Color Changes In Response Research Articles

FsHemF is involved in the formation of yellow Forsythia leaves by regulating chlorophyll synthesis in response to light intensity

The leaves of Forsythia koreana ‘Suwon Gold’ are yellow under natural light condition and can revert to green when the light intensity is reduced. To understand the molecular mechanism of leaf color changes in response to light intensity, we compared the chlorophyll content and precursor content between yellow- and green-leaf Forsythia under shade and light-recovery conditions. We identified the conversion of coproporphyrin III (Coprogen III) to protoporphyrin IX (Proto IX) as the primary rate-limiting step of chlorophyll biosynthesis in yellow-leaf Forsythia. Further analysis of the activity of the enzymes that catalyze this step and the expression pattern of the chlorophyll biosynthesis-related genes under different light intensities revealed that the negatively regulated expression of FsHemF by light intensity was the major cause affecting the leaf color change in response to light intensity in yellow-leaf Forsythia. To further understand the cause of differential expression pattern of FsHemF in yellow- and green-leaf lines, we compared the coding sequence and promoter sequence of FsHemF between yellow- and green-leaf Forsythia. We found that one G-box light-responsive cis-element was absent in the promoter region of green-leaf lines. To investigate the functional role of FsHemF, we performed virus-induced gene silencing (VIGS) of FsHemF in green-leaf Forsythia, which leads to yellowing leaf veins, decreased chlorophyll b content, and inhibition of chlorophyll biosynthesis. The results will assist in elucidating the mechanism of yellow-leaf Forsythia in response to light intensity.

A Ratiometric Fluorescent Sensor Based on Silicon Quantum Dots and Silver Nanoclusters for Beef Freshness Monitoring

A ratiometric fluorescent sensor with hydrogen sulfide (H2S) and methanthiol (CH3SH) sensitivity was developed to real-time monitor beef freshness. A silicon quantum dots (SiQD) and silver nanoclusters (AgNC) complex, namely SiQD-AgNC, was used as the dual emission fluorescence materials. Due to the fluorescence resonance energy transfer (FRET) effect between SiQD and AgNC, when the fluorescence of AgNC (610 nm) was quenched by H2S or CH3SH, the fluorescence of SiQD (468 nm) recovered, resulting in an increase of the fluorescent intensity ratio (I468/I610). I468/I610 showed a linear relationship with the H2S concentration within the concentration range of 1.125-17 μM, with a limit of detection (LOD) value of 53.6 nM. Meanwhile, I468/I610 presented two linear relationships with the CH3SH concentration within the concentration range of 1.125-17 μM and 23.375-38.25 μM, respectively, with a LOD value of 56.5 nM. The SiQD-AgNC complex was coated on a polyvinylidene fluoride (PVDF) film to form a portable SiQD-AgNC/PVDF film sensor. This film showed purplish red-to-cyan color changes in response to H2S and CH3SH, with LOD values of 224 nM and 233 nM to H2S and CH3SH, respectively. When the film was used to monitor beef freshness at 4 °C, its fluorescent color gradually changed from purplish red to cyan. Hence, this study presented a new ratiometric fluorescent sensor for intelligent food packaging.

An intelligent label using sodium carboxymethyl cellulose and carrageenan for monitoring the freshness of fresh-cut papaya

A novel intelligent label (CNCB) was prepared by casting and drying a mixed solution of sodium carboxymethyl cellulose (CMC-Na) and carrageenan, to which bromothymol blue (BTB) was fixed as the pH indicator. The CNCB label can reply the freshness of fruit through color changes according to the CO2 concentration inside the package. Variations in the three label components were investigated using Fourier transform infrared spectroscopy. Furthermore, the label morphology and structure were evaluated using scanning electron microscopy and X-ray diffractometry. Lastly, the thermal stability of the labels was analyzed using a synchronous thermal analyzer. Carrageenan enhanced the water resistance of the CMC-Na label and improved the mechanical properties. Moreover, while the BTB dye was added to visually indicate color change, its addition improved not only the physical properties but also the thermal stability of the label. The CNCB label showed different color changes in response to different CO2 concentrations. When the CNCB label was stored with fresh-cut papaya, its color changed from blue to green, yellow-green, and eventually yellow-brown as the fruit lost its freshness, displaying a strong correlation with the CO2 concentration in the package. This label prepared from CMC-Na, carrageenan, and BTB, can be used as intelligent label in monitoring the freshness of fresh-cut papaya for the excellent pH sensitivity.

