Detectable Color Change Research Articles

Vapor-, thermo-, and mechanical-grinding-triggered tri-stimuli-responsive luminescence switching of cycloplatinated(II) complex bearing 8-quinolinol derivatives

Four novel cycloplatinated(II) complexes, Pt(ppy)(L1) (1), Pt(ppy)(L2) (2), Pt(ppy)(L3) (3) and Pt(ppy)(L4) (4) based on 5-[2-(4-substituent-phenyl)ethynyl]-8-quinolinol ligands {substituent = H (L1), Me(L2), Et(L3), t-Bu(L4)} were synthesized and characterized. Complex 4 has three main pseudopolymorphs, including orange 4·CH3CH2OH, red 4R, and dark-brown 4·½(CCl4). Complex 4 exhibits interesting tri-stimuli-responsive luminescence switching properties. Upon exposure to different VOC vapors, three pseudopolymorphs display unusual irreversible vapoluminescence that 4R and 4·½ (CCl4) can be exchanged with each other and be irreversibly converted to 4·CH3CH2OH. Furthermore, 4·½(CCl4) shows reversible thermochromic luminescence behaviour and can be reversibly converted to 4R upon heating. No detectable change in color and luminescence of 4·CH3CH2OH and 4R can be found during the heating process, although 4·CH3CH2OH lost its solvent and changed to desolvated 4O. In addition, 4·CH3CH2OH, and 4·½ (CCl4) also show the mechanoluminescent property that both of them will be converted to the same red amorphous 4G peaked at 742 nm after grinding. Systematic studies revealed that the tri-stimuli-responsive luminescence switching property of 4 is due to the structural conversion and resultant changes of the lowest-energy excited states. In contrast, complexes 1–3 have not any luminescent switching property. The reason is most likely due to the compact stacking structures of them which prevent their structural conversion triggered by external stimuli.

Paper-based colorimetric sensor for easy and simple detection of polygalacturonase activity aiming for diagnosis of Allium white rot disease

Polygalacturonase (PG) activity in plants can serve as an important index for plant disease. However, the conventional method to detect PG activity is a complex process and requires a skilled technician and expensive analytical equipment. In this study, a paper-based colorimetric sensor was developed based on the principle of the ruthenium red (RR) dye method for easy and simple measurement of PG activity. The proposed paper-based sensor has a three-layer structure for detection of PG activity in samples. The sensor sensitivity was enhanced by optimizing the pH of the sodium acetate buffer used in polygalacturonic acid (PGA)-RR complex formation and the reaction temperature for PG and the PGA-RR complex. Further, for quantitative analysis of PG activity, Delta RGB analysis was conducted to detect color changes in the sensing window of the sensor. Results presented that the linear measurement range of the paper sensor was 0.02–0.1 unit with the limit of detection of 0.02 unit, which showed a similar detection range, but a lower detection limit, compared to the spectrophotometry. Furthermore, PG activity based on culture condition was measured using samples from Sclerotium cepivorum to verify the potential application of the developed paper-based sensor in the field. The measured activity showed no statistically significant difference from the values obtained from the spectrophotometry at 95% confidence level. Therefore, the paper-based colorimetric sensor can be used to predict plant diseases in Allium crops during the stage of pathogen invasion, potentially contributing to the improvement of crop production.

A pH‐Dependent Colorimetric Probe Based on Sodium Dodecyl Sulfate Silver Nanoparticles for Cadmium(II) and Aluminum(III) Determination

AbstractA novel pH‐dependent sensitive and convenient assay was proposed for the determination of Cd2+ and Al3+ in aqueous medium using the sodium dodecyl sulfate (SDS) modified AgNPs as signal probes. In different pH values, the probe showed a visually detectable color change based on the strong interaction of Cd2+ and Al3+ with SDS. The color of SDS‐AgNPs solution would change from bright yellow to purple red in the presence of Cd2+ at pH 9.8, and to reddish brown in the presence of Al3+ at pH 5.5. Under the optimum experimental conditions, the ratio of A580 nm/A390 nm of SDS‐AgNPs gradually increased with increasing of Cd2+, and a good linear relationship was achieved when Cd2+ concentration ranging from 4.2×10−8 M to 3.0×10−6 M. Linear decreasing of A390 nm related to Al3+ concentration was over the range of 3.6×10−8 M to 2.0×10−6 M. The limit of detection was as low as 11.2 nM Cd2+ and 7.2 nM Al3+, respectively. Importantly, it has been successfully applied to detect Cd2+ and Al3+ in real samples.

