Electrochemical Analysis of Dopamine: Perspectives of Specific In Vivo Detection

Biofouling and performance of boron-doped diamond electrodes for detection of dopamine and serotonin in neuron cultivation media

Boron doped diamond has been considered as a fouling-resistive electrode material for in vitro and in vivo detection of neurotransmitters. In this study, its performance in electrochemical detection of dopamine and serotonin in neuron cultivation media Neurobasal™ before and after cultivation of rat neurons was investigated. For differential pulse voltammetry the limits of detection in neat Neurobasal™ medium of 2 µM and 0.2 µM for dopamine and serotonin, respectively, were achieved on the polished surface, which is comparable with physiological values. On oxidized surface twofold higher values, but increased repeatabilities of the signals were obtained. However, in Neurobasal™ media with peptides-containing supplements necessary for cell cultivation, the voltammograms were notably worse shaped due to biofouling, especially in the medium isolated after neuron growth. In these complex media, the amperometric detection mode at +0.75 V (vs. Ag/AgCl) allowed to detect portion-wise additions of dopamine and serotonin (as low as 1-2 µM), mimicking neurotransmitter release from vesicles despite the lower sensitivity in comparison with neat NeurobasalTM. The results indicate substantial differences in detection on boron doped diamond electrode in the presence and absence of proteins, and the necessity of studies in real media for successful implementation to neuron-electrode interfaces.

Disposable paper electrodes for detection of changes in dopamine concentrations in rat brain homogenates

Dopamine, the main catecholamine neurotransmitter plays an important role in renal, cardiovascular, central nervous systems, and pathophysiological processes. The abnormal dopamine levels can result in neurological disorders such as Parkinson's, Alzheimer's, schizophrenia, acute anxiety, neuroblastoma and also contribute to cognitive dysfunctions. Given the widespread importance of dopamine concentration levels, it is imperative to develop sensors that are able to monitor dopamine. Herein, we have developed pre-anodized disposable paper electrode modified with 1-pyrenebutyric acid, for the selective and sensitive determination of dopamine. The sensor was characterized with Fourier transform infrared spectroscopy, Energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and electrochemical techniques for addressing the robust formation and electrochemical activity. The modified electrode exhibited excellent electrocatalytic activity towards dopamine without the common interference from ascorbic acid. The calibration plot for the dopamine sensor resulted linear range from 0.003 μM to 0.5 μM with a detection limit of 0.11 nM. The sensor's potential utility was tested by monitoring dopamine concentration changes in rat brain homogenates when subjected to neurotoxicity. The developed sensor was validated with gold-standard UV-Vis spectroscopy studies and computational studies were performed to understand the interaction between 1-pyrenebutyric acid and dopamine.

Measurement of Neuropeptide Y in Aptamer-Modified Planar Electrodes

Electrochemical impedance spectroscopy (EIS) is a powerful technique for studying the interaction at electrode/solution interfaces. The adoption of EIS for obtaining analytical signals in biosensors based on aptamers is gaining popularity because of its advantageous characteristics for molecular recognition. Neuropeptide Y (NPY), the most abundant neuropeptide in the body, plays a crucial role with its stress-relieving properties. Quantitative measurement of NPY is imperative for understanding its role in these and other biological processes. Although aptamer-modified electrodes for NPY detection using EIS present a promising alternative, the correlation between the data obtained and the adsorption process on the electrodes is not fully understood. Various studies utilize the change in charge transfer resistance when employing an active redox label. In contrast, label-free measurement relies on changes in capacitance. To address these challenges, we focused on the interaction between aptamer-modified planar electrodes and their target, NPY. We proposed utilizing -ω*Zimag as the analytical signal, which facilitated the analysis of the adsorption process using an analogous Langmuir isotherm equation. This approach differs from implantable microelectrodes, which adhere to the Freundlich adsorption isotherm. Notably, our method obviates the need for a redox label and enables the detection of NPY at concentrations as low as 20 pg/mL. This methodology demonstrated exceptional selectivity, exhibiting a signal difference of over 20-to-1 against potential interfering molecules.

