Rapid Color Research Articles

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.

Use of Tris-NH4Cl in modified G4/hemin DNAzyme assay with duplexed probes extends life of colorized radical product

The split G-quadruplex/hemin DNAzyme exhibits peroxidase-like activity and catalyzes the oxidation of colorless 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS2−) to the green-colored radical ABTS∙− in the presence of H2O2. The two major challenges to overcome are the relatively low catalytic activity and the short color retention after catalytic action with the substrate ABTS2−. We improved the sensitivity of the G-quadruplex DNAzyme-based DNA assay by utilizing split (duplex) DNAzyme hybridization and adjusting reagent concentrations under limited temperature and pH conditions. Significant improvements in sensitivity and stability were achieved using the activator Triton X-100 and NH4+ as compared to traditional K+. In addition, we demonstrate that the rapid color bleaching of the catalytic substrate ABTS2− is due to the disproportionation of the green-colored reaction product ABTS∙− by H2O2 rather than the degradation of hemin by H2O2. Since residual H2O2 remains after the primary catalytic reaction, the Tris-NH4Cl buffer preserves the radical by removing H2O2 that remains after completion of the primary reaction before it scavenges the radical product. This improved split G-quadruplex DNAzyme formulation can be used to detect various targets conveniently and rapidly, and the test results are stable for more than three days.

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.

Early visualization of skin burn severity using a topically applied dye-loaded liquid bandage

Skin burns are a significant source of injury in both military and civilian sectors. They are especially problematic in low resource environments where non-fatal injuries can lead to high morbidity rates, prolonged hospitalization, and disability. These multifaceted wounds can be highly complex and must be quickly diagnosed and treated to achieve optimal outcomes. When the appropriate resources are available, the current gold standard for assessing skin burns is through tissue punch biopsies followed by histological analysis. Apart from being invasive, costly, and time-consuming, this method can suffer from heterogeneous sampling errors when interrogating large burn areas. Here we present a practical method for the early visualization of skin burn severity using a topically applied fluorescein-loaded liquid bandage and an unmodified commercial digital camera. Quantitative linear mixed effects models of color images from a four day porcine burn study demonstrate that colorimetric changes within the HSB colorspace can be used to estimate burn depth severity immediately after burning. The finding was verified using fluorescence imaging, tissue cross-sectioning, and histopathology. This low-cost, rapid, and non-invasive color analysis approach demonstrates the potential of dye-loaded liquid bandages as a method for skin burn assessment in settings such as emergency medicine triage and low resource environments.

First report of rapid eye color change in a non‐avian tetrapod

AbstractLike coloration of the integument, eye color can be a significant but understudied component of communication and reproductive behavior. Eye color can change with sexual maturation and become sexually dimorphic, but in a few birds and fish, eye color can also change rapidly in response to the environment. There are few cases of the latter, and we report here several instances of such change in eye color in the Eastern box turtle (Terrapene carolina carolina), the first non‐avian tetrapod in which this capability has been reported. In male turtles, the iris changed from a pale yellow color (often characteristic of juveniles) to a bright red color (characteristic of mature males) in a period of <5 s. The nature of the color change is similar to that observed in some birds and suggests a common mechanism and/or adaptive role, which could be further explored in Eastern box turtles.

A fluorimetric water-soluble polymeric pH chemosensor for extremely acidic conditions: Live-cell and bacterial imaging application

In this study, a novel water-soluble difluoroboron dipyrromethene (BODIPY)-based polymeric fluorescent probe (P1) suitable for extremely acidic conditions is synthesized. Compared to conventional small-molecule-based organic pH sensors, the P1 polymeric probe exhibits excellent solubility and long-term stability in water, with instantaneous fluorimetric response to pH changes. This extreme pH response is attributed to protonation of tertiary amine groups of the BODIPY segment, which suppresses photo-induced electron transfer (PET) from the tertiary amine to the BODIPY skeleton. This mechanism is supported by density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The P1 also displays high selectivity, reversibility, and low cytotoxicity even at high concentration. Also, its fluorescence response in acidic pH is investigated for in vitro cell imaging and E. coli bacterial imaging experiments. Additionally, the feasibility of immobilizing the P1 on test paper highlights potential as a real-time probe for rapid color change via drop-casting of the pH solution (below pH 4). Through alternative exposure of hydrochloric acid/ammonia (acid/base) vapor, the P1 is also projected as an indirect ammonia vapor indicator.

