PDA Films Research Articles

In vitro and in vivo anti-corrosion properties and bio-compatibility of 5β-TCP/Mg-3Zn scaffold coated with dopamine-gelatin composite

Mg alloy is an excellent biomaterial due to its ideal mechanical properties, bio-degradability and bio-compatibility. However, high local pH, subcutaneous gas pockets and compromised mechanical integrity caused by high degradation rate restrict its clinical application. The purpose of this study is to improve the anti-corrosion properties of 5β-TCP/Mg-3Zn scaffold using poly-dopamine/gelatin (PDA/G) composite coatings through an easy, convenient and cheap dipping method. We found that dopamine (C8H11NO2) slowed down corrosion by forming thin, surface-adherent PDA films on the scaffold surface. Gelatin formed a dense organic membrane cover on the rough surface which results from the processing of PDA membrane to seal the macrocracks and protect it from corrosion. As compared to bare 5β-TCP/Mg-3Zn alloy, electrochemical tests showed that the corrosion current density (icorr) decreased from 5.24 × 10−3 A/cm2 to 1.41 × 10−3 A/cm2, indicating improved anti-corrosion properties. The soaking results indicated that pH values of immersion solution, as well as the volumes of released hydrogen, were 9.83 and 9.25, 20 mL and 15 mL for bare and coated alloy, respectively, indicating that the composite coating enhanced the anti-corrosion property of Mg alloy. The in vitro cytotoxicity test showed that 10%, 50% and 100% concentration of the immersion solution were safe for cellular applications. The in vivo test showed that serum magnesium concentration for PDA/G was lower than that of the bare sample. In addition, the materials and coatings were nontoxic to muscle and other vital organs, including heart, liver, kidney, and muscle. Moreover, the PDA/G composite coating showed a better anti-corrosion property in vivo than the bare sample and displayed a longer service time. These results suggest that coating of 5β-TCP/Mg-3Zn scaffold with PDA/G slowed down the corrosion rate of Mg alloy.

Dopamine-based molecularly imprinted polymers for the recognition of biomacromolecules

Compared to natural antibodies or receptors, molecularly imprinted polymers (MIPs) have shown advantages of easy preparation, low cost, high stability and reusability. MIPs have been widely used in the fields of separation, chemical sensing, drug delivery and biocatalysis. The development of new imprinting methods such as surface imprinting, epitope imprinting, post-imprinting modification have promoted the synthesis and application of MIPs against biomacromolecules. Despite of the success, it remains a challenge to prepare MIPs with high affinity and specificity to the target proteins because the options of water-soluble monomers are very limited and the protein’s conformation is liable to change during the polymerization reaction. The majority of protein imprinting studies employ the five most common monomers: acrylamide (AAm), methacrylic acid (MAA), aminophenylboronic acid (APBA), acrylic acid (AA), and N-isopropylacrylamide (NiPAAm) and the two frequently used crosslinkers, methylenebisacrylamide (MBA) and ethylene glycol dimethacrylate (EGDMA) for preparation of protein imprinted polymers. In recent years, dopamine (DA) has been frequently used for surface modification as it can self-polymerize in alkaline medium at room temperature and generate polydopamine (pDA) films that can adhere onto almost all inorganic and organic surfaces with good biocompatibility. Thus, DA emerged as an appropriate monomer as well as a crosslinker for various imprinting reactions. In this review, we highlighted the recent advances in design and fabrication of DA-based MIPs for various biomacromolecules, including proteins, glycoproteins, bacteria or virus, with focus on protein imprinted polymers. First, we briefly introduced the DA self-polymerization reaction and the reported mechanisms for pDA formation. It is generally accepted that the initial driving force for the formation of pDA is the oxidation of DA to DA-indole by dissolved oxygen in an alkaline solution. Then, we summarized the recent work that employs common protein such as human/bovine serum albumin (HSA/BSA), lysozyme (Lyz), hemoglobin, trypsin and immunoglobulin (IgG) as the imprinting templates. These MIPs were mainly used for separation and purification of the template proteins. We also introduced the combination of protein imprinting with quartz crystal microbalance (QCM), cyclic voltammetry (CV), surface plasmon resonance (SPR) and mass spectroscopy (MS) for recognition and detection of the target proteins. In the following part, we summarized the strategies developed for imprinting of glycoproteins, most of which took advantage of boron affinity reaction or lectin-sugar interaction to improve the affinity and selectivity of the resultant MIPs. Then, we introduced recent work on imprinting of microorganisms such as viruses and bacteria, in which surface imprinting technique and potential analysis or chemiluminescence (ECL) technique are combined to construct biosensors that can selectively detect target species with high sensitivity. In addition, we also introduced the synthesis of a bio-inspired virus imprinted polymer and its application for prevention of viral infections. The techniques which were used for characterizing the properties of the MIP materials, e.g., adsorption capacity, imprinting factor and selectivity, as well as the proposed theoretical model were also mentioned in the review. Finally, we discussed current challenges and possible solutions for using DA as a monomer to prepare MIPs for biomacromolecules. We believe that the interactions between the intermediate products during dopamine polymerization and the template proteins deserve further investigation, as it may provide more possibilities to modulate the binding properties of the obtained MIPs.

