Gold Electrode Array Research Articles

Employing electrochemically derived pH gradients for Lab-on-PCB protein preconcentration devices

Protein preconcentration is an essential sample preparation step for analysis in which the targeted proteins exist in low concentrations, such as bodily fluids, water, or wastewater. Nonetheless, very few practical implementations of miniaturized protein preconcentration devices have been demonstrated in practice, and even fewer have been integrated with other microanalytical steps. Existing approaches rely heavily on additional chemicals and reagents and introduce complexity to the overall assay. In this paper, we propose a novel miniaturized isoelectric focusing-based protein preconcentration screening device based on electrochemically derived pH gradients rather than existing chemical reagent approaches. In this way, we reduce the need for additional chemical reagents to zero while enabling device incorporation in a seamlessly integrated full protein analysis microsystem via Lab-on-PCB technology. We apply our previously presented Lab-on-PCB approach to quantitatively control the pH of a solution in the vicinity of planar electrodes using electrochemical acid generation through redox-active self-assembled monolayers. The presented device comprises a printed circuit board with an array of gold electrodes that were functionalized with 4-aminothiophenol; this formed a self-assembled monolayer that was electropolymerized to improve its electrochemical reversibility. Protein preconcentration was performed in two configurations. The first was open and needed the use of a holder to suspend a well of fluid above the electrodes; the second used microfluidic channels to enclose small volumes of fluid. Reported here are the resulting data for protein preconcentration in both these forms, with a quantitative concentration factor shown for the open form and qualitative proof shown for the microfluidic.

One-step and real-time detection of Hg2+ in brown rice flour using a biosensor integrated with AC electrothermal enrichment.

Mercury (Hg2+) is one of the most toxic heavy metals in farm products, so rapid detection of trace Hg2+ has always been sought after with high interest. Herein, we report a biosensor to specifically recognize Hg2+ in leaching solutions of brown rice flour. This sensor is simple and of low cost, with a very short assay time of 30s. Another merit is the ultra-low limit of detection (LOD) at fM level. In addition, the specific aptamer probe realizes a good selectivity above 105: 1 against the interferences. This sensor is developed based on an aptamer-modified gold electrode array (GEA) for capacitive sensing. Alternating current electrothermal (ACET) enrichment is induced during the AC capacitance acquirement. Thus, the enrichment and detection are coupled as a single step, and pre-concentration is needless. Owing to the sensing mechanism of solid-liquid interfacial capacitance and ACET enrichment, Hg2+ level can be sensitively and rapidly reflected. Also, the sensor has a wide linear range from 1 fM to 0.1nM and a shelf life of 15days. This biosensor shows advantages on overall performance, enabling easy-to-operate, real-time, and large-scale Hg2+ detection in farm products.

Polymer nanofiber network reinforced gold electrode array for neural activity recording.

The online version contains supplementary material available at 10.1007/s13534-022-00257-5.

Test Strip Platform Spin-Off for Telomerase Activity Detection: Development of an Electrochemical Biosensor.

Telomerase overexpression has been associated directly with cancer, and the enzyme itself is recognized within the scientific community as a cancer biomarker. BIDEA’s biosensing strip (BBS) is an innovative technology capable of detecting the presence of telomerase activity (TA) using electrochemical impedance spectroscopy (EIS). This BBS is an interdigital gold (GID) electrode array similar in size and handling to a portable glucose sensor. For the detection of the biomarker, BBS was modified by the immobilization of a telomere-like single strand DNA (ssDNA) on its surface. The sensor was exposed to telomerase-positive extract from commercially available cancer cells, and the EIS spectra were measured. Telomerase recognizes the sequence of this immobilized ssDNA probe on the BBS, and the reverse transcription process that occurs in cancer cells is replicated, resulting in the ssDNA probe elongation. This surface process caused by the presence of TA generates changes in the capacitive process on the electrode array microchip surface, which is followed by EIS as the sensing tool and correlated with the presence of cancer cells. The telomerases’ total cell extraction protocol results demonstrate significant changes in the charge-transfer resistance (Rct) change rate after exposure to telomerase-positive extract with a detection limit of 2.94 × 104 cells/mL. Finally, a preliminary study with a small set of “blind” uterine biopsy samples suggests the feasibility of using the changes in the Rct magnitude change rate (Δ(ΔRct/Rcti)/Δt) to distinguish positive from negative endometrial adenocarcinoma samples by the presence or absence of TA.

