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Intelligent packaging, in addition to acting as a food protection barrier, can emit a signal (electric, colorimetric, among others) in real time in response to any change in the initial packaging conditions and food quality. Packaging with pH indicators or pH sensors usually consists of two parts, a solid base and a dye sensitive to the pH change that makes up the colorimetric sensor. The dyes are extracted from various sources of fruits and vegetables or synthetics. At the beginning of the food deterioration process, alteration of the pH occurs; this change is one of the indicators of product quality. Packaging with a pH indicator is a measure that could indicate the quality of the food at the time of purchase or before consumption, making it safer for consumers. Research is being carried out with the aim of improving the characteristics and applicability of these indicators. This review paper presents research results on intelligent pH indicator packaging, with studies covering pigments, polymers, food and packaging solutions, as well as an overview of the materials/technologies used for the development, and the perspectives/challenges that involve this new technology.

Firefly luciferases have been widely used for bioanalytical purposes during the last 5 decades. They usually emit yellow-green bioluminescence and are pH-sensitive, displaying a color change to red at acidic pH and higher temperature and in the presence of heavy metals. Besides the usual applications as bioanalytical reagents and as reporter genes, firefly luciferases' pH- and metal-sensitivities have been recently harnessed for intracellular metal and pH biosensing. Previously we cloned the luciferase of the Brazilian Amydetes vivianii firefly which displays the most blue-shifted color among known firefly luciferases. Here we purified it, characterized and investigated the kinetic properties and the pH, metal and thermal sensitivities of this firefly luciferase. This luciferase displays the lowest reported KM for ATP, the highest catalytic efficiencies, and the highest thermostability among the studied recombinant beetle luciferases, making this enzyme and its cDNA an ideal reagent for sensitive ATP assays and reporter gene. The blue-shifted spectrum, higher thermostability, lower pH- and thermal-sensitivities and protein fluorescence studies indicate a more rigid active site during light emission. This enzyme displays an unmatched selective spectral sensitivity for cadmium and mercury, making it a promising ratiometric indicator of such toxic metals. Finally, the weaker thermal-sensitivity compared to other firefly luciferases makes this enzyme a better ratiometric pH indicator at temperatures above 30 °C, suitable for mammalian cell assays.

In this paper, we clarify the interfacial pH behavior induced by allergic responses at a mast cell/gate insulator nanogap detected by laser scanning confocal fluorescence microscopy. In a previous work, the change in interfacial pH detected on the basis of allergic responses was monitored at a mast cell/gate insulator nanogap interface using a cell-cultured gate ion-sensitive field-effect transistor (ISFET), but the interfacial pH behavior at a mast cell/gate insulator nanogap has not been clarified using other methods. Here, the phospholipid fluorescein is employed as the extracellular pH indicator, which is fixed to the external side of the plasma membrane of mast cells cultured on a substrate. As a result, the interfacial pH at the mast cell/substrate nanogap increases after mast cells with IgE on their membrane are activated by the interaction between IgE and an allergen. This is due to the basicity of histamine molecules released from mast cells. Moreover, the change in the interfacial pH at the mast cell/substrate nanogap is larger than that at the mast cell/bulk solution interface. That is, molecules of substances secreted as a result of allergic responses are assumed to accumulate around the cell/substrate nanogap. The data obtained in this study support the idea that potentiometric ion sensors such as ISFETs can detect a cellular-function-induced change in pH at a cell/electrode nanogap in real time.

Due to the concern about the inadequate disposal of synthetic and non-biodegradable plastic packaging, a great number of researches pointing at the substitution of these materials by natural and biodegradable sources have been growing in recent years. Another important category recognizes as intelligent packaging has also received more prominence. The study intended to achieve the matter aforementioned developing starch-based films by thermocompression without and with blueberry residue as pH change indicator. Moisture content, water solubility, water vapor permeability, oxygen permeability, morphology, color, and mechanical properties of the films were analyzed. Moreover, analysis of color change and compounds migration were conduct in the films with blueberry. The residue insertion led to the formation of less compact films with high oxygen permeability. Despite the irregular dispersion of the blueberry residue on the polymer matrix identified by optical microscopy, the films showed equal values of water vapor permeability, hydrophilicity, and mechanical properties when compared to the samples without the residue. In addition, they exhibited visually perceptible color changes in the pH range between 2 and 12, which was confirmed by colorimetric analysis since the Δ E 94 ∗ values between the samples were greater than 3. The compounds migration after film immersion in aqueous simulant solution (acetic acid) showed a higher intensity in comparison to the samples immersed in a fatty simulant solution (ethanol) due to the anthocyanins hydrophilicity. Therefore, the film with blueberry has potential as intelligent packaging. Besides that, it present potential as active packaging due to the migration of phenolic compounds in aqueous solutions.

We report the synthesis and photophysical properties of a new fluorophore compound TPy-BDP, containing thienyl-pyridine group in meso position of dipyrrin ligand. UV–Vis spectroscopy and steady state fluorimetric methods have been utilized to determine the photophysical features of this chromophore in variety of solvents. The photostability of the chromophore has been examined in solution and the dependence of spectral shifts upon solvent parameter has been studied. Also, pH sensitivity of the compound was evaluated in aqueous solutions. On binding to H+ ions fluorescence quenching was observed by an approximately 94% reduction in the emission intensity within the pH range of 7.6–1.0 in solution. However, no obvious fluorescence change could be observed in the basic conditions. To identify the underlying mechanism of the probe depending on pH, ultrafast pump probe experiments have been performed. The results indicate that fast electron transfer known as photoinduced electron transfer between boron-dipyrromethene scaffold to the appended group are responsible to the fluorescence quenching. Experimental results proved the capability of TPy-BDP in terms of using under strongly acidic conditions as a pH indicator.

