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Wood’s strike bath. The substrate was loaded in a custom made jig that isolates the non-plated regions from the bath. The jig-wafer assembly was then placed in a stirred Wood’s strike (240 g L-1 NiCl2.6H2O and 160 g L-1 conc. HCl, 40 ℃). A depolarized, soluble Ni anode (Alan Baker Co.,South San Francisco, CA) was loaded in a canvas bag to prevent large particles of nickel from entering the solution. A constant current power supply (Keithley, Instruments Inc., Cleveland, OH) was used to maintain a current density of 100 A m-2 for 50 min, yielding a 5 mm layer of active nickel. After 50 min the power supply was turned off and the jig was carefully removed to ensure that a puddle of bath solution remained over the active area. Liquid must be maintained over the active area because the presence of nickel oxide is suspected to be responsible for poor adhesion between substrate and electro deposited film.36 After displacing this puddle from the wafer surface with deionized water the jig-wafer assembly was finally placed in the electroplating bath.
Conclusion
We have designed, developed, and implemented an injection molding process for the fabrication of disposable microfluidic chips with standard, integrated, ready-to-use interconnects that can withstand very high back pressures. In anticipation of detecting analytes via LIF we screened several commercially available polymers for low background fluorescence and identified a suitable grade of COC for device production. A robust solid metal mold insert defining the microfluidic channels was rapidly microfabricated using a process that eliminated unnecessary electroplating time. The burst pressure of the chips was measured and used to optimize the bonding conditions enabling an eventual maximum burst pressure of 15.6 MPa. Finally, the suitability of UV transparent highpressure disposable devices was demonstrated by the in situ preparation of a high surface area porous polymer monolith directly within the channels. With devices capable of withstanding such high back pressure we are now able to pursue truly high performance liquid chromatography (HPLC) on-chip. We are also targeting the integration of multiple monolithic modules in a single chip to perform preconcentration, digestion, and separation in the analysis of proteins.
Acknowledgements
Support of this research by a grant of the National Institute of General Medical Sciences, National Institutes of Health (GM-48364) is gratefully acknowledged. The authors also want to acknowledge Nerique Gomez for his assistance with SEM in the National Center for Electron Microscopy, Lawrence Berkeley National Laboratory. This work was supported by the Materials Sciences and Engineering Division of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. We also thank James Wu of the Materials Sciences Division of Lawrence Berkeley National Laboratory for assistance with substrate annealing for lithography and John Morto of the Department of Mechanical Engineering, University of California at Berkeley for his valuable input regarding the tooling of the mold base.
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