Search

Dissertação de mestrado em Biotechnology, A embalagem inteligente é uma tecnologia emergente no sector das embalagens alimentares utilizada como ferramenta para monitorizar a qualidade e segurança dos alimentos através da deteção de alterações no produto alimentar embalado e/ou no seu ambiente circundante. O desenvolvimento de embalagens inteligentes contribui para a diminuição do desperdício alimentar, tem o potencial de melhorar a segurança dos produtos, a logística alimentar e a rastreabilidade, aumentando a eficiência da indústria alimentar. Neste contexto, o principal objetivo deste trabalho foi desenvolver uma embalagem inteligente de base biológica como indicador de frescura (através de alterações colorimétricas), a fim de monitorizar e fornecer informações relativas à qualidade de pescado utilizando uma técnica não destrutiva, in situ e em tempo real. Deste modo, filmes de goma de alfarroba (LBG)/k-carragenina (k-car) incorporando extratos de mirtilo (BLE) e/ou beterraba (BEE) foram desenvolvidos. Os filmes foram caracterizados em relação às suas propriedades estruturais, térmicas, de barreira, mecânicas e óticas. Além disso, os filmes BLE e BEE foram avaliados quanto à sua resposta colorimétrica durante o armazenamento de pescado (pescada) a 4 ⁰C e 25 ⁰C durante 8 e 3 dias, respetivamente. Verificou-se que os filmes desenvolvidos sofreram uma mudança colorimétrica de roxo escuro para azul em paralelo com o aumento da contagem microbiana (4,61 ± 0,36 para 8,61 ± 0,21 log CFU/g), do azoto básico volátil total (TVB-N) (de 10,21 ± 1,97 para 66,78 ± 4,81 mg/100 g), e do pH (de 6,60 ± 0,04 para 8,02 ± 0,03) das amostras de pescado. As propriedades de barreira à água foram melhoradas após a adição dos extratos de mirtilo (solubilidade = 39.66 ± 0.11 %, conteúdo de humidade = 23.54 ± 0.98 %, ângulo de contacto = 41.43 ± 3.32 ⁰). Os resultados deste estudo são muito promissores, uma vez que foi possível desenvolver um filme inteligente (o filme BLE) indicador colorimétrico de pH consoante o estado de degradação do pescado, de acordo com o objetivo proposto., Intelligent packaging is an emerging technology in the food packaging sector used as a tool to monitor food quality and safety by detecting changes in the packaged food product and/or its surrounding environment. Intelligent packaging development contributes to the food waste reduction, has the potential to improve product safety, food logistics and traceability, increasing food industry efficiency. In this context, the main goal of this work was to develop a bio-based intelligent packaging as freshness indicator (by colorimetric changes), in order to monitor and provide information regarding food quality using a non-destructive, in situ and real-time technique. Locust bean gum (LBG)/k- carrageenan (k-car) films incorporating blueberry (BLE) and/or beetroot (BEE) extracts were developed. The films were characterized regarding their structural, thermal, barrier, mechanical and optical properties. Moreover, BLE and BEE films were evaluated to assess color response during fish (hake) storage under 4 ⁰C and 25 ⁰C during 8 and 3 days, respectively. A visual change in the color of the packaging label from dark purple to blue in parallel with the increase in the microbial count (from 4.61 ± 0.36 to 8.61 ± 0.21 log10 CFU/g), total volatile basic nitrogen (TVB-N) (from 10.21 ± 1.97 to 66.78 ± 4.81 mg/100 g), and pH (from 6.60 ± 0.04 to 8.02 ± 0.03) of the fish samples was detected. The water barrier properties were improved after blueberry extracts addition (WS = 39.66 ± 0.11 %, MC = 23.54 ± 0.98 %, WCA = 41.43 ± 3.32 ⁰). The results of this study are very promising, since it was possible to develop an intelligent pH responsive indicator film (BLE film) that changes its color due to fish degradation, according to the proposed thesis aim.