Methyl-3-(2-hidroxy-5-nitrophenyl amino)-3-phenylpropanoate Based Colorimetric Sensor for Oxyanions

A colorimetric anion sensor of methyl-3-(2-hydroxy-5-nitrophenyl amino)-3-phenylpropanoate bearing –OH and –NH groups as binding sites and nitrophenyl as a signaling unit, has been successfully accomplished. The compound functioned as a colorimetric chemosensor for H2PO4– and AcO–, in particular, the sensor showed significant naked-eye detectable color change from colorless to light yellow. In contrast, no color change was detected upon addition of other anions such as SO42–, NO3–, and CIO4–. The anion sensing ability of the sensor was further investigated by UV-Vis absorption spectroscopy in acetone. Characteristic UV-Vis spectra changes were revealed upon addition of H2PO4– and AcO–.

Colorimetric chemosensor based on a Ni2+ complex of a pyridylazo dye for detection of citrate in aqueous solution

We developed a colorimetric naked-eye chemosensor based on the complex between a pyridylazo dye and Ni2+ in a 2:1 stoichiometric ratio (BrPSAA2-Ni2+) for the selective detection of citrate in a pure aqueous solution via the indicator displacement assay. Upon the addition of citrate, BrPSAA2-Ni2+ exhibited a naked-eye detectable color change from red to orange over other anions including dicarboxylates with a blue shift in absorption spectra due to the regeneration of BrPSAA by the interaction of citrate with Ni2+. Furthermore, the citrate detection process was not significantly influenced by other coexisting anions. Therefore, BrPSAA2-Ni2+ can be utilized as a simple and practical colorimetric chemosensor for citrate with selectivity and fast response in aqueous solution.

Azobenzene–Hemicyanine Conjugated Polymeric Chemosensor for the Rapid and Selective Detection of Cyanide in Pure Aqueous Media

A water-soluble polymeric probe was designed and synthesized that can be used for the colorimetric selective detection of cyanide ions in pure aqueous media. In particular, P1, a water-soluble random terpolymer (P1) of N,N′-dimethylacrylamide, 2-((E)-4-((E)-(4-((2-(acryloyloxy)ethyl)(methyl)amino)phenyl)diazenyl)styryl)-1,3,3-trimethyl-3H-indol-1-ium (M1), and N-(4-benzoylphenyl)acrylamide was synthesized via traditional free-radical polymerization. Upon the addition of CN− ions to a P1 solution, a macroscopically detectable color change of the solution from brick red to light yellow took place, which was associated with a low limit of analyte detection (1.23 μM). Notably, P1 exhibited excellent selectivity toward CN− over other anions and biothiols, which may be present in the medium. Such highly selective colorimetric response to CN− by P1 originated from the nucleophilic attack of CN− anions onto the electron-deficient polarized CN bonds of P1's indolium moieties, resulting in the perturbation of the intramolecular charge transfer process occurring within the probe via destruction of the polymer's extended π-conjugation. P1 was also immobilized on a quartz slide by spin coating and then exposed to ultraviolet light. The resulting polymeric film displayed a rapid response to CN− consisting in a distinct color change, extending the scope of the usefulness of P1 as a cyanide-ion probe beyond the solution phase. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 124–131

Leucistic Woodcock (Scolopax rusticola L.) occurrences in Hungary from the second half of the 19th century to the present day

