Search

This work presents a colorimetric dye-based array for naked-eye detection of chicken meat spoilage. The array is obtained by fixing five acid-base indicators, m-cresol purple (1), o-cresol red (2), bromothymol blue (3), thymol blue (4), and chlorophenol red (5), and a sensing molecule specific for thiols, 5,5'-dithiobis(2-nitrodibenzoic acid), called Ellman's reagent (6), on a cellulose-based support. The dyes, being permanently charged, are fixed on the support via ion-exchange. The entire degradation process of beast poultry meat, at ambient temperature and in a domestic fridge, is followed by the change of the color of the array, placed in the headspace over the meat samples. The device is set after selection of the most suitable starting form, which could be the acidic or the basic color of indicators, being the proper dye concentration and the dimension of the spots already established. Basing on sensors colors, we identified three levels of the degradation process of chicken meat, named SAFE, WARNING, and HAZARD. By instrumental analysis, we demonstrated that sensors response was correlated to volatile organic compounds (VOCs) composition in the headspace and, thus, to meat spoilage progress. We demonstrated that biogenic amines (BAs), commonly considered a critical spoilage marker, are indeed produced into the samples but never present in the headspace, even in traces, during the investigated time-lapse. The VOC evolution nevertheless allows one to assign the sample as WARNING and further HAZARD. Some indicators turned out to be more informative than others, and the best candidates for a future industrial application resulted in a bromothymol blue (3)-, chlorophenol red (5)-, and Ellman's reagent (6)-based array.

South Africa is a water-scarce country due to the shortage of rainfall. This scarcity is further exacerbated by the loss of water through leakage from faulty pipes. This paper reports on the use of a simple microfluidic device in the early detection of water leakages. The microfluidic paper-based device (µPADs) were prepared by printing patterns of wax (100 μm width) on the paper surface and melting the wax into the paper to form hydrophobic barriers. Solutions of lower to higher pH were also prepared and were introduced to the chlorophenol red test strips and a range of colours from yellow (lower pH) to purple (higher pH) were obtained. The digital images obtained with the μPADs were analysed using the CIELab colour system. The optimized pH range was wider than the typical grayscale-based image analysis and was successful for a wide pH range of 2–12. The QR codes attached to the strips enable tracking to obtain the real-time location from which leakage was detected. The study conclusively shows that the combination of digital image analysis and a μPAD device is highly efficient for quantitative analysis, and thus useful for the detection of household water leaks.

Microfluidic paper-based analytical devices (mPADs) have gained significant attention in recent years for applications ranging from clinical diagnostics to environmental testing. However, separation on mPADs remain challenging to implement, particularly in complex samples. This has revived interest in revisiting paper chromatography and paper electrophoresis in mPADs to address these needs. Here, laminated Parafilm-paper (l-paper) is applied to fabricate electrophoretic devices. This approach yields a free-standing channel, leading to improved peak resolution relative to previous electrophoretic separations in traditional wax-printed mPADs. Major factors influencing the separation, including Joule heating, electroosmotic flow, and electrophoretic mobility, were investigated. As a result of paper’s high ratio of surface area (78%) to pore volume (22%) resulting in slow heat dissipation, a usable applied field strength range of 0 – 200 V cm(−1) was employed to avoid Joule heating. The electroosmotic flow of the system was found to be 2.5 × 10(−5) ± 7.7 × 10(−7) cm(2) V(−1)s(−1) and the electrophoretic mobility of chlorophenol red was 1.2 × 10(−4) ± 7.7 × 10(−7) cm(2) V(−1)s(−1). Basic separation protocols were optimized using colorimetric detection of chlorophenol red and indigo carmine dyes as representative molecules. Paper type, channel width, and applied potential were then used to optimize the separations. Addition of an injection port to the device improved resolution and reduced peak broadening. Finally, the separation of fluorescein isothiocyanate (FITC) and L-glutamic acid (Glu) labeled with FITC, was successfully carried out using the l-paper electrophoretic device. Imaging with a microscope was found to achieve reduced peak broadening and increased resolution relative to imaging with a mobile camera, due to elimination of background signal, achieving a 72 ± 4% conjugation of Glu and FITC.

