Rapid Color Change Research Articles

Bioinspired Stimuli‐Responsive Hydrogel with Reversible Switching and Fluorescence Behavior Served as Light‐Controlled Soft Actuators

AbstractStimuli‐responsive materials with multiple functions occupy a significant position in the research of bionic artificial intelligence materials. It is a challenge to integrate rapid shape deformation and color change synergistically by a simple method in the same system. Herein, an effective strategy to develop an anisotropic bilayer hydrogel actuator with unified complex deformation and color change is proposed via combining the near‐infrared (NIR) light‐responsive graphene oxide/poly(N‐isopropylacrylamide) (GO‐PNIPAM) active hydrogel layer and an UV light‐responsive fluorescent poly(acrylic acid [4‐(1,2,2‐triphenylvinyl)] benzyl ester/N‐isopropylacrylamide) passive hydrogel layer. The actuator can undergo light‐controlled sapphire fluorescence color change and complex shape deformation simultaneously or separately under light irradiation. It can be remotely manipulated without the requirement for additional reagents, and the irradiation dosage can be accurately modulated through adjusting the irradiation parameters. This work provides new perspectives of intelligent systems with synergistic multiple functions, including smart robots, environmental sensors, and intelligent biomimetic devices.

Investigation of 4D printing of lotus root-compound pigment gel: Effect of pH on rapid colour change

The feasibility was investigated of 4D printing of lotus root gel compounded with a pigment that responds to pH change and alters colour. The pigment comprised of a combination of anthocyanins and lemon yellow; it was used in gel preparation for printing. The flowability and self-support properties of the lotus root-pigment gel were studied to evaluate its 3D printing performance. The gel viscosity decreased with the increase of printing temperature over the range 40, 50, and 60 °C. The gel with a ratio (lotus root powder/compound pigment) of 0.35 extruded smoothly and maintained high formability at temperatures below 60 °C. The pH response of compound pigment enabled the printed sample to change colour from reddish/yellowish to green after spraying with NaHCO3. The a* and b* values decreased significantly (p < 0.05) after spraying for 1 min. The gel with ratios of 0.30 and 0.35 achieved rapid colour change both superficially and internally. Through several different model designs (apple, Christmas tree, letters, and Chinese characters), high-quality 4D printing could be realized without problem. Thus, lotus root gel can be mixed with suitable pigments in correct proportion for 4D printing at appropriate temperature to ensure good flowability.

Synthesis and biological activities of alcohol extract of black cumin seeds (Bunium persicum)-based gold nanoparticles and their catalytic applications

Abstract Fast, simple, and environmentally friendly gold nanoparticles (Au-NPs) capped and stabilized with black cumin (Bunium persicum) seed alcohol extract are reported. The aqueous gold ions (Au3+) were treated with B. persicum (BP) seed extract, which resulted in a rapid color change to red, indicating the synthesis of Au-NPs. UV-Vis spectroscopy, FTIR, SEM, energy dispersive X-ray (EDX), and X-ray diffraction (XRD) techniques were used to further characterize the Au-NPs. Its stability was assessed against various pH levels and sodium chloride levels (NaCl), different salts of same concentration as well as at a range of temperature (30–100°C). The UV-Vis spectrum in the Au-NPs produced a 540 nm plasmon surface resonance, and a 25–50 nm range of particulates was shown in the SEM analysis. In addition, the FTIR spectra confirmed the inclusion in the capping and decrease of Au-NPs of amines, amide groups, and alcohols. The EDX analysis confirmed the presence of element Au. Furthermore, Au-NPs were tested for enzyme inhibition and antibacterial and antifungal activities and showed remarkable response. These findings have concluded that BP seed extract is an effective bio-reductant of gold nanoparticle synthesis, which can be further applied in different biomedical and pharmaceutical industries.

Slot‐Die Coated Organic UV Indicators and Filters Processed from Green Solvents

AbstractThis work reports the use of the slot‐die (SD) coating solution processing method to fabricate large‐area organic thin films composed of photochromic dyes as UV indicators and UV light absorbers as UV filters on polyethylene terephthalate flexible substrates. This is the first demonstration of large‐area SD coated organic photochromic films and UV filters. Impressively, highly uniform photochromic films comprised of small molecules are formed in air, from green solvents (i.e., alcohols) and show rapid color changes upon external stimuli (i.e., light and heat). The UV filters processed under the same conditions and comprised of only small molecules show highly transparent films in the visible and near‐IR range with T% &gt; 97%@550 nm and excellent UV blocking ability. The work highlights the utility of roll‐to‐roll compatible SD‐coating methods to make prototype organic devices in an academic laboratory setting and opens the door for additive manufacturing of simple and low‐cost UV active films for healthcare and electronic applications.