Development of a Neuropeptide Y-Sensitive Implantable Microelectrode for Continuous Measurements

In this work, we present the development of the first implantable aptamer-based platinum microelectrode for continuous measurement of a nonelectroactive molecule, neuropeptide Y (NPY). The aptamer immobilization was performed via conjugation chemistry and characterized using cyclic voltammetry before and after the surface modification. The redox label, methylene blue (MB), was attached at the end of the aptamer sequence and characterized using square wave voltammetry (SWV). NPY standard solutions in a three-electrode cell were used to test three aptamers in steady-state measurement using SWV for optimization. The aptamer with the best performance in the steady-state measurements was chosen, and continuous measurements were performed in a flow cell system using intermittent pulse amperometry. Dynamic measurements were compared against confounding and similar peptides such as pancreatic polypeptide and peptide YY, as well as somatostatin to determine the selectivity in the same modified microelectrode. Our Pt-microelectrode aptamer-based NPY biosensor provides signals 10 times higher for NPY compared to the confounding molecules. This proof-of-concept shows the first potential implantable microelectrode that is selectively sensitive to NPY concentration changes.

Genetically encoded fluorescent sensors for imaging neuronal dynamics in vivo

The brain relies on many forms of dynamic activities in individual neurons, from synaptic transmission to electrical activity and intracellular signaling events. Monitoring these neuronal activities with high spatiotemporal resolution in the context of animal behavior is a necessary step to achieve a mechanistic understanding of brain function. With the rapid development and dissemination of highly optimized genetically encoded fluorescent sensors, a growing number of brain activities can now be visualized in vivo. To date, cellular calcium imaging, which has been largely used as a proxy for electrical activity, has become a mainstay in systems neuroscience. While challenges remain, voltage imaging of neural populations is now possible. In addition, it is becoming increasingly practical to image over half a dozen neurotransmitters, as well as certain intracellular signaling and metabolic activities. These new capabilities enable neuroscientists to test previously unattainable hypotheses and questions. This review summarizes recent progress in the development and delivery of genetically encoded fluorescent sensors, and highlights example applications in the context of in vivo imaging.

Acupuncture Needle-Based Transistor Neuroprobe for In Vivo Monitoring of Neurotransmitter

Chemical communication via neurotransmitters is central to brain functions. Nevertheless, in vivo real-time monitoring of neurotransmitters released in the brain, especially the electrochemically inactive molecules, remains a great challenge. In this work, a novel needle field-effect transistor (FET) microsensor based on an acupuncture needle is proposed, which is demonstrated to be capable of real-time monitoring dopamine molecules as well as neuropeptide Y in vivo. The FET microstructure is fabricated by successively wrapping an insulating layer and a gold layer on the top of the needle, where the needle and the Au served as the source and drain, respectively. After assembling reduced graphene oxide (RGO) between the source and drain electrodes, the specific aptamer is immobilized on the RGO, making this needle-FET biosensor highly selective and sensitive to real-time monitor neurotransmitters released from rat brain, even in a Parkinson's diseases model. Furthermore, the needle-FET biosensor is applied to detect a variety of targets including hormones, proteins, and nucleic acid. By constructing a FET sensing interface on an acupuncture needle and implanting the sensor in a rat's brain for in vivo detection, this work provides a new sight in the FET domain and further expands the species of real-time in vivo detection.

Surface Nanostructure Effects on Dopamine Adsorption and Electrochemistry on Glassy Carbon Electrodes

