Signal-On Detection of Dopamine and Tyrosinase Using Tris(hydroxypropyl)phosphine as a New Lucigenin Chemiluminescence Coreactant.

Dopamine (DA) is a very imperative neurotransmitter in our body, since it contributes to several physiological processes in our body, for example, memory, feeling, cognition, cardiovascular diseases, and hormone secretion. Meanwhile, tyrosinase is a critical biomarker for several dangerous skin diseases, including vitiligo and melanoma cancer. Most of the reported chemiluminescent (CL) methods for monitoring DA and tyrosinase are signal-off biosensors. Herein, we introduce a new chemiluminescent "signal-on" system, lucigenin-tris(hydroxypropyl)phosphine (THPP), for the selective determination of DA and tyrosinase. THPP is well known as a versatile and highly water-soluble sulfhydryl-reducing compound that is more highly stable against air oxidation than common disulfide reductants. By employing THPP for the first time as an efficient lucigenin coreactant, the lucigenin-THPP system has shown a high CL response (approximately 16-fold) compared to the lucigenin-H2O2 classical CL system. Surprisingly, DA can remarkably boost the CL intensity of the lucigenin-THPP CL system. Additionally, tyrosinase can efficiently catalyze the conversion of tyramine to DA. Therefore, lucigenin-THPP was employed as an ultrasensitive and selective signal-on CL system for the quantification of DA, tyrosinase, and THPP. The linear ranges for the quantification of DA, tyrosinase, and THPP were 50-1000 nM, 0.2-50 µg/mL, and 0.1-800 µM, respectively. LODs for DA and tyrosinase were estimated to be 24 nM and 0.18 µg/mL, respectively. Additionally, the CL system has been successfully employed for the detection of tyrosinase in human serum samples and the assay of DA in human serum samples as well as in dopamine injection ampules with excellent obtained recoveries.

Etched-suppressed gold nanorods providing highly distinctive plasmonic patterns: Towards multiplex analysis of neuroblastoma biomarkers.

BACKGROUND: On-site monitoring of vanillylmandelic acid (VMA), homovanillic acid (HVA), and dopamine (DA) as key diagnostic biomarkers for a wide range of neurological disorders holds utmost significance in clinical settings. Numerous colorimetric sensors with mechanistic approaches based on aggregation or silver metallization have been introduced for this purpose. However, these mechanisms have drawbacks, such as sensitivity to environmental factors and probe toxicity. Therefore, there is a great demand for a robust yet non-toxic colorimetric sensor that employs a novel route to monitor these biomarkers effectively. RESULTS: Here, we present a single-component multi-colorimetric probe based on the controllable etching suppression of gold nanorods (AuNRs) upon exposure to the mild etchant N-bromosuccinimide (NBS), designed to accurately detect and discriminate VMA, HVA, DA, and their corresponding mixtures, i.e. , VMA: HVA, VMA:DA, HVA:DA, and VMA:HVA:DA. To enhance the sensitivity and automation capabilities of the designed multi-colorimetric sensor, two machine learning techniques were employed: linear discriminant analysis (LDA) for the qualitative classification and partial least-squares regression (PLSR) for the quantitative analysis of pure biomarkers and their mixtures. The outcomes revealed a high correlation between measured and predicted values, covering a linear range of 0.8-25, 1.2-25, and 2.7-100 µmol L-1, with remarkably low detection limits of 0.260, 0.397, and 0.913 µmol L-1 for VMA, HVA, and DA, respectively. Lastly, the performance of the probe was validated by successfully detecting the neuroblastoma biomarker VMA:HVA in human urine. SIGNIFICANCE: Our designed multi-colorimetric probe introduces a rapid, cost-effective, user-friendly, non-toxic, and non-invasive approach to detecting and discriminating not only the pure biomarkers but also their corresponding binary and ternary mixtures. The distinctive response profiles produced by the probe in the presence of different mixture ratios can indicate various disease states in patients, which is highly crucial in clinical diagnostics.

Fabrication of a graphite-paraffin carbon paste electrode and demonstration of its use in electrochemical detection strategies.

