Pure Buffer Solution Research Articles

Selective separation of dyes and tetracycline hydrochloride in polymer‐nucleotide coacervate droplets

AbstractThis paper reports the formation of coacervates by the electrostatic interaction of poly (diallyldimethylammonium chloride) (PDDA) and adenosine triphosphate (ATP) in aqueous solution, examining its formation conditions, stability, and efficiency in separation. The ideal concentration for creating coacervate droplets in pure water, HEPES buffer, and NaCl solution was determined to be 20 mM of PDDA and ATP. Enhancing the stability of coacervates was achieved by incorporating phospholipid vesicles on their surface, presenting a novel strategy for building cell models. Ostwald Ripening was employed to comprehend the growth mechanism of the coacervates, while the Hofmeister Ion Series and Schulze‐Hardy's rule were utilized to elucidate the stability differences in solutions containing NaCl, Na2SO4, and MgCl2. These coacervates were stable at concentrations below 90 mM NaCl, 200 mM Na2SO4, and 30 mM MgCl2, respectively. We also explored the specific separation of dyes and tetracycline hydrochloride (TC) in the coacervates. Separation efficiencies of 92.98% for methylene blue (MB), 94.19% for methyl orange (MO), and 85.94% for TC, were achieved by the coacervates, which can be attributed to the synergistic effects of hydrophobicity, electrostatic forces, and π‐π interactions. The proposed coacervates have great potential in cell mimicry and water treatment.

Simultaneous noninvasive ultrasensitive detection of prostate specific antigen and lncRNA PCA3 using multiplexed dual optical microfibers with strong plasmonic nanointerfaces

Low accuracy of diagnosing prostate cancer (PCa) was easily caused by only assaying single prostate specific antigen (PSA) biomarker. Although conventional reported methods for simultaneous detection of two specific PCa biomarkers could improve the diagnostic efficiency and accuracy, low detection sensitivity restrained their use in extreme early-stage PCa clinical assay applications. In order to overcome above drawbacks, this paper herein proposed a multiplexed dual optical microfibers separately functionalized with gold nanorods (GNRs) and Au nanobipyramids (Au NBPs) nanointerfaces with strong localized surface plasmon resonance (LSPR) effects. The sensors could simultaneously detect PSA protein biomarker and long noncoding RNA prostate cancer antigen 3 (lncRNA PCA3) with ultrahigh sensitivity and remarkable specificity. Consequently, the proposed dual optical microfibers multiplexed biosensors could detect the PSA protein and lncRNA PCA3 with ultra-low limit-of-detections (LODs) of 3.97 × 10−15 mol/L and 1.56 × 10−14 mol/L in pure phosphorus buffer solution (PBS), respectively, in which the obtained LODs were three orders of magnitude lower than existed state-of-the-art PCa assay technologies. Additionally, the sensors could discriminate target components from complicated physiological environment, that showing noticeable biosensing specificity of the sensors. With good performances of the sensors, they could successfully assay PSA and lncRNA PCA3 in undiluted human serum and urine simultaneously, respectively. Consequently, our proposed multiplexed sensors could real-time high-sensitivity simultaneously detect complicated human samples, that providing a novel valuable approach for the high-accurate diagnosis of early-stage PCa individuals.

Three-Dimensional Microfluidic Capillary Device for Rapid and Multiplexed Immunoassays in Whole Blood.

