PDMS however requires a surface treatment step in order to produce strong, conformal bonds between surfaces. Plasma treatment of PDMS increases the exposure of silanol groups (-OH) at the surface of the PDMS layers so that they form strong covalent bonds (Si– O–Si) when brought together with glass.
What is the plasma treatment of glass and PDMS?
The plasma treatment modifies the surface properties and namely the hydrophobicity of the glass and PDMS. A good treatment makes the surface hydrophilic. A first test consists in putting a water droplet (about 20µl) on each surface and measure the angle contact with the surface.
How do you bond PDMS to glass?
Glass / PDMS plasma bonding. The plasma bonding step enables to finish your microfluidic chip fabrication. To permanently bond the PDMS chip to the glass slide, researchers use a plasma cleaner to change the surface properties of glass and PDMS.
How does PDMS work?
Following plasma activation, the PDMS is immediately placed in contact with another oxidized PDMS or glass surface to form bridging Si-O-Si bond at the interface, creating an irreversible seal. This water-tight covalent bond is ideal for microchannel formation and function.
How long does it take for PDMS plasma bonding to occur?
With plasma usually used for soft lithography, the perfect time to have the most powerful bond is generally between 20 and 60 seconds. Right after the plasma treatment, the chemical bonds of the surface begin to recombine, and after a few minutes the surface becomes not enough activated for glass PDMS plasma bonding.
Why does PDMS stick to glass?
The simple answer to the question is hydrogen bonding to the glass. Glass has silanol (>Si-OH) groups on the surface.
What does plasma treatment do to PDMS?
Plasma treatment of PDMS increases hydophilic (-OH) groups on the PDMS surface which subsequently form strong covalent bonds (Si– O–Si) when brought together with glass. These covalent bonds form the basis of a practically inseparable seal between the layers.
What does plasma treatment do to glass?
Application of plasma to glass can make it hydrophilic, increase its surface energy and improve wettability, so that inks, paints or adhesives can wet better. In addition, it can remove organic, inorganic and microbial surface contaminants that form due to exposure to air.
What is PDMS bonding?
Harrick Plasma → PDMS Bonding. Poly(dimethylsiloxane) (PDMS) is a silcone-based organic polymer used extensively in professional and academic research laboratories for its low cost and high versatility.
How do you bond PDMS to glass?
You can use simple thermal bonding method to seal PDMS to glass. Make sure both surfaces are flat and clean. Just put these two pieces together with gentle pressure, then bake in oven at 80 oC for over 1 hour. We use this method to bond microfluidics devices, which can hold pressure at least to 10 Psi.
How does plasma bonding work?
Plasma bonding is the process of modifying a surface so that it may be bonded to or printed on. Often used on Teflon, rubber, or plastics, this process actually modifies the surface, leaving free radicals behind and allowing any material to bond reliably with glue or ink.
How does surface plasma treatment work?
Plasma treatment is used to alter the top few molecular layers of surfaces. When plasma is applied to the surface, the energy applied to the surface “activates” the surface. This freshly energized surface improves the adhesion characteristics of paints, coatings, and adhesives.
How does plasma treatment increase surface energy?
Plasma treatments aim to convert low energy surfaces to higher energy surfaces by removing hydrogen from the surface and attaching oxygen-containing species in its place. Other 'functional groups' can also be formed at the surface to give different and interesting properties.
What is plasma treatment of polymers?
Polymer surfaces can be modified by a plasma treatment in different ways (etching, cleaning, activation, cross-linking), for example to improve wetting properties, to enhance the adhesion of plasma-deposited coatings, or to reduce friction.
How do I bond PDMS to silicon?
You can try to use an epoxy-based resist like SU-8 as the glue. Indee. You could try using the PDMS as an adhesive by spinning a thin film of uncured PDMS onto one of the surfaces. If all else fails, try double-sided tape.
How do you glue PDMS together?
A plasma oxygen treatment, followed by a mild heating, can be used for permanently bonding PDMS and glass. This method can also be exploited with other substrates as long as they expose a sufficient amount of –OH groups on their surface upon plasma treatment.
