Gerwin Dijk

All Publications

• Thermal Processing Creates Water-Stable PEDOT:PSS Films for Bioelectronics. Advanced materials (Deerfield Beach, Fla.) Doshi, S., Forner, M. O., Wang, P., Hadwe, S. E., Jin, A. T., Dijk, G., Brinson, K., Lim, J., Dominguez-Alfaro, A., Lim, C. Y., Salleo, A., Barone, D. G., Hong, G., Brongersma, M. L., Melosh, N. A., Malliaras, G. G., Keene, S. T. 2025: e2415827

  Abstract

  Organic mixed ionic-electronic conductors have emerged as a key material for the development of bioelectronic devices due to their soft mechanical properties, biocompatibility, and high volumetric capacitance. In particular, PEDOT:PSS has become a choice material because it is highly conductive, easily processible, and commercially available. However, PEDOT:PSS is dispersible in water, leading to delamination of films when exposed to biological environments. For this reason, chemical cross-linking agents such as (3-glycidyloxypropyl)trimethoxysilane (GOPS) are used to stabilize PEDOT:PSS films in water, but at the cost of decreased electrical performance. Here, it is shown that PEDOT:PSS thin films become water-stable by simply baking at high temperatures (>150 °C) for a short time (≈ 2 min). It is shown that heat-treated PEDOT:PSS films are as stable as their chemically-cross-linked counterparts, with their performance maintained for >20 days both in vitro and in vivo. The heat-treated films eliminate electrically insulating cross-linkers, resulting in a 3× increase in volumetric capacitance. Applying thermal energy using a focused femtosecond laser enables direct patterning of 3D PEDOT:PSS microstructures. The thermal treatment method is compatible with a wide range of substrates and is readily substituted into existing workflows for manufacturing devices, enabling its rapid adoption in the field of bioelectronics.

  View details for DOI 10.1002/adma.202415827

  View details for PubMedID 40025942

• NeuroRoots, a bio-inspired, seamless brain machine interface for long-term recording in delicate brain regions. AIP advances Ferro, M. D., Proctor, C. M., Gonzalez, A., Jayabal, S., Zhao, E., Gagnon, M., Slézia, A., Pas, J., Dijk, G., Donahue, M. J., Williamson, A., Raymond, J., Malliaras, G. G., Giocomo, L., Melosh, N. A. 2024; 14 (8): 085109

  Abstract

  Scalable electronic brain implants with long-term stability and low biological perturbation are crucial technologies for high-quality brain-machine interfaces that can seamlessly access delicate and hard-to-reach regions of the brain. Here, we created "NeuroRoots," a biomimetic multi-channel implant with similar dimensions (7 μm wide and 1.5 μm thick), mechanical compliance, and spatial distribution as axons in the brain. Unlike planar shank implants, these devices consist of a number of individual electrode "roots," each tendril independent from the other. A simple microscale delivery approach based on commercially available apparatus minimally perturbs existing neural architectures during surgery. NeuroRoots enables high density single unit recording from the cerebellum in vitro and in vivo. NeuroRoots also reliably recorded action potentials in various brain regions for at least 7 weeks during behavioral experiments in freely-moving rats, without adjustment of electrode position. This minimally invasive axon-like implant design is an important step toward improving the integration and stability of brain-machine interfacing.

  View details for DOI 10.1063/5.0216979

  View details for PubMedID 39130131

  View details for PubMedCentralID PMC11309783

• The impact of hydrogen peroxide production in OECTs for <i>in vitro</i> applications JOURNAL OF MATERIALS CHEMISTRY C Lubrano, C., Bettucci, O., Dijk, G., Salleo, A., Giovannitti, A., Santoro, F. 2023

  View details for DOI 10.1039/d3tc02849f

  View details for Web of Science ID 001144727300001

• PEDOT:PSS-coated platinum electrodes for neural stimulation. APL bioengineering Dijk, G., Pas, J., Markovic, K., Scancar, J., O'Connor, R. P. 2023; 7 (4): 046117

