Flat Gold Electrodes Research Articles

Electrochemical Monitoring of Respiratory Infectious Disease on Nanostructured Surface Functionalized with Biosynthetic Multimer Aptamers

Multivalent aptamers have gained substantial interest owing to their enhanced affinity towards target analytes compared to their monomeric counterparts due to their capability to bind simultaneously to diverse regions of a target molecule, fostering more robust and enduring interactions. This study focuses on engineering the surface-based production and modification of multivalent aptamers through room temperature rolling circle amplification technique and chemically modified primers. This process starts with immobilizing modified primers onto an electrode to generate and arrange biosynthesised multivalent aptamers. These bio-engineered multivalent aptamers are utilized as bio-receptors for capturing a specific target (in this case, the SARS-CoV-2 spike protein). The entire surface amplification procedure is extensively characterized using electrochemical, microscopy, and spectroscopy methods, determining the optimal amplification duration for biosensing applications. Impressively, multivalent aptasensors shows substantially increased response signals and affinity compared to monomeric aptasensors. Moreover, the influence of surface structures on response signals is explored by employing both flat screen-printed gold electrodes and nano-/microisland (NMI) electrodes. NMIs-based multimeric aptasensors demonstrate notably heightened sensitivity in detecting SARS-CoV-2 spike protein within the range of 10 to 106 fg/mL in saliva and buffer media. Finally, the signal of the proposed aptasensor has been successfully assessed using several patient samples.

Electrochemical behavior of a flat gold electrode in an acetonitrile solution of 1,2,4,5-tetraoxane

Electrochemical behavior of a flat gold electrode in an acetonitrile solution of 1,2,4,5-tetraoxane

Conjugated Polyelectrolyte/Bacteria Living Composites in Carbon Paper for Biocurrent Generation.

Successful practical implementation of bioelectrochemical systems (BES) requires developing affordable electrode structures that promote efficient electrical communication with microbes. Recent efforts have centered on immobilizing bacteria with organic semiconducting polymers on electrodes via electrochemical methods. This approach creates a fixed biocomposite that takes advantage of the increased electrode's electroactive surface area (EASA). Here, it is demonstrated that a biocomposite comprising the water-soluble conjugated polyelectrolyte CPE-K and electrogenic Shewanella oneidensis MR-1 can self-assemble with carbon paper electrodes, thereby increasing its biocurrent extraction by ≈6-fold over control biofilms. A ≈1.5-fold increment in biocurrent extraction is obtained for the biocomposite on carbon paper relative to the biocurrent extracted from gold-coated counterparts. Electrochemical characterization revealed that the biocomposite stabilized with the carbon paper more quickly than atop flat gold electrodes. Cross-sectional images show that the biocomposite infiltrates inhomogeneously into the porous carbon structure. Despite an incomplete penetration, the biocomposite can take advantage of the large EASA of the electrode via long-range electron transport. These results show that previous success on gold electrode platforms can be improved when using more commercially viable and easily manipulated electrode materials.

Redox-controlled conductance of polyoxometalate molecular junctions

We demonstrate the reversible in situ photoreduction of molecular junctions of a phosphomolybdate [PMo12O40]3- monolayer self-assembled on flat gold electrodes, connected by the tip of a conductive atomic force microscope. The conductance of the one electron reduced [PMo12O40]4- molecular junction is increased by ∼10, and this open-shell state is stable in the junction in air at room temperature. The analysis of a large current-voltage dataset by unsupervised machine learning and clustering algorithms reveals that the electron transport in the pristine phosphomolybdate junctions leads to symmetric current-voltage curves, controlled by the lowest unoccupied molecular orbital (LUMO) at 0.6-0.7 eV above the Fermi energy with ∼25% of the junctions having a better electronic coupling to the electrodes than the main part of the dataset. This analysis also shows that a small fraction (∼18% of the dataset) of the molecules is already reduced. The UV light in situ photoreduced phosphomolybdate junctions systematically feature slightly asymmetric current-voltage behaviors, which is ascribed to the electron transport mediated by the single occupied molecular orbital (SOMO) nearly at resonance with the Fermi energy of the electrodes and by a closely located single unoccupied molecular orbital (SUMO) at ∼0.3 eV above the SOMO with a weak electronic coupling to the electrodes (∼50% of the dataset) or at ∼0.4 eV but with a better electrode coupling (∼50% of the dataset). These results shed light on the electronic properties of reversible switchable redox polyoxometalates, a key point for potential applications in nanoelectronic devices.

