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.

A bimetallic peroxidase-mimicking nanozyme with antifouling property for construction of sensor array to identify phosphoproteins and diagnose cancers.

Protein phosphorylation is a significant post-translational modification that plays a decisive role in the occurrence and development of diseases. However, the rapid and accurate identification of phosphoproteins remains challenging. Herein, a high-throughput sensor array has been constructed based on a magnetic bimetallic nanozyme (Fe3O4@ZNP@UiO-66) for the identification and discrimination of phosphoproteins. Attributing to the formation of Fe-Zr bimetallic dual active centers, the as-prepared Fe3O4@ZNP@UiO-66 exhibits enhanced peroxidase-mimicking catalytic activity, which promotes the electron transfer from Zr center to Fe(II)/Fe(III). The catalytic activity of Fe3O4@ZNP@UiO-66 can be selectively inhibited by phosphoproteins due to the strong interaction between phosphate groups and Zr centers, as well as the ultra-robust antifouling capability of zwitterionic dopamine nanoparticle (ZNP). Considering the diverse binding affinities between various proteins with the nanozyme, the catalytic activity of Fe3O4@ZNP@UiO-66 can be changed to various degree, leading to the different absorption responses at 420 nm in the hydrogen peroxide (H2O2) - 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) system. By simply extracting different absorbance intensities at various time points, a sensor array based on reaction kinetics for the discrimination of phosphoproteins from other proteins is constructed through linear discriminant analysis (LDA). Besides, the quantitative determination of phosphoproteins and identification of protein mixtures have been realized. Further, based on the differential level of phosphoproteins in cells, the differentiation of cancer cells from normal cells can also be implemented by utilizing the proposed sensor array, showing great potential in disease diagnosis.

Engineering injectable hyaluronic acid-based adhesive hydrogels with anchored PRP to pattern the micro-environment to accelerate diabetic wound healing.

Diabetic wounds remain a global challenge due to disordered wound healing led by inflammation, infection, oxidative stress, and delayed proliferation. Therefore, an ideal wound dressing for diabetic wounds not only needs tissue adhesiveness, injectability, and self-healing properties but also needs a full regulation of the microenvironment. In this work, adhesive wound dressings (HA-DA/PRP) with injectability were fabricated by combining platelet rich plasma (PRP) and dopamine-modified-hyaluronic acid (HA-DA). The engineered wound dressings exhibited tissue adhesiveness, rapid self-healing, and shape adaptability, thereby enhancing stability and adaptability to irregular wounds. The in vitro experiments demonstrated that HA-DA/PRP adhesives significantly promoted fibroblast proliferation and migration, attributed to the loaded PRP. The adhesives showed antibacterial properties against both gram-positive and negative bacteria. Moreover, in vitro experiments confirmed that HA-DA/PRP adhesives effectively mitigated oxidative stress and inflammation. Finally, HA-DA/PRP accelerated the healing of diabetic wounds by inhibiting bacterial growth, promoting granulation tissue regeneration, accelerating neovascularization, facilitating collagen deposition, and modulating inflammation through inducing M1 to M2 polarization, in an in vivo model of infected diabetic wounds. Overall, HA-DA/PRP adhesives with the ability to comprehensively regulate the microenvironment in diabetic wounds may provide a novel approach to expedite the diabetic wounds healing in clinic.

All-in-one hydrogel patches with sprayed bFGF-loaded GelMA microspheres for infected wound healing studies.

The current wound healing process faces numerous challenges such as bacterial infection, inflammation and oxidative stress. However, wound dressings used to promote wound healing, are not well suited to meet the clinical needs. Hyaluronic acid (HA) not only has excellent water absorption and good biocompatibility but facilitates cell function and tissue regeneration. Dopamine, on the other hand, increases the overall viscosity of the hydrogel and possesses antioxidant property. Furthermore, chitosan exhibits outstanding performance in antimicrobial, anti-inflammatory and antioxidant activities. Basic fibroblast growth factor (bFGF) is conducive to cell proliferation and migration, vascular regeneration and wound healing. Hence, we designed an all-in-one hydrogel patch containing dopamine and chitosan framed by hyaluronic acid (HDC) with sprayed gelatin methacryloyl (GelMA) microspheres loaded with bFGF (HDC-bFGF). The hydrogel patch exhibits excellent adhesive, anti-inflammatory, antioxidant and antibacterial properties. In vitro experiments, the HDC-bFGF hydrogel patch not only showed significant inhibitory effect on RAW cell inflammation and Staphylococcus aureus (S. aureus) growth but also effectively scavenged free radicals, in addition to promoting the migration of 3 T3 cells. In the mice acute infected wound model, the HDC-bFGF hydrogel patch adhered to the wound surface greatly accelerated the healing process via its anti-inflammatory and antioxidant activities, bacterial inhibition and pro-vascularization effects. Therefore, the multifunctional HDC-bFGF hydrogel patch holds great promise for clinical application.

