A novel electrochemical platform for sensitive and simultaneous determination of dopamine, uric acid and ascorbic acid based on Fe3O4SnO2Gr ternary nanocomposite

Chitosan-stabilized copper oxide nanoparticles: A novel colorimetric approach for ascorbic acid sensing

Ascorbic acid is implicated in various diseases such as scurvy, oxidative stress, cardiovascular diseases, etc. Herein, for the first time, a simple and efficient strategy was used to synthesize cross-linked chitosan-stabilized copper oxide nanoparticles (CuO@C-CS) as a non-toxic and biodegradable-based approach. Various spectroscopic techniques, including FTIR, XRD, SEM, EDX, TGA, and elemental mapping, confirmed the synthesis of the material. The synthesized nanozyme (CuO@C-CS) was used as a peroxidase mimic for the detection of ascorbic acid, through the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) with the assistance of hydrogen peroxide. The synthesized mimic enzyme transforms colorless TMB into oxTMB. The sensing of ascorbic acid was achieved through the peroxidase-like inhibitory activity of the mimic enzyme along with the reduction of oxTMB. The sensor system was fine-tuned, and it showed a limit of detection, a limit of quantification, a linear range, and regression coefficient values of 0.24 μM, 0.80 μM, 1-96 μM, and 0.999, respectively. The fabricated sensor was very selective in the presence of various potential interferents. The proposed sensor was successfully applied to commercially available orange juices for the qualitative and quantitative determination of ascorbic acid. The sensor can be used for the determination of ascorbic acid in biomedical and food samples.

A systematic review on electrochemical sensors for the detection of acetaminophen

Considerable progress has been made in the electrochemical determination of acetaminophen (AP) over the past few decades. Nanomaterials or enzymes as electrode modifiers greatly improve the performance of AP electrochemical sensors. This review focuses on the development potential, detection principles and techniques for the electrochemical analysis of AP. In particular, the design and construction of AP electrochemical sensors are discussed from the perspective of non-enzyme materials (such as nanomaterials, including precious metals, transition metals and non-metals) and enzyme substances (such as aryl acylamidase, polyphenol oxidase and horseradish peroxidase). Moreover, the influencing factors for AP electrochemical sensors and the simultaneous detection of AP and other targets are summarized, and the future prospective of AP electrochemical sensors is outlined. This review provides a reference and guidance for the development and application of electrochemical sensors for AP detection.

Simultaneous recognition of dopamine and uric acid in real samples through highly sensitive new electrode fabricated using ZnO/carbon quantum dots: bio-imaging and theoretical studies

Dopamine (DA) and uric acid (UA), which are vital components in human metabolism, cause several health problems if they are present in altered concentrations; thus, the determination of DA and UA is essential in real samples using selective sensors. In the present study, graphite carbon paste electrodes (CPE) were fabricated using ZnO/carbon quantum dots (ZnO/CQDs) and employed as electrochemical sensors for the detection of DA and UA. These electrodes were fully characterized via different analytical techniques (XRD, SEM, TEM, XPS, and EDS). The electrochemical responses from the modified electrodes were evaluated using cyclic voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy. The results showed that the present electrode has exhibited high sensitivity towards DA, recognizing even at low concentrations (0.12 μM), and no inference was observed in the presence of UA. The ZnO/CQD electrode was applied for the simultaneous detection of co-existing DA and UA in real human urine samples and the peak potential separation between DA and UA was found to be greatly associated with the synergistic effect originated from ZnO and CQDs. The limit of detection (LOD) of the electrode was analyzed, and compared with other commercially available electrodes. Thus, the ZnO/CQD electrode was used to detect DA and UA in real samples, such as Saccharomyces cerevisiae cells.

