosensors have the distinct advantage of "self-referencing," a method providing high selectivity while retaining outstanding temporal resolution. Here, we provide a step-by-step user guide for a commercially available system and its application for in vitro systems such as reprogrammed cells.

A ratiometric electrochemical sensor for selectively monitoring monoamine oxidase A in the live brain.

Herein, an electrochemical method for selectively sensing and accurately quantifying monoamine oxidase A (MAO-A) in the cortex and thalamus of a live mouse brain was reported. Using this tool, it was found that MAO-A increased Ca2+ entry into neurons via the TPRM2 channel in the live mouse brain of an AD model.

Electrochemical Sensing and Characterization of Aerobic Marine Bacterial Biofilms on Gold Electrode Surfaces.

Reliable and accurate in situ sensors capable of detecting and quantifying troublesome marine biofilms on metallic surfaces are increasingly necessary. A 0.2 mm diameter gold electrochemical sensor was fully characterized using cyclic voltammetry in abiotic and biotic artificial seawater media within a continuous culture flow cell to detect the growth and development of an aerobic Pseudoalteromonas sp. biofilm. Deconvolution of the abiotic and biotic responses enable the constituent extracellular electron transfer and biofilm responses to be resolved. Differentiation of enhanced oxygen reduction kinetics within the aerobic bacterial biofilm is linked to enzyme and redox mediator activities.

Aptamer-Integrated Multianalyte-Detecting Paper Electrochemical Device.

On-site detection of multiple small-molecule analytes in complex sample matrixes would be highly valuable for diverse biosensing applications. Paper electrochemical devices (PEDs) offer an especially appealing sensing platform for such applications due to their low cost, portability, and ease of use. Using oligonucleotide-based aptamers as biorecognition elements, we here for the first time have developed a simple, inexpensive procedure for the fabrication of aptamer-modified multiplex PEDs (mPEDs), which can robustly and specifically detect multiple small molecules in complex samples. These devices are prepared via an ambient vacuum filtration technique using carbon and metal nanomaterials that yields precisely patterned sensing architecture featuring a silver pseudo-reference electrode, a gold counter electrode, and three gold working electrodes. The devices are user-friendly, and the fabrication procedure is highly reproducible. Each working electrode can be readily modified with different aptamers for sensitive and accurate detection of multiple small-molecule analytes in a single sample within seconds. We further demonstrate that the addition of a PDMS chamber allows us to achieve detection in microliter volumes of biological samples. We believe this approach should be highly generalizable, and given the rapid development of small-molecule aptamers, we envision that facile on-site multi-analyte detection of diverse targets in a drop of sample should be readily achievable in the near future.

Electrochemical sensing technology for liquid biopsy of circulating tumor cells-a review.

In recent years, a lot of new detection techniques for circulating tumor cells (CTCs) have been developed. Among them, electrochemical sensing technology has gradually developed because of its advantages of good selectivity, high sensitivity, low cost and rapid detection. Especially in the latest decade, the field of electrochemical biosensing has witnessed great progress, thanks to the merging of biosensing research area with nanotechnology, immunotechnology, nucleic acid technology, and microfluidic technology. In this review, the recent progress for the detection of CTCs according to the principle of detection was summarized and how they can contribute to the enhanced performance of such biosensors was explained. The latest electrode construction strategies such as rolling circle amplification reaction, DNA walker and microfluidic technology and their advantages were also introduced emphatically. Moreover, the main reasonswhy the existing biosensors have not been widely used clinically and the next research points were clearly put forward.

Metal-Free Multilayer Hybrid PENG Based on Soft Electrospun/-Sprayed Membranes with Cardanol Additive for Harvesting Energy from Surgical Face Masks.

