Frank S. Tsai

Human mammalian cell sorting using a highly integrated micro-fabricated fluorescence-activated cell sorter (μFACS)

We demonstrate a high performance microfabricated FACS system with highly integrated microfluidics, optics, acoustics, and electronics. Single cell manipulation at a high speed is made possible by the fast response time (approximately 0.1 ms) of the integrated PZT actuator and the nozzle structure at the sorting junction. A Teflon AF-coated optofluidic waveguide along the microfluidic channel guides the illumination light, enabling multi-spot detection, while a novel space-time coding technology enhances the detection sensitivity of the microFACS system. The real-time control loop system is implemented using a field-programmable-gate-array (FPGA) for automated and accurate sorting. The microFACS achieves a high purification enrichment factor: up to approximately 230 fold for both polystyrene microbeads and suspended human mammalian cells (K562) at a high throughput (>1000 cells s(-1)). The sorting mechanism is independent of cell properties such as size, density, and shape, thus the presented system can be applied to sort out any pure sub-populations. This new lab-on-a-chip FACS system, therefore, holds promise to revolutionize microfluidic cytometers to meet cost, size, and performance goals.

Specific Sorting of Single Bacterial Cells with Microfabricated Fluorescence-Activated Cell Sorting and Tyramide Signal Amplification Fluorescence in Situ Hybridization

When attempting to probe the genetic makeup of diverse bacterial communities that elude cell culturing, researchers face two primary challenges: isolation of rare bacteria from microbial samples and removal of contaminating cell-free DNA. We report a compact, low-cost, and high-performance microfabricated fluorescence-activated cell sorting (μFACS) technology in combination with a tyramide signal amplification fluorescence in situ hybridization (TSA-FISH) to address these two challenges. The TSA-FISH protocol that was adapted for flow cytometry yields a 10-30-fold enhancement in fluorescence intensity over standard FISH methods. The μFACS technology, capable of enhancing its sensitivity by ~18 dB through signal processing, was able to enrich TSA-FISH-labeled E. coli cells by 223-fold. The μFACS technology was also used to remove contaminating cell-free DNA. After two rounds of sorting on E. coli mixed with λ-phage DNA (10 ng/μL), we demonstrated over 100,000-fold reduction in λ-DNA concentration. The integrated μFACS and TSA-FISH technologies provide a highly effective and low-cost solution for research on the genomic complexity of bacteria as well as single-cell genomic analysis of other sample types.

Lab-on-a-chip flow cytometer employing color-space-time coding

We describe a fluorescent detection technique for a lab-on-a-chip flow cytometer. Fluorescent emission is encoded into a time-dependent signal as a fluorescent cell or bead traverses a waveguide array with integrated spatial filters and color filters. Different from conventional colored filters with well-defined transmission spectral window, the integrated color filters are designed to have broad transmission characteristics, similar to the red-green-blue photoreceptors in the retina of human eye. This unique design allows us to detect multiple fluorescent colors with only three color filters based on the technique of color-space-time coding using only one single photomultiplier tube or avalanche photodetector.

Fluidic lens laparoscopic zoom camera for minimally invasive surgery.

We developed a miniaturized laparoscopic zoom camera that is 17 mm long, has >4X optical zoom, and works under 300 lux. This camera is suitable for advancing minimally invasive surgery. Demonstration surgery (cholecystectomy) was performed.

Micro-fabricated fluorescence-activated cell sorter

We demonstrate a high sensitivity, high throughput microfabricated cell sorting device with the integrated piezoelectric actuator and optofluidic waveguide on a chip. For automated sorting, field-programmable-gate-array (FPGA) embedded real time control loop system is built. The sorting is performed under high flow rate (~10 cm/sec), and the sorting system can achieve a high throughput (> 1kHz) with high purity. Moreover, to enhance its sensitivity, Teflon AF coated liquid core waveguide (LCW) structure is demonstrated. Teflon AF has a lower refractive index (n=1.31) than water (n=1.33) and forms the cladding layer of the LCW. Incident light is confined and guided along the Teflon AF coated fluidic channel, and interact with samples flowing along the same channel. This enables flexible device design and gives high sensitivity to the fluorescence detection system. The preliminary results demonstrate sorting fluorescent beads at a sorting efficiency of ~70% with no false sorting.

