Clamp Amplifier Research Articles

Modified Decoupled Sense Amplifier with Improved Sensing Speed for Low-Voltage Differential SRAM

A modified decoupled sense amplifier (MDSA) and modified decoupled sense amplifier with NMOS foot-switch is proposed for improved sensing in differential SRAM for low-voltage operation at the 22-nm technology node. The MDSA and MDSANF both offer notable improvements to read delay over conventional voltage and current sense amplifiers. At an operating voltage of 0.8 V, the MDSA exhibited a reduced delay of 28.6%, 41.79%, 37.74%, and 30.94% compared to modified clamped sense amplifier (MCSA), double tail sense amplifier (DTSA), modified hybrid sense amplifier (MHSA), and conventional latch-type sense amplifier (LSA), respectively. Similarly, the MDSANF demonstrated a delay reduction of 26.13%, 39.78%, 35.58%, and 28.55% over MCSA, DTSA, MHSA, and LSA, respectively. To validate the performance, the MDSA and MDSANF are evaluated using the variation in delay and power consumption across various supply voltages, process corners, input differential bit line voltage (ΔV BL ), bit line capacitance (C BL ), and the sizing of decoupling transistors. Monte Carlo simulations were conducted to analyse the impact of voltage threshold variations on transistor mismatch which leads to an increased occurrence of read failures and a decline in SRAM yield. The performance analysis of various voltage and current sense amplifiers is presented along with MDSA and MDSANF. Area consideration for selection of sensing scheme is important and as such layout of MDSA and MDSANF was performed conforming to the design rules and estimated area for MDSA is 0.297 μm 2 whereas MDSANF occupies 0.5192 μm 2 .

A 146-dB-Ohm Gain 14-pARMS Noise Patch-Clamp Amplifier for Whole-Cell Ion Current Detection

The membrane clamp technique is an important tool to reflect the electrophysiological characteristics of cells by recording the ionic currents of cellular channels. Embedded systems work in systems designed for specific user groups and are used to implement specific functions. The membrane clamp amplifier built with embedded technology has the advantages of miniaturization, specialization, low power consumption, high integration, high resource utilization, and a long life cycle, which can avoid the inconvenience to developers and experimenters due to the update of general-purpose computer software and hardware. In this paper, a patch-clamp amplifier (PCA) based on a transimpedance amplifier (TIA) is proposed, which includes a glass microelectrode series resistance/capacitance compensation circuit and feedback resistor parasitic capacitance compensation. The prototype is designed using 180 nm CMOS technology and occupies an area of 720 μ m × 630 μ m . The prototype achieves a transimpedance gain of 145.6 dB-Ohm, a -3 dB bandwidth greater than 15 kHz, and an input reference noise current of 13.98 pARMS. Experimental results show that the proposed PCA is capable of compensating up to 30 pF of electrode capacitance and up to 10 MΩ for 86% of the series resistance, respectively. In addition, when the feedback resistor parasitic capacitance compensation circuit is enabled, the overshoot phenomenon disappears, overcoming the shortcomings of the conventional diaphragm clamp amplifier current clamp and maintaining the original key performance.

Ion Channel-Based Reporters for cAMP Detection.

In the last 20years tremendous progress has been made in the development of single cell cAMP sensors. Sensors are based upon cAMP binding proteins that have been modified to transduce cAMP concentrations into electrical or fluorescent readouts that can be readily detected using patch clamp amplifiers, photomultiplier tubes, or cameras. Here, we describe two complementary approaches for the detection and measurement of cAMP signals near the plasma membrane of cells using cyclic nucleotide (CNG) channel-based probes. These probes take advantage of the ability of CNG channels to transduce small changes in cAMP concentration into ionic flux through channel pores that can be readily detected by measuring Ca2+ and/or Mn2+ influx or by measuring ionic currents.

