Functional cardiac cell constructs on cellulose-based scaffolding

This article provides a brief review on the development and applications of optical and fiber-optic pH sensors in the 1990s. Various methods and materials for immobilization of pH indicators are surveyed. Different spectroscopic methods used for measurement with pH sensors are briefly discussed. Several special optical and fiber-optic pH sensors are reviewed, including pH sensors based on conductive polymers, imaging fibers, microparticles and nanospheres, as well as micron and submicron fiber-optic pH sensors, distributed fiber-optic pH sensors, pH sensors for high acidity and alkalinity, pH sensors with broad dynamic range and linear response, and CO2 and NH3 sensors based on pH indicators. Applications of fiber-optic sensors in environmental detection, biomedical research, medical monitoring and industrial process control are summarized.

Recent development and applications of optical and fiber-optic pH sensors

This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and pKa values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

A novel type of chemodosimeters has been developed on the basis of a displacement reaction. N-Acyl-triazenes are found to be highly selective and tunable chemodosimeters toward cyanide. When N-acetyl-triazene 1a was titrated with various anions (-CN, F-, Cl-, AcO-, H2PO4-, -SCN, ClO4-, and HSO4-) in acetonitrile, significant absorption changes (from colorless to deep purple) resulted in the cases of -CN and F-, and small changes in the cases of AcO- and H2PO4-. N-Isopropanoyl-triazene 1b showed significant response only toward -CN, weaker response toward F-, and little response toward other anions in acetonitrile. Both of the triazenes 1a and 1b responded only to -CN in methanol−water, because of the analyte's strong nucleophilicity toward the acyl group and weak hydrogen-bonding ability as compared to other anions examined. The N-acyl-triazenes can be used for the naked eye detection of cyanide.

N-acyl triazenes as tunable and selective chemodosimeters toward cyanide ion.

An implantable biosensor for detecting an analyte in vivo in body fluids comprises an analyte-sensitive hydrogel filament chemically configured to vary its displacement volume according to changes in concentration of an analyte, such as glucose, in a patient's body fluid. A photometric displacement transducer placed inside the biosensor is configured to quantifiably detect changes in the displacement volume of the hydrogel filament, such as by detecting the light intensity on a photoreceptor arranged to receive light of varying intensity depending upon the displacement of the hydrogel filament. A battery powered telemeter operably engaged to the photometric displacement transducer sends a radio data signal representing glucose concentration level to a receiver containing an alarm system. The alarm system can automatically notify a person that the analyte level is outside desired predetermined parameters, and/or to automatically inject an agent to counteract the adverse analyte levels.

Photometric glucose measurement system using glucose-sensitive hydrogel

Membranes for optical pH sensors

Artificial multienzyme complexes were prepared in which enzymes were covalently bound to polysaccharide structures activated with urea and formaldehyde. Double enzyme complexes of glucose oxidase and catalase, a glucose oxidase and invertase, were prepared by immobilization on to cellulose fabric. Also, catalase was covalently bound to soluble dextran. The resulting multienzyme systems were highly active and stable, making them suitable for use in measuring the concentrations of glucose and saccharose in solutions. The measurements were performed using an amperometric oxygen electrode and multienzyme membranes containing glucose oxidase and catalase for the first substrate, as well as glucose oxidase bound to cheese-cloth and a 'liquid' membrane of dextran-bound catalase. To determine the concentration of saccharose, a multienzyme membrane with bound glucose oxidase and invertase was used in combination with a 'liquid' dextran-catalase. The enzyme electrodes exhibited a measuring range of 0.1-5 mol dm-3 and a response time of 2-3 min. The electrodes may be used for measuring saccharose and glucose concentrations both in fermentation broths and food products.

Milka A. Krysteva

Papers

Membranes for optical pH sensors

Multienzyme membranes for biosensors.