Lab on a Chip - Science topic

I have started working on microfluidics and their application as organ-on-a-chip. I want to learn about the fluidodynamic and theoretical/practical aspects of this technology. What references would you recommend? Thank you.

Hi All,

Normally when we are preparing the PDMS, we usually use Si as mold . Assume that you fabricate your PDMS mold in 3D-Printer instead of patterns on Si fabricated by SU-8 . Do you think that it negatively leads to bonding of PDMS-Glass because of the surface roughness of PDMS pilled off from 3D-printed mold ? Which type of mold for obtaining PDMS is the good for glass-pdms bonding? If you have any experiences about 3D-printed mold for PDMS, would you share us ?

The second question is that Oxygen/air plasma cleaning or RF etch is widely used to make PDMS blocks stickable on to glass. Is there any other way to achieve the same?

Third Question is that lets say that you remove PDMS from your chip. Then, if you want to clean it, which type of solvent should be used or prepared to clean PDMS dirtiness?

Sincerely,

Osman

Hi all,

I am trying to fabricate PDMS based microfluidic devices, after plasma treatment the PDMS does not bond to glass for some reason. I have tried to drop a water droplet to see if it changes the contact angle and I have seen increased hydrophilicity on PDMS. I cannot control the plasma power nor the pressure since the device I am using has no pressure gauge or power control.

Briefly, after 2 min of vacuum I apply 2 min of plasma ( I can see the plasma forming). I have tried to silanize the glass and PDMS, wash the glass with ethanol, heat treatment after plasma and PDMS-PDMS bonding. None of which worked out. Can anyone comment on what is the issue here?

Thanks in advance.

Hello everyone,

I'm looking for a software thats adapted for drawing complex designs of microchannels. Typically i have 2 inlets, 3 outlets and 100 microchannels in between. For the time being, i am using Clewin and Klayout, but i seek something more adapted for such complex features and this considerable number of channels. Do you have any recommendations. Do you know of a software to design such chips and able to export in .cif format that permits me to make my lithography masks ?

Thanks in advance,

Mohammad Baz

Is it necessary to do SAM before Fibronectin? With this modification, how long does it take for cells to spread on top of an electrode?

I have been recently trying to cast and cure Sylgard in 3D printed master molds made of resin but the sylgard doesn't cure. I have tried to cure it at different temperatures but still it doesn't cure.

I wonder if anyone has ever had this problem before and how you could fix it.

Thank you.

Hello fellow researchers!

I am trying to find a fluorocarbon oil that has a refractive index same as or greater than that of water (1.33). The closest one I can find so far is 1.3 (FC-170).

Dear All,

I have to align PDMS on LiNbO3, my channel size is 100 micron.

My process parameters are 0.3 Torr, O2 plasma treatment for 2 mins. 

I put a drop of ethanol on PDMS to align on LiNbO3, I use my finger to move 2-3 times, after that heat at 80 C.

The problem is PDMS always has leakage near the inlet.

Anyone has an idea what should I do ?

Best Regards,

Yannapol S.

I have used a glass（soda-lime glass）bonding with PDMS after treating with plasma, however, the bonding is too weak or otherwise it can only bond on part of the whole structure.

SO I'm eager to know what kind of glass should use when I need to bond PDMS.(the plasma treatment procedure is sure OK, and I'm doing the lab on a CD, so a hole need to be drilled in the center of the glass disc )

I am looking to fabricate PDMS pillars which are 0.5um or 1um in diameter, and up to 10um tall. Pattern definition and etch on a silicon substrate to create the mould, using E-beam and RIE etching doesn't present too much of a problem.

When I come to mould my PDMS against this, does anyone have any advice on getting decent demoulding without too much breakage/stretching/deformation? Will this even present a problem?

Hi! After weeks of testing we get control of the drop size, by put oil pump vertical and adjust the oil flow rate. However, we found the drop size becomes crazily deviated when trying to get drop smaller than the channel size. The chip adopt classical "+" geometry. We have 2 chip: diameter 70um and 80um. Both hard to get drop <70 and <80.

Is it necessary to get a smaller chip if we want drop diameter in 65um!

