Photoelectric hybrid integrated implantable flexible waveguide integrated optical genetic probe and preparation method thereof

Abstract

The invention discloses a photoelectric hybrid integrated implantable flexible waveguide integrated optical genetic probe and a preparation method thereof, and the method comprises the steps: further depositing a polymer material with a relatively low refractive index on a hard substrate deposited with a sacrificial layer as a lower cladding layer, and then depositing an inorganic material with a relatively high refractive index above the lower cladding layer as a waveguide core layer; the flexible waveguide integrated optical genetic probe is prepared by taking a hard substrate as a substrate, depositing a polymer material with a relatively low refractive index on the hard substrate as an upper cladding, preparing an active functional layer in a penetrating manner, defining the shape of the probe through cutting, and finally soaking a photoelectric probe chip in a corrosive liquid to partially strip the hard substrate to obtain the flexible waveguide integrated optical genetic probe. The deposition is only performed on the single chip from bottom to top, the step of pattern transfer is not needed, and the technological process is simple and convenient; the biological tissue inflammatory response caused in the long-term implantation process of the probe is small; the cladding-core layer-cladding structure and the active functional layer enable the probe to be suitable for realizing multi-site and adjustable light emission, and the optical and electrical functions of the probe are enriched.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of micro-nano waveguide integrated optoelectronic devices and neuroscience research, specifically to an optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe and its preparation method. Background Technology

[0002] Optogenetics, as a cutting-edge tool, typically utilizes visible light to precisely manipulate neuronal activity. However, brain tissue exhibits severe absorption and scattering of visible light, significantly limiting its effective transmission distance. To address this challenge, implantable optogenetic probes have emerged. Brain tissue is suspended within the cranial cavity and undergoes micromotion. Traditional rigid optogenetic probes have a significantly different Young's modulus compared to brain tissue, making them prone to inflammation upon interaction. The resulting glial scarring degrades signal quality and shortens probe lifespan. Given the excellent mechanical flexibility of flexible optogenetic probes, the relative displacement between the probe and brain tissue is smaller, effectively reducing interaction and significantly mitigating inflammation. This extends probe lifespan and provides a reliable platform for long-term recording and manipulation of neuronal activity.

[0003] To create more detailed brain maps, deepen our understanding of neuroscience, and advance the research and treatment of brain diseases, high spatiotemporal resolution neural recording and manipulation are indispensable. Optical fibers are currently the most commonly used tool in optogenetics; however, the Young's modulus of optical fibers differs from that of brain tissue by three orders of magnitude, potentially causing brain tissue damage during use. To address this issue, although various flexible polymer fiber-based optogenetic probes have been developed in recent years based on flexible polymer materials, problems such as a limited number of stimulation channels and integrated recording electrodes remain. Another widely researched technology is flexible micro-light-emitting diodes (LEDs), which have achieved remarkable breakthroughs in system miniaturization and wireless connectivity, but still face challenges such as a limited number of optical stimulation channels and beam divergence. Compared to fiber-based and micro-LED-based optogenetic probes, waveguide-integrated optogenetic probes, based on integrated optics, can emit low-divergence beams with beam profile dimensions matching the size of a single neuron, enabling high spatial resolution optical stimulation. Reconfigurable technology based on integrated optics can achieve microsecond-level time responses, matching the sub-millisecond response of photosensitive proteins, enabling high temporal resolution single-cell stimulation. In addition, waveguide-integrated optogenetic probes, by introducing micro- and nano-optical structures, have the characteristics of small device size, which can realize compact multi-channel stimulation site integration, thereby achieving high-pass neuron manipulation.