Thermal Decomposition Enhancement of HMX by Bonding with TiO2 Nanoparticles

AbstractThe appropriate structure and properties of a composite material, including the morphology, particle size, and bond strength, are very important for its performance and practical applications. The energetic material HMX (C4H8N8O8, cyclotetramethylenetetranitramine) is typically mixed with nanocatalysts to improve its thermal decomposition, which is advantageous for its detonation performance in practical applications. Inspired by the bioadhesion of mussels, a HMX@PDA@TiO2 (HMX first coated with PDA film and second coated with TiO2 nanoparticles) composite was developed in this study to greatly advance the thermal decomposition temperatures. A simple stirring process was used to prepare the composite from HMX and TiO2 nanoparticles under dopamine solutions with different pH values. Nanocatalyst TiO2 nanoparticles were anchored on the surface of HMX by reacting with the dopamine and polydopamine coatings. Compared with other reference samples, the thermal behavior of the obtained composite showed that the starting decomposition temperature was lower, at approximately 60 °C, and that the decomposition peak decreased by 35 °C, indicating that the composite properties should have great effects on the thermal performance of the materials. The findings offer a valuable composite preparation method to enhance the thermal behavior and the effect of the catalyst on the composite via bonding effects.

Antibiofilm Nitric Oxide-Releasing Polydopamine Coatings.

The growing number of patient morbidity related to nosocomial infections has placed an importance on the development of new antibacterial coatings for medical devices. Here, we utilize the versatile adhesion property of polydopamine (pDA) to design an antibacterial coating that possesses low-fouling and nitric oxide (NO)-releasing capabilities. To demonstrate this, glass substrates were functionalized with pDA via immersion in alkaline aqueous solution containing dopamine, followed by grafting of low-fouling polymer (poly(ethylene glycol) (PEG)) via Michael addition and subsequent formation of N-diazeniumdiolate functionalities (NO precursors) by purging with NO gas. X-ray photoelectron spectroscopy confirmed the successful grafting of PEG and formation of N-diazeniumdiolate on polydopamine-coated substrates. NO release from the coating was observed over 2 days, and NO loading is tunable by the pDA film thickness. The antibacterial efficiency of the coatings was assessed using Gram-negative Pseudomonas aeruginosa (i.e., wild-type PAO1 and multidrug-resistant PA37) and Gram-positive Staphylococcus aureus (ATCC 29213). The NO-releasing PEGylated pDA film inhibited biofilm attachment by 96 and 70% after exposure to bacterial culture solution for 24 and 36 h, respectively. In contrast, films that do not contain NO failed to prevent biofilm formation on the surfaces at these time points. Furthermore, this coating also showed 99.9, 97, and 99% killing efficiencies against surface-attached PAO1, PA37, and S. aureus bacteria. Overall, the combination of low-fouling PEG and antibacterial activity of NO in pDA films makes this coating a potential therapeutic option to inhibit biofilm formation on medical devices.