Hypothesis Water contamination from heavy metal ions is a major global environmental concern. Adsorbents based on biomaterials have been demonstrated to possess remarkable removal efficiency for metal ions, but the adsorption model of biosorbents is not clear and much efforts should be devoted to study the adsorption behaviors and understand the adsorption mechanism. Experiments The multifunctional rhodamine-modified chitosan (RMC) hydrogel for Hg2+ adsorption with fluorescent turn-ON properties was fabricated through grafting the rhodamine-modified poly (ethylene glycol) benzaldehyde (RM-PEG) onto the hydrogel network serving as the fluorescence/colorimetric sensing receptor. The adsorption behaviors and colorimetric sensing mechanism of RMC hydrogel towards Hg2+ were investigated in detail. Findings RMC hydrogel can remove more than 96.5% of Hg2+ from aqueous solution with significant fluorescence response and colorimetric change. The high adsorption selectivity and colorimetric sensing mechanism of RMC hydrogel towards Hg2+ can be explained by the hard and soft acid/base (HSAB) theory. The O atom in hydroxyl and carbonyl groups together with the N atom in amine/imine groups of RMC hydrogel play a vital role in the adsorption of Hg2+, while the colorimetric response and fluorescence enhancement of the hydrogel after adsorption are attributed to the specific spiro-lactam structure of rhodamine moieties. The adsorption isotherms and kinetics were investigated and well described by Freundlich isotherm and pseudo-second-order kinetic model. Furthermore, RM-PEG showed low cytotoxicity towards mouse embryonic fibroblast cells and RMC hydrogel can be used as a fluorescent pH indicator from 4.2 to 7.4, demonstrating the potential applications of RMC hydrogel in biological diagnosis.

An easy-to-use food packaging label with pH and ammonia sensitivity was developed by adding betacyanin (5, 10 and 15 mg per g of starch) from flowers of paperflower (Bougainvillea glabra) to potato starch film made using the solvent casting method. The betacyanin was well dispersed into the starch matrix and formed new interactions with it as revealed by FTIR. The film containing 15 mg/g of betacyanin showed a color change from light pink to yellow as a response to pH adjustment of between 2 to 13. It was also able to detect the presence of ammonia in a range of 0.1 and 0.01 mg of ammonia per ml of water. Surface hydrophobicity and water vapor barrier capacity of the starch film increased by addition of the betacyanin, yet their mechanical strength decreased in the presence of the betacyanin. The ability of the film in the real-time indication of fish quality as a label was also evaluated during the storage of Caspian sprat at 4 °C. A visual change in the color of the packaging label from pink to yellow in parallel with the increase in the total volatile basic nitrogen (TVB-N), microbial count of the fish samples was detected. The starch/betacyanin film could be a novel intelligent label for application in food packaging.

The design of functional metalloenzymes is attractive for the biosynthesis of biologically important compounds, such as phenoxazinones and phenazines catalyzed by native phenoxazinone synthase (PHS). To design functional heme enzymes, we used myoglobin (Mb) as a model protein and introduced an artificial CXXC motif into the heme distal pocket by F46C and L49C mutations, which forms a de novo disulfide bond, as confirmed by the X-ray crystal structure. We further introduced a catalytic Tyr43 into the heme distal pocket and found that the F43Y/F46C/L49C Mb triple mutant and the previously designed F43Y/F46S Mb exhibit PHS-like activity (80-98% yields in 5-15 min), with the catalytic efficiency exceeding those of natural metalloenzymes, including o-aminophenol oxidase, laccase, and dye-decolorizing peroxidase. Moreover, we showed that the oxidative coupling product of 1,6-disulfonic-2,7-diaminophenazine is a potential pH indicator, with the orange-magenta color change at pH 4-5 (pKa = 4.40). Therefore, this study indicates that functional heme enzymes can be rationally designed by structural modifications of Mb, exhibiting the functionality of the native PHS for green biosynthesis.

Soil salinity negatively affects the growth, development and yield of plants. Acidification of the cytosol in cells of glycophytes was reported under salinity, while various types of plant cells can have a specific reaction under the same conditions. Transgenic Arabidopsis plants expressing the pH sensor Pt-GFP in the cytosol were used in this work for determination of morphometric changes and cytosolic pH changes in the superficial cells of Arabidopsis roots under chronic salinity in vitro. We did not find changes in the length of the root cap cells, while there was a decrease in the length of the differentiation zone under 50, 75 mM NaCl and the size of the epidermal cells of the differentiation zone under 75 mM NaCl. The most significant changes of cytosolic pH to chronic salinity was noted in columella (decrease by 1 pH unit at 75 mM NaCl) and epidermal cells of the differentiation zone (decrease by 0.6 and 0.4 pH units at 50 and 75 mM NaCl, respectively). In developed lateral root cap cells, acidification of cytosol by 0.4 units occurred only under 75 mM NaCl in the medium. In poorly differentiated lateral cells of the root cap, there were no changes in pH under chronic salinity.