Fabrication of aspherical polymer lenses using a tunable liquid-filled mold.

We demonstrated a tunable molding process to fabricate aspherical polymer lenses that can reduce aberrations and the total length of an optical system. Radius of curvature and conic constant are shown to be the key parameters to characterize the lens profile. The good agreement between the measured profiles and the simulated profiles allows us to design and fabricate lenses of a wide range of user-specified properties. Compared to the conventional aspherical lens fabrication method using injection molding with a diamond-turned mold, the proposed method may yield savings in time and cost.

Scattering-Based Cytometric Detection Using Integrated Arrayed Waveguides With Microfluidics

Scattering-based on-chip excitation and detection on the arrayed-waveguide platform has been developed and implemented. Detected signals were processed with the proposed multiplication-based cross-correlation algorithm. The algorithm is capable of not only achieving signal enhancement (80 dB relative to the untreated signals) but also velocity measurement. Thus, particles flowing at different speed could also be accurately detected. Processed signals were verified by comparison to frame-by-frame video images, showing excellent correspondence. The signal processing algorithm can be easily extended to real-time on-chip detection

Fluidic Intraocular Lens With a Large Accommodation Range

Fluidic lenses with tunable focal distances were experimented in a human eye model as intraocular lenses (IOLs). Fluidic IOL shows superior performance to fixed or optic-shift accommodating IOLs because of their much wider accommodation range. Our results demonstrate that fluidic IOL can achieve an accommodation range of eight diopters, equivalent to the performance of young adults. Finite-element analysis shows that the required force for the fluidic IOL to achieve the desired amount of accommodation is comparable to the force generated from ciliary muscles of human eyes, as an initial indication that an implanted fluidic IOL may be controllable by eye muscles.

Microfluidic Photonic Integrated Circuits.

We report on the development of an inexpensive, portable lab-on-a-chip flow cytometer system in which microfluidics, photonics, and acoustics are integrated together to work synergistically. The system relies on fluid-filled twodimensional on-chip photonic components such as lenses, apertures, and slab waveguides to allow for illumination laser beam shaping, light scattering and fluorescence signal detection. Both scattered and fluorescent lights are detected by photodetectors after being collected and guided by the on-chip optics components (e.g. lenses and waveguides). The detected light signal is imported and amplified in real time and triggers the piezoelectric actuator so that the targeted samples are directed into desired reservoir for subsequent advanced analysis. The real-time, closed-loop control system is developed with field-programmable-gate-array (FPGA) implementation. The system enables high-throughput (1- 10kHz operation), high reliability and low-powered (<1mW) fluorescence activated cell sorting (FACS) on a chip. The microfabricated flow cytometer can potentially be used as a portable, inexpensive point-of-care device in resource poor environments.

Miniaturized unified imaging system using bio-inspired fluidic lens

Miniaturized imaging systems have become ubiquitous as they are found in an ever-increasing number of devices, such as cellular phones, personal digital assistants, and web cameras. Until now, the design and fabrication methodology of such systems have not been significantly different from conventional cameras. The only established method to achieve focusing is by varying the lens distance. On the other hand, the variable-shape crystalline lens found in animal eyes offers inspiration for a more natural way of achieving an optical system with high functionality. Learning from the working concepts of the optics in the animal kingdom, we developed bio-inspired fluidic lenses for a miniature universal imager with auto-focusing, macro, and super-macro capabilities. Because of the enormous dynamic range of fluidic lenses, the miniature camera can even function as a microscope. To compensate for the image quality difference between the central vision and peripheral vision and the shape difference between a solid-state image sensor and a curved retina, we adopted a hybrid design consisting of fluidic lenses for tunability and fixed lenses for aberration and color dispersion correction. A design of the worlds smallest surgical camera with 3X optical zoom capabilities is also demonstrated using the approach of hybrid lenses.