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In this research, novel electroencephalogram (EEG) electrodes were developed to detect high-quality EEG signals without the requirement of conductive gels, skin treatments, or head shaving. These electrodes were created using electrically conductive hook fabric with a resistance of 1 Ω/sq. The pointed hooks of the conductive fabric establish direct contact with the skin and can penetrate through hair. To ensure excellent contact between the hook fabric electrode and the scalp, a knitted-net EEG bridge cap with a bridging effect was employed. The results showed that the hook fabric electrode exhibited lower skin-to-electrode impedance compared to the dry Ag/AgCl comb electrode. Additionally, it collected high-quality signals on par with the standard wet gold cups and commercial dry Ag/AgCl comb electrodes. Moreover, the hook fabric electrode displayed a higher signal-to-noise ratio (33.6 dB) with a 4.2% advantage over the standard wet gold cup electrode. This innovative electrode design eliminates the need for conductive gel and head shaving, offering enhanced flexibility and lightweight characteristics, making it ideal for integration into textile structures and facilitating convenient long-term monitoring. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) black phosphorus (BP) is considered an ideal building block for field-effect transistors (FETs) owing to its unique structure and intriguing properties. To achieve high-performance BP-FETs, it is essential to establish a reliable and low-resistance contact between the BP and the electrodes. In this study, we employed a localized Joule heating method to improve the contact between the 2D BP and gold electrodes, resulting in enhanced BP-FET performance. Upon applying a sufficiently large source–drain voltage, the zero-bias conductance of the device increased by approximately five orders of magnitude, and the linearity of the current–voltage curves was also enhanced. This contact improvement can be attributed to the formation of gold phosphide at the interface of the BP and the gold electrodes owing to current-generated localized Joule heat. The fabricated BP-FET demonstrated a high on/off ratio of 4850 and an on-state conductance per unit channel width of 1.25 μS μm−1, significantly surpassing those of the BP-FETs without electrical annealing. These findings offer a method to achieve a low-resistance BP/metal contact for developing high-performance BP-based electronic devices. [ABSTRACT FROM AUTHOR]

Bimetallic nanocomposites and nanoparticles have received tremendous interest recently because they often exhibit better properties than single-component materials. Improved electron transfer rates and the synergistic interactions between individual metals are two of the most beneficial attributes of these materials. In this review, we focus on bimetallic nanoporous gold (NPG) because of its importance in the field of electrochemical sensing coupled with the ease with which it can be made. NPG is a particularly important scaffold because of its unique properties, including biofouling resistance and ease of modification. In this review, several different methods to synthesize NPG, along with varying modification approaches are described. These include the use of ternary alloys, immersion–reduction (chemical, electrochemical, hybrid), co-electrodeposition–annealing, and under-potential deposition coupled with surface-limited redox replacement of NPG with different metal nanoparticles (e.g., Pt, Cu, Pd, Ni, Co, Fe, etc.). The review also describes the importance of fully characterizing these bimetallic nanocomposites and critically analyzing their structure, surface morphology, surface composition, and application in electrochemical sensing of chemical and biochemical species. The authors attempt to highlight the most recent and advanced techniques for designing non-enzymatic bimetallic electrochemical nanosensors. The review opens up a window for readers to obtain detailed knowledge about the formation and structure of bimetallic electrodes and their applications in electrochemical sensing. [ABSTRACT FROM AUTHOR]

Developing neural electrodes with high stretchability and stable conductivity is a promising method to explore applications of them in biological medicine and electronic skin. However, considering the poor mechanical stretchability of typical conductive materials, maintaining the connection of electrode conductive paths under high stretching is still a challenge. Herein, for the first time, a double‐microcrack coupling strategy for highly stretchable neural electrodes is proposed. Compared with single‐layer stretchable microcrack electrodes, the design utilizes the complement between two gold microcrack films to contribute more conductive paths. It shows that the resistance change (R/R0) of the electrode under 100% strain is about 5.6 times, which is much lower than other electrodes and exhibits a high stretchability of ≈200%. Simultaneously, this design is an encapsulation‐free design which avoids the electrode performance degradation caused by encapsulation. Furthermore, it is found that the adhesion strength between metal electrode and substrate is critical to the stretchability and stability of electrodes, so polydimethylsiloxane0.9‐isophorone diisocyanate elastomer (PDMS0.9‐IPDI), whose adhesion to gold electrode is 4.5 times higher than that of the commercial polydimethylsiloxane (PDMS), is synthesized. Finally, the electrophysiological communication between different organisms by electrodes is successfully demonstrated. [ABSTRACT FROM AUTHOR]

To date the electroactive species of selective aldehyde oxidation to carboxylates at gold electrodes is usually assumed to be the diolate. It forms with high concentration only in very alkaline electrolytes, when OH− binds to the carbonyl carbon atom. Accordingly, the electrochemical upgrading of biomass‐derived aldehydes to carboxylates is believed to be limited to very alkaline electrolytes at many electrode materials. However, OH−‐induced aldehyde decomposition in these electrolytes prevents application of electrochemical aldehyde oxidation for the sustainable upgrading of biomass to value‐added chemicals at industrial scale. Here, we demonstrate the successful oxidation of aliphatic aldehydes at a rotating gold electrode at pH 12, where only 1 % of the aldehyde resides as the diolate species. This concentration is too small to account for the observed current, which shows that also other aldehyde species (i. e. the geminal diol and the non‐hydrated aldehyde) are electroactive. This insight allows developing strategies to omit aldehyde decomposition while achieving high current densities for the selective aldehyde oxidation, making its future industrial application viable. [ABSTRACT FROM AUTHOR]

Redox-active polymers have garnered significant attention as promising materials for redox capacitors, which are energy-storage devices that rely on reversible redox reactions to store and deliver electrical energy. Our focus was on optimizing the electrochemical performance in the design and synthesis of redox-active polymer electrodes. In this study, a redox-active polymer was prepared through step-by-step synthesis on a gold electrode. To achieve this, we designed an automatic sequential polymerization equipment that minimizes human intervention and enables a stepwise polymerization reaction. The electrochemical properties of the polymer gold electrodes were investigated. The degree of polymerization of the polymer grown on the gold electrode can be controlled by adjusting the cycle of the sequential operation. As the number of cycles increases, the amount of accumulated charge increases proportionally, indicating the potential for enhanced electrochemical performance. [ABSTRACT FROM AUTHOR]

Accurate and efficient detection of pathogenic bacteria plays a crucial role in the diagnosis of infectious diseases. However, rapid and highly sensitive detection of specific bacteria in clinical samples remains challenging. In this study, we developed a ratiometric dual‐signal electrochemical biosensor for ultrasensitive detection of pathogenic bacteria, based on an aptamer recognition‐induced rolling circle amplification (RCA)/G‐quadruplex strategy. On the surface of a gold electrode chip, we used an aptamer sequence (P1) conjugated to ferrocene (Fc) to capture the target bacterium. This capture released a different, previously bound sequence (P2) sequence that initiated the RCA/G‐quadruplex cascade, which, in the presence of potassium ions, was able to bind the electrochemical indicator methylene blue (MB). We integrated the signals from the loss of Fc and the appearance of MB (IMB/IFC ratio) to quantify the target bacteria concentration. This biosensor showed excellent detection performance and specificity, with a detection limit of 10 CFU/mL. Notably, it showed great diagnostic potential for clinical infectious diseases caused by pathogenic bacteria in precise/personalized medicine applications. [ABSTRACT FROM AUTHOR]

