Silicon Probe Research Articles

AFM observation of Si-HPMC hydrogel cross-linking

Event Abstract Back to Event AFM observation of Si-HPMC hydrogel cross-linking Fabienne Jordana1, 2, 3, Hassan Saadaoui4, 5, Khalid Khairoun1, Jean-Marc Olive6 and Pierre Weiss1, 2, 3 1 INSERM, LIOAD, U S 791 INSERM, France 2 University of Nantes, Faculty of Dentistry, France 3 CHU of Nantes, France 4 CNRS, Paul Pascal Research Center (CRPP), UPR 8641, France 5 University of Bordeaux, France 6 CNRS, I2M, UMR 5295, France Introduction: Silated hydroxypropylmethylcellulose (Si-HPMC) is an injectable and self-setting hydrogel used as a three-dimensional synthetic matrix for tissue engineering. Si-HPMC is a gel based on a derivate from HPMC, a cellulose derivative polymer. This biocompatible polysaccharide forms a covalently crosslinked hydrogel due to silanol condensation[1]-[3]. Materials and Methods: A thin layer of Si-HPMC hydrogel disks was transferred to a freshly cleaved mica surface. The Si-HPMC hydrogel was applied to the top surface of the mica. Images of Si-HPMC hydrogel were obtained by atomic force microscopy (AFM) (Bruker© Icon, 2010). During 24 hours, Si-HPMC hydrogel surface was observed. The thin hydrogel layer adhering to the mica surface was scanned with the AFM operating in tapping mode using an etched single crystal silicon probe. The drive frequency, amplitude, gains, and amplitude set point ratio were adjusted to give height and phase images with the clearest image details. AFM (height and phase shift) images analysis and examination in Fourier transformed operation mode were performed with the software NanoScope Analysis 1.30 (Bruker Corporation©, 2011). Results and Discussion: Polymerization and cross-linking of the polymer begin in the first seconds and continue during the whole time of observation. Height and phase shift images reflect the surface topography and relative mechanical responses of the sample, respectively. Images demonstrated a network-like structure with pores. The gels consisted of branched structures where the branch points may be interpreted as points where junctions between silanol cross-linked chains occur. The nanosized pore range from approximately 10-20 nm. Some of the pores were interconnected. Surface topography and relative mechanical responses regularly changes over time (fig. 1 and fig. 2). Fig. 1: AFM phase image of Si-HPMC hydrogel layer, after 30 minutes of AFM scanning. Scale is 1µm. Fig. 2: AFM phase image of Si-HPMC hydrogel layer, after 7 hours of AFM scanning. Scale is 1µm. The network becomes more complex with time. Examination of AFM images, in Fourier transformed operation mode of tapping mode-AFM, revealed that Si-HPMC hydrogel is characterized by an isotropic structure. Conclusion: These images revealed for the first time how the network is organized within Si-HPMC hydrogel and demonstrated that Si-HPMC hydrogel is characterized by an isotropic structure.

Direct Drive Simulation - Sound-Simulation of the Vibrant Soundbridge®

The Direct-Drive-Simulation (DDS) tends to simulate the sound quality of hearing with the active middle ear implant Vibrant Soundbridge(®) (VSB). Up to now a scientific evaluation of the validity is missing. Furthermore, the test procedure has not been described yet. Aim of this study was to evaluate the test validity and to describe the test realization in detail. 10 patients evaluated their sound impression on scales from 1 to 10 concerning sound quality during DDS, postoperative free field testing at least 3 month after the first fitting of the VSB and in the everyday life situation. 3 patients were implanted bilaterally. Together, 36 data sets could be analyzed. Coupling of the Floating Mass Transducer (FMT), which was placed inside of a silicone probe during DDS was successful in all cases. In 11 out of 13 cases the coupling quality was judged as "good" an only in 2 cases as "medium". None of the patients needed local anesthesia. Comparing the evaluation of the sound impression during DDS preoperatively, and with the implanted VSB in free field testing and in everyday life no significant differences were found. The DDS offers the possibility of a realistic preoperative sound simulation of the "VSB-hearing" in case of sensorineural hearing loss. Thus, the test is supposed to facilitate the patient's decision towards possible treatment options. The specialist gets additional information regarding the indication especially when audiologic indication criteria are critical. The DDS should be a basic part of the preoperative diagnostic prior to VSB-implantation.