Does PDMS stick to silicon?
PDMS Bonding PDMS can be successfully bonded to glass, silicon, and itself using a standard oxygen plasma in a reactive ion etcher (RIE). PDMS is quite hydrophobic with an overall non-reactive surface, making it difficult for it to bond with other surfaces.
What happens when PDMS is exposed to plasma?
When PDMS is exposed to plasma, some of the surface is modified to have -OH groups that will interact with -OH groups on the opposing surface through a condensation reaction which results in a covalent bond between the two surfaces.
How to clean PDMS glass?
1. Before plasma treating your PDMS/glass, wearing powder free gloves, clean it with scotch tape. The ultra sticky packing tape is good. You have to make sure there is no dust, oil, or dirt residue on your surfaces. For ultra precise microfluidics, a clean room is usually required, but doing this under a chemical hood is ok. 2.
How long does it take for PDMS to contact glass?
Vanderbilt University. Try exposing your PDMS and the glass for 20 seconds and make sure that you make contact between the glass and PDMS within 45 seconds after removal from plasma. Once the PDMS makes contact with the glass, you will not be able to move it again.
Can you use plasma to treat PDMS?
It is really easy to treat PDMS to much with plasma so that it will not bond, and that without seeing anything on the PDMS surface yet. If you cannot control the power of your DIY plasma, there are other cheap alternatives: 30s treatment on each face with a handheld corona discharge gun.
Can you put methanol on glass before applying PDMS?
If you need to align it, you can put some methanol on the glass before applying the PDMS. This will help preserve the active surfaces until the methanol evaporates. The methanol will make the PDMS slide on the glass very easily so you'll have to hold it in place until the methanol has evaporated completely.
Do PDMS stick to plasma chamber?
One additional comment: be sure that your PDMS does not stick/partially bond to the tray of the plasma chamber. If it does so, some pulling force is needed to release it which deforms the PDMS. Once the PDMS has been deformed the free -OH groups disappear and you won't able to bond it anymore.
Highlights
Flow cells constructed with PDMS were investigated for use in motility assays.
Abstract
In vitro motility assays are readily used to simplify the complex environments within the cell and in muscle tissue. These assays have afforded considerable insight into the fundamentals of their underlying biophysics, interactions with cargo, intracellular regulation, and motor cooperation/competition.
1. Introduction
Understanding how bionanomachines function is hoped to someday lead to the development of new types of manmade structures that could be used to perform several types of useful work at the nanoscale.
2. Materials and methods
Sodium bicarbonate and potassium chloride were purchased from Sigma–Aldrich. Rhodamine phalloidin was purchased from Invitrogen. FisherFinest Premium Cover Glasses (18 mm × 18 mm, No. 1), Fisherbrand Microscope Cover Glass (18 mm × 18 mm, No. 2), concentrated sulfuric acid, and pentane were from Fisher Scientific.
3. Results and discussion
Before beginning motility experiments, we had to ensure that incomplete polymer products leaching from the PDMS would not affect our motility assays. Common methods to eliminate uncured PDMS include thermal aging [52] and solvent extraction [50].
4. Conclusions
Extension of the standard in vitro motility assay into a more automated and cost-effective fluidic design while providing availability to the scientific community without expertise in lithographic fabrication is critical for the continued advancement of the field.
Acknowledgements
The authors would like to thank Hideyo Takatsuki and Kazuhiro Kohama for comments and assistance in setting up the standard motility assay and in the fascin purification, David Neff for help in collecting the SEM images, and very helpful comments from the reviewers. B.S.D. thanks the department of chemistry for start-up funds.
How is PDMS oxidized?
After patterning a PDMS substrate by replica molding from a master mold, the PDMS is oxidized in air or oxygen (O2) plasma. An air or O2 plasma removes organic, hydrocarbon material by chemical reaction with highly reactive oxygen radicals and ablation by energetic oxygen ions. This leaves silanol (SiOH) groups on the surface, rendering the surface more hydrophilic and increasing surface wettability. Following plasma activation, the PDMS is immediately placed in contact with another oxidized PDMS or glass surface to form bridging Si-O-Si bond at the interface, creating an irreversible seal. This water-tight covalent bond is ideal for microchannel formation and function.
