All Publications

  • Palette of Rechargeable Mechanoluminescent Fluids Produced by a Biomineral-Inspired Suppressed Dissolution Approach. Journal of the American Chemical Society Yang, F., Wu, X., Cui, H., Jiang, S., Ou, Z., Cai, S., Hong, G. 2022


    Mechanoluminescent materials, which emit light in response to mechanical stimuli, have recently been explored as promising candidates for photonic skins, remote optogenetics, and stress sensing. All mechanoluminescent materials reported thus far are bulk solids with micron-sized grains, and their light emission is only produced when fractured or deformed in bulk form. In contrast, mechanoluminescence has never been observed in liquids and colloidal solutions, thus limiting its biological application in living organisms. Here, we report the synthesis of mechanoluminescent fluids via a suppressed dissolution approach. We demonstrate that this approach yields stable colloidal solutions comprising mechanoluminescent nanocrystals with bright emissions in the range of 470-610 nm and diameters down to 20 nm. These colloidal solutions can be recharged and discharged repeatedly under photoexcitation and hydrodynamically focused ultrasound, respectively, thus yielding rechargeable mechanoluminescent fluids that can store photon energy in a reversible manner. This rechargeable fluid can facilitate a systemically delivered light source gated by tissue-penetrant ultrasound for biological applications that require light in the tissue, such as optogenetic stimulation in the brain.

    View details for DOI 10.1021/jacs.2c06724

    View details for PubMedID 36190898

  • A biomineral-inspired approach of synthesizing colloidal persistent phosphors as a multicolor, intravital light source. Science advances Yang, F., Wu, X., Cui, H., Ou, Z., Jiang, S., Cai, S., Zhou, Q., Wong, B. G., Huang, H., Hong, G. 2022; 8 (30): eabo6743


    Many in vivo biological techniques, such as fluorescence imaging, photodynamic therapy, and optogenetics, require light delivery into biological tissues. The limited tissue penetration of visible light discourages the use of external light sources and calls for the development of light sources that can be delivered in vivo. A promising material for internal light delivery is persistent phosphors; however, there is a scarcity of materials with strong persistent luminescence of visible light in a stable colloid to facilitate systemic delivery in vivo. Here, we used a bioinspired demineralization (BID) strategy to synthesize stable colloidal solutions of solid-state phosphors in the range of 470 to 650 nm and diameters down to 20 nm. The exceptional brightness of BID-produced colloids enables their utility as multicolor luminescent tags in vivo with favorable biocompatibility. Because of their stable dispersion in water, BID-produced nanophosphors can be delivered systemically, acting as an intravascular colloidal light source to internally excite genetically encoded fluorescent reporters within the mouse brain.

    View details for DOI 10.1126/sciadv.abo6743

    View details for PubMedID 35905189

  • Tether-free photothermal deep-brain stimulation in freely behaving mice via wide-field illumination in the near-infrared-II window. Nature biomedical engineering Wu, X., Jiang, Y., Rommelfanger, N. J., Yang, F., Zhou, Q., Yin, R., Liu, J., Cai, S., Ren, W., Shin, A., Ong, K. S., Pu, K., Hong, G. 2022


    Neural circuitry is typically modulated via invasive brain implants and tethered optical fibres in restrained animals. Here we show that wide-field illumination in the second near-infrared spectral window (NIR-II) enables implant-and-tether-free deep-brain stimulation in freely behaving mice with stereotactically injected macromolecular photothermal transducers activating neurons ectopically expressing the temperature-sensitive transient receptor potential cation channel subfamily V member 1 (TRPV1). The macromolecular transducers, ~40 nm in size and consisting of a semiconducting polymer core and an amphiphilic polymer shell, have a photothermal conversion efficiency of 71% at 1,064 nm, the wavelength at which light attenuation by brain tissue is minimized (within the 400-1,800 nm spectral window). TRPV1-expressing neurons in the hippocampus, motor cortex and ventral tegmental area of mice can be activated with minimal thermal damage on wide-field NIR-II illumination from a light source placed at distances higher than 50 cm above the animal's head and at an incident power density of 10 mW mm-2. Deep-brain stimulation via wide-field NIR-II illumination may open up opportunities for social behavioural studies in small animals.

    View details for DOI 10.1038/s41551-022-00862-w

    View details for PubMedID 35314800

  • Sono-optogenetics facilitated by a circulation-delivered rechargeable light source for minimally invasive optogenetics. Proceedings of the National Academy of Sciences of the United States of America Wu, X. n., Zhu, X. n., Chong, P. n., Liu, J. n., Andre, L. N., Ong, K. S., Brinson, K. n., Mahdi, A. I., Li, J. n., Fenno, L. E., Wang, H. n., Hong, G. n. 2019


    Optogenetics, which uses visible light to control the cells genetically modified with light-gated ion channels, is a powerful tool for precise deconstruction of neural circuitry with neuron-subtype specificity. However, due to limited tissue penetration of visible light, invasive craniotomy and intracranial implantation of tethered optical fibers are usually required for in vivo optogenetic modulation. Here we report mechanoluminescent nanoparticles that can act as local light sources in the brain when triggered by brain-penetrant focused ultrasound (FUS) through intact scalp and skull. Mechanoluminescent nanoparticles can be delivered into the blood circulation via i.v. injection, recharged by 400-nm photoexcitation light in superficial blood vessels during circulation, and turned on by FUS to emit 470-nm light repetitively in the intact brain for optogenetic stimulation. Unlike the conventional "outside-in" approaches of optogenetics with fiber implantation, our method provides an "inside-out" approach to deliver nanoscopic light emitters via the intrinsic circulatory system and switch them on and off at any time and location of interest in the brain without extravasation through a minimally invasive ultrasound interface.