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.

Detection of Dopamine Based on Aptamer-Modified Graphene Microelectrode.

In this paper, a novel aptamer-modified nitrogen-doped graphene microelectrode (Apt-Au-N-RGOF) was fabricated and used to specifically identify and detect dopamine (DA). During the synthetic process, gold nanoparticles were loaded onto the active sites of nitrogen-doped graphene fibers. Then, aptamers were modified on the microelectrode depending on Au-S bonds to prepare Apt-Au-N-RGOF. The prepared microelectrode can specifically identify DA, avoiding interference with other molecules and improving its selectivity. Compared with the N-RGOF microelectrode, the Apt-Au-N-RGOF microelectrode exhibited higher sensitivity, a lower detection limit (0.5 µM), and a wider linear range (1~100 µM) and could be applied in electrochemical analysis fields.

Hydrogel/MOF Dual-Modified Photoelectrochemical Biosensor for Antibiofouling and Biocompatible Dopamine Detection.

For accurate in vivo detection, nonspecific adsorption of biomacromolecules such as proteins and cells is a severe issue. The adsorption leads to electrode passivation, significantly compromising both the sensitivity and precision of sensing. Meanwhile, common antibiofouling modifications, such as polymer coatings, still grapple with issues related to biocompatibility, electrode passivation, and miniaturization. Herein, we propose a composite antibiofouling coating strategy based on zwitterionic metal-organic frameworks (Z-MOFs) and a combination of acrylamide hydrogels. On a well-designed TiO2/Z-MOF/hydrogel photoelectrode, we achieve highly sensitive and selective detection of dopamine in complex biological environments. The hydrogel's three-dimensional porous structure combined with unique microporous architecture of Z-MOF ensures effective sieving of interfering macromolecules while preserving efficient small molecules and electron transport. This innovative approach paves the way for constructing miniature, in vivo antibiofouling sensors for molecule monitoring in living organisms with complicated chemical environments.

Modulation of macrophage polarization by secondary cross-linked hyaluronan-dopamine hydrogels.

The inflammatory response plays a critical role in standard tissue repair processes, wherein active modulation of macrophage polarization is necessary for wound healing. Dopamine, a mussel-inspired bioactive material, is widely involved in wound healing, neural/bone/myocardial regeneration, and more. Recent studies indicated that dopamine-modified biomaterials can potentially alter macrophages polarization towards a pro-healing phenotype, thereby enhancing tissue regeneration. Nevertheless the immunoregulatory activity of dopamine on macrophage polarization remains unclear. This study introduces a novel interpenetrating hydrogel to bridge this research gap. The hydrogel, combining varying concentrations of oxidized dopamine with hyaluronic acid hydrogel, allows precise regulation of mechanical properties, antioxidant bioactivity, and biocompatibility. Surprisingly, both in vivo and in vitro outcomes demonstrated that dopamine concentration modulates macrophage polarization, but not linearly. Lower concentration (2 mg/mL) potentially decrease inflammation and facilitate M2 type macrophage polarization. In contrast, higher concentration (10 mg/mL) exhibited a pro-inflammatory tendency in the late stages of implantation. RNA-seq analysis revealed that lower dopamine concentrations induced the M1/M2 transition of macrophages by modulating the NF-κB signaling pathway. Collectively, this research offers valuable insights into the immunoregulation effects of dopamine-integrated biomaterials in tissue repair and regeneration.

Bovine Serum Albumin Template-Mediated Fabrication of Ruthenium Dioxide/Multiwalled Carbon Nanotubes: High-Performance Electrochemical Dopamine Biosensing in Human Serum.

