A biomineral-inspired approach of synthesizing colloidal persistent phosphors as a multicolor, intravital light source

Size and Structural Control of Mechanoluminescent ZnS:Mn2+ Nanocrystals for Optogenetic Neuromodulation

Mechanoluminescent materials hold immense potential for various transformative applications, from medical imaging and diagnostics to health monitoring and wearable displays. Conventionally produced as bulk powders or microparticles, they face significant size limitations for advanced applications, particularly in biological systems and microscale devices. This work presents an approach to ZnS:Mn2+ nanocrystal synthesis that involves self-assembly and subsequent calcination. In addition to effective size control within the nanoscale, this approach promotes the formation of abundant stacking faults, significantly enhancing piezoelectric and mechanoluminescent properties by increasing trap density and reducing trap depth. Unlike mechanoluminescent materials produced using conventional methods, these nanocrystals demonstrate strong mechanoluminescence without requiring UV pre-excitation, and the light emission persists even after mechanical stress is removed. These advantageous properties make them promising candidates for optogenetic neuromodulation, as they can effectively trigger electrical signals in neurons upon ultrasound stimulation both with and without UV pre-excitation. The persistent mechanoluminescence prolongs the duration of neuronal electrical activity, providing an extended temporal window for neuromodulation compared to conventional mechanoluminescent materials. This study provides a scalable method for producing efficient mechanoluminescent nanoparticles and reveals the crucial role of particle size and defect structures in determining their mechanoluminescent behavior.

Ultrasound-Activated Near-Infrared-II Afterglow Luminescence for Precise Cancer Imaging

Afterglow fluorescence imaging has been extensively assessed in ultrasensitive bioimaging. Since it eliminates the need for real-time excitation light and thereby circumvents the autofluorescence background of tissue, it holds tremendous potential in accurate biomedical imaging. However, current afterglow probes are rare and emit light only in the visible to near-infrared (NIR) range, which is inadequate for in vivo imaging. To resolve this issue, an ultrasound (US)-activated NIR-II afterglow luminescence probe (NPs-Ce4-SN) emitting afterglow luminescence with a peak at ∼1100 nm was developed. This peak is nearly 400 nm red-shifted compared with other reported afterglow probes. Of note, after US termination, NPs-Ce4-SN undergoes energy transformation to produce 1O2 and subsequently undergoes internal oxidation-reduction reaction to produce NIR-II afterglow, generating high signal-to-noise ratio and high-penetration depth imaging. In vitro and in vivo NIR-II afterglow imaging experiments revealed that NPs-Ce4-SN has good biocompatibility and deep tissue penetration depth, suggesting a diagnostic strategy for in vivo tumor imaging with a high signal-to-noise ratio.

Synthesis of SrZnOSe Crystals with Low Phonon Energy for Enhancing Near-Infrared Mechanoluminescence

Near-infrared (NIR) light is promising for bioimaging and information technology due to its high penetration ability and resistance to interference with environmental radiation. Here, a new class of lanthanide-doped SrZnOSe crystals are developed for the self-sustainable generation of NIR emissions under mechanical excitation. It is shown that the SrZnOSe crystals render ≈5-fold stronger NIR emissions than the well-established CaZnOS due to the low phonon energies of the selenide host, as confirmed by Raman spectroscopy. The potential utility of the crystals is demonstrated by integration with a mouthguard, which can generate bright NIR emissions by bite force to transmit encrypted optical signals through thick tissues (up to 8 mm) in ambient environments. The findings provide a powerful addition to the toolbox of self-recovery mechanoluminescent materials and open new possibilities for applied research.