Thermochromic materials exhibit a color change in response to a change in temperature. Creating nontoxic microcapsules containing thermochromic materials for applications in ink and film materials is historically challenging. In this study, we develop a nontoxic chlorophenol red (CPR)–water thermochromic system and its microcapsules with silicone shells via a reaction between water and octadecyltrichlorosilane (OTS) at the interface of a w/o emulsion. The obtained microcapsules exhibit a clear color change with full reversibility and are successfully used as inks by screen printing and as additives in films. Nontoxicity of both microcapsules and films is demonstrated through cell cytotoxicity assays. These features make these novel materials applicable to the next generation of intelligent sensors, coating, and food packaging materials.

NH 3 and CO 2 are often involved in the spoilage of foods. In this study, a colorimetric array indicator was evaluated for the detection of NH 3 and CO 2 using pH-sensitive dyes (dimethyl yellow, methyl red, chlorophenol red, methyl orange, phenol red, thymol blue, m -cresol purple) encapsulated within ethylcellulose matrices. The pH dyes were doped either with hydrochloric acid or tetrabutylammonium hydroxide to manipulate the colorimetric responses. The sensing dyes were applied onto a plastic substrate to produce array indicators consisting of 4 × 4 elements. Digital images of the indicator array, before and after the exposure to NH 3 , CO 2 or NH 3 /CO 2 mixtures, were taken to monitor the change in color for each of the array elements. Unique ΔRGB patterns for NH 3 , CO 2 , and their mixture were observed. At 4 °C, principal component analysis discriminated samples into two clusters that were higher and lower than 15 μg/mL NH 3 respectively. For CO 2 , at both 4 and 25 °C, the array indicator discriminated air samples with lower than 5% CO 2 from those higher than 20% CO 2 . For NH 3 /CO 2 mixtures, the array indicator differentiated air samples of high NH 3 /low CO 2 and low NH 3 /high CO 2 combinations. These results show that the array indicator may be useful for intelligent packaging application of food products.

L’élimination de la couleur de solutions aqueuses du rouge de chlorophénol a été étudiée par adsorption sur une hydrotalcite de synthèse calcinée. Le solide [Mg-Al-CO3] a été préparé par coprécipitation à pH constant et selon un rapport molaire Mg/Al = 2. Les études par diffraction des rayons X et spectroscopie infrarouge à transformée de Fourier (FTIR) ont montré que le matériau obtenu correspond aux composés de type hydrotalcite avec une bonne cristallinité. L’interaction de ce matériau avec le colorant montre que la cinétique d’adsorption est rapide et suit une expression de vitesse d’adsorption du second ordre. Les influences du pH, de la concentration de l’adsorbant, de la concentration en rouge de chlorophénol de la solution et d’ions compétiteurs tels que chlorure et carbonate ont été étudiées afin d’optimiser l’adsorption. Le traitement de solutions contenant de 0,015 à 1,5 mmol ∙L-1 de rouge de chlorophénol a donné des résultats prometteurs. La capacité d’adsorption de l’hydrotalcite calcinée est d’environ 1,7 mmol∙g-1. Les hydrotalcites calcinées pourraient constituer d’intéressants supports pour le piégeage du rouge de chlorophénol., The color removal from aqueous solutions of chlorophenol red by adsorption on a calcined synthetic hydrotalcite was investigated. The solid [Mg-Al-CO3] was prepared by coprecipitation at constant pH and with an Mg/Al molar ratio of 2. The studies by X-ray diffraction (XRD) and infrared spectroscopy FTIR (Fourier Transform InfraRed spectroscopy) have shown that the material obtained corresponds to the hydrotalcite-like compounds with good crystallinity. The interaction dye-hydrotalcite shows that the kinetic of adsorption is fast and follows the second order model. The effects of the pH, adsorbent concentration, chlorophenol red concentration and competitive ions such as chloride and carbonate on the adsorption were studied. Solutions containing from 0.015 to 1.5 mmol∙L-1 of chlorophenol red were successfully treated. The adsorption capacity of the calcined hydrotalcite is close to 1.7 mmol∙g-1. This suggests that the calcined hydrotalcites could constitute interesting supports for the trapping of chlorophenol red.