Cholesteric Liquid Crystal Polymeric Coatings for Colorful Artificial Muscles and Motile Humidity Sensor Skin Integrated with Magnetic Composites.

Structural colorful cholesterics show impressive susceptibility to external stimulation, leading to applications in electro/mechano-chromic devices. However, out-of-plane actuation of structural colorful actuators based on cholesterics and the integration with other stimulation remains underdeveloped. Herein, colorful actuators and motile humidity sensors are developed using humidity-responsive cholesteric liquid crystal networks (CLCNs) and magnetic composites. The developed colorful actuator can exhibit synergistic out-of-plane shape morphing and color change in response to humidity, with CLCNs as colorful artificial muscles. Through the integration with magnetic control, the motile sensor can be navigated to open and confined spaces with the aid of friction to detect local relative humidity. The integration of multi-stimulation actuation of cholesteric magnetic actuators will expand the research frontier of structural colorful actuators and motile sensors for confined spaces.

Antioxidant and ammonia-sensitive films based on starch, κ-carrageenan and Oxalis triangularis extract as visual indicator of beef meat spoilage

In this study, we first investigated the rheological property of sweet potato starch (SPS), κ-carrageenan (KC) and Oxalis triangularis extract (OTE) blends and found that the blends exhibited high apparent viscosity with an apparent shear thinning behavior. And then films based on SPS, KC and OTE were developed and their structural and functional properties were studied. The physico-chemical test results showed that OTE exhibited different colors in solutions with different pH values and the incorporation with OTE and KC could significantly increase the thickness, water vapor permeability, light barrier ability, tensile strength and elongation at break as well as the pH- and ammonia-sensitive properties of the SPS film. The structural property test results showed that some intermolecular interactions between OTE and SPS/KC occurred in SPS-KC-OTE films. Finally, the functional properties of SPS-KC-OTE films were examined and SPS-KC-OTE films showed significant DPPH radical scavenging activity as well as a visible color change in response to changes in beef meat freshness. Our results suggested that the SPS-KC-OTE films could be used as an active and intelligent food packaging material in food industry.

A metastable molecular array guided by the synergy of confinement and charge repulsion for piezochromic sensors

Piezochromic fluorescent materials have attracted the interest of the scientific community due to their obvious fluorescence emission or color change in response to external pressure or mechanical grinding stimulation.

Taisho-Sanshoku koi have hardly faded skin and show attenuated melanophore sensitivity to adrenaline and melanin-concentrating hormone.

Koi carp, an ornamental fish derived from the common carp Cyprinus carpio (CC), is characterized by beautiful skin color patterns. However, the mechanism that gives rise to the characteristic vivid skin coloration of koi carp has not been clarified. The skin coloration of many teleosts changes in response to differences in the background color. This change in skin coloration is caused by diffusion or aggregation of pigment granules in chromatophores and is regulated mainly by sympathetic nerves and hormones. We hypothesized that there would be some abnormality in the mechanism of skin color regulation in koi carp, which impairs skin color fading in response to background color. We compared the function of melanin-concentrating hormone (MCH), noradrenaline, and adrenaline in CC and Taisho-Sanshoku (TS), a variety of tri-colored koi. In CC acclimated to a white background, the skin color became paler and pigment granules aggregated in melanophores in the scales compared to that in black-acclimated CC. There were no clear differences in skin color or pigment granule aggregation in white- or black-acclimated TS. The expression of mch1 mRNA in the brain was higher in the white-acclimated CC than that in the black-acclimated CC. However, the expression of mch1 mRNA in the brain in the TS did not change in response to the background color. Additionally, plasma MCH levels did not differ between white- and black-acclimated fish in either CC or TS. In vitro experiments showed that noradrenaline induced pigment aggregation in scale melanophores in both CC and TS, whereas adrenaline induced pigment aggregation in the CC but not in the TS. In vitro administration of MCH induced pigment granule aggregation in the CC but not in the TS. However, intraperitoneal injection of MCH resulted in pigment granule aggregation in both CC and TS. Collectively, these results suggest that the weak sensitivity of scale melanophores to MCH and adrenaline might be responsible for the lack of skin color change in response to background color in the TS.

