Adsorption Of Dopamine Research Articles

Uncovering efficient sensing properties of vanadium disulfide (VS2) nanosheets towards specific neurotransmitters: A DFT prospective

Designing efficient nanosensors based on ultrathin materials for the detection of neurotransmitters is crucial for biosensing applications. In this work, using spin-polarized density functional theory (DFT) calculations, structural, electronic, magnetic, and adsorption of the selected neurotransmitters, such as dopamine (DA) and histamine (HA), were investigated using light transition metals dichalcogenides, vanadium disulfide (VS2) nanosheets. It was revealed that DA and HA adsorbed relatively weakly on pristine (p-VS2) as well as single sulfur (S) Vacancy-induced (SV-VS2). However, the introduction of selected transition metals (TMs) dopants, such as cobalt (Co), iron (Fe), and nickel (Ni), significantly improved the adsorption of DA and HA. Among the studied systems, Ni-doped VS2 (Fe-doped VS2) exhibited the strongest adsorption toward DA (HA) with an adsorption energy of −2.00 (−1.28) eV, which is promising for practical sensing applications. Charge analysis revealed that both DA and HA acted as charge donors to the TMs-doped VS2. Upon DA/HA adsorptions, quantifiable variations were observed in the electronic structures and magnetic properties of TMs-doped VS2, which were studied through band structures, spin-polarized density of states, and work function calculations. Lastly, for the practical detection capabilities at diverse pressure and temperature settings, we employed the Langmuir adsorption model. It was found that TMs-doped VS2 detected DA and HA at concentrations ranging from tens of ppt to ppm levels, respectively. We strongly believe that our findings will contribute towards the development of highly effective nanosensors based on TMs-doped VS2 nanosheets for the detection of DA, and HA.

Flexible electrospun test strips functionalized with a graphene oxide/doxorubicin complex for dopamine detection

A novel flexible test strip has been developed for the selective and sensitive detection of dopamine (DA) using an electrospun polyacrylonitrile nanofiber membrane as a substrate and doxorubicin (DOX)-functionalized graphene oxide (GO) as a fluorescent ligand. Employing the Langmuir-Blodgett technique, the fluorescent probe of GO/DOX was controllably and flatly applied onto the surface of nanofiber membranes. The adsorption behavior of DA and DOX on GO in solution and on the surface of solid test strips has been investigated, respectively. The results showed that DA exhibited a higher affinity for GO, both in solution and on the surface of test strips, compared to DOX. Due to the competitive adsorption of DOX and DA onto GO, the addition of DA to the GO/DOX complex led to a significant fluorescence enhancement, attributed to the replacement of the GO-supported DOX with DA of a higher adsorption affinity to GO, enabling the detection of DA. This nanofiber-based method proves to be simple, sensitive, selective, and effectively minimizes interference from common biomolecules and small molecules in serum. Thus, this portable, cost-effective, and selective nanofiber strip holds great promise for early diagnosis of neurodegenerative diseases by measuring DA levels.

A high-performance wearable microneedle sensor based on a carboxylated carbon nanotube-carbon nanotube composite electrode for the simultaneous detection of uric acid and dopamine

Uric acid (UA) and dopamine (DA) are crucial biomarkers in the human body. However, there is limited research on detecting UA or DA in subcutaneous interstitial fluid (SISF), and no studies on their simultaneous detection in SISF. Here, we developed an electrochemical microneedle sensor based on the carboxylated carbon nanotubes/multiwalled carbon nanotubes (CCNT/CNT) composite electrode for the simultaneous detection of UA and DA. Highly carboxylated CCNT was prepared and mixed with CNT and organosilicon-modified acrylic resin to form the CCNT/CNT composite. The carboxyl functional groups of CCNT enhance the electrode’s adsorption of UA and DA, while CNT improves electron conduction. The sensor achieves a wide linear detection range for UA (5–600 μM) with high sensitivity (7.13 μA μM−1 cm−2) and linearity (R2 = 0.994), as well as a wide linear range for DA (2–200 μM) with high sensitivity (13.31 μA μM−1 cm−2) and linearity (R2 = 0.994). The sensor achieved simultaneous detection of DA and UA in artificial interstitial fluid (ISF), with sensitivity and linearity remaining nearly unchanged compared to that in PBS, and is not affected by high levels of ascorbic acid (AA). Finally, the sensor successfully detected changes in UA levels in ISF of subjects before and after alcohol consumption in vivo, demonstrating its practical application capabilities. This study presents a practical strategy for detecting human biomarkers characterized by low cost, easy fabrication and excellent performance of electrode materials, and a well-designed microneedle sensor preparation scheme, making it highly promising for further research extension.

