Dopamine Molecules Research Articles

Graphene oxide sensors of high sensitivity fabricated using cold atmospheric-pressure hydrogen plasma for use in the detection of small organic molecules

A novel electrochemical sensor was fabricated by means of solution-processed graphene oxide (GO) ink on fluorine-doped tin oxide (FTO), followed by rapid reduction of the GO surface to reduced graphene oxide (rGO) by cold diffuse atmospheric plasma generated in pure hydrogen gas. The FTO/rGO electrode was then employed in the detection of ascorbic acid, uric acid, dopamine, and acetaminophen molecules with low limits of detection; in these cases, 0.03, 0.06, 0.07, and 0.04 μM, respectively. While traditional methods for the reduction of GO are time-consuming, in the order of tens of minutes, and involve high-temperature (450 °C) sintering in argon, the novelty of this work lies in the rapid manufacture of the sensing material through cold plasma-assisted reduction of a GO surface. Since the temperature of the plasma procedure is below 70 °C, with the elapsed time lesser than 10 s, and the plasma unit is capable of processing an area of up to 160 cm2, FTO/rGO electrode preparation can be performed at high throughput. This fabrication method may be easily deployed in rapid and low-cost roll-to-roll manufacture, a factor essential for the future commercialization of cost-effective flexible and printed electronics based on a wide range of sensors.

Are nickel- and titanium- doped fullerenes suitable adsorbents for dopamine in an aqueous solution? Detailed DFT and AIM studies

Dopamine is one of the biological-based drugs that play a vital role in treating several human diseases. The controllable adsorption and release pattern of dopamine is an essential factor in dopamine effectiveness. Recently, the use of nanostructured materials has received much attention as a carrier (adsorption-desorption) for drug-delivery. The fullerene C60 is a promising adsorbent due to its unique structure. However, the fullerene C60 possess relatively low polarity in water that hinders its application for biological application. In this research, we investigated the enhancement of fullerene C60 polarity in water by doping titanium and nickel atoms and investigated dopamine adsorption on generated metallofullerenes. In this research, dopamine adsorption on two kinds of metallofullerenes (C59Ti and C59Ni) was investigated using density functional theory (DFT). The most energetically favorable positions showed the adsorption energy values of −311.4 and − 157.8 kJ/mol using Ti- and Ni-doped fullerene, respectively. Atom in molecule (AIM) calculations revealed that the ionic bond is responsible for attaching dopamine molecule to each metallofullerene. The calculations were performed for water media, and the results were examined in detail from the perspective of quantum chemistry. Finally, electrical charge analysis, dipole moment, and molecular orbitals were depicted and investigated.

PSII-25 Detection of neurotransmitter-related molecules by untargeted metabolomic analysis of rumen fluid from monensin-treated temperate and tropically adapted beef cattle

Abstract The effect of an ionophore on the ruminal metabolome of temperate and tropically-adapted cattle was evaluated. For 21 d, five Angus, 5 Brahman, and 5 BrahmanXAngus F1 steers (264 kg BW) with 5 steers per pen within breedtype, were fed Tifton bermudagrass hay ad libitum, at the conclusion of which rumen fluid (100-to-250 mL) was collected and stored at -80°C (PRE). During a subsequent 21-d period, all steers were fed Tifton hay ad libitum plus a supplement (908 g corn, 217 g soybean meal, 60 g dried molasses) with monensin (220 mg·steer−1·d−1) individually, at the conclusion of which rumen fluid (100-to-250 mL) was collected and stored at -80°C (POST). Rumen fluid samples were processed for an untargeted analysis by LC/MS on Compound Discoverer v.3.1. Approximately 2,043 compounds were detected with 825 being annotated by ChemSpider and other databases, of which several were associated with four neurotransmitters; acetylcholine (ACh), dopamine, γ-aminobutyric acid (GABA), and serotonin. After monensin, several ACh-related molecules increased (P < 0.003) in Angus (POST:PRE ratio=7.906) but ACh decreased (P < 0.043) in the F1 (ratio= 0.391) steers. Dopamine and dopamine-related molecules decreased (P < 0.01) in Angus (ratio= 0.149) and F1 steers (ratio= 0.206) after monensin. No changes for rumen presence of ACh or dopamine occurred in Brahman steers after monensin. Multiple molecules related to GABA increased in Angus (P < 0.03) and Brahman (P < 0.02) steers. Serotonin-related molecules such as the metabolite 5-hydroxyindoleacetic acid (5-HIAA; ratio= 4.389) increased (P < 0.005) only in Brahman steers. The addition of monensin to the diet differentially altered the presence of neurotransmitter-related molecules in the rumen fluid of temperate and tropically adapted beef cattle. Further research regarding physiological roles of ruminal neurotransmitters and modulation by ionophores that affect ruminal microbiota is warranted. Support: USDA FAH

