Stanford Advisors

All Publications

  • Multiplexed neurochemical sensing with sub-nM sensitivity across 2.25 mm2 area. Biosensors & bioelectronics Mintz Hemed, N., Hwang, F. J., Zhao, E. T., Ding, J. B., Melosh, N. A. 2024; 261: 116474


    Multichannel arrays capable of real-time sensing of neuromodulators in the brain are crucial for gaining insights into new aspects of neural communication. However, measuring neurochemicals, such as dopamine, at low concentrations over large areas has proven challenging. In this research, we demonstrate a novel approach that leverages the scalability and processing power offered by microelectrode array devices integrated with a functionalized, high-density microwire bundle, enabling electrochemical sensing at an unprecedented scale and spatial resolution. The sensors demonstrate outstanding selective molecular recognition by incorporating a selective polymeric membrane. By combining cutting-edge commercial multiplexing, digitization, and data acquisition hardware with a bio-compatible and highly sensitive neurochemical interface array, we establish a powerful platform for neurochemical analysis. This multichannel array has been successfully utilized in vitro and ex vivo systems. Notably, our results show a sensing area of 2.25 mm2 with an impressive detection limit of 820 pM for dopamine. This new approach paves the way for investigating complex neurochemical processes and holds promise for advancing our understanding of brain function and neurological disorders.

    View details for DOI 10.1016/j.bios.2024.116474

    View details for PubMedID 38870827

  • Elevated shear stress modulates heterogenous cellular subpopulations to induce vascular remodeling. Tissue engineering. Part A Fischer, K., Henn, D., Zhao, E., Sivaraj, D., Litmanovich, B., Hahn, W., Hostler, A. C., Mojadidi, S., Gonzalez, J., Knochel, A., Mora Pinos, M. G., Holley, J., Kussie, H., Granoski, M., Yasmeh, J. P., Kneser, U., Chen, K., Gurtner, G. C. 2024


    Elevated shear stress induces vascular remodeling in veins exposed to arterial blood flow, which can lead to arterio-venous (AV) fistula failure. The molecular mechanisms driving remodeling have not been comprehensively examined with single cell resolution before.Using an in vivo animal mode, single-cell RNA-sequencing (scRNA-seq), and histopathology, we precisely manipulate blood flow to comprehensively characterize all cell subpopulations important during vascular remodeling.AV loops were created in saphenous vessels of rats using a contralateral saphenous vein interposition graft to promote elevated shear stress (ESS). Saphenous veins with no elevated shear stress (NSS) were anastomosed as controls.ESS promoted transcriptional homogeneity, and NSS cells promoted considerable heterogeneity. Specifically, ESS ECs showed a more homogeneous transcriptional response promoting angiogenesis and upregulating Endothelial-to-Mesenchymal-Transition (EndMT) inhibiting genes (Klf2). NSS ECs upregulated anti-proliferation genes such as Cav1, Cst3 and Btg1. In macrophages, ESS promoted a large homogeneous subpopulation, creating a mechanically activated pro-inflammatory M1-like, thus pro-angiogenic myeloid phenotype, while NSS myeloid cells expressed the anti-inflammatory and anti-angiogenetic marker Mrc1.ESS activates unified gene expression profiles to induce adaption of the vessel wall to hemodynamic alterations. Targeted depletion of the identified cellular subpopulations may lead to novel therapies to prevent excessive venous remodeling, intimal hyperplasia, and AV fistula failure.

    View details for DOI 10.1089/ten.TEA.2023.0362

    View details for PubMedID 38753711

  • Enhanced Thin-Film Encapsulation Through Micron-Scale Anchors ADVANCED FUNCTIONAL MATERIALS Hemed, N., Pham, A., Zhao, E. T., Wang, P., Melosh, N. A. 2024
  • Spiral NeuroString: High-Density Soft Bioelectronic Fibers for Multimodal Sensing and Stimulation. bioRxiv : the preprint server for biology Khatib, M., Zhao, E. T., Wei, S., Abramson, A., Bishop, E. S., Chen, C., Thomas, A., Xu, C., Park, J., Lee, Y., Hamnett, R., Yu, W., Root, S. E., Yuan, L., Chakhtoura, D., Kim, K. K., Zhong, D., Nishio, Y., Zhao, C., Wu, C., Jiang, Y., Zhang, A., Li, J., Wang, W., Salimi-Jazi, F., Rafeeqi, T. A., Hemed, N. M., Tok, J. B., Chen, X., Kaltschmidt, J. A., Dunn, J. C., Bao, Z. 2023