Engineering FeOOH/Fe2O3@Carbon Interfaces With Biomass-Derived Carbon Nanodot/Iron Colloids for Efficient Redox-Modulated Dopamine Voltammetric Detection.

The Fe2+/Fe3+ redox couple is effective for voltammetric detection of trace dopamine (DA). However, achieving adequate concentrations with high electroactive surface area (ECSA), DA affinity, and fast interfacial charge transfer is challenging. Consequently, most reported Fe-based sensors have a high nanomolar range detection limit (LOD). Herein, we address these limitations by manipulating the phase and morphology of FeOOH/Fe2O3 heterojunctions anchored on sp2-carbon. FeOOH/Fe2O3 is synthesized by variable temperature aging of unique Fe5H9O15/Fe2O3@sp2-carbon colloidal nanoparticles, which form via chelation between biomass-derived carbon nanodots (CNDs) and Fe2+ ions. At 27 °C and 120 °C, Fe5H9O15/Fe2O3@sp2-carbon transforms into β-FeOOH/Fe2O3 nanoparticles and α-FeOOH/Fe2O3 nanosheet, respectively. The β-FeOOH/Fe2O3 interface exhibits higher eg orbital electron occupancy than α-FeOOH/Fe2O3, thereby facilitating oxygen adsorption and the generation of Fe2+/Fe3+ sites near the polarization potential of DA. This facilitates interfacial electron transfer between Fe3+ and DA. Moreover, its nanoparticle morphology enhances ECSA and DA adsorption compared to α-FeOOH/Fe2O3 nanosheets. With a LOD of ~3.11 nM, β-FeOOH/Fe2O3 surpasses the lower threshold in humans (~10 nM) and matches noble-metal sensors. Furthermore, it exhibits selective detection of DA over 10 biochemicals in urine. Therefore, the β-FeOOH/Fe2O3@sp2-C platform holds promise as a low-cost, easy-to-synthesize, and practical voltammetric DA monitor.

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.

Density functional theory analysis of iodine coadsorbed OH-copper phthalocyanine for dopamine sensing

Density functional theory (DFT) was employed to investigate the sensing behaviour of the neurotransmitter dopamine (DA) when interacting with OH-functionalised copper phthalocyanines (CuPcs) and copper phthalocyanines coadsorbed with iodine (CuIPc), both in gaseous and aqueous media. This study revealed that CuIPc demonstrates a superior capacity for detecting dopamine molecules compared to CuPc. Within these complexes, hydrogen bonds and coordination bonds were observed, with hydrogen bonds playing a pivotal role in the dopamine adsorption process. The enhanced electrical conductivity of the CuPc sheets after iodine adsorption, along with the high adsorption energy of the iodine-coadsorbed CuPc/DA complexes, underscores the significance of iodine in this context. Notably, the utilisation of iodine significantly enhances the sensing response for dopamine. In summary, copper phthalocyanine coadsorbed with iodine has emerged as a promising material for dopamine sensors, offering possibilities for further advancements in this field.

