Vivid Color Change Research Articles

A Chromo-Fluorogenic Naphthoquinolinedione-Based Probe for Dual Detection of Cu2+ and Its Use for Various Water Samples.

The presence of an abnormal amount of Cu2+ in the human body causes various health issues. In the current study, we synthesized a new naphthoquinolinedione-based probe (probe 1) to monitor Cu2+ in different water systems, such as tap water, lakes, and drain water. Two triazole units were introduced into the probe via a click reaction to increase the binding affinity to a metal ion. In day-light, probe 1 dissolved in a mixed solvent system (HEPES: EtOH = 1:4) showed a vivid color change from light greenish-yellow to pink in the presence of only Cu2+ among various metal ions. In addition, the green luminescence and fluorescence emission of the probe were effectively bleached out immediately after Cu2+ addition. The limit of detection (LOD) of the probe was 0.5 µM when a ratio-metric method was used for metal ion detection. The fluorescence titration data of the probe with Cu2+ showed a calculated LOD of 41.5 pM. Hence, probe 1 possesses the following dual response toward Cu2+ detection: color change and fluorescence quenching. Probe 1 was also useful for detecting Cu2+ spiked in tap/lake water as well as the cytoplasm of live HeLa cells. The current system was investigated using ultraviolet-visible and fluorescence spectroscopy as well as density functional theory calculations (DFT).

Colorimetric detection and determination of glutathione based on superoxide radical-assisted etching approach

Rapid and ultrasensitive detection of biomarkers of diseases is of great importance in early diagnosis and monitoring the patient health conditions. Herein, we report a simple design for a naked-eye colorimetric biosensor for detection and determination of Glutathione (GSH) in human serum. In the presence of Horseradish peroxidase (HRP) and trace concentration of H2O2 and flavone apigenin, and of course GSH, oxidation of GSH results in generation of large amount of superoxide radicals (O2•−) which leads to etching of Au nanorods (AuNRs). The etching of AuNRs results in a blue-shift in the localized surface plasmon resonance (LSPR) of AuNRs, accompanied by a vivid color change from grey to blue then pink. The etching mechanism was well understood by carrying out a series of control experiments. The as-design naked-eye colorimetric biosensor possessed limit of detection of 34 nM, where the whole test was completed in only 5 min. Furthermore, proposed sensor showed an excellent selectivity toward interference substances. The practical tests were performed using human serum as a complex biological medium, where the as-designed biosensor was able to detect and determine GSH with an acceptable accuracy. Our findings suggest that the as-designed biosensor could be used for practical detection and determination of GSH level in for real samples, which could be a breakthrough in diagnosis of several GSH-related diseases.

Simple easy to make xanthene based optical probe for solid and liquid state Hg2+ ion detection

An easy to make xanthene based optical probe synthesized, precise recognition towards mercury ion been achieved by the probe RP and can detect Hg2+ effectively in both for solid and liquid state with a vivid color change. The other tested ion showed no interference, visual and instrumental methods confirms the probe selectivity. Stoichiometry (1:1) confirmed by job’s plot, plausible binding of Hg2+ ion with the probe confirmed by mass and NMR studies. Test strip prepared for the prompt onsite detection in aqueous medium with outstanding color variation in daylight.

Creation and Reconstruction of Thermochromic Au Nanorods with Surface Concavity.

Conventional colloidal syntheses typically produce nanostructures with positive curvatures due to thermodynamic preference. Here, we demonstrate the creation of surface concavity in Au nanorods through seed-mediated growth in confined spaces and report their thermochromic responses to temperature changes. The unique surface concavity is created by templating against Fe3O4 nanorods, producing a new concavity-sensitive plasmonic band. Due to the high surface energy, the metastable nanorods can be reconstructed at a moderate temperature, enabling convenient and precise tuning of their plasmonic properties by aging in different solvents. Such structural reconstruction of concave Au nanorods enables the fabrication of thermochromic plasmonic films that can display images with vivid color changes or exhibit encrypted, invisible information upon aging. This templating strategy is universal in creating concave nanostructures, which may open the door to designing new nanostructures with promising applications in sensing, anticounterfeiting, information encryption, and displays.

Carbazole-Based Colorimetric Anion Sensors.

