High Sensitivity Recording Research Articles

Bioelectrical interfaces with cortical spheroids in three-dimensions

Objective. Three-dimensional (3D) neuronal spheroid culture serves as a powerful model system for the investigation of neurological disorders and drug discovery. The success of such a model system requires techniques that enable high-resolution functional readout across the entire spheroid. Conventional microelectrode arrays and implantable neural probes cannot monitor the electrophysiology (ephys) activity across the entire native 3D geometry of the cellular construct. Approach. Here, we demonstrate a 3D self-rolled biosensor array (3D-SR-BA) integrated with a 3D cortical spheroid culture for simultaneous in vitro ephys recording, functional Ca2+ imaging, while monitoring the effect of drugs. We have also developed a signal processing pipeline to detect neural firings with high spatiotemporal resolution from the ephys recordings based on established spike sorting methods. Main results. The 3D-SR-BAs cortical spheroid interface provides a stable, high sensitivity recording of neural action potentials (<50 µV peak-to-peak amplitude). The 3D-SR-BA is demonstrated as a potential drug screening platform through the investigation of the neural response to the excitatory neurotransmitter glutamate. Upon addition of glutamate, the neural firing rates increased notably corresponding well with the functional Ca2+ imaging. Significance. Our entire system, including the 3D-SR-BA integrated with neuronal spheroid culture, enables simultaneous ephys recording and functional Ca2+ imaging with high spatiotemporal resolution in conjunction with chemical stimulation. We demonstrate a powerful toolset for future studies of tissue development, disease progression, and drug testing and screening, especially when combined with native spheroid cultures directly extracted from humans.

Methodological improvements for fluorescence recordings in Xenopus laevis oocytes.

Xenopus laevis oocytes are a widely used model system because of their capacity to translate exogenous mRNA, but their high intrinsic background fluorescence is a disadvantage for fluorescence recordings. Here, we developed two distinct methods for improving fluorescence recordings from oocytes. One was a pharmacological method in which a small-molecule salt-inducible kinase inhibitor was co-injected with the mRNA of interest to stimulate melanin production. We interrogated the oocytes using cut-open voltage clamp with simultaneous fluorescence recording and found that by increasing the amount of light-absorbing melanin in these oocytes, we decreased their intrinsic background fluorescence. The treated oocytes produced fluorescence signals that were approximately four times larger. The second method consisted of direct injection of synthetic melanin. This method also significantly improved (doubled) fluorescence signals and allowed any oocyte to be used for fluorescence recording. These two methods provide significant improvements of the signal quality for fluorescent oocyte recordings and allow all healthy oocytes to be used for high-sensitivity recordings.

Achieving Ultra-Conformability With Polyimide-Based ECoG Arrays.

Micro-electrode arrays for electrocorticography (ECoG) represent the best compromise between invasiveness and signal quality, as they are surface devices that still allow high sensitivity recordings. In this work, an assessment of different technical aspects determining the ultimate performance of ultra-conformable polyimide-based μECoG arrays is conducted via a finite element model, impedance spectroscopy measurements and recordings of sensorimotor evoked potentials (SEPs) in rats. The finite element model proves that conformability of thin-film arrays can be achieved with polyimide, a non-stretchable material, by adjusting its thickness according to the curvature of the targeted anatomical area. From the electrochemical characterization of the devices, intrinsic thermal noise of platinum and gold electrodes is estimated to be 3-5 μV. Results show that electrode size and in vitro impedance do not influence the amplitude of the recorded SEPs. However, the use of a reference on-skull (a metal screw), as compared to reference on-array (a metal electrode surrounding the recording area), provides higher-amplitude SEPs. Additionally, the incorporation of a grounded metal shield in the thin-film devices limits crosstalk between tracks and does not compromise the recording capabilities of the arrays.

CRDS with a VECSEL for broad-band high sensitivity spectroscopy in the 2.3 μm window.

