High Ionic Strength Solutions Research Articles

Rapid detection of NT-proBNP from whole blood using FET based biosensors for homecare

Detection of protein biomarkers in blood has diagnostic and prognostic potential in diseases such as heart failure (HF). But currently diagnostics for short term HF biomarkers such as NT-proBNP are only available in the clinical settings which require sophisticated laboratory-based instruments that are costly, complex and time-consuming. We have developed a portable and biosensor system to carry out a rapid whole blood immunoassay to detect NT-proBNP using a field effect transistor (FET) based biosensor. The biosensor has short response time (5 min) and does not require additional sample pre-processing. The biosensor utilizes an electrical double layer (EDL) gated FET, with enhanced sensitivity in high ionic strength solution. The FET biosensor adopts an extended gate format with high electric modulation which enables very high sensitivity, selectivity and wide dynamic range of detection in whole blood. The sensitivity is also correlated with the surface functionalization of the FET biosensor. A portable, hand-held biosensor measurement unit is used to measure and record the electrical signals from the sensor chips which can be used in a ‘dispose after use’ format. In this study, we have demonstrated the detection of NT-proBNP in 1X PBS and whole blood. This sensor is intended for personal home-care diagnostics.

Green fluorescent carbon quantum dots as a label-free probe for rapid and sensitive detection of hematin.

Hematin is an oxidized form of heme, and the abnormal levels of hematin in the human body can lead to various inflammatory lesions. Hence, there is still a need to establish a rapid, sensitive and efficient method for hematin detection. Herein, the green fluorescent carbon quantum dots (CQDs) are synthesized by using L-cysteine and hydrogen peroxide as precursors. The synthesized CQDs exhibit some fascinating characters including excellent water solubility, high fluorescence quantum yield, and good stability in a broad pH range of 7.0-11.0 and high ionic strength solution. Excitingly, the fluorescence of CQDs can be rapidly and selectively quenched by hematin via the inner filter effect. Moreover, the detection of hematin by the CQDs fluorescent probe shows a good linearity in the concentration range of 0.5-30 μM with a minimum detection limit of 0.1 μM. Finally, the proposed approach is successfully applied to detect hematin in human blood samples.

A label-free aptamer-based nanogap capacitive biosensor with greatly diminished electrode polarization effects.

A significant impediment to the use of impedance spectroscopy in bio-sensing is the electrode polarization effect that arises from the movement of free ions to the electrode-solution interface, forming an electrical double layer (EDL). The EDL screens the dielectric response of the bulk and its large capacitance dominates the signal response at low frequency, masking information particularly relevant for biological samples, such as molecular conformation changes and DNA hybridization. The fabrication of nanogap capacitors with electrode separation less than the EDL thickness can significantly reduce electrode polarization effects and provide enormous improvement in sensitivity due to better matching of the sensing volume with the size of the target entities. We report on the fabrication of a horizontal thin-film nanogap capacitive sensor with electrode separation of 40 nm that shows almost no electrode polarization effects when measured with water and ionic buffer solutions, thereby allowing direct quantification of their relative permittivity at low frequencies. Surface modification of the electrodes with thiol-functionalized single strand DNA aptamers transforms the device into a label-free biosensor with high sensitivity and selectivity towards the detection of a specific protein. Using this approach, we have developed a biosensor for the detection of human alpha thrombin. In addition, we also examine frequency dependent permittivity measurements on high ionic strength solutions contained within the nanogap and discuss how these support recent experimental observations of large Debye lengths. A large shift in the Debye relaxation frequency to lower frequency is also found, which is consistent with water molecules being in a rigid-like state, possibly indicating the formation of an ordered "ice-like" phase. Altogether, this work highlights the need for better understanding of fluids in confined, nanoscale geometries, from which important new applications in sensing may arise.