Smart packaging can provide real-time information about changes in food quality and impart a protective effect to the food product by using active agents. This study aimed to develop a smart bilayer film (alginate/agar) with a cellulose nanosphere (CNs) from corncob. The bilayer films were prepared using 1.5% (w/w) sodium alginate with 0.25%% (w/v) butterfly pea extract incorporated (indicator layer) and 2% (w/w) agar containing 0.5% (w/v) catechin–lysozyme (ratio 1:1) (active layer). The CNs were incorporated into the alginate layer at different concentrations (0, 5, 10, 20, and 30% w/w-based film) in order to improve the film’s properties. The thickness of smart bilayer film dramatically increased with the increase of CNs concentration. The inclusion of CNs reduced the transparency and elongation at break of the smart bilayer film while increasing its tensile strength (p < 0.05). The integration of CNs did not significantly affect the solubility and water vapor permeability of the smart bilayer film (p > 0.05). The smart bilayer film displayed a blue film with a glossy (without CNs) or matte surface (with CNs). The developed bilayer film shows excellent pH sensitivity, changing color at a wide range of pHs, and has a good response to ammonia and acetic acid gases. The film possesses exceptional antimicrobial and antioxidant activities. The integration of CNs did not influence the antibacterial activity of the film, despite the presence of a higher level of DPPH in film containing CNs. The smart bilayer film was effectively used to monitor shrimp freshness. These findings imply that smart bilayer films with and without CNs facilitate food safety and increase food shelf life by monitoring food quality.

A novel optical sensor for ammonia concentration in water is demonstrated using up-conversion (UC) fluorescence intensity ratio (FIR). The sensor element consists of (i) an Er 3+ -Yb 3+ co-doped tellurite glass microsphere integrated inside a section of suspended tri-core hollow fiber (STCHF) and (ii) the pH indicator phenol red. When 980 nm pump is coupled into the microsphere, the Er 3+ ions produce green and red UC emissions. Exposure to ammonia results in a strong increase in the 560 nm absorption of the phenol red, which acts as a filter for the green emission, while the red emission is unaffected. A simple linear relation between the FIR and the ammonia aqueous concentration has been established.

This work provides an algorithm to describe the salinity (SP) and temperature (T) dependence of the equilibrium and molar absorptivity characteristics of purified bromocresol purple (BCP, a pH indicator) over a river-to-sea range of salinity (0 ≤ SP ≤ 40). Based on the data obtained in this study, the pH of water samples can be calculated on the seawater pH scale as follows: pHSW = −log(K2e2) + log((R – e1)/(1 – Re4)) where −log(K2e2) = 4.981 – 0.1710SP0.5 + 0.09428SP + 0.3794SP1.5 + 0.0009129SP2 + 310.2/T – 17.33S1.5/T – 0.05895SP1.5 ln T – 0.0005730SP0.5T, e1 = 0.00049 ± 0.00029, and e4 = −7.101 × 10–3 + 7.674 × 10–5T + 1.361 × 10–5SP. The term pHSW is the negative log of the hydrogen ion concentration determined on the seawater pH scale; R is the ratio of BCP absorbances (A) at 432 and 589 nm; K2 is the equilibrium constant for the second BCP dissociation step; and e1, e2, and e4 are BCP molar absorptivity ratios. A log(K2e2) equation is also presented on the total pH scale. The e4 value determined for purified BCP in this study can be used with previously published procedures to correct BCP absorbance measurements obtained using off-the-shelf (unpurified) BCP. This work provides a method for purifying BCP, fills a critical gap in the suite of available purified sulfonephthalein indicators, enables high-quality spectrophotometric measurements of total alkalinity, and facilitates pH measurements in freshwater, estuarine, and ocean environments within the range 4.0 ≤ pH ≤ 7.5.

