WO3 nanoparticles based direct electrochemical dopamine sensor in the presence of ascorbic acid

Progress in CO2 Gas Sensing Technologies: Insights into Metal Oxide Nanostructures and Resistance-Based Methods

The demand for reliable and cost-effective CO2 gas sensors is escalating due to their extensive applications in various sectors such as food packaging, indoor air quality assessment, and real-time monitoring of anthropogenic CO2 emissions to mitigate global warming. Nanostructured materials exhibit exceptional properties, including small grain size, controlled morphology, and heterojunction effects, rendering them promising candidates for chemiresistive CO2 gas sensors. This review article provides an overview of recent advancements in chemiresistive CO2 gas sensors based on nanostructured semiconducting materials. Specifically, it discusses single oxide structures, metal-decorated oxide nanostructures, and heterostructures, elucidating the correlations between these nanostructures and their CO2 sensing properties. Additionally, it addresses the challenges and future prospects of chemiresistive CO2 gas sensors, aiming to provide insights into the ongoing developments in this field.

Dopamine fast determination in pharmaceutical products using disposable printed electrodes modified with bimetal oxides carbon nanotubes nanocomposite

Dopamine is an essential neurotransmitter involved in the regulation of our pleasure, motivation, and other biological functions. Thus, tracking and monitoring the biological dopamine level is crucial for the rapid and effective treatment as well as for the diagnosis of the neurodegenerative and neurological disorders. Nanostructured electrochemical systems are tested and validated as promising methods for dopamine detection. In this study, carbon nanotube-anchored bimetallic manganese/copper bi-oxides nanocomposite-modified screen-printed carbon electrodes (Mn/Cu oxides @CNTs-SPCEs) were exploited for the electrocatalytic oxidation and direct determination of dopamine. From the morphological analysis, the particle size of the bimetallic oxides spherical nanoparticles was ranged from 9.0 to 45 nm, while the electrocatalytic activity of nanocomposite towards dopamine oxidation was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) to demonstrate the acquired high sensitivity and selectivity. The optimized DPV assay provided a wide linear dynamic range of dopamine concentrations (from 0.001 to 140 µM), and a low detection limit of 0.3 nM. Eventually, the newly modified electrochemical method was applied for dopamine detection in pharmaceutical products with high accuracy.

Electrochemical sensing of dopamine using nanostructured silver chromate: Development of an IoT-integrated sensor

Dopamine, one of the most important neurotransmitters, plays a crucial role in the functions of human metabolism, as well as the cardiovascular, central nervous and hormonal systems. This study focuses on the synthesis of nanostructured silver chromate and their application in dopamine sensing. The nanoparticles were synthesized using a complexation-mediated route using aminosalicylic acid as a stabilizer, resulting in uniform particles ranging from 3 to 15 nm in size. The synthesized silver chromate was characterized using X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy techniques. Electrochemical studies revealed that the silver chromate exhibit excellent catalytic activity for the detection of dopamine. The electroanalysis provided the selective recognition of dopamine with the limit of detection of 1.05 μM and sensitivity of 2.68 μA μM-1 cm-2 in a linear range of 5-45 μM. Additionally, a portable, IoT (internet of things)-integrated sensor based on the synthesized silver chromate was developed using Arduino Uno R4 Wi-Fi module, enabling real-time monitoring of dopamine with data transmission to a cloud platform.

A grain-like cerium oxide nanostructure: synthesis and uric acid sensing application

Utilizing nanomaterials on the working electrode of sensors enables the fabrication of highly sensitive devices for the detection of various analytes. Herein, a facile synthesis method is used to formulate a grain-like cerium oxide (CeO2) nanostructure. The structural features and surface properties of the synthesized CeO2 nanostructure were studied, which showed that the CeO2 nanostructure exhibited grain-like morphology, good crystalline structure, and excellent vibrational properties. To evaluate the sensing properties of grain-like CeO2 nanostructure, nanomaterial slurry was prepared in butyldiglycol acetate binder. Then, the nanomaterial slurry was drop-casted onto the working electrode of the screen-printed carbon electrode (SPCE) to fabricate the CeO2-modified SPCE sensor. The sensor's electrochemical properties were analysed, which showed excellent charge-transfer behavior compared to the bare SPCE. CV-based electrochemical sensing of uric acid (UA) on a CeO2-modified SPCE sensor exhibited excellent linear performance up to 1070 μM UA. Moreover, the sensor offers good sensitivity, low detection limit, reproducibility, selectivity, and long-term stability. The CeO2-modified SPCE sensor demonstrated a promising application for UA detection in real samples, addressing the need for timely UA concentration monitoring.

