Preparation of electro-reduced graphene oxide supported walnut shape nickel nanostructures, and their application to selective detection of dopamine

Graphene and Carbon Nanotube-based Electrochemical Sensing Platforms for Dopamine

Dopamine (DA) is an important neurotransmitter, which is created and released from the central nervous system. It plays a crucial role in human activities, like cognition, emotions, and response to anything. Maladjustment of DA in human blood serum results in different neural diseases, like Parkinson's and Schizophrenia. Consequently, researchers have started working on DA detection in blood serum, which is undoubtedly a hot research area. Electrochemical sensing techniques are more promising to detect DA in real samples. However, utilizing conventional electrodes for selective determination of DA encounters numerous problems due to the coexistence of other materials, such as uric acid and ascorbic acid, which have an oxidation potential close to DA. To overcome such problems, researchers have put their focus on the modification of bare electrodes. The aim of this review is to present recent advances in modifications of most used bare electrodes with carbonaceous materials, especially graphene, its derivatives, and carbon nanotubes, for electrochemical detection of DA. A brief discussion about the mechanistic phenomena at the electrode interface has also been included in this review.

Fabrication and Characterization of Taurine Functionalized Graphene Oxide with 5-Fluorouracil as Anticancer Drug Delivery Systems

Recently, nanocarrier systems for cancer drugs, especially GO-based drug delivery systems, have become a boon for cancer patients. In this study, we choose Tau to functionalize the GO surface to improve its biocompatibility. Firstly, nano-scale GO was synthesized by the modified Hummer's method and ultrasonic stripping method. The taurine-modified graphene oxide carrier (Tau-GO) was synthesized by chemical method to obtain Tau-GO that has a good dispersibility and stability in water, with a zeta potential of - 38.8 mV and a particle size of 242 nm. Based on the encapsulation efficiency evaluation criteria, the optimal formulation was determined to combine Tau-GO and 5-FU by non-covalent bonding. The 5-FU-Tau-GO was more stable in neutral environment than in acidic environment, and with a certain PH response and sustained release effect. In vivo, we compared oral and intravenous administrations of 5-FU and 5-FU-Tau-GO, respectively, using pharmacokinetic tests and related parameters and showed that 5-FU-Tau-GO oral or intravenous administration prolongs the action time of 5-FU in the body and improves its bioavailability. In addition, the inhibition of HepG2 cells that was measured by the MTT assay, showed that the IC₅₀ value of 5-FU was 196 ± 8.73 μg/mL, and the IC₅₀ value of 5-FU-Tau-GO was 65.2 ± 0.7 μg/mL, indicating that 5- FU-Tau-GO is more potent against HepG2 cells and has a stronger inhibitory effect on cancer cells. The effect on cell morphology that was measured using the AO/EB staining also showed that 5-FU-Tau-GO not only disrupted cells, but also significantly induced apoptosis compared to 5-FU. We also verified by computer aided design that Tau-GO can bind better to 5-FU than to the unmodified GO, and that the formed 5-FU-Tau-GO system is more stable, and conducive to the transfer and release of 5-FU in vivo.

Magnetic nanomaterials with unique nanozymes-like characteristics for colorimetric sensors: A review

Colorimetric sensors for the rapid detection of numerous analytes have been widely applied in many fields such as biomedicine, food industry and environmental science due to their highly sensitive and selective response, easy operation and visual identification by naked eyes. In this review, the recent progress of the colorimetric sensors based on the magnetic nanomaterials with unique nanozymes-like catalytic activity (magnetic nanozyme) and their colorimetric sensing applications are presented. Emerging magnetic nanozyme-based colorimetric sensors, such as metal oxide/sulfides-based, metal-based, carbon-based, and aptamer-conjugated magnetic nanomaterials, offer many desirable features for target analytes detection. And due to the unique nanoscale physical-chemical properties, magnetic nanozymes have been used to mimic the catalytic activity of natural enzymes such as peroxidases, oxidases and catalases. This review also highlights the catalytic mechanisms of enzyme-like reactions, and promising colorimetric sensing system for the detection of chemical compounds like H₂O₂, pesticide, ascorbic acid, dopamine, tetracyclines, perfluorooctane sulfonate, phenolic compounds, heavy metal ion and sulfite have been deeply discussed. In addition, the remaining challenges and future directions in utilizing magnetic nanozyme for colorimetric sensors are addressed.