Electrochemical Detection of Electrolytes Using a Solid-State Ion-Selective Electrode of Single-Piece Type Membrane.

This study aimed to develop simple electrochemical electrodes for the fast detection of chloride, sodium and potassium ions in human serum. A flat thin-film gold electrode was used as the detection electrode for chloride ions; a single-piece type membrane based solid-state ion-selective electrode (ISE), which was formed by covering a flat thin-film gold electrode with a mixture of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and ion-selective membrane (ISM), was developed for sodium and potassium ions detection. Through cyclic voltammetry (CV) and square-wave voltammetry (SWV), the detection data can be obtained within two minutes. The linear detection ranges in the standard samples of chloride, sodium, and potassium ions were 25–200 mM, 50–200 mM, and 2–10 mM, with the average relative standard deviation (RSD) of 0.79%, 1.65%, and 0.47% and the average recovery rates of 101%, 100% and 96%, respectively. Interference experiments with Na+, K+, Cl−, Ca2+, and Mg2+ ions demonstrated that the proposed detection electrodes have good selectivity. Moreover, the proposed detection electrodes have characteristics such as the ability to be prepared under relatively simple process conditions, excellent detection sensitivity, and low RSD, and the detection linear range is suitable for the Cl−, Na+ and K+ concentrations in human serum.

Effect of surface roughness, porosity and roughened micro-pillar structures on the early formation of microbial anodes

The early formation of electroactive biofilms was investigated with gold electrodes inoculated with Geobacter sulfurreducens. Biofilms were formed under an applied potential of 0.1 V/SCE, with a single batch of acetate 10 mM, on flat gold electrodes with different random surface roughness. Roughness with arithmetical mean height (Sa) ranging from 0.5 to 6.7 μm decreased the initial latency time, and increased the current density by a factor of 2.7 to 6.7 with respect to nano-rough electrodes (Sa = 4.5 nm). The current density increased linearly with Sa up to 14.0 A·m−2 for Sa of 6.7 μm. This linear relationship remained valid for porous gold. In this case, the biofilm rapidly formed a uniform layer over the pores, so porosity impacted the current only by modifying the roughness of the upper surface. The current density thus reached 14.8 ± 1.1 A·m−2 with Sa of 7.6 μm (7 times higher than the nano-rough electrodes). Arrays of 500-μm-high micro-pillars were roughened following the same protocol. In this case, roughening resulted in a modest gain around 1.3-fold. A numerical model showed that the modest enhancement was due to ion transport not being sufficient to mitigate the local acidification of the structure bottom.

Coreactant electrochemiluminescence at nanoporous gold electrodes

The electrochemiluminescence (ECL) performances were comparatively investigated at flat and nanoporous gold (NPG) electrodes of different thicknesses (120 and 200 nm) and roughness factors (fr). The phenomena were studied using either tripropylamine (TPrA) or peroxydisulfate (S2O82−) as sacrificial coreactant and Ruthenium (II)-tris(2,2′-bipyridine) as emitting species. The experiments performed using TPrA showed, at first glance, a linear dependence of the ECL emission with respect to the effective surface area of the NPG electrodes. However, ECL signals were not stable in the measuring conditions, presumably due to amine absorption on the metal surface, leading to electrode corrosion and modification of the surface morphology. The experiments made using peroxydisulfate as coreactant provided conversely a stable ECL response, about proportional to the effective electrode surface area, in the considered range of thicknesses.

