Preparation of polydiacetylene immobilized optically encoded beads

Polydiacetylene (PDA), which can change the chromic and fluorescence properties by inducing environmental perturbations, is immobilized on planar solid supports for many biological applications. In this work, we immobilize PDA onto optically encoded spherical beads (PDA-SERS beads). The prepared PDA immobilized beads (36 μm) exhibit a blue color without fluorescence. By inducing stress, their color and fluorescence properties are changed to red with fluorescence. The SERS spectra of the PDA-SERS beads can be recognized over the PDA background. Moreover, our PDA immobilization methods are successfully applied to silica-surface SERS-encoded beads (5 μm) and proven to also be useful in fluorescence encoding systems.     

PDA/SiO2大孔复合材料固定化荧光假单胞菌脂肪酶

以具有三维骨架结构的大孔聚合物为模板制备SiO_2大孔材料,通过多巴胺在SiO_2大孔材料孔道表面的原位聚合制得聚多巴胺表面功能化修饰的二氧化硅大孔材料(PDA/SiO_2)。应用SEM、EDX、MIP、BET、TG-DTA和FTIR等技术对修饰前后的材料进行表征。以PDA/SiO_2为载体固定荧光假单胞菌脂肪酶(PFL),优化固定化条件并对比游离脂肪酶和固定化脂肪酶的性质。结果表明SiO_2大孔材料具有三维连续贯通的孔道结构,孔径分布在300~500 nm,聚多巴胺修饰后形成聚多巴胺/二氧化硅复合纳米薄膜构筑的大孔材料。在固定化时间为14 h、p H值为8、初始脂肪酶浓度为0.4 mg·m L-1时,固定化效果最佳,酶活回收率达246%。与游离脂肪酶相比,固定化脂肪酶有更宽的温度和p H适用范围、热稳定性显著提高,并展现出良好的储存稳定性和操作稳定性,固定化脂肪酶的Km低于游离脂肪酶的,酶与底物的亲和性较好。     

Donor–Acceptor Heterojunction Configurations Based on DNA–Multichromophore Arrays

Multichromophore arrays of bis(2‐thienyl)diketopyrrolopyrrole (DPP) and naphthalenediimide (NDI) with two Zn^II‐cyclens were constructed using thymidine DNA as a scaffold through the binding of the Zn^II‐cyclens with thymine bases. We demonstrate photocurrent generation in a donor–acceptor heterojunction configuration consisting of the DPP (donor) and NDI (acceptor) arrays co‐immobilized on an Au electrode. The co‐immobilized electrode exhibited good photocurrent responses because of the efficient charge separation between the DPP and NDI arrays. In contrast, an immobilized electrode consisting of randomly assembled DPP‐NDI arrays generated no photocurrent response because DPP formed ground‐state charge‐transfer complexes with NDI in the randomly assembled arrays. Therefore, our approach to generate donor–acceptor heterojunctions based on DNA–multichromophore arrays is a useful method to efficiently generate photocurrent.     

Micro‐Patterning of Polydiacetylene Supramolecules using Micromolding in Capillaries (MIMIC)

Micrometer‐sized polydiacetylene (PDA) vesicle patterns on titanium substrates have been successfully fabricated by using a micromolding in capillaries (MIMIC) technique. The shape and width of the PDA patterns are well matched with polydimethylsiloxane (PDMS) molds used in the MIMIC process. However, the thicknesses of the patterned films are less than the depths of the PDMS molds, which may be a consequence of the poor water wettability of the PDMS and/or low concentrations of the PDA solutions. Heat‐treatment of the solid substrate, immobilized with blue‐phase PDAs, induces a blue‐to‐red‐phase transition and results in the formation of patterned fluorescence images.

     

Surface molecularly imprinted polydopamine films for recognition of immunoglobulin G

We have prepared a surface imprinted polymer (SIP) film for label-free recognition of immunoglobulin G (IgG). The IgG-SIPs were obtained by covalent immobilization of IgG via a cleavable covalent bond and a suitable spacer unit to a gold electrode, followed by electrodepostion of a nm-thin film of polydopamine (PDA). The IgG was then removed by destruction of the cleavable bond so that complementary binding sites were created on the surface of the film. IgG-SIPs with various thicknesses of the PDA films were compared with respect to their affinity to IgG using a quartz crystal microbalance combined with flow injection analysis. The films were also characterized by cyclic voltammetry and scanning electron microscopy. The IgG-SIPs with a film thickness of around 17 nm showed the most pronounced imprinting effect (IF 1.66) and a binding constant of 296 nM.

