We fabricated YBa2Cu3O7 (YBCO) direct current (dc) nano superconducting quantum interference devices (nanoSQUIDs) based on grain boundary Josephson junctions by focused ion beam patterning. Characterization of electric transport and noise properties at 4.2 K in magnetically shielded environment yields a very small inductance L of a few pH for an optimized device geometry. This in turn results in very low values of flux noise < 50 nΦ0/Hz 1/2 in the thermal white noise limit, which yields spin sensitivities of a few µB/Hz 1/2 (Φ0 is the magnetic flux quantum and µB is the Bohr magneton). We observe frequency-dependent excess noise up to 7 MHz, which can only partially be eliminated by bias reversal readout. This indicates the presence of fluctuators of unknown origin, possibly related to defect-induced spins in the SrTiO3 substrate. We demonstrate the potential of using YBCO nanoSQUIDs for the investigation of small spin systems, by placing a 39 nm diameter Fe nanowire, encapsulated in a carbon nanotube, on top of a non-optimized YBCO nanoSQUID and by measuring the magnetization reversal of the Fe nanowire via the change of magnetic flux coupled to the nanoSQUID. The measured flux signals upon magnetization reversal of the Fe nanowire are in very good agreement with estimated values, and the determined switching fields indicate magnetization reversal of the nanowire via curling mode.

One of the main challenges for implantable biomedical sensing schemes is obtaining a reliable signal while maintaining biocompatibility. In this work, we demonstrate that a combination of medical ultrasound imaging and smart hydrogel micromechanical resonators can be employed for continuous monitoring of analyte concentrations. The sensing principle is based on the shift of the mechanical resonance frequencies of smart hydrogel structures induced by their volume-phase transition in response to changing analyte levels. This shift can then be measured as a contrast change in the ultrasound images due to resonance absorption of ultrasound waves. This concept eliminates the need for implanting complex electronics or employing transcutaneous connections for sensing biomedical analytes in vivo. Here, we present proof-of-principle experiments that monitor in vitro changes in ionic strength and glucose concentrations to demonstrate the capabilities and potential of this versatile sensing platform technology.

We present an electrically addressable optrode array capable of delivering light to 181 sites in the brain, each providing sufficient light to optogenetically excite thousands of neurons in vivo, developed with the aim to allow behavioral studies in large mammals. The device is a glass microneedle array directly integrated with a custom fabricated microLED device, which delivers light to 100 needle tips and 81 interstitial surface sites, giving two-level optogenetic excitation of neurons in vivo. Light delivery and thermal properties are evaluated, with the device capable of peak irradiances >80 mW∕mm 2 per needle site. The device consists of an array of 181 80 μm × 80 μm 2 microLEDs, fabricated on a 150-μm-thick GaN-on-sapphire wafer, coupled to a glass needle array on a 150-μm thick backplane. A pinhole layer is patterned on the sapphire side of the microLED array to reduce stray light. Future designs are explored through optical and thermal modeling and benchmarked against the current device.

Objective. Brain functions such as perception, motor control, learning, and memory arise from the coordinated activity of neuronal assemblies distributed across multiple brain regions. While major progress has been made in understanding the function of individual neurons, circuit interactions remain poorly understood. A fundamental obstacle to deciphering circuit interactions is the limited availability of research tools to observe and manipulate the activity of large, distributed neuronal populations in humans. Here we describe the development, validation, and dissemination of flexible, high-resolution, thin-film (TF) electrodes for recording neural activity in animals and humans. Approach. We leveraged standard flexible printed-circuit manufacturing processes to build high-resolution TF electrode arrays. We used biocompatible materials to form the substrate (liquid crystal polymer; LCP), metals (Au, PtIr, and Pd), molding (medical-grade silicone), and 3D-printed housing (nylon). We designed a custom, miniaturized, digitizing headstage to reduce the number of cables required to connect to the acquisition system and reduce the distance between the electrodes and the amplifiers. A custom mechanical system enabled the electrodes and headstages to be pre-assembled prior to sterilization, minimizing the setup time required in the operating room. PtIr electrode coatings lowered impedance and enabled stimulation. High-volume, commercial manufacturing enables cost-effective production of LCP-TF electrodes in large quantities. Main Results. Our LCP-TF arrays achieve 25× higher electrode density, 20× higher channel count, and 11× reduced stiffness than conventional clinical electrodes. We validated our LCP-TF electrodes in multiple human intraoperative recording sessions and have disseminated this technology to >10 research groups. Using these arrays, we have observed high-frequency neural activity with sub-millimeter resolution. Significance. Our LCP-TF electrodes will advance human neuroscience research and improve clinical care by enabling broad access to transformative, high-resolution electrode arrays.

Micro- and nanoelectromechanical oscillators driven at or close to their resonance frequency are used as sensors in many fields of science and technology. A decrease in the oscillator's effective spring constant and/or mass holds great potential for an increase in the sensor's sensitivity. This is usually accompanied by a reduction in spatial dimensions, which in most cases requires more complex detection methods. By analyzing the complex behavior of a simple asymmetric coupled harmonic oscillator model we propose a novel sensor concept which combines the advantages of bigger and smaller oscillators, i.e. ease of detection and high sensitivity. The concept is based on matching the resonance frequencies of two otherwise very different oscillators. To support our theoretical considerations, we present an experimental implementation of such a sensor and respective experimental data, verifying a substantial signal enhancement by several orders of magnitude.