Fresh fruit storage is very important for the exporter in order to keep the fruit in good quality. Modified atmosphere packaging is one of the useful methods but it can cause fruit fermentation, abnormal ripening and off flavours. The application of the pH indicator label for monitoring 'Nam Dok Mai See Thong' mango fruit in modified atmosphere packaging was investigated. 'Nam Dok Mai See Thong' mango fruit, sized 300-400 g, were packed individually in a zip locked polypropylene bag with 4, 6, 8 and 10 holes (0.5 mm diameter hole(‑1)). The pH indicator label for monitoring quality was applied in all bags. All fruit was stored at 11°C for 3 days (mimicking transportation time). The fruits were removed and allowed to ripen at 25°C. Changes of the label colour were observed and gas condition in the package and the quality of mango fruit was determined. The results found that the mango fruit in packages where the indicator label colour did not change colour, showed normal ripening. The fruit in packages that had the indicator label where the colour changed, displayed fermentation and high concentrations of carbon dioxide and ethanol. By increasing the number of holes the abnormal ripening could be prevented. The results indicate that the use of pH indicator labels, combined with the modified atmosphere packaging, were able to indicate and inform the seller to open the package in order to prevent the fruit from abnormal ripening. Moreover, 85% of consumers accepted packaging with indicator labels.

In this supplement to our second-year supercapacitor lab (Bringing Real-World Energy-Storage Research into a Second-Year Physical-Chemistry Lab Using a MnO2-Based Supercapacitor. J. Chem. Educ. 201...

Summary The ability of Pseudomonas species to thrive in all major natural environments (i.e. terrestrial, freshwater and marine) is based on its exceptional capability to adapt to physicochemical changes. Thus, environmental bacteria have to tightly control the maintenance of numerous physiological traits across different conditions. The intracellular pH (pH i) homoeostasis is a particularly important feature, since the pH i influences a large portion of the biochemical processes in the cell. Despite its importance, relatively few reliable, easy‐to‐implement tools have been designed for quantifying in vivo pH i changes in Gram‐negative bacteria with minimal manipulations. Here we describe a convenient, non‐invasive protocol for the quantification of the pH i in bacteria, which is based on the ratiometric fluorescent indicator protein PHP (pH indicator for Pseudomonas). The DNA sequence encoding PHP was thoroughly adapted to guarantee optimal transcription and translation of the indicator in Pseudomonas species. Our PHP‐based quantification method demonstrated that pH i is tightly regulated over a narrow range of pH values not only in Pseudomonas, but also in other Gram‐negative bacterial species such as Escherichia coli. The maintenance of the cytoplasmic pH homoeostasis in vivo could also be observed upon internal (e.g. redirection of glucose consumption pathways in P. putida) and external (e.g. antibiotic exposure in P. aeruginosa) perturbations, and the PHP indicator was also used to follow dynamic changes in the pH i upon external pH shifts. In summary, our work describes a reliable method for measuring pH i in Pseudomonas, allowing for the detailed investigation of bacterial pH i homoeostasis and its regulation.

Water hardness has implications for both human health and industry. The main components that make water hard are calcium and magnesium. The magnesium in hard water may provide a moderate health benefit, but calcium can cause serious problems in industrial processes. This paper presents a rapid-response, reliable and convenient device developed to measure calcium and magnesium ion concentrations continuously in water samples by using a smartphone analysis of colorness change. The ion detection is based on phase extraction equilibria in a specific ion-exchange substance membrane that contains an ionophore (selectively binding to specific ions), a chromoionophore (a lipophilic pH indicator), an ionic salt (a cation exchanger), a polymer (PVC) and a plasticizer. The device is built on a PDMS fluidic layer with six parallel detection chambers that allows the water samples to flow through at a specific rate to these chambers. An Android smartphone App was developed to acquire the color images after the ions exchange across the membrane, and the analysis of target ion concentration can be realized by the pre-loaded calibration curves. The results show that the colorimetric sensor is capable of determining Ca2+ concentration in an acetate buffer solution (pH = 5.3) and total hardness in a Tris-HCl buffer solution (pH = 7.2), covering the range of normal water hardness (from soft to very hard). The measurements on real samples were analyzed by both Image J and the App and were compared with results from a commercial hardness kit and inductively coupled plasma mass spectrometry (ICP-MS), demonstrating the accuracy and precision of our colorimetric sensor compared to a commercial sensor. This cost-effective device and automatic analytical smartphone app can be combined easily as a ready-to-go sensor for monitoring Ca2+ and Mg2+ continuously and simultaneously, which is convenient for use in resource-limited areas.

