The present invention relates generally to the field of integrated optics, and more particularly to an optical waveguide comprising multiple layers of solid-state material disposed on a substrate, whereby one of the layers is a lifting-gate valve made of a high refractive index material.
Movable microvalves have been introduced for controlling liquids on microfluidic devices (“labs-on-chip”). One attractive implementation is the lifting-gate technology, e.g., a pneumatically actuated micro-valve. (See, e.g., [1] Jensen, E. C., Bhat, B. P., and Mathies, R. A., “A digital microfluidic platform for the automation of quantitative biomolecular assays”, Lab Chip 10, 685-£91 (2010); [2] Kim, J., Kang, M., Jensen, E. C., and Mathies, R. A., “Lifting gate PDMS microvalves and pumps for microfluidic control”, Anal. Chern. 84, 2067-2071 (2012); [3] Erik C. Jensen, E. C., Stockton, A., Chisel, T., Kim, J., and Mathies, R. A., “Digital Microfluidic automaton for multi-scale combinatorial mixing and sample processing”, Lab Chip 13, 288-96 (2013); [4] Kim, J., Jensen, E., Stockton, A., and Mathies, R. A., “Universal Microfluidic Automaton for Autonomous Sample Processing: Application to the Mars Organic Analyzer”, Anal. Chern. 85, 7682-88 (2013).) A lifting-gate valve is raised as vacuum is applied to the pneumatic channel on the top, allowing fluid motion through the channel below. Lifting-gate microvalves can be operated sequentially using computer control, thus creating devices with reconfigurable fluidic functions.
A lifting-gate network (automaton) has recently been combined with dedicated optical sensing chips made on a silicon platform. The automaton was to implement advanced sample preparation steps, exemplified by the sequence-specific nucleic acid extraction protocol (See, e.g., Parks, J. W., Olson, M. A., Kim, J., Ozcelik, D., Cai, H., Carrion Jr., R., Patterson, J. L., Mathies, R. A., Hawkins, A. R., and Schmidt, H., “Integration of programmable microfluidics and on-chip fluorescence detection for biosensing applications”. Biomicrofluidics 8, 054111 (2014).) As an example, synthetic nucleic acids corresponding to Zaire Ebola virus were mixed with matching molecular beacon probes, magnetic microbeads with another matching pull-down sequence, and other random DNA. After mixing and incubation in one of the microvalves, beads with multiple attached target-probe complexes were pulled to the valve bottom with a magnet, and remaining nucleic acids were washed off. Subsequently, the beads were pumped into a Si-based anti-resonant reflecting optical waveguide (ARROW) chip for detection.
The present invention relates to an optical waveguide comprising multiple layers of solid-state material disposed on a substrate, wherein one of the layers is a lifting-gate valve made of a high refractive index material (i.e., the refractive index of the lifting-gate valve is higher than the refractive index of the surrounding material). The invention introduces concepts for directing and providing better optical signal confinement in microfluidic channels. Specifically, the invention introduces a microvalve optical waveguide device having the capability to integrate both optical signals and sample processing. For example, referring to the lifting-gate embodiment of
The present invention addresses the implementation of flexible optical layouts on microfluidic and optofluidic labs-on-chip. By designing a movable microvalve such that it can also guide, distribute, and collect light in different ways, we can dynamically change light paths on a chip. Current devices have fixed optical paths. The invention can be implemented with established microfluidic soft lithography techniques using, e.g., inexpensive polydimethylsiloxane (PDMS) silicon for rapid prototyping.
An illustrative embodiment of an optical waveguide in accordance with the present invention comprises a substrate characterized by a first refractive index, a pneumatic layer disposed on the substrate and characterized by a second refractive index, a channel between the substrate and the pneumatic layer and configured to receive a sample fluid, and a pneumatically actuated micro-valve comprising a gate. The gate is characterized by a third refractive index that is greater than the first refractive index and the second refractive index. An optical channel for guiding an optical signal is disposed between the substrate and the pneumatic layer transversely to the channel. The micro-valve is configured to be pneumatically actuated to switch from a first state in which the gate is positioned to block fluid flow in the channel, and a second state in which the gate is sufficiently withdrawn from the channel to permit fluid flow in the channel. Moreover, the high-index gate is configured for guiding the optical signal transversely through the channel when in the first state.
We also disclose a method for operating an optical waveguide. Other aspects of the inventive technology are described below.
The present invention relates to the field of integrated optics, and more particularly to an optical waveguide comprising multiple layers of solid-state material disposed on a substrate, wherein one of the layers is a pneumatically actuated micro-valve (an example of which is a lifting-gate valve) made of a high refractive index material. The present invention introduces concepts for directing and providing better optical signal confinement in microfluidic channels. Specifically, the present invention introduces a single microvalve optical waveguide device that has the capability to integrate both optical signals and sample processing.
In the following subsections, we discuss our inventive methods for fabricating lifting-gate valves using high refractive index materials, and our inventive flexible optofluidic waveguide platform with multi-dimensional reconfigurability. The disclosed methods for fabricating lifting-gate valves are discussed with reference to
Fabricating Lifting-Gate Using a High Refractive Index Material
In one embodiment, improvement in the confinement of optical signals in an optical waveguide device includes the usage of a high refractive index material. The key material here is the high refractive index, which is strategically fabricated in a lifting-gate valve. This allows optical signals to be re-directed or re-distributed as signals flow through the channels of the optical waveguide. With more control of the signals that flow through the channels, the confinement of the signals in the channels is improved.
