Chong Hou

Multifunctional fibers for simultaneous optical, electrical and chemical interrogation of neural circuits in vivo

Brain function depends on simultaneous electrical, chemical and mechanical signaling at the cellular level. This multiplicity has confounded efforts to simultaneously measure or modulate these diverse signals in vivo. Here we present fiber probes that allow for simultaneous optical stimulation, neural recording and drug delivery in behaving mice with high resolution. These fibers are fabricated from polymers by means of a thermal drawing process that allows for the integration of multiple materials and interrogation modalities into neural probes. Mechanical, electrical, optical and microfluidic measurements revealed high flexibility and functionality of the probes under bending deformation. Long-term in vivo recordings, optogenetic stimulation, drug perturbation and analysis of tissue response confirmed that our probes can form stable brain-machine interfaces for at least 2 months. We expect that our multifunctional fibers will permit more detailed manipulation and analysis of neural circuits deep in the brain of behaving animals than achievable before.

All-in-Fiber Chemical Sensing

A new all-in-fiber trace-level chemical sensing approach is demonstrated. Photoconductive structures, embedded directly into the fiber cladding along its entire length, capture light emitted anywhere within the fibers hollow core and transform it directly into an electrical signal. Localized signal transduction circumvents problems associated with conventional fiber-optics, including limited signal collection efficiency and optical losses. This approach facilitates a new platform for remote and distributed photosensing.

Crystalline silicon core fibres from aluminium core preforms

Traditional fibre-optic drawing involves a thermally mediated geometric scaling where both the fibre materials and their relative positions are identical to those found in the fibre preform. To date, all thermally drawn fibres are limited to the preform composition and geometry. Here, we fabricate a metre-long crystalline silicon-core, silica-cladded fibre from a preform that does not contain any elemental silicon. An aluminium rod is inserted into a macroscopic silica tube and then thermally drawn. The aluminium atoms initially in the core reduce the silica, to produce silicon atoms and aluminium oxide molecules. The silicon atoms diffuse into the core, forming a large phase-separated molten silicon domain that is drawn into the crystalline silicon core fibre. The ability to produce crystalline silicon core fibre out of inexpensive aluminium and silica could pave the way for a simple and scalable method of incorporating silicon-based electronics and photonics into fibres.

Flexible and stretchable nanowire-coated fibers for optoelectronic probing of spinal cord circuits

Stretchable optoelectronic fibers interrogate spinal cord circuits during free behavior. Studies of neural pathways that contribute to loss and recovery of function following paralyzing spinal cord injury require devices for modulating and recording electrophysiological activity in specific neurons. These devices must be sufficiently flexible to match the low elastic modulus of neural tissue and to withstand repeated strains experienced by the spinal cord during normal movement. We report flexible, stretchable probes consisting of thermally drawn polymer fibers coated with micrometer-thick conductive meshes of silver nanowires. These hybrid probes maintain low optical transmission losses in the visible range and impedance suitable for extracellular recording under strains exceeding those occurring in mammalian spinal cords. Evaluation in freely moving mice confirms the ability of these probes to record endogenous electrophysiological activity in the spinal cord. Simultaneous stimulation and recording is demonstrated in transgenic mice expressing channelrhodopsin 2, where optical excitation evokes electromyographic activity and hindlimb movement correlated to local field potentials measured in the spinal cord.

Direct atomic-level observation and chemical analysis of ZnSe synthesized by in situ high-throughput reactive fiber drawing.

