Electrodeposited reduced graphene oxide-PEDOT:PSS/Nafion hybrid interface for the simultaneous determination of dopamine and serotonin.

The electrochemically deposited reduced graphene oxide-PEDOT:PSS/Nafion (rGO-PP/NF) hybrid material has provided a favorable interface for the simultaneous detection of dopamine (DA) and serotonin (5-HT). The rGO-PP/NF onto the Au seed layer of the flexible substrate was simple, and it was followed by the sequential electrophoretic deposition of GO, reduction at the optimal pH buffer media, electropolymerization of EDOT:PSS, and Nafion coating. The strong electron-transport capacity between rGO-PEDOT:PSS and the negatively charged Nafion matrix might allow the highly sensitive, simultaneous, and selective detection of DA and 5-HT due to its high affinity for cations. In the results of the electrochemical response, well-separated oxidation peaks were observed in a mixture that contained various concentrations of DA and 5-HT. It showed the dynamic sensing of DA and 5-HT in the ranges of 0.5-75 µM and 0.05-50 µM, respectively, and the detection limits of 0.17 and 0.16 µM, respectively. In the mixture of DA and 5-HT, the sensor had a detection limit of 0.1 µM for 5-HT and DA, and its sensitivities of DA and 5-HT were 99.3 and 86 µA/µMcm2. Furthermore, it demonstrated high selectivity, reproducibility, stability, and a recovery property in the human serum spike test that was good enough for the practical use.

Vibroacoustic Characteristics of a Specific Patterned Polymer with Graphene for an Electrostatic Speaker.

Graphene/polymer actuators were developed using bilayer graphene and various polymer substrates for use as transparent, flexible, and robust electrostatic speaker units. Additionally, a resonant frequency shift was induced using a polymer substrate on which various micropatterns were transferred to boost bass. The total sound pressure level (SPL) in the graphene/polymer actuator was measured by a sweep, and the frequency of the spectrum was confirmed to be one-third that of the octave band frequency. The change in the vibroacoustic characteristic with changes in Young's modulus and density was studied for the polymers of the same size and thickness. Particularly, the possibility of boosting bass was confirmed by inducing a resonant frequency shift and increasing the total SPL by adding micropatterns on a polymer substrate under the same conditions. The resonance frequency of 523 Hz and the SPL of 54 dBA in flat polymer film became 296 Hz and 69 dBA in a specific pattern, which produced a sound of >15 dB based on the same flat polymer. We expect that the design and information provided herein can provide the key parameters required to change the resonant frequency in small-size devices for the application of graphene/polymer thin-film actuators.

Flexible sensor with electrophoretic polymerized graphene oxide/PEDOT:PSS composite for voltammetric determination of dopamine concentration.

We demonstrate a novel, flexible sensor with graphene oxide/PEDOT:PSS (GO/PEDOT:PSS) composite for voltammetric determination of selective low levels of dopamine. The well-distributed GO and EDOT:PSS suspension in water were deposited simply and polymerized. Consequently, the EDOT:PSS provided a strong interaction between GO and PEDOT:PSS, and it also had well-tailored interfacial properties that allowed the highly selective and sensitive determination of DA. Since the interfacial net charge is well-constructed, the sensor satisfies both the requirements of selectivity and the highly sensitive detection of low amounts of DA. In the results, the sensor with the GO/PEDOT:PSS composite exhibited a low interfacial impedance of about 281.46 ± 30.95 Ω at 100 Hz and a high charge storage capacity (53.94 ± 1.08 µC/cm2) for the detection of dopamine. In addition, the interference from ascorbic acid was reduced effectively to a minimum by electrostatic charge repelling of the AA and the distinct difference for the oxidation peak of the UA. Due to the fact that the GO/PEDOT:PSS composite had a net negative charge and, enhanced interfacial properties, the sensor showed a dopamine detection limit of 0.008 µM and a sensitivity of 69.3 µA/µMcm2.

Sensitive and non-invasive cholesterol determination in saliva via optimization of enzyme loading and platinum nano-cluster composition.

An excessive cholesterol level can lead to cardiovascular diseases, such as stroke, hypertension, and myocardial infarction. A non-invasive, painless method of determining the cholesterol level in blood would improve the user's convenience. To provide rapid and accurate determination of cholesterol, we have developed a simple, disposable, enzyme-based electrochemical biosensor that can detect salivary cholesterol. It is possible to detect low concentrations of cholesterol in saliva using the optimized vertical structure of the platinum nano-cluster (Pt-NC) and the immobilization of a proper volume of an enzyme. The biosensor exhibited a linear range from 2 to 486 µM, the limit of detection was about 2 µM, and the sensitivity of the sensor was calculated to be 132 µA mM-1 cm-2. It also showed good specificity for ascorbic acid, uric acid, dopamine, glucose, and lactate. In a test with an actual sample, the performance of the biosensor was confirmed by measuring total cholesterol in the saliva of a patient with hyperlipidemia. The cholesterol levels measured in the saliva of three patients with hyperlipidemia were 520, 460, and 290 µM. Therefore, the Pt-NC based enzyme sensor is a promising candidate for the detection of cholesterol in human saliva.