Mechanism of SDBS functionalized PPy enhancing the electrochemical sensitivity of SPGE to dopamine and uric acid: Experimental and DFT investigations

A novel approach to enhance the electrochemical sensitivity of screen-printed graphene electrode (SPGE) to dopamine (DA) and uric acid (UA) utilizing sodium dodecylbenzene sulfonate (SDBS) functionalized polypyrrole (PPy) is presented. The functionalized PPy nanosheets (SDBS/PPy) were synthesized via low-temperature polymerization. The introduced dodecylbenzene sulfonate (DBS-) facilitated the dispersion of functionalized PPy nanosheets, resulting in a notably increased specific surface area. DA and UA adsorption behavior on PPy and SDBS/PPy surface was investigated using density functional theory (DFT). The adsorption energy of DA and UA on SDBS/PPy was 0.15 eV and 0.05 eV higher than that on PPy. The adsorption ability of DA and UA was greatly improved after doping DBS- in PPy. The electrochemical response of SDBS/PPy-modified SPGE (SDBS/PPy/SPGE) to different concentrations of DA and UA was evaluated. Compared with SPGE, the oxidation current sensitivity of SDBS/PPy/SPGE to DA increased from 0.08 μA·μM−1 to 0.13 μA·μM−1, the oxidation current sensitivity of SDBS/PPy/SPGE to UA increased from 0.01 μA·μM−1 to 0.04 μA·μM−1. Electrochemical measurement demonstrated that PPy doping with DBS- caused a unique improvement in DA and UA performance of SPGE.

A DFT investigation for the Dopamine adsorption on the pristine and defected blue arsenic-phosphorus monolayers

In this study, the adsorption mechanism of the Dopamine (DA) molecule on the pristine and vacancy-defected b-AsP monolayers was investigated using DFT methods in order to reveal the drug carrying and sensing potential of b-AsP. For this purpose, the structural and electronic properties of many possible adsorption models on the pristine and defected b-AsP surfaces were calculated. According to the results, vacancy defects in the monolayer significantly increase the adsorption energy of the DA molecule. Additionally, the presence of defects triggers some important changes in the electronic and magnetic structure, revealing a prediction that b-AsP can be used as a sensor for DA-type molecules. The spin dependence of electronic properties also points out that these defected structures may be good candidates for some spintronic applications. The flattening of the DA molecule parallel to the surface in some models indicates the possibility that AsP could be a substrate candidate for molecule polymerization.

Dopamine adsorption on OH-functionalized metal phthalocyanines [MPc] (M = Mg, Co) in gas and solvent (water, ethanol) medium: A DFT study

The sensing behavior of the neurotransmitter dopamine (DA) on metal phthalocyanines (MPcs), specifically containing cobalt (CoPc) and magnesium (MgPc) in the presence of solvents (water and ethanol), was investigated using density functional theory (DFT). The outcomes of our study demonstrate that both Mg-Pc and Co-Pc exhibit a higher affinity towards dopamine molecules. The negative values of enthalpy and Gibbs free energy and entropy suggest that the adsorption process is exothermic, spontaneous, reversible, and thermodynamically favorable. Further, the charge transfer and conduction capacity of both Mg-Pc and Co-Pc indicate their potential as sensitive materials for dopamine biosensors. Furthermore, the high recovery time and sensitivity indicate both the materials perform exceptionally well in water, as dopamine sensors with slight edges favouring the DA/CoPc complex.

Development of functionalized polymeric nanomaterial by organosiliconic reagent for boronate affinity-based dopamine recognition

The dopamine neurotransmitter is mainly responsible for endocrine functions in our body. The increase in the level of dopamine in the human body leads to many disorders such as schizophrenia, uncontrollable tics, addiction, increased tension, desire to act excessively, and carelessness. Decreased levels of dopamine cause problems such as malnutrition, stress, insomnia, and the use of antidepressants. Recognition of dopamine is crucial for clinical experiments. Therefore, the development of recognition surfaces of dopamine is essential for isolation, purification, and determination processes. This study, it was aimed to produce a polymeric nanomaterial that can recognize dopamine. For this purpose, p(HEMA) polymer was synthesized with surfactant-free emulsion polymerization method and silanized by organosilicon reagent (3-aminopropyl) triethoxylsilane (APTES) and modified with phenylboronic acid (PBA). Characterization of the p(HEMA)-APTES-PBA nanopolymeric system for dopamine recognition was performed with Scanning Electron Microscope(SEM), Energy Dispersive Spectrometry (EDS), Fourier Transform Infrared Spectroscopy (FTIR), Zeta-size/zeta-potential analysis, surface area calculations. Dopamine affinity of the p(HEMA)-APTES-PBA was optimized in terms of pH, time, concentration, buffer concentration, and buffer type parameters. Dopamine adsorption of p(HEMA)-APTES-PBA nanopolymers was 4,8 times more than epinephrine in specificity analysis. After the 7 adsorption–desorption cycles, the desorption rate was found to be 74.8 %. The developed nanopolymeric system is a convenient method with high adsorption capacity which allows easy and rapid extraction, isolation, and purification of dopamine.

