Vertical Conductive Metal-Organic Framework Single-Crystalline Nanowire Arrays for Efficient Electrocatalytic Hydrogen Evolution.

The construction of crystalline metal-organic frameworks with regular architectures supportive of enhanced mass transport and bubble diffusion is imperative for electrocatalytic applications; however, this poses a formidable challenge. Here, a method is presented that confines the growth of nano-architectures to the liquid-liquid interface. Using this method, vertically oriented single crystalline nanowire arrays of an Ag-benzenehexathiol (BHT) conductive metal-organic framework (MOF) are fabricated via an "in-plane self-limiting and out-of-plane epitaxial growth" mechanism. This material has excellent electrocatalytic features, including highly exposed active sites, intrinsically high electrical conductivity, and superhydrophilic and superaerophobic properties. Leveraging these advantages, the carefully designed material demonstrates superior electrocatalytic hydrogen evolution activity, resulting in a low Tafel slope of 66 mV dec-1 and a low overpotential of 275 mV at a high current density of 1 A cm-2. Finite element analysis (FEA) and in situ microscopic verification indicates that the nanowire array structure significantly enhances the electrolyte transport kinetics and promotes the rapid release of gas bubbles. The findings highlight the potential of using MOF-based ordered nanoarray structures for advanced electrocatalytic applications.

COVID-19 diagnosis by SARS-CoV-2 Spike protein detection in saliva using an ultrasensitive magneto-assay based on disposable electrochemical sensor.

The outbreak of the COVID-19 pandemic, caused by Severe Acute Respiratory Syndrome of Coronavirus 2 (SARS-CoV-2), has fueled the search for diagnostic tests aiming at the control and reduction of the viral transmission. The main technique used for diagnosing the Coronavirus disease (COVID-19) is the reverse transcription-polymerase chain reaction (RT-PCR) technique. However, considering the high number of cases and the underlying limitations of the RT-PCR technique, especially with regard to accessibility and cost of the test, one does not need to overemphasize the need to develop new and less expensive testing techniques that can aid the early diagnosis of the disease. With that in mind, we developed an ultrasensitive magneto-assay using magnetic beads and gold nanoparticles conjugated to human angiotensin-converting enzyme 2 (ACE2) peptide (Gln24-Gln42) for the capturing and detection of SARS-CoV-2 Spike protein in human saliva. The technique applied involved the use of a disposable electrochemical device containing eight screen-printed carbon electrodes which allow the simultaneous analysis of eight samples. The magneto-assay exhibited an ultralow limit of detection of 0.35 ag mL-1 for the detection of SARS-CoV-2 Spike protein in saliva. The magneto-assay was tested in saliva samples from healthy and SARS-CoV-2-infected individuals. In terms of efficiency, the proposed technique - which presented a sensitivity of 100.0% and specificity of 93.7% for SARS-CoV-2 Spike protein-exhibited great similarity with the RT-PCR technique. The results obtained point to the application potential of this simple, low-cost magneto-assay for saliva-based point-of-care COVID-19 diagnosis.

Simple, fast, and instrumentless fabrication of paper analytical devices by novel contact stamping method based on acrylic varnish and 3D printing.

A new contact stamping method for fabrication of paper-based analytical devices (PADs) is reported. It uses an all-purpose acrylic varnish and 3D-printed stamps to pattern hydrophobic structures on paper substrates. The use of 3D printing allows quickly prototyping the desired stamp shape without resorting to third-party services, which are often expensive and time consuming. To the best of our knowledge, this is the first report regarding the use of this material for creation of hydrophobic barriers in paper substrates, as well as this 3D printing-based stamping method. The acrylic varnish was characterized and the features of the stamping method were studied. The PADs developed here presented better compatibility with organic solvents and surfactants compared with similar protocols. Furthermore, the use of this contact stamping method for fabrication of paper electrochemical devices was also possible, as well as multiplexed microfluidic devices for lateral flow testing. The analytical applicability of the varnish-based PADs was demonstrated through the image-based colorimetric quantification of iron in pharmaceutical samples. A limit of detection of 0.61 mg L-1 was achieved. The results were compared with spectrophotometry for validation and presented great concordance (relative error was < 5% and recoveries were between 104 and 108%). Thus, taking into account the performance of the devices explored here, we believe this novel contact stamping method is a very interesting alternative for production of PADs, exhibiting great potentiality. In addition, this work brings a new application of 3D printing in analytical sciences.

Highly transparent sustainable biogel electrolyte based on cellulose acetate for application in electrochemical devices.