Artificial Neural Network (ANN) had been used in this study to extend the response range of the pH indicator. The input from absorbance values of the absorbance spectra of chlorophenol red at different pH was used to train the ANN. During the training process, the coefficient values of the ANN will be adjusted to obtain the desire output. In this research, back propagation algorithm had been used for optimizing the response range of the pH indicator chlorophenol red in solution. The result indicates that the use of ANN enable the pH response range to be extended from 4.8-6.8 to 1.0-10.0.

A colorimetric strip sensor array based on the naked-eye detection has been reported as a simple instrument-free device able to visually display a concentration level of gaseous analytes with basicity. The array has a vertically aligned configuration of five sensing elements and their detection sensitivities to basic analytes are controlled to decrease downwardly. The colorimetric sensors were fabricated by drop-casting a dye solution containing a pH indicator, an acid compound, and hydrophilic polyethylene glycol on a polyacrylonitrile nanofiber mat. The detection sensitivity was regulated by using different amounts of the acid compound in addition to variation in pH Indicator. When sensors containing a pH indicator of bromophenol blue (BPB), bromocresol green (BCG), or chlorophenol red (CPR) were exposed to ammonia gas, coloration happens considerably in the regions of 0–1, 0–5 and 10–100 ppm for BPB, BCG and CPR sensors, respectively. Furthermore, the detection sensitivity could be controlled to decrease by increasing an amount of citric acid, which reveals that the color-changing acid-base reactions between pH indicator and basic analytes are reduced by competitive interactions between the analytes and acid additive. As illustrations, two strip sensor arrays based on BPB and BCG dyes were fabricated and confirmed the successful naked-eye discrimination of a NH 3 concentration level in the ranges of 1–50 and 5–100 ppm, respectively. The concentration level can be determined by a number of coloration elements in the strip device while its resolution relies on a total number of sensing elements.

A simple on package indicator label for grapes (Vitis vinifera L.) ripeness has been developed based on chlorophenol red (CPR). The CPR was immobilized onto the filter paper via absorption method to make the CPR membrane. The membrane as a colorimetric label for grape ripeness works based on pH increase as the volatile organic acids decreased gradually in the package headspace due to the formation of sugars during berry ripening process. Subsequently, the color of the indicator label will change from white to beige then finally to yellow for over-ripe indication, which is easily detected by naked eye. The results show that the indicator label could be used to monitor the ripeness of grapes since the color changes of indicator label toward the ripeness of the grapes are in similar tendency and have a good linear correlation. Thus, the indicator label can be used as an effective tool for on-line ripeness monitoring of grapes packaging. Finally, the indicator label was successfully used as on-package indicator label for on-line ripeness monitoring of grapes in ambient and chilled conditions.

In the present paper a novel cone shaped nano-fiber (CSNF) pH sensor using multi-mode fiber (MMF) has been fabricated and demonstrated. Three different pH indicators, chlorophenol red, bromothymol blue and cresol red with precursor tetraethyl orthosilicate (TEOS) have been used for fabrication of pH sensing layer. A significant enhancement in sensing properties of pH sensor with TiO 2 thin film has been observed. The pH sensor with TiO 2 thin film shows the quite high sensitivity (1.16 dBm/pH) as compared to sensor with simple pH coating (0.81 dBm/pH) at 1550 nm with a good linear response. Moreover, the sensor with TiO 2 film exhibits fast response time of ∼ 25 s for pH values ranging from 4 to 11 with excellent stability and durability.

