Cyclic Olefin Copolymer Surface Research Articles

Surface functionalization of cyclic olefin copolymer by plasma‐enhanced chemical vapor deposition using atmospheric pressure plasma jet for microfluidic applications

AbstractLab‐On‐A‐Chips promise solutions for high throughput and specific analysis for environmental and health applications, with the challenge to develop materials allowing fast, easy, and cheap microfabrication and efficient surface treatment. Cyclic olefin copolymer (COC) is a promising thermoplastic, easily microfabricated for both rapid prototyping and low‐cost mass production of microfluidic devices but still needing efficient surface modification strategies. This study reports for the first time the optimization of an easy COC silica coating process by plasma‐enhanced chemical vapor deposition at atmospheric pressure with plasma jet and tetraethylorthosilicate as precursor, leading to a 158 ± 7 nm thickness and a 14‐day‐stability of hydrophilic properties for a COC‐embedded microchannel (100 µm), paving the way for a simplified and controlled COC surface modification.

Functionalization of cyclic olefin copolymer substrates with polyethylene glycol diacrylate for the in situ synthesis of immobilized nanoparticles

Nanoparticles as novel stationary phase could enhance chromatographic performance (efficiency and resolution). However, their implementation in columns is rather challenging. The methodological approach we propose is an in situ synthesis of such nanoparticles through photopolymerization of a miniemulsion containing hexyl acrylate monomers. While the miniemulsion composition was previously optimized, resulting in highly spherical monodisperse nanoparticles with a mean size inferior to 200 nm, the immobilization of such particles is not straightforward. The strategy consists in carrying out the miniemulsion polymerization in the very close vicinity of a reactive surface, namely cyclic olefin copolymer (COC), from which covalent bond can grow thanks to hydrogen abstraction. While the hydrophobic nature of COC appears to disturb the stability of the miniemulsion, a more polar surface allows simultaneous polymerization and anchoring of nanoparticles on the surface. Surface functionalization of COC with different monomers was tested in this work and polyethylene glycol dimethacrylate photografting was found to provide an adequate surface modification. It appears however that the extent of surface modification and especially the amount of initiator that is applied on the COC surface have consequences on both the spherical aspect and the number of resulting nanoparticles. An optimization of the PEGDA surface modification by central composite design in regards to PEGDA and BME amounts and irradiation time is proposed. SEM images after miniemulsion photopolymerization for different conditions of PEGDA photografting showed the impact of photografting on nanoparticle shape.

Wetting characteristics of bare micro-patterned cyclic olefin copolymer surfaces fabricated by ultra-precision raster milling

A micro-directional grooved cyclic olefin copolymer surface fabricated by ultra-precision raster milling gives a good sliding performance for a water droplet.

Superhydrophobic hierarchical structures produced through novel low-cost stamp fabrication and hot embossing of thermoplastic film

We present a simple and cost-effective method to produce superhydrophobic surfaces in thermoplastic polymer substrates, which contain hierarchical micro/nano structures that resemble lotus leaves. The method involved the fabrication of an Al stamp through the sequential application of laser ablation and anodization to create micro- and nano-structures, respectively. The fabricated patterns on the Al stamp were replicated on the thermoplastic Cyclic olefin copolymer (COC) film surfaces through a hot embossing technique. Static water contact angles were measured to evaluate the hydrophobicity of the patterned COC surfaces. The static water contact angle on the micro/ nano hierarchical structured COC surface was measured to be 162.3° on average. The hot embossing process was repeated 31 times with a nano-structured Al stamp, and the replicated COC surfaces showed consistent water contact angles.

Atmospheric Solid Analysis Probe-Ion Mobility Mass Spectrometry: An Original Approach to Characterize Grafting on Cyclic Olefin Copolymer Surfaces.

A cyclic olefin copolymer (COC) was grafted with aryl layers from aryldiazonium salts, and then we combined infrared spectrometry, atomic force microscopy (AFM), and ion mobility mass spectrometry with atmospheric solid analysis probe ionization (ASAP-IM-MS) to characterize the aryl layers. ASAP is a recent atmospheric ionization method dedicated to the direct analysis of solid samples. We demonstrated that ASAP-IM-MS is complementary to other techniques for characterizing bromine and sulfur derivatives of COC on surfaces. ASAP-IM-MS was useful for optimizing experimental grafting conditions and to elucidate hypotheses around aryl layer formation during the grafting process. Thus, ASAP-IM-MS is a good candidate tool to characterize covalent grafting on COC surfaces.

