Tetraedrinen amorfinen hiili – grafeeni hybridielektrodi dopamiinin havaitsemiseen

The real time in vivo detection of dopamine and other neurotransmitters in awake behaving animals is a long-standing goal. Carbon nanomaterials have emerged as promising candidates for electrochemical detection of dopamine. Diamond-like carbon films have wide water window, low capacitive background current and high chemical stability. By combining ultrathin tetrahedral amorphous carbon (ta-C) with Ti under layer the electron transfer properties can be enhanced without deterioration in the desired properties of ta-C. Such a bilayer thin films can also be modified with other carbon allotropes, such as graphene. To the best knowledge of the author this reports for the first time a ta-C electrode modified with reduced graphene oxide (rGO) for electrochemical detection of dopamine. Ti/ta-C bilayer electrodes with varying ta-C top layer thickness were fabricated and optimized in terms of electron transfer properties. Both types of electrodes were subjected to cyclic voltammetry experiments, Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy. The ta-C thickness was found to affect the electron transfer kinetics, while the dopamine detection limit of 5 μM remained unchanged. The electron transfer properties were found to improve with decreasing ta-C thickness and best performance was observed with 7 nm ta-C thickness. At a thickness below 7 nm the electron transfer properties start deteriorating due to excessive oxidation of the Ti/ta-C interface. The ta-C electrode showed poor selectivity towards dopamine. An order of magnitude improvement in sensitivity and a significant increase in selectivity towards dopamine was achieved. The rGO modified electrodes were able to detect 500 nM DA without any data treatment. Modification with rGO also resulted in significant improvement in electron transfer kinetics of dopamine. The amount of added rGO and the stacking of the graphene sheets were found to affect electron transfer in both inner and outer sphere systems. Finally oxidative treatments of the rGO resulted in increased current response and selectivity towards dopamine of all rGO electrodes, highlighting the role of oxygen containing functional groups in the electro-oxidation of both L-ascorbic acid and dopamine. By combining the stability, good electron transfer properties, and the reasonably low capacitive currents of the Ti/ta-C bilayer electrode with the more electrochemically active rGO, an electrode with low detection limit and improved selectivity towards dopamine was achieved. This electrode also exhibited wide enough water window and sufficiently low capacitive background currents for electrochemical detection of dopamine.Dopamiinin ja muiden hermovälittäjäaineiden reaaliaikainen havaitseminen elävissä organismeissa on pitkäaikainen tavoite. Hiilinanomateriaalit ovat osoittautuneet lupaaviksi materiaaleiksi dopamiinin havaitsemiseen. Timantinkaltaisella hiilellä on laaja vesi-ikkuna, matala kapasitiivinen taustavirta ja se on kemiallisesti stabiili. Yhdistämällä ultraohut tetraedrinen amorfinen hiili (ta-C) titaanin kanssa saadaan aikaan kaksikerroksinen elektrodi, jonka elektroninsiirto-ominaisuuksia voidaan säätää muuttamalla ta-C –kalvon paksuutta. Tämän elektrodin pintaa voidaan myös modifioida muilla hiilen allotroopeilla, kuten grafeenilla. Modifioimme ensimmäistä kertaa Ti/ta-C -elektrodeja grafeenilla dopamiinin havaitsemista varten. Ti/ta-C elektrodien elektroninsiirto-ominaisuudet optimoitiin ensin muuttamalla ta-C kerroksen paksuutta. Molemmat elektrodit karakterisoitiin syklisellä voltametrialla, Raman ja FT-IR spektroskopialla sekä pyyhkäisyelektronimikroskopialla. Elektroninsiirron havaittiin olevan riippuvainen ta-C:n paksuudesta, vaikka paksuudella ei ollut vaikutusta dopamiinin 5 μM havaitsemisrajaan. Elektroninsiirto kasvoi, kun ta-C:n paksuutta pienennettiin. Alle 4 nm paksuudella elektroninsiirto kuitenkin hidastui johtuen Ti -alikerroksen passivoitumisesta. Ti/ta-C elektrodi ei ollut selektiivinen, eivätkä askorbiinihapon ja dopamiinin hapetuspiikit olleet erotettavissa. Grafeenin avulla saavutettiin yhden kertaluokan aleneminen havaitsemisrajassa. Grafeeni-Ti/ta-C -elektrodilla saatiin 500 nM havaitsemisraja dopamiinille. Grafeeni myös nopeutti dopamiinin hapetus-pelkistysreaktion kinetiikkaa ja paransi selektiivisyyttä. Askorbiinihapon ja dopamiinin hapetuspiikit voitiin erottaa toisistaan. Lisäksi grafeenin määrän ja agglomeraattien mikrorakenteen havaittiin vaikuttavan elektroninsiirtoon sekä ulko- että sisäkehän hapetus-pelkistysreaktioissa. Lopuksi grafeenia hapetettiin väkevällä typpihapolla, minkä voitiin todeta kasvattavan dopamiinin virtavastetta sekä elektrodin selektiivisyyttä. Yhdistämällä Ti/ta-C -elektrodin elektroninsiirto-ominaisuudet ja matala taustavirta sähkökemiallisesti aktiivisemman grafeenin kanssa saatiin aikaan selektiivinen elektrodi, jolla on tarpeeksi matala havaitsemisraja dopamiinin havaitsemiseen solujen ulkoisessa nesteessä aivoissa. Lisäksi tämän elektrodin vesi-ikkuna on riittävän suuri ja taustavirta tarpeeksi pieni dopamiinin sähkökemiallista havaitsemista varten