Color Stability of Alkasite Restorative Material: in vitro Studies

The purpose of this study is was to compare the color stability of alkasite and other restorative materials commonly used in the field of pediatric dentistry and to study a color change in response to various beverages. Test specimens of glass ionomer, resin modified glass ionomer, alkasite restorative material, and composite resin were prepared, and the color stability was measured after thermocycling. Each specimen was also subdivided into 5 groups and submerged in PBS, coffee, green tea, coke, and orange juice to analyze the color change from the original CIE <i>L*a*b*</i> values after 7, 14, 21, and 28 days. Composite resin showed the best color stability after thermocycling, followed by alkasite restorative material, glass ionomer, and resin modified glass ionomer. Submerging in various beverages for 7 days resulted in color change in all test specimens, with alkasite restorative material showing less color change than glass ionomer but greater change than composite resin. Alkasite restorative material showed the greatest color change in coffee, followed by green tea and orange juice, but almost no change in coke and PBS even after 28 days of submersion.

Independent dual-responsive luminous composite fibers with controllable full-color emissions

Accumulated ultraviolet (UV) under high temperature is prone to cause photoaging, skin burns, and even induce skin cancers during outdoor activities. Fiber-based wearable sensors with color-tunable luminescent ability are urgently demanded for real-time monitoring of human health conditions to enhance personal awareness of these hazards. To achieve tunable full-color emission, a set of three primary colors (red, green, and blue) of rare-earth doped persistent luminescent phosphors are successfully synthesized. After simply mixing them with particular ratios, a tunable full-color emission system can be realized. Herein, by integrating the thermochromic dyes, photochromic dyes, and luminescent phosphors directly into polyacrylonitrile (PAN) matrix, novel thermo-UV-sensing composite fibers with color-tunable luminescent ability are prepared via the facile wet-spinning process. The obtained fibers can be switched among four different colors with brilliant reversible color changes in response to temperature and UV irradiation both independently and in combination. Besides, the fibers can emit tunable emissions under in full spectral range 365 nm excitation. This work paves the way for as-prepared fibers for diverse applications including energy-free, wearable real-time monitors of the temperature/UV, and high-level information encryption.

Alginic Acid Beads Containing Fluorescent Solvatochromic Dyes Display an Emission Color Response to a Cationic Surfactant.

Lipophilic fluorescent dyes can be employed as sensors for surfactants present in concentrations above the critical micellar concentration (CMC) where the dyes are monodispersed in micelles. However, the surfactant concentration range over which these dyes are effective is narrowed because by the sigmoidal nature of their responses. To overcome this limitation, we developed a novel sensor material comprised of a labeled fluorescent solvatochromic dye covalently bonded to alginate gel, which is known to strongly adsorb cationic surfactants. We hypothesized that the dye-alginate conjugate would undergo fluorescent color changes in response to binding of surfactants which alter the polarity of the surrounding environment. Indeed, addition of the representative cationic surfactant, cetylpyridinium chloride (CPC), to an aqueous solution of the alginate conjugated fluorescent solvatochromic dye leads to a visible fluorescent color change when the concentration of CPC is below the CMC. The average values of the color appearance parameter, referred to as a hue, of light emitted from gels, calculated by analysis of fluorescence microscopy images using ImageJ software, were found to be approximately linearly dependent on the concentration of CPC encapsulated in the alginate-fluorescent dye complex. This finding shows that absorbed CPC can be quantitatively determined over a wide concentration range in the form of simple fluorescence wavelength or visible responses.