Synthesis of rod-like CeO2 nanoparticles and their application to catalyze the luminal-O2 chemiluminescence reaction used in the determination of oxcarbazepine and ascorbic acid

Rod-like CeO₂ nanoparticles (NPs) were produced by the quick precipitation approach and employed as a catalyzer to increase the chemiluminescence (CL) intensity of the luminol-O₂ reaction. The transmission electron microscopy (TEM) images of the CeO₂ NPs showed that rod-like particles with the length and diameter about 15 nm and 5 nm, respectively, were produced. Furthermore, pharmaceuticals including oxcarbazepine (OXP) and ascorbic acid (AA) showed an inhibitory effect against the CL intensity such that the more concentration of the pharmaceuticals, the less was the CL intensity. Therefore, the new CeO₂ NPs-luminol-O₂ CL reaction was developed to determine OXP and AA in the pharmaceutical formulations. It is the first CL method established for the quantification of OXP. The linear dynamic range of this method for OXP was from 6.0 × 10^-7 to 6.0 × 10^-5 mol L^-1 and for AA from 1.0 × 10^-6 to 1.0 × 10^-4 mol L^-1.

A highly selective and sensitive electrochemical sensor for dopamine based on a functionalized multi-walled carbon nanotube and poly(N-methylaniline) composite

Dopamine (DA) is an important neurotransmitter used for diagnosing various diseases from its abnormal concentrations in human fluids. Herein, an electrochemical sensor based on a composite of re-doped poly(N-methylaniline) (rePNMA) and modified multi-walled carbon nanotubes (fMWCNTs), termed fMWCNT-rePNMA, was developed to measure DA concentration. The successful modification of the fMWCNT surface was confirmed by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Cyclic voltammetry (CV) displayed an excellent electrocatalytic activity of the fMWCNTs-rePNMA composite towards the oxidation of DA. The developed fMWCNTs-rePNMA composite demonstrated a broad linear range from 5 to 90 μmol L^-1 with a low limit of detection (LOD) value of 2.23 μmol L^-1, and a fast response with a high sensitivity of 251.5 nA μmol^-1 L as determined from the calibration curve of the DA determination. In addition, the fMWCNTs-rePNMA composite selectively identified and quantified DA in the presence of ascorbic acid (AA) and uric acid (UA). Therefore, the fMWCNTs-rePNMA composite sensor shows potential to determine the level of DA in human urine.

Using Graphene-Based Biosensors to Detect Dopamine for Efficient Parkinson's Disease Diagnostics

Parkinson's disease (PD) is a neurodegenerative disease in which the neurotransmitter dopamine (DA) depletes due to the progressive loss of nigrostriatal neurons. Therefore, DA measurement might be a useful diagnostic tool for targeting the early stages of PD, as well as helping to optimize DA replacement therapy. Moreover, DA sensing appears to be a useful analytical tool in complex biological systems in PD studies. To support the feasibility of this concept, this mini-review explores the currently developed graphene-based biosensors dedicated to DA detection. We discuss various graphene modifications designed for high-performance DA sensing electrodes alongside their analytical performances and interference studies, which we listed based on their limit of detection in biological samples. Moreover, graphene-based biosensors for optical DA detection are also presented herein. Regarding clinical relevance, we explored the development trends of graphene-based electrochemical sensing of DA as they relate to point-of-care testing suitable for the site-of-location diagnostics needed for personalized PD management. In this field, the biosensors are developed into smartphone-connected systems for intelligent disease management. However, we highlighted that the focus should be on the clinical utility rather than analytical and technical performance.

Gold Nanoparticles/Carbon Nanotubes and Gold Nanoporous as Novel Electrochemical Platforms for L-Ascorbic Acid Detection: Comparative Performance and Application