In this study, we demonstrate whole blood immunoassays using a microfluidic device optimized for conducting rapid and multiplexed fluorescence-linked immunoassays. The device is capable of handling whole blood samples without any preparatory treatment. The three-dimensional channels in poly(methyl methacrylate) are designed to passively load bodily fluids and, due to their linearly tapered profile, facilitate size-dependent immobilization of biofunctionalized particles. The channel geometry is optimized to allow for the unimpeded flow of cellular constituents such as red blood cells (RBCs). Additionally, to make the device easier to operate, the biofunctionalized particles are pretrapped in a first step, and the channel is dried under vacuum, after which it can be loaded with the biological sample. This novel approach and design eliminated the need for traditionally laborious steps such as filtering, incubation, and washing steps, thereby substantially simplifying the immunoassay procedures. Moreover, by leveraging the shallow device dimensions, we show that sample loading to read-out is possible within 5 min. Our results also show that the presence of RBCs does not compromise the sensitivity of the assays when compared to those performed in a pure buffer solution. This highlights the practical adaptability of the device for simple and rapid whole-blood assays. Lastly, we demonstrate the device's multiplexing capability by pretrapping particles of different sizes, each functionalized with a different antigen, thus enabling the performance of multiplexed on-chip whole-blood immunoassays, showcasing the device's versatility and effectiveness toward low-cost, simple, and multiplexed sensing of biomarkers and pathogens directly in whole blood.

An electrochemical sensor based on CS-MWCNT and AuNPs for the detection of mycophenolic acid in plasma

For patients receiving organ transplants, monitoring the blood concentration of MPA can provide timely information on whether MPA has reached the effective therapeutic window to better function while reducing the incidence of rejection or adverse reactions. In this study, an electrochemical sensor for the detection of MPA was built using a nanocomposite made of CS-MWCNT and AuNPs. At the same time, the high performance liquid phase (HPLC) method for MPA was established and compared with this sensor. The surface morphology, structure, and roughness of the material on the electrode were characterized by scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), and atomic force microscopy (AFM). In addition, the electrochemical behavior of the modified electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The standard curve was obtained in blank plasma, not pure buffer solution. The peak current was linearly related to the MPA concentration in the linear range of 0.001–0.1 mM with a detection limit of 0.05 μM and good anti-interference ability. Moreover, the sensor was employed with success for the determination of MPA in rat plasma with good recovery. The electrochemical sensor presented here is eco-friendly, and sensitive, and offers a great possibility for practical applicability.

Viscoelastic properties of thermosensitive gelatin/tragacanth hydrogel as novel ink suitable for additive manufacturing: Effect of various additives on system's viscoelastic characteristics and printability

AbstractIn this study, a novel hydrogel ink made from gelatin and tragacanth gum was prepared. Two additives and a crosslinking agent were added to improve the viscoelastic properties of the material during gelation and its printability. Alginic acid was introduced as a crosslinking agent along with additives such as rice starch and halloysite nanotubes (HNT). Two rheological measurement modes, rotational and oscillatory, were utilized to measure the steady state viscosity and complex moduli, respectively. Auxiliary measurements such as Fourier‐transform spectroscopy infrared and gel permeation chromatography were implemented to determine the bonds formed and the molecular weight of gelatin and tragacanth gum, respectively. We have demonstrated how these additives can affect fluid uptake by examining them in water at ambient temperature and also in 1× PBS at both ambient and normal body temperatures. The printability was analyzed by the grid pattern dispensed by interconnected filaments. It was observed that the sample containing HNT and rice starch show the best properties. The hydrogel nanocomposite, unlike the pure gelatin films, retains water and buffer solution for 72 h with minimum changes. Moreover, the printability criterion (Pr) was improved from 0.3 for pure gelatin to about 1 for the sample containing alginate, HNT, and rice starch.

Combined Ultrasensitive Detection of Renal Cancer Proteins and Cells Using an Optical Microfiber Functionalized with Ti3C2 MXene and Gold Nanorod-Nanosensitized Interfaces.

The ultrasensitive and quantitative detection of renal cancer protein biomarkers present at ultralow concentrations for early-stage cancer diagnosis requires a biosensing probe possessing ultrahigh detection sensitivity and remarkable biosensing selectivity. Here, we report an optical microfiber integrated with Ti3C2-supported gold nanorod hybrid nanointerfaces for implementation in ultrasensitive sensing of the carbonic anhydrase IX (CAIX) protein and renal cancer cells. Because the evanescent field of the fiber is strongly coupled with nanointerfaces in the near-infrared region, the proposed optical microfiber biosensor achieves ultrahigh-sensitivity detection of the CAIX protein biomarker with ultralow limits of detection (LODs) of 13.8 zM in pure buffer solution and 0.19 aM in 30% serum solution. In addition, the proposed sensor also successfully and specifically recognizes living renal cancer cells in cell culture media with a LOD of 180 cells/mL. This strategy may serves as a powerful biosensing platform that combines the quantification of protein biomarkers and cancer cells, resulting in a higher accuracy of early-stage renal cancer diagnosis and screenings.

