PDA Films Research Articles

Microscale Metal Patterning on Any Substrate: Exploring the Potential of Poly(dopamine) Films in High Resolution, High Contrast, Conformal Lithography.

We have explored the potential of poly(dopamine) (PDA) thin films as versatile, high resolution conformal photoresists, using catalytic photoreduction of silver ions to micropattern the film. The combination of photosensitivity, biocompatibilty, and straightforward deposition under mild conditions into thin (∼45 nm) conformal coatings on nearly any material makes PDA films of interest in lithographic patterning on highly nonplanar geometries as well as on soft and biological materials where standard photoresists cannot be used. PDA and poly(norepinephrine) (PNE) films deposited with a standard autoxidation process were investigated along with PDA film deposited with a fast oxidation (FO) technique. Notably, we find that nonspecific deposition of silver off the lithographic pattern is strongly suppressed in PNE and nearly absent in FO-PDA films, which makes very high contrast lithography possible. We attribute this to a lower ratio of catechol to quinone moieties in these films compared to standard PDA films. PNE and FO-PDA films also exhibit smaller silver grain sizes (<40 nm) than standard PDA films, where grains are up to 200 nm in size. We demonstrate laser-scanning lithography patterns at 1.7 μm spatial resolution near the optical resolution limit of the experiment. Continuous silver films can readily be deposited on PDA, PNE, and FO-PDA with blue ( = 473 nm) and UV-A (375 nm) light, but not with green (515 nm) light. The UV light at lower intensities deposits silver several times faster than the blue light but also degrades the deposited silver at high light intensities. Silver films deposited in this way reach the percolation threshold at optical doses (at = 473 nm) in the range of 10-50 kJ/cm2, and SEM images of the films appear nearly pinhole free at comparable doses.

Uptake of Magnetite Nanoparticles on Polydopamine Films Deposited on Gold Surfaces: A Study by AFM and XPS.

Polydopamine has the capacity to adhere to a large variety of materials and this property offers the possibility to bind nanoparticles to solid surfaces. In this work, magnetite nanoparticles were deposited on gold substrates coated with polydopamine films. The aim of this work was to investigate the effects of the composition and morphology of the PDA layers on the sticking of magnetite nanoparticles. The polydopamine coating of gold surfaces was achieved by the oxidation of alkaline solutions of dopamine with various reaction times. The length of the reaction time to form PDA was expected to influence the composition and surface roughness of the PDA films. Magnetite nanoparticles were deposited on these polydopamine films by immersing the samples in aqueous dispersions of nanoparticles. The morphology at the nanometric scale and the composition of the surfaces before and after the deposition of magnetite nanoparticles were investigated by means of AFM and XPS. We found that the amount of magnetite nanoparticles on the surface did not vary monotonically with the reaction time of PDA formation, but it was at the minimum after 20 min of reaction. This behavior may be attributed to changes in the chemical composition of the coating layer with reaction time.

Reversible electronic modulation of polydiacetylenes for sensing in dynamic conditions

AbstractPolydiacetylenes (PDAs) are renowned for their exceptional optical properties intricately linked to the polymer conformation, yet they exhibit poor conductivity in their undoped state. Despite this drawback, PDAs have garnered significant interest as sensing materials owing to their ability to undergo colorimetric shifts from blue to red in response to external stimuli. However, the irreversible nature of this transition has limited their utility in dynamic environments. In this study, we augment the sensing capabilities of PDA films beyond their irreversible optical response by inducing a reversible electronic response through conductivity modulation. We investigated polyamine‐substituted PDAs with enriched hydrogen‐bonding interaction sites for the concurrent changes in colorimetry and conductivity upon acetic acid (AA) vapor exposure. Coated on a flexible interdigitated electrode (IDE), we monitor the conductivity change throughout the blue‐to‐red phase transition. Remarkably, AA molecules act as dopants, significantly amplifying the system's conductivity. Although the PDA coating retains its red phase at postdopant removal, the electronic response reverts to its initial state, demonstrating reversibility. This reversible electronic response offers invaluable real‐time insights into the specific triggers within dynamic environments, underscores the adaptability of responsive conjugated polymers, and highlights a promising avenue for their utilization in various sensing and monitoring applications.