Comparison of Deep Learning Models for Fully Automated Single Channel Idealization

Single ion channel analysis can reveal high resolution data about kinetics of single molecules, but has been described as “slow and laborious”. Typically, the first stage in such analysis is the creation of an idealized record with each timepoint classified as the number ion channels open. Whilst there have been a number of semi-automatic methods developed to assist with this, in situations with multiple channels in the patch or generally poor signal to noise ratio, these methods could be difficult to upscale these analysis for industrial use. With this in mind we are working on artificial intelligence methods that may one day supersede existing methods. One recent approach, called DeepChannel, used developments in deep learning (a branch of artificial intelligence) to fully idealize data fully automatically. Deep learning is heavily dependent on large datasets to train, which in DeepChannel's case were generated by passing simulated ion channel events through a real patch clamp amplifier. This method was thus limited to real-time recording resulting in the size of datasets to still be relatively small. Here, we describe new, completely digital data generation pipeline simulated data ion channel data and use these to train and compare new and old deep learning models including one based on the acclaimed image classification model “ResNet”. Additionally, we then use these models to idealise real world data, and compare with an expert annotation to judge relative model performance. Deep learning models show great potential for fully automated single molecule analysis and in the future we will release example models as a web app for easy use by other ion channel biologists.

English

Annona senegalensis Pers. is a plant used in Burkina folkloric medicine for the treatment of epilepsy. The stem-bark, roots and leaves of A. senegalensis are used for an array of human disorders, including epilepsy. Previous studies have demonstrated some genuine effects of A. senegalensis fractions in vivo models of temporal lobe epilepsy. In the present work, we have compared the pharmacological profile of the most promising A. senegalensis fraction obtained up-to-date with anticonvulsant drugs targeting voltage-activated channels namely Carbamazepine (Na+ channels) and Retigabine (KCNQ Channels). In an in vitro model of temporal lobe epilepsy, we could observe a dose-dependent reduction of electrically evoked epileptiform bursts in the CA1 region of the rat hippocampus when applying carbamazepine, retigabine or the F4 fraction of A. senegalensis. The intrinsic excitability of CA1 pyramidal neurons was dose-dependently reduced by A. senegalensis. Since A. senegalensis effects could not anymore be observed when endogenous voltage-dependent sodium channels were blocked and intrinsic excitability restored with a dynamic clamp amplifier, it was concluded that A. senegalensis contains molecules that target voltage-dependent sodium channels. Key words: Hippocampus, epilepsy, Annona senegalensis, Burkina Faso plant extracts, sodium channel, KCNQ channel, M-current, retigabine, carbamazepine.

Dynamic Clamp on a Windows PC.

Dynamic clamp is a powerful tool for interfacing computational models and real cells. We describe here how to set up and carry out dynamic clamp experiments using a patch clamp amplifier, a National Instruments data acquisition card, and the freely available QuB software that operates on a PC running MS Windows.

Patch Clamp Technology in the Twenty-First Century.

In the almost four decades since its inception, the patch clamp technique has transitioned from a specialist skill to a method commonly used among many others in a lab. Development of patch clamp instrumentation has not been steady: A boost of product releases in rapid succession by multiple manufacturers in the 1990s had slowed to a trickle by the mid-2000s. In 2016, Sutter Instrument's entry into the market of turnkey patch clamp amplifier systems, defined as an amplifier with matching data acquisition hardware and software, caused a fresh breeze in a field in danger of going stale. Sutter has meanwhile completed the product line, culminating in the flagship dPatch® Ultra-fast, Low-noise Digital Amplifier. The dPatch System constitutes a contemporary, digital design that features many firsts, including digital signalcompensation, an extremely high bandwidth and fully integrated dynamic clamp capability, paired with the increasingly popular SutterPatch® Software.This chapter compares feature sets of the new Sutter instrumentation with the established platforms by the other two providers of turnkey systems, Axon Instruments by Molecular Devices and HEKA Elektronik by Harvard Bioscience. A variety of products from other manufacturers, who rely on combination with components from other sources rather than offering turnkey systems, are listed, but for their conceptual diversity not compared at a great level of detail. The chapter further covers architectural considerations for patch clamp systems, headstage design, data acquisition strategies and efficient structuring of the recorded data, controlling and monitoring periphery, advanced technologies, such as software lock-in amplifier capability and dynamic clamp features, and application modules for efficient analysis of action potentials and postsynaptic events.