A fluorescein-based fluorescent probe for real-time monitoring hypochlorite

Hypochlorite is an important reactive oxygen species in environment and pathophysiological processes. Abnormal level of ClO− can be destructive and lead to many diseases. Herein, to real-time and sensitively monitoring ClO−, a fluorescein-based fluorescence turn-on probe for ClO− in almost pure PBS buffer solution was successfully developed. After sensing hypochlorite, the spirolactam ring of the probe was opened and fluorescence at 525 nm greatly enhanced (∼1800 fold). The probe has a low detection limit (9.6 nM), short response time (∼1 min) and wide pH work range (5.0–9.0). Furthermore, the probe has been successfully applied to detect ClO− in disinfectant and actual water samples. Based on its fast response rate and almost pure buffer detection condition, the probe can be used to real time monitor ClO− in actual water environment.

Molecular crowders modulate ligand binding affinity to G-quadruplex DNA by decelerating ligand association

The study of kinetics of ligand binding to G-quadruplex DNA (GqDNA) structures is of paramount importance for comprehending (possible) ligand-induced anticancer activity involving GqDNA within cells. However, cellular environment is crowded with variety of small- and macro-molecules that occupy ∼30–40 % of cell-volume. While only few earlier studies dealt with deciphering the kinetics of ligands’ interactions with GqDNA in dilute solution, such studies in cell-like crowded milieu are absent. Here we investigate the effect of small and macro molecular crowders, glucose, sucrose and ficoll 70, on the kinetic steps of association and dissociation of a benzophenoxazine-ligand (Cresyl Violet: CV) with human telometic (hybrid) GqDNA structure using fluorescence correlation spectroscopy (FCS), aided by other methods. We find that the binding constants of the ligand to GqDNA change appreciably with nearly fivefold decrease in the presence of ficoll 70, compared to that in pure buffer solution. FCS measurements unfold that this decrease of binding constants is mainly modulated by the viscosity-induced deceleration of the association of the ligand to GqDNA in the crowded solution; however, the rate-determining dissociation rates remain nearly unchanged in the presence of all three crowders. These results have important implications in the context of ligand/GqDNA interactions within cellular environment, which indicate that even if the binding affinity of a ligand to GqDNA structures may be influenced by cellular crowders, they may not influence the unbinding rate of the ligand from a stable ligand/GqDNA complex formed by strong π-π stacking interactions.

Bioinspired Polysaccharide Derivative with Efficient and Stable Lubrication for Silicon-Based Devices.

It is becoming increasingly important to synthesize efficient biomacromolecule lubricants suitable for medical devices. Even though the development of biomimetic lubricants has made great progress, the current system suitable for hydrophobic silicone-based medical devices is highly limited. In this work, we synthesize one kind of novel polysaccharide-derived macromolecule lubricant of chitosan (CS) grafted polyethylene glycol (PEG) chains and catechol groups (CT) (CS-g-PEG-g-CT). CS-g-PEG-g-CT shows good adsorption ability by applying quantitative analysis of quartz crystal microbalance (QCM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and confocal fluorescence imaging technique, as well as the typical shear-thinning feature. CS-g-PEG-g-CT exhibits low and stable coefficients of friction (COFs) (0.01-0.02) on polydimethylsiloxane (PDMS) surfaces at a wide range of mass concentrations in diverse media including pure water, physiological saline, and PBS buffer solution and is even tolerant to various normal loads and sliding frequencies for complex pressurizing or shearing environments. Subsequently, systematic surface characterizations are used to verify the dynamic attachment ability of the CS-g-PEG-g-CT lubricant on the loading/shearing process. The lubrication mechanism of CS-g-PEG-g-CT can be attributed to the synergy of strong adsorption from catechol groups to form a uniform assembly layer, excellent hydration effect from PEG chains, and typical shear-thinning feature to dissipate viscous resistance. Surprisingly, CS-g-PEG-g-CT exhibits efficient lubricity on silicone-based commercial contact lenses and catheters. The current macromolecule lubricant demonstrates great real application potential in the fields of medical devices and disease treatments.

