Accurate measurement of the steady-state swelling behavior of SU-8 negative photo resist

The swelling behaviour of SU-8 2000 series is investigated. This is done using on-wafer micro machined stress indicator structures. The indicator structures convert the stress in the material to a measurable displacement. When SU-8 is submersed into a solvent, the polymer matrix of the SU-8 can absorb some of the solvent molecules. As a result, the SU-8 can expand and the built in tensile stress is partially relieved. The swelling can thus be measured directly and independently of lithography parameters. For this study, the indicator structures are immersed in Propyle Glycol Methyl Ether Acetate (PGMEA), isopropyl alcohol (IPA) and water.     

Design and fabrication of integrated solid-phase extraction-zone electrophoresis microchip

Integrated solid-phase extraction-zone electrophoresis (SPE-ZE) device has been designed and fabricated on microchip. The structures were fabricated by using multiple layers of SU-8 polymer with a novel technique that enables easy alignment and high yield of the chips. SU-8 adhesive bonding has two major advantages: it enables bonding of high aspect ratio pillars and it results in fully SU-8 microchannels with uniform electrokinetic flow properties. The SPE-ZE device has a fluidic reservoir with 15:1 high aspect ratio pillars for bead filters that act as a SPE part in the chip structure. The separation unit is a 25 mm long electrophoresis channel starting from the outlet of SPE reservoir. Argon laser-induced fluorescence (LIF) detector was used to monitor simultaneously the SPE reservoir and the detection site at the end of the electrophoresis channel. Flow characteristics and electric field distributions were simulated with Femlab software. Fluorescein was used as the analyte for detecting the operational performance of the chip. Adsorption, bead rinsing, elution and detection were tested to verify functioning of the chip design.     

Simple photografting method to chemically modify and micropattern the surface of SU-8 photoresist

SU-8 has gained widespread acceptance as a negative photoresist. It is also finding increasing use as a structural material in microanalytical devices. Consequently, methods to tailor the surface properties of SU-8 as well as to micropattern coatings on the surface of SU-8 are needed. The SU-8 photoresist consists of EPON SU-8 resin mixed with the photoacid generator triarylsulfonium hexafluoroantimonate. This photoacid generator can also serve as a photoinitiator generating free radicals when illuminated with UV light. Under the appropriate conditions, sufficient triarylsulfonium hexafluoroantimonate remains within cured SU-8 to act as a source of free radicals and initiate UV-mediated grafting of polymers onto the surface of the SU-8. UV-mediated grafting was used to coat SU-8 surfaces with poly(acrylic acid) and other water-soluble monomers. The SU-8 surface was chemically micropatterned by placing a mask between the UV light and SU-8. The X-Y spatial resolution of micropatterned poly(acrylic acid) on the SU-8 surface was 2 mum. Three applications of these chemically modified SU-8 surfaces were demonstrated. In the first, poly(ethylene glycol) was used to protect the SU-8 from interactions with proteins, yielding a surface resistant to biofouling. In the second demonstration, the SU-8 surface was micropatterned with a cell-resistant layer to guide cellular attachment and growth. In the final application, SU-8 micropallets were encoded with polymer lines. The bar codes were read by either absorbance or fluorescence measurements. Thus, UV-mediated graft polymerization is an efficient and effective method to micropattern coatings onto the surface of SU-8.     

A rigid poly(dimethylsiloxane) sandwich electrophoresis microchip based on thin-casting method

We present a novel concept of glass/poly(dimethylsiloxane) (PDMS)/glass sandwich microchip and developed a thin-casting method for fabrication. Unlike the previously reported casting method for fabricating PDMS microchip, several drops of PDMS prepolymer were first added on the silanizing SU-8 master, then another glass plate was placed over the prepolymer as a cover plate, and formed a glass plate/PDMS prepolymer/SU-8 master sandwich mode. In order to form a thin PDMS membrane, a weight was placed on the glass plate. After the whole sandwich mode was cured at 80 degrees C for 30 min, the SU-8 master was easily peeled and the master microstructures were completely transferred to the PDMS membrane which was tightly stuck to the glass plate. The microchip was subsequently assembled by reversible sealing with the glass cover plate. We found that this PDMS sandwich microchip using the thin-casting method could withstand internal pressures of >150 kPa, more than 5 times higher than that of the PDMS hybrid microchip with reversible sealing. In addition, it shows an excellent heat-dissipating property and provides a user-friendly rigid interface just like a glass microchip, which facilitates manipulation of the microchip and fix tubing. As an application, PDMS sandwich microchips were tested in the capillary electrophoresis separation of fluorescein isothiocyanate-labeled amino acids.     

