Linear pH Range Research Articles

A Highly fluorescent vinylene-linked covalent organic framework for chemical sensing of pH and NH3 gas with wide dynamic range

Herein, a vinylene-linked covalent organic framework (TMT-BPDA-COF) was prepared via the Aldol condensation of 2,4,6-trimethyl-1,3,5-triazine (TMT) and 4,4'-biphenyl dimethyl formaldehyde (BPDA). TMT-BPDA-COF displayed high crystallinity and thermal stability, and robust chemical stability in strong acid, strong base and common organic solvents. TMT-BPDA-COF nanosheets emitted strong yellow fluorescence with the quantum yield of 14.9% and showed fast reversible response toward pH with a wide range (pH 0.0 ∼ 14.0) based on the intramolecular charge transfer effect. Furthermore, portable fluorescent sensors were prepared by incorporated TMT-BPDA-COF nanosheets into agarose gel and cellulose acetate butyrate (CAB), respectively. TMT-BPDA-COF gel showed a wide pH response range over pH 0.0 ∼ 14.0 with a linear range of pH 4.0 ∼ 14.0. TMT-BPDA-COF CAB film exhibited high sensitivity for sensing of NH3 gas with a limit of detection of 1.6 ppb. TMT-BPDA-COF agarose gel and CAB film also exhibited good reversibility and reproducibility in response to pH and NH3 gas, respectively. We expect TMT-BPDA-COF-based sensors, which feature fast response, high sensitivity, wide response range, good reproducibility and reversibility, can apply to detect pH and NH3 gas in the field of environment and industry.

MoS2‐Polyaniline Based Flexible Electrochemical Biosensor: Toward pH Monitoring in Human Sweat

AbstractWearable pH sensors for sweat analysis have garnered significant scientific attention for the detection of early signs of many physiological diseases. In this study, a MoS2‐polyaniline (PANI) modified screen‐printed carbon electrode (SPCE) is fabricated and used as a sweat biosensor. The exfoliated MoS2 nanosheets are drop casted over an SPCE and are functionalized by a conducting polymer, polyaniline (PANI) via the electropolymerization technique. The as‐fabricated biosensor exhibits high super‐Nernstian sensitivity of −70.4 ± 1.7 mV pH−1 in the linear range of pH 4 to 8 of 0.1 m standard phosphate buffer solution (PBS), with outstanding reproducibility. The sensor exhibits excellent selectivity against the common sweat ions including Na+, Cl−, K+, and NH4+ with tremendous long‐term stability over 180 min from pH 4 to 6. The enhanced active surface area and better electrical conductivity as a consequence of the synergistic effect between MoS2 and PANI are correlated with the boosted performance of the as‐produced biosensor. The feasibility of the sensor is further examined using an artificial sweat specimen and the successful detection confirms the potential of the biosensor for a real‐time noninvasive, skin attachable, and flexible wearable pH sensor.

One-step laser synthesis platinum nanostructured 3D porous graphene: A flexible dual-functional electrochemical biosensor for glucose and pH detection in human perspiration

There has been a recent increase in the demand for wearable sensors for sweat glucose monitoring to facilitate diabetes management in a patient-friendly and non-invasive manner. To address this issue, the key challenge lies in the design of flexible sensors with high conductivity, miniaturized patterning, and environmental friendliness. Herein, we introduce a flexible electrochemical sensing system for glucose and pH detection based on one-step laser-scribed PtNPs nanostructured 3D porous laser-scribed graphene (LSG). The as-prepared nanocomposites can synchronously possess hierarchical porous graphene architectures, whereas PtNPs can significantly enhance their sensitivity and electrocatalytic activity. Benefiting from these advantages, the fabricated Pt-HEC/LSG biosensor exhibited a high sensitivity of 69.64 μA mM−1 cm−2 as well as a low limit of detection (LOD) of 0.23 μM at a detection range of 5–3000 μM (covering the glucose range in sweat). Moreover, the pH sensor was functionalized with polyaniline (PANI) on a Pt-HEC/LSG electrode, and it also exhibited high sensitivity (72.4 mV/pH) in the linear range of pH 4–8. The feasibility of the biosensor was confirmed by analyzing human perspiration during physical exercise. This dual-functional electrochemical biosensor displayed excellent performance, including a low detection limit, high selectivity, and great flexibility. These results confirm that the proposed dual-functional flexible electrode and fabrication process are highly promising for application in human sweat-based electrochemical glucose and pH sensors.

