Counter Transport Research Articles

THE ARABIDOPSIS NHX1 GENE: OVEREXPRESSION AND ITS IMPACT ON SALT TOLERANCE IN TRANSGENIC PLANTS

Abiotic stresses, such as salinity, negatively impact crop growth, development and overall production. The discovery and operational confirmation of new genes will provide the framework for successful genetic engineering techniques to increase crop plants' resistance to salinity stress. The most effective method for maintaining ionic balance in plants under stress due to saltiness is provided by the membrane and vacuolar Na+/H+ counter transporter. The function of AtNHX1, the initially identified vacuolar antiporter from more advanced crops, was extensively researched. In this article, we will review the possible function of the Arabidopsis NHX1 gene that is responsible for salt tolerance and its transformation into Wheat, Barley, Poplar, Fescue, Petunia hybrid, Alfalfa & Soybean. Reason to engineer higher plants' genomes using Arabidopsis NHX1 genes to provide food sustainably in salinity-affected locations.

Computational analysis of sodium-dependent phosphate transporter SLC20A1/PiT1 gene identifies missense variations C573F, and T58A as high-risk deleterious SNPs

SLC20A1/PiT1 is a sodium-dependent inorganic phosphate transporter, initially recognized as the retroviral receptor for Gibbon Ape Leukemia Virus in humans. SNPs in SLC20A1 is associated with Combined Pituitary Hormone Deficiency and Sodium Lithium Counter transport. Using in silico techniques, we have screened the nsSNPs for their deleterious effect on the structure and function of SLC20A1. Screening with sequence and structure-based tools on 430 nsSNPs, filtered 17 nsSNPs which are deleterious. To evaluate the role of these SNPs, protein modeling and MD simulations were performed. A comparative analysis of model generated with SWISS-MODEL and AlphaFold shows that many residues are in the disallowed region of Ramachandran plot. Since SWISS-MODEL structure has a 25-residue deletion, the AlphaFold structure was used to perform MD simulation for equilibration and structure refinement. Further, to understand perturbation of energetics, we performed in silico mutagenesis and ΔΔG calculation using FoldX on MD refined structures, which yielded SNPs that are neutral (3), destabilizing (12) and stabilizing (2) on protein structure. Furthermore, to elucidate the impact of SNPs on structure, we performed MD simulations to discern the changes in RMSD, Rg, RMSF and LigPlot of interacting residues. RMSF profiles of representative SNPs revealed that A114V (neutral) and T58A (positive) were more flexible & C573F (negative) was more rigid compared to wild type, which is also reflected in the changes in number of local interacting residues in LigPlot and ΔΔG. Taken together, our results show that SNPs can lead to structural perturbations and impact the function of SLC20A1 with potential implications for disease. Communicated by Ramaswamy H. Sarma

Effect of total pressure difference on counter transport of gases with different molecular weights through solid oxide fuel cell anode

The counter transport of gases with different molecular weights is experimentally and numerically investigated to clarify gas transport phenomena of a hydrogen–steam binary mixture in a solid oxide fuel cell (SOFC) anode during operation. The crossover fluxes through the anodes with different porous microstructures are measured and the effect of total pressure difference on the counter gas transport is evaluated. Without the total pressure difference, an imbalance is found in the diffusion fluxes of gases with different molecular weights in accordance with Graham's diffusion law. Therefore, for the equimolar transport, a total pressure difference is required to enhance the transport of the gas with a larger molecular weight. A numerical model based on the cylindrical pore interpolation model (CPIM) is developed and confirmed to be able to reproduce the experimental results accurately. In addition, the limiting current density of an SOFC predicted using the model we developed agrees with that of the cell evaluated in the experiment. The total pressure at the anode–electrolyte interface is found to be about 20 kPa higher than that on the anode surface at 1 A cm−2, which is non-negligible. Therefore, we must take this into account when we perform numerical simulation of anode-supported SOFCs.