High quantum-yield carbon dots embedded metal-organic frameworks for selective and sensitive detection of dopamine

By embedding high quantum yield blue-emitting carbon dots (CDs) into zeolitic imidazolate framework-8 (ZIF-8), the luminescent metal-organic frameworks (LMOFs) - CDs@ZIF-8 composites were fabricated facilely and served as the fluorescent probe for selective and sensitive detection of dopamine (DA). In which the sustainable pores within ZIF-8 would not only provide a natural habitat for analyte but also can selectively capture and concentrate the DA molecules via the interaction between the analyte DA and the basic site of the frame. Meanwhile, the CDs can be served as the signal probes to transform chemical signals of the interaction between CDs and analytes into fluorescent signals. Thus, the as-synthesized CDs@ZIF-8 composites generate new sensing performance when compared with CDs. As a consequence, a wide concentration dynamic range of 0.1–200 μM with a low detection limit (LOD) 16.64 nM was favorably obtained for the CDs@ZIF-8 composites based detection method for DA. Besides, the practicality and viability of the fluorescent composites were also successfully verified via challenging the CDs@ZIF-8 based sensing method to detect DA in complicated serum and urine.

Upconversion-luminescent hydrogel optical probe for in situ dopamine monitoring

Dopamine (DA), as a neurotransmitter in human brain, plays a crucial role in reward motivation and motor control. An improper level of DA can be associated with neurological disorders such as schizophrenia and Parkinson’s disease. To quantify DA, optical DA sensors have emerged as an attractive platform due to their capability of high-precision and label-free measurement, and immunity to electromagnetic interference. However, the lack of selectivity, limited biocompatibility, and complex fabrication processes are challenges that hinder their clinical applications. Here, we report a soft and biocompatible luminescent hydrogel optical sensor capable of recognizing and quantifying DA with a simple and compact interrogation setup. The sensor is made of a hydrogel optical fiber (HOF) incorporated with upconversion nanoparticles (UCNPs). DA molecules are detected through the luminescence energy transfer (LET) between the UCNPs and the oxidation products of DA, while the light-guiding HOF enables both excitation and emission collection of the UCNPs. The hydrogel sensor provides an optical readout that shows a linear response up to 200 μmol/L with a detection limit as low as 83.6 nmol/L. Our results show that the UCNP-based hydrogel sensor holds great promise of serving as a soft and biocompatible probe for monitoring DA in situ.

Amperometric determination of dopamine based on an interface platform comprising tetra-substituted Zn2+ phthalocyanine film layer with embedment of reduced graphene oxide

