Research

12 pages, 3506 KiB

Open AccessArticle

Micro-Structured Polydopamine Films via Pulsed Electrochemical Deposition

by Jing Lin, Sven Daboss, Dominik Blaimer and Christine Kranz

Nanomaterials 2019, 9(2), 242; https://doi.org/10.3390/nano9020242 - 11 Feb 2019

Cited by 15 | Viewed by 4130

Polydopamine (PDA) films are interesting as smart functional materials, and their controlled structured formation plays a significant role in a wide range of applications ranging from cell adhesion to sensing and catalysis. A pulsed deposition technique is reported for micro-structuring polydopamine films using [...] Read more.

Polydopamine (PDA) films are interesting as smart functional materials, and their controlled structured formation plays a significant role in a wide range of applications ranging from cell adhesion to sensing and catalysis. A pulsed deposition technique is reported for micro-structuring polydopamine films using scanning electrochemical microscopy (SECM) in direct mode. Thereby, precise and reproducible film thicknesses of the deposited spots could be achieved ranging from 5.9 +/− 0.48 nm (1 pulse cycle) to 75.4 nm +/− 2.5 nm for 90 pulse cycles. The obtained morphology is different in comparison to films deposited via cyclic voltammetry or films formed by autooxidation showing a cracked blister-like structure for high pulse cycle numbers. The obtained polydopamine spots were investigated in respect to their electrochemical properties using SECM approach curves. Quantitative kinetic data in dependence of the film thickness, the substrate potential, and the used redox species were obtained. Full article

(This article belongs to the Special Issue Nanomaterials for Electrocatalytic Applications in Energy and Sensing)

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20 pages, 6270 KiB

Open AccessArticle

Voltammetric Detection of Caffeine in Beverages at Nafion/Graphite Nanoplatelets Layer-by-Layer Films

by Sandra Hernandez-Aldave, Afshin Tarat, James D. McGettrick and Paolo Bertoncello

Nanomaterials 2019, 9(2), 221; https://doi.org/10.3390/nano9020221 - 07 Feb 2019

Cited by 16 | Viewed by 4368

Abstract

We report for the first time a procedure in which Nafion/Graphite nanoplatelets (GNPs) thin films are fabricated using a modified layer-by-layer (LbL) method. The method consists of dipping a substrate (quartz and/or glassy carbon electrodes) into a composite solution made of Nafion and [...] Read more.

We report for the first time a procedure in which Nafion/Graphite nanoplatelets (GNPs) thin films are fabricated using a modified layer-by-layer (LbL) method. The method consists of dipping a substrate (quartz and/or glassy carbon electrodes) into a composite solution made of Nafion and GNPs dissolved together in ethanol, followed by washing steps in water. This procedure allowed the fabrication of multilayer films of (Nafion/GNPs)_n by means of hydrogen bonding and hydrophobic‒hydrophobic interactions between Nafion, GNPs, and the corresponding solid substrate. The average thickness of each layer evaluated using profilometer corresponds to ca. 50 nm. The as-prepared Nafion/GNPs LbL films were characterized using various spectroscopic techniques such as X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), FTIR, and optical microscopy. This characterization highlights the presence of oxygen functionalities that support a mechanism of self-assembly via hydrogen bonding interactions, along with hydrophobic interactions between the carbon groups of GNPs and the Teflon-like (carbon‒fluorine backbone) of Nafion. We showed that Nafion/GNPs LbL films can be deposited onto glassy carbon electrodes and utilized for the voltammetric detection of caffeine in beverages. The results showed that Nafion/GNPs LbL films can achieve a limit of detection for caffeine (LoD) of 0.032 μM and linear range between 20‒250 μM using differential pulse voltammetry, whereas, using cyclic voltammetry LoD and linear range were found to be 24 μM and 50‒5000 μM, respectively. Voltammetric detection of caffeine in beverages showed good agreement between the values found experimentally and those reported by the beverage producers. The values found are also in agreement with those obtained using a standard spectrophotometric method. The proposed method is appealing because it allows the fabrication of Nafion/GNPs thin films in a simple fashion using a single-step procedure, rather than using composite solutions with opposite electrostatic charge, and also allows the detection of caffeine in beverages without any pre-treatment or dilution of the real samples. The proposed method is characterized by a fast response time without apparent interference, and the results were competitive with those obtained with other materials reported in the literature. Full article