Detecting bacteria is important in the fields of human health, environmental monitoring, and food safety. Foodborne pathogens alone are estimated to cause 420 »000 deaths annually, with low-income regions affected most. Despite improvements in bacterial detection, fast, disposable, low-cost, sensitive, and user-friendly methods are still needed. Traditional methods for detecting bacteria rely primarily on cell culturing or polymerase chain reaction (PCR), which require highly trained personnel and a central laboratory and take several hours or even days to deliver results. Low-cost methods like lateral flow immunoassays exist but frequently suffer from poor sensitivity and/or lack quantitative results. Here, a rapid method for detecting bacteria at very low concentrations is presented using two sequential preconcentration steps. In the first preconcentration step, the sample is mixed with antibody-modified magnetic particles and free antibodies conjugated to β-galactosidase (β-gal). The target bacteria are isolated and concentrated using immunomagnetic separation. The isolated bacteria are then incubated with chlorophenol red-β-d-galactopyranoside (CPRG), which reacts with β-gal to produce chlorophenol red (CPR) in a bacteria concentration-dependent manner. In the second step, CPR and CPRG are separated and focused using an isotachophoretic microfluidic paper-based analytical device, significantly improving the final detection limit relative to paper-based devices lacking the focusing mechanism. Moreover, CPR and CPRG form two visible color bands that act as test and control bands, respectively, improving assay robustness. The method was tested with E. coli DH5-α and successfully detected concentrations as low as 9.2 CFU/mL in laboratory samples and 920 CFU/mL in apple juice samples in ∼90 min. Fil: Schaumburg, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Carrell, Cody S.. State University of Colorado - Fort Collins; Estados Unidos Fil: Henry, Charles S.. State University of Colorado - Fort Collins; Estados Unidos

The use of coliforms and Escherichia coli as indicator species for assessing the quality of water is well established and a large variety of methods based on β-galactosidase (B-GAL) activity, inherent to the microbes within this classification, have arisen to enable their detection and enumeration. Chlorophenol red (CPR) is widely used as a chromogenic label, but its capacity for translation to electroanalytical devices has yet to be fully explored. The CPR moiety is capable of undergoing oxidation at carbon substrates (+0.7 V) giving rise to a variety of phenolic intermediates. Electrochemical, XPS and enzymatic techniques were employed to characterise the underpinning chemistry and the intermediate identified as a 1,2-quinone derivative in which the chlorine substituent is retained. The latter was found to accumulate at the electrode and, in contrast to the parent CPR, was found to be detected at a significantly less positive potential (+0.3 V). Bacterial hydrolysis of a CPR labelled substrate was demonstrated with the 1,2-quinone oxidation product found to accumulate at the electrode and detected using square wave voltammetry. Proof of concept for the efficacy of the alternative electrode pathway was established through the detection of E.coli after an incubation time of 2.5 h with no interference from the labelled substrates.

Biosensors have been used as first-step monitoring tools to detect on-site samples in a simple and cost-effective manner. Numerous recombinant microbial biosensors have been exploited for monitoring on-site toxic chemicals and biological signals. Herein, a recombinant microbial biosensor was constructed for monitoring cadmium. The cadmium responding cadC regulatory gene and it’s promoter from Staphylococcus aureus was amplified through PCR, fused with the lacZ gene, and transformed into Escherichia coli BL21 (DE3) cells. In the presence of cadmium, the biosensor cells express β-galactosidase showing red color development with chlorophenol red β-galactopyranoside (CPRG) as the enzymatic substrate. The biosensor cells showed the best β-galactosidase activity after 3 hr induction with cadmium at pH 5 and a detection range from 0.01 μM to 10 mM cadmium with a linearity from 0.01 to 0.1 μM cadmium (y = 0.98 x + 0.142, R² = 0.98). Among the heavy metals, cadmium and lead showed good responses, tin and cobalt showed medium responses, and mercury and copper showed no responses. The biosensor cells showed good responses to several waste waters similar to buffer solution, all spiked with cadmium. The biosensor described herein could be applied for on-site cadmium monitoring in a simple and cost-effective manner without sample pretreatments.