Dopamine (DA) adsorption and electron-transfer kinetics are strongly sensitive to the structure and composition of carbon electrodes. Activation of carbon surfaces is a popular method to improve DA detection, but the role of carbon structural features on DA behavior remains uncertain. Herein, we use scanning electrochemical cell microscopy (SECCM) for local anodization of glassy carbon (GC) electrodes in acid media followed by electrochemical imaging of DA adsorption and electrochemistry covering both unmodified and anodized GC regions of the same electrode. Electrochemical measurements of adsorbed DA involve the delivery of DA from the SECCM meniscus (30 μM) for 1 s periods followed by voltammetric analysis at a reasonable sweep rate (47 V s^-1). This general approach reduces effects from interelectrode variability and allows for considerable numbers of measurements and statistical analysis of electrochemical data sets. Localized electrode activity is correlated to surface structure and chemistry by a range of characterization techniques. Anodization enhances DA electron-transfer kinetics and provides more sites for adsorption (higher specific surface area). A consequence is that adsorption takes longer to approach completion on the anodized surface. In fact, normalizing DA surface coverage by the electrochemical surface area (ECSA) reveals that adsorption is less extensive on anodized surfaces compared to as-prepared GC on the same time scale. Thus, ECSA, which has often been overlooked when calculating DA surface coverage on carbon electrodes, even where different activation methods would be expected to result in different surface roughness and nanostructure, is an important consideration. Lower graphitic and higher oxygen content on anodized GC also suggest that oxygen-containing functional groups do not necessarily enhance DA adsorption and may have the opposite effect. This work further demonstrates SECCM as a powerful technique for revealing surface structure-function relationships and correlations at heterogeneous electrodes.

Optical Sensing Strategies for Probing Single-Cell Secretion

Measuring cell secretion events is crucial to understand the fundamental cell biology that underlies cell-cell communication, migration, proliferation, and differentiation. Although strategies targeting cell populations have provided significant information about live cell secretion, they yield ensemble profiles that obscure intrinsic cell-to-cell variations. Innovation in single-cell analysis has made breakthroughs allowing accurate sensing of a wide variety of secretions and their release dynamics with high spatiotemporal resolution. This perspective focuses on the power of single-cell protocols to revolutionize cell-secretion analysis by allowing real-time and real-space measurements on single live cell resolution. We begin by discussing recent progress on single-cell bioanalytical techniques, specifically optical sensing strategies such as fluorescence-, surface plasmon resonance-, and surface-enhanced Raman scattering-based strategies, capable of in situ real-time monitoring of single-cell released ions, metabolites, proteins, and vesicles. Single-cell sensing platforms which allow for high-throughput high-resolution analysis with enough accuracy are highlighted. Furthermore, we discuss remaining challenges that should be addressed to get a more comprehensive understanding of secretion biology. Finally, future opportunities and potential breakthroughs in secretome analysis that will arise as a result of further development of single-cell sensing approaches are discussed.

Perspective-Electrochemical Sensors for Neurotransmitters and Psychiatrics: Steps toward Physiological Mental Health Monitoring

Therapeutic monitoring of neurotransmitters (NTs) and psychiatric medications is essential for the diagnosis and treatment of mental illness. However, in-vivo monitoring of NTs in humans as well as continuous physiological monitoring of psychiatrics have yet to be realized. In pursuit of this goal, there has been a plethora of work to develop electrochemical sensors for both in-vivo NT monitoring as well as in-vitro detection of psychiatric medications. We review these sensors here while discussing next steps needed to achieve concurrent, continuous physiological monitoring of NTs and psychiatric medications as part of a closed-loop feedback system that guides medication administration.

Electrochemical sensor based on Ti3C2 membrane doped with UIO-66-NH2 for dopamine

A Ti₃C₂ membrane was prepared by doping UIO-66-NH₂ with Ti₃C₂ through hydrogen bonds. When the doping mass ratio of Ti₃C₂ and UIO-66-NH₂ was 6:1, the electrochemical performance was optimal. Characterization was done by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS) which exhibited hierarchical cave-like physiognomy, large specific area, outstanding electronic conductive network, and excellent film-forming property. Moreover, the Ti₃C₂ film was analyzed via atomic force microscopy (AFM), which displayed good mechanical properties and rough surface morphology. The fabricated Ti₃C₂ membrane/GCE sensor was applied to the detection of dopamine (working potential of + 0.264 V vs. Ag/AgCl) with LOD of 0.81 fM and a sensitivity of 14.72 µA fM⁻¹ cm⁻². It was demonstrated that the Ti₃C₂ membrane can be used to construct nonenzymatic sensors with excellent performance. The fabricated sensor has high selectivity and stability and has good practicability with recoveries of 101.2–103.5% and a relative standard deviation (RSD) of 1.2–2.4%.