Nondestructive inspection of packaged microcircuits by aperture-type terahertz near-field imaging

A scanning aperture-type terahertz near-field imaging system is developed to perform precise nondestructive testing on packaged aluminum etched antenna arrays, and surface imaging of a flexible gold electrode array, to obtain subsurface imaging and surface imaging. The resolution of subsurface imaging is 110 and 500 μm when the packaging (polyethylene terephthalate) thickness is 50 and 200 μm respectively, and the surface imaging resolution is 6 μm at 0.11 THz. An adaptive threshold segmentation algorithm of Hilbert scan combined with wavelet transform were employed to successfully suppress the noise of the imaging results due to the change of near-field distance. We also proposed a derivative filtering extremum threshold segmentation algorithm to effectively suppress severely uneven threshold distribution of the packaged aluminum etched antenna arrays.

Comparative study of platinum electroplating to improve micro gold electrode arrays with LCP laminate.

Decoding the cellular network interaction of neurons and glial cells are important in the development of new therapies for diseases of the central nervous system (CNS). Electrophysiological in vivo studies in mice will help to understand the highly complex network. In this paper, the optimization of epidural liquid crystal polymer (LCP) electrodes for different platinum electroplating parameters are presented and compared. Constant current and pulsed current electroplating varied in strength and duration was used to decrease the electrode impedance and to increase the charge storage capacity (CSCC). In best cases, both methods generated similar results with an impedance reduction of about 99%. However, electroplating with pulsed currents was less parameter-dependent than the electroplating with constant current. The use of ultrasound was essential to generate platinum coatings without plating defects. Electrode model parameters extracted from the electrode impedance reflected the increase in surface porosity due to the electroplating processes.

Design and fabrication of an integrated heart-on-a-chip platform for construction of cardiac tissue from human iPSC-derived cardiomyocytes and in situ evaluation of physiological function

In vitro model of the human cardiac tissues generated from human induced pluripotent stem cells (hiPSCs) could facilitate drug discovery and patient-specific studies of physiology and disease. However, the immature state of hiPSC-derived cardiomyocytes (hiPSC-CMs) compared to adult myocardium is a key defect that must be overcome to enable the potential applications of hiPSC-CMs in drug testing. For this purpose, we developed a heart-on-a-chip device that contains microfluidic channels for long-term dynamic culture of cells, platinum wire electrodes for electrical stimulation of hiPSC-CMs, and gold electrode arrays as acquisition electrodes for real-time recording electrophysiological signals of cardiac tissues. Human iPSC-CMs cultured on biocompatible hydrogels in the chip chamber can be electrically stimulated to prompt the maturation of cardiomyocytes (CMs) and generate functional cardiac tissues. Drug tests were performed with calcium transient measurements to evaluate drug responsiveness of electrical stimulated and unstimulated cardiac tissues. The results show that only the electrical-stimulated cardiac tissues respond correctly to drug treatment of verapamil and isoprenaline, indicating the reliability of this engineered cardiac tissues for drug testing. The above integrated heart-on-a-chip device provides a promising platform for drug efficacy testing and cardiactoxicity.

Gold nanostructure-programmed flexible electrochemical biosensor for detection of glucose and lactate in sweat

Flexible electrochemical biosensors used for sweat analysis have aroused great interests in the field of intelligent instruments. Due to the complexity of body fluids, development of ultrasensitive and miniaturized sensors for analysis of sweat is always challengeable. In this research, we fabricate a sensitive and flexible sensor for real-time monitoring of glucose and lactate in sweat at micromolar level and millimolar level by using gold nanopine needles (AuNNs) as the signal amplification strategy. A flexible chip with gold electrode arrays was fabricated in a standard semi-conductor laboratory. AuNNs were deposited on the working electrode by electrochemical deposition method. Enzyme immobilization was carried out on the electrode surface via a cross-linker poly(ethylene glycol) diglycidylether (PEGDE), which is an important component of redox hydrogels capable of retaining the activity of the enzyme to a greater extent than other linkers like glutaraldehyde. The catalytic behavior of AuNNs under different conditions was investigated. The as-fabricated electrochemical sweat biosensor was found to achieve low detection limit down to 7 μmol L −1 for glucose, 54 μmol L −1 for lactate, respectively. The sensor also exhibited great selectivity, reproducibility and stability. In addition, human sweat samples were analyzed by the sensor, indicating its potential applications in determination of glucose and lactate as a wearable skin sensor. • A flexible electrochemical sensor is fabricated. • Au nanostructure is utilized for signal amplification. • Both glucose and lactate in sweat are detected. • High sensitivity is achieved due to Au nanostructure. • The developed sensor shows satisfactory selectivity.