TiO2 coated microfluidic devices for recoverable hydrophilic and hydrophobic patterns

We report a simple method for modifying the surfaces of plastic microfluidic devices through dynamic coating process with a nano-colloidal TiO2 sol. The surface of the thermoplastic, cyclic olefin copolymer (COC) was coated with the TiO2 film, that displayed an effective photocatalytic property. The hydrophilic surface is obtained in the TiO2-coated zone of a microfluidic channel, and TiO2 coated surface degradation can be reversed easily by UV irradiation. The present work shows a photocatalytic activity concerning the effect of TiO2 coating density, which is controlled by the number of coating cycles. The hydrophilized surface was characterized by the contact angle of water and the TiO2 coated COC surface reduced the water contact angle from 85° to less than 10° upon UV irradiation. The photocatalytic effect of the layer that was coated five times with TiO2 was excellent, and the super-hydrophilicity of the TiO2 surface could be promptly recovered after 10 months of storage at atmospheric conditions. The COC microfluidic devices, in which TiO2 has been freshly deposited and aged for 10 months, were capable of generating water-in oil-in water (W/O/W) double emulsions easily and uniformly by simple control of the flow rates for demonstration of excellent hydrophilic patterning and recovery of the TiO2 coated in the microchannels.

Immobilization of Antibody on a Cyclic Olefin Copolymer Surface with Functionalizable, Non-Biofouling Poly[Oligo(Ethylene Glycol) Methacrylate

We report a perfluoroaryl azide-based photoreaction for synthesizing functionalizable and nonbiofouling poly[oligo(ethylene glycol) methacrylate] (pOEGMA) films on a chemically inert COC substrate, and an estimation of a surface coverage of the antibody immobilized onto the surface with the immuno-gold nanoparticles. The processes were confirmed by water contact angle measurement, FT-IR spectroscopy, and FE-SEM. The strategy demonstrated in this work could be applied to functionalizations of other polymeric materials and determination of the binding capacity of analytes in biosensors and microfluidic devices.

Direct assembly of cyclic olefin copolymer microfluidic devices helped by dry photoresist

A generic method for rapid, reproducible, and robust selective bonding of microfluidic chips made of Cyclic Olefin Copolymer (COC) has been developed and optimized. In this work we propose an adhesive bonding technique using ORDYL negative dry film photo-resist as glue to perform the packaging of COC micro-patterned structures. The ORDYL resist is qualified in terms of resolution, biocompatibility and fluidic sealing. The adhesive bonding is achieved by laminating a thin layer of ORDYL SY300 (<17μm) on top of the microfluidic part and then bonded to the other COC part. In this research, an oxygen plasma treatment for adhesion improvement was performed on COC surfaces at various plasma times. The bonding method is described in detail and the bonding quality of the chips was evaluated by a shear strength testing procedure and a leak test by pressurizing a microfluidic channel with an aqueous solution using an external peristaltic pump. Results are reported emphasizing the efficiency of the proposed approach and the developed process features high yields (>70%).

Surface functionalization of cyclic olefin copolymer with aryldiazonium salts: A covalent grafting method

Covalent immobilization of biomolecules on the surface of cyclic olefin copolymer (COC) is still a tough challenge. We developed a robust method for COC surface grafting through reaction with aryldiazonium. Chemical diazonium reduction generated an aryl radical and the formation of a grafted film layer on the organic surface. We also demonstrated that the chemical reduction of diazonium salt was not sufficient to form a film on the COC surface. UV illumination had to be combined with chemical reduction to graft an aryl layer onto the COC surface. We optimized organic film deposition by using different chemical reducers, different reaction times and reagent proportions. We characterized surface modifications by fluorescence microscopy and contact angle measurements, infrared spectroscopy, X-ray photoemission spectroscopy and Raman spectroscopy, and assessed the topography of the aryl film by atomic force microscopy. This original strategy allowed us to evidence various organic functions to graft biomolecules onto COC surfaces with a fast and efficient technique.