In this study, an easy and low-cost production method for a cellulose acetate-based gel polymer containing lithium perchlorate and propylene carbonate is described, as well as the investigation of its properties for potential use as an electrolyte in electrochemical devices. Cellulose acetate, a biopolymer derived from natural matrix, is colourless and transparent, as confirmed by the UV-Vis spectroscopy, with 85 % transparency in visible spectrum. The gels were prepared and tested at different concentrations and proportions to optimise their properties. Thermogravimetry, XRD, and FTIR analyses revealed crucial characteristics, including a substantial 90 % mass loss between 150 and 250 °C, a semi-crystalline nature with complete salt dissociation within the polymer matrix, and a decrease in intensity at 1780 cm-1 with increasing Li+ ion concentration, suggesting an improvement in ionic conduction capacity. In terms of electrochemical performance, the gel containing 10 % by mass of cellulose acetate and 1.4 M of LiClO4 emerged as the most promising. It exhibited a conductivity of 2.3 × 10-4 S.cm-1 at 25 °C and 3.0 × 10-4 S.cm-1 at 80 °C. Additionally, it demonstrated an ideal shape of cyclic voltammetry curves and stability after 400 cycles, establishing its suitability as an electrolyte in electrochemical devices.

Investigating Electrode-Ionomer Interface Phenomena for Electrochemical Energy Applications.

The endeavor to develop high-performance electrochemical energy applications has underscored the growing importance of comprehending the intricate dynamics within an electrode's structure and their influence on overall performance. This review investigates the complexities of electrode-ionomer interactions, which play a critical role in optimizing electrochemical reactions. Our examination encompasses both microscopic and meso/macro scale functions of ionomers at the electrode-ionomer interface, providing a thorough analysis of how these interactions can either enhance or impede surface reactions. Furthermore, this review explores the broader-scale implications of ionomer distribution within porous electrodes, taking into account factors like ionomer types, electrode ink formulation, and carbon support interactions. We also present and evaluate state-of-the-art techniques for investigating ionomer distribution, including electrochemical methods, imaging, modeling, and analytical techniques. Finally, the performance implications of these phenomena are discussed in the context of energy conversion devices. Through this comprehensive exploration of intricate interactions, this review contributes to the ongoing advancements in the field of energy research, ultimately facilitating the design and development of more efficient and sustainable energy devices.

Analytical chemistry toward on-site diagnostics.

Analytical Chemistry, through quantitative and/or qualitative analysis (identification), is a discipline that involves the development of methodologies and the exploration of new principles to obtain answers to given problems. In situ analysis techniques have attracted attention for its ability to elucidate phenomena occurring and to evaluate amount of a certain component in substances at real time and biological samples as applications of such analysis technology. Lots of techniques have been performed to understand the fundamental phenomena in varied fields such as X-ray, vibrational, and electrochemical impedance spectroscopies and also analytical reagents that enable to semi-quantitative analysis just observation. In fact, applying various in situ techniques in analytical chemistry expands to the medical diagnosis, which leads to be able to detect early diseases. Here, we describe some of previous researches in many fields such as electrochemical device for energy storage, biology, environment, and pathology and briefly introduce our recent challenges to analytical chemistry toward the on-site diagnosis.

A stack-up electrochemical device based on metal-organic framework modified carbon paper for ultra-trace lead and cadmium ions detection.

A portable device is conducive to the on-site detection of heavy metal ions at trace level in food and the prevention of related food safety issues. In this work, an electrochemical device stacked up with flat electrodes was developed for the detection of Pb2+ and Cd2+. The top layer of the device is a carbon paper as working electrode, which is modified with amino functionalized cobalt-based metal-organic framework and gold nanoparticles. The bottom layer was constructed with the carbon counter electrode and Ag/AgCl reference electrode, and a punched sample cell (Φ = 8 mm) was in the middle. The proposed method could simultaneously determinate Pb2+ and Cd2+ via anodic stripping voltammetry with the detection limit of 7.0 × 10-2 ng mL-1 and 1.1 × 10-2 ng mL-1, and was applied in real food samples (drinking water, juice, tea, grain, fruits, vegetables, liver and aquatic products) with the recovery of 91.2-105.4 % and 90.2-111.2 %, respectively.

Study of Innovative GO/PBI Composites as Possible Proton Conducting Membranes for Electrochemical Devices.