Owing to their strong carbazole chromophore and fluorophore, as well as to their powerful and convergent hydrogen bond donors, 1,8-diaminocarbazoles are amongst the most attractive and synthetically versatile building blocks for the construction of anion receptors, sensors, and transporters. Aiming to develop carbazole-based colorimetric anion sensors, herein we describe the synthesis of 1,8-diaminocarbazoles substituted with strongly electron-withdrawing substituents, i.e., 3,6-dicyano and 3,6-dinitro. Both of these precursors were subsequently converted into model diamide receptors. Anion binding studies revealed that the new receptors exhibited significantly enhanced anion affinities, but also significantly increased acidities. We also found that rear substitution of 1,8-diamidocarbazole with two nitro groups shifted its absorption spectrum into the visible region and converted the receptor into a colorimetric anion sensor. The new sensor displayed vivid color and fluorescence changes upon addition of basic anions in wet dimethyl sulfoxide, but it was poorly selective; because of its enhanced acidity, the dominant receptor-anion interaction for most anions was proton transfer and, accordingly, similar changes in color were observed for all basic anions. The highly acidic and strongly binding receptors developed in this study may be applicable in organocatalysis or in pH-switchable anion transport through lipophilic membranes.

Multicolorimetric ELISA biosensors on a paper/polymer hybrid analytical device for visual point-of-care detection of infection diseases.

Enzyme-linked immunosorbent assay (ELISA) is widely used for the detection of disease biomarkers. However, it utilizes time-consuming procedures and expensive instruments, making it infeasible for point-of-care (POC) analysis especially in resource-limited settings. In this work, a multicolorimetric ELISA biosensor integrated on a paper/polymer hybrid microfluidic device was developed for rapid visual detection of disease biomarkers at point of care, without using costly equipment. This multicolormetric ELISA platform was built on multiple distinct color variants resulted from the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) and the etching of gold nanorods (AuNRs). The vivid color changes could be easily distinguished by the naked eye, and their red mean values allowed quantitative biomarker detection, without using any sophisticated instruments. When this multicolorimetric ELISA was integrated on a paper/polymer hybrid analytical device, it not only provided integrated processing and high portability but also enabled fast assays in about 50 min due to the unique advantages of paper/polymer hybrid devices. The limit of detection of 9.1 ng/μL of the hepatitis C virus core antigen, a biomarker for hepatitis C, was achieved using this multicolorimetric ELISA platform. This multicolor ELISA analytical device provides a new versatile, user-friendly, affordable, and portable immunosensing platform with high potential for on-site detections of various viruses, proteins, and biomarkers for low-resource settings such as at home, public venues, rural areas, and developing nations.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s00216-021-03359-8.

Sensitive Colorimetric Sensor for Lead Ions and VOCs Based on Histidine-Functionalized Polydiacetylene

Due to the high toxicity of lead ions (Pb2+) and volatile organic compounds (VOCs) to human health and the environment, increasing attention has been paid by scientists to the development of simple, flexible and sensitive sensors or methods that are capable of tracing Pb2+ ions or VOCs with colorimetric visualization. In this study, the fabrication of colorimetric sensors based on histidine-functionalized diacetylene (His-DA), chromatic π-conjugated liposomes, for tracing Pb2+ ions was described. With a suitable molar ratio (4:1) between the10,12-pentacosadiynoic acid (PCDA) and His-DA monomers, the histidine units of the hybrid liposomes could rationally interrupt the efficient backbone length of polydiacetylene (PDA) chains, which causes the probe to be highly sensitive and selective for colorimetric visualization of tracing Pb2+ ions. Moreover, the His-PDA films also displayed sensitivity to volatile organic solvents or vapors, which could promote vivid color changes from blue to purple or pink. These interesting findings indicate that histidine-functionalized diacetylene may offer a promising way to design smart devices for real applications of sensing or tracing hazardous substances in the future.