Signal Processing for Single Biomolecule Identification Using Nanopores: A Review

Nanopore sensors provide an innovative platform for rapid and label-free biomolecule detection. The analytical information extracted from resistive pulse sensing (RPS) measurement, though powerful has several limitations. To address these challenges, various signal conditioning algorithms have been researched which include efficient clustering and classification of data, applying probabilistic models to reduce information overlap and also leveraging transient analysis of ionic current instead of the steady state RPS measurement. Additionally, as the current is typically in few picoampere regime with high transition rates, its faithful measurement requires precision instrumentation like a patch clamp amplifier with low noise and high bandwidth. However, for practical deployment of such systems, it is necessary to develop portable electronic interface. Significant efforts have been directed globally to develop on-chip customized integrated circuits with low noise, high bandwidth amplifiers. Thus, it is absolutely timely and pertinent to conduct a review on the various signal processing schemes and electronic interfaces for single biomolecule identification using nanopores which will enable to comprehend the current status for its deployment as a commercial platform for genomics and ultrasensitive detection. To the best of our knowledge, the data extraction methodologies and electronic interface schemes for nanopores have not yet been summarized. In this paper, a comprehensive review emphasizing the signal processing algorithms for DNA sequencing and protein identification in complex analyte using functionalized and non-functionalized nanopores has been presented along with the on-chip low noise electronic interfaces required for field deployable measurement.

Array Design of High-Density Emerging Memories Making Clamped Bit-Line Sense Amplifier Compatible with Dummy Cell Average Read Scheme

Array Design of High-Density Emerging Memories Making Clamped Bit-Line Sense Amplifier Compatible with Dummy Cell Average Read Scheme

Robust Two-Layer Model Predictive Control for Full-Bridge NPC Inverter-Based Class-D Voltage Mode Amplifier

Finite control set model predictive control (FCS-MPC) is able to handle multiple control objectives and constraints simultaneously with good dynamic performance. However, its industrial application is limited by its high dependence on system model and the huge computational effort. In this paper, a novel robust two-layer MPC (RM-MPC) with strong robustness is proposed for the full-bridge neutral-point clamped (NPC) voltage mode Class-D amplifier (CDA) aiming at this problem. The errors caused by the parameter mismatches or uncertainties of the LC filter and the load current are regarded as lumped disturbance and estimated by the designed Luenberger observer. The robust control can be achieved by compensating the estimated disturbance to the used predictive model. In order to reduce computation of the controller, a two-layer MPC is proposed for the full-bridge NPC inverter with an LC filter. The first layer is used to calculate the optimal output level which minimizes the tracking error of the output voltage. The second layer is used to determine the switching state for the purpose of capacitor voltage balancing. The experimental results show that the lumped model error is observed centrally through only one observer with low complexity. The two-layer MPC further reduced the computation without affecting the dynamic performance.

The mechanosensitive ion channel TRAAK is localized to the mammalian node of Ranvier.

TRAAK is a membrane tension-activated K+ channel that has been associated through behavioral studies to mechanical nociception. We used specific monoclonal antibodies in mice to show that TRAAK is localized exclusively to nodes of Ranvier, the action potential propagating elements of myelinated nerve fibers. Approximately 80 percent of myelinated nerve fibers throughout the central and peripheral nervous system contain TRAAK in what is likely an all-nodes or no-nodes per axon fashion. TRAAK is not observed at the axon initial segment where action potentials are first generated. We used polyclonal antibodies, the TRAAK inhibitor RU2 and node clamp amplifiers to demonstrate the presence and functional properties of TRAAK in rat nerve fibers. TRAAK contributes to the 'leak' K+ current in mammalian nerve fiber conduction by hyperpolarizing the resting membrane potential, thereby increasing Na+ channel availability for action potential propagation. We speculate on why nodes of Ranvier contain a mechanosensitive K+ channel.