The present study of ectrochemical zinc tetra [4-{2-[(E)-2-phenylethenyl]-1H-benzimidazol-1-yl}] phthalocyanine (Zn(II)TPEBiPc) film layer embedded reduced graphene oxide (rGO) based sensor was used for the determination of dopamine (DA) is reported. We present reduced graphene oxide with substituted zinc(II)phthalocyanine immobilized composite sensor in comparison with the phthalocyanine film layer onto a thin surface of the glassy carbon electrode (GCE). The composite hybrid material was prepared and characterized by spectral and electroanalytical spectroscopy. The substituted zinc(II)phthalocyanine with reduced graphene oxide composite modified electrode shows more competitive results in the detection of Dopamine molecule. The electrochemical behavior was investigated using cyclic voltammetry, differential pulse voltammetry. The amperometry sensor shows an excellent analytical performance in the concentration range 20 nM to 1.0 μM with detection limit (LOD) of 06 nM and sensitivity of 2.8784 μAμM–1 cm−2 respectively for GCE/rGO-Zn(II)TPEBiPc and GCE/Zn(II)TBPc. The rGO-Zn(II)TPEBiPc modified electrode exhibited better performance. Furthermore, the composite sensor demonstrated long-term storage stability, good repeatability and reproducibility. The practical applicability of the sensor has been assessed in pharmaceutical drugs. The illustrated method efficiently bridges the very good physicochemical properties of reduced graphene oxide with rich redox chemistry of Zinc(II)phthalocyanine.

2D-titanium carbide (MXene) based selective electrochemical sensor for simultaneous detection of ascorbic acid, dopamine and uric acid

Two-dimensional (2D) titanium carbide (MXene) nanosheets exhibited excellent conductivity, flexibility, high volumetric capacity, hydrophilic surface, thermal stability, etc. So, it has been exploited in various applications. Herein, we report synthesis of mixed phase 2D MXene as a catalytic material for simultaneous detection of important biomolecules such as ascorbic acid (AA), dopamine (DA) and uric acid (UA). Crystalline structure, surface morphology and elemental composition of mixed phase titanium carbide (Ti-C-Tx) MXene (Tx = –F, −OH, or −O) nanosheets were confirmed by X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), high-resolution scanning electron microscopy (HR-SEM) and Energy-dispersive X-ray spectroscopy (EDS) mapping analysis. Furthermore, Ti-C-Tx modified glassy carbon electrode (GCE) was prepared and its electrochemical properties are studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that Ti-C-Tx modified GCE (Ti-C-Tx/GCE) showed excellent electrocatalytic activity and separated oxidation peaks of important biomolecules such as AA (at 0.01 V), DA (at 0.21 V) and UA (at 0.33 V). Also, Ti-C-Tx/GCE sensor is enabled their simultaneous detection in physiological pH from 100 to 1000 μM for AA, 0.5–50 μM for DA and 0.5–4 μM & 100–1500 μM for UA. The limit of detection’s (LOD) was estimated as 4.6 μM, 0.06 μM and 0.075 μM for AA, DA and UA, respectively. Moreover, real sample analysis indicated that spiked AA, DA and UA can be determined accurately by Ti-C-Tx/GCE with the recovery ratio in the range between 100.5%–103% in human urine samples. The proposed Ti-C-Tx modified electrode exhibited good stability, selectivity and reproducibility as an electrochemical sensor for the detection of AA, DA and UA molecules.

Nitrogen-doped carbon nanotubes towards electrochemical sensing: Effect of synthesis temperature

Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized at various temperatures ranging from 650 to 950 °C, at 100 °C intervals, by chemical vapor deposition technique (CVD). The synthesized N-CNTs were employed as modifiers of glassy carbon paste electrodes (GCPE), which were further used as electrochemical sensors for the determination of dopamine (DA) and epinephrine (EP), two important catecholamines that display biological roles as neurotransmitters and hormones. The results revealed that electrodes modified with the N-CNTs synthesized at 650 °C (GCPE/N-CNT650) and 950 °C (GCPE/N-CNT950) presented better electrocatalytic activities and sensing capabilities than the others (GCPE/N-CNT750 and GCPE/N-CNT850). N-CNT950 had the highest graphitization and the highest powder conductivity, whereas N-CNT650 had the lowest graphitization and the lowest powder conductivity. However, both N-CNT950 and N-CNT650 had the highest nitrogen contents, 3.5 and 3.8 at.%, respectively, which probably enhanced their number of electroactive sites to interact with DA and EP molecules. This result is of high significance, because the use of the lowest temperature (650 °C) in the CVD process, yielded N-CNTs with improved electrocatalytic activity and less energy consumption during CVD.