Disposable surgical face masks are usually used by medical/nurse staff but the current Covid-19 pandemic has caused their massive use by many people. Being worn closely attached to the people's face, they are continuously subjected to routine movements, i.e., facial expressions, breathing, and talking. These motional forces represent an unusual source of wasted mechanical energy that can be rather harvested by electromechanical transducers and exploited to power mask-integrated sensors. Typically, piezoelectric and triboelectric nanogenerators are exploited to this aim; however, most of the current devices are too thick or wide, not really conformable, and affected by humidity, which make them hardly embeddable in a mask, in contact with skin. Different from recent attempts to fabricate smart energy-harvesting cloth masks, in this work, a wearable energy harvester is rather enclosed in the mask and can be reused and not disposed. The device is a metal-free hybrid piezoelectric nanogenerator (hPENG) based on soft biocompatible materials. In particular, poly(vinylidene fluoride) (PVDF) membranes in the pure form and with a biobased plasticizer (cardanol oil, CA) are electrospun onto a laser-ablated polyimide flexible substrate attached on a skin-conformable elastomeric blend of poly(dimethylsiloxane) (PDMS) and Ecoflex. The multilayer structure of the device harnesses the piezoelectricity of the PVDF nanofibers and the friction triboelectric effects. The ultrasensitive mechanoelectrical transduction properties of the composite device are determined by the strong electrostatic behavior of the membranes and the plasticization effect of cardanol. In addition, encapsulation based on PVDF, PDMS, CA, and parylene C is used, allowing the hPENG to exhibit optimal reliability and resistance against the wet and warm atmosphere around the face mask. The proposed device reveals potential applications for the future development of smart masks with coupled energy-harvesting devices, allowing to use them not only for anti-infective protection but also to supply sensors or active antibacterial/viral devices.

Enhanced response of sensor on serotonin using nickel-reduced graphene oxide by atomic layer deposition.

Atomic layer deposition (ALD) is a promising method for preparing nanomaterials. The thickness and uniformity of nanomaterials can be precisely controlled. Hence, the uniform Ni nanoparticles (Ni NPs) deposited on reduced graphene oxide (rGO) by ALD and got the optimal combination interface. The morphology, structure, and electrochemical behavior of Ni NPs-rGO nanocomposite are investigated. By experiment results, the Ni NPs could occupy some active surface of rGO, resulting in high conductivity and large specific surface area of Ni NPs-rGO nanocomposite. The Ni NPs-rGO nanocomposite exhibits high electrocatalytic activity for serotonin and speeds up the electron transfer between the surface of the electrode and the solution. Therefore, the sensor is prepared by Ni NPs-rGO nanocomposite modified glassy carbon electrode (GCE) and used to sensitive detection of serotonin. By differential pulse voltammetric, the Ni NPs-rGO/GCE enhanced the current responses and showed a wide linear range of 0.02-2 µM with a low detection of 0.01 µM for serotonin (S/N = 3). The Ni NPs-rGO/GCE exhibited good stability, selectivity, and anti-interference ability that can be used for real sample detection. According to these results, the Ni NPs-rGO nanocompositeis successfully prepared by ALD. The properties of Ni NPs-rGO nanocomposite make it an attractive material for potential applications in sensors and catalysis.

A high-performance voltammetric methodology for the ultra-sensitive detection of riboflavin in food matrices based on graphene oxide-covered hollow MnO2 spheres.

A high-performance voltammetric methodology was developed to achieve ultra-sensitive detection of riboflavin, employing an electrode modified by graphene oxide-covered hollow MnO2 spheres nanocomposite with high catalytic activity, large surface area, and hierarchical layered structure. Under the optimal conditions, the current responses of the oxidation peak located at -0.39 V showed a good linear relationship versus the concentration of riboflavin in the range of 1.0 nM-4.0 µM in acetate buffer (pH 5.4). The limit of detection was determined as 0.26 nM. Moreover, the proposed electrode exhibited high reproducibility (relative standard deviation of 1.7%, n = 10) and excellent stability (97.6% sensitivity within two months), which has been successfully applied to the quantification of riboflavin in complicated food matrices, with results in good accordance with those obtained by chromatography as a reference method, indicating it is an effective sensing platform for ultra-sensitive determination of riboflavin in practical applications.

Voltammetric detection of arsenic (III) using gold nanoparticles modified carbon screen printed electrodes: Application for facile and rapid analysis in commercial apple juice.