Differential Amperometric Microneedle Biosensor for Wearable Levodopa Monitoring of Parkinson's Disease

Levodopa (L-Dopa) is considered to be one of the most effective therapies available for Parkinson's disease (PD) treatment. The therapeutic window of L-Dopa is narrow due to its short half-life, and long-time L-Dopa treatment will cause some side effects such as dyskinesias, psychosis, and orthostatic hypotension. Therefore, it is of great significance to monitor the dynamic concentration of L-Dopa for PD patients with wearable biosensors to reduce the risk of complications. However, the high concentration of interferents in the body brings great challenges to the in vivo monitoring of L-Dopa. To address this issue, we proposed a minimal-invasive L-Dopa biosensor based on a flexible differential microneedle array (FDMA). One working electrode responded to L-Dopa and interfering substances, while the other working electrode only responded to electroactive interferences. The differential current response of these two electrodes was related to the concentration of L-Dopa by eliminating the common mode interference. The differential structure provided the sensor with excellent anti-interference performance and improved the sensor's accuracy. This novel flexible microneedle sensor exhibited favorable analytical performance of a wide linear dynamic range (0-20 μM), high sensitivity (12.618 nA μM^-1 cm^-2) as well as long-term stability (two weeks). Ultimately, the L-Dopa sensor displayed a fast response to in vivo L-Dopa dynamically with considerable anti-interference ability. All these attractive performances indicated the feasibility of this FDMA for minimal invasive and continuous monitoring of L-Dopa dynamic concentration for Parkinson's disease.

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.

Graphene and Carbon Nanotube-based Electrochemical Sensing Platforms for Dopamine

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

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.

Recent Advances in In Vivo Neurochemical Monitoring

The brain is a complex network that accounts for only 5% of human mass but consumes 20% of our energy. Uncovering the mysteries of the brain's functions in motion, memory, learning, behavior, and mental health remains a hot but challenging topic. Neurochemicals in the brain, such as neurotransmitters, neuromodulators, gliotransmitters, hormones, and metabolism substrates and products, play vital roles in mediating and modulating normal brain function, and their abnormal release or imbalanced concentrations can cause various diseases, such as epilepsy, Alzheimer's disease, and Parkinson's disease. A wide range of techniques have been used to probe the concentrations of neurochemicals under normal, stimulated, diseased, and drug-induced conditions in order to understand the neurochemistry of drug mechanisms and develop diagnostic tools or therapies. Recent advancements in detection methods, device fabrication, and new materials have resulted in the development of neurochemical sensors with improved performance. However, direct in vivo measurements require a robust sensor that is highly sensitive and selective with minimal fouling and reduced inflammatory foreign body responses. Here, we review recent advances in neurochemical sensor development for in vivo studies, with a focus on electrochemical and optical probes. Other alternative methods are also compared. We discuss in detail the in vivo challenges for these methods and provide an outlook for future directions.

Single-atom electrocatalysts templated by MOF for determination of levodopa

To overcome the problem of incorrect levodopa (LD) dosage in the treatment of Parkinson's disease, a new analytical tool is urgently needed for accurately determining the concentration of LD in human fluids. Herein, an effective and stable sensor based on a Co-single-atomic-site catalyst (Co-SASC)-modified glassy carbon electrode (Co-SASC/GCE) was developed for the determination of LD concentration. The physicochemical characterization of Co-SASC is systematically investigated. It has excellent thermal stability, graphitization degree, and a large specific surface area. Benefiting from its porous structure for kinetically fast catalysis and component advantages for fix a single cobalt atom to improve stability, Co-SASC/GCE exhibits a superior electrochemical response. Under optimal conditions (pH 2.0, coating amount is 10 μg), an ideal linear relationship is achieved between the logarithm of the peak current of the sensor and the logarithm of LD concentration. The linear range is 0.1-200 μM, and the limit of detection (LOD) is 0.033 μM. After a simple pretreatment, LD in human serum is detected by Co-SASC/GCE with excellent stability and selectivity. As such, this work enlarges the existing electrochemical sensor toolbox by offering a reasonable design and synthesis protocol for advanced materials to accurately determine LD in human fluids for the clinical treatment of Parkinson's disease.