Development of tungsten trioxide nano-flakes intercalated on tannic acid-functionalized reduced graphene oxide for flexible acebutolol sensors

Acebutolol (ACE) is commonly used to treat hypertension and high blood pressure. Large doses of ACE can have adverse effects with potentially life-threatening consequences. It is, therefore, essential to develop a simple, low-cost, reliable, and reproducible device for detecting ACE in biofluids. This study explores the potential of unique two-dimensional nano-flakes, such as tungsten trioxide (WO3). Graphene oxide (GO) typically exhibits lower electrical conductivity than pristine graphene due to the presence of oxygen-containing functional groups that interfere with the π-conjugated structure. Functionalizing GO with tannic acid (TA) can partially reinstate the π-conjugation and limit the amount of oxygen, resulting in enhanced electrical conductivity. Ultrasonic techniques were utilized to create WO3 NFs@TA-rGO, and a range of spectroscopic and microscopic methods were applied to examine the formation of the resulting WO3 NFs@TA-rGO nanocomposites. Under optimal conditions, modified sensors resulted in lower limits of detection (0.0055 μM) and good sensitivity (0.40 μA μM-1 cm-2). They also exhibited a broad linear range spanning from 0.009 to 568.6 μM. Fabricated sensors have significant anti-interference properties with high specificity and excellent storage stability (RSD = 4.3 %), reproducibility (RSD = 3.9 %), and repeatability (RSD = 3.3 %). Ultimately, the sensor's efficacy was confirmed through the successful detection of ACE in biological samples (with recoveries ranging from 99.1 to 99.6 %). Lastly, this study highlights the substantial potential of ACE detection and extends its applications in biomedical diagnostics and pharmaceutical research.

Electrochemical sensors based on the composite of reduced graphene oxide and a multiwalled carbon nanotube-modified glassy carbon electrode for simultaneous detection of hydroquinone, dopamine, and uric acid

Using a simple drop-casting technique, we successfully fabricated a sensitive electrochemical sensor based on the composite of reduced graphene oxide (RGO) and multiwalled carbon nanotubes (MWCNT) deposited on the surface of a glassy carbon electrode (GCE) for individual and simultaneous measurements of hydroquinone (HQ), dopamine (DA), and uric acid (UA). The nanocomposite of RGO/MWCNT was further characterized in terms of its structural properties, surface morphology, and topography using Raman, FT-IR spectroscopy, SEM, HRTEM, and AFM. Then, the proposed sensor for simultaneous measurement of HQ, DA, and UA based on RGO/MWCNT-modified GCE was investigated for its electrochemical behavior and electroanalytical performances using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). In addition, the composition ratio between RGO and MWCT was 1 : 1 showing the highest electrochemical response for simultaneous detection of HQ, DA, and UA. Owing to the synergistic effect between RGO and MWCNT leading to excellent conductivity properties, the proposed sensor exhibited improved electrochemical response at pH 7 toward the oxidation processes of HQ, DA, and UA on the surface of modified electrode. The proposed sensor demonstrated three well-defined anodic peaks of these analytes with their linear concentrations ranges of 3.0-150.0 μM for HQ, 4.0-100.0 μM for DA, and 2.0-70.0 μM for UA. The limit of detection values for the simultaneous detection of HQ, DA, and UA were found as follows 0.400 ± 0.014, 0.500 ± 0.006, and 0.300 ± 0.016 μM, respectively. The additional features of this proposed sensor are high reproducibility and stability for the simultaneous detection of HQ, DA, and UA with negligible interference effect from interferents such as Mg2+, K+, Cl-, ascorbic acid, and glucose. An acceptable percentage of recovery was also shown by this sensor for simultaneous measurements of HQ, DA, and UA using 6 samples of human urine. In summary, the RGO/MWCNT nanocomposite has been shown to be a promising platform for rapid, simple, and reliable determination of simultaneous measurements of HQ, DA, and UA in practical applications.