Continuously Processed, Long Electrochromic Fibers with Multi-Environmental Stability.

Smart textiles and clothing with highly controllable and tunable color changes are gaining interest because of their promising functionality. However, practical applications are still restricted by the lack of continuously processed long color-changing fibers that are suitable for industrial weaving. This work presents smart electrochromic (EC) fibers with long-range controllability and multi-environmental stability that were continuously prepared using custom-built equipment. By introducing various EC-active materials (viologens) and a unique device design (parallel dual-counter-electrode structure), multiple uniform and rapid color changes were achieved over long time ranges, including blue, magenta, green, and dull red. Furthermore, an electrochemical anticorrosive layer and outer polymer protective layer were used to enhance the electrochemical, mechanical, washing, irradiation, and thermal stabilities of the EC fibers. These fibers were knitted to form large-area, smart color-changing textiles and implanted into textiles with complex patterns to demonstrate two potential EC fiber applications in adaptive camouflage and wearable displays.

Toward Easy-to-Assemble, Large-Area Smart Windows: All-in-One Cross-Linked Electrochromic Material and Device.

Conventional electrochromic devices with a sandwich structure consist of multiple interfaces, which enhance electron trapping on the interfaces. Furthermore, crack generation in the electrochromic layer is inevitable due to repeated ion insertion and extraction during the service process. These problems increase the fabrication complexity and lead to poor performance and stability, which are severely limiting and prime concerns for the future development of the electrochromism field. Here, a strategy of synthesizing an all-in-one self-healing electrochromic material, TAFPy-MA, is presented, which has been utilized for the fabrication of a high-reliability, large-scale, and easy-assembly smart electrochromic window. The all-in-one self-healing electrochromic material can undergo in situ redox reactions with Li+ ions to reduce resistance transfer and avoid interface obstacles, and the reversible Diels-Alder cross-linking network structure can heal the cracks to improve the reliability of the electrochromic layer. High ion diffusivity (1.13 × 10-5 cm2 s-1), rapid color switching (3.9/3.7 s), high coloration efficiency (413 cm2 C-1), excellent stability (sustains 88.7% after 1000 cycles) and reliability (crack can be healed in 110 s), and large-scale smart windows (30 × 35 cm2) are achieved using the all-in-one electrochromic material, which exhibits fascinating and promising features for a wide range of applications in buildings, airplanes, etc.

Smart pH response flexible sensor based on calcium alginate fibers incorporated with natural dye for wound healing monitoring

A kind of smart calcium alginate fiber having pH indicating properties was proposed to monitor wound healing. The smart calcium alginate fiber was prepared by dyeing the hydroxypropyl trimethyl ammonium chloride chitosan (HACC) modified calcium alginate fiber with alizarin dye and anthocyanin dye, respectively. It was worth noting that modification of calcium alginate fibers with HACC enhanced the dyeing and antibacterial properties, simultaneously. When the concentration of HACC was 10 g/L, the modified calcium alginate fiber had the best dyeing performance. At the same time, the dyeing process had no significant influence on the mechanical properties of the fibers with the strength loss only around 0.2 cN/dtex. The smart calcium alginate fibers exhibited a rapid and significant color change and reversible color response at pH 2–11. Moreover, the color change could be easily observed by naked eye. Therefore, the prepared calcium alginate fibers could be a good candidate for intelligent wound dressings for visual monitoring of wound healing.

Robust, rapid, and ultrasensitive colorimetric sensors through dye chemisorption on poly-cationic nanodots

Colorimetric sensors were fabricated by incorporation of anionic colorimetric probes on a hierarchical nanofibrous membrane containing poly-cationic nanodots through intense electrostatic interaction. Unique poly-cationic nanodots were covalently grown on poly (4-vinylpyridine)/polyacrylonitrile nanofibrous membrane through a self-propagation reaction of 2-diethylaminoethyl chloride (DEAE-Cl). The nanodots on the nanofiber surfaces possess strong adsorption affinity and high adsorption capacity toward anionic probes, which contributed to excellent detection sensitivity and sensor stability compared with the co-electrospun sensor. As a proof-of-concept study, phenol red was selected to functionalize the as-fabricated substrate (polyDEAE@P4VP/PAN NFM) to a colorimetric sensor, which shows responses to alkaline vapors. The as-fabricated sensor showed rapid color changes to ammonia and triethylamine (response time < 10 s), whose detection limits reached 1 ppm and 5 ppm, respectively. The sensor can be repeatedly used for at least 20 cycles by regenerating it in air for 1 min. Taking advantage of the intense attractive force between poly-cationic nanodots and anionic probes, polyDEAE@P4VP/PAN NFM is a promising media to be used for the development of robust, rapid, and ultrasensitive colorimetric sensors.