Preparation and characterization of antioxidant and pH-sensitive films based on arrowhead (Sagittaria sagittifolia) starch, κ-carrageenan and black chokeberry (Aronia melanocarpa) extract for monitoring spoilage of chicken wings

In this study, we firstly developed an antioxidant and pH-sensitive film based on arrowhead starch (AS), κ-carrageenan (KC) and black chokeberry extract (BCE) and its physical and structural properties were investigated. We found BCE showed different colors in different pH solutions and incorporation with KC and BCE could significantly decrease light transmittance, increase thickness, elongation at break and pH-sensitive property of AS film. The results of structural property assay indicated that there were some intermolecular interactions between BCE and AS/KC in AS-KC-BCE films. Secondly, we investigated the rheological property of AS, AS-KC and AS-KC-BCE suspensions and found the suspensions showed an obvious shear-thinning behavior with high apparent viscosity. Finally, the functional properties of AS-KC-BCE films were investigated and AS-KC-BCE films showed strong scavenging activity on DPPH free radical and presented visible colour changes in response to the changes of the chicken wing qualities. The results suggest that AS-KC-BCE films can be used in active and intelligent packaging of food industry.

Liquid Crystal Nanoparticle Actuator by Polymer Surfactant-Assisted Assembly for Fabricating Bioinspired Smart Interface with Adjustable Light and Changeable Color

Fabrication of bioinspired intelligent materials with adjustable light, self-shading, and tunable color performances is a significant challenge in the fields of advanced materials. In this work, a liquid crystal nanoparticle actuator (LCNA) with photo-humidity stimuli responses was designed, which was supramolecular self-assembled by the surfactant-assisted method from a functional liquid crystal molecule 2-(3′,3′-dimethyl-6-nitrospiro[chromene-2,2′-indolin]-1′-yl)ethyl dodecyl phthalate (EDP-SP). Bionic films containing the LCNA showed adjustable light, self-shading, and color changes in response to environmental light and humidity stimuli. The self-assembled amphiphilic nanoparticles greatly improved the stimuli-responsive sensitivity. A bionic nanoactuator was triggered by multiple supramolecular interactions, such as the rearrangement of liquid crystal molecules, the interactions of intermolecular hydrogen bonds, and the photoisomerization in the nanoparticles. They show excellent dimming and color-changing sensitivity and reversibility in real time. Bionic interfaces containing the self-assembled LCNA attract much interest and have many potential applications in 3D printing, smart textiles, and artificial bionic skin.

Structural Color Controllable Humidity Response Chiral Nematic Cellulose Nanocrystalline Film.

Through self-assembly, environmentally friendly cellulose nanocrystals (CNCs) can form films with a photonic crystal structure whose pitch size can be adjusted in a variety of ways at the fabrication stage. Moreover, the films exhibit response performance to multiple stimuli, which offers extensive applications. Poly(ethylene glycol) (PEG) and CNCs combine to form a smaller chiral nematic domain that develops a solid film with a uniform spiral structure when slowly dried. By changing the composition of CNCs and PEG, flexible and flat photonic composite films with uniform structural colors from blue to red are prepared. Benefiting from the change in pitch size by insertion and detachment of water molecules into the chiral nematic structure, CNCs films and CNC-PEG composite films exhibit a reversible structural color change in response to different humidity. In addition, the chiral nematic films formed by the combination of glycerol and CNCs have a reversible stimulation response to hydrochloric acid gas. Similarly, adjusting the ratio of glycerol can control the pitch size of the films and, thus, the reflective color. In summary, the pitch size of the photonic crystal structure of the films can be precisely tuned by regulating the additive ratio, and the two prepared films have reversible responses to humidity and hydrochloric acid gas, respectively. The CNC-based films show promise in the application of colorimetric biosensors.