Herein, the effects of nanostructured modifications of a gold electrode surface in the development of electrochemical sensors for L-ascorbic acid detection have been investigated. In particular, a bare gold electrode has been modified by electrodeposition of gold single-walled carbon nanotubes (Au/SWCNTs) and by the formation of a highly nanoporous gold (h-nPG) film. The procedure has been realized by sweeping the potential between +0.8 V and 0 V vs. Ag/AgCl for 25 scans in a suspension containing 5 mg/mL of SWCNTs in 10 mM HAuCl4 and 2.5 M NH4Cl solution for Au/SWCNTs modified gold electrode. A similar procedure was applied for a h-nPG electrode in a 10 mM HAuCl4 solution containing 2.5 M NH4Cl, followed by applying a fixed potential of −4 V vs. Ag/AgCl for 60 s. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the properties of the modified electrodes. The developed sensors showed strong electrocatalytic activity towards ascorbic acid oxidation with enhanced sensitivities of 1.7 × 10−2 μA μM−1cm−2 and 2.5 × 10−2 μA μM−1cm−2 for Au/SWCNTs and h-nPG modified electrode, respectively, compared to bare gold electrode (1.0 × 10−2 μA μM−1cm−2). The detection limits were estimated to be 3.1 and 1.8 μM, respectively. The h-nPG electrode was successfully used to determine ascorbic acid in human urine with no significant interference and with satisfactory recovery levels.

Electrochemical dual signal sensing platform for the simultaneous determination of dopamine, uric acid and glucose based on copper and cerium bimetallic carbon nanocomposites

A highly sensitive electrochemical sensor for the simultaneous dual signal determination of dopamine (DA), uric acid (UA) and glucose (Glu) has been obtained using nanocomposites based on the copper and cerium bimetallic nanoparticles and carbon nanomaterials of graphene and single-walled carbon nanotubes in the presence of Tween 20 (GR-SWCNT-Ce-Cu-Tween 20) modified glassy carbon electrode. The surface morphology of the nanocomposites was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the electrochemical behavior of the sensor was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with potassium ferricyanide as probe. In the coexistence system of DA, UA and Glu, three clear and well-isolated voltammetric peaks were obtained by CV and differential pulse voltammetry (DPV), and oxidation peak currents of DA and UA are positively correlated with their concentrations respectively, while the peak current of Glu is negatively correlated with its concentration. Linearity was obtained in the ranges of 0.1-100 µM for dopamine, 0.08-100 µM for uric acid and 1-1000 µM for glucose with DPV, and the detection limits (S/N = 3) of 0.0072 µM, 0.0063 µM, and 0.095 µM for DA, UA and Glu, respectively. The method was successfully applied to the determination of DA, UA and Glu in blood serum samples, which provided a reference for further sensor research.

Simultaneous Detection of Ascorbic Acid, Dopamine, and Uric Acid Using a Novel Electrochemical Sensor Based on Palladium Nanoparticles/Reduced Graphene Oxide Nanocomposite

A fresh strategy based on two-step electrochemical reduction for the fabrication of palladium nanoparticles/reduced oxide nanocomposite-modified glass carbon electrode (PdNPs/rGO/GCE) was established in this study. Field emission scanning electron microscopy (FESEM) images showed that spherical PdNPs were evenly distributed on the surface of rGO-modified electrode (rGO/GCE), and the introduction of PdNPs has no effect on the morphology of rGO. Electrochemical impedance spectroscopy (EIS) studies revealed that the conductivity of PdNPs/rGO/GCE was higher than that of rGO/GCE and bare GCE. The electrochemical performances of PdNPs/rGO/GCE sensor were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry using ascorbic acid (AA), dopamine (DA), and uric acid (UA) as analytes. At the optimized conditions, wide linear ranges of 0.5–3.5 mM (R² = 0.99), 3–15 μM (R² = 0.99) and 15–42 μM (R² = 0.99), and 0.3–1.4 mM (R² = 0.99) towards AA, DA, and UA in ternary mixture were observed, respectively. In addition to superior anti-interference capability, fast response (≤5 s), excellent reproducibility, and good long-term stability were also given by this sensor. These results suggested that PdNPs/rGO/GCE is promising for the simultaneous detection of AA, DA, and UA in practical application.

