Real-time monitoring of tissue oxygenation within the nervous system is imperative for advancements in neuroscience research and the improvement of clinical diagnostics. Unlike blood oxygenation levels, the partial pressure of oxygen in brain tissue (PbtO2) offers a more direct insight into the localized neural activities and metabolic states. Here, we present a microscale optoelectronic probe for the wireless, real-time monitoring of in vivo partial brain tissue oxygen (PbtO2) levels. This probe measures local PbtO2 concentrations via the luminescent quenching mechanism of phosphorescent dyes. An integrated light-emitting diode (LED) and photodetector are used to generate and capture the optical signals. To facilitate capturing and wirelessly transmitting PbtO2 signals, the device includes miniaturized electronic circuits that can be powered by a battery or an inductive coil. In vitro and in vivo experiments demonstrate the ability to dynamically record oxygen partial pressure (pO2), offering novel exploration opportunities in neuroscience research and clinical applications.
The monitoring of partial pressure of oxygen in brain tissue (PbtO2) holds paramount importance in both neuroscience research and the management of brain-related disorders. While imaging techniques offer avenues to directly or indirectly assess brain oxygenation, their applicability is limited in the study of certain disease models involving behaving animals. Here, we present an optoelectronic probe for real-time and continuous PbtO2 monitoring, offering wireless capabilities and providing high temporal and spatial resolutions. This probe measures oxygen partial pressure (PO2) through phosphorescence quenching, and the implantable probe integrates a micro-scale violet light-emitting diode (LED), a thin-film filter, a micro-scale photodetector, and an oxygen-sensing film. An implantable optoelectronic probe and a wireless control circuit miniaturized to centimeter scales form a system for monitoring PbtO2. Implanted into the brain of rats, this battery-free system demonstrates efficacy in capturing PbtO2 changes in response to alterations in the fraction of inspired oxygen (FiO2).
Photon upconversion with the transformation of low-energy photons to high-energy photons is of significant interest for broad applications. Here, we present self-powered, micrometer-scale optoelectronic devices based on III-V materials for high-performance near-infrared to visible upconversion. By taking advantage of its unique photon – “free electron” – photon processes, these thin-film, ultra-miniaturized devices realize fast upconversion that is linearly dependent on incoherent, low-power excitation, with a quantum yield of ~1.5%. By exploiting the advanced manufacturing method, encapsulated, freestanding devices are transferred onto heterogeneous substrates and show desirable biocompatibilities within biological fluids and tissues. These devices as the microscale light sources are implanted in behaving animals, with in vitro and in vivo experiments demonstrating their utility for optogenetic neuromodulation. These results provide routes for high-performance upconversion materials and devices and their unprecedented potential as optical biointerfaces.
Photon upconversion with the transformation of low-energy photons to high-energy photons is of significant interest for broad applications in biomedicine for stimulation, sensing, and imaging. Conventional upconversion materials rely on non-linear light-matter interactions, exhibit incidence dependent efficiencies and require high power excitation. Here, we present self-powered, micrometer-scale optoelectronic devices for high-performance near-infrared (~810 nm) to visible (630 nm red or 590 nm yellow) photon upconversion. Thanks to its unique photon–electron conversion process, these thin-film, ultra-miniaturized devices realize fast upconversion that is linearly dependent on incoherent, low-power excitation, with a quantum yield of ~1.5%. Encapsulated, freestanding devices are transferred onto heterogeneous flexible substrates and show desirable biocompatibilities within biological fluids and tissues. Demonstrations of optogenetic stimulation with upconversion devices as implantable light sources have successfully performed in vitro and in vivo scenarios. This approach provides a versatile route to achieve upconversion throughout the entire visible spectral range at lower power and higher efficiency than has previously been possible.
We exploit microscale, thin-film gallium arsenide (GaAs) lasers integrated onto silicon (Si) substrates via transfer printing, with a thermally conductive interface material for continuous wave (CW) operation at room temperature. Concepts that bypass existing challenges for III-V/Si integration are presented, and we demonstrate them in strategies for releasing and transfer printing fully formed, functional thin-film microscale GaAs based lasers onto Si substrates where a metallic thin film serves as an adhesive and a thermally conductive interface. Numerical simulations reveal the key considerations in thermal management, with an emphasis on the role of this interface layer. Electrically pumped devices printed on Si exhibit continuous-wave (CW) lasing in the near-infrared range (around 820 nm) at room temperature, with performance comparable to unreleased devices on their native substrates. The spectral shift is consistent with thermal modeling. In addition, preliminary experiments show that the laser devices are possible to be integrated with Si waveguide arrays as well as flexible substrates. The results presented here have promise as generalized routes for advanced heterogeneous integration in next-generation electronic and photonic circuits.
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