[0004] Currently, there are few reports on research into flexible waveguide-integrated optogenetic probes. Although some researchers have fabricated a flexible waveguide-integrated probe based on biocompatible materials Parylene C and PDMS using silicon oxide as a sacrificial layer, the low refractive index difference between Parylene C and PDMS results in a large device size, making it difficult to achieve multi-stimulation channel integration within a limited implantation probe area. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes an optoelectronic hybrid integrated implantable flexible waveguide-integrated optogenetic probe and its fabrication method. On a rigid substrate with a deposited sacrificial layer, a flexible lower cladding, an inorganic waveguide core, and a flexible upper cladding are sequentially fabricated. An active functional layer can be interspersed during the fabrication of the upper cladding. Then, the defined probe outline is cut, and finally, the rigid substrate is partially peeled off to obtain the flexible probe. Compared to previously reported flexible waveguide-integrated probes, this invention, using inorganic materials as the waveguide and polymers as the cladding, possesses a high refractive index contrast structure, enabling smaller size and higher density optical integration. The introduction of the electrical functional layer allows for active modulation of the optical link and recording of neural potentials, ultimately achieving a small-sized, multi-site, and flexibly modulated implantable flexible waveguide-integrated optogenetic probe.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for fabricating an optoelectronic hybrid integrated implantable flexible waveguide optical genetic probe includes the following steps:

[0008] Step 1: Deposit a sacrificial layer on a hard substrate;

[0009] Step 2: Deposit a polymer layer on the sacrificial layer as the lower cladding of the waveguide;

[0010] Step 3: When the waveguide material is an oxide, a polymer protective layer is deposited on the polymer layer using atomic layer deposition (ALD), and then a waveguide material layer is further deposited on the polymer protective layer using reactive sputtering. When the waveguide material is not an oxide, the waveguide material layer is directly deposited on the polymer layer using reactive sputtering.

[0011] Step 4: Patterning and etching the waveguide material layer to fabricate the waveguide;

[0012] Step 5: When the prepared probe is an active probe, metal electrodes for recording neural potentials, metal wiring, and metal electrodes for encapsulation are prepared around the waveguide using a patterning-metal deposition-stripping method. Then, a polymer layer is deposited on the surface of the waveguide material layer as the upper cladding of the waveguide, and the polymer on the upper surface of the metal electrodes is removed to expose the metal electrodes. When the prepared probe is a passive probe, a polymer layer is directly deposited on the surface of the waveguide material layer obtained in step 4 as the upper cladding of the waveguide.

[0013] Step 6: Divide the waveguide chip obtained in Step 6 into implanted and non-implanted parts, release the implanted part, remove the sacrificial layer and hard substrate, and obtain an optoelectronic hybrid integrated implantable flexible waveguide optical genetic probe.

[0014] Furthermore, before releasing the implanted portion in step six, a metal for optical field modulation in the waveguide is prepared on the upper cladding surface of the waveguide in step six by patterning-metal deposition-stripping. Subsequently, a polymer layer is deposited on top of the metal, and finally the polymer on the surface of the metal electrode used for external encapsulation is removed.

[0015] Furthermore, to facilitate easier peeling, the sacrificial layer in step one is silicon dioxide or germanium dioxide with a thickness of 200-1000 nm.

[0016] Furthermore, to ensure the flexibility of the lower cladding polymer, the lower cladding polymer of the waveguide is selected from any one of SU-8, colorless polyimide, polydimethylsiloxane, cellulose, and polyurethane, and the thickness of the lower cladding is 1-50 μm.

[0017] Furthermore, in order to ensure the high transmittance of the waveguide material layer in the visible light band to meet the low transmission loss characteristics of the waveguide, the material of the waveguide layer is selected from any one of silicon nitride, titanium dioxide, gallium oxide and zinc oxide.

[0018] Furthermore, the polymer protective layer in step three is selected from any one of alumina, zinc oxide, zirconium oxide, and titanium oxide, and the thickness of the polymer protective layer is in the range of 5-50 nm.

[0019] Furthermore, in order to adapt to the thickness of the flexible polymer substrate or cladding, the polymer of the upper cladding of the waveguide is selected from any one of SU-8, Epocore, PMMA and colorless polyimide.

[0020] Furthermore, in order to achieve efficient release of the probe, when releasing the probe implantation part in step six, a wet chemical method is used to etch the sacrificial layer, thereby peeling off the hard substrate; or, a dry etching method is used to etch away the hard substrate and the sacrificial layer.

[0021] An optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe prepared by the above preparation method.

[0022] Furthermore, in order to obtain the probe outline shape, the outline can be obtained by laser cutting or photolithography patterning-etching. The width of the implanted part of the probe is 20-500μm and the length is 1mm-10mm. The tip of the implanted part of the probe is a pointed shape with an angle of 45°-150°. The length and width of the non-implanted part of the probe chip are both in the range of 0.5-3.5cm.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) This invention avoids the pattern transfer step in the common flexible waveguide integrated device fabrication method and realizes a simple and intuitive bottom-up deposition process. The fabrication process is simple and easy to industrialize.