Thank You

Hi,

I have a microfluidic channel with a very low aspect ratio (100 um tall x 2 mm wide). When I flow cells though this channel I notice cells move at two separate speeds. I am trying to figure out exactly why this is and how to resolve the issue.

The channel is made on 3 sides with PDMS and on the last side by SU-8.

My thinking thus far is that in a low aspect ratio channel the cells will inertially focus into two equilibrium positions in the vertical axis of the channel: But these two positions are not at the same spot on the parabolic velocity profile and thus have different speeds.

Where the cells find an equilibrium is a function of the wall interaction and the sheer gradient lift force. Cells at each equilibrium will have the same fluid velocity, density and size. Thus there must be a difference in the velocity profile to cause this discrepancy. I assume this would be because the materials are different. Something to do with the slip length, the surface charge (zeta potential) or surface roughness.

Has anyone had a similar issue? Any suggestions for how I could resolve this issue (excluding changing the geometry much)? Does my thinking make sense, perhaps there is another way to explain why I see cells moving at two different speeds?

Best,

David

Hi!

We realise the dripping in our microfluid chip (the + cross).

Yet we wonder how can we control our droplet size to ~=70um sphere (the channel is a semicircle in 70um diameter)

Can we calculate the drop size, using Weber number and capillary number or any other parameter?

Thanks!

I am working with an microfluidic chip engineering company whose manufacturing approach can create super smooth round channels with integrated connectors and no tooling requirements, they are interested in creating new configurations to support various applications in biodiscovery and analysis but would like to understand the current limitations of microfluidic chips and systems - is it cell damage, bubbles, poor mixing, cost to mfg, engineering limitations, etc? If you are working with cell analysis or other biologic applications what adaptations to your microfluidic system would make your research easier?

I am performing a 2-d simulation in COMSOL in which a microfluidc device separates different cell particles using dielectrophoresis. I want to compute drag and dielectrophoretic forces acting on different particles at different locations. I have tried the built-in expressions from COMSOL, but they do not work (maybe I do not know how to do such an action). Does anyone know how I could do that?

Sincerely,

Hi everyone. I'm currently working with Dolomite Microfluidic system for preparation on PLGA based microparticles, but I seem to be encountering some issues which have been giving me some trouble for some time already.

1) I'm using a PLGA/DCM solution as my droplet phase and I have a feeling that I'm having a loss of DCM which impacts my particles as the PLGA solution then gets more concentrated.

2) The flow throughout the run is also somehow inconsistent and flow rate starts decreasing and pressure increasing after some time, even though no clogging or blockage is visible under the microscope. I believe this second issue might be related to the first question, despite the blockage also occasionally coming from tubes/pump containing the continuous phase (PVA aqueous solution).

Would anyone be able to help me for a way to reduce this apparent loss of solvent? For information, I use a glass vial that fits into the P-pump pressure chamber, and screw the chamber lid on with the tube placed in the glass vial.

Thanks in advance! - Julia Shih

Lateral Flow Immunoassay system were used for newborn screening test and these systems consist of some parts including plasma separation membrane part, I found lots of plasma separation membrane pad but they used for lower hematocrit sample like adult blood and because of higher hematocrit blood of neonates I think that these systems use special filters for separating plasma from blood and I want to know about that.

thank you

What simulation program do you advise me to perform the simulation of the movement of a magnetic nanoparticle in a fluid in a lab_on_a_chip, influenced by an external magnetic field?

I was wondering how to find non fluorescent plastic coverslips for optical in vivo imaging. We now use glass coverslips 3mm in diameter, 0,15mm thick, but want to find a plastic substitute. According to this paper http://www.ncbi.nlm.nih.gov/pubmed/16286964, PDMS seems to be good. But I cannot find any commercial supplier of coverslips made of this material. Could anyone be so kind to provide some advice?

I'm using su-8 2025 on glass and want it to be part of my final fluidic device, but I'm having a lot of detaching problems even before entering water. How could I improve it, and what kind of promotors can I use?

Hello,

I am spin coating PDMS over a glass wafer with patterned metal. It is important to me that this PDMS surface is smooth. Is there an easy way to measure the surface roughness?

I was planning on using Bruker Contour GT-K Optical Optical Profilometer, but I have been informed that since the PDMS is transparent it will be difficulty to get accurate measurement.

