pH-induced Colour Research Articles

PH-Induced color changeable AIE-featured polymeric micelles for self-indicating anticancer drug delivery

Multifunctional polymeric micelles, which possess capabilities for tracking, bioimaging, stimuli-responsive drug release and tumor targeting, are essential in facilitating the effective delivery of anticancer drugs. Hence, a novel copolymer (CD-CS-Bio-TPAA, CCBT) was synthesized with biotin and hydroxypropyl-β-cyclodextrin conjugated chitosan as the hydrophilic segment and aggregation-induced emission (AIE) featured tetraphenylethene derivative (TPAA) as the hydrophobic segment. Interestingly, under acidic conditions, CCBT exhibited color-tunable AIE behavior as a result of the cleavage of benzoic imine bonds in TPAA molecules, transitioning from red to yellow. Furthermore, CCBT could also self-assemble into polymeric micelles and be used as drug carriers to encapsulate paclitaxel (PTX) (PTX/CCBT PMs) for self-indicating cancer therapy. In vitro release experiments demonstrated that PTX/CCBT PMs could release drugs specifically under acidic conditions. Fluorescence imaging experiments demonstrated that CCBT PMs exhibited excellent cell imaging capabilities and could be tracked due to their unique color-changing behavior. Moreover, PTX/CCBT PMs exhibited notable cytotoxic effects on MCF-7 cells and showed selective internalization by MCF-7 cells through biotin receptor-mediated active targeting. In vivo antitumor experiments confirmed that PTX/CCBT PMs possessed remarkable tumor-inhibiting effects and low systemic toxicity. This work suggested that PTX/CCBT PMs provided new ideas for self-indicating breast cancer treatment.

Composite Materials Based on Biocompatible Metal-Organic Framework and Anthocyanins from Hibiscus sabdariffa for Active Food Packaging

The biocompatible metal-organic framework [Zn4(GA)4(H2O)4] · 4H2O (H2GA = glutamic acid) was used as a container for anthocyanins from Hibiscus sabdariffa in composite films based on kappa-carrageenan and hydroxypropyl methylcellulose. The obtained composite materials showed high antioxidant activity and ability to undergo pH-induced color change upon reactions with gaseous products of pathogen development and, hence, possess the potential for practical application as functional materials for food packaging.

Photo-modulated activation of organic bases enabling microencapsulation and on-demand reactivity

A method is developed for facile encapsulation of reactive organic bases with potential application for autonomous damage detection and self-healing polymers. Highly reactive chemicals such as bases and acids are challenging to encapsulate by traditional oil-water emulsion techniques due to unfavorable physical and chemical interactions. In this work, reactivity of the bases is temporarily masked with photo-removable protecting groups, and the resulting inactive payloads are encapsulated via an in situ emulsion-templated interfacial polymerization method. The encapsulated payloads are then activated to restore the organic bases via photo irradiation, either before or after being released from the core-shell carriers. The efficacy of the photo-activated capsules is demonstrated by a damage-triggered, pH-induced color change in polymeric coatings and by recovery of adhesive strength of a damaged interface. Given the wide range of potential photo-deprotection chemistries, this encapsulation scheme provides a simple but powerful method for storage and targeted delivery of a broad variety of reactive chemicals, promoting design of diverse autonomous functionalities in polymeric materials.

Novel Halochromic Disazo Stilbene Dye with Intramolecular Color Mixing Effect for Textile Sensor Material

A stilbene-based halochromic dye was synthesized, which possesses the effect of intramolecular color matching. By dyeing cotton fabric with the synthesized dye, a textile sensor material was prepared to visually monitor the acidity of the biologically significant pH range (4.5–8.0). The sensitivity of the sensor material to changes in the acidity of the environment, as well as the color stability to the action of saline solutions simulating biological fluids (sweat and blood plasma), were explored. A visually noticeable pH-induced color change of the material is observed in the pH range of 3.0–10.0. In the pH range of buffer solutions at pH 3, the color of the samples is green, from 6 to 8, orange, and from 9 and above, purple. The average color change time was 3 s. The results obtained show the promise of using the studied azo compound in technologies for designing multifunctional pH-sensitive textile sensor materials.

Orange Carotenoid Protein in Mesoporous Silica: A New System towards the Development of Colorimetric and Fluorescent Sensors for pH and Temperature.

