Facile DNA Immobilization on Surfaces through a Catecholamine Polymer

One-Step Surface Modification to Graft DNA Codes on Paper: The Method, Mechanism, and Its Application

Glass slides have been widely used for DNA immobilization in DNA microarray and numerous bioassays for decades, whereas they are faced with limitations of low probe density, time-consuming modification steps, and expensive instruments. In this work, a simple one-step surface modification method using 3-aminopropyl trimethoxysilane (APTMS) has been developed and applied to graft DNA codes on paper. Higher DNA immobilization efficiency was obtained in comparison with that in a conventional method using glass slides. Fluorescence detection, X-ray photoelectron spectroscopy (XPS), infrared spectra (FT-IR), and pH influence studies were employed to characterize the surface modification and subsequent DNA immobilization, which further reveals a mechanism in which this method lies in ionic interactions between the positively charged APTMS-modified paper surface and negatively charged DNA probes. Furthermore, an APTMS-modified paper-based device has been developed to demonstrate application in low-cost detection of a foodborne pathogen, Giardia lamblia, with high sensitivity (the detection limit of 22 nM) and high specificity. Compared with conventional methods using redundant cross-linking reactions, our method is simpler, faster, versatile, and lower-cost, enabling broad applications of paper-based bioassays especially for point-of-care detection in resource-poor settings.

Target capturing performance of microfluidic channel surface immobilized aptamers: the effects of spacer lengths

Aptamers have been widely used to recognize and capture their targets in sensitive detection applications, such as in detections of circulating tumor cells. In this study, we investigate the effects of different lengths of oligo-T spacers on surface tethered sgc8 aptamers and their target capturing performances. To achieve this, sgc8 aptamers were immobilized onto microfluidic channel surfaces via oligo-T spacers of different lengths, and the target capturing performances of these immobilized aptamers were studied using CCRF-CEM cells. We demonstrate that the capturing performances of the immobilized aptamers were significantly affected by steric hindrance. Our results also show that aptamers immobilized on surfaces via spacers of ten Ts demonstrated the best cell capturing performances; aptamers with either too short or too long oligo-T spacers showed reduced cell capturing performances. Therefore it can be concluded that spacer optimizations are critically important for surface tethered aptamers that are commonly used in microfluidic devices for sensitive target sensing and detections.

Polydopamine Surface Chemistry: A Decade of Discovery

Polydopamine is one of the simplest and most versatile approaches to functionalizing material surfaces, having been inspired by the adhesive nature of catechols and amines in mussel adhesive proteins. Since its first report in 2007, a decade of studies on polydopamine molecular structure, deposition conditions, and physicochemical properties have ensued. During this time, potential uses of polydopamine coatings have expanded in many unforeseen directions, seemingly only limited by the creativity of researchers seeking simple solutions to manipulating surface chemistry. In this review, we describe the current state of the art in polydopamine coating methods, describe efforts underway to uncover and tailor the complex structure and chemical properties of polydopamine, and identify emerging trends and needs in polydopamine research, including the use of dopamine analogs, nitrogen-free polyphenolic precursors, and improvement of coating mechanical properties.

Construction of catechol-containing semi-fluorinated asymmetric polymer brush via successive RAFT polymerization and ATRP

This article reports the synthesis of a semi-fluorinated compositional heterogeneous polymer brush for anti-fouling surface.

Stability research on polydopamine and immobilized albumin on 316L stainless steel

In this study, the polydopamine (PDA) film was coated on polished 316Lss and then thermally treated at 150 °C (labeled as PDA-Th150), and the stability of coatings was also investigated. Straining test indicated that PDA-Th150 coating performed better in affording sufficient adherence to 316 L SS substrate. Moreover, both PDA and PDA-Th150 coating suffered slight swelling during immersion in deionized water (pH = 6.5). X-ray photoelectron spectroscopy results showed that during immersion, latent nucleophilic reaction via amines inside PDA coating occurred. This led to an enhanced cross-linking and thus gradually promoted the coating stability. Moreover, larger amount of bovine serum albumin (BSA) was immobilized onto PDA-Th150 coating and performed well in anti-platelet adhesion. A high retention of immobilized BSA was observed even after immersion for 30 days. These tests suggested that PDA was stable enough and performed well in surface functionalization, which might enrich the research and application of PDA.

