Frequency response of electrolyte-gated graphene electrodes and transistors

The interface between graphene and aqueous electrolytes is of high importance for applications of graphene in the field of biosensors and bioelectronics. The graphene/electrolyte interface is governed by the low density of states of graphene that limits the capacitance near the Dirac point in graphene and the sheet resistance. While several reports have focused on studying the capacitance of graphene as a function of the gate voltage, the frequency response of graphene electrodes and electrolyte-gated transistors has not been discussed so far. Here, we report on the impedance characterization of single layer graphene electrodes and transistors, showing that due to the relatively high sheet resistance of graphene, the frequency response is governed by the distribution of resistive and capacitive circuit elements along the graphene/electrolyte interface. Based on an analytical solution for the impedance of the distributed circuit elements, we model the graphene/electrolyte interface both for the electrode and the transistor configurations. Using this model, we can extract the relevant material and device parameters such as the voltage-dependent intrinsic sheet and series resistances as well as the interfacial capacitance. The model also provides information about the frequency threshold of electrolyte-gated graphene transistors, above which the device exhibits a non-resistive response, offering an important insight into the suitable frequency range of operation of electrolyte-gated graphene devices

Flexible Graphene Solution-Gated Field-Effect Transistors : Efficient Transducers for Micro-Electrocorticography

Brain-computer interfaces and neural prostheses based on the detection of electrocorticography (ECoG) signals are rapidly growing fields of research. Several technologies are currently competing to be the first to reach the market; however, none of them fulfill yet all the requirements of the ideal interface with neurons. Thanks to its biocompatibility, low dimensionality, mechanical flexibility, and electronic properties, graphene is one of the most promising material candidates for neural interfacing. After discussing the operation of graphene solution-gated field-effect transistors (SGFET) and characterizing their performance in saline solution, it is reported here that this technology is suitable for μ-ECoG recordings through studies of spontaneous slow-wave activity, sensory-evoked responses on the visual and auditory cortices, and synchronous activity in a rat model of epilepsy. An in-depth comparison of the signal-to-noise ratio of graphene SGFETs with that of platinum black electrodes confirms that graphene SGFET technology is approaching the performance of state-of-the art neural technologies

EGNITE : Engineered Graphene for Neural Interface

La tecnologia d'implants neuronals en medicina té com a objectiu restaurar la funcionalitat del sistema nerviós en casos de degeneració o dany greu registrant o estimulant l'activitat elèctrica del teixit nerviós. Els implants neuronals disponibles actualment ofereixen una eficàcia clínica modesta, en part a causa de les limitacions que tenen els metalls utilitzats en la interfície elèctrica amb el teixit. Aquests materials comprometen la resolució de la interfície i, per tant, la restauració funcional amb el rendiment i l'estabilitat. En aquest treball presento uns implants neuronals flexibles basats en una pel·lícula prima de grafè porós nanoestructurat i biocompatible que proporciona una interfície neural bidireccional estable i d'alt rendiment. En comparació amb els dispositius de microelectrodos de platí estàndard, elèctrodes de 25 μm de diàmetre basats en grafè ofereixen una impedància significativament menor i poden injectar de manera segura 200 vegades més càrrega durant més de 100 milions de polsos. N'evaluo les seves capacitats in vivo registrant activitat epicortical amb alta fidelitat i alta resolució, estimulant subconjunts d'axons dins del nervi ciàtic amb llindars de corrent baixos i alta selectivitat i modulant l'activitat de la retina amb alta precisió. La tecnologia de pel·lícula fina de grafè aquí descrita té el potencial de convertir-se en el nou punt de referència per la pròxima generació de tecnologia d'implants neuronals.La tecnología de implantes neuronales en medicina tiene como objetivo restaurar la funcionalidad del sistema nervioso en casos de degeneración o daño grave registrando o estimulando la actividad eléctrica del tejido nervioso. Los implantes neurales disponibles actualmente ofrecen una eficacia clínica modesta, en parte debido a las limitaciones que plantean los metales utilizados en la interfaz eléctrica con el tejido. Dichos materiales comprometen la resolución de la interfaz y, por lo tanto, la restauración funcional con el rendimiento y la estabilidad. En este trabajo presento unos implantes neuronales flexibles basados en una película delgada de grafeno poroso nanoestructurado y biocompatible que proporciona una interfaz neural bidireccional estable y de alto rendimiento. En comparación con los dispositivos de microelectrodos de platino estándar, electrodos de 25 μm de diámetro basados en grafeno ofrecen una impedancia significativamente menor y pueden inyectar de forma segura 200 veces más carga durante más de 100 millones de pulsos. Aquí evaluo sus capacidades in vivo registrando actividad epicortical con alta fidelidad y alta resolución, estimulando subconjuntos de axones dentro del nervio ciático con umbrales de corriente bajos y alta selectividad y modulando la actividad de la retina con alta precisión. La tecnología de película fina de grafeno aquí descrita tiene el potencial de convertirse en el nuevo punto de referencia para la próxima generación de tecnología de implantes neuronales.Neural implants technology in medicine aims to restore nervous system functionality in cases of severe degeneration or damage by recording or stimulating the electrical activity of the nervous tissue. Currently available neural implants offer a modest clinical efficacy partly due to the limitations posed by the metals used at the electrical interface with the tissue. Such materials compromise interfacing resolution, and therefore functional restoration, with performance and stability. In this work, I present flexible neural implants based on a biocompatible nanostructured porous graphene thin film that provides a stable and high performance bidirectional neural interface. Compared to standard platinum microelectrode devices, the graphene-based electrodes of 25 μm diameter offer significantly lower impedance and can safely inject 200 times more charge for more than 100 million pulses. I assessed their performance in vivo by recording high fidelity and high resolution epicortical activity, by stimulating subsets of axons within the sciatic nerve with low thresholds and high selectivity and by modulating the retinal activity with high precision. The graphene thin film technology I describe here has the potential to become the new performance benchmark for the next generation of neural implant technology.Universitat Autònoma de Barcelona. Programa de Doctorat en Enginyeria Electrònica i de Telecomunicaci

