Electrochemical detection of dopamine in the presence of ascorbic acid using graphene modified electrodes

Platinum nanowires/MXene nanosheets/porous carbon ternary nanocomposites for in situ monitoring of dopamine released from neuronal cells

Dopamine is an important neurotransmitter in the body and closely related to many neurodegenerative diseases. Therefore, the detection of dopamine is of great significance for the diagnosis and treatment of diseases, screening of drugs and unraveling of relevant pathogenic mechanisms. However, the low concentration of dopamine in the body and the complexity of the matrix make the accurate detection of dopamine challenging. Herein, an electrochemical sensor is constructed based on ternary nanocomposites consisting of one-dimensional Pt nanowires, two-dimensional MXene nanosheets, and three-dimensional porous carbon. The Pt nanowires exhibit excellent catalytic activity due to the abundant grain boundaries and highly undercoordinated atoms; MXene nanosheets not only facilitate the growth of Pt nanowires, but also enhance the electrical conductivity and hydrophilicity; and the porous carbon helps induce significant adsorption of dopamine on the electrode surface. In electrochemical tests, the ternary nanocomposite-based sensor achieves an ultra-sensitive detection of dopamine (S/N = 3) with a low limit of detection (LOD) of 28 nM, satisfactory selectivity and excellent stability. Furthermore, the sensor can be used for the detection of dopamine in serum and in situ monitoring of dopamine release from PC12 cells. Such a highly sensitive nanocomposite sensor can be exploited for in situ monitoring of important neurotransmitters at the cellular level, which is of great significance for related drug screening and mechanistic studies.

Graphene Nanocomposite Ink Coated Laser Transformed Flexible Electrodes for Selective Dopamine Detection and Immunosensing

Novel and flexible disposable laser-induced graphene (LIG) sensors modified with graphene conductive inks have been developed for dopamine and interleukin-6 (IL-6) detection. The LIG sensors exhibit high reproducibility (relative standard deviation, RSD = 0.76%, N = 5) and stability (RSD = 4.39%, N = 15) after multiple bendings, making the sensors ideal for wearable and stretchable bioelectronics applications. We have developed electrode coatings based on graphene conductive inks, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (G-PEDOT:PSS) and polyaniline (G-PANI), for working electrode modification to improve the sensitivity and limit of detection (LOD). The selectivity of LIG sensors modified with the G-PANI ink is 41.47 times higher than that of the screen-printed electrode with the G-PANI ink modification. We have compared our fabricated bare laser-engraved Kapton sensor (LIG) with the LIG sensors modified with G-PEDOT (LIG/G-PEDOT) and G-PANI (LIG/G-PANI) conductive inks. We have further compared the performance of the fabricated electrodes with commercially available screen-printed electrodes (SPEs) and screen-printed electrodes modified with G-PEDOT:PSS (SPE/G-PEDOT:PSS) and G-PANI (SPE/G-PANI). SPE/G-PANI has a lower LOD of 0.632 μM compared to SPE/G-PEDOT:PSS (0.867 μM) and SPE/G-PANI (1.974 μM). The lowest LOD of the LIG/G-PANI sensor (0.4084 μM, S/N = 3) suggests that it can be a great alternative to measure dopamine levels in a physiological medium. Additionally, the LIG/G-PANI electrode has excellent LOD (2.6234 pg/mL) to detect IL-6. Also, the sensor is successfully able to detect ascorbic acid (AA), dopamine (DA), and uric acid (UA) in their ternary mixture. The differential pulse voltammetry (DPV) result shows peak potential separation of 229, 294, and 523 mV for AA-DA, DA-UA, and UA-AA, respectively.

Facile Synthesis of Fe-Doped, Algae Residue-Derived Carbon Aerogels for Electrochemical Dopamine Biosensors

An abnormal level of dopamine (DA), a kind of neurotransmitter, correlates with a series of diseases, including Parkinson's disease, Willis-Ekbom disease, attention deficit hyperactivity disorder, and schizophrenia. Hence, it is imperative to achieve a precise, rapid detection method in clinical medicine. In this study, we synthesized nanocomposite carbon aerogels (CAs) doped with iron and iron carbide, based on algae residue-derived biomass materials, using Fe(NO3)3 as the iron source. The modified glassy carbon electrode (GCE) for DA detection, denoted as CAs-Fe/GCE, was prepared through surface modification with this composite material. X-ray photoelectron spectroscopy and X-ray diffraction characterization confirmed the successful doping of iron into the as-prepared CAs. Additionally, the electrochemical behavior of DA on the modified electrode surface was investigated and the results demonstrate that the addition of the CAs-Fe promoted the electron transfer rate, thereby enhancing their sensing performance. The fabricated electrochemical DA biosensor exhibits an accurate detection of DA in the concentration within the range of 0.01~200 µM, with a detection limit of 0.0033 µM. Furthermore, the proposed biosensor is validated in real samples, showing its high applicability for the detection of DA in beverages.

Bimetallic Coordination Polymers: Synthesis and Applications in Biosensing and Biomedicine

Bimetallic coordination polymers (CPs) have two different metal ions as connecting nodes in their polymer structure. The synthesis methods of bimetallic CPs are mainly categorized into the one-pot method and post-synthesis modifications according to various needs. Compared with monometallic CPs, bimetallic CPs have synergistic effects and excellent properties, such as higher gas adsorption rate, more efficient catalytic properties, stronger luminescent properties, and more stable loading platforms, which have been widely applied in the fields of gas adsorption, catalysis, energy storage as well as conversion, and biosensing. In recent years, the study of bimetallic CPs synergized with cancer drugs and functional nanomaterials for the therapy of cancer has increasingly attracted the attention of scientists. This review presents the research progress of bimetallic CPs in biosensing and biomedicine in the last five years and provides a perspective for their future development.