Dual fluorescent hollow silica nanofibers for in situ pH monitoring using an optical fiber.

This study reports a sensitive and robust pH sensor based on dual fluorescent doped hollow silica nanofibers (hSNFs) for in situ and real-time pH monitoring. Fluorescein isothiocyanate (FITC) and tris(2,2'-bipyridyl)dichlororuthenium(ii) hexahydrate (Ru(BPY)3) were chosen as a pH sensitive dye and reference dye, respectively. hSNFs were synthesized using a two-step method in a reverse micelle system and were shown to have an average length of 6.20 μm and average diameter of 410 nm. The peak intensity ratio of FITC/Ru(BPY)3 was used to calibrate to solution pH changes. An optical-fiber-based fluorescence detection system was developed that enabled feasible and highly efficient near-field fluorescence detection. The developed system enables fully automated fluorescence detection, where components including the light source, detector, and data acquisition unit are all controlled by a computer. The results show that the developed pH sensor works in a linear range of pH 4.0-9.0 with a fast response time of less than 10 s and minimal sample volume of 50 μL, and can be stored under dark conditions for one month without failure. In addition, the as-prepared hSNF-based pH sensors also have excellent long-term durability. Experimental results from ratiometric sensing confirm the high feasibility, accuracy, stability and simplicity of the dual fluorescent hSNF sensors for the detection of pH in real samples.

The New Reliable pH Sensor Based on Hydrous Iridium Dioxide and Its Composites.

The new reliable sensor for pH determination was designed with the use of hydrous iridium dioxide and its composites. Three different hIrO2-based materials were prepared and applied as solid-contact layers in pH-selective electrodes with polymeric membrane. The material choice included standalone hydrous iridium oxide; composite material of hydrous iridium oxide, carbon nanotubes, and triple composite material composed of hydrous iridium oxide; carbon nanotubes; and poly(3-octylthiophene-2,5-diyl). The paper depicts that the addition of functional material to standalone metal oxide is beneficial for the performance of solid-state ion-selective electrodes and presents the universal approach to designing this type of sensors. Each component contributed differently to the sensors' performance-the addition of carbon nanotubes increased the electrical capacitance of sensor (up to 400 µF) while the addition of conducting polymer allowed it to increase the contact angle of material changing its wetting properties and enhancing the stability of potentiometric response. Hydrous iridium oxide contacted electrodes exhibit linear response in wide linear range of pH (2-11) and stable potentiometric response (the lowest potential drift of 0.036 mV/h is attributed to the electrode with triple composite material).

A facile fluorescent sensor based on nitrogen-doped carbon dots derived from Listeria monocytogenes for highly selective and visual detection of iodide and pH.

Sensitive and visual analysis of iodide (I−) and pH is significant in environmental and food applications. Herein, we present a facile fluorescent sensor for highly selective and visual detection of I− and pH based on nitrogen-doped carbon dots derived from Listeria monocytogenes (NCDs-LM). The NCDs-LM-based fluorescent sensor showed a good linear relationship to I− concentrations, and the detection limit was calculated as 20 nmol L−1. The developed sensor was successfully applied to the detection of I− in drinking water and milk samples. Meanwhile, the as-synthesized NCDs-LM sensor can be used to detect pH, achieving a wide linear pH range. Furthermore, fluorescent test papers based on NCDs-LM were designed for semi-quantitative detection of I− and pH via the naked-eye colorimetric assay. The present work indicates that the NCDs-LM-based fluorescent sensor has high potential for use in environmental monitoring and food analysis.