Distance dependence of atomic-resolution near-field imaging on α-Al2O3 (0001) surface with respect to surface photovoltage of silicon probe tip

Recently, we achieved atomic-resolution optical imaging with near-field scanning optical microscopy using photon-induced force detection. In this technique, the surface photovoltage of the silicon-tip apex induced by the optical near field on the surface is measured as the electrostatic force. We demonstrated atomicresolution imaging of the near field on the α-Al2O3 (0001) surface of a prism. We investigated the spatial distribution of the near field by scanning at different tip-sample distances and found that the atomic corrugation of the near-field signal was observed at greater distances than that of the atomic force microscopy signal. As the tip-sample distance increased, the normalized signal-to-noise ratio of the near field is in a gradual decline almost twice that of the frequency shift (Δf).

Single-crystal diamond pyramids: synthesis and application for atomic force microscopy

Here we present the results of investigations aimed at the development and testing of robust, chemically inert single-crystal diamond probes for atomic force microscopy (AFM). The probes were prepared by assembling common silicon probes with micrometer-sized pyramid- shaped single-crystal diamonds (SCD). The SCD were obtained by the selective thermal oxi- dation of the polycrystalline films grown by chemical vapor deposition. Electrostatic spray of adhesive coating onto silicon probes was used to attach individual SCD. Geometrical parameters of produced AFM SCD probes were revealed with transmission electron microscopy: the apex angle of the pyramidal diamond crystallite was ∼10 deg, and the curvature radius at the apex was ∼2 to 10 nm. The diamond AFM probes were used for surface imaging of deoxyribonucleic acid deposited on graphite substrate. Obtained results demonstrate high efficiency of the dia- mond AFM probes, allowing improvement of the image quality compared to standard silicon probes. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.10

Evolution of temporal and spectral dynamics of pathologic high-frequency oscillations (pHFOs) during epileptogenesis.

In temporal lobe epilepsy (TLE), pathologic high frequency oscillations (pHFOs, 200-600 Hz) are present in the hippocampus, especially the dentate gyrus (DG). The pHFOs emerge during a latent period prior to the onset of spontaneous generalized seizures. We used a unilateral suprahippocampal injection of kainic acid (KA) mouse model of TLE to characterize the properties of hippocampal pHFOs during epileptogenesis. In awake head-fixed mice, 4-14 days after KA-induced status epilepticus (SE), we recorded local field potentials (LFPs) with 64-channel silicon probes spanning from CA1 alveus to the DG hilus, or with glass pipettes in the DC mode in the CA1 str radiatum. The pHFOs, are observed simultaneously in the CA1 and the DG, or in the DG alone, as early as 4 days post-SE. The pHFOs ride on top of DC deflections, occur during motionless periods, persist through the onset of TLE, and are generated in bursts. Burst parameters remain remarkably constant during epileptogenesis, with a random number of pHFOs generated per burst. In contrast, pHFO duration and spectral dynamics evolve from short events at 4 days post-SE to prolonged discharges with complex spectral characteristics by 14 days post-SE. Simultaneous dural EEG recordings were exceedingly unreliable for detecting hippocampal pHFOs; therefore, such recordings may deceptively indicate a "silent" period even when massive hippocampal activity is present. Our results demonstrate that hippocampal pHFOs exhibit a dynamic evolution during the epileptogenic period following SE, consistent with their role in transitioning to the chronic stage of TLE.

