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ABSTRACT: In this paper we describe the status of a silicon-based microelectrode for neural recording and an advanced neural interface.
We have developed a silicon neural probe, using a combination of plasma and wet etching techniques. This process enables the
probe thickness to be controlled precisely. To enhance the CMOS compatibility in the fabrication process, we investigated
the feasibility of the site material of the doped polycrystalline silicon with small grains of around 50 nm in size. This
silicon electrode demonstrated a favorable performance with respect to impedance spectra, surface topography and acute neural
recording. These results showed that the silicon neural probe can be used as an advanced microelectrode for neurological applications.
Biotechnology and Bioprocess Engineering 04/2012; 8(4):252-256. · 1.28 Impact Factor
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ABSTRACT: We demonstrate a highly sensitive THz molecular imaging (TMI) technique involving differential modulation of surface plasmons induced on nanoparticles and obtain target specific in vivo images of cancers. This technique can detect quantities of gold nanoparticles as small as 15 µM in vivo. A comparison of TMI images with near infrared absorption images shows the superior sensitivity of TMI. Furthermore, the quantification property of TMI is excellent, being linearly proportional to the concentration of nanoparticles. The target specificity issue is also addressed at the ex vivo and cell levels. The high thermal sensitivity of TMI can help extend photonic-based photothermal molecular imaging researches from the in vitro level to the in vivo level. The TMI technique can be used for monitoring drug delivery processes and for early cancer diagnosis.
Optics Express 02/2011; 19(5):4009-16. · 3.59 Impact Factor
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ABSTRACT: A retrospective study of clinical results of operative treatment for degenerative lumbar scoliosis.
To determine the risk factors of sagittal decompensation after long instrumentation and fusion to L5 or S1.
Little is known about the risk factors for sagittal decompensation, which was defined in this study as sagittal C7 plumb falling anterior >8 cm from the posterosuperior corner of the sacrum.
Forty-five patients (mean age: 64.4 year) with adult degenerative lumbar scoliosis were reviewed retrospectively with a minimum 2 years. The mean number of levels fused was 6.1 +/- 1.6 segments. The upper instrumented vertebra ranged from T9 to L2. The lower instrumented vertebra was L5 and S1 in 24 and 21 patients, respectively.
Sagittal decompensation (SD) developed in 19 patients. The most significant risk factors of SD were preoperative sagittal imbalance and high pelvic incidence. The preoperative sagittal C7 plumb was more positive (67.9 mm) in the decompensation group than in the balance group (37.0 mm) (P = 0.002). There was a significant difference in pelvic incidence between 61.7 degrees in the decompensation and 54.9 degrees in the balance group (P = 0.01). The preoperative lumbar lordosis was hypolordotic in the decompensation group, however, it was not found to be a risk factor. Pseudarthrosis was identified at the lumbosacral junction in 5 patients, and 4 of them (80%) had SD. SD developed in 55% of patients who had loosening of the distal screws and 50% of patients with hypolordotic lumbar fusion. Distal adjacent segment disease was more likely to cause SD than proximal adjacent segment disease.
Sagittal decompensation is common after long posterior instrumentation and fusion for degenerative lumbar scoliosis. It is mostly associated with complications at the distal segments, including pseudarthrosis and implant failure at the lumbosacral junction. Restoration of optimal lumbar lordosis and secure lumbosacral fixation is necessary especially in patients with preoperative sagittal imbalance and high pelvic incidence in order to prevent sagittal decompensation after surgery.
Spine 04/2010; 35(17):1595-601. · 2.08 Impact Factor
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ABSTRACT: In this study, we measured the conformational-state-dependent power absorptions, refractive indices and dielectric constants of beta-glucans in laminarin, and the two states, SSH and TSH, of beta-glucans were compared.
Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe - EQEC 2009. European Conference on; 07/2009
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Advanced Materials 06/2009; 21(43):4339 - 4342. · 13.88 Impact Factor
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ABSTRACT: The penetration property of the terahertz electromagnetic (THz) wave is relevant to its use. We used the THz wave spectroscopy system which easily penetrates some materials that do not contain water, e.g., plastic and ceramics. The system has been developed for several purposes, including measuring the properties of semiconductors and bio-materials, and detecting plastic bombs and ceramic knives at airports. It is also used for medical imaging systems, such as magnetic resonance imaging (MRI), at some research institutes. It can show not only the difference in amplitude, but also the difference of the phase of each point of sample. MRI technology usually uses contrast agents to enhance the quality of the image. Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA), made with a heavy metal ion, is commonly used as a clinical MRI contrast agent. Gadolinium oxide (Gd{sub 2}O{sub 3}) nanoparticle is a new contrast agent. It serves to equip the core of each particle with antibodies or ligands. It can freely circulate in blood vessels without amassing in the liver or lungs. This study shows the characteristics of gadolinium oxide nanoparticles to further advance terahertz medical imaging.
