pH Sensor System Research Articles

Label-free detection of pH based on the i-motif using an aggregation-caused quenching strategy

A label-free and biocompatible pH sensor system based on the aggregation-caused quenching (ACQ) probe has been reported herein. The DNA i-motif, a kind of pH-triggered structure, affects the aggregation of PTCDI derivatives by structural switch that would provide significant fluorescence signals responding to the different pH values. Our method not only shows sensitive and reversible response to pH changes, but also could expand the detection range by allosteric control of the DNA i-motif.

Hyaluronic Acid Immobilized Polyacrylamide Nanoparticle Sensors for CD44 Receptor Targeting and pH Measurement in Cells

Our ability to design receptor-targeted nanocarriers aimed at drug release after endocytosis is limited by the current knowledge of intracellular nanoparticle (NP) trafficking. It is not clear if NP size, surface chemistry, and/or targeting of cell surface receptors changes the intracellular fate of NPs; i.e., will all NPs enter acidic compartments and eventually end up in lysosomes or are there escape mechanisms or receptor-specific signaling that can be induced to change the cellular processing of an internalized NP? To give new insight into the intracellular trafficking of NPs that target the CD44 receptor, which is overexpressed on the surface of a broad variety of cancer cells, we have synthesized an NP pH sensor system that targets CD44. We used a polyacrylamide nanoparticle matrix bearing hyaluronic acid (HA) on the surface as a CD44 targeting ligand. The HA-coated NPs were prepared by radical polymerization followed by post functionalization with sensor fluorophores and physically absorbed or chemically conjugated HA. Cell uptake studies showed significant uptake of HA-coated nanosensors in HeLa cells and no uptake under the same conditions without the HA targeting ligand. The pH distribution profile in cells was measured for nanosensors with HA, cationic, and noncharged NP surface coatings giving a clear indication of the intracellular pH environment that the different NPs experience after internalization. The pH profile of cationic nanosensors in comparison to HA conjugated nanosensors indicates that the intracellular trafficking is aimed at lysosomes regardless of whether CD44 receptor-specific or unspecific uptake is induced.

The Buddha Relics and Evidence of Physical Space Conditioning with Unimprinted Intention Host Devices

The objective of this study was to experimentally determine whether an unimprinted intention host device (IHD), electrically activated in the near presence of the Maitreya Buddhist relics for about 72 hours (3 nights), could be imprinted by its loving kindness essence into the IHD. This will be referred to as a "first-degree relic IHD." This first-degree relic IHD was placed in an unused, unconditioned room in a Scottsdale, AZ home in the presence of a water vessel (pH ~ 5.6) being continuously monitored via a pH-sensor system that was computer recorded. This particular IHD was electrically switched on. Initially, no intention instructions were given to the system. After about 2200 hours, an intention statement was written to respectfully ask the first-degree relic IHD that the excess thermodynamic free energy aspect of this loving kindness essence be made manifest in this space so that its thermodynamic magnitude could be experimentally measured via the pH-sensor reading. It was shown that during the first 3 months, only a small increase in water pH was recorded. However, during the postintention period, the pH increased by about +2.5 pH units or ~ 60 meV increase in the thermodynamic free energy of the physical space, a very significant change. The excess thermodynamic free energy suggests that a fundamental change of the gauge symmetry state of the unconditioned room had occurred to a higher state. The following were concluded in this study: (1) Imprinting meaningful information onto a simple unimprinted IHD via passive exposure to the Buddha relics is possible. (2) Activating this IHD information to, in turn, imprint itself onto the space of a particular room so that a quantitative thermodynamic measure of its energetic essence can be physically realized is also possible. (3) Crucially, a verbal request from a deep meditative state by four humans appeared to be a necessary condition for this "imbedded loving kindness essence" to manifest itself in this way.

Evaluation of pH‐Sensitive Poly(β‐amino ester)‐graft‐poly(ethylene glycol) and its Usefulness as a pH‐Sensor and Protein Carrier

In this study, some possible biomedical applications of a pH-sensitive and amphiphilic copolymer as a pH sensor and protein delivery system are reported. PAE-g-PEG was used as a pH-sensitive polymer that can exhibit a sharp pH-dependent transition. Various fluorescent dyes including pyrene and RITC can be used to label the pH-sensitive polymer PAE-g-PEG, which was evaluated for protein encapsulation. pH-sensing was possible by observing excimer formation of the labeled pyrene via pH-dependent expansion of the polymeric chain. Also, it was confirmed that FITC-BSA could be entrapped in RITC-labeled pH-sensitive micelles of PAE-g-PEG by FRET. As a result, PAE-g-PEG can be a pH sensor and carrier for protein delivery.