A Dopamine Detection Sensor Based on Au-Decorated NiS2 and Its Medical Application

This article reports a simple hydrothermal method for synthesizing nickel disulfide (NiS2) on the surface of fluorine-doped tin oxide (FTO) glass, followed by the deposition of 5 nm Au nanoparticles on the electrode surface by physical vapor deposition. This process ensures the uniform distribution of Au nanoparticles on the NiS2 surface to enhance its conductivity. Finally, an Au@NiS2-FTO electrochemical biosensor is obtained for the detection of dopamine (DA). The composite material is characterized using transmission electron microscopy (TEM), UV-Vis spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The electrochemical properties of the sensor are investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and time current curves in a 0.1 M PBS solution (pH = 7.3). In the detection of DA, Au@NiS2-FTO exhibits a wide linear detection range (0.1~1000 μM), low detection limit (1 nM), and fast response time (0.1 s). After the addition of interfering substances, such as glucose, L-ascorbic acid, uric acid, CaCl2, NaCl, and KCl, the electrode potential remains relatively unchanged, demonstrating its strong anti-interference capability. It also demonstrates strong sensitivity and reproducibility. The obtained Au@NiS2-FTO provides a simple and easy-to-operate example for constructing nanometer catalysts with enzyme-like properties. These results provide a promising method utilizing Au coating to enhance the conductivity of transition metal sulfides.

A PEDOT: PSS/GO fiber microelectrode fabricated by microfluidic spinning for dopamine detection in human serum and PC12 cells

Rapid and accurate in situ determination of dopamine is of great significance in the study of neurological diseases. In this work, poly (3,4-ethylenedioxythiophene): poly (styrenesulfonic acid) (PEDOT: PSS)/graphene oxide (GO) fibers were fabricated by an effective method based on microfluidic wet spinning technology. The composite microfibers with stratified and dense arrangement were continuously prepared by injecting PEDOT: PSS and GO dispersion solutions into a microfluidic chip. PEDOT: PSS/GO fiber microelectrodes with high electrochemical activity and enhanced electrochemical oxidation activity of dopamine were constructed by controlling the structure composition of the microfibers with varying flow rate. The fabricated fiber microelectrode had a low detection limit (4.56 nM) and wide detection range (0.01-8.0 µM) for dopamine detection with excellent stability, repeatability, and reproducibility. In addition, the PEDOT: PSS/GO fiber microelectrode prepared was successfully used for the detection of dopamine in human serum and PC12 cells. The strategy for the fabrication of multi-component fiber microelectrodes is a new and effective approach for monitoring the intercellular neurotransmitter dopamine and has high potential as an implantable neural microelectrode.

Tungsten-based Nanomaterials in the Biomedical Field: A Bibliometric Analysis of Research Progress and Prospects

Tungsten-based nanomaterials (TNMs) with diverse nanostructures and unique physicochemical properties have been widely applied in the biomedical field. Although various reviews have described the application of TNMs in specific biomedical fields, there are still no comprehensive studies that summarize and analyze research trends of the field as a whole. To identify and further promote the development of biomedical TNMs, a bibliometric analysis method is used to analyze all relevant literature on this topic. First, general bibliometric distributions of the dataset by year, country, institute, referenced source, and research hotspots are recognized. Next, a comprehensive review of the subjectively recognized research hotspots in various biomedical fields, including biological sensing, anticancer treatments, antibacterials, and toxicity evaluation, is provided. Finally, the prospects and challenges of TNMs are discussed to provide a new perspective for further promoting their development in biomedical research.

Investigation of the one-step electrochemical deposition of graphene oxide-doped poly(3,4-ethylenedioxythiophene)-polyphenol oxidase as a dopamine sensor

In this paper, we fabricated poly(3,4-ethylenedioxythiophene) (PEDOT)-graphene oxide-polyphenol oxidase (PEDOT-GO-PPO) as a dopamine sensor. The morphology of PEDOT-GO-PPO was observed using scanning electron microscopy. Cyclic voltammetry was conducted to study the oxidation-reduction characteristics of dopamine. To optimize the pH, potential and limit of detection of dopamine, the amperometric technique was employed. The found limit of detection was 8 × 10-9 M, and the linear range was from 5 × 10-8 to 8.5 × 10-5 M. The Michaelis-Menten constant (K m) was calculated to be 70.34 μM, and the activation energy of the prepared electrode was 32.75 kJ mol-1. The electrode shows no significant change in the interference study. The modified electrode retains up to 80% of its original activity after 2 months. In the future, the biosensor can be used for the quantification of dopamine in human urine samples. The present modified electrode constitutes a tool for the electrochemical analysis of dopamine.

