Organic plasma process for simple and substrate-independent surface modification of polymeric BioMEMS devices

Characterization of Mechanical Stability and Immunological Compatibility for Functionalized Modification Interfaces

Surface modification layers are performed on the surfaces of biomaterials and have exhibited promise for decoupling original surface properties from bulk materials and enabling customized and advanced functional properties. The physical stability and the biological compatibility of these modified layers are equally important to ensure minimized delamination, debris, leaching of molecules, and other problems that are related to the failure of the modification layers and thus can provide a long-term success for the uses of these modified layers. A proven surface modification tool of the functionalized poly-para-xylylene (PPX) system was used as an example, and in addition to the demonstration of their chemical conjugation capabilities and the functional properties that have been well-documented, in the present report, we additionally devised the characterization protocols to examine stability properties, including thermostability and adhesive strength, as well as the biocompatibility, including cell viability and the immunological responses, for the modified PPX layers. The results suggested a durable coating stability for PPXs and firmly attached biomolecules under these stability and compatibility tests. The durable and stable modification layers accompanied by the native properties of the PPXs showed high cell viability against fibroblast cells and macrophages (MΦs), and the resulting immunological activities created by the MΦs exhibited excellent compatibility with non-activated immunological responses and no indication of inflammation.

Properties and reactivity of polyoxazoline plasma polymer films

Polyoxazolines arise as a promising new class of polymers for biomedical applications, but creating oxzoline-based coatings via conventional methods is challenging. Herein, nanoscale polyoxazoline coatings were generated via a single step plasma deposition process. The effects of plasma deposition conditions on the film stability, structure and chemical group density were investigated. Detailed examination of the physical and chemical properties of plasma deposited polyoxazoline via XPS, FTIR, contact angle and ellipsometry unravels the complex functionality of the films. Partial retention of the oxazoline ring facilitates a covalent reaction with the carboxylic acid groups present on nanoparticles and biomolecules. Surface bound proteins effectively retain their bioactivity, therefore a vast range of potential applications unlocks for plasma deposited polyoxazoline coatings in the field of biosensing, medical arrays and diagnosis.

Highly selective trapping of enteropathogenic E. coli on Fabry-Pérot sensor mirrors

Untreated recycled water, such as sewage and graywater, will almost always contain a wide range of agents that are likely to present risks to human health, including chemicals and pathogenic microorganisms. The microbial hazards, such as large numbers of enteric pathogens that can cause gastroenteric illness if ingested, are the main cause of concern for human health. The presence of the enteropathogenic Escherichia coli (EPEC) serotype is of particular concern, as this group of bacteria is responsible for causing severe infant and travelers' diarrhea, gastroenteritis and hemolytic uremic syndrome. A biosensing system based on an optical Fabry-Pérot (FP) cavity, capable of directly detecting the presence of EPEC within 5 min, has been developed using a simple micro-thin double-sided adhesive tape and two semi-transparent FP mirror plates. The system utilizes a poly(methyl methacrylate) (PMMA) or glass substrates sputtered by 40-nm-thick gold thin films serving as FP mirrors. Mirrors have been activated using 0.1M mercaptopropionic acid, influencing an immobilization density of the translocated intimin receptor (TIR) of 100 ng/cm(2). The specificity of recognition was confirmed by exposing TIR functionalized surfaces to four taxonomically related and/or distantly related bacterial strains. It was found that the TIR-functionalized surfaces did not show any bacterial capture for these other bacterial strains within a 15 min incubation period.

Nanostructure protein repellant amphiphilic copolymer coatings with optimized surface energy by Inductively Excited Low Pressure Plasma

Statistically designed amphiphilic copolymer coatings were deposited onto Thermanox, Si wafer, and quartz crystal microbalance (QCM) substrates via Plasma Enhanced Chemical Vapor Deposition of 1H,1H,2H,2H-perfluorodecyl acrylate and diethylene glycol vinyl ether in an Inductively Excited Low Pressure Plasma reactor. Plasma deposited amphiphilic coatings were characterized by Field Emission Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy, Atomic Force Microscopy, and Water Contact Angle techniques. The surface energy of the coatings can be adjusted between 12 and 70 mJ/m(2). The roughness of the coatings can be tailored depending on the plasma mode used. A very smooth coating was deposited with a CW (continuous wave) power, whereas a rougher surface with R(a) in the range of 2 to 12 nm was deposited with the PW (pulsed wave) mode. The nanometer scale roughness of amphiphilic PFDA-co-DEGVE coatings was found to be in the range of the size of the two proteins namely BSA and lysozyme used to examine for the antifouling properties of the surfaces. The results show that the statistically designed surfaces, presenting a surface energy around 25 mJ/m(2), present no adhesion with respect to both proteins measured by QCM.