Bacterial cellulose-based re-swellable hydrogel: Facile preparation and its potential application as colorimetric sensor of sweat pH and glucose

Direct deposition of the negatively charged polyelectrolyte, carboxymethyl cellulose (CMC), into a bacterial cellulose (BC) matrix was used as a simple route to fabricate a re-swellable and biocompatible cellulose-based hydrogel. As a result of this non-destructive approach, the physical and mechanical property of the original BC were well-preserved within the resulting BC/CMC hydrogel. As a BC/CMC-based colorimetric pH sensor, it exhibited a rapid response with an easy color differentiation between each pH by the naked eye, and wide linear range of pH 4.0–9.0 with good linearity. For the detection of glucose in sweat, the BC/CMC-based colorimetric glucose sensor provided a low limit of detection (25 μM) with a wide linear detection range (0.0–0.5 mM) and high accuracy. These BC/CMC based sensors could potentially be applied as non-invasive semi-quantitative sensors for on-skin health monitoring.

Ultrasonic atomizer based development of pH sensor for real time analysis

Fluorescent pH biosensors have gained importance owing to their low cost utilization in real time monitoring of biological and food samples in comparison to conventional pH meters. The research reports a novel method of ultrasonic atomization for developing a fluorescent pH sensor for real-time analysis made of Fluorescein isothiocyanate (FITC)-dextran/FITC-dextran-Tris (2, 2′-bipyridyl) dichlororuthenium (II) hexahydrate as indicator and reference fluorophores, respectively. The process of ultrasonic atomization ensures formation of monodisperse dye immobilized alginate microspheres ensuring efficient pH sensing. The developed biosensor was tested on milk samples, which has a short life span and shows a significant fall in pH with time due to microbial spoilage. The proposed biosensor showed a linear range of pH 4–8 (R2 between 0.96–0.99 for different single/dual fluorophore biosensors) which suitably cover the pH of milk during the entire storage period and spoilage. The % recovery for predicted pH falls between 90–110% compared against standard pH meter, indicating a good accuracy of estimation and low turnaround time (10 min). Thus, real-time monitoring using fluorescent pH biosensor for milk samples may profoundly improve the economics of losses occurring in processing and storage with capability of in-package continuous quality assessment.

Highly flexible and conductive poly (3, 4-ethylene dioxythiophene)-poly (styrene sulfonate) anchored 3-dimensional porous graphene network-based electrochemical biosensor for glucose and pH detection in human perspiration

The patterned LIG flakes are generally not interconnected due to the line gap of the laser ray, leading to lower uniform conductivity and fragile graphene. Thus, the fabrication of a highly conductive and mechanically robust LIG-based biosensing platform remains challenging. In this study, the fabrication of a flexible electrochemical biosensor is reported based on poly (3, 4-ethylene dioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) modified 3-dimensional (3D) stable porous laser-induced graphene (LIG) for the detection of glucose and pH. PEDOT:PSS was spray-coated on the LIG to improve electrode robustness and deliver uniform electrical conductivity. The as-prepared PEDOT:PSS modified LIG (PP/LIG) was characterized using field-emission scanning electron microscopy (FESEM), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). Platinum and palladium nanoparticles (Pt@Pd) were successfully electrodeposited on PP/LIG, markedly enhancing the electrocatalytic activity for glucose detection. The fabricated biosensor exhibited an excellent amperometric response to glucose with a wide linear range of 10 μM − 9.2 mM, a high sensitivity of 247.3 μAmM−1cm−2, and a low detection limit (LOD) of 3 μM, with high selectivity. In addition, the pH sensor was functionalized by the polyaniline (PANI) on PP/LIG, and it also exhibited excellent potentiometric response with a high sensitivity of 75.06 mV/pH in the linear range of pH 4 − 7. Ultimately, the feasibility of the biosensor was confirmed by the analysis of human perspiration collected during physical exercise. This approach validates the utility of the novel fabrication procedure, and the potential of the LIG-conductive polymer composite for biosensing applications.