We present a novel and easy approach using a silicon-based impedance chip to determine the concentration of the given aqueous buffer solution. An accurate determination of the post-dilution concentration of the buffers is necessary for ensuring optimal buffer capacity, pH stability, and to assess solution reproducibility. In this study, we focused on phosphate buffer as the test liquid to achieve precise post-dilution concentration determinations. The impedance chip consisting of a top gold ring electrode, where a test volume of 20 μL to 30 μL of phosphate buffer was introduced for impedance measurements within the frequency range of 40 Hz to 1 MHz. For impedance investigation, we used phosphate buffers with three different pH values, and the impedance was measured after diluting the phosphate buffers to a concentration of 1.00 M, 0.75 M, 0.50 M, 0.25 M, 0.10 M, 0.05 M, and 0.01 M. In order to analyze the distinctive changes in the measured impedance, an equivalent circuit was proposed and modeled. From the impedance modeling, we report that the circuit parameter RAu/Si showed exponential dependence on the concentration of phosphate buffer and no dependence on the pH values of the phosphate buffer and on the added volume inside the ring electrode. The proposed silicon-based impedance chip is quick and uses reduced liquid volume for post-dilution concentration measurements of buffers and has perspective applications in the pharmaceutical and biological domains for regulating, monitoring, and quality control of the buffers. [ABSTRACT FROM AUTHOR]

Several electrochemical conversion reactions occur under high cathodic currents, where electrocatalysts can experience substantial alterations in their surface structure through cathodic corrosion, influencing their electrocatalytic performance. Thus, understanding the structural changes of metal surfaces upon cathodic polarization is crucial for the rational design of active and stable electrocatalysts in the context of a transition towards green technologies. In this work, we probe the structural changes of Au surfaces after cathodic corrosion in 10 M NaOH and 10 M KOH at different potentials, using metal deposition and electrocatalytic surface-sensitive reactions. Cathodic polarization increases the electrochemically active surface area and alters the distribution of crystal facets, as evidenced by underpotential deposition of Pb and the electrochemical behaviour in 0.1 M H2SO4. The Au electrode surfaces obtained in NaOH and KOH exhibit different distributions and sizes of (111)-facets. The electrocatalytic activity of the restructured Au electrodes towards the formic acid oxidation reaction (FAOR) and the hydrogen evolution reaction (HER) is evaluated. The nanostructured Au electrodes obtained after polarization in NaOH show superior HER activity compared to those obtained in KOH, which is related to the formed nanostructures and the influence of low-coordination sites. Furthermore, the FAOR activity of the Au electrodes with higher (111)-contribution, achieved through polarization in 10 M KOH, is comparable to well-ordered Au(111) single crystals, emphasizing the key role of terraces in FAOR rather than surface steps as active sites responsible for the extraordinary HER activity. To further explore the electrocatalytic performance, we demonstrate the electrochemical fabrication of Pd–Au bimetallic nanostructures with varying contributions of (111)-facets, obtained through a combination of cathodic corrosion and electrodeposition. Remarkably, the electrocatalytic activity of Pd films on nanostructured Au electrodes towards FAOR in HClO4 and H2SO4 solutions is significantly enhanced compared to as-polished Au electrodes and is dependent on the contribution of (111)-facets. The present findings are relevant to the stability and long-term performance of cathodes in a variety of applications including electrosynthesis. [ABSTRACT FROM AUTHOR]

One dimensional (1-D) nano-structures are expected to be the most suitable candidates for analyte sensing, owing to their high surface area to volume ratio. In the present work, SnO2-ZnO composite solutions with different viscosity have been synthesized and thickness of electrospun nanofibers is optimized to obtain uniformly distributed nanofibers without formation of bead-like structures. The nanofibers in the range of 75 to 250 nm have been successfully deposited on Interdigitated gold electrode (IDGE) for ethanol analyte sensing. The effect of the fiber width on the analyte sensing properties of the nanofibers has been studied to provide the optimum fiber thickness for ethanol sensing. The SnO2-ZnO nanofibers-based sensor, with the average fiber thickness 106.2 nm, has shown response of 41.66% towards 0.5 ppm ethanol with fast response time of 11 s. The crystallite size of the SnO2-ZnO composite is observed to 44.38 nm. The sensor has exhibited significant and appreciable selectivity towards ethanol as compared to other tested volatile organic compounds (VOCs). The crystallographic structure, valence states analysis and surface morphological analysis has been provided using XRD, XPS and FESEM characterization. The formation of n–n heterojunction further enhances the response of the sensor and the ethanol analyte sensing mechanism based on redox reaction at the surface and heterojunction interface is also presented. [ABSTRACT FROM AUTHOR]

Prostate specific antigen (PSA) is considered as an important biomarker in prostate cancer diagnosis. Herein, an ultrasensitive ratiometric electrochemical aptasensor was constructed for analyzing PSA. The ferrocene (Fc)-labeled thiolated hairpin probe 2 (Fc-HP2) was conjugated to the gold nanoparticles (AuNPs)-modified gold electrode (AuE) surface by Au-S bonds. With the introduction of PSA, the aptamer region of hairpin probe 1 (HP1) preferred to bind with PSA, and the rest of HP1 could hybridize with Fc-HP2 to form Fc-HP2/HP1/PSA complex with a blunt 3′ terminus, which triggered the exonuclease III (Exo III) cleavage process accompanied by Fc leaving from the electrode and recycling of HP1/PSA. The remaining Fc-HP2 fragments left on the electrode surface were then hybridized with methylene blue-labeled DNA (MB-DNA). This resulted in an enhancement of MB signal (IMB) and a decrement of Fc signal (IFc). Under the optimal conditions, the proposed aptasensor showed good analytical performance for sensitive detection of PSA with a linear range from 100 fg·mL−1 to 10 ng·mL−1 and a detection limit of 34.7 fg·mL−1. The fabricated aptasensor had been applied to detect PSA in diluted human serum samples and obtained satisfied results, suggesting it had great potential in clinical diagnosis. [ABSTRACT FROM AUTHOR]

Taktic, an Amitraz-based insecticide, is commonly used in sub-Saharan Africa to treat cattle for ticks. Due to misuse in rural dipping pools, some ticks are showing resistance to Taktic. This work presents a low-cost e-nose with commercial sensors to monitor Taktic levels in dipping pool water. The device shows distinctly different measurements for the odours of air, distilled water, farm water, and four levels of Taktic insecticide in farm water. A naive Bayes algorithm with a Gaussian distribution is trained on the data and a validation set achieves a 96.5% accuracy. This work also compares two sol-gel ZnO nanoparticle solutions with an off-the-shelf ZnO nanoparticle ink for use as active material in chemiresistive gas sensors to be employed in an e-nose array. The ZnO solutions are screen-printed onto gold electrodes, auto-sintered with a built in heater, and used with UV illumination to operate as low-power, room temperature gas sensors. All of the screen-printed ZnO sensors show distinct changes in resistance when exposed to Taktic vapours under room temperature and humidity conditions. The custom room temperature ZnO gas sensors fabricated via facile and low-cost processes are suitable for future integration in a point-of-need microsystem for the detection of Taktic in water. [ABSTRACT FROM AUTHOR]