Rapid and ultrasensitive E. coli O157:H7 quantitation by combination of ligandmagnetic nanoparticles enrichment with fluorescent nanoparticles based two-color flow cytometry

A novel, fast and sensitive determination strategy for E. coli O157:H7 has been developed by combination of ligandmagnetic nanoparticles (LMNPs) enrichment with a fluorescent silica nanoparticles (FSiNPs) based two-color flow cytometry assay (LMNPs@FSiNPs-FCM). E. coli O157:H7 was first captured and enriched through the lectin concanavalin A (Con A) favored strong adhesion of E. coli O157:H7 to the mannose-conjugated magnetic nanoparticles. The enriched E. coli O157:H7 was further specially labeled with goat anti-E. coli O157:H7 antibody modified RuBpy-doped FSiNPs, and then stained with a nucleic acid dye SYBR Green I (SYBR-I). After dual-labeling with FSiNPs and SYBR-I, the enriched E. coli O157:H7 was determined using multiparameter FCM analysis. With this method, the detection sensitivity was greatly improved due to the LMNPs enrichment and the signal amplification of the FSiNPs labelling method. Furthermore, the false positives caused by aggregates of FSiNPs conjugates and nonspecific binding of FSiNPs to background debris could be significantly decreased. This assay allowed the detection of E. coli O157:H7 in PB buffer at levels as low as 7 cells mL(-1). The total assay time including E. coli O157:H7 sample enrichment and detection was less than 4 h. An artificially contaminated bottled mineral water sample with a concentration of 6 cells mL(-1) can be detected by this method. It is believed that the proposed method will find wide applications in biomedical fields demanding higher sensitive bacterial identification.

Wireless, remote-query, and high sensitivity Escherichia coli O157:H7 biosensor based on the recognition action of concanavalin A

Escherichia coli O157:H7 is detected using a remote-query (wireless, passive) magnetoelastic sensor platform to which a 1 microm thick layer of Bayhydrol 110 and then a layer of functionalized mannose is applied. The multivalent binding of lectin concanavalin A (Con A) to the E. coli surface O-antigen and mannose favors the strong adhesion of E. coli to the mannose-modified magnetoelastic sensor; E. coli is rigidly and strongly attached on the mannose-modified sensor through Con A, which works as a bridge to bind E. coli to the mannose-modified sensor surface. As E. coli is bound to the sensor, its resonance frequency shifts, enabling quantification of E. coli concentration with a limit of detection of 60 cells/mL and a linear logarithmic response range of 6.0 x 10(1) to 6.1 x 10(9) cells/mL. The analysis can be directly conducted without incubation and completed in 3 h or less.

Cold plasma functionalized TeraHertz BioMEMS for enzyme reaction analysis

In this paper, we describe the development, functionalization and functionality testing of a TeraHertz (THz) Bio-MicroElectroMechanical System (BioMEMS) dedicated to enzyme reaction analysis. The microdevice was fabricated by mixing clean room microfabrication with cold plasma deposition. The first is used to build the microfluidic circuits and the THz sensor, while the later serves for the polymerization of allylamine using a homemade glow discharge plasma reactor for a subsequent immobilization of enzymatic biocatalysts. Thermal stability of the deposited plasma polymer has been investigated by infrared spectroscopy. Fluorescent detection confirmed the efficiency of the immobilization and the enzyme hydrolysis into the BioMEMS microchannels. For the first time, the progression of the hydrolysis reaction over time was monitored by the THz sensor connected to a vectorial network analyzer. Preliminary results showed that sub-THz transmission measurements are able to discriminate different solid films, various aqueous media and exhibit specific transmission behavior for the enzyme hydrolysis reaction in the spectral range 0.06-0.11 THz.