Effect of surface nano/micro-structuring on the early formation of microbial anodes with Geobacter sulfurreducens: Experimental and theoretical approaches

Smooth and nano-rough flat gold electrodes were manufactured with controlled Ra of 0.8 and 4.5nm, respectively. Further nano-rough surfaces (Ra 4.5nm) were patterned with arrays of micro-pillars 500μm high. All these electrodes were implemented in pure cultures of Geobacter sulfurreducens, under a constant potential of 0.1V/SCE and with a single addition of acetate 10mM to check the early formation of microbial anodes. The flat smooth electrodes produced an average current density of 0.9A·m−2. The flat nano-rough electrodes reached 2.5A·m−2 on average, but with a large experimental deviation of ±2.0A·m−2. This large deviation was due to the erratic colonization of the surface but, when settled on the surface, the cells displayed current density that was directly correlated to the biofilm coverage ratio.The micro-pillars considerably improved the experimental reproducibility by offering the cells a quieter environment, facilitating biofilm development. Current densities of up to 8.5A·m−2 (per projected surface area) were thus reached, in spite of rate limitation due to the mass transport of the buffering species, as demonstrated by numerical modelling. Nano-roughness combined with micro-structuring increased current density by a factor close to 10 with respect to the smooth flat surface.

Electrochemical Behavior of Aromatic Compounds on Nanoporous Gold Electrode

This study aimed at investigating the electrochemical behavior of benzene and its substituted derivatives on nanoporous gold and assessing the possibility of utilizing this electrode as a platform for simultaneous detection of different aromatic compounds. Cyclic voltammetric studies were performed with benzene, hydroquinone, catechol, phenol, 2-aminophenol, 2-chlorophenol as well as their mixtures on the nanoporous gold prepared from dealloying of AuxSi1-x films. The nanoporous structure was found to provide enhanced electro-oxidation of hydroquinone, catechol, phenol, 2-aminophenol and 2-chlorophenol and remarkable fouling resistance in the electro-oxidation of phenol and 2-aminophenol compared to the compact and flat gold electrode. Interestingly, oxidation potentials of these aromatics appear to be affected significantly by the attachment of functional groups to the benzene ring. Based on the onset oxidation potentials, the easiness of oxidation at nanoporous gold was found to follow the order: hydroquinone > catechol > 2-aminophenol > 2-chlorophenol, phenol > benzene. Moreover, nanoporous gold was found to be advantageous over nanoporous platinum for potential application in simultaneous analysis employing voltammetric techniques as it could offer discernable peak potential separation in the electro-oxidation of the different aromatics.

Control of Rectification in Molecular Junctions: Contact Effects and Molecular Signature.

Thin layers of oligomers with thickness between 7 and 9 nm were deposited on flat gold electrode surfaces by electrochemical reduction of diazonium reagents, then a Ti(2 nm)/Au top contact was applied to complete a solid-state molecular junction. The molecular layers investigated included donor molecules with relatively high energy HOMO, molecules with high HOMO-LUMO gaps and acceptor molecules with low energy LUMO and terminal alkyl chain. Using an oligo(bisthienylbenzene) based layer, a molecule whose HOMO energy level in a vacuum is close to the Fermi level of the gold bottom electrode, the devices exhibit robust and highly reproducible rectification ratios above 1000 at low voltage (2.7 V). Higher current is observed when the bottom gold electrode is biased positively. When the molecular layer is based on a molecule with a high HOMO-LUMO gap, i.e., tetrafluorobenzene, no rectification is observed, while the direction of rectification is reversed if the molecular layer consists of naphtalene diimides having low LUMO energy level. Rectification persisted at low temperature (7 K), and was activationless between 7 and 100 K. The results show that rectification is induced by the asymmetric contact but is also directly affected by orbital energies of the molecular layer. A "molecular signature" on transport through layers with thicknesses above those used when direct tunneling dominates is thus clearly observed, and the rectification mechanism is discussed in terms of Fermi level pinning and electronic coupling between molecules and contacts.

