Basic electrochemical properties of sputtered gold film electrodes

Molecular Shape-Preserving Au Electrode for Progesterone Detection

Quantifying progesterone levels in the body is an important indicator of early pregnancy and health. Molecular shape-preserving electrodes have garnered attention in electrochemical biosensors because they can detect targets without the need for expensive enzymes or antibodies. However, some of the currently used methods typically have low electrode durability. Here, progesterone, for which antibodies are typically expensive, was used to develop a molecular shape-preserving electrode using Au to enhance its long-term stability. The physical properties of the electrodes were characterized using scanning electron microscopy (SEM), the electrochemical surface area (ECSA), and cyclic voltammetry (CV). The specific structure of the electrode demonstrated an electrochemical double layer comparable to that of a smooth Au electrode, confirming its high durability. The detection performance was assessed using CV, square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS). The current response to progesterone increased in a concentration-dependent manner, but decreased from the saturated state owing to electrodeposition on the surface. Additionally, electrochemical impedance measurements showed high selectivity compared with hormones with similar structures. The fabricated molecular shape-preserving electrode exhibits an excellent durability, stability, and detection performance, confirming its suitability for long-term use. These findings pave the way to new possibilities for electrode fabrication.

Terahertz Transmission through a Gold Mirror or Electrode

Hundreds of nanometer-thick metal layers are used as electrical conductors in various technologies and research fields. The intensity of the radiation transmitted by such devices is a small fraction and is often neglected. Here, it is shown that intense terahertz time-domain spectroscopy can probe the absolute electro-optical properties of a 100 nm thick gold sample in transmission geometry without the need to apply electrical contacts or handle wires. The terahertz conductivity of the metal film agrees with that obtained from standard contact measurements of the static component within the error bars. This experimental approach can help to quantify the electrical properties of opaque and conductive materials such as the composite electrodes used in photovoltaic or electrochemical applications, and in the quality control of metal films.

Evaluation of Transducer Elements Based on Different Material Configurations for Aptamer-Based Electrochemical Biosensors

The selection of an appropriate transducer is a key element in biosensor development. Currently, a wide variety of substrates and working electrode materials utilizing different fabrication techniques are used in the field of biosensors. In the frame of this study, the following three specific material configurations with gold-finish layers were investigated regarding their efficacy to be used as electrochemical (EC) biosensors: (I) a silicone-based sensor substrate with a layer configuration of 50 nm SiO/50 nm SiN/100 nm Au/30-50 nm WTi/140 nm SiO/bulk Si); (II) polyethylene naphthalate (PEN) with a gold inkjet-printed layer; and (III) polyethylene terephthalate (PET) with a screen-printed gold layer. Electrodes were characterized using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) to evaluate their performance as electrochemical transducers in an aptamer-based biosensor for the detection of cardiac troponin I using the redox molecule hexacyanoferrade/hexacyaniferrade (K3[Fe (CN)6]/K4[Fe (CN)6]. Baseline signals were obtained from clean electrodes after a specific cleaning procedure and after functionalization with the thiolate cardiac troponin I aptamers "Tro4" and "Tro6". With the goal of improving the PEN-based and PET-based performance, sintered PEN-based samples and PET-based samples with a carbon or silver layer under the gold were studied. The effect of a high number of immobilized aptamers will be tested in further work using the PEN-based sample. In this study, the charge-transfer resistance (Rct), anodic peak height (Ipa), cathodic peak height (Ipc) and peak separation (∆E) were determined. The PEN-based electrodes demonstrated better biosensor properties such as lower initial Rct values, a greater change in Rct after the immobilization of the Tro4 aptamer on its surface, higher Ipc and Ipa values and lower ∆E, which correlated with a higher number of immobilized aptamers compared with the other two types of samples functionalized using the same procedure.