Direct Evidence for the Polymeric Nature of Polydopamine

AbstractInspired by the adhesive proteins of mussels, polydopamine (pDA) has emerged as one of the most widely employed materials for surface functionalization. Despite numerous attempts at characterization, little consensus has emerged regarding whether pDA is a covalent polymer or a noncovalent aggregate of low molecular weight species. Here, we employed single‐molecule force spectroscopy (SMFS) to characterize pDA films. Retraction of a pDA‐coated cantilever from an oxide surface shows the characteristic features of a polymer with contour lengths of up to 200 nm. pDA polymers are generally weakly bound to the surface through much of their contour length, with occasional “sticky” points. Our findings represent the first direct evidence for the polymeric nature of pDA and provide a foundation upon which to better understand and tailor its physicochemical properties.

Direct Evidence for the Polymeric Nature of Polydopamine.

Inspired by the adhesive proteins of mussels, polydopamine (pDA) has emerged as one of the most widely employed materials for surface functionalization. Despite numerous attempts at characterization, little consensus has emerged regarding whether pDA is a covalent polymer or a noncovalent aggregate of low molecular weight species. Here, we employed single-molecule force spectroscopy (SMFS) to characterize pDA films. Retraction of a pDA-coated cantilever from an oxide surface shows the characteristic features of a polymer with contour lengths of up to 200 nm. pDA polymers are generally weakly bound to the surface through much of their contour length, with occasional "sticky" points. Our findings represent the first direct evidence for the polymeric nature of pDA and provide a foundation upon which to better understand and tailor its physicochemical properties.

Development of Antimicrobial and Antifouling Universal Coating via Rapid Deposition of Polydopamine and Zwitterionization.

Biomaterials-associated infections (BAIs) are related to bacterial colonization on medical devices, which lead to a serious medical burden, such as increased healthcare cost, prolonged hospital stays, and high mortality and morbidity. To reduce the risk of infections, in this work, a new approach which makes use of a bioinspired coating with dual antimicrobial and antifouling functions was developed through rapid deposition of functional polydopamine (pDA) and antimicrobial copper ions, and subsequent conjugation of zwitterionic antifouling sulfobetaine (SB) moieties by the aza-Michael addition reaction. pDA permits surface-independent versatile functionalization on a variety of substrates, such as TiO2, SiO2, gold, plastics, and Nitinol alloy. The characterizations for chemical elemental compositions and hydrophilicity by X-ray photoelectron spectroscopy and contact angle goniometer, respectively, indicating the successful grafting of SB moieties and the presence of copper ions in the pDA adlayers. Ellipsometric thicknesses of the thin films were followed to monitor the formation of pDA films and the changes after the post conjugation. UV-vis spectroscopy and inductively coupled plasma-mass spectrometry revealed the coordination structure of catechol-Cu, and release profile of Cu2+ from the constructed functional coatings. The superhydrophilic and charge-balanced SB interface allowed effective resistance of bacterial adsorption. Intriguingly, we scrutinized that the release of bactericidal copper ions enables killing the residual amount of adsorbed bacteria. Moreover, viability tests for fibroblast cells indicate the excellent biocompatibility of the developed medical coatings. For real-world implementation, the antifouling and antimicrobial coatings were applied on commercially available silicone-based urinary catheters, and the existence of bacteria was evaluated by using the plate-counting assay. The results showed an undetectable level of living bacteria. Consequently, the dual functional medical coating offers a promising approach to eliminate BAIs for practical applications.

In Situ Structural Elucidation and Selective Pb2+ Ion Recognition of Polydopamine Film Formed by Controlled Electrochemical Oxidation of Dopamine.