Synthesis of α-N-Ethylamino Acids and their Derivatives

Summary.  A new synthesis of α-N-ethylamino acids starting from α-amino acids using hexafluoroacetone as protecting and activating agent is described. The hexafluoroacetone-protected N-ethylamino acid derivatives obtained are activated lactons. Therefore, they can be directly transformed without the need of an additional activation step with various nucleophiles into the corresponding carboxylic acid derivatives. Received March 24, 2000. Accepted (revised) April 20, 2000     

Control of the water adhesion on hydrophobic micropillars by spray coating technique

We present an alternative approach for controlling the water adhesion on solid superhydrophobic surfaces by varying their coverage with a spray coating technique. In particular, micro-, submicro-, and nanorough surfaces were developed starting from photolithographically tailored SU-8 micropillars that were used as substrates for spraying first poly(tetrafluoroethylene) submicrometer particles and subsequently iron oxide nanoparticles. The sprayed particles serve to induce surface submicrometer and nanoscale roughness, rendering the SU-8 patterns superhydrophobic (apparent contact angle values of more than 150°), and also to tune the water adhesion between extreme states, turning the surfaces from “non-sticky” to “sticky” while preserving their superhydrophobicity. The influence of the chemical properties and of the geometrical characteristics of the functionalized surfaces on the wetting properties is discussed within the frame of the theory. This simple method can find various applications in the fabrication of microfluidic devices, smart surfaces, and biotechnological and antifouling materials.     

Surface modification of SU-8 for enhanced biofunctionality and nonfouling properties

SU-8 is a chemically amplified, epoxy-based negative photoresist typically used for producing ultrathick resist layers during device manufacturing in the semiconductor industry. As a simple resist, SU-8 has garnered attention as a possible material for a variety of biomedical applications, including tissue engineering, drug delivery, as well as cell-based screening and sensing. However, as a hydrophobic material, the use of SU-8 is limited due to a high degree of nonspecific adsorption of biomolecules, as well as limited cell attachment. In this work, surface chemistry is utilized to modify the SU-8 surface by covalently attaching poly(ethylene glycol) (PEG) to increase biofunctionality and improve its nonfouling properties. Different molecular weights and concentrations of PEG were used to form films of various grafting densities on SU-8 surfaces. X-ray photoelectron spectroscopy (XPS) was used to verify the presence of PEG moieties on the SU-8 surface. High-resolution C1s spectra show that, with an increase in concentration and immobilization time, the grafting density of PEG also increases. Further, a standard overlayer model was used to calculate the thickness of the PEG films formed. The effect of PEG-modified SU-8 was examined in terms of protein adsorption on the surface and fibroblast-surface interactions.     

Effect of exposure dose on the replication fidelity and profile of very high aspect ratio microchannels in SU-8

We are interested in using SU-8 dense gratings with very high aspect ratio microchannels as the master mold for fabrication of child molds needed for replication. For such applications, the sidewall taper angle and mask replication fidelity of SU-8 are very important. Increasing the exposure time was experimentally observed to decrease the width of the microchannel and the sidewall angle of SU-8 bars. A new diffraction-refraction-reflection model was also developed. The calculated microchannel width and sidewall angle at high exposure dose agreed well with the experimentally observed values indicating that reflection at the silicon substrate was significant. The larger than calculated actual microchannel width for low exposure dose was shown to be due to leaching of unreacted SU-8 in the developer. Dense gratings of high aspect ratio SU-8 bars separated by high aspect ratio (19.1) microchannels were also demonstrated.     

C3‐symmetric trialkyl phosphites as starting compounds of asymmetric synthesis

Chiral C₃‐symmetric trialkyl phosphites, derivatives, of (−)‐(1R,2S,5R)‐menthol, and (−)‐di‐O‐isopropylidene‐1,2:5,6‐α‐D ‐glucofuranose, have been studied as starting reagents for the preparation of chiral organophosphorus compounds. The reactions involve induction at the α‐carbon atom of substituted α‐alkylphosphonates. The stereoselectivity of the reaction depends on the structure of the starting compounds and the reaction conditions. The configurations of the alkylphosphonates were defined by means of NMR spectroscopy and by transformation into corresponding alkylphosphonic acids. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:138–143, 2000     