Tunable micropatterned substrates based on poly(dopamine) deposition via microcontact printing

A simple technique was developed to fabricate tunable micropatterned substrates based on mussel-inspired surface modification. Polydopamine (PDA) was developed on polydimethylsiloxane (PDMS) stamps and was easily imprinted to several substrates such as glass, silicon, gold, polystyrene, and poly(ethylene glycol) via microcontact printing. The imprinted PDA retained its unique reactivity and could modulate the chemical properties of micropatterns via secondary reactions, which was illustrated in this study. PDA patterns imprinted onto a cytophobic and nonfouling substrates were used to form patterns of cells or proteins. PDA imprints reacted with nucleophilic amines or thiols to conjugate molecules such as poly(ethylene glycol) for creating nonfouling area. Gold nanoparticles were immobilized onto PDA-stamped area. The reductive ability of PDA transformed silver ions to elemental metals as an electroless process of metallization. This facile and economic technique provides a powerful tool for development of a functional patterned substrate for various applications.     

Surface‐Independent and Oriented Immobilization of Antibody via One‐Step Polydopamine/Protein G Coating: Application to Influenza Virus Immunoassay

For the construction of high‐performance biosensor, it is important to interface bioreceptors with the sensor surface densely and in the optimal orientation. Herein, a simple surface modification method that can optimally immobilize antibodies onto various kinds of surfaces is reported. For the surface modification, a mixture of polydopamine (PDA) and protein G was employed. PDA is a representative mussel‐inspired polymer, and protein G is an immunoglobulin‐binding protein that enables an antibody to have an optimal orientation. The surface characteristics of PDA/Protein G mixture‐coated substrates are analyzed and the PDA/protein G ratio is optimized to maximize the antibody binding efficiency. Moreover, the antibody‐immobilized substrates are applied to the detection of influenza viruses with the naked eye, providing a detection limit of 2.9 × 10³ pfu mL^‐1. Importantly, the several substrates (glass, SiO₂, Si, Al₂O₃, polyethylene terephthalate, polyethylene, polypropylene, and paper) can be modified by simple incubation with the mixture of PDA/protein G, and then the anti‐influenza A H1N1 antibodies can be immobilized on the substrates successfully. Regardless of the substrate, the influenza viruses are detectable after the sandwich immunoreaction and silver enhancement procedure. It is anticipated that the developed PDA/protein G coating method will extend the range of applicable materials for biosensing.     

Highly controlled coating of biomimetic polydopamine in TiO2 nanotubes

Highly controlled coating of biomimetic polydopamine (PDA) was achieved on titanium dioxide nanotubes (TiO₂ NTs) by exposing TiO₂ NT arrays to a slightly alkaline dopamine solution. The thin films act as photonic sensitizers (enhancing photocurrents and photodegradation) in the visible light range. The PDA coatings can furthermore be used as a platform for decorating the TiO₂ NTs with different co-catalysts and metal nanoparticles (NPs).     

Polydopamine-Assisted Rapid One-Step Immobilization of L-Arginine in Capillary as Immobilized Chiral Ligands for Enantioseparation of Dansyl Amino Acids by Chiral Ligand Exchange Capillary Electrochromatography

Herein, a novel L-arginine (L-Arg)-modified polydopamine (PDA)-coated capillary (PDA/L-Arg@capillary) was firstly fabricated via the basic amino-acid-induced PDA co-deposition strategy and employed to constitute a new chiral ligand exchange capillary electrochromatography (CLE-CEC) method for the high-performance enantioseparation of D,L-amino acids (D,L-AAs) with L-Arg as the immobilized chiral ligand coordinating with the central metal ion Zn(II) as running buffer. Assisted by hydrothermal treatment, the robust immobilization of L-Arg on the capillary inner wall could be facilely achieved within 1 h, prominently improving the synthesis efficiency and simplifying the preparation procedure. The successful preparation of PDA/L-Arg coatings in the capillary was systematically characterized and confirmed using several methods. In comparison with bare and PDA-functionalized capillaries, the enantioseparation capability of the presented CLE-CEC system was significantly enhanced. Eight D,L-AAs were completely separated and three pairs were partially separated under the optimal conditions. The prepared PDA/L-Arg@capillary showed good repeatability and stability. The potential mechanism of the greatly enhanced enantioseparation performance obtained by PDA/L-Arg@capillary was also explored. Moreover, the proposed method was further utilized for studying the enzyme kinetics of L-glutamic dehydrogenase, exhibiting its promising prospects in enzyme assays and other related applications.     

