Microelectrodes provide a direct pathway to investigate brain activities electrically from the external world, which has advanced our fundamental understanding of brain functions and has been utilized for rehabilitative applications as brain-machine interfaces. However, minimizing the tissue response and prolonging the functional durations of these devices remain challenging. Therefore, the development of next-generation microelectrodes as neural interfaces is actively progressing from traditional inorganic materials toward biocompatible and functional organic materials with a miniature footprint, good flexibility, and reasonable robustness. In this study, we developed a miniaturized all polymer-based neural probe with carbon nanofiber (CNF) composites as recording electrodes via the scalable thermal drawing process. We demonstrated that in situ CNF unidirectional alignment can be achieved during the thermal drawing, which contributes to a drastic improvement of electrical conductivity by 2 orders of magnitude compared to a conventional polymer electrode, while still maintaining the mechanical compliance with brain tissues. The resulting neural probe has a miniature footprint, including a recording site with a reduced size comparable to a single neuron and maintained impedance that was able to capture neural activities. Its stable functionality as a chronic implant has been demonstrated with the long-term reliable electrophysiological recording with single-spike resolution and the minimal tissue response over the extended period of implantation in wild-type mice. Technology developed here can be applied to basic chronic electrophysiological studies as well as clinical implementation for neuro-rehabilitative applications.

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We studied kinetic roughening of copper which was electrodeposited at slow rates. The surfaces showed a unique scaling. In the shorter length regime, the interface width scaled with the length scale L as L (u = 0.87~0.05). In the longer length regime, the width scaled with the deposition time t as t~( P = 0.45~0.05). The value of a + a/P, 2.8, is much larger than 2 predicted for the case where the growing direction is normal to the surface everywhere.The scaling behavior is interpreted as the result of enhanced growth of the protrusions owing to nonlocal Laplacian growth effect. PACS numbers: 68.55.Jk, 05.70.Ln, 68.70.+w, 82.65.Dp Surface roughness of growing films on Aat substrates has been shown to exhibit scaling behavior over large variations of length scales, and thus considerable interest [1,2] has been recently directed to the physics of dynamic scaling. Theory [1,3) predicts that the interface width (the mean surface height fluctuation) W(L, t) for length scale L and growth time t scales as W(L, t)~L, for L (( L, ,Z = cr/P. (4) The scaling behavior is equivalent to scale invariance of the surface height deviation from the average plane at point x and t, h(x, t): The statistical properties of h(x, t) coincides with those of b h(bx, b't), where b is an arbitrary rescaling factor [2].In many growth processes, growth is determined solely by the local conditions at the growing site such as reaction rates, surface relaxation rates, and stochastic noise. Kardar, Parisi, and Zhang (KPZ) [3] studied such growing surfaces based on a nonlinear Langevin continuum equation using renormalization-group techniques. The ballistic deposition model [4, 5] and Eden growth model [6] are believed to belong to the same universality class as the KPZ growth, and many theoretical and numerical simulation studies have been done [1,2]. For the KPZ type local growth model, the value of a is predicted to be 0.4 (Ref. [2]) for a planar substrate and the surface is compact and self-affine. On the other hand, in a nonlocal growth process called Laplacian growth, the motion of the growing interface is controlled by a fieldlike quantity (e.g., concentration of a diffusing particle and electric potential) which satisfies the Laplace equation. In this case, deposition occurs preferentially on protrusions. This causes an instability, known as the Mullins-Sekerka instability [7], which can often lead to much rougher bulk-fractal (self-similar) structures where a -1. Surface growth in physical systems is likely to have both local and nonlocal growth effects.Electrochemical deposition is an ideal system for studying the competition between these growth processes because the local and the nonlocal growth effects can be controlled by changing the growth conditions [8,9]. Deposition near the mass-transfer-limited current condition [10] corresponds to diffusion limited growth and leads to unstable morphologies such as fractal and densebranching morphologies, which have been studied extensively [9, 11, 12]. At slow growth rates, the growth is control...

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A light-addressable potentiometric sensor (LAPS) is a semiconductor-based chemical sensor, in which a measurement site on the sensing surface is defined by illumination. This light addressability can be applied to visualize the spatial distribution of pH or the concentration of a specific chemical species, with potential applications in the fields of chemistry, materials science, biology, and medicine. In this review, the features of this chemical imaging sensor technology are compared with those of other technologies. Instrumentation, principles of operation, and various measurement modes of chemical imaging sensor systems are described. The review discusses and summarizes state-of-the-art technologies, especially with regard to the spatial resolution and measurement speed; for example, a high spatial resolution in a submicron range and a readout speed in the range of several tens of thousands of pixels per second have been achieved with the LAPS. The possibility of combining this technology with microfluidic devices and other potential future developments are discussed.

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