Another suggestion was AFM, but I am not trained on it so it would take time for me to be able to get measurement.

Any other suggestions?

Thank you for the help,

David

For a microfluidic device of mine, cells are sticking to a PDMS surface (not oxidized). Are there any surface treatments that can be used to reduce this effect? It may also be that the surface of the PDMS is not perfectly smooth. In that case how can I ensure the PDMS being spin coated is smoother?

I am looking for the microchannel's most important applications between:

- Micro-electronic Thermal Management

- Solar Collectors

- Space Machines Cooling

- Drilling Devices

and etc ...

Hello,

For a microfluidic device I have built, I have a layer of PDMS acting as a gasket. I would like to be able to sterilized this device such that it can be reused. I am aware of multiple sterilization techniques (UV light, NaOH, bleach etc.) but ideally I would like to be able to put my devices in an autoclave.

My first question is, can PDMS be autoclaved? The layer I have now is approx. 20 um thick, spin coated on borosilicate glass. My lab members think not, but Millet et al. seems to suggest it is possible.

My follow-up question would be if the PDMS cannot be autoclaved, is there a material which could substitute as a gasket that CAN withstand being autoclaved? Ideally I could also create a layer of this material approx. 20 um thick on my device.

Any suggestions would be appreciated!

I had used a closed micro-channel (0.5 mm height, 5 mm wide) for an immunological reaction. I wish to re-use the same for some minor experiments, and need to remove a small layer of the acrylic surface (say 1 micron or less), such that the surface is as good as new. How can this be done?

Getting new channels for such indicative experiments is not economical and rather time consuming, and this is why we wish to reuse the channels.

Has anyone published their work in Microsystems and Nanoengineering journal which is published by Nature? Is it comparable with Lab-on-a-chip journal by RSC?

Dear Experts,

I have struggled with bonding issue for quite sometime. Initially, I plasma bonded (Oxygen and Nitrogen) the PDMS on LiNbO3. The bonding worked for the 1st time, but after a while there was a leakage, so I removed the PDMS and replace with the new PDMS microchannel.

However, the 2nd, 3rd.. time bonding of PDMS on LiNbO3 is very weak and causes internal leakages. Even I wiped/rubbed LiNbO3 with acetone every time before bonding.

Anyone has suggestion on this bonding issue ?

- is it due to a change of LiNbO3 surface composition, with oxygen ?

- any suggestion ?

Best Regards,

Yannapol Sriphutkiat

I recently experienced the shrinking of PDMS. I mean the structures don't have the same size once removed from the SU8 mold. I need to align and bond it on a set of electrodes and because of the shrinking they do not fit together. Something like 10 or 20µm over 4mm.

Is there a way to avoid PDMS shrinking? Lower temperature reticulation? Any ideas?

We need a new device to do cell research. CellASIC of Merck Millipore is a choice, but we need comparisons among different instruments.

I am using syringe pump with the flowrate set to 5ul/min. When I flow water which is in plastic syringe through a 1mm 0.5mm tube and collect the liquid for 10min. Then I see that ~50ul liquid is collected. But if I flow water using the same setting through a 6um glass capillary the liquid collected is only ~44ul. This can happen only if the flowrate is reduced incase of micro capillary. But why does this happen? Is there any theory to calculate the loss?

Hello, 

in my current project, I have to create tiny microstructures in PDMS. The mold is a photoresist containing holes with a diameter of 5-10 micrometer and a depth of around 150 micrometer. 

The most common way in microfluidics is to degas the PDMS polymer properly and to pour it directly on the mold. After that, most of the people degas the casted polymer or bake it. 

In my case, I am concerned that the air which is trapped during the casting process is not released due to the very tiny holes. Has anyone experienced that even in very small structures air bubbles will be soaked out? Which pressure level would you recommend? 

I have thought to pour the PDMS on the wafer in vacuum with a small setup inside a desiccator. Has anyone ever tried this? 