Light/X-ray/ultrasound activated delayed photon emission of organic molecular probes for optical imaging: mechanisms, design strategies, and biomedical applications

Conventional optical imaging, particularly fluorescence imaging, often encounters significant background noise due to tissue autofluorescence under real-time light excitation. To address this issue, a novel optical imaging strategy that captures optical signals after light excitation has been developed. This approach relies on molecular probes designed to store photoenergy and release it gradually as photons, resulting in delayed photon emission that minimizes background noise during signal acquisition. These molecular probes undergo various photophysical processes to facilitate delayed photon emission, including (1) charge separation and recombination, (2) generation, stabilization, and conversion of the triplet excitons, and (3) generation and decomposition of chemical traps. Another challenge in optical imaging is the limited tissue penetration depth of light, which severely restricts the efficiency of energy delivery, leading to a reduced penetration depth for delayed photon emission. In contrast, X-ray and ultrasound serve as deep-tissue energy sources that facilitate the conversion of high-energy photons or mechanical waves into the potential energy of excitons or the chemical energy of intermediates. This review highlights recent advancements in organic molecular probes designed for delayed photon emission using various energy sources. We discuss distinct mechanisms, and molecular design strategies, and offer insights into the future development of organic molecular probes for enhanced delayed photon emission.

Strain-Programmed Adhesive Patch for Accelerated Photodynamic Wound Healing

As an alternative to tissue adhesives, photochemical tissue bonding is investigated for advanced wound healing. However, these techniques suffer from relatively slow wound healing with bleeding and bacterial infections. Here, the versatile attributes of afterglow luminescent particles (ALPs) embedded in dopamine-modified hyaluronic acid (HA-DOPA) patches for accelerated wound healing are presented. ALPs enhance the viscoelastic properties of the patches, and the photoluminescence and afterglow luminescence of ALPs maximize singlet oxygen generation and collagen fibrillogenesis for effective healing in the infected wounds. The patches are optimized to achieve the strong and rapid adhesion in the wound sites. In addition, the swelling and shrinking properties of adhesive patches contribute to a nonlinear behavior in the wound recovery, playing an important role as a strain-programmed patch. The protective patch prevents secondary infection and skin adhesion, and the patch seamlessly detaches during wound healing, enabling efficient residue clearance. In vitro, in vivo, and ex vivo model tests confirm the biocompatibility, antibacterial effect, hemostatic capability, and collagen restructuring for the accelerated wound healing. Taken together, this research collectively demonstrates the feasibility of HA-DOPA/ALP patches as a versatile and promoting solution for advanced accelerated wound healing, particularly in scenarios involving bleeding and bacterial infections.

Enabling Visible-Light-Charged Near-Infrared Persistent Luminescence in Organics by Intermolecular Charge Transfer

Visible light is a universal and user-friendly excitation source; however, its use to generate persistent luminescence (PersL) in materials remains a huge challenge. Herein, the concept of intermolecular charge transfer (xCT) is applied in typical host-guest molecular systems, which allows for a much lower energy requirement for charge separation, thus enabling efficient charging of near-infrared (NIR) PersL in organics by visible light (425-700 nm). Importantly, NIR PersL in organics occurs via the trapping of electrons from charge-transfer aggregates (CTAs) into constructed trap states with trap depths of 0.63-1.17 eV, followed by the detrapping of these electrons by thermal stimulation, resulting in a unique light-storage effect and long-lasting emission up to 4.6 h at room temperature. The xCT absorption range is modulated by changing the electron-donating ability of a series of acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile-based CTAs, and the organic PersL is tuned from 681 to 722 nm. This study on xCT interaction-induced NIR PersL in organic materials provides a major step forward in understanding the underlying luminescence mechanism of organic semiconductors and these findings are expected to promote their applications in optoelectronics, energy storage, and medical diagnosis.

Nano-optogenetics for Disease Therapies

Optogenetic, known as the method of 21 centuries, combines optic and genetic engineering to precisely control photosensitive proteins for manipulation of a broad range of cellular functions, such as flux of ions, protein oligomerization and dissociation, cellular intercommunication, and so on. In this technique, light is conventionally delivered to targeted cells through optical fibers or micro light-emitting diodes, always suffering from high invasiveness, wide-field illumination facula, strong absorption, and scattering by nontargeted endogenous substance. Light-transducing nanomaterials with advantages of high spatiotemporal resolution, abundant wireless-excitation manners, and easy functionalization for recognition of specific cells, recently have been widely explored in the field of optogenetics; however, there remain a few challenges to restrain its clinical applications. This review summarized recent progress on light-responsive genetically encoded proteins and the myriad of activation strategies by use of light-transducing nanomaterials and their disease-treatment applications, which is expected for sparking helpful thought to push forward its preclinical and translational uses.