Neuronal network activity in the hippocampus of tau transgenic (Tg4510) mice

Development of neurofibrillary tangles in Alzheimer's disease correlates with neuronal loss and dementia. Transgenic Tg4510 mice model the tauopathy of the disease, with these mice exhibiting progressive, region-specific neuronal loss, and behavioral deficits. In the present study, neuronal network activity in the hippocampus of 7-month-old Tg4510 mice was investigated and compared with age-matched wild-type (WT) mice. Multisite field potentials were recorded using 16-site silicon probes, inserted across the hippocampus in urethane anesthetized mice. The hippocampal network theta oscillation was evaluated in these mice by stimulating the brainstem nucleus pontis oralis. Subsequently, population spikes in the dentate gyrus were identified in response to perforant path stimulation, and long-term potentiation was elicited by theta burst stimulation. Tg4510 mice showed dramatically reduced dentate gyrus population spike amplitude; however, the magnitude of theta burst stimulation-induced long-term potentiation was identical in WT and transgenic mice. WT and Tg4510 mice showed identical increase in frequency to nucleus pontis oralis stimulation, whereas absolute theta power was severely reduced in the Tg4510 animals. Because total signal power over the entire frequency band range was reduced, there was no difference in relative theta power between WT and Tg4510 mice. These presently described electrophysiological findings can be directly attributed to the drastic reduction of pyramidal/granule neurons in Tg4510 mice, which could be the main contributing factor to their impaired behavior and cognitive function. However, the remaining synapses and neuronal circuitry seem to function properly in these assays.

Three-dimensional macroporous nanoelectronic networks as minimally invasive brain probes.

Direct electrical recording and stimulation of neural activity using micro-fabricated silicon and metal micro-wire probes have contributed extensively to basic neuroscience and therapeutic applications; however, the dimensional and mechanical mismatch of these probes with the brain tissue limits their stability in chronic implants and decreases the neuron-device contact. Here, we demonstrate the realization of a three-dimensional macroporous nanoelectronic brain probe that combines ultra-flexibility and subcellular feature sizes to overcome these limitations. Built-in strains controlling the local geometry of the macroporous devices are designed to optimize the neuron/probe interface and to promote integration with the brain tissue while introducing minimal mechanical perturbation. The ultra-flexible probes were implanted frozen into rodent brains and used to record multiplexed local field potentials and single-unit action potentials from the somatosensory cortex. Significantly, histology analysis revealed filling-in of neural tissue through the macroporous network and attractive neuron-probe interactions, consistent with long-term biocompatibility of the device.

Development of Silicon Probe With Acute Study on <italic>In Vivo</italic> Neural Recording and Implantation Behavior Monitored by Integrated Si-Nanowire Strain Sensors

The silicon probe with highly P-doped Si electrodes was realized on 8-in Silicon on insulator wafer through standard Complementary metal-oxide semiconductor process. By leveraging the same thin Si device layer ( $\sim 100$ nm), the built-in piezoresistive Si-nanowires (SiNWs) configured in full-bridge structure were also equipped along the probe shank for strain sensing. After additional coatings of nanocomposite (Carbon nanotubes + Au nanoparticles) on silicon electrodes, the functionality of neural recording was validated with a low noise level ( $ ) during in vivo neural recording on rat brain (CA1 region). The additional capability of monitoring probe mechanical behavior was first verified through the probe buckling experiments and further examined with implantations on rat brain (S1 region). Besides the large buckling mechanics, the physiological brain micromotion (e.g., caused by respiration) was successfully picked up by integrated SiNWs strain sensors, which would provide the research platform to practically understand the correlation between the electrical neural signal and the brain micromotion. [2014-0370]

Efficient population coding of naturalistic whisker motion in the ventro-posterior medial thalamus based on precise spike timing

The rodent whisker-associated thalamic nucleus (VPM) contains a somatotopic map where whisker representation is divided into distinct neuronal sub-populations, called “barreloids”. Each barreloid projects to its associated cortical barrel column and so forms a gateway for incoming sensory stimuli to the barrel cortex. We aimed to determine how the population of neurons within one barreloid encodes naturalistic whisker motion. In rats, we recorded the extracellular activity of up to nine single neurons within a single barreloid, by implanting silicon probes parallel to the longitudinal axis of the barreloids. We found that play-back of texture-induced whisker motion evoked sparse responses, timed with millisecond precision. At the population level, there was synchronous activity: however, different subsets of neurons were synchronously active at different times. Mutual information between population responses and whisker motion increased near linearly with population size. When normalized to factor out firing rate differences, we found that texture was encoded with greater informational-efficiency than white noise. These results indicate that, within each VPM barreloid, there is a rich and efficient population code for naturalistic whisker motion based on precisely timed, population spike patterns.