Abstract Publications about curiosities are known in the Hungarian and international ornithological literature since the 1800s. Although studies explaining the processes of pigmentation dysfunctions have been known since the mid-nineteenth century, these specimens still appear only as curiosities in the professional press and the terminology used to specify them is generally incorrect. The analysed genetic abnormalities causing white colour varieties in Woodcock (albinism, leucism, Ino) are due to mutations. By briefly describing the biological background of the defects, this work helps detect colour changes. In this article, we provide a broad overview of partially or completely white Woodcocks (n = 23 expl.) found in international (8 countries) and Hungarian literature. We have supplemented the literature background with our own studies. The large-scale analysis of the variability of colours and patterns was made possible by the countrywide wing sample collection within the biometric module of Woodcock Monitoring, which has been running under the coordination of the Hungarian Hunting Conservation Association since 2010. Within this framework, 12,078 samples were analysed between 2010–2018. We found that pigment deficiency occurred in the sample set only with a proportion of 0.01%. Based on the Hungarian literature and our own samples, we presented the known occurrences on maps of the state territory with boundaries before and after 1921, indicating the causes of patterns of occurrence by migration and frequencies of occurrence.

Synthesis and Spectroscopic Studies of an Azo-Azomethine Receptor for Naked-Eye Detection of Hydrogen Carbonate Ions in Aqueous Media

In this research, we have designed and synthesized a new receptor, namely 4-((E)-(2,5-dichlorophenyl)diazenyl)-2-((E)-((4-hydroxyphenyl)imino)methyl)phenol (L) for detection of hydrogen carbonate anions by naked-eye and UV–Vis spectroscopy. This compound revealed visual changes with HCO3 − anion in aqueous media. No detectable color changes were observed upon the addition of any other tested anions. The sensitivity and selectivity of the receptor (L) to hydrogen carbonate anion was investigated by UV–Vis spectroscopy and 1H-NMR titration methods. The receptor (L) had a detection limit of 2.18 × 10−7 mol L−1 toward HCO3 − anions. Therefore, this compound was highly suitable for detection of hydrogen carbonate anion in aqueous solutions. The stability constant of the receptor (L)-HCO3 − complex was determined by Benesi–Hildebrand plot method. The stoichiometry of this complex was determined (receptor (L)/anion = 1:1) by Job’s plot technique. Overall, the designed chemosensor can be used for quick detection of hydrogen carbonate anions within the basic pH range.

Target-Induced Aggregation of Gold Nanoparticles for Colorimetric Detection of Bisphenol A

Bisphenol A (BPA) is used in a wide variety of consumer products owing to its beneficial properties of optical clarity, shatter resistance, and heat resistance. However, leached BPA has been shown to disturb the endocrine system and could cause cancer even at low concentrations, which has led to public concern. To reduce the toxic effects caused by BPA, it is important to monitor the BPA levels and its presence in products in a simple, rapid, and on-site manner. Here, we propose a new colorimetric strategy for the simple and rapid detection of BPA employing a DNA aptamer, a cationic surfactant, and gold nanoparticles (AuNPs). Using the developed system, the presence of BPA can be successfully determined based simply on a visually detectable color change from red to blue, triggered by aggregate formation of the AuNPs, which can be monitored even with the naked eye. Under the optimized conditions, this system could detect BPA with excellent selectivity and sensitivity, and its high performance was validated in the receipt obtained from local market and BPA-spiked tap water samples, ensuring its practical applicability. Moreover, the limit of the detection of the system was determined to be 97 nM, which is below the current tolerable daily intake level, demonstrating its suitability for toxicity assessment and on-site quality control in a more economical manner when compared with conventional methods.

Azobenzene–Hemicyanine Conjugated Polymeric Chemosensor for the Rapid and Selective Detection of Cyanide in Pure Aqueous Media