Investigation of a vapor-deposited thin silica film: morphological and spectral characterization

Surface modification reactions by organosilicon compounds have demonstrated great success in a wide variety of applications. However, they are of limited usefulness in that they only proceed appreciably on surfaces that have an abundance of reactive hydroxyl groups, thus preventing their application to some materials of technological relevance, such as plastics and polymers. A process capable of depositing a surface rich in reactive hydroxyl groups onto a wide variety of substrates could potentially enable the extension of organosilane surface modification reactions to new materials, but conventional processes for depositing oxide layers require temperatures that are too high for most polymers and plastics. It has been shown that silica layers can be deposited from the vapor-phase hydrolysis of tetrachlorosilane at room temperature, but little if any work has been done to characterize the resulting films. In this work, ellipsometry, atomic force microscopy, and Fourier transform infrared spectroscopy are employed to study the characteristics of films formed from this process. Interestingly, very different film morphologies can be obtained by changing key processing parameters. Furthermore, isotopic exchange experiments and dehydration studies show that the surfaces of the silica films obtained by this method are composed entirely of hydrogen-bonded silanol groups and do not exhibit any freely vibrating surface silanol groups, a result that is in contrast with conventionally prepared silica materials. Still, this layer has been shown to behave very similarly to conventional silica materials with respect to surface reactions. Finally, infrared spectral data and contact angle data demonstrate that this method can be employed to deposit silica layers onto poly(methyl methacrylate) and polystyrene surfaces.

DNA immobilization/hybridization on plasma-polymerized pyrrole

The present work describes the fabrication and characterization of the conducting polymer coatings prepared by the continuous wave plasma polymerization and the applications as adhesion layers for studying DNA immobilization/hybridization. The stability of plasma polymerized pyrrole (ppPY) in the aqueous solution was characterized by ellipsometry. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to investigate polymer matrix properties and oligonucleotide/DNA binding interaction. The successful DNA immobilization on ppPY surfaces was found to depend on the macromolecular architecture of plasma polymerized films. The plasma polymers with similar thickness deposited at different input powers showed various comparable immobilization properties. The plasma-polymerized films prepared at the low input power showed a lower sensitivity toward DNA binding than those films deposited at the high input power. This result will be important to study plasma polymerized films as potential DNA biosensors in the future.

Photochemically patterned poly(methyl methacrylate) surfaces used in the fabrication of microanalytical devices

We report here the photochemical surface modification of poly(methyl methacrylate), PMMA, microfluidic devices by UV light to yield pendant carboxylic acid surface moieties. Patterns of carboxylic acid sites can be formed from the micrometer to millimeter scale by exposure of PMMA through a contact mask, and the chemical patterns allow for further functionalization of PMMA microdevice surfaces to yield arrays or other structured architectures. Demonstrated here is the relationship between UV exposure time and PMMA surface wettability, topography, surface functional group density, and electroosmotic flow (EOF) of aqueous buffer solutions in microchannels made of PMMA. It is found that the water contact angle on PMMA surfaces decreases from 70 degrees to 24 degrees after exposure to UV light as the result of the formation of carboxylic acid sites. However, upon rinsing with 2-propanol, the water contact angle increases to approximately 80 degrees , and this increase is attributed to changes in surface roughness resulting from removal of low molecular weight PMMA formed from scission events. In addition, the surface roughness and surface coverage of carboxylic acid groups exhibit a characteristic trend with UV exposure time. Electroosmotic flow (EOF) in PMMA microchannels increases upon UV modification and is pH dependent. The possible photolysis mechanism for formation of carboxylic acid groups on PMMA surfaces under the conditions outlined in this work is discussed.

Room-temperature bonding for plastic high-pressure microfluidic chips

A generic method for the rapid, reproducible, and robust bonding of microfluidic chips fabricated from plastics has been developed and optimized. One of the bonding surfaces is exposed to solvent vapor prior to bringing the mating parts into contact and applying a load. Nanoindentation measurements performed by atomic force microscopy show that a reversible material softening occurs upon exposure to solvent vapor. Subsequent exposure of the bonded chip to UV light then strengthens the bond between mating parts and increases the burst pressure by 50% due to partial cross-linking and chain scission reactions as measured by size exclusion chromatography-multiangle light scattering (SEC-MALS). Performing all steps of this procedure at room temperature eliminates channel distortion observed during thermal bonding and affords channels with highly uniform cross-sectional dimensions. Our technique enables chips resistant to pressures as high as 34.6 MPa.