A Portable Electrochemical Dopamine Detector Using a Fish Scale-Derived Graphitized Carbon-Modified Screen-Printed Carbon Electrode

In this paper, a highly conductive alkali-activated graphitized carbon (a-GC) was prepared using tilapia fish scales as precursors through enzymolysis, activation and pyrolytic carbonization methods. The prepared a-GC was modified on the surface of a screen-printed carbon electrode to construct a flexible portable electrochemical sensing platform, which was applied to the differential pulse voltametric detection of dopamine (DA) using a U-disk electrochemical workstation combined with a smart phone and Bluetooth. The prepared a-GC possesses good electrical conductivity, a large specific surface area and abundant active sites, which are beneficial for the electrooxidation of DA molecules and result in excellent sensitivity and high selectivity for DA analysis. Under the optimal conditions, the oxidation peak current of DA increased gradually, with its concentrations in the range from 1.0 μmol/L to 1000.0 μmol/L, with the detection limit as low as 0.25 μmol/L (3S/N). The proposed sensor was further applied to the determination of DA in human sweat samples, with satisfactory results, which provided an opportunity for developing noninvasive early diagnosis and nursing equipment.

Microinstrumentation for Brain Organoids

Brain organoids are three-dimensional aggregates of self-organized differentiated stem cells that mimic the structure and function of human brain regions. Organoids bridge the gaps between conventional drug screening models such as planar mammalian cell culture, animal studies, and clinical trials. They can revolutionize the fields of developmental biology, neuroscience, toxicology, and computer engineering. Conventional microinstrumentation for conventional cellular engineering, such as planar microfluidic chips; microelectrode arrays (MEAs); and optical, magnetic, and acoustic techniques, has limitations when applied to three-dimensional (3D) organoids, primarily due to their limits with inherently two-dimensional geometry and interfacing. Hence, there is an urgent need to develop new instrumentation compatible with live cell culture techniques and with scalable 3D formats relevant to organoids. This review discusses conventional planar approaches and emerging 3D microinstrumentation necessary for advanced organoid-machine interfaces. Specifically, this article surveys recently developed microinstrumentation, including 3D printed and curved microfluidics, 3D and fast-scan optical techniques, buckling and self-folding MEAs, 3D interfaces for electrochemical measurements, and 3D spatially controllable magnetic and acoustic technologies relevant to two-way information transfer with brain organoids. This article highlights key challenges that must be addressed for robust organoid culture and reliable 3D spatiotemporal information transfer.

Crater-like nanoelectrode arrays for electrochemical detection of dopamine release from neuronal cells

Stem cell therapy has shown great potential in treating various incurable diseases using conventional chemotherapy. Parkinson's disease (PD)-a neurodegenerative disease-has been reported to be caused by quantitative loss or abnormal functionality of dopaminergic neurons (DAnergic neurons). To date, stem cell therapies have shown some potential in treating PD throughex vivoengraftment of stem-cell-derived neurons. However, accurately identifying the differentiation and non-invasively evaluating the functionality and maturity of DAnergic neurons are formidable challenges in stem cell therapies. These strategies are important in enhancing the efficacy of stem cell therapies. In this study, we report a novel cell cultivation platform, that is, a nanocrater-like electrochemical nanoelectrode array (NCENA) for monitoring dopamine (DA) release from neurons to detect exocytotic DA release from DAnergic neurons. In particular, the developed NCENA has a nanostructure in which three-dimensional porous gold nanopillars are uniformly arranged on conductive electrodes. The developed NCENA exhibited great DA sensing capabilities with a linear range of 0.39-150μM and a limit of detection of 1.16μM. Furthermore, the nanotopographical cues provided by the NCENA are suitable for cell cultivation with enhanced cellular adhesion. Finally, we successfully analysed the functionality and maturity of differentiated neurons on the NCENA through its excellent sensing ability for exocytotic DA.

Electrochemical Sensing of Dopamine Using Polypyrrole/Molybdenum Oxide Bilayer-Modified ITO Electrode

The electrochemical sensing of biomarkers has attracted more and more attention due to the advantages of electrochemical biosensors, including their ease of use, excellent accuracy, and small analyte volumes. Thus, the electrochemical sensing of biomarkers has a potential application in early disease diagnosis diagnosis. Dopamine neurotransmitters have a vital role in the transmission of nerve impulses. Here, the fabrication of a polypyrrole/molybdenum dioxide nanoparticle (MoO₃ NP)-modified ITO electrode based on a hydrothermal technique followed by electrochemical polymerization is reported. Several techniques were used to investigate the developed electrode's structure, morphology, and physical characteristics, including SEM, FTIR, EDX, N₂ adsorption, and Raman spectroscopy. The results imply the formation of tiny MoO₃ NPs with an average diameter of 29.01 nm. The developed electrode was used to determine low concentrations of dopamine neurotransmitters based on cyclic voltammetry and square wave voltammetry techniques. Furthermore, the developed electrode was used for monitoring dopamine in a human serum sample. The LOD for detecting dopamine by using MoO₃ NPs/ITO electrodes based on the SWV technique was around 2.2 nmol L^-1.

Nitrogen-Doped 4H Silicon Carbide Single-Crystal Electrode for Selective Electrochemical Sensing of Dopamine

In this work, we designed, fabricated, and characterized the first nitrogen (N)-doped single-crystalline 4H silicon carbide (4H-SiC) electrode for sensing the neurotransmitter dopamine. This N-doped 4H-SiC electrode showed good selectivity for redox reactions of dopamine in comparison with uric acid (UA), ascorbic acid (AA), and common cationic ([Ru(NH₃)₆]³⁺), anionic ([Fe(CN)₆]^3-), and organic (methylene blue) redox molecules. The mechanisms of this unique selectivity are rationalized by the unique negative Si valency and adsorption properties of the analytes on the N-doped 4H-SiC surface. Quantitative electrochemical detection of dopamine by the 4H-SiC electrode was achieved in the linear range from 50 nM to 10 μM with a detection limit of 0.05 μM and a sensitivity of 3.2 nA.μM^-1 in a pH = 7.4 phosphate buffer solution. In addition, the N-doped 4H-SiC electrode demonstrated excellent electrochemical stability. This work forms the foundation for developing 4H-SiC as the next-generation robust and biocompatible neurointerface material for a broad range of applications such as the in vivo sensing of neurotransmitters.