Electrochemical detection methods hold many advantages over their optical counterparts, such as operation in complex sample matrices, low-cost and high volume manufacture and possible equipment miniaturisation. Despite these advantages, the use of electrochemical detection is currently limited in the clinical setting. There is a wide range of potential electrode materials, selected for optimal signal-to-noise ratios and reproducibility when detecting target analytes. The use of carbon paste electrodes (CPEs) for electrochemical detection can be limited by their analytical performance, however they remain very attractive due to their low cost and biocompatibility. This paper presents the fabrication of an easy-to-make and use graphite powder/paraffin wax paste combined with a substrate produced via additive manufacturing and confirms its functionality for both direct and indirect electrochemical measurements. The produced CPEs enable the direct voltammetric detection of hexaammineruthenium(III) chloride and dopamine at an experimental limit of detection (ELoD) of 62.5 µM. The key inflammatory biomarker Interleukin-6 through an enzyme-linked immunosorbant assay (ELISA) was also quantified, yielding a clinically-relevant ELoD of 150 pg ml-1 in 10% human serum. The performance of low-cost and easy-to-use CPEs obtained in 0.5 hours is showcased in this study, demonstrating the platform's potential uses for point-of-need electroanalytical applications.

Laser-induced stripping defect for highly selective electrochemical quantification of dopamine: Anti-interference from other catecholamine neurotransmitters.

Detecting dopamine (DA) is critical for early diagnosis of neurological and psychiatric disorders. However, the presence of other catecholamine neurotransmitters with structural similarities to DA causes significant interference in its detection. Herein, we introduce S stripping defects via laser-induced MoS2 to functionalize MoS2 electrodes and improve their selectivity for DA electrochemical detection. The sensing results show its excellent immunity to interference from other neurotransmitters, ensuring the preservation of the DA electrochemical signal even in the mixed neurotransmitters such as acetylcholine (ACh), γ-aminobutyric acid (GABA), epinephrine (EP), norepinephrine (NP), and serotonin (5-HT). DFT calculations further reveal that the negatively charged S-stripping defects enhance DA adsorption on the surface of the functionalized MoS2 electrode, contributing to its excellent performance. Moreover, this functionalized electrodes successfully monitor DA released from living PC12 cells in the presence of other interference, highlighting its potential applicability in intercellular signaling communication.

A New BODIPY-Based Receptor for the Fluorescent Sensing of Catecholamines.

The human body synthesizes catecholamine neurotransmitters, such as dopamine and noradrenaline. Monitoring the levels of these molecules is crucial for the prevention of important diseases, such as Alzheimer's, schizophrenia, Parkinson's, Huntington's, attention-deficit hyperactivity disorder, and paragangliomas. Here, we have synthesized, characterized, and functionalized the BODIPY core with picolylamine (BDPy-pico) in order to create a sensor capable of detecting these biomarkers. The sensing properties of the BDPy-pico probe in solution were studied using fluorescence titrations and supported by DFT studies. Catecholamine sensing was also performed in the solid state by a simple strip test, using an optical fiber as the detector of emissions. In addition, the selectivity and recovery of the sensor were assessed, suggesting the possibility of using this receptor to detect dopamine and norepinephrine in human saliva.

Multi-walled carbon nanotubes-metal-organic framework nanocomposite based sensor for the monitoring of multiple monoamine neurotransmitters in living cells.

The levels of monoamine neurotransmitters (MNTs) including dopamine (DA), adrenaline (Adr), norepinephrine (NE) and 5-hydroxytryptamine (5-HT) in cells are useful indicators to explore the pathogenesis of MNTs-related diseases such as Alzheimer's disease, Parkinson's disease and depression. Herein, we constructed a novel electrochemical sensing platform based on multi-walled carbon nanotubes (MWCNTs)-amine functionalized Zr (IV) metal-organic framework (UIO-66-NH2) nanocomposite for the detection of multiple MNTs including DA, Adr, NE and 5-HT. The synergistic effect between MWCNTs and UIO-66-NH2 endowed the nanocomposite with high specific surface area, low interface impedance and superior electrocatalytic activity, which effectively enhance the electrochemical performance of the sensor. The MWCNTs-UIO-66-NH2 nanocomposite-based sensor exhibited satisfied sensitivity for the quantitative measurement of DA, Adr, NE and 5-HT, as well as low detection limit. The outstanding biocompatibility of the constructed sensor permitted it to be successfully implemented for the real-time monitoring of DA released by PC12 and C6 cells, providing a promising strategy for clinical diagnosis of MNTs-related disorders and diseases.

