Direct electrodeposition of reduced graphene oxide on carbon fiber electrode for simultaneous determination of ascorbic acid, dopamine and uric acid

Laser-induced graphene electrodes on polyimide membranes modified with gold nanoparticles for the simultaneous detection of dopamine and uric acid in human serum

The level control of biological active molecules in human body fluids is important for the surveillance of several human diseases. Dopamine (DA) and uric acid (UA) are two important biomarkers of neurological and bone diseases, respectively. Design of sensitive and cost-effective sensors for their detection is an effervescent research field. We report on the straightforward design of laser-induced graphene electrodes (LIGEs) from the laser ablation of a polyimide substrate and their modification by electrochemical deposition of gold nanoparticles (AuNPs/LIGE) and their uses as chemosensors. Electrochemical investigations showed that the presence of gold nanoclusters onto the electrode surface improved the electrochemical surface area (ECSA) and the heterogenous electron transfer (HET) rate. Furthermore, the AuNPs/LIGEs can be used to detect simultaneously low concentrations of DA and UA in presence of ascorbic acid (AA) as an potentially interfering substance at redox potentials of 300 mV, 230 mV and 450 mV and 91 mV, respectively, compared with the Ag/AgCl (3 M KCl) reference electrode in cyclic voltametric. The method displayed linear ranges varying from 2 to 20 μM and 5 to 50 μM, led to limits of detection of 0.37 μM and 0.71 μM for DA and UA, respectively. The AuNPs/LIGE was applied to simultaneously detect both analytes in scarcely diluted human serum with good recoveries. The data show that the recovery percentages ranged from 94% ± 2.1 to 102 % ± 0.5 and from 94% ±0.3 to 112% ± 1.4 for dopamine and uric acid, respectively. Thus, the AuNPs/LIGEs are promising candidates for the detection of other biologically active molecules such as drugs, pesticides, and metabolites.

Graphene-Based Flexible Sensors for Simultaneous Detection of Ascorbic Acid, Dopamine, and Uric Acid

Many diseases are closely related to abnormal concentrations of ascorbic acid (AA), dopamine (DA), and uric acid (UA). Therefore, the detection of these small molecules is significant for monitoring life metabolism and healthy states. Electrochemical detection has been widely used to detect small molecules due to its good selectivity, high sensitivity, and good economics. Fabrication and application are two sides of the coin, and we cannot give up one for the other. Graphene (GN) is a very suitable material for electrochemical sensing due to its excellent catalytic performance and large specific surface area. It possesses many excellent properties but cannot hold itself alone due to its nanoscale thickness. Herein, we have fabricated three-dimensional (3D) GN nanosheets (GNSs) on flexible carbon cloth (CC) by thermal chemical vapor deposition (CVD). The GNSs/CC can successfully detect AA, DA, and UA simultaneously. We find that these GNSs/CC sensors show good performance with 7 h CVD modification. The linear ranges of AA, DA, and UA are 0.02-0.1, 0.0005-0.02, and 0.0005-0.02 mM, respectively. The detection sensitivity rates of AA, DA, and UA are 5,470, 60,500, and 64,000 μA mM-1 cm-2, respectively. Our GNSs/CC flexible sensors can be successfully applied in the human serum for UA detection. The result matches with commercial sensors very well.

Biological applications of microchip electrophoresis with amperometric detection: in vivo monitoring and cell analysis

Microchip electrophoresis with amperometric detection (ME-EC) is a useful tool for the determination of redox active compounds in complex biological samples. In this review, a brief background on the principles of ME-EC is provided, including substrate types, electrode materials, and electrode configurations. Several different detection approaches are described, including dual-channel systems for dual-electrode detection and electrochemistry coupled with fluorescence and chemiluminescence. The application of ME-EC to the determination of catecholamines, adenosine and its metabolites, and reactive nitrogen and oxygen species in microdialysis samples and cell lysates is also detailed. Lastly, approaches for coupling of ME-EC with microdialysis sampling to create separation-based sensors that can be used for near real-time monitoring of drug metabolism and neurotransmitters in freely roaming animals are provided. Graphical abstract.

Ultrathin Ni-MOF Nanobelts-Derived Composite for High Sensitive Detection of Nitrite

In this paper, the Ni/NiO ultrathin nanobelts were successively synthesized by a facile in suit conversion process using pre-synthesized Ni-based metal-organic frameworks (MOFs) nanobelts as parent materials to detect the nitrite (NaNO2). The synthesized Ni/NiO composites have the advantages in structure, as follows: (I) Interleaved 3D reticulated structure has strong mechanical stability; (II) Ultrathin nanobelt structures allow more active sites to be exposed and make the transfer of charge faster; (III) A large number of ultrafine Ni nanoparticles decorate the building blocks of the NiO nanobelt and enhance the electrical conductivity. Ni/NiO/GCE has an obvious oxidation peak at 0.78 V, when the concentration is between 0.5 and 1000 μM, the oxidation peak current of NaNO2 is linearly related to the concentration, and the sensitivity is 1.5319 μA mM-1 cm-2 (S/N = 3). Moreover, the experimental results also concluded that the Ni/NiO ultrathin nanobelts not only indicated wonderful reproducibility in the determination of NaNO2 in the pickled pork samples, but also could be well-recovered and keep stable for a long time.