Controllable synthesis of MoS2@TiO2 nanocomposites for visual detection of dopamine secretion with highly-efficient enzymatic activity

Dopamine (DA) plays an essential role in dopaminergic neuronal behavior and disease. However, current detection methods for discriminating the secretion of DA are hampered by the limitations of the requirement for bulky instrumentation and non-intuitive signals. Herein, we have controllably and proportionately integrated molybdenum disulfide (MoS₂) with titanium dioxide (TiO₂) to prepare MoS₂@TiO₂ nanocomposites (MoS₂@TiO₂ NCs) via a facile synthesis method. MoS₂@TiO₂ NCs with a certain reactant mass ratio have shown a significant enhancement in peroxidase-like activity with superiority of the nanocomposite structure compared to single MoS₂ or natural enzyme. The method for catalyzing the decomposition of H₂O₂ by MoS₂@TiO₂ NCs and competition for hydroxyl radicals (˙OH) between the chromogenic agent and DA enable a sensitive, specific, and colorimetric DA analysis with a low detection limit of 0.194 μM and a wide linear detection range (0.8 to 100 μM). Because of the favorable detection performance, we were encouraged to explore and finally realize the visual detection of cellular DA secretion that is stimulated in a High-K⁺ neurocyte environment. Collectively, this method will provide a promising strategy for basic research in neuroscience with its portable, sensitive, and naked-eye detectable performance.

A photoluminescence sensor for in-situ monitoring of the dopamine neurotransmitters released from PC12 cells

Constructing simple, stable, fast, and sensitive neurotransmitter-based sensors is a promising tool to diagnose neurological diseases. Dopamine (DA), "a catecholamine neurotransmitter" is important in transmitting nerve impulses. Therefore, great attention is taken to monitor DA concentrations received. The challenge in developing a DA-based sensor is to enhance its stability and sensitivity. Thus, we have used o-phthalaldehyde (OPA)/2-mercapto ethanol (2ME)/mesoporous silica instated of 2ME in solution. Here we have successfully developed a fluorescence DA neurotransmitters sensor. The sensor was used for detecting a wide range of concentrations of DA (5 nM to 5 µM). Effects of pH (4.3-11.4) and temperatures (25-70 °C) on the sensor efficiency were investigated. The detection limit was 1.35 × 10^-11 mol/dm³, which is lower than the normal DA level in the central nervous system. The results indicated that using OPA/2ME/MSNPs has long-time stability over a year of its preparation. Moreover, the developed sensor showed high specificity towards DA in the presence of different interferences such as ascorbic acid or another catecholamine neurotransmitter such as γ-aminobutyric acid. Finally, the fabricated biosensor was used to monitor the DA neurotransmitter released from PC12 cells. Hence, it was successfully developed a simple and stable probe for accurate photoluminescence detection of DA neurotransmitters.

Using Nanomaterials as Excellent Immobilisation Layer for Biosensor Design

The endless development in nanotechnology has introduced new vitality in device fabrication including biosensor design for biomedical applications. With outstanding features like suitable biocompatibility, good electrical and thermal conductivity, wide surface area and catalytic activity, nanomaterials have been considered excellent and promising immobilisation candidates for the development of high-impact biosensors after they emerged. Owing to these reasons, the present review deals with the efficient use of nanomaterials as immobilisation candidates for biosensor fabrication. These include the implementation of carbon nanomaterials-graphene and its derivatives, carbon nanotubes, carbon nanoparticles, carbon nanodots-and MXenes, likewise their synergistic impact when merged with metal oxide nanomaterials. Furthermore, we also discuss the origin of the synthesis of some nanomaterials, the challenges associated with the use of those nanomaterials and the chemistry behind their incorporation with other materials for biosensor design. The last section covers the prospects for the development and application of the highlighted nanomaterials.

Neuro-nanotechnology: diagnostic and therapeutic nano-based strategies in applied neuroscience

Artificial, de-novo manufactured materials (with controlled nano-sized characteristics) have been progressively used by neuroscientists during the last several decades. The introduction of novel implantable bioelectronics interfaces that are better suited to their biological targets is one example of an innovation that has emerged as a result of advanced nanostructures and implantable bioelectronics interfaces, which has increased the potential of prostheses and neural interfaces. The unique physical-chemical properties of nanoparticles have also facilitated the development of novel imaging instruments for advanced laboratory systems, as well as intelligently manufactured scaffolds and microelectrodes and other technologies designed to increase our understanding of neural tissue processes. The incorporation of nanotechnology into physiology and cell biology enables the tailoring of molecular interactions. This involves unique interactions with neurons and glial cells in neuroscience. Technology solutions intended to effectively interact with neuronal cells, improved molecular-based diagnostic techniques, biomaterials and hybridized compounds utilized for neural regeneration, neuroprotection, and targeted delivery of medicines as well as small chemicals across the blood-brain barrier are all purposes of the present article.

Multi-Responsive Sensor Based on Porous Hydrogen-Bonded Organic Frameworks for Selective Sensing of Ions and Dopamine Molecules

Hydrogen-bonded organic frameworks (HOFs), as an emerging porous material, have attracted increasing research interest in fluorescence sensing due to their inherent fluorescence emission units with unique physicochemical properties. Herein, based on the organic building block 3,3',5,5'-tetrakis-(4-carboxyphenyl)-1,1'-biphenyl (H₄TCBP), the porous material HOF-TCBP was successfully synthesized using hydrogen bond self-assembly in a DMF solution. The fluorescence properties of the HOF-TCBP solution showed that when the concentration was high, excimers were easily formed, the PL emission was red-shifted, and the fluorescence intensity became weaker. HOF-TCBP showed good sensitivity and selectivity to metal ions Fe³⁺, Cr³⁺, and anion Cr₂O₇^2-. In addition, HOF-TCBP can serve as a label-free fluorescent sensor material for the sensitive and selective detection of dopamine (DA). HOF-based DA sensing is actually easy, low-cost, simple to operate, and highly selective for many potential interfering substances, and it has been successfully applied to the detection of DA in biological samples with satisfactory recoveries (101.1-104.9%). To our knowledge, this is the first report of HOF materials for efficient detection of the neurotransmitter dopamine in biological fluids. In short, this work widely broadens the application of HOF materials as fluorescent sensors for the sensing of ions and biological disease markers.