Robust Nanoparticle-DNA Conjugates Based on Mussel-Inspired Polydopamine Coating for Cell Imaging and Tailored Self-Assembly

We have demonstrated that mussel-inspired polydopamine can serve as an intermediate coating layer for covalently attaching oligonucleotides on nanostructures of diverse chemical nature, which are made possible by the universal adhesion and spontaneous reactivity of polydopamine. Our results have shown that polydopamine can strongly bond to representative nanoparticles (i.e., Au nanoparticles and magnetic polymer nanobeads) and form a thin layer of coating that allows for attachment of commercially available DNA with thiol or amine end functionality. The resulting DNA-nanoparticle conjugates not only show excellent chemical and thermal stability and high loading density of DNA, but the linked DNA also maintain their biological functions in directing cancer cell targeting and undergo DNA hybridization to form multifunctional magnetic core-plasmonic satellite assemblies. The generally applicable strategy opens new opportunities for easy adoption of DNA-nanoparticle conjugates for broad applications in biosensors and nanomedicine.

Versatile Method for Coating Surfaces with Functional and Responsive Polymer-Based Films

A versatile surface modification technique was developed to yield poly(N-isopropylacrylamide) (pNIPAm) microgel-based thin films on a variety of substrates, e.g., metals, nonmetals, and polymers. Because the chemistry, and hence functionality and responsivity, of the pNIPAm-based microgels is easily tuned, multifunctional and responsive thin films could be generated on many different surfaces without varying the coating conditions. In one case, we showed that fluorescent/light emitting thin films could be generated using crystal violet-modified microgels. Antibacterial films could be obtained using silver nanoparticle-modified pNIPAm-based microgels. Finally, we show that thin films fabricated via the methods here could be used as a component in optical sensors. Although we show only a few examples of the utility of this approach, we feel that the apparent universality of the technique can be extended to countless other applications.

Biomedical and Clinical Importance of Mussel-Inspired Polymers and Materials

The substance secreted by mussels, also known as nature's glue, is a type of liquid protein that hardens rapidly into a solid water-resistant adhesive material. While in seawater or saline conditions, mussels can adhere to all types of surfaces, sustaining its bonds via mussel adhesive proteins (MAPs), a group of proteins containing 3,4-dihydroxyphenylalanine (DOPA) and catecholic amino acid. Several aspects of this adhesion process have inspired the development of various types of synthetic materials for biomedical applications. Further, there is an urgent need to utilize biologically inspired strategies to develop new biocompatible materials for medical applications. Consequently, many researchers have recently reported bio-inspired techniques and materials that show results similar to or better than those shown by MAPs for a range of medical applications. However, the susceptibility to oxidation of 3,4-dihydroxyphenylalanine poses major challenges with regard to the practical translation of mussel adhesion. In this review, various strategies are discussed to provide an option for DOPA/metal ion chelation and to compensate for the limitations imposed by facile 3,4-dihydroxyphenylalanine autoxidation. We discuss the anti-proliferative, anti-inflammatory, anti-microbial activity, and adhesive behaviors of mussel bio-products and mussel-inspired materials (MIMs) that make them attractive for synthetic adaptation. The development of biologically inspired adhesive interfaces, bioactive mussel products, MIMs, and arising areas of research leading to biomedical applications are considered in this review.

Development of a catheter functionalized by a polydopamine peptide coating with antimicrobial and antibiofilm properties

Catheter-associated urinary tract infections (CAUTIs) are the most common hospital-acquired infections worldwide, aggravating the problem of antimicrobial resistance and patient morbidity. There is a need for a potent and robust antimicrobial coating for catheters to prevent these infections. An ideal coating agent should possess high antimicrobial efficacy and be easily and economically conjugated to the catheter surface. In this study, we report a simple yet effective immobilization strategy to tether a potent synthetic antimicrobial peptide, CWR11, onto catheter-relevant surfaces. Polydopamine (PD) was deposited as a thin adherent film onto a polydimethylsiloxane (PDMS) surface to facilitate attachment of CWR11 onto the PD-functionalized polymer. Surface characterization of the CWR11-tethered surfaces confirmed the successful immobilization of peptides onto the PD-coated PDMS. The CWR11-immobilized PDMS slides displayed excellent antimicrobial (significant inhibition of 5×10(4) colony-forming units of CAUTI-relevant microbes) and antibiofilm (∼92% enhanced antibacterial adherence) properties. To assess its clinical relevance, the PD-based immobilization platform was translated onto commercial silicone-coated Foley catheters. The CWR11-impregnated catheter displayed potent bactericidal properties against both Gram-positive and Gram-negative bacteria, and retained its antimicrobial functionality for at least 21days, showing negligible cytotoxicity against human erythrocyte and uroepithelial cells. The outcome of this study demonstrates the proof-of-concept potential of a polydopamine-CWR11-functionalized catheter to combat CAUTIs.