Recent Advances in Electrochemical and Optical Sensing of Dopamine

Nowadays, several neurological disorders and neurocrine tumours are associated with dopamine (DA) concentrations in various biological fluids. Highly accurate and ultrasensitive detection of DA levels in different biological samples in real-time can change and improve the quality of a patient's life in addition to reducing the treatment cost. Therefore, the design and development of diagnostic tool for in vivo and in vitro monitoring of DA is of considerable clinical and pharmacological importance. In recent decades, a large number of techniques have been established for DA detection, including chromatography coupled to mass spectrometry, spectroscopic approaches, and electrochemical (EC) methods. These methods are effective, but most of them still have some drawbacks such as consuming time, effort, and money. Added to that, sometimes they need complex procedures to obtain good sensitivity and suffer from low selectivity due to interference from other biological species such as uric acid (UA) and ascorbic acid (AA). Advanced materials can offer remarkable opportunities to overcome drawbacks in conventional DA sensors. This review aims to explain challenges related to DA detection using different techniques, and to summarize and highlight recent advancements in materials used and approaches applied for several sensor surface modification for the monitoring of DA. Also, it focuses on the analytical features of the EC and optical-based sensing techniques available.

Highly sensitive and rapid determination of sunset yellow in drinks using a low-cost carbon material-based electrochemical sensor

Starting from simple graphite flakes, an electrochemical sensor for sunset yellow monitoring is developed by using a very simple and effective strategy. The direct electrochemical reduction of a suspension of exfoliated graphene oxide (GO) onto a glassy carbon electrode (GCE) surface leads to the electrodeposition of electrochemically reduced oxide at the surface, obtaining GCE/ERGO-modified electrodes. They are characterized by cyclic voltammetry (CV) measurements and field emission scanning electron spectroscopy (FE-SEM). The GCE/ERGO electrode has a high electrochemically active surface allowing efficient adsorption of SY. Using differential pulse voltammetry (DPV) technique with only 2 min accumulation, the GCE/ERGO sensor exhibits good performance to SY detection with a good linear calibration for concentration range varying 50-1000 nM (R² = 0.996) and limit of detection (LOD) estimated to 19.2 nM (equivalent to 8.9 μg L^-1). The developed sensor possesses a very high sensitivity of 9 μA/μM while fabricated with only one component. This electrochemical sensor also displays a good reliability with RSD value of 2.13% (n = 7) and excellent reusability (signal response change < 3.5% after 6 measuring/cleaning cycles). The GCE/ERGO demonstrates a successful practical application for determination of sunset yellow in commercial soft drinks. Graphical abstract.

Simultaneous determination of ascorbic acid, dopamine and uric acid by a novel electrochemical sensor based on N2/Ar RF plasma assisted graphene nanosheets/graphene nanoribbons

A novel nitrogen/argon (N₂/Ar) radio frequency (RF) plasma functionalized graphene nanosheet/graphene nanoribbon (GS/GNR) hybrid material (N₂/Ar/GS/GNR) was developed for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Various nitrogen mites introduced into GS/GNR hybrid structure was evidenced by a detailed microscopic, spectroscopic and surface area analysis. Owing to the unique structure and properties originating from the enhanced surface area, nitrogen functional groups and defects introduced on both the basal and edges, N₂/Ar/GS/GNR/GCE showed high electrocatalytic activity for the electrochemical oxidations of AA, DA, and UA with the respective lowest detection limits of 5.3, 2.5 and 5.7 nM and peak-to-peak separation potential (ΔE_P) (vs Ag/AgCl) in DPV of 220, 152 and 372 mV for AA/DA, DA/UA and AA/UA respectively. Moreover, the selectivity, stability, repeatability and excellent performance in real time application of the fabricated N₂/Ar/GS/GNR/GCE electrode suggests that it can be considered as a potential electrode material for simultaneous detection of AA, DA, and UA.

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

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.

Electrochemical synthesis of gold nanoparticles decorated flower-like graphene for high sensitivity detection of nitrite

In this paper, the spherical Au nanoparticles and 3D flower-like structure graphene were successively deposited on glassy carbon electrode (GCE) (Au/f-GE/GCE) via a facile and two-step electrodeposition method for the detection of nitrite ions (NaNO₂). The morphology and composition elements were confirmed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction measurements (XRD). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to evaluate the electrochemical behaviors of NaNO₂ on the as-prepared electrode. Compared to f-GE/GCE and Au/GCE, Au/f-GE/GCE showed a sharp and obvious oxidation peak at 0.78V. The oxidation peak current of NaNO₂ was linearly proportional to its concentration in the range from 0.125 to 20375.98μM, with a detection limit of 0.01μM (at S/N=3). Furthermore, the experiment results also showed that the as-prepared electrode exhibited excellent reproducibility and long-term stability, as well as good recovery when applied to the determination of NaNO₂ in pickled pork samples.