Sexual selection in a tropical toad: Do female toads choose brighter males in a species with rapid colour change?

AbstractConspicuous visual signals play an important role in animal communication, both within and between species. Bright, colourful signals allow animals to discriminate between individuals and can inform behavioural decisions and social interactions. In many instances, conspicuous colouration appears to have evolved through sexual selection via female mate choice or male–male competition. Male Neotropical yellow toads, Incilius luetkenii, display bright‐yellow colouration during their brief explosive mating events and then revert to a cryptic, female‐like, brown colour following amplexus and fertilization. Recent research has revealed that the yellow colouration of males may serve as a sex identification signal and that males remain yellow in the presence of both males and females but darken without conspecific stimulus. However, there is considerable variation in the brightness of yellow colouration in courting males, ranging from dull olive‐green to vibrant lemon‐yellow. The function of this variation remains unknown. In this study, we conducted two‐choice model presentation trials to test one mechanism of sexual selection that may drive this variation: intersexual selection. Specifically, we set out to determine whether females differentiate between males based on their colouration. We presented females with two hyper‐realistic robotic model toads, with one model painted to match a bright‐yellow male and the other a dull‐yellow male. Using several metrics of choice, we found that females did not show a preference for bright or dull colouration. Our research suggests that variation in the intensity of male breeding colouration is not driven by female choice in this species. Our study is consistent with the idea that there may be limited opportunity for female choice to influence male‐trait expression in explosive breeders. Future research will address whether intrasexual selection may influence colour variation in male yellow toads.

Untangling the structural and molecular mechanisms underlying colour and rapid colour change in a lizard, Agama atra.

With functions as diverse as communication, protection and thermoregulation, coloration is one of the most important traits in lizards. The ability to change colour as a function of varying social and environmental conditions is thus an important innovation. While colour change is present in animals ranging from squids, to fish and reptiles, not much is known about the mechanisms behind it. Traditionally, colour change was attributed to migration of pigments, in particular melanin. More recent work has shown that the changes in nanostructural configuration inside iridophores are able to produce a wide palette of colours. However, the genetic mechanisms underlying colour, and colour change in particular, remain unstudied. Here we use a combination of transcriptomic and microscopic data to show that melanin, iridophores and pteridines are the main colour-producing mechanisms in Agama atra, and provide molecular and structural data suggesting that rapid colour change is achieved via melanin dispersal in combination with iridophore organization. This work demonstrates the power of combining genotypic (gene expression) and phenotypic (microscopy) information for addressing physiological questions, providing a basis for future studies of colour change.

Synthesis and characterization of novel tricyanofuran hydrazone probe: solvatochromism, density-functional theory calculation and selective fluorescence, and colorimetric determination of iron (III).

A tricyanofuran hydrazone (TCFH) spectroscopic probe was produced to visually recognize Fe(III) ions in aqueous environments. The synthesis was started by reacting tricyanofuran with 4-aminophenol diazonium chloride. All the synthesized compounds were characterized by spectroscopic analyses. TCFH showed distinctive solvatochromic behaviour in various organic polar solvents due to intramolecular charge transfer. Its behaviour towards sensing Fe(III) was studied using ultraviolet-visible spectrophotometry. The sensing behaviours of the proposed probe for other metal ions, namely Co(II), Cr(III), Mg(II), Pb(II), Cd(II), Ba(II), Hg(II), Mn(II), Ni(II), Cu(II), Zn(II), Ca(II), Al(III), Na(I) and K(I), were also investigated, but no spectral changes were observed, indicating the probe's potential use as a highly selective and Fe(III)-sensitive colorimetric and fluorescent chemical sensor. The TCFH probe using EtOH/H2 O (5:1; v/v) served as a colorimetric and fluorescent chemosensor for identification of Fe(III) by the naked eye owing to both its high sensitivity and selectivity towards Fe(III) compared with the other examined metal ions. The proposed TCFH probe can therefore be utilized as an effective spectroscopic sensor for Fe(III). Both colorimetric and fluorescence recognition of the analyte depended on the concentration of Fe(III) ions and was accomplished at a pH of 7. A rapid colour change from yellow to red occurred when an aqueous solution of Fe(III) ions was added. The intensity of the colour increased at higher Fe(III) concentrations. Cyclic voltammetry measurements in the dimethylformamide solvent indicated a nonreversible redox potential. This study also explained the possible mechanisms for both solvatochromism and the detection of Fe(III) through TCFH-Fe(III) complex formation. The binding constant of the generated TCFH-Fe(III) complex was explored. Computational modelling was conducted to explain the deprotonation-triggered changes that occur in the photophysical properties of TCFH dyes.

