Browsing by Author "Fan, Bo"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Flexible microelectrodes for high quality in vivo single-unit recording
    (2020-04-24) Fan, Bo; Robinson, Jacob
    Single-unit recording using microelectrodes has been a key technique to help us understand how the brain functions. For long-term, high-quality and high-density recording, neural electrodes have been developed to be small and flexible to place more channels and to minimize tissue damage. However, small electrodes naturally have higher impedance, which results in higher thermal noise and reduces the recording quality. Here, we introduce a sputtered porous Pt coating for flexible microelectrodes, which is highly compatible with existing manufacturing process. We compare the sputtered porous Pt with conventional flat Pt, and find consistent impedance reduction up to 9-fold, as well as noise reduction from both in vitro (PBS solution) and in vivo (noise in suppression). We demonstrated that the porous Pt is mechanically robust for handling, implantation, recording single-unit activity and retrieval from the brain. In addition, we designed differently-shaped electrodes and found that both surface area and perimeter determine total impedance. (Adapted from Bo Fan & Alex Rodriguez et al. 2020 [1])
  • Thumbnail Image
    Item
    Flexible sensors for high-quality recording and human-computer interface
    (2022-12-01) Fan, Bo; Robinson, Jacob T.
    Human-computer interfaces have been widely developed to bridge the gap in information transmission and enable the interaction between humans and computers. It provides unique opportunities to understand, augment, assist and repair the cognitive, sensory, and motor functions. Due to the soft nature of human skin and tissues, the conventional rigid human-computer interfaces face challenges in biocompatibility, wearability, comfortability, and high signal-to-noise (SNR) ratio for long-term and stable recording. Flexible devices are emerging. The flexible human-machine interface requires fundamental research in materials, mechanism, device design, and fabrication. This work focuses on developing flexible devices for human-computer interfaces which collect high-quality physical and physiological signals from animals. We have developed low impedance flexible electronic devices for high SNR recording in the motor cortex of rats: With a simple direct sputtering method, we can reduce the impedance of flexible Pt microelectrodes by 5-9-fold and reduce the thermal noise from both in vitro and in vivo recording. We also demonstrated that in addition to the surface area, the shape also affects the total impedance. We then further investigated how the design and materials of the electrodes affect the impedance, which is important for balancing the electrode sizes and recording SNR. We discovered that for materials associated with a diffusion-limited process, in small electrodes with a radius of fewer than 10 microns, the impedance transitions from area-dependent to perimeter-dependent. This indicates that when pushing for small electrodes, materials that have interactions with diffusion species in the electrolyte should be preferred. Finally, similar fabrication techniques for flexible microelectrodes can be applied to flexible photonic devices for temperature monitoring. We designed a micro-ring-resonator (MRR) based temperature sensor and demonstrated that the flexible temperature sensor doubled the temperature sensitivity compared to the conventional silicon-based MRR temperature sensor, which opens opportunities for biomedical applications in wearable devices or high sensitivity temperature monitoring. In summary, this work reports a novel method for wafer-scale low-impedance microelectrodes fabrication and provides insights into flexible device design, mechanism, and materials for high-quality recording and human-computer interfaces.
  • Thumbnail Image
    Item
    Impedance scaling for gold and platinum microelectrodes
    (IOP Publishing, 2021) Fan, Bo; Wolfrum, Bernhard; Robinson, Jacob T.; Bioengineering; Electrical and Computer Engineering
    Objective. Electrical measurement of the activity of individual neurons is a primary goal for many invasive neural electrodes. Making these ‘single unit’ measurements requires that we fabricate electrodes small enough so that only a few neurons contribute to the signal, but not so small that the impedance of the electrode creates overwhelming noise or signal attenuation. Thus, neuroelectrode design often must strike a balance between electrode size and electrode impedance, where the impedance is often assumed to scale linearly with electrode area. Approach and main results. Here we study how impedance scales with neural electrode area and find that the 1 kHz impedance of Pt electrodes (but not Au electrodes) transitions from scaling with area (r −2) to scaling with perimeter (r −1) when the electrode radius falls below 10 µm. This effect can be explained by the transition from planar to spherical diffusion behavior previously reported for electrochemical microelectrodes. Significance. These results provide important intuition for designing small, single unit recording electrodes. Specifically, for materials where the impedance is dominated by a pseudo-capacitance that is associated with a diffusion limited process, the total impedance will scale with perimeter rather than area when the electrode size becomes comparable with the diffusion layer thickness. For Pt electrodes this transition occurs around 10 µm radius electrodes. At even lower frequencies (1 Hz) impedance approaches a constant. This transition to r −1 scaling implies that electrodes with a pseudo-capacitance can be made smaller than one might expect before thermal noise or voltage division limits the ability to acquire high-quality single-unit recordings.
  • Thumbnail Image
    Item
    A microfluidic-induced C. elegans sleep state
    (Springer Nature, 2019) Gonzales, Daniel L.; Zhou, Jasmine; Fan, Bo; Robinson, Jacob T.; Bioengineering; Electrical and Computer Engineering
    An important feature of animal behavior is the ability to switch rapidly between activity states, however, how the brain regulates these spontaneous transitions based on the animal’s perceived environment is not well understood. Here we show a C. elegans sleep-like state on a scalable platform that enables simultaneous control of multiple environmental factors including temperature, mechanical stress, and food availability. This brief quiescent state, which we refer to as microfluidic-induced sleep, occurs spontaneously in microfluidic chambers, which allows us to track animal movement and perform whole-brain imaging. With these capabilities, we establish that microfluidic-induced sleep meets the behavioral requirements of C. elegans sleep and depends on multiple factors, such as satiety and temperature. Additionally, we show that C. elegans sleep can be induced through mechanosensory pathways. Together, these results establish a model system for studying how animals process multiple sensory pathways to regulate behavioral states.