Proteases from haloalkaliphilic microorganisms are biocatalyst with a great interest to be studied in biotechnological implications. Nevertheless, available methods for assay haloalkaliphilic proteases on protein substrates are few, are carry out to end point and implies the use of complicated steps. A new high throughput screening assay is described involving pH indicators at haloalkaline conditions. Rapid Enzymatic Determination method use casein as natural substrate and salts: NaCl and KCl to measure the activity of halophilic proteases. When a peptide bond is cleaved by a protease a proton is released changing the color of the indicator, proteolysis is followed by monitoring the decrease in absorbance. This is the easiest, quickest, and cheapest kinetic assay. Moreover, amounts of about 40 ng×mL-1 of proteolytic enzyme could be detected by this method in a pH range from 7.5 to 10.9 and salt concentrations from 0 to 4 M.

An hydroxythiophene-conjugated benzothiazole (T2(OH)B) was synthesized as a pH sensitive fluorescent probe. T2(OH)B displayed dual emission behavior due to the excited state intramolecular proton transfer (ESIPT) process, while the methoxy analogs, T2(OMe)B, did not. T2(OH)B showed strong fluorescence enhancement above physiological pHs. The applicability of T2(OH)B as a biological pH indicator was demonstrated by its use for staining mitochondrial compartment and H. pylori. Owing to its strong fluorescence emission with a large stokes shift and its effective response to pH, T2(OH)B serves as a platform for the design of new types of fluorescent probes.

An optical biosensor employing immobilized haloalkane dehalogenase (HLD), the halide degrading enzyme for the detection of halogenated organic in environmental water and drinking water samples was developed. The enzymatic biosensor was fabricated by incorporating H+ ion selective chromoionophore ETH5294 and HLD enzyme in a stacked chitosan films system on a glass slide. Hydrolytic dehalogenation of dichloroethane (DCA) by the carbon-halide degrading HLD enzyme resulting in the release of a halogen, a proton and a primary alcohol. The halocarbon concentration was optically transduced by the pH transducer layer as a result of protonation reaction of the chromoionophore pH indicator dye embedded in the underneath layer. The resulting colour change of the protonated chromoionophore was measured by fiber optic reflectance spectrophotometry method. Under optimized conditions the detection limit of the proposed reflectance-based enzymatic biosensor membrane was estimated to be 1 mg L−1 with a wide dynamic linear concentration range of 5–60 mg L−1 DCA (R2 = 0.9792) and satisfactory reproducibility within the relative standard deviation (RSD) range of 3.4–4.3%. Validation test demonstrated that the optical halocarbon biosensor could be a promising tool for rapid (6 min) in situ and direct evaluation of organohalide in river water, tap water and bottled water samples without any sample pre-treatment or extraction steps.

A paper based litmus test has been developed using modulation of urease enzyme activity for detection of C-C mismatch single nucleotide polymorphisms (SNPs) by the naked eye. Urease is first inactivated with silver ions and printed onto paper microzones. Addition of DNA containing C-C mismatches reactivates urease via binding of Ag(I), allowing restoration of urease activity, hydrolysis of urea to produce ammonia, and an increase in pH, which is monitored colorimetrically using a pH indicator with a limit of detection of 11 nM DNA in 40 min. The assay system is easy to use, portable, and stable for at least 30 days at ambient temperature. To assess the versatility and practical application of the paper sensor, we used it to identify a G > C transversion present in human genomic DNA from a ductal carcinoma cell line, a mutation commonly found in breast cancer. We believe this new assay system has the potential to be a low-cost method for rapidly identifying DNA with the C-C mismatch SNP as a means of cancer screening in resource-limited areas.

The use of organosilanes to produce hybrid materials, also known as ORMOSILs (organically modified silicas) can be a good strategy to tune a material’s properties, enabling, for example, the optimization of important features of chemical sensors such as specificity, sensitivity and response time. Thus, different hybrid silicas were prepared by the sol-gel method to be employed as a colorimetric sensor. The investigated organic groups for producing hybrid materials included methyl, octyl, octadecyl, vinyl, phenyl, aminopropyl, isocyanatopropyl, mercaptopropyl, chloropropyl, iodopropyl and glycidoxypropyl groups, and the pH indicator alizarin red was used as the encapsulated receptor element. The sensors were characterized using a set of complementary techniques such as UV–vis spectroscopy, cyclic and differential pulse voltammetry, nuclear magnetic resonance, nitrogen porosimetry, small-angle X-ray scattering and transmission electronic microscopy. The performance was evaluated according to the color change (ΔE*ab) by conducting a colorimetric analysis and measuring the response time after ammonia exposure, with results varying from 48 to 95 s. Additionally, other characteristics of the hybrid materials, such as their surface area, reticulation degree, texture and morphologic properties, were altered depending on the organic modification present in the silica network. The potentiality for material optimization, to achieve better sensor performance, depends on the employed organosilane.