Orange carotenoid protein (OCP) is a photochromic carotenoprotein involved in the photoprotection of cyanobacteria. It is activated by blue-green light to a red form OCPR capable of dissipating the excess of energy of the cyanobacterial photosynthetic light-harvesting systems. Activation to OCPR can also be achieved in the dark. In the present work, activation by pH changes of two different OCPs-containing echinenone or canthaxanthin as carotenoids-is investigated in different conditions. A particular emphasis is put on OCP encapsulated in SBA-15 mesoporous silica nanoparticles. It is known that in these hybrid systems, under appropriate conditions, OCP remains photoactive. Here, we show that when immobilised in SBA-15, the OCP visible spectrum is sensitive to pH changes, but such a colorimetric response is very different from the one observed for OCP in solution. In both cases (SBA-15 matrices and solutions), pH-induced colour changes are related either by orange-to-red OCP activation, or by carotenoid loss from the denatured protein. Of particular interest is the response of OCP in SBA-15 matrices, where a sudden change in the Vis absorption spectrum and in colour is observed for pH changing from 2 to 3 (in the case of canthaxanthin-binding OCP in SBA-15: λMAX shifts from 454 to 508 nm) and for pH changing from 3 to 4 (in the case of echinenone-binding OCP in SBA-15: λMAX shifts from 445 to 505 nm). The effect of temperature on OCP absorption spectrum and colour (in SBA-15 matrices) has also been investigated and found to be highly dependent on the properties of the used mesoporous silica matrix. Finally, we also show that simultaneous encapsulation in selected surface-functionalised SBA-15 nanoparticles of appropriate fluorophores makes it possible to develop OCP-based pH-sensitive fluorescent systems. This work therefore represents a proof of principle that OCP immobilised in mesoporous silica is a promising system in the development of colorimetric and fluorometric pH and temperature sensors.

Effects of casein on the stability, antioxidant activity, and bioavailability of lotus anthocyanins.

Effects of casein on the stability, antioxidant activity, and bioavailability of lotus anthocyanins were investigated. Casein could inhibit the unsatisfactory pH-induced color change of lotus anthocyanins, and improved their photo, oxidation, and thermal stabilities. During the simulated digestion, the anthocyanin retention increased from 65.39 to 76.14 mg C3G/L with the protection of casein, while the DPPH and ABTS scavenging activities of lotus anthocyanins with casein increased to 62.33% and 46.58%, respectively. However, casein with lower concentration showed a better protective effect on lotus anthocyanins due to its self-aggregation tendency at high dose. The zebrafish model further verified that casein could enhance the bioavailability of lotus anthocyanins. Furthermore, molecular docking revealed that casein could interact with anthocyanin by hydrogen bond and hydrophobic interaction, which led to the stronger stability and bioavailability of lotus anthocyanins. The results conveyed that casein could be used as a wall material to protect anthocyanins. PRACTICAL APPLICATIONS: Anthocyanins are natural colorants with multiple biological activities, but the poor stability during processing and digestion limits their application in food industry. In the present research, casein exhibited conspicuous ability to enhance the stability of lotus anthocyanins toward detrimental conditions. Additionally, casein could preserve anthocyanins from degradation during digestion and thus improve the bioavailability. These findings indicated that casein could serve as a potential carrier for encapsulating and delivering anthocyanins. The better stability and bioavailability would promote the application of anthocyanins in food products and human health.

Protection of anthocyanin-rich extract from pH-induced color changes using water-in-oil-in-water emulsions

The food, cosmetics, and personal care industries are increasingly interested in replacing synthetic colorants with natural alternatives. Anthocyanin is a renewable and sustainable source of plant-derived pigment. However, their application in commercial products is often limited because of their susceptibility to chemical degradation, which leads to color fading and/or a change in hue. In this study, we examined the possibility of protecting anthocyanin from degradation by encapsulating them within the inner water phase of a water-in-oil-in-water (W/O/W) emulsion. Polyglycerol polyricinoleate (PGPR) was used as a hydrophobic emulsifier, while quillaja saponin was used as a hydrophilic emulsifier. First, W/O emulsions containing 20% aqueous phase and 80% oil phase (PGPR in corn oil) were prepared using a microfluidizer. Second, W/O/W emulsions were prepared by blending 20% W/O emulsion with 80% aqueous phase (saponin in water) using a high-shear mixer. Changes in color, particle size, charge, and anthocyanin leakage of the emulsions were measured when the external aqueous phase was changed from pH 7 to 3. Anthocyanin encapsulation significantly slowed down pH-induced color changes, possibly because the internal aqueous phase had a different pH to the external one. Anthocyanin transfer between aqueous phases depended on pH, temperature, and initial location. Our results suggest that multiple emulsions may be useful for encapsulation and protection of natural colors.