The appeal of combining polybenzimidazole (PBI) and graphene oxide (GO) for the manufacturing of membranes is increasingly growing, due to their versatility. Nevertheless, GO has always been used only as a filler in the PBI matrix. In such context, this work proposes the design of a simple, safe, and reproducible procedure to prepare self-assembling GO/PBI composite membranes characterized by GO-to-PBI (X:Y) mass ratios of 1:3, 1:2, 1:1, 2:1, and 3:1. SEM and XRD suggested a homogenous reciprocal dispersion of GO and PBI, which established an alternated stacked structure by mutual π-π interactions among the benzimidazole rings of PBI and the aromatic domains of GO. TGA indicated a remarkable thermal stability of the composites. From mechanical tests, improved tensile strengths but worsened maximum strains were observed with respect to pure PBI. The preliminary evaluation of the suitability of the GO/PBI X:Y composites as proton exchange membranes was executed via IEC determination and EIS. GO/PBI 2:1 (IEC: 0.42 meq g-1; proton conductivity at 100 °C: 0.0464 S cm-1) and GO/PBI 3:1 (IEC: 0.80 meq g-1; proton conductivity at 100 °C: 0.0451 S cm-1) provided equivalent or superior performances with respect to similar PBI-based state-of-the-art materials.

Hyaluronic Acid Methacrylate Hydrogel-Modified Electrochemical Device for Adsorptive Removal of Lead(II).

This paper presents the development of a compact, three-electrode electrochemical device functionalized by a biocompatible layer of hyaluronic acid methacrylate (HAMA) hydrogel for the adsorptive removal of detrimental lead (Pb(II)) ions in aqueous solutions. An adsorption mechanism pertaining to the observed analytical performance of the device is proposed and further experimentally corroborated. It is demonstrated that both the molecular interactions originating from the HAMA hydrogel and electrochemical accumulation originating from the electrode beneath contribute to the adsorption capability of the device. Infrared spectral analysis reveals that the molecular interaction is mainly induced by the amide functional group of the HAMA hydrogel, which is capable of forming the Pb(II)-amide complex. In addition, inductively coupled plasma mass spectrometric (ICP-MS) analysis indicates that the electrochemical accumulation is particularly valuable in facilitating the adsorption rate of the device by maintaining a high ion-concentration gradient between the solution and the hydrogel layer. ICP-MS measurements show that 94.08% of Pb(II) ions present in the test solution can be adsorbed by the device within 30 min. The HAMA hydrogel-modified electrochemical devices exhibit reproducible performance in the aspect of Pb(II) removal from tap water, with a relative standard deviation (RSD) of 1.28% (for n = 8). The experimental results suggest that the HAMA hydrogel-modified electrochemical device can potentially be used for the rapid, on-field remediation of Pb(II) contamination.

Quality evaluation of cell spheroids for transplantation by monitoring oxygen consumption using an on-chip electrochemical device.

Three-dimensional cell spheroids are superior cell-administration form for cell-based therapy which generally exhibit superior functionality and long-term survival after transplantation. Here, we nondestructively measured the oxygen consumption rate of cell spheroids using an on-chip electrochemical device (OECD) and examined whether this rate can be used as a marker to estimate the quality of cell spheroids. Cell spheroids containing NanoLuc luciferase-expressing mouse mesenchymal stem cell line C3H10T1/2 (C3H10T1/2/Nluc) were prepared. Spheroids of high or low quality were prepared by altering the medium change frequency. After transplantation into mice, the high-quality C3H10T1/2/Nluc spheroids exhibited a higher survival rate than the low-quality ones. The oxygen consumption rate of the high-quality C3H10T1/2/Nluc spheroids was maintained at high levels, whereas that of the low-quality spheroids decreased with time. These results indicate that OECD-based measurement of the oxygen consumption rate can be used to estimate the quality of cell spheroids without destructive analysis of the spheroids.

A Review of Applications, Prospects, and Challenges of Proton-Conducting Zirconates in Electrochemical Hydrogen Devices.

In the future, when fossil fuels are exhausted, alternative energy sources will be essential for everyday needs. Hydrogen-based energy can play a vital role in this aspect. This energy is green, clean, and renewable. Electrochemical hydrogen devices have been used extensively in nuclear power plants to manage hydrogen-based renewable fuel. Doped zirconate materials are commonly used as an electrolyte in these electrochemical devices. These materials have excellent physical stability and high proton transport numbers, which make them suitable for multiple applications. Doping enhances the physical and electronic properties of zirconate materials and makes them ideal for practical applications. This review highlights the applications of zirconate-based proton-conducting materials in electrochemical cells, particularly in tritium monitors, tritium recovery, hydrogen sensors, and hydrogen pump systems. The central section of this review summarizes recent investigations and provides a comprehensive insight into the various doping schemes, experimental setup, instrumentation, optimum operating conditions, morphology, composition, and performance of zirconate electrolyte materials. In addition, different challenges that are hindering zirconate materials from achieving their full potential in electrochemical hydrogen devices are discussed. Finally, this paper lays out a few pathways for aspirants who wish to undertake research in this field.