Effects of reactive oxygen species-responsive antibacterial microneedles on the full-thickness skin defect wounds with bacterial colonization in diabetic mice

Effects of reactive oxygen species-responsive antibacterial microneedles on the full-thickness skin defect wounds with bacterial colonization in diabetic mice

Optical cryomicroscopy and differential scanning calorimetry of buffer solutions containing cryoprotectants

In the pharmaceutical industry, cryoprotectants are added to buffer formulations to protect the active pharmaceutical ingredient from freeze- and thaw damage. We investigated the freezing and thawing of aqueous sodium citrate buffer with various cryoprotectants, specifically amino acids (cysteine, histidine, arginine, proline and lysine), disaccharides (trehalose and sucrose), polyhydric alcohols (glycerol and mannitol) and surfactants (polysorbate 20 and polysorbate 80). Hereby, we employed optical cryomicroscopy in combination with differential scanning calorimetry in the temperature range to −80 °C. The effect of cryoprotectants on the morphology of the ice crystals, the glass transition temperature and the initial melting temperature is presented. Some of the cryoprotectants have a significant impact on ice crystal size. Disaccharides restrict ice crystal growth, whereas surfactants and glycerol allow ice crystals to increase in size. Cysteine and mannitol cause dehydration after thawing. Either one or two glass transition temperatures were detected, where arginine, surfactants, glycerol, proline and lysine suppress the second, implying a uniform freeze-concentrated solution. The initial melting temperature of pure buffer solution can be shifted up by adding mannitol, both disaccharides and both surfactants; but down by glycerol, proline and lysine.

Magnetic-Optical Core-Shell Nanostructures for Highly Selective Photoelectrochemical Aptasensing.

Selectivity is a crucial parameter for photoelectrochemical (PEC) sensing in a practical setting. Despite the use of specific probes such as aptamers, antibodies, and enzymes, coexisting interferences can still result in inaccuracies in PEC sensing, especially for complex biosample matrixes. Here we report the design of an Fe3O4@SiO2@TiO2 magnetic-optical bifunctional beacon applied in a novel PEC sensor that can selectively capture progesterone in complex biosamples, be magnetically separated and cleaned, and be detected in pure phosphate buffer solution (PBS). The magnetic separation strategy efficiently removes the complex coexisting species from the modified electrode surface and drastically enhances the selectivity of the as-designed PEC sensor. The as-designed PEC sensor is cost-effective, easy to fabricate, highly selective and sensitive, and highly reliable, making it a promising platform for efficient aptasensing.

Electrokinetic instability in microchannel viscoelastic fluid flows with conductivity gradients

Electrokinetic instability (EKI) is a flow instability that occurs in electric field-mediated microfluidic applications. It can be harnessed to enhance sample mixing or particle trapping but has to be avoided in particle separation. Current studies on EKI have been focused primarily on the flow of Newtonian fluids. However, many of the chemical and biological solutions exhibit non-Newtonian characteristics. This work presents the first experimental study of the EKI in viscoelastic fluid flows with conductivity gradients through a T-shaped microchannel. We find that the addition of polyethylene oxide (PEO) polymer into Newtonian buffer solutions alters the threshold electric field for the onset of EKI. Moreover, the speed and temporal frequency of the instability waves are significantly different from those in the pure buffer solutions. We develop a three-dimensional preliminary numerical model in COMSOL, which considers the increased viscosity and conductivity as well as the suppressed electroosmotic flow of the buffer-based PEO solutions. The numerically predicted threshold electric field and wave parameters compare favorably with the experimental data except at the highest PEO concentration. We attribute this deviation to the neglect of fluid elasticity effect in the current model that increases with the PEO concentration.