Pyocyanin Biomarker Imprinted Polydopamine for Rapid and Simple Indirect Detection of Pseudomonas Aeruginosa

Abstract This paper reports the first successful preparation of pyocyanin (PYO)-imprinted polydopamine-modified glassy carbon electrodes (PDA-GCE) using potentiodynamic electropolymerization. The molecularly imprinted PDA films showed an enhanced current response to pyocyanin compared to non-imprinted polydopamine (NIP) on GCE. The MIP-GCE sensor exhibited improved sensitivity, offering a linear range of 10 µM to 100 µM (r2 = 0.993), with a low limit of detection (6.45 µM) and limit of quantitation (21.5 µM). The MIP-PDA/GCE is a sensitive, selective electrochemical sensor for PYO.

19 nm‐Thick Grafted‐To Polymer Brushes onto Optimized Poly(Dopamine)‐Coated Surfaces

AbstractGrafting‐to polymer coatings are typically easy to apply, but the thickness of such coatings is typically limited to a few nanometers, which may hamper applications. This paper presents a grafting‐to coating approach that yields polymer brushes up to an unprecedented thickness of 19 nm. To this aim, an easy‐to‐apply poly(dopamine) (PDA) primer layer is optimized. PDA is an easy‐to‐apply, but highly complex and chemically not well understood primer layer. In this study, PDA is deposited on silicon substrates using several deposition protocols (pH 4–7 in presence of NaIO4, and from Tris solution at pH 8.5). The modified surfaces are characterized using X‐ray photoelectron spectroscopy, spectroscopic ellipsometry, static water contact angle measurements, and atomic force microscopy. Subsequently, block copolymers of poly(glycidyl methacrylate)20‐b‐poly(N‐isopropylacrylamide)n are attached onto the PDA films using a grafting‐to approach. The results indicate that the conditions of PDA deposition and the PDA film thickness strongly influence the stability and grafting efficiency of the block copolymers. PDA films deposited at pH 7 with NaIO4 are stable, and yield the most efficient grafting, with grafted polymer layers as thick as 19 nm. Polymer layers of such thickness are rarely achieved using grafting‐to procedures from solution.

Highly sensitive capacitance-based nitrite sensing using polydopamine/AuNPs-modified screen-printed carbon electrode.

Regulatory bodies play a crucial role in establishing limits for food additives to ensure food quality and safety of food products, as excessive usage poses risks to consumers. In the context of processed animal-based foodstuffs, nitrite is commonly utilized as a means to slow down bacterial degradation. In this study, we have successfully leveraged the redox activity of an electrochemically deposited polydopamine (pDA) film onto gold nanoparticle (AuNP)-modified screen-printed electrodes (SPCE) to develop a sensitive and versatile methodology for the detection of nitrite using redox capacitance spectroscopy. By exploiting the interaction of the AuNPs/pDA electroactive interface with the target nitrite ions, we observed distinct changes in the redox distribution, subsequently leading to modifications in the associated redox capacitance. This alteration enables the successful detection of nitrite, exhibiting a linear response within the concentration range of 10 to 500 μM, with a limit of detection of 1.98 μM (S/N = 3). Furthermore, we applied the developed sensor to analyze nitrite levels in processed meats, yielding good recoveries. These results demonstrate the potential of our approach as a promising method for routine detection of ions.

Dopamine as a bioinspired adhesion promoter for the metallization of multi-responsive phase change microcapsules

This work reports on an environmentally friendly method to produce encapsulated phase change material with a thin nickel coating, applicable for heat conversion, storage and thermal management of heat-sensitive components and suitable for active heating by electromagnetic radiation. A critical issue for the metallization is the adhesion between the polymer capsule shell and the metal layer. Based on previous studies using the bio-molecule dopamine as adhesion promoter in composites and for plastics metallization, commercial paraffin microcapsules were coated with an ultrathin polydopamine film via a simple wet chemical process. Subsequently, a thin, uniform and compact nickel layer was produced by electroless metallization. The successful deposition of both layers was verified with a broad range of imaging and spectroscopic techniques. For the first time, surface-enhanced IR spectroscopy was used to study the deposition of ultrathin PDA films. The combination of SEM and energy-dispersive X-ray spectroscopy allowed resolving the spatial distribution of the elements Ni, N, and O in the MC shell. Electrically conducting paths in the Ni shell were verified by conductive AFM. Thermal analysis revealed that the coated microcapsules show a phase change enthalpy of approx. 170 J/g, suitable for thermal storage and management. Additionally, the nickel layer enhanced the thermal diffusivity of the microcapsule powders and enables a fast heating of the PCM microcapsules by microwave radiation, demonstrating the applicability of the metallized MCs for controlled heating applications.Graphical abstract