Multicolor visual screening of total dithiocarbamate pesticides in foods based on sulfydryl-mediated growth of gold nanobipyramids

Dithiocarbamates (DTCs) pesticides were extensively used as fungicides in a variety of crops during their growth, storage and shipment. The DTCs residue in foods will seriously harm human health. In this study, a novel multicolor colorimetric sensor was developed for visual screening of total DTCs (total of ziram, thiram and zineb) based on sulfhydryl-mediated growth of gold nanobipyramids (AuNBPs). We demonstrated that DTCs can absorb on AuNBPs seed’s surface via the formation of Au–S bonds and thus impede the 8-hydroxyquinoline (8-HQ)-promoted AuNBPs growth, which generates DTCs concentration-corresponding color changes. The developed sensor has vivid color changes, short analysis time, higher sensitivity and excellent specificity. It can be used to detect as low as 50 nM of total DTCs by bare eye observation and 17–18 nM of total DTCs by UV–visible spectrometry. By using the multicolor sensor, we have successfully screened total DTCs in apple and black tea by bare eye observation, and detected total DTCs in apple and black tea by UV–visible spectrometry with a recovery of 90%–104% and a relative standard deviation (RSD, n = 5) < 5%. The results obtained with our method consisted well with those obtained with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), verifying that our method had good accuracy and reliability. Especially, the visual detection limit of our method is much lower than the maximum residue limit of total DTCs in vegetable and fruits. All above features make our sensor a promising method for rapid on-site screening of total DTCs in vegetable and fruits by only bare eye observation.

Manganese dioxide nanosheet-mediated etching of gold nanorods for a multicolor colorimetric assay of total antioxidant capacity

A simple and efficient strategy based on the manganese dioxide (MnO2) nanosheet-mediated etching of gold nanorods (AuNRs) has been demonstrated, affording an effective and convenient way to develop a high-resolution multicolor colorimetric method for the visual detection of antioxidants. The UV−visible absorption spectroscopy and transmission electron microscopy results revealed that the MnO2 nanosheets etched the AuNRs quickly in weakly acidic solutions at room temperature, resulting in a significant blue shift in the AuNR longitudinal local surface plasmon resonance peak and vivid color changes. The feasibility of the etching process was theoretically evaluated by comparing the standard electron potentials of Au(I)/Au(0) and Mn(IV)/Mn(II). Changes in the chemical valencies of Au and Mn during the etching process were analyzed via X-ray photoelectron spectroscopy, which further confirmed that the etching process occurred. Key factors, including the concentrations of the MnO2 nanosheets, cetyltrimethylammonium bromide, and H+, and incubation time, were then investigated. The application of MnO2 nanosheet-mediated AuNR etching for antioxidant analysis was based on the antioxidant-induced decomposition of MnO2 nanosheets. With the merits of simplicity and user-friendliness, this method provides a promising platform for the visual detection of total antioxidant capacity in real beverages.

Detection of ferrous ion by etching-based multi-colorimetric sensing of gold nanobipyramids

Colorimetric sensing methods based on non-spherically symmetric gold (Au) nanoparticles have become a powerful tool in the field of biomedical detection due to their intriguing plasmonic properties. In this study, Au nanobipyramids (Au NBPs) were used as colorimetric sensing probes to detect ferrous ions (Fe2+) through tip etching. The quick etching of Au NBPs along the longitudinal direction by superoxide radicals generated by the reaction of Fe2+ and H2O2 led local surface plasmon resonance (LSPR) to blue shift and produced vivid color change that could be used for visual inspection. Under the optimal reaction conditions, the peak shift of the Au NBPs and the logarithm of the concentrations of Fe2+ had a linear relationship in the range of 10 nM to 10 μM, with a very low detection limit of 1.29 nM. During the etching process, a different end shape of the Au nanoparticles results in a different process for the morphology transition, which makes the degree of spectral change and detection sensitivity significantly different. In the presence of trace amounts of Fe2+ (<1000 nM), the detection sensitivity of Au NBPs with sharp ends which rely on aspect ratio and truncation is nine times higher than that of gold nanorods with round ends which only rely on aspect ratio. Although the color change of larger-sized Au NBPs was not clear during detection, the LSPR peak shift was more severe. Therefore, the system provides different modes for detecting Fe2+ according to Au NBPs with different sizes and characteristics.

Macroscopic Au@PANI Core/Shell Nanoparticle Superlattice Monolayer Film with Dual-Responsive Plasmonic Switches.

