Color Change Response Research Articles

Engineering DNA tetrahedron as a sensing surface of lateral flow test strips and ratiometric visual detection of exosomal microRNA-150–5p

We here report that DNA tetrahedral probe-based sensing surfaces are capable of efficiently capturing gold nanoparticles (AuNPs) on lateral flow test strips, and we have developed a ratiometric biosensor for exosomal microRNAs by integrating a tetrahedral probe and a catalytic hairpin assembly (CHA). DNA tetrahedrons were devised with barcodes and labeled with biotin as capture probes on the test and control lines of the strip. The CHA system consists of two hairpin substrates that can form stable duplexes via a programmable assembly reaction triggered by exosomal miRNAs. The duplexes hybridized with barcoded tetrahedra via complementary sequences and bound to streptavidin-modified AuNPs (SA-AuNPs) via biotin. Thus, a red line was observed on the test line owing to the immobilized SA-AuNPs. The remaining SA-AuNPs were captured by using a biotinylated tetrahedron on the control line. Because the barcoded and biotinylated tetrahedra consume SA-AuNPs simultaneously, a stronger signal in the test line results in a weaker signal in the control line, thus forming a ratiometric result. Tetrahedral probes avoid movement along with sample flow on sensing zones like single-stranded probes. The strip can have a detection limit of 58.90 fM with high selectivity due to the use of ratiometric color changing response, CHA signal amplification and tetrahedral capture probes. This system is able to rapidly detect exosomal microRNA-150–5p and may have a potential utility in point-of-care diagnosis of incipient diabetic nephropathy.

Optimized formulation of polyaniline-pectin optical film sensor for pH measurement

Novel polyaniline-pectin (PAN-PEC) composite sensing films were prepared for optical pH measurement. Box–Behnken experiment design and the response surface method were used to optimize the PAN-PEC synthesis to produce films with a maximum color change response to pH change in the pH range of 2 to 12. The pH sensing PAN-PEC nanoparticles for incorporation in the sensing film were made by oxidative polymerization of aniline using ammonium persulfate as the oxidant and pectin as the stabilizer. The experimental factors were the quantity of aniline, the concentration of hydrochloric acid, and the mass of ammonium persulfate in the reaction mixture, for a fixed quantity of pectin. A relationship between spectrophotometric absorption at 420 nm and the pH was developed for estimating the pH of the samples.

Cellulose-Based Fluorescent Material for Extreme pH Sensing and Smart Printing Applications.

Environment-responsive fluorescence materials are being widely investigated for instrument-free determination of various environmental factors. However, developing an eco-friendly cellulose-based fluorescent pH sensor for sensing extreme acidity and alkalinity is still challenging. Herein, a highly fluorescent and multifunctional material is developed from biopolymer-based cellulose acetate. A biopolymer-based structure containing responsive functional groups such as -C═O and -NH is constructed by chemically bonding 5-amino-2,3-dihydrophthalazine-1,4-dione (luminol) onto cellulose acetate using 4,4'-diphenylmethane diisocyanate (MDI) as a cross-linking agent. The prepared material (Lum-MDI-CA) is characterized by UV-vis, Fourier transform infrared, 1H NMR, 13C NMR spectroscopies, and fluorescence techniques. The material exhibits excellent aqua blue fluorescence and demonstrates extreme pH sensing applications. Interesting results are further revealed after adding a pH-unresponsive dye such as MTPP as the reference to develop the ratiometric method. The ratiometric system clearly differentiates the extreme acidic pH 1 from pH 2 and extreme alkaline pH 12, 13, and 14 by visual and fluorescence color change response under a narrow pH range. In addition, the material is fabricated into transparent flexible fluorescent films which demonstrate an outstanding UV shielding, security printing, and haze properties for smart food packaging and printing applications.