Redox cycling-based signal amplification at alkanethiol modified nanoporous gold interdigitated microelectrodes.

Interdigitated electrodes (IDEs) enable electrochemical signal enhancement through repeated reduction and oxidation of the analyte molecule. Porosity on these electrodes is often used to lower the impedance background. However, their high capacitive current and signal interferences with oxygen reduction limit electrochemical detection ability. We present utilization of alkanethiol modification on nanoporous gold (NPG) electrodes to lower their background capacitance and chemically passivate them from interferences due to oxygen reduction, while maintaining their fast electron transfer rates, as validated by lower separation between anodic and cathodic peaks (ΔE) and lower charge transfer resistance (Rct) values in comparison to planar gold electrodes. Redox amplification based on this modification enables sensitive detection of various small molecules, including pyocyanin, p-aminophenol, and selective detection of dopamine in the presence of ascorbic acid. Alkanethiol NPG arrays are applied as a multiplexed sensor testbed within a well plate to screen binding of various peptide receptors to the SARS COV2 S-protein by using a sandwich assay for conversion of PAPP (4-aminophenyl phosphate) to PAP (p-aminophenol), by the action of AP (alkaline phosphatase), which is validated against optical ELISA screens of the peptides. Such arrays are especially of interest in small volume analytical settings with complex samples, wherein optical methods are unsuitable.

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.

Colorimetric array sensor based on bimetallic nitrogen-doped carbon-based nanozyme material to detect multiple antioxidants.

Copper-cobalt bimetallic nitrogen-doped carbon-based nanoenzymatic materials (CuCo@NC) were synthesized using a one-step pyrolysis process. A three-channel colorimetric sensor array was constructed for the detection of seven antioxidants, including cysteine (Cys), uric acid (UA), tea polyphenols (TP), lysine (Lys), ascorbic acid (AA), glutathione (GSH), and dopamine (DA). CuCo@NC with peroxidase activity was used to catalyze the oxidation of TMB by H2O2 at three different ratios of metal sites. The ability of various antioxidants to reduce the oxidation products of TMB (ox TMB) varied, leading to distinct absorbance changes. Linear discriminant analysis (LDA) results showed that the sensor array was capable of detecting seven antioxidants in buffer and serum samples. It could successfully discriminate antioxidants with a minimum concentration of 10 nM. Thus, multifunctional sensor arrays based on CuCo@NC bimetallic nanoenzymes not only offer a promising strategy for identifying various antioxidants but also expand their applications in medical diagnostics and environmental analysis of food.

An Ultramicroelectrode Electrochemistry and Surface Plasmon Resonance Coupling Method for Cell Exocytosis Study.

Exocytosis of a single cell has been extensively researched in recent years due to its close association with numerous diseases. However, current methods only investigate exocytosis at either the single-cell or multiple-cell level, and a method for simultaneously studying exocytosis at both levels has yet to be established. In this study, a combined device incorporating ultramicroelectrode (UME) electrochemistry and surface plasmon resonance (SPR) was developed, enabling the simultaneous monitoring of single-cell and multiple-cell exocytosis. PC12 cells were cultured directly on the SPR sensing Au film, with a carboxylated carbon nanopipette (c-CNP) electrode employed for electrochemical detection in the SPR reaction cell. Upon exocytosis, the released dopamine diffuses onto the inner wall of c-CNP, undergoing an electrochemical reaction to generate a current peak. Concurrently, exocytosis can also induce changes in the refractive index of the Au film surface, leading to the SPR signal. Consequently, the device enables real-time monitoring of exocytosis from both single and multiple cells with a high spatiotemporal resolution. The c-CNP electrode exhibited excellent resistance to protein contamination, high sensitivity for dopamine detection, and the capability to continuously monitor dopamine exocytosis over an extended period. Analysis of both SPR and electrochemical signals revealed a positive correlation between changes in the SPR signal and the frequency of exocytosis. This study introduces a novel method and platform for the simultaneous investigation of single-cell and multiple-cell exocytosis.