Polydopamine inner wall-coated hypodermic needle as microextraction device and electrospray emitter for the direct analysis of illicit drugs in oral fluid by ambient mass spectrometry

In this article, polydopamine inner wall-coated hypodermic needles (PDA-HNs) are evaluated as both microextraction devices and electrospray ionization (ESI) emitters for determining selected illicit drugs (methamphetamine, cocaine, and methadone) in oral fluid samples. The PDA film, located in the inner wall of the needle, allows the extraction of the analytes at alkaline pH, where their hydrophobic character is promoted. The extracted analytes are finally eluted in a methanol/formic acid mixture that also acts as ESI solution. For this purpose, a dedicated interface based on the connection of a PEEK tube with the needle hub is proposed. This assembly allows delivering the ESI solution by the infusion syringe pump of the mass spectrometer, providing an efficient ESI on the tip of the needle. The double use of the PDA-HNs as microextraction devices and ESI emitters permits the determination of the target analytes with limits of detection and precision (expressed as relative standard deviation) values better than 2.4 μg/L and 17.6%, respectively. The accuracy was evaluated by analyzing independent spiked oral fluid samples, obtaining good results.

Enhancement of Thermoplasmonic Neural Modulation Using a Gold Nanorod-Immobilized Polydopamine Film.

Photothermal neural activity inhibition has emerged as a minimally invasive neuromodulation technology with submillimeter precision. One of the techniques involves the utilization of plasmonic gold nanoparticles (AuNPs) to modulate neural activity by photothermal effects ("thermoplasmonics"). A surface modification technique is often required to integrate AuNPs onto the neural interface. Here, polydopamine (pDA), a multifunctional adhesive polymer with a wide light absorption spectrum, is introduced both as a primer layer for the immobilization of gold nanorods (GNRs) on the neural interface and as an additional photothermal agent by absorbing near-infrared red (NIR) lights for more efficient photothermal effects. First, the optical and photothermal properties of pDA as well as the characteristics of GNRs attached onto the pDA film are investigated for the optimized photothermal neural interface. Due to the covalent bonding between GNR surfaces and pDA, GNRs immobilized on pDA showed strong attachment onto the surface, yielding a more stable photothermal platform. Lastly, when photothermal neural stimulation was applied to the primary rat hippocampal neurons, the substrate with GNRs immobilized on the pDA film allowed more laser power-efficient photothermal neuromodulation as well as photothermal cell death. This study suggests the feasibility of using pDA as a surface modification material for developing a photothermal platform for the inhibition of neural activities.

Bioinspired Synthesis of ZnO@polydopamine/Au for Label-Free Photoelectrochemical Immunoassay of Amyloid-β Protein.

Amyloid-β protein (Aβ) is an important biomarker and plays a key role in the early stage of Alzheimer’s disease (AD). Here, an ultrasensitive photoelectrochemical (PEC) sensor based on ZnO@polydopamine/Au nanocomposites was constructed for quantitative detection of Aβ. In this sensing system, the ZnO nanorod array decorated with PDA films and gold nanoparticles (Au NPs) have excellent visible-light activity. The PDA film was used as a sensitizer for charge separation, and it also was used for antibody binding. Moreover, Au NPs were loaded on the surface of PDA film by in situ deposition, which further improved the charge transfer efficiency and the PEC activity in visible light due to the localized surface plasmon resonance effect of Au NPs. Therefore, in ZnO@polydopamine/Au nanocomposites, a significantly enhanced photocurrent response was obtained on this photoelectrode, which provides a good and reliable signal for early detection of AD. Under the optimized conditions, the PEC immunosensor displayed a wide linear range from 1 pg/mL to 100 ng/mL and a low detection limit of 0.26 pg/mL. In addition, this PEC immunosensor also presented good selectivity, stability, and reproducibility. This work may provide a promising point-of-care testing method toward advanced PEC immunoassays for AD biomarkers.