The ratiometric fluorescent probe with high quantum yield for quantitative imaging of intracellular pH

Intracellular pH, especially cytoplasmic pH (~7.2) plays a crucial role in cell functions and metabolism. A ratiometric fluorescent probe namely, 6-(2-(benzothiazol-2-yl)vinyl)naphthalen-2-ol (BTNO) was facilely synthesized by the condensation of 6-hydroxy-2-naphthaldehyde and 2-methylbenzothiazole. BTNO exhibited a remarkable ratiometric emission (F456/F526) enhancement in response to a pH change with a linear range of pH = 9.50–7.00 and a pKa value of 7.91 ± 0.03, which is desirable for measuring and monitoring the cytoplasmic pH fluctuations. In addition, because of the high fluorescence quantum yield of BTNO (Φ = 0.88 in DMSO and 0.61 in water relative to quinine sulfate solution in 0.1 M H2SO4), the interferences of the probe on the physiological functions could be greatly reduced. This could also provide enhanced measurement sensitivity. The successful demonstration of BTNO in detecting and monitoring the intracellular pH changes in live HeLa cells via a ratiometric approach confirmed that BTNO held a practical potential in biomedical research.

An Optical Sensor with Polyaniline-Gold Hybrid Nanostructures for Monitoring pH in Saliva.

Saliva contains important personal physiological information that is related to some diseases, and it is a valuable source of biochemical information that can be collected rapidly, frequently, and without stress. In this article, we reported a new and simple localized surface plasmon resonance (LSPR) substrate composed of polyaniline (PANI)-gold hybrid nanostructures as an optical sensor for monitoring the pH of saliva samples. The overall appearance and topography of the substrates, the composition, and the wettability of the LSPR surfaces were characterized by optical and scanning electron microscope (SEM) images, infrared spectra, and contact angles measurement, respectively. The PANI-gold hybrid substrate readily responded to the pH. The response time was very short, which was 3.5 s when the pH switched from 2 to 7, and 4.5 s from 7 to 2. The changes of visible-near-infrared (NIR) spectra of this sensor upon varying pH in solution showed that—for the absorption at given wavelengths of 665 nm and 785 nm—the sensitivities were 0.0299 a.u./pH (a.u. = arbitrary unit) with a linear range of pH = 5–8 and 0.0234 a.u./pH with linear range of pH = 2–8, respectively. By using this new sensor, the pH of a real saliva sample was monitored and was consistent with the parallel measurements with a standard laboratory method. The results suggest that this novel LSPR sensor shows great potential in the field of mobile healthcare and home medical devices, and could also be modified by different sensitive materials to detect various molecules or ions in the future.

Hydroquinone monosulfonate-doped polypyrrole electrodeposited on very low cost commercial junction field effect transistors as a novel ion sensitive field effect transistor pH sensor

In this study, for the first time, we introduce a simple and low cost pH sensor based on a commercial junction field effect transistor. The transistor was mechanically treated, isolated and used as an ion sensitive field effect transistor for pH detection, after electrodeposition of the sensing membrane on its surface. Polypyrrole, as a suitable sensing membrane, was electrodeposited on the copper metal gate of transistor from a solution containing pyrrole monomer, hydroquinone monosulfonate as a proper ligand and sodium salicylate for avoiding the substrate oxidation, under a two-step deposition conditions. The prepared sensor showed a near-Nernstian response of 52.3 mV pH−1 over a linear pH range of 2.75–12.20, an ultra low hysteresis of 0.56 mV, a very low drift of 0.14 mV h−1 and a low response time of less than 8 s.