The study reports preparation and detailed comparison of four new pH sensor materials for seawater measurements. The composition of the sensors is optimized in several iterations to ensure optimal dynamic range, fast response time at low temperatures, low cross-sensitivities to temperature (dpKa/dT ∼ -0.013 pH units/K) and negligible cross sensitivity to ionic strength above salinity 15 PSU. The first generation (material “pH-1″) utilizes a pH indicator which is physically entrapped into a polyurethane hydrogel. This material shows satisfactory performance only at comparably high temperatures with response times being extremely long at low temperatures (t95 > 2 h at 5 °C). The three other materials utilize cross-linked hydrophilic polymers based on poly(acryloylmorpholine) with indicator dye covalently coupled to the polymer. They feature fast response times at low temperatures (t90

Edible films are made from canna tuber starch, glycerol, aloe vera gel, and addition of purple cabbage extract (Brassica oleracea) aimed to determine the effect of temperature variation on the results of edible film synthesis and anthocyanin effectivenes s of purple cabbage as a pH indicator. The stages in this study include isolation of canna tuber starch, extraction of purple cabbage, making aloe vera gel, determination of anthocyanin extract proportions, synthesis of edible films with varied temperatures, and characterization of edible film results. Optimal composition of cabbage extract as a pH bio-indicator is used for synthesis of edible film with temperature variations between 75-90oC and elongation of 26.6% and WVTR value of 4.750 g/m2h at 85oC.

This study investigated the potential of chitosan/PVA films containing black carrot anthocyanins as a natural pH indicator and bentonite as a nano-filler, for intelligent packaging applications. Two series of chitosan/PVA (CP) films, with different concentrations of bentonite (CPB3%, CPB5%) and with a constant concentration of anthocyanin (CPA, CPAB3%, CPAB5%) were prepared by solution casting method. The colorimetric parameter b* showed an increase from 1.0 ± 0.2 for CP films to 2.7 ± 0.2 and 8.8 ± 1.1 for CPB3% and CPB5% films, respectively which indicates that addition of bentonite increases the intensity of yellow color in the nanocomposite films. The presence of anthocyanins caused to shifting of a* values from negative to positive values which indicated the color change of films from greenness to redness. Addition of bentonite reduced the tensile strength from 100.6 for CP film to 86.5 and 67.2 for CPB3% and CPB5% films which was related to the solution intercalation method used for preparation of nanocomposite films. In contrast, addition of anthocyanins increased the tensile strength for CPA, CPAB3% and CPAB5% due to the hydrogen bonding interactions between its OH groups and PVA and chitosan chains. Water vapor permeability (WVP) of the films was decreased from 1.140 (mg.mm/m2.kPa.h) for CP film to 0.5620 and 0.3515 for CPB3% and CPB5% films, respectively. In contrast, anthocyanins caused to increase WVP of the samples compared to the anthocyanin free films. Thermo-gravimetric analysis showed that the films containing bentonite and anthocyanins have a better thermal stability. Finally, CPAB5% showed the highest bacterial growth inhibition against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, respectively 75.20%, 69.95% and 44.38%.

A simple and low cost analytical device is described for the determination of ammonium in the vitreous humor suitable for inferring the post mortem interval in forensic cases. The device is based on ammonia formation from ammonium ion by means of NaOH addition to the vitreous humor sample and its detection with a pH chemical indicator in the gas phase above the vitreous humor sample. From the gas phase, ammonia diffuses through a polymeric membrane and it is trapped and detected with a droplet of pH indicator thymol blue. The color change of the droplet is measured using a smartphone camera. Under optimal conditions, the device showed a limit of detection of 0.2mM, with between days precision of ≤ 15% expressed as relative standard deviation, and an accuracy between days from 88.3% to 114.5%. This homemade gas diffusion analytical device was successfully used for the determination of ammonia in vitreous humor samples from forensic autopsies. The results obtained with the proposed method, although for a limited number, showed a close correlation with the data obtained with an instrumental analysis based on capillary electrophoresis. Moreover a significant correlation was also found between the results of the present method and the time elapsed since death by a simple evaluation of the color intensity. In conclusion, this preliminary study showed that the proposed device, after adequate validation, could be a promising tool for a presumptive estimation of the time since death directly at the crime scene.

A non-invasive textile-based colorimetric sensor for the simultaneous detection of sweat pH and lactate was created by depositing of three different layers onto a cotton fabric: 1.) chitosan, 2.) sodium carboxymethyl cellulose, and 3.) indicator dye or lactate assay. This sensor was characterized using field emission scanning electron microscopy and fourier transform infrared spectroscopy. Then, this sensor was used to measure pH and lactate concentration using the same sweat sample. The sensing element for sweat pH was composed of a mixture of methyl orange and bromocresol green while a lactate enzymatic assay was chosen for the lactate sensor. The pH indicator gradually shifted from red to blue as the pH increased, whereas the purple color intensity increased with the concentration of lactate in the sweat. By comparing these colors with a standard calibration, this platform can be used to estimate the sweat pH (1−14) and the lactate level (0–25 mM). Fading of the colors of this sensor was prevented by using cetyltrimethylammonium bromide (CTAB). The flexibility of this textile based sensor allows it to be incorporated into sport apparels and accessories hence potentially enabling real-time and continuous monitoring of sweat pH and lactate. This non-invasive sensing platform might open a new avenue for personal health monitoring and medical diagnosis as well as for determining of the physiological conditions of endurance athletes.

