Voltammetric dopamine sensor based on a gold electrode modified with reduced graphene oxide and Mn3O4 on gold nanoparticles

Metal Oxide Nanocatalysts for the Electrochemical Detection of Propofol

Propofol is one of the most widely used intravenous drugs for anaesthesia and sedation and is one of the most commonly used drugs in intensive care units for the sedation of mechanically ventilated patients. The correct dosage of propofol is of high importance, but there is currently a lack of suitable point-of-care techniques for determining blood propofol concentrations. Here, we present a cytochrome P450 2B6/carbon nanotube/graphene oxide/metal oxide nanocomposite sensor for discrete measurement of propofol concentration. Propofol is converted into a quinol/quinone redox couple by the enzyme and the nanocomposite enables sensitive and rapid detection. The metal oxide nanoparticles are synthesised via green synthesis and a variety of metal oxides and mixed metal oxides are investigated to determine the optimal nanocatalyst. Converting propofol into the redox couple allows for the measurement to take place over different potential ranges, enabling interference from common sources such as paracetamol and uric acid to be avoided. It was found that nanocomposites containing copper titanium oxide nanoparticles offered the best overall performance and electrodes functionalised with such nanocomposites demonstrated a limit of detection in bovine serum of 0.5 µg/mL and demonstrated a linear response over the therapeutic range of propofol with a sensitivity of 4.58 nA/μg/mL/mm2.

Microfluidic flow injection analysis system for the electrochemical detection of dopamine using diazonium-grafted copper nanoparticles on multi-walled carbon nanotube-modified surfaces

In this proof-of-concept study, a microfluidic flow injection analysis (FIA) system was developed using multi-walled carbon nanotube-modified screen-printed carbon electrodes (CNTSPEs) that were modified with copper nanoparticles (CuNPs) following the electrodeposition of the diazonium salt of 4-aminothiophenol to form 4-thiophenol-conjugated CuNPs (CuNPs-CNTSPE). Transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) were used to characterize the size of CuNPs, morphology and elemental analysis of CuNPs-CNTSPE, respectively. Using electrochemical impedance spectroscopy (EIS), the charge-transfer resistance (Rct) of CuNPs-CNTSPE was found to be 20-fold lower than that of CNTSPE. The CuNPs-CNTSPE displayed an oxidation peak for dopamine at -0.08 V which is ∼80 mV lower than the one detected using CNTSPE. The modified electrode was used in microfluidic flow injection analysis and offline systems for sensitive detection of dopamine (DA). The pH, flow rate, loop volume, concentration, and type of surfactant were all optimized for on-chip detection. Under the optimal conditions, using phosphate electrolyte solution (pH 6) containing 0.05% (w/v) Tween 20® as the carrier at a flow rate of 0.6 mL min-1 and a loop volume of 50 μL, the calibration curve was linear from 1.5 to 500 nM with a limit of detection of 0.33 nM. This technique was used for the successful detection of DA in real samples with recovery ranging from 96.5% to 103.8%. The microfluidic FIA system described here has the potential to be used as an electrochemical point-of-care device for rapid DA detection with high sensitivity and reproducibility.

Electrochemical Biosensing of Dopamine Neurotransmitter: A Review

Neurotransmitters are biochemical molecules that transmit a signal from a neuron across the synapse to a target cell, thus being essential to the function of the central and peripheral nervous system. Dopamine is one of the most important catecholamine neurotransmitters since it is involved in many functions of the human central nervous system, including motor control, reward, or reinforcement. It is of utmost importance to quantify the amount of dopamine since abnormal levels can cause a variety of medical and behavioral problems. For instance, Parkinson's disease is partially caused by the death of dopamine-secreting neurons. To date, various methods have been developed to measure dopamine levels, and electrochemical biosensing seems to be the most viable due to its robustness, selectivity, sensitivity, and the possibility to achieve real-time measurements. Even if the electrochemical detection is not facile due to the presence of electroactive interfering species with similar redox potentials in real biological samples, numerous strategies have been employed to resolve this issue. The objective of this paper is to review the materials (metals and metal oxides, carbon materials, polymers) that are frequently used for the electrochemical biosensing of dopamine and point out their respective advantages and drawbacks. Different types of dopamine biosensors, including (micro)electrodes, biosensing platforms, or field-effect transistors, are also described.