Force-Based Neuromodulation

Technologies for neuromodulation have rapidly developed in the past decade with a particular emphasis on creating noninvasive tools with high spatial and temporal precision. The existence of such tools is critical in the advancement of our understanding of neural circuitry and its influence on behavior and neurological disease. Existing technologies have employed various modalities, such as light, electrical, and magnetic fields, to interface with neural activity. While each method offers unique advantages, many struggle with modulating activity with high spatiotemporal precision without the need for invasive tools. One modality of interest for neuromodulation has been the use of mechanical force. Mechanical force encapsulates a broad range of techniques, ranging from mechanical waves delivered via focused ultrasound (FUS) to torque applied to the cell membrane.Mechanical force can be delivered to the tissue in two forms. The first form is the delivery of a mechanical force through focused ultrasound. Energy delivery facilitated by FUS has been the foundation for many neuromodulation techniques, owing to its precision and penetration depth. FUS possesses the potential to penetrate deeply (∼centimeters) into tissue while maintaining relatively precise spatial resolution, although there exists a trade-off between the penetration depth and spatial resolution. FUS may work synergistically with ultrasound-responsive nanotransducers or devices to produce a secondary energy, such as light, heat, or an electric field, in the target region. This layered technology, first enabled by noninvasive FUS, overcomes the need for bulky invasive implants and also often improves the spatiotemporal precision of light, heat, electrical fields, or other techniques alone. Conversely, the second form of mechanical force modulation is the generation of mechanical force from other modalities, such as light or magnetic fields, for neuromodulation via mechanosensitive proteins. This approach localizes the mechanical force at the cellular level, enhancing the precision of the original energy delivery. Direct interaction of mechanical force with tissue presents translational potential in its ability to interface with endogenous mechanosensitive proteins without the need for transgenes.In this Account, we categorize force-mediated neuromodulation into two categories: 1) methods where mechanical force is the primary stimulus and 2) methods where mechanical force is generated as a secondary stimulus in response to other modalities. We summarize the general design principles and current progress of each respective approach. We identify the key advantages of the limitations of each technology, particularly noting features in spatiotemporal precision, the need for transgene delivery, and the potential outlook. Finally, we highlight recent technologies that leverage mechanical force for enhanced spatiotemporal precision and advanced applications.

Modulating Smart Mechanoluminescent Phosphors for Multistimuli Responsive Optical Wood

Mechanoluminescence is a smart light-emitting phenomenon in which applied mechanical energy is directly converted into photon emissions. In particular, mechanoluminescent materials have shown considerable potential for applications in the fields of energy and sensing. This study thoroughly investigates the mechanoluminescence and long afterglow properties of singly doped and codoped Sr2 MgSi2 O7 (SMSO) with varying concentrations of Eu2+ and Dy3+ ions. Subsequently, a comprehensive analysis of its multimode luminescence properties, including photoluminescence, mechanoluminescence, long afterglow, and X-ray-induced luminescence, is conducted. In addition, the density of states mapping is acquired through first-principles calculations, confirming that the enhanced mechanoluminescence properties of SMSO primarily stem from the deep trap introduced by Dy3+ . In contrast to traditional mixing with Polydimethylsiloxane, in this study, the powders are incorporated into optically transparent wood to produce a multiresponse with mechanoluminescence, long afterglow, and X-ray-excited luminescence. This structure is achieved by pretreating natural wood, eliminating lignin, and subsequently modifying the wood to overall modification using various smart phosphors and epoxy resin composites. After natural drying, a multifunctional composite wood structure with diverse luminescence properties is obtained. Owing to its environmental friendliness, sustainability, self-power, and cost-effectiveness, this smart mechanoluminescence wood is anticipated to find extensive applications in construction materials and energy-efficient displays.