ABSTRACTA water‐soluble polymeric probe was designed and synthesized that can be used for the colorimetric selective detection of cyanide ions in pure aqueous media. In particular, P1, a water‐soluble random terpolymer (P1) of N,N′‐dimethylacrylamide, 2‐((E)‐4‐((E)‐(4‐((2‐(acryloyloxy)ethyl)(methyl)amino)phenyl)diazenyl)styryl)‐1,3,3‐trimethyl‐3H‐indol‐1‐ium (M1), and N‐(4‐benzoylphenyl)acrylamide was synthesized via traditional free‐radical polymerization. Upon the addition of CN− ions to a P1 solution, a macroscopically detectable color change of the solution from brick red to light yellow took place, which was associated with a low limit of analyte detection (1.23 μM). Notably, P1 exhibited excellent selectivity toward CN− over other anions and biothiols, which may be present in the medium. Such highly selective colorimetric response to CN− by P1 originated from the nucleophilic attack of CN− anions onto the electron‐deficient polarized CN bonds of P1's indolium moieties, resulting in the perturbation of the intramolecular charge transfer process occurring within the probe via destruction of the polymer's extended π‐conjugation. P1 was also immobilized on a quartz slide by spin coating and then exposed to ultraviolet light. The resulting polymeric film displayed a rapid response to CN− consisting in a distinct color change, extending the scope of the usefulness of P1 as a cyanide‐ion probe beyond the solution phase. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 124–131

Improving sensitivity of mercury detection using learning based smartphone colorimetry

Detection of various contaminations in drinking water such as heavy metal ions and toxic chemicals is costly, time-consuming and requires an accompanying computing device to capture and analyze the data. Hence, there is an extensive need for a rapid, user-friendly, cost-effective, sensitive and ubiquitous detection technique. Smartphones are an effective means to measure, analyze and share the results. In this work, a gadget was designed and printed using a lightweight 3D material, which can be attached to any smartphone and integrated with optical components. A full color TFT LCD display was used as the uniform source of any color of light. Aptamer conjugated gold nanoparticles were employed to determine the concentration of Hg2+ as the basis of a colorimetric sensor. Interaction between the aptamer and the analytes leads to a color change in the solution due to aggregation of gold nanoparticles. For the corresponding color change detection, a novel image processing protocol using RGB value was introduced for each captured image. Multiple linear regression analysis was also exploited to achieve a better sensor response model. Light source enhancement, colorimetry at more points of visible spectrum (470, 540, 640 nm) and a powerful post process technique including machine learning made it possible to obtain an excellent level of sensitivity (1 nM–0.2 ppb).

The Role of Working Memory in Dual-Target Visual Search.

Visual search (VS) for multiple targets is especially error prone. One of these errors is called subsequent search misses (SSM) and represents a decrease in accuracy at detecting a second target after a first target has been found. One of the possible explanations of SSM errors is working memory (WM) resource depletion. Three experiments investigated the role of WM in SSM errors using a dual task paradigm. The first experiment investigated the role of object WM using a classical color change detection task. In the second and the third experiments, a modified change detection task was applied, using shape as the relevant feature. The results of our study revealed no effect of additional WM task on second target detection in dual-target VS. To this end, SSM errors are not related to WM resource depletion. On the contrary, WM task performance was violated by dual-target VS as compared to single-target VS, when the targets in VS task were defined by the same feature used in the WM task.

Solid-phase colorimetric apta-biosensor for thrombin detection

Herein, we developed a solid-phase colorimetric apta-biosensor for thrombin detection. Aggregation of gold nanoparticles (AuNPs) deposited on a 3-aminopropyltriethoxysilane (APTES) substrate was utilized to form the colorimetric sensor. The APTES-coated substrate with primary aptamer (TBA1)-conjugated AuNPs (AuNP-TBA1) was used to construct the solid-phase sensing platform, where an enhancement of the localized surface plasmon resonance due to the AuNPs was observed upon incubation with a target molecule (thrombin). The introduction of secondary aptamer-conjugated AuNPs (AuNP-TBA2) induced plasmonic coupling of the AuNPs, resulting in significantly enhanced spectral signals and peak shifts and visually detectable color changes. This sensing platform not only includes several advantages, such as simplicity and rapid detection, but also allows naked-eye detection sensitivity at 3 μg/mL with no analytical equipment and a limit of detection of 1.33 μg/mL using UV–vis.

Enabling Room-Temperature Mechanochromic Activation in a Glassy Polymer: Synthesis and Characterization of Spiropyran Polycarbonate.