Data and code from "Nanoporous graphene-based thin-film microelectrodes for in vivo high-resolution neural recording and stimulation"

Data and code for reproducing the main results of the paper "Nanoporous graphene-based thin-film microelectrodes for in vivo high-resolution neural recording and stimulation".Peer reviewe

Occurrence of Nonylphenol and Bisphenol-A in Surface Waters from Portugal

The occurrence of the endocrine disruptor compounds, such as 4-nonylphenol isomers and bisphenol A was determined in surface water samples from Portugal. The analytical method used involved the preconcentration of 200 mL of water sample by solid phase extraction (SPE) using a OASIS (Waters) cartridge, followed by Gas Chromatography-Mass Spectrometry (GC/MS) determination. Recoveries and limits of detection of 4-nonylphenol isomers and bisphenol-A were 73 % and 119 %, respectively, 0.01 mg L-1 and 0.002 mg L-1. The method was applied to the determination of these estrogenic pollutants in river and coastal waters during three months (August-October/1999). The total samples analyzed were 135. Concentrations of 4-nonylphenol isomers and bisphenol-A ranged from 0.03-30 mg L-1 and 0.07-4.0 mg L-1, respectively. Only in two river samples, concentrations of 4-nonylphenol isomers were above 10 mg L-1 and bisphenol-A were above 2 mg L-1. These values can cause estrogenic effects in fish and these sampling points require further investigation in order to verify the maintenance of these levels.D. A. A. acknowledges a grant from CNPq. Direção Geral do Ambiente, Ministério do Ambiente (Portugal), the EU project of the waste water cluster SANDRINE (ENV4-CT98-0801) and CICYT (AMB/999-1705-CE) are acknowledged for financial support to this project. Rosa Alonso and Roser Chaler are acknowledged for technical assistance.Peer reviewe

Occurrence of nonylphenol and bisphenol-A in surface waters from Portugal

The occurrence of the endocrine disruptor compounds, such as 4-nonylphenol isomers and bisphenol A was determined in surface water samples from Portugal. The analytical method used involved the preconcentration of 200 mL of water sample by solid phase extraction (SPE) using a OASIS (Waters) cartridge, followed by Gas Chromatography-Mass Spectrometry (GC/MS) determination. Recoveries and limits of detection of 4-nonylphenol isomers and bisphenol-A were 73 % and 119 %, respectively, 0.01 mug L-1 and 0.002 mug L-1. The method was applied to the determination of these estrogenic pollutants in river and coastal waters during three months (August-October/1999). The total samples analyzed were 135. Concentrations of 4-nonylphenol isomers and bisphenol-A ranged from 0.03-30 mug L-1 and 0.07-4.0 mug L-1, respectively. Only in two river samples, concentrations of 4-nonylphenol isomers were above 10 mug L-1 and bisphenol-A were above 2 mug L-1. These values can cause estrogenic effects in fish and these sampling points require further investigation in order to verify the maintenance of these levels