The self-assembled gold nanoparticle (NP) superlattice displays unusual but distinctive features such as high mechanical and free-standing performance, electrical conductivity, and plasmonic properties, which are widely employed in various applications especially in biological diagnostics and optoelectronic devices. For a two-dimensional (2D) superlattice monolayer film composed of a given metal nanostructure, it is rather challenging to tune either its plasmonic properties or its optical properties in a reversible way, and it has not been reported. It is therefore of significant value to construct a free-standing 2D superlattice monolayer film of gold nanoparticles with an intelligent response and desired functions. Herein, we developed an easy and efficient approach to construct a gold nanoparticle superlattice film with a dual-responsive plasmonic switch. In this system, gold nanoparticles werecoated by polyaniline (PANI) and then interracially self-assembled into a monolayer film at the air-liquid interface. The PANI shell plays two important roles in the superlattice monolayer film. First, the PANI shell acts as a physical spacer to provide a steric hindrance to counteract the van der Waals (vdW) attraction between densely packed nanoparticles (NPs), resulting in the formation of a superlattice by adjusting the thickness of the PANI shell. Second, the PANI shells provide the superlattice film with multiple stimuli such as electrical potential and pH change, leading to reversible optical and plasmonic responsiveness. The superlattice monolayer film can show a vivid color change from olive green to pink, or from olive green to violet by the change of the corresponding stimuli. Also, the localized surface plasmonic resonance (LSPR) of the superlattice monolayer film can be reversibly modulated by both by changing the local pH and applying an electric potential. Notably, a significant plasmonic shift of 157 nm can be achieved in the superlattice monolayer film when the PANI shell with a thickness of 35 nm and gold nanorods as a core were used. The superlattice monolayer film with dual-responsive plasmonic switches is promising for a range of potential applications in optoelectronic devices, plasmonic and colorimetric sensors, and surface-enhanced Raman scattering (SERS).

Electrochromism and electrochromic devices of new extended viologen derivatives with various substituent benzene

New electrochromic devices based on six extended viologen derivatives with various aromatic substituents were manufactured and systematically investigated. With the introduction of various substituents, six extended viologen derivatives exhibit an unprecedented electrochromic property among previous researches on viologens. Electrochromic devices containing these derivatives as the working electrode present vivid color changes, high optical contrast, fast response and excellent durability. Additionally, the extended skeletal pyridine π-system endows these viologens derivatives with unanticipated electrofluorochromic behavior, which provides the devices of these extended viologens multifunction. To sum up, preeminent optical and electrical performances indicate that these extended viologen derivatives are promising for new-generation electrochromic applications.

Hydroxychalcone dyes that serve as color indicators for pH and fluoride ions.

A chalcone, which is composed of two aromatic rings bridged by an α,β-unsaturated carbonyl group, exhibits a variety of biological activities. With an objective to develop a novel chalcone-based functional dye, we have synthesized a chalcone diol CLN1, bearing two OH groups at the 2-positions on both phenyl rings, as well as reference compounds CLN2–6, and found that it serves as color indicators for pH and fluoride ions. CLN1 showed a vivid color change from colorless to yellow (halochromism) in water at pH ≥ 10. Furthermore, it presented a selective color change from colorless to red upon the addition of TBAF in an organic solvent such as CH3CN. CLN1 provided a strong red-shifted absorption band in the visible region under alkaline conditions in water and upon the addition of TBAF in CH3CN. The absorption spectral study together with TD-DFT calculations and X-ray crystallographic analysis revealed that the characteristic π-resonant structures of CLN1 caused by the ionization or OH–F− interactions and the planar conformation due to its intramolecular hydrogen bonding may provide a strong charge transfer (CT) absorption in the visible region.