Ultrasound-Induced Cascade Amplification in a Mechanoluminescent Nanotransducer for Enhanced Sono-Optogenetic Deep Brain Stimulation

Remote and genetically targeted neuromodulation in the deep brain is important for understanding and treatment of neurological diseases. Ultrasound-triggered mechanoluminescent technology offers a promising approach for achieving remote and genetically targeted brain modulation. However, its application has thus far been limited to shallow brain depths due to challenges related to low sonochemical reaction efficiency and restricted photon yields. Here we report a cascaded mechanoluminescent nanotransducer to achieve efficient light emission upon ultrasound stimulation. As a result, blue light was generated under ultrasound stimulation with a subsecond response latency. Leveraging the high energy transfer efficiency of focused ultrasound in brain tissue and the high sensitivity to ultrasound of these mechanoluminescent nanotransducers, we are able to show efficient photon delivery and activation of ChR2-expressing neurons in both the superficial motor cortex and deep ventral tegmental area after intracranial injection. Our liposome nanotransducers enable minimally invasive deep brain stimulation for behavioral control in animals via a flexible, mechanoluminescent sono-optogenetic system.

UCNPs-based nanoreactors with ultraviolet radiation-induced effect for enhanced ferroptosis therapy of tumor

The limitations of light source limit the clinical application of optical therapy technology. How to improve the application efficiency of radiant light has become the focus of researchers. Here, we synthesize a kind of UCNPs@PVP-GOx-PpIX-Fe3+ (UPGPF) nanoreactors with rare earth upconversion nanoparticles (UCNPs) as the substrate for the enhancement of ferroptosis effect by the synergistic starvation/photodynamic therapies. Firstly, glucose oxidase (GOx) and Fe3+ loaded in UPGPF nanoreactors are used to directly face the problems of insufficient H2O2 level in tumor tissue and low Fenton reaction efficiency. Further, UCNPs can absorb NIR light at 980 nm and convert low-energy photons into high-energy photons, thereby cleverly generating ultraviolet (UV) radiation induction in vivo, which can produce a synergistic effect of enhancing iron death. The in vivo experimental results of breast cancer model mice show that the UPGPF nanoreactors have significant anticancer effect and good biosafety. With the help of the optical conversion characteristics of UCNPs, this kind of treatment idea of building a UV radiation-induced microplatform in the tumor microenvironment, which leads to the synergistic enhancement of iron death effect, provides a promising innovative design strategy for tumor research.

Activation of mechanoluminescent nanotransducers by focused ultrasound enables light delivery to deep-seated tissue in vivo

Light is used extensively in biological and medical research for optogenetic neuromodulation, fluorescence imaging, photoactivatable gene editing and light-based therapies. The major challenge to the in vivo implementation of light-based methods in deep-seated structures of the brain or of internal organs is the limited penetration of photons in biological tissue. The presence of light scattering and absorption has resulted in the development of invasive techniques such as the implantation of optical fibers, the insertion of endoscopes and the surgical removal of overlying tissues to overcome light attenuation and deliver it deep into the body. However, these procedures are highly invasive and make it difficult to reposition and adjust the illuminated area in each animal. Here, we detail a noninvasive approach to deliver light (termed 'deLight') in deep tissue via systemically injected mechanoluminescent nanotransducers that can be gated by using focused ultrasound. This approach achieves localized light emission with sub-millimeter resolution and millisecond response times in any vascularized organ of living mice without requiring invasive implantation of light-emitting devices. For example, deLight enables optogenetic neuromodulation in live mice without a craniotomy or brain implants. deLight provides a generalized method for applications that require a light source in deep tissues in vivo, such as deep-brain fluorescence imaging and photoactivatable genome editing. The implementation of the entire protocol for an in vivo application takes ~1-2 weeks.

