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FJaser micromachining of microfluidic channels and vias for biophotonic chip applications Peter R Herman, Andrew Yick, Jianzhao Li Department ofEIectrica1 and Computer Engineering, University of Toronto, IO Kings College Rd , Toronto, ON, M5S 3G4, Canada, Tel 41 6-978-7722F a r 416-971-3020;
[email protected]
Nigel Munce, Lothar Lilge Department ofMedica1 Biophysics, University of Toronto, 610 University Avenue, Toronto, ON, M5G 2M9, Canada,
Eric Jervis Chetnical Engineering, University of Waterloo, 200 University Ave. W., Waterloo, ON,N2L 3G1, Canada;
Sergey Krylov Department of Chemisty, York University, Toronto, ON, M3J 1P3, Canada;
Abstract: Deep-ultraviolet F2-laser radiation drives strong interactions in optically transparent glasses for smooth and crack-free shaping of microfluidic channels, microvias, and arrays for cellon-a-chip applications. We describe cell manipulation and imaging applications in custom fabricated biophotonic chips. 02002 Optical Society of Amenca OCIS codes: (350.3390) Laser materials processing, (170.1530) Cell analysis
1. Introduction
Laser microprocessing tools offer attractive approaches for rapid prototyping and testing of biological chips at the nano-scale dimensions necessary for defining microfluidic channels, reservoirs, cell traps, gates, mixing channels, and microvias-monolithically on a common transparent substrate-for manipulating and probing of cells, genes, proteins, and other biological agents. Glasses are highly attractive substrate materials because of their high optical tmnsparency, low fluorescence, and benign surface. However, transparent glasses are challenging to process with conventional lasers, which are weakly interacting at visible or near-visible wavelengths. Our group is addressing these challenges with deep ultraviolet Fz-laser light, which provides strong interactions at the band-edge of fused silica glasses for nano-milling of small surface features that are smooth and crack free. In this paper, we describe the formation of electrophoretic channels for cell manipulation, hole arrays for stem cell trapping, and micro-hole arrays for multi-cell aligners in glass and other transparent materials.
2. F2 Laser Microfabrication The Fz-laser micro-fabrication station has been described previously [l, 21. Briefly, a 5mm x 5mm uniform (*So/,> beam is formed at the projection mask, which is demagnified 25x onto the target surface with a Schwarzschild objective (NA = 0.4). A Cr-coated (-90-nm) CaF2grating mask or laser-milled metal foils provide the basic beam shapes while a 100-nm precision X Y Z motion stage (Newport Model TSPI) and a high-resolution target viewing camera system control the patterns and alignment of features onto lab-on-a-chip or so called micro total analysis systems (pTASs). On-target laser fluence of up to 5 J/cm2was available at 100-Hz repetition rate.
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3. Microfluidic Channels
Laser exposures were optimized for defining 1:1 aspect ratio channels with near-vertical walls as shown in the end view of a glass slide in Fig. 1. The channels were formed at 5 Hz, single-pulse fluence of 9 J/cm2,with 100 and 200 pulses respectively. High fluence of 9-J/cm2provided the best wall geometly.
Fig. 1. Optical end-view of micro-channels fabricated in microscope glass slides (Coming 2947) with single pulse fluence of 9 J/cm2.
Microfluidic c l m e l s for electrophoretic manipulation of cellular material were ablated into glass- and PMMAbased lab-on-a-chip devices in the locations identified in the microscope photograph of Fig. 2 for the case of a commercial glass device Wcronit Microfluidics, the Netherlands). A cover slip was sealed onto the chip. Cells were labeled with fluorescein derivative and were then manipulated to the microfluidic channel for laser membrane fracture and probing of the cellular material in the microfluidic channel. Fig. 2 (right) shows the close match of the cell size to the microfluidic channel. Etchmg by F2 microfabrication thus permits a wide range of channel geometries for custom application purposes.
Fig.2. Biochip (9 cm x 4.5 cm) with Fz-laser fabricated micro-fluidic channels. A commercial microfluidics device (Micronit Microfluidics, the Netherlands) modified by FZlaser ablation to form parallel electrophoretic channels, identified by the white horizontal lines (a). An illustration of a cell (fluorescein-labelled)that has been brought to the entrance of one of the channels with optical tweezers (b).
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4. Stem Cell Arrays and Multi-Cell Aligners
Micro-vias of cellular (10 pm) and smaller Qmensions are hghly desired in many cell or gene chip applications. Fig. 3a shows a microscope photograph of a cell-chip array on 200-pm centers, designed to trap stem cells onto glass surfaces. A closer view is shown in the SEM photograph in Fig 3b, whch revealed a slightly astigmatic hole diameter of -17 pm at the top and -12 pm at the bottom- well matched to the size of stem cells. A 3-D profile of the hole in Fig. 3c, obtained by confocal-microscope scanning under oil immersion, reveals a flat geometry along the bottom of the hole. Each hole was formed with 100 laser pulses at 10 Hz (10 second exposure), using 6-J/cm2 fluence on the surface. With appropriate masking and 100-Hz operation, dozens of holes may be excised per second. Fig. 3b also reveals accumulation of ablation debris. No cleaning methods were applied in the present case and methods to reduce the debris accumulation are under further investigation. The paper will also describe the formation of 8-pm diameter through holes in fused silica cover slips for the purpose of fabricating multi-cell aligners.
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Fig. 3. Optical photograph of a stem cell m a y (200 pm centers) drilled with an F2-laser (a), SEM micrograph close-up of a typical hole in the array @), montage of pictures of a typical hole in the array using scanning confocal microscopy (c).
5. Conclusion Non-isotropic etching of glass and plastic materials have broad applications in handling and analyzing biological material at the single cell level. As biology begins to focus on studying diversity at the single cell level in fields such as cancer and stem cells, new tools will be needed to be developed. The F2 laser is a powerful tool for nanomilling of surface relief structures and micro-vias in glass and plastic substrates for custom fabrication of biologcal devices. 6. References 1.
2.
P. R. Herman, K. P. Chen, h4. Wei, J. Zhang, J. Ihlemann, D. Schafer, G. Marowsky, P.'Oesterlin, B. Burghardt, "F~-lasers:high-resolution micromachining system for shaping photonic components", in OSA TOPS 56, 574-577 (2001). Jianzhao Li, Peter R. Herman, Midori Wei, Kevin P. Chen, Jurgen Ihlemann, Gerd Marowsky, Peter Oesterlin and Berthold Burghardt, "High-Resolution F2-Laser Machining of Micro-Optic Components", in Photon Processing in Microelectronics and Photonics, SPIE 4637, 228-234 (2002).