Development of a photodiode array biochip using a bipolar semiconductor and its application to detection of human papilloma virus

We describe a DNA microarray system using a bipolar integrated circuit photodiode array (PDA) chip as a new platform for DNA analysis. The PDA chip comprises an 8 × 6 array of photodiodes each with a diameter of 600 μm. Each photodiode element acts both as a support for an immobilizing probe DNA and as a two-dimensional photodetector. The usefulness of the PDA microarray platform is demonstrated by the detection of high-risk subtypes of human papilloma virus (HPV). The polymerase chain reaction (PCR)-amplified biotinylated HPV target DNA was hybridized with the immobilized probe DNA on the photodiode surface, and the chip was incubated in an anti-biotin antibody-conjugated gold nanoparticle solution. The silver enhancement by the gold nanoparticles bound to the biotin of the HPV target DNA precipitates silver metal particles at the chip surfaces, which block light irradiated from above. The resulting drop in output voltage depends on the amount of target DNA present in the sample solution, which allows the specific detection and the quantitative analysis of the complementary target DNA. The PDA chip showed high relative signal ratios of HPV probe DNA hybridized with complementary target DNA, indicating an excellent capability in discriminating HPV subtypes. The detection limit for the HPV target DNA analysis improved from 1.2 nM to 30 pM by changing the silver development time from 5 to 10 min. Moreover, the enhanced silver development promoted by the gold nanoparticles could be applied to a broader range of target DNA concentration by controlling the silver development time. Figure An optical image of the PDA chip and target DNA detection through silver enhancement Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Signal enhancement of a micro-arrayed polydiacetylene (PDA) biosensor using gold nanoparticles

Polydiacetylene (PDA) liposomes possess unique properties that allow liposomes to change color and emit fluorescence in response to stimuli such as temperature, antibody-antigen interaction, pH, mechanical stress, and organic solvent. They have been studied extensively as signal transducers in biosensor applications. Here, we describe an antibody-based biosensor using PDA liposomes for detection of human immunoglobulin E (hIgE). Target hIgE chemically bound to hIgE monoclonal antibodies immobilized on PDA liposomes and the fluorescent signals were slightly increased depending on the target protein concentration. As the primary response, the hIgE could be detected to below 10 ng mL(-1). However, fluorescent signals were dramatically increased depending on the target protein concentration when gold nanoparticle-conjugated polyclonal antibody probes were added on the PDA liposomes after the primary immune reaction. A PDA liposome biosensor could detect the hIgE as low as 0.1 ng mL(-1) and the sensitivity was increased up to one hundred times higher than the primary response. As a result, we confirmed that gold nanoparticle-conjugated polyclonal antibody probes efficiently enhanced the fluorescent signal of the PDA liposome biosensor chip. This strategy can be useful to detect proteins of ultra-low concentration.     

Polydiacetylene/Anti‐HBs Complexes for Visible and Fluorescent Detection of Hepatitis B Surface Antigen on a Nitrocellulose Membrane

The immunochromatographic assay (ICA) using a nitrocellulose (NC) membrane offers several advantages. This technique is a rapid and straightforward method in contrast to other immunoassays. Polydiacetylene (PDA) vesicles have unique optical properties, displaying red color and red fluorescence at the same time. In this system, red‐phase PDA vesicles are used as a fluorescent dye as well as a surface for immobilized hepatitis B surface antibody (HBsAb). PDA has a remarkable stability compared with other fluorescent dyes. In this study, the most suitable PDA/HBsAb complexes are introduced for detecting hepatitis B surface antigen (HBsAg). Then, the PDA/HBsAb complexes affixed antibody is attached to NC membrane, which has two lines to confirm detection of HBsAg. The main advantage of this system is that the detection of HBsAg can be observed in both visible and fluorescent images due to the optical properties of polydiacetylene. Detection of HBsAg is observed up to 0.1 ng mL⁻¹ by fluorescent analysis and confirmed by red line on the NC membrane up to 1 ng mL⁻¹ (HBsAg) using the naked eye. Consequently, these results show that PDA/HBsAb complexes were successfully applied to ICA for the diagnosis of hepatitis B.     