"Efficacy of Treatment Regimens for Sodium-Glucose Counter Transporter 2 Inhibitor (Emaglyf) with Metformin and DPP-4 Inhibitor (Januvia) in Patients with Type 2 Diabetes Mellitus with Stage 1-3 Chronic Kidney Disease"

"Efficacy of Treatment Regimens for Sodium-Glucose Counter Transporter 2 Inhibitor (Emaglyf) with Metformin and DPP-4 Inhibitor (Januvia) in Patients with Type 2 Diabetes Mellitus with Stage 1-3 Chronic Kidney Disease"

Effect of Total Pressure Difference on Counter Transport of Gases with Different Molecular Weights Through Solid Oxide Fuel Cell Anode

Effect of Total Pressure Difference on Counter Transport of Gases with Different Molecular Weights Through Solid Oxide Fuel Cell Anode

Biomimetic Membranes without Proteins but with Aqueous Nanochannels and Facilitated Transport. Minireview

Imitation of biological membranes and aqueous channels attracts more and more attention. In this review, we mention both the early and very recent papers in this area. Still, we concentrate our attention on less known biomimetic membranes, which are commercial nitrocellulose ultrafilters, impregnated by esters of fatty acids. Pores in filters are filled with lipid-like oils, but aqueous nanochannels are spontaneously formed on the inner pore surfaces with carboxylic groups fixed on nitrocellulose. This combination imitates the most fundamental barrier properties of biological membranes, including specific (per unit thickness) permeability of respiratory gases, transport of nonelectrolytes, water, and ions, cation/anion selectivity, electric impedance, etc. The activation energy for water transport in nanochannels is similar to that in aquaporin. In the presence of fatty acids and other carriers, it is possible to observe facilitated and coupled active counter transport of different metal cations in exchange to H+ and without any transmembrane pressure, voltage or ATP. When quinones are dissolved in oils, light-sensitive co-transport of electrons and H+ through oil is possible. In this case, redox-active substances are separated by the membrane. They are not mixed, but they still react. Small biomimetic membranes can be used as electrochemical drug sensors in drug detection and screening, medium size membranes—for smart transdermal drug -delivery, and large membranes—for industrial separation and purification. For example, after small modifications, they can be used for metal recovery, including radioactive strontium removal from nuclear waste accumulated and stored since the Cold War.

Influence of ultraviolet radiation on kinetic characteristics in erythrocytes

Erythrocytes were irradiated with an ultraviolet lamp of the VMT type (λ = 253.7 nm). The kinetic characteristics in irradiated and non-irradiated blood samples were compared by the acid (chemical) erythrogram method and by the counter transport method. Obtained:
 - by the method of acidic erythrograms it was found that in ultraviolet-irradiated blood samples there is a decrease in the time of half hemolysis.
 - ultraviolet radiation increases the speed of counter movement of ions through erythrocyte membranes.
 - a decrease in the time of half hemolysis and an increase in the rate of counter transfer of ions, irradiated blood samples, is due to a decrease in the "effective" thickness of the near-membrane diffusion layer - an immiscible layer of water adjacent to the erythrocyte membrane.
 A decrease in the "effective thickness" of the near-membrane water layer changes the rate of metabolic processes in the "cell - intercellular medium" system, changing the mode of cell functioning. The altered mode of functioning is a biological response to light radiation. Red blood cells with an altered mode of functioning are stimulus signals that force the body to mobilize resources to fight pathology. These circumstances can predict the creation of a universal phototherapeutic equipment for extracorporeal blood irradiation based on LEDs with certain exposure parameters. Figs.: 4. Tabl.: 3. Refs.: 12 titles.

Occupational risk of COVID-19 in the first versus second epidemic wave in Norway, 2020.

BackgroundThe occupational risk of COVID-19 may be different in the first versus second epidemic wave.AimTo study whether employees in occupations that typically entail close contact with others were at higher risk of SARS-CoV-2 infection and COVID-19-related hospitalisation during the first and second epidemic wave before and after 18 July 2020, in Norway.MethodsWe included individuals in occupations working with patients, children, students, or customers using Standard Classification of Occupations (ISCO-08) codes. We compared residents (3,559,694 on 1 January 2020) in such occupations aged 20–70 years (mean: 44.1; standard deviation: 14.3 years; 51% men) to age-matched individuals in other professions using logistic regression adjusted for age, sex, birth country and marital status.ResultsNurses, physicians, dentists and physiotherapists had 2–3.5 times the odds of COVID-19 during the first wave when compared with others of working age. In the second wave, bartenders, waiters, food counter attendants, transport conductors, travel stewards, childcare workers, preschool and primary school teachers had ca 1.25–2 times the odds of infection. Bus, tram and taxi drivers had an increased odds of infection in both waves (odds ratio: 1.2–2.1). Occupation was of limited relevance for the odds of severe infection, here studied as hospitalisation with the disease.ConclusionOur findings from the entire Norwegian population may be of relevance to national and regional authorities in handling the epidemic. Also, we provide a knowledge foundation for more targeted future studies of lockdowns and disease control measures.