Activation of Glassy Carbon Surfaces by Alkaline Anodization Enhances Dopamine Adsorption and Electron‐Transfer Kinetics

AbstractSurface activation can increase the sensitivity of carbon electrodes for electrochemical detection of neurotransmitters, such as dopamine (DA). However, fully understanding the changes in DA behavior after electrode activation remains elusive. Herein, we use scanning electrochemical cell microscopy (SECCM) to investigate DA adsorption and electrochemistry on glassy carbon (GC) after anodization in alkaline media. Through localized microscale anodization to different extents (two distinct times and same potential), followed by spatially‐resolved SECCM, we achieve direct visualization of DA electrochemistry across unmodified and anodized GC regions, with complementary microscopy and spectroscopy unraveling the effects of co‐located carbon surface chemistry and structure. Our findings reveal that short anodization times (60 s) enhance DA adsorption, rapidly reaching nearly complete monolayer coverage. Longer anodization (300 s) induces further changes in electrochemical surface area so that although the DA surface concentration increased based on geometric area, it was smaller based on specific surface area. This work highlights that even small differences in surface properties after activation can significantly impact electrode performance for neurotransmitter sensing, and separating the individual contribution of chemical and topographical factors remains challenging. SECCM provides an excellent platform to assess activation methods in a high throughput format to help accelerate the discovery of optimal modified electrodes.

Ab-Initio study of dopamine, absorbic acid and uric acid adsorption on graphene and InBi monolayer with effects of charging and green’s function method

Dopamine (DA) is a crucial molecule for the central nervous system, and the ability to detect it in samples containing molecules such as Ascorbic Acid (AA) and Uric Acid (UA) could facilitate early diagnosis of related disorders. In this work, the interaction of DA, UA, and AA with InBi and Graphene (GR) monolayers under charging was investigated using Density Functional Theory (DFT) calculations with van der Waals (vdW) correction and nonequilibrium Green’s function method for the first time. According to our calculations, the most influential factor in the interaction was observed to arise from the [Formula: see text]–[Formula: see text] and [Formula: see text]–O interaction between molecules and surfaces. It has been concluded that InBi is a better adsorbent than GR for DA, AA, and UA, where the adsorption energies from the highest to lowest were found as [Formula: see text]. Furthermore, the charge transfers between molecules and surfaces were investigated, and it was demonstrated that the molecules on GR act as charge acceptors. In contrast, for InBi–molecule systems, electronic drift from molecules to the InBi surface was observed. The Partial Density of States (P-DOS) plots were examined, and the results were discussed in detail. The consequences of adding/removing charges to/from the systems were also examined, and it was shown that removing [Formula: see text][Formula: see text]e/cell from the GR–molecule systems effectively detected DA molecules from the others. Charging also broke the topological state of InBi, leading to semiconductor to metal, except for the [Formula: see text][Formula: see text]e/cell case. Finally, the changes in transmittance due to adsorption were simulated, and our results show that InBi is a possible candidate for DA sequencing biosensor applications compared to GR. The findings of this work provide a theoretical framework for the development and creation of highly precise biodevices and biosensors.

