Novel Micro-Photodiodes for Retina Stimulation

2000 ◽  
Vol 609 ◽  
Author(s):  
M. Rojahn ◽  
M.B. Schubert
Keyword(s):  
Amorphous Silicon ◽  
Ganglion Cells ◽  
Light Exposure ◽  
Open Circuit ◽  
In Vitro Tests ◽  
Buffer Solution ◽  
Long Term Stability ◽  
Current Voltage

ABSTRACTWe present a new design of micro-photodiodes for in-vitro tests to electrically stimulate the ganglion cells of chicken and rat retinae upon light exposure of the photodiodes. Based on amorphous silicon, our laterally series connected double-stacked micro-photodiodes provide an open circuit voltage of 2.3 volts. Photolithographic steps as well as etching procedures for patterning the back contact, the amorphous silicon layers and the front contact are described. We analyse current- voltage-measurements performed with direct contact of the metal needles of a micro-positioning system to the device's electrodes. In order to test the performance of an individual micro-photodiode in an electrolyte environment, the stimulation electrode of the device is also contacted with a micro-droplet of buffer solution. Further improvement is needed, mainly addressing the problem of long-term stability of the device in electrolyte environments.

Use of Transparent Conductive Oxide Materials with Low Indices of Refraction in Amorphous Silicon-Based Solar Cell Technology

2005 ◽  
Vol 862 ◽  
Author(s):  
Scott J. Jones ◽  
Joachim Doehler ◽  
Tongyu Liu ◽  
David Tsu ◽  
Jeff Steele ◽  
...  
Keyword(s):  
Solar Cell ◽  
Amorphous Silicon ◽  
Transparent Conductive Oxide ◽  
Open Circuit ◽  
Long Term Stability ◽  
Back Reflectors ◽  
Stability Issues ◽  
Silicon Based ◽  
Solar Cell Technology

AbstractNew types of transparent conductive oxides with low indices of refraction have been developed for use in optical stacks for the amorphous silicon (a-Si) solar cell and other thin film applications. The alloys are ZnO based with Si and MgF added to reduce the index of the materials through the creation of SiO2 or MgF2, with n=1.3-1.4, or the addition of voids in the materials. Alloys with 12-14% Si or Mg have indices of refraction at λ=800nm between 1.6 and 1.7. These materials are presently being used in optical stacks to enhance light scattering by Al/multi-layer/ZnO back reflectors in a-Si based solar cells to increase light absorption in the semiconductor layers and increase open circuit currents and boost device efficiencies. In contrast to Ag/ZnO back reflectors which have long term stability issues due to electromigration of Ag, these Al based back reflectors should be stable and usable in manufactured PV products. In this manuscript, structural properties for the materials will be reported as well as the performance of solar cell devices made using these new types of materials.

THE ROLE OF POLYETHYLENIMINE IN ENHANCING PERFORMANCE OF GLUTAMATE BIOSENSORS

2018 ◽  
Vol 8 (3) ◽  
pp. 36-41
Author(s):  
Diep Do Thi Hong ◽  
Duong Le Phuoc ◽  
Hoai Nguyen Thi ◽  
Serra Pier Andrea ◽  
Rocchitta Gaia
Keyword(s):  
First Generation ◽  
Good Reproducibility ◽  
Complex Matrices ◽  
Long Term Stability ◽  
In Vitro Characterization ◽  
Glutamate Oxidase

Background: The first biosensor was constructed more than fifty years ago. It was composed of the biorecognition element and transducer. The first-generation enzyme biosensors play important role in monitoring neurotransmitter and determine small quantities of substances in complex matrices of the samples Glutamate is important biochemicals involved in energetic metabolism and neurotransmission. Therefore, biosensors requires the development a new approach exhibiting high sensibility, good reproducibility and longterm stability. The first-generation enzyme biosensors play important role in monitoring neurotransmitter and determine small quantities of substances in complex matrices of the samples. The aims of this work: To find out which concentration of polyethylenimine (PEI) exhibiting the most high sensibility, good reproducibility and long-term stability. Methods: We designed and developed glutamate biosensor using different concentration of PEI ranging from 0% to 5% at Day 1 and Day 8. Results: After Glutamate biosensors in-vitro characterization, several PEI concentrations, ranging from 0.5% to 1% seem to be the best in terms of VMAX, the KM; while PEI content ranging from 0.5% to 1% resulted stable, PEI 1% displayed an excellent stability. Conclusions: In the result, PEI 1% perfomed high sensibility, good stability and blocking interference. Furthermore, we expect to develop and characterize an implantable biosensor capable of detecting glutamate, glucose in vivo. Key words: Glutamate biosensors, PEi (Polyethylenimine) enhances glutamate oxidase, glutamate oxidase biosensors