A colourimetric vacuum air pressure indicator is described, based on the very low level of CO2 in air. The indicator uses the pH indicator dye, ortho-cresolphthalein, OCP, which is violet coloured in its deprotonated form and colourless when protonated. When the violet coloured OCP anion is ion-paired with the tetrabutylammonium cation, the product is readily dissolved in a non-aqueous solution containing the polymer ethyl cellulose to create an ink which, when cast and allowed to dry, responds to levels of CO2 well below that in air, i.e.≪0.041%; the indicator's halfway colour changing point is at 0.062 atm of air at 22 °C, which is interesting in that in food vacuum packaging the pressure in the pack is usually ca. 0.04 atm. The indicator can be used as a qualitative and quantitative indicator of vacuum air pressure. The latter requires the use of digital photography, coupled to RGB colour analysis, in the analysis of the indicator's colour. As with most CO2 indicators, the indicator's response is temperature sensitive, with ΔH = 78 ± 5 kJ mol-1. The indicator's 90% response and recovery times to a cycle of vacuum and air are 16.2 and 2.7 min, respectively. The efficacy of the indicator as a vacuum-package integrity indicator for food packaging is illustrated and other potential applications are discussed briefly. This is the first reported example of an ink-based, inexpensive, colourimetric vacuum air pressure indicator.

Dental caries is one of the most prevalent human oral diseases. The pH of the oral environment is lower than the critical pH point, which causes the demineralization of the hard tissues of teeth and finally leads to dental caries. Therefore, it is important to have an accurate, sensitive detecting assay of the critical pH. An electrospun fibrous membrane was reported to modulate immobilized bromocresol green (BCG), a common pH indicator, by shifting the acid dissociation constant (pKa) from 4.6 to 5.3. Based on spectroscopic and colorimetric characterizations, it was demonstrated that the BCG–polystyrene/polyvinylpyrrolidone (BCG–PS/PVP) electrospun fibrous membrane achieved a sensitive and fast response; moreover, its use exhibits a convenient sensing strategy for visualizing the critical pH point of 5.5 that induces tooth demineralization. Compared with a common pH meter or pH test papers, the BCG–PS/PVP electrospun fibrous membrane could distinguish pH 5.5 from its adjacent pH value with higher accuracy and much more convenience. We could also evaluate the inhibitory effect of the anti-caries agents on bacterial growth and acid production by the platform. The BCG–PS/PVP electrospun fibrous membrane is expected to have potential applications in the monitoring and prevention of early caries.

For the characterization of the quality and pollution degree of the water or solution, quality indicators are used. These can be classified after their nature, and after their nature and their effects they have on water: organoleptical, physical, chemical, bacteriological, biological, ad radioactive. Under physical indicators we can find the pH also. To guarantee an adequate quality of a product which will be painted in an electrostatic field, this has to be undertaken to a chemical pre-treatment process using of some chemical solutions, and water for rinsing. During the pre-treatment process, without the use of the pH indicator, the maxim quality level couldn’t be reached; the influence would be so significant that it could compromise the whole painting process in an electrostatic field.

Intelligent pH-indicator films based on soy protein isolate (SPI) were prepared using pH-sensitive dyes (bromothymol blue and methyl red). The addition of mixed indicators imparts pH-indicator films with an appreciable microstructure, acceptable water resistance, and favorable optical properties. The incorporation of the mixed indicators did not lead to significant improvement in the mechanical properties of films due to weak ionic cross-linking by hydrogen bonding between the SPI macromolecules and low-molecular-weight indicators. Fourier-transform infrared spectroscopy indicated hydrogen bond-mediated intermolecular interactions, and scanning electron microscopy showed that BB/MR were well dispersed in the SPI film. The indicator addition hindered the sorption and passage of water molecules. The water vapor permeability, moisture sorption, moisture content, and total soluble matter were 4.32 to 6.12 ×10-12 g·cm/cm2 ·s·Pa, 36.70% to 73.33%, 25.28% to 44.11%, and 8.21% to 25.56%, respectively. Also, the addition of indicators reduced UV light transmittance with minimal effect on the transparency of the film. The presence of indicators enhanced the pH sensitivity, seen as a visible color reaction at different pHs (total color difference, ΔE > 5). When the pH-indicator film containing 8 ml/100 ml final film emulsions was used to monitor the fresh-cut apple freshness, a green color for fresh status was observed, which turned blue after 60 h. Collectively, our findings suggested that indicator-containing SPI films have the potential for monitoring the freshness of fruits. PRACTICAL APPLICATION: pH-indicator films can help consumers to identify the freshness of packaged food by a change in the color of the packaging material, which is easily visible to the unaided eye without the need for opening the packaging. This protects consumers' interests.

A library of 2,4,6,7-tetrasubstituted-2H-pyrazolo[4,3-c]pyridines was prepared from easily accessible 1-phenyl-3-(2-phenylethynyl)-1H-pyrazole-4-carbaldehyde via an iodine-mediated electrophilic cyclization of intermediate 4-(azidomethyl)-1-phenyl-3-(phenylethynyl)-1H-pyrazoles to 7-iodo-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridines followed by Suzuki cross-couplings with various boronic acids and alkylation reactions. The compounds were evaluated for their antiproliferative activity against K562, MV4-11, and MCF-7 cancer cell lines. The most potent compounds displayed low micromolar GI50 values. 4-(2,6-Diphenyl-2H-pyrazolo[4,3-c]pyridin-7-yl)phenol proved to be the most active, induced poly(ADP-ribose) polymerase 1 (PARP-1) cleavage, activated the initiator enzyme of apoptotic cascade caspase 9, induced a fragmentation of microtubule-associated protein 1-light chain 3 (LC3), and reduced the expression levels of proliferating cell nuclear antigen (PCNA). The obtained results suggest a complex action of 4-(2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-7-yl)phenol that combines antiproliferative effects with the induction of cell death. Moreover, investigations of the fluorescence properties of the final compounds revealed 7-(4-methoxyphenyl)-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridine as the most potent pH indicator that enables both fluorescence intensity-based and ratiometric pH sensing.