U današnje vrijeme sve je veći interes za korištenjem prirodnih materijala pri izradi nosivih kemijskih senzora (engl. wearable chemical sensors), uslijed njihove netoksičnosti, biorazgradivosti i općenito manjeg utjecaja na okoliš. Antocijanini su pigmenti topljivi u vodi, koji se dobivaju izoliranjem iz biljaka, poput voća i povrća. Pokazuju širok spektar boja ovisno o pH medija, zbog čega se mogu koristiti kao pH indikatori. Spektroskopske karakteristike otkrivaju mnogo o kemijskom ponašanju pigmenata te su neizostavan korak prilikom izrade optičkih senzora. Najčešće korištene su UV-Vis apsorpcijska, reflektancijska, fluorescencijska spektroskopija te kolorimetrija. Celuloza je najrašireniji prirodni polimer glukoze, koji pokazuje razna korisna svojstva, primjerice obnovljivost, visoku adsorpciju i mogućnost modifikacije. Njena mikrofibrilna struktura čini pogodni matriks za imobilizaciju antocijanina u senzorima baziranim na prirodnim materijalima. Od mnogobrojnih derivata, karboksimetilceluloza (CMC) pokazuje velik potencijal zbog topivosti u vodi, čime se izbjegava korištenje toksičnih otapala. U ovom radu istraživana su optička svojstva antocijanina izoliranog iz crvenog kupusa, otopljenog u otopini, imobiliziranog u CMC trakicama te CMC filmovima osušenim na stakalcima. UV-Vis spektrofotometrija je korištena za karakterizaciju antocijanina u otopini te imobiliziranog u CMC trakicama, dok je za karakterizaciju CMC filmova osušenih na stakalcima korištena reflektancija. Promjena boje pri različitim pH imobiliziranog antocijanina usporediva je s promjenom boje u otopini. Najpogodnija svojstva u vidu najprimijetnije promjene boje, jasno definiranog reflektancijskog spektra i prikladne konzistencije filma postignuta su za filmove s najvećom korištenom koncentracijom antocijanina. Prikazani rezultati najavljuju mogućnost daljnjih istraživanja ove teme i razvoja nosivih pH osjetljivih materijala u potpunosti načinjenih od prirodnih, netoksičnih, štoviše jestivih materijala, čija primjena bi bila posebno atraktivna u nosivim kemijskim senzorima. Nowadays there is a growing interest to apply natural materials into wearable chemical sensors, due to their lower impact on the environment, nontoxicity and biodegradability. Anthocyanins are water soluble pigments isolated from plants, like fruits and vegetables. They exhibit a broad spectrum of color depending on the pH, therefore could be used as pH indicators. Spectroscopic characteristics are important for defining chemical properties of the pigments and are a mandatory step in preparing an optical sensor. Characterization methods usually include UV-Vis absorbance, reflectance and fluorescence spectroscopy, as well as colorimetry. Cellulose is the most abundant glucose polymer, which shows great variety of properties, namely reusability, high adsorption and reactivity with other chemicals. Its microfiber structure allows to be utilized as an ideal matrix to immobilize anthocyanin in sensors based on natural materials. Out of many derivatives, carboxymethylcellulose shows great potential due to its solubility in water, thus avoiding the use of toxic solvents. In this work the optical properties of anthocyanin isolated from red cabbage are investigated in solution as well as in immobilized forms as carboxymethylcellulose (CMC) film strips and as dried CMC spots on glass slides. To characterize the anthocyanin in solution and immobilized in CMC film strips UV-Vis spectroscopy was used, while reflectance spectroscopy measurements were used to characterize spots dried on glass slides. Color change of immobilized anthocyanin films exposed to solution of different pH value was comparable with changes obtained with anthocyanins dissolved in solution. Best properties in terms of most noticeable color change, well defined reflectance spectra and appropriate consistency were achieved for the films with highest concentration of anthocyanins. The results obtained here show great promise for development of new pH sensitive materials entirely made of natural, nontoxic and even edible materials, especially suitable for wearable sensing applications.

Nowadays, worldwide challenges such as global warming, pollution, unsustainable consumption patterns, and scarcity of natural resources are key drivers toward future-oriented bioeconomy strategies, which rely on renewable biobased resources, such as bacterial pigments and bacterial cellulose (BC), for materials production. Therefore, the purpose of this study was to functionalize bacterial cellulose with violacein, flexirubin-type pigment, and prodigiosin and test their suitability as pH indicators, due to the pigments’ sensitivity to pH alterations. The screening of the most suitable conditions to obtain the BC-pigment indicators was achieved using a full factorial design, for a more sustainable functionalization process. Then, the pH response of functionalized BC to buffer solutions was assessed, with color changes at acidic pH (BC-violacein indicator) and at alkaline pH (BC-violacein, BC-prodigiosin, and BC-flexirubin-type pigment indicators). Moreover, the indicators also revealed sensitivity to acid and base vapors. Furthermore, leaching evaluation of the produced indicators showed higher suitability for aqueous foods. Additionally, color stability of the functionalized BC indicators was carried out, after light exposure and storage at 4 °C, to evaluate the indicators’ capacity to maintain color/sensitivity. Thus, BC membranes functionalized with bacterial pigments have the potential to be further developed and used as pH indicators.