The Crystal Structure of the Ca2+-ATPase 1 from Listeria monocytogenes reveals a Pump Primed for Dephosphorylation

Many bacteria export intracellular calcium using active transporters homologous to the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA). Here we present three crystal structures of Ca2+-ATPase 1 from Listeria monocytogenes (LMCA1). Structures with BeF3- mimicking a phosphoenzyme state reveal a closed state, which is intermediate between the outward-open E2P and the proton-occluded E2-P* conformations known for SERCA. It suggests that LMCA1 in the E2P state is pre-organized for dephosphorylation upon Ca2+ release, consistent with the rapid dephosphorylation observed in single-molecule studies. An arginine side-chain occupies the position equivalent to calcium binding site I in SERCA, leaving a single Ca2+ binding site in LMCA1, corresponding to SERCA site II. Observing no putative transport pathways dedicated to protons, we infer a direct proton counter transport through the Ca2+ exchange pathways. The LMCA1 structures provide insight into the evolutionary divergence and conserved features of this important class of ion transporters.

Hydrodynamic modeling and radiotracer investigations in Kolkata Port Trust, Kolkata, West Bengal, India

In this study, hydrodynamic modeling and radiotracer investigations were conducted in Kolkata Port Trust, Kolkata, West Bengal, India to investigate the dispersion of sediments and to evaluate the suitability of three different dumping sites (Upper Auckland, Lower Auckland and Eden) for dredged sediments along a navigation channel. Scandium-46 (148-240 GBq) comprising scandium glass powder with a particle size distribution ranging from 75-100 μm was used as a radiotracer. The radiotracer was injected onto the seabed at the selected site using a remotely operated injection system and its movement on the seabed was tracked over a period of three months using waterproof NaI(Tl) scintillation detector. The tracer concentration curves were plotted on a site map of the area for different trackings and isocount contours were plotted. Qualitative information was obtained from the isocount contours such as the general direction of movement and spread of the radiotracer. The isocount contours showed that the sediment predominantly moved away from the navigation channel. From the isocount, a transport diagram was plotted based on isocount counter and sediment transport parameters such as the general direction of movement by sediments on the seabed, transport velocity, transport thickness and bed load movement rate were determined for all the sites. The dispersion patterns obtained for the sediments by modeling were compared with the experimental results and they were found to be similar. Thus, the model results were validated and the proposed sites were found to be suitable for dumping the dredged material because the sediments did not return to the navigation channel.

Tenapanor: new approach to counter irritable bowel syndrome with constipation

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder chronic in nature and characterized predominantly by abdominal pain or discomfort associated with altered bowel habits, diagnosis requires characteristic symptoms during the last 3 months and onset ≥6 months ago. Symptom-based approaches for functional bloating, constipation and diarrhea are best utilised to identify IBS. IBS with constipation exerts significant impairment on work productivity by hampering quality of life. Inadequate relief by existing modalities, persistent hard stools and visceral abdominal pain demanded further clinical research. Tenanapor a novel molecule acts locally on gastrointestinal sodium/hydrogen exchanger isoform 3 (NHE3), an antiporter a counter transporter and exert antinociceptive effects on visceral sensation thereby decreases the frequency of abdominal pain. Action on NHE3 receptors located on small intestine and colon’s apical surface reduces the absorption of sodium and phosphate, with minimal systemic exposure. NHE3 Inhibition induced sodium absorption results in increase in water secretion into intestinal lumen resultant an accelerated intestinal transit time and softer stool consistency. Most common adverse reactions (≥2%) are diarrhea, abdominal distension, flatulence and dizziness. The drug is metabolised mainly by CYP3A4/5 and excreted in feaces (70%) and urine (7%). Tenapanor’s minimal systemic absorption is likely to be associated with a relatively inert safety and tolerability profile. Based on positive results from the phase III T3MPO trial program, tenapanor demonstrated promising results for IBS-C management and received US Food and Drug Administration approval as IBSRELA @ Ardelyx Pharma in September 2019 and augment existing modalities for management of IBS-C.

In-Line Seawater Phosphate Detection with Ion-Exchange Membrane Reagent Delivery.