Mechanochromic functionality realized through force-responsive molecules (i.e., mechanophores) has great potential for spatially localized damage warning in polymers. However, in structural plastics, for which damage warning is most critical, this approach has had minimal success because brittle failure typically precedes detectable color change. Herein, we report on the room-temperature mechanochromic activation of spiropyran in high Tg bisphenol A polycarbonate. The mechanochromic functionality was introduced by polymerization of dihydroxyspiropyran as a comonomer while retaining the excellent thermomechanical properties of the polycarbonate. The mechanochromic behavior is thoroughly evaluated in response to changes in stress, deformation, and time, providing new insights regarding how loading history controls stress accumulation in polymer chains. In addition, a new method to incorporate mechanochromic functionality in structures without dispersing costly mechanophores in the bulk is demonstrated by using a mechanochromic laminate. The room-temperature mechanochromic activation in a structural polymer combined with the new and efficient preparation and processing methods bring us closer to the application of mechanochromic smart materials.

Can short-term memory be trained?

Is the capacity of short-term memory fixed, or does it improve with practice? It is already known that training on complex working memory tasks is more likely to transfer to untrained tasks with similar properties, but this approach has not been extended to the more basic short-term memory system responsible for verbal serial recall. Here we investigated this with adaptive training algorithms widely applied in working memory training. Serial recall of visually presented digits was found to improve over the course of 20 training sessions, but this improvement did not extend to recall of either spoken digits or visually presented letters. In contrast, training on a nonserial visual short-term memory color change detection task did transfer to a line orientation change detection task. We suggest that training only generates substantial transfer when the unfamiliar demands of the training activities require the development of novel routines that can then be applied to untrained versions of the same paradigm (Gathercole, Dunning, Holmes, & Norris, 2019). In contrast, serial recall of digits is fully supported by the existing verbal short-term memory system and does not require the development of new routines.

Development of highly selective chemosensor for chomium(III) estimation in aqueous environment

A new antipyrine Schiff's base, 2-((2,5-dimethyl-3-oxo-1-phenyl-2,3-dihydro-1H-pyrazol-4-yl)imino)-1H-indene-1,3(2H)-dione (L) has been synthesized by simple condensation of ninhydrin with 4-aminoantipyrine. The sensing ability of L was studied with selected metal ions from s-block and d-block elements by visual and UV–Vis spectrometry in water: methanol (8:2, v/v) media. The naked-eye detectable colour change of L was occurred from pink to colourless upon interacting with Cr3+ while other metal ions did not change the colour of L. The two main absorption bands appeared at 425 nm and 540 nm of L were quenched upon interaction with Cr3+ while other tested metal ions failed to perturb the absorption bands of L. The Jobs plot and UV–visible spectral studies indicate the formation of a 2:1 complex between the L and Cr3+ with an association constant of 3.0 × 104 M−1. The limit of detection (LOD) of L for the analysis of Cr3+ found to be 5.4 × 10−7 M. The CrL2 complex formation in solution is reversed after treatment with ethylenediaminetetracetic acid (EDTA). The colorimetric sensing ability of Schiff's base L was successfully utilized in the preparation of test paper strips and solid supported silica for the real samples analysis to detect Cr3+ ions from 100% aqueous environment.

A smartphone biosensor based on analysing structural colour of porous silicon.

We report a smartphone compatible, low-cost porous silicon biosensor, which correlates the structural colour of a porous silicon microcavity (PSiM) to spectral peak position. Molecules captured in the PSiM cause a colour change that can be quantified through image analysis. Minimal external accessories are employed. Spectrometer measurements of the PSiM reflectance spectrum shifts are carried out concurrently with the smartphone measurements to benchmark the accuracy of the smartphone biosensor. We estimate that the smartphone biosensor supports an equivalent accuracy of 0.33 nm for the detection of colour changes corresponding to spectral shifts of the PSiM. Biosensing functionality is demonstrated using a biotin-streptavidin assay with an estimated detection limit of 500 nM. The PSiM-smartphone biosensor is a promising platform for label-free point of care diagnostics.

Symmetry Breaking-Induced Plasmonic Mode Splitting in Coupled Gold-Silver Alloy Nanodisk Array for Ultrasensitive RGB Colorimetric Biosensing.