A novel fluorescent sensor based on an enzyme-free system for highly selective and sensitive detection of glyphosate and malathion in real samples

Malathion (Mal) and glyphosate (Glyp) are widely used organophosphorus pesticides to prevent or control insects and weed in agriculture. Unfortunately, the extensive and frequent commercial use of these compounds on farmland has caused their presence as residues in crops and livestock. Therefore, the design of new sensors with enhanced analyte selectivity and sensitivity is critical in this field. Here, we developed an optical sensor for the detection of malathion and glyphosate. The sensor, N,N-dimethyl-4-(3-(pyrazin-2-ylimino)prop-1-en-1-yl)aniline (CNP), was synthesized in a one-step reaction by condensation of 4-(dimethylamino)cinnamaldehyde with 2-aminopyrazine. CNP gives a rapid color change, absorbance and fluorescence response to Glyp and Mal in the presence of the metal ions and pesticides tested in the working system. The binding stoichiometry between the sensor and the pesticides (Glyp and Mal) was investigated by some spectrophotometric methods and the sensing mechanisms were eludicated by NMR titration experiments, suggesting that CNP responds to Glyp via H-bonding and to Mal via the coordination. The sensor has a high selectivity and rapid response to the pesticides (Glyp and Mal) with low detection limits. The sensor was also successfully used to monitor the pesticides in real samples; Mal in apple and tap water samples, and Glyp in potato, tap water and soil samples.

Dye-surfactant co-assembly as the chromogenic indicator for nanomolar level detection of Cu(I) ions via a color-changing response.

Polyaromatic amphiphilic probes have been developed, that can be involved in chromogenic detection of Cu+ ions in anionic micelles. A rapid change in solution color from yellow to orange was observed in the presence of Cu+ ions. The detection limit was found at the nanomolar range. To the best of our knowledge, this is the first report of the visible detection of Cu+ ions in aqueous medium using anionic micelles as a stabilizing agent. Interestingly, the compound can also detect Cu+ ions, generated in situ from physiological redox processes. The mechanistic investigation suggests that the probe molecule forms a diamagnetic tetrahedral complex with the Cu+ ion, coordinating through a pyridyl ketone unit. In addition, we have also followed the interaction with Cu+ on a bilayer surface made of anionic phospholipids. Further, a Cu2+-probe ensemble is used to assay the reducing ability of different biogenic thiols depending upon the pKa of their sulfhydryl (-SH) group. This allows us to determine the amount of reducing thiols present in human urine samples. Considering the high sensitivity of the present system, we screened water samples collected from different natural sources for Cu+ ions. Nearly 100% recovery values with considerably small relative standard deviations (<5%) indicate that the present system is indeed suitable for real-life sample analysis. Finally, low-cost, reusable, chemically-modified paper strips have been developed for rapid, on-location detection of Cu+ ions.

Integrated Transcriptome and Metabolome Analysis of Color Change and Low-Temperature Response during Flowering of Prunus mume

In China, Prunus mume is a famous flowering tree that has been cultivated for 3000 years. P. mume grows in tropical and subtropical regions, and most varieties lack cold resistance; thus, it is necessary to study the low-temperature response mechanism of P. mume to expand the scope of its cultivation. We used the integrated transcriptomic and metabolomic analysis of a cold-resistant variety of P. mume 'Meiren', to identify key genes and metabolites associated with low temperatures during flowering. The 'Meiren' cultivar responded in a timely manner to temperature by way of a low-temperature signal transduction pathway. After experiencing low temperatures, the petals fade and wilt, resulting in low ornamental value. At the same time, in the cold response pathway, the activities of related transcription factors up- or downregulate genes and metabolites related to low temperature-induced proteins, osmotic regulators, protective enzyme systems, and biosynthesis and metabolism of sugars and acids. Our findings promote research on the adaptation of P. mume to low temperatures during wintering and early flowering for domestication and breeding.

A rapid responsive coumarin-naphthalene derivative for the detection of cyanide ions in cell culture

Cyanide ion (CN−) is widely used in many industrial processes; however, it causes several diseases in humans. Therefore, rapid and accurate detection of CN− is very important and urgent. In this study, a CN− sensor (MH-2) which was capable of detecting CN− ions in living cell was developed. MH-2 gives a rapid color change, absorbance and fluorescence response to CN− in the presence of the anions tested in the working system. The binding ratio between the sensor and CN− was demonstrated by some spectrophotometric methods and the sensing mechanism was investigated by NMR titration experiments, suggesting that MH-2 gives response to CN− via the nucleophilic addition reaction. The fluorescence detection limit and the absorbance detection limit were calculated as 0.056 μM and 0.11 μM, respectively. Both of these detection limits are below the tolerable limit recommended by WHO for CN− in the drinking water (1.9 μM). MH-2 was also applied to living cells for bio-imaging and the results showed that the sensor penetrates the cells and can detect cyanide ions in living cells.