Development of CuAlO2-Encapsulated Reduced Graphene Oxide Nanocomposites: An Efficient and Selective Electrocatalyst for Detection of Neurodegenerative Disorders

Carbon-based nanomaterials continue to simulate wide interest in diverse disciplines including electrochemical biosensors, which have great ability to function as next-generation clinical diagnostics. Motivated by this point, we for the first time developed a CuAlO₂-encapsulated reduced graphene oxide (rGO) nanocomposite by a facile wet-chemical process to modify a glassy carbon electrode for dopamine detection with high selectivity and good sensitivity. The size, shape, phase purity, chemical composition, and surface area were investigated for the samples through transmission electron microscopy, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Brunauer-Emmett-Teller analysis. The electrocatalytic performance was studied using cyclic voltammetry and amperometric technique. The modified rGO/CuAlO₂ nanocomposite electrode showed an enhanced electrochemical performance compared to other electrodes and pure CuAlO₂ electrodes due to the strong promoting effect between rGO and CuAlO₂. Both the oxidation current and concentration were proportional and show a linear range of 9.2 × 10^-8 to 1.6 × 10^-7 M having a detection limit of 15 nM at S/N = 3. Further, the biosensor successfully neglected the interference of ascorbic and uric acid and exhibited enhanced selectivity, improved sensitivity, and stability toward dopamine formulations. Most obviously, the real-time analysis of the electrochemical biosensor may be proved using the clinical diagnostics in the near future.

Electroless deposition of gold nanoparticles on carbon nanopipette electrode for electrochemical detection of catecholamines released from PC12 cells

An electroless deposition method is reported for the fabrication of gold nanoparticles (Au NPs) modified carbon nanopipette electrode (CNPE) for sensitive electrochemical detection of dopamine (DA) in aqueous solution and catecholamines released from PC12 cells. A CNPE is fabricated by chemical vapor deposition with a carbon layer onto nanocapillary and then contacted with copper (Cu) wire. Cu wire of CNPE is able to serve as reducing agent for electroless deposition of Au NPs on the CNPE because the potential of Cu²⁺/Cu is more negative than that of AuCl₄^-/Au. The method is simple, time-saving, and environmentally friendly. Field emission scanning electron microscopy, energy-dispersive X-ray analysis, and electrochemical techniques confirm the successful fabrication of the Au NPs/CNPE. Furthermore, Au NPs/CNPE exhibits a good sensing activity for DA oxidation with a wide linear determination range of 0.1-8 μmol/L and a low detection limit of 6 nmol/L. The Au NPs/CNPE can be potentially applied for measurement of catecholamines released from PC12 cells. This present work is believed to be beneficial to the design and development of active metal catalysts onto nanoelectrodes for the detection of electroactive biological molecules in living cells.Graphical abstract An electroless deposition method was developed for the fabrication of gold nanoparticles onto the carbon nanopipette electrode, which was served as an enhanced electrochemical sensing platform for highly sensitive detection of dopamine with a linear range of 0.1-8 μmol/L and a detection limit of 6 nmol/L, and was also applied in the detection of catecholamines released from PC12 cells.

Electrochemical Detection of Dopamine and Serotonin in the Presence of Interferences in a Rotating Droplet System

In this Article, a rotating droplet system is used for simultaneous detection of dopamine and serotonin. Carbon nanoparticles functionalized with sulfonic groups on the electrode surface enables potential discrimination between the neurotransmitters and the most common interferences, whereas the efficient and low-volume hydrodynamic system helps to lower the detection limit toward physiologically relevant concentrations. Here, we present results with a 10 nM limit of detection for serotonin and a 100 nM to 2 μM linear response range from the system in a sample containing an equimolar concentrations of dopamine and serotonin and 0.5 mM concentration of both uric and ascorbic acids. Demonstrating the practical applicability of this method, we measure the concentration of serotonin in 70 μL of mice blood serum samples without additional pretreatment.