AIP Conference Proceedings 04/2009; 1119(1).
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ABSTRACT: This paper demonstrates the principle of the nanoparticle-contrast-agent-enabled terahertz imaging (CATHI) technique, which yields a dramatic sensitivity of the differential signal from cancer cells with nanoparticles. The terahertz (THz) reflection signal increased beam by 20% in the cancer cells with nanoparticles of gold nano-rods (GNRs) upon their irradiation with a infrared (IR) laser, due to the temperature rise of water in cancer cells by surface plasma ploritons. In the differential mode, the THz signal from the cancer cells with GNRs was 30 times higher than that from the cancer cells without GNRs. As the high sensitivity is achieved by the surface plasmon resonance through IR laser irradiation, the resolution of the CATHI technique can be as good as a few microns and THz endoscopy becomes more feasible.
Optics Express 04/2009; 17(5):3469-75. · 3.59 Impact Factor
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ABSTRACT: We measured the binding-state-dependent power absorptions, refractive indices, and dielectric constants of triple-stranded helices (TSHs) and single-stranded helices (SSHs) β-glucans in laminarin using terahertz time-domain spectroscopy (TDS). The SSH β-glucan was obtained from a TSH β-glucan laminarin by a chemical treatment with NaOH solution. The power absorption of TSH β-glucan increased more rapidly than that of the SSH β-glucan with the frequency increment. The refractive index and dielectric constants of TSH β-glucan were also larger than those of the SSH β-glucan. This result implies that terahertz-TDS is a very effective method in classifying the conformational state of β-glucans.
Applied Physics Letters 03/2009; 94(11):111911-111911-3. · 3.84 Impact Factor
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ABSTRACT: We measured the optical constants of aqueous biomaterial mixtures with various electrolyte concentrations using terahertz time-domain spectroscopy. The mixtures were divided into water and other electrolyte parts in mass fractions for analysis. The optical constants of the electrolyte, excluding water, were obtained by applying the ideal mixture equation, and the power absorption of the electrolyte was observed to be larger than that of water above 1 THz. Data from the measurement were fitted with the modified double Debye model, and the reorientation and hydrogen-bond formation decomposition times were found to decrease as the electrolyte concentration increased.
Journal of Applied Physics 10/2007; 102(7):074702-074702-5. · 2.17 Impact Factor
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ABSTRACT: The authors investigated the carrier dynamics of n-type modulation-doped InAs/GaAs quantum dots (QDs) using terahertz time-domain spectroscopy to estimate the total number of electrons captured by the QDs. The terahertz power absorption of the sample with QDs was less than that of the sample without QDs. This is attributed to the fact that the carriers are confined in the QDs. The experiment results were fitted into the Drude model and the number of electrons captured by QDs was determined through the difference in the numbers of free electrons of the samples with and without QDs.
Applied Physics Letters 03/2007; 90(13):131906-131906-3. · 3.84 Impact Factor
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ABSTRACT: The electrical and optical properties of double-walled carbon nanotubes (DWNTs) have been characterized and compared with those of single-walled carbon nanotubes (SWNTs) utilizing terahertz time-domain spectroscopy. The power absorption and the complex refractive indices of DWNTs are smaller than those of SWNTs. The conductivity of DWNTs was also observed to be smaller. The experimental results have been fitted with the Bruggman effective medium approximations, which has yielded the transport parameters of DWNTs such as plasma frequency, damping rate, etc.
Applied Physics Letters 01/2007; 90(5):051914-051914-3. · 3.84 Impact Factor
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ABSTRACT: There is a great need for silicon microelectrodes that can simultaneously monitor the activity of many neurons in the brain. However, one of the existing processes for fabricating silicon microelectrodes-reactive-ion etching in combination with anisotropic KOH etching-breaks down at the wet-etching step for device release. Here we describe a modified wet-etching sidewall-protection technique for the high-yield fabrication of well-defined silicon probe structures, using a Teflon shield and low-pressure chemical vapor deposition (LPCVD) silicon nitride. In the proposed method, a micro-tab holds each individual probe to the central scaffold, allowing uniform anisotropic KOH etching. Using this approach, we obtained a well-defined probe structure without device loss during the wet-etching process. This simple method yielded more accurate fabrication and an improved mechanical profile.