Chondroitin sulfate increases cell transfection efficiency by DNA-PEI complexes

One of the most popular nonviral delivery systems for gene therapy constructs are carriers based on polyethylenimine (PEI) DNA complexes. A number of disadvantages associated with the lack of targeted delivery and increased cytotoxicity are overcome by adding auxiliary molecules to the complexes. An example of this is chondroitin sulfate (CS). The purpose of this work was to assess the effect of CS on the transfection properties of DNA–PEI complexes under different conditions of their preparation and transfection protocols. All complexes were prepared in solutions with high and low ionic strength. Transfection of C26 cells was performed according to two protocols differing in the presence of serum in the medium. The portion of transfected cells, transgene expression level, and cell viability were the main parameters of assessing the transfection efficiency. In binary DNA–PEI complexes prepared in different salt conditions, using different transfection protocols, the difference in the portion of transfected cells reached ten times. Addition of CS improved this transfection efficiency indicator up to 6.5 times, while the maximum difference in this indicator for the corresponding ternary complexes was reduced to 2.5 times. Changes in the proportion of CS in the composition of the complexes had an insignificant effect on their transfection properties. In the case of complexes prepared in high ionic strength solutions, the order of CS addition was also important. The best results of transfection efficiency were achieved with ternary complexes prepared in low ionic strength solutions, using a serum-free protocol, while these indicators were comparable with the data for Lipofectamine 2000. The addition of chondroitin sulfate improves the transfection properties of DNA–PEI complexes and makes them less dependent on the methods of preparation and transfection.

Wettability of Amphoteric Surfaces: The Effect of pH and Ionic Strength on Surface Ionization and Wetting.

We present a novel theory to predict the contact angle of water on amphoteric surfaces, as a function of pH and ionic strength. To validate our theory, experiments were performed on two commonly used amphoteric materials, alumina (Al2O3) and titania (TiO2). We find good agreement at all pH values, and at different salt concentrations. With increasing salt concentration, the theory predicts the contact angle-pH curve to get steeper, while keeping the same contact angle at pH = PZC (point of zero charge), in agreement with data. Our model is based on the amphoteric 1-pK model and includes the electrostatic free energy of an aqueous system as well as the surface energy of a droplet in contact with the surface. In addition, we show how our theory suggests the possibility of a novel responsive membrane design, based on amphoteric groups. At pH ∼ PZC, this membrane resists flow of water but at slightly more acidic or basic conditions the wettability of the membrane pores may change sufficiently to allow passage of water and solutes. Moreover, these membranes could act as active sensors that only allow solutions of high ionic strength to flow through in wastewater treatment.

Quantitation of carbohydrate monomers and dimers by liquid chromatography coupled with high-resolution mass spectrometry

As remnants of plant wastes or plant secretions, carbohydrates are widely found in various environmental matrices. Carbohydrate-containing feedstocks represent important carbon sources for engineered bioproduction of commodity compounds. Routine monitoring and quantitation of heterogenous carbohydrate mixtures requires fast, accurate, and precise analytical methods. Here we present two methods to quantify carbohydrates mixtures by coupling hydrophilic interaction liquid chromatography with electrospray ionization high-resolution mass spectrometry. Method 1 was optimized for eleven different carbohydrates: three pentoses (ribose, arabinose, xylose), three hexoses (glucose, fructose, mannose), and five dimers (sucrose, cellobiose, maltose, trehalose, lactose). Method 1 can monitor these carbohydrates simultaneously, except in the case of co-elution of xylose/arabinose and lactose/maltose/cellobiose peaks. Using the same stationary and mobile phases as in Method 1, Method 2 was developed to separate glucose and galactose, which were indistinguishable in Method 1. Both methods have low limits of detection (0.019–0.40 μM) and quantification (0.090–1.3 μM), good precision (2.4–13%) except sucrose (18%), and low mass error (0.0–2.4 ppm). Method 1 was robust at analyzing high ionic strength solutions, but a moderate matrix effect was observed. Finally, we apply Method 1 to track concurrently the extracellular depletion of five carbohydrates (xylose, glucose, fructose, mannose, and maltose) by Pseudomonas protegens Pf-5, a biotechnologically-important soil bacterial species.