An intensity-modulated fiber optic pH sensor is fabricated and demonstrated in the present work. Three pH indicators, bromothymol blue, cresol red and chlorophenol red along with titania-silica composite are used as pH sensitive layers. The sensing principle is based on evanescent field absorption and then transmitted power loss of light guided within the fiber. The sensor parameters were studied by changing the volume ratio of the composite layer, and a maximum sensitivity of 1.76 μW/pH is obtained for 1:3 (TiO2:SiO2) composite layer with excellent linear response for pH value from 2 to 11. The TiO2 content induces strong interaction between guided light and outer medium and the concentration of SiO2 was increased to improve porosity in the sol-gel matrix to achieve enhanced sensitivity. A straight forward way has been introduced to utilize the temperature cross-sensitivity feature of the optical fiber pH sensor with high temperature sensitivity. In addition to its high sensitivity, the proposed sensor has additional characteristics of fast time response and good stability which are very useful in biomedical, environmental, food processing and industrial applications.

Making use of the sol-gel technique, an optical pH sensor was prepared, which was made from an organic carrier with four indictors including congo red, bromophenol blue, cresol red, and chlorophenol red, cross-linked by tetraethyl orthosilicate (TEOS) and cellulose acetate. The actual detection range of the optical pH sensor is 2.5&ndash, 11.0. The optimal ratio of ethyl orthosilicate, absolute ethanol, deionized water, and hydrochloric acid in glue precursor of the sensor-sensitive membrane was explored. The orthogonal experiment was designed to optimize the dosage of cellulose acetate, N,N-dimethylformamide (DMF), indicator, hydrochloric acid, and precursor glue in preparing the sensor-sensitive membrane. The linearity, measurement accuracy, repeatability, stability, and response time of the prepared pH sensor were tested. The measurement results were analyzed using a support vector machine and linear regression. The experimental results show that the optical pH sensor has a measurement accuracy of up to 0.2 pH and better stability and repeatability than the traditional pH glass electrode.

The article describes a simple and rapid method for colorimetric detection of bacteria. It is based on competitive binding of positively charged polyethyleneimine-coated gold nanoparticles (PEI-AuNPs) to negatively charged enzymes and bacteria. The PEI-AuNPs are electrostatically attracted by both the bacterial surface and the enzyme β-galactosidase (β-Gal). Binding to the latter results in the inhibition of enzyme activity. However, in the presence of a large number of bacteria, the PEI-AuNPs preferentially bind to bacteria. Hence, the enzyme will not be inhibited and its activity can be colorimetrically determined via hydrolysis of the chromogenic substrate chlorophenol red β-D-galactopyranoside (CPRG). The detection limit of this assay is as low as 10 cfu·mL−1, and the linear range extends from 106 to 108 cfu·mL−1. The assay is applicable to both Gram-negative (such as enterotoxigenic Escherichia coli; ETEC) and Gram-positive (Staphylococcus aureus; S. aureus) bacteria. Results are obtained within 10 min using an optical reader, and within 2–3 h by bare-eye detection. The method was applied to the identification of ETEC contamination at a level of 10 cfu·mL−1 in spiked drinking water. Given its low detection limit and rapidity (sample preconcentration is not required), this method holds great promise for on-site detection of total bacterial contamination.