Characterization of SU-8 for electrokinetic microfluidic applications

The characterization of SU-8 microchannels for electrokinetic microfluidic applications is reported. The electroosmotic (EO) mobility in SU-8 microchannels was determined with respect to pH and ionic strength by the current monitoring method. Extensive electroosmotic flow (EOF), equal to that for glass microchannels, was observed at pH > or =4. The highest EO mobility was detected at pH > or =7 and was of the order of 5.8 x 10(-4) cm(2) V(-1) s(-1) in 10 mM phosphate buffer. At pH < or =3 the electroosmotic flow was shown to reverse towards the anode and to reach a magnitude of 1.8 x 10(-4) cm(2) V(-1) s(-1) in 10 mM phosphate buffer (pH 2). Also the zeta-potential on the SU-8 surface was determined, employing lithographically defined SU-8 microparticles for which a similar pH dependence was observed. SU-8 microchannels were shown to perform repeateably from day to day and no aging effects were observed in long-term use.     

Accumulation of Poly[(<Emphasis Type="Italic">R</Emphasis>)-3-hydroxyalkanoates] in <Emphasis Type="Italic">Enterobacter cloacae</Emphasis> SU-1 During Growth with Two Different Carbon Sources in Batch Culture

Polyhydroxyalkanoates (PHAs) are polymers of hydroxyalkanoate, which are accumulated by many bacteria as food storage material under excess carbon source and limited nitrogen source. In our study, Enterobacter cloacae SU-1 isolated from the rhizospheric soil of Arachis hypogea was allowed to grow as batch culture in minimal media containing either glucose or lactose, and the pattern of PHA accumulation by E. cloacae SU-1 was studied. E. cloacae SU-1 was found to accumulate 94% of PHA/dry weight of the organism in 8 g/l lactose-containing medium. When the monomeric units of PHA of E. cloacae SU-1 was analyzed by gas chromatography, it was also found to accumulate medium chain length PHA 3-hydroxyoctanoate (3HO)/3-hydroxyhexanoate (3HH) in the presence of glucose and lactose, but the ratio of these monomers differed as 11:1 and 6:1, respectively.     

高聚物微流控芯片镍阳模的简易加工技术

提出了一种简便快速制作高聚物微流控芯片镍阳模的新方法。采用抛光镍片作为电铸基底,涂覆SU-8光胶层后,光刻得到SU-8微结构。以镍基片作为阳极,用16～30A/dm2的电流密度电解刻蚀5min,清除SU-8微结构间隙底部镍片表面的氧化物,并刻蚀得到10～20μm深的凹坑,有效地提高了随后电沉积镍结构和基底镍片间结合力。利用SU-8微结构作为电铸模板,以镍基片作为阴极,电铸5h后制得了微结构倾角为83°深宽比较大的镍阳模。实现了在普通化学实验室中长寿命镍阳模的制作。用热压法制得500多片聚甲基丙烯酸甲酯(PMMA)聚合物芯片,并成功用于DNA片段的分离。     

电沉积技术制作高聚物微流控芯片模具

利用电沉积技术制作微流控芯片金属模具,方法是:使用新型超厚光刻胶SU8胶作近紫外光刻,并在光刻后的图案上电沉积金属Ni,之后去胶,最终获得金属模具.该法减小了电沉积工作量.采用反向电流预处理基底、并适当增加电铸液的添加剂以及脱模后真空退火,即可明显提高电沉积微结构与基底的结合力.用此金属模具成功热压了PMMA,制成了微流控芯片.     

Fabrication of enclosed SU-8 tips for electrospray ionization-mass spectrometry

We describe a novel electrospray tip design for MS which is fabricated completely out of SU-8 photoepoxy. A three-layer SU-8 fabrication process provides fully enclosed channels and tips. The tip shape and alignment of all SU-8 layers is done lithographically and is therefore very accurate. Fabrication process enables easy integration of additional fluidic functions on the same chip. Separation channels can be made with exactly the same process. Fluidic inlets are made in SU-8 during the fabrication process and no drilling or other postprocessing is needed. Channels have been fabricated and tested in the size range of 10 microm x 10 microm-50 microm x 200 microm. Mass spectrometric performance of the tips has been demonstrated with both pressure-driven flow and EOF. SU-8 microtips have been shown to produce stable electrospray with EOF in a timescale of tens of minutes. With pressure driven flow stable spray is maintained for hours. Taylor cone was shown to be small in volume and well defined even with the largest channel cross section. The spray was also shown to be well directed with our tip design.     