Micro electro-mechanical systems (MEMS) combining sensing and microfluidics functionalities, as are common in Lab-on-Chip (LoC) devices, are increasingly based on polymers. Benefits of polymers include tunable material properties, the possibility of surface functionalization, compatibility with many micro and nano patterning techniques, and optical transparency. Often, additional materials, such as metals, ceramics, or silicon, are needed for functional or auxiliary purposes, e.g., as electrodes. Hybrid patterning and integration of material composites require an increasing range of fabrication approaches, which must often be newly developed or at least adapted and optimized. Here, a microfabrication process concept is developed that allows one to implement attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and electrochemistry on an LoC device. It is designed to spatially resolve chemical sensitivity and selectivity, which are instrumental for the detection of chemical distributions, e.g., during on-flow chemical and biological reaction chemistry. The processing sequence involves (i) direct-write and soft-contact UV lithography in SUEX dry resist and replication in polydimethylsiloxane (PDMS) elastomers as the fluidic structure; (ii) surface functionalization of PDMS with oxygen plasma, 3-aminopropyl-triethoxysilane (APTES), and a UV-curable glue (NOA 73) for bonding the fluidic structure to the substrate; (iii) double-sided patterning of silicon nitride-coated silicon wafers serving as the ATR-FTIR-active internal reflection element (IRE) on one side and the electrode-covered substrate for microfluidics on the back side with lift-off and sputter-based patterning of gold electrodes; and (iv) a custom-designed active vacuum positioning and alignment setup. Fluidic channels of 100 μm height and 600 μm width in 5 mm thick PDMS were fabricated on 2" and 4" demonstrators. Electrochemistry on-chip functionality was demonstrated by cyclic voltammetry (CV) of redox reactions involving iron cyanides in different oxidation states. Further, ATR-FTIR measurements of laminar co-flows of H2O and D2O demonstrated the chemical mapping capabilities of the modular fabrication concept of the LoC devices. [ABSTRACT FROM AUTHOR]

Using liquid secondary ion mass spectrometry, we in situ unraveled that the single walled carbon nanotubes-modified gold electrode surface is free of a dense adsorption phase and abundant in water molecules, which facilitated the electro-oxidation reaction of ascorbate. Such an understanding will expedite the knowledge-based development of electrochemical interfaces. [ABSTRACT FROM AUTHOR]

Phosphorous is an important environmental health parameter as the availability of phosphorus within water systems plays an essential role in the prevalence of harmful algal blooms (cyanobacteria blooms). Currently, phosphates are detected using sensitive chromatographic and colorimetric techniques; however, major disadvantages stem from the lack of anion selectivity in samples with complex matrices, as well as the high cost of analysis. Electrochemical techniques utilizing self-assembled monolayers can provide a cheaper yet sensitive method of detection. This work explores the modification of a gold working electrode using pyridine–zinc(II) complexes. The implementation of self-assembled monolayers allows for an ultrasensitive and selective method of indirect detection of the H2PO4− species, ranging in concentrations between 0.0 and 1.2 fmol/L phosphate. Electrochemical techniques such as cyclic voltammetry and square-wave voltammetry were explored for their phosphate-detection abilities, with detection limits of 4.0 × 10−16 and 9.0 × 10−17 mol/L H2PO4−, respectively. X-ray photoelectron spectroscopy measurements were also taken to confirm the modification of the electrode. The selectivity of this sensor towards phosphate anions was successfully explored for this sensor in the presence of potential interfering agents (sulfate, chlorine, carbonate, fluoride, nitrite, and hypochlorite ions), and applicability of sensor was also explored through the detection of phosphate in a tap and lake water sample. [ABSTRACT FROM AUTHOR]

Context: This study aims to tune the transport properties of tetracene single-molecule junctions with the proper choice and placement of side and anchoring groups. For the operationalization of the molecule that was anchored with thiol or isocyanide groups, two different side groups, amine and nitro, in two different positions, were taken into consideration. For unperturbed tetracene molecule, a prominent negative differential resistance (NDR) feature at 1.8 V was observed with the isocyanide anchoring group while the thiol anchoring group exhibits a plateau region over a bias voltage of 2.2 to 3.2 V. At a bias voltage that is dependent on the chemical or structural change of side or anchoring groups, NDR feature of varying degree was seen in all configurations. Results show that the current flowing through the thiol-anchored molecule perturbed with the amine group at S' position is relatively larger than other configurations because of the smaller HOMO-LUMO gap and broader transmission peaks resulting in a peak to valley current ratio (PVCR) of 1.22. In addition, multiple NDR regions were realized in nitro-perturbed isocyanide-anchored molecule at S position. These results suggest their promising applications in switches, logic cells, and storage devices. Methods: The modeling and simulation of side-group mediated anchored tetracene molecule through two electrodic systems were studied using density functional theory (DFT) combined with non-equilibrium Green's function (NEGF) in Virtual NanoLab-AtomistixToolkit (ATK). The electron transport properties were calculated using Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) exchange-correlation function. To optimize computing time, gold electrodes were single zeta polarized whereas the molecule, anchor groups, and side groups were double zeta polarized. [ABSTRACT FROM AUTHOR]

Phosphate detection using Cobalt nanoparticle modified gold electrode has been carried out. Cobalt oxide nanoparticles were produced by mixing a solution of cobalt chloride with 10 % glycerol and adding Ammonium hydroxide solution with stirring for 2 hours at 50° C using a magnetic stirrer. The solution was then allowed to stand for 12 hours. The precipitate obtained was filtered and calcined at 700° C for one hour. The obtained cobalt nanoparticles are mixed with nafion, then attached to a gold wire to form a modified cobalt nanoparticle electrode. The performance of this electrode was tested against a phosphate solution using a three-electrode system of the Autolab Metrohm type AUT 84948. Measurements were made by immersing a modified cobalt gold electrode connected to the Metrohm Autolab three-electrode system. All phosphate measurements were carried out in KHP and KCl buffer solutions. Voltammograms of KHP did not show peaks of anodic and cathodic currents but in phosphate solution (10 ppm NaH2PO4) showed peaks of cathodic currents at a potential of – 1.009 V. This indicated that the electrode was sensitive to phosphate ion solutions. The cathodic current increases with the phosphate concentration. The measurement detection limit is 0.47 ppm. [ABSTRACT FROM AUTHOR]

Hyaluronic acid (HA) is the main non-sulfated glycosaminoglycan of the extracellular matrix that is synthesized by fibroblasts and other specialized connective tissue cells. The accumulation of HA on different tissues is a characteristic of disorders that are associated with progressive tissue fibrosis. HA is also known to play a critical role in tumorigenesis and tumor metastasis. It is overproduced by many types of tumors and promotes tumor progression and multidrug resistance. There is a great necessity for the development of an easy and cost-effective detection method for the monitoring of HA for both the diagnosis and efficient treatment of related disorders. In the present study, an innovative immune device was designed for the rapid and sensitive recognition of HA in human plasma samples. For this purpose, an efficient alloy (Pt@Au) was fabricated on the surface of the gold electrode. Thus, a novel substrate was used for the preparation of an efficient transducer, which is necessary for the immobilization of biotinylated antibodies. CHA was applied for the electrochemical deposition of Pt@Au nano-alloy on Au electrodes. Additionally, the morphological study of the used nanocomposite was assessed using FESEM at a working voltage of 3 kV, and the chemical structures of the electrode were analyzed using the EDS apparatus. For the first time, a biocompatible alloy-based substrate was prepared for the study of antigen–antibody identification. The developed immunosensor has a linear response within the range of 0.156–160 ng.mL−1 with a limit of detection of 0.039 ng.mL−1 in human plasma samples. This research study offers a novel promising technique for HA analyses and is anticipated to be used in the early diagnosis of some disorders related to abnormal levels of HA in human bio-fluids. Thus, a constructed (pt@Au) nano-alloy provides a useful interface for the dense loading of AB. This excellent design loads high sensations of the biosensor for the selective detection of HA in real samples (human bio-fluids). [ABSTRACT FROM AUTHOR]