The presence of abnormal dopamine (DA) levels may cause serious neurological disorders, therefore, the quantitative analysis of DA and its related research are of great significance for ensuring health. Herein, the bovine serum albumin (BSA) template method has been proposed for the preparation of catalytically high-performance ruthenium dioxide/multiwalled carbon nanotube (RuO2/MWCNT) nanocomposites. The incorporation of MWCNTs has improved the active surface area and conductivity while effectively preventing the aggregation of RuO2 nanoparticles. The outstanding electrocatalytic performance of RuO2/MWCNTs has promoted the electro-oxidation of DA at neutral pH. The electrochemical sensing platform based on RuO2/MWCNTs has demonstrated a wide linear range (0.5 to 111.1 µM), low detection limit (0.167 µM), excellent selectivity, long-term stability, and good reproducibility for DA detection. The satisfactory recovery range of 94.7% to 103% exhibited by the proposed sensing podium in serum samples signifies its potential for analytical applications. The aforementioned results reveal that RuO2/MWCNT nanostructures hold promising aptitude in the electrochemical sensor to detect DA in real samples, further offering broad prospects in clinical and medical diagnosis.

Hydrazo Pyrazole-Pyridone Fluorescent tag for NLO, Live cell imaging, LFPs visualization, Photophysical probing, and Electrochemical sensor for Dopamine detection.

The present communication reports on the synthesis of a novel methyl-pyridone azo fluorescent tag (MPAFT) were proven through 1H (NMR), FT-IR, UV-vis, and high-resolution mass spectrometry. The quantum chemical parameters of MPAFT were evaluated using density functional theory (DFT) analysis. It was further investigated for its latent fingerprint (LFPs) in various surfaces and anticounterfeiting applications. By exposing Level I-Level III, ridge features to UV light with a wavelength of 365 nm, a bioimaging investigation has also demonstrated the potential of MPAFT's emission behaviour. The cyclic voltammetry (CV) and linear sweep voltammetry (LSV) at MPAFT/MGCE (modified glassy carbon electrode) were used to explore the electrochemical sensitivity and reliable detection of dopamine (DA) in neutral PBS (pH 7) electrolyte solution, and the results show good sensitivity and detection. The lower detection limit for LSV was 0.81 µM under optimum conditions.

Hydroxylase-like Biomimetic Nanozyme Synthesized via a Urea-Mediated MOF Pyrolytic Reconstruction Strategy for Non-"o-Phenol hydroxyl"-Dependent Dopamine Electrochemical Sensing.

Dopamine (DA), an essential neurotransmitter, is closely associated with various neurological disorders, whose real-time dynamic monitoring is significant for evaluating the physiological activities of neurons. Electrochemical sensing methods are commonly used to determine DA, but they mostly rely on the redox reaction of its o-phenolic hydroxyl group, which makes it difficult to distinguish it from substances with this group. Here, we design a biomimetic nanozyme inspired by the coordination structure of the copper-based active site of dopamine ß-hydroxylase, which was successfully synthesized via a urea-mediated MOF pyrolysis reconstruction strategy. Experimental studies and theoretical calculations revealed that the nanozyme with Cu-N3 coordination could hydroxylate the carbon atom of the DA ß-site at a suitable potential and that the active sites of this Cu-N3 structure have the lowest binding energy for the DA ß-site. With this property, the new oxidation peak achieves the specific detection of DA rather than the traditional electrochemical signal of o-phenol hydroxyl redox, which would effectively differentiate it from neurotransmitters, such as norepinephrine and epinephrine. The sensor exhibited good monitoring capability in DA concentrations from 0.05 to 16.7 µM, and its limit of detection was 0.03 µM. Finally, the sensor enables the monitoring of DA released from living cells and can be used to quantitatively analyze the effect of polystyrene microplastics on the amount of DA released. The research provides a method for highly specific monitoring of DA and technical support for initial screening for neurocytotoxicity of pollutants.

Dopamine- and Grape-Seed-Extract-Loaded Solid Lipid Nanoparticles: Interaction Studies between Particles and Differentiated SH-SY5Y Neuronal Cell Model of Parkinson's Disease.

Parkinson's disease (PD) is a prevalent neurodegenerative disorder, primarily associated with dopaminergic neuron depletion in the Substantia Nigra. Current treatment focuses on compensating for dopamine (DA) deficiency, but the blood-brain barrier (BBB) poses challenges for effective drug delivery. Using differentiated SH-SY5Y cells, we investigated the co-administration of DA and the antioxidant Grape Seed Extract (GSE) to study the cytobiocompability, the cytoprotection against the neurotoxin Rotenone, and their antioxidant effects. For this purpose, two solid lipid nanoparticle (SLN) formulations, DA-co-GSE-SLNs and GSE-ads-DA-SLNs, were synthesized. Such SLNs showed mean particle sizes in the range of 187-297 nm, zeta potential values in the range of -4.1--9.7 mV, and DA association efficiencies ranging from 35 to 82%, according to the formulation examined. The results showed that DA/GSE-SLNs did not alter cell viability and had a cytoprotective effect against Rotenone-induced toxicity and oxidative stress. In addition, this study also focused on the evaluation of Alpha-synuclein (aS) levels; SLNs showed the potential to modulate the Rotenone-mediated increase in aS levels. In conclusion, our study investigated the potential of SLNs as a delivery system for addressing PD, also representing a promising approach for enhanced delivery of pharmaceutical and antioxidant molecules across the BBB.

