Rapid Color Research Articles

Colorimetric and Electrochemical Dual-Signal Method for Water Toxicity Detection Based on Escherichia coli and p-Benzoquinone.

The development of simple and rapid toxicity detection methods has important practical significance. In this work, a dual-signal method with colorimetric and electrochemical properties for water toxicity detection was proposed for the first time based on a rapid color reaction between Escherichia coli (E. coli) and p-benzoquinone (BQ). Here, E. coli was used as a biocatalyst and BQ was used as a mediator. An IC50 value of 0.75 mg L-1 for Cu2+ was obtained using a two-step electrochemical detection method. Strikingly, toxicity could also be estimated visually by the naked eye, and the minimum detection limit was 3.2 mg L-1 for Cu2+. The dual-signal toxicity detection method extends the function of BQ, and the result is more reliable than the traditional single-signal method. This simple and rapid toxicity detection method shows certain application prospects.

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% > 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.

Flashing spots on the dorsal trunk of hardyhead silverside fish.

A large number of living creatures are able to use ambient light effectively in biological signalling. Atherinomorus lacunosus, a teleost fish has alignments of circular spots on its dorsal trunk. The spot consists of iridophores, whose diameters are approximately 7–10 µm. The iridophore contains guanine crystals with diameters of 1–3 µm. Here, it is found that more than one spot with a diameter of approximately 0.1 mm causes a rhythmic flashing of light when viewed under white light. The typical light flash has a pulse width of approximately one second. When a pulsed train of flashes appears, the flash repeats at a typical frequency of 0.5–1 Hz. The observed phenomenon is one example of the evidence for the existence of rapid colour changing teleost fish.

Rapid detection of ceftriaxone resistance in clinical isolates of extensively drug resistant Salmonella enterica serovar Typhi.

To see the efficacy of rapid colour test for the sensitivity of ceftriaxone against clinical isolates of salmonella typhi. The cross-sectional validation study was conducted at the Department of Microbiology, Pakistan Navy Ship Shifa Hospital, Karachi, from Nov 2018 to April 2019, and comprised clinical isolates of salmonella typhi that were obtained from five different hospitals in Karachi and Hyderabad. The isolates were tested using the rapid colour test. All the isolates were also tested using the conventional disc diffusion method and minimum inhibitory concentrations on the Vitek-2 version 8.01. Of the 97 isolates, 83(85.5%) were ceftriaxone-resistant and 14(14.4%) were ceftriaxone-sensitive. Sensitivity and specificity of the rapid colour test were 100% when compared with the results of the other methods. All the results were readable within 2 hours on the colour test. The colour test was found to be a rapid, accurate and inexpensive tool to screen for ceftriaxone resistance in typhoid-endemic areas.

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.

Evaluation of Stone Features That Cause the Color Doppler Ultrasound Twinkling Artifact

The color Doppler ultrasound twinkling artifact is a rapid color shift that appears on 43%–96% of kidney stones. Surface microbubbles on kidney stones are theorized to cause twinkling as exposure to elevated static pressures of 0.41–1.13 MPa (approximately 0.5–1 times diagnostic ultrasound pressure and 5–10 times ambient pressure) reduced twinkling. However, it is unclear what external and internal stone features support bubbles. Thirteen ex vivo kidney stones were scanned with color Doppler ultrasound at 2.5, 5 and 18.5 MHz. Select stones were imaged with environmental scanning electron microscopy or underwater micro-computed tomography to evaluate features that may cause twinkling. Results revealed that the lower frequencies produced larger volumes of twinkling. Condensation first occurred in the smallest (∼1 µm diameter) surface pores and may be indicative of where bubbles form. Gas pockets were seen inside two of three tested stones that may contribute to twinkling. Overall, these results provide evidence of cavity structures both externally and internally and their correlation to the twinkling artifact. This indicates that microbubbles may be present on and within kidney stones and may contribute to the twinkling artifact.