Aim. This work was aimed at developing a new design of an enzyme biosensor for highly sensitive determination of creatinine. Methods. The electrochemical transducers consist of two identical pairs of gold interdigitated electrodes obtained by gold sputtering onto ceramic plate. The sensitive surface of each electrode pair was approximately 1.0×1.5 mm. The transducers were connected to the measuring device “MХP-3”. The immobilization procedure was performed as follows. The enzyme solution was prepared by dissolving 20% creatinine deiminase (microbial, EC 3.5.4.21, with activity of 36 U/mg, from SigmaAldrich, Japan) in 20 mM phosphate buffer solution (PBS), pH 6.5, containing 10% bovine serum albumin (BSA) and 10% glycerol. The mixture for reference membrane was prepared by the same procedure using BSA instead of enzymes. The solutions were mixed with 1% aqueous solution of glutaraldehyde (GA) in 1:1 ratio and were deposited on the electrodes. Then the membranes were dried in open air at room temperature. Before starting the experiments, the electrodes with membranes were washed out excess of unbound components used PBS. Measurements were carried out at room temperature in an open cell filled with 5 mM PBS, pH 7.35, with constant stirring. The required substrate concentration in the cell was obtained by adding the aliquots of substrates stock solutions in the cell with PBS. Non-specific changes in the output signal associated with fluctuations of temperature, medium pH, and electrical noise, were compensated by using differential mode of measurement. At least three series of experiments were performed. Results and Discussion. Various immobilization procedures of the bioselective element were tested. Immobilization method with 1% GA solution was chosen. The optimal conditions for biosensors operation were found. The biosensors were characterized by high signal reproducibility at determination of substrate (RSD = 6%). The linear range of determination of creatinine was 0.01–1 mM. Conclusions. The new construction of enzyme biosensor based on creatinine deiminase was developed for the creatinine determination. The production and measurement conditions of proposed biosensor were optimized. The biosensor was characterized by high reproducibility of responses and showed high storage stability. In future the developed biosensor can be used for express evaluation of the creatinine in biological samples. [ABSTRACT FROM AUTHOR]

Tetracycline antibiotics are used extensively in veterinary medicine, but the majority of the administrated dose is eliminated unmodified from the animal through various excretion routes including urine, faeces and milk. In dairy animals, limits on residues secreted in milk are strictly controlled by legislation. Tetracyclines (TCs) have metal chelation properties and form strong complexes with iron ions under acidic conditions. In this study, we exploit this property as a strategy for low cost, rapid electrochemical detection of TC residues. TC-Fe(III) complexes in a ratio of 2:1 were created in acidic conditions (pH 2.0) and electrochemically measured on plasma-treated gold electrodes modified with electrodeposited gold nanostructures. DPV measurements showed a reduction peak for the TC-Fe(III) complex that was observed at 50 mV (vs. Ag/AgCl QRE). The limit of detection in buffer media was calculated to be 345 nM and was responsive to increasing TC concentrations up to 2 mM, added to 1 mM FeCl3. Whole milk samples were processed to remove proteins and then spiked with tetracycline and Fe(III) to explore the specificity and sensitivity in a complex matrix with minimal sample preparation, under these conditions the LoD was 931 nM. These results demonstrate a route towards an easy-to-use sensor system for identification of TC in milk samples taking advantage of the metal chelating properties of this antibiotic class. [ABSTRACT FROM AUTHOR]

Metal oxide-based sensors have the benefit of inexpensive, quick response, and high sensitivity in detecting specific biological species. In this article, a simple electrochemical immunosensor was fabricated using antibody-chitosan coated silver/cerium oxide (Ab-CS@Ag/CeO2) nanocomposites on a gold electrode for sensitive alpha-fetoprotein (AFP) diagnosis in human serum samples. Successfully synthesis of AFP antibody-CS@Ag/CeO2 conjugates was confirmed through Fourier transform infrared spectra of the prototype. The amine coupling bond chemistry was then used to immobilize the resultant conjugate on a gold electrode surface. It was observed that the interaction of the synthesized Ab-CS@Ag/CeO2 nanocomposites with AFP prevented an electron transfer and reduced the voltammetric Fe(CN)63−/4− peak current, which was proportional to the amount of AFP. The linear ranges of AFP concentration were found from 10−12–10−6 g.ml−1. The limit of detection was calculated using the calibration curve and came out to be 0.57 pg.ml−1. The designed label-free immunosensor successfully detected AFP in human serum samples. As a result, the resulting immunosensor is a promising sensor plate form for AFP detection and could be used in clinical bioanalysis. [ABSTRACT FROM AUTHOR]

Near-infrared spectroscopy (NIRS) is a promising research tool that found its way into the field of brain-computer interfacing (BCI). BCI is crucially dependent on maximized usability thus demanding lightweight, compact, and low-cost hardware. We designed, built, and validated a hybrid BCI system incorporating one optical and two electrical modalities ameliorating usability issues. The novel hardware consisted of a NIRS device integrated with an electroencephalography (EEG) system that used two different types of electrodes: Regular gelled gold disk electrodes and tri-polar concentric ring electrodes (TCRE). BCI experiments with 16 volunteers implemented a two-dimensional motor imagery paradigm in off- and online sessions. Various non-canonical signal processing methods were used to extract and classify useful features from EEG, tEEG (EEG through TCRE electrodes), and NIRS. Our analysis demonstrated evidence of improvement in classification accuracy when using the TCRE electrodes compared to disk electrodes and the NIRS system. Based on our synchronous hybrid recording system, we could show that the combination of NIRS-EEG-tEEG performed significantly better than either single modality only. [ABSTRACT FROM AUTHOR]

An electrochemical aptasensor for the detection of tetracycline (TET) is prepared based on a methylene blue (MB)-tagged DNA aptamer, with the sequence 5′-MB-CCC CCG GCA GGC CAC GGC TTG GGTTGG TCC CAC TGC GCG-thiol-3′. The DNA aptamer is chemisorbed on a gold electrode and differential pulse voltammetry (DPV) is utilized for the detection. In particular, upon binding of the TET with the purpose-designed aptamer, there is an increase in the current intensity, as a result of the increased proximity of the MB molecule to the gold surface. The sensor is tested using aqueous samples spiked with TET concentrations between 1 and 1000 nM and a limit of detection (LOD) of 1.2 nM is determined. Furthermore, the dissociation constant is estimated to be 1.4 nM using a Lineweaver–Burk plot. [ABSTRACT FROM AUTHOR]