In this study, a colorimetric pH indicator was developed using nanofibrous mats of polylactide (PLA) including turmeric, a natural dye. Firstly, nanofibrous mats were produced by dissolving PLA at different concentrations in chloroform (CHL)/dimethylformamide (DMF) at various volume ratios, and morphological analysis was performed. Subsequently, turmeric was added at a concentration of 2% wt. to the polymer solution having a PLA concentration of 10% in 75/25 CHL/DMF, and nanofibrous pH indicators were produced. Then, pH indicators containing turmeric were immersed into pH buffer solutions (pH 1, 4, 7 and 10), and color variations were measured using a spectrophotometer. It was foreseen that the produced pH indicators have the potential to be used in intelligent food packaging applications., u çalışmada, doğal bir boyarmadde olan turmerik içeren, polilaktit (PLA) esaslı nanolif yüzeyler kullanılarak kolorimetrik pH indikatörü geliştirilmiştir. Öncelikle, farklı konsantrasyonlarda PLA polimeri, çeşitli hacim oranlarında kloroform (CHL)/dimetilformamid (DMF) içerisinde çözdürülüp, elde edilen karışımlarla elektroeğirme yöntemi ile nanolif yüzeyler üretilmiş ve morfolojik analizler gerçekleştirilmiştir. Ardından, ağırlıkça %2 oranında turmerik, %10 PLA konsantrasyonuna sahip 75/25 CHL/DMF çözeltisi içerisine ilave edildikten sonra bu karışımdan nanolifli pH indikatörü üretilmiştir. Turmerik içeren bu pH indikatörlü, pH tampon çözeltilerine daldırılarak, spektrofotometrede renk değişimleri ölçülmüştür. Üretilen pH indikatörlerinin, akıllı gıda paketlemelerinde potansiyel olarak kullanılabileceği öngörülmüştür.

Dysfunction of mitochondria is closely related to neurodegenerative diseases, heart diseases, cancers, and so on. Because both proton and oxygen participate in vital biochemical reactions occurring in mitochondria such as adenosine triphosphate (ATP) generation, measuring proton and oxygen concentrations in mitochondria is therefore crucial for monitoring mitochondria activities and understanding cellular behavior. For this purpose, we developed a ratiometric fluorescent nanosensor for simultaneously sensing and imaging O2 and pH in mitochondria. The steps are as follows: (1) Styrene was copolymerized with 2-aminoethyl methacrylate hydrochloride to produce amino-functionalized polymer nanoparticles. (2) The reference dye rhodamine B isothiocyanate (RBITC) and oxygen-sensitive dye platinum(II) octaethylporphyrin (PtOEP) were encapsulated into a polymer sphere during polymerization, while the pH indicator fluorescein isothiocyanate (FITC) and mitochondrial-targeting molecule (3-carboxypropyl)triphenylphosphonium bromide (TPP) were further modified on the surface of the nanoparticles. The developed nanosensor shows a narrow distribution of particle size, high sensitivity toward O2 and pH, excellent stability, and low cytotoxicity. These remarkable features of the dual nanosensor render them capable of real-time sensing and imaging of O2 and pH in mitochondria with high spatial resolution. Applying the mitochondrial-targeted dual nanosensor in HeLa cells, we quantitatively measured and imaged mitochondrial proton and oxygen concentration variations after carbonyl cyanide m-chlorophenylhydrazone (CCCP) treatment.

Purpose Development of thin film sensors with pH function for noninvasive real-time monitoring of spoilage of packed seafood such as fish, crab and shrimp are described in this study. It is also the purpose of this study to enhance the leaching resistance of the sensors by using a suitable strategy and to quantitatively correlate the sensor’s halochromism with the total volatile amine. Design/methodology/approach To prepare halochromic sensors with better leaching resistance, biocompatible materials such as starch, agar, polyvinyl alcohol and cellulose acetate along with a halochromic dye were used to prepare the thin film sensors. These thin films were evaluated for monitoring the spoilage of packed seafood at room temperature, 4°C and −2°C up to 30 days. The halochromic sensors were characterized using UV-visible and FT-IR spectroscopy. Findings CIELab analyses of the halochromism of the thin film sensors revealed that the color changes exhibited by the sensors in response to the spoilage of seafood are visually distinguishable. Further, the halochromic response of the thin films was directly proportional to the amount of total volatile base nitrogen that evolved from the packed seafood. Excellent leaching resistance was observed for the developed thin film sensors. The halochromic property of the sensors is reversible and thus the sensors are recyclable. Besides, the thin film sensors exhibited significant biodegradability. Originality/value This study provides insights for use of different biocompatible polymers for obtaining enhanced leaching resistance in halochromic sensors. Further, the color changes exhibited by the sensors are in line with the total volatile amines evolved from the packed seafood. These results highlight the importance of the developed halochromic thin film sensors for real-time monitoring of the spoilage of packed seafood.