An exploratory analysis of ammonia sensing hybrid material encapsulating Bromocresol purple were synthesized; using two types of matrices: (i) Silica produced by acid- or alkaline-catalyzed sol-gel processes was used as the inorganic matrix, and (ii) polymethacrylic acid (using methacrylic acid as the monomer) was used as the organic matrix. Eleven different sensitive structures were prepared by intercalating the pH indicator in both matrices. The resulting materials were tested for potential applications as colorimetric sensitive materials for alkaline vapors using ammonia as the probe gas. The response time and reversibility were evaluated by colorimetric analysis employing the CIELAB color space model with the illuminant D65. The color difference (∆E*ab) was measured from a Euclidian distance between the color coordinates (L*, a* and b*). Almost all the sensitive materials presented values of ∆E*ab > 5; i.e., it was possible to visually observe the difference between the two colors. The data showed that silica-based structures have faster time responses (4 min 50 s) than those of the polymer-based ones (11 min 50 s) and lower rates of reversibility, although the changes in color tone are similar (ΔE*ab, 28 and 21, respectively, for silica and polymer matrices).

Three new aza‐BODIPY dyes incorporating fused fluorene or carbazole moieties have been prepared. The dyes show significant enhancement of photophysical properties compared to the parent 1,3,5,7‐tetraphenyl aza‐BODIPY (TPAB): a bathochromic shift of the absorption maximum (up to 2700 cm−1) and emission maximum (up to 2270 cm−1); an almost threefold increase in molar absorption coefficients (to ca. 230 000 M−1 cm−1) and a significant increase in the fluorescence quantum yield to 49–66 %. Owing to the combination of these properties, the new aza‐BODIPY dyes belong to the brightest NIR dyes reported. The dyes also show excellent photostability. Due to their outstanding properties, the new dyes represent a promising platform for further exploration in biomedical research. A pH indicator containing only one fused carbazole unit was also prepared and shows absorption and emission spectra that are bathochromically shifted by about 110 and 100 nm, respectively, compared to the indicator dye based on the TPAB chromophore., Look on the bright side: Three new fluorescent aza‐BODIPY dyes fused with fluorene or carbazole substituents show strong bathochromic shifts (up to 139 nm) of absorption and emission maxima compared to the parent 1,3,5,7‐tetraphenyl aza‐BODIPY (TPAB) and are highly photostable. Two of the dyes show excellent fluorescence brightness due to exceptionally high molar absorption coefficients (ca. 230 000 M−1 cm−1) and emission quantum yields (up to 0.66); the third dye was rendered pH sensitive by introducing a chlorophenol motif.

The intelligent pH indicator films were prepared by incorporating curcumin-loaded Pickering emulsion with corn starch (CS) and polyvinyl alcohol (PVA) matrix. The mechanical properties, barrier properties and functional characteristics of the films were studied and the films were applied to monitor fish freshness. Fourier transform infrared (FTIR) spectroscopy and Scanning electron microscopy (SEM) showed that Pickering emulsion can form hydrogen bonds with CS and PVA. The antioxidant activity of the films was detected, which showed that Pickering emulsion could reduce the decomposition of curcumin during the process of preparation and storage. Bactericidal tests showed that the films can inhibit the growth of S. aureus, B. subtilis, and E. coli, and the effect of the films on Gram-positive (G+) bacteria is stronger than Gram-negative (G−) bacteria. Application of the films presented here is supported by an activation test of Pangasius bocouti. With time changed, the color of films changed from yellow to red, and the color change of films prepared with curcumin-loaded Pickering emulsion was more evident than the films prepared with curcumin solution. Therefore, the films prepared with curcumin-loaded Pickering emulsion had better performance and can be used to indicate the quality of food.

The surface pH is a critical factor in the quality and longevity of materials and products. Traditional fast colorimetric pH detection-based tests such as water quality control or pregnancy tests, when results are determined by the naked eye, cannot provide quantitative values. Using standard pH papers, paper-printed comparison charts, or colorimetric microfluidic paper-based analytical devices is not suitable for such technological applications and quality management systems (QMSs) where the particular tested material should contain a suitable indicator in situ, in its structure, either before or after the process, the technology or the apparatus that are being tested. This paper describes a method based on the combination of impregnation of a tested material with a pH indicator in situ, its exposure to a process of technology whose impact on pH value is to be tested, colorimetric pH measurement, and approximation of pH value using derived pH characteristic parameters (pH-CPs) based on CIE orthogonal and cylindrical color variables. The hypotheses were experimentally verified using the methyl red pH indicator, impregnating the acid lignin-containing paper, and preparing a calibration sample set with pH in the range 4 to 12 using controlled alkalization. Based on the performed measurements and statistical evaluation, it can be concluded that the best pH-CPs with the highest regression parameters for pH are √∆E, ln (a),√∆H (ab), a/L, h/b and ln (b/a). The experimental results show that the presented method allows a good estimation of pH detection of the material surfaces.