Efficient naked eye sensing of tartrate/malate based on a Zn-Xylenol orange complex in water and membrane-based test strips

A new strategy for the real-time and naked-eye quantitative determination of tartrate and malate in aqueous solutions at physiological pH and with practical polypropylene membrane-based tests strips was developed by straightforward assembly Zn2+ ions and xylenol orange (3,3-bis [N,N-bis(carboxymethyl) aminomethyl]-o-cresolsulfonephthalein tetrasodium sodium salt, XO). The chromogenic dinuclear complex [Zn2 (XO) (H2O)x], 1 was studied in-deep as visual chemosensor for aliphatic dicarboxylates, oxyanions and nucleoside triphosphates. Complex 1 was highly sensitive and selective for visual detection of α-hydroxydicarboxylates such as tartrate and malate over non-hydroxylated dicarboxylates (oxalate, malonate, maleate, fumarate and succinate), citrate, oxyanions and nucleoside triphosphates in micromolar concentration range. Addition of tartrate and malate at pH = 7.4, gave rise to rapid color change from purple to golden with detection limit of 11 μmolL−1 for tartrate. On the basis of spectroscopic tools (UV–Vis, 1H NMR) and DFT calculations the efficient colorimetric change upon addition tartrate is attributed to a complexation process, through simultaneous coordination of the carboxylate and hydroxyl groups, to the Zn atoms with high affinity (log K = 5.08) and binding energy calculated in 8.7 kcal mol−1. The complex 1 is an order the magnitude more selective for tartrate than malate.Finally, the combination of complex 1 with polypropylene membranes negatively charged with carboxylate groups on surface generates flexible and cheap tests strips allows for the selective visual detection of tartrate in micromolar concentration range with good selectivity over other common dicarboxylates and oxyanions.

Rapid beard darkening predicts contest outcome, not copulation success, in bearded dragon lizards

Rapid colour change is widespread in animals and allows them to respond dynamically to the physical and social environment. However, few studies have examined the information conveyed by dynamic colour signals in different social contexts, such as courtship and rivalry contests. Furthermore, dynamic colour change on different body regions may be subject to different selection pressures and therefore serve different functions. We tested whether male colour or colour change predicts contest outcome in male–male interactions or the likelihood of copulation attempts in male–female interactions in the central bearded dragon, Pogona vitticeps . The extent of beard darkening strongly predicted contest outcome, but neither colour (beard, dorsal) nor colour change predicted copulation attempts. Dorsal colour showed little consistent change and did not predict contest outcome or copulation attempts. Previous work shows that dorsal but not beard colour change occurs in response to both background colour and temperature in the laboratory and in the wild. Taken together, these results indicate that dynamic colour change in bearded dragons varies in relation to social context and can serve different functions depending on the body region. Our results add to the growing appreciation of how rapid colour change enables animals to accommodate the multiple functions of colour, including communication to different receivers, camouflage and thermoregulation. • Male bearded dragon lizards change colour during interactions with other lizards. • Winners had darker beards, and their beard changed more than those of losers. • Residency was the strongest predictor of contest outcome. • Neither colour nor the extent of colour change predicted copulation attempts.