Potentiometric MIP-Modified Screen-Printed Cell for Phenoxy Herbicides Detection

In this study, a molecularly imprinted polymer (MIP)-based screen-printed cell is developed for detecting phenoxy herbicides using 2-methyl-4-chlorophenoxyacetic acid (MCPA) as the template. MCPA is a phenoxy herbicide widely used since 1945 to control broadleaf weeds via growth regulation, primarily in pasture and cereal crops. The potentiometric cell consists of a silver/silver chloride pseudo-reference electrode and a graphite working electrode coated with a MIP film. The polymeric layer is thermally formed after drop-coating of a pre-polymeric mixture composed of the reagents at the following molar ratio: 1 MCPA: 15 MAA (methacrylic acid): 7 EGDMA (ethylene glycol dimethacrylate). After template removal, the recognition cavities function as the ionophore of a classical ion selective electrode (ISE) membrane. The detected ion is the deprotonated MCPA specie, negatively charged, so the measurements were performed in phosphate buffer at pH 5.5. A linear decrease of the potential with MCPA concentration, ranging from 4 × 10^-8 to 1 × 10^-6 mol L^-1, was obtained. The detection limit and the limit of quantification were, respectively, 10 nmol L^-1 and 40 nmol L^-1. A Nernstian slope of about -59 mV/dec was achieved. The method has precision and LOD required for MCPA determination in contaminated environmental samples.

Three-Dimensional Graphene-TiO2-SnO2 Ternary Nanocomposites for High-Performance Asymmetric Supercapacitors

Ternary nanocomposites synergistically combine the material characteristics of three materials, altering the desired charge storage properties such as electrical conductivity, redox states, and surface area. Therefore, to improve the energy synergistic of SnO₂, TiO₂, and three-dimensional graphene, herein, we report a facile hydrothermal technique to synthesize a ternary nanocomposite of three-dimensional graphene-tin oxide-titanium dioxide (3DG-SnO₂-TiO₂). The synthesized ternary nanocomposite was characterized using material characterization techniques such as XRD, Raman spectroscopy, FTIR spectroscopy, FESEM, and EDXS. The surface area and porosity of the material were studied using Brunauer-Emmett-Teller (BET) studies. XRD studies showed the crystalline nature of the characteristic peaks of the individual materials, and FESEM studies revealed the deposition of SnO₂-TiO₂ on 3DG. The BET results show that incorporating 3DG into the SnO₂-TiO₂ binary nanocomposite increased its surface area compared to the binary composite. A three-electrode system compared the electrochemical performances of both the binary and ternary composites as a battery-type supercapacitor electrode in different molar KOH (1, 3, and 6 M) electrolytes. It was determined that the ternary nanocomposite electrode in 6 M KOH delivered a maximum specific capacitance of 232.7 C g^-1 at 1 A g^-1. An asymmetric supercapacitor (ASC) was fabricated based on 3DG-SnO₂-TiO₂ as a positive electrode and commercial activated carbon as a negative electrode (3DG-SnO₂-TiO₂//AC). The ASC delivered a maximum energy density of 28.6 Wh kg^-1 at a power density of 367.7 W kg^-1. Furthermore, the device delivered a superior cycling stability of ∼97% after 5000 cycles, showing its prospects as a commercial ASC electrode.

Ascorbic acid does not necessarily interfere with the electrochemical detection of dopamine

It is widely stated that ascorbic acid (AA) interferes with the electrochemical detection of neurotransmitters, especially dopamine, because of their overlapping oxidation potentials on typical electrode materials. As the concentration of AA is several orders of magnitude higher than the concentration of neurotransmitters, detection of neurotransmitters is difficult in the presence of AA and requires either highly stable AA concentration or highly selective neurotransmitter sensors. In contrast to the common opinion, we show that AA does not always interfere electrochemical detection of neurotransmitters. The decay of AA is rapid in cell culture medium, having a half-time of 2.1 hours, according to which the concentration decreases by 93% in 8 hours and by 99.75% in 18 hours. Thus, AA is eventually no longer detected by electrodes and the concentration of neurotransmitters can be effectively monitored. To validate this claim, we used unmodified single-wall carbon nanotube electrode to measure dopamine at physiologically relevant concentration range (25-1000 nM) from human midbrain organoid medium with highly linear response. Finally, AA is known to affect dopamine oxidation current through regeneration of dopamine, which complicates precise detection of small amounts of dopamine. By designing experiments as described here, this complication can be completely eliminated.

Facile and controllable synthesis of monodisperse gold nanoparticle bipyramid for electrochemical dopamine sensor

We demonstrated potential features of gold nanoparticle bipyramid (AuNB) for an electrochemical biosensor. The facile synthesis method and controllable shape and size of the AuNB are achieved through the optimization of cetyltrimethylammonium chloride (CTAC) surfactant over citric acid (CA) ratio determining the control of typically spherical Au seed size and its transition into a penta-twinned crystal structure. We observe that the optimized ratio of CTAC and CA facilitates flocculation control in which Au seeds with size as tiny as ∼14.8 nm could be attained and finally transformed into AuNB structures with an average length of ∼55 nm with high reproducibility. To improve the electrochemical sensing performance of a screen-printed carbon electrode, surface modification with AuNB via distinctive linking procedures effectively enhanced the electroactive surface area by 40%. Carried out for the detection of dopamine, a neurotransmitter frequently linked to the risk of Parkinson's, Alzheimer's, and Huntington's diseases, the AuNB decorated-carbon electrode shows outstanding electrocatalytic activity that improves sensing performance, including high sensitivity, low detection limit, wide dynamic range, high selectivity against different analytes, such as ascorbic acid, uric acid and urea, and excellent reproducibility.

Simultaneous Determination of Dopamine and Uric Acid in Real Samples Using a Voltammetric Nanosensor Based on Co-MOF, Graphene Oxide, and 1-Methyl-3-butylimidazolium Bromide

A chemically modified carbon paste electrode, based on a CoMOF-graphene oxide (GO) and an ionic liquid of 1-methyl-3-butylimidazolium bromide (CoMOF-GO/1-M,3-BB/CPE), was fabricated for the simultaneous determination of dopamine (DA) and uric acid (UA). The prepared CoMOF/GO nanocomposite was characterized by field emission-scanning electron microscopy (FE-SEM), the X-ray diffraction (XRD) method, a N₂ adsorption-desorption isotherm, and an energy dispersive spectrometer (EDS). The electrochemical sensor clearly illustrated catalytic activity towards the redox reaction of dopamine (DA), which can be authenticated by comparing the increased oxidation peak current with the bare carbon paste electrode. The CoMOF-GO/1-M,3-BB/CPE exhibits a wide linear response for DA in the concentration range of 0.1 to 300.0 µM, with a detection limit of 0.04 µM. The oxidation peaks' potential for DA and uric acid (UA) were separated well in the mixture containing the two compounds. This study demonstrated a simple and effective method for detecting DA and UA in real samples.

