No abstract

Active tunability of photonic resonances is of great interest for various applications such as optical switching and modulation based on optoelectronic materials. Manipulation of charged excitons in atomically thin transition metal dichalcogenides (TMDCs) like monolayer MoS offers an unexplored route for diverse functionalities in optoelectronic nanodevices. Here, we experimentally demonstrate the dynamic photochemical and optoelectronic control of the photonic crystal Fano resonances by optical and electrical tuning of monolayer MoS refractive index via trions without any chemical treatment. The strong spatial and spectral overlap between the photonic Fano mode and the active MoS monolayer enables efficient modulation of the Fano resonance. Our approach offers new directions for potential applications in the development of optical modulators based on emerging 2D direct band gap semiconductors.

Owing to their unique electrical and optical properties, two-dimensional transition metal dichalcogenides have been extensively studied for their potential applications in biosensing. However, simultaneous utilization of both optical and electrical properties has been overlooked, yet it can offer enhanced accuracy and detection versitility. Here, we demonstrate a dual-mode optoelectronic biosensor based on monolayer molybdenum disulfide (MoS2) capable of producing simultaneous electrical and optical readouts of biomolecular signals. On a single platform, the biosensor exhibits a tunable photonic Fano-type optical resonance while also functioning as a field-effect transistor (FET) based on a optically transparent gate electrode. Furthermore, chemical vapor deposition grown MoS2 provides a clean surface for direct immobilization of a water-soluble variant of the μ-opioid receptor (wsMOR), via a nickel ion-mediated linker chemistry. We utilize a synthetic opioid peptide to show the operation of the electronic and optical sensing modes. The responses of both modes exhibit a similar trend with dynamic ranges of four orders of magnitude and detection limits of  <1 nM. Our work explores the potential of a versatile multimodal sensing platform enabled by monolayer MoS2, since the integration of electrical and optical sensors on the same chip can offer flexibility in read-out and improve the accuracy in detection of low concentration targets.

Spatial dispersion of a photonic crystal manifests itself as an angle dependent optical response. Here, we use the emerging two-dimensional transition metal dichalcogenides (TMDCs) as a photon source to directly image the spatial dispersion in the reciprocal space. Excitonic emission from a monolayer MoS 2 is coupled to the delocalized Fano resonances supported by the photonic crystal slab, recreating isofrequency contours in the far-field. This integration of monolayer TMDCs and photonic crystal not only reveals the band structure of a photonic crystal but also provides a new route to controllable and directional excitonic light sources.

To investigate chronic durability of transparent graphene electrodes fabricated on polyethylene terephthalate (PET) and SU-8 substrates for chronic in vivo studies. Methods: We perform systematic accelerated aging tests to understand the chronic reliability and failure modes of transparent graphene microelectrode arrays built on PET and SU-8 substrates. We employ graphene microelectrodes fabricated on PET substrate in chronic in vivo experiments with transgenic mice. Results: Our results show that graphene microelectrodes fabricated on PET substrate work reliably after 30 days accelerated aging test performed at 87 °C, equivalent to 960 days in vivo lifetime. We demonstrate stable chronic recordings of cortical potentials in multimodal imaging/recording experiments using transparent graphene microelectrodes fabricated on PET substrate. On the other hand, graphene microelectrode arrays built on SU-8 substrate exhibit extensive crack formation across microelectrode sites and wires after one to two weeks, resulting in total failure of recording capability for chronic studies. Conclusion: PET shows superior reliability as a substrate for graphene microelectrode arrays for chronic in vivo experiments. Significance: Graphene is a unique neural interface material enabling cross-talk free integration of electrical and optical recording and stimulation techniques in the same experiment. To date, graphene-based microelectrode arrays have been demonstrated in various multi-modal acute experiments involving electrophysiological sensing or stimulation, optical imaging and optogenetics stimulation. Understanding chronic reliability of graphene-based transparent interfaces is very important to expand the use of this technology for long-term behavioral studies with animal models.