Selective detection of morphine in the presence of paracetamol with anodically pretreated dual layer Ti/tetrahedral amorphous carbon electrodes

We investigated the effect of anodic treatment of titanium/tetrahedral amorphous carbon electrodes on the electrochemical detection of morphine and paracetamol. The anodic treatment caused both oxidation of the carbon and, more importantly, exposure and oxidation of the underlying Ti layer. This treatment anodically shifted the oxidation potential of paracetamol while that of morphine remained unaffected. The resulting electrode also showed better selectivity than a ta-C electrode without Ti. After anodic treatment at 2.5 V, selective detection of morphine with a physiologically meaningful detection limit of 9.8 nM and a linear range of 0.1-10 mu M was obtained in the presence of 100 mu M paracetamol.Peer reviewe

Simultaneous electrochemical detection of tramadol and O-desmethyltramadol with Nafion-coated tetrahedral amorphous carbon electrode

Tramadol (TR) is a member of the opioid family and is widely used for pain treatment in clinical patient care. The analgesic effect of tramadol is induced primarily by its main metabolite Odesmethyltramadol (ODMT). Due to interindividual differences in the TR metabolism to ODMT, the responses to TR vary highly between patients. Thus, a fast and selective method for simultaneous detection of TR and ODMT would increase the patient safety and pain treatment efficacy. In this study, a tetrahedral amorphous carbon (ta-C) electrode coated with a thin dip-coated recast Nafion membrane was fabricated for selective electrochemical determination of TR and ODMT. With this Nafion/ta-C electrode, simultaneous detection of TR and ODMT was achieved with linear ranges of 1-12.5 mu M and 1-15 mu M, respectively. The limits of detection were 131 nM for TR and 209 nM for ODMT. Both analytes were also measured in the presence of several common interferents, demonstrating the high selectivity of the fabricated electrode. In addition, the effect of pH on the peak potential was studied to observe the electrochemical behavior of the analytes at the electrode. Finally, clinically relevant concentrations of TR and ODMT were simultaneously detected from diluted human plasma to assess the applicability of the electrode in real samples. The fabricated Nafion/ta-C electrode was found successful in the simultaneous electrochemical detection of TR and ODMT in both buffer solution and in human plasma. (C) 2018 Elsevier Ltd. All rights reserved.Peer reviewe

Protein Adsorption and Its Effects on Electroanalytical Performance of Nanocellulose/Carbon Nanotube Composite Electrodes

Protein fouling is a critical issue in the development of electrochemical sensors for medical applications, as it can significantly impact their sensitivity, stability, and reliability. Modifying planar electrodes with conductive nanomaterials that possess a high surface area, such as carbon nanotubes (CNTs), has been shown to significantly improve fouling resistance and sensitivity. However, the inherent hydrophobicity of CNTs and their poor dispersibility in solvents pose challenges in optimizing such electrode architectures for maximum sensitivity. Fortunately, nanocellulosic materials offer an efficient and sustainable approach to achieving effective functional and hybrid nanoscale architectures by enabling stable aqueous dispersions of carbon nanomaterials. Additionally, the inherent hygroscopicity and fouling-resistant nature of nanocellulosic materials can provide superior functionalities in such composites. In this study, we evaluate the fouling behavior of two nanocellulose (NC)/multiwalled carbon nanotube (MWCNT) composite electrode systems: one using sulfated cellulose nanofibers and another using sulfated cellulose nanocrystals. We compare these composites to commercial MWCNT electrodes without nanocellulose and analyze their behavior in physiologically relevant fouling environments of varying complexity using common outer- and inner-sphere redox probes. Additionally, we use quartz crystal microgravimetry with dissipation monitoring (QCM-D) to investigate the behavior of amorphous carbon surfaces and nanocellulosic materials in fouling environments. Our results demonstrate that the NC/MWCNT composite electrodes provide significant advantages for measurement reliability, sensitivity, and selectivity over only MWCNT-based electrodes, even in complex physiological monitoring environments such as human plasma.</p

Electrochemical Detection of Oxycodone and Its Main Metabolites with Nafion-Coated Single-Walled Carbon Nanotube Electrodes