A pH indicator film was prepared by mixing natural polymeric chitosan (CH) with natural dye from butterfly pudding extract (BP). The films were determined by color changes at different pH value, absorbance, thickness, moisture content, swelling property, water contact angle, mechanical property, barrier property, and microstructure of films. The structural change of film was analyzed by Fourier transform infrared spectra. The application to monitor fish freshness was also studied. The prepared film was sensitive to the changes in pH value and showed distinct color changes from pink purple to yellow, with pH value ranging from 1 to 14. The films showed visible color changes from purple-blue to dark green during fish preservation. The total volatile basic nitrogen (TVB-N) content and pH value changes of tilapia were closely related to the visual color changes in film. The result indicated that the fabricated film was a highly pH-sensitive film for monitoring fish freshness.

Hybrid hydrogels were prepared by copolymerization of 2-hydroxyethyl methacrylate and diallyldimethylammonium chloride mixed with alginate, bromothymol blue, and fume silica. The polymerization reaction occurred by free radical polymerization using potassium persulfate and N,N,N/, N/−tetramethyethylenediamine as a redox initiator and N,N/−methylenebisacrylamide as a crosslinker. The results showed that the hydrogels responded to pH and exhibited color change. The bromothymol blue ionization was the main reason for the color change of the hydrogels. Also, the alginate and fume silica incorporated in the hydrogels moved the color from light shade to dark shade. The alginate, fume silica, and diallyldimethylammonium chloride affected the swelling property of the hydrogels. The alginate and fume silica increased water absorption. However, the diallyldimethylammonium chloride decreased the swelling property. The hydrogel can be used as a sensor to detect acids or bases, such as urine, causing irritation in the elderly or bed-bound patients.

The present study demonstrated the evaluation of starch based film formulated with ClitoriaTernatea flowers extracts which act as pH indicator. Maceration, sonication and infusion extraction were employed to determine the percentage yield of the flower extracts. Extract solutions (1mg/mL) were subjected to UPLC-QTOF/MS in order to detect and identify the chemical constituents of C. ternatea. UV-Vis analysis is done by treating the extracts (4mg/mL) with prepared buffer solution in various pH value ranged (2.0 – 11.0) and the absorbance were observed within a broad range of wavelength (400-700 nm). 100 mL solution of 4g starch, C. ternatea extracts and glycerol (19g plasticizer/100g starch) in distilled water were undergo gelatinization process to form the desired thin film. The functional group presented in the film and raw materials were detected and defined by analyzing through FTIR spectroscopy. From the results, maceration techniques produced the higher yield of extracts with 41.48% compared to sonication and infusion method. Variation colours of C. ternatea solution were displayed in different value of pH. At pH lower than 3, the extract solution illustrated light red to purple in colour while at higher pH value to the more basic pH (4,5,6,7,8 and 9), the colour can be perceived as blue. From the gelatinization process, the blue smooth thin layer of film was produced. FTIR analysis showed that all of samples contain C-O bond (3300 cm-1). Starch based film formulated with C. ternatea as pH indicator can be applied to detect the spoilage of foods in the production of food wrapper and packaging.

In the present investigation, a paper-based pH indicator was developed using anthocyanin from purple rice bran for rapid food quality monitoring. The efficiency of the indicator was studied in different buffer solutions of pH range 2–10. The indicator was made with 150 mg/L anthocyanin concentration shows a distinct L, a, and b values of color. Furthermore, the indicator was tested in different liquid foods with varying pH and indicating distinct color in every pH value. The degradation behavior of a value (redness) of the indicator was investigated in 4 and 25 °C. The degradation behavior at 4 and 25 °C was best fitted with first-order kinetics (R2 = 0.99 and 0.97) than zero-order (R2 = 0.98 and 0.96). In addition, the performance of the indicator was compared with the previous research observations. The present study manifested a green route of monitoring for liquid food quality using low-cost and highly sensitive pH indicator.