This paper describes a voltammetric method and data analysis program developed for the detection of arsenic(III) in commercial apple juice. Arsenic(III) was detected using square wave stripping voltammetry with gold nanoparticle modified screen printed electrodes. The only sample pretreatment performed was the addition of a 100 mM phosphate buffer with a pH of 7. To compensate for interference from high ascorbic acid concentrations, a data analysis program was developed in MATLAB to fit a non-linear baseline, allowing for accurate peak height measurement. With this data analysis program, the developed methodology had a sensitivity of 0.1007 µA (µg L-1)-1 and a limit of detection of 16.73 µg L-1. A comparison between the voltammetric method and graphite furnace atomic absorption spectroscopy showed no bias in the voltammetric results and a good correlation between the two sets of predicted concentrations, with an R2 of 0.939.

Fructose determination in fruit juices using an electrosynthesized molecularly imprinted polymer on reduced graphene oxide modified electrode.

The present work reports the development of a novel electrochemical sensor for the selective detection of fructose. The sensor was developed through electropolymerization of a molecularly imprinted polymer film on a reduced graphene oxide modified electrode. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, atomic force microscopy and RAMAN spectroscopy. Through the application of the modified electrode, the recognition of fructose molecules occurred in a concentration range of 1.0 × 10-14 to 1.0 × 10-11 mol L-1, under a Langmuir adsorption isothermal model. The sensitivity and limits of detection and quantification obtained for the sensor were 9.9 × 107 A L mol-1, 3.2 × 10-15 mol L-1 and 1.1 × 10-14 mol L-1, respectively. The analytical method used for the detection of fructose presented good reproducibility, stability and accuracy, and was successfully applied for the quantification of this sugar in orange, apple and grape juices.

Carbon cloth-supported nanorod-like conductive Ni/Co bimetal MOF: A stable and high-performance enzyme-free electrochemical sensor for determination of glucose in serum and beverage.

In this work, we propose a electrochemical enzyme-free glucose sensor by direct growth of conductive Ni/Co bimetal MOF on carbon cloth [Ni/Co(HHTP)MOF/CC] via a facile hydrothermal method. Due to excellent conductivity between Ni/Co(HHTP)MOF and CC, synergic catalytic effect of Ni and Co elements, the Ni/Co(HHTP)MOF/CC not only provides larger surface area and more effective active sites, but also boosts the charge transports and electro-catalytic performance. Under optimized conditions, the Ni/Co(HHTP)MOF/CC shows excellent activity with a linear range of 0.3 µM-2.312 mM, a low detection limit of 100 nM (S/N = 3), a fast response time of 2 s and a high sensitivity of 3250 µA mM-1 cm-2. Furthermore, the Ni/Co(HHTP)MOF/CC was successfully applied for the detection of glucose in real serum and beverages with competitive performances. This facile and cost-effective method provides a novel strategy for monitoring of glucose in biological and food samples.

Delta-9-tetrahydrocannabinol (Δ9-THC) sensing using an aerosol jet printed organic electrochemical transistor (OECT).

Recreational use of marijuana/cannabis was legalized in Canada in 2018 and has been decriminalized in several other countries; however, the detection of impairment has remained elusive for law enforcement. The psychoactive ingredient in cannabis, delta-9-tetrahydrocannabinol (Δ9-THC), can be detected in saliva and be correlated well with the intake of cannabis. Organic electrochemical transistors (OECTs) have been used for a variety of biosensing applications like glucose, pH, ions, etc. In this work, we demonstrate the use of unfunctionalized OECTs for the detection of Δ9-THC down to 0.1 nM and 1 nM diluted in DI water and synthetic saliva buffer, respectively. These OECTs have been aerosol jet printed entirely with PEDOT:PSS as the channel material. Using a platinum gate coupled with an aerosol jet printed OECT, Δ9-THC concentration can be detected due to its oxidation reaction at the gate. These results were consistent with cyclic voltammetry measurements of Δ9-THC using Pt as the working and counter electrode. Utilizing these OECT based sensors, we have achieved high sensitivity of detection of Δ9-THC in the range from 0.1 nM to 5 µM. These OECT based Δ9-THC sensors demonstrate less than 3% error indicating good repeatability which is averaged over 15 measurements on multiple devices.