Uterosacral Nerve Stimulation via Cuff Electrode: A Preliminary Animal Study for Potential Application to Treatment of Preterm Labor.

Preterm labor occurs in about 12% of all pregnancies, accounting for at least 75% of neonatal deaths. The neonatal outcomes depend on mainly the gestational age at delivery. The lower the gestational age, the higher the risk of morbidity and mortality. The management of preterm labor involves early detection of high-risk women, prevention and treatment. In this study, the feasibility and stability of implantable cuff electrodes detection and inhibition of uterine contractions for preterm labor treatment were investigated by in-vivo mouse test. In order to check functionality of implanted electrodes, acute in-vivo test at mouse uterosacral ligament was performed by using cuff electrode which stimulate and record nerve activity. As results, the electrical stimulation via a stimulating cuff electrode at mouse uterosacral ligament was properly applied and nerve fiber's signal was recorded via the recording electrode. In addition, the implanted cuff electrodes could obtain stable recording signal to the periodic electrical stimulation for 7 weeks.

Biological assessments of multifunctional hydrogel-decorated implantable neural cuff electrode for clinical neurology application.

The implantable cuff electrode is an effective neuroprosthetic device in current nerve tissue engineering. However, biocompatibility and stability are still a serious dispute in terms of in vivo function and continuous monitoring. In this regard, assessing the host's biological response to biomaterials is one of the key factors of chronic implantation. In this article, we analyzed the peripheral nerve specific-biological responses to the application of multi-functional hydrogel-coated electrodes. The surface of the cuff electrode was modified using a multifunctional hydrogel composed of PEG hydrogel, cyclosporin A(CsA)-microsphere(MS) and electrodeposited PEDOT:PSS. Through our approach, we have found that the multifunctional hydrogel coatings improve the neural electrode function, such as peak-to-peak amplitude increase. Additionally, the multifunctional hydrogel coated electrodes exhibited improved biocompatibility, such as reduced apoptotic properties and increased axonal myelination. Furthermore, 12 genes (BDNF, Gfra1, IL-6, Sox 10, S100B, P75 NTR , GAP43, MBP, MPZ, NrCAM, NE-FL, CB1) were upregulated at 5 weeks post-implant. Finally, double immunofluorescence revealed the effect of endocannabinoid system on neuroprotective properties and tissue remodeling of peripheral nerves during cuff electrode implantation. These results clearly confirmed that multifunctional hydrogel coatings could improve electrode function and biocompatibility by enhancing neuroprotective properties, which may provide a valuable paradigm for clinical neurology application.

Flexible and Highly Biocompatible Nanofiber-Based Electrodes for Neural Surface Interfacing.

Polyimide (PI)-based electrodes have been widely used as flexible biosensors in implantable device applications for recording biological signals. However, the long-term quality of neural signals obtained from PI-based nerve electrodes tends to decrease due to nerve damage by neural tissue compression, mechanical mismatch, and insufficient fluid exchange between the neural tissue and electrodes. Here, we resolve these problems with a developed PI nanofiber (NF)-based nerve electrode for stable neural signal recording, which can be fabricated via electrospinning and inkjet printing. We demonstrate an NF-based nerve electrode that can be simply fabricated and easily applied due to its high permeability, flexibility, and biocompatibility. Furthermore, the electrode can record stable neural signals for extended periods of time, resulting in decreased mechanical mismatch, neural compression, and contact area. NF-based electrodes with highly flexible and body-fluid-permeable properties could enable future neural interfacing applications.

Biofunctionalization of Nerve Interface via Biocompatible Polymer-Roughened Pt Black on Cuff Electrode for Chronic Recording.