Evaluation of the Rapid Polymyxin NP Test for Polymyxin B Resistance Detection Using Enterobacter cloacae and Enterobacter aerogenes Isolates.

Polymyxin resistance is an increasing problem worldwide. Currently, determining susceptibility to polymyxins is problematic and lengthy. Polymyxins diffuse poorly into agar, potentially giving inaccurate disk diffusion and Etest results. A rapid screening test (2 h) for the detection of polymyxin resistance in Enterobacteriaceae, developed by P. Nordmann and L. Poirel (rapid polymyxin NP test) in 2016, detects glucose metabolization in the presence of polymyxin E (PE) and PB via pH-induced color change. The sensitivity and specificity were 99.3 and 95.4%, respectively, with results obtained in ≤2 h. Our goal was to evaluate this test using PB against larger numbers of Enterobacter A total of 143 nonduplicate Enterobacter isolates (102 E. cloacae complex, 41 E. aerogenes) were tested, including 136 collected from Ochsner Health System patients from March to May 2016 and 7 previously determined PB-resistant E. cloacae isolates from JMI Laboratories. MICs were determined via broth microdilution. For the rapid polymyxin NP test, a color change from orange to yellow is positive; a weak/no color change is deemed negative after 4 h. Of 143 Enterobacter isolates, 25 were determined to be PB resistant by broth microdilution (MIC > 2 μg/ml), including all 7 JMI isolates. Of these 25, 7 were positive by the rapid polymyxin NP test (included 3/7 JMI isolates). All 118 isolates determined to be PB susceptible by broth microdilution were NP test negative. The sensitivity and specificity for the rapid polymyxin NP test were 25 and 100%, respectively, compared to broth microdilution. Although the rapid polymyxin NP test is a much faster method (2 to 4 h) for polymyxin resistance determination compared to broth microdilution (16 to 20 h), our study indicates that it may be subject to limitations when testing Enterobacter.

Stabilising phycocyanin by anionic micelles

Phycocyanins are pigment-protein complexes with potential application as natural food colourants. The perceived colour of phycocyanins varies with pH, and a method to stabilise the colour over a broad range of pH values is requested by the food industry. In this work, the stabilising effect of sodium dodecyl sulphate (SDS) micelles on pH-induced colour variations of phycocyanin was examined. SDS was shown to stabilise the blue conformation of phycocyanin, preventing formation of the green conformation, which is prevalent at low pH. The studies indicated that the stabilising effect occurred through interaction or entrapment of the non-protonated, circular helical (blue) structure of phycocyanin and the anionic SDS micelles. The interaction prevented conversion into protonated, partially unfolded (green) phycocyanin species. This information opens for new possibilities to stabilise the blue conformation of phycocyanin and to apply the stabilised form in food products as a natural blue food colourant.

Improving beef meat colour scores at carcass grading

Unacceptable meat colour scores at the time of carcass grading are associated with reduced meat quality and consumer rejection. We hypothesised that the meat colour at carcass grading would be influenced by the pH and temperature decline post slaughter, as these would be determined by animal and processing factors. Beef carcasses (n = 1512) at seven Australian processing plants were assessed, at grading, for the meat colour of the M. longissimus thoracis. Statistical modelling determined the animal, carcass and processing factors contributing to the meat colour score at carcass grading. The occurrence of unacceptably dark meat dropped from 8 to 3% when the time of grading was increased from 14 to 31 h post slaughter (P < 0.01). A high temperature at pH 6 (rigor temperature), high final pH (pHF), pasture feeding and older animals were associated with dark M. longissimus thoracis at carcass grading (P < 0.05 for all). Less than 30% of carcasses with non-compliant pHF displayed a dark non-compliant meat colour >3, indicative of an opportunity to determine the mechanism behind this pH-induced colour development and thus reduce the incidence of non-compliance. It is recommended that when there is a high occurrence of carcasses with a dark meat colour >3 that the time from slaughter to grading is checked to ensure carcasses are in full rigor at the grading point. This will assist in minimising economic penalties due to dark-coloured carcasses. Finally, animal factors, such as maturity and feeding regime also had a considerable impact on the meat colour at carcass grading.