Wireless deep-brain neuromodulation using photovoltaics in the second near-infrared spectrum

Conventional electrical neuromodulation techniques are constrained by the need for invasive implants in neural tissues, whereas methods using optogenetic are subjected to genetic alterations and hampered by the poor tissue penetration of visible light. Photovoltaic neuromodulation using light from the second near-infrared (NIR-II) spectrum, which minimizes scattering and enhances tissue penetration, shows promise as an alternative to existing neuromodulation technologies. NIR-II light has been used in deep-tissue imaging and in deep-brain photothermal neuromodulation via nanotransducers. This Perspective will provide an overview for the underpinning mechanisms of photovoltaic neuromodulation and identify avenues for future research in materials science and bioengineering that can further advance NIR-II photovoltaic neuromodulation methods.

Nanotransducer-Enabled Deep-Brain Neuromodulation with NIR-II Light

The second near-infrared window (NIR-II window), which ranges from 1000 to 1700 nm in wavelength, exhibits distinctive advantages of reduced light scattering and thus deep penetration in biological tissues in comparison to the visible spectrum. The NIR-II window has been widely employed for deep-tissue fluorescence imaging in the past decade. More recently, deep-brain neuromodulation has been demonstrated in the NIR-II window by leveraging nanotransducers that can efficiently convert brain-penetrant NIR-II light into heat. In this Perspective, we discuss the principles and potential applications of this NIR-II deep-brain neuromodulation technique, together with its advantages and limitations compared with other existing optical methods for deep-brain neuromodulation. We also point out a few future directions where the advances in materials science and bioengineering can expand the capability and utility of NIR-II neuromodulation methods.

Principles and applications of sono-optogenetics

Optogenetics has revolutionized neuroscience research through its spatiotemporally precise activation of specific neurons by illuminating light on opsin-expressing neurons. A long-standing challenge of in vivo optogenetics arises from the limited penetration depth of visible light in the neural tissue due to scattering and absorption of photons. To address this challenge, sono-optogenetics has been developed to enable spatiotemporally precise light production in a three-dimensional volume of neural tissue by leveraging the deep tissue penetration and focusing ability of ultrasound as well as circulation-delivered mechanoluminescent nanotransducers. Here, we present a comprehensive review of the sono-optogenetics method from the physical principles of ultrasound and mechanoluminescence to its emerging applications for unique neuroscience studies. We also discuss a few promising directions in which sono-optogenetics can make a lasting transformative impact on neuroscience research from the perspectives of mechanoluminescent materials, ultrasound-tissue interaction, to the unique neuroscience opportunities of "scanning optogenetics".

Ultrasound-activated luminescence with color tunability enabled by mechanoluminescent colloids and perovskite quantum dots

Ultrasound represents a wireless and non-contact route for energy delivery and device control, owing to its ability to propagate and focus in various mediums including biological tissue. Specifically, ultrasound-activated mechanoluminescence from a colloidal suspension of mechanoluminescent (ML) nanocrystals offers a wireless means to remotely control a light source, such as wirelessly addressing a multicolor display. However, the limited color purity and tunability, as well as the large sizes of conventional ML materials prevent their use in an ultrasound-mediated flexible color display. Here, we apply a biomineral-inspired suppressed dissolution approach to synthesize ML colloids with bright blue emission under ultrasound and small sizes down to 20 nm. In addition, we leverage the bandgap engineering strategy of all-inorganic perovskite quantum dots (PQDs) to achieve wavelength tunability of the mechanoluminescence of ML colloid/PQD composites. Remarkably, the ultrasound-activated emission of the ML colloid/PQD composites exhibits a highly saturated color gamut covering the entire visible spectrum. Based on these advantages, we assembled a pixel array composed of different ML colloid/PQD composites in a silicone elastomer and demonstrated the proof-of-concept of a flexible and wireless multicolor display with each pixel individually addressed by scanning focused ultrasound.