Peripheral nerve cuff electrodes with roughened Pt black (BPt) are coated with polyethylene glycol (PEG) and Nafion (NF). Although the influence of coated PEG and Nafion on roughened BPt on the electrical properties is weak, the cuff electrode with BPt/PEG and BPt/Nafion exhibits some very important properties. For example, it markedly decreases interfacial impedance, increases charge storage capacity (CSC) due to retaining the BPt surface structure, good stability without exfoliation in repetitive cyclic voltammetry scanning because it is protected by PEG or Nafion coating. In cell viability test, Nafion-coated BPt does not show cytotoxicity to rat Schwann cell line (S16) at 24 and 72 h with the Nafion coating ranging from 0.1 to 10 mg cm-2 . In addition, real-time polymerase chain reaction (PCR) analysis indicates that Schwann cell differentiation (S100 calcium-binding protein B, myelin basic protein, peripheral myelin protein 22), proliferation (proliferating cell nuclear antigen, cyclin-dependent kinase 1 (CDK1)), and adhesion molecules (neural cell adhesion molecule, laminin, fibronectin) are upregulated up to 5 mg cm-2 of Nafion. In animal study, the BPt/Nafion reduces infiltration of fibrotic tissue with high axonal maintenance with upregulation of proliferation (CDK1), adhesion (laminin, neuronal cell adhesion molecule), and neurotrophic factor receptor-related (gdnf family receptor alpha 1) mRNA expressions.

Multifunctional hydrogel coatings on the surface of neural cuff electrode for improving electrode-nerve tissue interfaces.

UNLABELLED: Recently, implantable neural electrodes have been developed for recording and stimulation of the nervous system. However, when the electrode is implanted onto the nerve trunk, the rigid polyimide has a risk of damaging the nerve and can also cause inflammation due to a mechanical mismatch between the stiff polyimide and the soft biological tissue. These processes can interrupt the transmission of nerve signaling. In this paper, we have developed a nerve electrode coated with PEG hydrogel that contains poly(lactic-co-glycolic) acid (PLGA) microspheres (MS) loaded with anti-inflammatory cyclosporin A (CsA). Micro-wells were introduced onto the electrode in order to increase their surface area. This allows for loading a high-dose of the drug. Additionally, chemically treating the surface with aminopropylmethacrylamide can improve the adhesive interface between the electrode and the hydrogel. The surface of the micro-well cuff electrode (MCE) coated with polyethylene glycol (PEG) hydrogel and drug loaded PLGA microspheres (MS) were characterized by SEM and optical microscopy. Additionally, the conductive polymers, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT/PSS), were formed on the hydrogel layer for improving the nerve signal quality, and then characterized for their electrochemical properties. The loading efficiencies and release profiles were investigated by High Performance Liquid Chromatography (HPLC). The drug loaded electrode resulted in a sustained release of CsA. Moreover, the surface coated electrode with PEG hydrogel and CsA loaded MP showed a significantly decreased fibrous tissue deposition and increased axonal density in animal tests. We expect that the developed nerve electrode will minimize the tissue damage during regeneration of the nervous system. STATEMENT OF SIGNIFICANCE: The nerve electrodes are used for interfacing with the central nervous system (CNS) or with the peripheral nervous system (PNS). The interface electrodes should facilitate a closed interconnection with the nerve tissue and provide for selective stimulation and recording from multiple, independent, neurons of the neural system. In this case, an extraneural electrodes such as cuff and perineural electrodes are widely investigated because they can completely cover the nerve trunk and provide for a wide interface area. In this study, we have designed and prepared a functionalized nerve cuff electrode coated with PEG hydrogel containing Poly lactic-co-glycol acid (PLGA) microspheres (MS) loaded with cyclosporine A (CsA). To our knowledge, our findings suggest that surface coating a soft-hydrogel along with an anti-inflammatory drug loaded MS can be a useful strategy for improving the long-term biocompatibility of electrodes.

Fabrication and characterization of stimulus nerve cuff electrode with highly roughened surface for chronic implant.

Nerve cuff electrodes for peripheral nerve prostheses are required chronically implanted electrodes which simultaneously stimulate and record nerve activity. It is inevitable challenge to investigate electrode material with low interfacial impedance and enhanced charge transfer capacity. In this study, stimulus nerve cuff electrodes on polyimide with Pt, conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT), black Pt, and IrOx were fabricated and characterized. The electrochemical properties were investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and voltage transient measurements. From th experimental results, stimulus nerve cuff electrodes with black Pt showed the highest charge delivery capacity (80 times higher than Pt), charge injection capacity (6 times higher than Pt), and lowest interfacial impedance (3.8 times lower than Pt).

Characterization of electroplated multilayered nanoporous platinum films for electrochemical sensor applications.

We newly fabricated and characterized the double layered nanoporous Pt (NPt) thin film on silicon substrate for enzyme-free glucose sensing applications. The surface morphologies of the fabricated NPt film were characterized using field emission scanning electron microscopy (FESEM). The fabricated NPt films exhibited highly dense nanopores with irregularly arranged grain boundaries and thicknesses of 0.77 microm, which were highly affected by the structural geometries of the bottom layer. The electrochemical properties of the double layered NPt films were tested in 1 M sulfuric acid and phosphate buffered saline (PBS, pH 7.4) with different concentrations of glucose. The NPt film on silicon substrate exhibited extremely high electrochemical roughness factor (RF) of 901.35 (mean values) and sensitivities of 33.34 microA mM(-1) cm(-2) in glucose concentrations up to 16 mM.