Pt-Decorated Boron Nitride Nanosheets as Artificial Nanozyme for Detection of Dopamine

Over the past decade, nanosized metal oxides, metals, and bimetallic particles have been actively researched as enzyme mimetic nanomaterials. However, the common issues with individual nanoparticles (NPs) are stabilization, reproducibility, and blocking of active sites by surfactants. These problems promote further studies of composite materials, where NPs are spread on supports, such as graphene derivatives or dichalcogenide nanosheets. Another promising type of support for NPs is the few-layered hexagonal boron nitride (hBN). In this study, we develop surfactant-free nanocomposites containing Pt NPs dispersed on chemically modified hydrophilic hBN nanosheets (hBNNSs). Ascorbic acid was used as a reducing agent for the chemical reduction of the Pt salt in the presence of hBNNS aqueous colloid, resulting in Pt/hBNNS nanocomposites, which were thoroughly characterized with X-ray diffraction, transmission electron microscopy, dynamic light scattering, and X-ray photoelectron and infrared spectroscopies. Similar to graphene oxide binding the metal NPs more efficiently than pure graphene, hydrophilic hBNNSs well stabilize Pt NPs, with particle size down to around 8 nm. We further demonstrate for the first time that Pt/hBNNS nanocomposites exhibit peroxidase-like catalytic activity, accelerating the oxidation of the classical colorless peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) to its corresponding blue-colored oxidized product in the presence of H₂O₂. Kinetic and mechanism studies involving terephthalic acid and isopropanol as a fluorescent probe and an ^•OH radical scavenger, respectively, proved that Pt/hBNNSs assist H₂O₂ decomposition to active oxygen species (^•OH), which are responsible for TMB oxidation. The Pt/hBNNS nanocomposite-assisted oxidation of TMB provides an effective platform for the colorimetric detection of dopamine, an important biomolecule. The presence of increased amounts of dopamine gradually inhibits the catalytic activity of Pt/hBNNSs for the oxidation of TMB by H₂O₂, thus enabling selective sensing of dopamine down to 0.76 μM, even in the presence of common interfering molecules and on real blood serum samples. The present investigation on Pt/hBNNSs contributes to the knowledge of hBN-based nanocomposites and discovers their new usage as nanomaterials with good enzyme-mimicking activity and dopamine-sensing properties.

Antibody-functionalized reduced graphene oxide films for highly selective capture and purification of aflatoxins

Pyrenylbutyric acid and streptavidin were coupled to films of reduced graphene oxide (rGO) and then conjugated to a biotinylated broad-spectrum monoclonal antibody against aflatoxins (AFs). It is shown that such films can efficiently and selectively capture AFs inculding AFB₁, AFB₂, AFG₁, AFG₂, AFM₁ and AFM₂. The rGO films were characterized by using scanning electron microscopy, energy-dispersive spectroscopy, and raman spectroscopy. The selectivity and purification performance of the antibody-loaded rGO films were investigated. They were applied to the purification of extremely small samples (100 μL) of AFs-spiked rabbit serum after enzymatic hydrolysis. The AFs were analyzed by ultra-performance liquid chromatography coupled to tandem mass spectrometry. The limits of detection for the six AFs investigated ranged from 50 to 170 pg·mL^-1. The average recoveries of AFs in spiked rabbit serum samples ranged from 55% to 75%, with relative standard deviations of less than 9.4%. Graphical abstract Design of a multifunctional sandwich film that consists of a reduced graphene oxide film base, a pyrenylbutyric acid middle layer and a broad-specificity anti-AF monoclonal antibody surface layer. It was successfully applied to the determination of aflatoxins in only 100 μL of rabbit serum samples with satisfactory selectivity and acceptable accuracy.

A facile one-pot synthesis of cobalt-doped magnetite/graphene nanocomposite as peroxidase mimetics in dopamine detection

Cobalt-doped magnetite/graphene nanocomposites (Co-MGNCs) were prepared by a facile one-pot electrochemical method.