    Bioelectronic fibers hold promise for both research and clinical applications due to their compactness, ease of implantation, and ability to incorporate various functionalities such as sensing and stimulation. However, existing devices suffer from bulkiness, rigidity, limited functionality, and low density of active components. These limitations stem from the difficulty to incorporate many components on one-dimensional (1D) fiber devices due to the incompatibility of conventional microfabrication methods (e.g., photolithography) with curved, thin and long fiber structures. Herein, we introduce a fabrication approach, ‶spiral transformation, to convert two-dimensional (2D) films containing microfabricated devices into 1D soft fibers. This approach allows for the creation of high density multimodal soft bioelectronic fibers, termed Spiral NeuroString (S-NeuroString), while enabling precise control over the longitudinal, angular, and radial positioning and distribution of the functional components. We show the utility of S-NeuroString for motility mapping, serotonin sensing, and tissue stimulation within the dynamic and soft gastrointestinal (GI) system, as well as for single-unit recordings in the brain. The described bioelectronic fibers hold great promises for next-generation multifunctional implantable electronics.

    View details for DOI 10.1101/2023.10.02.560482

    View details for PubMedID 37873341

  • Allometrically scaling tissue forces drive pathological foreign-body responses to implants via Rac2-activated myeloid cells. Nature biomedical engineering Padmanabhan, J., Chen, K., Sivaraj, D., Henn, D., Kuehlmann, B. A., Kussie, H. C., Zhao, E. T., Kahn, A., Bonham, C. A., Dohi, T., Beck, T. C., Trotsyuk, A. A., Stern-Buchbinder, Z. A., Than, P. A., Hosseini, H. S., Barrera, J. A., Magbual, N. J., Leeolou, M. C., Fischer, K. S., Tigchelaar, S. S., Lin, J. Q., Perrault, D. P., Borrelli, M. R., Kwon, S. H., Maan, Z. N., Dunn, J. C., Nazerali, R., Januszyk, M., Prantl, L., Gurtner, G. C. 2023


    Small animals do not replicate the severity of the human foreign-body response (FBR) to implants. Here we show that the FBR can be driven by forces generated at the implant surface that, owing to allometric scaling, increase exponentially with body size. We found that the human FBR is mediated by immune-cell-specific RAC2 mechanotransduction signalling, independently of the chemistry and mechanical properties of the implant, and that a pathological FBR that is human-like at the molecular, cellular and tissue levels can be induced in mice via the application of human-tissue-scale forces through a vibrating silicone implant. FBRs to such elevated extrinsic forces in the mice were also mediated by the activation of Rac2 signalling in a subpopulation of mechanoresponsive myeloid cells, which could be substantially reduced via the pharmacological or genetic inhibition of Rac2. Our findings provide an explanation for the stark differences in FBRs observed in small animals and humans, and have implications for the design and safety of implantable devices.

    View details for DOI 10.1038/s41551-023-01091-5

    View details for PubMedID 37749310

    View details for PubMedCentralID 2966551

  • A CMOS-based highly scalable flexible neural electrode interface. Science advances Zhao, E. T., Hull, J. M., Mintz Hemed, N., Uluşan, H., Bartram, J., Zhang, A., Wang, P., Pham, A., Ronchi, S., Huguenard, J. R., Hierlemann, A., Melosh, N. A. 2023; 9 (23): eadf9524


    Perception, thoughts, and actions are encoded by the coordinated activity of large neuronal populations spread over large areas. However, existing electrophysiological devices are limited by their scalability in capturing this cortex-wide activity. Here, we developed an electrode connector based on an ultra-conformable thin-film electrode array that self-assembles onto silicon microelectrode arrays enabling multithousand channel counts at a millimeter scale. The interconnects are formed using microfabricated electrode pads suspended by thin support arms, termed Flex2Chip. Capillary-assisted assembly drives the pads to deform toward the chip surface, and van der Waals forces maintain this deformation, establishing Ohmic contact. Flex2Chip arrays successfully measured extracellular action potentials ex vivo and resolved micrometer scale seizure propagation trajectories in epileptic mice. We find that seizure dynamics in absence epilepsy in the Scn8a+/- model do not have constant propagation trajectories.