Three-dimensional space representation by echolocation in bats

Echolocating bats are equipped with a biological sonar system that permits spatial navigation and target tracking in complete darkness. By actively controlling the directional aim, timing, frequency content, and duration of echolocation signals to “illuminate” the environment, the bat directly influences the acoustic input available to its sonar imaging system. Detailed analyses of the bat’s sonar behavior suggest that the animal’s actions play into a rich 3-D representation of the environment, which then guides motor commands for subsequent call production, head aim, and flight control in an adaptive feedback system. Studies of the bat’s sonar behavior have motivated neurophysiological studies of the midbrain superior colliculus (SC), a structure implicated in sensorimotor integration and spatial orientation. Using multichannel silicon probe recordings from the freely echolocating big brown bat, we characterized response profiles of single neurons, as the animal tracked moving targets from a stationary position on a platform and in free flight. Our data show premotor activity prior to sonar vocalizations and responses to echoes from objects. Echo responses depended on both the azimuth and delay of sonar returns. These findings demonstrate both auditory and premotor specializations in the bat SC, which contribute to the animal’s 3-D representation of space.

Two-step sharpening process for silicon probe in quartz-based atomic force microscopy sensor

A two-step sharpening process for a Si pillar in a quartz tuning fork sensor was developed for use in frequency modulation atomic force microscopy (FM-AFM). By combining electrochemical etching in HF solution and anisotropic etching in KOH solution, the tip radius was decreased to 120 nm. The Si-probe-attached sensor showed a higher resonance frequency than a tungsten-probe attached sensor, which would lead to a higher force sensitivity. We demonstrated FM-AFM imaging on a cleaved mica surface in aqueous solution by using the fabricated sensor, and atomic resolution was successfully achieved.

Status Epilepticus Induced Spontaneous Dentate Gyrus Spikes: In Vivo Current Source Density Analysis.

The dentate gyrus is considered to function as an inhibitory gate limiting excitatory input to the hippocampus. Following status epilepticus (SE), this gating function is reduced and granule cells become hyper-excitable. Dentate spikes (DS) are large amplitude potentials observed in the dentate gyrus (DG) of normal animals. DS are associated with membrane depolarization of granule cells, increased activity of hilar interneurons and suppression of CA3 and CA1 pyramidal cell firing. Therefore, DS could act as an anti-excitatory mechanism. Because of the altered gating function of the dentate gyrus following SE, we sought to investigate how DS are affected following pilocarpine-induced SE. Two weeks following lithium-pilocarpine SE induction, hippocampal EEG was recorded in male Sprague-Dawley rats with 16-channel silicon probes under urethane anesthesia. Probes were placed dorso-ventrally to encompass either CA1-CA3 or CA1-DG layers. Large amplitude spikes were detected from EEG recordings and subject to current source density analysis. Probe placement was verified histologically to evaluate the anatomical localization of current sinks and the origin of DS. In 9 of 11 pilocarpine-treated animals and two controls, DS were confirmed with large current sinks in the molecular layer of the dentate gyrus. DS frequency was significantly increased in pilocarpine-treated animals compared to controls. Additionally, in pilocarpine-treated animals, DS displayed current sinks in the outer, middle and/or inner molecular layers. However, there was no difference in the frequency of events when comparing between layers. This suggests that following SE, DS can be generated by input from medial and lateral entorhinal cortex, or within the dentate gyrus. DS were associated with an increase in multiunit activity in the granule cell layer, but no change in CA1. These results suggest that following SE there is an increase in DS activity, potentially arising from hyperexcitability along the hippocampal-entorhinal pathway or within the dentate gyrus itself.