Morphology-dependent MnO2/nitrogen-doped graphene nanocomposites for simultaneous detection of trace dopamine and uric acid

Four nanostructured MnO₂ with various controllable morphologies, including nanowires, nanorods, nanotubes and nanoflowers were synthesized, and then further composited with nitrogen-doped graphene (NG) with the assistance of ultrasonication. The surface morphologies, phase structures, and electrochemical performances of the proposed MnO₂/NG nanohybrids were investigated by various techniques, and their catalytic activities on the electrooxidation of dopamine (DA) and uric acid (UA) were compared systematically. The sensing performances were found to be highly correlated with their morphologies. Among these morphologies, the nanoflower-like MnO₂, composited with NG, displayed the most sensitive response signals for DA and UA. The boosted electrocatalytic activity was ascribed to the unique porous structure, large electroactive area, and low charge transfer resistance (R_ct), which facilitated the electron transfer between electrode and analytes. Two linear response ranges (0.1 μM-10 μM and 10 μM-100 μM) were accompanied with very low detection limits of 34 nM and 39 nM for DA and UA, respectively. Moreover, the successful application of the MnO₂NFs/NG composites for the simultaneous detection of DA and UA in human serum was realized using second-derivative linear sweep voltammetry (SDLSV). These findings give valuable insights for understanding the morphology-dependent sensing properties of MnO₂ based nanomaterials, which is conducive to the rapid development of ubiquitous MnO₂-based electrochemical sensors.

Electroanalysis of Catecholamine Drugs using Graphene Modified Electrodes

Background:

Catecholamine drugs are a family of electroactive pharmaceutics, which are widely analyzed through electrochemical methods. However, for low level online determination and monitoring of these compounds, which is very important for clinical and biological studies, modified electrodes having high signal to noise ratios are needed. Numerous materials including nanomaterials have been widely used as electrode modifies for these families during the years. Among them, graphene and its family, due to their remarkable properties in electrochemistry, were extensively used in modification of electrochemical sensors.

Objective:

In this review, working electrodes which have been modified with graphene and its derivatives and applied for electroanalyses of some important catecholamine drugs are considered.

Nonenzymatic amperometric dopamine sensor based on a carbon ceramic electrode of type SiO2/C modified with Co3O4 nanoparticles

An amperometric nonenzymatic dopamine sensor has been developed. Cobalt oxide (Co₃O₄) nanoparticles were uniformly dispersed inside mesoporous SiO₂/C. A sol-gel process was used for the preparation of this mesoporous composite material (SiO₂/C). This mesoporous composite has a pore size of around 13-14 nm, a large surface area (S_BET 421 m²·g^-1) and large pore volume (0.98 cm³·g^-1) as determined by the BET technique. The material compactness was confirmed by SEM images which showing that there is no phase segregation at the magnification applied. The chemical homogeneity of the materials was confirmed by EDX mapping. The SiO₂/C/Co₃O₄ nanomaterial was pressed in desk format to fabricate a working electrode for nonenzymatic amperometric sensing of dopamine at a pH value of 7.0 and at a typical working potential of 0.25 V vs SCE. The detection limit, linear response range and sensitivity are 0.018 μmol L^-1, 10-240 μmol L^-1, and 80 μA·μmol L^-1 cm^-2, respectively. The response timé of the electrode is less than 1 s in the presence of 60 μmol L^-1 of dopamine. The sensor showed chemically stability, high sensitivity and is not interfered by other electroactive molecules present in blood. The repeatability of this sensor was evaluated as 1.9% (RSD; for n = 10 at a 40 μmol L^-1 dopamine level. Graphical abstract Schematic presentation of the preparation of a nanostructured composite of type SiO₂/C/Co₃O₄ for electrooxidative sensing of dopamine.

Rational design and facile synthesis of binary metal sulfides VS2-SnS2 hybrid with functionalized multiwalled carbon nanotube for the selective detection of neurotransmitter dopamine

In this work, we report a sensitive and selective electrochemical sensor for the detection of dopamine (DA) neurotransmitter based on VS₂-SnS₂/f-MWCNT hybrids. Herein, the binary metal sulfide (VS₂-SnS₂) was synthesized via single step hydrothermal route and hybrids with f-MWCNT via the ultrasonication process. The as-prepared VS₂-SnS₂/f-MWCNT hybrids were characterized through the FESEM, EDX and elemental mapping, TEM, XPS, Raman and XRD techniques. The electrochemical performance and catalytic activity of the modified electrodes were probed using electrochemical impedance spectra (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Interestingly, DPV results exhibits an appreciable linear range from 0.025 to 1017 μM and LOD of 0.008 μM. The selectivity study was performed to prove the high selectivity of the VS₂-SnS₂/f-MWCNT hybrids modified electrode. Furthermore, the practical applicability of the DA sensor was scrutinized in human serum sample and rat brain sample.