RETRACTED: Construction of an excellent eco-friendly anti-corrosion system based on epoxy@Sm2O3-polydopamine biopolymer on the mild steel surface

Abstract Metals' surface treatment by chemical conversion coatings (CCs) is one of the most promising methods for improving the organic coatings adhesion strength as well as the corrosion protection properties on the metal substances. Since most of the recently used conventional CCs, i.e., chromate/phosphate-based ones, have undesired environmental problems; nowadays, several non-hazardous chemical treatment solutions based on the rare earth metals (REM), such as Sm-CC, are applied to improve the EC/steel substrate interfacial adhesion level and corrosion resistance of the organic coatings. Despite the eco-friendly nature of the REM-based CCs, they cannot provide high corrosion resistance due to some structural problems. Therefore, finding appropriate and bio-compatible approaches for improving Sm-CC properties is the new topic of research. In the present work, a green/non-toxic surface treatment approach has been used to improve the corrosion resistance of the epoxy coating (EC) on the mild steel (MS) surface. For this objective, a green anti-corrosion composite film based on samarium CC-poly-dopamine (SmPDA) was applied on the MS surface. PDA NPs were obtained by oxidation of dopamine molecules in two different ways, i.e., self-polymerization (PDA1) and oxidant-induced polymerization (PDA2). The deposited SmPDA film morphology and chemical structures were characterized by SEM/EDS and Raman spectroscopy methods. The EC corrosion protection performance evaluation was conducted by electrochemical impedance spectroscopy (EIS) and salt-spray test. Besides, the cathodic delamination (CD) rate and adhesion strength were measured. SEM/EDS analysis and Raman spectroscopy results revealed that nanostructure samarium and graphene-like PDA films were developed on the MS surface via SmPDA chemical modification. Moreover, EIS achievements demonstrated that the Rt values of the EC and scratched EC samples applied on the surface treated MS substrates are 37600 MΩ.cm2 and 90830 Ω.cm2, respectively. These values ​​are about 1375 and 19 fold more than the Rt of those applied on the un-treated MS coupons, respectively. The qualitative salt-spray test results illustrated that via SmPDA treatment, the less disbonding and blistering have occurred on the EC. The EC applied to SmPDA2 treated MS showed better corrosion protection performance than SmPDA1. In addition, by SmPDA2 surface treatment, the CD rate of the EC decreased about 92%, and its adhesion strength increased by about 118%.

Tunable electronic properties of TiO2 nanocrystals by in situ dopamine functionalization for planar perovskite solar cells

A high-quality TiO2 electron transport layer (ETL) should possess a good energy-level alignment, perfect electron mobility, and excellent charge extraction efficiency. Nevertheless, the poor conductivity of amorphous TiO2 film from low-temperature preparation is an inherent problem while the high-crystallined TiO2 after high-temperature sintering (>450 °C) limits its application in the low-cost fabrication and flexible substrates. Here, we develop a low-temperature approach to in situ functionalize TiO2 nanocrystals with dopamine molecules (DA-TiO2 NCs) in the synthesis of the nanocrystals through a non-aqueous sol-gel method. We systematically investigate the tunable electronic properties of TiO2 NCs with the variable DA modification and confirm that DA-TiO2 can tailor the energy level alignment as well as increase the charge-extraction capacity, substantially reducing charge accumulation between the TiO2 and perovskite layer. The in situ anchored amino groups (-NH3+) not only preferentially boost the in-plane growth of perovskite grains but also induce the red-shift absorption of perovskite via the strong electrostatic interaction with Br− ions. Based on the DA-TiO2 NCs ETLs, the power conversion efficiency of the fully ambient-processed planar FAxMA1-xPbBryI3-y PSCs is optimized to 19.45%.