Exploiting Principal Component Analysis (PCA) to reveal temperature, buffer and metal ions' role in neuromelanin (NM) synthesis by dopamine (DA) oxidative polymerization.

Neuromelanin (NM) plays a well-established role in neurological disorders pathogenesis; the mechanism of action is still discussed and the investigations in this field are limited by NM's complex and heterogeneous composition, insolubility, and low availability from human brains. An alternative can be offered by synthetic NM obtained from dopamine (DA) oxidative polymerization; however, a deep knowledge of the influence of both physicochemical parameters (T, pH, ionic strength) and other compounds in the reaction media (buffer, metal ions, other catecholamines) on DA oxidation process and, consequently, on synthetic NM features is mandatory to develop reliable NM preparation methodologies. To partially fulfill this aim, the present work focuses on defining the role of temperature, buffer and metal ions on both DA oxidation rate and DA oligomer size. DA oxidation in the specific conditions is monitored by UV-Vis spectroscopy and Principal Component Analysis (PCA) is run either on the raw spectra to model the background absorption increase, related to small DA oligomers formation, or on their first derivative to rationalize DA consumption. After having studied three case studies, 3-Way PCA is applied to directly evaluate the effect of temperature and buffer type on DA oxidation in the presence of different metal ions. Despite the proof-of-concept nature of the work and the number of compounds still to be included in the investigation, the preliminary results and the possibility to further expand the chemometric approach represent an interesting contribution to the field of in vitro simulation of NM synthesis.

Facile fabricate sandwich-structured molecularly imprinted dopamine polymer for simultaneously specific capture of Low-density lipoprotein and eliminate "bad cholesterol".

A simplified approach for preparation of sandwich type molecularly imprinted polymers (PPDA-MIPs) is proposed for simultaneously identify Low-density lipoprotein (LDL) and dispose "bad cholesterol". Porous polydopamine nanosphere (PPDA) is applied as a matrix for immobilization of LDL, and the imprinted layer is formed by dopamine acting as a functional monomer. Since imprinted cavities exhibit shape memory effects in terms of recognizing selectivity, the PPDA-MIPs exhibit excellent selectivity toward LDL and a substantial binding capacity of 550.3 µg mg-1. Meanwhile, six adsorption/desorption cycles later, the adsorption efficiency of 83.09 % is still achieved, indicating the adequate stability and reusability of PPDA-MIPs. Additionally, over 80 % of cholesterol is recovered, indicating the completeness of "bad cholesterol" removal in LDL. Lastly, as demonstrated by gel electrophoresis, PPDA-MIPs performed satisfactory behavior for the removal of LDL from the goat serum sample.

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.

Dopamine-Derived Guanidine Alkaloids from a Didemnidae Tunicate: Isolation, Synthesis, and Biological Activities.

Mellpaladines A-C (1-3) and dopargimine (4) are dopamine-derived guanidine alkaloids isolated from a specimen of Palauan Didemnidae tunicate as possible modulators of neuronal receptors. In this study, we isolated the dopargimine derivative 1-carboxydopargimine (5), three additional mellpaladines D-F (6-8), and serotodopalgimine (9), along with a dimer of serotonin, 5,5'-dihydroxy-4,4'-bistryptamine (10). The structures of these compounds were determined based on spectrometric and spectroscopic analyses. Compound 4 and its congeners dopargine (11), nordopargimine (15), and 2-(6,7-dimethoxy-3,4-dihydroisoquinolin-1-yl)ethan-1-amine (16) were synthetically prepared for biological evaluations. The biological activities of all isolated compounds were evaluated in comparison with those of 1-4 using a mouse behavioral assay upon intracerebroventricular injection, revealing key functional groups in the dopargimines and mellpaladines for in vivo behavioral toxicity. Interestingly, these alkaloids also emerged during a screen of our marine natural product library aimed at identifying antiviral activities against dengue virus, SARS-CoV-2, and vesicular stomatitis Indiana virus (VSV) pseudotyped with Ebola virus glycoprotein (VSV-ZGP).

