MOABC Summary
The proposed P41 resource will be focused on the integration of optics into microscale and microfluidic systems, a need becoming increasingly apparent as bioassaying devices and other sensors are being developed for portable applications. Though commercial microfluidic systems have been under development for the past decade, these have been focused on very high return markets such as pharmaceuticals. The systems that are currently sold are, for the most part, microfluidic cartridge based and require an associated large-scale “box”, either benchtop or larger scale, for actual function. Such systems can be quite expensive due to the optics and other systems that are integrated within the overall system. If these devices are to move into broader markets, they must be developed for portable (i.e. non lab-based) application.
After a sample has been prepared, introduced into the analytical device and processed, it must then be detected. This detection is still commonly accomplished by a microscope located off-chip. Having the microfluidic chip as just a small part of a system in which sample introduction and detection are much more complicated than the chip’s operation may be appropriate in some circumstances, but does detract from the potential advantages of microfluidic devices.
…it (microfluidics) must become successful commercially, rather than remain a field based on proof-of-concept demonstrations and academic papers. The impact of microfluidic systems…will only become apparent when everyone is using them. Microfluidics must be able to solve problems for users who are not experts in fluid physics or nanolithography, such as clinicians, cell biologists, police officers or public health officials.
-George M. Whitesides1
(Nature July, 2006)
Many of the promises of micro total analysis systems have yet to be realized: integration and packaging of several functionalities into a single system is proving to be a complex task…robust approaches to fabrication, integration, and packaging (such as communication with the macroenvironment) remain major areas of research.
-Klavs F. Jensen2
(Nature July, 2006)
To do so however, many of the tasks associated with the associated hardware must be integrated directly within the microfluidic platform. This includes not only the more obvious macroscale optical needs associated with scattering measurements or fluorescence excitation and detection, it include the need to control and direct transport within microfluidic systems. Often the need to control cell direction or pump fluids comprises a significant fraction of the associated hardware. If many of these tasks were accomplished optically and in a highly-integrated fashion, a significant scale down and step toward portable applications will be achieved. The proposed center will push the integration of optics within microsystems and provide a resource for those needing to move proof-of-concept techniques towards the commercial marketplace, aiding not only the typical consumer of medical care in the US but extending the reach of many technologies to the 3rd world3.
What is the current state of the art in microfluidics and optics? What other commercial microfluidic devices are there other than genechips, caliper drug discovery chips, or fluidigm protein chips?
Gene Chips -Affymetrix. Nanogen
Drug Discovery Chips - Caliper/Agilent
Protein Chips - Fluidigm
Cytometry Companies – Guava, Beckman,
What about DARPA and defense related microfluidic work? (http://www.darpa.mil/MTO/mFlumes)
This emerging and growing requirement for integrated optical capabilities will be supported by unique facilities and expertise that will serve as the foundation of a very useful community resource. CSM is presently home to a world-class ultrafast optical science laboratory, featuring three state-of-the-art, high-intensity chirped pulse amplification systems and a large array of femtosecond laser oscillators for imaging and spectroscopy. Such femtosecond optical capabilities require significant infrastructure, facilities not readily available at most institutions. These sources are capable of generating and controlling electromagnetic radiation spanning from the x-ray regime to millimeter waves (terahertz).
Given these unique capabilities, the proposed resource will center around the use of optical techniques for the characterization, manufacturing, and manipulation of biological systems. Though each of these research cores will focus around its own set of specific aims, they tie strongly together with results feeding into the research and development efforts of the other thrusts (see Figure 1). Specifically, the core aims include:
Core #1 Characterization: Microscale biophotonic measurement systems integrating optical and microscale systems for characterizing cells and other biologically significant molecules. Aims will include:
Specific Aim 1.1: Develop intra-microfluidic molecular spectroscopy capabilities.
Specific Aim 1.2: Develop intra-microfluidic cellular characterization capabilities.
Core #2 Manufacturing: Built around femtosecond laser micromachining this technological core will utilize the proven capability of these sources to produce precision, 3D integrated optical/microfluidic (or other microscale) devices. Aims will include:
Specific Aim 2.1: Non-writing based instrument development and demonstration optical device components fabricated in glass
Specific Aim 2.2: Extend machining capabilities to three-dimensional integrated structures
Specific Aim 2.3: Extend micromachining capabilities to new materials with relevance to optical microsystem integration, biological imaging, or biomedical device development.