Use of biocompatible natural product ‘quinine’ for naked-eye sensing of Sarin-surrogate both in solution-state and vapor phase

A fluorescent, biocompatible natural product, quinine (commercially available at low-cost), has been employed for ratiometric, dual-mode sensing of diethyl chlorophosphate (DCP, a sarin surrogate) in the aqueous medium (using pH 7.0 buffer). The addition of DCP induces a rapid (< 30s) change in solution color from colorless to yellow, accompanied by an appearance of intense blue-colored fluorescence (detection limit: 18 nM). Mechanistic investigation indicates phosphorylation of the hydroxyl unit of quinine in the presence of DCP, followed by protonation at the quinoline nitrogen end. The chemodosimetric adduct, so formed, possesses a conformationally-locked structure with a significantly different charge-transfer state as compared to the parent molecule. Such a bifunctional labeling reaction is found to be highly selective towards DCP, no other warfare chemicals, including diethyl cyanophosphate (DCNP, a tabun surrogate) could render any detectable interference. Further, a solid-supported sensing device has been designed as a sustainable strategy for on-site vapor phase detection of DCP.

Synergistic effects of combinatorial chitosan and polyphenol biomolecules on enhanced antibacterial activity of biofunctionalized silver nanoparticles

The present study reports the synergistic antibacterial activity of biosynthesized silver nanoparticles (AgNPs) with the aid of a combination of chitosan and seaweed-derived polyphenols as a green synthetic route. Under optimum synthesis conditions, the rapid color change from yellowish to dark brown and UV–visible absorption peak at 425 confirmed the initial formation of AgNPs. DLS, TEM, XRD, and EDX analyses revealed the spherical shape of pure biogenic AgNPs with a mean diameter size of 12 nm ± 1.5 nm, and a face-centered cubic crystal structure, respectively. FTIR and TGA results indicated the significant contribution of chitosan and polyphenol components into silver ions bioreduction and thermal stability of freshly formed AgNPs. Long-term colloidal stability of AgNPs was obtained after 6-month storage at room temperature. The bio-prepared AgNPs possessed a negative surface charge with a zeta potential value of − 27 mV. In contrast to naked chemical silver nanoparticles, the green Ag nanosamples demonstrated the distinct synergistic antibacterial in vitro toward all selected human pathogens presumably due to the presence of high content of biomolecules on their surface. The results show that synergy between chitosan and polyphenol results in the enhancement of bactericidal properties of biogenic AgNPs. We also highlighted the underlying mechanism involved in AgNPs formation based on nucleophile–electrophile interaction.

5,7,3\u02b9,4\u02b9-Tetrahydroxyflav-2-en-3-ol 3-O-glucoside, a new biosynthetic precursor of cyanidin 3-O-glucoside in the seed coat of black soybean, Glycine max

The seed coat of mature black soybean, Glycine max, accumulates a high amount of cyanidin 3-O-glucoside (Cy3G), which is the most abundant anthocyanin in nature. In the pod, it takes two months for the seed coat color change from green to black. However, immature green beans rapidly adopt a black color within one day when the shell is removed. We analyzed the components involved in the color change of the seed coat and detected a new precursor of Cy3G, namely 5,7,3ʹ,4ʹ-tetrahydroxyflav-2-en-3-ol 3-O-glucoside (2F3G). Through quantitative analysis using purified and synthetic standard compounds, it was clarified that during this rapid color change, an increase in the Cy3G content was observed along with the corresponding decrease in the 2F3G content. Chemical conversion from 2F3G to Cy3G at pH 5 with air and ferrous ion was observed. Our findings allowed us to propose a new biosynthetic pathway of Cy3G via a colorless glucosylated compound, 2F3G, which was oxidized to give Cy3G.

Facile development of microporous cellulose acetate xerogel immobilized with hydrazone probe for real time vapochromic detection of toxic ammonia

Exposure to colorless ammonia vapor could result in failure of human organs or even death. Thus, it is of great significance to build up a portable quick onsite recognition technique for ammonia vapor. In this context, we report the preparation of highly sensitive, reversible, portable, fast detection time, cost effective solid state microporous cellulose test strips that exhibit a naked-eye colorimetric responsiveness within a fraction of second to ammonia vapor. An easy-to-prepare pH- responsive tricyanofuran-hydrazone (TCFH) dye was developed. The hydrazone recognition unit is able to selectively monitor ammonia over a series of other alkaline organic compounds and solvents. This TCFH was diffused in-situ within the as-prepared microporous cellulose acetate (CA). The size, sensitivity, and subsecond response of this spectroscopic hydrazone probe made them suitable for inclusion into cellulose acetate strips sensor assays (CA-TCFH) and ammonia vapor detection. The aqueous ammonia concentration range between 0.4 and 72 ppb displayed a color shift of the spectroscopic hydrazone dye from yellow to purple. The color shift of CA-TCFH was monitored from yellow to orange, red and purple with increasing the aqueous ammonia concentration, which was studied by color strength and CIE Lab measurements. Cellulose acetate test strip displayed a good detection limit as low as 0.4 ppb of aqueous ammonia. When cellulose sensor strip is subjected to ammonia vapor, the conversion of spectroscopic hydrazone probe into the hydrazone anion form causes a rapid color change. The microporous cellulose acetate showed high porosity with a pore diameter in the range of 4.5–7.5 μm.