Miniaturized and integrated devices for fast determination of clinical biomarkers are in high demand in the current healthcare environment. In this work, we present a functionalized self-assembled monolayer (SAM) on the gold surface of a screen-printed electrode (Au-SPE). The device was applied for uric acid (UA) detection, a biomarker associated with arthritis, diabetes mellitus, and kidney function. Prior to SAM formation, AuSPE was subjected to pretreatment with KOH and Au electrodeposition to provide additional roughness to the substrate. The SAM was formed in the AuSPE/KOH/AuNP surface by the cysteamine method—carried out for working surface dipping in the cysteamine (CYS) solution at 20 mM for 24 h (rinsed with ethanol and milli-Q water). Then, the uricase enzyme was immobilized through physical absorption at room temperature for 1 h to obtain the AuSPE/KOH/AuNPs/SAM/Uox biosensor. The physical and electrochemical characterization of AuSPE modification was carried out by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The calibrated data of the Au/KOH/AuNPs/SAM/Uox biosensor showed a linear relation in the range of 50–1000 µM, a sensibility of 0.1449 µA/[(µM)cm2], and a limit of detection (LOD) of 4.4669 µM. The Au/KOH/AuNPs/SAM/Uox also exhibited good selectivity for UA in the presence of ascorbic acid. Moreover, the methodology showed good reproducibility, stability, and sensitive detection of UA. This performance of the proposed biosensor is in good accordance with clinical needs and can be compared with previous biosensors based on nanostructured surfaces of high-fabrication complexity. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors that emulate the sensation and characteristics of natural skins are of great importance in wearable medical devices, intelligent robots, and human–machine interfaces. The microstructure of the pressure-sensitive layer plays a significant role in the sensor's overall performance. However, microstructures usually require complex and costly processes such as photolithography or chemical etching for fabrication. This paper proposes a novel approach that combines self-assembled technology to prepare a high-performance flexible capacitive pressure sensor with a microsphere-array gold electrode and a nanofiber nonwoven dielectric material. When subjected to pressure, the microsphere structures of the gold electrode deform via compressing the medium layer, leading to a significant increase in the relative area between the electrodes and a corresponding change in the thickness of the medium layer, as simulated in COMSOL simulations and experiments, which presents high sensitivity (1.807 kPa−1). The developed sensor demonstrates excellent performance in detecting signals such as slight object deformations and human finger bending. [ABSTRACT FROM AUTHOR]

Nanoporous gold (NPG) has excellent catalytic activity and has been used in the recent literature on this issue as a sensor in various electrochemical and bioelectrochemical reactions. This paper reports on a new type of metal–oxide–semiconductor field-effect transistor (MOSFET) that utilizes NPG as a gate electrode. Both n-channel and p-channel MOSFETs with NPG gate electrodes have been fabricated. The MOSFETs can be used as sensors and the results of two experiments are reported: the detection of glucose and the detection of carbon monoxide. A detailed comparison of the performance of the new MOSFET to that of the older generation of MOSFETs fitted with zinc oxide gate electrodes is given. [ABSTRACT FROM AUTHOR]

Phospholipase C (PLC) has important biological functions in specific cancer types, immune disorders and neurodegeneration. Here, an ultrasensitive electrochemical sensor for PLC was developed via signal amplification based on breathing atom transfer radical polymerization (ATRP). First, phosphatidylethanolamine (PE) was immobilized on the surface of a gold electrode by L -cysteine and cross-linker. Then, PE was specially hydrolyzed by PLC to obtain the phosphate groups and tethered with the ATRP initiator α-bromophenacetic acid (BPAA) by the coordination action of Zr4+. After the breathing ATRP, a large number of electroactive monomers (ferrocenylmethyl methacrylate, FcMMA) were successfully grafted from BPAA. The experimental results indicated that the detection signal of the obtained electrode (sensor) was proportional to the concentration of PLC. The sensor showed a low detection limit of 0.270 U L−1 and a wide linear range of 1–40 U L−1 (R2 = 0.997). Most importantly, the sensor was successfully applied to detect PLC in breast cancer cells (MCF-7, MDA-MB-231) and nontumor cells (MCF-10A). The value obtained by our electrochemical sensor had no obvious difference from that determined by the commercial ELISA kit. These results showed that the fabricated PLC sensor had acceptable potential in clinical applications. [ABSTRACT FROM AUTHOR]

Screen-printed carbon electrodes (SPCEs) were modified with gold particles to improve luminol electrochemiluminescence (ECL) in the presence of H2O2 as the co-reactant. Gold particles with sizes ranging from 10 to 50 nm were successfully deposited by the electrochemical technique with around 3.4% (w/w) gold on the carbon surface. The gold-modified SPCE (Au-SPCE) increases the ECL intensity of luminol around 2.5 times more than that using the unmodified SPCE. These signals were also found to be linearly correlated to H2O2 concentration. At an optimum pH of 9, the ECL signals of 1 mM luminol in 0.1 M phosphate buffer solution using the Au-SPCE are linear in the H2O2 concentration range from 0.5 to 200 pM (R2 = 0.99) with an estimated detection limit of 4.78 pM. The developed sensor also showed the excellent repeatability and reproducibility of the ECL signals. Moreover, H2O2 detection in milk and tap water samples was also successfully demonstrated, indicating that the developed sensor is promising for H2O2 detection applications. [ABSTRACT FROM AUTHOR]

A method for the synthesis of a conjugate of 4-substituted phenylterpyridine and lipoic acid, containing a triethylene glycol linker group between the terpyridine and sulfur-containing fragments, has been developed. A coordination compound of the resulting terpyridine with Rh(III) was obtained. Cyclic voltammetry was used to explore the ability of the synthesized ligand and its rhodium complex to be chemisorbed on the surface of gold electrodes to form an Au–S bond. [ABSTRACT FROM AUTHOR]

A key challenge for sensor miniaturization is to create electrodes with smaller footprints, while maintaining or increasing sensitivity. In this work, the electroactive surface of gold electrodes was enhanced 30‐fold by wrinkling followed by chronoamperometric (CA) pulsing. Electron microscopy showed increased surface roughness in response to an increased number of CA pulses. The nanoroughened electrodes also showed excellent fouling resistance when submerged in solutions containing bovine serum albumin. The nanoroughened electrodes were used for electrochemical detection of Cu2+ in tap water and of glucose in human blood plasma. In the latter case, the nanoroughened electrodes allowed highly sensitive enzyme‐free sensing of glucose, with responses comparable to those of two commercial enzyme‐based sensors. We anticipate that this methodology to fabricate nanostructured electrodes can accelerate the development of simple, cost‐effective, and high sensitivity electrochemical platforms. [ABSTRACT FROM AUTHOR]

The preparation of an electroactive matrix for the immobilization of the bioprobe shows great promise to construct the label-free biosensors. Herein, the electroactive metal-organic coordination polymer has been in-situ prepared by pre-assembly of a layer of trithiocynate (TCY) on a gold electrode (AuE) through Au-S bond, followed by repetitive soaking in Cu(NO3)2 solution and TCY solutions. Then the gold nanoparticles (AuNPs) and the thiolated thrombin aptamers were successively assembled on the electrode surface, and thus the electrochemical electroactive aptasensing layer for thrombin was achieved. The preparation process of the biosensor was characterized by an atomic force microscope (AFM), attenuated total reflection-Fourier transform infrared (ATR-FTIR), and electrochemical methods. Electrochemical sensing assays showed that the formation of the aptamer-thrombin complex changed the microenvironment and the electro-conductivity of the electrode interface, causing the electrochemical signal suppression of the TCY-Cu2+ polymer. Additionally, the target thrombin can be label-free analyzed. Under optimal conditions, the aptasensor can detect thrombin in the concentration range from 1.0 fM to 1.0 μM, with a detection limit of 0.26 fM. The spiked recovery assay showed that the recovery of the thrombin in human serum samples was 97.2–103%, showing that the biosensor is feasible for biomolecule analysis in a complex sample. [ABSTRACT FROM AUTHOR]