Study on microstructure and stimuli-responsive optical characteristics of wing scales of Madagascan sunset moth

To explore the optical characteristics and bionic application potentials of the wing scales of the Madagascan sunset moth, the mapping relationship between the micronano structure and the optical response characteristics was established, and the optical stimuli-responsive mechanism of the structure-colored scales was deeply revealed. The multilevel fine structure of structure-colored scales on the forewings of the Madagascan sunset moth was formed by coupling the linear strip surface and the layered cross-section. The layered film structure system of wing scales was similar to a set of bioresponsive nanophotonic crystals, had a sensitive color change response to the external environment changes such as liquid infiltration and incident angle, and had a highly adjustable reflectivity in the near-infrared range. The unique optical characteristics of the wing scales of the Madagascan sunset moth could provide new ideas for the development of adaptive bionic stealth materials and components.

Damage detection of fiber reinforced composite based on mechanoresponsive aggregation induced emission luminogen

Mechanoresponsive luminescence (MRL) have great potential applications in the fields of sensing, displaying, optical information storage and damage detection because of their light emission or color changing response under mechanical stimulation. In this work, 1,1,2,2-tetrakis (4-nitrophenyl) ethane (TPE-4N) has been synthesized as a MRL with aggregation induced emission (AIE) properties. Taking advantage of the high contrast of mechanically sensitive fluorescence of TPE-4N under mechanical stimulation, it has been coated on the various laminated fiber reinforced composites (FRCs) to successfully realize the on-site visualization of stress distribution of composites. V-shear experiments were carried out on three types of laminated FRCs coated with TPE-4N coatings. The experimental results show that TPE-4N can transform the invisible stress distribution information into visible fluorescence information. Moreover, the matrix cracking, fibre fracture and delamination of the composites can be qualitatively analyzed by using the fluorescence visualization images. By considering the repairability of FRC, early warning values were introduced by calculating the fluorescence areas. The fluorescence visualization method proposed in this work demonstrates the great potential in on-site monitoring the structural health condition of engineering composite structures.

Monitoring Local pH of Membranous Aggregates via Ratiometric Color Changing Response.

A series of oxidized di(indolyl)arylmethanes (DIAM) with polyaromatic signaling moieties have been designed for monitoring local pH at the interfacial region of surfactant aggregates, such as micelles and vesicles. The oxidized DIAMs show changes in solution color from red to yellow when incorporated in cationic surfactants (at pH 7.4) and yellow to reddish pink when exposed to negatively-charged surfactants (at pH 5.0). The changes in surface charge can influence the interfacial pH (distinct from bulk pH of the medium) of the surfactant aggregates. The mechanistic studies indicate that the red-shifted absorption maxima observed in the presence of anionic amphiphiles (acidic local pH) originated from the protonated species. On the contrary, maxima in the blue region, triggered by positively charged amphiphiles (basic local pH), is attributed to the zwitterionic species. Such prototropic equilibrium affects charge transfer states of the molecules along with their self-assembly properties. Thus, it is evident that probes can predict as well as quantify the local pH change using the pseudophase ion exchange formalism. Also, the probes can detect the presence of anionic amphiphiles even when bound to phospholipid membranes.

Moisture-Sensitive Ratiometric Color-Changing Response: a Useful Tool for Precision Farming

Anthra[1,2-d]imidazole-6,11-dione-based charge transfer probes have been developed for the detection of water impurities in a wide range of laboratory-used organic solvents. The deprotonated (anionic) forms of the probe molecules, obtained upon addition of basic anions such as fluoride, demonstrate a ratiometric color-changing response (blue to yellow in presence of F– and red to yellow with CN– ion) even in the presence of a trace amount of moisture (detection limit: 0.008 wt %). Considering their high sensitivity and “naked-eye” response, the anionic receptors are utilized for the quantification of moisture level or water impurity in a wide range of real-life samples, such as building raw materials, packaged food items, soil, plant leaves, and so on. Determination of the moisture level of plant leaves or soil samples is particularly important for precision farming as it helps the farmers to schedule the irrigation events. Finally, low-cost, reusable, and optical kit-based dye-coated paper strips were developed for rapid, on-location detection as well as quantification purposes. Since such a sustainable approach does not involve any sophisticated instruments or complex sample preparation steps, the general public with little knowledge of science or technology will be able to use it without much difficulty.