A Promising Electrochemical Platform for Dopamine and Uric Acid Detection Based on a Polyaniline/Iron Oxide-Tin Oxide/Reduced Graphene Oxide Ternary Composite

A ternary polyaniline/Fe₂O₃-SnO₂/reduced graphene oxide (PFSG) nanocomposite was prepared using a simple two-step hydrothermal treatment. The composite was applied as a glassy carbon electrode modifier (GCE) to enhance dopamine (DA) and uric acid (UA) detection. The ternary PFSG composite was compared with its binary precursor Fe₂O₃-SnO₂/reduced graphene oxide (FSG). The influence of the modified GCE electrodes on their performance as a sensing platform was determined. GCE/PFSG showed better sensing parameters than GCE/FSG due to the introduction of polyaniline (PANI), increasing the electrocatalytic properties of the electrode towards the detected analytes. GCE/PFSG enabled the detection of low concentrations of DA (0.076 µM) and UA (1.6 µM). The peak potential separation between DA and UA was very good (180 mV). Moreover, the DA oxidation peak was unaffected even if the concentration of UA was ten times higher. The fabricated sensor showed excellent performance in the simultaneous detection with DA and UA limits of detection: LOD_DA = 0.15 µM and LOD_UA = 6.4 µM, and outstanding long-term stability towards DA and UA, holding 100% and 90% of their initial signals respectively, after one month of use.

Three-dimensional voltammetry: Use of chronoamperometric E-t-i data to achieve second-order advantage

This work studied the use of three-dimensional voltammetry, particularly potential-time-current (E-t-i) data, on the development of electroanalytical methods. E-t-i data was obtained by taking chronoamperograms at potentials applied as pulses on a staircase waveform. By using this three-way kind of data and appropriate calibration algorithms, the possibility of achieving the second-order advantage was evaluated in the determination of ferrocyanide in the presence of the uncalibrated interference hydroquinone as a model system. The determination of acetaminophen in urine samples, where ascorbic acid and uric acid play the major roles as interferents was also studied. Parallel factor analysis (PARAFAC) and multivariate curve resolution alternating least-squares (MCR-ALS) were the algorithms employed in this work. Both algorithms successfully achieved the second-order advantage by correctly predicting the concentrations of the validation synthetic samples. Excellent predictions were obtained in the direct analysis of acetaminophen-spiked urine samples by E-t-i data and MCR-ALS.

Smartphone-Based Electrochemical Potentiostat Detection System Using PEDOT: PSS/Chitosan/Graphene Modified Screen-Printed Electrodes for Dopamine Detection

In this work, a smartphone-based electrochemical detection system was designed and developed for rapid and real-time detection of dopamine (DA). The system included a screen-printed electrode (SPE) used as a sensor, a hand-held electrochemical potentiostat and a smart phone with a specially designed app. During the detection period, the SPEs modified with poly(3,4-ethylenedioxythiophene) (PEDOT), chitosan (CS) and graphene (G) were used to convert and amplify the electrochemical reaction signals. The electrochemical potentiostat was used to generate excitation electrical signals and collect the electrical signals converted from the sensor. The smartphone—connected to the detector via Bluetooth-was used to control the detector for tests, further process the uploaded data, and plot graphs in real time. Experimental results showed that the self-designed sensing system could be employed for highly selective detection of DA in the presence of interfering substances such as ascorbic acid (AA) and uric acid (UA). CV was carried out to characterize the electrochemical properties of the modified SPEs and the electrochemical behaviors of DA on the modified SPEs. Finally, according to the analysis of DPV responses of DA, the system could detect DA with a detection sensitivity of 0.52 ± 0.01 μA/μM and a limit of detection of 0.29 μM in the linear range of DA concentrations from 0.05 to 70 μM.

Gold nanoparticle decorated polypyrrole/graphene oxide nanosheets as a modified electrode for simultaneous determination of ascorbic acid, dopamine and uric acid

AuNPs, GO and PPy are combined effectively to form a novel composite showing a huge enhancement in electrochemical performance compared to the single materials.