Adsorption of glucose oxidase onto plasma-polymerized film characterized by atomic force microscopy, quartz crystal microbalance, and electrochemical measurement

Adsorption of glucose oxidase (GOD) onto plasma-polymerized thin films (PPF) with nanoscale thickness was characterized by atomic force microscopy (AFM), quartz crystal microbalance (QCM), and electrochemical measurements. The PPF surface is very flat (less than 1-nm roughness), and its properties (charge and wettability) can be easily changed while retaining the backbone structure. We focused on three types of surfaces: (1) the pristine surface of hexamethyldisiloxane (HMDS) PPF (hydrophobic and neutral surface), (2) an HMDS PPF surface with nitrogen-plasma treatment (hydrophilic and positive-charged surface), and (3) an HMDS PPF surface treated with oxygen plasma (hydrophilic and negative-charged surface). The AFM image showed that the GOD molecules were densely adsorbed onto surface 2 and that individual GOD molecules could be observed. The longer axis of GOD ellipsoid molecules were aligned parallel to the surface, called the "lying position", because of electrostatic association. On surface 1, clusters of GOD molecules did not completely cover the original PPF surface (surface coverage was ca. 60%). The 10-nm-size step height between the GOD clusters and the PPF surface suggests that the longer axes of individual GOD molecules were aligned perpendicular to the surface, called the "standing position". On surface 3, only a few of the GOD molecules were adsorbed because of electrostatic repulsion. These results indicate that the plasma polymerization process can facilitate enhancement or reduction of protein adsorption. The AFM images show a corresponding tendency with the QCM profiles. The QCM data indicate that the adsorption behavior obeys the Langmuir isotherm equation. The amperometric biosensor characteristics of the GOD-adsorbed PPF on a platinum electrode showed an increment in the current because of enzymatic reaction with glucose addition, indicating that enzyme activity was mostly retained in spite of irreversible adsorption.

Chitosan-mediated in situ biomolecule assembly in completely packaged microfluidic devices

We report facile in situ biomolecule assembly at readily addressable sites in microfluidic channels after complete fabrication and packaging of the microfluidic device. Aminopolysaccharide chitosan's pH responsive and chemically reactive properties allow electric signal-guided biomolecule assembly onto conductive inorganic surfaces from the aqueous environment, preserving the activity of the biomolecules. A transparent and nonpermanently packaged device allows consistently leak-free sealing, simple in situ and ex situ examination of the assembly procedures, fluidic input/outputs for transport of aqueous solutions, and electrical ports to guide the assembly onto the patterned gold electrode sites within the channel. Both in situ fluorescence and ex situ profilometer results confirm chitosan-mediated in situ biomolecule assembly, demonstrating a simple approach to direct the assembly of biological components into a completely fabricated device. We believe that this strategy holds significant potential as a simple and generic biomolecule assembly approach for future applications in complex biomolecular or biosensing analyses as well as in sophisticated microfluidic networks as anticipated for future lab-on-a-chip devices.

Capillarity Induced Solvent-Actuated Bonding of Polymeric Microfluidic Devices

Rapid, robust, and economical fabrication of fluidic microchannels is of fundamental importance for the successful development of disposable lab-on-a-chip devices. In this work, we present a solvent-actuated bonding method for fabricating polymeric microfluidic devices at room temperature. A PMMA sheet with an imprinted microchannel was clamped to a blank PMMA sheet, and then 80 +/- 5 muL of acetone (bonding solvent) was introduced at one end of the fluidic channel and aspirated out at the other end. As the solvent moved down the channel, capillary forces drew a fraction of the solvent into the interstitial space between the two polymeric substrates. After aspiration, the assembly was incubated in the clamp for 5 min for effective bond formation. The quantity of the bonding solvent, its water content and flow rate, along with residence time in the channel were found to have significant impact on the bond quality and the channel integrity. Microfluidic electrophoretic separations of a 400-base DNA ladder were performed in devices fabricated using this method in less than 8 min with efficiencies routinely between 2 x 10(6) and 3 x 10(6) plates/m. The simplicity and economy of this technique make it amenable for automation and mass production, which could make polymeric substrates more attractive for single-use chemical analysis devices.