State-of-the-art clinical detection methods typically involve standard immunoassay methods, requiring specialized equipment and trained personnel. This impedes their use in the Point-of-Care (PoC) environment, where ease of operation, portability, and cost efficiency are prioritized. Small, robust electrochemical biosensors provide a means with which to analyze biomarkers in biological fluids in PoC environments. Optimized sensing surfaces, immobilization strategies, and efficient reporter systems are key to improving biosensor detection systems. The signal transduction and general performance of electrochemical sensors are determined by surface properties that link the sensing element to the biological sample. We analyzed the surface characteristics of screen-printed and thin-film electrodes using scanning electron microscopy and atomic force microscopy. An enzyme-linked immunosorbent assay (ELISA) was adapted for use in an electrochemical sensor. The robustness and reproducibility of the developed electrochemical immunosensor were investigated by detecting Neutrophil Gelatinase-Associated Lipocalin (NGAL) in urine. The sensor showed a detection limit of 1 ng/mL, a linear range of 3.5–80 ng/mL, and a CV% of 8%. The results demonstrate that the developed platform technology is suitable for immunoassay-based sensors on either screen-printed or thin-film gold electrodes. [ABSTRACT FROM AUTHOR]

On‐skin electronics, which offers an interface for extracting electrophysiological signals from skin, is intensively investigated using electrodes mounted on flexible substrates. Despite numerous efforts toward substrate design to optimize user comfort, substrates with skin‐adhesion, skin‐breathability, skin‐compatibility, mechanical endurance, sterilizability, sustainability, and biodegradability remain desirable candidates for human‐ and environment‐friendly on‐skin electronics. To this end, a wood‐derived cellulose nanofiber paper (denoted nanopaper) with customized porous nanostructures is developed in this study. The customized porous nanopaper enables water‐assisted deformation for skin‐conformability, thereby realizing outstanding skin‐adhesion force, along with high skin‐breathability and compatibility, superior to those of conventional substrates reported for on‐skin electronics. By mounting gold electrodes on the porous nanopaper and adhering them to human skin, the real‐time monitoring of electroencephalogram, electromyogram, and electrocardiogram for diagnosing the human physiological state is successfully achieved. Furthermore, the gold‐electrode‐mounted porous nanopaper affords unique characteristics including durability against skin deformation, reusability, and even sterilizability, owing to its high mechanical endurance, and thermal stabilities. Thus, the as‐prepared porous nanopaper serves a fascinating platform for human‐ and environment‐harmonious on‐skin electronics. [ABSTRACT FROM AUTHOR]

An electrode composite containing a metal organic framework (Mn-MIL-100) was prepared by linkers including gold nanoparticles/polypyrrole and cysteine. The electrocatalytic application of this nanocomposite was evaluated via the oxidation of benzylic and aliphatic alcohols under open air conditions. Various active and inactive alcohol derivatives were successfully converted to the corresponding ketones with excellent yields. This advanced electrocatalyst proved to have remarkable stability over several recovery cycles from the reaction medium without significant change in its activity and selectivity and its regeneration potential. The active surface area of this electrocatalyst is very large due to its structural features, arising from the introduction of a metal organic framework (Mn-MIL-100) on a gold electrode, which provides more accessible surface sites, therefore boosting the electrocatalytic activity. The structure of the synthesized electrocatalyst has been characterized by FESEM, EDX, and AFM techniques. [ABSTRACT FROM AUTHOR]

Early detection can help control and treat ovarian cancer, which is one of the most deadly types of cancer among women. Nowadays, nanobiosensors as a time-saving tool with highly selective and sensitive properties applied in different biomarker detection. One of the most sensitive methods for diagnosing ovarian cancer is electrochemistry-based methods. This study was conducted to detect ovarian cancer antigen 125 (CA125) biomarkers using an electrochemical aptasensor based on voltammetric techniques. Graphitic carbon nitrides, magnetic nanoparticles, and polyaniline (g-C 3 N 4 /Fe 3 O 4 /PANI) were utilized to stabilize aptamer chains on the surface of a gold electrode (GE). The hexacyanoferrate redox system was used as the electroactive probe, and it was typically operated at around 0.3 V (vs. Ag/AgCl), with a 0.418 U.mL−1 detection limit in the hexacyanoferrate medium. As a redox-active medium, methylene blue was used to lower the electrochemical potential for the detection of CA125. The detection potential was reduced to − 0.2 V, and the electrochemical aptasensor exhibited a broad dynamic linear range (DLR) ranging between 5 and 60 U.mL−1, with an R2 of 0.993 and a limit of detection (LOD) of 0.298 U.mL−1. The results revealed that the modified electrode is highly selective for CA125 compared with other biomolecules. Additionally, the synthesized aptasensor exhibited excellent selectivity and stability. This electrochemical aptasensor demonstrated outstanding results for evaluating the serum of patients and healthy people. [Display omitted] • Graphitic carbon nitride (g-C 3 N 4)/Magnetic nanoparticles (Fe 3 O 4)/Polyaniline (PANI)/gold electrode (GE) was successfully prepared. • The nanocomposite can significantly improve electrochemical performance. • Electrochemical impedance spectroscopy and Squarewave voltammetry technics are used to detect cancer antigen 125 (CA 125). • The sensor has a linear range of 5–60 U.mL−1 with a 0.298 U.mL−1 limit of detection. [ABSTRACT FROM AUTHOR]

A new dipping robot is presented for the execution of layer‐by‐layer (LbL) deposition procedures for the modification of electrode surfaces. It is composed of low‐budget parts broadly available three‐dimensional (3D) printer. New extra hardware components produced by 3D printing and the open‐source software can turn such a device into a flexible dipping robot. The required changes in code as well as the printing instructions for the changed hardware components are documented and are made freely available together with tools that allow customizing LbL coating processes. The potential of this very flexible instrumentation is exemplified by a redox‐active film of nickel hexacyanoferrate on a gold electrode modified by a monolayer of 3′‐mercaptobiphenyl‐carbonitrile. Scanning electron microscopy confirm the absence of micometer‐sized cracks. It shows the typical voltammetric behavior of that material. [ABSTRACT FROM AUTHOR]

We studied here the influence of Li+ ions on the benzene rings of nematic mixture E7, which is electrochemically adsorbed onto gold electrode surface, to highlight the ability of this mixture for the applications in the field of the rechargeable Li+-ion batteries. Raman spectra support the changes observed in electrochemical analyses while contact angle measurements show that wetting properties of E7 layer were modified after deposition of this mixture onto gold support and the doping with Li+ ions. [ABSTRACT FROM AUTHOR]

Recently, the development of miniaturized electronic devices has accelerated the demand for the rate capability of planar on-chip micro-supercapacitors (POMSs). The POMSs based on reduced graphene oxide and carbon nanotube (rGO/CNT) composite electrodes (rGO/CNT-POMSs) were manufactured in the work and detailed electrochemical tests of devices were carried out over a wide range of scanning rates (0.01–10000 V s−1). The rGO/CNT composite electrode films without binder were prepared on silicon substrates by a modified liquid–air interface self-assembly method and a hydroiodic acid reduction method. The electrodes were fabricated into interdigital structure with 50 μm width of electrode and gap of electrode by photolithography. Interdigital POMSs based on different electrodes were prepared by gold sputtering on the electrode lugs. The area capacitance of the rGO/CNT-POMSs was 28.62 μF cm−2. They also had 0.004 μWh cm−2 of energy density and 1.068 μW cm−2 of power density. In addition, the charge–discharge time constant of the device was only 5.6 μs, and the charge–discharge rate was very quick. After 10,000 cycles of charge–discharge, the capacitance retention rate was still above 88%. At the ultra-high scan rate of 10000 V s−1, the devices still worked well. Compared with the POMSs based on reduced graphene oxide electrodes (rGO-POMSs) and the POMSs based on carbon nanotube electrodes (CNT-POMSs), the introduction of the CNT significantly increased the area capacitance, energy density and power density of rGO/CNT-POMSs, and significantly shortened the charge–discharge time constant. This indicated that the rGO/CNT composite electrodes had a good application prospect in the micro-chip accumulator devices. [ABSTRACT FROM AUTHOR]