Flexible molecularly imprinted glucose sensor based on graphene sponge and Prussian blue

To enhance the sensitivity of flexible glucose sensors made with 3-aminophenylboronic acid and pyrrole as functional molecules and a carbon tri-electrode as substrate, graphene sponge (GS) and Prussian blue (PB) were used to enhance the charge transfer between the molecularly imprinted cavities and the electrodes. Electrochemical impedance spectroscopy and cyclic voltammetry showed that modifying the electrode with GS and PB significantly reduced the charge transfer impedance and increased the redox current of the sensor. The sensor has a sensitivity of up to 25.81 µA⋅loge (µM)-1⋅cm-2 for the detection of glucose using differential pulse voltammetry in the range of 7.78 to 600 µM, with a low detection limit of 1.08 μM (S/N = 3). When the pH varies in the range of 5.5 to 7.5, the sensor maintains a certain level of stability for glucose detection. The presence of lactic acid, urea, and ascorbic acid had minimal impact on glucose detection by the sensor. After 20 days of storage at room temperature, the sensor maintains 80 % efficiency. This study supports the development of wearable glucose sensors with high sensitivity, specificity, and stability through molecular imprinting.

Design and characterization of an electrochemically-modulated membrane chromatography device

Membrane separations offer a compelling alternative to traditional chromatographic methods by overcoming mass transport limitations. We introduce an additional degree of freedom in modulating membrane chromatography by using metalized membranes in a potential-driven process. Investigating the impact of a gold coating on membrane characteristics, the sputtered gold layer enhances the surface conductivity with stable electrochemical behavior. However, this comes at the expense of reduced permeability, wettability, and static binding capacity (∼ 474 µg g-1 of maleic acid). The designed device displayed a homogenous flow distribution, and the membrane electrodes exhibit predominantly capacitive behavior during potential application. Modulating the electrical potential during the adsorption and desorption phase strongly influenced the binding and elution behavior of anion-exchange membranes. Switching potentials between ±1.0 V vs. Ag/AgCl induces desorption, confirming the process principle. Elution efficiency reaches up to 58 % at -1.0 V vs. Ag/AgCl in the desorption phase without any alteration of the mobile phase. Increasing the potential perturbation ranging from +1.0 V to -1.0 V vs. Ag/AgCl resulted in reduced peak width and improved elution behavior, demonstrating the feasibility of electrochemically-modulated membrane chromatography. The developed process has great potential as a gentle and sustainable separation step in the biotechnological and chemical industry.

A label-free electrochemical immunosensor based on PtCoCu PNPs/NB-rGO as a dual signal amplification platform for sensitive detection of β-Amyloid1-42

In this work, a label-free electrochemical immunosensor based on popcorn-shaped PtCoCu nanoparticles supported on N- and B-codoped reduced graphene oxide (PtCoCu PNPs/NB-rGO) was constructed to sensitively detect concentration level of β-Amyloid_1-42 oligomers (Aβ). The PtCoCu PNPs exhibits excellent catalytic ability due to its popcorn structure which improves the specific surface area and porosity, resulting in more active sites being exposed and fast transport paths for ion/electron. NB-rGO with large surface area and unique pleated structure could disperse PtCoCu PNPs through electrostatic adsorption and formation of d-p dative bonds between the metal ion and pyridinic N of NB-rGO. In addition, the doping of B atoms enhances the catalytic ability of GO enormously and achieves further signal amplification. Besides, both PtCoCu PNPs and NB-rGO are able to fix abundant antibodies through M(Pt, Co, Cu)-N bonds and amide bonds respectively without any other complex processing procedures such as carboxylation, ect. The designed platform achieved the dual amplification of electrocatalytic signal and effectively immobilization of antibodies. Under the optimum conditions, the designed electrochemical immunosensor presented wide linear rang (50.0 fg/mL ∼ 100 ng/mL) and low detection limits (3.5 fg/mL). The results demonstrated that the prepared immunosensor will be promising in sensitive detection of AD biomarkers.