Preparation of A Novel Type of Fluorescein Isothiocyanate-Doped Fluorescent Silica Nanoparticle and Its Application as pH Probe

Abstract In this study, a novel type of core-shell fluorescein isothiocyanate (FITC)-doped fluorescent silica nanoparticle was synthesized and used as an intracellular pH sensor. First, a silane reagent of 3-aminopropyl-trimethoxysilane (APTMS) was used to synthesize a novel precursor FITC-APTMS. Then, FITC-APTMS/SiO2 (FAS) nanoparticles were obtained using water-in-oil (W/O) microemulsion technique in the presence of tetraethoxysilane (TEOS). Characterizations by transmission electron microscopy (TEM) and fluorescence spectroscopy show that the nanoparticles are spherical, monodisperse, and uniform in size with the diameters being (150 ± 15) nm. They are also highly fluorescent and highly photostable. When the nanoparticles were dispersed in aqueous solution under ultrasonic treatment for 6 h, no obvious dye leaking was observed. It was found that the fluorescence of the nanoparticles was pH sensitive, and the pH response range was 3.6–9.7, with a linear range of pH 6.0–9.0. The FAS nanoparticles could be phagocytosed by murine neural stem cell and thus could be applied to detect intracellular pH value of single cell.

Protein repertoire of human uterine fluid duringthe mid-secretory phase of the menstrual cycle

This study is an attempt to construct a repository of polypeptide species in human uterine fluid during the mid-secretory phase of menstrual cycle. This information is essential to generate alternative and less invasive tools for the assessment of uterine functions. Two-dimensional polyacrylamide gel electrophoresis (2D PAGE) and mass spectrometric analysis were used to resolve and identify the major components of human uterine fluid. Uterine fluid collected during the mid-secretory phase (n = 6) demonstrated ca. 590 polypeptide spots in the linear range of pH 4-7 after 2D PAGE. Mass spectrometric analysis revealed the presence of heavy and light chains of immunoglobulins, alpha-1 anti-trypsin precursor, anti-chymotrypsin precursor, haptoglobin, apolipoprotein A4, apolipoprotein A1 fragment, beta-actin fragment, heat shock protein 27, hemopexin precursor and transferrin precursor. 2D protein profile of fluid collected during the proliferative phase (n = 5) revealed ca. 433 polypeptide spots, of which 279 could be paired with mid-secretory phase protein spots on the basis of their coordinates (isoelectric point and molecular weight) in 2D gels. Apolipoprotein A4, apolipoprotein A1 fragment and alpha-1 anti-trypsin precursor were 2-3-fold more abundant in uterine fluid collected during the mid-secretory phase as compared with that in the proliferative phase. Further, 86 uterine fluid polypeptides were conserved across species, being detected in human, rat and bonnet monkeys. The molecular repertoire of the mid-secretory phase human uterine fluid, when compared with that of the proliferative phase uterine fluid, is broadened due to differential expression of proteins. Further, some of the mid-secretory phase proteins were conserved across species.

Expression of psoriasis-associated fatty acid-binding protein in senescent human dermal microvascular endothelial cells.

Aging is associated with the progressive pathophysiologic modification of endothelial cells. In vitro endothelial cell senescence is accompanied by proliferative activity failure and by perturbations in gene and protein expressions. Moreover, this cellular senescence in culture has been proposed to reflect processes that occur in aging organisms. In order to observe the changing patterns of protein expression in senescent human dermal microvascular endothelial cells (HDMECs), proteins obtained from both early- and late-passaged HDMECs were separated by two-dimensional electrophoresis, visualized by silver staining, and quantified by image processing. Proteins of interest were extracted by in-gel digestion with trypsin and quantified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), by searching the National Center for Biotechnology Information protein-sequence database. More than 2000 spots were detected by 2D electrophoresis within a linear pH range of 3-10. Twenty-two major differentially expressed spots were observed in serially passaged HDMECs and identified with high confidence by MALDI-TOF-MS. One of these spots was found to be a 14-15 kDa psoriasis-associated fatty acid-binding protein (PA-FABP) with high affinity for long-chain fatty acids. The expression of PA-FABP was confirmed to be elevated in senescent HDMECs (passage 20) by fluorescence-activated cell sorting (FACS), confocal laser microscopy, and by immunohistochemistry in aged human skin tissue. Our results suggest that the overexpression of FABP in cultured senescent HDMECs is closely related to skin aging.