The integration of an industry ready packaged Sb-based Vertical-External-Cavity Surface-Emitting-Laser (VECSEL) into a Cavity Ring Down Spectrometer (CRDS) is presented. The instrument operates in the important 2.3 μm atmospheric transparency window and provides a high sensitivity (minimum detectable absorption of 9 × 10(-11) cm(-1)) over a wide spectra range. The VECSEL performances combine a large continuous tunability over 120 cm(-1) around 4300 cm(-1) together with a powerful (∼5 mW) TEM00 diffraction limited beam and linewidth at MHz level (for 1 ms of integration time). The achieved performances are illustrated by high sensitivity recordings of the very weak absorption spectrum of water vapor in the region. The developed method gives potential access to the 2-2.7 μm range for CRDS.

Monitoring Population Membrane Potential Signals from Neocortex.

Voltage-sensitive dyes (VSDs) and optical imaging are useful tools for studying spatiotemporal patterns of population neuronal activity in cortex. Because fast VSDs respond to membrane potential changes with microsecond temporal resolution, these are better suited than calcium indicators for recording rapid neural signals. Here we describe methods for using a 464 element photodiode array and fast VSDs to record signals ranging from large scale network activity in brain slices and in vivo mammalian preparations with sensitivity comparable to local field potential (LFP) recordings. With careful control of dye bleaching and phototoxicity, long recording times can be achieved. Absorption dyes have less photo-toxicity than fluorescent dyes. In brain slices, the total recording time in each slice can be 1,000-2,000s, which can be divided into hundreds of short recording trials over several hours. In intact brains when fluorescent dyes are used, reduced light intensity can also increase recording time. In this chapter, we will discuss technical details for the methods to achieve reliable VSD imaging with high sensitivity and long recording time.

High sensitivity recording of afferent nerve activity using ultra-compliant microchannel electrodes: an acute in vivo validation

Neuroprostheses interfaced with transected peripheral nerves are technological routes to control robotic limbs as well as convey sensory feedback to patients suffering from traumatic neural injuries or degenerative diseases. To maximize the wealth of data obtained in recordings, interfacing devices are required to have intrafascicular resolution and provide high signal-to-noise ratio (SNR) recordings. In this paper, we focus on a possible building block of a three-dimensional regenerative implant: a polydimethylsiloxane (PDMS) microchannel electrode capable of highly sensitive recordings in vivo. The PDMS ‘micro-cuff’ consists of a 3.5 mm long (100 µm × 70 µm cross section) microfluidic channel equipped with five evaporated Ti/Au/Ti electrodes of sub-100 nm thickness. Individual electrodes have average impedance of 640 ± 30 kΩ with a phase angle of −58 ± 1 degrees at 1 kHz and survive demanding mechanical handling such as twisting and bending. In proof-of-principle acute implantation experiments in rats, surgically teased afferent nerve strands from the L5 dorsal root were threaded through the microchannel. Tactile stimulation of the skin was reliably monitored with the three inner electrodes in the device, simultaneously recording signal amplitudes of up to 50 µV under saline immersion. The overall SNR was approximately 4. A small but consistent time lag between the signals arriving at the three electrodes was observed and yields a fibre conduction velocity of 30 m s−1. The fidelity of the recordings was verified by placing the same nerve strand in oil and recording activity with hook electrodes. Our results show that PDMS microchannel electrodes open a promising technological path to 3D regenerative interfaces.

Assembly of Lipid Bilayers in Large Scaffold Arrays

In this study we have addressed the assembly of lipid bilayers in arrays and the stability of established membranes in different scaffold geometries. To establish planar lipid membranes across large scale partition aperture arrays, we created a disposable single-use horizontal chamber design that supports combined optical-electrical measurements. Lipid bilayers could easily and efficiently be established across CO2 laser micro structured 8 × 8 aperture partition arrays with average aperture diameters of 301 ± 5 μm. To demonstrate the functionality of the lipid bilayers established across the 8 × 8 arrays, controllable reconstitution of the biotechnological and physiological relevant peptides valinomycin and gramicidin A, together with the membrane proteins α-Hemolysin and FomA were carried out. The results showed that the design supports low current (high sensitivity) recordings of membrane peptides and proteins by incorporating gramicidin A, α-Hemolysin and FomA into the established lipid bilayers.Finally, we tested the scalability of the assembly of lipid bilayers by creating rectangular 24 × 24 and hexagonal 24 ×27 lipid membrane arrays respectively. The two different geometries of the micro structured aperture arrays seem to support stable and functional membrane arrays, however, with somewhat different electrical properties. We propose that the presented design may be suitable for further developments of sensitive biosensor assays.