(This article belongs to the Special Issue Nanomaterials for Electrocatalytic Applications in Energy and Sensing)

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12 pages, 4772 KiB

Open AccessArticle

Plasma Activation of Copper Nanowires Arrays for Electrocatalytic Sensing of Nitrate in Food and Water

by Angela Maria Stortini, Sabrina Fabris, Gloria Saorin, Emanuele Verga Falzacappa, Ligia Maria Moretto and Paolo Ugo

Nanomaterials 2019, 9(2), 150; https://doi.org/10.3390/nano9020150 - 25 Jan 2019

Cited by 13 | Viewed by 3303

Abstract

Electrochemical methods for nitrate detection are very attractive since they are suitable for in-field and decentralized monitoring. Copper electrodes are often used to this aim as this metal presents interesting electrocatalytic properties towards nitrate reduction. In this research, we study improvements in the [...] Read more.

Electrochemical methods for nitrate detection are very attractive since they are suitable for in-field and decentralized monitoring. Copper electrodes are often used to this aim as this metal presents interesting electrocatalytic properties towards nitrate reduction. In this research, we study improvements in the electrochemical analysis of nitrate in natural water and food by taking advantage of the detection capabilities of ensembles of copper nanowire electrodes (CuWNEEs). These electrodes are prepared via template electrodeposition of copper within the nanopores of track-etched polycarbonate (PC) membranes. A critical step in the preparation of these sensors is the removal of the template. Here, we applied the combination of chemical etching with atmospheric plasma cleaning which proved suitable for improving the performance of the nanostructured copper electrode. Analytical results obtained with the CuWNEE sensor for nitrate analyses in river water samples compare satisfactorily with those achieved by standard chromatographic or spectroscopic methods. Experimental results concerning the application of the CuWNEEs for nitrate analysis in food samples are also presented and discussed, with focus on nitrate detection in leafy vegetables. Full article

(This article belongs to the Special Issue Nanomaterials for Electrocatalytic Applications in Energy and Sensing)

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12 pages, 3573 KiB

Open AccessArticle

Electrodeposition–Assisted Assembled Multilayer Films of Gold Nanoparticles and Glucose Oxidase onto Polypyrrole-Reduced Graphene Oxide Matrix and Their Electrocatalytic Activity toward Glucose

by Baoyan Wu, Shihua Hou, Yongyong Xue and Zhan Chen

Nanomaterials 2018, 8(12), 993; https://doi.org/10.3390/nano8120993 - 01 Dec 2018

Cited by 13 | Viewed by 4650

Abstract

The study reports a facile and eco-friendly approach for nanomaterial synthesis and enzyme immobilization. A corresponding glucose biosensor was fabricated by immobilizing the gold nanoparticles (AuNPs) and glucose oxidase (GOD) multilayer films onto the polypyrrole (PPy)/reduced graphene oxide (RGO) modified glassy carbon electrode [...] Read more.

The study reports a facile and eco-friendly approach for nanomaterial synthesis and enzyme immobilization. A corresponding glucose biosensor was fabricated by immobilizing the gold nanoparticles (AuNPs) and glucose oxidase (GOD) multilayer films onto the polypyrrole (PPy)/reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) via the electrodeposition and self-assembly. PPy and graphene oxide were first coated on the surface of a bare GCE by the electrodeposition. Then, AuNPs and GOD were alternately immobilized onto PPy-RGO/GCE electrode using the electrodeposition of AuNPs and self-assembly of GOD to obtain AuNPs-GOD multilayer films. The resulting PPy-RGO-(AuNPs-GOD)_n/GCE biosensors were used to characterize and assess their electrocatalytic activity toward glucose using cyclic voltammetry and amperometry. The response current increased with the increased number of AuNPs-GOD layers, and the biosensor based on four layers of AuNPs-GOD showed the best performance. The PPy-RGO-(AuNPs-GOD)₄/GCE electrode can detect glucose in a linear range from 0.2 mM to 8 mM with a good sensitivity of 0.89 μA/mM, and a detection limit of 5.6 μM (S/N = 3). This study presents a promising eco-friendly biosensor platform with advantages of electrodeposition and self-assembly, and would be helpful for the future design of more complex electrochemical detection systems. Full article

(This article belongs to the Special Issue Nanomaterials for Electrocatalytic Applications in Energy and Sensing)