Nanoscale covalent organic framework for the low-temperature treatment of tumor growth and lung metastasis

Photothermal therapy (PTT) has shown promising applications in tumor therapies. However, due to laser-induced nonspecific heating and heat diffusion, high levels of hyperthermia (>50°C) in tumor tissues often increase the risk of cancer recurrence and metastasis, which causes the patient pain and destroys the surrounding normal cells and tissues. It is therefore important to develop photothermal strategies that have excellent therapeutic efficiencies under low-temperature conditions (≤45°C). In addition, the heterogeneity and complexity of tumors require the development of combinatorial antitumor treatments as the therapeutic efficiency of monomodal PTT is not currently sufficient. Herein, we have adopted a stepwise synthetic approach to develop a highly efficient multimodal therapeutic agent GA@PCOF@PDA by successive bonding defect functionalization (BDF), guest encapsulation, and surface modification steps. The covalently grafted porphyrinic photosensitizers (Por), encapsulated gambogic acid (GA), and surface-modified PDA film are independently responsible for photodynamic therapy (PDT), heat-shock protein 90 (HSP90) down-regulation and chemotherapy (CT), and low-temperature PTT. This proof-of-concept study illustrates an efficient, generalized approach to design high-performance covalent organic framework (COF)-based nanoagents that can be easily tailored to combine different therapeutic modalities for improved cancer theranostics at low temperatures.

Enhanced performance of Si/PEDOT: PSS heterojunction solar cells via multi-walled carbons coated with polydopamine

n-Si/PEDOT: PSS heterojunction solar cells are expected to be the alternative for photovoltaic technique for the potentially excellent power conversion efficiency and ease of processing. Herein, a multi-walled carbon nanotubes network coated with polydopamine (MWCNTs&PDA) was applied as an interlayer between silicon substrate and PEDOT:PSS film to enhance the performance of Si/PEDOT:PSS heterojunction device in this study. When the film was applied as an interlayer, the average reflectance of the device within the wavelength range 400–1000 nm dropped from 13.6 % to 8.33 %. The enhanced antireflection ability meant more photon-generated carriers were excited. The introduction of PDA reduced the contact angle from 84.5° to 47° on Si surface, and the minority carrier lifetime (τ) was 2.16 times increase. The high charge separation and improved junction effect of MWCNTs&PDA films incorporated between PEDOT:PSS and Si substrate result in advantageous networks of charge carriers, which is confirmed by the excellent open-circuit voltage (Voc) 637 mV, short-circuit current density (Jsc) Jsc 34.76 mA/cm2 and fill factor (FF) 56.41 %. The power conversion efficiency improved to 12.49 % when the MWCNTs&PDA film was incorporated. The achievements of this study indicated that the MWCNTs coated with polydopamine as an interlayer is a promising material for excellent performance Si/PEDOT:PSS heterojunction solar devices.

Spherical Polydopamine-Modified Carbon-Felt Cathode with an Active Indole Structure for Efficient Hydrogen Peroxide Electroproduction

As one of the most promising methods for H2O2 production, H2O2 electroproduction has received increasingly more attention. In this study, a spherical particle polydopamine (pDA) modified carbon felt (noted as ht-pDA/ACF) for H2O2 production was fabricated. At a constant potential of 2.0 V and pH of 1.0, the H2O2 production of the ht-pDA/ACF cathode reached 220 mg/L after 6 h of electrolyzing, compared to the 30 mg/L H2O2 production of raw carbon felt. Firstly, the spherical pDA exposes more active sites that are favorable to the 2e− ORR compared to pDA film. Secondly, the ring cleavage and re-cyclization of indole structure in the pDA during electrolyzing could form the radicals that act as the intermediate to the H2O2 formation. This research exhibits a low-cost method to modify carbon materials for effective H2O2 electroproduction. The ht-pDA/ACF cathode is promising for green H2O2 production and wastewater treatment.

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%.

A Clean and Tunable Mussel-Inspired Coating Technology by Enzymatic Deposition of Pseudo-Polydopamine (ψ-PDA) Thin Films from Tyramine.