Kind regards, 

Karl Tschurtschenthaler 

Hello, I am working on protein detection sensor, and in one step, I need to incubate protein targets with the antibodies on the electrodes. However, antibodies are only functionalized on certain places of the electrodes with a width of 5 um, and length of 550 um, and it will be great if all proteins within the sample are within this area rather than the entire electrodes. So is there a way to do that? I am thinking of making a microchannel, but 5 um wide microchannel seems to be difficult to make (maybe cut it with FIB on PDMS?). Is there a easy way to make this microchannel? Many thanks!

Hello everyone,

I am experiencing a problem with double layer microfluidic fabrication. I am going to eventually use this device on human cells, thus the environment needs to be appropriate. I have been seeing some particles due to punching the inlet/outlet holes of the device. Has anyone had this experience before? I am new to two layer device fabrication, thus any tips on cleaning the holes after punching/the actual punching method, etc., would be appreciated.

Any tips on multilayer soft lithography protocol would be great as well. If there are researchers who can share their protocols, tips and tricks?

thank you and have a great experiment everyone!

I work in integrated microfluidics system and I like to bond my microfluidic chip to Epoxy substrate. Could anyone suggest me what are the possible ways to bond PDMS to Epoxy??

Hello everyone,

For those familiar with using PDMS microfluidic devices for biological experiments, to what extent is PDMS gas-permeable? I have seen this mentioned in a few review papers but never qualified. I have not read many material science papers on PDMS so this may be why. Is that to say that cell culture medium flowing through an enclosed PDMS microfluidic devices will be able to equilibrate to a neutral pH in an incubate? If this is the case, how thick can PDMS walls be before this is no longer viable?

Something like: this is the 2D CAD structure, material, this is input this output, medium=blood, pressure here, pressure there ...

and then show flow directions, velocity etc.

Maybe in AutoDesk Simulation CFD.

Never did such a simulation before.

I have electrode arrays and I would like to measure multichannel with SI 1260. Are you working with this machine? If you know, please help me.

Hello, 

I am wondering which FOXA1 antibody do you guys use to conduct your ChIP experiments? I've been using 17-10267 from Millipore. 

I am planning to ChIP low cell numbers (i.e <50 000 cells) and frozen tissue. The lower cell number I go with the EMD Millipore antibody, less enrichment I'm getting.

Raised in goat or rabbit would be preferred

Thanks in advance!

I would like to test the response of cancer cells (MDA and MCF7) on Cisplatin. I bought a bottle (15g) in powder.

Could you tell me how should I dilute it? Which concentration should I use? How long should I monitor?

I am using SU-8 2015 for my microfluidic channel structures. The substrate is 1mm thick glass wafer. 

Issue : SU-8 flows off the substrate during the developing process. The adhesion is poor apparently.

Solution/s to this problem are needed.

The protocol I am following is as follows.

1) Cleaning and dehydration bake of the wafer.

2) Spin coating of SU8 of desired thickness.

3) Soft baking process. 2 mins at 65C and 5 mins at 95C.

4) Exposure using MA-6 Mask Aligner.

5) Post Exposure baking. 2 min at 65C and 5-10 min at 95C.

6) Developing in solution for 1min.

7) Rinsing with IPA and drying with Nitrogen gas.

Hello,

I am working on colorimetric analysis of Lab-on-a-chip to determined the blood hematocrit. Usually, I prepare hematocrit samples of 10%-65% with 5% incrementation. Then in the colorimetric analysis, we have gray scale value (GSV) of different concentration. Relative GSV value is in principle linearly increases with hematocrit concentration. Could you please explain how to calculate LOD, sensitivity and resolution of the LOC device?

Hello,

I am working on colorimetric analysis of blood hematocrit using microfluidic chip. I have measured the relative gray scale value (GSV) of hematocrit of 10% to 65% with 5% incrementation. Observed GSV with different hematocrit levels is linear with correlation coefficient of R2=0.9854. Now I am asking about some specific method to calculate the resolution of the microfluidic chip. Pls be reminded that I have GSV data for blood hematocrit of 15% to 65% range.

The optical response in electrochromism is defined as the time that required to obtain 90 % of the needed coloration. Can I use some kind of analogy? Any experiences? 