Tyrosinase/Chitosan/Reduced Graphene Oxide Modified Screen-Printed Carbon Electrode for Sensitive and Interference-Free Detection of Dopamine

Tyrosinase, chitosan, and reduced graphene oxide (rGO) are sequentially used to modify a screen-printed carbon electrode (SPCE) for the detection of dopamine (DA), without interference from uric acid (UA) or ascorbic acid (AA). The use of tyrosinase significantly improves the detection’s specificity. Cyclic voltammetry (CV) measurements demonstrate the high sensitivity and selectivity of the proposed electrochemical sensors, with detection limits of 22 nM and broad linear ranges of 0.4–8 μM and 40–500 μM. The fabricated tyrosinase/chitosan/rGO/SPCE electrodes achieve satisfactory results when applied to human urine samples, thereby demonstrating their feasibility for analyzing DA in physiological samples.

Morphologically Tunable MnO2 Nanoparticles Fabrication, Modelling and Their Influences on Electrochemical Sensing Performance toward Dopamine

The morphology or shape of nanomaterials plays an important role in functional applications, especially in the electrochemical sensing performance of nanocomposites modified electrodes. Herein, the morphology-dependent electrochemical sensing properties of MnO2-reduced graphene oxide/glass carbon electrode (MnO2-RGO/GCE) toward dopamine detection were investigated. Firstly, various morphologies of nanoscale MnO2, including MnO2 nanowires (MnO2 NWs), MnO2 nanorods (MnO2 NRs), and MnO2 nanotubes (MnO2 NTs), were synthesized under different hydrothermal conditions. Then the corresponding MnO2-RGO/GCEs were fabricated via drop-casting and the subsequent electrochemical reduction method. The oxidation peak currents increase with the electrochemical activity area following the order of MnO2 NWs-RGO/GCE, MnO2 NTs-RGO/GCE, and MnO2 NRs-RGO/GCE. The spatial models for MnO2 NWs, MnO2 NTs, and MnO2 NRs are established and accordingly compared by their specific surface area, explaining well the evident difference in electrochemical responses. Therefore, the MnO2 NWs-RGO/GCE is selected for dopamine detection due to its better electrochemical sensing performance. The response peak current is found to be linear with dopamine concentration in the range of 8.0 × 10−8 mol/L–1.0 × 10−6 mol/L and 1.0 × 10−6 mol/L–8.0 × 10−5 mol/L with a lower detection limit of 1 × 10−9 mol/L (S/N = 3). Finally, MnO2 NWs-RGO/GCE is successfully used for the determination of dopamine injection samples, with a recovery of 99.6–103%. These findings are of great significance for understanding the relationship between unlimited nanoparticle structure manipulation and performance improvement.

Photoelectrochemical CdSe/TiO2 nanotube array microsensor for high-resolution in-situ detection of dopamine

A photoelectrochemical wire microelectrode was constructed based on the use of a TiO₂ nanotube array with electrochemically deposited CdSe semiconductor. A strongly amplified photocurrent is generated on the sensor surface. The microsensor has a response in the 0.05-20 μM dopamine (DA) concentration range and a 16.7 μM detection limit at a signal-to-noise ratio of 3. Sensitivity, recovery and reproducibility of the sensor were validated by detecting DA in spiked human urine, and satisfactory results were obtained. Graphical abstract Schematic of a sensitive photoelectrochemical microsensor based on CdSe modified TiO₂ nanotube array. The photoelectrochemical microsensor was successfully applied to the determination of dopamine in urine samples.