The tyrosinase-catalyzed oxidation of tyramine, leading to the deposition of pseudo-polydopamine (ψ-PDA) thin films, is disclosed herein as a superior technology for surface functionalization and coating at a neutral pH and at a low substrate concentration, compared to the standard autoxidative PDA coating protocols. Smooth ψ-PDA thin films of variable thickness up to 87 nm were obtained from 1 mM tyramine by varying tyrosinase concentrations (5–100 U/mL). Compared to the PDA films obtained by the similar enzymatic oxidation of 1 mM dopamine with tyrosinase (T-PDA), ψ-PDA displayed slower deposition kinetics, lower water contact angles in the range of 11°–28°, denoting higher hydrophilicity but similar UV-vis absorption profiles, as well as electrochemical properties and antioxidant activity. MALDI-MS analysis indicated for ψ-PDA a well defined pattern of peaks compatible with dopamine tetrameric structures degraded to a variable extent. The exposure to a tyramine solution of tyrosinase-loaded alginate spheres, or films deposited on glass or polyethylene, resulted in a rapid gel-confined ψ-PDA formation with no leakage or darkening of the solution, allowing the complete recovery and re-utilization of the unreacted tyramine. In contrast, an abundant PDA precipitation outside the gel was observed with dopamine under the same conditions. The ψ-PDA deposition by tyrosinase-catalyzed tyramine oxidation is thus proposed as a controllable and low-waste technology for selective surface functionalization and coating or for clean eumelanin particle production.

Electrochemiluminescence behaviour of m-CNNS quenched by CeO2@PDA composites for sensitive detection of BNP

Heart failure is one of the common disabling states and serious illness among medical disorders that may lead to death. Brain natriuretic peptide (BNP) has been recognized as a new biomarker of outstanding prognosis-predictive capability for heart failure. In this work, modified carbon nitride nanosheets (m-CNNS) were used as the part of this sensing platform could generate stronger ECL emission and the CeO2@Polydopamine (CeO2@PDA) composites firstly worked as effective ECL signal quencher. Moreover, there was a suitable overlap between the absorption spectra of CeO2@PDA and ECL spectra of m-CNNS, causing the remarkable decline in ECL signal. In particular, a novel ECL-RET (electrochemiluminescence resonance energy transfer) system between m-CNNS as ECL donor while CeO2@PDA as ECL acceptor was established. CeO2@PDA composites were tightly linked to the secondary antibody (Ab2) via covalent bonding owing to the reactive quinones on the surface of the PDA film. The primary antibody (Ab1) and m-CNNS are connected via carboxylic groups of 1-pyrene butyric acid (Py-COOH, sodium salt) easily employing EDC/NHS activation, a common crosslinking approach. By employing K2S2O8 as a coreactant, ECL behaviour of m-CNNS was observed. Under optimal conditions, BNP concentration was detected in the range of 0.5 pg/mL–100 ng/mL with the detection limit of 0.01 pg/mL (S/N = 3). Featuring high sensitivity, wider linear range, excellent repeatability and selectivity, this ECL-RET immunosensor opened a novel path to realize a reliable sensitive detection of BNP, which may also be applied to determine other biomarkers. It was noteworthy that the proposed method was applied to real serum samples accompanied by good recovery range of 102.8–103.2%, indicating that the recommended method was of good accuracy for BNP detection.

Lysine and α-Aminoisobutyric Acid Conjugated Bioinspired Polydopamine Surfaces for the Enhanced Antibacterial Performance of the Foley Catheter.

Microbial adhesion onto implanted devices was reduced by the immobilization of amino acid lysine and α-aminoisobutyric acid to polydopamine functionalized PET films and Foley catheters. The polydopamine functionalized film was prepared by a dip coating method followed by incorporation of biocompatible amino acids to prepared films. The purpose of development of the modified pDA film is to improve the anti-biofouling and antibacterial activity of the film which can be successfully applied for medical devices. The characterization of modification was done using different techniques such as contact angle measurement, ATR-FTIR, FE-SEM, AFM, and XPS analysis. ATR-FTIR spectroscopy and XPS confirmed the successful amino modification of film. The anti-biofouling and antimicrobial behavior of the prepared surfaces were evaluated using the bacterial attachment and death assay. The resulting coatings repelled bacterial cell attachment and killed clinically applicable Gram-negative and Gram-positive strains. The developed coatings were applied to the Foley catheters to study the antibacterial activity by the log reduction method. The results demonstrate that tested amino acid-modified film increases the antibacterial activity of the catheters and can significantly help in reduction of nosocomial infections.

Mechanical Enhancement of Bioinspired Polydopamine Nanocoatings.