Oxycodone is a strong opioid frequently used as an analgesic. Although proven efficacious in the management of moderate to severe acute pain and cancer pain, use of oxycodone imposes a risk of adverse effects such as addiction, overdose, and death. Fast and accurate determination of oxycodone blood concentration would enable personalized dosing and monitoring of the analgesic as well as quick diagnostics of possible overdose in emergency care. However, in addition to the parent drug, several metabolites are always present in the blood after a dose of oxycodone, and to date, there is no electrochemical data available on any of these metabolites. In this paper, a single-walled carbon nanotube (SWCNT) electrode and a Nafion-coated SWCNT electrode were used, for the first time, to study the electrochemical behavior of oxycodone and its two main metabolites, noroxycodone and oxymorphone. Both electrode types could selectively detect oxycodone in the presence of noroxycodone and oxymorphone. However, we have previously shown that addition of a Nafion coating on top of the SWCNT electrode is essential for direct measurements in complex biological matrices. Thus, the Nafion/SWCNT electrode was further characterized and used for measuring clinically relevant concentrations of oxycodone in buffer solution. The limit of detection for oxycodone with the Nafion/SWCNT sensor was 85 nM, and the linear range was 0.5-10 mu M in buffer solution. This study shows that the fabricated Nafion/SWCNT sensor has potential to be applied in clinical concentration measurements.Peer reviewe

Disposable Nafion-Coated Single-Walled Carbon Nanotube Test Strip for Electrochemical Quantitative Determination of Acetaminophen in a Finger-Prick Whole Blood Sample

A disposable electrochemical test strip for the quantitative point-of-care (POC) determination of acetaminophen (paracetamol) in plasma and finger-prick whole blood was fabricated. The industrially scalable dry transfer process of single-walled carbon nanotubes (SWCNTs) and screen printing of silver were combined to produce integrated electrochemical test strips. Nafion coating stabilized the potential of the Ag reference electrode and enabled the selective detection in spiked plasma as well as in whole blood samples. The test strips were able to detect acetaminophen in small 40 mu L samples with a detection limit of 0.8 mu M and a wide linear range from 1 mu M to 2 mM, well within the required clinical range. After a simple 1:1 dilution of plasma and whole blood, a quantitative detection with good recoveries of 79% in plasma and 74% in whole blood was achieved. These results strongly indicate that these electrodes can be used directly to determine the unbound acetaminophen fraction without the need for any additional steps. The developed test strip shows promise as a rapid and simple POC quantitative acetaminophen assay.Peer reviewe

Simultaneous Detection of Morphine and Codeine in the Presence of Ascorbic Acid and Uric Acid and in Human Plasma at Nafion Single-Walled Carbon Nanotube Thin-Film Electrode

In clinical settings, the dosing and differential diagnosis of the poisoning of morphine (MO) and codeine (CO) is challenging due to interindividual variations in metabolism. However, direct electrochemical detection of these analytes from biological matrices is inherently challenging due to interference from large concentrations of anions, such as ascorbic acid (AA) and uric acid (UA), as well as fouling of the electrode by proteins. In this work, a disposable Nafion-coated single-walled carbon nanotube network (SWCNT) electrode was developed. We show facile electron transfer and efficient charge separation between the interfering anions and positively charged MO and CO, as well as significantly reduced matrix effect in human plasma. The Nafion coating alters the voltammetric response of MO and CO, enabling simultaneous detection. With this SWCNT/Nafion electrode, two linear ranges of 0.05-1 and 1-10 mu M were found for MO and one linear range of 0.1-50 mu M for CO. Moreover, the selective and simultaneous detection of MO and CO was achieved in large excess of AA and UA, as well as, for the first time, in unprocessed human plasma. The favorable properties of this electrode enabled measurements in plasma with only mild dilution and without the precipitation of proteins.Peer reviewe

Amorphous carbon thin film electrodes with intrinsic Pt-gradient for hydrogen peroxide detection

Nanoscale amorphous carbon thin films with intrinsic Pt gradient show great promise as new electrode materials for electrochemical detection of hydrogen peroxide. Embedding the Pt particles in the carbon matrix during the fabrication process allows tighter integration than, for example, adding them after the fabrication on top of the substrate. Especially, this approach can offer excellent electrochemical properties combined with CMOS compatibility, which is crucial for further device development. Here we provide extensive in depth electrochemical and physicochemical characterization of these novel materials by cyclic voltammetry (CV), chronoamperometry (CA), rotating disk electrode (RDE) experiments, transmission electron microscopy (TEM), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Equipped with these detailed results on these materials we proceed to present some suggestions how the physicochemical properties correlate with the results from electrochemical measurements. (i) It is shown that coarsening of the initially very finely dispersed structure occurs both under electron bombardment during TEM imaging as well as during cyclic voltammetry in H2SO4. (ii) Further, it is shown that OH is adsorbed on small Pt islands much more strongly compared to the bulk Pt, which may heavily influence hydrogen peroxide redox reactions on these Pt-containing amorphous carbon films. (iii) Finally, we proceed to demonstrate that despite these complications, these materials show linear response for hydrogen peroxide reduction in neutral phosphate buffered saline combined with very fast response times.Academy of Finland (E.P. grant #274670, T.L. grants # 285015 and #285526), Biocentrum Helsinki, Finnish Cultural Foundation (N.I. grant #00160331) and Foundation for Aalto University Science and Technology are acknowledged for funding