A simple equivalent electrical circuit is used to obtain the physical parameters of electrical circuit elements from measured electrochemical impedance spectra. This model consists of four circuit elements with a clear physical meaning for each of the elements. Compared to complex models with multiple constant phase elements or Warburg impedances, our model is suitable for extracting physical values for important electrode parameters with low errors. The feasibility of the model was shown by investigating pure metal or polymer‐coated electrodes. Here, gold electrodes were coated either with Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT : PSS), Polypyrrole:poly(styrenesulfonate) (PPy : PSS), or (PEDOT/PPy) : PSS by means of electropolymerization. The model could demonstrate the ionic‐electronic differences such as the ion accessibility of the differently coated electrodes. To prove the correctness of the model, the obtained results were compared to the literature. [ABSTRACT FROM AUTHOR]

A novel voltammetric method was successfully applied for the determination of an anticholinergic drug, oxybutynin hydrochloride (OXB). The method is concerned with electrooxidation of the drug on the surface of pencil graphite electrode (PGE). In order to enhance the electrode sensitivity and peak current, the electrode was coated with gold nanoparticles (Au‐NPs) via electrochemical deposition using cyclic voltammetry from gold salt solution. The surface of Au‐NPs modified PGE has been characterized using scanning electron microscopy and X‐ray photoelectron spectroscopy. Various experimental variables were studied and optimized to enhance the sensor's response towards OXB. Quantitative determination of the drug was achieved in phosphate buffer pH 7.5 using differential pulse voltammetry by scanning the potential over range of 0.00 to 2.20 V with scan rate of 40 mV s−1. Validation of the method was achieved according to ICH guidelines. The method was found to be linear over concentration range (2.0×10−7–1.0×10−6 M). The suggested sensor was efficiently developed for the quantitative determination of OXB in pure form, pharmaceutical dosage form and spiked plasma samples. [ABSTRACT FROM AUTHOR]

A ratiometric electrochemical aptasensor based on gold nanoparticles (AuNPs) functionalization and hybridization chain reaction (HCR) assisted signal amplification has been for the first time designed for the detection of streptomycin (STR). The double-stranded DNA (dsDNA) formed by the hybridization of ferrocene (Fc)-labeled STR aptamer (Apt) and capture probe (CP) is first immobilized on the gold electrode (GE) surface via Au–S reaction. The specific binding of the target and Apt results in numerous Fc detachment from the sensing interface. Then, the remaining single-stranded CP is combined with AuNPs modified with initiator DNA (iDNA) by auxiliary DNA (aDNA). Among them, the iDNA triggers HCR between two hairpin probes (H1/H2), thus capturing a large number of methylene blue (MB) electrochemical probe, which generates a strong electrochemical signal of MB and a weak electrochemical signal of Fc. Signals are collected by square wave voltammetry (the potential window ranging from -0.5 V to 0.6 V, vs. Ag/AgCl), and the oxidation peak currents at -0.200 V (MB) and 0.416 V (Fc) are recorded. The use of the ratiometric method has effectively improved the accuracy and reliability of the analysis. The successful application of AuNPs and HCR greatly improves the sensitivity of the sensor, and the detection limit is as low as 0.08 pM. It can sensitively determine STR in the range 0.1 pM to 10 nM. In addition, the designed aptasensor has been successfully applied to the detection of STR in milk and honey samples. [ABSTRACT FROM AUTHOR]

We report the microfabrication and characterization of concentric gold nanoring electrodes (Au NREs), which were fabricated by patterning two gold nanoelectrodes on the same silicon (Si) micropillar tip. Au NREs of 165 ± 10 nm in width were micropatterned on a 6.5 ± 0.2 µm diameter 80 ± 0.5 µm height Si micropillar with an intervening ~ 100 nm thick hafnium oxide insulating layer between the two nanoelectrodes. Excellent cylindricality of the micropillar with vertical sidewalls as well as a completely intact layer of a concentric Au NRE including the entire micropillar perimeter has been achieved as observed via scanning electron microscopy and energy dispersive spectroscopy data. The electrochemical behavior of the Au NREs was characterized by steady-state cyclic voltammetry and electrochemical impedance spectroscopy. The applicability of Au NREs to electrochemical sensing was demonstrated by redox cycling with the ferro/ferricyanide redox couple. The redox cycling amplified the currents by 1.63-fold with a collection efficiency of > 90% on a single collection cycle. The proposed micro-nanofabrication approach with further optimization studies shows great promise for the creation and expansion of concentric 3D NRE arrays with controllable width and nanometer spacing for electroanalytical research and applications such as single-cell analysis and advanced biological and neurochemical sensing. [ABSTRACT FROM AUTHOR]

Biofuel cells (BFCs) with enzymatic electrocatalysts have attracted significant attention, especially as power sources for wearable and implantable devices; however, the applications of BFCs are limited owing to the limited O2 supply. This can be addressed by using air-diffusion-type bilirubin oxidase (BOD) cathodes, and thus the further development of the hierarchical structure of porous electrodes with highly effective specific surface areas is critical. In this study, a porous layer of gold is deposited over magnesium-oxide-templated carbon (MgOC) to form BOD-based biocathodes for the oxygen reduction reaction (ORR). Porous gold structures are constructed via electrochemical deposition of gold via dynamic hydrogen bubble templating (DHBT). Hydrogen bubbles used as a template and controlled by the Coulomb number yield a porous gold structure during the electrochemical deposition process. The current density of the ORR catalyzed by BOD without a redox mediator on the gold-modified MgOC electrode was 1.3 times higher than that of the ORR on the MgOC electrode. Furthermore, the gold-deposited electrodes were modified with aromatic thiols containing negatively charged functional groups to improve the orientation of BOD on the electrode surface to facilitate efficient electron transfer at the heterogeneous surface, thereby achieving an ORR current of 12 mA cm−2 at pH 5 and 25 °C. These results suggest that DHBT is an efficient method for the fabrication of nanostructured electrodes that promote direct electron transfer with oxidoreductase enzymes. [ABSTRACT FROM AUTHOR]

Transglutaminase 2 (TG2) is a ubiquitously expressed member of the transglutaminase family with Ca2+-dependent protein crosslinking activity. Its subcellular localization is crucial in determining its function, and indeed, TG2 is found in the extracellular matrix, mitochondria, recycling endosomes, plasma membrane, cytosol, and nucleus because it is associated with cell growth, differentiation, and apoptosis. It is involved in several pathologies, such as celiac disease, cardiovascular, hepatic, renal, and fibrosis diseases, carrying out opposite functions of up and down regulation in the progression of the same pathology. Therefore, this fine regulation requires a very sensitive and specific method of identification of TG2, which is to be detected in very small quantities in a deregulated condition. Here, we demonstrate the possibility of detecting TG2 down to attomolar concentration by using organic electrochemical transistors driven by gold electrodes functionalized with anti-TG2 antibodies. In particular, a direct correlation between the TG2 concentration and the transistor transconductance values, as extracted from typical transfer curves, was found. Overall, our findings highlight the potentialities of this new biosensing approach for the detection of TG2 in the context of pathological diseases, offering a rapid and cost-effective alternative to traditional methods. [ABSTRACT FROM AUTHOR]