Proton Spin Relaxation in Aqueous Solutions of Self-assembling Gadolinium Endofullerenols

The nuclear magnetic resonance (NMR)-relaxation characteristics of protons in pure aqueous and buffer solutions of highly hydroxylated endofullerenols with paramagnetic gadolinium ions at ambient temperature have been studied. These systems were thoroughly characterized by SANS and examined by NMR at various resonance frequencies: f = 2 kHz–500 MHz. In all the cases, we have discovered much higher longitudinal and transversal relaxation rates as compared to the reference salt solutions with Gd+3 ions in the same range of concentrations (0.1–10.0 mM/l). We suppose that this effect is due to the fact that the objects studied reveal well-manifested abilities to the self-assembly in acidic conditions. As a result, the transversal relaxation rate (1/T2) increases greatly, and also the longitudinal relaxation rate (1/T1) demonstrates a broad maximum at resonant frequencies f ~ 20–100 MHz that are determined by the time of fullerenol diffusive rotations. The relaxation rates, which increase linearly with fullerenol content (0.1–10.0 mM/l), testify the stable assembly. The studied features of fullerenol assembly and its strong influence on the proton relaxation make it possible to suppose good prospects of these metal–carbon structures for biomedical applications, in particular, as contrast agents in MRI.

DNA Interaction with 17α‐Ethinylestradiol Studied Using Electrochemical Biosensors and Biosensing in Solution

AbstractThe synthetic estrogen 17α‐ethinylestradiol (EE2) is an active component of oral contraceptives. It is considered as an endocrine disrupting compound that, once incorporated into an organism, affects the hormonal balance of animals and humans. In this study we characterized the DNA‐EE2 interaction using an electrochemical biosensor and biosensing in solution phase with the double stranded DNA from salmon sperm and deoxyguanosine monophosphate (dGMP). Differential pulse voltammetry method has been applied based on voltammetric anodic responses of the deoxyguanine (dGuo) and deoxyadenine (dAdo) as well as EE2 in the medium of phosphate buffer solution pH 7.0. Binding of EE2 to the nucleobases leads to a decrease of their anodic signals. Association constant for DNA‐EE2 interaction has been estimated to be about 1.1 ⋅ 103 L mol−1 and 1.4 ⋅ 103 L mol−1 for dGuo and dAdo responses, respectively. The association is reversible as indicated by decrease of the EE2 response in pure buffer solution due to leaching of EE2 from the surface attached DNA. The DNA‐EE2 association has been confirmed also by UV‐vis spectrometric experiments.

Observation of complex formation between l-histidine and heterocyclic compounds in water and aqueous buffer solution using calorimetric and spectroscopic methods

Interactions between the aromatic amino acid (l-histidine) and heterocyclic ligands (uracil, nicotinic acid) in pure water (pH 5.4) and in aqueous buffer solutions (pH 7.4) were studied by calorimetry and UV–vis spectroscopy. Stability constants (lgKc) and thermodynamic parameters of complex formation (ΔcG, ΔcH, ΔcS) have been calculated and presented in a table. The buffer solution was found to be a more suitable medium for complex formation between l-histidine (His) and uracil (Ura) and nicotinic acid (NA), since the amino acid forms more stable complexes with them in the buffer than in pure water: lgKpH7.4 > lgKpH5.4. It was shown that the complexes of NA with the His are mainly enthalpically stabilized, while those of Ura with His are stabilized by both enthalpic and entropic contributions to the free Gibbs energy for both buffer solution and pure water. The data obtained reveal the presence of complexes between His and ligands (Ura, NA) with 1:1 and 1:2 stoichiometry, respectively, for pure water and buffer solution.