Patterned gold electrode prepared from optical discs display largely enhanced electrochemical sensitivity as exemplified in a sensor for hydrogen peroxide

Gold film electrodes (Au-FE) with distinct nanostructured patterns were prepared from polycarbonate (PC) substrates and investigated with respect to their analytical sensitivity. The recordable (R) and read-only memory (ROM) discs, respectively, yield PC substrates with grooves (stripe pattern) or pits (indented pattern). The Au-FEs were characterized in terms of surface morphology and surface patterns, and it was found that the surface area of all Au-FEs does not significantly differ (by 0.2 to 7.4 %) compared to electrode with flat surfaces. However, the electrical signal of indented patterns is larger by 32 to 213 % when directly compared to stripe-patterned Au-FEs (at the same scale of groove and pit). An Au-FE prepared from a polycarbonate sheet from a Blu-ray disc read only memory (BD-ROM) as substrate displayed the best electrochemical performance towards reductive sensing of H2O2. The respective calibration plot, acquired at a working potential of −0.1 V vs. Ag/AgCl, covers the 0 to 10 mM hydrogen peroxide concentration range. The sensitivity is as high as 3.11 μA∙mM−1∙cm−2 which is larger by a factor of 28 compared to flat gold electrodes, and the detection limit (at a signal-to-noise ratio of 3) is 6 μM. Therefore, the results confirm that the indented nanopattern on the Au-FE significantly increases the efficiency of electrochemical detection. Conceivably, the surface patterns and structures may be designed in order to tune sensitivity with respect to future applications of Au-FEs in diagnostics, agriculture, and environmental monitoring.

A gold electrode modified with silver oxide nanoparticle decorated carbon nanotubes for electrochemical sensing of dissolved ammonia

We have prepared silver oxide nanoparticles with a diameter of ~ 15 nm and decorated with carbon nanotube nanocomposites (Ag2O/CNT NCs) by a facile wet chemical method using reducing agents in alkaline medium. These NCs were characterized by UV/vis, FTIR and energy dispersive X-ray spectroscopy, by X-ray powder diffraction and field emission scanning electron microscopy. The NCs were then deposited on a flat gold electrode with the help of a conducting binder to result in an electrochemical sensor for aqueous ammonia using the I-V technique. Response is based on surface oxidation of ammonium hydroxide with electrode-adsorbed oxygen to form nitrogen oxide, these simultaneously liberating free electrons in the conduction band. Sensor features include a sensitivity of 32.856 μA.μM‾1.cm‾2, a low detection limit (1.3 pM at a signal to noise ratio of 3), reliability, reproducibility, ease of integration, and long term stability. The response to dissolved ammonia is linear (r2: 0.9778) over the 0.01 nM to 0.1 mM concentration range.

Development of ionic-sensor based on sono-chemically prepared low-dimensional β-Fe2O3 nanoparticles onto flat-gold electrodes by an electrochemical approach

Iron oxide nanoparticles (NPs) was prepared sono-chemically in presence of ultrasonic irradiation in aqueous alkaline medium at room conditions, where ferric chloride and urea were used as starting materials. NPs were characterized using powder X-ray diffraction, field-emission scanning electron microscopy, UV/vis. X-ray photoelectron, Fourier-transform infra-red spectroscopy (FT-IR), and Raman spectroscopy, etc. They were deposited on a flat polycrystalline gold electrode (AuE, surface area, 0.0216cm2) to give a sensor with a fast response towards selective ion (i.e., fluoride ion, F−) in phosphate buffer system. The fabricated chemi-sensor also exhibits good sensitivity, lower detection limit, and long-term stability as well as enhanced electrochemical responses towards the target analyte. The calibration plot is linear (r2: 0.9598) over the 0.1nM to 1.0mM fluoride concentration ranges. The sensitivity and detection limit is ∼1.8718μAcm−2mM−1 and ∼0.092±0.02nM (at a Signal-to-Noise-Ratio of 3) respectively in short response time (10.0s). Finally it was confirmed that the nanostructures and the optical features of iron oxide can be extended to a large range in un-doped semiconductor nanomaterials for proficient chemical sensor applications.