Ion Conductance-Based Perfusability Assay of Vascular Vessel Models in Microfluidic Devices.

We present a novel methodology based on ion conductance to evaluate the perfusability of vascular vessels in microfluidic devices without microscopic imaging. The devices consisted of five channels, with the center channel filled with fibrin/collagen gel containing human umbilical vein endothelial cells (HUVECs). Fibroblasts were cultured in the other channels to improve the vascular network formation. To form vessel structures bridging the center channel, HUVEC monolayers were prepared on both side walls of the gel. During the culture, the HUVECs migrated from the monolayer and connected to the HUVECs in the gel, and vascular vessels formed, resulting in successful perfusion between the channels after culturing for 3-5 d. To evaluate perfusion without microscopic imaging, Ag/AgCl wires were inserted into the channels, and ion currents were obtained to measure the ion conductance between the channels separated by the HUVEC monolayers. As the HUVEC monolayers blocked the ion current flow, the ion currents were low before vessel formation. In contrast, ion currents increased after vessel formation because of creation of ion current paths. Thus, the observed ion currents were correlated with the perfusability of the vessels, indicating that they can be used as indicators of perfusion during vessel formation in microfluidic devices. The developed methodology will be used for drug screening using organs-on-a-chip containing vascular vessels.

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.

Highly sensitive interfaces of graphene electrical-electrochemical vertical devices for on drop atto-molar DNA detection.

The development of novel high-sensitivity DNA-based biosensors is beneficial, as these devices have applications in the identification of genetic risk factors, medical diagnostics, and environmental monitoring. Herein, we report on the first robust device capable of detecting DNA on a microliter drop with a zepto-molar (10-21) concentration. To accomplish this, we engineered an electrical-electrochemical vertical device (EEVD) that comprises a novel drain and source terminal in a short-circuited configuration, paired with an ideal non-polarizable reference electrode. Vertical electron transfer occurs perpendicularly to the graphene plane, while the electronic current flows through the graphene van der Waals (vdW) heterojunctions. Ferrocene adsorbed on graphene was strategically chosen as the vdW heterojunction redox component. Charge carrier insertion into the graphene makes the EEVD 10 times more sensitive than traditional graphene field-effect transistors. Interfacial potential changes were measured for single-stranded DNA detection with an unprecedented zepto-molar limit of detection.

Solid-State Organic Electrolyte-Gated Transistors Based on Doping-Controlled Polymer Composites with a Confined Two-Dimensional Channel in Dry Conditions.

We report comprehensive and comparative studies on chemical and electrochemical controls of doping characteristics of various poly(3,4-ethylenedioxythiophene) (PEDOT) composites complexed with sulfonates. Chemical treatment of PEDOT composites was conducted with a dedoping agent, tetrakis(dimethylamino)ethylene (TDAE), resulting in the changes in conformation and bulk charge-carrier density. Electrochemical control of doping states was done with a solid-state ionogel based on an ionic liquid dispersed in a polymer matrix. With this approach, we can fabricate solid-state organic electrolyte-gated transistors (OEGTs) with a large current modulation, a high mobility of holes, and a low driving voltage. Our OEGTs are operational in a dry environment and, surprisingly, form the two-dimensional channel of the interfacial charge carriers modulating the conductance under gate bias, unlike conventional liquid-based OEGTs. The charge-carrier mobility and the on-to-off current ratio reach up to ∼7 cm2 V-1 s-1 and over 104, respectively, from the chemically dedoped PEDOT composites. The ionogel-based gating of the layer of TDAE-treated PEDOT composites induces a reversible transition between a highly doped bipolaronic state and neutral/polaronic states, as revealed by the absorption profiles under gate bias. We also demonstrate in-plane OEGTs, in which the dedoped channel and the conductive source/drain electrodes are made of a single PEDOT composite layer.

Facile Synthesis of Co3O4-Incorporated Multichannel Carbon Nanofibers for Electrochemical Applications.

Considering their superior electrochemical performances, extensive studies have been carried out on composite nanomaterials based on porous carbon nanofibers. However, the introduction of inorganic components into a porous structure is complex and has a low yield. In this study, we propose a simple synthesis of cobalt-oxide-incorporated multichannel carbon nanofibers (P-Co-MCNFs) as electrode materials for electrochemical applications. The cobalt oxide component is directly formed in the carbon structure by a simple oxygen plasma exposure of the phase-separated polymer nanofibers. P-Co-MCNF displays high specific capacitance (815 F g-1 at 2.0 A g-1), rate capability (821 F g-1 at 1 A g-1 and 786 F g-1 at 20 A g-1), and cycle stability (92.1% for 5000 cycles) as a supercapacitor electrode. Moreover, excellent sensitivity (down to 1 nM) and selectivity to the glucose molecule is demonstrated for nonenzyme sensor applications.