Development of Solid-State Nanopore Life Detection Technology

Biomarkers collected from past and present life on Earth are a central guide in the development of flight-ready technologies designed to search for life on other planets and moons. Data from numerous laboratory and field studies have revealed the importance of incorporating capabilities that minimize the risk of false negatives or false positives during life detection missions. Biomolecules are the most unambiguous and information-rich of all known biosignatures. Indeed, the identification in a sample of biopolymers akin to DNA, RNA or proteins, would be difficult to refute as a successful life detection experiment. In the case of Mars, the search for biomolecules is inescapable, but few technological solutions exist for in situ identification. Thus, our work has focused on the development of technologies designed to detect biochemical polyelectrolyte molecules, which have been argued to be a universal signature for life due to their ability to store information while reducing their tendency to adopt complex tertiary structures that would prohibit their replication. To that end we have developed a solid-state nanopore device that has the ability to detect electrically charged organic polymers, such as those found in deoxyribonucleic acid. Our nanopore technology, when used as a biosensor, consists of two or three ion-filled chambers separated by voltage-biased thin layer (Figure 1). Nanopores are milled into the thin layer, allowing the chambers to be connected electrically via an ionic solution. Polyelectrolytes are introduced into one of the chambers, and a patch clamp amplifier is connected to the chip via electrodes that serve as a voltage source and an ammeter. When a voltage is applied across the membrane, the ionic current going only through this pore is measured. The polyelectrolytes are captured by the electric field in the pore, then and electrophoretically drawn through the nanopore (translocation) causing the nanopore conductance to decrease. This conductance decrease, or transient current blockage, is evaluated for: 1) mean blockage current (which is caused by the physical passage of the polyelectrolyte through the nanopore, and is measured by a sensitive ammeter in pA); 2) translocation duration (physical time of the translocation, for DNA this is typically 30 bases per second when translocation is controlled by a molecular motor [1]); and 3) integrated area of a blockage, revealing key features of the particle. Solid-state nanopore technology is being aggressively advanced for use as an electrochemistry sensor for a wide variety of biological molecules. Testing of the solid-state nanopore membranes includes the establishment of criteria used to distinguish informational from non-informational output signals. Our work highlights past, current, and future efforts in the development of solid-state nanopore technology for life detection.

Precise Construction and Tuning of an Aerolysin Single-Biomolecule Interface for Single-Molecule Sensing

Precise Construction and Tuning of an Aerolysin Single-Biomolecule Interface for Single-Molecule Sensing

Artifactual hyperpolarization during extracellular electrical stimulation: Proposed mechanism of high-rate neuromodulation disproved

BackgroundKilohertz-frequency electric field stimulation (kEFS) applied to the spinal cord can reduce chronic pain without causing the buzzing sensation (paresthesia) associated with activation of dorsal column fibers. This suggests that high-rate spinal cord stimulation (SCS) has a mode of action distinct from conventional, parasthesia-based SCS. A recent study reported that kEFS hyperpolarizes spinal neurons, yet this potentially transformative mode of action contradicts previous evidence that kEFS induces depolarization and was based on patch clamp recordings whose accuracy in the presence of kEFS has not been verified. ObjectivesWe sought to elucidate the basis for kEFS-induced hyperpolarization and to validate the effects of kEFS observed in patch clamp recordings by comparing with independent optical methods. MethodsUsing patch clamp electrophysiology and voltage-sensitive dye (VSD) imaging, we measured the response to kEFS applied in vitro to hippocampal and spinal neurons. ResultsThe kEFS-induced hyperpolarization observed with current clamp recordings was corroborated by VSD imaging and rheobase measurements in patched neurons. However, no hyperpolarization was observed when imaging unpatched neurons or when recording with a voltage-follower amplifier rather than with a patch clamp amplifier (PCA). We found that EFS induced an artifactual current in PCAs that was injected back into current clamped neurons. The artifactual current induced by single, charge-balanced EFS pulses caused modest hyperpolarization, but these unitary hyperpolarizations accumulated when EFS pulses were repeated at kilohertz frequencies. ConclusionOur results rule out hyperpolarization as the mechanism underlying kEFS-mediated analgesia and highlight the risk of recording artifacts caused by extracellular electrical stimulation.