There is an urgent need for reliable seawater phosphate measuring tools to better assess eutrophication. Today, most accepted sensing approaches are based on the established colorimetric molybdenum blue assay. It requires one to modify the sample to strongly acidic conditions and to add various reagents, principally molybdate and reducing agent (e.g., ascorbic acid), to form a blue colored phosphate complex that is subsequently detected spectrophotometrically. The associated need for large sample and mobile phase reservoirs and mixing coils are, unfortunately, not ideally adapted for the development of operationally simple in situ sensing instruments. It is here demonstrated for the first time that the key reagents needed to achieve phosphate detection by the molybdate method may be delivered by passive counter transport across ion-exchange membranes. A cation-exchange Donnan exclusion membrane placed in contact with a sample flow (450 μm thick) is shown to provide the strongly acidic conditions (pH ∼ 1) necessary for phosphate determination. Proton transport is driven, via cation-exchange, by the high sodium content of the seawater sample. Molybdate was similarly released through an anion-exchange membrane by chloride counter transport. Consequently, an in-line flow system containing the two membrane modules in series was used for delivering both hydrogen and molybdate ions into the sample to form the desired phosphomolybdate complex for subsequent spectrophotometric detection. A linear calibration in the range of 0.1-10 μM phosphate (3-300 ppb inorganic P) was achieved, which is sufficiently attractive for environmental work. A range of seawater samples was tested and the results from this membrane delivery device showed no significant differences compared to the classical molybdate assay chosen as the reference method.

The Intracellular Loop of the Na+/Ca2+ Exchanger Contains an "Awareness Ribbon"-Shaped Two-Helix Bundle Domain.

The Na+/Ca2+ exchanger (NCX) is a ubiquitous single-chain membrane protein that plays a major role in regulating the intracellular Ca2+ homeostasis by the counter transport of Na+ and Ca2+ across the cell membrane. Other than its prokaryotic counterpart, which contains only the transmembrane domain and is self-sufficient as an active ion transporter, the eukaryotic NCX protein possesses in addition a large intracellular loop that senses intracellular calcium signals and controls the activation of ion transport across the membrane. This provides a necessary layer of regulation for the more complex function of eukaryotic cells. The Ca2+ sensor in the intracellular loop is known as the Ca2+-binding domain (CBD12). However, how the signaling of the allosteric intracellular Ca2+ binding propagates and results in transmembrane ion transportation still lacks a detailed explanation. Further structural and dynamics characterization of the intracellular loop flanking both sides of CBD12 is therefore imperative. Here, we report the identification and characterization of another structured domain that is N-terminal to CBD12 in the intracellular loop using solution nuclear magnetic resonance (NMR) spectroscopy. The atomistic structure of this domain reveals that two tandem long α-helices, connected by a short linker, form a stable crossover two-helix bundle (THB), resembling an "awareness ribbon". Considering the highly conserved amino acid sequence of the THB domain, the detailed structural and dynamics properties of the THB domain will be common among NCXs from different species and will contribute toward the understanding of the regulatory mechanism of eukaryotic Na+/Ca2+ exchangers.

SAC1 degrades its lipid substrate PtdIns4P in the ER to maintain a steep electrochemical gradient on donor membranes

Phosphatidylinositol 4‐phosphate (PtdIns4P) is one of the most functionally diverse molecules utilized by eukaryotic cells. It is both a metabolic hub for other crucial signaling lipids such as PtdIns(4,5)P2 and PtdInsP3, and a key molecule for recruitment of membrane and lipid transport proteins in its own right. Most recently, it has been proposed to form a “phosphoinositide‐motive force”, whereby transport of PtdIns4P molecules down their concentration gradient from the plasma membrane (PM) or Golgi to the ER drives counter transport of other lipids up their own concentration gradients. A critical requirement for this model is that the main PtdIns4P degrading enzyme, the integral ER phosphatase SAC1, hydrolyzes PtdIns4P in the ER in a “cis” configuration. Alternatively, it has been suggested that other functions of PtdIns4P are regulated by SAC1 hydrolyzing PtdIns4P directly in the PM in a “trans” configuration at membrane contact sites (MCS). However, such activity would surely disrupt lipid counter transport. Therefore, we sought to determine whether SAC1 acts in “cis”, “trans”, or both in mammalian cells. Acute chemical ablation of SAC1 activity drives ectopic accumulation of PtdIns4P in the ER, revealing “cis” activity. Furthermore, endogenous or ectopically expressed SAC1 localizes to the ER and Golgi, but does not constitutively or dynamically enrich at ER‐PM MCS. Forced recruitment of SAC1 to experimentally induced MCS does not produce robust “trans” activity on PM PtdIns4P. However, “trans” activity can be induced by adding an approximately 6 nm long helical linker between the ER anchor and the catalytic domain. Together, our results reveal that SAC1 operates in a “cis” configuration. This ensures a “phosphoinositide‐motive force” for lipid transport is effective, and also implies regulation of PM phosphoinositide signaling is tightly linked to non‐vesicular traffic of PtdIns4P at ER‐PM MCS.Support or Funding InformationThis work was supported by National Institutes of Health grant 1R35GM119412‐01This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