Ultrasensitive electrochemical biosensors for dopamine and cholesterol: recent advances, challenges and strategies

The rapid and accurate determination of the dopamine (neurotransmitter) and cholesterol level in bio-fluids is significant because they are crucial bioanalytes for several lethal diseases, which require early diagnosis. The level of DA in the brain is modulated by the dopamine active transporter (DAT), and is influenced by cholesterol levels in the lipid membrane environment. Accordingly, electrochemical biosensors offer rapid and accurate detection and exhibit unique features such as low detection limits even with reduced volumes of analyte, affordability, simple handling, portability and versatility, making them appropriate to deal with augmented challenges in current clinical and point-of-care diagnostics for the determination of dopamine (DA) and cholesterol. This feature article focuses on the development of ultrasensitive electrochemical biosensors for the detection of cholesterol and DA for real-time and onsite applications that can detect targeted analytes with reduced volumes and sub-picomolar concentrations with quick response times. Furthermore, the development of ultrasensitive biosensors via cost-effective, simple fabrication procedures, displaying high sensitivity, selectivity, reliability and good stability is significant in the impending era of electrochemical biosensing. Herein, we emphasize on recent advanced nanomaterials used for the ultrasensitive detection of DA and cholesterol and discuss in depth their electrochemical activities towards ultrasensitive responses. Key points describing future perspectives and the challenges during detection with their probable solutions are discussed, and the current market is also surveyed. Further, a comprehensive review of the literature indicates that there is room for improvement in the miniaturization of cholesterol and dopamine biosensors for lab-on-chip devices and overcoming the current technical limitations to facilitate full utilization by patients at home.

Hydrothermal Generation of 3-Dimensional WO₃ Nanocubes, Nanobars and Nanobricks, Their Antimicrobial and Anticancer Properties

In our current endeavor, 3-dimensional (3D) tungsten oxide (WO₃) nanostructures (nanocubes, nanobars and nanobricks) have been swiftly generated via hydrothermal route at 160 °C for 24 h. Physico-chemical characterization of the resultant powder revealed formation of WO₃ nanostructures with predominantly faceted cube, brick and rectangular bar-like morphology. The present study was also aimed at exploring the antimicrobial and anticancer potential of WO₃ nanostructures. Antimicrobial activity was tested against different micro-organisms viz., Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli and Aspergillus fumigatus. The antibacterial and antifungal activity was ascertained against these micro-organisms by measuring the diameter of inhibition zone in agar well diffusion test which revealed that the resultant WO₃ nanostructures acted as excellent antibacterial agents against both bacteria and fungi but were more effective against the fungus, A. fumigatus. To examine the growth curves of bacterial cells, time kill assay was monitored for E. coli, against which significant antibacterial action of WO₃ nanostructures was noted. The anti-cancer activity of WO₃ nanostructures was found to be concentration-dependent against KB cell line by viable cell count method. In our pilot study, WO₃ nanostructures suspension with concentration in the range of 10^-1 to 10^-5 mg/ml was found to kill KB cells effectively.

Facile Post-deposition Annealing of Graphene Ink Enables Ultrasensitive Electrochemical Detection of Dopamine

A growing body of research focuses on engineering materials for electrochemical detection of dopamine (DA), a critical neurotransmitter involved in motor function, reward processes, and blood pressure regulation. Among various sensing materials, graphene is highly attractive due to its excellent electrical conductivity and, in particular, the π-π interaction between the aromatic rings of DA and graphene. However, the lowest detection limits reported solely using graphene are nominally 1 nM. To improve the sensor sensitivity, various strategies are being explored, including chemical functionalization, heterostructure/composite formation, elemental doping, and modification with biomolecules (aptamers, enzymes, etc.). In this work, we demonstrate that commercially available graphene ink can exhibit selective and highly sensitive detection of DA by tuning the surface chemistry utilizing a simple, one-step annealing process. The annealing condition directly impacts the sensor response to DA, with the optimal conditions (30 min at 300 °C under 3% H₂ + Ar) yielding a distinguishable and selective response to DA down to 5 pM. X-ray photoelectron spectroscopy (XPS) confirms that the improved selectivity is due to the increased fraction of oxygen functionalities (in particular, C-OH), while Raman spectroscopy shows a higher degree of defectiveness for this condition compared to others. Evaluation of the interaction of three molecular components of DA (i.e., aromatic ring, hydroxyl groups, and amine group) with graphene confirms that the π-π interaction and -OH groups play a prominent role in the improved adsorption of DA on the graphene surface. Furthermore, we demonstrate a proof-of-concept, all-solution processable sensor on polyimide substrates using graphene ink. Tuning the sensor response by varying the annealing condition offers a simple avenue for developing sensitive, selective, and low-cost point-of-care biosensors, while low-temperature annealing ensures compatibility with flexible substrates, such as polyimide.