Bioinspired Fabrication of Hierarchically Structured, pH-Tunable Photonic Crystals with Unique Transition

We herein report a new class of photonic crystals with hierarchical structures, which are of color tunability over pH. The materials were fabricated through the deposition of polymethylacrylic acid (PMAA) onto a Morpho butterfly wing template by using a surface bonding and polymerization route. The amine groups of chitosan in Morpho butterfly wings provide reaction sites for the MAA monomer, resulting in hydrogen bonding between the template and MAA. Subsequent polymerization results in PMAA layers coating homogenously on the hierarchical photonic structures of the biotemplate. The pH-induced color change was detected by reflectance spectra as well as optical observation. A distinct U transition with pH was observed, demonstrating PMAA content-dependent properties. The appearance of the unique U transition results from electrostatic interaction between the -NH3(+) of chitosan and the -COO(-) groups of PMAA formed, leading to a special blue-shifted point at the pH value of the U transition, and the ionization of the two functional groups in the alkali and acid environment separately, resulting in a red shift. This work sets up a strategy for the design and fabrication of tunable photonic crystals with hierarchical structures, which provides a route for combining functional polymers with biotemplates for wide potential use in many fields.

Dye-Loaded Porous Nanocapsules Immobilized in a Permeable Polyvinyl Alcohol Matrix: A Versatile Optical Sensor Platform

In this work we report on a versatile sensor platform based on encapsulated indicator dyes. Dyes are entrapped in hollow nanocapsules with nanometer-thin walls of controlled porosity. The porous nanocapsules retain molecules larger than the pore size but provide ultrafast access to their interior for molecules and ions smaller than the pore size. Dye-loaded nanocapsules are immobilized in a polyvinyl alcohol (PVA) matrix with high solvent permeability and rapid analyte diffusion. This approach provides robust sensing films with fast response and extended lifetime. To demonstrate the performance characteristics of such films, pH-sensitive indicator dyes were entrapped in vesicle-templated nanocapsules prepared by copolymerization of tert-butyl methacrylate, butyl methacrylate, and ethylene glycol dimethacrylate. As pH sensitive dyes, Nile blue A, bromophenol blue, and acid fuchsin were tested. Time-resolved absorbance measurements showed that the rate of the color change is controlled by the rate of diffusion of protons in the hydrogel. The pH-induced color change in a ~400 μm thick film is complete within 40 and 60 s. The porous nanocapsule loaded films showed excellent stability and reproducibility in long-term monitoring experiments. Compartmentalization of the indicator dyes within the nanocapsules increased their stability. The matrix caused a shift in the position of the color change of the dye compared to that in an aqueous buffer solution. The encapsulation/immobilization protocol described in this account is expected to be broadly applicable to a variety of indicator dyes in optical sensor applications.

Radio-frequency tag with optoelectronic interface for distributed wireless chemical and biological sensor applications

A battery-free, wireless optical chemical sensor with integral contactless power and data link is demonstrated. The chemical sensor and its optoelectronic interface form an integral part of a radio-frequency tag which we have developed specifically for use as a wireless chemical and biological sensor, and which is compatible with the International Standards Organisation ISO15693 radio-frequency identification (RFID) protocol. The chemical sensor, optoelectronic interface, RFID processor and antenna are designed and fabricated on a credit-card sized tag which is operated in a passive mode using wireless energy transfer to power the sensor and read its response. The optical chemical sensing capability of the RFID tag is demonstrated by measuring pH using a thin sol–gel film containing a pH-sensitive indicator dye, bromocresol green (BCG), as a model chemical sensor interface. The film exhibits a colourimetric response to pH in the range 5.0–8.5 pH units. The optoelectronic interface of the tag comprises a silicon photodiode and two light emitting diode (LED) sources measuring the optical absorption of the pH-induced colour change of the thin film at two discrete wavelengths. The pH response curve and the p K value of the immobilised indicator were determined using the RFID tag system and compared with the results obtained using a standard laboratory spectrophotometer. A good correlation between the measurements was achieved, demonstrating the viable integration of an optical absorption based chemical sensor onto a passive RFID tag. By combining the relative advantages of simple, tuneable, optical sol–gel sensing chemistries and integrating these onto the RFID wireless communication platform, it is possible to envisage in the near future a range of new wireless sensors for distributed industrial, scientific and medical applications, in particular for smart packaging, personal (wearable) diagnostics, and infrastructure-related applications.