Graphene oxide reinforced silk fibroin nanocomposite as an electroactive interface for the estimation of dopamine

The fabrication of 2D materials and polymer-based nanocomposites deposited on flexible conductive interfaces has unblocked new horizons to expedite reaction kinetics for developing highly selective and sensitive electrochemical biosensors. Herein, we developed a novel biosensing platform, comprising graphene oxide and a silk fibroin-based nanocomposite, drop-cast on a carbon cloth electrode. The fabricated interface was expected to be a robust and miniaturized sensing platform for precise detection of dopamine (DA). Characterization was performed by SEM, EDX, FTIR, XRD, UV-visible spectroscopy, contact angle measurement, fluorescence spectroscopy, particle size, and zeta potential analysis. CV, EIS, DPV, and chronoamperometry demonstrated the superior electrochemical properties of the working interface and revealed its enhanced active surface area, increased conductivity, and accelerated electron transfer rate. The designed interface exhibited low LoD (0.41 μM), admirable stability, good sensitivity (2.46 μA μM^-1 cm^-2), wide linearity ranging from 100-900 μM, excellent reproducibility, and superb selectivity against dopamine even in the presence of possible interfering analytes. These findings endorse the feasibility of the practical execution of such an integrated system in real sample analysis.

Epitaxial Self-Assembly of Interfaces of 2D Metal-Organic Frameworks for Electroanalytical Detection of Neurotransmitters

This paper identifies the electrochemical properties of individual facets of anisotropic layered conductive metal-organic frameworks (MOFs) based on M₃(2,3,6,7,10,11-hexahydroxytriphenylene)₂ (M₃(HHTP)₂) (M = Co, Ni). The electroanalytical advantages of each facet are then applied toward the electrochemical detection of neurochemicals. By employing epitaxially controlled deposition of M₃(HHTP)₂ MOFs on electrodes, the contribution of the basal plane ({001} facets) and edge sites ({100} facets) of these MOFs can be individually determined using electrochemical characterization techniques. Despite having a lower observed heterogeneous electron transfer rate constant, the {001} facets of the M₃(HHTP)₂ systems prove more selective and sensitive for the detection of dopamine than the {100} facets of the same MOF, with the limit of detection (LOD) of 9.9 ± 2 nM in phosphate-buffered saline and 214 ± 48 nM in a simulated cerebrospinal fluid. Langmuir isotherm studies accompanied by all-atom MD simulations suggested that the observed improvement in performance and selectivity is related to the adsorption characteristics of analytes on the basal plane versus edge sites of the MOF interfaces. This work establishes that the distinct crystallographic facets of 2D MOFs can be used to control the fundamental interactions between analyte and electrode, leading to tunable electrochemical properties by controlling their preferential orientation through self-assembly.

Studies of Monoamine Neurotransmitters at Nanomolar Levels Using Carbon Material Electrodes: A Review

Neurotransmitters (NTs) with hydroxyl groups can now be identified electrochemically, utilizing a variety of electrodes and voltammetric techniques. In particular, in monoamine, the position of the hydroxyl groups might alter the sensing properties of a certain neurotransmitter. Numerous research studies using electrodes modified on their surfaces to better detect specific neurotransmitters when other interfering factors are present are reviewed to improve the precision of these measures. An investigation of the monoamine neurotransmitters at nanoscale using electrochemical methods is the primary goal of this review article. It will be used to determine which sort of electrode is ideal for this purpose. The use of carbon materials, such as graphite carbon fiber, carbon fiber micro-electrodes, glassy carbon, and 3D printed electrodes are only some of the electrodes with surface modifications that can be utilized for this purpose. Electrochemical methods for real-time detection and quantification of monoamine neurotransmitters in real samples at the nanomolar level are summarized in this paper.

Spatially-directed magnetic molecularly imprinted polymers with good anti-interference for simultaneous enrichment and detection of dual disease-related bio-indicators

As the changes of biomarkers directly reflect the occurrence of degenerative diseases, accurate detection of biomarkers is of great significance for disease diagnosis and control. However, single index detection has high uncertainties to accurately reflect the pathological characteristics because of the complexity of the human internal environment and the extremely trace concentration of indicators. To this end, a method for simultaneous detection of dual-biomarkers based on anti-interference magnetic molecularly imprinted polymers (D-mag-MIPs) is thereby proposed, and successfully applied in human urine analysis for the detection of Parkinson's disease bio-indicators 4-dihydroxyphenylacetic acid (DOPAC) and dopamine (DA). In this work, carboxyl functionalized ferric oxide served as a magnetic core, laying a solid foundation for batch detection. Hyperbranched polyethylenimine, whose abundant amino groups can provide multiple interaction forces to templates with high affinity, is employed as a functional monomer. Relative to single-template MIPs, D-mag-MIPs achieve the detection of dual bio-indicators in a one-time test, reducing the false positive result probability and enhancing the detection accuracy. The proposed methodology has been evaluated to exhibit good anti-interference, satisfactory precision, low detection limits, wide linear ranges and fast batch detection for DA and DOPAC. This work thus offers an alternative and efficient pathway for convenient batch detection of dual bio-indicators from biofluids at once.

Carbon-Related Materials: Graphene and Carbon Nanotubes in Semiconductor Applications and Design

As the scaling technology in the silicon-based semiconductor industry is approaching physical limits, it is necessary to search for proper materials to be utilized as alternatives for nanoscale devices and technologies. On the other hand, carbon-related nanomaterials have attracted so much attention from a vast variety of research and industry groups due to the outstanding electrical, optical, mechanical and thermal characteristics. Such materials have been used in a variety of devices in microelectronics. In particular, graphene and carbon nanotubes are extraordinarily favorable substances in the literature. Hence, investigation of carbon-related nanomaterials and nanostructures in different ranges of applications in science, technology and engineering is mandatory. This paper reviews the basics, advantages, drawbacks and investigates the recent progress and advances of such materials in micro and nanoelectronics, optoelectronics and biotechnology.