One-pot green synthesis of optical fluorescent sensor for selective detection of Ni2+ ions and hydro gel studies

Abstract A Schiff base chemosensor derived from 2-aminophenol and 9-anthracenecarboxaldehyde (APAI) was designed and synthesized in a greener approach. It was prepared by microwave irradiation using few drops of acetic acid. The synthesized chemosensor was characterized by 1H NMR and HR-LCMS mass analysis. Its excellent selectivity towards Ni2+ was examined by both colorimetric and fluorometric sensing techniques. A rapid colour change from yellow to dark brown was observed when Ni2+ was added. Among the employed metals only Ni2+ has notable colour change. In the UV–Visible spectrum a new peak apart from the sensor appeared which confirms the selectivity in sensing. A significant enhancement in fluorescence was observed in presence of Ni2+. Among the various metals Cu2+, Co2+, Zn2+, Cr3+,Mg2+, Hg2+, Fe2+, Fe3+, Cd2+, Pb2+ Al3+, Pd2+, K+, Na+, Cr2O42− investigated no major interference was observed even in higher concentration of analytes with a comparatively lowest detection limits of 0.04 μM. The experimental results are further supported by the DFT studies. The chemosensor is likely to find application in the recovery of contaminated water and hydrogel experiments were carried out in order to support the selective colorimetric detection of Ni2+ by APAI.

Electrostatic spray deposition of chemochromic WO3-Pd sensor for hydrogen leakage detection at room temperature

We demonstrate the chemochromic sensor, which is used to detect hydrogen leaks at room temperature. The structure of the sensor is fabricated via electrostatic spray deposition (ESD) of a solution of Pd and WO3 nanoparticles. ESD enables the uniform distribution of Pd nanoparticles on WO3, with droplets of sub-micron size being generated during the process. With 1% of hydrogen diluted in N2, the optimized sensor shows a rapid color change at room temperature that can be recognized with the naked eye within 15 s. The sensor exhibits a deep blue color in the presence of hydrogen, and this change is quantified by a color difference value of 18.5 in 10 min. The developed sensor is reversible, implying that it can recover its original color when exposed to air, and its reversibility is maintained over 20 cycles. Moreover, the sensor exhibits long-term stability for 40 d. The sensor is also fabricated on adhesive tape, which enables it to demonstrate prompt color change at the hydrogen leakage site.

Rapid colorimetric detection of arsenic (III) by glutathione functionalized gold nanoparticles based on RGB extracting system

A sensitive and selective method for the colorimetric detection of arsenic (AsIII) ions has been demonstrated using glutathione functionalized gold nanoparticles (GSH-AuNPs). When arsenic ions are added to the GSH-AuNPs solution, the binding of arsenic ions with GSH ligands induces the aggregation of AuNPs, resulting in a rapid color change of the solution. With the implementation of a home-developed RGB extracting software, excellent linear correlation has been established between the calculated RGB color values and the arsenic concentrations (R2 = 0.99488). The limit of detection (LOD) of arsenic ions is as low as 0.12 ppb. More significantly, the GSH-AuNPs solution shows excellent detection selectivity to other metal ions (Fe3+, Co2+, Ni2+, K+, Na+, Mg2+, Ca2+, Cu2+, Hg2+, and Pb2+). This method could be applied to on-site and real-time fast detection of low level arsenic ions.