A chip-based 128-channel potentiostat for high-throughput studies of bioelectrochemical systems: Optimal electrode potentials for anodic biofilms

The presence of microorganisms performing extracellular electron transfer has been established in many environments. Research to determine their role is moving slowly due to the high cost of potentiostats and the variance of data with small number of replicates. Here, we present a 128-channel potentiostat, connected to a 128 gold electrode array. Whereas the system is able to perform simultaneously 128 (bio)electrochemical measurements with an independent electrical signal input, the present manufacturing of the array limited the number of effective channels for this study to 77. We assessed the impact of 11 electrode potentials ranging from −0.45V to +0.2V vs. Ag/AgCl (7 replicates per potential) on the growth and electrochemical characteristics of anodic electroactive biofilms (EABs) formed by acetate-fed microbial communities. After 7 days of growth, maximum current was reached for electrodes poised at −0.3V, closely followed by −0.25V and −0.1V to +0.1V, a range well-fitting the midpoint potential of minerals naturally reduced by electroactive bacteria such as Geobacter Sulfurreducens. There was no significant difference in apparent midpoint potential of the EABs (−0.35V), suggesting that the mechanism of heterogeneous electron transfer was not affected by the electrode potential. The EABs poised below current plateau potential (≤−0.3V) exhibited slower growth but higher charge transfer parameters. The high-throughput and high reproducibility provided by the array may have a major facilitating impact on the field of electromicrobiology. Key aspects to improve are data processing algorithms to deal with the vast amount of generated data, and manufacturing of the electrode array itself.

Amperometric Detection of Creatinine in Clinical Samples Based on Gold Electrode Arrays Fabricated Using Printed Circuit Board Technology

AbstractHerein we report a reliable and stable biosensor for the amperometric detection of creatinine through the ammonium produced in its reaction with creatinine deiminase linked to a Nafion®/polyaniline gold coated surface. The gold electrode array was produced using a low cost printed board circuit technology. A linear range of 1–1000 μM was obtained with standard deviations of less than 5 % (n=3) obtained. Stability studies were carried out and 80 % activity was maintained after one month. The sensors were tested with 142 serum samples from patients with renal dysfunction at different stage of the disease and validated using a commercial colorimetric method.

Modeling and Fabrication of a Piezoelectric Artificial Cochlea Electrode Array With Longitudinal Coupling

In this study, inspired from human cochlea, we propose an artificial basilar membrane structure based on an array of gold electrodes microfabricated along the opposite surfaces of a piezoelectric continuum. The proposed piezoelectric continuum features an isosceles trapezoidal geometry and is situated atop an elastomer matrix with embedded electrode grooves and a duct. At first, a detailed analytical model is presented, which formulates the continuum’s planar deflection equation, governing its elastodynamic behavior. Subsequently, in order to verify the analytical outcomes, a multiphysics finite-element analysis is performed in COMSOL®. Both analytical and numerical models demonstrate desired frequency selectivity akin to the capability of a biological basilar membrane. Subsequently, a proof-of-concept model of the proposed structure is custom-fabricated through standard photo- and soft lithography techniques using Polyvinylidene Difluoride (PVDF), gold, and Polydimethylsiloxane (PDMS) materials. Finally, the fabricated artificial basilar membrane that is intended to be used as a broad band sensor, and artificial cochlea for seamless human-robot interaction is experimentally characterized using a custom-built acoustic exciter, and its effective performance is validated within the frequency range of 3 kHz to 8 kHz.