Amine-based volatile compounds released bymicroorganisms offer an alternative diagnostic approach for the identification of foodborne pathogens. Our objective has been to solvent cast cellulose acetate membranes to immobilise dyes and to use the resultant membranes as a plastic device to discriminate between different types of amines (triethylamine, isobutylamine, isopentylamine). The plastic device consisted of an array of membranes with five pH indicators (namely alizarin, bromophenol blue, chlorophenol red, methyl red and thymol blue). To analyse the data using a portable instrument, we used an iPhone (R) to obtain images and to extract red, green and blue colours (RGB) using in-house software before and after contact with each individual amine. All the RGB values extracted for each analyte allowed us to generate a unique colour pattern, which was used as input for non-supervised pattern recognition methods. Based on this analysis, it was possible to clearly discriminate between the amines studied without any misclassification, demonstrating that the device is well-suited for large-scale applications such as non-destructive methods to discriminate amines and, in future, for smart packaging applications in order to give early warning of rotting food that may lead to food poisoning. Additionally, a semi-quantitative analysis was performed and we have demonstrated that it is possible to quantify concentrations of amines down to 1 ppm.

The present work describes the fabrication and characterization of an optical fiber pH sensor using a sol–gel technique. The sensing head configuration is incorporated using a short section of no-core fiber, coated with tetraethyl orthosilicate and spliced at the end of a single mode fiber with a bulge. Different types of indicators (bromophenol blue, cresol red, and chlorophenol red) were used to achieve a wide pH range from 2 to 13. High sensitivities of the fabricated device were found to be 1.02 and ? 0.93 ?? nm / pH for acidic and alkaline solutions, respectively. From the characterization results, it was noted that there is an impact of ionic strength and an effect of the temperature of liquid on the response characteristic, which is an advantage of the existing device over the other pH sensors. The fabricated sensor exhibited good reflection spectrum, indicating a blueshift in resonance wavelength for alkaline solutions and a redshift for acidic solutions.

Aromatic hydrocarbons are toxic environmental pollutants that are detrimental to the ecosystem and human health. Among them, chlorotoluene and nitrotoluene are toxic to hydrobios and irritate the skin, eyes, and respiratory organs of humans. We herein report the development of recombinant microbial biosensors for cheap and rapid monitoring of chlorotoluene and nitrotoluene compounds. Plasmids were constructed by inserting the xylR regulatory gene for BTEX (benzene, toluene, ethylbenzene, and xylene) degradation into upstream of Po’ (the DmpR activator promoter Po with the deletion of its own upstream activating sequences) or Pu (the cognate promoter of XylR)::lacZ (the β-galactosidase gene) and transformed into Escherichia coli DH5α. In the presence of inducers, the biosensor cells immobilized in agarose developed a red color in 1-2 h due to the hydrolysis of chlorophenol red β-D-galactopyranoside (CPRG), a substrate of β-galactosidase that was expressed by the inducers. Among BTEX, high responses were specifically observed with o-, m-, p-chlorotoluene (0.1 ㎛-100 mM) and o-, m-, p-nitrotoluene (0.1 mM-100 mM). Po’ demonstrated higher responses than those with Pu. The biosensors immobilized in agarose showed good stability after 21 days’ storage at 4℃, and responses in untreated wastewater spiked with chlorotoluene and nitrotoluene, suggesting they can be used to detect compounds in wastewater.

An optical fiber formaldehyde biosensor based on a modified single sol–gel film consisting of alcohol oxidase (AOX) and chlorophenol red (CPR) was developed. The modification relies on addition of poly(vinyl alcohol) (PVA) into sol–gel matrix, in order to increase the function of AOX. The biosensing element on a sol–gel film has been placed inside the flow-cell for the flow system measurements. In the presence of a constant AOX, a color change of the CPR was measured in term of its reflected signal intensity at the wavelength 555 nm. This color change could be related to the formaldehyde concentration in the sample solutions. The performance of optical formaldehyde biosensor in the flow system has been optimized. The formaldehyde biosensor exhibited a dynamic linear response range in the formaldehyde concentration range of 0–10 mg/L with linear correlation (r ) was 0.996. The detection limit of the biosensor was 0.035 mg/L while reproducibility was < 1% RSD (relative standard deviation). Tofu as real food sample were analysis using the biosensor revealed that it was promising for food analysis of formaldehyde.