Paper Strip Based on Nanoemulsion of Curcumin as Boric Acid Detection

Boric acid is a toxic contaminant chemical that is found not only in food but also in the environment, especially the water environment so that its existence needs to be detected. In this work, we design the paper strip using nanoemulsion curcumin for boric acid detection. Curcumin is a bioactive compound that is able to provide a color change response to boron. However, curcumin is not stable to certain environmental conditions, so it needs to be encapsulated. Since it has a low solubility so that the proper encapsulation technique is nanoemulsion. This study investigates nanoemulsion curcumin paper strips' performance as a colorimteric biosensor for the detection of boric acid. The results showed that nanoemulsion curcumin reagent (CURNnsr) as a boric acid detection had a smooth spherical shape with a size of 25.70 nm. Interaction between created curcumin paper strips and boric acid led to a color change from yellow to red. Curcumin paper strip was selective towards sole boric acid after being reacted with various chemicals such as Pb2+, Zn2+ , Fe2+, Mg2+, NaCl, sodium nitrite, monosodium glutamate, sodium benzoate, and formalin with a concentration of 10000 ppm, respectively. The detection limit (LOD) for curcumin paper strips was 105.56 ppm in the range 200-700 ppm of boric acid. This research results are pledging to develop disposable biosensors that are sensitive, selective, and stable, low cost, easy to use and detect quickly.

Anion-induced deprotonation as a simple strategy to improve analytical performance of an amphiphilic probe at mesoscopic interface

A systematic improvement in the metal ion binding ability of a pyrene functionalized oxidized bisindolyl compound was investigated in the aqueous medium. In water, a color-changing response from orange to red was observed upon the addition of Hg2+ ion. However, in this condition, the compound suffered issues like poor selectivity (interference from Cu2+, Cd2+, and Zn2+) and low sensitivity (∼1.6-fold increment in absorbance). Incorporating nonionic surfactant as solubilizing agent alters the protonation equilibrium of the compound and improves its analytical performance to some extent (∼2.5-fold increment in absorbance by Hg2+ and minor interference from Cu2+ and Zn2+ ions). However, an excellent selectivity (no interference) towards Hg2+ ion was achieved when the probe molecules were undergone anion-induced deprotonation reaction before the interaction with metal ions. Also, the deprotonated receptor demonstrated superior sensitivity for Hg2+ (yellow to red color change, ∼5.2-fold increment in absorbance). Thus, in this work, we have developed anion-triggered deprotonation as an alternative strategy for improving the analytical performance of an oxidized bisindolyl probe.

Development of a PCL-PEO double network colorimetric pH sensor using electrospun fibers containing Hibiscus rosa sinensis extract and silver nanoparticles for food monitoring

Major anthocyanin, cyanidin-3-sophoroside (318.1 mg/mL), and other minor copigments were identified in the ethanol extract of Hibiscus rosa sinensis. The extracts can be coelectrospun with polycaprolactone and polyethylene oxide into fiber mats and were sensitive to pH changes from 1 to 13 with a unique color code (ΔE > 5). The pH sensor was used to monitor shrimp quality under isothermal conditions to obtain the respective activation energy (Ea in kJ/mol) of the sensors’ color-change response (20.2), measured pH (20.6), and trimethylamine nitrogen (24.6), indole (27.1), and total microbial counts (30.8). Together with the Pearson correlation coefficient, the results showed high correlations between the sensors’ color change and other quality parameters (p < 0.001). The regression equation developed by conducting the kinetic analysis was also suitable for predicting shrimp quality at refrigeration temperatures (4–10 °C) and can be used as a marker to monitor shrimp quality by visually inspecting the item condition.

