The present work aims to provide new tools for the manipulation and detection of biological samples. They can be envisioned as individual components of an integrated, lab-on-a-chip system.
A novel SU-8 microgripper is introduced for the manipulation of single cells or other biological species in solution with minimal undesired interactions. The electrothermally activated polymer gripper consists of two SU-8 ‘hot-and-cold-arm’ actuators that are fabricated in a two-mask surface micromachining process. The high thermal expansion coefficient of SU-8 (52 ppm/oC) compared to silicon and metals, allows the actuation of the microgripper with small average temperature elevations (10 - 32 OC) at low voltages (1 - 2 Volts). Attached to an external manipulator, the gripper is capable of positioning single cells in 3-D space. The various material properties of SU-8 photoresist are also discussed.
A more advanced system – a three-degree-of-freedom SU-8-based microrobotic workstation – was also developed. It can replace the above-mentioned bench-sized setup, providing at the same time autonomous on-chip single cell manipulation. The construction of SU-8 chevron and ‘hot-and-cold-arm’ microactuators that are able to operate in physiological media at low voltages (1.5-2.6 V) and with small temperature increases (~22 oC) is the key element of the design.
The rest of the thesis discusses the development of optical components for bio-detection and imaging on-chip.
The use of a total internal reflection (TIR)-based biochip is proposed for imaging surface dynamics. The chip utilizes a polymer-filled cavity with a micromirror sidewall. The implementation of the micromirror sidewall cavity facilitates precise alignment of the excitation light beam into the system. The incident angle of illumination can be easily modified by selecting polymers of different indices of refraction while optical losses are minimized. The design enables the hybrid, vertical integration of a laser diode and a CCD camera, resulting in a compact optical system. Brownian motion of fluorescent microspheres and real-time photobleaching of rhodamine 6G molecules is also demonstrated.
Finally, a tunable microlens array can be used to collect and direct fluorescent emitted light. The microlens array, integrated on top of a microfluidic network, is formed from a PDMS (polydimethylsiloxane) slab patterned from an SU-8 mold. The simultaneous control of the focal length of all the microlenses composing the elastomeric array is accomplished by pneumatically regulating the pressure of the microfluidic network. A focal length tuning range of hundreds of microns to several millimeters is achieved. The microlens array can be furthermore integrated on top of the TIR biochip resulting in an integrated bio-detection system for various high throughput imaging applications.
November 30, 2004
Chronis, N. S. (2004). Lab-on-a-Chip Mechanical and Optical Components for the Manipulation and Detection of Biological Species. United States: University of California, Berkeley.