Rapid desorption of radium isotopes from black shale during hydraulic fracturing. 1. Source phases that control the release of Ra from Marcellus Shale

Hydraulic fracturing of the Marcellus Shale produces wastewaters that are hypersaline and highly enriched in isotopes of radium. Radium is understood to derive from the Marcellus Shale itself, but its source phases and their contributions to wastewater production have not been described. Using sequential extractions and experimental leachates, we characterize two distinct end-members that could contribute Ra to wastewaters, (1) a mineral phase, which hosts labile228Ra and has 226Ra/228Ra atom ratios ~250, and (2) an organic phase, which hosts exchangeable226Ra and has 226Ra/228Ra ~10,000. In leaching experiments we observed rapid extraction of Ra from these phases, with high ionic strength solutions leaching up to 14% of Ra from the shale in just hours. Radium concentrations and 226Ra/228Ra ratios increase with [Ca2+] of the leaching solution, and solutions approaching 1 M Ca2+ produce 226Ra/228Ra ratios compatible with Marcellus wastewaters. In contrast, pure water removes <0.5% of Ra from the shale with low 226Ra/228Ra ratios incompatible with wastewaters. Experimental results and wastewater data together provide a coherent picture, that the distinctive Ra isotopic signature of Marcellus wastewaters results from contemporaneous water-rock interactions that promote desorption of 226Ra from organics during hydraulic fracturing.

Miniaturized Biomedical Sensors for Enumeration of Extracellular Vesicles.

In this research, we have realized a rapid extracellular vesicle (EV) quantification methodology using a high field modulated AlGaN/GaN high electron mobility (HEMT) biosensor. The unique sensing structure facilitated the detection of the sub-cellular components in physiological salt environment without requiring extensive sample pre-treatments. The high field operation of GaN HEMT biosensor provides high sensitivity and wide dynamic range of detection of EVs (107–1010 EVs/mL). An antibody specific to the known surface marker on the EV was used to capture them for quantification using an HEMT biosensor. Fluorescence microscopy images confirm the successful capture of EVs from the test solution. The present method can detect EVs in high ionic strength solution, with a short sample incubation period of 5 min, and does not require labels or additional reagents or wash/block steps. This methodology has the potential to be used in clinical applications for rapid EV quantification from blood or serum for the development of diagnostic and prognostic tools.

Direct label-free protein detection in high ionic strength solution and human plasma using dual-gate nanoribbon-based ion-sensitive field-effect transistor biosensor

We report on direct label-free protein detection in high ionic strength solution and human plasma by a dual-gate nanoribbon-based ion-sensitive field-effect transistor (NR-ISFET) biosensor system with excellent sensitivity and specificity in both solution-gate (SG) and dual-gate (DG) modes. Compared with previously reported results, the NR-ISFET biosensor enables selective prostate specific antigen (PSA) detection based on antibody-antigen binding in broader detection range with lower LOD. For the first time, real-time specific detection of PSA of 10 pM to 1 μM in 100 mM phosphate buffer (PB) was demonstrated by conductance measurements using the polyethylene glycol (PEG)-modified NR-ISFET biosensors in DG mode with the back-gate bias (VBG) of 20 V. Due to larger maximum transconductance value resulting from the modulation of NR-ISFET channel by the back gate in DG mode, the detection range can be broadened with larger linear detection region (100 pM to 100 nM) and lower limit of detection (LOD, 10 pM) as compared to those in SG mode. Moreover, the influence of different back-gate bias from VBG = 5 V to VBG = 25 V on the biosensor performance has been investigated. Furthermore, direct PSA detection of 100 pM to 1 μM in human plasma was demonstrated by using the PEG-modified NR-ISFET in DG mode, enabling direct detection of protein in human blood for clinical applications since the LOD of 100 pM PSA can meet the clinical requirements.

Direct detection of DNA using electrical double layer gated high electron mobility transistor in high ionic strength solution with high sensitivity and specificity

In this research, we have realized an electrical double layer (EDL) gated high electron mobility transistor (HEMT) as DNA sensor. The sensing area on the gate electrode which is separated from the transistor channel is immobilized with probe DNA to capture target DNA from physiological salt environment. The detection limit of the sensor can be as low as 1 fM with very high sensitivity. The specificity of the DNA sensor is also demonstrated by controlling the hybridization temperature. By choosing the hybridization temperature slightly lower than the melting temperature of the well-matched sequence, the binding ratio can be controlled between the fully-matched and mismatched one. The sensor has demonstrated specificity, with the ability to achieve single base mismatch resolution. The sensor has the potential for rapid DNA sensing applications in cells, biomarkers and viruses.