Turn-on fluorescence sensor for selective detection of fluoride ion and its molecular logic gates behavior

Loutonin based emissive probe (L) for the dual sensing of fluoride (F−) and bisulphate (HSO4−) anions in aqueous media. The development is based on reports that the interaction between fluoride and loutonin based fluorescent probe exhibits rapid and remarkable color changes in both colorimetrically as well as fluorimetrically. More amusingly, on the introduction of bisulphate ion into the medium containing loutonin fluoride ion complex (L-F−) which shows both the color and fluorescence has been recovered. The limit of detection for fluoride ions by the probe was determined as 8.62 × 10−7 M by fluorescence titrations. Further the probe L can be employed for the removal of fluoride ions. The need for a dual anion detection system with such an outstanding reversible and reproducible process characteristics led us to consider loutonin as a feasible nominee for the construction of molecular keypad lock and molecular logic circuits. The fluorescence change of loutonin after appendage of fluoride ions is mainly due to the hydrogen bonding interaction. Further, the probe could be potentially incorporated into the test strips and silica gel plates, with better selectivity for fluoride and bisulphate anions in aqueous media.

Cephalopod‐Inspired High Dynamic Range Mechano‐Imaging in Polymeric Materials

AbstractCephalopods, such as squid, cuttlefish, and octopuses, use an array of responsive absorptive and photonic dermal structures to achieve rapid and reversible color changes for spectacular camouflage and signaling displays. Challenges remain in designing synthetic soft materials with similar multiple and dynamic responsivity for the development of optical sensors for the sensitive detection of mechanical stresses and strains. Here, a high dynamic range mechano‐imaging (HDR‐MI) polymeric material integrating physical and chemical mechanochromism is designed providing a continuous optical read‐out of strain upon mechanical deformation. By combining a colloidal photonic array with a mechanically responsive dye, the material architecture significantly improves the mechanochromic sensitivity, which is moreover readily tuned, and expands the range of detectable strains and stresses at both microscopic and nanoscopic length scales. This multi‐functional material is highlighted by creating detailed HDR mechanographs of membrane deformation and around defects using a low‐cost hyperspectral camera, which is found to be in excellent agreement with the results of finite element simulations. This multi‐scale approach to mechano‐sensing and ‐imaging provides a platform to develop mechanochromic composites with high sensitivity and high dynamic mechanical range.

From extraocular photoreception to pigment movement regulation: a new control mechanism of the lanternshark luminescence

The velvet belly lanternshark, Etmopterus spinax, uses counterillumination to disappear in the surrounding blue light of its marine environment. This shark displays hormonally controlled bioluminescence in which melatonin (MT) and prolactin (PRL) trigger light emission, while α-melanocyte-stimulating hormone (α-MSH) and adrenocorticotropic hormone (ACTH) play an inhibitory role. The extraocular encephalopsin (Es-Opn3) was also hypothesized to act as a luminescence regulator. The majority of these compounds (MT, α-MSH, ACTH, opsin) are members of the rapid physiological colour change that regulates the pigment motion within chromatophores in metazoans. Interestingly, the lanternshark photophore comprises a specific iris-like structure (ILS), partially composed of melanophore-like cells, serving as a photophore shutter. Here, we investigated the role of (i) Es-Opn3 and (ii) actors involved in both MT and α-MSH/ACTH pathways on the shark bioluminescence and ILS cell pigment motions. Our results reveal the implication of Es-Opn3, MT, inositol triphosphate (IP3), intracellular calcium, calcium-dependent calmodulin and dynein in the ILS cell pigment aggregation. Conversely, our results highlighted the implication of the α-MSH/ACTH pathway, involving kinesin, in the dispersion of the ILS cell pigment. The lanternshark luminescence then appears to be controlled by the balanced bidirectional motion of ILS cell pigments within the photophore. This suggests a functional link between photoreception and photoemission in the photogenic tissue of lanternsharks and gives precious insights into the bioluminescence control of these organisms.

CMC and CNF-based alizarin incorporated reversible pH-responsive color indicator films

Smart color-changing indicator films were prepared using two different types of cellulose (CMC and CNF) and pH-sensitive dye, alizarin. pH-responsive color indicator films were produced by ionization and deprotonation of hydroxyl groups of alizarin phenolic compounds. The X-ray diffraction pattern of the color indicator film showed a new weak diffraction peak at 2θ = 13°, indicating the semi-crystalline character of alizarin. The indicator film showed UV–vis light screening properties and radical scavenging activity with enhanced thermal stability. The indicator film showed a distinct color change of alizarin from yellow to purple in the pH range of 2−12. In addition, the color indicator film showed stable and reversible color changes even after repeated changes in environmental pH. The pH-responsive color indicator films are likely to be used as an acid or base gas sensor due to the rapid response and reversible color change to the pH change in the packaging environment.