Protein-polysaccharide nanocomplexes system could improve the low stability of ACNs, making ACNs become a potential and stable pH indicator. In this study, intelligent colorimetric film was designed to monitor pork freshness by incorporating ACNs-loaded ovalbumin-propylene glycol alginate nanocomplexes (ACNs-loaded OVA-PGA) into polyvinyl alcohol/ glycerol (PG) matrix. The intelligent film (PG/ACNs-loaded OVA-PGA film) presented well barrier performance (lower water vapor permeability and light transmittance at 200–600 nm). Fourier transform infrared spectroscopy further confirmed the hydrogen bonds among film-forming components. Moreover, Scanning electron microscope and X-ray diffraction showed that ACNs-loaded OVA-PGA was uniformly distributed in film matrix but decreased the crystallinity of polyvinyl alcohol. PG/ACNs-loaded OVA-PGA film had distinguishable colorimetric response to pH 2.0–11.0 buffers and volatile ammonia. In the test, PG/ACNs-loaded OVA-PGA film displayed visible color alterations from purplish-red to dark-blue as pork freshness decreased, suggesting it can be used in intelligent packaging for real-time monitoring freshness of meat products.

Several different diagnostic tests have been reported for rapid, sensitive, and economical detection of bacterial pathogens, but most lack widespread and practical use in the clinic. In this study, we used anthocyanins from red cabbage (Brassica oleracea) as a natural pH indicator and, for the first time, incorporated this agent into a simple, rapid, and economical colorimetric strategy for the detection of Helicobacter pylori (H. pylori) (RCE@test). We prepared two sets of RCE@test solutions (test 1 is purple, and test 2 is blue) in different forms, including liquid, adsorbed filter paper, and agar, and investigated the performance of each RCE@test as a function of the test volume, H. pylori concentration, and reaction time. To elucidate the effect of the pathophysiological environment on these RCE@tests, H. pylori in an artificial gastric fluid was also detected. The 10 and 1 CFU/mL H. pylori suspensions were detected in 15 min and 3 h, respectively, and the limit of detection was determined down to 1 CFU/mL. We experimentally demonstrated the advantages of the RCE@test for detection of H. pylori by comparing it to a commercially available rapid urease test, the CLO test (Campylobacter-like organism test). In addition to colorimetric detection by the naked eyes, RGB (Red Green Blue) and Delta-E analysis in image-processing software was run to quantitatively monitor changes of color in the RCE@test using a smartphone application. Finally, we propose that this test provides simple, effective, rapid, and inexpensive detection and that it can be easily implemented for clinical use. 2020 BAGEP Award of the Science Academy; Turkish Academy of Sciences (2018 TUBA GEBIP Award) This work was supported by the 2020 BAGEP Award of the Science Academy and Turkish Academy of Sciences (2018 TUBA GEBIP Award). We would like to thank Mucahit Osman Turkan and Busra Aydin for their assistance in drawing and designing TOC. WOS:000643539400033 2-s2.0-85104943598 PubMed: 33825433

In the present work, DNA recombination of three homologous tau class glutathione transferases (GSTUs) allowed the creation of a library of tau class GmGSTUs. The library was activity screened for the identification of glutathione transferase (GST) variants with enhanced catalytic activity towards the herbicide alachlor (2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide). One enzyme variant (GmGSTsf) with improved catalytic activity and binding affinity for alachlor was identified and explored for the development of an optical biosensor for alachlor determination. Kinetics analysis and molecular modeling studies revealed a key mutation (Ile69Val) at the subunit interface (helix α3) that appeared to be responsible for the altered catalytic properties. The enzyme was immobilized directly on polyvinylidenefluoride membrane by crosslinking with glutaraldehyde and was placed on the inner surface of a plastic cuvette. The rate of pH changes observed as a result of the enzyme reaction was followed optometrically using a pH indicator. A calibration curve indicated that the linear concentration range for alachlor was 30–300 μM. The approach used in the present study can provide tools for the generation of novel enzymes for eco-efficient and environment-friendly analytical technologies. In addition, the outcome of this study gives an example for harnessing protein symmetry for enzyme design.

Colorimetric analysis is being broadly applied in chemical sensing today; however, detection ranges and resolution limits are typically modest. In this paper, we introduce a methodology to quantify the colorimetric chemical response on a paper-based microfluidic device that enables high-resolution colorimetric detection over a broad pH range. We have achieved this by combining data from various indicators displaying sensitivity on partially overlapping small pH ranges and training machine learning classification models to the colorimetric output. The training dataset consists of images taken from the colorimetric response of three different pH indicators previously deposited on circular spots of a multilayer paper-based device, captured with a reference lab-grade camera. Instead of restricting the use of each pH indicator to their linear response regime within the RGB space, the models are trained against data spanning the entire range of pH values, from 3 to 9, in increments of 0.1, exploring the optimum combination of feature engineering and classification model to maximize the overall model accuracy. The combined analysis of image data captured simultaneously with the three indicators resulted in a pH detection accuracy above 85% with over the entire pH range with resolution down to 0.2 pH points. The demonstrated detection range and resolution are well-suited to support various applications in environmental and industrial analysis.