[0025] (2) In the device fabrication method of the present invention, a polymer protective layer is prepared on the flexible polymer substrate by means of atomic layer deposition process, so that the thin film preparation process using physical vapor deposition (e.g., magnetron sputtering) is compatible with the flexible polymer substrate, and the types of materials for the core layer are broadened.

[0026] (3) The flexible probe prepared by the present invention has a Young's modulus that is more compatible with brain tissue than that of the rigid probe, and exhibits better biocompatibility in long-term biological experiments, resulting in less tissue inflammatory response.

[0027] (4) In the cladding-core-cladding structure adopted in this invention, the core layer can be combined with integrated optical unit devices to design various optical waveguide paths, realize multi-point light emission, and can be further combined with active functional layers to perform external optical control of the waveguide, realize reconfigurable light emission. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the method for fabricating the optoelectronic hybrid integrated flexible waveguide optical genetic probe of the present invention.

[0029] Figure 2 This is a schematic diagram of the passive flexible waveguide integrated optogenetic probe prepared in Example 1.

[0030] Figure 3 This is a schematic diagram of the optoelectronic hybrid integrated active flexible waveguide photogenetic probe prepared in Example 2. Detailed Implementation

[0031] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The purpose and effects of the present invention will become clearer. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0032] This invention proposes an optoelectronic hybrid integrated implantable flexible waveguide optical genetic probe and its fabrication method. The method involves depositing a waveguide core material and an upper cladding material on a flexible lower cladding layer. An active functional layer can be interspersed within the upper cladding material. Then, the implanted and non-implanted portions of the probe are defined. Finally, the rigid substrate of the implanted portion is peeled off, achieving the fabrication of a complete flexible waveguide optical genetic probe. The overall process flow diagram of this fabrication method is shown below. Figure 1 .

[0033] Example 1: Flexible passive titanium dioxide waveguide integrated optical genetic probe with 1×8 channels

[0034] (1) A silicon dioxide layer with a thickness of 1 μm was deposited on a silicon wafer by thermal oxidation.

[0035] (2) A 10 μm thick SU-8 was spin-coated on a silicon dioxide layer, and a flexible polymer was obtained by photolithography overexposure process, which was used as the lower cladding layer of the waveguide.

[0036] (3) An aluminum oxide film with a thickness of 40 nm was deposited on the SU-8 layer using atomic layer deposition process as a polymer protective layer; then a titanium oxide film with a thickness of 150 nm was deposited on the aluminum oxide layer by magnetron sputtering.

[0037] (4) Waveguide patterns are prepared by photolithography and inductively coupled plasma reactive ion etching, which are manifested as a tree-like cascade of 7 1×2 multimode interference couplers, ultimately forming a 1×8 channel optical waveguide path.

[0038] (5) A SU-8 layer with a thickness of 10 μm was spin-coated on the upper surface of the waveguide and the SU-8 layer was solidified and stabilized by photolithography overexposure process.

[0039] (6) The probe shape is defined on the waveguide chip by laser cutting, dividing it into implanted and non-implanted sections. The implanted probe has a width of 200 μm, a length of 5 mm, and a tip angle of 120°. The non-implanted chip has a length of 2 cm and a width of 2 cm. The chip is then placed in a hydrofluoric acid solution to peel off the hard substrate beneath the implanted section, ultimately obtaining the following... Figure 2 The 1×8 channel flexible passive titanium oxide waveguide integrated optical genetic probe is shown.

[0040] Example 2: A flexible silicon nitride reconfigurable visible waveguide with 1×4 channels integrates a multimodal optogenetic probe.

[0041] (1) Spin-coating a colorless polyimide with a thickness of 7 μm onto a silicon wafer that already has a silicon dioxide layer with a thickness of 1 μm.

[0042] (2) A silicon nitride thin film with a thickness of 200 nm was deposited on a colorless polyimide layer by magnetron sputtering.