The impedance-titrator : A novel setup to perform automated pH-dependent electrochemical experiments

A new device for performing electrochemical experiments under automatic change or control of the solution pH was developed. The electrochemical cell consists of a thermostatted glass cell, counter electrode, reference electrode and working electrode, pH sensor, stirrer and gas purging system. A control box and a potentiostat equipped with a frequency response analyser form the electronic equipment, while a piston buret allows dosing the solution of interest e.g. a sodium hydroxide solution. Various modes are available for scanning the pH range or keeping the pH constant if a hydroxide consuming reaction shall be observed at a constant pH value, all during electrochemical experiments are performed. Two application examples are given to demonstrate the versatility of the impedance titrator. One addresses the determination of the breakdown pH value of anodised aluminium and the other quantifies the consumption of zinc during transient formation of zincate precipitates.

Development of Photochemical Polymerized Optical pH-Sensors

A photochemical polymerized optical pH-sensor system was fabricated. The portable sensor system consists of a blue LED for exciting the optical source and metal packaged photomultiplier tubes for detecting fluorescence. As an acidic indicator, Fluorescein sodium salt was used. Intensity of the fluorescent emission was proportional to the pH value of the acid solutions used. 5-Carboxyfluorescein was used for an alkaline indicator. However, intensity of the fluorescent emission was decreased as the pH value of the alkali solutions increased. We accomplished to measure pH from pH 3 to pH 10 by subtracting output voltages from two kinds of sensors. Using the pH multi-measuring system, we succeeded in pH-measurement during alkaline solutions are spreading.

An electrokinetic bioreactor: using direct electric current for enhanced lactic acid fermentation and product recovery

The microbiological production of organic acids by fermentation processes is growing in commercial importance. However, the removal of product and pH control are two main issues that limit the technical and commercial viability of such processes. A laboratory scale bioreactor combining conventional electrodialysis and bipolar membrane electrodialysis has been developed for in situ product removal and pH control in lactic acid fermentation. The electrokinetic process enabled removal of the biocatalytic product (lactic acid) directly from the bioreactor system, in a concentrated form, as well as enabling good pH control without generation of troublesome salts. Moreover, end-product inhibition of glucose catabolism was reduced, resulting in a greater generation of the end-product lactic acid. An automatic pH sensor and current application system was developed and successfully implemented for lactic acid fermentation in the electrokinetic bioreactor.

Lifetime-based pH sensor system based on a polymer-supported ruthenium(II) complex

A new luminescence lifetime-based pH sensor system is described. The system is based on [Ru(Ph2phen)2DCbpy]2+ (DCbpy = 4,4'-dicarboxy-2,2'-bipyridine) immobilized in a mixed domain network copolymer utilizing hydrophobic regions in a hydrophilic, water-swellable, poly(ethylene oxide) matrix. The metal complex binds irreversibly to the hydrophobic domains leaving the pH-sensing COOHs projecting into an aqueous-rich poly(ethylene oxide) region. The complex shows a strong pH dependence of its lifetime (3-4-fold) and provides a usable pH range of about 3-5. The long (approximately 1 micros) excited-state lifetime and visible absorption of the sensor simplifies measurements. A model for the combined pH and oxygen-quenching sensitivity of the complex is provided; this allows use of the pH system over a wide range of oxygen concentrations. The combined polymer sensor is easy to prepare and requires no covalent chemistry. Further, the polymers enhance the luminescence of the complex and minimize interference from oxygen quenching.