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17 pages, 5378 KiB

Open AccessArticle

Biosynthesis of Copper Oxide (CuO) Nanowires and Their Use for the Electrochemical Sensing of Dopamine

by Sasikala Sundar, Ganesh Venkatachalam and Seong Jung Kwon

Nanomaterials 2018, 8(10), 823; https://doi.org/10.3390/nano8100823 - 12 Oct 2018

Cited by 168 | Viewed by 7838

Abstract

A facile one-step, eco-friendly, and cost-effective approach for the formation of copper oxide (CuO) nanowires by a green method using saponin-rich Sapindus mukorossi fruit extract (SMFE). The physio-chemical characteristics of the synthesized CuO nanowires have been characterized by X-ray Diffractometry (XRD), X-ray Photoelectron [...] Read more.

A facile one-step, eco-friendly, and cost-effective approach for the formation of copper oxide (CuO) nanowires by a green method using saponin-rich Sapindus mukorossi fruit extract (SMFE). The physio-chemical characteristics of the synthesized CuO nanowires have been characterized by X-ray Diffractometry (XRD), X-ray Photoelectron Spectroscopy (XPS), FT-IR (Fourier Transform Infrared Spectroscopy, FE-SEM (Scanning Electron Microscopy), and High-Resolution Transmission Electron Microscopy (HR-TEM). Further, the electrocatalytic activity of the CuO nanowires synthesized with SMFE has been investigated, and they have been used as dopamine (DA) sensors. Because of their unique properties, the CuO nanowires/GCE exhibited remarkable electrochemical response for the detection of DA with enhanced current response. The anodic current demonstrated that the CuO nanowires/GCE linearly detects the concentration of DA over the range of 0.1 µM to 0.105 mM of DA with a regression co-efficient of 0.9960. The obtained results illustrated that the synthesized CuO nanowires can easily stimulate the electron transfer reaction between DA and the nanowires modified electrode with the improvement of the conductivity and stability of the electrode. This remarkable electrocatalytic property of CuO nanowires makes it a unique electrochemical sensor for the detection of DA. Furthermore, the sensor is free from the interference of ascorbic acid, uric acid, and other interfering species. Moreover, the anti-interference performance also showed that the CuO nanowires/GCE could be employed for the determination of DA in real samples with good selectivity and sensitivity. Full article

(This article belongs to the Special Issue Nanomaterials for Electrocatalytic Applications in Energy and Sensing)

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13 pages, 2910 KiB

Open AccessArticle

Galvanic Replacement of Electrochemically Restructured Copper Electrodes with Gold and Its Electrocatalytic Activity for Nitrate Ion Reduction

by Ali Balkis, Jessica Crawford and Anthony P. O’Mullane

Nanomaterials 2018, 8(10), 756; https://doi.org/10.3390/nano8100756 - 25 Sep 2018

Cited by 10 | Viewed by 3880

Abstract

The electrochemical formation of nanostructured materials is a cost effective route to creating substrates that can be employed in a variety of applications. In this work the surface of a copper electrode was electrochemically restructured in an alkaline solution containing ethanol as an [...] Read more.

The electrochemical formation of nanostructured materials is a cost effective route to creating substrates that can be employed in a variety of applications. In this work the surface of a copper electrode was electrochemically restructured in an alkaline solution containing ethanol as an additive to modify the surface morphology, and generate a Cu/Cu₂O surface, which is known to be active for the electrocatalytic reduction of environmentally harmful nitrate ions. To increase the activity of the nanostructured surface it was decorated with gold prisms through a facile galvanic replacement approach to create an active Cu/Cu₂O/Au layer. The surface was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, as well as electrochemical techniques. It was found that the presence of recalcitrant oxides, and Au was beneficial for the increased activity compared to unmodified copper and undecorated restructured copper and was consistent with the incipient hydrous oxide adatom mediator model of electrocatalysis. This approach to generating nanostructured metal/metal oxide surfaces that can be galvanically replaced to create these types of composites may have other applications in the area of electrocatalysis. Full article

(This article belongs to the Special Issue Nanomaterials for Electrocatalytic Applications in Energy and Sensing)

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14 pages, 4370 KiB

Open AccessArticle

Modification of Microelectrode Arrays with High Surface Area Dendritic Platinum 3D Structures: Enhanced Sensitivity for Oxygen Detection in Ionic Liquids

by Ghulam Hussain, Anthony P. O’Mullane and Debbie S. Silvester

Nanomaterials 2018, 8(9), 735; https://doi.org/10.3390/nano8090735 - 17 Sep 2018

Cited by 9 | Viewed by 4134

Abstract

Electrochemical gas sensors are often used for identifying and quantifying redox-active analyte gases in the atmosphere. However, for amperometric sensors, the current signal is usually dependent on the electroactive surface area, which can become small when using microelectrodes and miniaturized devices. Microarray thin-film [...] Read more.