A novel sensor based on WO3·0.33H2O nanorods modified electrode for the detection and degradation of herbicide, carbendazim

In the present-day scenario, it is necessary to establish more flexible, effective and selective analytical methods that are easy to operate and less expensive. Cyclic voltammetry (CV) can be a useful technique to assess minute quantity of pollutants and in this work, an effort has been made to detect the trace quantification from the environmental samples. Herein, electrochemical sensor was fabricated using tungsten oxide nanorod (WO₃·0.33H₂O) for sensitive detection of fungicide, carbendazim (CBZ). Under optimal conditions, while studying the effect of pH on peak current, the highest peak current was observed at pH 4.2. The degradation of CBZ followed the mixed diffusion-adsorption controlled and quasi-reversible processess at the WO₃·0.33H₂O/GC electrode surface. Using WO₃·0.33H₂O/GCE sensor in SWV provided the lowest limit of detection (LOD) and limit of quantification (LOQ) values of 2.21 × 10^-8 M and 7.37 × 10^-8 M, respectively over the concentration ranges of 1.0 × 10^-7 M to 2.5 × 10^-4 M. The proposed method demonstrates potential applicability of the fabricated sensor for soil and water samples analysis in the management of creating a benign environment.

"Nano": An Emerging Avenue in Electrochemical Detection of Neurotransmitters

The growing importance of nanomaterials toward the detection of neurotransmitter molecules has been chronicled in this review. Neurotransmitters (NTs) are chemicals that serve as messengers in synaptic transmission and are key players in brain functions. Abnormal levels of NTs are associated with numerous psychotic and neurodegenerative diseases. Therefore, their sensitive and robust detection is of great significance in clinical diagnostics. For more than three decades, electrochemical sensors have made a mark toward clinical detection of NTs. The superiority of these electrochemical sensors lies in their ability to enable sensitive, simple, rapid, and selective determination of analyte molecules while remaining relatively inexpensive. Additionally, these sensors are capable of being integrated in robust, portable, and miniaturized devices to establish point-of-care diagnostic platforms. Nanomaterials have emerged as promising materials with significant implications for electrochemical sensing due to their inherent capability to achieve high surface coverage, superior sensitivity, and rapid response in addition to simple device architecture and miniaturization. Considering the enormous significance of the levels of NTs in biological systems and the advances in sensing ushered in with the integration of nanotechnology in electrochemistry, the analysis of NTs by employing nanomaterials as interface materials in various matrices has emerged as an active area of research. This review explores the advancements made in the field of electrochemical sensors for the sensitive and selective determination of NTs which have been described in the past two decades with a distinctive focus on extremely innovative attributes introduced by nanotechnology.

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.

Electrocatalytic detection of herbicide, amitrole at WO3·0.33H2O modified carbon paste electrode for environmental applications

Environmental pollution by the heavy usage of pesticides has been a pandemic issue in view of the rising farming operations for increasing the crop yield to meet the requirements of food chain supply. Throughout the world, environmental pollution by the presence of pesticides, particularly the use of herbicides in large quantities to protect the crops, has posed many environmental issues. In this research, an electrochemical sensor based on tungsten oxide hydrates (WO₃·0.33H₂O) nanorod modified carbon paste electrode (CPE) was developed for the detection of herbicide, amitrole (AMT) by the cyclic voltammeter. Hydrothermally synthesized and characterized WO₃·0.33H₂O nanorod was found to be sensitive towards the detection of AMT due to its superior sensing property as the sensor showed enhanced current and catalytic property when used in phosphate buffer solution (PBS) of pH 5.0 by the cyclic voltammetric (CV) and square wave voltammetric (SWV) techniques. The influence of electro kinetic parameters viz., scan rate, pH, accumulation time and temperature with respect to AMT oxidation was studied using CV. The linearity range was in between 1.0 × 10^-8 M and 24 × 10^-5 M and limit of detection (LOD) and limit of quantification (LOQ) was calculated to be 2.33 nM and 7.8 nM respectively. The proposed simple method demonstrated the potential applicability to detect AMT from the soil and water samples.