Colloidal lithography as a novel approach for the development of Ni-nanocavity insulin sensor

In this study, a highly sensitive, fast, and selective enzyme-free electrochemical sensor based on the deposition of Ni cavities on conductive glass was proposed for insulin detection. Considering the growing prevalence of diabetes mellitus, an electrochemical sensor for the determination of insulin was proposed for the effective diagnosis of the disease. Colloidal lithography enabled deposition of nanostructured layer (substrate) with homogeneous distribution of Ni cavities on the electrode surface with a large active surface area. The morphology and structure of conductive indium tin oxide glass modified with Ni cavities (Ni-c-ITO) were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The diameter of the resulting cavities was approximately 500 nm, while their depth was calculated at 190 ± 4 nm and 188 ± 18 nm using AFM and SEM, respectively. The insulin assay performance was evaluated by cyclic voltammetry. Ni-c-ITO exhibited excellent analytical characteristics, including high sensitivity (1.032 µA µmol^-1 dm³), a low detection limit (156 µmol dm^-3), and a wide dynamic range (500 nmol dm^-3 to 10 µmol dm^-3). Finally, the determination of insulin in buffer with interferents and in real blood serum samples revealed high specificity and demonstrated the practical potential of the method.

Highly sensitive and selective detection of dopamine with boron and sulfur co-doped graphene quantum dots

In this work, we report, the synthesis of Boron and Sulfur co-doped graphene quantum dots (BS-GQDs) and its applicability as a label-free fluorescence sensing probe for the highly sensitive and selective detection of dopamine (DA). Upon addition of DA, the fluorescence intensity of BS-GQDs were effectively quenched over a wide concentration range of DA (0–340 μM) with an ultra-low detection limit of 3.6 μM. The quenching mechanism involved photoinduced electron transfer process from BS-GQDs to dopamine-quinone, produced by the oxidization of DA under alkaline conditions. The proposed sensing mechanism was probed using a detailed study of UV–Vis absorbance, steady state and time resolved fluorescence spectroscopy. The high selectivity of the fluorescent sensor towards DA is established. Our study opens up the possibility of designing a low-cost biosensor which will be suitable for detecting DA in real samples.

Graphene as a Piezoresistive Material in Strain Sensing Applications

High accuracy measurement of mechanical strain is critical and broadly practiced in several application areas including structural health monitoring, industrial process control, manufacturing, avionics and the automotive industry, to name a few. Strain sensors, otherwise known as strain gauges, are fueled by various nanomaterials, among which graphene has attracted great interest in recent years, due to its unique electro-mechanical characteristics. Graphene shows not only exceptional physical properties but also has remarkable mechanical properties, such as piezoresistivity, which makes it a perfect candidate for strain sensing applications. In the present review, we provide an in-depth overview of the latest studies focusing on graphene and its strain sensing mechanism along with various applications. We start by providing a description of the fundamental properties, synthesis techniques and characterization methods of graphene, and then build forward to the discussion of numerous types of graphene-based strain sensors with side-by-side tabular comparison in terms of figures-of-merit, including strain range and sensitivity, otherwise referred to as the gauge factor. We demonstrate the material synthesis, device fabrication and integration challenges for researchers to achieve both wide strain range and high sensitivity in graphene-based strain sensors. Last of all, several applications of graphene-based strain sensors for different purposes are described. All in all, the evolutionary process of graphene-based strain sensors in recent years, as well as the upcoming challenges and future directions for emerging studies are highlighted.

Graphene nanosheet-sandwiched platinum nanoparticles deposited on a graphite pencil electrode as an ultrasensitive sensor for dopamine

An ultra-sensitive sensor of dopamine is introduced. The sensor is constructed by encapsulating platinum nanoparticles (PtNPs) between reduced graphene oxide (GR) nanosheets. The sandwiched PtNPs between GR layers acted as a spacer to prevent aggregation and provided a fine connection between the GR nanosheets to provide fast charge transfer. This specific orientation of the GR nanosheets and PtNPs on the graphite pencil electrode (GPE) substantially improved the electrocatalytic activity of the sensor. The synthesized graphene oxide and the fabricated sensor were comprehensively characterized by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, field emission-scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and square wave voltammetry (SWV). The value of the charge transfer coefficient (α), apparent heterogeneous electron transfer rate constant (k_s), and electroactive surface area for dopamine were found to be about 0.57, 8.99 s⁻¹, and 0.81 cm², respectively. The developed sensor is highly sensitive towards dopamine, and the detection limit is 9.0 nM. The sensor response is linear for dopamine concentration from 0.06 to 20 μM (R² = 0.9991). The behavior of the sensor for dopamine in the presence of a high concentration of l(+) Ascorbic acid and other potential interferents was satisfactory. High recovery percentage between 90% and 105% in the human urine sample, good reproducibility, and facile fabrication of the electrode make it a good candidate for dopamine sensing.

An efficient, highly sensitive, and selective electrochemical sensor using PtNPs sandwiched graphene layered modified graphite pencil electrode.

Multiwalled carbon nanotube nanofiller-polyindole polymer matrix-based efficient biosensor for the rapid detection of swine flu

Pictorial representation of the synthesis of the electrode material, fabrication and electrochemical response of the biosensing platform for swine flu detection.

Fabrication of NiFeB flexible electrode via electroless deposition towards selective and sensitive detection of dopamine

The abstract should be a single paragraph that summarises the content of the article A novel cost effective and eco-friendly flexible electrochemical sensor was designed to deal with the problems...