EVALUATION OF KINETIC CONSTANTS AND TRANSPORT EFFICIENCIES AT MEMBRANE INTERFACES TO OPTIMIZE Co(II) RECOVERY BY BULK LIQUID MEMBRANES

The harms of heavy metals to the environment and public health joined to their character of valuable resource, have lead to an increasing interest in the search of efficient processes for their removal/recovery. In this paper we study the optimization of cobalt(II) recovery by bulk liquid membranes through a carrier facilitated counter transport mechanism, using DP8R as carrier and H2SO4 as stripping agent (protons as counter-ions), by analyzing the influence of different operational parameters (carrier concentration in the membrane, stripping agent concentration in the product phase, stirring rate and organic phase volume) on both the extraction/stripping kinetic constants and the Co(II) transport efficiencies through the feed/membrane and the membrane/product interfaces.

Photo-Induced Ionic Noise in Si and Quartz Based Solid-State Nanopore Device

In the past two decades there has been a tremendous amount of research into the use of nanopores as single molecule sensors, which has been inspired by the Coulter counter and molecular transport across biological pores. Recently, the desire to increase structural resolution and analytical throughput has led to the integration of additional detection methods such as fluorescence spectroscopy. For structural information to be probed electronically high bandwidth measurements are crucial due to the high translocate on velocity of molecules. The most commonly used solid-state nanopore sensors consist of a silicon nitride membrane and bulk silicon substrate. Unfortunately, the photoinduced noise associated with illumination of these platforms limits their applicability to high-bandwidth, high-laser-power synchronized optical and electronic measurements. Here, we investigate the influence of light illumination in the solid-state nanopore device fabricated either on Si substrate and quartz substrate. As has been well known, the noise signal in the solid state nanopore structure has been one of the major concerns. And the strong increase of ionic noise upon laser light illumination has been investigated before. Without light illumination, the noise signal which is characterized either by RMS value or more importantly by the power spectrum (pA2/Hz versus frequency Hz) typically shows about 40 pA in a Si substrate and 5.3 pA in a quartz substrate in RMS values and shows much improved noise characteristics on quartz substrate both in low frequency and high frequency. In general, it has been known that there are four different types of noise sources of ionic current obtained from the patch clamp system which shows different frequency dependency; 1. Voltage noise including RC noise showing f2 relationship, 2. dielectric noise which is proportional to f, 3. Johnson noise (thermal noise or Nyquist noise) and shot noise which are independent to f, and 4. Flicker noise related to a combination of noise showing 1/fa characteristics. However, upon irradiation with laser light in Si device, a completely different PSD was observed. PSD has the corner frequency, which is located at few hundreds Hz. This frequency dependence of this noise source is inconsistent with that of surface charge protonation noise or temperature-dependent thermal and dielectric noise. And, this peaks absence within the quartz-SiNx platforms power spectrum suggests the source of noise is related to the Si substrate. The optical transparency of the SiNx membrane and photon energy (2.54 eV) is sufficient for electron-hole pair generation in the Si substrate (band gap ∼1.1 eV), reported to promote photoreduction of H+ at p-type Si interfaces. Therefore, the increase in noise is via electrochemical reaction at the silicon/electrolyte surface by the excitation electron-hole pairs. In this sense, quartz device has only insignificant increase with laser illumination. Increase in thermal and dielectric noise term by localized heating can explain the small noise increase. This observation may also be quite important since there are many researchers who would like to utilize spectroscopic way of sequencing the DNA in a nanopore system.

