Andres de los Santos Pereira

Biomimetic non-fouling surfaces: extending the concepts

In this study, we propose a substrate-independent biomimetic modification route for the creation of antifouling polymer brushes. This modification route consists of the formation/deposition of a biomimetic polydopamine anchor layer followed by a well-controlled surface-initiated atom transfer radical polymerization of antifouling polymer brushes initiated by 2-bromo-2-methylpropanoyl groups covalently attached to the hydroxyl and amine groups present in the anchor layer. In this way, we synthesized polymer brushes of methoxy- and hydroxy-capped oligoethylene glycol methacrylate, 2-hydroxyethyl methacrylate and carboxybetaine acrylamide. Spectroscopic ellipsometry (SE) indicated well-controlled polymerization kinetics of the brushes, thus the thickness of the ultra-thin films could be precisely tuned at a nanometer scale. The covalent structure and organization of the brushes grown from the polydopamine anchor layer were accessed by infrared reflection-adsorption spectroscopy (IRRAS) while the change in hydrophilicity caused by the presence of the brush was determined by dynamic water contact angle measurements. Surface plasmon resonance as well as ex situ IRRAS and SE measurements were applied to investigate the adsorption of model protein solutions and undiluted human blood plasma to the brushes. The biomimetic brushes completely suppressed the fouling from single protein solutions and reduced the fouling from plasma to less than 3% from the fouling measured on bare gold surfaces. The proposed modification procedure is non-destructive and does not require any chemical pre-activation or the presence of reactive groups on the substrate surface. Contrary to other antifouling modifications the coating can be performed on various classes of substrates and preserves its properties even in undiluted blood plasma. This work offers a promising technology for the facile fabrication of different surface-based biotechnological and biomedical devices able to perform tailor-made functions while resisting the fouling from the complex biological media where they operate.

Functionalized ultra-low fouling carboxy- and hydroxy-functional surface platforms: functionalization capacity, biorecognition capability and resistance to fouling from undiluted biological media.

The non-specific binding of non-target species to functionalized surfaces of biosensors continues to be challenge for biosensing in real-world media. Three different low-fouling and functionalizable surface platforms were employed to study the effect of functionalization on fouling resistance from several types of undiluted media including blood plasma and food media. The surface platforms investigated in this work included two polymer brushes: hydroxy-functional poly(2-hydroxyethyl methacrylate) (pHEMA) and carboxy-functional poly(carboxybetaine acrylamide) (pCBAA), and a standard OEG-based carboxy-functional alkanethiolate self-assembled monolayer (AT-SAM). The wet and dry polymer brushes were analyzed by AFM, ellipsometry, FT-IRRAS, and surface plasmon resonance (SPR). The surfaces were functionalized by the covalent attachment of antibodies, streptavidin, and oligonucleotides and the binding and biorecognition characteristics of the coatings were compared. We found that functionalization did not substantially affect the ultra-low fouling properties of pCBAA (plasma fouling of ~20 ng/cm(2)), a finding in contrast with pHEMA that completely lost its resistance to fouling after the activation of hydroxyl groups. Blocking a functionalized AT-SAM covalently with BSA decreased fouling down to the level comparable to unblocked pCBAA. However, the biorecognition capability of blocked functionalized AT-SAM was poor in comparison with functionalized pCBAA. Limits of detection of Escherichia coli O157:H7 in undiluted milk were determined to be 6×10(4), 8×10(5), and 6×10(5) cells/ml for pCBAA, pHEMA, and AT-SAM-blocked, respectively. Effect of analyte size on biorecognition activity of functionalized coatings was investigated and it was shown that the best performance in terms of overall fouling resistance and biorecognition capability is provided by pCBAA.

Synthesis of non-fouling poly[N-(2-hydroxypropyl)methacrylamide] brushes by photoinduced SET-LRP

Surface-initiated photoinduced single-electron transfer living radical polymerization (SET-LRP) was employed to assemble brushes of poly[N-(2-hydroxypropyl) methacrylamide] (poly(HPMA)) from silicon surfaces. The linear increase in thickness of the poly(HPMA) brushes with time and the ability to prepare block copolymers indicate the living nature of this grafting-from process. Copper concentrations as low as 80 ppb were sufficient for this surface-initiated SET-LRP. Micropatterns of poly(HPMA) brushes on the silicon surface were constructed for the first time by this method. Negligible fouling was observed after contact with undiluted blood plasma. This report provides the first example of non-fouling polymer brushes prepared by SET-LRP of HPMA.

Use of pooled blood plasmas in the assessment of fouling resistance

The ability of a surface to resist fouling from blood plasma cannot be realistically estimated without measuring adsorption from real samples directly. Due to the variability of biological samples, pooled blood plasma is normally used. We show that even when using pooled plasma, a comparison of antifouling surfaces strongly depends on its source.