[0043] (3) Waveguide patterns are prepared by photolithography and inductively coupled plasma reactive ion etching, which are manifested as a tree-like cascade of three multimode interference couplers-Mach-Zehnder interferometers to form a 1×4 channel optical waveguide path.

[0044] (4) A 100 nm thick gold layer is deposited next to the waveguide using a photolithography-electron beam thermal evaporation-stripping process as a recording electrode for recording neural potentials, along with corresponding metal wiring and a packaging electrode for packaging.

[0045] (5) A 1 μm thick SU-8 layer is spin-coated on the upper layer of the waveguide and photolithography is performed to expose the metal electrodes used for recording electrophysiological signals and for packaging.

[0046] (6) Above the SU-8 layer, a 100nm thick platinum metal is deposited using a photolithography-electron beam thermal evaporation-stripping process to modulate the optical field in the waveguide. The modulation electrode is designed above the two arms of the Mach-Zehnder interferometer, and the external packaging electrode is designed near the edge of the waveguide chip.

[0047] (7) A 4μm thick SU-8 layer is spin-coated on top of the electrode layer, and the SU-8 layer is cured by photolithography overexposure process to expose the electrode window.

[0048] (8) Define the probe shape on the waveguide chip by laser cutting to separate the implanted and non-implanted parts. Remove the hard substrate and sacrificial layer at the bottom of the implanted part using a dry etching process.

[0049] The 1×4 channel flexible silicon nitride reconfigurable visible light waveguide integrated multimodal optogenetic probe prepared in this embodiment is as follows: Figure 3 As shown. The implanted probe is 150μm wide, 6mm long, and has a tip angle of 130°. The non-implanted portion of the chip is 3cm long and 2cm wide.

[0050] Example 3: Flexible passive gallium oxide waveguide integrated optical genetic probe with 1×8 channels

[0051] (1) A 1 μm silicon dioxide layer was deposited on a silicon wafer using a thermal oxidation method;

[0052] (2) A colorless polyimide with a thickness of 3 μm was spin-coated on a silicon dioxide layer, and a flexible polymer was obtained by thermosetting process, which was used as the lower cladding layer of the waveguide.

[0053] (3) An aluminum oxide film with a thickness of 30 nm was deposited on a colorless polyimide layer using atomic layer deposition process as a polymer protective layer; then a gallium oxide film with a thickness of 200 nm was deposited on the aluminum oxide layer by magnetron sputtering.

[0054] (4) Waveguide patterns are prepared by photolithography and inductively coupled plasma reactive ion etching, which are manifested as a tree-like cascade of 7 1×2 multimode interference couplers, ultimately forming a 1×8 channel optical waveguide path.

[0055] (5) A 3 μm thick layer of colorless polyimide is spin-coated onto the upper surface of the waveguide and cured by a thermosetting process.

[0056] (6) The probe shape was defined on the waveguide chip by laser cutting, dividing it into implanted and non-implanted parts. The implanted probe had a width of 250 μm, a length of 8 mm, and a tip angle of 100°. The non-implanted part of the chip had a length of 2 cm and a width of 2 cm. The chip was then placed in a hydrofluoric acid solution to peel off the hard substrate beneath the implanted part, ultimately obtaining a 1×8 channel flexible passive gallium oxide waveguide integrated optogenetic probe.

[0057] Example 4: Flexible passive zinc oxide waveguide integrated optogenetic probe with 1×8 channels

[0058] (1) A 1 μm silicon dioxide layer was deposited on a silicon wafer using a thermal oxidation method;

[0059] (2) A colorless polyimide with a thickness of 5 μm was spin-coated on a silicon dioxide layer, and a flexible polymer was obtained by thermosetting process, which served as the lower cladding layer of the waveguide.

[0060] (3) An aluminum oxide film with a thickness of 50 nm was deposited on a colorless polyimide layer using atomic layer deposition as a polymer protective layer; then a zinc oxide film with a thickness of 200 nm was deposited on the aluminum oxide layer by magnetron sputtering.

[0061] (4) Waveguide patterns are prepared by photolithography and inductively coupled plasma reactive ion etching, which are manifested as a tree-like cascade of 7 1×2 multimode interference couplers, ultimately forming a 1×8 channel optical waveguide path.