Pt deposited on magnetic CoFe2O4 nanoparticles: Double enzyme-like activity, catalytic mechanism and fast colorimetric sensing of dopamine

Pt deposited on magnetic CoFe2O4 nanoparticles (Pt/CoFe2O4) were prepared successfully via a two-step method. Pt/CoFe2O4 possessed the superior intrinsic peroxidase-like performance together with a weak oxidase-like activity and fast catalyzed to oxidize the colorless 3, 3, 5, 5-tetramethylbenzidine (TMB) into a blue oxTMB, accompanied with a fast color reaction only in 15 s. Dopamine (DA) molecules attached with phenol hydroxyl groups, have some reducibility, resulting in consuming H2O2 and causing the blue fade of the TMB solution. The peroxidase-like performance of Pt/CoFe2O4 was consistent with the Michaelis-Menten kinetics. The catalytic mechanism of Pt/CoFe2O4 from the generated active species (O2− and OH) in the catalytic system was comprehensively investigated by florescent probe and ESR. Valuably, due to the strong magnetism, Pt/CoFe2O4 is easy to be separated from liquid mixtures avoiding of the secondary pollution in practical application. The method realizes simple, rapid (15 s), sensitive and visual detection of H2O2 and dopamine, which has potential application in real-time monitoring of small biomolecules.

Custom-made sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) nanocomposite membranes for vanadium redox flow battery applications

Sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) (SPVDF-co-HFP) based nanocomposite proton exchange membranes (PEM) are fabricated by simple solution casting method using polydopamine coated exfoliated molybdenum disulfide (PDA-MoS2) nanosheets as an alternative for Nafion® in vanadium redox flow batteries (VRFBs). PDA-MoS2 is synthesized by the etching of exfoliated MoS2 nanosheets with dopamine molecule by self-polymerization method. Various characteristic results clearly demonstrated that the incorporated PDA-MoS2 nanosheets homogeneously distributed into the SPVDF-co-HFP matrix and the presence of NH/NH2 group electrostatically interacts with SPVDF-co-HFP to form a strong acid-base pair and thus enhances the proton transport via Grotthuss type mechanism. Besides, the improvement in surface hydrophilicity provides the vehicle type conduction also. As a result, SPVDF-co-HFP/PM nanocomposite membranes showed higher proton conductivity in comparison with the pristine membrane. Especially SPVDF-co-HFP/PM-1 membrane demonstrated the excellent proton conductivity of 5.24 × 10−3 Scm−1 at 25 °C, lower vanadium-ion permeability of 1.05 × 10−8 cm2min−1 and highest membrane selectivity of 49.9 × 104 Scm−3min. On the other hand, vanadium-ion stability of the membrane increased by adding the PD-MoS2 content is attributed to their strong electrostatic attraction towards the polymer matrix. Overall results suggested that the SPVDF-co-HFP/PM-1 nanocomposite membrane is found to be a better alternative for commercially costly Nafion in VRFB applications.

Theoretical study of interaction of Fe13O8@Zn48O48 cluster with dopamine: Magnetic and optical properties

In this study, we modelled the interaction of Fe13O8 and Fe13O8@Zn48O48 (core@shell) cluster with a biologically active dopamine molecule using density functional theory. First, the electronic, magnetic and optical properties of core@shell, Fe13O8@Zn48O48 cluster investigated and compared with isolated Fe13O8 and Zn48O48 clusters. Fe13O8@Zn48O48 cluster is found to be energetically stable. For Fe13O8 and Fe13O8@Zn48O48 clusters have the net magnetic moment 42 μB. The decrease in HOMO-LUMO gap of core@shell cluster as compared to that of isolated clusters reflects the higher reactivity. The results of the site dependent interaction of Fe13O8 and Fe13O8@Zn48O48 clusters with dopamine molecule are presented. The interaction strength is determined in terms of the cluster-dopamine complex binding energy and found to be enhanced for core@shell cluster than the Fe13O8. Furthermore, the calculated results predict that in presence of dopamine, the magnetic moment of Fe13O8 and Fe13O8@Zn48O48 cluster remains unaffected. The analysis of optical spectra of core@shell indicates the obvious red shift compared to Zn48O48 clusters. The optical spectra of Fe13O8@Zn48O48-dopamine shows the higher oscillator strength as compared to that of Fe13O8-dopamine complex. Fe13O8-dopamine complex gives rise to more quenched oscillator strengths as compared to that of bare iron oxide cluster. These results indicate interesting magneto-optical behaviour, which can be useful for biomedical applications.