scholarly journals An updated protocol based on CLSI document C37 for preparation of off-the-clot serum from individual units for use alone or to prepare commutable pooled serum reference materials

2020 ◽  
Vol 58 (3) ◽  
pp. 368-374 ◽  
Author(s):  
Uliana Danilenko ◽  
Hubert W. Vesper ◽  
Gary L. Myers ◽  
Patric A. Clapshaw ◽  
Johanna E. Camara ◽  
...  
Keyword(s):  
Human Serum ◽  
Reference Materials ◽  
Frozen Storage ◽  
Metrological Traceability ◽  
Medical Laboratory ◽  
Serum Samples ◽  
Long Term Stability ◽  
Individual Human

AbstractManufacturers of in vitro diagnostic medical devices, clinical laboratories, research laboratories and calibration laboratories require commutable reference materials that can be used in the calibration hierarchies of medical laboratory measurement procedures used for human specimens to establish metrological traceability to higher order reference systems. Commutable materials are also useful in external quality assessment surveys. In order to achieve these goals, matrix-based reference materials with long-term stability, appropriate measurand concentrations and commutability with individual human specimens are required. The Clinical and Laboratory Standards Institute (CLSI) guideline C37-A (now archived) provided guidance to prepare commutable pooled serum reference materials for use in the calibration hierarchies of cholesterol measurement procedures. Experience using the C37-A guideline has identified a number of technical enhancements as well as applications to measurands other than cholesterol. This experience is incorporated into this updated protocol to ensure the procedure will continue to meet the needs of the medical laboratory. The updated protocol describes a procedure for preparing frozen human serum units or pools with minimal matrix alterations that are likely to be commutable with individual human serum samples. The protocol provides step-by-step guidance for the planning phase, collection of individual serum units, processing the units, qualifying the units for use in a pool and frozen storage of aliquots of pooled sera to manufacture frozen serum pools. Guidance on how to perform quality control of the final product and suggestions on documentation are also provided.

scholarly journals Long-Term Stability of a RAFT-Modified Bulk-Fill Resin-Composite under Clinically Relevant versus ISO-Curing Conditions

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5350
Author(s):  
Niklas Graf ◽  
Nicoleta Ilie
Keyword(s):  
Fracture Mechanism ◽  
Resin Composite ◽  
Bending Test ◽  
Depth Sensing ◽  
Matrix Formulation ◽  
Curing Conditions ◽  
Term Stability ◽  
Long Term Stability

The addition of RAFT (reversible addition-fragmentation chain transfer) agents to the matrix formulation of a bulk-fill resin composite can significantly decrease the required curing time down to a minimum of 3 s. Evaluating the long term-stability of this resin composite in relation to varied curing conditions in an in-vitro environment was this study’s goal. Specimens were produced according to either an ISO or one of two clinical curing protocols and underwent a maximum of three successive aging procedures. After each one of the aging procedures, 30 specimens for each curing condition were extracted for a three-point bending test. Fragments were then stereo-microscopically characterized according to their fracture mechanism. Weibull analysis was used to quantify the reliability of each aging and curing combination. Selected fragments (n = 12) underwent further testing via depth-sensing indentation. Mechanical values for either standardized or clinical curing were mostly comparable. However, changes in fracture mechanism and Weibull modulus were observed after each aging procedure. The final procedure exposed significant differences in the mechanical values due to curing conditions. Curing conditions with increased radiant exposure seemingly result in a higher crosslink in the polymer-matrix, thus increasing resistance to aging. Yet, the clinical curing conditions still resulted in acceptable mechanical values, proving the effectiveness of RAFT-polymerization.