Phenotypic flexibility in background-mediated color change in sticklebacks.

Phenotypic flexibility may incur a selective advantage in changing and heterogeneous environments, and is increasingly recognized as an integral aspect of organismal adaptation. Despite the widespread occurrence and potential importance of rapid and reversible background-mediated color change for predator avoidance, knowledge gaps remain regarding its adaptive value, repeatability within individuals, phenotypic correlates, and whether its expression is context dependent. We used manipulative experiments to investigate these issues in two fish species, the three-spined stickleback (Gasterosteus aculeatus) and nine-spined stickleback (Pungitius pungitius). We sequentially exposed individuals to dark and light visual background treatments, quantified color change from video recordings, and examined associations of color change with phenotypic dimensions that can influence the outcome of predator-prey interactions. G. aculeatus expressed a greater degree of color change compared to P. pungitius. In G. aculeatus, the color change response was repeatable within individuals. Moreover, the color change response was independent of body size but affected by sex and boldness, with males and bolder individuals changing less. Infection by the parasite Schistocephalus solidus did not affect the degree of color change, but it did modulate its association with sex and boldness. G. aculeatus adjusted the expression of color change in response to predation risk, with enhanced color change expression in individuals exposed to either simulated attacks, or olfactory cues from a natural predator. These results provide novel evidence on repeatability, correlated traits, and context dependence in the color change response and highlight how a suite of factors can contribute to individual variation in phenotypic flexibility.

Luminescent Sm(III) complex bearing dynamic imine bonds as a multi-responsive fluorescent sensor for F− and PO43− anions together with Zn2+ cation in water samples

We have designed and synthesized a new luminescent mononuclear samarium (III) complex Sm-2h based on the [1 + 1] Schiff-base macrocycle H2L2h, derived from the cyclocondensation reaction between dialdehyde and diamine precursors, and its exact architecture is determined to be [Sm(HL2h) (NO3)2]. The sensing ability of complex Sm-2h is carefully evaluated for various common inorganic ions in solution. It is shown that complex Sm-2h is a multi-responsive fluorimetric sensor with high selectivity for F− and PO43− anions together with Zn2+ cation. The sensing process is rapid within 60 s for F− and PO43− ions and 300 s for Zn2+ ion. Further detailed responsive investigations suggest that its sensing behavior has excellent linear relationship between the fluorescence intensity (or absorption value) and ion concentration. The limit of detection (LOD) for sensing F−, PO43− and Zn2+ ions are as low as 2.61 μM (2.94 μM), 1.92 μM (1.64 μM) and 5.67 μM (3.53 μM), respectively, verified by fluorimetric (or colorimetric) titration experiments. ESI mass spectra prove that these efficient detections originate from the structure collapse of sensor Sm-2h because of the ion-induced imine bond breakage. Moreover, sensor Sm-2h shows excellent sensing performances for F−, PO43− and Zn2+ ions in real water samples, and we also have developed a convenient method to detect these three ions by use of the sensor impregnated test paper strips, providing rapid and distinguishable fluorimetric color changes. Therefore, the macrocyclic Sm(III) complex Sm-2h could be regarded as a valuable candidate for monitoring F−, PO43− and Zn2+ ions in practical applications.

Urchin peroxidase-mimicking Au@Pt nanoparticles as a label in lateral flow immunoassay: impact of nanoparticle composition on detection limit of Clavibacter michiganensis.