In this study we report a method for the rapid and sensitive estimation of bacterial cell concentration in solution based on a colorimetric enzyme/gold nanoshells conjugate system. The CTAB capped gold nanoshells are electrostatically attracted by both the bacterial surface and the enzyme β-galactosidase. The preferential binding of cationic (CTAB)-functionalized gold nanoshells to the more negative bacterial surfaces leaves active β-galactosidase in solution, providing an enzyme-amplified colorimetric response of the binding event. A progressive increase in the enzyme activity is evidenced by the conversion of the yellow-orange CPRG substrate into the red chromophore chlorophenol red, which can be correlated with increasing bacterial cell numbers. Using this strategy, the quantification of bacteria at concentrations as low as 10 bacteria/mL of solution has been achieved. The present method of bacterial cell load assessment offers a distinct potential advantage over other conventional methods such as plate counting in terms of ease of operation, rapidity, high sensitivity and quantitative detection of bacterial cells.

The pH of polar ice is important for the stability and mobility of impurities in ice cores and can be strongly influenced by volcanic eruptions or anthropogenic emissions. We present a simple optical method for continuous determination of acidity in ice cores based on spectroscopically determined color changes of two common pH-indicator dyes, bromophenol blue, and chlorophenol red. The sealed-system method described here is not equilibrated with CO2, making it simpler than existing methods for pH determination in ice cores and offering a 10–90% peak response time of 45 s and a combined uncertainty of 9%. The method is applied to Holocene ice core sections from Greenland and Antarctica and compared to standard techniques such as electrical conductivity measurement (ECM) conducted on the solid ice, and electrolytic meltwater conductivity, EMWC. Acidity measured in the Greenland NGRIP ice core shows good agreement with acidity calculated from ion chromatography. Conductivity and dye-based acidity Hdye+ are f...

Among all time–temperature integrator (TTI) types, microbial-based TTIs prevail since their response is directly related to food spoilage. For the development of lactic acid bacteria-based TTIs, optimum pH-indicators were chosen as follows. Five kinds of potential pH-indicators and four species of lactic acid bacteria were used to create microbial-based TTIs. The qualifying standards for pH-indicator selection were defined as (1) the effect of microorganism inhibition, (2) the simplicity of mechanistic interpretation of the color development reaction, and (3) intensity of color development. In particular, the reaction of TTI color development could be enhanced from non zero-order to zero-order. Overall, the optimum pH-indicator for the microbial TTIs was bromocresol green, followed by bromocresol purple, bromophenol blue, chlorophenol red, and congo red, in descending rank order. In conclusion, the choice of pH-indicators was found to be selective to assure effective color development of TTI.

A simple, accurate, and rapid extraction spectrophotometric procedure has been developed for the determination of some phenothiazine drugs such as chlorpromazine hydrochloride (CPH) and trifluoperazine dihydrochloride (TFPH) in pure form and their pharmaceutical preparations. The procedures are based on the reaction between the examined drugs (CPH and TFPH) and Alizarin Red S (AR), Bromocresol Purple (BCP), Chlorophenol Red (CPR) and Cresol Red (CR) producing ion-pair complexes which can be measured at the optimum wavelengths. The optimizations of the reaction conditions were investigated. Beer’s law is obeyed in the concentration ranges 1.77–96 μg ml −1 . The molar absorptivity and Sandell sensitivity are also calculated. The correlation coefficient for both drugs was ⩾0.9995 ( n = 5) with a relative standard deviation (R.S.D.) ⩽0.38. The methods are successfully applied to determine CPH and TFPH in pharmaceutical formulations.

