A MEMS ultrasound stimulation system for modulation of neural circuits with high spatial resolution in vitro.

Neuromodulation by ultrasound has recently received attention due to its noninvasive stimulation capability for treating brain diseases. Although there have been several studies related to ultrasonic neuromodulation, these studies have suffered from poor spatial resolution of the ultrasound and low repeatability with a fixed condition caused by conventional and commercialized ultrasound transducers. In addition, the underlying physics and mechanisms of ultrasonic neuromodulation are still unknown. To determine these mechanisms and accurately modulate neural circuits, researchers must have a precisely controllable ultrasound transducer to conduct experiments at the cellular level. Herein, we introduce a new MEMS ultrasound stimulation system for modulating neurons or brain slices with high spatial resolution. The piezoelectric micromachined ultrasonic transducers (pMUTs) with small membranes (sub-mm membranes) generate enough power to stimulate neurons and enable precise modulation of neural circuits. We designed the ultrasound transducer as an array structure to enable localized modulation in the target region. In addition, we integrated a cell culture chamber with the system to make it compatible with conventional cell-based experiments, such as in vitro cell cultures and brain slices. In this work, we successfully demonstrated the functionality of the system by showing that the number of responding cells is proportional to the acoustic intensity of the applied ultrasound. We also demonstrated localized stimulation capability with high spatial resolution by conducting experiments in which cocultured cells responded only around a working transducer.

Redox Additive-Improved Electrochemically and Structurally Robust Binder-Free Nickel Pyrophosphate Nanorods as Superior Cathode for Hybrid Supercapacitors.

For several decades, one of the great challenges for constructing a high-energy supercapacitor has been designing electrode materials with high performance. Herein, we report for the first time to our knowledge a novel hybrid supercapacitor composed of battery-type nickel pyrophosphate one-dimensional (1D) nanorods and capacitive-type N-doped reduced graphene oxide as the cathode and anode, respectively, in an aqueous redox-added electrolyte. More importantly, ex situ microscopic images of the nickel pyrophosphate 1D nanorods revealed that the presence of the battery-type redox additive enhanced the charge storage capacity and cycling life as a result of the microstructure stability. The nickel pyrophosphate 1D nanorods exhibited their maximum specific capacitance (8120 mF cm-2 at 5 mV s-1) and energy density (0.22 mWh cm-2 at a power density of 1.375 mW cm-2) in 1 M KOH + 75 mg K3[Fe(CN)6] electrolyte. On the other side, the N-doped reduced graphene oxide delivered an excellent electrochemical performance, demonstrating that it was an appropriate anode. A hybrid supercapacitor showed a high specific capacitance (224 F g-1 at a current density of 1 A g-1) and high energy density (70 Wh kg-1 at a power density of 750 W kg-1), as well as a long cycle life (a Coulombic efficiency of 96% over 5000 cycles), which was a higher performance than most of those in recent reports. Our results suggested that the materials and redox additive in this novel design hold great promise for potential applications in a next-generation hybrid supercapacitor.

Radio frequency based label-free detection of glucose.

We investigated the frequency based mediator-free glucose sensor in the radio-frequency (RF) range. Frequency dependent power signal showed clear dependence on the glucose concentration with free enzymatic condition. Also, the passive electrical components such as the resistance, inductance, shunt conductance, and capacitance were extracted based on the transmission line model for further analysis. These various parameters proposed by the signal processing provided more effective verification for instant multi-components in-situ readings without any added supporters. Additionally the residual signal (RS), impedance (Z), and propagation constant (γ) were also calculated from measured S-parameters for glucose analysis. These parameters basically showed amplitude variation and interestingly, some parameters such as inductance and impedance showed frequency shift of resonance dip. The results support that the frequency based sensing technique including the parameter based analysis can enable effective multi-dimensional detection of glucose. Moreover, this technique showed that glucose sensing is also possible over a diabetic patient's serum.

Controlling the luminescence emission from palladium grafted graphene oxide thin films via reduction.

The role of palladium (Pd) in the reduction of graphene oxide (GO) thin films was investigated using a Pd assisted grafting technique. The structural and optical characteristics of these thin films were obtained from various spectroscopic analyses, which confirmed increased C[double bond, length as m-dash]C-C aromatic ring vibration and oxidation of Pd with Ar annealing. In Pd free GO, annealing of films resulted in restoration of sp(2) clusters; however, Pd grafting with non-annealed film enhanced the possibility of restoration and further annealing dramatically increased the restoration rate with enhanced blue photoluminescence (PL) emission. The blue PL emission originates from sp(2) cluster sites and the yellow-green PL from defect trapped states. As reduction of GO increased, yellow-green emission decreased and blue PL became the prominent emission. These experimental findings open up a new feasible pathway for controlling the luminescence emission from graphene oxide that furthers the technological advancement of graphene based optoelectronic devices.