Phototriggered Functionalization of Hierarchically Structured Polymer Brushes

The precise design of bioactive surfaces, essential for the advancement of many biomedical applications, depends on achieving control of the surface architecture as well as on the ability to attach bioreceptors to antifouling surfaces. Herein, we report a facile avenue toward hierarchically structured antifouling polymer brushes of oligo(ethylene glycol) methacrylates via surface-initiated atom transfer radical polymerization (SI-ATRP) presenting photoactive tetrazole moieties, which permitted their functionalization via nitrile imine-mediated tetrazole-ene cyclocloaddition (NITEC). A maleimide-functional ATRP initiator was photoclicked to the side chains of a brush enabling a subsequent polymerization of carboxybetaine acrylamide to generate a micropatterned graft-on-graft polymer architecture as evidenced by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Furthermore, the spatially resolved biofunctionalization of the tetrazole-presenting brushes was accessed by the photoligation of biotin-maleimide and subsequent binding of streptavidin. The functionalized brushes bearing streptavidin were able to resist the fouling from blood plasma (90% reduction with respect to bare gold). Moreover, they were employed to demonstrate a model biosensor by immobilization of a biotinylated antibody and subsequent capture of an antigen as monitored in real time by surface plasmon resonance.

Antifouling Polymer Brushes Displaying Antithrombogenic Surface Properties

The contact of blood with artificial materials generally leads to immediate protein adsorption (fouling), which mediates subsequent biological processes such as platelet adhesion and activation leading to thrombosis. Recent progress in the preparation of surfaces able to prevent protein fouling offers a potential avenue to mitigate this undesirable effect. In the present contribution, we have prepared several types of state-of-the-art antifouling polymer brushes on polycarbonate plastic substrate, and investigated their ability to prevent platelet adhesion and thrombus formation under dynamic flow conditions using human blood. Moreover, we compared the ability of such brushes--grafted on quartz via an adlayer analogous to that used on polycarbonate--to prevent protein adsorption from human blood plasma, assessed for the first time by means of an ultrahigh frequency acoustic wave sensor. Results show that the prevention of such a phenomenon constitutes one promising route toward enhanced resistance to thrombus formation, and suggest that antifouling polymer brushes could be of service in biomedical applications requiring extensive blood-material surface contact.

Surface Grafting via Photo‐Induced Copper‐Mediated Radical Polymerization at Extremely Low Catalyst Concentrations

Surface-initiated photo-induced copper-mediated radical polymerization is employed to graft a wide range of polyacrylate brushes from silicon substrates at extremely low catalyst concentrations. This is the first time that the controlled nature of the reported process is demonstrated via block copolymer formation and re-initiation experiments. In addition to unmatched copper catalyst concentrations in the range of few ppb, film thicknesses up to almost 1 μm are achieved within only 1 h.

Quantifying bacterial adhesion on antifouling polymer brushes via single-cell force spectroscopy

Bacterial adhesion poses serious problems in food safety and biomedical applications. Antifouling polymer brushes have been shown to be effective as surface modifications to prevent biofilm formation from pathogenic bacteria. In this work, the adhesion of Yersinia pseudotuberculosis on seven types of brushes is examined by single-cell force spectroscopy. The brushes, known to possess excellent resistance to protein adsorption, greatly reduced the maximum force and the work required to detach the bacterium.

Grafting of functional methacrylate polymer brushes by photoinduced SET-LRP

Photoinduced surface-initiated single electron transfer living radical polymerization (SET-LRP) is a versatile technique for the preparation of polymer brushes. The vast diversity of compatible functional groups, together with a high end-group fidelity that enables precise control of the architecture, makes this approach an effective tool for tuning the properties of surfaces. We report the application of photoinduced SET-LRP for the surface-initiated grafting of polymer brushes from a wide range of methacrylate monomers for the first time. The living character of the process was demonstrated by the linear evolution of the polymer brush thickness in time, the ability to reinitiate the polymerization for the preparation of well-defined block copolymers, and also by X-ray photoelectron spectroscopy depth profiling. The surface patterning with these brushes could be achieved simply by restricting the irradiated area. The ability of poly(methacrylate) brushes prepared in this way to prevent non-specific protein adsorption is also demonstrated, indicating the suitability of this procedure for advanced applications.

Catalyst-free site-specific surface modifications of nanocrystalline diamond films via microchannel cantilever spotting

The properties of nanocrystalline diamond (NCD) films offer great potential for the creation of various sensing and photonic devices. A great challenge in order to materialize such applications lies in achieving the micrometrically resolved functionalization of NCD surfaces. In the present work, we introduce a facile approach to meet this challenge employing the novel strain-promoted alkyne–azide cycloaddition “click” chemistry reaction, a catalyst-free ligation protocol compatible with biomolecules. The ability to achieve well-resolved multicomponent patterns with high reproducibility is demonstrated, paving the way for the fabrication of novel devices based on micropatterned NCD films.