Electrochemical gas sensors are often used for identifying and quantifying redox-active analyte gases in the atmosphere. However, for amperometric sensors, the current signal is usually dependent on the electroactive surface area, which can become small when using microelectrodes and miniaturized devices. Microarray thin-film electrodes (MATFEs) are commercially available, low-cost devices that give enhanced current densities compared to mm-sized electrodes, but still give low current responses (e.g., less than one nanoamp), when detecting low concentrations of gases. To overcome this, we have modified the surface of the MATFEs by depositing platinum into the recessed holes to create arrays of 3D structures with high surface areas. Dendritic structures have been formed using an additive, lead acetate (Pb(OAc)₂) into the plating solution. One-step and two-step depositions were explored, with a total deposition time of 300 s or 420 s. The modified MATFEs were then studied for their behavior towards oxygen reduction in the room temperature ionic liquid (RTIL) [N_8,2,2,2][NTf₂]. Significantly enhanced currents for oxygen were observed, ranging from 9 to 16 times the current of the unmodified MATFE. The highest sensitivity was obtained using a two-step deposition with a total time of 420 s, and both steps containing Pb(OAc)₂. This work shows that commercially-available microelectrodes can be favorably modified to give significantly enhanced analytical performances. Full article

(This article belongs to the Special Issue Nanomaterials for Electrocatalytic Applications in Energy and Sensing)

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14 pages, 3786 KiB

Open AccessArticle

Platinum Nanoparticle Inclusion into a Carbonized Polymer of Intrinsic Microporosity: Electrochemical Characteristics of a Catalyst for Electroless Hydrogen Peroxide Production

by Robert K. Adamik, Naiara Hernández-Ibáñez, Jesus Iniesta, Jennifer K. Edwards, Alexander G. R. Howe, Robert D. Armstrong, Stuart H. Taylor, Alberto Roldan, Yuanyang Rong, Richard Malpass-Evans, Mariolino Carta, Neil B. McKeown, Daping He and Frank Marken

Nanomaterials 2018, 8(7), 542; https://doi.org/10.3390/nano8070542 - 18 Jul 2018

Cited by 8 | Viewed by 5395

Abstract

The one-step vacuum carbonization synthesis of a platinum nano-catalyst embedded in a microporous heterocarbon (Pt@cPIM) is demonstrated. A nitrogen-rich polymer of an intrinsic microporosity (PIM) precursor is impregnated with PtCl₆²⁻ to give (after vacuum carbonization at 700 °C) a nitrogen-containing heterocarbon [...] Read more.

The one-step vacuum carbonization synthesis of a platinum nano-catalyst embedded in a microporous heterocarbon (Pt@cPIM) is demonstrated. A nitrogen-rich polymer of an intrinsic microporosity (PIM) precursor is impregnated with PtCl₆²⁻ to give (after vacuum carbonization at 700 °C) a nitrogen-containing heterocarbon with embedded Pt nanoparticles of typically 1–4 nm diameter (with some particles up to 20 nm diameter). The Brunauer-Emmett-Teller (BET) surface area of this hybrid material is 518 m² g⁻¹ (with a cumulative pore volume of 1.1 cm³ g⁻¹) consistent with the surface area of the corresponding platinum-free heterocarbon. In electrochemical experiments, the heterocarbon-embedded nano-platinum is observed as reactive towards hydrogen oxidation, but essentially non-reactive towards bigger molecules during methanol oxidation or during oxygen reduction. Therefore, oxygen reduction under electrochemical conditions is suggested to occur mainly via a 2-electron pathway on the outer carbon shell to give H₂O₂. Kinetic selectivity is confirmed in exploratory catalysis experiments in the presence of H₂ gas (which is oxidized on Pt) and O₂ gas (which is reduced on the heterocarbon surface) to result in the direct formation of H₂O₂. Full article

(This article belongs to the Special Issue Nanomaterials for Electrocatalytic Applications in Energy and Sensing)