SU-8 as a structural material for labs-on-chips and microelectromechanical systems

Since its introduction in the nineties, the negative resist SU-8 has been increasingly used in micro- and nanotechnologies. SU-8 has made the fabrication of high-aspect ratio structures accessible to labs with no high-end facilities such as X-ray lithography systems or deep reactive ion etching systems. These low-cost techniques have been applied not only in the fabrication of metallic parts or molds, but also in numerous other micromachining processes. Its ease of use has made SU-8 to be used in many applications, even when high-aspect ratios are not required. Beyond these pattern transfer applications, SU-8 has been used directly as a structural material for microelectromechanical systems and microfluidics due to its properties such as its excellent chemical resistance or the low Young modulus. In contrast to conventional resists, which are used temporally, SU-8 has been used as a permanent building material to fabricate microcomponents such as cantilevers, membranes, and microchannels. SU-8-based techniques have led to new low-temperature processes suitable for the fabrication of a wide range of objects, from the single component to the complete lab-on-chip. First, this article aims to review the different techniques and provides guidelines to the use of SU-8 as a structural material. Second, practical examples from our respective labs are presented.     

Development of an optical ammonia sensor based on polyaniline/epoxy resin (SU-8) composite

Polyaniline (PANI)/glycidyl ether of bisphenol A (SU-8) composite film is elaborated in order to detect ammonia gas. These composite films are characterized by ultraviolet-visible (UV-vis) spectroscopy, Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The sensitivity to ammonia is measured by optical absorption changes. The ammonia sensing properties of PANI/SU-8 composite films are studied, and then are compared to pure PANI films elaborated by chemical way. Experimental results show that the PANI/SU-8 optical sensor has simultaneously a rapid response to ammonia gas and regenerates easily, that is advantageous compared to pure PANI films.     

Polyimide and SU-8 microfluidic devices manufactured by heat-depolymerizable sacrificial material technique

The following paper describes a sacrificial layer method for the manufacturing of microfluidic devices in polyimide and SU-8. The technique uses heat-depolymerizable polycarbonates embedded in polyimide or SU-8 for the generation of microchannels and sealed cavities. The volatile decomposition products originating from thermolysis of the sacrificial material escape out of the embedding material by diffusion through the cover layer. The fabrication process was studied experimentally and theoretically with a focus on the decomposition of the sacrificial materials and their diffusion through the polyimide or SU-8 cover layer. It is demonstrated that the sacrificial material removal process is independent of the actual channel geometry and advances linearly with time unlike conventional sacrificial layer techniques. The fabrication method provides a versatile and fast technique for the manufacturing of microfluidic devices for applications in the field of microTAS and Lab-on-a-Chip.     

Fabrication of SU-8 based microchip electrophoresis with integrated electrochemical detection for neurotransmitters

A new SU-8 based microchip capillary electrophoresis (MCE) device has been developed for the first time with integrated electrochemical detection. Embedded electrophoretic microchannels have been fabricated with a multilayer technology based on bonding and releasing steps of stacked SU-8 films. This technology has allowed the monolithic integration in the device of the electrochemical detection system based on platinum electrodes. The fabrication of the chips presented in this work is totally compatible with reel-to-reel techniques, which guarantee a low cost and high reliability production. The influence of relevant experimental variables, such as the separation voltage and detection potential, has been studied on the SU-8 microchip with an attractive analytical performance. Thus, the effective electrical isolation of the end-channel amperometric detector has been also demonstrated. The good performance of the SU-8 device has been proven for separation and detection of the neurotransmitters, dopamine (DA) and epinephrine (EP). High efficiency (30,000-80,000 N/m), excellent precision, good detection limit (450 nM) and resolution (0.90-1.30) has been achieved on the SU-8 microchip. These SU-8 devices have shown a better performance than commercial Topas (thermoplastic olefin polymer of amorphous structure) microchips. The low cost and versatile SU-8 microchip with integrated platinum film electrochemical detector holds great promise for high-volume production of disposable microfluidic analytical devices.     

石墨烯/SU-8复合导电光刻胶的制备及传感应用

将导电导热性石墨烯(GR)引入光刻胶SU-8中, 制备了具有导电性的复合光刻胶. 采用超景深显微镜和万用表表征了石墨烯在复合光刻胶中的分散性及复合光刻胶的导电性. 通过光刻法将设计的图案转移到氧化铟锡(ITO)玻璃表面制备了一种新型的GR/SU-8图案化电极元件. 进一步在GR/SU-8/ITO表面电化学原位还原CuNPs, 制备了一种新型无酶传感器. 实验结果表明, 该传感器具有优异的电子转移性能, 在110 mmol/L浓度范围内对过氧化氢具有良好的响应(R²=0.999), 同时稳定性优异, 15 d后电流响应仍可保持90%以上, 表明该导电光刻胶可用于电化学传感领域.