Collisions of Ir Oxide Nanoparticles with Carbon Nanopipettes: Experiments with One Nanoparticle.

Investigating the collisions of individual metal nanoparticles (NPs) with electrodes can provide new insights into their electrocatalytic behavior, mass transport, and interactions with surfaces. Here we report a new experimental setup for studying NP collisions based on the use of carbon nanopipettes to enable monitoring multiple collision events involving the same NP captured inside the pipet cavity. A patch clamp amplifier capable of measuring pA-range currents on the microsecond time scale with a very low noise and stable background was used to record the collision transients. The analysis of current transients produced by oxidation of hydrogen peroxide at one IrOx NP provided information about the origins of deactivation of catalytic NPs and the effects of various experimental conditions on the collision dynamics. High-resolution TEM of carbon pipettes was used to attain better understanding of the NP capture and collisions.

Current Comparison based Domino with Clamped Bit-Line Current Amplifier for Wide Fan-In Gates

A greater part of the low power design methodology is allocated for reducing leakage current. This plays a vital role in static power dissipation. In this project, a current comparison domino pull-up network with its worst case leakage current is compared with Current comparison based Domino (CCD) with Clamped bit-line Current-sensing Amplifier circuit. Thus, the contention current and consequently power consumption and delay are reduced. The leakage current is also decreased by utilizing the footer transistor in diode configuration, which results in increased noise immunity. The simulation results of wide fan-in gates designed using a 16-nm high-performance predictive technology model demonstrates 46 % power reduction and at least 2.36× noise-immunity improvement at the same delay compared to the standard domino circuits for wide fan – in OR gates.

What Type of Ion Channels are Identified on Osteosarcoma Cells Membrane?

Human Osteosarcoma (SaOs-2) cell line is a good and recognized model for in vitro calcification. These cells present osteoblast-like properties and can be mineralized under appropriate conditions. There is not a full electrophysiological characterization on these cells. Our goal was to screen ion channels on SaOs-2 cells membrane. SaOs-2 cells were obtained from tissue bank at UFRJ (BCRJ # 0217) and maintained in an incubator at 37°C with 5% CO2. For these experiments, cells were maintained in DMEM supplemented with 10% FBS, 1mM L-glutamine and 50 units/ml Penicillin and 50 μg/ml Streptomycin. Cells were detached from culture flasks using trypsin-EDTA. After centrifugation at 1.000 rpm for 2 minutes, cells were recovered in culture medium and plated into a small single plate and allowed to attach for at least 1 hour. Electrophysiological recording was performed in the whole-cell configuration using a patch clamp amplifier in voltage clamp mode. The signal was registered in 5 KHz. Micropipette tip resistance 3-5 MΩ. Solutions used were composed in mM: Pipette (KCl 130; NaCl 10; EGTA 5; Hepes 10) and external (NaCl 140; KCl 54; CaCl2 2.0; MgCl2 0.5; Glucose 10; Hepes 10). Tetraethylammonium (TEA), Iberotoxin (IBTX) and Tetrodotoxin (TTX) (10 mM, 100 nM and 100mM, respectively) were used as inhibitors for Ca++-activated K+ channel (IKCa) and rectifier K+ current channels (IKDR). Slow activation current similar to IKDR and another one as fast activation current similar to IKCa channel were observed. Both currents (IKCa; IKDR) were decreased approximately 65 % (n=3) by TEA when compared to relative control condition. IKCa was decreased approximately 86 % (n=3) to IBTX specifically. The inward current was entirely abolished by TTX application. Further experiments are still under investigation to determine more channels on SaOs-2 cells.