Controllable in situ fabrication of portable AuNP/mussel-inspired polydopamine molecularly imprinted SERS substrate for selective enrichment and recognition of phthalate plasticizers

A bio-inspired polydopamine (PDA) molecularly imprinted substrate is fabricated by one-step oxidative self-polymerization of dopamine and template molecules in weakly alkaline medium on screen-printed electrode (SPE). Through the catechol and amine groups on PDA surface, Au nanoparticles (AuNPs) can be easily anchored and growth on PDA-MIP coating, thereby forming a three-dimensional (3D) architecture. By adjusting the reaction conditions, the particle size and distribution of PDA and AuNPs can be well controlled. Benefiting from the “hot spots” generated by AuNPs and recognition sites produced by MIP, the AuNP/PDA-MIP nanocomposite can serve as excellent SERS substrate enabling selective enrichment and identification of phthalate plasticizers (PAEs). Using this substrate, an enhancement factor (EF) up to 1.70 × 107 for dimethyl phthalate (DMP) is achieved with a detection limit as low as 1.0 × 10−10 M. Furthermore, the rebinding kinetics study demonstrates that the portable MIP-based SERS substrate can promptly reach the adsorption equilibrium within 10 min. Thanks to its highly selectivity, the substrate exhibits low SERS interference for structural analogues benzyl butyl phthalate (BBP) and di(2-ethylhexyl) phthalate (DEHP). Besides, the straightforward SERS recognition of DMP in surface water, commercial bottled water and liquor samples are successfully realized using this substrate. This green and environmental-friendly fabrication method is promising for synthesis of highly performance sensing substrate, adsorbent or catalysts. Combining with portable Raman spectrometer, the fabricated MIP-based SERS substrate has exhibited a great potential as on-site device for environmental monitoring, food safety and homeland security.

Structural and Functional Tailoring of Melanin-Like Polydopamine Radical Scavengers

Melanin is a ubiquitous but poorly understood polymeric, dark brown to black pigment biomaterial found both in nature and by organic synthesis. Its structural heterogeneity and disordered covalent/...

A unifying theory for the pathoetiologic mechanism of tardive dyskinesia

IntroductionChronic treatment with dopamine D2 receptor antagonists has been proposed to lead to dopamine receptor supersensitivity. Frequently, this is conceptualized as upregulation or changes in the structure or function of the post-synaptic D2 receptor. However, the measured 1.4-fold increase in D2 receptor density and the lack of actual receptor supersensitivity are probably inadequate to explain outcomes such as tardive dyskinesia (TD) and dopamine supersensitivity psychosis. HypothesisRecent data suggest that TD may result from a combination of presynaptic, synaptic, and postsynaptic changes. DiscussionPresynaptic increase in dopamine release occurs when super-therapeutic blockade of postsynaptic D2 receptors results in excess synaptic unbound dopamine which ultimately ends up being reuptaken by the presynaptic neuron through the dopamine transporter. The increased availability of recycled dopamine results in higher vesicular dopamine concentrations. Since the quantity of neurotransmitter released (known as quanta) is determined by the number of presynaptic neurotransmitter vesicles, the increase in the number (concentration) of dopamine molecules in the vesicles results in a higher concentration of synaptic dopamine with successive depolarization events. Synaptic changes such as the appearance of perforated synapses which is an early step in new synapse formation have been shown in animal models of TD. Finally, postsynaptic increases in D2 receptor expression without demonstration of increased sensitivity or potency has been demonstrated. ConclusionTD likely develops due to changes across the synapse and terminology such as ‘dopamine receptor supersensitivity’ can be misleading. ‘Synaptic upregulation’ may be a more correct term.