Fluorescence sensing probe based on functionalized mesoporous MOFs for non-invasive and detection of dopamine in human fluids.

Abnormal amount of dopamine (DA) in human body is closely relate to various diseases, such as Parkinson's disease, pheochromocytoma. Real-time monitoring DA is crucial for disease warning, diagnosis and treatment. Currently, most methods rely on invasive blood testing for detecting DA, which is only completed with the aid of the medical staffs in hospitals. Herein, a non-invasive fluorescence visual strategy is developed for the real-time monitoring DA, based on luminescent nanoparticles and modified mesoporous zeolite imidazole framework (ZIF-8-NH2) dodecahedrons. During the reaction process, DA is enriched through the spatial configuration of ZIF-8-NH2 and hydrogen bonding effect. The luminescence of Cr3+-doped zinc gallate (ZnGa2O4:Cr3+, ZGC) is inhibited by the photo-induced electron transfer (PET) mechanism to realize sensitively detecting DA. The intelligent sensing platform based on the designed fluorescence probe and color recognition system is structured for real-time detection of DA in urine. Furthermore, a skin-fitting hydrogel patch is prepared by combining a fluorescent probe with chitosan, which enables sensitive and accurate detection of DA in sweat without the complex sample pretreatment. The non-invasive fluorescence detection method provides an effective strategy for quantitatively monitoring DA in human fluids.

One-pot hydrothermal synthesis of silicon, nitrogen co-doped carbon dots for enhancing enzyme activity of acid phosphatase (ACP) to dopamine and for cell imaging.

Developing water-soluble nanomaterials with high photoluminescence emission and high yield for biological analysis and imaging is urgently needed. Herein, water-soluble blue emitting silicon and nitrogen co-doped carbon dots (abbreviated as Si-CDs) of a high photoluminescence quantum yield of 80 % were effectively prepared with high yield rate (59.1 %) via one-step hydrothermal treatment of N-[3-(trimethoxysilyl)propyl]ethylenediamine (DAMO) and trans-aconitic acid. Furthermore, the Si-CDs demonstrate environmental robustness, photo-stability and biocompatibility. Given the importance of the potentially abnormal levels of acid phosphatase (ACP) in cancer diagnosis, developing a reliable and sensitive ACP measurement method is of significance for clinical research. The Si-CDs unexpectedly promote the catalytic oxidation of ACP on dopamine (DA) to polydopamine under acidic conditions through the produced reactive oxygen species (ROS). Correspondingly, a fluorescence response strategy using Si-CDs as the dual functions of probes and promoting enzyme activity of ACP on catalyzing DA was constructed to sensitively determine ACP. The quantitative analysis of ACP displayed a linear range of 0.1-60 U/L with a detection limit of 0.056 U/L. The accurate detection of ACP was successfully achieved in human serum through recovery tests. As a satisfactory fluorescent probe, Si-CDs were successfully applied to fluorescent imaging of A549 cells in cytoplasmic with long-term and safe staining. The Si-CDs have the dual properties of outstanding fluorescent probes and auxiliary oxidase activity, indicating their great potential in multifunctional applications.

Electrochemical and quantum chemical approaches to the study of dopamine sensing using bentonite and l-cysteine modified carbon paste electrode.

This work presents a significant investigation involving both electrochemical experiment and quantum chemical simulation approaches. The objective was to characterize the electrochemical detection of dopamine (DA). The detection was carried out using a modified carbon paste electrode (CPE) incorporating bentonite (Bent) and l-cysteine (CySH) (named as CySH/Bent/CPE). To understand and explain the oxidation mechanism of DA on the CySH/Bent modified electrode surface, the coupling of the two approaches were exploited. The CySH/Bent/CPE showed excellent electroactivity toward DA such as good sensibility, selectivity, stability, and regenerative ability. The developed sensor shows a dynamic linear range from 0.8 to 80 µM with a limit of detection and quantification of 0.5 µM and 1.5 µM, respectively. During the quantitative analysis of DA in presence of ascorbic acid (AA) and uric acid (UA) the electrochemical oxidation signals of AA, DA, and UA distinctly appear as three separate peaks. The potential differences between the peaks are 190 mv, 150 mv, and 340 mV for the AA-DA, DA-UA, and AA-UA oxidation pairs, respectively. These observations stem from square wave voltammetry (SWV) studies, along with the corresponding redox peak potential separations. The developed sensor is simple and accurate to monitor DA in human serum samples. On the other hand, CySH acts as an electrocatalyst on the CySH/Bent/CPE surface by increasing its active electron transfer sites, as suggested by the quantum chemical modeling with analytical results of Fukui. Furthermore, the voltammetric results obtained agree well with the theoretical calculations.