A review on recent advancements in electrochemical biosensing using carbonaceous nanomaterials

This review, with 201 references, describes the recent advancement in the application of carbonaceous nanomaterials as highly conductive platforms in electrochemical biosensing. The electrochemical biosensing is described in introduction by classifying biosensors into catalytic-based and affinity-based biosensors and statistically demonstrates the most recent published works in each category. The introduction is followed by sections on electrochemical biosensors configurations and common carbonaceous nanomaterials applied in electrochemical biosensing, including graphene and its derivatives, carbon nanotubes, mesoporous carbon, carbon nanofibers and carbon nanospheres. In the following sections, carbonaceous catalytic-based and affinity-based biosensors are discussed in detail. In the category of catalytic-based biosensors, a comparison between enzymatic biosensors and non-enzymatic electrochemical sensors is carried out. Regarding the affinity-based biosensors, scholarly articles related to biological elements such as antibodies, deoxyribonucleic acids (DNAs) and aptamers are discussed in separate sections. The last section discusses recent advancements in carbonaceous screen-printed electrodes as a growing field in electrochemical biosensing. Tables are presented that give an overview on the diversity of analytes, type of materials and the sensors performance. Ultimately, general considerations, challenges and future perspectives in this field of science are discussed. Recent findings suggest that interests towards 2D nanostructured electrodes based on graphene and its derivatives are still growing in the field of electrochemical biosensing. That is because of their exceptional electrical conductivity, active surface area and more convenient production methods compared to carbon nanotubes. Graphical abstract Schematic representation of carbonaceous nanomaterials used in electrochemical biosensing. The content is classified into non-enzymatic sensors and affinity/ catalytic biosensors. Recent publications are tabulated and compared, considering materials, target, limit of detection and linear range of detection.

A carbon paste electrode modified with Al2O3-supported palladium nanoparticles for simultaneous voltammetric determination of melatonin, dopamine, and acetaminophen

The authors have modified a carbon paste electrode with Al₂O₃-supported palladium nanoparticles (PdNP@Al₂O₃) to obtain a sensor for simultaneous voltammetric determination of melatonin (MT), dopamine (DA) and acetaminophen (AC). The PdNP@Al₂O₃ was characterized by scanning electron microscopy and energy-dispersive X-ray spectra. The sensor can detect DA, AC, MT and their mixtures by giving distinct signals at working voltages of typically 236, 480 and 650 mV (vs. Ag/AgCl), respectively. Differential pulse voltammetric peak currents of DA, AC and MT increase linearly in the 50 nmol L^-1 - 1.45 mmol L^-1, 40 nmol L^-1 -1.4 mmol L^-1, and 6.0 nmol L^-1 - 1.4 mmol L^-1 concentration ranges. The limits of detection are 36.5 nmol L^-1 for DA, 36.5 nmol L^-1 for AC, and 21.6 nmol L^-1 for MT. The sensor was successfully used to detect the analytes in (spiked) human serum and drug samples. Graphical abstract Schematic presentation of Al2O3-supported palladium nanoparticles (PdNP@Al2O3) for modification of a carbon paste electrode (CPE) to develop a voltammetric sensor for the simultaneous determination of dopamine (DA), acetaminophen (AC) and melatonin (MT).

Golf ball-like MoS2 nanosheet arrays anchored onto carbon nanofibers for electrochemical detection of dopamine

Arrays of molybdenum(IV) disulfide nanosheets resembling the shape of golf balls (MoS₂ NSBs) were deposited on carbon nanofibers (CNFs), which are shown to enable superior electrochemical detection of dopamine without any interference by uric acid. The MoS₂ NSBs have a diameter of ∼ 2 μm and are made up of numerous bent nanosheets. MoS₂ NSBs are connected by the CNFs through the center of the balls. Figures of merit for the resulting electrode include (a) a sensitivity of 6.24 μA·μM^-1·cm^-2, (b) a low working voltage (+0.17 V vs. Ag/AgCl), and (c) a low limit of detection (36 nM at S/N = 3). The electrode is selective over uric acid, reproducible and stable. It was applied to the determination of dopamine in spiked urine samples. The recoveries at levels of 10, 20 and 40 μM of DA are 101.6, 99.8 and 107.8%. Graphical abstract Schematic presentation of the golf ball-like MoS₂ nanosheet balls/carbon nanofibers (MoS₂ NSB/CNFs) by electrospining and hydrothermal process to detect dopamine (DA).