Cell type- and activity-dependent extracellular correlates of intracellular spiking.

Despite decades of extracellular action potential (EAP) recordings monitoring brain activity, the biophysical origin and inherent variability of these signals remain enigmatic. We performed whole cell patch recordings of excitatory and inhibitory neurons in rat somatosensory cortex slice while positioning a silicon probe in their vicinity to concurrently record intra- and extracellular voltages for spike frequencies under 20 Hz. We characterize biophysical events and properties (intracellular spiking, extracellular resistivity, temporal jitter, etc.) related to EAP recordings at the single-neuron level in a layer-specific manner. Notably, EAP amplitude was found to decay as the inverse of distance between the soma and the recording electrode with similar (but not identical) resistivity across layers. Furthermore, we assessed a number of EAP features and their variability with spike activity: amplitude (but not temporal) features varied substantially (∼ 30-50% compared with mean) and nonmonotonically as a function of spike frequency and spike order. Such EAP variation only partly reflects intracellular somatic spike variability and points to the plethora of processes contributing to the EAP. Also, we show that the shape of the EAP waveform is qualitatively similar to the negative of the temporal derivative to the intracellular somatic voltage, as expected from theory. Finally, we tested to what extent EAPs can impact the lowpass-filtered part of extracellular recordings, the local field potential (LFP), typically associated with synaptic activity. We found that spiking of excitatory neurons can significantly impact the LFP at frequencies as low as 20 Hz. Our results question the common assertion that the LFP acts as proxy for synaptic activity.

Atomic-Resolution Imaging of the Optical Near Field Based on the Surface Photovoltage of a Silicon Probe Tip

Atomic-Resolution Imaging of the Optical Near Field Based on the Surface Photovoltage of a Silicon Probe Tip

Long-range intralaminar noise correlations in the barrel cortex.

Identifying the properties of correlations in the firing of neocortical neurons is central to our understanding of cortical information processing. It has been generally assumed, by virtue of the columnar organization of the neocortex, that the firing of neurons residing in a certain vertical domain is highly correlated. On the other hand, firing correlations between neurons steeply decline with horizontal distance. Technical difficulties in sampling neurons with sufficient spatial information have precluded the critical evaluation of these notions. We used 128-channel "silicon probes" to examine the spike-count noise correlations during spontaneous activity between multiple neurons with identified laminar position and over large horizontal distances in the anesthetized rat barrel cortex. Eigen decomposition of correlation coefficient matrices revealed that the laminar position of a neuron is a significant determinant of these correlations, such that the fluctuations of layer 5B/6 neurons are in opposite direction to those of layers 5A and 4. Moreover, we found that within each experiment, the distribution of horizontal, intralaminar spike-count correlation coefficients, up to a distance of ∼1.5 mm, is practically identical to the distribution of vertical correlations. Taken together, these data reveal that the neuron's laminar position crucially affects its role in cortical processing. Moreover, our analyses reveal that this laminar effect extends over several functional columns. We propose that within the cortex the influence of the horizontal elements exists in a dynamic balance with the influence of the vertical domain and this balance is modulated with brain states to shape the network's behavior.

Formation of wear-resistant coatings on silicon probes for atomic force microscopy by thermal vacuum evaporation

The possibility has been shown to modify silicon probes for atomic force microscopes by thin wear-resistant carbide coatings, which leads to the improvements of their operating properties (decreases the probability of appearing artifacts of scanning by 20–22% and increases the probes service life by 45–55%). Optimal conditions for the deposition of such coatings by thermal evaporation in a vacuum with a subsequent low-energy electron-beam microprocessing have been proposed. The quality of deposited coatings has been checked and the tests showed a decrease of the probe surface subroughness by a factor of 15–25 and increase of the microhardness and wear resistance of coatings by a factor of 1.1–1.35.

Hippocampal neuro-networks and dendritic spine perturbations in epileptogenesis are attenuated by neuroprotectin d1.