Nitrodopamine modified MnO2 NS-MoS2QDs hybrid nanocomposite for the extracellular and intracellular detection of glutathione.

We have developed a highly sensitive and reliable fluorescence resonance energy transfer (FRET) probe using nitro-dopamine (ND) and dopamine (DA) coated MnO2 nanosheet (ND@MnO2 NS and DA@MnO2 NS) as an energy acceptor and MoS2 quantum dots (QDs) as an energy donor. By employing surface-modified MnO2 NS, we can effectively reduce the fluorescence intensity of MoS2 QDs through FRET. It can reduce MnO2 NS to Mn2+ and facilitate the fluorescence recovery of the MoS2 QDs. This ND@MnO2 NS@MoS2 QD-based nanoprobe demonstrates excellent sensitivity to GSH, achieving an LOD of 22.7 nM in an aqueous medium while exhibiting minimal cytotoxicity and good biocompatibility. Moreover, our sensing platform shows high selectivity to GSH towards various common biomolecules and electrolytes. Confocal fluorescence imaging revealed that the nanoprobe can image GSH in A549 cells. Interestingly, the ND@MnO2 NS nanoprobe demonstrates no cytotoxicity in living cancer cells, even at concentrations up to 100 µg mL-1. Moreover, the easy fabrication and eco-friendliness of ND@MnO2 NS make it a rapid and simple method for detecting GSH. We envision the developed nanoprobe as an incredible platform for real-time monitoring of GSH levels in both extracellular and intracellular mediums, proving valuable for biomedical research and clinical diagnostics.

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.

Iron-driven self-assembly of dopamine into dumbbell-shaped nanozyme for visual and rapid detection of norfloxacin on a smartphone-assisted platform.

Antibiotics in aquatic environments raise health concerns. Therefore, the rapid, on-site, and accurate detection of antibiotic residues is crucial for protecting the environment and human health. Herein, a dumbbell-shaped iron (Fe3+)-dopamine coordination nanozyme (Fe-DCzyme) was developed via an iron-driven self-assembly strategy. It exhibited excellent peroxidase-like activity, which can be quenched by adding l-cysteine to prevent Fe3+/Fe2+ electron transfer but restored by adding norfloxacin. Given the 'On-Off-On' effect of peroxidase-like activity, Fe-DCzyme was used as a colourimetric sensor for norfloxacin detection, and showed a wide linear range from 0.05 to 6.00 µM (R2 = 0.9950) and LOD of 27.0 nM. A portable smartphone-assisted detection platform using Fe-DCzyme was also designed to convert norfloxacin-induced color changes into RGB values as well as to realise the rapid, on-site and quantitative detection of norfloxacin. A good linear relation (0.10-6.00 µM) and high sensitivity (LOD = 79.3 nM) were achieved for the smartphone-assisted Fe-DCzyme detection platform. Its application was verified using norfloxacin spiking methods with satisfactory recoveries (92.66%-119.65%). Therefore, the portable smartphone-assisted Fe-DCzyme detection platform with low cost and easy operation can be used for the rapid, on-site and visual quantitative detection of antibiotic residues in water samples.

In situ detection of dopamine in single living cells by molecularly imprinted polymer-functionalized nanoelectrodes.