A novel electrochemical sensor based on self-assembled platinum nanochains - Multi-walled carbon nanotubes-graphene nanoparticles composite for simultaneous determination of dopamine and ascorbic acid

In this study, platinum nanochains (PtNCs), multi-walled carbon nanotubes (MWCNTs) and graphene nanoparticles (GNPs) were assembled together to form a novel nanocomposite by a facile ultrasonic-assisted blending process. The PtNCs-MWCNTs-GNPs nanocomposite was characterized by high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The nanocomposite was used for the modification of glass carbon electrode (GCE) and simultaneous determination of dopamine (DA) and ascorbic acid (AA) by differential pulse voltammetry (DPV) and cycle voltammetry (CV). Under the optimum conditions, the calibration curves obtained are linear for the currents versus DA and AA concentrations over the range 2.00-50.0 μM and 100-1200 μM, respectively. And the detection limits for DA and AA are 0.500 μM and 10.0 μM, respectively. The detection and quantitative analysis of DA and AA in human serum and vitamin C tablets on PtNCs-MWCNTs-GNPs/GCE gave the recoveries of 104-110% and 101-108% with relative standard deviations (RSD) of 4.36-7.48% and 0.620-2.90%, respectively. The proposed PtNCs-MWCNTs-GNPs composite could provide a new platform for the routine analysis of DA and AA in terms of its good anti-interference ability, excellent reproducibility and repeatability, and feasibility of use.

Porous tal palm carbon nanosheets: preparation, characterization and application for the simultaneous determination of dopamine and uric acid

A novel porous tal palm carbon nanosheet (PTPCN) material was synthesized from the leaves of Borassus flabellifer (tal palm) and used for developing an electrochemical sensor through modifying a glassy carbon electrode (GCE) simply by drop-casting on it a solution of the material for the sensitive simultaneous detection of dopamine (DA) and uric acid (UA), even in the presence of interfering species. The drop-casting solution was prepared by simply dispersing the PTPCNs in ethanol without using any other binding materials (e.g. Nafion). The surface morphologies of the PTPCNs were studied through field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction spectroscopy (XPS) studies revealed the chemical composition of the PTPCNs' surface. Their structural properties were studied using X-ray diffraction (XRD) and Raman spectroscopy. Brunauer-Emmett-Teller (BET) analysis confirmed the surface area and pore volume to be 1094.53 m² g^-1 and 0.74 cm³ g^-1, respectively, while Barrett-Joyner-Halenda (BJH) pore-size distribution showed the average pore size to be 22 nm. The sufficiently large surface area and pore-size distribution suggested better electrocatalytic properties compared to the average modifying materials. The modified electrode (PTPCNs/GCE) was characterized through impedimetric and CV techniques in standard potassium ferricyanide solution for evaluating their charge-transfer resistance and electrochemical properties. The limits of detection (S/N = 3) were 0.17 μM and 0.078 μM and the sensitivities were 1.2057 μA μM^-1 cm^-2 and 2.693 μA μM^-1 cm^-2 for UA and DA, respectively. The possible interactions that took place between the PTPCNs and the analytes that aided in the enhancement of the electroanalytical performance of the PTPCNs/GCE are discussed based on the experimental findings and established theoretical concepts. The PTPCNs/GCE was successfully employed for analyzing real samples, like dopamine injection and urine.