A customizable cost-effective design for printed circuit board-based nanolayered gold screen-printed electrode: From fabrication to bioapplications

Screen-printed electrodes (SPEs) are promising candidates for fabricating biosensing platforms in the laboratory and industry due to the various advantages they involve. The primary method for fabricating SPEs is 2D printing. However, commercial SPEs have some limitations due to the specific ports and connections they require, inflexible design, high prices, and decreased efficiency after a short time. This article introduces high performance, feasible, and cost-effective gold SPEs based on the combination of printed circuit board substrate (PCBs) and sputtering methods for electrochemical biosensing platforms. First, we discuss a general gold SPE development procedure that helps researchers to develop specific designs. The final developed version of SPEs was characterized in the second step, showing positive performance in electrochemical parameters because of the optimization of design and fabrication steps. In the study’s final phase, SPEs were used to fabricate a simple platform for breast cancer cell detection as a proof of concept without using any linker or labeling step. The designed immunosensor is very simple and cost-effective, showing a linear calibration curve in the range of 10 − 2× 102 cells mL−1 (R2 = 0.985, S/N = 3). This research can be used as a reference for future studies in SPEs-based biosensors because of the flexibility of its design and the accessibility of the manufacturing equipment required.

Vanadium-Substituted Dawson-Type Polyoxometalate–TiO2 Nanowire Composite Film as Advanced Cathode Material for Bifunctional Electrochromic Energy-Storage Devices

Polyoxometalates (POMs) demonstrate potential for application in the development of integrated smart energy devices based on bifunctional electrochromic (EC) optical modulation and electrochemical energy storage. Herein, a nanocomposite thin film composed of a vanadium-substituted Dawson-type POM, i.e., K₇[P₂W₁₇VO₆₂]·18H₂O, and TiO₂ nanowires were constructed via the combination of hydrothermal and layer-by-layer self-assembly methods. Through scanning electron microscopy and energy-dispersive spectroscopy characterisations, it was found that the TiO₂ nanowire substrate acts as a skeleton to adsorb POM nanoparticles, thereby avoiding the aggregation or stacking of POM particles. The unique three-dimensional core−shell structures of these nanocomposites with high specific surface areas increases the number of active sites during the reaction process and shortens the ion diffusion pathway, thereby improving the electrochemical activities and electrical conductivities. Compared with pure POM thin films, the composite films showed improved EC properties with a significant optical contrast (38.32% at 580 nm), a short response time (1.65 and 1.64 s for colouring and bleaching, respectively), an excellent colouration efficiency (116.5 cm² C⁻¹), and satisfactory energy-storage properties (volumetric capacitance = 297.1 F cm⁻³ at 0.2 mA cm⁻²). Finally, a solid-state electrochromic energy-storage (EES) device was fabricated using the composite film as the cathode. After charging, the constructed device was able to light up a single light-emitting diode for 20 s. These results highlight the promising features of POM-based EES devices and demonstrate their potential for use in a wide range of applications, such as smart windows, military camouflage, sensors, and intelligent systems.

Development of GO/Co/Chitosan-Based Nano-Biosensor for Real-Time Detection of D-Glucose

Electrochemical nano-biosensor systems are popular in the industrial field, along with evaluations of medical, agricultural, environmental and sports analysis, because they can simultaneously perform qualitative and quantitative analyses with high sensitivity. However, real-time detection using an electrochemical nano-biosensor is greatly affected by the surrounding environment with the performance of the electron transport materials. Therefore, many researchers are trying to find good factors for real-time detection. In this work, it was found that a composite composed of graphite oxide/cobalt/chitosan had strong stability and electron transfer capability and was applied to a bioelectrochemical nano-biosensor with high sensitivity and stability. As a mediator-modified electrode, the GO/Co/chitosan composite was electrically deposited onto an Au film electrode by covalent boding, while glucose oxidase as a receptor was immobilized on the end of the GO/Co/chitosan composite. It was confirmed that the electron transfer ability of the GO/Co/chitosan composite was excellent, as shown with power density analysis. In addition, the real-time detection of D-glucose could be successfully performed by the developed nano-biosensor with a high range of detected concentrations from 1.0 to 15.0 mM. Furthermore, the slope value composed of the current, per the concentration of D-glucose as a detection response, was significantly maintained even after 14 days.