A scalable two-dimensional moving electric lattice on a chip for polar molecules

Cold atoms and polar molecules have long been candidates for the implementation of quantum information processing. Although many schemes of two-dimensional (2D) moving optical or magnetic lattices have been proposed for atomic shift register, little work has been done on 2D electric lattice for molecular shift register, mainly due to the complexity of molecular energy level structures as well as the challenge to build micropotentials that are scalable, smoothly moving and accurately controlled. Here we present a design of chip-based 2D electric lattice for molecular shift register capable of scaling and controlling, which mainly consists of arrays of equidistant gold electrodes for generating a moving electric lattice. Our theoretical analysis and trajectory calculations, based on the polar molecules ammonia-D3 (ND3) and methylidyne radical (CH), show explicitly that the 2D lattice is able to directly slow down arrays of polar molecules from supersonic speeds to a standstill over a distance of a few centimeters, and then hold them for a certain time or shift them back in a smooth manner. Besides, it also enables decelerating and trapping of the two molecular species simultaneously, which contributes to the understanding towards new phenomena such as novel quantum mechanical collisions and cold chemistry.

Micro Electrode Arrays Fabrication Using Flexible Perfluoroalkoxy Alkane Films.

Perfluoroalkoxy alkane (PFA) film-based microelectrode arrays were fabricated in monolithic structure with pretreatment of plasma on the surface followed by patterning gold electrode array without additional adhesion metal layer. The encapsulation of patterned fluoropolymer layer was thermally laminated at the temperature of under its melting point, interleaved between Polytetrafluoroethylene (PTFE) sheets which indicate formation of micro-corrugated pattern. The fabricated device was optically opaque, however, transparent in solution due to the diffraction of light. Packaged substrate was easily processable with focused ion beam laser machine in high resolution. According to excellent reliability, PFA based micro gold electrode can be applied in a variety of biomedical application such as artificial retina, neural sensors with chronic implantation.

Thickness Dependence Impact on Proton Transport Proton Properties of Nafion® Thin-Film on Platinum Model Electrode

Introduction Improving oxygen reduction reaction (ORR) activity of cathode catalyst is required for wide spread of polymer electrolyte fuel cells. Because ORR occurs at the three-phase-boundary among the cathode catalyst, ionomer and oxygen gas, understanding the impact the ionomer on the cathode catalyst is important to achieve the high performance PEFCs. Especially, the structure of the ionomer on the cathode is strongly influenced by humidity, thickness, annealing treatment [1-3]. In this study, we examined the proton conductivity the Nafion® thin-film with various thickness from 5 to 200 nm. The correlation between structure and proton conductivity of the Nafion on Pt electrode was discussed. Experimental For proton conductivity measurements, Nafion thin-films were prepared on interdigitated array of gold electrodes on SiO2 substrate by soaking the electrode on Nafion dispersion. For GISAXS measurements, Nafion thin-films were prepared on Pt sputtered P doped-silicon substrates by spin casting of Nafion dispersion. Proton conductivity under humidity was measured by applying an alternating potential of amplitude 100 mV over a frequency 7 MHz to 0.01 Hz. GISAXS measurements were performed under humidity in beamline BL40B2 at SPring-8, Japan. Results and Discussion In the Nafion thin-films with thickness more than 50 nm, EIS results indicated that the hydrophilic domains grew gradually as the thickness increases. In contrast, the hydrophilic domains, which works as the protonic path, grows larger with increase of the thickness, leading to reduce the activation energy of proton conductivity. According to GISAXS, the hydrophilic domain disappears in the Nafion thin-film with thickness less than 50 nm. These results indicate that the structure of Nafion thin-film drastically changes with the thickness. It is anticipated that the proton conductivity of the in-plane in the Nafion film is larger than that of the out-of-plane because the hydrophilic domain of the in-plane grows larger than that of the out-of-plane. The anisotropy of the ordered structure in the Nafion thin-film is enhanced by the interaction between the ionomer and substrate. These results indicate that the proton conductivity in the Nafion is largely influenced by the amount of the hydrophobic domain. Acknowledgments This research is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Reference: [1] A. Kusoglu, D. Kushner, D. K. Paul, D. Karan, M. Hickner, A. Weber, Adv. Funct. Mater., 24, 4763 (2014) [2] D. K. Paul, H. K. Shim, J. B. Giorgi, K. Karan, J. Polym. Sci. B Polym. Phys., 54, 1267 (2016) [3] D. K. Paul, R. McCreery, K. Karan, J. Electrochem. Soc., 161, F1395 (2014)