Gold nanorods decorated with graphene oxide and multi-walled carbon nanotubes for trace level voltammetric determination of ascorbic acid

An ultra-sensitive sensor is described for the voltammetric determination of ascorbic acid (AA). A glassy carbon electrode (GCE) was modified with graphene oxide (GO), multi-walled carbon nanotubes (MWCNTs) and gold nanorods (AuNRs). GO was used to prevent the aggregation of MWCNTs. The integration of positively charged AuNRs reduces the overpotential and increases the peak current of AA oxidation. Figures of merit of this sensor, typically operated at a low working potential of 0.036 V (vs. Ag/AgCl), include a low detection limit (0.85 nM), high sensitivity (7.61 μA·μM^-1·cm^-2) and two wide linear ranges (from 1 nM to 0.5 μM and from 1 μM to 8 mM). The use of GO simplifies the manufacture and results in a highly reproducible and stable sensor. It was applied to the quantification of AA in spiked serum. Graphical abstract Graphical abstract contains poor quality and small text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.We have provided the original format with the attachments named g.tif. Graphene oxide (GO) in combination with multiwalled carbon nanotubes (MWCNTs) and gold nanorods (AuNRs) were used to construct a sensing interface with outstanding electrocatalytic performance for ascorbic acid detection.

Detection of Neurotransmitters by Three-Dimensional Laser-Scribed Graphene Grass Electrodes

Carbon nanomaterials possess superb properties and have contributed considerably to the advancement of integrated point-of-care chemical and biological sensing devices. Graphene has been widely researched as a signal transducing and sensing material. Here, a grass-like laser-scribed graphene (LSG) was synthesized by direct laser induction on common polyimide plastics. The resulting LSG grass was employed as a disposable electrochemical sensor for the detection of three neurotransmitters, dopamine (DA), epinephrine (EP), and norepinephrine (NE), and in the presence of uric acid and ascorbic acid as potential interferants, using differential pulse voltammetry and cyclic voltammetry. The LSG grass sensor achieved sensitivities of 0.243, 0.067, and 0.110 μA μM^-1 for DA, EP, and NE, respectively, whereas the limits of detection were 0.43, 1.1, and 1.3 μM, respectively. The selectivity of LSG grass was excellent for competing biomarkers with high structural similarity (EP vs NE and EP vs DA). The exceptional performance of LSG grass for DA, EP, and NE detection holds a promising future for carbon nanomaterial sensors with unique surface morphologies.

Self-stacking of exfoliated charged nanosheets of LDHs and graphene as biosensor with real-time tracking of dopamine from live cells

This study introduces a new strategy for periodic stacking of positively charged NiAl layered double hydroxides (LDHs) nanosheets with negatively charged monolayers of graphene (G) by systematically optimizing several parameters in a controlled co-feeding fashion and resultant heterostacked NiAl LDH/G LBL nanocomposites have been practically applied in sensitive detection of dopamine released from live cells as early Parkinson's disease (PD) diagnostic tool. PD is the second most chronic neurodegenerative disorder with gradual progressive loss of movement and muscle control causing substantial disability and threatening the life seriously. Unfortunately majority of dopaminergic neurons present in substantia nigra of PD patients are destroyed before it is being clinically diagnosed, so early stages PD diagnosis is essential. Because of direct neighboring of extremely conductive graphene to semiconductive LDHs layers, enhanced intercalation capability of LDHs, and huge surface area with numerous active sites, good synergy effect is harvested in heteroassembled NiAl LDH/G LBL material, which in turn shows admirable electrocatalytic ability in DA detection. The interference induced by UA and AA is effectively eliminated especially after the modifying the electrode with Nafion. The outstanding electrochemical sensing performance of NiAl LDH/G LBL modified electrode has been achieved in terms of broad linear range and lowest real detection limit of 2 nM (S/N = 3) towards DA oxidation. Benefitting from superior efficiency, biosensor has been successfully used for real-time in-vitro tracking of DA efflux from live human nerve cell after being stimulated. We believe that our biosensing platform of structurally integrated well-ordered LBL heteroassembly by inserting graphene directly to the interlayer galleries of LDHs material will open up new avenue in diseases determination window.