A dual-signal output electrochemical immunosensor based on Au-MoS2/MOF catalytic cycle amplification strategy for neuron-specific enolase ultrasensitive detection

In this work, a dual-signal output electrochemical immunosensor based on the Au-MoS₂/MOF high-efficiency catalytic cycle amplification strategy for the sensitive detection of neuron-specific enolase (NSE). The mixed-valence structure MOF (Fe²⁺/Fe³⁺-MOF) exhibits high-speed charge mobility and excellent electrochemical performance. Notably, nanoflowers-like MoS₂ (MoS₂ NFs), as a co-catalyst, were introduced into Fe²⁺/Fe³⁺-MOF to successfully ensure the stable cycle of Fe²⁺/Fe³⁺ at the electrode interface. The constantly emerging of "fresh" active sites significantly amplified the current signal response. According to the electrochemical behavior, the catalytic cycle mechanism and electron transfer pathways between MoS₂ and Fe²⁺/Fe³⁺-MOF were further discussed. The two output signals of a sample realized the self-calibration of the immunoassay results, which improved the reliability and sensitivity of the immunosensor. Under optimal conditions, the linear range was 1.00 pg/mL∼100 ng/mL, and the low detection limits were 0.37 pg/mL and 0.52 pg/mL. The results suggest that the as-proposed immunosensor will be promising in the biological analysis and early clinical diagnosis of cancer biomarkers.

Development of a Mechanically Flexible 2D-MXene Membrane Cathode for Selective Electrochemical Reduction of Nitrate to N2: Mechanisms and Implications

The contamination of water resources by nitrate is a major problem. Herein, we report a mechanically flexible 2D-MXene (Ti₃C₂T_x) membrane with multilayered nanofluidic channels for a selective electrochemical reduction of nitrate to nitrogen gas (N₂). At a low applied potential of -0.8 V (vs Ag/AgCl), the MXene electrochemical membrane was found to exhibit high selectivity for NO₃^- reduction to N₂ (82.8%) due to a relatively low desorption energy barrier for the release of adsorbed N₂ (*N₂) compared to that for the adsorbed NH₃ (*NH₃) based on density functional theory (DFT) calculations. Long-term use of the MXene membrane for treating 10 mg-NO₃-N L^-1 in water was found to have a high faradic efficiency of 72.6% for NO₃^- reduction to N₂ at a very low electrical cost of 0.28 kWh m^-3. Results of theoretical calculations and experimental results showed that defects on the MXene nanosheet surfaces played an important role in achieving high activity, primarily at the low-coordinated Ti sites. Water flowing through the MXene nanosheets facilitated the mass transfer of nitrate onto the low-coordinated Ti sites with this enhancement of particular importance under cathodic polarization of the MXene membrane. This study provides insight into the tailoring of nanoengineered materials for practical application in water treatment and environmental remediation.

Flexible electrochemical biosensors for healthcare monitoring

As the interest in wearable devices has increased recently, increasing biosensor flexibility has begun to attract considerable attention. Among the various types of biosensors, electrochemical biosensors are uniquely suited for the development of such flexible biosensors due to their many advantages, including their fast response, inherent miniaturization, convenient operation, and portability. Therefore, many studies on flexible electrochemical biosensors have been conducted in recent years to achieve non-invasive and real-time monitoring of body fluids such as tears, sweat, and saliva. To achieve this, various substrates, novel nanomaterials, and detection techniques have been utilized to develop conductive flexible platforms that can be applied to create flexible electrochemical biosensors. In this review, we discussed recently reported flexible electrochemical biosensors and divided them into specific categories including materials for flexible substrate, fabrication techniques for flexible biosensor development, and recently developed flexible electrochemical biosensors to externally monitor target molecules, thereby providing a means to noninvasively examine cells and body fluid samples. In conclusion, this review will discuss the materials, methods, recent studies, and perspectives on flexible electrochemical biosensors for healthcare monitoring and wearable biosensing systems.

How to Improve the Performance of Electrochemical Sensors via Minimization of Electrode Passivation

It follows from critical evaluation of possibilities and limitations of modern voltammetric/amperometric methods that one of the biggest obstacles in their practical applications in real sample analysis is connected with electrode passivation/fouling by electrode reaction products and/or matrix components. This review summarizes possibilities how to minimise these problems in the field of detection of small organic molecules and critically compares their potential and acceptability in practical laboratories. Attention is focused on simple and fast electrode surface renewal, the use of disposable electrodes just for one and/or few measurements, surface modification minimising electrode fouling, measuring in flowing systems, application of rotating disc electrode, the use of novel separation methods preventing access of passivating particles to electrode surface and the novel electrode materials more resistant toward passivation. An attempt is made to predict further development in this field and to stress the need for more systematic and less random research resulting in new measuring protocols less amenable to complications connected with electrode passivation.