A Thermodynamic Model for ZrO2(am) Solubility at 25 °C in the Ca2+–Na+–H+–Cl−–OH−–H2O System: A Critical Review

Zirconium is an important element in the nuclear fuel cycle. Thermodynamic data and models to reliably predict Zr–OH system behavior in various conditions including high ionic strengths are required and currently are unavailable. Most available experimental data are rather old, obtained using inadequate methodologies, and provide equilibrium constant values that differ by many orders of magnitude. Previous reviews have recommended values based on available data. These reviews used all of the available data, including poor quality data, in a global fit to determine these values. This has resulted in recommended thermodynamic models with a large number of polynuclear species and a number of mononuclear species with values of thermodynamic constants for the solubility product of ZrO2(am) and Zr–OH hydrolysis constants that are many orders of magnitude different from those for the reliable analogous Hf reactions. In this critical review, we have evaluated the quality of the available data, selected only those data that are of high quality, and reinterpreted all of the high quality data using SIT and Pitzer models for applications to high ionic strength solutions. Herein for 25 °C we (1) present formation constant values for ZrOH3+, $$ {\text{Zr}}\left( {\text{OH}} \right)_{2}^{2 + } $$ , Zr(OH)4(aq), $$ {\text{Zr}}\left( {\text{OH}} \right)_{5}^{ - } $$ , and $$ {\text{Zr}}\left( {\text{OH}} \right)_{6}^{2 - } $$ , and the solubility product for ZrO2(am) which are consistent with the Hf system, (2) report a revised value for the formation constant of $$ {\text{Ca}}_{3} {\text{Zr}}\left( {\text{OH}} \right)_{6}^{4 + } $$ , (3) show that several hypothetical polynuclear species ( $$ {\text{Zr}}_{3} \left( {\text{OH}} \right)_{9}^{3 + } $$ , Zr4(OH) 15 + , and Zr4(OH)16(aq)) proposed in previous reviews are not needed, and (4) show that polynuclear species ( $$ {\text{Zr}}_{3} \left( {\text{OH}} \right)_{4}^{8 + } $$ and $$ {\text{Zr}}_{4} \left( {\text{OH}} \right)_{8}^{8 + } $$ ) are not important in a very extensive H+ concentration range (0.1–10−15.4 mol·kg−1). Our review has also resulted in SIT and Pitzer ion-interaction parameters applicable to as high ionic strength solutions as 5.6 mol·kg−1 in NaCl, 2.11 mol·kg−1 in CaCl2, and 23.5 mol·kg−1 in NaOH.

Casuarina equisetifolia cone as sustainable adsorbent for removal of Malachite green dye from aqueous solution using batch experiment method

Various methods have been devised in order to treat the wastewaters before they are disposed into water bodies such as the rivers and the seas. One of the methods used is adsorption as it has the advantages of cheap, environmentally friendly and wide range of materials can be used. In this study Casuarina equisetifolia cone (CEC) was used to remove malachite green (MG) from aqueous solution and the adsorption process was investigated through contact time, pH, temperature, ionic strength and dye concentration. The experimental results indicated that CEC can operate well in high ionic strength solution and was not significantly affected by temperature. The adsorption process followed the pseudo-2 nd order and can be described using the Langmuir model where the maximum adsorption capacity was determined as 58 mg g -1 .

Risk stratification of heart failure from one drop of blood using hand-held biosensor for BNP detection

Continued risk assessment by evaluating cardiac biomarkers in healthy and unhealthy individuals can lower the mortality rate of cardiovascular diseases (CVDs). In this research, we have developed a hand-held biosensor system to rapidly screen for brain natriuretic peptide (BNP) from a single drop of whole blood. The sensor methodology is based on extended gate design of electrical double layer (EDL) field effect transistor (FET), that can directly detect BNP in whole blood, without extensive sample pre-treatments, thereby eliminating the limitations of charge screening in high ionic strength solutions. A simple sensor array chip is fabricated to integrate with the MOSFET sensor system. Sensing characteristics are elucidated using purified BNP samples in 1 × PBS (with 4% BSA), spiked BNP samples in whole blood and clinical whole blood samples. The blood cells can be gravitationally separated without the use of any external actuation. The sensor exhibits very high sensitivity over wide dynamic range of detection. The sensing characteristics are not adversely affected by the presence of background proteins or blood cells, even without gravitational blood cell separation. Thus, the biosensor system can allow users to perform rapid whole blood diagnostics with minimal user protocols, in 5 min. The features of high sensitivity, cost-effectiveness and convenience of usage empower this technology to revolutionize the mobile diagnostics and healthcare industry.