Fabrication of the lifting-gate valve may be achieved by bonding high and low-index layers together. Alternatively, spinning the low-index layer on top of the structured high-index layer would also provide for a dual layer of lifting-gate valves where light can be re-directed to a different layer in the optical waveguide. This refers to a lifting gate comprising a high and low index region, in which case one can implement the gate by making these two layers separately and bonding them with UV light or oxygen plasma (i.e., PDMS bonding), or by patterning the lower high index layer and then adding the second layer directly on top. This can be done by dropping the liquid precursor material on top and then spinning the whole thing rapidly. This creates a thin layer of uniform thickness, which can be controlled by spin duration and speed.
With high refraction index material fabricated in the lifting-gate valves, optical waveguides can be dropped into the channels of the device to create new light paths on the fly. These lifting-gate valves may be operated by the same pneumatic controls already used for the sample preparation valves.
Several embodiments are discussed below and with reference to the attached drawings. These descriptions and drawings are for explanatory purposes and do not exhaustively represent all combinations of waveguide configurations and mechanical assemblies provided by this invention. Those of ordinary skill in the art will readily appreciate that many other variations could be derived from these descriptions and the cited technical findings.
An exemplary embodiment of the invention is represented in
The optical waveguide 300 may be configured as an anti-resonant reflecting optical waveguide (ARROW) waveguide, slot waveguide, hollow-core photonic crystal fiber, omniguide, dual-hollow-core waveguide, or Bragg waveguide. Furthermore, the substrate 310 may comprise silicon, PDMS, or glass material. And the pneumatic and fluidic layers 330, 320 may comprise SiO2 and SiN or PDMS material. The lifting-gate valve 320 in
Flexible Optofluidic Waveguide Platform with Multi-Dimensional Reconfigrrability
We will now discuss our new optofluidic platform that provides both multi-modal photonic reconfiguration and advanced fluidic sample handling in a single chip. On-chip photonic devices are based on a combination of solid-core and liquid-core PDMS waveguides as shown in
In order to demonstrate the physical implementation of the PDMS waveguide platform and the ability to tune an optical device using both fluid control and pressure, we first consider a multi-mode interference (MMI) waveguide.26 MMIs create length and wavelength dependent spot patterns upon propagation of multiple waveguide modes, and have recently been used to implement spectrally multiplexed detection of single viruses flowing through intersecting fluidic channels.21 Our liquid-core optofluidic MMI is schematically shown in
The multimode interference leads to the formation of N images of the input mode for a given length, L, and pressure, P, according to
This pattern formation is visualized in
Next, we turn to dynamic tuning of these optofluidic elements. The first mechanism is through replacement of guiding liquid, i.e the waveguide core refractive index, nc.
Thin sidewalls made from a pliable material (PDMS) allow for controlling a microfluidic channel's width through both inward and outward pressure.28 Here, we use this principle for pressure-based dynamic tuning of the optofluidic MMI devices. Inward pneumatic pressure applied to the side channels causes a decrease in the MMI width, (
We now turn to introducing a new approach for a fully—optically and fluidically—reconfigurable optofluidic platform. At its heart is an actuatable microvalve that simultaneously acts as an optical waveguide and actively moderates fluid flow, dubbed here as a “lightvalve”. Our implementation is based on lifting-gate microvalves that have been used in microfluidic devices for complex bioassays.29,30
The obvious Litmus test for photonic functionality of the lightvalve is operation as an on-off switch, which is reported in
Next, we analyzed the on-off optical switching efficiency for different length lightvalves operated in lift-up mode. The results are displayed in
Push-down operation, on the other hand, is relatively length-independent as it relies only on deformation of the waveguide structure at the beginning of the lightvalve, which leads to poor mode coupling between the excitation and valve waveguides.
Finally, we demonstrate an implementation of the lightvalve as a functional element that unites both fluid handling and photonic functions of a bio-detection assay. To this end, the lightvalve is built as an annular structure shown schematically in
Lastly, we demonstrate the lightvalve trap's ability to analyze single, trapped bioparticles—here, fluorescently stained E. coli bacteria.
In summary, we have introduced a new optofluidic platform that seamlessly marries optical and fluidic functions in a single chip. Based on combining solid- and liquid-core PDMS waveguides whose fabrication is compatible with purely microfluidic chips, we created devices that offer multi-modal photonic reconfigurability using core liquids, mechanical pressure and motion. The potential of this approach was illustrated using widely tunable liquid-core MMI waveguides and by the introduction of novel lightvalves that regulate both liquid and light flow. Extremely efficient optical switching and definition of physical particle traps for optical analysis were demonstrated. The fluidic valve shape and optical pathways created by the lightvalve can be designed independently and with great flexibility, making the lightvalve a powerful building block for future optofluidic devices.
While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.
This application is a National Stage Application filed under 35 U.S.C. 371 of International Application No. PCT/US2016/049999, “Reconfigurable Microvalve Optical Waveguide,” filed on Sep. 1, 2016, which claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application No. 62/213,022, “Reconfigurable Microvalve Optical Waveguide,” filed on Sep. 1, 2015, the contents of which are incorporated herein by reference in their entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/US2016/049999 | 9/1/2016 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2017/040856 | 3/9/2017 | WO | A |
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20060171846 | Marr et al. | Aug 2006 | A1 |
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