Immobilization of DNA aptamers via plasma polymerized allylamine film to construct an endothelial progenitor cell-capture surface

The endothelial progenitor cells (EPCs) capture stent has drawn increasing attentions and become one of the most promising concepts for the next generation vascular stent. In this regard, it is of great significance to immobilize a molecule with the ability to bind EPC for rapid in vivo endothelialization with high specificity. In this work, a facile two-step method aimed at constructing a coating with specific EPC capturing aptamers is reported. The processes involves as the first-step deposition of plasma polymerized allylamine (PPAam) on a substrate to introduce amine groups, followed by the electrostatic adsorption of a 34 bases single strand DNA sequence to the PPAam surface as a second step (PPAam-DNA). Grazing incidence attenuated total reflection Fourier transform infrared spectroscopy (GATR-FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed the successful immobilization of the aptamers. Quartz crystal microbalance with dissipation (QCM-D) real time monitoring result shows that about 175 ng/cm(2) aptamers were conjugated onto the PPAam surface. The interactions between the modified surfaces and human umbilical vein endothelial cells (ECs), smooth muscle cells (SMCs), and murine induced EPCs derived from mesenchymal stem cells (MSCs) were also investigated. It was demonstrated that PPAam-DNA samples could capture more EPCs, and present a cellular friendly surface for the proliferation of both EPCs and ECs but no effect on the hyperplasia of SMCs. Also, the co-culture results of 3 types of cells confirmed that the aptamer could specifically bond EPCs rather than ECs and SMCs, suggesting the competitive adhesion advantage of EPCs to ECs and SMCs. These data demonstrate that the EPC aptamer has large potential for designing an EPC captured stent and other vascular grafts with targeted in situ endothelialization.

Enzymatic amplification detection of peanut allergen Ara h1 using a stem-loop DNA biosensor modified with a chitosan-mutiwalled carbon nanotube nanocomposite and spongy gold film

In this paper, a highly sensitive biosensor was constructed for peanut allergen Ara h1 detection. The biosensor was constructed by coating a glassy carbon electrode with a chitosan-mutiwalled carbon nanotube nanocomposite and then adding a spongy gold film via electro-deposition to increase the effective area. The probe switched from an "on" to an "off" state in the presence of target DNA, which detached biotin from the electrode surface. This also detached streptavidin-horseradish peroxidase (HRP-SA), which was bound to the electrode via specific interaction with biotin. The HRP-SA catalyzed chemical oxidation of hydroquinone by H2O2 to form benzoquinone, and when it was detached, electrochemical reduction of the signal of benzoquinone could be used to monitor DNA hybridization via chronoamperometry. Under optimum conditions, a wide dynamic detection range (3.91 × 10(-17)-1.25 × 10(-15) mol L(-1)) and a low detection limit (1.3 × 10(-17) mol L(-1)) were achieved for the complementary sequence. Furthermore, the DNA biosensor exhibited an excellent ability to discriminate between a complementary target and a one-base mismatch or non-complementary sequence. The sensor was successfully applied to Ara h1 analysis in peanuts.

A novel technique for in situ aggregation of Gluconobacter oxydans using bio-adhesive magnetic nanoparticles

Here, we present a novel technique to immobilize magnetic particles onto whole Gluconobacter oxydans in situ via a synthetic adhesive biomimetic material inspired by the protein glues of marine mussels. Our approach involves simple coating of a cell adherent polydopamine film onto magnetic nanoparticles, followed by conjugation of the polydopamine-coated nanoparticles to G. oxydans which resulted in cell aggregation. After optimization, 21.3 mg (wet cell weight) G. oxydans per milligram of nanoparticle was aggregated and separated with a magnet. Importantly, the G. oxydan aggregates showed high specific activity and good reusability. The facile approach offers the potential advantages of low cost, easy cell separation, low diffusion resistance, and high efficiency. Furthermore, the approach is a convenient platform technique for magnetization of cells in situ by direct mixing of nanoparticles with a cell suspension.