We demonstrate a high-throughput method for synthesizing zinc selenide (ZnSe) in situ during fiber drawing. Central to this method is a thermally activated chemical reaction occurring across multiple interfaces between alternately layered elemental zinc- (Zn-) and selenium- (Se-) rich films embedded in a preform and drawn into meters of fiber at a temperature well below the melting temperature of either Zn or ZnSe. By depositing 50 nm thick layers of Zn interleaved between 1 μm thick Se layers, a controlled breakup of the Zn sheet is achieved, thereby enabling a complete and controlled chemical reaction. The thermodynamics and kinetics of this synthesis process are studied using thermogravimetric analysis and differential scanning calorimetry, and the in-fiber compound is analyzed by a multiplicity of materials characterization tools, including transmission electron microscopy, Raman microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, all resulting in unambiguous identification of ZnSe as the compound produced from the reactive fiber draw. Furthermore, we characterize the in-fiber ZnSe/Se97S3 heterojunction to demonstrate the prospect of ZnSe-based fiber optoelectronic devices. The ability to synthesize new compounds during fiber drawing at nanometer scale precision and to characterize them at the atomic-level extends the architecture and materials selection compatible with multimaterial fiber drawing, thus paving the way toward more complex and sophisticated functionality.

Optoelectronic Fibers via Selective Amplification of In-Fiber Capillary Instabilities

Thermally drawn metal-insulator-semiconductor fibers provide a scalable path to functional fibers. Here, a ladder-like metal-semiconductor-metal photodetecting device is formed inside a single silica fiber in a controllable and scalable manner, achieving a high density of optoelectronic components over the entire fiber length and operating at a bandwidth of 470 kHz, orders of magnitude larger than any other drawn fiber device.

Sub‐Micrometer Surface‐Patterned Ribbon Fibers and Textiles

The worldwide annual production volume of textiles is nearly one hundred million metric tons. Most of these undergo treatments to achieve specific properties, such as color, hydrophobicity, antimicrobial, or UV protection, using chemicals that lead to collateral environmental consequences. There is great interest in developing alternative and sustainable strategies to achieve textile functionality that do not involve chemical treatment. Here we present a thermal drawing approach to achieve fiber surface gratings on a rectangular cross-section. We demonstrate directional wetting properties as well as structural coloration based on the gratings. Periods down to ≈ 600 nm were established on the surface of a fiber. Fabrics displaying higher-order diffraction peaks in the visible regime were produced from surface-patterned fibers using convetional weaving machinery.

Confined in-fiber solidification and structural control of silicon and silicon−germanium microparticles

Significance Water freezing into ice has a number of fascinating outcomes: Dendritic solidification of water results in beautiful snowflakes, a sealed bottle of beer shatters in a freezer, and ice covering salty oceans at the poles is salt-free due to compositional segregation. A silicon–germanium (SiGe) material system, ubiquitous in microelectronics, is surprisingly similar to water in its solidification behavior. Quenching of molten SiGe microdroplets sealed inside a glass fiber leads to dendritic morphology, with potential use in solar cells. Slow cooling induces compression of these spheres to tens of thousands of atmospheres, potentially changing the band structure of these materials. Moreover, slow solidification results in compositionally segregated SiGe Janus particles, useful for high-frequency microelectronic and nanorobotic applications. Crystallization of microdroplets of molten alloys could, in principle, present a number of possible morphological outcomes, depending on the symmetry of the propagating solidification front and its velocity, such as axial or spherically symmetric species segregation. However, because of thermal or constitutional supercooling, resulting droplets often only display dendritic morphologies. Here we report on the crystallization of alloyed droplets of controlled micrometer dimensions comprising silicon and germanium, leading to a number of surprising outcomes. We first produce an array of silicon−germanium particles embedded in silica, through capillary breakup of an alloy-core silica-cladding fiber. Heating and subsequent controlled cooling of individual particles with a two-wavelength laser setup allows us to realize two different morphologies, the first being a silicon−germanium compositionally segregated Janus particle oriented with respect to the illumination axis and the second being a sphere made of dendrites of germanium in silicon. Gigapascal-level compressive stresses are measured within pure silicon solidified in silica as a direct consequence of volume-constrained solidification of a material undergoing anomalous expansion. The ability to generate microspheres with controlled morphology and unusual stresses could pave the way toward advanced integrated in-fiber electronic or optoelectronic devices.