Coordination complexes as molecular glue for immobilization of antibodies on cyclic olefin copolymer surfaces

A novel metal-based chelating method has been used to provide an order of magnitude increase in immunoassay performance on cyclic olefin copolymer (COC) plastics compared with passive binding. COCs are hydrophobic, and without surface modification they are often unsuitable for applications where protein adhesion is desired. When interacting with the bare plastic, the majority of the bound proteins will be denatured and become nonfunctional. Many of the surface modification techniques reported to date require costly equipment setup or the use of harsh reaction conditions. Here, we have successfully demonstrated the use of a simple and quick metal chelation method to increase the sensitivity, activity, and efficiency of protein binding to COC surfaces. A detailed analysis of the COC surfaces after activation with the metal complexes is presented, and the immunoassay performance was studied using three different antibody pairs.

Construction of DNA microarrays on cyclic olefin copolymer surfaces using confined photocatalytic oxidation

A novel strategy for DNA immobilization on cyclic olefin copolymer surfaces.

Polymeric Functionalization of Cyclic Olefin Copolymer Surfaces with Nonbiofouling Poly(oligo(Ethylene Glycol) Methacrylate)

Polymeric Functionalization of Cyclic Olefin Copolymer Surfaces with Nonbiofouling Poly(oligo(Ethylene Glycol) Methacrylate)

High-density immobilization of antibodies onto nanobead-coated cyclic olefin copolymer plastic surfaces for application as a sensitive immunoassay chip

Our research efforts have been devoted to development of nanobead multilayer-based sensitive immunoassays on cyclic olefin copolymer (COC) plastic surfaces. To facilitate nanobead attachment and impart antibiofouling properties to a COC substrate, we used an amphiphilic copolymer comprising benzyl, polyethylene glycol, and reactive ester moieties to coat the hydrophobic COC surface in an aqueous environment. Subsequently, NH2-modified polystyrene nanobeads were reacted with the polymer-coated COC surface and further assembled into multilayers that increased the overall surface area available for attaching capture antibodies. After treatment of the nanobead multilayers with an amine-reactive homobifunctional crosslinker, a model capture antibody (anti-rabbit IgG) was covalently immobilized onto the activated surface of nanobeads. Finally, a sandwich immunoassay was carried out using rabbit IgG as a target analyte and rhodamine-labeled anti-rabbit IgG as a probe. Compared with a nanobead-free, polymer-coated COC surface, the nanobead multilayer-based immunoassay exhibited ~4-fold higher fluorescence intensity. In addition, our nanobead-based assay system exhibited a wide dynamic range of detection (0.1 to 1,000ng/mL) and high specificity for rabbit IgG. Furthermore, much better detection sensitivity for rabbit IgG was attained in the nanobead multilayer-based immunoassay than with a conventional ELISA system (0.1ng/mL versus 10ng/mL), indicating the potential value of the proposed immunoassay system in plastic-based portable biochip applications.

Facile Immobilization of Biomolecules onto Various Surfaces Using Epoxide-Containing Antibiofouling Polymers

The surface modifications of plastic or glass substrate and the subsequent immobilization of biomolecules onto the surfaces has been a central feature of the fabrication of biochips. To this end, we designed and synthesized new epoxide-containing random copolymers that form stable polymer adlayers on plastic or glass surface and subsequently react with amine or sulfhydryl functional groups of biomolecules under aqueous conditions. Epoxide-containing random copolymers were synthesized by radical polymerization of three functional monomers: a monomer acting as an anchor to the surfaces, a PEG group for preventing nonspecific protein adsorption, and an epoxide group for conjugating to biomolecules. Polymer coating layers were facilely formed on cyclic olefin copolymer (COC) or glass substrate by simply dipping each substrate into a solution of each copolymer. The polymer-coated surfaces characterized by a contact angle analyzer and X-ray photoelectron spectroscopy (XPS) showed very low levels of nonspecific immunoglobulin G (IgG) adsorption compared to the uncoated bare surface (control). Using a microcontact printing (μCP) method, antibodies as representative biomolecules could be selectively attached onto the copolymers-coated glass or COC surface with high signal-to-noise ratios.