IEEE Transactions on Biomedical Engineering 03/2006; 53(2):351-4. · 2.28 Impact Factor
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ABSTRACT: The frequency-dependent optical constants and electrical conductivities of hydrogen-functionalized single-walled carbon nanotubes have been measured from the 0.2- to 1.5-THz region using a terahertz time domain spectroscopy. The indices of refraction and electrical conductivities of the sample after hydrogen functionalization were smaller than those of the sample before hydrogen functionalization. The experimental results were fitted using the Maxwell-Garnett model, and a reduction of plasma frequency was observed. This can be attributed to the fact that the hydrogen functionalization has reduced the number of free carriers with the bonding change from sp<sup>2</sup>to sp<sup>3</sup>.
Microwave Photonics, 2005. MWP 2005. International Topical Meeting on; 11/2005
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ABSTRACT: Effects of hypothermia on the afferent somatosensory transmission to the ventroposteromedial (VPM) thalamus were determined in anesthetized rats and hamsters. Hamsters showed a gradual suppression of afferent sensory transmission during cooling (to 18 degrees C) and disinhibition during subsequent warming of body temperature (Tb). However, rats exhibited steep inhibition from Tb 26 degrees C to complete absence of sensory transmission at Tb 20 degrees C and abrupt disinhibition during subsequent warming. Species difference at thalamic level was quite similar to our previous results in the primary somatosensory (SI) cortex, suggesting that changes of sensory transmission observed in the SI cortex may have already occurred at thalamic level. Differences between the cortex and the thalamus were observed only during deep hypothermia in rat and during the final period of warming in hamster. Conduction latencies of thalamocortical system of both species were not influenced during Tb lowering until 24 degrees C (equivalent to brain temperature 25-26 degrees C). These results suggest inherently different adaptability to hypothermia in processing somatosensory information between hibernator and non-hibernator, but similar sustainability of sensory functions of the thalamocortical system during hypothermia in both species.
Brain Research 05/2004; 1003(1-2):122-9. · 2.73 Impact Factor
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Journal of Materials Science Letters 12/2002; 22(2):131-133.
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ABSTRACT: Microelectrode arrays have been developed for simultaneous multi-channel recordings from nervous systems, typically using silicon substrates. However, it has been known that it is difficult to meet the biocompatibility and durability requirements using silicon and other dielectric materials (SiO2, Si3N4), due to environmental moisture and ions. Additional disadvantage of silicon being the rigid material makes it hard to apply these materials in chronic recording situations.Liquid Crystal Polymer (LCP) was recently introduced as a candidate material for electronic packaging purposes. The material acts as efficient barrier against ions and moisture, a desirable feature for a substrate material of microelectrode arrays. In this paper, we report on the neural recording performed using the LCP-based microelectrode arrays.The cell adhesion on the new material was compared very favorably with that using silicon, SiO2, or polyimide material. The microelectrode arrays were patterned with Ti (500 Å)/Au (3500 Å) on the LCP film and were employed in both stimulation and recording from rat sciatic nerve. The electrical characteristic of the recorded signal was as good as those using other substrate materials, proving this material as an excellent candidate for next generation microelectrode arrays.
Materials Science and Engineering: C.
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ABSTRACT: Insertion of prosthetic device is elicits reactive responses from both nervous tissue and vasculature that prevent successful integration of these devices. Their chronic use is limited due to glial encapsulation that electrically isolates devices from cellular networks. We examined time-dependent changes of reactive responses in neocortex, hippocampus, and thalamus using immunohistochemistry and confocal microscopy. Results show dramatic differences in the magnitude of cellular response in different brain regions and time-courses. These experiments will provide important new information for the design of improved biomaterials and nano/micro-device to control dynamic biological events in the central nervous system.
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ABSTRACT: This study characterized hydrogen-functionalized carbon nanotube films and compared their characteristics before and after they were hydrogen functionalized, using terahertz (THz) time-domain spectroscopy. Reduction of the power absorption of the samples was observed with hydrogen functionalization. To analyze the experimental results, the effective medium approximation (EMA) was adopted. Through the EMA, the effective plasma frequencies, damping rates, and other physical parameters located in the THz region were determined. In this way, decreases in the plasma frequencies and the damping rates were observed after hydrogen functionalization, which implies a decrease in the carrier density.
Phys. Rev. B. 75(8).