Non-enzymatic electrochemical dopamine sensing probe based on hexagonal shape zinc-doped cobalt oxide (Zn-Co2O4) nanostructure

A non-enzymatic dopamine electrochemical sensing probe was developed. A hexagonal shape zinc-doped cobalt oxide (Zn-Co₂O₄) nanostructure was prepared by a facile hydrothermal approach. The combination of Zn, which has an abundance of electrons, and Co₃O₄ exhibited a synergistically electron-rich nanocomposite. The crystallinity of the nanostructure was investigated using X-ray diffraction. A scanning electron microscope (SEM) was used to examine the surface morphology, revealing hexagonal nanoparticles with an average particle size of 400 nm. High-resolution transmission electron microscopy (HR-TEM) was used to confirm the nanostructure of the doped material. The nanostructure's bonding and functional groups were verified using Fourier transform infrared spectroscopy (FTIR). The electrochemical characterization was conducted by using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and amperometry. The resistivity of the electrode was confirmed through EIS and showed that the bare glassy carbon electrode (GCE) exhibited higher charge transfer resistance as compared to modified Zn-Co₂O₄/GCE. The sensing probe was developed by modifying the surface of GCE with Zn-Co₂O₄ nanostructure and tested as an electrochemical sensor for dopamine oxidation; it operated best at a working potential of 0.17 V (vs Ag/AgCl). The developed sensor exhibited a low limit of detection (0.002 µM), a high sensitivity (126 µA. µM^-1 cm^-2), and a wide linear range (0.2 to 185 µM). The sensor showed a short response time of < 1 s. The sensor's selectivity was investigated in the presence of coexisting species (uric acid, ascorbic acid, adrenaline, epinephrine, norepinephrine, histamine, serotonin, tyramine, phenethylamine, and glucose) with no effects on dopamine determination results. The developed sensor was also successfully used for determining dopamine concentrations in a real sample.

Achievements of Graphene and Its Derivatives Materials on Electrochemical Drug Assays and Drug-DNA Interactions

Graphene, emerging as a true two-dimensional (2D) material, has attracted increasing attention due to its unique physical and electrochemical properties such as high surface area, excellent conductivity, high mechanical strength, and ease of functionalization and mass production. The entire scientific community recognizes the significance and potential impact of graphene. Electrochemical detection strategies have advantages such as being simple, fast, and low-cost. The use of graphene as an excellent interface for electrode modification provides a promising way to construct more sensitive and stable electrochemical (bio)sensors. The review presents sensors based on graphene and its derivatives for electrochemical drug assays from pharmaceutical dosage forms and biological samples. Future perspectives in this rapidly developing field are also discussed. In addition, the interaction of several important anticancer drug molecules with deoxyribonucleic acid (DNA) that was immobilized onto graphene-modified electrodes has been detailed in terms of dosage regulation and utility purposes.

Construction of a Au@MoS2 composite nanosheet biosensor for the ultrasensitive detection of a neurotransmitter and understanding of its mechanism based on DFT calculations

MoS₂ nanosheets can be applied as electrochemical biosensors to selectively and sensitively respond to the surrounding environment and detect various biomolecules due to their large specific surface area and unique physicochemical properties. In this paper, single-layer or few-layer MoS₂ nanosheets were prepared by an improved liquid phase stripping method, and then combining the unique material characteristics of MoS₂ and the metallic property of Au nanoparticles (AuNPs), Au@MoS₂ composite nanosheets were synthesized based on MoS₂ nanosheets. Then, the structure and properties of MoS₂ nanosheets and Au@MoS₂ composite nanosheets were comprehensively characterized. The results proved that AuNPs were successfully loaded on MoS₂ nanosheets. At the same time, on the basis of the successful preparation of Au@MoS₂ composite nanosheets, an electrochemical biosensor targeting dopamine was successfully constructed by cyclic voltammetry. The linear detection range was 0.5–350 μM, and the detection limit was 0.2 μM. The high-sensitive electrochemical detection of dopamine has been achieved, which provides a new idea for the application of MoS₂-based nanomaterials in the biosensing of neurotransmitters. In addition, density functional theory (DFT) was used to explore the electrochemical performance of Au@MoS₂ composite nanosheets. The results show that the adsorption of Au atoms on the MoS₂ 2D structure improves the conductivity of MoS₂ nanosheets, which theoretically supports the possibilities of its application as a platform for the ultrasensitive detection of neurotransmitters or other biomolecules in the field of disease diagnosis.

An electrochemical biosensor based on Au@MoS₂ composite nanosheets was successfully prepared for the high-sensitivity detection of dopamine.

Effect of graphite oxide and exfoliated graphite oxide as a modifier for the voltametric determination of dopamine in presence of uric acid and folic acid

In the present work, exfoliated graphite oxide (E-GO) was prepared by sonicating graphite oxide (GO) (prepared by modified Hummer's and Offemam methods). Prepared GO and E-GO were characterized using infrared absorption spectroscopy, X-ray diffraction, and scanning electron microscopy. The electrocatalytic properties of GO and E-GO towards detection of dopamine (DA), uric acid (UA), and folic acid (FA) were investigated using cyclic voltammetry and differential pulse voltammetry. Our results revealed that E-GO has a slighter advantage over the GO as an electrode modifier for detection DA, UA, and FA, which might be ascribed to the good conductivity of E-GO when compared to the GO.

Non-enzymatic electrochemical determination of salivary cortisol using ZnO-graphene nanocomposites

Electrochemically deposited ZnO nanoparticles on a pencil graphite electrode (PGE) coated with graphene generate a noteworthy conductive and selective electrochemical sensing electrode for the estimation of cortisol. Electrochemical techniques such as cyclic voltammetry (CV) analysis and electrochemical impedance spectroscopic (EIS) tests were adopted to analyze and understand the nature of the modified sensor. Surface morphological analysis was done using various spectroscopic and microscopic techniques like X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Structural characterization was conducted by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The effect of scan rate, concentration, and cycle numbers was optimized and reported. Differential pulse voltammetric (DPV) analysis reveals that the linear range for the detection of cortisol is 5 × 10⁻¹⁰M − 115 × 10⁻¹⁰ M with a very low-level limit of detection value (0.15 nM). The demonstrated methodology has been excellently functional for the determination of salivary cortisol non-enzymatically at low-level concentration with enhanced selectivity despite the presence of interfering substances.

Electrochemically deposited ZnO nanoparticles on a pencil graphite electrode (PGE) coated with graphene generate a noteworthy conductive and selective electrochemical sensing electrode for the estimation of cortisol.