Glucose‐sensitive structural color change of cholesteric liquid crystal formed by hydroxypropyl cellulose with phenylboronic acid moieties

AbstractDeveloping durable and simple glucose sensing materials is essential to enable the general population an easy method for testing their glucose levels under different environmental conditions. Hence, materials that enable enzyme‐free and intuitive glucose sensing are required. In this study, a system based on an aqueous solution, which enables simple colorimetric glucose detection without the use of enzymes, was developed. The solutions were prepared by dissolving hydroxypropyl cellulose with phenylboronic acid (PBA) moieties (PBA‐HPC) in water. The aqueous solutions with a high concentration of PBA‐HPC formed a lyotropic cholesteric liquid crystal (ChLC) and exhibited structural color originating from the selective reflection of circularly polarized light. PBA‐HPC ChLC aqueous solutions exhibited a color change in response to the increase in the glucose concentration in the solutions. This can be attributed to the change in the side‐chain structure of the PBA‐HPC caused by the formation of a complex between the PBA moieties and glucose, which induced a change in the cholesteric helical pitch. Thus, the proposed system can be used as a durable and simple enzyme‐free glucose sensing material.

Development of highly stable color indicator films based on κ-carrageenan, silver nanoparticle and red grape skin anthocyanin for marine fish freshness assessment

Color indicator films for fish freshness were fabricated by incorporating κ-carrageenan (CAR) polymer with red grape skin extract (GSE) as a pH-sensing agent and silver nanoparticles (AgNPs) as an antimicrobial agent. Anthocyanins in GSE exhibited distinguished pH responsive color changes. GSE and AgNPs were well compatible with CAR with intramolecular interactions, approved by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis, thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). GSE-containing films displayed distinguished color changes in response to pH variations and volatile ammonia. Enhanced UV blocking ability and strong antioxidant activity were revealed for GSE included films without sacrificing the physico-chemical properties of the CAR film. Films containing AgNPs showed improved mechanical strength and strong antimicrobial ability against both Escherichia coli and Staphylococcus aureus. The CAR/AgNPs/GSE film displayed a distinctive color change corresponding to changes in the total volatile basic nitrogen (TVB-N) of fish during storage. In addition, the CAR/AgNPs/GSE film showed excellent color stability to consecutive UV exposure and its storage time at 25 °C is expected to be at least 240 days, which indicates that it has high potential as an intelligent food freshness indicator film.

Colorimetric indicators of açaí anthocyanin extract in the biodegradable polymer matrix to indicate fresh shrimp

Colorimetric indicator or freshness indicators hold great potential to reduce food waste. Films off açaí anthocyanins extract (AE) with different concentrations molars of two plasticizers glycerol (GLY) or triethyl citrate (TEC), for application fresh shrimp, real time were evaluated. The AE undergoes a visible pink/violet to green/yellowish color change in response to different pH's, which is an indicator of microbial spoilage in shrimp. The CI were exposed to ammonia, and analyzed through infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), ultraviolet spectroscopy, and visual colorimetric. The immobilization of the plasticizers into the CA polymer matrices were confirmed through FT-IR spectra and SEM micrographs. In vitro chromatic transition of the indicators exposed to ammonia vapors, were visually more perceptible when they were produced with 7.2 mols of GLY or 1.8, 3.6, and 7.2 mols of TEC. For the real-time analysis of the application of colorimetric indicators in gray shrimp samples, the indicators that had plasticizers showed perfect color change at the exact time of food deterioration. The colorimetric indicators developed in this study using different molar concentrations of plasticizers are simple, effective and a great eco-friendly alternative to chemical sensors already developed so far.

Direct Ink Writing of 4D Structural Colors

AbstractAdditive manufacturing with stimuli‐responsive materials—4D printing—is a rapidly growing field, with direct ink writing allowing deposition of a wide variety of materials. The synthesis of a humidity‐sensitive cholesteric liquid crystal oligomer ink is reported. With the responsive cholesteric ink, demonstrator devices exhibiting the ink's “four dimensionality” are printed in disparate fashions: as a structural color change or as a preprogrammed deformation mode. After printing, the photonic ink changes color in response to atmospheric humidity, demonstrated as a hydrochromic coating precisely deposited atop a 3D‐printed beetle. After activation in aqueous acid, the beetle exhibits vibrant color shifts across the visible spectrum. Alternatively, a scallop‐inspired actuator with a 3D‐programmed structural color is selectively treated with acid, to allow reversible “opening” and “closing” when exposed to humid and dry air, respectively. The ink enables additive manufacturing of both monolithic and multimaterial stimuli‐responsive, shape‐changing, structurally colored objects, toward broad application of cholesterics in future “smart,” 4D structurally colored devices.