Electrochemical genosensor for the direct detection of tailed PCR amplicons incorporating ferrocene labelled dATP

An electrochemical genosensor for the detection and quantification of Karlodinium armiger is presented. The genosensor exploits tailed primers and ferrocene labelled dATP analogue to produce PCR products that can be directly hybridised on a gold electrode array and quantitatively measured using square wave voltammetry. Tailed primers consist of a sequence specific for the target, followed by a carbon spacer and a sequence specifically designed not to bind to genomic DNA, resulting in a duplex flanked by single stranded binding primers. The incorporation of the 7-(ferrocenylethynyl)-7-deaza-2′-deoxyadenosine triphosphate was optimised in terms of a compromise between maximum PCR efficiency and the limit of detection and sensitivity attainable using electrochemical detection via hybridisation of the tailed, ferrocene labelled PCR product. A limit of detection of 277aM with a linear range from 315aM to 10 fM starting DNA concentration and a sensitivity of 122 nA decade−1 was achieved. The system was successfully applied to the detection of genomic DNA in real seawater samples.

Influence of phenylethylammonium iodide as additive in the formamidinium tin iodide perovskite on interfacial characteristics and charge carrier dynamics

A combined electrical and time-resolved optical investigation of the perovskite formamidinium tin iodide (FASnI3) and its phenylethylammonium (PEA) derivative PEA0.08FA0.92SnI3, which recently achieved a power conversion efficiency of 9%, is presented to study the specifics of contact characteristics and charge carrier dynamics. Microstructured gold electrode arrays were used to investigate the charge transport across a metal-perovskite interface and through micrometers of the perovskite films. Symmetrical contact configuration enabled detailed polarization studies. Hysteresis in the current-voltage characteristics and a corresponding current-time behavior indicated limitations by charge transfer in the contacts. Hysteresis was less pronounced in PEA0.08FA0.92SnI3 compared with FASnI3. This is explained by a 2-dimensional interlayer at the contacts, which leads to decreased field-induced migration of ions at the contact. Carrier recombination in the bulk of FASnI3 films, however, was only slightly modified by the presence of PEA. Femtosecond broadband transient absorption experiments up to 1.5 ns provided rate constants for the Auger and bimolecular recombination processes in FASnI3 of k3 = 1 × 10−29 cm6 s−1 and k2 = 3.1 × 10−10 cm3 s−1, respectively. In PEA0.08FA0.92SnI3, no significant differences in k2 and an only slightly increased k3 = 2 × 10−29 cm6 s−1 were measured. In extension to previous photoluminescence studies, we found efficient cooling of hot carriers by coupling to optical phonons (τcop = 0.5 ps), which is even faster than in lead perovskites.

Gold-Plated Electrode with High Scratch Strength for Electrophysiological Recordings

Multi electrode arrays (MEA) have been exploited in different electrophysiological applications. In neurological applications, MEAs are the vital interfaces between neurons and the electronic circuits with dual role; transmitting electric signal to the neurons and converting neural activity to the electric signal. Since the performance of the electrodes has a direct effect on the quality of the recorded neuronal signal, as well as the stimulation, the true choice of electrode material for MEA is crucial. Gold is one of the best candidates for fabrication of MEAs due to its high electrical conductivity, biocompatibility and good chemical stability. However, noble metals such as gold do not adhere well to the glass substrate. Consequently while exposing to the water, gold films are damaged, which impose limitations in the exploiting of gold thin films as the electrode. In this paper, a simple and cost effective method for the fabrication of gold electrode arrays is proposed. Using various mechanical (adhesion test and scratch strength), morphological (AFM and SEM) and electrochemical methods, the fabricated electrodes are characterized. The results show that the fabricated electrode arrays have significantly high scratch strength and stability within the aqueous medium. In addition, the electrical properties of the electrodes have been improved. The proposed electrodes have the potential to be exploited in other applications including electronics, electrochemistry, and biosensors.