Effects of sonochemical approach and induced contraction of core-shell bismuth sulfide/graphitic carbon nitride as an efficient electrode materials for electrocatalytic detection of antibiotic drug in foodstuffs.

Ultrasonic-enhanced surface-active bismuth trisulfide based core-shell nanomaterials were developed and used as an efficient modified electrode material to construct a highly sensitive antibiotic sensor. The core-shell Bi2S3@GCN electrode material was directly synthesized by in-situ growth of GCN on Bi2S3 to form core-shell like nanostar (Ti-horn, 30 kHz, and 70 W/cm2). The electrocatalyst of Bi2S3@GCN nanocomposites was efficaciously broadened towards electrochemical applications. As synthesized Bi2S3@GCN promoted the catalytic ability and electrons of GCN to transfer to Bi2S3. The single-crystalline GCN layers were uniformly grown on the surface of the Bi2S3 nanostars. Under the optimal conditions of electrochemical analysis, the CPL sensor exhibited responses directly proportional to concentrations (toxic chemical) over a range of 0.02-374.4 µM, with a nanomolar detection limit of 1.2 nM (signal-to-noise ratio S/N = 3). In addition, the modified sensor has exhibited outstanding selectivity under high concentrations of interfering chemicals and biomolecules. The satisfactory CPL recoveries in milk product illustrated the credible real-time application of the proposed Bi2S3@GCN sensors for real samples, indicating promising potential in food safety department and control. Additionally, the proposed electrochemical antibiotic sensor exhibited outstanding performance of anti-interfering ability, high stability and reproducibility.

Redox Potential Heterogeneity in Fixed-Bed Electrodes Leads to Microbial Stratification and Inhomogeneous Performance.

Bed electrodes provide high electrode area-to-volume ratios represent a promising configuration for transferring bioelectrochemical systems close to industrial applications. Nevertheless, the intrinsic electrical resistance leads to poor polarization behavior. Therefore, the distribution of Geobacter spp. and their electrochemical performance within exemplary fixed-bed electrodes are investigated. A minimally invasive sampling system allows characterization of granules from different spatial locations of bed electrodes. Cyclic voltammetry of single granules (n=63) demonstrates that the major share of electroactivity (134.3 mA L-1 ) is achieved by approximately 10 % of the bed volume, specifically that being close to the current collector. Nevertheless, analysis of the microbial community reveals that Geobacter spp. dominated all sampled granules. These findings clearly demonstrate the need for engineered bed electrodes to improve electron exchange between microorganisms and granules.

An electrodialytic device for automated inorganic anion preconcentration with determination by ion chromatography-conductivity detection.

A 4-layer sandwiched device (4LSD) well suited for coupling to online ion chromatography (IC) systems was described and simultaneously performed target anion enrichment, matrix removal and sample injection within seconds. The basic assembly consisted of an extraction solution channel, a sample solution channel and two electrolyte channels. Cation-exchange resin (CER) was utilized to support the solution chamber, increase electrical conductivity and improve pressure resistance to achieve compatibility with a peristaltic pump. Filter placement ensured loop circulation of the 4LSD and prevented resin leakage. The 4LSD showed comparable performance to that of conventional solid-phase extraction (SPE) pretreatment in terms of matrix interference removal while enabling automation. The applied current, sample/extraction solution flow rate ratio, and initial concentration were discussed and optimized. Controllable 1-40-fold enrichment can be ensured. The migration phenomenon of different anions was discussed. F-, Cl-, NO2-, Br-, NO3-, SO42- and ClO4- exhibited satisfactory linear detection ranges within 2.5-1000 µg·L-1, and the calculated limits of detection (LODs) in milk formula were within the 0.097-0.79 mg·kg-1 range. The 4LSD was successfully applied to the determination of anions in milk formula with good spiked recoveries ranging between 92.54% and 107.2%, except for the NO2- recovery. The relative standard deviations (RSDs) ranged from 0.69% to 8.29%.