The influence of Au@Pt nanoparticles' composition, morphology, and peroxidase-mimicking activity on the limit of detection (LOD) of lateral flow immunoassay (LFIA) has been investigated. Fourteen types of nanoparticles were synthesized by varying the concentration of Pt4+ (20-2000μM), using gold nanoparticles (GNP, diameter 20.0 ± 2.6nm) as the seeds and ascorbic acid as a reducing agent. Au@Pt nanoparticles and GNPs were conjugated with antibodies specific to the target analyte, a widespread and dangerous phytopathogenic bacteria species (Clavibacter michiganensis). We found that the 100-fold growth of the Pt4+ concentration was accompanied by an increase of the Au@Pt nanoparticle diameter (24-55nm) and surface area with the formation of urchin-shaped morphology. These changes led to a 70-fold increase in peroxidase-mimicking activity in the solution (specific activity 0.06-4.4Umg-1) and a 30-fold decrease in LOD using the catalytic activity of Au@Pt. The Au@Pt nanoparticles synthesized at 1000-2000μM of Pt4+ demonstrated statistically indistinguishable catalytic activity. The highest sensitivity of LFIA was reached for Au@Pt nanoparticles synthesized at Pt4+ concentration equal to1000μM. Au@Pt nanoparticles saved most of their peroxidase-mimicking activity, whereas endogenous plant peroxidases were completely inhibited by sodium azide. The LOD of LFIA with Au@Pt nanoparticles synthesized at 1200μM of Pt4+ was 300colony-forming units (CFU) per mL of buffer and 500CFU per mL of potato tuber extract, which provides 330- and 200-fold improvement compared tothe conventional LFIA with GNPs. The assay consists of three rapid 5-min stages, namely, extraction, lateral flow, and color enhancement (oxidation of diaminobenzidine by Au@Pt nanoparticles). LFIA with the urchin Au@Pt nanoparticles allows the detection of latent bacterial infections rapidly without equipment or special skills. Graphical abstract.

Effect of Temperature on the Composition of a Synthetic Hydrocarbon Aviation Lubricating Oil.

Synthetic hydrocarbon aviation lubricating oils (SHALOs) gradually degrade over time when subjected to high temperatures, resulting in their composition and properties varying over the operation lifetime. Therefore, understanding the SHALO degradation properties by elucidating the mechanism on a molecular level, as a function of high temperature, is of interest. A SHALO was subjected to thermal treatment (TT) at 180, 200, 230, 250, 270, or 300 °C for 2 h. The chemical compositions of six TT samples and one fresh oil were analyzed by fourier transform infrared F spectroscopy, advanced polymer chromatography, and gas chromatography/mass spectrometry. Furthermore, the physicochemical properties, such as kinematic viscosity, pour point, and acid number, of seven samples were determined. The oil samples were grouped by cluster analysis (CA) using a statistical method. The SHALO was identified to comprise 20 functional groups, including comb-like alkanes, long-chain diesters, amines, phenols, and other compounds. TT at <230 °C caused partial cracking of the SHALO base oils, with a concomitant change in the antioxidant content and type, and the polycondensation reactions were dominant. The observed antioxidant changes were not obvious from TT at >230 °C. A large number of small-molecule compounds were detected, including n-alkanes and olefins. TT at 250 °C was shown to be an important threshold for the kinematic viscosity, pour point, and acid number of the samples. Below 250 °C, the sample properties were relatively stable; but at elevated TT temperatures (>250 °C), the properties were observed to dramatically degrade. As the sample color was highly sensitive to temperature, the TT temperature induced rapid and significant color changes. The CA analysis results for the oil compounds at the molecular level were in good agreement with observed changes in the physicochemical properties at the macro level.

Interactively Full‐Color Changeable Electronic Fiber Sensor with High Stretchability and Rapid Response

AbstractSmart interactive electronic devices can dynamically respond to and visualize environmental stimuli. Inspired by the rapid color changes of natural creatures, an interactive electronic fiber sensor with high stretchability and tunable coloration is presented. It is based on an ingenious multi‐sheath design on a piezoresistive electronic fiber coupled with a mechanochromic photonic crystal microtubule. It has the unique capabilities of sensing and visualizing its deformation simultaneously, by reconstructing conductive paths and regulating the lattice spacing of the photonic sheath. In particular, it exhibits dynamic color switching spanning the full visible region (from red to blue), fast optical/electrical response (≈80 ms), and a large working range (0–200%), allowing its application as a user‐interactive sensor for dynamically monitoring large joint movements and muscle microvibrations of the human body in real time. This investigation provides a general platform for emerging interactive devices, which are promising for applications in wearable electronics, human–machine interactions, and intelligent robots.