Adsorption characteristics of dopamine by activated carbon: Experimental and theoretical approach

In this work, we investigate the adsorption mechanism of dopamine (DP) drug using an activated carbon (AC) type through experimental and theoretical data. Experiment series were carried out at different initial values of solution pH, temperature, reaction time and initial drug concentration. The effect of protonation and deprotonation of DP molecule was also investigated. The equilibrium isotherm data were evaluated using the Dubinin-Radushkevich, Langmuir, Temkin and Freundlich models. Elovich, pseudo-first and pseudo-second order kinetic models were used to analyze kinetic data. Here we also used molecular dynamic (MD) simulation and DFT-based computational methods to reach information about the electronic properties of DP drug and its adsorption mechanism that have not been experimentally observed. Experimental results show that the Elovich kinetic model and Langmuir model best describe the adsorption phenomenon. In parallel, the experimental analysis revealed that the adsorption process is spontaneous and endothermic. Dopamine adsorption on AC occurs quickly and is pH and temperature-dependent. Frontier molecular orbital (FMO) energies for neutral, deprotonated and protonated forms of DP were determined and thoroughly explained. The basic medium significantly impacts DP drug adsorption behavior, which has the greatest adsorption energy when the pH is less than 12. It was found that DP adsorption occurs in a bidentate geometry by forming strong bonds between molecular oxygens and carbon atoms on the AC surface. Based on theoretical calculations interaction mechanisms of DP on the AC (001) surface were proposed.

Prussian Blue Analogue-Derived Iron Sulfide–Cobalt Sulfide Nanoparticle-Decorated Hollow Nitrogen-Doped Carbon Nanocubes for the Selective Electrochemical Detection of Dopamine

Hollow nanostructures have gained much attention in the electroanalytical field. This work describes the synthesis of CoS2–FeS2 nanoparticle-decorated hollow nitrogen-doped carbon nanocubes (CoS2–FeS2/HNCC) by a direct sulfidation of the Co–Fe Prussian blue analogue at a high temperature. By integrating dual-phase metal sulfides and a nitrogen-doped carbon matrix, this hollow nanocubic structure provides rich catalytic centers, enhanced conductivity, large surface area, and 3D-porous channels, which all contribute to the adsorption and catalysis of dopamine. The CoS2–FeS2/HNCC-modified glassy carbon electrode demonstrates excellent electrocatalytic activity for dopamine. Under the optimal parameters, the electrochemical sensor exhibits a wide detection range (0.05–90 μM), a low limit of detection (9.3 nM, S/N = 3), and a high sensitivity (91.6 μA μM–1 cm–2) along with excellent selectivity, reproducibility, reusability, and stability. This method has also been applied for the detection of dopamine in human urine samples and displays satisfactory results.

Plasmonic Refractive Index Sensor Enhanced with Chitosan/Au Bilayer Thin Film for Dopamine Detection.

Surface plasmonic sensors have received considerable attention, found extensive applications, and outperformed conventional optical sensors. In this work, biopolymer chitosan (CS) was used to prepare the bilayer structure (CS/Au) of a plasmonic refractive index sensor for dopamine (DA) detection. The sensing characteristics of the developed plasmonic sensor were evaluated. Increasing DA concentrations significantly shifted the SPR dips. The sensor exhibited stability and a refractive index sensitivity of 8.850°/RIU in the linear range 0.1 nM to 1 µM with a detection limit of 0.007 nM and affinity constant of 1.383 × 108 M-1. The refractive index and thickness of the CS/Au structure were measured simultaneously by fitting the obtained experimental findings to theoretical data based on Fresnel equations. The fitting yielded the refractive index values n (1.5350 ± 0.0001) and k (0.0150 ± 0.0001) for the CS layer contacting 0.1 nM of DA, and the thickness, d was (15.00 ± 0.01) nm. Then, both n and d values increased by increasing DA concentrations. In addition, the changes in the FTIR spectrum and the variations in sensor surface roughness and structure obtained by AFM analysis confirmed DA adsorption on the sensing layer. Based on these observations, CS/Au bilayer has enhanced the performance of this plasmonic sensor, which showed promising importance as a simple, low-cost, and reliable platform for DA sensing.

Improving electrochemical sensitivity of screen‐printed carbon electrodes by atmospheric pressure plasma jet treatment and electrochemical detection of dopamine

AbstractScreen‐printed carbon electrode (SPCE) has various crucial applications as biosensors. The binders used in the ink formulation of the SPCEs reduce the electron transfer from an electrolyte to it. In this study, we used an argon atmospheric pressure plasma jet (APPJ), a cost‐effective device, to modify the SPCE surface. Scanning electron microscopy and X‐ray photoelectron spectroscopy results show binder removal and oxidation of the APPJ‐treated SPCE surface. Due to binder removal and exposure of graphitic surface, the hydrophilicity of the APPJ‐treated SPCE surface enhances significantly. Moreover, oxidation makes the electrode more suitable for dopamine adsorption, resulting in enhanced sensitivity. The detection limit for the APPJ‐treated electrode is 1 μm, as observed in this study. Cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy have been performed on APPJ‐treated and untreated SPCEs.