PurposeLimbic epileptogenesis triggers molecular and cellular events that foster the establishment of aberrant neuronal networks that, in turn, contribute to temporal lobe epilepsy (TLE). Here we have examined hippocampal neuronal network activities in the pilocarpine post-status epilepticus model of limbic epileptogenesis and asked whether or not the docosahexaenoic acid (DHA)-derived lipid mediator, neuroprotectin D1 (NPD1), modulates epileptogenesis.MethodsStatus epilepticus (SE) was induced by intraperitoneal administration of pilocarpine in adult male C57BL/6 mice. To evaluate simultaneous hippocampal neuronal networks, local field potentials were recorded from multi-microelectrode arrays (silicon probe) chronically implanted in the dorsal hippocampus. NPD1 (570 μg/kg) or vehicle was administered intraperitoneally daily for five consecutive days 24 hours after termination of SE. Seizures and epileptiform activity were analyzed in freely-moving control and treated mice during epileptogenesis and epileptic periods. Then hippocampal dendritic spines were evaluated using Golgi-staining.ResultsWe found brief spontaneous microepileptiform activity with high amplitudes in the CA1 pyramidal and stratum radiatum in epileptogenesis. These aberrant activities were attenuated following systemic NPD1 administration, with concomitant hippocampal dendritic spine protection. Moreover, NPD1 treatment led to a reduction in spontaneous recurrent seizures.ConclusionsOur results indicate that NPD1 displays neuroprotective bioactivity on the hippocampal neuronal network ensemble that mediates aberrant circuit activity during epileptogenesis. Insight into the molecular signaling mediated by neuroprotective bioactivity of NPD1 on neuronal network dysfunction may contribute to the development of anti-epileptogenic therapeutic strategies.

半導体検査用片持ち梁型シリコンプローブの三次元配線プロセス

A fabricating method of three-dimensional wirings on a cantilever-type silicon probe has been developed for a semiconductor testing. The cantilever-type silicon probe consists of probe-tips, cantilevers, apertures and three-dimensional wirings. The wiring is connected from probe-tip to back-side electrode via cantilever edge, cantilever backside and aperture side-wall. The problem of the cantilever-type silicon probe is that breakings of wiring occur at the cantilever edge and the aperture edge. The shapes of the cantilever edge and the aperture edge are optimized by applying a compensation mask and a roof-removal mask, respectively. We fabricate the cantilever-type silicon probe without breaking of wiring in 1216 pins, and confirm to be able to contact aluminum electrodes on the semiconductor.

Fluorescent porous silicon biological probes with high quantum efficiency and stability.

We demonstrate porous silicon biological probes as a stable and non-toxic alternative to organic dyes or cadmium-containing quantum dots for imaging and sensing applications. The fluorescent silicon quantum dots which are embedded on the porous silicon surface are passivated with carboxyl-terminated ligands through stable Si-C covalent bonds. The porous silicon bio-probes have shown photoluminescence quantum yield around 50% under near-UV excitation, with high photochemical and thermal stability. The bio-probes can be efficiently conjugated with antibodies, which is confirmed by a standard enzyme-linked immunosorbent assay (ELISA) method.

Quantitative electrostatic force microscopy with sharp silicon tips

Electrostatic force microscopy (EFM) probes are typically coated in either metal (radius ∼ 30 nm) or highly-doped diamond (radius ∼ 100 nm). Highly-doped silicon probes, which offer a sharpened and stable tip apex (radius ∼ 1–10 nm) and are usually used only in standard atomic force microscopy, have been recently shown to allow enhanced lateral resolution in quantitative EFM and its application for dielectric constant measurement. Here we present the theoretical modelling required to quantitatively interpret the electrostatic force between these sharpened tips and samples. In contrast to a sphere-capped cone geometry used to describe metal/diamond-coated tips, modelling a sharpened silicon tip requires a geometry comprised of a cone with two different angles. Theoretical results are supported by experimental measurements of metallic substrates and ∼10 nm radius dielectric nanoparticles. This work is equally applicable to EFM and other electrical scanned probe techniques, where it allows quantifying electrical properties of nanomaterials and 3D nano-objects with higher resolution.