New “one-step” method for the simultaneous synthesis and anchoring of organic monolith inside COC microchip channels

A new method for monolith synthesis and anchoring inside cyclic olefin copolymer (COC) microchannels in a single step is proposed. It is shown that type I photoinitiators, typically used in a polymerization mixture to generate free radicals during monolith synthesis, can simultaneously act as type II photoinitiators and react with the plastic surface through hydrogen abstraction. This mechanism is used to "photograft" poly(ethylene glycol) methacrylate (PEGMA) on COC surfaces. Contact angle measurements were used to observe the changes in surface hydrophilicity when increasing initiator concentration and irradiation duration. The ability of type I photoinitiators to synthesize and anchor a monolith inside COC microchannels in a single step was proved through SEM observations. Different concentrations of photoinitiators were tried. Finally, electrochromatographic separations of polycyclic aromatic hydrocarbons were realized to illustrate the beneficial effect of anchoring on chromatographic performances. The versatility of the method was demonstrated with two widely used photoinitiators: benzoin methyl ether (BME) and azobisisobutyronitrile (AIBN).

Toward immunoassay chips: Facile immobilization of antibodies on cyclic olefin copolymer substrates through pre-activated polymer adlayers

Our research efforts have focused on the surface modification and the potential as a biochip material of commercially available cyclic olefin copolymer (COC) substrates. For the surface modification of hydrophobic COC substrates we synthesized two types of amphiphilic polymers having three important functions: hydrophobic (dodecyl or benzyl) groups, serving to anchor the COC substrate; a PEG component, which acts as a repellent of non-specific biomolecules; and an NHS ester group for conjugation of biomolecules. Formation of the polymer adlayers on COC surface was confirmed using a contact angle analyzer. The anti-biofouling property of the polymer-coated COC surface was examined by measuring the extent of nonspecific adsorption of immunoglobulin G (IgG), resulting in a very low level of the protein adsorption compared to uncoated COC surfaces (control). In addition, antibodies, used as representative biomolecules for immunoassay, could be selectively immobilized on the polymer-coated COC surface. Sandwich immunoassay using anti-rabbit IgG immobilized COC surface showed linear response to rabbit IgG of model analyte over a range from 1 to 1000 ng/mL with detection limit of 1–10 ng/mL. We also fabricated a Lab-On-a Chip type of COC biochip, which could detect a cardiac marker protein, troponin I (TnI), with detection limit of 10 ng/mL.

Surface Modification of COC Microfluidic Devices: A Comparative Study of Nitrogen Plasma Treatment and its Advantages Over Argon and Oxygen Plasma Treatments

AbstractControl of surface properties is very important in high performance microfluidic devices because appropriate functionalization of the surface of the microchannel helps to minimize adsorption of certain analytes thus improving its performance. In this regard, both the argon and oxygen plasma techniques have been used to improve the adaption of polymer surfaces to biological environments. However, the less common nitrogen plasma technique has not been used for surface modification of cyclic olefin copolymer (COC) in microfluidic applications. This paper presents a comparative study between the argon, oxygen, and nitrogen plasma treatments with the aim to identify the most suitable process for the development of a smart, disposable chip for the Bio‐MEMS application. The chemical and morphological changes of the plasma modified COC surfaces were characterized using X‐ray photoelectron spectroscopy, atomic force microscopy, and water contact angle measurements. The effect of plasma treatment on the strength of thermally bonded lap‐shear specimens was studied. The influence of plasma treatment on the integrity of thermally sealed microdevices was assessed using burst pressure tests. The plasma treatments had a significant impact on the electroosmosis flow mobility in the microchannels. The hemocompatibility of the various plasma‐modified COC surfaces was determined using the static platelets adhesion experiment. It was shown that the nitrogen plasma treatment was more effective than the argon and oxygen treatments for the modification of COC based microfluidic devices. magnified image