Owing to the versatility and biocompatibility, a self-polymerized DA (in the presence of air at pH 8.5 tris buffer solution) as a polydopamine (pDA) film has been used for a variety of applications. Indeed, instability under electrified condition (serious surface-fouling) and structural ambiguity of the pDA have been found to be unresolved problems. Previously, pDA films (has hygroscopic and insoluble property) prepared by various controlled chemical oxidation methods have been examined for the structural analysis using ex situ solid-state NMR and mass spectroscopic techniques. In this work, a new in situ approach has been introduced using an electrochemical quartz crystal microbalance (EQCM) technique for the improved structural elucidation of pDA that has been formed by a controlled electrochemical oxidation of DA on a carboxylic acid functionalized multiwalled carbon nanotube-Nafion (cationic perfluoro polymer) modified electrode (f-MWCNT-Nf) system in pH 7 phosphate buffer solution. Key intermediates like 5,6-dihydroxy indole (DHI; 150.7 g mol-1), dopamine (154.1 g mol-1), Na+, PO42-, and polymeric product of high molecular weight, 2475 g mol-1, have been trapped on f-MWCNT-Nf surface via π-π (sp2 carbon of MWCNT and aromatic e-s), covalent (amide-II bonding, minimal), hydrogen, and ionic bonding and identified its molecular weights successfully. The new pDA film system showed well-defined peaks at E°' = 0.25 V and -0.350 vs Ag/AgCl corresponding to the surface-confined dopamine/dopamine quinone and DHI/5,6-indolequinone redox transitions without any surface-fouling complication. As an electroanalytical application of pDA, selective recognition of Pb2+ ion via {(pDA)-hydroquinone-Pb0} complexation with detection limit (signal-to-noise ratio = 3) 840 part-per-trillion has been demonstrated.

Electrochemiluminescence immunosensor based on quenching effect of SiO2@PDA on SnO2/rGO/Au NPs-luminol for insulin detection

A sandwich quenching electrochemiluminescence (ECL) immunosensor was constructed for insulin detection. In this work, the SnO2/reduced graphene oxide/gold nanoparticles (SnO2/rGO/Au NPs) nanocomposites combined with luminol (Lu) were utilized to construct the base of the immunosensor, and the SiO2@Polydopamine (SiO2@PDA) nanomaterials acted as efficient ECL signal quencher. SiO2@PDA was firmly anchored secondary antibody (Ab2) by covalent bonding due to the reactive quinones at the surface of PDA film. Au NPs which functionalized SnO2/rGO were acted as the bridge to incubate with primary antibody (Ab1) by Au-N bond and simultaneously enhanced the sensitivity of immunosensor. In addition, we used the luminol-O2 system to obtain more stable ECL signal. Under the optimal experimental conditions, a reliable determination of insulin was realized within a linear range of 0.0001–50 ng/mL and with a detection limit of 26 fg/mL (S/N = 3). Therefore, the ECL immunosensor exhibited good sensitivity, acceptable selectivity and high repeatability. Meanwhile, the proposed sandwich quenching ECL immunosensor was also evaluated by detecting insulin in real samples, this immunosensor has potential application value in insulin detection.

Synthesis of superhydrophobic polydopamine-Ag microbowl/nanoparticle array substrates for highly sensitive, durable and reproducible surface-enhanced Raman scattering detection

Surface-enhanced Raman scattering (SERS) sensor allows for fingerprinting and label-free molecular detection with a high sensitivity, but the simple fabrication of SERS active substrates with a well-control over the SERS performance, e.g. an ultra-high sensitivity, superior reproducibility and long-term stability remain a great challenge. Here, we introduce an easy strategy for synthesizing polydopamine-Ag microbowl/nanoparticle array (PDA-Ag MNA) substrates with a tunable superhydrophobic surface, applicable for ultra-highly sensitive SERS detection. First, the periodically dented PDA films are prepared by polymerizing dopamine onto 2D polystyrene colloidal crystals formed at the liquid/air interface, and followed with an in-situ reduction of Ag ions to Ag nanoparticles after removing polystyrene. The surface morphology, i.e. microbowl/nanoparticle structure, is well-controlled, therefore, allowing that the SERS activity of the substrate is under control. Inspired by the superhydrophobic hierarchical surface of the rose petals, this analogous MNA surface is subsequently endowed to be superhydrophobic. This way, the SERS detection of ultra-dilute solute (10−14M) can be achieved by concentrating analytes within a localized region. Moreover, this substrate also shows a superior reproducibility in result and durability in use. This strategy exhibits a realistic paradigm for further improving the sensitivity of the SERS technique.