Polymer brushes grafted from graphene via bioinspired polydopamine chemistry and activators regenerated by electron transfer atom transfer radical polymerization

Polymer brushes decorated reduced GO (rGO) with advanced applications have been prepared by bioinspired polydopamine (PDA) chemistry integrated with activators regenerated by electron transfer atom transfer radical polymerization (ARGET‐ATRP) technique. First, rGO/PDA was obtained by the process for graphene oxide (GO) coated with a homogeneous bio‐adhesive PDA layer. Then the initiator 2‐bromoisobutyryl bromide (BIBB) was immobilized on the surface of PDA functionalized rGO. Finally, rGO/PDA‐Br was polymerized with N, N‐diethylaminoethyl methacrylate (DEAEMA) and glycidyl methacrylate (GMA) to obtain rGO/PDA‐g‐polymer brushes by ARGET‐ATRP process. The prepared rGO/PDA‐g‐PGMA brush would be subjected to further functionalization with ethylenediamine (EDA), which would impart the obtained products (rGO/PDA‐g‐PGMA‐NH₂) with good adsorption ability toward cationic dyes. The chemical structures and morphologies of the functionalized GO products have been characterized in detail by Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, thermal gravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscope(TEM), and atomic force microscopy (AFM). The distinctive pH‐responsive character of rGO/PDA‐g‐PDEAEMA and adsorption ability of rGO/PDA‐g‐PGMA‐NH₂ for cationic dyes have been explored by UV–vis spectrophotometer. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 689–698     

Surface molecularly imprinted polydopamine films for recognition of immunoglobulin G

We have prepared a surface imprinted polymer (SIP) film for label-free recognition of immunoglobulin G (IgG). The IgG-SIPs were obtained by covalent immobilization of IgG via a cleavable covalent bond and a suitable spacer unit to a gold electrode, followed by electrodepostion of a nm-thin film of polydopamine (PDA). The IgG was then removed by destruction of the cleavable bond so that complementary binding sites were created on the surface of the film. IgG-SIPs with various thicknesses of the PDA films were compared with respect to their affinity to IgG using a quartz crystal microbalance combined with flow injection analysis. The films were also characterized by cyclic voltammetry and scanning electron microscopy. The IgG-SIPs with a film thickness of around 17 nm showed the most pronounced imprinting effect (IF 1.66) and a binding constant of 296 nM.

A strategy for preparation of the IgG-Surface Imprinted Polymeric (IgG-SIP) thin films was developed. IgG was covalently immobilized via a cleavable cross-linker to a gold electrode surface followed by electrochemical deposition of a nanometer thin PDA film. After cleaving S-S bond in the linker the IgG was removed leaving behind the complementary binding sites confined in the surface of the polymer film. The prepared IgG-SIPs were applied for IgG recognition.

     

Fluorescence, XPS, and TOF-SIMS surface chemical state image analysis of DNA microarrays

Performance improvements in DNA-modified surfaces required for microarray and biosensor applications rely on improved capabilities to accurately characterize the chemistry and structure of immobilized DNA molecules on micropatterned surfaces. Recent innovations in imaging X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) now permit more detailed studies of micropatterned surfaces. We have exploited the complementary information provided by imaging XPS and imaging TOF-SIMS to detail the chemical composition, spatial distribution, and hybridization efficiency of amine-terminated single-stranded DNA (ssDNA) bound to commercial polyacrylamide-based, amine-reactive microarray slides, immobilized in both macrospot and microarray diagnostic formats. Combinations of XPS imaging and small spot analysis were used to identify micropatterned DNA spots within printed DNA arrays on slide surfaces and quantify DNA elements within individual microarray spots for determination of probe immobilization and hybridization efficiencies. This represents the first report of imaging XPS of DNA immobilization and hybridization efficiencies for arrays fabricated on commercial microarray slides. Imaging TOF-SIMS provided distinct analytical data on the lateral distribution of DNA within single array microspots before and after target hybridization. Principal component analysis (PCA) applied to TOF-SIMS imaging datasets demonstrated that the combination of these two techniques provides information not readily observable in TOF-SIMS images alone, particularly in identifying species associated with array spot nonuniformities (e.g., "halo" or "donut" effects often observed in fluorescence images). Chemically specific spot images were compared to conventional fluorescence scanned images in microarrays to provide new information on spot-to-spot DNA variations that affect current diagnostic reliability, assay variance, and sensitivity.     