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.

Exploring the Complex Impact of Proteins on Dopamine Polymerization: Mechanisms and Strategies for Modulation.

Polydopamine (pDA) is a valuable material with wide-ranging potential applications. However, the complex and debated nature of dopamine polymerization complicates our understanding. Specifically, the impact of foreign substances, especially proteins, on pDA formation adds an additional layer of subtlety and complexity. This study delves into specific surface features of proteins that predominantly shape their impact on dopamine polymerization. Notably, the biotin-binding site emerges as a critical region responsible for the pronounced inhibitory effect of avidin and neutravidin on the dopamine polymerization process. The binding of biotin successfully mitigates these inhibitory effects. Moreover, several nucleases demonstrated a significant hindrance to pDA formation, with their impact substantially alleviated through the introduction of DNA. It is speculated that hydrogen bonding, electrostatic, cation-π, and/or hydrophobic interactions may underlie the binding between protein surfaces and diverse oligomeric intermediates formed by the oxidation products of dopamine. Additionally, we observed a noteworthy blocking effect on the dopamine polymerization reaction induced by erythropoietin (EPO), a glycoprotein hormone known for its role in stimulating red blood cell production and demonstrating neuroprotective effects. The inhibitory influence of EPO persisted even after deglycosylation. These findings not only advance our comprehension of the mechanisms underlying dopamine polymerization but also provide strategic insights for manipulating the reaction to tailor desired biomaterials.

Structural insights into vesicular monoamine storage and drug interactions.

Biogenic monoamines-vital transmitters orchestrating neurological, endocrinal and immunological functions1-5-are stored in secretory vesicles by vesicular monoamine transporters (VMATs) for controlled quantal release6,7. Harnessing proton antiport, VMATs enrich monoamines around 10,000-fold and sequester neurotoxicants to protect neurons8-10. VMATs are targeted by an arsenal of therapeutic drugs and imaging agents to treat and monitor neurodegenerative disorders, hypertension and drug addiction1,8,11-16. However, the structural mechanisms underlying these actions remain unclear. Here we report eight cryo-electron microscopy structures of human VMAT1 in unbound form and in complex with four monoamines (dopamine, noradrenaline, serotonin and histamine), the Parkinsonism-inducing MPP+, the psychostimulant amphetamine and the antihypertensive drug reserpine. Reserpine binding captures a cytoplasmic-open conformation, whereas the other structures show a lumenal-open conformation stabilized by extensive gating interactions. The favoured transition to this lumenal-open state contributes to monoamine accumulation, while protonation facilitates the cytoplasmic-open transition and concurrently prevents monoamine binding to avoid unintended depletion. Monoamines and neurotoxicants share a binding pocket that possesses polar sites for specificity and a wrist-and-fist shape for versatility. Variations in this pocket explain substrate preferences across the SLC18 family. Overall, these structural insights and supporting functional studies elucidate the mechanism of vesicular monoamine transport and provide the basis to develop therapeutics for neurodegenerative diseases and substance abuse.

Fluorometric "AND" logic gate for detection of tyramine and tyrosinase based on in-situ formation of silicon-containing nanoparticles.

BACKGROUND: Tyramine is an important index of food freshness degree, and tyrosinase that can specifically oxidized monophenolamine to catecholamine plays a crucial part in the occurrence and development of melanin-related skin diseases. Therefore, it is crucial to develop sensitive and efficient methods for the detection of tyramine and tyrosinase. RESULTS: In this work, encouraged by tyrosinase-triggered specific oxidation of tyramine to dopamine and the unique fluorescent reaction between dopamine and amino silane, we have developed a one-step synthetic strategy of silicon containing nanoparticles (Si CNPs) for "turn-on" detection of tyramine and tyrosinase. The Si CNPs formed with thoroughly studied mechanism exhibit uniform structure and robust yellow-green fluorescence. The low detection limits for tyramine (1.87 µM) and tyrosinase (0.0029 U/mL) demonstrate admirable sensitivity outstripping most methods. The proposed assay achieves satisfactory results in the determination of tyramine and tyrosinase activity in real samples. Furthermore, we leverage this new fluorescent assay to enable the fabrication of an "AND" Boolean logic gate. SIGNIFICANCE: The entire process can be completed at easily available temperature and pressure with rapid response, convenient operation and visual observation. This fluorescent assay featured with excellent sensitivity, selectivity and stability has considerable prospects in the application of biosensors and disease diagnosis.