an inexpensive method for pdms-pdms bonding in fabrication of microfluidic device

1. AMN & APLOC 2011 an inexpensive method for pdms-pdms bonding in fabrication of microfluidic device The Second Conference on Advances in Microfluidics and Nanofluidics and Asian-Pacific International Symposium on Lab on Chip 5th-7th January 2011, Singapore Koh Kai Seng, The University of Notitngham Malaysia Campus

2. AMN & APLOC 2011 Table of content • Introduction • Experiments • Result and discussion • Conclusion

3. AMN & APLOC 2011 Introduction • Poly(dimethylsiloxane) (PDMS) has been widely used in microfluidic applications. • Sealing has been the key challenges in microfluidic fabrication. • Reversible bonding, • irreversible bonding.

4. AMN & APLOC 2011 • Conventional sealing techniques require • Costly equipments.(Oxygen plasma) • Time consuming. (Partial curing technique) • Involve complicated steps. (Oxygen plasma) • Reliability and repeatability are always at the centre of argument. • Piranha solution is used because • More economical, • Time saving, • Involve less complicated steps. • Relatively high reliability and repeatability

5. AMN & APLOC 2011 Bonding mechanism First stage: • Dehydration of hydrogen and oxygen into water unit. Second stage: • H2SO4 + H2O2 → H3O+ +H2O4- + O∙ Reactive atomic oxygen species +

6. AMN & APLOC 2011 O∙ • Bonding mechanism: OH PDMS surface CH3 CH3O· Si O Si O Si n OH- O∙ → H2O → OH- + OH-

7. AMN & APLOC 2011 Experiment Method • Sealing procedure: • PDMS samples with strings embedded in it were solidified. • The samples were cut into 2cm × 2cm square piece each. • Piranha solution concentrated Sulfuric acid (96wt%) & Hydrogen peroxide(30wt%) at 3:1 weight ratio. • Interfaces of two PDMS are drenched into the solution for a define interval. • Next, both surfaces attached and bounded together followed by thermally curing of 70°C for 60 minutes.

8. AMN & APLOC 2011 Result & Discussion • 2 methods are used to test bonding power: • Tensile strength test • Leakage test

9. AMN & APLOC 2011 Table 1: Tensile strength (kPa) against drenching time (sec) at 3:1 weight ratio of Piranha solution Table 2: Calibration of tensile strength of string (kPa)

10. AMN & APLOC 2011 Piranha solution using HNO3 (65wt%) + H2O2 at 3:1 weight ratio Table 3: Tensile strength (kPa) against drenching time (sec) at 3:1 weight ratio of Piranha solution

11. AMN & APLOC 2011 Figure 1: Graph average tensile strength (kPa) against drenching time (sec) Sustaining time of the PDMS-PDMS interfaces is within the range of 20-30 seconds.

12. AMN & APLOC 2011 • Optimum drenching time is 45 seconds. • Reaction ends at around 65±5seconds. • Pure Sulfuric acid remains. (limiting reactant is Hydrogen peroxide). • PDMS surface will be attacked.

13. AMN & APLOC 2011

14. AMN & APLOC 2011 • Leakage test • Water is pumped into closed channels for 5 minutes at 5,20,50µl/min. • No leakage detected!!

15. AMN & APLOC 2011 Conclusion • An inexpensive polymer-based sealing technique, using piranha solution (3:1 weight ratio) is demonstrated and quantitative result is shown. • This irreversible bonding techniques is able to sustain a mechanical strength of (200±20kPa). • Water is injected into closed microchannels at different flowrates and no leakage occurred up to a flowrate 0.3ml/hr. • In future work, optimization of the bonding strength using the same method will be investigated.

16. AMN & APLOC 2011 Thank you for your attention.