Recent Advances in Nanomaterial-Enabled Wearable Sensors: Material Synthesis, Sensor Design, and Personal Health Monitoring

Wearable sensors have gained much attention due to their potential in personal health monitoring in a timely, cost-effective, easy-operating, and noninvasive way. In recent studies, nanomaterials have been employed in wearable sensors to improve the sensing performance in view of their excellent properties. Here, focus is mainly on the nanomaterial-enabled wearable sensors and their latest advances in personal health monitoring. Different kinds of nanomaterials used in wearable sensors, such as metal nanoparticles, carbon nanomaterials, metallic nanomaterials, hybrid nanocomposites, and bio-nanomaterials, are reviewed. Then, the progress of nanomaterial-based wearable sensors in personal health monitoring, including the detection of ions and molecules in body fluids and exhaled breath, physiological signals, and emotion parameters, is discussed. Furthermore, the future challenges and opportunities of nanomaterial-enabled wearable sensors are discussed.

Label-free silver triangular nanoplates for spectrophotometric determination of catecholamines and their metabolites

A novel method towards spectrophotometric determination of catecholamines and their metabolites differing in their functional groups has been developed. This method is based on a change in morphology of silver triangular nanoplates upon the action of cateсholamines and their metabolites, which is manifested by the decrease of the nanoparticle local surface plasmon resonance (LSPR) band intensity or its shift to the short-wavelength region of the spectrum. The shift value of the LSPR band or the change of its intensity increases with increasing concentration of catecholamines or their metabolites, which is proposed for their spectrophotometric determination. The limits of detection of catecholamines and their metabolites under selected conditions increase in the series homovanillic acid < vanillylmandelic acid < L-epinephrine < L-norepinephrine < dopamine and are 0.25, 1.2, 3.0, 64, and 130 μmol L^-1, respectively. The selectivity of the proposed method was assessed using vanillylmandelic acid as example. It was found that the determination of vanillylmandelic acid does is not interfered in the presence of 4000-fold excess of Na⁺, K⁺, CH₃COO^-, and 1000-fold excess of Mg²⁺, Ca²⁺, Al³⁺, NO₃^-. The method also allows for the selective determination of vanillylmandelic acid in the presence of a 1000-fold excess of structurally related substances that do not contain either a catechol fragment or an electron donor substituent. The proposed approach was successfully applied to the determination of catecholamines in pharmaceuticals and artificial urine. Graphical abstract.

Single-atom doping of MoS2 with manganese enables ultrasensitive detection of dopamine: Experimental and computational approach

Two-dimensional transition metal dichalcogenides (TMDs) emerged as a promising platform to construct sensitive biosensors. We report an ultrasensitive electrochemical dopamine sensor based on manganese-doped MoS2 synthesized via a scalable two-step approach (with Mn ~2.15 atomic %). Selective dopamine detection is achieved with a detection limit of 50 pM in buffer solution, 5 nM in 10% serum, and 50 nM in artificial sweat. Density functional theory calculations and scanning transmission electron microscopy show that two types of Mn defects are dominant: Mn on top of a Mo atom (MntopMo) and Mn substituting a Mo atom (MnMo). At low dopamine concentrations, physisorption on MnMo dominates. At higher concentrations, dopamine chemisorbs on MntopMo, which is consistent with calculations of the dopamine binding energy (2.91 eV for MntopMo versus 0.65 eV for MnMo). Our results demonstrate that metal-doped layered materials, such as TMDs, constitute an emergent platform to construct ultrasensitive and tunable biosensors.

Hypha-templated synthesis of carbon/ZnO microfiber for dopamine sensing in pork

Carbon/ZnO coaxial microfibers were synthesized with the hypha of Penicillium expansum as low-cost and green template. The SEM images, XRD and Raman spectra were used to characterize the morphology and chemical components of the prepared microfibers. The formation of the coaxial structure could be attributed to the attachment of Zn²⁺ onto the hypha surface through coordination and electrostatic interactions. Sensing performance of the carbon/ZnO microfibers toward Dopamine (DA) were evaluated by dropping method. Results showed that the proposed sensor exhibited good selectivity, reproducibility, and stability with a detection limit of 0.106 μM. Two linear ranges were obtained from 0 to 50 and 50 to 300 μM. The practicality of the carbon/ZnO microfibers was supported by the successful detection of DA in pork with recovery ranging from 96.85% to 104.51%. Based on the excellent electrochemical performance and easy preparation, the proposed sensor provides a promising method for determination of DA.