Dopamine-functionalized graphene oxide as a high-performance material for biosensing

We describe a nanocomposite material for the electrochemical detection of β-nicotinamide adenine dinucleotide (NADH), a coenzyme involved in redox reactions of all living cells and in the detection of many organic species by electrochemical biosensors. The composite is made of nanosheets of electrochemically exfoliated graphene oxide (EGO) covalently functionalized with dopamine (DP) molecules. The EGODP material finally obtained is rich of 1,2-dihydroxyphenyl moieties and is able to detect NADH at a particular low potential value with higher sensitivity with respect to pristine EGO.To study the effectiveness of 1,2-dihydroxyphenyl moieties in inducing electrocatalytic oxidation of NADH, we combined standard voltammetric techniques with UV–Vis absorption spectroelectrochemistry, which allowed us to measure the variations in composition occurring at the electrode|solution interface, i.e. to measure the consumption rate of NADH.Spectroelectrochemical tests performed by polarising the electrode at a fixed potential value were finally used to compare the performance of EGODP with both EGO and EGO-DP blend (MIX) for the detection of NADH. The covalently functionalized EGO (EGODP) shows sensitivity to NADH up to 300 M−1, around 180 % and 140 % better than either pristine EGO or MIX, respectively.

Tripeptide-dopamine fluorescent hybrids: a coassembly-inspired antioxidative strategy.

Unmodified tripeptides and dopamine molecules can coassemble into fluorescent hybrid nanostructures, which break the intrinsic emission limit of both dopamines and peptides with an over-50 nm red-shift. We demonstrate that the coassembly method can effectively resist the oxidation of dopamine molecules, thus inhibiting their melanin pathway.

Surface area measurements of graphene and graphene oxide samples: Dopamine adsorption as a complement or alternative to methylene blue?

The possible use of dopamine, monitored spectroscopically, as a probe molecule for surface area measurements is investigated. Using high surface area carbon materials, including both graphene and graphene oxide (GO), the method is established as a complement or alternative to methylene blue or conventional N2 (BET) adsorption. The molecular reorientation (flat to vertical) of dopamine on the graphene and GO surface provides a direct indication of the monolayer coverage and the rapid adsorption (within 10 min to saturation) offers high convenience. The smaller dopamine molecule size and less self-repulsion compared to methylene blue can be considered to yield a more closely-packed surface coverage on the materials of interest. Especially for materials with complex morphologies and internal structures, the dopamine adsorption will therefore lead to a more ‘correct’ measurement.

Dipole moment effects in dopamine/N-doped-graphene systems

In the present work the effect exerted by N-doping on parameters characterizing dopamine adsorption on modified graphene substrate is theoretically studied. Moreover, an analysis of dipole moment properties of dopamine/N-doped-graphene system was performed in order to predict the feasibility of N-doped graphene system as a sensor material. Dopamine molecule anchors preferentially according to parallel modes of adsorption, stabilizing predominantly through dispersive interactions and showing very small atomic charges. On the other hand, the anchoring on sites with one nitrogen atom in the carbon monovacancy border is much more favored than on other sites, owing to non-covalent hydrogen bonding interactions. An analysis carried out about the modifications of polarization along the normal direction to the basal planes of graphene-based substrates, considering the most representative parallel modes of dopamine adsorption, indicated that N-doping enhances such dipole moment changes, compared with regular graphene, particularly when dopamine anchors on N-graphitic defects with four nitrogen atoms as impurities and N-pyridinic defects with one impurity nitrogen atom.