Extraordinary Dynamic Near Vision in Champion Shotgun Shooters: PDI Check Evaluation of Stereo and Color without Floor Effect.

BackgroundConventional near and stereo tests have a “floor effect;” inability to discriminate normal from super-normal. Shotgun champions require unique performance in binocularity and rapid color discrimination.Patients and MethodsTwenty-nine champion clay-target shooters, 14 normal Army and 12 color-normal subjects were tested with conventional near vision tests and on PDI-Check, a series of dynamic, near vision tests on the autostereoscopic Nintendo console.ResultsConventional tested shotgunners had all perfect Ishihara and 75% best 40 sec Stereo fly while Army had 92%perfect Ishihara and 69% best stereo fly. On PDI-Check, experienced shotgunners with median stereo of 17 (IQR 12–41) arc sec were better than Army volunteers 59 (IQR 30 to 487) arc seconds (Mann–Whitney U=62, p=0.04). Median PDI-Check for shotgun compared to Army was 88% compared to 84% for blue cone, 90% compared to 84% for green and 77% compared to 72% (red, Mann–Whitney p=0.05). Adding dark cherry filter shooting glasses improved the red and green color detection (p<0.01). This study lacked power to detect eye dominance using PDI Check color or stereo.ConclusionMany champion shotgun shooters had outstanding dynamic near stereo and better-than-average color vision which could be optimized with dark filter spectacles for red and green hues. PDI Check not only helps identify abnormal binocularity and color vision, but it can clarify supranormal vision as well.

Penta-nuclear [Ag5I6] Cluster-Based Photochromic Hybrid: Synthesis, Structure, Dye Sorption, and Separation

An [Ag5I6] cluster-based coordination polymer has been successfully constructed with the assistance of a polydentate organic amine hexamethylenetetramine (Hmta) as the linker, [NH4][Ag5I6(Hmta)] (1). Compound 1 features an anionic 2D bilayer network wherein the combination of Ag(I) with I– and N atom gives rise to a novel [Ag5I6] secondary building unit and further generates the final architecture with free NH4+ being located in the space of the framework. Interestingly, compound 1 exhibits a cation exchange behavior which can efficiently capture and separate methylene blue (MB) in a binary mixture of dye solution. Desorption experiments have been performed, showing that the MB molecules in dye-loaded samples can be readily discharged when triggered by Na+. Moreover, reversible photochromism is observed for solid 1, displaying a rapid color response to light illumination.

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.

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.

Constant temperature during postharvest storage delays fruit ripening and enhances the antioxidant capacity of mature green tomato

The aim of this study was to evaluate the effect of storage temperature fluctuation (TF) (15 ± 5°C, 15 ± 1°C, and 15 ± 0°C) on the ripening quality and antioxidant capacity of mature green tomato. Results indicated that tomato subjected to high TF (15 ± 5°C) had higher respiration rate and weightlessness rate, earlier ethylene release peak, and developed rapid color transfer greater than that to 15 ± 0°C. Besides, tomato exposed to high TF (15 ± 5°C) reveal low lycopene, total phenols, and ascorbic acid content, and inferior activity of superoxide dismutase and catalase later in the storage period. Indicated in this study is the fact that a consistent storage temperature (15 ± 0°C) helps to delay ripening and the senescence process of mature green tomato, and a good sensory quality and high antioxidant capacity after storage is maintained. Practical applications Storage temperature fluctuation in cold chain logistics of fresh fruits and vegetables is one of the main factors leading to quality loss. In this experiment, the effects of different temperature fluctuations on ripening quality and antioxidant properties of mature green tomato were evaluated. The results showed that the high TF would lead to the abnormal ripening of tomatoes and reduce the ripening quality and antioxidant capacity, while the constant storage temperature had the opposite effect. Operators should ensure as far as possible that the temperature of any link in the cold chain logistics of fresh food is stable, so as to extend the full-ripening time of green mature tomato after harvest, and improve their edible quality and antioxidant capacity.

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.