A high-toughness anti-pollution polyethersulfone membrane for efficient separation of oil-in-water emulsions

Stable emulsion is the most difficult of all forms of oily wastewater to treat. Membrane separation technology has more advantages in solving related problems because of its high selectivity. The existence of hydroxyapatite containing more hydrophilic groups makes the membrane materials with high hydrophilicity obtained. In this work, hydroxyapatite was modified by strong adsorption of dopamine to prepare modified nanoparticles with good compatibility, which were more easily dispersed in the solution. Then the modified hydroxyapatite was introduced into the casting solution to avoid agglomeration and uneven distribution. The phase separation process was then completed by reverse thermal separation (RTIPS). After water flux and oil-water separation tests, high permeability (1515.46 L/m2 h, 14 times higher than the raw membranes) and high selectivity (99.80 % and 99.92 %) were obtained. At the same time, the membrane materials with the optimal conditions also achieved better performance in the cycle test. In addition, the bond between materials was improved due to the presence of hydroxyapatite, which ultimately makes the membrane materials more ductile and reduces the possibility of breakage.

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

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

Structure and Dynamics of Adsorbed Dopamine on Solvated Carbon Nanotubes and in a CNT Groove.

Advanced carbon microelectrodes, including many carbon-nanotube (CNT)-based electrodes, are being developed for the in vivo detection of neurotransmitters such as dopamine (DA). Our prior simulations of DA and dopamine-o-quinone (DOQ) on pristine, flat graphene showed rapid surface diffusion for all adsorbed species, but it is not known how CNT surfaces affect dopamine adsorption and surface diffusivity. In this work, we use molecular dynamics simulations to investigate the adsorbed structures and surface diffusion dynamics of DA and DOQ on CNTs of varying curvature and helicity. In addition, we study DA dynamics in a groove between two aligned CNTs to model the spatial constraints at the junctions within CNT assemblies. We find that the adsorbate diffusion on a solvated CNT surface depends upon curvature. However, this effect cannot be attributed to changes in the surface energy roughness because the lateral distributions of the molecular adsorbates are similar across curvatures, diffusivities on zigzag and armchair CNTs are indistinguishable, and the curvature dependence disappears in the absence of solvent. Instead, adsorbate diffusivities correlate with the vertical placement of the adsorbate’s moieties, its tilt angle, its orientation along the CNT axis, and the number of waters in its first hydration shell, all of which will influence its effective hydrodynamic radius. Finally, DA diffuses into and remains in the groove between a pair of aligned and solvated CNTs, enhancing diffusivity along the CNT axis. These first studies of surface diffusion on a CNT electrode surface are important for understanding the changes in diffusion dynamics of dopamine on nanostructured carbon electrode surfaces.

Theoretical insight on dopamine, ascorbic acid and uric acid adsorption on graphene as material for biosensors

In the present work, the interaction of dopamine (DA), ascorbic acid (AA) and uric acid (UA) molecules with graphene, with and without divacancies, has been theoretically studied within the framework of Density Functional Theory (DFT), in particular, paying attention on those surface properties relevant for field effect transistor (FET) and electrochemical biosensor applications. Several adsorption modes for these molecules were examined, and the main sources of adsorbate–substrate bonding were considered. The electric dipole moment for these molecules, when adsorbed, suffers in some cases large modifications due to conformational changes. The perpendicular component of dipole moment has a main molecular contribution molecule and another from the adsorbate–substrate polarization. The proposed reaction models of DA, AA and UA oxidations, show a good agreement with the oxidation potential ordering obtained in electrochemical experiments, i.e., UA > DA > AA. A spreading of reaction energies is observed due to the heterogeneity in adsorption modes.