    View details for DOI 10.1126/sciadv.adf9524

    View details for PubMedID 37285436

    View details for PubMedCentralID PMC10246892

  • Direct-print three-dimensional electrodes for large- scale, high-density, and customizable neural inter- faces. bioRxiv : the preprint server for biology Wang, P., Wu, E. G., Uluşan, H., Phillips, A. J., Rose Hays, M., Kling, A., Zhao, E. T., Madugula, S., Vilkhu, R. S., Vasireddy, P. K., Hier-Lemann, A., Hong, G., Chichilnisky, E. J., Melosh, N. A. 2023


    Silicon-based planar microelectronics is a powerful tool for scalably recording and modulating neural activity at high spatiotemporal resolution, but it remains challenging to target neural structures in three dimensions (3D). We present a method for directly fabricating 3D arrays of tissue-penetrating microelectrodes onto silicon microelectronics. Leveraging a high-resolution 3D printing technology based on 2-photon polymerization and scalable microfabrication processes, we fabricated arrays of 6,600 microelectrodes 10-130 μm tall and at 35-μm pitch onto a planar silicon-based microelectrode array. The process enables customizable electrode shape, height and positioning for precise targeting of neuron populations distributed in 3D. As a proof of concept, we addressed the challenge of specifically targeting retinal ganglion cell (RGC) somas when interfacing with the retina. The array was customized for insertion into the retina and recording from somas while avoiding the axon layer. We verified locations of the microelectrodes with confocal microscopy and recorded high-resolution spontaneous RGC activity at cellular resolution. This revealed strong somatic and dendritic components with little axon contribution, unlike recordings with planar microelectrode arrays. The technology could be a versatile solution for interfacing silicon microelectronics with neural structures and modulating neural activity at large scale with single-cell resolution.

    View details for DOI 10.1101/2023.05.30.542925

    View details for PubMedID 37398164

    View details for PubMedCentralID PMC10312573

  • On-Demand, Reversible, Ultrasensitive Polymer Membrane Based on Molecular Imprinting Polymer. ACS nano Mintz Hemed, N., Leal-Ortiz, S., Zhao, E. T., Melosh, N. A. 2023


    The development of in vivo, longitudinal, real-time monitoring devices is an essential step toward continuous, precision health monitoring. Molecularly imprinted polymers (MIPs) are popular sensor capture agents that are more robust than antibodies and have been used for sensors, drug delivery, affinity separations, assays, and solid-phase extraction. However, MIP sensors are typically limited to one-time use due to their high binding affinity (>107 M-1) and slow-release kinetics (<10-4 muM/sec). To overcome this challenge, current research has focused on stimuli-responsive MIPs (SR-MIPs), which undergo a conformational change induced by external stimuli to reverse molecular binding, requiring additional chemicals or outside stimuli. Here, we demonstrate fully reversible MIP sensors based on electrostatic repulsion. Once the target analyte is bound within a thin film MIP on an electrode, a small electrical potential successfully releases the bound molecules, enabling repeated, accurate measurements. We demonstrate an electrostatically refreshed dopamine sensor with a 760 pM limit of detection, linear response profile, and accuracy even after 30 sensing-release cycles. These sensors could repeatedly detect <1 nM dopamine released from PC-12 cells in vitro, demonstrating they can longitudinally measure low concentrations in complex biological environments without clogging. Our work provides a simple and effective strategy for enhancing the use of MIPs-based biosensors for all charged molecules in continuous, real-time health monitoring and other sensing applications.