In Situ Study of Oxygen Reduction in Dimethyl Sulfoxide (DMSO) Solution: A Fundamental Study for Development of the Lithium–Oxygen Battery

To develop a lithium–oxygen (Li-O2) battery with an extremely high specific energy, mechanisms for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) on a flat gold electrode in the aprotic polar solvent of dimethyl sulfoxide (DMSO) has been systematically investigated by electrochemistry in combination with in situ UV–vis absorption spectroscopy, surface-enhanced Raman vibrational spectroscopy (SERS), and ex situ infrared spectroscopy. In the Li-free DMSO solution, O2 is efficiently reduced to the superoxide, which forms an ion-pair with the tetrabutylammonium (TBA) cation and shows an excellent stability in DMSO. The adsorption of the superoxide on the gold electrode surface has been observed by an in situ SERS measurement. When the Li-ion is included in the DMSO, O2 can be further electrochemically reduced to lithium peroxide (Li2O2) and deposited on the electrode surface, although a large amount of superoxide is still produced in the solution. The latter oxide shows a UV–vis a...

Gold/ Polypyrrole Multilayer Electrode for Biochip Applications

Novel gold/ polypyrrole/ gold electrodes for biochip applications are presented. The electrodes demonstrated better conductivity than polypyrrole electrodes and better sensitivity than conventional gold electrodes. We describe the device fabrication and the electrical properties of the electrodes. Polypyrrole was deposited by electrochemical polymerization, and a thin top gold layer was electro-deposited on the Polypyrrole. A study of the nucleation and growth of the top gold using high resolution scanning electron microscope is presented. Under stagnant conditions a significant electro-crystallization was observed. Electrochemical characterization essential for future bio-sensing application was demonstrated. The electrochemical behavior of the metal/Ppy/metal electrodes was tested by CV and impedance spectroscopy. The novel electrode system was tested for their application as whole cell biosensors using substrate - enzyme interaction by product electrochemical activity. We studied the response of the new electrode in biological solutions (PBS). We found that depositing Ppy on thin metal seed layer dramatically increases the measured current of the electrodes, as compared to Au electrode. This effect was also demonstrated by CV measurements as well as in amperometric detection of alkaline-phosphatase enzymatic activity using biological chips. This high current produces noise that interferes with the proper operation. However, when sufficient metal is electrodeposited on the Ppy, the behavior of the electrode becomes similar to that of a metal electrode, as demonstrated by CV and by amperometric detection of enzymatic activity. The CV curve has the same characteristics as that of the planar gold electrode, with a considerably higher current peak (Ip). The modified Au/Ppy/Au electrode yielded an improved signal, compared with that from a flat gold electrode. The electrodeposition of Ppy followed by Au, on the surface of the biochip’s Au seed layer, affected the electrocrystallization of the Au particles on the Ppy (Fig 1) resulting in a high surface area. This electrode can serve as a highly sensitive, high surface area and flexible sensor for biological species. Figure 1

Nanostructured Surface Effect of Electrode on Doxorubicin Determination

In this study, we compared two types of nanostructured electrodes with gold nanocolumns and flat gold electrodes by measurements with doxorubicin. Nanostructured electrodes were fabricated by electrochemical anodic oxidation followed by deposition of gold to the porous alumina. Flat gold electrodes were fabricated by physical evaporation of gold layer to the silicon substrate. All electrodes were characterized by electrochemical impedance spectroscopy and then the electrochemical determination of doxorubicin was studied by differential pulse voltammetry. The impedance spectroscopy measurements proved a bigger electroactive area for nanostructured electrodes. The gold nanocolumns have been found as an important factor in increasing of electrodes active area. This fact is very important for sensors sensitivity. Fabricated electrodes were successfully used for determination of doxorubicin.