Fabrication of Amine-Modified Magnetite-Electrochemically Reduced Graphene Oxide Nanocomposite Modified Glassy Carbon Electrode for Sensitive Dopamine Determination

Amine-modified magnetite (NH₂-Fe₃O₄)/reduced graphene oxide nanocomposite modified glassy carbon electrodes (NH₂-Fe₃O₄/RGO/GCEs) were developed for the sensitive detection of dopamine (DA). The NH₂-Fe₃O₄/RGO/GCEs were fabricated using a drop-casting method followed by an electrochemical reduction process. The surface morphologies, microstructure and chemical compositions of the NH₂-Fe₃O₄ nanoparticles (NPs), reduced graphene oxide (RGO) sheets and NH₂-Fe₃O₄/RGO nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The electrochemical behaviors of DA on the bare and modified GCEs were investigated in phosphate buffer solution (PBS) by cyclic voltammetry (CV). Compared with bare electrode and RGO/GCE, the oxidation peak current (i_pa) on the NH₂-Fe₃O₄/RGO/GCE increase significantly, owing to the synergistic effect between NH₂-Fe₃O₄ NPs and RGO sheets. The oxidation peak currents (i_pa) increase linearly with the concentrations of DA in the range of 1 × 10^-8 mol/L - 1 × 10^-7 mol/L, 1 × 10^-7 mol/L - 1 × 10^-6 mol/L and 1 × 10^-6 mol/L - 1 × 10^-5 mol/L. The detection limit is (4.0 ± 0.36) ×10^-9 mol/L (S/N = 3). Moreover, the response peak currents of DA were hardly interfered with the coexistence of ascorbic acid (AA) and uric acid (UA). The proposed NH₂-Fe₃O₄/RGO/GCE is successfully applied to the detection of dopamine hydrochloride injections with satisfactory results. Together with low cost, facile operation, good selectivity and high sensitivity, the NH₂-Fe₃O₄/RGO/GCEs have tremendous prospects for the detection of DA in various real samples.

Preparation of Cu₂O-Reduced Graphene Nanocomposite Modified Electrodes towards Ultrasensitive Dopamine Detection

Cu₂O-reduced graphene oxide nanocomposite (Cu₂O-RGO) was used to modify glassy carbon electrodes (GCE), and applied for the determination of dopamine (DA). The microstructure of Cu₂O-RGO nanocomposite material was characterized by scanning electron microscope. Then the electrochemical reduction condition for preparing Cu₂O-RGO/GCE and experimental conditions for determining DA were further optimized. The electrochemical behaviors of DA on the bare electrode, RGO- and Cu₂O-RGO-modified electrodes were also investigated using cyclic voltammetry in phosphate-buffered saline solution (PBS, pH 3.5). The results show that the oxidation peaks of ascorbic acid (AA), dopamine (DA), and uric acid (UA) could be well separated and the peak-to-peak separations are 204 mV (AA-DA) and 144 mV (DA-UA), respectively. Moreover, the linear response ranges for the determination of 1 × 10⁻⁸ mol/L~1 × 10⁻⁶ mol/L and 1 × 10⁻⁶ mol/L~8 × 10⁻⁵ mol/L with the detection limit 6.0 × 10⁻⁹ mol/L (S/N = 3). The proposed Cu₂O-RGO/GCE was further applied to the determination of DA in dopamine hydrochloride injections with satisfactory results.

A highly sensitive gold nanoparticle-based electrochemical aptasensor for theophylline detection

Theophylline is a common bronchodilator for the treatment of diseases like asthma, bronchitis and emphysema. However, it should be strictly used and monitored due to its toxicity when the concentration is above certain levels. In this work, an electrochemical biosensor for theophylline detection is proposed by recognition of RNA aptamer and gold nanoparticle (AuNP)-based amplification technique. First, RNA aptamer is splitted into two single-stranded RNA probes. One is hybridized with DNA tetrahedron and the resulted nanostructure is then immobilized onto a gold electrode; the other is modified on the surface of AuNPs which is also labeled with methylene blue (MB) as electrochemical species. The recognition process between the two RNA probes and theophylline causes the localization of AuNPs and the enrichment of MB on the electrode interface. A significant electrochemical response is thus generated which is related to the concentration of initial theophylline. This proposed aptasensor shows excellent sensitivity and selectivity which could also be applied in quantitatively detection of theophylline in serums samples.

The novel sulfonated polyaniline-decorated carbon nanosphere nanocomposites for electrochemical sensing of dopamine

Herein, a novel dopamine (DA) electrochemical sensor was developed by combining carbon nanospheres (CNSs) and sulfonated polyaniline (SPANI) with their own excellent characteristics.