A novel fluorescent indicator for Ba2+ in aqueous micellar solutions

The highly selective and sensitive fluorescence detection of Ba(2+) among alkali metal and alkaline earth metal cations was successfully achieved in aqueous media by the combination of a novel monoazacryptand type of fluorophore and micelles of Triton X-100.     

A novel fluorescent indicator displacement assay for sensing the anticancer drug gefitinib

Fluorescent indicator displacement assays have become popular for converting synthetic receptors into optical sensors. We have now shown that a 1:2 host–guest complex between cucurbit[8]uril (Q[8]) and proflavine (PF) can be used as a fluorescent indicator for sensing the anticancer drug gefitinib. The 2PF@Q[8] complex can be used to detect gefitinib with high selectivity using fluorescence spectrometry with a detection limit of 6.63 × 10^?8 mol^?L. The proposed sensing mechanism was investigated using ¹H nuclear magnetic resonance spectroscopy (¹H NMR), isothermal titration calorimetry and electrospray ionisation mass spectrometry. The 2PF@Q[8] complex was shown to be suitable for imaging gefitinib in prostate cancer (PC3) cells, which may help to elucidate relevant biological processes at the molecular level. We have developed a novel F-IDA to detect the anticancer drug GEF with high selectivity. The new indicator has excellent selectivity and a low detection limit for GEF. We have also demonstrated that the F-IDA can be used for the practical determination of drugs in living cells.     

A novel genetically encoded fluorescent protein as a Cu(I) indicator

We constructed the copper(I)-binding domain of Mycobacterium tuberculosis (Mtb) CDC 1551 (residues 1-162) between cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP), and formed a novel genetically encoded fluorescent copper(I) responsive protein (PMtb). The sensitivity and selectivity to copper(I) of the PMtb was sought. The experiments showed that the copper(I)-binding domain of the PMtb was highly sensitive and selective towards copper(I).     

A novel indicator series for measuring pKa values in acetonitrile

A series of substituted azobenzene dyes was found to span a range of 8 pK_a units in acetonitrile. The UV absorption spectra of the dyes are responsive to protonation, changing in both absorption maximum and intensity. These characteristics make the dyes useful as indicators for the measurement of pK_a values of neutral organic bases that absorb in the visible region of the spectrum.     

Development of a novel UV indicator and dosimeter film

A novel UV indicator is described, comprising nanocrystalline particles of titania dispersed in a film of a polymer, hydroxyl ethyl cellulose (HEC), containing: a mild reducing agent, triethanolamine (TEOA) and a redox indicator, methylene blue (MB). The UV indicator film is blue-coloured in the absence of UV light and loses colour upon exposure to UV light, attaining within a few min a steady-state degree of bleaching that can provide a measure of the irradiance of the incident light. The original blue colour of the film returns once the source of UV light is removed. The spectral characteristics of a typical UV indicator film, and its components, are discussed and the UV-absorbing action of the titania particles highlighted. From the measured %bleaching undergone by a typical UV indicator as a function of light irradiance the indicator appears fully bleached, within 7 min, by a UV irradiance of 3 mW cm(-2) or greater. The mechanism by which the UV indicator works is described. The reversible nature of the UV indicator is removed by covering a typical UV indicator with a thin, largely oxygen impermeable, polymer film, such as the regenerated cellulose found in Sellotape. The product is a UV dosimeter, the response of which is related to the intensity and duration of the incident UV light, as well as the amount of titania in the film. A typical UV dosimeter film is fully bleached by 250 mJ cm(-2) of UV light. The possible use of these novel indicators to measure UV exposure levels, irradiance and dose, is discussed.     

A New acid-base indicator

The Fe(III)-1,2-dihydroxybenzene-3,5-disulfonic acid complex absorption characteristics are pH dependent. An intensive study has shown that these characteristics are reversible and reproducible.This system is, therefore, well-suited for use as a pH indicator. It serves for double indicator titrations (acid → base; base → acid) and as a universal wide-range indicator.     