Improved stability of self-healing hydrogel pore-filled membranes with ionic cross-links

A self-healing water filtration membrane that can autonomously recover from rejection loss due to physical damage is a promising solution to deal with prevalent membrane integrity deterioration problems. While hydrogel-composite membranes fabricated using poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) hydrogel and a polyethersulfone support exhibit strong self-healing property, the stability of these membranes in high ionic strength solutions is uncertain. This study investigates the effect of changes in the ionic strength of the swelling medium due to the presence of saline and acidic solutions on PAMPS pore-filled membranes. Acidic conditions had a deleterious effect on the pore-filled membranes, resulting in loss of rejection to 50%. However, the presence of cations such as calcium and sodium ions in saline solutions improved the stability and self-healing property of PAMPS pore-filled membranes substantially. Ionically cross-linked membranes showed rejection recovery from values as low as 13%, which is a marked improvement over previous pore-filled membranes which did not show any self-healing property when the rejection fell below 30%. The results of this study suggest that ionic cross-links provide a facile approach to improve the performance of self-healing hydrogel pore-filled membranes.

Choosing mineral flotation collectors from large nanoparticle libraries

Polystyrene nanoparticles can promote froth flotation of mineral particles if the nanoparticles are sufficiently hydrophobic and are colloidally stable in the high ionic strength solutions typical of commercial flotation operations. A library of 80 unique polystyrene nanoparticle types was prepared with click chemistry and used to determine if particles that were sufficiently hydrophilic to be colloidally stable in high ionic strength and high pH solutions, were also capable of promoting flotation. The conflicting requirements of colloidal stability and hydrophobicity can be achieved in 9 mM sodium carbonate, a very challenging environment. Instead of testing all 80 samples with laborious flotation testing, automated assays measuring colloid stability and nanoparticle hydrophobicity were employed. The colloid stability assay measured the critical coagulation concentrations (CCC). Nanoparticle hydrophobicity was characterized by water contact angle, measurements (CA). A smaller cohort of the most promising nanoparticle candidates for detailed flotation testing were identified by mapping nanoparticle properties on the CA versus CCC plain – a “Flotation Domain Diagram”. We believe that this work was the first time that combinatorial synthesis and high throughput screening have been used in the development of flotation chemicals. Finally, based on the accumulated evidence, effective nanoparticle flotation collectors are likely to be ∼50 nm in diameter, with a soft hydrophobic polymer shell and with surface functional group densities in the order of magnitude of 0.1 nm−2.

Highly sensitive and rapid MicroRNA detection for cardiovascular diseases with electrical double layer (EDL) gated AlGaN/GaN high electron mobility transistors

This study reports the development of an efficient and sensitive method to directly sense microRNA (miRNA) in high ionic strength solutions with the use of electrical double layer (EDL) gated AlGaN/GaN high electron mobility transistor (HEMT). This FET structure uses a complementary DNA probe functionalized gate electrode which is separated from the transistor channel. In this research, we focus on the detection of miRNA samples, miR-126, miR-208a and miR-21 which are biomarkers of cardiovascular diseases (CVD). The sensor has a dynamic range that is comparable to the clinically relevant concentration range with a detection limit as low as 1 fM. Selectivity of the sensor is demonstrated by evaluating sensor response at fully complementary and slightly mismatched sequences. The miniaturized sensor can be used in point of care or homecare diagnostics for rapid miRNA detection to evaluate CVDs at an early stage.

