Sensitivity optimization of a rhodopsin-based fluorescent voltage indicator

The ability to optically image cellular transmembrane voltage at millisecond-timescale resolution can offer unprecedented insight into the function of living brains in behaving animals. The chemigenetic voltage indicator Voltron is bright and photostable, making it a favorable choice for long in vivo imaging of neuronal populations at cellular resolution. Improving the voltage sensitivity of Voltron would allow better detection of spiking and subthreshold voltage signals. We performed site saturation mutagenesis at 40 positions in Voltron and screened for increased ΔF/F0 in response to action potentials (APs) in neurons. Using a fully automated patch-clamp system, we discovered a Voltron variant (Voltron.A122D) that increased the sensitivity to a single AP by 65% compared to Voltron. This variant (named Voltron2) also exhibited approximately 3-fold higher sensitivity in response to sub-threshold membrane potential changes. Voltron2 retained the sub-millisecond kinetics and photostability of its predecessor, with lower baseline fluorescence. Introducing the same A122D substitution to other Ace2 opsin-based voltage sensors similarly increased their sensitivity. We show that Voltron2 enables improved sensitivity voltage imaging in mice, zebrafish and fruit flies. Overall, we have discovered a generalizable mutation that significantly increases the sensitivity of Ace2 rhodopsin-based sensors, improving their voltage reporting capability.

A positively tuned voltage indicator reveals electrical correlates of calcium activity in the brain

Neuronal activity is routinely recorded in vivo using genetically encoded calcium indicators (GECIs) and 2-photon microscopy, but calcium imaging is poorly sensitive for single voltage spikes under typical population imaging conditions, lacks temporal precision, and does not report subthreshold voltage changes. Genetically encoded voltage indicators (GEVIs) offer better temporal resolution and subthreshold sensitivity, but 2-photon detection of single spikes in vivo using GEVIs has required specialized imaging equipment. Here, we report ASAP4b and ASAP4e, two GEVIs that brighten in response to membrane depolarization, inverting the fluorescence-voltage relationship of previous ASAP-family GEVIs. ASAP4b and ASAP4e feature 180% and 210% fluorescence increases to 100-mV depolarizations, respectively, as well as modestly prolonged deactivation and high photostability. We demonstrate single-trial detection of spikes and oscillations in vivo with standard 1 and 2-photon imaging systems, and confirm improved temporal resolution in comparison to calcium imaging on the same equipment. Thus, ASAP4b and ASAP4e GEVIs extend the uses of existing imaging equipment to include multi-unit voltage imaging in vivo.

FinFET Response under Radiation and Bias Stress: A Review

Electronics devices are made on IC’s, the basic building block of these IC’s are transistors. Transistors are continuously upgraded to new forms from conventional BJT to the latest FinFET. The purpose of this paper is to provide a clear and exhaustive understanding of the state of the art, challenges, and future trends of silicon based devices to produced reliable output for a longer time period even in abnormal conditions like in space. The modeling techniques for the conventional transistor, different strategies have been proposed over the last years to model the FinFET behavior and increasing the storage capacity of the IC by increasing the number of transistors without occupying more space on the same IC. The behavior of the device is impacted by radiation, heat, and temperature, by which the overall performance of the devices is affected a lot. Keywords: CMOS, MOSFET, FinFET, diode, transistor, subthreshold voltage, threshold voltage, electromigration, and charge trapping.

Study on Cross-Coupled-Based Sensing Circuits for Nonvolatile Flip-Flops Operating in Near/Subthreshold Voltage Region

To date, most studies focus on complex designs to realize offset cancelation characteristics in nonvolatile flip-flops (NV-FFs). However, complex designs using switches are ineffective for offset cancelation in the near/subthreshold voltage region because switches become critical contributors to the offset voltage. To address this problem, this paper proposes a novel cross-coupled NMOS-based sensing circuit (CCN-SC) capable of improving the restore yield, based on the concept that the simplest is the best, of an NV-FF operating in the near/subthreshold voltage region. Measurement results using a 65 nm test chip demonstrate that with the proposed CCN-SC, the restore yield is increased by more than 25 times at a supply voltage of 0.35 V, compared to that with a cross-coupled inverter-based SC, at the cost of 18× higher power consumption.