Core #3 Manipulation: Optical-based control of cells and label-free sensing of cell properties. Aims will include:
Figure 1: The research cores are designed to
complement one another with results of each
feeding throughout the entire center.
Specific Aim 3.1: Develop integrated optical trapping techniques for microdevices.
Specific Aim 3.2: Develop integrated optical stretching techniques for microdevices.
Core #1 Characterization: Integrated optics for molecular and cellular characterization within microfluidic systems
A1. Specific Aims
Microfluidics hold tremendous potential as important tools for simultaneously advancing biomedical research and health care. The microfluidic platform provides several substantial advantages in biomedical research – key biomolecules are not available in large quantities, and the relevant dynamics of complex biomolecules takes place over a significant time expanse. Microfluidics are an optimal system for quantitative measurements of kinetics when sample size is limited, and the microfluidic geometry is readily configured to enable examination over times scales ranging from femtoseconds to seconds.
Similarly, from a health care point-of-view, the microfluidic platform is a tool that can be used to provide a significant measure of a broad range of cellular attributes from small samples. It can be done rapidly - statistically meaningful results can, in principle, be achieved in minutes.
Thus, the focus of the characterization core is to incorporate proven integrated optical techniques to enable the production of truly practical microfluidic devices that can be used for 1) biomedical research at the molecular and cellular level, and 2) as a health care diagnostics tool.
To achieve these goals, our specific aims include:
A1.1: Develop intra-microfluidic molecular spectroscopy capabilities. In order to produce devices optimized for studying biomolecular kinetics, microfluidic devices with fast mixing times and long delay lines must be created. Using nonlinear optical techniques we can quantitatively characterize device performance and, in conjunction with three-dimensional computer models, rapidly iterate on optimal designs for molecular spectroscopy applications. Further, using advanced micromachining methods, integrated optics will be designed and employed to provide robust, simplified optical excitation and detection systems into the microfluidic. Finally, in addition to traditional linear and nonlinear spectroscopic capability, new linear optical methods for measuring important parameters such as temperature will be incorporated, creating a comprehensive microfluidic platform for biomolecular studies.
A1.2: Develop intra-microfluidic cellular characterization capabilities. This aim will build on the capability of the integrated optical technology developed for the molecular spectroscopy applications. First, these same integrated, intra-microfluidic excitation and detection optics can be immediately incorporated as a linear optical system that is capable of characterizing cell size. This capability will be further developed to provide functional imaging of individual cells through a variety of contrast mechanisms including linear and nonlinear imaging techniques. The focus of the nonlinear imaging techniques is to be able to measure important cell attributes indicative of cell health without the necessity of adding exogenous contrast agents.
Core #2 Manufacturing: Ultrafast Laser Micromachining for Integrated Optical-Microfluidic Device Manufacturing
A2. Specific Aims
Point-of-care (POC) diagnostic technologies are considered a disruptive technology capable of revolutionizing national and global public health care in the next generation1. Already, the development of sophisticated new POC biomedical technologies have steadily advanced diagnosis and treatment, improved patient outcomes, and increased survivability. However, these technologies have proven to be and are expected to continue to be quite expensive. The extensive cost of emerging microfluidic POC technologies, based primarily upon microfluidic technologies, is due to the cumbersome processes by which they are manufactured. Descended from microelectronics processing and adapted for biomedical device fabrication, these protocols do not lend themselves well to scale-up in this new application arena. Furthermore, manufacturing scale-up problems are compounded by the need to seamlessly integrate fluidic, optical and electronic components. As a result the point-of-care potential of such technologies remains substantially unfulfilled and their use limited to laboratories and medical centers that can house, staff and afford to offer them. Clearly, the next generation microscale biomedical devices must be developed with a strong emphasis upon manufacturing cost, which will in turn assure more universal access and implementation.
Figure 2.
The focus of this core will be to develop novel optical manufacturing technologies that serve the mission of the MOABC Resource Center. The initial stages of this project will be immediately focused upon instrument development. We shall build upon demonstrated feasibility of an optical manufacturing platform that employs ultrafast lasers to sculpt both optical waveguides and fluidic channels into glass substrates. Subsequent work will focus upon scaling up the manufacturing equipment and employing it to prototype disposable components of novel integrated microfluidic-optical diagnostic platforms. Examples of the hybrid microfluidic-optical tools that we will focus upon as core cross-over efforts include cell sorters and on-chip flow cytometers.