We report the first observation of symmetry breaking-induced mode splitting in coupled gold-silver alloy nanodisk array (ANA). According to the plasmonic hybridization picture, the original localized surface plasmon resonance (LSPR) of individual nanodisk is split into a pair of high and low energy modes when placed in between a superstrate and a substrate. Although well studied in single silver nanoparticles, the high energy mode has been largely suppressed in gold nanoparticles, which nevertheless are more chemically robust and have superior environmental stability. Herein, we show that the high energy mode can be partially restored and precisely engineered to ∼540 nm for silver-rich alloy nanodisk which has excellent environmental stability. However, peak broadening and red-shifting occur due to plasmonic dephasing when the nanodisk diameter increases. We next demonstrate that a far-field coupled ANA fabricated by low-cost nanosphere lithography can fully restore the high energy mode with electric field concentration extended into the superstrate, thereby imparting greater sensitivity to local refractive index changes. The high energy mode at 540 nm is of key importance for color change detection using low-cost RGB cameras/human vision and broadband light sources (e.g., the sun). The index sensitivity of ANA is the highest among existing plasmonic arrays (particles or holes) within a similar resonance wavelength region. We demonstrate colorimetric detection of sub-nanomolar and sub-monolayer biotin-streptavidin surface binding with a smartphone camera and a white light lamp. The high performance yet low-cost fabrication and detection technology could potentially result in affordable point-of-care biosensing technologies.

Development of the Smartphone-Assisted Colorimetric Detection of Thorium by Using New Schiff's Base and Its Applications to Real Time Samples.

In this paper, a new Th4+ ion-selective chromogenic sensor (L) was developed by reacting 1,10-phenanthroline-2,9-dicarbohydrazide with 2-hydroxy naphthaldehyde. The sensing ability of L toward Th4+ was investigated in solution and paper strips loaded with L using spectrophotometric and colorimetric methods. The selective interaction of L was examined with various f-metal ions and other selected metal ions from s-block and d-block elements. Results show that by the colorimetric method in solution-phase dimethyl sulfoxide/H2O (7:3, v/v) and paper strip methods, the naked-eye detectable color change of L occurred from colorless solution to yellow-orange and pale yellow colour upon interacting with Th4+ and Al3+, respectively, whereas other metal ions did not interfere. The ligand L exhibits two absorbance bands at 320 and 375 nm because of ligand-to-ligand charge transfer. Upon interaction with Th4+, L undergoes red shift of both absorption bands and the formation of a new UV-vis band at 335 and 440 nm. The UV-visible spectral studies indicate the formation of a 1:1 host-guest complex between L and Th4+ with an association constant of 4.7 × 103 M-1. The limit of quantification and limit of detection of L for the analysis of Th4+ are found to be 167 and 50 nM, respectively. The visually detectable color change of L has been well integrated with a smartphone RGB color value to make it an analytical signal for real-time analysis of Th4+ with the detection limit down to 116 nM. Besides, L was applied for the analysis of Th4+ content present in various real water samples, monazite, and lantern mantle samples by spectrophotometry and RGB color values. The binding mode of L with Th4+ is investigated by 1H NMR, electrospray ionization-mass, and theoretical studies.

Colorimetric Co2+ sensor based on an anionic pyridylazo dye and a cationic polyelectrolyte in aqueous solution

AbstractA new naked‐eye colorimetric sensor for detecting Co2+ in a pure aqueous solution at pH 7.0 was developed by mixing an anionic organic dye, 2‐(5‐bromo‐2‐pyridylazo)‐5‐(N‐propyl‐N‐sulfopropylamino)phenol (5‐Br‐PAPS) with a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC). Upon addition of Co2+, the absorption maximum exhibited a remarkable bathochromic shift from 426 to 635 nm (Δ = 209 nm) with a detectable color change from yellow, green to blue, while other metal ions did not induce such a change. The results showed that the 5‐Br‐PAPS and PDADMAC mixture can be used as a selective and sensitive naked‐eye colorimetric chemosensor for Co2+. This study afforded a simple strategy to construct a novel chemosensor by a simple mixture of an organic dye and an oppositely charged polyelectrolyte. © 2018 Society of Chemical Industry