Sonochemical synthesis of graphitic carbon nitrides-wrapped bimetal oxide nanoparticles hybrid materials and their electrocatalytic activity for xanthine electro-oxidation

A novel network-like magnetic nanoparticle was fabricated on a graphitic carbon nitride through a facile sonochemical route at frequency 20 kHz and power 70 W. To enhance the electrocatalytic activity of the modified materials, the graphitic carbon nitrides (g-C₃N₄) was prepared from melamine. Monitoring of xanthine concentration level in biological fluids is more important for clinical diagnosis and medical applications. As modified CuFe₂O₄/g-C₃N₄ nanocomposite exhibits better electrochemical activity towards the oxidation of xanthine with higher anodic current compared to other modified and unmodified electrode for the detection of xanthine with larger linear range (0.03-695 µM) and lower limit of detection (13.2 nM). To compare with these methods, the electrochemical techniques may be an alternative high sensitive method due to their simplicity and rapid detection time. In addition, the practical feasibility of the sensor was inspected with biological samples, reveals the acceptable recovery of the sensor in real samples.

Electrochemical Micropyramid Array-Based Sensor for In Situ Monitoring of Dopamine Released from Neuroblastoma Cells

Abnormal dopamine neurotransmission is associated with several neurological and psychiatric disorders such as Parkinson's disease, schizophrenia, attention deficiency and hyperactivity disorder, and addiction. Developing highly sensitive, selective, and fast dopamine monitoring methods is of high importance especially for the early diagnosis of these diseases. Herein, we report a new ultrasensitive electrochemical sensing platform for in situ monitoring of cell-secreted dopamine using Au-coated arrays of micropyramid structures integrated directly into a Petri dish. This approach enables the monitoring of dopamine released from cells in real-time without the need for relocating cultured cells. According to the electrochemical analyses, our dopamine sensing platform exhibits excellent analytical characteristics with a detection limit of 0.50 ± 0.08 nM, a wide linear range of 0.01-500 μM, and a sensitivity of 0.18 ± 0.01 μA/μM. The sensor also has remarkable selectivity toward DA in the presence of different potentially interfering small molecules. The developed electrochemical sensor has great potential for in vitro analysis of neuronal cells as well as early diagnosis of different neurological diseases related to abnormal levels of dopamine.

A feasible sonochemical approach to synthesize CuO@CeO2 nanomaterial and their enhanced non-enzymatic sensor performance towards neurotransmitter

A nanostructured and high conductive cupric oxide (CuO NPs) with hierarchical CeO₂ sheets-like structure was synthesized by a facile sonochemical approach. Furthermore, CuO/CeO₂ nanostructure is synthesized by high-intensity ultrasonic probe (Ti-horn, 50 kHz and 100 W) at ambient air. Moreover, the synthesized CuO/CeO₂ material was characterized by various analytical techniques including FESEM, EDX, XRD and electrochemical methods. Then, the synthesized CuO/CeO₂ composite was applied for the electrocatalytic detection of dopamine using CV and DPV techniques. In addition, the CuO/CeO₂ modified electrode has good electrocatalytic performance with high linear range from 0.025 to 98.5 µM towards the determination of dopamine drug and high sensitivity of the CuO/CeO₂ modified drug sensor was calculated as 16.34 nM and 4.823 μA·µM^-1·cm^-2, respectively. Moreover, a repeatability, reproducibility and stability of the CuO@CeO₂ mixture modified electrode were analyzed towards the determination of dopamine biomolecule. Interestingly, the real time application of CuO@CeO₂ modified electrode was established in different serum and drug samples.

A novel electrochemical sensing platform for detection of dopamine based on gold nanobipyramid/multi-walled carbon nanotube hybrids

Dopamine homeostasis is an important clinical diagnostic index, because an abnormal level in the human body is closely related to certain serious diseases. Herein, a novel electrochemical sensing platform based on gold nanobipyramid/multi-walled carbon nanotube hybrids (AuNBP/MWCNTs) is developed to detect dopamine in human fluids. Using field emission scanning electron microscopy, it is observed that AuNBPs of about 60 nm with two pyramids are well dispersed on the surface of MWCNTs. Energy-dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy confirm that AuNBPs are self-assembled onto the surface of MWCNTs to form the hybrids. Cyclic voltammetry reveals that the AuNBP/MWCNTs exhibit good electrocatalytic activity toward dopamine oxidation owing to the synergistic effects of AuNBPs and MWCNTs. In addition, both cyclic voltammetry and differential pulse voltammetry display three well-resolved and distinct oxidation peaks on the AuNBP/MWCNT-modified glassy carbon electrode. Based on AuNBP/MWCNTs, the newly developed electrochemical sensor is used to detect dopamine in the presence of ascorbic acid and uric acid over a wide linear range from 50 nM to 2.7 mM and a low detection limit of 15 nM (at S/N = 3). The electrochemical sensor can also be applied for the quantitative analysis of dopamine in real samples. Graphical abstract A novel electrochemical sensing platform based on gold nanobipyramid/multi-walled carbon nanotube hybrids (AuNBP/MWCNTs) was proposed to detect dopamine in the presence of ascorbic acid and uric acid.