How long does it take for PDMS to recover from plasma?
It is recommended that PDMS bonding and other subsequent processing steps be performed within 15 minutes to an hour of plasma treatment.
What are plasma treatments?
Plasma treatment has been used to facilitate the fabrication of microfluidic devices for applications such as: 1 Study of chemical reactions and fluid flow on micron scale 2 Detection of biological organism or chemical species 3 Clinical diagnostics and drug screening for medical research 4 Manipulation of fluid on cellular length scale 5 Cell Culture, Tissue Culture, Organoid Studies
Why is high temperature important for PDMS?
The high temperature provides activation energy for additional bond formation. Cleanliness: the presence of particulates or oil can block bonds from forming. Avoid touching the surfaces to be bonded when removing PDMS from the plasma chamber.
Who is Harrick Plasma?
Harrick Plasma is a leading supplier of plasma equipment to the research community. We have been providing quality tabletop plasma devices specifically designed for laboratory and R&D use for over 30 years.
What is plasma bonding?
The plasma bonding step enables to finish your microfluidic chip fabrication. To permanently bond the PDMS chip to the glass slide, researchers use a plasma cleaner to change the surface properties of glass and PDMS. The plasma treatment will modify the surface chemicals and allows to stick the PDMS with the channels against other substrates (PDMS or glass).
Why bake PDMS?
A bake to improve the glass PDMS plasma bonding quality. To make the chemical link easier after the contact between the PDMS and the glass or PDMS, it is recommended to heat the set. The time, the temperature and the device can change between the laboratory and the user. A baking at 80-90°C during 15-30 minutes is usually enough to have ...
How long does it take for plasma to bond?
With plasma usually used for soft lithography, the perfect time to have the most powerful bond is generally between 20 and 60 seconds.
What is the most common polluting gas in plasma cleaners?
Some impurities even in very low quantity will pollute your surface. The most common polluting is oil coming from the vacuum pump or from the compressors around.
What happens when you bond a chip?
When you bond your chip, at the contact point the part becomes darker, so you can follow the contact. After the plasma treatment, drop off gently the PDMS on the glass or on an other piece of PDMS. The contact front should progress of itself quickly and easily.
What is the best indicator of plasma quality?
A good indicator of the quality of the plasma is generally its color/luminosity (which depends on the pressure and the gas used). Since the color may change, what you have to remember is, if your plasma color changes with the same parameters, a problem probably has occurred.
How to remove dust from glass?
There are other methods to remove dust, you can use 3M Scotch tape to remove particles on the surface or more efficiently you can dive your chip in Isopropanol and use sound wave to detach all unwanted particles on the surface and inside the holes in the PDMS. To clean the glass use successively acetone, isopropanol, water, and dry it.
Why does PDMS require a surface treatment?
PDMS however requires a surface treatment step in order to produce strong, conformal bonds between surfaces. Plasma treatment of PDMS increases the exposure of silanol groups (-OH) at the surface of the PDMS layers so that they form strong covalent bonds (Si– O–Si) when brought together with glass. These covalent bonds form the basis ...
How to treat PDMS?
PLASMA TREATMENT OF PDMS 1 Removal of hydrocarbon groups 2 Exposure of hydrophilic -OH groups 3 Improved bonding to PDMS, PC and glass 4 Improve analyte flow 5 Possibility of patterned surfaces with alternating hydrophilic/hydrophobic regions
What is PDMS in medical?
Polydimethylsiloxane (PDMS) – is a member of a group of polymeric organosilicon compounds that are widely known as silicones. It is the most widely used of these compounds and is featured in applications ranging from medicines and cosmetics to silly putty. In this application we concentrate on the use of PDMS in microfluidic device fabrication.
What is XPS in plasma?
XPS is a widely used technique to analyze the functional groups present on the surface of a substrate. Here we use XPS to show how C-O groups are absent prior to plasma treatment (in this case with oxygen plasma) and present after the treatment. Thus indicating a successful surface modification.