Sodium, potassium, magnesium and calcium salts of gamma-hydroxybutyrate have been synthesised from gamma-butyrolactone and the corresponding group 1 or 2 hydroxide. Although the group 2 salts are non-hygroscopic, FT-IR spectroscopy and elemental analysis revealed them to be hydrated. X-ray powder diffraction was found to be a quick, non-destructive method of discriminating between the four salts. The Smith and the chlorophenol red/modified Schweppes reagent presumptive colour tests gave positive results regardless of the salt tested. Microcrystalline tests for NaGHB were in accordance with previous literature reports, but results for the other three salts were not reliable.

We herein report the development of an agarose-gel-immobilized recombinant bacterial biosensor simple system for the field monitoring of phenolic compounds. Escherichia coli cells harboring the pLZCapR plasmid, which was previously designed to express the -galactosidase reporter gene in the presence of phenolic compounds, were co-immobilized with a substrate [chlorophenol red -galactopyranoside (CPRG) in agarose gel, and dispensed to the wells of a 96-well plate. Field samples were added to the wells and color development was monitored. In the presence of 5 to 10 mM of phenol, the biosensor developed a red (representing hydrolysis of CPRG) color. Other phenolic compounds were also detected by this immobilized system, with the pattern resembling that previously reported for the corresponding non-immobilized biosensor. The immobilized cells showed optimum activity when the gel was simultaneously supplemented with 6% dimethyl formamide (DMF), 0.1% SDS and 10 mM . The immobilized biosensor described herein does not require the addition of a substrate or the use of unwieldy instruments or sample pretreatments that could complicate field studies.

Ammonia sensors have broad spectrum of applications for industrial process control as well as for environ-mental monitoring. An optical fiber ammonia sensor probe has been developed by using a bent optical fiber having dual poly(methyl methacrylate) (PMMA)/chlorophenol red (CPR) coatings as a transducer. This sen-sor probe was tested for monitoring trace ammonia in gas samples using air as sample matrix. The reaction of ammonia with CPR causes a color change of the reagent, which was detected by using fiber optic evanes-cent wave absorption spectrometry as a sensing signal. By adopting a dual layer coating structure, the sensor probe has faster response compared to a sensor using a broadly accepted sensing reagent-immobilized poly-mer coating structure. The sensor developed in this work is sensitive, has a detection limit of 2.7 ppb NH3 in air, which is the most sensitive among the reported optical fiber ammonia sensors to the best knowledge of the authors. The sensor is also reversible and has a response time of 25 minutes. The features of high sensi-tivity, reversibility and reasonable response time make this sensor technique very attractive for air quality monitoring.

A commercially-available sulfonphthalein derivative was demonstrated to be a chemodosimeter for Fe2+ and its sensing behavior was further investigated by UV-vis spectroscopy in aqueous media under the optimum conditions. In the presence of chlorophenol red (CPR) and H2O2, the absorption maximum at 435 nm decreased upon addition of Fe2+, resulting in a significant color change of the CPR solution from yellow to colorless. The chemosensor system did not show significant responses to a series of other metal ions including Al3+, Zn2+, Cd2+, Hg2+, Mn2+, Co2+, Fe3+, Ni2+, Cu2+, La3+, Ce4+, Th4+, Pd2+, Pb2+, Sb3+, Cr3+, Au3+, Ag+, Nd3+, Sm3+, alkali and alkaline earth metal cations, allowing for highly selective naked-eye detection of Fe2+. Quantitative analysis was carried out kinetically for practicable the Fe2+ assay when either fixed time method or the initial rate method was applied. When the detecting time was set, the decrease of absorbance signal was linear with Fe2+ concentration in the range of 0 to 7.50 × 10−5 mol L−1 and the regression equation was ΔA = 0.00759 + 0.00593C Fe with a correlation coefficient r = 0.9953. The chemodosimetric system has employed an irreversible Fenton reagent-promoted oxidation of the CPR free chromophore and the hydroxyl radicals were generated in the presence of both Fe2+ and hydrogen peroxide. The mechanistic interpretation of the signaling process was partially confirmed by the radical scavenging experiment and the FT-IR analysis of the intermediates formed at different reaction periods.