Preparation of polydopamine-coated graphene oxide/Fe3O4 imprinted nanoparticles for selective removal of fluoroquinolone antibiotics in water

Antibiotics in water have recently caused increasing concerns for public health and ecological environments. In this work, we demonstrated polydopamine-coated graphene oxide/Fe3O4 (PDA@GO/Fe3O4) imprinted nanoparticles coupled with magnetic separation for fast and selective removal of fluoroquinolone antibiotics in water. The nanoparticles were prepared by the self-polymerization of dopamine using sarafloxacin as a template. The imprinted PDA film of 10~20 nm uniformly covered the surface of GO/Fe3O4 providing selective binding sites. The nanoparticles showed rapid binding and a large capacity (70.9 mg/g). The adsorption data fitted well the Langmuir and pseudo-second order kinetic equations. The nanoparticles could be easily separated by a magnet following the adsorption and then regenerated by simple washing for repetitive adsorptions. The nanoparticles were successfully used for the removal of fluoroquinolone antibiotics in seawater, with removal efficiencies of more than 95%. The proposed strategy has potentials for efficient removal of antibiotics in environmental water.

A flexible transparent colorimetric wrist strap sensor.

A flexible, transparent, and portable wrist strap sensor device has been well developed from a hierarchical polydiacetylene/MoS2 nanocomposite (PDA/MoS2) film. MoS2 with a nanoflake structure and chelation ability acts as a supporter for PDA films to enhance the porosity as well as the transparency of films, which increases the sensitivity, selectivity, and application potential of a PDA sensor. The PDA/MoS2 film sensor shows a linear detection range for N,N-dimethylformamide (DMF) vapor from 0.01% to 4% with a visible blue to red color change detected by the naked eye, which is more sensitive than other organic vapors. Exploiting the high transparency, vivid color change, remarkable flexibility and reliability, a wearable wrist strap sensor device with visible DMF sensing ability is fabricated based on PDA/MoS2 films, indicating their great potential for smart wearable devices.

Determination of the extinction coefficient of “polydopamine” films obtained by using NaIO4 as the oxidant

Understanding the molecular origin of the broadband optical absorption spectrum of eumelanin in solution remains a challenging task both from an experimental and a theoretical point of view. Eumelanin like materials can now be deposited on solid surfaces from dopamine solutions in oxidizing conditions allowing to easily functionalize the surface of almost all materials. The optical spectra of those “polydopamine” (PDA) films are close to the spectra of eumelanin but not identical. This article is a first attempt to quantify the optical absorption coefficient of PDA films which is made complicated by the uncertainty due to the need to know the density of this material. Using dissolved NaIO4 as the oxidant, at 0.5, 1 or 10 mM, the film thickness versus time does superimpose with the absorbance versus time curves suggesting intrinsic film homogeneity and allowing to calculate the product of the extinction coefficient by the concentration of PDA in the film.

Patterned Poly(dopamine) Films for Enhanced Cell Adhesion.

Engineered materials that promote cell adhesion and cell growth are important in tissue engineering and regenerative medicine. In this work, we produced poly(dopamine) (PDA) films with engineered patterns for improved cell adhesion. The patterned films were synthesized via the polymerization of dopamine at the air-water interface of a floating bed of spherical particles. Subsequent dissolution of the particles yielded free-standing PDA films with tunable geometrical patterns. Our results show that these patterned PDA films significantly enhance the adhesion of both cancer cells and stem cells, thus showing promise as substrates for cell attachment for various biomedical applications.

Functionalization of Polydopamine via the Aza-Michael Reaction for Antimicrobial Interfaces.