A Double-Deck Structure of Reduced Graphene Oxide Modified Porous Ti3C2Tx Electrode towards Ultrasensitive and Simultaneous Detection of Dopamine and Uric Acid

Considering the vital physiological functions of dopamine (DA) and uric acid (UA) and their coexistence in the biological matrix, the development of biosensing techniques for their simultaneous and sensitive detection is highly desirable for diagnostic and analytical applications. Therefore, Ti₃C₂T_x/rGO heterostructure with a double-deck layer was fabricated through electrochemical reduction. The rGO was modified on a porous Ti₃C₂T_x electrode as the biosensor for the detection of DA and UA simultaneously. Debye length was regulated by the alteration of rGO mass on the surface of the Ti₃C₂T_x electrode. Debye length decreased with respect to the rGO electrode modified with further rGO mass, indicating that fewer DA molecules were capable of surpassing the equilibrium double layer and reaching the surface of rGO to achieve the voltammetric response of DA. Thus, the proposed Ti₃C₂T_x/rGO sensor presented an excellent performance in detecting DA and UA with a wide linear range of 0.1-100 μM and 1-1000 μM and a low detection limit of 9.5 nM and 0.3 μM, respectively. Additionally, the proposed Ti₃C₂T_x/rGO electrode displayed good repeatability, selectivity, and proved to be available for real sample analysis.

Electrochemical Determination of Levodopa Using Zinc Sulfide Nanospheres-Reduced Graphene Oxide

Zinc sulfide nanospheres (ZnS NSs) were prepared by hydrothermal synthesis and graphene oxide (GO) was prepared by the Hummer's method. ZnS NSs-rGO/ITO electrode was synthesized by heat treatment at a certain temperature, which was used for the detailed electrochemical determination of levodopa (LD). Finally, they were annealed to form the ZnS NSs-rGO/ITO electrode for detecting levodopa (LD). The results reveal that the ZnS NSs with the diameter of ~1 μm are covered by rGO. The ZnS NSs-rGO/ITO electrode has a good sensitivity of 1.43 μA μM ^-1 for the determination of LD in the concentration range of 1-40 μM. Moreover, it also shows a good selectivity, reproducibility and stability. In order to verify the practicability, we also use the electrode to detect LD in human serum. The detection results also prove that the electrode can be used in real life.

Rosaniline Hydrochloride Encapsulated MCM-48: Fluorescent and Electrochemical Sensor for Dopamine

The dye Rosaniline hydrochloride (RANH) has been successfully incorporated in MCM-48 (designated as RANH@MCM-48) and characterized by various spectroscopic methods including FT-IR, SEM, EDX and N₂ adsorption-desorption isotherm. RANH@MCM-48 in aqueous medium acts as fluorescence "on" sensor for neurotransmitter dopamine (DA) in presence of its main biological interfering agent ascorbic acid or vitamin c (AA) along with Glucose, Cholesterol and Uric acid (UA). The limits of detection (LOD) were found to be 65 nM and 51 nM respectively in absence and in presence of AA. The interaction of DA to RANH@MCM-48 is found to be reversible with respect to EDTA^2-. The fluorescence intensity vs. pH plot shows a narrow fluorescence window of 7.2 to 8.8. RANH@MCM-48 has been successfully applied for DA detection in artificial cerebrospinal fluid (ACF) and bovine serum albumin (BSA) with LOD values 27 nM and 22.5 nM respectively. Platinum disc electrode has been modified with RANH@MCM-48 which showed distinct oxidation peaks with a separation of 0.188 V in cyclic voltammetry (CV). The LOD for DA in presence of AA determined from oxidation current is 77.5 nM. The voltammetric detection of DA is found to be free from common interfering species Na⁺, K⁺, Ca²⁺, Fe²⁺, UA, Cholesterol and Glucose. RANH@MCM-48 has been found to be a very effective fluorescence and voltammetric sensor for DA with very low  LOD.

A selective sensing platform for the simultaneous detection of ascorbic acid, dopamine, and uric acid based on AuNPs/carboxylated COFs/Poly(fuchsin basic) film

In this study, an electrochemical sensing strategy was developed based on the synergies of gold nanoparticles (AuNPs) doped carboxylated covalent organic frameworks (ACOFs) and poly(fuchsin basic) film for the simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA). This strategy not only took advantage of the adopted materials but also made use of the H-bonding and electrostatic interaction between the three compounds and materials. For this sensing, a poly-BFu film was formed on the surface of bare glass carbon electrode (GCE) under a constant potential. AuNPs was highly dispersed and immobilized on the constructed ACOF-TaTp to obtain AuNPs@ACOF. The constructed sensor AuNPs@ACOF/p-BFu/GCE combined the merits of high surface area, hydrophilicity, conductivity, and selective affinity, consequently exhibiting high sensitivity and selectivity toward the simultaneous detection of AA, DA, and UA with wide linear response ranges of 25-1500 μM, 0.75-40 μM, and 1-200 μM, respectively. The corresponding detection limits were 12.0 μM, 0.15 μM, and 0.22 μM. The simultaneous determination of UA in real human urine sample further confirmed the practicability of the designed electrode.

Unveiling the effect of the crystalline phases of iron oxyhydroxide for highly sensitive and selective detection of dopamine

Electrocatalysis is key to the development of several important energy and biosensing applications. In this regard, the crystalline phase-dependent electrocatalytic activity of materials has been extensively studied for reactions such as hydrogen evolution, oxygen reduction, etc. But such comprehensive studies for evaluating the phase-dependence of electrochemical biosensing have not been undertaken. Herein, three crystalline phases (α-, β-, and γ-) of iron oxyhydroxide (FeOOH) have been synthesized and characterized by spectroscopic and microscopy techniques. Electrochemical studies revealed their high sensitivity and selectivity towards dopamine (DA) detection. Amongst the three electrocatalysts, β-FeOOH shows the highest sensitivity (337.15 μA mM^-1 cm^-2) and the lowest detection limit (0.56 μM). The enhanced electrocatalytic activity of β-FeOOH, as compared to that of α- and γ-FeOOH, was attributed to its higher active site percentage and facile electrode kinetics. Furthermore, theoretical studies probed into the DA-FeOOH interactions by evaluating the charge transfer characteristics and hydrogen adsorption energies of the three phases to support the experimental findings.