Holographic optical elements recorded in silver halide sensitized gelatin emulsions. Part 2. Reflection holographic optical elements.

Silver halide sensitized gelatin (SHSG) holograms are similar to holograms recorded in dichromated gelatin (DCG), the main recording material for holographic optical elements (HOEs). The drawback of DCG is its low energetic sensitivity and limited spectral response. Silver halide materials can be processed in such away that the final hologram will have properties like a DCG hologram. Recently this technique has become more interesting since the introduction of new ultra-fine-grain silver halide (AgHal) emulsions. In particular, high spatial-frequency fringes associated with HOEs of the reflection type are difficult to construct when SHSG processing methods are employed. Therefore an optimized processing technique for reflection HOEs recorded in the new AgHal materials is introduced. Diffraction efficiencies over 90% can be obtained repeatably for reflection diffraction gratings. Understanding the importance of a selective hardening process has made it possible to obtain results similar to conventional DCG processing. The main advantage of the SHSG process is that high-sensitivity recording can be performed with laser wavelengths anywhere within the visible spectrum. This simplifies the manufacturing of high-quality, large-format HOEs, also including high-quality display holograms of the reflection type in both monochrome and full color.

Holographic optical elements recorded in silver halide sensitized gelatin emulsions Part I Transmission holographic optical elements

Silver halide sensitized gelatin (SHSG) holograms are similar to holograms recorded in dichromated gelatin (DCG), the main recording material for holographic optical elements (HOE's). The drawback of DCG is its low sensitivity and limited spectral response. Silver halide materials can be processed in such a way that the final hologram will have properties like a DCG hologram. Recently this technique has become more interesting since the introduction of new ultra-high-resolution silver halide emulsions. An optimized processing technique for transmission HOE's recorded in these materials is introduced. Diffraction efficiencies over 90% can be obtained for transmissive diffraction gratings. Understanding the importance of the selective hardening process has made it possible to obtain results similar to conventional DCG processing. The main advantage of the SHSG process is that high-sensitivity recording can be performed with laser wavelengths anywhere within the visible spectrum. This simplifies the manufacturing of high-quality, large-format HOE's.

Dynamic Response of Reflectivity of Metal/GeS2 Systems during Laser Irradiation in Nanosecond Range.

We constructed an equipment for measuring rapid changes in reflectivity of optical recording materials on test pieces during recording laser irradiation, which is very important in a development of these kinds of materials, with a time resolution less than 10 ns. Using this equipment, we examined the metal/GeS2 systems in the performance as recording materials for Write Once Read Many (WORM) optical disks. Seven kinds of metals were tested. Differences in the profiles of the reflectivity changes during the laser irradiation were clearly elucidated depending on the metal layer materials. In/GeS2 and Sn-Bi/GeS2 (Sn-Bi:Sn-57wt%Bi eutectic alloy) samples showed the most rapid decreases in the reflectivity with low laser power absorbed in the samples. These results suggest that In/GeS2 and Sn-Bi/GeS2 are promising for the WORM optical recording material with high sensitivity and high recording speed.

Ultrasonic two-axis rotation detector

A two-axis rotation monitor is described which determines the relative displacement between a pair of ultrasonic detectors using the phase difference of a continuous ultrasound wave generated by a single, distant source. The monitor has been used to measure head rotations around the vertical and horizontal axes, but can easily be adopted to other body segment rotations or translations. The device produces high sensitivity recordings of wide spatial and dynamic range. Although the device is quite linear with good isolation between channels, a computer-based linearization/calibration routine is described which further increases linearity and reduces crosstalk. The device is unobtrusive, inexpensive, and has proven reliable and easy to use.