Inspired by the catechol and amine-rich adhesive proteins of mussels, polydopamine (pDA) has become one of the most widely employed methods for functionalizing material surfaces, powered in part by the versatility and simplicity of pDA film deposition that takes place spontaneously on objects immersed in an alkaline aqueous solution of dopamine monomer. Despite the widespread adoption of pDA as a multifunctional coating for surface modification, it exhibits poor mechanical performance. Attempts to modify the physical properties of pDA by incorporation of oxidizing agents, cross-linkers, or carbonization of the films at ultrahigh temperatures have been reported; however, improving mechanical properties with mild post-treatments without sacrificing the functionality and versatility of pDA remains a challenge. Here, we demonstrate thermal annealing at a moderate temperature (130 °C) as a facile route to enhance mechanical robustness of pDA coatings. Chemical spectroscopy, X-ray scattering, molecular force spectroscopy, and bulk mechanical analyses indicate that monomeric and oligomeric species undergo further polymerization during thermal annealing, leading to fundamental changes in molecular and bulk mechanical behavior of pDA. Considerable improvements in scratch resistance were noted in terms of both penetration depth (32% decrease) and residual depth (74% decrease) for the annealed pDA coating, indicating the enhanced ability of the annealed coating to resist mechanical deformations. Thermal annealing resulted in significant enhancement in the intermolecular and cohesive interactions between the chains in the pDA structure, attributed to cross-linking and increased entanglements, preventing desorption and detachment of the chains from the coating. Importantly, improvements in pDA mechanical performance through thermal annealing did not compromise the ability of pDA to support secondary coating reactions as evidenced by electroless deposition of a metal film adlayer on annealed pDA.

Antibacterial Performance of a Mussel-Inspired Polydopamine-Treated Ag/Graphene Nanocomposite Material.

Graphene-based nanocomposites have attracted tremendous attention in recent years. In this study, a facile yet effective approach was developed to synthesize reduced graphene oxide and an Ag–graphene nanocomposite. The basic strategy involved in the preparation of reduced graphene oxide includes reducing graphene oxide with dopamine, followed by in situ syntheses of the Ag-PDA-reducing graphene oxide (RGO) nanocomposite through adding AgNO3 solution and a small amount of dopamine. The nanocomposite was characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), FTIR spectra, Raman spectra, ultraviolet-visible (UV-vis), and X-ray photoelectron spectroscopy (XPS), results indicated that a uniform PDA film is formed on the surface of the GO and GO is successfully reduced. Besides, the in situ synthesized Ag nanoparticles (AgNPs) were evenly distributed on the RGO surface. To investigate antibacterial properties Ag-PDA-RGO, different dosages were selected for evaluating the antibacterial activity against Gram-positive bacteria Staphylococcus aureus and Gram-negative bacteria Escherichia coli. The Ag-PDA-RGO nanocomposites displayed excellent antibacterial property. The antibacterial ratio reached 99.9% against S. aureus and 90.9% against E. coli when the dosage of 100 mg/L Ag-PDA-RGO nanocomposites was 100 μL. The novel Ag-PDA-RGO nanocomposite prepared by a facile yet effective, environmentally friendly, and low-cost method holds great promise in a wide range of modern biomedical applications.

Hexamethylenediamine-Mediated Polydopamine Film Deposition: Inhibition by Resorcinol as a Strategy for Mapping Quinone Targeting Mechanisms.

Hexamethylenediamine (HMDA) and other long chain aliphatic diamines can induce substrate-independent polymer film deposition from dopamine and several other catechols substrates at relatively low concentrations, however the mechanism of the diamine-promoted effect has remained little understood. Herein, we report data indicating that: (a) film deposition from 1 mM HMDA and dopamine is not affected by chemical oxidation with periodate but is markedly inhibited by resorcinol, which also prevents PDA film formation at 10 mM monomer concentration in the absence of HMDA; (b) N-acetylation of HMDA completely inhibits the effect on PDA film formation; (c) HMDA enables surface functionalization with 1 mM 5,6-dihydroxyindole (DHI) polymerization at pH 9.0 in a resorcinol-inhibitable manner. Structural investigation of the polymers produced from dopamine and DHI in the presence of HMDA using solid state 13C and 15N NMR and MALDI-MS suggested formation of covalent cross linked structures. It is concluded that HMDA enhances polydopamine adhesion by acting both on dopamine quinone and downstream, e.g., via covalent coupling with DHI. These results provide new insights into the mechanisms of PDA adhesion and disclose resorcinol as a new potent tool for targeting/mapping quinone intermediates and for controlling polymer growth.