Responsive Bio‐Composites from Magnesium Carbonate Filled Polycaprolactone and Curcumin‐Functionalized Cellulose Fibers

AbstractDevelopment of responsive bio‐based and biodegradable materials is particularly important in food preservation and monitoring technologies. Although replacing conventional plastic products with sustainable alternatives is still a challenge, promising advances have been reported. In this work, the fabrication of responsive bio‐composite films from polycaprolactone (PCL) and magnesium carbonate (MgCO3), known as food additive E504 with melt impregnation into cellulose, is reported. Cellulose fibers are stained/coated with ethanoic curcumin solutions, primarily to protect them against oxidative degradation. The films demonstrate a strong antioxidant effect against fatty and aqueous food simulants with improved oxygen gas barrier properties. Interestingly, the natural chelation of curcumin with magnesium within the composites improves the bioavailability and antioxidant potency of curcumin. Moreover, the composites show reversible color change response detectable by the naked eye in basic solutions or vapors. This response is tested by placing the composite film inside a sealed plastic container containing shrimp at room temperature, but not in direct contact. Due to spoilage, a noticeable color change in the bio‐composites is recorded. These simple, cost‐effective, non‐toxic, and paper‐like flexible bio‐composites can be fabricated on large scale and be used in diverse applications ranging from sustainable packaging to medical applications and freshness indicators.

Dual Temperature and Metal Salts-Responsive Interpenetrating Polymer Networks Composed of Poly (N-isopropylacrylamide) and Polyethylene Glycol.

Novel interpenetrating polymer networks (IPNs) composed of poly(N-isopropylacrylamide) (poly-NIPAM) and polyethers—namely, polyethylene glycol (PEG) and poly(tetramethylene oxide)—were synthesized in the absence and presence of polysiloxane containing a silanol residue. Gelation was accomplished using end-capped polyethers with trimethoxysilyl moieties and proceeded through simultaneous radical gelation of NIPAM and condensation of the silyl groups to form siloxane linkages. Thus, a novel one-step method constructing an IPN structure was provided. The obtained IPNs showed a gentle temperature-responsive volume change in water owing to the constructed poly-NIPAM gel component. In addition, a specific color-change response to chemical stimuli, such as CuCl2 and AgNO3 in water, was observed only when both components of poly-NIPAM and PEG existed in a gel form. For example, a single network gel composed of poly-NIPAM or PEG was isolated as a pale blue hydrogel, whereas IPNs composed of poly-NIPAM and PEG components turned yellow after swelling in an aqueous CuCl2 solution (0.1 M, pale blue). Dual-responsive functionalities of the synthesized hydrogels to temperature and metal salts, along with volume and color changes, were demonstrated.

A learning-based approach for solving shear stress vector distribution from shear-sensitive liquid crystal coating images

A learning-based approach for solving wall shear stresses from Shear-Sensitive Liquid Crystal Coating (SSLCC) color images is presented in this paper. The approach is able to learn and establish the mapping relationship between the SSLCC color-change responses in different observation directions and the shear stress vectors, and then uses the mapping relationship to solve wall shear stress vectors from SSLCC color images. Experimental results show that the proposed approach can solve wall shear stress vectors using two or more SSLCC images, and even using only one image for symmetrical flow field. The accuracy of the approach using four or more observations is found to be comparable to that of the traditional multi-view Gauss curve fitting approach; the accuracy is slightly reduced when using two or fewer observations. The computational efficiency is significantly improved when compared with the traditional Gauss curve fitting approach, and the wall shear stress vectors can be solved in nearly real time. The learning-based approach has no strict requirements on illumination direction and observation directions and is therefore more flexible to use in practical wind tunnel measurement when compared with traditional liquid crystal-based methods.