ZnO-Associated Carbon Dot-Based Fluorescent Assay for Sensitive and Selective Dopamine Detection

This paper presents a simple and highly efficient method for dopamine detection using water-soluble carbon dot nanoparticles. The ZnO-associated carbon dots (CDZs) were synthesized using a green chemical strategy. An examination of the effects of biomolecules on the fluorescence of CDZs revealed selective dopamine-induced quenching. In a phosphate buffer (pH = 7.4) medium, a detection limit of 1.06 nM was obtained. This "turn off" phenomenon was attributed to the electronic interaction between CDZs and dopamine, during the oxidation of dopamine. At lower pH, however, the effects of dopamine on the fluorescence of CDZs were insignificant as the oxidation of dopamine was hindered when the proton concentration was increased. This method was found to be free from the interference of coexisting molecules, that is, ascorbic acid and uric acid. This sensing platform was applied successfully in biological fluids to confirm the practical significance of the as-designed sensor.

Ultrasound-assisted synthesis of tungsten trioxide entrapped with graphene nanosheets for developing nanomolar electrochemical (hormone) sensor and enhanced sensitivity of the catalytic performance

Herein, we have reported a simple sonochemical synthesis of multi-layer graphene covered tungsten trioxide nanoballs (WO₃ NBs) and the nanocomposite was characterized by FESEM, HRTEM, XRD, XPS, CV and EIS. Furthermore, progesterone (PGT) is a preferred marker for various biological problems like pregnancy problem, mood swings, anxiety, depression, nervousness and body pain. Therefore, its selective and sensitive determination in various biological fluids is beneficial for the evaluation of malformation problems. We describe the fabrication of an amperometric and non-enzymatic biosensor based on WO₃ NBs@GR nanocomposite modified electrode for nanomolar detection of PGT. The results showed that the nanocomposite modified electrode exhibit well-defined electro-oxidation peak compared to bare and control electrodes, demonstrating the superior electrocatalytic ability and performances. The fabricated modified sensor was facilitates the analysis of PGT in the concentration ranges of 0.025-1792.5 µM with a low detection limit of 4.28 nM. Further, the as-prepared WO₃ NBs@GR electrode has been applied to determination of PGT in human blood samples with outstanding recovery results and more importantly, the facile and environment-friendly sonochemical construction strategy extended here, may be open a cost-effective way for setting up the nanocomposites based (bio) sensing platform.

Nicotinamide adenine dinucleotide immobilized tungsten trioxide nanoparticles for simultaneous sensing of norepinephrine, melatonin and nicotine

Herein, we report the anionic surfactant, ethylene diamine tetraacetic acid (EDTA), mediated synthesis of WO₃ nanoparticles and its subsequent modification through gamma irradiation (GI) and electrochemical immobilization with nicotinamide adenine dinucleotide (NAD). Glassy carbon electrode (GCE) modified with GI-WO₃ NPs and the enzyme NAD exhibited strong electro-oxidation of three important biomolecules such as norepinephrine (NEP), melatonin (MEL) and nicotine (NIC) in 0.1 M phosphate buffer saline (PBS) at physiological pH of 7. Square wave voltammetry (SWV) studies exhibited three well-defined peaks at potentials of 120, 570 and 840 mV, corresponding to the oxidation of NEP, MEL and NIC respectively, indicating that simultaneous determination of these compounds is feasible at the NAD/GI EDTA-WO₃/GCE. The proposed sensor displayed a wide linear range of 0.010-1000 μM with the lowest detection limit of 1.4 nM for NEP, 2.6 nM for MEL and 1.7 nM for NIC respectively. Furthermore, the modified electrode was successfully applied to detect NEP, MEL and NIC in pharmaceutical and cigarette samples with excellent selectivity and reproducibility.