    View details for DOI 10.1073/pnas.1914387116

    View details for PubMedID 31811026

  • Shedding light on neurons: optical approaches for neuromodulation. National science review Jiang, S., Wu, X., Rommelfanger, N. J., Ou, Z., Hong, G. 2022; 9 (10): nwac007


    Today's optical neuromodulation techniques are rapidly evolving, benefiting from advances in photonics, genetics and materials science. In this review, we provide an up-to-date overview of the latest optical approaches for neuromodulation. We begin with the physical principles and constraints underlying the interaction between light and neural tissue. We then present advances in optical neurotechnologies in seven modules: conventional optical fibers, multifunctional fibers, optical waveguides, light-emitting diodes, upconversion nanoparticles, optical neuromodulation based on the secondary effects of light, and unconventional light sources facilitated by ultrasound and magnetic fields. We conclude our review with an outlook on new methods and mechanisms that afford optical neuromodulation with minimal invasiveness and footprint.

    View details for DOI 10.1093/nsr/nwac007

    View details for PubMedID 36196122

    View details for PubMedCentralID PMC9522429

  • Shedding light on neurons: optical approaches for neuromodulation NATIONAL SCIENCE REVIEW Jiang, S., Wu, X., Rommelfanger, N. J., Ou, Z., Hong, G. 2022
  • How is flexible electronics advancing neuroscience research? Biomaterials Chen, Y., Rommelfanger, N. J., Mahdi, A. I., Wu, X., Keene, S. T., Obaid, A., Salleo, A., Wang, H., Hong, G. 2020; 268: 120559


    Innovative neurotechnology must be leveraged to experimentally answer the multitude of pressing questions in modern neuroscience. Driven by the desire to address the existing neuroscience problems with newly engineered tools, we discuss in this review the benefits of flexible electronics for neuroscience studies. We first introduce the concept and define the properties of flexible and stretchable electronics. We then categorize the four dimensions where flexible electronics meets the demands of modern neuroscience: chronic stability, interfacing multiple structures, multi-modal compatibility, and neuron-type-specific recording. Specifically, with the bending stiffness now approaching that of neural tissue, implanted flexible electronic devices produce little shear motion, minimizing chronic immune responses and enabling recording and stimulation for months, and even years. The unique mechanical properties of flexible electronics also allow for intimate conformation to the brain, the spinal cord, peripheral nerves, and the retina. Moreover, flexible electronics enables optogenetic stimulation, microfluidic drug delivery, and neural activity imaging during electrical stimulation and recording. Finally, flexible electronics can enable neuron-type identification through analysis of high-fidelity recorded action potentials facilitated by its seamless integration with the neural circuitry. We argue that flexible electronics will play an increasingly important role in neuroscience studies and neurological therapies via the fabrication of neuromorphic devices on flexible substrates and the development of enhanced methods of neuronal interpenetration.

    View details for DOI 10.1016/j.biomaterials.2020.120559

    View details for PubMedID 33310538

  • A wearable helical organic-inorganic photodetector with thermoelectric generators as the power source JOURNAL OF MATERIALS CHEMISTRY C Sa, C., Xu, X., Wu, X., Chen, J., Zuo, C., Fang, X. 2019; 7 (42): 13097–103

    View details for DOI 10.1039/c9tc04696h

    View details for Web of Science ID 000494705100009

  • Mode-splitting based optofluidic sensing at exceptional points in tubular microcavities OPTICS COMMUNICATIONS Wang, Y., Li, S., Kiravittaya, S., Wu, X., Wu, K., Li, X., Mei, Y. 2019; 446: 128–33
  • Ultrathin Silicon Nanomembrane in a Tubular Geometry for Enhanced Photodetection ADVANCED OPTICAL MATERIALS Xu, C., Pan, R., Guo, Q., Wu, X., Li, G., Huang, G., An, Z., Li, X., Mei, Y. 2019
  • Rolled-up Nanotechnology: Materials Issue and Geometry Capability ADVANCED MATERIALS TECHNOLOGIES Xu, C., Wu, X., Huang, G., Mei, Y. 2019; 4 (1)
  • Infrared tubular microcavity based on rolled-up GeSn/Ge nanomembranes. Nanotechnology Wu, X., Tian, Z., Cong, H., Wang, Y., Edy, R., Huang, G., Di, Z., Xue, C., Mei, Y. 2018; 29 (42): 42LT02


    Germanium-Tin (GeSn) alloys have attracted great amounts of attention as these group IV semiconductors present direct band-gap behavior with high Sn content and are compatible with current complementary metal oxide semiconductor technology. In this work, three dimensional tubular GeSn/Ge micro-resonators with a diameter of around 7.3 μm were demonstrated by rolling up GeSn nanomembranes (NM) grown on a Ge-on-insulator wafer via molecular beam epitaxy. The microstructural properties of the resonators were carefully investigated and the strain distributions of the rolled-up GeSn/Ge microcavities along the radial direction were studied by utilizing micro-Raman spectroscopy with different excitation laser wavelengths. The values of the strains calculated from Raman shifts agree well with the theoretical prediction. Coupled with fiber tapers, as-fabricated devices present a high quality factor of up to 800 in the transmission spectral measurements. The micro-resonators fabricated via rolled-up nanotechnology and GeSn/Ge NMs in this work may have great potential in photonic micro- and nanodevices.

    View details for DOI 10.1088/1361-6528/aad66e

    View details for PubMedID 30052202