Recent Advances in Electrochemiluminescence-Based Systems for Mammalian Cell Analysis.

Mammalian cell analysis is essential in the context of both fundamental studies and clinical applications. Among the various techniques available for cell analysis, electrochemiluminescence (ECL) has attracted significant attention due to its integration of both electrochemical and spectroscopic methods. In this review, we summarize recent advances in the ECL-based systems developed for mammalian cell analysis. The review begins with a summary of the developments in luminophores that opened the door to ECL applications for biological samples. Secondly, ECL-based imaging systems are introduced as an emerging technique to visualize single-cell morphologies and intracellular molecules. In the subsequent section, the ECL sensors developed in the past decade are summarized, the use of which made the highly sensitive detection of cell-derived molecules possible. Although ECL immunoassays are well developed in terms of commercial use, the sensing of biomolecules at a single-cell level remains a challenge. Emphasis is therefore placed on ECL sensors that directly detect cellular molecules from small portions of cells or even single cells. Finally, the development of bipolar electrode devices for ECL cell assays is introduced. To conclude, the direction of research in this field and its application prospects are described.

Accelerated Hydrogen Diffusion and Surface Exchange by Domain Boundaries in Epitaxial VO2 Thin Films.

Electronic phase modulation based on hydrogen insertion/extraction is kinetically limited by the bulk hydrogen diffusion or surface exchange reaction, so slow hydrogen kinetics has been a fundamental challenge to be solved for realizing faster solid-state electrochemical switching devices. Here we accelerate electronic phase modulation that occurs by hydrogen insertion in VO2 through vertically aligned 2D defects induced by symmetry mismatch between epitaxial films and substrates. By using domain-matching epitaxial growth of monoclinic VO2 films with lattice rotation and twinning on hexagonal Al2O3 substrates, the domain boundaries naturally align vertically; they provide a "highway" for hydrogen diffusion and surface exchange in VO2 films and overcome the limited rates of bulk diffusion and surface reaction. From the quantitative analysis of the deuterium (2H) isotope tracer exchange, it is confirmed that the tracer diffusion coefficient (D*) and surface exchange coefficient (k*) were increased by several orders of magnitude in VO2 films that had domain boundaries. These results yield fundamental insights into the mechanism by which mobile ions are inserted along extended defects and provide a strategy to overcome a limitation to switching speed in electrochemical devices that exploit ion insertion.

A new disposable microfluidic electrochemical paper-based device for the simultaneous determination of clinical biomarkers.

A new disposable microfluidic electrochemical paper-based device (ePAD) consisting of two spot sensors in the same working electrode for the simultaneous determination of uric acid and creatinine was developed. The spot 1 surface was modified with graphene quantum dots for direct uric acid oxidation and spot 2 surface modified with graphene quantum dots, creatininase and a ruthenium electrochemical mediator for creatinine oxidation. The ePAD was employed to construct an electrochemical sensor (based on square wave voltammetry analysis) for the simultaneous determination of uric acid and creatinine in the 0.010-3.0 µmol L-1 range. The device showed excellent analytical performance with a very low simultaneous detection limit of 8.4 nmol L-1 to uric acid and 3.7 nmol L-1 to creatinine and high selectivity. The ePAD was applied to the rapid and successful determination of those clinical biomarkers in human urine samples.

A chemiresistor sensor based on a cobalt(salen) metallopolymer for dissolved molecular oxygen.

A resistance detection device for dissolved molecular oxygen in aqueous solutions is prepared using a chemiresistor material as sensor platform. The chemiresistive circuit element is fashioned from a thin film of a cobalt-salen metallopolymer electrodeposited on a platinum electrode. Electrochemical impedance spectroscopy shows that the resistive and capacitive properties of the sensor platform depend on the presence of dissolved oxygen. The electrical circuit models are R(Q/R)(Q/R) and R(Q/R)(Q/RW) in the absence and presence of oxygen, respectively. The chemiresistor sensor exhibits good sensitivity (0.483 kΩ L mg-1), excellent reversibility and excellent linearity over a range of dissolved oxygen concentrations typically found under environmental conditions (2.72-40.9 mg L-1). The sensor fabricated in this work can potentially serve as an alternative sensor for the detection of dissolved oxygen in environmental samples.