A wireless, implantable optoelectrochemical probe for optogenetic stimulation and dopamine detection

Physical and chemical technologies have been continuously progressing advances in neuroscience research. The development of research tools for closed-loop control and monitoring neural activities in behaving animals is highly desirable. In this paper, we introduce a wirelessly operated, miniaturized microprobe system for optical interrogation and neurochemical sensing in the deep brain. Via epitaxial liftoff and transfer printing, microscale light-emitting diodes (micro-LEDs) as light sources and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-coated diamond films as electrochemical sensors are vertically assembled to form implantable optoelectrochemical probes for real-time optogenetic stimulation and dopamine detection capabilities. A customized, lightweight circuit module is employed for untethered, remote signal control, and data acquisition. After the probe is injected into the ventral tegmental area (VTA) of freely behaving mice, in vivo experiments clearly demonstrate the utilities of the multifunctional optoelectrochemical microprobe system for optogenetic interference of place preferences and detection of dopamine release. The presented options for material and device integrations provide a practical route to simultaneous optical control and electrochemical sensing of complex nervous systems.

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.

Deciphering Electron-Shuttling Characteristics of Neurotransmitters to Stimulate Bioelectricity-Generating Capabilities in Microbial Fuel Cells

This first-attempt study used electrochemical methods to quantitatively assess electron-shuttling capabilities of different neurotransmitters crucial to catecholamine biosynthesis in human brain. As prior studies mentioned, aromatics bearing ortho- or para-dihydroxybenzenes could reveal promising electroactivities to stimulate bioenergy generation in microbial fuel cells (MFCs). This feasibility study extended to investigate the electrochemical characteristics of catecholamines and trace amines (e.g., 14 model compounds selected from neurotransmitters) synthesized by human brain via cyclic voltammetry methods (CVs) and MFCs. Dopamine (DA), levodopa (L-DOPA), epinephrine (EP), norepinephrine (NP), and 3,4-dihydroxyphenylacetic acid (DOPAC) would perform the electron-shuttling characteristics, and the rest would not. In particular, DA formed by decarboxylation of L-DOPA could exhibit relatively higher electrochemical activities than their precursors. In addition, carboxylic acids formed by deamination and carboxylation of trace monoamines would reveal more significant reductive potential (E_pc); however, their oxidative electric currents seemed to be reduced. That is, chemical structure significantly influenced whether the electrochemical characteristics could be effectively expressed. This work also clearly revealed that neurotransmitters with ortho-dihydroxybenzenes exhibited promising stimulation to bioelectricity-generating capabilities of MFCs in the ranking of DA ~ EP > NP > L-DOPA > DOPAC. This was consistent with ES behaviors as CV analyses indicated.

α-MoO3 nanostructure on carbon cloth substrate for dopamine detection

Orthorhombic molybdenum oxide (α-MoO₃) nanostructures were deposited on the surface of carbon cloth (CC) as a flexible and high conductive scaffold by reactive RF magnetron sputtering technique. Structure and morphology of the as prepared molybdenum coated carbon cloth (MoO₃CC) were thoroughly characterized with field emission scanning electron microscopy, x-ray diffraction, energy dispersive x-ray and Raman spectroscopy. Benefiting from high surface area and superior conductivity of CC as well as electrocatalytic activity of α-MoO₃ nanostructures, an electrochemical sensor was fabricated. The electrochemical behavior of this new sensor toward determination of dopamine was studied in detail by cyclic voltammetry, amperometry (AM) and square wave voltammetry (SWV). Results reported here reveal that using SWV not only enhances the sensitivity of sensors to dopamine by more than 14 times compared to AM, but also offers higher linear dynamic range (1-700 μM compared to 5-550 μM). Limit of detection, for signal to noise ratio 3, was calculated to be 0.48 μM. Applicability of the proposed sensor for measurement of dopamine in real samples, like urine and pharmaceutical formulation, was also evaluated that concluded to satisfactory results.