A laboratory technique for examining the flight activity of insects under controlled environment conditions

A technique was developed for studying the flight activity of the, black fly,Simulium arcticum, under controlled environment conditions. Wind speed, light, temperature and humidity could be controlled and monitored in the flight chambers. Accurate measurement and recording of individual insect activity were achieved with a high-sensitivity video recording and monitoring system. The controlled-environment monitoring system is adaptable for investigations of the environmental behaviour and physiology of various insect species.

Superfluid cryostage for high-resolution electron microscopy

Structural study using electron microscopy is indispensable in the fields of physics, chemistry and biology because electron microscopy provides structural images from only small regions of a specimen. The high sensitivity of structure analysis in electron microscopy, however, results in the inevitable problem of irradiation damage in biological and organic materials. Many methods have been tried to reduce the irradiation damage, for example, by raising accelerating voltage, developing high sensitivity recording systems, cooling specimen temperature, etc. Cryoprotection may be the most promising method available for reducing damage at present. The cryoprotection effect from room temperature to liquid helium temperature has interested many researchers for about 15 years, although it is still open to controversy. Recently, the International Experimental Study Group made an interesting attempt to resolve the problem of the cryoprotection factor by cooling specimens in electron microscopes in independent experiments, as closely coordinated as possible with one another. In that paper, although the critical doses measured in each laboratory agree satisfactorily at room temperature, no agreement among the values was observed at very low temperatures.

Recording mechanisms in antireflection trilayer structures

Any recording mechanism which produces a high-reflectivity spot by disrupting the interference condition which results in the initially low reflectivity of the trilayer structure is a potential mode of recording and data storage. Experimental results are presented for deep pit and bubble modes of recording. In the deep pit mode both the absorber and dielectric layers are melted so that the pit penetrates to the reflector layer. In the bubble mode, outgassing of the dielectric layer results in a micron-sized raised blister or bubble in the absorber layer. The bubble mode, in particular, offers the potential for high sensitivity and high SNR recording characteristics without the use of low melting point absorber layer materials.

Video with Wide-Field SPecular Microscopy

The addition of a high-sensitivity video camera and recording system has augmented and simplified the use of the wide-field specular microscope. In the noncontact mode, the tape is replayed and the clearest image frozen for analysis. When used as a contact instrument, video recording as the cornea is scanned allows examination of broad areas for endothelial pathologic involvement.

Comparison of dark-field and bright-field incident illumination for in vivo measurements of reduced pyridine nucleotides

Bright-field and dark-field illumination techniques for in vivo measurements of reduced pyridine nucleotide fluorescence were compared in 15 rats during periods of normocapnia, hypocapnia, hypercapnia, and anoxia. Parameters investigated included fluorescence, cortical reflectance, cortical blood flow, and electroencephalograms. In normal brain, with preserved autoregulation, reduced pyridine nucleotide fluorescence was constant through a wide range in P a(CO 2), cortical blood flow, and cerebral blood volume in animals studied using vertical illumination (bright-field) techniques. There was a marked increase in reduced pyridine nucleotide fluorescence at death from anoxia. Artifacts were reduced by monochromators for excitation, emission, and reflected light; low-intensity vertical excitation energy and high-sensitivity recording instrumentation; and a small avascular (123 μm) field. Potential sources of error include photodecomposition, hemoglobin interference from absorption and reflectance, and light scattering. Vertical excitation techniques using a small field appeared to give more reliable and reproducible results than circumferential techniques using a larger field of observation.