Lysosomes, the acidic degradation compartments of eukaryotic cells, play an essential role in many physiological processes. Their dysfunction is associated with a number of diseases, which are often related to an altered localization or luminal pH. Thus, the in-depth characterization of lysosomes within the intact eukaryotic cell is of utmost interest. For microscopic evaluation of lysosomal distribution and acidity, a number of labels have been developed, but many showed poor organelle specificity or rapid clearing from lysosomes, rendering them unsuitable for long-term observations. Here, we describe the synthesis and spectroscopic properties of a novel small molecule marker for lysosomes based on naphthalene monoimide with reversible, pH-dependent spectral shifts in both the absorption and the emission spectrum and acidity-associated changes in fluorescence lifetime. The dye can be excited either with single- or two-photon excitation and appears to be very stably associated with lysosomes for several days. We used this chromophore to detect chemically-induced changes of lysosomal pH in HeLa cells by ratiometric and FLIM imaging.

pH sensors based on up-conversion nanoparticles (UCNPs) are widely studied due to their effective elimination of background signals. However, ratiometric pH measurement depending on blue and red luminescence under NIR irradiation has been seldom reported for the lack of simultaneous strong blue and red emissions for traditional UCNPs. In this work, we designed NaGdF4:Yb,Tm@NaYF4:Yb,Eu@NaYF4:Yb,Nd@NaYF4 core–triple shell (CTS) UCNPs as fluorescent materials to realize blue/red ratiometric pH measurement. On the basis of Gd3+-mediated interfacial energy transfer and Yb3+-mediated energy migration, CTS particles present intense luminescence and a high red/blue (615 nm/450 nm) peak intensity ratio of 0.47 at 808 nm excitation. Composed of these particles and pH indicator bromocresol green, the pH sensor exhibits ratiometric responses in a pH range of 4–7 according to blue/red luminescence intensity ratios, avoiding the common errors as well as potential mutual fluorescence signal interference. Owing to strong overall luminescence and additional red emission of CTS UCNPs distinctly improving the signal-to-noise ratio, this ratiometric sensor reveals high sensitivity. Moreover, the employed excitation wavelength of 808 nm can not only eliminate autofluorescence signals, but also alleviate severe temperature rise in biosamples under continuous irradiation, ensuring accurate pH determination. More intriguingly, a CCD RGB camera serves as a collector to record luminescence signals, further promoting commercial feasibility. The successful application of CTS UCNPs on sensors indeed realizes blue/red ratiometric measurement towards pH under 808 nm irradiation, also pointing out a novel way for pH sensors with high sensitivity and accuracy.

Background: Nucleic acid (NA)-based diagnostics enable a rapid response to various diseases, but current techniques often require multiple labor-intensive steps, which is a major obstacle to successful translation to a clinical setting. Methods: We report on a surface-engineered single-chamber device for NA extraction and in situ amplification without sample transfer. Our system has two reaction sites: a NA extraction chamber whose surface is patterned with micropillars and a reaction chamber filled with reagents for in situ polymerase-based NA amplification. These two sites are integrated in a single microfluidic device; we applied plastic injection molding for cost-effective, mass-production of the designed device. The micropillars were chemically activated via a nature-inspired silica coating to possess a specific affinity to NA. Results: As a proof-of-concept, a colorimetric pH indicator was coupled to the on-chip analysis of NA for the rapid and convenient detection of pathogens. The NA enrichment efficiency was dependent on the lysate incubation time, as diffusion controls the NA contact with the engineered surface. We could detect down to 1×103 CFU by the naked eye within one hour of the total assay time. Conclusion: We anticipate that the surface engineering technique for NA enrichment could be easily integrated as a part of various types of microfluidic chips for rapid and convenient nucleic acid-based diagnostics.

While wearable chemical sensors often rely on electrochemical techniques, optical chemical sensors coupled with a smartphone or a miniaturized camera represent an attractive approach to the monitoring of sweat composition. In this paper, we modify real sports fabrics such as polyester–spandex fabrics with rational combinations of sensing chemicals including a pH indicator, an ion exchanger, and an ionophore via one-step inkjet printing. Highly selective and fully reversible pH optodes as well as Na+- and K+-selective optodes are obtained only when the most hydrophobic sensing chemicals are used (e.g., sodium ionophore VIII vs. sodium ionophore VI). These sensors exhibit large color-based responses that can be readily identified by naked eye or analyzed via an iPhone app. Their dynamic ranges well cover the physiological sweat concentrations of the analytes. Compared to most other sensors created on garments, our fabric-based optodes are cost-effective, mass-reproducible by the digital printing technology currently used in the textile industry, and do not significantly compromise the essential properties of fabrics such as flexibility, stretchability, wickability, and breathability.