The Novel Functional Chromophores Based on Squarylium Dyes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The Novel Functional Chromophores Based on Squarylium Dyes

Squarylium or squaraine dyes are derived from 1,2-dihydroxycyclobuten-3,4-dione, otherwise known as squaric acids. They are two principal types: the 1,2-bisdonorsubstituted derivatives, and the 1,3-bisdonorsubstituted derivatives. The former are essentially merocyanines and have no distinctive properties, whereas the latter represent a unique type of chromophore, which is neither a merocyanines nor cyanine and has exceptional light absorption characteristics. They also have many functional applications based on their special properties. Thus it was the objective of this research project to synthesize a range of 1,3-squarylium dyes of widely differing structural types, and to investigate their light absorption and fluorescence properties in general, and the color change properties of appropriate examples in particular. Also in this study, the various pHinduced colour change processes were examined.

Properties of 3-deoxyanthocyanins from sorghum.

There is increasing interest in natural food colorants with functional properties. Anthocyanins from black, brown (containing tannins), and red sorghums were characterized by spectrophotometric and HPLC techniques. The antioxidant activity and pH stability of the anthocyanins were also determined. Sorghum brans had 3-4 times higher anthocyanin contents than the whole grains. Black sorghum had the highest anthocyanin content (average = 10.1 mg/g in bran). The brown and red sorghum brans had anthocyanin contents of 2.8-4.3 mg/g. Only 3-deoxyanthocyanidins were detected in sorghum. These compounds are more stable to pH-induced color change than the common anthocyanidins and their glycosides. Additionally, crude sorghum anthocyanin extracts were more stable than the pure 3-deoxyanthocyanidins. The antioxidant properties of the 3-deoxyanthocyanidins were similar to those of the anthocyanins. Pigmented sorghum bran has high levels of unique 3-deoxyanthocyanidins, which are stable to change in pH and have a good potential as natural food pigments.

Chitosan Membranes for Optical pH Chemical Sensors

A three-layer membrane for optical pH chemical sensors has been developed consisting of layers of polyester support, chitosan-indicator and polyvinly alcohol-titanium dioxide for reflection. The chitosan membrane was more stable and easier for immobilizing of benzopurprine 4B or fluorescein isothiocyanate than a cellulose membrane on which polyvinyl alcohol with titanium dioxide and calcium carbonate was coated and heated at 140°C in nitrogen atmosphere followed by dissolving of calcium carbonate to form a porous water-resistant membrane for reflection of light. The sensor membrane shows a pH-induced color change than makes it capable of measuring pH in the 3-7 range.

Optical sensor for the pH 10?13 range using a new support material

A pH-sensitive membrane has been developed consisting of a polyester support covered with a thin layer of cellulose onto which a pH-indicator is covalently immobilized. The sensor membrane is completely transparent and shows a pH-induced colour change that makes it capable of measuring pH in the 10–13 range. Its performance was studied with respect to relative signal change, reproducibility, and long-term use. The response time for 90% of the total signal change to occur was 1 min. The material has a response that is stable over hours of operation at high pHs. This is in contrast to conventional glass electrodes which tend to become unstable at high pH, but also suffer from interferences due to the so-called alkali error. Hence, this optrode sensor presents an attractive alternative for measuring the pH of highly alkaline solutions as occurring in chemical industry, scrubbers, and waste water treatment plants. The immobilization scheme is of general interest in that it allows immobilization of vinylsulfonyl dyes with a broad variety of pKa-values, thereby allowing the design of a variety of pH (and other) sensors possessing the same mechanical support.