Occurrence and specific congener profile of 40 polybrominated diphenyl ethers in river and coastal sediments from Portugal

7 pages, 5 figures, 1 table.-- PMID: 12666918 [PubMed].-- Printed version published Mar 1, 2003.Forty polybrominated diphenyl ethers (PBDEs), from mono- through hepta-brominated, were analyzed in river and coastal sediment samples of the eight main river basins of Portugal to investigate the occurrence, geographical distribution, and detailed congener profiles. Thirty-two sediment samples taken along the different rivers from inland to the open sea revealed an increase toward the river mouth with a total PBDE concentration of 20 ng/g-dw, and levels decreased to 0.5 ng/g-dw in coastal sediments. PBDEs were detected in all samples analyzed, indicating a diffuse source of pollution in the aquatic environments. Maximum levels were encountered in sediments collected close to urban and industrial areas. Of 40 congeners included in the analytical work, 17 congeners were detected in river sediments. BDE 47 was found in all samples analyzed whereas BDEs 100 and 99 were found in more than 26 out of 32 samples analyzed at concentrations from 0.03 to 10 ng/g-dw. This study is unique in showing the presence of previously nondescribed lower brominated PBDEs in riverine and marine sediments. BDEs 7, 11, 12+13, 15, 30, 32, 17, 25, 28+33, 49, 75, and 71 were identified in two to five samples with a median of 0.03−0.55 ng/g-dw. The analytical method developed consisted of the use of Soxhlet extraction with a novel cleanup method employing alumina cartridges and analysis by gas chromatography−mass spectrometry operated in negative chemical ionization mode.This work has been financed by the Instituto do Ambiente of Portugal (Ministry of Environment).Peer reviewe

Concentrations and sources of legacy and novel flame retardants in outdoor and indoor environments

Levels of particle-phase legacy polybrominated diphenyl ethers (PBDEs), and novel brominated and chlorinated flame retardants, such as decabromodiphenyl ethane (DBDPE) and Dechlorane Plus (DP), were measured in ambient outdoor air, indoor workplace air and indoor dust, in different locations across Spain. PBDE concentrations were generally higher in outdoor ambient air samples than in indoor air, ranging between 1.18 and 28.6 pg m−3, while DP was the main flame retardant (FR) in indoor air (2.90–42.6 pg m−3). A different behavior of legacy versus novel FRs was observed in all the environments and matrices considered, which seemed to indicate a progressive replacement of the former. Although the emission sources could not be fully identified, certain evidences suggested that high outdoor PBDE concentrations could be associated with old goods in landfills and recycling centers, while high indoor DP concentrations were linked to the presence of new electronic devices. A direct impact of land use on outdoor atmospheric DP concentrations was observed, with DP concentrations correlating with high density of buildings within a city. In addition, DP concentrations outdoors correlated with inorganic species with FR properties (e.g., Cr, Cu). Significant differences in the fraction of anti-DP to the total DP (Fanti ratio) were observed between indoor air (PM2.5) and dust (PM10), which could be related with: a) a dependence on particle size, suggesting a higher relative abundance of the anti-isomer in PM10 than in PM2.5, while similar concentrations were recorded for the syn-isomer; b) a higher deposition rate of the anti-isomer compared to the syn-isomer; and/or c) a more accentuated preferential degradation of the anti-isomer linked to artificial light or other agents coexisting in the air. The detectable presence of all the FR families analyzed in indoor air and dust points to the importance of monitoring these compounds in order to minimize human exposure. © 2018This work was partially funded by the Spanish Ministry of Economy, Industry and Competitiveness (MINEC) and the Agencia Estatal de Investigación (AEI) through project CGL2017-82093-ERC. The authors acknowledge the support from AGAUR SGR41 and SGR1404.Peer reviewe