Polydopamine (pDA) coatings afford tremendous versatility due to their capabilities to provide substrate-independent functionalization with a wide range of amine- and thiol-containing molecules. In this work, we developed a new and facile conjugation approach to the formation of β-amino carbonyl linkages between pDA and acrylate/acrylamide molecules via the aza-Michael reaction. Sulfobetaine acrylamide (SBAA), sulfobetaine methacrylate (SBMA), and poly(ethylene glycol) methacrylate (PEGMA) were employed to graft onto pDA films, giving rise to formation of antifouling coatings. Because of the universal adhesive property of pDA, the coating strategy was applied to different substrates, including TiO2, gold, SiO2, Nitinol alloy, polystyrene, and poly(dimethylsiloxane). The variation of surface chemistry and surface wettability upon pDA modification and subsequent conjugation was monitored with X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Antifouling properties of coatings were challenged by three common Gram-negative and Gram-positive bacteria. Cytocompatibility of the coatings with NIH-3T3 fibroblasts was accessed using MTT assay. The results showed that pDA coatings grafted with SBAA exhibited superhydrophilicity and excellent fouling resistance likely due to the high chemical reactivity of acrylamide, leading to high grafting density. In addition, dual functional coatings containing passive and active antibacterial components were constructed through the in situ deposition of antimicrobial agent, silver nanoparticles, in pDA, followed by the grafting of SBAA for bacterial repellence. The composite coatings allowed reducing adsorption of E.coli by >95%, while killing attached bacteria by up to 98% upon the releasing of Ag(+) ions as measured by inductively coupled plasma mass spectrometry. Consequently, this work paves a new avenue to the grafting strategy to engineer pDA and to the functional bioinspired antifouling interfaces in a substrate-independent fashion.

Tunable fabrication of hierarchical hybrids via the incorporation of poly(dopamine) functional interlayer

Two kinds of ternary hybrids were prepared by anchoring different shapes and loadings of Au nanoparticles (NPs) on poly(dopamine) (PDA) functionalized polystyrene (PS) microspheres with two different strategies, i.e., in situ reduction and self-assembly approach. PDA coatings were firstly introduced to functionalize the hydrophobic PS surface with sufficient amino and hydroxyl groups, which enhanced the interaction between Au NPs and the polymer spheres. Thus, Au NPs could be easily immobilized onto the surface of the PDA/PS microspheres, and the hierarchical composite microspheres exhibited a well-defined core/shell structure without sacrificing the spherical PS morphology. PS/PDA/Au-R and PS/PDA/Au-A microspheres fabricated by in situ reduction and self-assembly approach showed different distinct Au nano-shell morphology with the corresponding optical, catalytic and electrochemical properties. Field emission scanning electron microscopy and transmission electronic microscopy verified these hierarchical structures with the ultrathin PDA film incorporating between the inner PS core and the outer Au NPs shell. X-ray diffraction and X-ray photoelectron spectroscopy confirmed the presence of PDA and Au layer on the surface of the composite particles. These green and facile methods with mild experimental conditions can extend to fabricate other polymer or inorganic substrates coated by various noble metals.

Electrochemical glucose biosensor with improved performance based on the use of glucose oxidase and Prussian Blue incorporated into a thin film of self-polymerized dopamine

We report on the use of self-polymerized dopamine (PDA) in an enzyme-based biosensor with improved performance. This is due to the fact that poly-DA strongly improves the stability of the electrocatalyst Prussian Blue (PB) in neutral and alkaline solution. The polymer also effectively entraps the enzyme glucose oxidase (GOx) while retaining its activity. A glucose biosensor was fabricated by modifying a glassy carbon electrode with a thin film of PB into which GOx was incorporated with the assistance of PDA film. The PB films enable a facile electrochemical reduction, and thus the determination, of enzymatically generated H2O2 at a remarkably low potential of 0.0V (versus Ag/AgCl). The biosensor responds linearly to glucose in the 200μM to 3.4mM concentration range, with a sensitivity of 1.59nAμM−1, a 46.2μM detection limit, a response time of 15s, and with storage stabilities of 3 months at 4–8°C and of >4 weeks at room temperature. The biosensor is highly selective over many other electroactive species, reproducible, and stable even at weakly alkaline pH values. The stabilized PB films by PDA will widen horizons of its applications both as H2O2 sensor and for elaboration of the oxidase-based biosensors in physiological environment.

Characterization of 10,12-pentacosadiynoic acid Langmuir-Blodgett monolayers and their use in metal-insulator-metal tunnel devices.