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9 pages, 2890 KiB

Open AccessArticle

Preparation of Cuprous Oxide Mesoporous Spheres with Different Pore Sizes for Non-Enzymatic Glucose Detection

by Jingwen Ma, Jun Wang, Min Wang, Guoliang Zhang, Wenchao Peng, Yang Li, Xiaobin Fan and Fengbao Zhang

Nanomaterials 2018, 8(2), 73; https://doi.org/10.3390/nano8020073 - 29 Jan 2018

Cited by 18 | Viewed by 4408

Abstract

Mass transfer plays a significant role in a sensor’s performance, because the substrate can be detected only when it contacts with the active catalytic surface. In this work, cuprous oxide mesoporous nanospheres (Cu₂O MPNS) with different pore size distributions are fabricated [...] Read more.

Mass transfer plays a significant role in a sensor’s performance, because the substrate can be detected only when it contacts with the active catalytic surface. In this work, cuprous oxide mesoporous nanospheres (Cu₂O MPNS) with different pore size distributions are fabricated and applied as electrocatalysts for glucose detection. The small pore Cu₂O (SP-Cu₂O, mean pore size of 5.3 nm) and large pore Cu₂O (LP-Cu₂O, mean pore size of 16.4 nm) spheres are prepared by the template method and an etching treatment. The obtained two kinds of Cu₂O MPNS exhibit high porosity with a similar specific surface area of 61.2 and 63.4 (m²·g⁻¹), respectively. The prepared Cu₂O MPNS are used to construct an electrochemical non-enzymatic glucose sensor. The results show that the LP-Cu₂O exhibits better performance than SP-Cu₂O, which illustrates that the internal diffusion takes a great impact on the performance of the sensor. The LP-Cu₂O modified electrode possesses a high and reproducible sensitivity of 2116.9 μA mM⁻¹·cm⁻² at the applied potential of 0.6 V with a wide detection range of 0.003–7.8 mM and a low detection limit of 0.42 μM. Full article

(This article belongs to the Special Issue Nanomaterials for Electrocatalytic Applications in Energy and Sensing)

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4111 KiB

Open AccessArticle

One-Step Electrochemical Fabrication of Reduced Graphene Oxide/Gold Nanoparticles Nanocomposite-Modified Electrode for Simultaneous Detection of Dopamine, Ascorbic Acid, and Uric Acid

by Chang-Seuk Lee, Su Hwan Yu and Tae Hyun Kim

Nanomaterials 2018, 8(1), 17; https://doi.org/10.3390/nano8010017 - 30 Dec 2017

Cited by 86 | Viewed by 7818

Abstract

Here, we introduce the preparation of the hybrid nanocomposite-modified electrode consisting of reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) using the one-step electrochemical method, allowing for the simultaneous and individual detection of dopamine (DA), ascorbic acid (AA), and uric acid (UA). RGO/AuNPs [...] Read more.

Here, we introduce the preparation of the hybrid nanocomposite-modified electrode consisting of reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) using the one-step electrochemical method, allowing for the simultaneous and individual detection of dopamine (DA), ascorbic acid (AA), and uric acid (UA). RGO/AuNPs nanocomposite was formed on a glassy carbon electrode by the co-reduction of GO and Au³⁺ using the potentiodynamic method. The RGO/AuNPs nanocomposite-modified electrode was produced by subjecting a mixed solution of GO and Au³⁺ to cyclic sweeping from −1.5 V to 0.8 V (vs. Ag/AgCl) at a scan rate 10 mV/s for 3 cycles. The modified electrode was characterized by scanning electron microscopy, Raman spectroscopy, contact angle measurement, electrochemical impedance spectroscopy, and cyclic voltammetry. Voltammetry results confirm that the RGO/AuNPs nanocomposite-modified electrode has high catalytic activity and good resolution for the detection of DA, AA, and UA. The RGO/AuNPs nanocomposite-modified electrode exhibits stable amperometric responses for DA, AA, and UA, respectively, and its detection limits were estimated to be 0.14, 9.5, and 25 μM. The modified electrode shows high selectivity towards the determination of DA, AA, or UA in the presence of potentially active bioelements. In addition, the resulting sensor exhibits many advantages such as fast amperometric response, excellent operational stability, and appropriate practicality. Full article

(This article belongs to the Special Issue Nanomaterials for Electrocatalytic Applications in Energy and Sensing)

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