The determination of pH in fermented milk is an important parameter for monitoring the production of acid by lactic acid bacteria (LAB). In this work, a colorimetric method is proposed that allows a fast determination of LAB acidification ability by evaluation of pH drop in whey fermentation. The proposed method uses spectrophotometry to measure the pH change by bacteria and uses bromocresol purple as a pH indicator dye. The absorbance at 430 nm of a buffer solution with bromocresol purple was found to be correlated with pH values. This colorimetric assay was linear within the pH range of 4.6–7.0. Upon regression analysis, linear equation y = −0.1267× + 0.9196 was obtained having r 2 value of 0.9927. The assay was validated by the use of LAB fermentation in sweet whey and comparison to the values obtained by glass electrode/pH meter. Estimation of acidification activity of LAB in whey was found to be similar in both methods (r = 0.801, p > 0.05). The proposed procedure presents a viable alternative to the measurement of pH by the standard method and allows the simultaneous and fast screening of LAB acidifying activity.

Bacterial vaginosis (BV) and its recurrence are most commonly associated with the formation of Gardnerella species biofilm. Probiotics are typically used to treat BV; however, the optimal period of Lactobacillus probiotic application in BV treatment remains uncertain. The present study aimed to explore the effects of Lactobacillus rhamnosus and Lactobacillus casei on various stages of biofilm formation in Gardnerella species. The biofilm-forming ability of seven strains, including one Gardnerella vaginalis ATCC 14018 and six clinically isolated Gardnerella species, was determined via gentian violet staining assay. Moreover, the sensitivity of the planktonic and biofilm forms toward metronidazole and clindamycin was assessed via microdilution broth method. L. rhamnosus Xbb-LR-1 and L. casei Xbb-LC-1 were added during various stages of biofilm formation in Gardnerella species and were cocultured for 24 h. The biofilm thickness of each sample was determined via confocal laser scanning microscopy (CLSM). The absolute quantities of Gardnerella species in each sample was obtained via real time polymerase chain reaction method, and the pH value was obtained using a pH indicator paper. Biofilm formation by Gardnerella species in a medium with distinct pH values was observed via gentian violet staining, CLSM, and scanning electron microscopy (SEM). The biofilm increased the resistance of Gardnerella species toward metronidazole and clindamycin. L. rhamnosus added at the initial biofilm formation stage in Gardnerella species exhibited highest inhibitory effect, with a percentage inhibition of 38.17% ± 1.35%. When the pH value of the culture medium was 6.5, ATCC 14018 could hardly form a biofilm; however, at pH ≥4.5 and ≤6.5, it was able to form a stronger biofilm. The amount of biofilm attained maximum value at optical density of 3.29 ± 0.28 (595 nm), pH 5.5, and at 36 h. Biofilm formation increases the resistance of Gardnerella species toward antibiotics. Maintaining an acidic vaginal environment with pH Lactobacillus remarkably prevents the formation of Gardnerella species biofilm at the initial stage, which further has a significant impact on the treatment and prevention of biofilm-related infections.

We describe a study of the binding of anions to the surface of an octanuclear coordination cage HW, which carries a 16+ charge, in aqueous solution. Anionic aromatic fluorophores such as fluorescein (and derivatives) and hydroxypyrene tris-sulfonate (HPTS) bind strongly to an extent depending on their charge and hydrophobicity. Job plots indicated binding of up to six such fluorescent anions to HW, implying that one anion can bind to each face of the cubic cage, as previously demonstrated crystallographically with small anions such as halides. The quenching of these fluorophores on association with the cage provides the basis of a fluorescence displacement assay to investigate binding of other anions: addition of analyte (organic or inorganic) anions in titration experiments to an HW/fluorescein combination results in displacement and restoration of the fluorescence from the bound fluorescein, allowing calculation of 1 : 1 binding constants for the HW/anion combinations. Relative binding affinities of simple anions for the cage surface can be approximately rationalised on the basis of ease of desolvation (e.g. F− < Cl− < Br−), electrostatic factors given the 16+ charge on the cage (monoanions < dianions), and extent of hydrophobic surface. The interaction of a di-anionic pH indicator (bromocresol purple) with HW results in a pKa shift, with the surface-bound di-anionic form stabilised by approximately 1 pKa unit compared to the non-bound neutral form due to the charge on the cage.

In electroanalysis, solution pH is a critical parameter that often needs to be adjusted and controlled for the detection of particular analytes. This is most commonly performed by the addition of chemicals, such as strong acids or bases. Electrochemical in-situ pH control offers the possibility for the local adjustment of pH at the point of detection, without additional reagents. FEA simulations have been performed to guide experimental design for both electroanalysis and in-situ control of solution pH. No previous model exists that describes the generation of protons at an interdigitated electrode array in buffered solution with one comb acting as a protonator, and the other as the sensor. In this work, FEA models are developed to provide insight into the optimum conditions necessary for electrochemical pH control. The magnitude of applied galvanostatic current has a direct relation to the flux of protons generated and subsequent change in pH. Increasing the separation between the electrodes increases the time taken for protons to diffuse across the gap. The final pH achieved at both, protonators and sensor electrodes, after 1 second, was shown to be largely uninfluenced by the initial pH of the solution. The impact of buffer concentration was modelled and investigated. In practice, the pH at the electrode surface was probed by means of cyclic voltammetry, i.e., by cycling a gold electrode in solution and identifying the potential of the gold oxide reduction peak. A pH indicator, methyl red, was used to visualise the solution pH change at the electrodes, comparing well with the model’s prediction