Modeling mass transfer in solid oxide fuel cell anode: I. Comparison between Fickian, Stefan-Maxwell and dusty-gas models

Fickian, Stefan-Maxwell and dusty-gas model have been widely used in modeling mass transfer in porous electrodes of solid oxide fuel cells. Suwanwarangkul et al. (J. Power Sources 122 (2003) 9–18) implement a survey for performance comparison among these models to predict the concentration overpotential of a solid oxide fuel cell anode. In their work, the flux ratio of species is calculated by Graham's law and contradictorily the equimolar counter transport is used for isobaric assumption. Focused on the flux-ratio approaches and usually neglected pressure gradient, a comparison between Fickian, Stefan-Maxwell and dusty-gas model is done again in this article. The dusty gas model combined with the ‘Stoich’ flux-ratio approach, i.e. the species flux is dictated by its stoichiometry of the electrochemical reaction, is validated to make the best performance. And all models by the ‘Graham’ flux-ratio approach, i.e. the flux of species satisfies Graham's law, underestimate the concentration overpotential when the molecular weights of species are quite different. The extended Stefan-Maxwell model is an alternative, although it generally exaggerates the role of Knudsen diffusion. The effect of pore size on the Knudsen diffusion and pressure gradient is also discussed.

Formation and development of salt crusts on soil surfaces

The salt concentration gradually increases at the soil free surface when the evaporation rate exceeds the diffusive counter transport. Eventually, salt precipitates and crystals form a porous sodium chloride crust with a porosity of 0.43 ± 0.14. After detaching from soils, the salt crust still experiences water condensation and salt deliquescence at the bottom, brine transport across the crust driven by the humidity gradient, and continued air-side precipitation. This transport mechanism allows salt crust migration away from the soil surface at a rate of 5 μm/h forming salt domes above soil surfaces. The surface characteristics of mineral substrates and the evaporation rate affect the morphology and the crystal size of precipitated salt. In particular, substrate hydrophobicity and low evaporation rate suppress salt spreading.

In Ovo injection of betaine affects hepatic cholesterol metabolism through epigenetic gene regulation in newly hatched chicks.

Betaine is reported to regulate hepatic cholesterol metabolism in mammals. Chicken eggs contain considerable amount of betaine, yet it remains unknown whether and how betaine in the egg affects hepatic cholesterol metabolism in chicks. In this study, eggs were injected with betaine at 2.5 mg/egg and the hepatic cholesterol metabolism was investigated in newly hatched chicks. Betaine did not affect body weight or liver weight, but significantly increased the serum concentration (P < 0.05) and the hepatic content (P < 0.01) of cholesterol. Accordingly, the cholesterol biosynthetic enzyme HMGCR was up-regulated (P < 0.05 for both mRNA and protein), while CYP7A1 which converts cholesterol to bile acids was down-regulated (P < 0.05 for mRNA and P = 0.07 for protein). Moreover, hepatic protein content of the sterol-regulatory element binding protein 1 which regulates cholesterol and lipid biosynthesis, and the mRNA abundance of ATP binding cassette sub-family A member 1 (ABCA1) which mediates cholesterol counter transport were significantly (P < 0.05) increased in betaine-treated chicks. Meanwhile, hepatic protein contents of DNA methyltransferases 1 and adenosylhomocysteinase-like 1 were increased (P < 0.05), which was associated with global genomic DNA hypermethylation (P < 0.05) and diminished gene repression mark histone H3 lysine 27 trimethylation (P < 0.05). Furthermore, CpG methylation level on gene promoters was found to be increased (P < 0.05) for CYP7A1 yet decreased (P < 0.05) for ABCA1. These results indicate that in ovo betaine injection regulates hepatic cholesterol metabolism in chicks through epigenetic mechanisms including DNA and histone methylations.

Synchronized optical and electronic detection of biomolecules using a low noise nanopore platform.

In the past two decades there has been a tremendous amount of research into the use of nanopores as single molecule sensors, which has been inspired by the Coulter counter and molecular transport across biological pores. Recently, the desire to increase structural resolution and analytical throughput has led to the integration of additional detection methods such as fluorescence spectroscopy. For structural information to be probed electronically high bandwidth measurements are crucial due to the high translocation velocity of molecules. The most commonly used solid-state nanopore sensors consist of a silicon nitride membrane and bulk silicon substrate. Unfortunately, the photoinduced noise associated with illumination of these platforms limits their applicability to high-bandwidth, high-laser-power synchronized optical and electronic measurements. Here we present a unique low-noise nanopore platform, composed of a predominately Pyrex substrate and silicon nitride membrane, for synchronized optical and electronic detection of biomolecules. Proof of principle experiments are conducted showing that the Pyrex substrates have substantially lowers ionic current noise arising from both laser illumination and platform capacitance. Furthermore, using confocal microscopy and a partially metallic pore we demonstrate high signal-to-noise synchronized optical and electronic detection of dsDNA.