Hello,

I am doing a Passive Particle Separation application in PDMS microchannels. Due to the nature of the process, I am using quite high volumetric flow rates (up to 2.5 ml/min in a 40µm x 500µm microchannel.) The main problem that I have at high flow rates is the leaking of the fluid between inlet fittings and PDMS (i.e., There is no problem about the plasma bonding which I used to bond PDMS and glass base.)

Firstly, I though that the metal fittings that I have used (which can be seen at the image below) are so thin which makes the flow even faster at the inlet of the microchannel and it leads to leaking. For this reason, I decided to use wider plastic fittings to connect my microchannel to the syringe pump that I have been using. However, at this time, PDMS has teared when I was punching it with a wider puncher compatible to the wider plastic inlets. Later on, I decided to place the plastic fittings on the photoresist mold and then cast PDMS to eliminate punching process. At the end, I obtained a PDMS channel integrated to plastic inlets; however there was again leaking between plastic fittings and PDMS.

In all these cases, I used silicon grease around the inlets to isolate little cracking around the inlets through which leaking occurs, but I did not work neither.

Are there anyone who have also experienced this kind of leaking problem, and found a possible solution? I am eager to listen their recomendations.

Thank you in advance,

Utku. 

HI, I am trying to perform ChIP on low cell numbers (1x10⁶, 200.000) and after sonication and reverse crosslinking to check the chromatin, I see a very sharp band around 1000 bp but nearly no visible smear. Did anybody ever experience the same problem?

My problem is clear as it can be seen above. Is it possible produce box-shaped hollow part with SU8 ? 

DMEM - dulbecco's modified eagle's medium, consisting of the typical Amino Acids, Glucose, pH indicator, Salts and Vitamins

We want to find a technique for determining of glucose concentrations in this culture from impedance spectroscopy data

Can it be that the most authors and researchers have neglected and still do not follow the demands of the following ISO norms (with year of coming into effect): 15193 (2002); 15194 (2002); 15195 (2003); 17511 (2003); 18153 (2003) and especially: ISO/PDTS 25680.8: Use of external quality assessment schemes in the assessment of the performance of in vitro diagnostic examination procedures? This European Standard was approved by CEN on 2 March 2004 as EN 14136. Why do most published papers in this area not perform the minimum performance test by taking part in an inter-laboratory trial with real samples and not with pure aqueous solutions without a possibly interfering matrix (e.g., in bio-sensing: enzyme-poisoning, denaturing reagents, proteases, drug-metabolites, etc.)?

The antibody was already conjugated with quantum dots and the unconjugated proteins was already removed by centrifugal concentrator. While checking via ELISA reader the unconjugated protein was found to be more than the total volume added for the reaction. Please suggest any other method to check the concentration of antibody conjugated Qds.

I fabricate PDMS micropillars with LIGA-made casting mold (Nickel Metal Sheet) consisting sinking holes of 240µm depth and around 18µm diameter. My casting setup is as the figure attached. A cannula with a diameter 5mm is clipped tightly together with the casting sheet with one or two clips. Sylgard 182 Silicone for casting the pillars is moved into the cannula by a pipette. Then after the degassing process and the baking process the silicone becomes cured.

My question is concerning the peel-off process. Currently I first remove the clips and then put the whole thing into a vibrating bath (the bath is filled with isopropanol) and wait for the cannula with pillars and the casting sheet to become apart. The pillars are expected to be 240µm high (same as the hole depth). However, most pillars I get suffer from not enough height, that is they are torn apart after the silicone get cured. 

May I ask if anyone has similar experiences and do you have any suggestions concerning the peeling off process? Or maybe anyone has some other ways for peeling them off?

Thanks very much!

Typically the ACF needs a curing process under 150-200 centidegree. Now we want to do the bonding at room temperature so we can not use conventional ACF. Is is feasible to mix the metal particles of ACF with UV curable epoxy for a bonding process?

I am reviewing existing literature that deals with magnetophoresis separation in microfluidic systems and in which the passive magnetic elements (like Ni or permalloy) are integrated with the system as flow-invasive and not side-wall embedded. I appreciate your help in doing this literature survey.

Oxygen/air plasma cleaning or RF etch is widely used to make PDMS blocks stickable on to glass. Is there any other way to achieve the same?

I have three electrodes: WE, CE and RE. How can I connect with SI 1260 to measure V1/V2?