Developing a versatile electrochemical platform with optimized electrode configuration through screen-printing technology toward glucose detection

Rapid on-site detection of glucose has been attracting considerable attention nowadays. Screen-printed electrodes (SPEs) were assessed as ideal detection platforms due to their advantages such as, disposability, portability, ease of miniaturization, and mass production. The topology and shape of electrodes have a crucial impact on their electrical conductivity and electrochemical properties. In this study, a versatile electrochemical platform with optimized three-electrode configuration was developed through screen-printing technology. Three types of SPEs were prepared, and their electrocatalytic properties toward glucose detection were investigated. Based on this platform, both enzyme-based (denoted as GOD/rGO) and non-enzymatic (denoted as Co@MoS2/rGO) bioactive compounds were deposited on the working electrode of the circular SPE through simply drop-casting, respectively. Their morphology was characterized through scanning electron microscopy (SEM). Cycle sweep voltammetry was used to study the electrocatalytic activity of these biosensors. The circular SPE exhibited satisfying electrochemical redox activity and much higher sensitivity towards glucose detection, which rendered it a promising candidate for point-of-care detection.

Highly efficient electrosynthesis of hydrogen peroxide on a superhydrophobic three-phase interface by natural air diffusion

Hydrogen peroxide (H₂O₂) synthesis by electrochemical oxygen reduction reaction has attracted great attention as a green substitute for anthraquinone process. However, low oxygen utilization efficiency (<1%) and high energy consumption remain obstacles. Herein we propose a superhydrophobic natural air diffusion electrode (NADE) to greatly improve the oxygen diffusion coefficient at the cathode about 5.7 times as compared to the normal gas diffusion electrode (GDE) system. NADE allows the oxygen to be naturally diffused to the reaction interface, eliminating the need to pump oxygen/air to overcome the resistance of the gas diffusion layer, resulting in fast H₂O₂ production (101.67 mg h^-1 cm^-2) with a high oxygen utilization efficiency (44.5%–64.9%). Long-term operation stability of NADE and its high current efficiency under high current density indicate great potential to replace normal GDE for H₂O₂ electrosynthesis and environmental remediation on an industrial scale.

H₂O₂ electrosynthesis has garnered great attention as a green alternative to the anthraquinone process. Here the authors propose a cost-effective cathode to greatly improve the O₂ diffusion coefficient, resulting in a high H₂O₂ production without the need for aeration.

Bifunctional electrochromic-energy storage materials with enhanced performance obtained by hybridizing TiO2 nanowires with POMs

A bifunctional electrochromic-energy storage film with enhanced performance is designed and fabricated by hybridizing TiO₂ nanowires with POMs.

Detection of Protein Toxin Simulants from Contaminated Surfaces by Paper Spray Mass Spectrometry

Proteinaceous toxins are harmful proteins derived from plants, bacteria, and other natural sources. They pose a risk to human health due to infection and also as possible biological warfare agents. Paper spray mass spectrometry (PS-MS) with wipe sampling was used to detect proteins from surfaces as a potential tool for identifying the presence of these toxins. Proteins ranging in mass between 12.4 and 66.5 kDa were tested, including a biological toxin simulant/vaccine for Staphylococcal enterotoxin B (SEBv). Various substrates were tested for these representative proteins, including a laboratory bench, a notebook cover, steel, glass, plant leaf and vinyl flooring. Carbon sputtered porous polyethylene (CSPP) was found to outperform typical chromatography paper used for paper spray, as well as carbon nanotube (CNT)-coated paper and polyethylene (PE), which have been previously shown to be well-suited for protein analysis. Low microgram quantities of the protein toxin simulant and other test proteins were successfully detected with good signal-to-noise from surfaces using a porous wipe. These applications demonstrate that PS-MS can potentially be used for rapid, sample preparation-free detection of proteins and biological warfare agents, which would be beneficial to first responders and warfighters.