Review—High Field Modulated FET Biosensors for Biomedical Applications

In here, we have reviewed the major FET sensor methodologies developed for biosensing applications. Each of the methodologies offer different approaches to mitigate the effects of charge screening in high ionic strength solutions. We focus in detail on the study of high field gated FET biosensors developed to directly detect target analytes in physiological salt environments, without extensive sample pre-treatments. Several biomedical applications are illustrated in this review cum original research article, such as protein detection in buffer/serum/whole blood, nucleotide detection in buffer, whole cell-based sensor and characterization of biological tissues. The mechanism of detection beyond Debye length in high ionic strength solutions is investigated. The integrated portable biosensor system developed based on the high field gated FET biosensor demonstrates potential for clinical applications in point of care and home-care diagnostics.

A Comprehensive Model for Whole Cell Sensing and Transmembrane Potential Measurement Using FET Biosensors

In this research, the development of a highly sensitive FET based biosensor technology for whole cell sensing and cellular transmembrane potential measurement is discussed and a quantitative model is proposed to elucidate the sensor mechanism. Electrical double layer (EDL) gated FET biosensor platform offers high sensitivity target analyte detection, even in high ionic strength solutions, thereby eliminating the need for complex sample pre-processing methods. Using this sensor platform, we have developed a whole cell sensing technology that can detect and count cells, and monitor cellular bioelectric signals such as transmembrane potential changes. A quantitative model is developed to explain the sensor mechanism and theoretical prediction shows good agreement with experimental results. The changes in the cellular transmembrane potential upon extracellular stimulus is modeled based on the EDL FET sensor response. Our investigation reveals that EDL FET biosensor platform can be used to study the bioelectric signals of cells, dynamically which is highly relevant to cell biology in applications of drug development, ion channel studies and disease model establishment. This sensor technology can also be used for point of care diagnostics, in the diagnosis and prognosis of diseases such as cancer.

Biomolecule Detection in High Ionic Strength With Enhanced Sensitivity Using Graphene Nanogrid FET Immunosensor

Detecting charges in high ionic strength solutions is a challenge due to the inherent problem of ionic screening in small Debye length. There have been some efforts to improve the sensing in high ionic strength buffer but the sensitivity and detection limit is poor. To address this challenge, we report high frequency sensing using smooth graphene nanogrid FET immunosensor. These sensors have certain intrinsic advantages: firstly, in the nanopores, the biomolecules usually reside within a distance shorter than the original pore radius which statistically raises the charge transfer probability between the biomolecules and the surface even at high ionic strength of the buffer and secondly, such a graphene nanostructure has a size dependent effective energy gap which increases the transconductance of the device. These features coupled with high frequency sensing have enabled detection down to 0.1 fMHep-B in a high ionic strength buffer (150mM) at 8 MHz with a sensitivity as high as 445.45%. This is an enhancement by more than 18 times compared to the existing reports.

An ultrasensitive conformation-dependent colorimetric probe for the detection of mercury(II) using exonuclease III-assisted target recycling and gold nanoparticles

An ultrasensitive conformation-dependent colorimetric assay has been developed for the detection of mercury(II) ions. It is based on the use of exonuclease III (Exo III)-assisted target recycling and gold nanoparticles (AuNPs). In the absence of Hg(II), the hairpin-shaped DNA probe (H-DNA) binds to AuNPs and stabilizes them in solutions of high ionic strength. In the presence of Hg(II), on the other hand, the sticky termini of the H-DNA form a rigid DNA duplex stem with a blunt 3'-terminus. Thus, Exo III is activated as a biocatalyst for selective and stepwise removal of mononucleotides from the 3'-terminus of the H-DNA. As a result, Hg(II) is released from the T-Hg(II)-T complexes. The guanine-rich sequences released from the H-DNA are then self-assembled with potassium ion to form a stable G-quadruplex conformation. In solutions of high ionic strength, this results in aggregation of AuNPs and a color change from red to blue which can be seen with bare eyes. The method is highly sensitive and selective. It has a linear response in the 10 pM to 100nM Hg(II) concentration range, and the detection limit is as low as 3.2 pM (at an S/N ratio of 3). The relative standard deviation at a level of 0.5nM of Hg(II) is 4.9% (for n = 10). The method was applied to the detection of Hg(II) in spiked environment water samples, with recoveries ranging from 92% to 106%. Graphical abstract A conformation-dependent colorimetric system was fabricated for label-free detection of mercury(II) by utilizing exonuclease III(Exo III)-assisted target recycling and gold nanoparticles (AuNPs).