Fabrication of Diverse Microcapsule Arrays of High Density and Good Stability

Microcapsule arrays attract a lot of interest due to their potential applications in sensing technology. A strategy for fabricating diverse microcapsule arrays through covalent linking is reported here. The self‐assembly of microcapsules was directed by using a poly(allylamine hydrochloride) (PAH)‐patterned template, which was created via microcontact printing. The microcapsules with PAH as the outermost layer were treated with glutaraldehyde and then covalently immobilized on the PAH regions, resulting in ordered microcapsule arrays. The arrays had a high density of capsules and the aggregate number in a pattern could be well controlled by adjusting the area of the PAH pattern. A single microcapsule array could be obtained if the diameter of the PAH region was smaller than that of the microcapsules. These covalently assembled arrays could survive through successive incubation in solutions of high ionic strength and extreme pHs. Such good stability ensures further treatments, such as chemical reactions and loading of functional substances.

     

Size‐Controlled Fabrication of Polydiacetylene‐Embedded Microfibers on a Microfluidic Chip

A microfluidic technique was employed to fabricate polydiacetylene (PDA)‐embedded hydrogel microfibers. By taking advantage of calcium ion‐induced insoluble hydrogel formation, supramolecularly assembled diacetylene (DA)‐surfactant complexes were successfully immobilized in the calcium alginate fibers. Thus, instantaneous microfiber formation was observed when the core flow of DA supramolecules‐containing alginate solution met the sheath flow of calcium ions. UV irradiation of the resulting fibers afforded blue colored PDAs, and the formation of a conjugated polymer was confirmed by heat‐induced phase transition and by Raman spectroscopy. By adjusting the core and sheath flow rates, PDA‐embedded hydrogel fibers of various sizes were obtained.     

Mussel‐Inspired One‐Pot Synthesis of a Fluorescent and Water‐Soluble Polydopamine–Polyethyleneimine Copolymer

Inspired by the molecular mechanics of mussel adhesive formation, a novel water‐soluble fluorescent macromolecule (polydopamine–polyethyleneimine (PDA–PEI)) is prepared by one‐pot copolymerization of dopamine (DA) and PEI. In this method, DA is polymerized to form PDA, which is then coupled with PEI mainly through Michael addition. The fluorescence property of PDA–PEI is mainly attributed to the Michael addition of PEI on the 5,6‐dihydroxyindole (DHI) units of PDA, where PEI can form hydrogen bonds with oxidative products such as DHI and force the DHI units to twist out of plane, resulting in a decrease in the intra‐ and intermolecular coupling of PDA. In addition, the influence of various metal cations on the fluorescence of the PDA–PEI copolymer is investigated. This work may facilitate the development of new strategies for controlling the emission characteristics of PDA.

     

Mussel‐Inspired Photografting on Colloidal Spheres: A Generalized Self‐Template Route to Stimuli‐Responsive Hollow Spheres for Controlled Pesticide Release

A thermo‐controlled pesticide release system composed of poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) thin film grafted polydopamine (PDA) (PDMAEMA‐g‐PDA) microcapsules is reported. SiO₂ microparticles are used as a template to prepare PDA‐coated SiO₂ microparticles. The thermally‐responsive PDMAEMA thin films are grafted on PDA surfaces using a metal‐free surface‐initiated photopolymerization approach without adding any photo­initiator or photosensitizer under UV light irradiation. The subsequent acid etching yields PDMAEMA‐g‐PDA hollow microcapsules. PDMAEMA‐g‐PDA microcapsules exhibit well‐controlled release of avermectin (Av). The results show that the loading ability of PDMAEMA‐g‐PDA microcapsules of Av is up to 52.7% (w/w). The release kinetics of Av demonstrate that Av@PDMAEMA‐g‐PDA microcapsules exhibit temperature‐controlled release performance. This work is significant for controlled release systems. This simple design is expected to be used in various applications, such as in controlled drug release and agriculture‐related fields.

     

Carbohydrate arrays for the evaluation of protein binding and enzymatic modification

This paper reports a chemical strategy for preparing carbohydrate arrays and utilizes these arrays for the characterization of carbohydrate-protein interactions. Carbohydrate chips were prepared by the Diels-Alder-mediated immobilization of carbohydrate-cyclopentadiene conjugates to self-assembled monolayers that present benzoquinone and penta(ethylene glycol) groups. Surface plasmon resonance spectroscopy showed that lectins bound specifically to immobilized carbohydrates and that the glycol groups prevented nonspecific protein adsorption. Carbohydrate arrays presenting ten monosaccharides were then evaluated by profiling the binding specificities of several lectins. These arrays were also used to determine the inhibitory concentrations of soluble carbohydrates for lectins and to characterize the substrate specificity of beta-1,4-galactosyltransferase. Finally, a strategy for preparing arrays with carbohydrates generated on solid phase is shown. This surface engineering strategy will permit the preparation and evaluation of carbohydrate arrays that present diverse and complex structures.