Electrolyte-Induced Electrical Disconnection between Single Graphene Nanoplatelets and an Electrode

We report the influence of electrolyte on the electrical contact between graphene nanoplatelets (GNPs) and an electrode via a single entity electrochemical technique. The current "steps" were observed in the absence of electrolyte due to the GNPs impacting on and bridging across an interdigitated gold electrode array (IDE); in contrast, current spikes of short duration were obtained in the presence of electrolyte. This result indicates that in the latter case the constant short-circuit bridging current was switched off and replaced solely by impacts of GNPs with single electrodes. These observed current spikes measured in the presence of electrolyte are evidenced to be of a capacitative nature, demonstrating the high sensitivity of the electronic properties of the GNP/metal junction to the ionic strength of the electrolytic solution.

Effect of Annealing Treatment for the Morphology and Proton Transport Property of Nafion Thin-Film on Platinum Electrode

Introduction Improving oxygen reduction reaction (ORR) activity of cathode catalyst is required for wide spread of polymer electrolyte fuel cells. Because ORR occurs at the interface between cathode catalyst and ionomer (Nafion), understanding the structure of Nafion on the cathode catalyst is important to design reaction field with high activity. The morphology of the Nafion on the cathode is strongly influenced by humidity, thickness, annealing treatment and so on[1-3]. The proton conductivity of Nafion increases with humidification, and the change degree depends on the thickness of Nafion.[3] However, the correlation between morphology and proton conductivity of the Nafion on the cathode have not still been clearly understood. In this study, we examined the correlation between morphology and proton conductivity under humidity of Nafion thin-film with annealing treatment via grazing incidence small angle X-ray scattering (GISAXS) and electrochemical impedance spectroscopy. Experimental For proton conductivity measurements, Nafion thin-films were prepared on interdigitated array of gold electrodes on SiO2 substrate by soaking the electrode on Nafion dispersion. For GISAXS measurements, Nafion thin-films were prepared on Pt sputtered P doped-silicon substrates by spin casting of Nafion dispersion. Annealing treatment was conducted under 160oC under N2 atmosphere for 1 hour for each thin-film prepared by the different methods. Proton conductivity under humidity was measured by applying an alternating potential of amplitude 100 mV over a frequency 7 MHz to 0.01 Hz. GISAXS measurements were performed under humidity in beamline BL40B2 at SPring-8, Japan. Results and Discussion The proton conductivity of the Nafion thin-film without annealing treatment was larger than that of the thin-film with annealing treatment under 20-80% relative humidity. Figure 1 shows that 1 D line profiles parallel to the substrate obtained from 2D GISAXS patterns of Nafion thin-films with or without annealing treatment under various relative humidity (RH). For the non-annealed thin-film (Figure 1 (a)), a broad peak, which is attributed to water domain in Nafion [4], appeared around q = 1.5 nm-1. The peak shifted lower q and the intensity increased with humidification. In the annealed thin-film (Figure 1(b)), the peak appeared around higher q (2.0 nm-1) higher than non-annealed thin-film, and the degree of intensity change with humidification was smaller. These results mean that annealing treatment suppresses growth of water domain in Nafion with humidity, which decreases proton conductivity. Acknowledgments This research is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Reference [1] A. Kusoglu, D. Kushner, D. K. Paul, D. Karan, M. Hickner, A. Weber, Adv. Funct. Mater., 24, 4763 (2014) [2] D. K. Paul, H. K. Shim, J. B. Giorgi, K. Karan, J. Polym. Sci. B Polym. Phys., 54, 1267 (2016) [3] D. K. Paul, R. McCreery, K. Karan, J. Electrochem. Soc., 161, F1395 (2014) [4] A. Kusgglu, T. J. Dursch, A. Z. Weber, Adv. Funct. Mater., 26, 4961 (2016)

Comparing the effect of different surfactants on the aggregation and electrical contact properties of graphene nanoplatelets

We report the influence of different surfactants, Triton X-100, sodium dodecyl sulfate (SDS) and cetrimonium bromide (CTAB), on the suspended graphene nanoplatelets (GNPs) in aqueous solution studied via a single entity electrochemical technique. This method simply requires recording the current responses resulting from the impacts of individual and aggregated GNPs with an interdigitated gold electrode array. Upon impact the nanomaterial can bridge across two interdigitated gold microbands creating an electrical contact. The current magnitude reflects both the agglomeration state of the material and the contact resistance between the gold array and the carbon nanomaterial. The sensitivity of the magnitude of the current steps to the identity of the used surfactant was further evidenced, indicating the influence of these surfactants upon the electrical connectivity of the nanomaterial to the electrode substrate.