The characterization of Langmuir–Blodgett thin films of 10,12-pentacosadiynoic acid (PDA) and their use in metal–insulator–metal (MIM) devices were studied. The Langmuir monolayer behavior of the PDA film was studied at the air/water interface using surface tension–area isotherms of polymeric and monomeric PDA. Langmuir–Blodgett (LB, vertical deposition) and Langmuir–Schaefer (LS, horizontal deposition) techniques were used to deposit the PDA film on various substrates (glass, quartz, silicon, and nickel-coated film on glass). The electrochemical, electrical and optical properties of the LB and LS PDA films were studied using cyclic voltammetry, current–voltage characteristics (I–V), and UV–vis and FTIR spectroscopies. Atomic force microscopy measurements were performed in order to analyze the surface morphology and roughness of the films. A MIM tunnel diode was fabricated using a PDA monolayer assembly as the insulating barrier, which was sandwiched between two nickel layers. The precise control of the thickness of the insulating monolayers proved critical for electron tunneling to take place in the MIM structure. The current–voltage characteristics of the MIM diode revealed tunneling behavior in the fabricated Ni–PDA LB film–Ni structures.

Effects of Nanoparticle Concentration and Plasticizer Type on Colorimetric Behavior of Polydiacetylene/Silica Nanocomposite as Time-temperature Indicator

Effects of silica nanoparticle concentration and plasticizer type on color transition of PDA/SiO2 nanocomposite were investigated. Four types of plasticizer were poly(ethylene glycol-400), glycerol, xylitol and sorbitol. The number of hydroxyl groups in polyol affected to the stability of PDA/SiO2 nanocomposite molecules. The color of plasticized PDA films exhibited a stronger purple color tone than those of plasticized PDA/SiO2 films. As increasing time and temperature, the color change of plasticized PDA films occurred faster than plasticized PDA/SiO2 (10wt.%) films and plasticized PDA/SiO2 (20wt.%) films, respectively. Higher concentration of silica nanoparticles yielded higher stability of PDA/SiO2 nanocomposite molecules. Plasticized PDA and plasticized PDA/SiO2 films clearly changed the color from blue to purple, reddish purple and finally red stored at higher temperature (35°C), whereas they only shifted the color from blue to purple kept at lower temperature (5°C) throughout storage time. This study confirmed that it is possible to develop a time-temperature indicator for applying with chilled food products.

Facile preparation of protein stationary phase based on polydopamine/graphene oxide platform for chip-based open tubular capillary electrochromatography enantioseparation

A novel chip-based enantioselective open-tubular capillary electrochromatography (OT-CEC) was developed employing bovine serum albumin (BSA) conjugated polydopamine–graphene oxide (PDA/GO) nanocomposites (PDA/GO/BSA) as stationary phase. After the poly(dimethylsiloxane) (PDMS) microfluidic chip was filled with a freshly prepared solution containing dopamine and graphene oxide, PDA/GO nanocomposites were formed and deposited on the inner wall of microchannel as permanent coating via the oxidation of dopamine by the oxygen dissolved in the solution. The PDA/GO-coated PDMS microchips not only have the adhesion of PDA that make them easily immobilized in the microchannel, but also have the larger surface and excellent biocompatibility of graphene which can incorporate much more biomolecules and well maintain their biological activity. In addition, incorporation of GO in PDA film can make surface morphology more rough, which is beneficial for enhancing the loading capacity of proteins in the microchannels and increasing sample capacity of OT-CEC columns. BSA was stably immobilized in the PDMS microchannel to fabricate a protein-stationary phase. Compared with the native PDMS microchannels, the modified surfaces exhibited much better wettability, more stable electroosmotic mobility, and less nonspecific adsorption. The efficient separation of chiral amino acids (tryptophan and threonine) and chiral dipeptide demonstrate that the constructed OT-CEC columns own ideal enantioselectivity. The presented strategy using PDA/GO coating as a versatile platform for facile conjugation of proteins may offer new processing strategies to prepare a functional surface designed on microfluidic chips.