Electrical characteristics of snake distal tubules: studies of I-V relationships

1980 ◽  
Vol 239 (5) ◽  
pp. F402-F411 ◽  
Author(s):  
B. M. Koeppen ◽  
K. W. Beyenbach ◽  
W. H. Dantzler ◽  
S. I. Helman
Keyword(s):  
Chemical Potential ◽  
Distal Tubule ◽  
Ringer Solution ◽  
Open Circuit ◽  
Transepithelial Resistance ◽  
Constant Current ◽  
Toad Urinary Bladder ◽  
Current Voltage ◽  
Distal Tubules

Distal tubules of Thamnophis spp. were perfused in vitro with Ringer solution containing either 16 or 150 mM Na and bathed with 150 mM Na Ringer. Current-voltage relationships were obtained by injecting pulses of constant current, Io, into the tubule lumen and recording changes in voltage, delta Vo, at the proximal end of the perfused tubule segment. The Io-Vo plots showed a distinct break at a voltage E1 (approximately 85 mV) that was greater than the open-circuit voltage, VToc, and similar to values of ENa, the transepithelial driving force for Na transport estimated by other methods. The resistance of the shunt pathway, Rs, was estimated from the values of the transepithelial resistance after luminal addition of 10(-5) M amiloride, which caused a rapid fall of the VToc to 0 mV with concurrent increases of the transepithelial resistance. These estimates of Rs were the same as the values of E1/I1 obtained from the Io-Vo plots. The VToc, RT, and Rs were independent of the bath [Na] and were not influenced by the addition of amiloride to the bath. As in frog skin and toad urinary bladder, the ENa and Rs of the snake distal tubule can be estimated from studies of their Io-Vo plots, and the E1 appears to be independent of the transepithelial chemical potential for Na.

scholarly journals Circadian Photoentrainment in Mice and Humans

Biology ◽  
2020 ◽  
Vol 9 (7) ◽  
pp. 180
Author(s):  
Russell G. Foster ◽  
Steven Hughes ◽  
Stuart N. Peirson
Keyword(s):  
Ganglion Cells ◽  
Light Exposure ◽  
Bright Light ◽  
Functional Expression ◽  
Time Of Day ◽  
High Irradiance ◽  
Intermittent Light ◽  
Long Duration ◽  
Light History

Light around twilight provides the primary entrainment signal for circadian rhythms. Here we review the mechanisms and responses of the mouse and human circadian systems to light. Both utilize a network of photosensitive retinal ganglion cells (pRGCs) expressing the photopigment melanopsin (OPN4). In both species action spectra and functional expression of OPN4 in vitro show that melanopsin has a λmax close to 480 nm. Anatomical findings demonstrate that there are multiple pRGC sub-types, with some evidence in mice, but little in humans, regarding their roles in regulating physiology and behavior. Studies in mice, non-human primates and humans, show that rods and cones project to and can modulate the light responses of pRGCs. Such an integration of signals enables the rods to detect dim light, the cones to detect higher light intensities and the integration of intermittent light exposure, whilst melanopsin measures bright light over extended periods of time. Although photoreceptor mechanisms are similar, sensitivity thresholds differ markedly between mice and humans. Mice can entrain to light at approximately 1 lux for a few minutes, whilst humans require light at high irradiance (>100’s lux) and of a long duration (>30 min). The basis for this difference remains unclear. As our retinal light exposure is highly dynamic, and because photoreceptor interactions are complex and difficult to model, attempts to develop evidence-based lighting to enhance human circadian entrainment are very challenging. A way forward will be to define human circadian responses to artificial and natural light in the “real world” where light intensity, duration, spectral quality, time of day, light history and age can each be assessed.

scholarly journals Inhibition of prostaglandin E2 restores defective lymphocyte proliferation and cell-mediated lympholysis in recipients after allogeneic marrow grafting