[0062] (5) Spin-coating a 3μm thick PMMA layer onto the upper surface of the waveguide and curing the PMMA layer by a thermosetting process.

[0063] (6) The probe shape was defined on the waveguide chip by laser cutting, dividing it into implanted and non-implanted parts. The implanted probe had a width of 300 μm, a length of 10 mm, and a tip angle of 90°. The non-implanted part of the chip had a length of 2.5 cm and a width of 2 cm. The chip was then placed in a hydrofluoric acid solution to peel off the hard substrate beneath the implanted part, ultimately obtaining a 1×8 channel flexible passive zinc oxide waveguide integrated optogenetic probe.

[0064] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for fabricating an optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe, characterized in that, Includes the following steps: Step 1: Deposit a sacrificial layer on a hard substrate; Step 2: Deposit a polymer layer on the sacrificial layer as the lower cladding of the waveguide; Step 3: When the waveguide material is an oxide, a polymer protective layer is deposited on the polymer layer using atomic layer deposition (ALD), and then a waveguide material layer is further deposited on the polymer protective layer using reactive sputtering. When the waveguide material is not an oxide, the waveguide material layer is directly deposited on the polymer layer using reactive sputtering. Step 4: Patterning and etching the waveguide material layer to fabricate the waveguide; Step 5: When the prepared probe is an active probe, metal electrodes for recording neural potentials, metal wiring, and metal electrodes for encapsulation are prepared around the waveguide through patterning-metal deposition-stripping. Then, a polymer layer is deposited on the surface of the waveguide material layer as the upper cladding of the waveguide, and the polymer on the upper surface of the metal electrodes is removed to expose the metal electrodes. When the prepared probe is a passive probe, a polymer layer is directly deposited on the surface of the waveguide material layer obtained in step 4 as the upper cladding of the waveguide. Step 6: Divide the waveguide chip obtained in Step 6 into implanted and non-implanted parts, release the implanted part, remove the sacrificial layer and hard substrate, and obtain an optoelectronic hybrid integrated implantable flexible waveguide optical genetic probe.

2. The method for fabricating the optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe according to claim 1, characterized in that, Before releasing the implanted portion in step six, a metal for optical field modulation in the waveguide is prepared on the upper cladding surface of the waveguide in step six by patterning-metal deposition-stripping. Then, a polymer layer is deposited on the metal, and finally the polymer on the surface of the metal electrode used for external encapsulation is removed.

3. The method for fabricating the optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe according to claim 1, characterized in that, The sacrificial layer in step one is silicon dioxide or germanium dioxide, with a thickness of 200-1000 nm.

4. The method for fabricating the optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe according to claim 1, characterized in that, The polymer of the lower cladding of the waveguide is selected from any one of SU-8, colorless polyimide, polydimethylsiloxane, cellulose and polyurethane, and the thickness of the lower cladding is 1-50 μm.

5. The method for fabricating the optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe according to claim 1, characterized in that, The waveguide material layer is selected from any one of silicon nitride, titanium dioxide, gallium oxide, and zinc oxide.

6. The method for fabricating the optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe according to claim 1, characterized in that, The polymer protective layer in step three is selected from any one of alumina, zinc oxide, zirconium oxide, and titanium oxide, and the thickness of the polymer protective layer is in the range of 5-50 nm.

7. The method for fabricating the optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe according to claim 1, characterized in that, The polymer of the upper cladding of the waveguide is selected from any one of SU-8, Epocore, PMMA and colorless polyimide.

8. The method for fabricating the optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe according to claim 1, characterized in that, In step six, when releasing the probe implantation portion, a wet chemical method is used to etch the sacrificial layer, thereby peeling off the hard substrate; or, a dry etching method is used to etch away the hard substrate and the sacrificial layer.

9. An optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe prepared by the preparation method of any one of claims 1 to 8.

10. The optoelectronic hybrid integrated implantable flexible waveguide optogenetic probe according to claim 9, characterized in that, The implanted portion of the probe has a width of 20-500μm and a length of 1mm-10mm. The tip of the implanted portion of the probe has a pointed shape with an angle of 45°-150°. The length and width of the non-implanted portion of the probe chip are both in the range of 0.5-3.5cm.

Images