Low-temperature (below Tg) thermal bonding of COC microfluidic devices using UV photografted HEMA-modified substrates: high strength, stable hydrophilic, biocompatible surfaces

Cyclic olefin copolymer (COC) based microfluidic devices offer unique opportunities in developing high quality chips for a variety of applications but critical issues such as the bonding strength, biocompatibility and flow need to be addressed before this can be realized. In this study, we introduce a simple microfluidic device fabricated on COC (Topas) substrates that were modified by ultraviolet (UV) photo-grafting of a hydrophilic monomer 2-hydroxyethyl methacrylate (HEMA). This water soluble acrylic monomer was used to increase the bond strength, surface wettability and hemocompatibility. Thermal bonding of the microfluidic chips was accomplished at temperatures well below the glass transition temperature (Tg) of the COC polymer. Moreover, this process produced COC microchannels with modified surfaces that had stable permanent hydrophilic properties. Therefore, it can be used for Bio-MEMS applications in electrophoretic analysis where stable electro-osmotic flow (EOF) is important. The bond strength and burst pressure of the HEMA modified chips increased significantly to 1.70 MPa and 4.20 MPa for bonding at 10 °C below Tg. The COC surfaces were characterized using contact angle, EOF measurements, and Fourier transform infrared spectroscopy. The hydrophilicities of the substrates improved significantly with increase in degree of poly-HEMA immobilization and a maximum grafting yield of about 0.13% was obtained for a short irradiation time of 12 min with 25% of HEMA monomer. In vitrofibrinogen and fluorescent labeled bovine serum albumin adsorption results indicated that the COC surface can easily be tuned against protein adsorption by controlling the grafting yield. The in vitroplatelet adhesion tests confirmed that the hydroxyl functionality greatly improved the surface hemocompatibility of COC by reducing the number and the degree of activation of the adherent platelets.

Surface analysis, hydrophilic enhancement, ageing behavior and flow in plasma modified cyclic olefin copolymer (COC)-based microfluidic devices

Radio frequency (RF) argon and argon-oxygen plasma were used to improve hydrophilicity and increase wettability of the COC (Topas) surface to enhance its surface properties for applications in microfluidic devices. This is necessary because the hydrophobic nature of COC can lead to adsorption of specific compounds from biological fluids in the channel which can impair precise quantification and cause clogging. The significant loss in hydrophilicity during ageing was found to be associated with the decrease in –OH groups on the plasma modified surface. A correlation was found between the surface oxygen/carbon ratio and hydrophobicity of the treated surface. Plasma power ratings of 60 W and 100 W with exposure times from 15 s to 240 s were carried out. The surface roughness was characterized using atomic force microscopy (AFM) and wettability was determined using contact angle measurements. The oxygenated-argon plasma treatment improved surface wettability more effectively as compared to the argon treatment. The changes in surface properties due to treatment and during ageing were characterized using FTIR and XPS (X-ray photoelectron spectroscopy) revealing the presence of polar species such as carbonyl, carboxyl and hydroxyl groups. The probable chemical surface mechanisms were identified. The study indicates that plasma modified COC-based microfluidic devices ought to be vacuum-packed for storage to ensure that their performance will not be impaired.

Versatile surface functionalization of cyclic olefin copolymer (COC) with sputtered SiO2 thin film for potential BioMEMS applications

Cyclic olefin copolymer (COC) is a new class of thermoplastic polymers used for a variety of applications ranging from bio-sensing to optics. However, lack of functional groups and intense surface hydrophobicity hamper further development and application of this material. Here, we describe fabrication and characterization of SiO2–COC hybrid material (oxCOC), which provides a desirable substrate for microfluidic devices and subsequent surface modifications. The deposited SiO2 thin film on COC surface was characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The new SiO2–COC hybrid was found to have similar high optical transmission properties as that of pristine COC. Profilometric and AFM analysis revealed no dramatic change in morphology or surface roughness of functionalized COC. The SiO2–COC hybrid appeared to be stable in most of the solvents evaluated and could be further modified by other compounds, such as 3-aminopropyltriethoxy silane (APTES). The new SiO2–COC hybrid material and the robust fabrication method are expected to enable a variety of BioMEMS applications.