I want to modified my screen printed electrode (SPCE) with OH group. Later, OH modified SPCE will be treated with APTES to introduce NH2 group on SPCE. Can anyone let me know a simple method to produce OH group on SPCE?

I need to study the flow behavior of emulsion (oil-in-water/water-in-oil) through a microchannel (hydrophilic/hydrophodic). Can you please help me regarding this?

Especially when your patterns are small like individual pillars. They just get washed off when developing.

.

I made a die from polycarbonate. Now I want to cast a low viscosity polymer into small channels on the polycarbonate die. These channels are 0.4 mm in width, so when I pour the polymer on the first die, I need time to take bubbles out of it. I think around 10 minute is enough.

I already tried PMMA, but it sticks to polycarbonate. Also I used polyvinyl siloxane but it it's working time is a few minutes.

What do you suggest?

Extracting membrane and cytoplasmic properties from electrorotation experiments.

I am interested in modeling and simulation.

How we can modify gold electrode with graphene? What are advantages in using graphene based electrode for cell-based sensor?

Has anybody tried to make PDMS electrically conductive? Which material (metal) and methods have you tried?

Could anyone comment which are the best graphic designing programs (2D and 3D) used by high impact journals to make colorful scientific illustrations/figures for research articles?

We are looking for any experience in the field of storage protein detection in wheat using new devices/techniques instead of SDS-PAGE.

What are the parameters to be measured (in lab or on site) in order to assess if the water is fit for drinking in the Indian sub-continent?

I have SU8 structure on top of Au electrode? If I put the chip in the oven, at which maximum temperature can I set up which SU8 structure will not damage?

I would like to modify our gold electrode by GO or r-GO. Does anyone have any experience?

Could you tell me about the process to clean gold electrode before doing experiment with cells? Our system consists of thin film gold (100nm) electrode inside microchannel by SU-8.

Thank you so much

The fluid in my case is blood with suspended elements like RBCs etc. i.e. a non-Newtonian fluid.

I would like to record the SEM image of a cell on top of a Gold electrode? How should I prepare the sample? If you have experience, please let me know. Thank you so much

I am looking to aquire a reliable, yet affordable, visulization system to track and record the motion of poly-sized magnetic beads flowing through a magneteophoresis microfluidic separation device. The smallest bead can have a diameter less than 0.5 microns. The beads are expected to have distinct separation and deflections (based on their magnetic dealings) into different sub-microchannels. The more resolved tracking and the more the systems that are integrated are preferred.

I measured impedance between 2 planar gold electrodes inside a microchannel filled with medium for cell culture. Which electrical elements should I put in the circuit and how are they connected together? Should I use Randles circuit for this system?

I would like to modify our Gold electrode by Fibronectin or Poly-L_Lysin to reduce the time for cell attach on surface of electrode. If you have experiences, please help me.

I would like to use Matrigel for cell culture but I don't know which concentration of Matrigel to use. Can anyone give some advice?

I would like to use protein for reducing the time for breast cancer cell attach on the gold electrode.

After finish fabricating, I coated a thin layer of AZ1518 to protect the gold electrode for dicing. Before bonding, chips were already cleaned with Axetol in ultrasonic for 3 min, isopropanol for 3 min and water. But the surface of the electrodes don't seem to be clean. I would like to use Piranha to clean and remove photoresist. Could you share your experience with me.

Is there any LOC-SERS application?

The bottom of 96 well plate will be coverslip glass. Inherent spin coating is not possible since I require varying ratios in one 96 well. Upon polymerization the coated/deposited 96 well will be subjected to 02 plasma/chemical activation for studying adherence of protein in high content microscope with 63 x objective.

The recipe I followed: place wafer on Hotplate in 15min at 150 degree - Spin coating - softbake at 95 degree in 15min - Exposure - Hardbake: 65 deg in 1min and 95 deg in 5 min - Develope in 8 min.

Had an array of silicon nanowires, now I want to deposit a metal particle on the top of it. I do not want to use the VLS method to get this. Anyone have any suggestion?

I am interested in applying COMSOL Multiphysics to simulate microfluidic devices. Can any one recommend me any book/reference to start with?