Dynamic Anticounterfeiting Through Novel Photochromic Spiropyran-Based Switch@Ln-MOF Composites.

Fluorescent materials presenting unique color changes in response to external stimuli have wide applications in information storage and anticounterfeiting. However, developing intelligent fluorescent materials with high security levels and dynamically displaying encrypted information is still a challenge. Herein, we report a new method for constructing excellent fluorescent materials by loading the photochromic molecule spiropyran into a lanthanide metal-organic framework. Controlling the isomerization of the spiropyran unit regulates the fluorescence resonance energy transfer (FRET) mechanism between the spiropyran acceptor and the lanthanide donor, leading to an exceptional reversible absorption/luminescence modulation ability. As the irradiation time is extended, the fluorescent color changes continuously from yellow-greenish to orange and then to red through the FRET process within 60 s. This composite system has great potential in anticounterfeiting because of the following advantages: (1) the materials have different fluorescence emissions and optical colors regulated by ultraviolet radiation, which is convenient for designing complex anticounterfeiting patterns; (2) the system can be repeatedly verified quickly and exhibit dynamic fluorescence color within 60 s, having great potential in advanced anticounterfeiting, where time is key in encryption/decryption. These unique advantages will greatly enhance the reliability of anticounterfeiting measures and increase the difficulty of anticounterfeiting.

Functionalized organic–inorganic hybrid composites used as colorimetric chemosensors for hydrogen sulfide detection

AbstractDetection of trace‐level hydrogen sulfide (H2S) gas is of great importance both in industrial production and disease diagnosis. In this article, two simple but smart colorimetric chemosensors for H2S detection were designed based upon the principle of colorimetric reaction. Ag NPs, as the main detection agent was loaded onto the primary carrier, silica sulfonic acid. Thus, a silver‐modified silica sulfonic acid (Ag‐SSA) was prepared successfully. Then the Ag‐SSA was integrated with two kinds of secondary substrate materials. One is the cotton‐woven textile and the other one is polyvinyl alcohol (PVA) nanofibrous membrane. Finally, two functionalized organic–inorganic hybrid composite systems for H2S detection were formed. Both of them were able to exhibit a rapid visual color change in response to H2S. Ag‐SSA/cotton textile was tested in the aqueous state and the limit of detection (LOD) of H2S solution was around 10−6 mol/L. For the Ag‐SSA/PVA nanofibers membrane detected in the atmospheric condition, the LOD of H2S gas reached 6.5 ppm. This research has been successfully demonstrated for the application in sensitive and selective detection of hydrogen sulfide in aqueous solution and gaseous state.

Pt/WO3 Nanoparticle-Dispersed Polydimethylsiloxane Membranes for Transparent and Flexible Hydrogen Gas Leakage Sensors.

Hydrogen gas is a promising, clean, and highly efficient energy source. However, to use combustible H2 gas safety, high-performance and safe gas leakage sensors are required. In this study, transparent and flexible platinum-catalyst-loaded tungsten trioxide (Pt/WO3) nanoparticle-dispersed membranes were prepared as H2 gas leakage sensors. The nanoparticle-dispersed membrane with a Pt:W compositional ratio of 1:13 was transparent and exhibited a sufficient color change in response to H2 gas. The membrane containing 0.75 wt.% of Pt/WO3 nanoparticles exhibited high transparency over a wide wavelength range and the largest transmittance change in response to H2 gas among the others. The heat treatment of the particles at 573 K provided sufficient crystallinity and an accessible area for a gasochromic reaction, resulting in a rapid and sensitive response to the presence of H2 gas. The lower limit of detection of the optimized Pt/WO3 nanoparticle-dispersed membrane by naked eye was 0.4%, which was one-tenth of the minimum explosive concentration. This novel membrane was transparent as well as flexible and exhibited a clear and rapid color response to H2. Therefore, it is an ideal candidate sensor for the safe and easy detection of H2 gas leakage.