Highly selective and sensitive electrochemical detection of dopamine using a nafion coated hybrid macroporous gold modified electrode with platinum nanoparticles.

A coral-like macroporous Au electrode with electroplated Pt nanoparticles (hybrid macroporous Au-/nPts) coated with Nafion has been fabricated for the first time and used for highly selective and sensitive determination of dopamine (DA). The physically characterized results indicated that the electroplated Pt nanoparticles were dispersed uniformly on the macroporous Au electrode. The porosity and window pore size of the fabricated macroporous Au electrode were 50% and 100-300 nm, respectively. Also the electroplated Pt nanoparticles size was approximately 10-20 nm. The cyclic voltammograms results showed that the hybrid macroporous Au-/nPts exhibited a much larger surface activation area, a roughness factor (RF) of 2024.7, much higher than that of the macroporous Au electrode, which is 46.07. The electrochemical experimental results showed that the hybrid macroporous Au-/nPts coated with Nafion exhibited a dramatic electrocatalytic effect on the oxidation of DA. At 0.1 V, it responded linearly to DA concentrations ranging from 20 µ M to 160 µ M with a detection sensitivity of 90.9 µA mM (-1) cm (-2). Furthermore, it showed wide detection ranging from 20 nM to 900 µ M. At the same time, the interference of ascorbic acid (AA) was effectively avoided because of the Nafion film coated on the surface of the hybrid electrode.

Nonenzymatic free-cholesterol detection via a modified highly sensitive macroporous gold electrode with platinum nanoparticles.

A sensitive macroporous Au electrode with a highly rough surface obtained through the use of with Pt nanoparticles (macroporous Au-/nPts) is reported. It has been designed for nonenzymatic free-cholesterol biosensor applications. A macroporous Au-/nPts electrode was fabricated by electroplating Pt nanoparticles onto a coral-like shaped macroporous Au electrode structure. The macroporous Au-/nPts electrode was physically characterized by field emission scanning electron microscopy (FESEM). It was confirmed that the Pt nanoparticles were well deposited on the surface of the macroporous Au electrode. The porosity and window pore size of the macroporous Au electrode were 50% and 100-300 nm, respectively. The electroplated Pt nanoparticle size was approximately 10-20 nm. Electrochemical experiments showed that the macroporous Au-/nPts exhibited a much larger surface activation area (roughness factor (RF)=2024.7) than the macroporous Au electrode (RF=46.07). The macroporous Au-/nPts also presented a much stronger electrocatalytic activity towards cholesterol oxidation than does the macroporous Au electrode. At 0.2 V, the electrode responded linearly up to a 5 mM cholesterol concentration in a neutral media, with a detection limit of 0.015 mM and detection sensitivity of 226.2 µA mM(-1) cm(-2). Meanwhile, interfering species such as ascorbic acid (AA), acetaminophen (AP), and uric acid (UA), were effectively avoided. This novel nonenzymatic detection electrode has strong applications as an electrochemically based cholesterol biosensor.

Fabrication and Optimization of a Nanoporous Platinum Electrode and a Non-enzymatic Glucose Micro-sensor on Silicon.

In this paper, optimal conditions for fabrication of nanoporous platinum (Pt) were investigated in order to use it as a sensitive sensing electrode for silicon CMOS integrable non-enzymatic glucose micro-sensor applications. Applied charges, voltages, and temperatures were varied during the electroplating of Pt into the formed nonionic surfactant C16EO8 nano-scaled molds in order to fabricate nanoporous Pt electrodes with large surface roughness factor (RF), uniformity, and reproducibility. The fabricated nanoporous Pt electrodes were characterized using atomic force microscopy (AFM) and electrochemical cyclic voltammograms. Optimal electroplating conditions were determined to be an applied charge of 35 mC/mm2, a voltage of -0.12 V, and a temperature of 25 °C, respectively. The optimized nanoporous Pt electrode had an electrochemical RF of 375 and excellent reproducibility. The optimized nanoporous Pt electrode was applied to fabricate non-enzymatic glucose micro-sensor with three electrode systems. The fabricated sensor had a size of 3 mm x 3 mm, air gap of 10 µm, working electrode (WE) area of 4.4 mm2, and sensitivity of 37.5 µA•L/mmol•cm2. In addition, it showed large detection range from 0.05 to 30 mmolL-1 and stable recovery responsive to the step changes in glucose concentration.