Origin of light instability in amorphous IGZO thin-film transistors and its suppression

Radiating amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) with deep ultraviolet light (λ = 175 nm) is found to induce rigid negative threshold-voltage shift, as well as a subthreshold hump and an increase in subthreshold-voltage slope. These changes are attributed to the photo creation and ionization of oxygen vacancy states (VO), which are confined mainly to the top surface of the a-IGZO film (backchannel). Photoionization of these states generates free electrons and the transition from the neutral to the ionized VO is accompanied by lattice relaxation, which raises the energy of the ionized VO. This and the possibility of atomic exchange with weakly bonded hydrogen leads to metastability of the ionized VO, consistent with the rigid threshold-voltage shift and increase in subthreshold-voltage slope. The hump is thus a manifestation of the highly conductive backchannel and its formation can be suppressed by reduction of the a-IGZO film thickness or application of a back bias after radiation. These results support photo creation and ionization of VO as the main cause of light instability in a-IGZO TFTs and provide some insights on how to minimize the effect.

The organization of the sino-atrial node microvasculature varies regionally to match local myocyte excitability

The cardiac cycle starts when an action potential is produced by pacemaking cells in the sino-atrial node. This cycle is repeated approximately 100,000 times in humans and 1 million times in mice per day, imposing a monumental metabolic demand on the heart, requiring efficient blood supply via the coronary vasculature to maintain cardiac function. Although the ventricular coronary circulation has been extensively studied, the relationship between vascularization and cellular pacemaking modalities in the sino-atrial node is poorly understood. Here, we tested the hypothesis that the organization of the sino-atrial node micro-vasculature varies regionally, reflecting local myocyte firing properties. We show that vessel densities are higher in the superior versus inferior sino-atrial node. Accordingly, sino-atrial node myocytes are closer to vessels in the superior versus inferior regions. Superior and inferior sino-atrial node myocytes produce stochastic subthreshold voltage fluctuations and action potentials. However, the intrinsic action potential firing rate of sino-atrial node myocytes is higher in the superior versus inferior node. Our data support a model in which the micro-vascular densities vary regionally within the sino-atrial node to match the electrical and Ca2+ dynamics of nearby myocytes, effectively determining the dominant pacemaking site within the node. In this model, the high vascular density in the superior sino-atrial node places myocytes with metabolically demanding, high frequency action potentials near vessels. The lower vascularization and electrical activity of inferior sino-atrial node myocytes could limit these cells to function to support sino-atrial node periodicity with sporadic voltage fluctuations via a stochastic resonance mechanism.

Impact of interface trap charges on Junctionless double and triple metal gate High-k Gate All Around Nanowire FET based Alzheimer Biosensor

In this work, junctionless double and triple metal gate high-k gate all around nanowire field-effect transistor-based APTES biosensor has been developed to study the impact of ITCs on device sensitivity. The analytical results were authenticated using ‘‘ATLAS-3D’’ device simulation tool. Effect of different interface trap charge on the output characteristics of double and triple metal gate high-k gate all around junctionless NWFET biosensor was studied. Output characteristics, like transconductance, output conductance,drain current, threshold voltage, subthreshold voltage and switching ratio, including APTES biomolecule, have been studied in both devices. 184% improvement has been investigated in shifting threshold voltage in a triple metal gate compared to a double metal gate when APTES biomolecule immobilizes on the nanogap cavity region under negative ITCs. Based on this finding, drain off-current ratio and shifting threshold voltage were considered as sensing metrics when APTES biomolecule immobilizes in the nanogap cavity under negative ITCs which is significant for Alzheimer's disease detection. We signifies a negative ITC has a positive impact on our proposed biosensor device compared to positive and neutral ITCs.