One-step porous gold fabricated electrode for electrochemical impedance spectroscopy immunosensor detection

A porous gold electrode fabricated by a simple one-step electro-process was employed for the first time to enhance a label-free immunosensor detection based on electrochemical impedance spectroscopy (EIS). The porous gold surface was simply fabricated using an applied potential of 1.50V in 100s, providing a 19±1 times larger surface area than the flat gold electrode. The larger surface area enhanced the performance of an immunosensor by increasing the amount of the immobilized antibody. The antibody–antigen pair of anti-human serum albumin (anti-HSA) and human serum albumin (HSA) was use as a model for the direct immunosensor detection. Porous and flat gold electrodes were modified with anti-HSA via a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) and thiourea and a polymer layer of polytyramine and their performance was tested by EIS technique. The effect of two blocking solutions bovine serum albumin (BSA) and 1-dodecanethiol were also tested. The porous electrode modified with anti-HSA via the SAM of 11-MUA and blocked with BSA provided the highest sensitivity and the lowest detection limit, of up to 8.7 times and two order of magnitude compared with the flat electrode, respectively. The electrode can be reused for up to 40 times. The system was used to analyze albumin in serum and urine samples and the results agreed well with the photometric bromocresal green method for serum sample and an immunoturbidimetric assay for urine sample (P>0.05). This method could be easily applied to other label-free affinity pairs.

A gold–gold oil microtrench electrode for liquid–liquid anion transfer voltammetry

Two flat gold electrodes are placed vis-à-vis with an epoxy spacer layer that is etched out to give a ca. 100 μm-deep electrochemically active trench. A water-insoluble oil phase, here the redox system N,N-diethyl-N'N'-didodecyl-phenylenediamine (DDPD) in 4-(3-phenylpropyl)-pyridine (PPP), is immobilized into the trench to allow anion transfer upon oxidation of DDPD (oil) to DDP⁺ (oil). In "mono-potentiostatic mode" quantitative transfer/expulsion of anions into the trench oil phase occurs. However, in "bi-potentiostatic mode" feedback currents dominated by rapid plate-to-plate diffusion normal to the electrode surfaces are observed. Comparison of "normal" diffusion and "lateral" diffusion shows that the rate of diffusion-migration charge transport across the oil film is anion hydrophobicity dependent.

Fabrication of nanoporous thin-film working electrodes and their biosensingapplications

Electrochemical detection for point-of-care diagnostics is of great interest due to its high sensitivity, fast analysis time and ability to operate on a small scale. Herein, we report the fabrication of a nanoporous thin-film electrode and its application in the configuration of a simple and robust enzymatic biosensor. The nanoporous thin-film was formed in a planar gold electrode through an alloying/dealloying process. The nanoporous electrode has an electroactive surface area up to 40 times higher than that of a flat gold electrode of the same size. The nanoporous electrode was used as a substrate to build an enzymatic electrochemical biosensor for the detection of glucose in standard samples and control serum samples. The example glucose biosensor has a linear response up to 30mM, with a high sensitivity of 0.50μAmM−1mm−2, and excellent anti-interference ability against lactate, uric acid and ascorbic acid. Abundant catalyst and enzyme were stably entrapped in the nanoporous structure, leading to high stability and reproducibility of the biosensor. Development of such nanoporous structure enables the miniaturization of high-performance electrochemical biosensors for point-of-care diagnostics or environmental field testing.

Constructing LBL-assembled functional bio-architecture using gold nanorods for lactate detection

Layer-by-layer assembly technique was employed to fabricate functional bio-architecture on 3D gold nanorods suitable for working electrode for lactate detection. Successive immobilization of horseradish peroxidase and lactate oxidase on the nanorods was carried out by direct adsorption and specific interaction. The bio-architecture constructed using 3D gold nanorods electrode shows higher sensitivity compared to 2D flat gold electrode due to an increased amount of accessible enzymes and a high transduction capacity. This functional structure system was applied to the determination of l-lactate concentration. The CV results showed a linear response at the 0.1mM level of l-lactate with a sensitivity of 1.02μA/mM.