  Abstract

  Safe and long-term electrical stimulation of neurons requires charge injection without damaging the electrode and tissue. A common strategy to diminish adverse effects includes the modification of electrodes with materials that increases the charge injection capacity. Due to its high capacitance, the conducting polymer PEDOT:PSS is a promising coating material; however, the neural stimulation performance in terms of stability and safety remains largely unexplored. Here, PEDOT:PSS-coated platinum (Pt-PEDOT:PSS) microelectrodes are examined for neural stimulation and compared to bare platinum (Pt) electrodes. Microelectrodes in a bipolar configuration are used to deliver current-controlled, biphasic pulses with charge densities ranging from 64 to 255 μC cm-2. Stimulation for 2 h deteriorates bare Pt electrodes through corrosion, whereas the PEDOT:PSS coating prevents dissolution of Pt and shows no degradation. Acute stimulation of primary cortical cells cultured as neurospheres shows similar dependency on charge density for Pt and Pt-PEDOT:PSS electrodes with a threshold of 127 μC cm-2 and increased calcium response for higher charge densities. Continuous stimulation for 2 h results in higher levels of cell survival for Pt-PEDOT:PSS electrodes. Reduced cell survival on Pt electrodes is most profound for neurospheres in proximity of the electrodes. Extending the stimulation duration to 6 h increases cell death for both types of electrodes; however, neurospheres on Pt-PEDOT:PSS devices still show significant viability whereas stimulation is fatal for nearly all cells close to the Pt electrodes. This work demonstrates the protective properties of PEDOT:PSS that can be used as a promising approach to extend electrode lifetime and reduce cell damage for safe and long-term neural stimulation.

  View details for DOI 10.1063/5.0153094

  View details for PubMedID 38075207

  View details for PubMedCentralID PMC10699886

• Fabrication and in vivo 2-photon microscopy validation of transparent PEDOT:PSS microelectrode arrays. Microsystems & nanoengineering Dijk, G., Kaszas, A., Pas, J., O'Connor, R. P. 2022; 8: 90

  Abstract

  Transparent microelectrode arrays enable simultaneous electrical recording and optical imaging of neuronal networks in the brain. Electrodes made of the conducting polymer poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) are transparent; however, device fabrication necessitates specific processes to avoid deterioration of the organic material. Here, we present an innovative fabrication scheme for a neural probe that consists of transparent PEDOT:PSS electrodes and demonstrate its compatibility with 2-photon microscopy. The electrodes show suitable impedance to record local field potentials from the cortex of mice and sufficient transparency to visualize GCaMP6f-expressing neurons underneath the PEDOT:PSS features. The results validate the performance of the neural probe, which paves the way to study the complex dynamics of in vivo neuronal activity with both a high spatial and temporal resolution to better understand the brain.

  View details for DOI 10.1038/s41378-022-00434-7

  View details for PubMedID 36051746

  View details for PubMedCentralID PMC9424218

• Electroporation Microchip With Integrated Conducting Polymer Electrode Array for Highly Sensitive Impedance Measurement IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING Dijk, G., Poulkouras, R., OConnor, R. P. 2022; 69 (7): 2363-2369

  Abstract

  Monitoring of impedance changes during electroporation-based treatments can be used to study the biological response and provide feedback regarding treatment progression. However, seamless integration of the sensing electrodes with the setup can be challenging and high impedance sensing electrodes limit the recording sensitivity as well as the spatial resolution. Here, we present an all-in-one microchip containing stimulation electrodes, as well as an array of low impedance, micro-scale sensing electrodes for highly sensitive impedance monitoring.An in vitro platform is fabricated with integrated stimulation and sensing electrodes. To reduce the impedance, the sensing electrodes are coated with the conducting polymer PEDOT:PSS. The performance is studied during the growth of a confluent cell layer and treatment with electrical pulses.Coated electrodes, compared to uncoated electrodes, show more pronounced impedance changes in a broader frequency range throughout the formation of a confluent cell layer and after electrical treatment.PEDOT:PSS coatings enhance the monitoring of impedance changes with micro-scale electrodes, enabling high spatial resolution and increased sensitivity.Such monitoring systems can be used to study electroporation dynamics and monitor treatment progression for better understanding of underlying mechanisms and improved outcomes.

  View details for DOI 10.1109/TBME.2022.3143542

  View details for Web of Science ID 000812532300029

  View details for PubMedID 35041593

• PEDOT:PSS-Coated Stimulation Electrodes Attenuate Irreversible Electrochemical Events and Reduce Cell Electropermeabilization ADVANCED MATERIALS INTERFACES Dijk, G., Ruigrok, H. J., O'Connor, R. P. 2021; 8 (19)

  View details for DOI 10.1002/admi.202100214

  View details for Web of Science ID 000694628000001

• Influence of PEDOT:PSS Coating Thickness on the Performance of Stimulation Electrodes ADVANCED MATERIALS INTERFACES Dijk, G., Ruigrok, H. J., O'Connor, R. P. 2020; 7 (16)

  View details for DOI 10.1002/admi.202000675

  View details for Web of Science ID 000541502200001

• Stability of PEDOT:PSS-Coated Gold Electrodes in Cell Culture Conditions ADVANCED MATERIALS TECHNOLOGIES Dijk, G., Rutz, A. L., Malliaras, G. G. 2020; 5 (3)

  View details for DOI 10.1002/admt.201900662

  View details for Web of Science ID 000492386500001