Structure and biosensor characteristics of complex between glucose oxidase and plasma-polymerized nanothin film

The structure and biosensor characteristics of complex between glucose oxidase (GOD) and plasma-polymerized nanothin film (PPF), in which the thickness is several nanometers, were investigated by atomic force microscopy (AFM) and electrochemical measurement. The GOD molecules were densely adsorbed onto the PPF surface treated by nitrogen plasma and the individual GOD molecules were observed. Subsequently, the GOD densely packed array on the PPF surface was subsequently treated by plasma polymerization (overcoating). AFM image showed that the thicker film gave the smoother surface, indicating that the GOD adsorbed on the surface was embedded more deeply in PPF. The amperometric biosensor characteristics of the GOD-PPF complex on a platinum electrode showed the current increment due to the enzymatic reaction with glucose addition, indicating that enzyme activity was retained although the enzyme has been exposed to the plasma gas related to diffusion of the substrate. This means that under mild exposure to organic plasma, the enzyme does not become seriously dysfunctional. Amperometric biosensor characteristics were strongly affected by monomer and thickness of PPF overcoating related with the diffusion of the substrate (glucose). Considering that the film deposition was performed using microfabrication-compatible organic plasma, our new method for protein architecture has a great potential of enabling high throughput production of bioelectronic devices.

Electron transfer mediator micro-biosensor fabrication by organic plasma process

We propose a new strategy for constructing a mediator-type biosensor as a Bio-MicroElectroMechanical Systems (BioMEMS) application. A vinylferrocene plasma-polymerized film (PPF) was deposited directly onto the surface of an electrode under dry conditions. The resulting redox film was extremely thin, adhered well onto a substrate (electrode), and had a highly crosslinked network structure. This technique, capable of polymeric deposition of any kind of monomer, can also serve the purpose of anti-fouling coating, or layer-to-layer interface creation. With a subsequent plasma process, additional polymeric layer of hydrophilic acetonitrile was superimposed onto the existing vinylferrocene-PPF surface to offer crucial features such that the wettability could be adjusted for a better electron transfer, and amino functional groups could be attached to immobilize a large amount of enzyme. Based upon this scheme, the device fabrication could be designed in a manner that the whole procedure was made up of dry wafer-handling processes, which is compatible with mass production. A prototype device was fabricated to have an array of needle-shaped amperometric micro-biosensors. The resultant thin polymer layer carried a large number of the mediator molecules, accomplishing a lower overpotential (+410 mV) and a rapid response time (<5s). Stressing the advantages of the plasma polymerization process together with some additional features accomplished in our device fabrication, we would discuss new possibilities in the field of BioMEMS.

Fabrication and characterization of poly(methylmethacrylate) microfluidic devices bonded using surface modifications and solvents

The fabrication of polymer microchips allows inexpensive, durable, high-throughput and disposable devices to be made. Poly(methylmethacrylate) (PMMA) microchips have been fabricated by hot embossing microstructures into the substrate followed by bonding a cover plate. Different surface modifications have been examined to enhance substrate and cover plate adhesion, including: air plasma treatment, and both acid catalyzed hydrolysis and aminolysis of the acrylate to yield carboxyl and amine-terminated PMMA surfaces. Unmodified PMMA surfaces were also studied. The substrate and cover plate adhesion strengths were found to increase with the hydrophilicity of the PMMA surface and reached a peak at 600 kN m(-2) for plasma treated PMMA. A solvent assisted system has also been designed to soften less than 50 nm of the surface of PMMA during bonding, while still maintaining microchannel integrity. The extent to which both surface modifications and solvent treatment affected the adhesion of the substrate to the cover plate was examined using nanoindentation methods. The solvent bonding system greatly increased the adhesion strengths for both unmodified and modified PMMA, with a maximum adhesion force of 5500 kN m(-2) achieved for unmodified PMMA substrates. The bond strength decreased with increasing surface hydrophilicity after solvent bonding, a trend that was opposite to what was observed for non-solvent thermal bonding.