Blood ◽  
1986 ◽  
Vol 68 (1) ◽  
pp. 102-107 ◽  
Author(s):  
HG Klingemann ◽  
MS Tsoi ◽  
R Storb
Keyword(s):  
Prostaglandin E2 ◽  
Lymphocyte Proliferation ◽  
Chronic Gvhd ◽  
Interleukin 2 ◽  
In Vitro Tests ◽  
Lymphocyte Function ◽  
T Lymphocyte Proliferation ◽  
Long Term Survivors

Abstract Prostaglandins are said to influence T and B cell function by inhibiting the generation of interleukin 2 (IL 2) and the formation of suppressor lymphocytes. After bone marrow transplantation, patients usually have a profound immunodeficiency that persists in recipients with chronic graft-v-host disease (GVHD) and generally resolves in long- term survivors without GVHD. In vitro tests of lymphocyte function such as allogeneic mixed lymphocyte culture (MLC) and cell-mediated lympholysis (CML) have been shown to be impaired in many patients. We postulated that prostaglandin E2 (PGE2) plays a role in the impaired in vitro tests. To test this hypothesis, we studied in vitro tests in the presence of PGE2 antagonists, indomethacin, and anti-PGE2 antiserum with cells from 22 short-term patients (less than 100 days postgrafting) and 32 long-term survivors with or without GVHD. Results show that blockade of PGE2 release by indomethacin and anti-PGE2 significantly (P less than .01) enhanced the MLC (+67%) and the CML responses (+10.5%) of cells from long-term survivors with chronic GVHD but not from those of long-term, stable recipients. No enhancement of MLC and CML activity was observed with cells from donors of long-term recipients. In patients shortly after marrow grafting, enhancement in the MLC was not significant. However, CML activity in this patient group was significantly increased (+12.5% in recipients with no GVHD, 8.5% in those with acute GVHD, P less than .01). Indomethacin also suppressed the activity of nonspecific suppressor cells in patients with chronic GVHD. When cells from patients with chronic GVHD were treated with recombinant IL 2 and IL 2 combined with indomethacin, it was possible to get an additional augmentation of lymphocyte proliferation after the addition of indomethacin to IL 2-treated cultures. Thus it is very likely that PGE2 inhibits T lymphocyte proliferation, not exclusively by inhibition of IL2 production or activity. We conclude that PGE2, among other factors, may play a role in the pathogenesis of the immunodeficiency after transplantation. PGE2 does not act primarily by interfering with IL2 but presumably by inducing a suppressorlike activity.

scholarly journals Development and test for long-term stability of a synthetic standard for a quantitative Cryptosporidium parvum LightCycler™ PCR assay

2005 ◽  
Vol 3 (1) ◽  
pp. 15-25 ◽  
Author(s):  
Renata Filkorn-Kaiser ◽  
Konrad Botzenhart ◽  
Albrecht Wiedenmann
Keyword(s):  
Cryptosporidium Parvum ◽  
Surrogate Marker ◽  
Target Sequence ◽  
Positive Trend ◽  
Long Term Stability ◽  
Synthetic Standard ◽  
One Year

A recently described quantitative rapid cycle real time PCR (LightCycler™) assay detects Cryptosporidium parvum after in vitro excystation, which is a surrogate marker for the viability of the organisms. In the original assay the quantification standard is a dilution series of C. parvum oocysts with a microscopically determined excystation rate. The need to keep suspensions of viable oocysts in stock and to continuously monitor their excystation rate, however, renders the assay impracticable for routine application. A synthetic standard was developed to replace the in vivo standard and was calibrated using oocysts with known excystation rates. The standard consists of a 486 bp DNA segment ranging from 229 bp upstream to 79 bp downstream of the actual PCR target site. Aliquots of the standard were frozen and stored at −20 °C and at −70 °C or lyophilised and stored at room temperature in the dark. For a period of one year samples preserved with each of the three methods were restored every four or five weeks. They were amplified in the LightCycler™ and the crossing points (CP) were monitored. No significant trend in the raw CP values could be observed for any of the three storage methods. However, when the methods were compared to each other by calculating the CP ratios (−20 °C/−70 °C; −20 °C/lyophilised; −70 °C/lyophilised) at the 10 monitoring dates, the CP ratios −20 °C/−70 °C and −20 °C/lyophilised showed a highly significant positive trend (p<0.0001) while the CP ratio −70 °C/lyophilised did not differ from the null hypothesis (p=0.53). It can be concluded that the latter two preservation methods are both appropriate, while storage at −20 °C is less advisable. Calculations based on the molecular weight of the standard and on the assumption of an average yield of three sporozoites per oocyst led to the conclusion that the target sequence is probably located on a double copy gene