Development of a novel colorimetric indicator pad for detecting aldehydes

A colorimetric indicator was developed and a colorimetric indicator pad was fabricated for the rapid detection of aldehydes. The detection pad has two sides: an observation side on top and a barrier on the bottom. The top side contains a reagent which reacts directly with aldehydes to produce a color change, while the bottom side is coated with a double-sided plastic tape barrier to prevent the escape of chemicals. Sensitivity of the indicator pads was determined using the vapor sensitive ASTM F739 technique with the presence of the indicator. A significant indicator color change (yellow to red) occurred about 5 min before the infrared analyzer response of the ASTM method. The chemical principle and reaction characterization of the test are described. The stability and potential interferences of the indicator pad were also examined by directly spiking aldehydes and compounds with other functional groups, respectively, onto the indicator pads. The newly developed aldehyde indicator pad should find utility in detecting aldehydes in both liquid and vapor phases and in collecting aldehyde permeation through PPE for further study.     

Haematoxylin,a novel indicator by the determination of phosphorus

Determination of phosphate was performed with lanthanum nitrate in an aqueous medium in the presence of a haematoxylin indicator. Following processing of the organic phosphorus compound in a Schöniger flask the mixture was acidified and boiled off and then the pH was adjusted to 6.1–6.3 with hexamethylene tetramine. The hot solution was titrated with lanthanum nitrate. The orange colour of haematoxylin changed to violet-blue at the point of equivalence, while precipitation of lanthanum phosphate was observed.     

A novel acidotropic pH indicator and its potential application in labeling acidic organelles of live cells.

BACKGROUND: Ratio imaging has received intensive attention in the past few decades. The growing potential of ratio imaging is significantly limited, however, by the lack of appropriate fluorescent probes, for acidic organelles in particular. The classic fluorescent dyes (such as fluoresceins, rhodamines and coumarins) are not suitable for studying acidic organelles (such as lysosomes) because their fluorescence is significantly decreased under neutral or acidic conditions. This has motivated us to develop probes that can be used in ratio imaging that are strongly fluorescent even in acidic media. RESULTS: The compound 2-(4-pyridyl)-5-((4-(2-dimethylaminoethyl-aminocarbamoyl) methoxy)phenyl)oxazole (PDMPO) was prepared and characterized as a new acidotropic dual-excitation and dual-emission pH indicator. It emits intense yellow fluorescence at lower pH and gives intense blue fluorescence at higher pH. This unique pH-dependent fluorescence property was readily explored to selectively stain lysosomes and to determine the pH of the organelle in an emission-ratio-imaging mode. PDMPO is selectively localized to lysosomes and exhibits a pH-dependent dual excitation and emission. CONCLUSIONS: PDMPO selectively labels acidic organelles (such as lysosomes) of live cells and the two distinct emission peaks can be used to monitor the pH fluctuations of live cells in ratio measurements. Additionally, the very large Stokes shift and excellent photostability of PDMPO make the compound an ideal fluorescent acidotropic probe. The unique fluorescence properties of PDMPO might give researchers a new tool with which to study acidic organelles of live cells.     

A mechanically controlled indicator displacement assay

Push a host: Mechanical compression was applied to a host monolayer at an interface, which facilitated an indicator displacement assay. The fluorescence resonance energy transfer (FRET) between the host and indicator was switched on by this compression. Addition of D-glucose caused the indicator to be displaced, effectively quenching the FRET process.     

A viologen-based UV indicator and dosimeter

A UV indicator/dosimeter based on benzyl viologen (BV²⁺) encapsulated in polyvinyl alcohol (PVA) is described. Upon exposure to UV light, the BV²⁺/PVA film turns a striking purple colour due to the formation of the cation radical, BV^•+. The usual oxygen sensitivity of BV^•+ is significantly reduced due to the very low oxygen permeability of the encapsulating polymer, PVA. Exposure of a typical BV²⁺/PVA film, for a set amount of time, to UVB light with different UV indices produces different levels of BV^•+, as measured by the absorbance of the film at 550 nm. A plot of the change in absorbance at this wavelength, ΔAbs(550), as a function of UV index, UVI, produces a linear calibration curve which allows the film to be used as a UVB indicator, and a similar procedure could be employed to allow it to be used as a solar UVI indicator. A typical BV²⁺/PVA film generates a significant, semi-permanent (stable for >24 h) saturated purple colour (absorbance ~0.8–0.9) upon exposure to sunlight equivalent to a minimal erythemal dose associated with Caucasian skin, i.e. skin type II. The current drawbacks of the film and the possible future use of the BV²⁺/PVA film as a personal solar UV dosimeter for all skin types are briefly discussed.      