Immunological Rapid Urease Test for Detecting Helicobacter pylori: Comparative Study of Biopsy Specimens and Gastric Mucus

Abstract: A variety of reliable methods are available for the detection of H. pylori during upper gastrointestinal endoscopy. We evaluated the clinical utility of an analyzer for H. pylori urease composed of a solid‐phase tip coated with a monoclonal antibody against H. pylori urease and ion‐sensitive field effect transistor‐based pH sensor system. Samples of both gastric mucus and gastric mucosal specimens were collected and the results from this system were compared. Sensitivity and specificity were 97% and 100% for mucus samples and 92% and 97% for mucosal specimens in the present system; compared to 95% and 96% for histological examination, 92% and 100% for bacteriological test, and 89% and 100% for rapid urease test, respectively. These results confirmed that the present system had high clinical sensitivity and specificity, especially for testing of mucus samples. This method has the advantage of requiring only one sample per patient because mucus can be collected from a broad area of the stomach lumen by stroking the mucosal surface with a brush. (Dig Endosc 1999; 11: 42–46)

A fiber-optic broad-range pH sensor system for gastric measurements

Abstract The construction and performance of a fiber-optic broad-range pH sensor system are described. The general construction of the sensor is similar to the original fiber-optic pH sensor, but two dyes with three p K values have been immobilized to provide resonse over the pH range of 0.5–7 with a precision better than 0.1 pH unit. The range extends to pH9 with less precision. The primary objective of the design is for gastric measurements. The system is based on absorbance dyes bound to polyacrylamide gel containing light-scattering particles. The sensor is constructed on a single 0.25-mm diameter plastic optical fiber. The optical system consists of a tungsten lamp, fiber-optic splitter and CCD/grating detector connected to a computer for spectral analysis, using two wavelength regions. The computer displays the pH graphically over 24 h. The system shows stability within 0.2 pH unit over 24 h, and has been tested with gastric samples in a dog.

Integrated pO 2, pCO 2, pH sensor system for online blood monitoring

A self-calibrating sample-taking sensor system for online pO 2, pCO 2 and pH monitoring is presented. The system consists of a two-lumen catheter with a sensor flow-through cell, a pump unit with instrumentation and a personal computer. The sensor device is based on an integrated silicon chip containing chemically sensitive field-effect transistors (ChemFETs) with CMOS signal-processing and thin film electrode systems for potentiometric and amperometric transducers. In vitro measurements and animal studies with anaesthetized pigs show good correlation with standard analyzer equipment.

Measurements of pH 60 in pork using ISFET/REFET and glass electrode methods

pH values of 180 pork longissimus dorsi muscles were obtained using different measurement methods. A glass combined penetration electrode and an ISFET/REFET pH sensor system were used directly in the muscle, whereas in the homogenate, pH was assessed with a glass combined electrode. The results showed that no statistically significant differences were obtained between the methods in all tested samples. However, samples where pH 60 stood below 5·9, produced a better agreement between methods. Comparing the values obtained from the two direct puncture methods in the first group of samples (pH<5·9) the I/R probe appeared to agree with those obtained from the homogenates. While working, the ISFET/REFET system proved to be a good device to detect carcasses with fast post mortem pH decline. Nevertheless, the excessive time required display stabilisation prohibits its use for continuous measurements on high speed slaughter-lines.

魚介類鮮度計測用ｐＨセンサシステムの試作

A pH sensor system, by which β-buffer capacity in fish muscle is determined continuously, was prepared from a pH electrode, a flow cell, a peristaltic pump, and a recorder. The optimum conditions for the proposed system were established, and then β-buffer capacity in fish muscles was determined by the the sensor system and a conventional method. Good correlation were obtained between β-buffffer capacities obtained by the output of the sensor and the conventional method. The results obtained by the system were also in good correlation with the K values. From these results, the possibility of determination of fish freshness with the proposed sensor system was suggested. The conditions for the determination of the buffer capacity in fish muscles were as follows: pH of buffer 7.0, flow rate 1.4 ml/min, and sample volume 50μl.

The possible danger of excessive early maternal vocal stimulation on infant development

The construction and performance of a fiber-optic broad-range pH sensor system are described. The general construction of the sensor is similar to the original fiber-optic pH sensor, but two dyes with three pK values have been immobilized to provide resonse over the pH range of 0.5–7 with a precision better than 0.1 pH unit. The range extends to pH9 with less precision. The primary objective of the design is for gastric measurements. The system is based on absorbance dyes bound to polyacrylamide gel containing light-scattering particles. The sensor is constructed on a single 0.25-mm diameter plastic optical fiber. The optical system consists of a tungsten lamp, fiber-optic splitter and CCD/grating detector connected to a computer for spectral analysis, using two wavelength regions. The computer displays the pH graphically over 24 h. The system shows stability within 0.2 pH unit over 24 h, and has been tested with gastric samples in a dog.