scholarly journals Performance of Polyester-Based Electrospun Scaffolds under In Vitro Hydrolytic Conditions: From Short-Term to Long-Term Applications

Nanomaterials ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 786 ◽  
Author(s):  
Oscar Gil-Castell ◽  
José David Badia ◽  
Jordi Bou ◽  
Amparo Ribes-Greus
Keyword(s):  
Molar Mass ◽  
Pure Water ◽  
Phosphate Buffer Solution ◽  
Short Term ◽  
Buffer Solution ◽  
Electrospun Scaffolds ◽  
The Stability ◽  
Short Time

The evaluation of the performance of polyesters under in vitro physiologic conditions is essential to design scaffolds with an adequate lifespan for a given application. In this line, the degradation-durability patterns of poly(lactide-co-glycolide) (PLGA), polydioxanone (PDO), polycaprolactone (PCL) and polyhydroxybutyrate (PHB) scaffolds were monitored and compared giving, as a result, a basis for the specific design of scaffolds from short-term to long-term applications. For this purpose, they were immersed in ultra-pure water and phosphate buffer solution (PBS) at 37 °C. The scaffolds for short-time applications were PLGA and PDO, in which the molar mass diminished down to 20% in a 20–30 days lifespan. While PDO developed crystallinity that prevented the geometry of the fibres, those of PLGA coalesced and collapsed. The scaffolds for long-term applications were PCL and PHB, in which the molar mass followed a progressive decrease, reaching values of 10% for PCL and almost 50% for PHB after 650 days of immersion. This resistant pattern was mainly ascribed to the stability of the crystalline domains of the fibres, in which the diameters remained almost unaffected. From the perspective of an adequate balance between the durability and degradation, this study may serve technologists as a reference point to design polyester-based scaffolds for biomedical applications.

scholarly journals Requirement of the C-terminal proline residue for stability of the Ca2+-activated photoprotein aequorin

1993 ◽  
Vol 293 (1) ◽  
pp. 181-185 ◽  
Author(s):  
N J Watkins ◽  
A K Campbell
Keyword(s):  
Light Emission ◽  
Specific Activity ◽  
In Vitro Transcription ◽  
Wild Type ◽  
Proline Residue ◽  
Long Term Stability ◽  
Recombinant Aequorin

cDNA coding for the Ca(2+)-activated photoprotein aequorin from the jellyfish Aequorea victoria has been engineered to investigate the role of the C-terminal proline residue in bioluminescence. Recombinant aequorin proteins were synthesized by PCR followed by in vitro transcription/translation, and characterized by specific activity, stability, and affinity for coelenterazine. The C-terminal proline residue of aequorin was shown to be essential for the long-term stability of the bound coelenterazine. Aequorin minus proline had only 1% of the specific activity of the wild-type after 2 h, and was virtually inactive after 18 h. The instability of this variant was further demonstrated by re-activating with a coelenterazine analogue (epsilon-coelenterazine), where maximum reactivation was reached in 15 min, and the luminescent activity was almost completely abolished within 3 h. Replacement of the C-terminal proline residue with histidine or glutamic acid decreased the specific activity to 10 and 19% of that of the wild-type respectively. However these variants were also unstable, having t1/2 values of 2.4 h and 2.3 h respectively. Enhancement of the Ca(2+)-independent light emission when proline was replaced by histidine confirmed the stabilizing role of the C-terminal proline. No significant effect of removal of the C-terminal proline was detected on the affinity for coelenterazine.

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