Expanding neurochemical investigations with multi-modal recording: simultaneous fast-scan cyclic voltammetry, iontophoresis, and patch clamp measurements.

Multi-modal recording describes the simultaneous collection of information across distinct domains. Compared to isolated measurements, such studies can more easily determine relationships between varieties of phenomena. This is useful for neurochemical investigations which examine cellular activity in response to changes in the local chemical environment. In this study, we demonstrate a method to perform simultaneous patch clamp measurements with fast-scan cyclic voltammetry (FSCV) using optically isolated instrumentation. A model circuit simulating concurrent measurements was used to predict the electrical interference between instruments. No significant impact was anticipated between methods, and predictions were largely confirmed experimentally. One exception was due to capacitive coupling of the FSCV potential waveform into the patch clamp amplifier. However, capacitive transients measured in whole-cell current clamp recordings were well below the level of biological signals, which allowed the activity of cells to be easily determined. Next, the activity of medium spiny neurons (MSNs) was examined in the presence of an FSCV electrode to determine how the exogenous potential impacted nearby cells. The activities of both resting and active MSNs were unaffected by the FSCV waveform. Additionally, application of an iontophoretic current, used to locally deliver drugs and other neurochemicals, did not affect neighboring cells. Finally, MSN activity was monitored during iontophoretic delivery of glutamate, an excitatory neurotransmitter. Membrane depolarization and cell firing were observed concurrently with chemical changes around the cell resulting from delivery. In all, we show how combined electrophysiological and electrochemical measurements can relate information between domains and increase the power of neurochemical investigations.

An Accessory Agonist Binding Site Promotes Activation of α4β2* Nicotinic Acetylcholine Receptors

Neuronal nicotinic acetylcholine receptors containing α4, β2, and sometimes other subunits (α4β2* nAChRs) regulate addictive and other behavioral effects of nicotine. These nAChRs exist in several stoichiometries, typically with two high affinity acetylcholine (ACh) binding sites at the interface of α4 and β2 subunits and a fifth accessory subunit. A third low affinity ACh binding site is formed when this accessory subunit is α4 but not if it is β2. Agonists selective for the accessory ACh site, such as 3-[3-(3-pyridyl)-1,2,4-oxadiazol-5-yl]benzonitrile (NS9283), cannot alone activate a nAChR but can facilitate more efficient activation in combination with agonists at the canonical α4β2 sites. We therefore suggest categorizing agonists according to their site selectivity. NS9283 binds to the accessory ACh binding site; thus it is termed an accessory site-selective agonist. We expressed (α4β2)2 concatamers in Xenopus oocytes with free accessory subunits to obtain defined nAChR stoichiometries and α4/accessory subunit interfaces. We show that α2, α3, α4, and α6 accessory subunits can form binding sites for ACh and NS9283 at interfaces with α4 subunits, but β2 and β4 accessory subunits cannot. To permit selective blockage of the accessory site, α4 threonine 126 located on the minus side of α4 that contributes to the accessory site, but not the α4β2 sites, was mutated to cysteine. Alkylation of this cysteine with a thioreactive reagent blocked activity of ACh and NS9283 at the accessory site. Accessory agonist binding sites are promising drug targets.

Channel-based reporters for cAMP detection.

In the last 15 years, tremendous progress has been made in the development of single-cell cAMP sensors. Sensors are based upon cAMP-binding proteins that have been modified to transduce cAMP concentrations into electrical or fluorescent readouts that can be readily detected using patch clamp amplifiers, photomultiplier tubes, or cameras. Here we describe two complementary approaches for the detection and measurement of cAMP signals near the plasma membrane of cells. These probes take advantage of the ability of cyclic nucleotide-gated (CNG) channels to transduce small changes in cAMP concentrations into ionic flux through channel pores that can be readily detected by measuring Ca(2+) and/or Mn(2+) influx or by measuring ionic currents.