Development of pH sensor based on aromatic polyurethane matrix

The synthesized aromatic polyurethane (APU)-based all-solid-state (ASS) pH sensor was developed with the same APU-based reference site in an ASS multi sensing electrode. The best analytical performance (the linear range of pH 3.0–11.5, slopes of ∼57 mV pH −1) was obtained with the membrane composition of 33:66:1 (wt.%) of APU/plasticizer (NPOE)/ionophore ( N, N-dioctadecylmethylamine) with the addition of lipophilic additive (KTpClPB, 5 mol.%). This ASSE exhibits more advantages of increasing stability, reducing membrane resistance and reducing anion interference.

Purification, Cloning, and Expression of a Pathogen Inducible UDP-glucose:Salicylic Acid Glucosyltransferase from Tobacco

Salicylic acid (SA) plays an important role in plant disease resistance. Inoculation of tobacco leaves with incompatible pathogens triggers the biosynthesis of SA which accumulates primarily as the SA 2-O-beta-D-glucoside (SAG) and glucosyl salicylate (GS). The tobacco UDP-glucose:salicylic acid glucosyltransferase (SA GTase) capable of forming both SAG and GS was purified, characterized, and partially sequenced. It has an apparent molecular mass of 48 kDa, a pH optimum of 7.0, and an isoelectric point at pH 4.4. UDP-glucose was the sole sugar donor for the enzyme. However, SA and several phenolics served as glucose acceptors. The apparent K(m) values for UDP-glucose and SA were 0.27 and 1-2 mM, respectively. Zn(2+) and UDP inhibited its activity. The corresponding cDNA clone which encoded a protein of 459 amino acids was isolated from an SA-induced tobacco cDNA library and overexpressed in Escherichia coli. The recombinant protein catalyzed the formation of SAG and GS, and exhibited a broad specificity to simple phenolics, similar to that of the purified enzyme. Northern blot analysis showed that the SA GTase mRNA was induced both by SA and incompatible pathogens. The rapid induction timing of the mRNA by SA indicates that it belongs to the early SA response genes.

Construção e avaliação de um eletrodo tubular sensível ao íon hidrogênio como detector em sistemas de análise em fluxo

The construction of a tubular hydrogen ion-selective potentiometric electrode without inner reference solution, based on the tridodecylamine (TDDA) ionophore, and its evaluation in a flow system are described. TDDA was dissolved in 2-nitrophenyl octyl ether, dispersed in a PVC membrane and applied directly to a conducting support which consisted of an epoxy resin and graphite mixture. The electrode was designed with a tubular geometry to effort facilities to be coupled as part of a flow injection network. The main working characteristics such as response time, linear pH range, selectivity and life time were evaluated and compared with those obtained which a conventionally shaped electrode based on the same sensor. The electrode showed a slope of 51-52 mV dec-1 within a linear pH range from 4.0 up to 12.0.

Isoelectric focusing of proteins in capillary electrophoresis with pressure-driven mobilization

An isoelectric focusing (IEF) method in the capillary format with wide linear pH range (pH 3–10) and high resolution has been developed for separations of proteins. The methodology involves applying pressure and voltage simultaneously during the mobilization step of the IEF process, to elute the focused protein zones for detection. Capillary isoelectric focusing (CIEF) is performed in neutral, hydrophilic, coated capillaries of 50 μm I.D., using various concentrations of methyl cellulose to reduce the distortion of focused zone by parabolic laminar flow. A linear relationship between the retention time and isoelectric point (pI) of protein standards was observed. The high resolution of this technique was demonstrated by the separation of hemoglobin variants F and A with pI difference of 0.05 pH units, and by the resolution of the isoforms of an anti-carcinoembryonic antigen monoclonal antibody.

The rheological and technological properties of silicon carbide suspensions

An investigation was carried out of the rheological and technological properties of silicon carbide suspensions. The optimal linear pH range of silicon carbide suspensions not containing an additive is 8.5–11. Within this range the ξ-potential is at a maximum and viscosity, sedimentation and the build-up rate of the casting at minima; the slip settles only very slightly, the porosity of the fired casting is at a minimum while the density and bending strength are at maxima.