In situ detection of dopamine (DA) at single-cell level is critical for exploring neurotransmitter-related biological processes and diseases. However, the low content of DA and a variety of distractors with similar oxidation potentials as DA in cells brought great challenges. Here, a sensitive and specific electrochemical nanosensor was proposed for in situ detection of DA in single living cells based on nanodiamond (ND) and molecularly imprinted polymer (MIP)-functionalized carbon fiber nanoelectrode (ND/MIP/CFNE). Due to its excellent electrocatalytic property, ND was modified to the surface of CFNE based on amide bonding. Compared with bare CFNE, ND-modified CFNE can enhance oxidation currents of DA by about 4-fold, improving signal-to-noise ratio and detection sensitivity. MIP was further electropolymerized on the surface of nanoelectrodes to achieve specific capture and recognition of DA, which could avoid the interference of complex matrix and analogs in cells. Taking advantage of the precise positioning capability of a single-cell analyzer and micromanipulator, ND/MIP/CFNE could be precisely inserted into different locations of single cells and monitor oxidation signal of DA. The concentration of DA in the cytoplasm of single pheochromocytoma (PC12) cell was measured to be about 0.4 µM, providing a sensitive and powerful method for single-cell detection. Furthermore, the nanoelectrodes can monitor the fluctuation of intracellular DA under drug stimulation, providing new ideas and methods for new drug development and efficacy evaluation.

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.

New insight into interference-free and highly sensitive dopamine electroanalysis.

Early diagnosis of Parkinson's disease and hyperprolactinemia based on electrochemical dopamine (DA) sensing appears as an efficient and promising practical diagnostic method. However, the coexistence of DA in real samples with ascorbic acid (AA) and uric acid (UA), which oxidize at potentials close to its own, prevents the accurate electrochemical DA sensing and therefore, hinders the effective diagnosis of these diseases. In this work, we successfully combined the electrostatic proprieties of GO, the electron transfer properties of an AuNPs@MWCNTs nanocomposite and the ability of thiol group of the amino acid l-cysteine to react chemically with carbonyl groups of UA, to develop a novel approach that enabled complete suppression of interference from AA and UA and hence, accurate DA electroanalysis in the conditions close to those of human blood serum. The chemical reaction between l-cysteine and UA was evidenced by monitoring the DPV responses of UA under different conditions. XRD, Raman spectroscopy, XPS and FE-SEM revealed the successful synthesis of GO and AuNPs@MWCNTs. The study of the electrode material (GO-AuNPs@MWCNTs) morphology via FE-SEM and HR-TEM showed that AuNPs@MWCNTs are distributed throughout the exfoliated GO layers. The fabricated sensor was calibrated in the concentration range of 0.5-5 µM, in the presence of the highest blood concentrations of AA and UA for healthy individuals. A linear relationship was observed and the LOD was found to be 1.31 nM (S/N = 3). Furthermore, the sensor showed good electron transfer kinetics, good repeatability and reproducibility, satisfactory long-term stability, and recoveries in human blood serum.

Gold nanoparticles-decorated peptide hydrogel for antifouling electrochemical dopamine determination.

A reliable and brief ultralow fouling electrochemical sensing system capable of monitoring targets in complex biological media was constructed and validated based on gold nanoparticles-peptide hydrogel-modified screen-printed electrode. The self-assembled zwitterionic peptide hydrogel was prepared by a newly designed peptide sequence of Phe-Phe-Cys-Cys-(Glu-Lys)3 with the N-terminal modified with a fluorene methoxycarbonyl group. The thiol groups on cysteine of the designed peptide are able to self-assemble with AuNPs to form a three-dimensional nanonetwork structure, which showed satisfactory antifouling capability in complex biological media (human serum). The developed gold nanoparticles-peptide hydrogel-based electrochemical sensing platform displayed notably sensing properties for dopamine determination, with a wide linear range (from 0.2 nM to 1.9 µM), a low limit of detection (0.12 nM), and an excellent selectivity. This highly sensitive and ultralow fouling electrochemical sensor was fabricated via simple preparation with concise components that avoid the accumulation of layers with single functional material and complex activation processes. This ultralow fouling and highly sensitive strategy based on the gold nanoparticles-peptide hydrogel with a three-dimensional nanonetwork offers a solution to the current situation of various low-fouling sensing systems facing impaired sensitivity and provides a potential path for the practical application of electrochemical sensors.