Synthesis of oriented core/shell hexagonal tungsten oxide/amorphous titanium dioxide nanorod arrays and its electrochromic-pseudocapacitive properties

In this work, well-aligned core/shell hexagonal tungsten oxide/amorphous titanium dioxide nanorod arrays (denoted as core/shell WTNRAs) were synthesized on FTO substrates by a hydrothermal-spin coating approach and has been proved to have enhanced electrochromic-pseudocapacitive properties compared with initial WO3 nanorod arrays (h-WNRAs). The influence of spin-coated amorphous TiO2 (a-TiO2) layer on the microstructure, electrochromic (EC) and pseudocapacitive (PC) properties of the core/shell WTNRAs was intensively investigated. With the suitable a-TiO2 shell, the core/shell WTNRAs presented good EC performance including larger optical modulation (682 nm, 78%), faster response (coloring time 15 s, bleaching time 12 s), higher coloration efficiency (800 nm, 122.3 cm2·C−1) and good cyclic stability. In the meantime, the core/shell structures achieved excellent PC properties such as higher charge storage capacity (426.8 F·g−1 at 1 A·g−1), good charge-discharge cycle efficiency (81%) and rate performance. The mechanism of improving the bifunctional properties was also discussed. Furthermore, the energy storage stages of the material could be visually monitored by rapid and reversible colour changes at different current densities.

Colorimetric Determination of Singlet Oxygen Scavengers Using a Protein Photosensitizer

Despite the diverse roles of singlet oxygen (1O2) in plants and animals, simple detection of 1O2 has been limited due to technical difficulties. Here we report a colorimetric method for visualizing the generation and suppression of 1O2 using a protein photo-sensitizer, mini singlet oxygen generator (miniSOG). Upon external light irradiation, miniSOG strongly produced 1O2 and oxidized a universal chromogenic reagent, tetramethylbenzidine, leading to a rapid color change in solution. We used this finding to demonstrate the 1O2 scavenging effects of well-known anti-oxidants and of natural compounds extracted from plants. Owing to its high usability and simplicity, our developed assay platform will be useful for screening potential scavengers for reactive oxygen species and will promote the development of various antioxidants.

Spectrophotometric Determination of Copper(II) in Water based on Fluorescein Diacetate

Two novel methods for spectrophotometric determination of Cu2+ ion using synthesized and characterized furfuraldehyde fluorescein diacetate hydrazone (FFDH) and furfuraldehyde fluorescein hydrazone (FFH) have been proposed. Addition of Cu2+ to FFDH and FFH solutions results in a rapid color change from colorless to dark yellow. Experimental results show that FFH and FFDH both can provide a rapid, selective and sensitive response to Cu2+ within a linear dynamic range of 7–33 µM and the detection limits of 1.1 × 10–7 and 7 × 10–8 M, respectively. Apparently, the detection limit of FFDH is lower than that of FFH, which indicates that FFDH forms a more stable complex with Cu2+. In addition, the detection of Cu2+ in water samples was also studied; as a result, the developed FFDH was found to be more applicable than FFH for spectrophotometric determination of Cu2+ in environmental water samples. Particularly, as a lipid chemical compound, FFDH may be transported across the cell membrane to detect Cu2+ in vivo. It is of great significance in many fields, such as biology, biochemistry, medicine and environment.

Luminescent macrocyclic Sm(III) complex probe for turn-off fluorescent and colorimetric water detection in organic solvents and liquid fuels

The rapid and sensitive detection of water has attracted wide interests in the chemical and energy industry for its harmful influences, which encourage researchers to explore kinds of materials for sensing water. Herein, we report the sensing performance of a Schiff-base macrocyclic Sm(III) complex Sm-2g as the turn-off fluorescent and colorimetric probe for water detection in organic solvents (DMF, methanol and acetone) and liquid fuels (bioethanol and avgas). It is especially encouraging that the probe Sm-2g exhibits a rapid and sensitive response for water, and it could be easily distinguished by the distinct fluorescence quenching and absorption shift. Electrospray ionization mass spectra prove that this efficient detection is achieved based on the transformation from complex Sm-2g to corresponding dialdehyde precursor, originating from the imine bond cleavage after the addition of water. Furthermore, the Sm-2g impregnated paper strip also provides a convenient way to detect water by its rapid and distinguishable fluorescent color changes in organic media. Therefore, the luminescent Sm(III) complex Sm-2g shows promise as a valuable candidate for the detection of water.