Usually, electronic tongues (e-tongue) do not require specific interactions to discriminate aqueous solutions. Among the several factors which determine the electrical properties of sensing units, the interactions between liquids and interfaces have a crucial role. Here, we explore the interaction between dioctadecyldimethylammonium bromide (DODAB) lipid and carbendazim (MBC) pesticide in an e-tongue to discriminate different MBC concentrations in aqueous solutions. The sensing units were fabricated of gold interdigitated electrodes (IDEs) coated with layer-by-layer (LbL) films of DODAB and nickel tetrasulfonated phthalocyanine (NiTsPc), perylene and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (DPPG), namely (DODAB/NiTsPc)5 and (Perylene/DPPG)5, respectively. Besides, a bare electrode also constituted the e-tongue to distinguish MBC concentrations from 1.0 × 10−7 up to 1.0 × 10−10 mol L−1, by impedance spectroscopy. In addition, the experiment was optimized using two IDE geometries. The LbL films were manually fabricated obtaining linear growth monitored via UV-Vis absorption spectroscopy. Optical images associated with chemical mapping reveals the presence of small aggregates in the DODAB/NiTsPc LbL film surface. Although the e-tongue was able to discriminate all MBC concentrations by means of the interactive document map (IDMAP), only the sensing unit covered with DODAB/NiTsPc LbL film presented a satisfactory response. According to the equivalent circuit, the main contribution arises from the bulk and film surface due to the interaction between DODAB and MBC, indicating THE sensitivity of the sensing unit. Finally, the adsorption of MBC molecules onto the film surface induced an irreversible process, although there are some frequencies at which the sensing unit response seems to be reversible, as shown by parallel coordinates. [ABSTRACT FROM AUTHOR]

Redox active labels on DNA SAMs are used for transducing hybridization via the change in the rate of contact-mediated redox with the electrode surface. This change in the fraction hybridized can be measured using CV or SWV. Here, we detail the use of EIS to quantify the change in the redox rate and thereby assess the hybridization characteristics for DNA SAMs. EIS of methylene blue (MB) labeled DNA SAMs on smooth single crystal bead electrodes were measured and the results fit to a series of equivalent circuits representing one redox rate, two redox rates or a distribution of redox rates. The rate of MB redox decreased with increasing complementary strand (cDNA) concentration, interpreted as an increase in the amount of hybridized dsDNA in the SAM. The EIS method was able to accurately measure the average rate of MB redox, but EIS was unable to independently measure the ssDNA and dsDNA populations as the redox rates were not sufficiently distinct. A majority of the redox active MB was one average time constant, but a consistent 10% of the MB had much faster redox rates which were interpreted as due to non-specifically adsorbed MB-labeled DNA. The EIS fits were not improved by using a CPE in place of C d l. However, the EIS fits were improved by replacing the RC circuit element with a distributed circuit element based on the Cole-Cole model, replacing a R with a CPE in one RC branch of the equivalent circuit. This distributed model better explained the EIS results giving the most probable redox rate and a distribution of rates. The EIS measurement approach was verified with a higher coverage DNA SAM which showed slower redox rates as expected. Interestingly, in all cases the amount of redox active MB (Γ M B) decreased with an increase in the [cDNA], suggesting that some MB was in an environment that prevented it from reaching the surface. This decrease in Γ M B with [cDNA] was reflected in the SWV results since it was sensitive to both the change in redox rate and the amount of redox active MB. In contrast, the EIS results were found to measure the k E T independent of the amount of redox active MB. Hybridization isotherms produced using either SWV or EIS results showed a significant difference between SWV (50 Hz) and k E T when fit to a Langmuir-Hill isotherm. These results suggested the SWV results must be interpreted with caution as the K A and Hill co-operativity coefficient (n) were different than the EIS measurements, but in a way that strongly depended on the coverage and the SWV frequency chosen. Overall, EIS of the redox labeled DNA SAM was successfully interpreted using a distributed redox rate expression based on the Cole-Cole model. EIS measured k E T provided a hybridization isotherm that was not convoluted with the amount of redox active MB, enabling an accurate assessment of the DNA SAM interface. [Display omitted] • EIS was used to characterize redox(MB)-labelled DNA SAMs prepared on a gold electrode. • EIS results suggest the presence of at least two populations of redox active MB • The slow redox process represented contact-mediated electron transfer • The fast redox process may be due to non-specifically adsorbed MB-labelled DNA. • Fitting was improved with a Cole-Cole model using a distribution of redox rates. • Hybridization isotherms from SWV and the redox rate constant from EIS were compared [ABSTRACT FROM AUTHOR]

The investigation of biomolecules is essential due to abnormalities in biological metabolism in the human body. Dopamine (DA) and uric acid (UA) are important chemicals that coexist in biological systems and play crucial roles in various physiological processes related to human metabolism. This study explores the application of carbon and SnO 2 nanoparticles for DA and UA sensing, focusing on the preparation of Sn/SnO 2 nanocomposites through electrospinning and plasma treatment. The research aims to measure these concentrations quickly and accurately, offering advantages such as low manufacturing costs and environmental friendliness. This study presents a novel Sn/SnO 2 nanocomposites as an electrocatalyst for the detection of dopamine (DA) and uric acid (UA) levels. Sn/SnO 2 nanocomposites were effectively obtained by argon microwave plasma (ArMP) treatment, a dry and green process, on electrospun fibers containing SnCl 2 within 120 s. The resultant Sn/SnO 2 nanocomposites provide excellent electrochemical catalytic effects to quantify the levels of DA and uric acid UA, which are the two important physiological molecules. To further incorporate graphite into ArMP-Sn/SnO 2 can modulate precise differentiation of the oxidation peaks of DA, UA, and ascorbic acid (AA), solving the problems of overlapped oxidation potential among biomolecules. The as-established nanocomposites revealed excellent applicability to be incorporated onto difference substrates including gold electrode (AuE), screen-printed carbon electrodes (SPCE), and flexible carbon electrodes (FCE), providing great potential for building point-of-care sensing platform. The 1%g-120s-ArMP-Sn/SnO 2 @AuE resulting the highest sensing performance for DA and UA, which the linear detection range was 0.1–400 μM and 0.1–900 μM, with sensitivity of 473.72 and 169.21 μA/mM.cm2, and LOD 0.003 and 0.010 μM, respectively. Additionally, in the areal human fluid matrix the sensor obtains a recovery rate between 95.28 % and 102.72 % with a high selectivity (less than 5 %) upon the presence of common interferences in body fluid. [Display omitted] • Sn/SnO 2 was synthesized by argon microwave plasma (ArMP) in 2 min as electrocatalyst to quantify dopamine (DA) and uric acid (UA) level. • The catalytic effect of the Sn/SnO 2 and graphite on electrode revealed high sensitivity, wide linear sensing on both DA and UA with low LOD. • The ArMP treated Sn/SnO 2 demonstrates great sensing performance on screen-printed carbon electrode (SPCE) and flexible carbon electrode (FCE). [ABSTRACT FROM AUTHOR]