A fast response membrane-based pH indicator optode

A cellulose acetate based optode membrane containing 4-dimethylamino-4'-octylazobenzene as an acid-base indicator is described. Other essential components of the membrane for a fast-responding and durable sensor are diethyl phthalate, triethyleneglycol and potassium tetrakis(4-chlorophenyl)borate. Factors affecting the sensor behaviour are discussed and an application in a flow-cell is demonstrated.     

A facile synthesis of phthalein indicator dyes

The use of methanesulfonic acid offers a novel and highly efficient method for the synthesis of phthalein indicator dyes in excellent yields on an industrial scale.     

Development of a novel colorimetric indicator label for monitoring freshness of intermediate-moisture dessert spoilage

A colorimetric mixed pH dye-based indicator with potential for the development of intelligent packaging, as a “chemical barcode” for real-time monitoring of intermediate-moisture dessert spoilage, is described. This on-package indicator contains mixed pH-sensitive dyes, bromothymol blue and methyl red, that respond through visible color change to carbon dioxide (CO₂) as a spoilage metabolite. Both indicator solution and indicator label characteristics were studied, as well as their response to CO₂. A kinetic approach was used to correlate the response of the indicator label to the changes in intermediate-moisture dessert spoilage. Color changes, in terms of total color difference of a mixed pH dye-based indicator, correlated well with CO₂ levels of intermediate-moisture dessert. Trials on golden drop have verified that the indicator response correlates with microbial growth patterns in dessert samples, thus enabling the real-time monitoring of spoilage either at various constant temperatures or with temperature fluctuation.     

A new water-soluble near-neutral ratiometric fluorescent pH indicator

Donor-pi-acceptor fluorene derivative 1c is a near-neutral pH indicator whose pKa of approximately 7.0 was determined by both absorption and fluorescence methods. 1c satisfies important criteria for a sensitive ratiomeric fluorescent pH indicator with a distinctive isoemissive point, good dispersion in cell cytosol, and low cytotoxicity. Furthermore, its 2PA cross section of 100 GM in its neutral form suggests its potential in two-photon fluorescence imaging applications.     

A new rhodamine B-based lysosomal pH fluorescent indicator

We designed and synthesized a new pH fluorescent probe, RCE, based on structural changes of rhodamine dye at different pH values. The probe exhibits high selectivity, high sensitivity and quick response to acidic pH, as well as low cytotoxicity, excellent photostability, reversibility and cell membrane permeability. Fluorescence intensity at 584 nm was increased more than 150-fold within pH range 7.51–3.53. This probe has pK_a value 4.71, which is valuable for studying acidic organelles. Because of its long absorption and emission wavelengths, RCE can avoid associated cell damage. The probe can selectively stain lysosomes and monitor lysosomal pH changes in living cells.     

A FRET-based indicator for imaging mitochondrial zinc ions

A strategy based on fluorescence resonance energy transfer (FRET) to transform a red-emitting fluorophore into a ratiometric indicator for mitochondrial Zn(II) is demonstrated.     

A new indicator for the complexometric determination of calcium

Glyoxal bis-(2-hydroxy-anil) is proposed as a new indicator for the complexoemetric titration of calcium. The end-point is indicated by a sharp change from pink to yellow.     

A turn-on fluorescent indicator for citrate with micromolar sensitivity

A turn-on fluorescent indicator for citric acid (citrate) has been developed, displaying high emission enhancement (+1500%) and low interference by other carboxylates. The sensor is based on the non-emissive copper(II) complex of a fluorescent amino amide, which, upon addition of citrate decomplexates to yield the emissive ligand. The detection limit estimated for this new chemosensing system is about 0.5 microM. This novel approach to the analysis of citrate constitutes an alternative ca. 10(2)-10(3) times more sensitive than the standard method based on the enzyme citrate lyase.