A rapid and highly sensitive paper-based colorimetric device for the on-site detection of ammonia (NH3) gas is presented in this study. The detection principle of this device is based upon a change of color from red to yellow on a paper that has been immobilized with a pH indicator, i.e., methyl orange (pKa = 3.4), in the presence of NH3 gas. The color signal of the device can be measured through the hue channel of an HSL system via the application of a smartphone. This device can detect the amount of NH3 gas within 3 min. The linear relationship between the NH3 gas concentration and the hue signal was found to be in the range from 6.0 to 54.0 ppbv with R2 = 0.9971, and the limit of detection was found to be 2.0 ppbv. In addition, this device showed remarkably high selectivity to NH3 gas amongst the other common volatile organic compounds and general gases that are present in environmental air without the assistance of any membrane material. Furthermore, we demonstrated the applicability of this device for the detection of total NH3 gas at a chicken farm and in a laboratory, with relative standard deviations of 6.2% and 5.4%, respectively. The developed NH3 gas device in the study is easy to operate and cost-effective, with the reduction of a large consumption of chemical reagents; also, its signals can be measured simply and then recorded through a smartphone. It is suitable for the application of routine on-site detection of NH3 gas, especially concerning regions which have limited resources.

BACKGROUND: Studies have documented the importance of alkaline pH for deposition of calcium phosphate, thereby aiding plaque mineralization. The ureolytic pH response promotes calculus formation by increasing the saturation level of calcium phosphate in plaque fluid. Therefore, AIM - A study was conducted to assess the effect of salivary pH and urea level in mild moderate and heavy calculus formers. METHODS: Group A- Mild calculus formers Group B- Moderate calculus formers Group C- Heavy calculus formers 10 subjects were assigned to each group. Salivary pH was recorded by using pH indicator strips as soon as saliva was collected in a sterile container. Thereafter, biochemical estimation of salivary urea was performed. RESULT-: There was no statistically significant difference in pH levels between Group A and Group B (p=0.97) but significant difference between Group A and Group C (p= 0.01).There was a highly significant difference between Group A and Group C in urea levels .(p

The catalytic enhancements of enzymes loaded on DNA nanostructures have been attributed to the characteristics provided by highly negative charges on the surface of the DNA scaffold, such as the modulation of the local pH near enzymes. In this study, two types of enzymes with optimal activity at pH 6 and 8 equally displayed significant catalytic enhancements on the DNA scaffold surface. By using a ratiometric pH indicator, a lower local pH shift of 0.8 was observed near the DNA scaffold surface. The postulated local pH change near the DNA scaffold surface is unlikely to play a general role in enhancing the activity of the scaffolded enzymes.

In this work, we have developed two single-molecular probes, (S)-3-(4-hydroxyphenyl)-2-((4-nitrobenzyl)amino)propanoic acid (H2Tyr-4-nitro, 1) and (S)-3-(4-hydroxyphenyl)-2-((3-nitrobenzyl)amino)propanoic acid (H2Tyr-3-nitro, 2), from cheap and readily available L-tyrosine and demonstrated their use as (i) a solvent mediated differential fluorescent sensor for iodide in aqueous methanol and fluoride in aqueous DMSO and (ii) a reversible chromogenic pH indicator in DMSO. A flip-flop halide sensor also acting as a pH indicator is unprecedented.

Methyl orange (MO) is a synthetic organic semiconductor, which is frequently used as pH indicator in food & beverages, pharmaceuticals, wastewater treatment, laboratory experimentation, agriculture and healthcare etc. It is a toxic and mutagenic substance. This azo dye is very difficult to decompose by common treatment methods and thereby causing environment pollution and health problems. To overcome this problem, a reusable pH indicator flexible film is prepared by the blending of polyvinyl alcohol (PVA) with MO using water as solvent at 100 °C. PVA is a synthetic non-toxic biodegradable polymer with good solution processability in water and it contains hydroxy functional groups. The intermolecular hydrogen bonding exists between PVA and MO will prevent the macro-phase separation of this new polymeric material. All polymeric materials showed good absorbance in the UV–Vis region of the electromagnetic spectrum and intensity of absorption increases with increase in the amount of MO in the polymer matrix. The pH indicating property of polymer film is studied by dipping the film in different acids and bases. It showed red colour in acid solution and orange-yellow in base solution. The absorption spectrum of PVA/MO film in 0.1 N HCl solution showed bathochromic shift of ∼ 42 nm than that measured in water solution due to the existence of MO in two different forms namely benzenoid and quinonoid form. The flexibility and reusability of this novel material will make it excellent pH indicator in many industrial and laboratory applications.