A microfabricated fluorescence activated cell sorter based on an optical switch enables low-stress sorting of small cell populations (i.e. 1,000 - 100,000 cells), a regime that is not addressed by current cell sorters. The glass microchannels are packaged in a self-contained plastic cartridge that enables "chip-to-world" interconnect for ease of use.
The sample is hydrodynamically focused using pneumatic pressure driven flow control and is biased to the waste reservoir by default. A 5 mW, 488 nm semiconductor laser is used for cell detection and fluorescence excitation. A sorting event is triggered based on the fluorescence and light scatter properties of the cell. The optical switch is produced from a 20 W CW 1070 nm Ytterbium fiber laser that is controlled by an acousto-optic modulator to deflect the target cell to the target reservoir. Cells can be recovered after the sort for further manipulations. Sorting performance was evaluated using a stably transfected, GFP expressing HeLa cell line spiked at varying ratios into parental HeLa cells. Throughputs ranged from 20-100 cells/sec depending on initial cell concentrations and flow parameters. Target purities greater than 90% were obtained in most cases with overall recoveries greater than 85%. A 1% subpopulation of GFP-HeLa cells could be enriched by 63-71 fold. Similar results were demonstrated using samples from pancreas and other primary tissues. Optical switching can be scaled to fluidic networks of greater complexity by multiplexing an optical source to multiple locations on a chip, and these locations can be arbitrarily reconfigurable.
A novel, non-invasive measurement technique for quantitative cellular analysis is presented that utilizes the forces generated by an optical beam to evaluate the physical properties of live cells in suspension. Analysis is performed by rapidly scanning a focused, near-infrared laser line with a high cross-sectional intensity gradient across a field of cells and monitoring their interaction with the beam. The response of each cell to the laser depends on its size, structure, morphology, composition, and surface membrane properties; therefore, using this technique, cell populations of different type, treatment, or biological state can be compared. To demonstrate the utility of this cell analysis platform we have evaluated the early stages of apoptosis induced in the U937 cancer cell line by the drug camptothecin and compared the results to established references assays. Measurements on our platform show detection of cellular changes earlier than either of the fluorescence-based annexin V or caspase assays. Because no labeling or additional cell processing is required and because accurate assays can be performed with a small number of cells, this measurement technique may find suitable applications in cell research, medical diagnostics, and drug discovery.
Cationic-induced two-photon photopolymerization is demonstrated at 710 nm, using an isopropylthioxanthone/diarylidonium salt initiating system for the cationic polymerization of an epoxide. The polymerization threshold J2th is found to be approximately 1 GW/cm2, with a dynamic range of > 100, i.e. the material can be fully polymerized at intensities > 100 times the threshold level without damage. The polymerization rate R is found to be proportional to the m equals 1.7 power of the intensity, or R equals [C (J-J2th)]m equals [C (J-J2th)]1.7, which implies a significantly stronger localization of the photochemical response than that of free radical photoinitiators. R and J2th significantly improve when the concentration z of the initiator (onium salt) increases.
Large-scale computer and data-communication systems have reached a bottleneck in performance in recent years due to the limitations of electronic interconnections for data transfer. One potential solution is based on the use of optoelectronic device arrays for free space optical interconnects. In this paper, we present the design and implementation of a 16 X 16 3D distributed optoelectronic crossbar switch.
We demonstrate a setup with 10 optically interconnected chips,k which can perform a distributed radix-2-butterfly calculation for fast Fourier transformation. The setup consists of a motherboard, five multi-chip-modules (MCMs, with processor/transceiver chips and laser/detector chips), four plug-on-top optics modules that provide the bi- directional optical links between the MCMs, and external control electronics. The design of the optics and optomechanics satisfies numerous real-world constraints, such as compact size (< 1 inch thick), suitability for mass-production, suitability for large arrays (up to 103 parallel channels), compatibility with standard electronics fabrication and packaging technology, and potential for active misalignment compensation by integrating MEMS technology.
Current biochip technologies typically rely on electrostatic or mechanical forces for the transport and sorting of biological samples such as single cells. In this paper we have investigated how optical pressure forces can be effectively used for the manipulation of cells and switching in a microfluidic system. By projecting the optical beams externally non-contact between the control devices and the sample chip is possible thus allowing the sample chips to be disposable which reduces the chance of cross-contamination. In one implementation we have shown that vertical cavity surface emitting laser (VCSEL) array devices used as parallel optical tweezer arrays can increase the parallelism of sample manipulation on a chip. We have demonstrated the use of a high-order Laguerre-Gaussian mode VCSEL for optical tweezing of polystyrene microspheres and live cells. We have also shown that optical pressure forces from higher- power sources can be used for the switching of particles within microfluidic channels. Both the attractive gradient force and the scattering force of a focused optical beam have been used to direct small particles flowing through junctions molded in PDMS. We believe that by integrating optical array devices for simultaneous detection and manipulation, highly parallel and low-cost analysis and sorting devices may be achieved.
It is demonstrated that threshold reduction of two-photon polymerization is achievable by means traditionally employed for sensitivity enhancement for single photon photoinitiation, such as heavy atom enhancement or intersystem crossing, electron donor agent, concentration increase of initiator. It is shown that measured threshold is in reverse proportion to square root of initiator concentration, whereas observed length of induction period exhibits reverse proportionality to the square of light intensity. Overall, experimentally observed threshold values of two-photon induced photopolymerization are effected by all intermediate stages of energy transformation in the photochemical sequences leading to photoinitiation, in particular inter-system crossing of excited initiating molecules as well as by monomer reactivity.
Three layer data recording has been demonstrated in monolithic disk media using two-photon absorption. Two dimensional data arrays have been recorded and retrieved in parallel. The recording process has been modeled and simulated. Fluorescence has been detected from a disk spinning at 1500 rpm with a signal to noise ratio of 10.