Highly selective probe of a copper(II) complex based on a coumarin derivative for hydrogen sulfide detection

A fluorescent probe 1 containing copper(II) had been designed and synthesized based on a coumarin derivative. The molecular structure of probe 1 was characterized by 1H NMR, HRMS, IR, and elemental analysis. The interactions of 1 with biologically important anions and amino acid were determined by UV–Vis, fluorescence, and HRMS titration experiments. Results indicated that probe 1 showed the highest binding ability for HS− among studied anions (AcO−, H2PO4 −, F−, Cl−, Br−, and I−) and cysteine in pure dimethyl sulfoxide (DMSO) and HEPES buffer solution. As we expected, the response of UV–Vis spectra in aqueous solution was stronger than that of pure DMSO solvent. In addition, the binding ability for HS− was not hindered by the existence of other anions. HRMS titration experiment showed that the interacted mechanism was that the copper(II) ion in 1 was captured by HS− and then free ligand released. Furthermore, the detection limit of probe 1 with HS− was carried out through UV–Vis titration showing 1 to be highly sensitive for HS−.

Proton Transfer Hydrogels: Versatility and Applications.

Proton transfer polymerization between thiol and epoxide groups is shown to be an adaptable and utilitarian method for the synthesis of hydrogels. For instance, the polymerization catalyst can be organic or inorganic, and the polymerization medium can be pure water, buffer solutions, or organic solvents. The gelation mechanism can be triggered at ambient conditions, at a physiological temperature of 37 °C, or through using light as an external stimulus. The ambient and photochemical methods both allow for nanoimprint lithography to produce freestanding patterned thick films. The required thiol- and epoxide-carrying precursors can be chosen from a long list of commercially available small molecular as well as polymeric materials. The water uptake, mechanical, and biodegradation properties of the gels can, therefore, be tuned through the choice of appropriate gelation precursors and polymerization conditions. Finally, the thio-ether groups of the cross-linked networks can be functionalized through a postgelation modification reaction to access sulfonium-based cationic structures. Such structural changes endow antibacterial properties to the networks. In their pristine form, however, the gels are biocompatible and nonadhesive, allowing cancer cells to grow in a cluster formation.

Enzyme activity of horseradish peroxidase in surfactant-free microemulsions

In the present contribution, we investigated the influence of the structuring of surfactant-free microemulsions (SFME) (water/1-propanol/limonene and water/tert-butanol/limonene) on the enzyme activity of horseradish peroxidase (HRP). To this purpose, the oxidation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) with hydrogen peroxide was chosen as a model reaction. Enzymatic activities in SFMEs of varying compositions were investigated by UV–Vis spectroscopy and compared to the enzyme activity in pure buffer solution. Dynamic light, small-angle-X-ray scattering and conductivity measurements were performed in order to obtain structural information on the used SFMEs.Findings presented in this study revealed that the ability of short-chain alcohols to form mesostructures (aqueous aggregates in oil) has a crucial effect on the enzyme activity in SFMEs. Mesoscale structuring with 1-propanol (NPA) was found to be more pronounced than for the more hydrophobic tert-butanol (TBA). It was concluded that the most pronounced mesoscale-structured SFMEs lead to the highest enzymatic activities.

MOF based fluorescent assay of xanthine oxidase for rapid inhibitor screening with real-time kinetics monitoring

The activity assay of xanthine oxidase (XO) is of great application value in clinical diagnosis because the abnormal level of this enzyme is related to a series of pathological states. In this work, a Zr based metal-organic framework (BTB-MOF) with stable photoluminescence in pure water and buffer solution was synthesized. The examination about the fluorescent responses of this material to xanthine and its oxidation product, uric acid, showed that, although both of them affected the emission of BTB-MOF in quenching form, the efficiencies presented much difference. Taking advantage of this feature, a fluorescent method was developed for the activity assay of XO, that is, BTB-MOF was added to the enzymatic oxidation system as a sensor to transduce the proceeding of the reaction real-timely to the signal of fluorescent intensity change. Our method can work under the interference of normal biologically related species, and precisely reflect XO activity in the range of 0.2–40 U L−1 (detection limit = 0.004 U L−1). With consecutive fluorescence intensity scan, this assay could be applied as a high speed screening method of XO inhibitors with the testing time of 1 min. This work shows the wide potential application of MOFs in enzyme analysis.