Application of Pulse-Test Methods in Oman

Single-well pulse testing using very short pulses is effective for measuring vertical permeability. A particular advantage is that, unlike the constant-rate method, it does not require fully built-up conditions. Introduction Major decisions concerning the future development of a reservoir must increasingly be made in the early stages. Numerical simulators are now used early to study the effect of various development schemes. The extent to which these model studies are useful as a method of comparing various possible development schemes depends largely on the reliability of the early available data. The lateral permeability development and the magnitude of the vertical permeability (for coning studies, for example) arc often critical parameters. Because subsequent production can disturb the reservoir to such an extent that representative permeability data can be obtained only initially, tests that can provide that early information are especially important. Recently, therefore, there has been a revival of interest in well tests, especially those that provide a direct measurement of the in-situ horizontal and vertical permeabilities. permeabilities. New test methods based on pulse disturbances (single or repeated) have been proposed to achieve this. The advantage of these methods over constant-rate methods is that, owing to the more complex response resulting from the pulses, they provide more selective information on the in-situ reservoir parameters. The pulse response can be characterized by only relative pulse response can be characterized by only relative pressures (see Fig. 1); therefore pulse tests can be pressures (see Fig. 1); therefore pulse tests can be performed even when a general back-ground pressure performed even when a general back-ground pressure trend is present. Although there are these theoretical advantages, they are counterbalanced by greater, experimental difficulties. The measured response usually is weak, so special high-sensitivity recording equipment must be used. Also, the weak response is more susceptible to small disturbances than the response of conventional tests. An additional problem is created by the fact that variable pressures must be recorded. To ensure that the pressures measured inside the observation wells truly reflect the pressure variations in the reservoir, these wells must be "hard" enough. This means that the time constant of the wellbore-perforation system must be smaller than the variations in pressure that are to be observed. A well can be made harder by reducing the total compressibility of the fluids inside the wellbore and additionally by reducing the resistance over the perforations (skin). This implies that it might be necessary to completely fill the well with a gas-free liquid or to use special packer arrangements. This is generally time-consuming and expensive. These interwell pulse methods generally are applied only to low-storage pulse methods generally are applied only to low-storage reservoirs with close spacing, since in such cases a reasonable response can be expected. In the Yibal oil field in Oman, an interwell pulse test was carried out over long distances. JPT P. 1025

Accelerated chromatographic method for determination of hydroxyproline

An automated method is described for the determination of urinary hydroxyproline. The method utilizes accelerated column chromatography on spherical sulfonated polystyrene resin, PA-35, and a Beckman/Spinco model 116 amino acid analyzer equipped with sample injection and high sensitivity recording. The effluent is monitored by ninhydrin analysis. The method requires only 30 min per analysis, and allows better than 98% reproducibility and recovery. Moreover, compared to other methods, less handling is required for each sample, and less time is required of the analyst. Eight normal subjects, whose sole source of collagen was derived from a controlled diet containing 10 oz of meat per day, excreted 38.71 mg of hydroxyproline per 24 hr. After correcting for the urinary hydroxyproline excretion arising from dietary collagen, the same urinary excretion of hydroxyproline was obtained as that reported by others for subjects on collagen-free diets.

An Automatic Zero Suppression Circuit

A practical technique is described for high sensitivity recording of input signals having a large dynamic range. The circuit senses when the input signal exceeds preset limits and applies a precise and stable baseline shift in the correct sense to maintain the output within these limits. The circuit may be regarded as a black box to be inserted between an analog signal source and a recording device and requiring no alteration to either. A system is presented in detail which permits recording of signals within the range −5.4 to +6.1 V on a recorder at 1.0 V full scale sensitivity. The drift introduced by this system is maintained at less than 1 mV/°C over a wide ambient temperature range. A discussion of the sources of error is presented and techniques for reducing these errors are described.

The fetal electrocardiogram. A new research tool.

CURRENT INTEREST in the field of human reproduction has created greater demands for accurate evaluation of intrauterine environment. The fetal heart has served as the main indicator of abnormal fetal physiology by evidencing altered myocardial contractility, producing both bradycardia and tachycardia, as well as irregularities in rate. Although one-half century has transpired since the accidental recording of the first fetal heart beat by Cremer in 1906, active interest and progress in this new field of fetal cardiology has been limited to the past decade. With our growing experience and understanding, fetal electrocardiographic (ECG) technique is beginning to emerge as a research tool of wide promise. Based on more than 4,500 fetal ECG case studies, this report will demonstrate the present and future vistas in the study of the fetal heart in the field of human reproduction. Technique A variety of high-sensitivity recording systems are utilized effectively in recording the fetal