The architecture of the integrated optical-microfluidic components that we will manufacture is unique: waveguides are integrated directly into the microfluidic channels, enabling optical manipulation and interrogation as cells flow through the system. The manufacturing approach described here will allow these architectures to be rapidly produced in a single, monolithic glass substrate. We have previously shown that waveguides, allowing direct integration of fluorescence, and transmission/absorption-based detection and fabricated in compatible materials, can be used to fabricate a truly miniaturized and portable device. (See Section 4, Preliminary Studies.) Current waveguide creation is a slow, serial process lacking real-time quantitative feedback—leading to ineffective commercialization efforts due to high cost. To make our integrated waveguiding/microfluidic approach inexpensive and truly practical, new waveguide fabrication technologies must be developed.
To create the integrated microchannels and waveguides we propose, an entirely new fabrication scheme is required. During the proposed project, femtosecond lasers will be used to fabricate waveguides for microfluidic devices using a micromachining parallelization technique pioneered by Professor Jeff Squier. This system employs an image-based approach to highly parallelize femtosecond pulsed lasers to enable fabrication and imaging simultaneously in real time with sub-micron precision. In addition to the important implications that the proposed work has for micromachining in general, this will be the first demonstration of highly parallel micromachining with simultaneous three-dimensional visualization.
To demonstrate that multi-focal machining is feasible, we have already used a simplified system to write structures such as waveguides and waveguide couplers by translation along the axial dimension of the beam. In that work, we used a beam-splitter array to produce four beamlets, which were focused to produce four foci spaced by 10 µm. (See Section 4.) Initially, we will fully validate and expand upon this initial work to clarify design parameters for construction of a capable manufacturing workstation. Specifically, we will pursue the following Specific Aims throughout the course of this core’s primary project:
A2.1: Instrument development and demonstration optical device components fabricated in glass. The primary focus of instrument development efforts will be machining in silicon dioxide substrates. The first specific aim will concentrate on multiplexed waveguide writing, which as we have demonstrated can be combined with conventional PDMS microchannel networks to create devices of hybrid materials. Hybrid device development will be pursued in a synergistic collaboration with the NIBIB sponsored BioMEMS Resource Center to immediately provide functioning devices to an established user base. The individual milestones of Specific Aim 1 are:
· A2.1.1 Develop imaging-based, as opposed to writing-based, techniques for cost-efficient waveguide fabrication. Multi-focal development and lithographic demonstration. We will prove that the multi-focal micromachining approach can be parallelized to “stamp” out a single layer of features with 5 mm resolution. This will provide the basis of our manufacturing technique in which 5 mm deep layers of features will be individually created and in this way a three dimensional device “swept” out of a monolithic substrate.
· A2.1.2 Demonstrate multi-focal ultrafast laser fabrication of vertical, linear waveguides and characterize the machined waveguides for optimal performance in fluorescence excitation/emission applications.
· A2.1.3 Demonstrate multi-focal ultrafast laser micromachining of channel structures. The overall project will demonstrate the feasibility of developing a multi-focal ultrafast laser micromachining workstation for the manufacture of microfluidic structures containing integrated optical components.
A2.2: Extend machining capabilities to three-dimensional integrated structures in glass. The second specific aim will shift from the point-wise thermodynamic restructuring of glass to the planar ablation of glass for the creation of microchannels. Combining the capabilities developed in aims 1 and 2 will enable the creation of monolithic, integrated waveguide/microchannel devices.
A2.3: Extend micromachining capabilities to new materials with relevance to optical microsystem integration, biological imaging, or biomedical device development. Obvious candidate materials include commonly used elastomers such as PDMS and fluorinated siloxanes. Silicon is a second substrate of tremendous interest because it enables electrical integration and is an ideal substrate for femtosecond machining due to its strong two-photon absorption.
Core #3 Manipulation: Optical-Based Cell Manipulation and Measurement
A3. Specific Aims
Microfluidics holds great promise as the basis for future sensing and analysis systems. Compared to instruments with traditional fluid-handling technology, it offers both rapid transport and the ability to manipulate smaller sample volumes than previously possible, advantages that are ideal for the investigation of precious or very expensive samples. These capabilities will allow samples of microliter or smaller volumes to be split for multiple diagnoses on one chip. As a consequence, biomedical analyses will move out of the laboratory to point of care situations. Handheld sensors capable of collecting samples from dynamic environments and providing immediate feedback are now being developed. One goal is the micro total analysis system (mTAS) where a single sample drop (blood, saliva, etc.) could be split, mixed with varying reagents, and analyzed in one small device (the “lab on a chip”).