The color change and stress response of Atlantic salmon (Salmo salar L.) infected with Aeromonas salmonicida

Fish challenged with pathogens often show behavioral disorders. The present study investigated the influence of Aeromonas salmonicida infection on the body color changes of Atlantic salmon (Salmo salar L.). In both conditions of a white background and transfer from the black background to the white background, the body color contrast of the fish infected with A. salmonicida (100 μL bacterium solution 8.2 × 109 CFU ml−1 in the dorsal muscle) declined significantly following an initial increase compared with the control group (100 μL 0.9 % NaCl); the greatest differences were observed on day 11, at 57.6 % and 52.7 % respectively (P<0.01). In the black background (transferred from white to the black background), A. salmonicida infection resulted an initial lower and then higher contrast in the challenged fish (P<0.01), and the greatest difference occurred on day 5, reaching 156.7 % (P<0.01). Meanwhile, the cortisol, melanocyte stimulating hormone (MSH) and melanin-concentrating hormone (MCH) levels in serum were also evaluated. Comparing the infected fish with the control fish, the cortisol (7.2 % ∼ 21.2 %), MSH (25.8 % ∼48.6 %) and MCH (36.4 % ∼ 54.4 %) levels of the infected fish were elevated to varying degrees after infection with A. salmonicida (P < 0.05). The results suggested that A. salmonicida challenge altered the color-change behavior, which might be regulated by MSH and MCH.

Improving functional properties of PVA/starch-based films as active and intelligent food packaging by incorporating propolis and anthocyanin

An active and intelligent starch-based biodegradable food packaging system is developed in this work. The growing environmental protection concerns have motivated researchers to look for biodegradable yet sustainable products for food packaging. The packaging is able to resist against undesirable bacterial attack and color-change response due to pH change in food. Polyvinyl alcohol and starch are cross-linked with Glutaraldehyde to improve their mechanical strength. Propolis Extract (PE) and anthocyanin (ATH) were added as an active and intelligent material, respectively. Different film formulations were prepared by varying concentration of PE. All film formulations were characterized by SEM, FTIR and XRD. The results proved good compatibility of the film mixture. The mechanical strength and other physical properties like water vapor transmission rate, moisture retention capability, swelling degree and biological leaching ability were investigated. Films containing 20% PE showed the best results alongside maximum mechanical strength of 15.9 MPa. Furthermore, the same formulation has shown maximum zone of inhibition of 25 mm and 20 mm against E. Coli and MRSA, respectively. Moreover, there was a clear color-change response when films were immersed in different pH solutions ranging from 1 to 14. Finally, to validate the potential application of prepared film formulations, films were tested on pasteurized milk and a color-change response is observed along with the anti-bacterial activity. Hence, this active and intelligent food packaging system is capable of inhibiting and alerting food spoilage.[Formula: see text]

Application of colorimetric indicators to predict the fermentation stage of kimchi.

Cabbage kimchi, a popular side dish in Korean cuisine, produces several fermentation by-products (FBPs). Kimchi is praised for its flavor, taste, and texture when suitably fermented at 0.7% to 0.9% total acidity, or a pH of approximately 4.1. Beyond this acidity level, the quality of the product decreases, negatively impacting consumers' purchase preferences. Therefore, the current study seeks to develop an optimally fermented (OptF) kimchi indicator that can be inserted into product packaging to evaluate its utility at 4 and 10 °C. A gradual change in the total color difference (ΔE) was observed during the kimchi fermentation stage, and the highest ΔE values were observed at 4 (34.87) and 10 °C (37.99), after 9 weeks. Moreover, the color-change response function value F(Xc) was more linear at 4 and 10 °C (0.981 and 0.984, respectively) compared to the ΔE over time, during kimchi fermentation. Coefficients of determination for F(Xc)-carbon dioxide (0.983), F(Xc)-pH (0.979), and F(Xc)-titratable acidity (0.974) were sufficient to meet the optimal polynomial regression model, while that for F(Xc)-lactic acid bacteria (0.881) was not. Standardized residuals of predicted data indicated that 95% of the residuals were in the range of -2.0 to 2.0. The regression analysis further suggested that the OptF kimchi indicator could be used as a kimchi fermentation indicator. PRACTICAL APPLICATION: Cabbage kimchi, a traditional Korean fermented food, produces several fermentation by-products. After the optimal fermenting stage, the sensory evaluation of cabbage kimchi and consumers' purchase preference decreases. This study describes an optimally fermented kimchi indicator and its utility at 4 and 10 °C. Our results demonstrate the ability of this indicator to predict the freshness and fermentation stage of kimchi without the need for sensory evaluation. This method could help increase the purchase preference for commercial kimchi.