Recent developments in optophysiology techniques such as optogenetics have revolutionized the ability to actuate cell activity. Further combining optophysiology and electrophysiology will integrate the advantages from both optical and electrical modalities and yield enabling technologies that allow simultaneous monitoring of cellular activity in response to modulation, which are crucial for biomedical applications. However, multifunctional devices that can deliver optical stimuli to regions beneath the electrodes and perform simultaneous sensing remain largely unexplored. Existing transparent microelectrode technologies depend on external bulk optical instruments for optical interventions. Here, innovative monolithic integrated multifunctional microsystems are demonstrated by applying transparent nanogrid electrodes onto microscale light sources to permit simultaneous electrophysiology and optical modulation at the same anatomical site. The nanogrid electrodes have transmittances > 70% with a low normalized impedance of 5.9 Ω cm2. Additional features of the devices include superior mechanical flexibility, minimized light‐induced electrical artifacts, and excellent biocompatibility. Ex vivo experiments demonstrate that the multifunctional devices can record abnormal heart rhythm in transgenic mouse hearts and simultaneously restore the sinus rhythm via optogenetic pacing. This work provides a versatile approach for constructing multifunctional colocalized biointerfaces containing crosstalk‐free optical and electrical modalities with expanded opportunities in both fundamental and applied biomedical research.

Transparent microelectrodes have recently emerged as a promising approach for crosstalk‐free multifunctional electrical and optical biointerfacing. High‐performance flexible platforms that allow seamless integration with soft tissue systems for such applications are urgently needed. Here, silver nanowires (Ag NWs)‐based transparent microelectrode arrays (MEAs) and interconnects are designed to meet this demand. The nanowire networks exhibit a high optical transparency >90.0% at 550 nm, and superior mechanical stability up to 100,000 bending cycles at 5 mm radius. The Ag NWs microelectrodes preserve low normalized electrochemical impedance of 3.4–15 Ω cm2 at 1 kHz, and the interconnects demonstrate excellent sheet resistance (Rsh) of 4.1–25 Ω sq−1. In vivo histological analysis reveals that the Ag NWs structures are biocompatible. Studies on Langendorff‐perfused mouse and rat hearts demonstrate that the Ag NWs MEAs enable high‐fidelity real‐time monitoring of heart rhythm during co‐localized optogenetic pacing and optical mapping. This proof‐of‐concept work illustrates that the solution‐processed, transparent, and flexible Ag NWs structures are a promising candidate for the next‐generation of large‐area multifunctional biointerfaces for interrogating complex biological systems in basic and translational research.

Flexible and transparent microelectrodes and interconnects provide the unique capability for a wide range of emerging biological applications, including simultaneous optical and electrical interrogation of biological systems. For practical biointerfacing, it is important to further improve the optical, electrical, electrochemical, and mechanical properties of the transparent conductive materials. Here, high‐performance microelectrodes and interconnects with high optical transmittance (59–81%), superior electrochemical impedance (5.4–18.4 Ω cm2), and excellent sheet resistance (5.6–14.1 Ω sq−1), using indium tin oxide (ITO) and metal grid (MG) hybrid structures are demonstrated. Notably, the hybrid structures retain the superior mechanical properties of flexible MG other than brittle ITO with no changes in sheet resistance even after 5000 bending cycles against a small radius at 5 mm. The capabilities of the ITO/MG microelectrodes and interconnects are highlighted by high‐fidelity electrical recordings of transgenic mouse hearts during co‐localized programmed optogenetic stimulation. In vivo histological analysis reveals that the ITO/MG structures are fully biocompatible. Those results demonstrate the great potential of ITO/MG interfaces for broad fundamental and translational physiological studies.

disease arises from asynchrony and abnormalities in the complex and coordinated electro-mechanical properties over time and space. Therefore, devices that allow monitoring and controlling of the spatiotemporal dynamics of cardiac activity are crucial for unraveling the pathophysiology of heart disease and developing effective treatment therapies in clinical cardiology practice. Implantable electronic pacemakers play an essential role in treating various types of arrhythmias and heart failure and studying cardiac physiology by changing the membrane potential and triggering an action potential with an electric current. [3,4] However, electrical stimulation can lead to adverse effects on cell health and integrity due to the cell membrane electroporation and redox processes. [5,6] The electrical fields created by the stimulation electrodes will generate electrical crosstalk between stimulation and recording electrodes and result in recording artifacts. [7] Furthermore, electrical stimulation is unable to target specific subtypes of cardiac cells. Optogenetics uses light to modulate the activity of genetically targeted cell types through photosensitive ion channels and pumps. [8] Despite its initial use in neuroscience research to control neural circuits, [8,9] optogenetics has now been applied as a promising tool in cardiology for pain-free, low-energy optical pacing, and defibrillation with cell-type specificity. [10][11][12] In addition, cardiac optogenetics generally interferes less with simultaneous electrical readout of cardiac activity compared to electrical stimulation. Currently, cardiac optogenetics is primarily used in in vitro and ex vivo cardiac studies with cell cultures or explanted perfused hearts. [13][14][15][16][17] More in vivo research is crucially needed to fully exploit the unique opportunities cardiac optogenetics offers for mechanistic investigations of heart function in health and disease.Small animal models such as mice and rats are the main rodent species that could be genetically engineered for in vivo cardiac optogenetics research and their heart electrophysiology is a good approximation of the human electrophysiology. [18] Implantable cardiac devices that combine precise light delivery to targeted heart regions of small animals with electrophysiological readout capabilities remain a major technological Bioelectronic devices that allow simultaneous accurate monitoring and control of the spatiotemporal patterns of cardiac activity provide an effective means to understand the mechanisms and optimize therapeutic strategies for heart disease. Optogenetics is a promising technology for cardiac research due to its advantages such as cell-type selectivity and high space-time resolution, but its efficacy is limited by the insufficient number of modulation channels and lack of simultaneous spatiotemporal mapping capabilities in current implantable cardiac optogenetics tools available for in vivo investigations. Here, soft implantable electro-optical cardiac devices integrating multilayered highly ...

Recently developed optically transparent microelectrode technology provides a promising approach for simultaneous high-resolution electrical and optical biointerfacing with tissues in vivo and in vitro. A critically unmet need is designing high-performance stretchable platforms for conformal biointerfacing with mechanically active organs. Here, we report silver nanowire (Ag NW) stretchable transparent microelectrodes and interconnects that exhibit excellent electrical and electrochemical performance, high optical transparency, superior mechanical robustness and durability by a simple selective-patterning process. The fabrication method allows the direct integration of Ag NW networks on elastomeric substrates. The resulting Ag NW interface exhibits a low sheet resistance (Rsh) of 1.52–4.35 Ω sq−1, an advantageous normalized electrochemical impedance of 3.78–6.04 Ω cm2, a high optical transparency of 61.3–80.5% at 550 nm and a stretchability of 40%. The microelectrode arrays (MEAs) fabricated with this approach exhibit uniform electrochemical performance across all channels. Studies on mice demonstrate that both pristine and stretched Ag NW microelectrodes can achieve high-fidelity electrophysiological monitoring of cardiac activity with/without co-localized optogenetic pacing. Together, these results pave the way for developing stretchable and transparent metal nanowire networks for high-resolution opto-electric biointerfacing with mechanically active organs, such as the heart.