Dopamine Binding and Analysis in Undiluted Human Serum and Blood by the RNA-Aptamer Electrode

Specific analysis of such neurotransmitters as dopamine by the aptamer electrodes in biological fluids is detrimentally affected by nonspecific adsorption of media, particularly pronounced at positive charges of the electrode surface at which dopamine oxidizes. Here, we show that dopamine analysis at the RNA-aptamer/cysteamine-modified electrodes is strongly inhibited in undiluted human serum and blood due to nonspecific interfacial adsorption of serum and blood components. We demonstrate that nonspecific adsorption of serum proteins (but not of blood components) could be minimized when analysis is performed in a flow and injections of serum samples are followed by washing steps in a phosphate buffer solution (PBS) carrier. Under those conditions, the dopamine-aptamer binding affinity in whole human serum of (1.9 ± 0.3) × 10⁴ M^-1 s^-1 was comparable to the (3.7 ± 0.3) × 10⁴ M^-1 s^-1 found in PBS, and the dopamine oxidation signal linearly depended on the dopamine concentration, providing a sensitivity of analysis of 73 ± 3 nA μM^-1 cm^-2 and a LOD of 114 ± 8 nM. The flow-injection apatmer-electrode system was used for direct analysis of basal levels of dopamine in undiluted human serum samples, without using any physical separators (membranes) or filtration procedures. The results suggest a simple strategy for combatting biosurface fouling, otherwise most pronounced at positive electrode potentials used for dopamine detection, and assist in designing more efficient antifouling strategies for biomedical applications.

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.

Facile, low-temperature synthesis of tungsten carbide (WC) flakes for the sensitive and selective electrocatalytic detection of dopamine in biological samples

Transition metal carbides have shown potential for use in electrochemical applications due to their excellent electronic conductivity, stability and electrocatalysis.

A selective colorimetric strategy for probing dopamine and levodopa through the mussel-inspired enhancement of Fe3O4 catalysis

Mussel-inspired enhancement of Fe₃O₄ catalysis was discovered toward the colorimetric analysis of dopamine and/or levodopa with bis-catechol structures.

Application of eukaryotic and prokaryotic laccases in biosensor and biofuel cells: recent advances and electrochemical aspects

Laccases exhibit a wide range of applications, especially in the electrochemical field, where they are regarded as a potential biotic component. Laccase-based biosensors have immense practical applications in the food, environmental, and medical fields. The application of laccases as biocathodes in enzymatic biofuel cells has promising potential in the preparation of implantable equipment. Extensive studies have been directed towards the potential role of fungal laccases as biotic components of electrochemical equipment. In contrast, the potential of prokaryotic laccases in electrochemistry has been not fully understood. However, there has been recent and rapid progress in the discovery and characterization of new types of prokaryotic laccases. In this review, we have comprehensively discussed the application of different sources of laccases as a biocatalytic component in various fields of application. Further, we described the potential of different types of laccases in bioelectrochemical applications.

Smartphone-based differential pulse amperometry system for real-time monitoring of levodopa with carbon nanotubes and gold nanoparticles modified screen-printing electrodes

Parkinson's disease caused by lack of dopamine in brain is a common neurodegenerative disorder. The traditional treatment is to replenish levodopa since it could pass through blood brain barrier and form dopamine. However, its accumulation can cause patients' movement disorders and uncontrollable emotion. Therefore, it is critical to control the levodopa dosage accuracy to improve the curative effect in clinical. In this study, a smartphone-based electrochemical detection system was developed for rapid monitoring of levodopa. The system involved a disposable sensor, a hand-held electrochemical detector, and a smartphone with designed application. Single-wall carbon nanotubes and gold nanoparticles modified screen-printed electrodes were used to convert and amplify the electrochemical current signals upon presence of levodopa molecules. The electrochemical detectors were used to generate electrochemical excitation signals and detect the resultant currents. Smartphone was connected to the detector, which was used to control the detector, calculate data, and plot graph in real-time. The smartphone-based differential pulse amperometry system was demonstrated to monitor levodopa at concentrations as low as 0.5 µM in human serum. Furthermore, it has also been verified to be able to distinguish levodopa from other representative substances in the body. Therefore, its performance was more sensitive and rapid than electrochemical workstation. With these advantages, the system can be used in the field of point-of-care testing (POCT) to detect levodopa and provide the possibility to solve clinical demand for levodopa detection.