    View details for DOI 10.1021/acsnano.2c11618

    View details for PubMedID 36913954

  • Decoding and Modulation of Spiking Activity of the Sciatic Nerve in an Awake and Moving Rodent Fischer, K. S., Zhao, E. T., Maan, Z., Barrera, J., Noishiki, C., Litmanovich, B., Henn, D., Mojadidi, S. M., Gonzalez, J., Sivaraj, D., Hostler, A., Hahn, W., Chen, K., Melosh, N., Gurtner, G. C. WILEY. 2023: 267-268
  • Wireless, closed-loop, smart bandage with integrated sensors and stimulators for advanced wound care and accelerated healing. Nature biotechnology Jiang, Y., Trotsyuk, A. A., Niu, S., Henn, D., Chen, K., Shih, C. C., Larson, M. R., Mermin-Bunnell, A. M., Mittal, S., Lai, J. C., Saberi, A., Beard, E., Jing, S., Zhong, D., Steele, S. R., Sun, K., Jain, T., Zhao, E., Neimeth, C. R., Viana, W. G., Tang, J., Sivaraj, D., Padmanabhan, J., Rodrigues, M., Perrault, D. P., Chattopadhyay, A., Maan, Z. N., Leeolou, M. C., Bonham, C. A., Kwon, S. H., Kussie, H. C., Fischer, K. S., Gurusankar, G., Liang, K., Zhang, K., Nag, R., Snyder, M. P., Januszyk, M., Gurtner, G. C., Bao, Z. 2022


    'Smart' bandages based on multimodal wearable devices could enable real-time physiological monitoring and active intervention to promote healing of chronic wounds. However, there has been limited development in incorporation of both sensors and stimulators for the current smart bandage technologies. Additionally, while adhesive electrodes are essential for robust signal transduction, detachment of existing adhesive dressings can lead to secondary damage to delicate wound tissues without switchable adhesion. Here we overcome these issues by developing a flexible bioelectronic system consisting of wirelessly powered, closed-loop sensing and stimulation circuits with skin-interfacing hydrogel electrodes capable of on-demand adhesion and detachment. In mice, we demonstrate that our wound care system can continuously monitor skin impedance and temperature and deliver electrical stimulation in response to the wound environment. Across preclinical wound models, the treatment group healed ~25% more rapidly and with ~50% enhancement in dermal remodeling compared with control. Further, we observed activation of proregenerative genes in monocyte and macrophage cell populations, which may enhance tissue regeneration, neovascularization and dermal recovery.

    View details for DOI 10.1038/s41587-022-01528-3

    View details for PubMedID 36424488

    View details for PubMedCentralID 5350204

  • Ag-Diamond Core-Shell Nanostructures Incorporated with Silicon-Vacancy Centers. ACS materials Au Li, S., Francaviglia, L., Kohler, D. D., Jones, Z. R., Zhao, E. T., Ogletree, D. F., Weber-Bargioni, A., Melosh, N. A., Hamers, R. J. 2022; 2 (2): 85-93


    Silicon-vacancy (SiV) centers in diamond have attracted attention as highly stable fluorophores for sensing and as possible candidates for quantum information science. While prior studies have shown that the formation of hybrid diamond-metal structures can increase the rates of optical absorption and emission, many practical applications require diamond plasmonic structures that are stable in harsh chemical and thermal environments. Here, we demonstrate that Ag nanospheres, produced both in quasi-random arrays by thermal dewetting and in ordered arrays using electron-beam lithography, can be completely encapsulated with a thin diamond coating containing SiV centers, leading to hybrid core-shell nanostructures exhibiting extraordinary chemical and thermal stability as well as enhanced optical properties. Diamond shells with a thickness on the order of 20-100 nm are sufficient to encapsulate and protect the Ag nanostructures with different sizes ranging from 20 nm to hundreds of nanometers, allowing them to withstand heating to temperatures of 1000 °C and immersion in harsh boiling acid for 24 h. Ultrafast photoluminescence lifetime and super-resolution optical imaging experiments were used to study the SiV properties on and off the core-shell structures, which show that the SiV on core-shell structures have higher brightness and faster decay rate. The stability and optical properties of the hybrid Ag-diamond core-shell structures make them attractive candidates for high-efficiency imaging and quantum-based sensing applications.

    View details for DOI 10.1021/acsmaterialsau.1c00027

    View details for PubMedID 36855764

    View details for PubMedCentralID PMC9888652

  • Etching- and intermediate-free graphene dry transfer onto polymeric thin films with high piezoresistive gauge factors JOURNAL OF MATERIALS CHEMISTRY C Li, R., Zhang, Q., Zhao, E., Li, J., Gu, Q., Gao, P. 2019; 7 (42): 13032–39

    View details for DOI 10.1039/c9tc04545g

    View details for Web of Science ID 000494705100004