Highly sensitive electrochemical determination of Sunset Yellow based on the ultrafine Au-Pd and reduced graphene oxide nanocomposites

A sensitive and novel electrochemical sensor with Au-Pd and reduced graphene oxide (RGO) nanocomposites modified glassy carbon electrode (Au-Pd-RGO/GCE) was successfully fabricated by one-step synthesis method for the detection of Sunset Yellow. The as-prepared composites were uniformly dispersed on the surface of electrode with an average diameter of approximately 3.44nm, and the ultrafine nanoparticles effectively enhanced the electrochemical active surface area of GCE. The modified electrode had been characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and electrochemical tests. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) results showed high stability and outstanding electrocatalytic activity of Au-Pd-RGO/GCE for the detection of SY with low detection limits (1.5 nM, S/N=3) and wide concentration ranges (0.686-331.686μM). The Au-Pd-RGO/GCE was further applied to detect SY in real samples with good recovery. Herein, the fabricated Au-Pd-RGO/GCE showed excellent sensitivity, stability and repeatability for the detection of SY and will be a promising application in electrochemical sensor.

Engineered Carbon-Nanomaterial-Based Electrochemical Sensors for Biomolecules

The study of electrochemical behavior of bioactive molecules has become one of the most rapidly developing scientific fields. Biotechnology and biomedical engineering fields have a vested interest in constructing more precise and accurate voltammetric/amperometric biosensors. One rapidly growing area of biosensor design involves incorporation of carbon-based nanomaterials in working electrodes, such as one-dimensional carbon nanotubes, two-dimensional graphene, and graphene oxide. In this review article, we give a brief overview describing the voltammetric techniques and how these techniques are applied in biosensing, as well as the details surrounding important biosensing concepts of sensitivity and limits of detection. Building on these important concepts, we show how the sensitivity and limit of detection can be tuned by including carbon-based nanomaterials in the fabrication of biosensors. The sensing of biomolecules including glucose, dopamine, proteins, enzymes, uric acid, DNA, RNA, and H2O2 traditionally employs enzymes in detection; however, these enzymes denature easily, and as such, enzymeless methods are highly desired. Here we draw an important distinction between enzymeless and enzyme-containing carbon-nanomaterial-based biosensors. The review ends with an outlook of future concepts that can be employed in biosensor fabrication, as well as limitations of already proposed materials and how such sensing can be enhanced. As such, this review can act as a roadmap to guide researchers toward concepts that can be employed in the design of next generation biosensors, while also highlighting the current advancements in the field.

A cost-effective disposable graphene-modified electrode decorated with alternating layers of Au NPs for the simultaneous detection of dopamine and uric acid in human urine

A disposable electrode based on a highly sensitive and readily fabricated arrangement of alternating AuNP and graphene layers was introduced for the simultaneous determination of dopamine and uric acid.

Electrodeposition of reduced graphene oxide on a Pt electrode and its use as amperometric sensor in microchip electrophoresis

This report describes the development and application of a novel graphene-modified electrode to be used as amperometric sensor in microchip electrophoresis (ME) devices. The modified electrode was achieved based on electroreduction of graphene oxide on an integrated Pt working electrode of a commercial ME device. The surface modification was characterized by SEM and cyclic voltammetry techniques. The results indicated that graphene sheets were successfully deposited exhibiting higher surface conductivity and greater electrode sensitivity. The performance of the modified electrode for the amperometric detection on ME devices has been demonstrated by the separation and detection of an anionic mixture containing iodide and ascorbate. The graphene-modified electrode provided significantly higher sensitivity (896.7 vs. 210.9 pA/μM for iodide and 217.8 vs. 127.8 pA/μM for ascorbate), better separation efficiencies (3400 vs. 700 plates/m for iodide and 10 000 vs. 2400 plates/m for ascorbate), enhanced peak resolutions (1.6 vs. 1.0), and LODs (1.5 vs. 5.3 μM for iodide and 3.1 vs. 7.3 μM for ascorbate) in comparison with the unmodified Pt electrode. The proposed amperometric sensor was successfully applied for the analysis of ascorbic acid (through its anionic form) in a commercial medicine sample, and the results achieved were in agreement with the value provided by the supplier. Based on the data here presented, the modified graphene electrode shows great promise for ME applications.

Electrodeposition synthesis of reduced graphene oxide–carbon nanotube hybrids on indium tin oxide electrode for simultaneous electrochemical detection of ascorbic acid, dopamine and uric acid

Reduced graphene oxide–carbon nanotube (rGO–CNT) hybrids have been synthesized by electrodeposition of GO stabilized CNT using indium tin oxide (ITO) as working electrode, followed by electrochemical reduction of GO–CNT into rGO–CNT.

Graphene and its nanocomposite material based electrochemical sensor platform for dopamine

In this review, the recent progress in the electrochemical sensing of dopamine with various graphene and their nanocomposite materials modified electrodes are presented.