A multifunctional perylenediimide-based dual-analyte chemodosimeter for specific and rapid detection of H2S and Pd0 in water, biofluids, live cells and solid state

We report design and synthesis of heterogeneously bay functionalized perylenedimide PN-PDI, endowed with two differentialy reacting functional groups –NO2 and propargyloxy, as dual analyte chemodosimeter for differential and instantaneous colorimetric (NIR) and fluorescence responses towards H2S and Pd0 with vivid color changes. The respective colorimetric and fluorescent detection limits for H2S (1.21 nM and 6.6 nM) and Pd0 (3.05 nM and 3.3 nM) are based on S/N = 3. Furthermore, the practical utility of PN-PDI for the detection of H2S and Pd0 has been demonstrated in blood serum, urine and live A549 cells. PN-PDI based test strips can be used to detect H2S 2.8 pg/cm2 and Pd0 11.5 pg/cm2 by the naked eye. The results of UV–vis, fluorescence spectroscopic and 1H NMR titration studies confirm that mechanism of H2S sensing is through both reduction of –NO2 group to –NH2 and thiolysis reactions, whereas mechanism of Pd0 sensing is through depropargylation reaction of propargyloxy group in PN-PDI. The multiple outputs have been further utilized to construct NOR and INH logic functions.

Phenothiazine-based fluorescence probe for ratiometric imaging of hydrazine in living cells with remarkable Stokes shift.

By modifying the 10-butyl-2-methoxy-10H-phenothiazine-3-carbaldehyde with malonontrile group, a new fluorescent sensor PBM for selective detection of hydrazine in ratiometric mode has been developed. Probe PBM owned the advantages of quick response (10 min), remarkable Stokes shift (168 nm for PBM, 161 nm for PBM-NH2), excellent selectivity, high sensitivity (detection limit of 63.2 nM was obtained from in vitro experiment), profound ratiometric change (82-fold) and low cytotoxicity in response to hydrazine. Additionally, it could be utilized to monitor hydrazine in gas state with various concentrations through vivid color changes and imaged hydrazine in living MCF-7 cells with excellent performance.

β-carboline-based turn-on fluorescence chemosensor for quantitative detection of fluoride at PPB level.

A novel β-carboline-based chemosensor, having an acidic NH proton that leads to fluoride-induced deprotonation involving a vivid color change from colorless to yellow is described. The absorption spectrum of the chemosensor in acetonitrile has a peak at 375 nm, which changes to 428 nm with the gradual addition of only fluoride in the solution with a clear isosbestic points at 357 nm and 392 nm. More interestingly, the chemosensor gives a turn-on type of fluorescence at 554 nm in the presence of fluoride. Further it was found that the sensor is highly selective towards fluoride over other anions including chloride, bromide, iodide, nitrate, borate, perchlorate and can quantitatively detect fluoride at ppb level with a limit of detection of 0.02 mg/ L or 20 ppb. The chemosensor was successfully demonstrated to assess the fluoride concentration in the tap water.

Cryptosporidium parvum oocyst directed assembly of gold nanoparticles and graphene oxide

Understanding the interactions between inorganic nanomaterials and biological species is an important topic for surface and environmental chemistry. In this work, we systematically studied the oocysts of Cryptosporidium parvum as a model protozoan parasite and its interaction with gold nanoparticles (AuNPs) and graphene oxide (GO). The as-prepared citrate-capped AuNPs adsorb strongly on the oocysts leading to a vivid color change. The adsorption of the AuNPs was confirmed by transmission electron microscopy. Heat treatment fully inhibited the color change, indicating a large change of surface chemistry of the oocysts that can be probed by the AuNPs. Adding proteases such as trypsin and proteinase K partially inhibited the color change. DNA-capped AuNPs, on the other hand, could not be adsorbed by the oocysts. GO was found to wrap around the oocysts forming a conformal shell reflecting the shape of the oocysts. Both citrate-capped AuNPs and GO compromised the membrane integrity of the oocysts as indicated by the propidium iodide staining experiment, and they may be potentially used for inactivating the oocysts. This is the first example of using nanomaterials to probe the surface of the oocysts, and it suggests the possibility of using such organisms to template the assembly of nanomaterials.

A morphology-based ultrasensitive multicolor colorimetric assay for detection of blood glucose by enzymatic etching of plasmonic gold nanobipyramids

An ultrasensitively multicolor colorimetric assay on the basis of enzyme-catalyzed reaction mediated etching of gold nanobipyramids (Au NBPs) is developed for detection of blood glucose with naked eye. This assay depends on the catalytic oxidation of H2O2 (generated from glucose oxidation) by horseradish peroxidase (HRP) to generate hydroxyl radicals (•OH) with strong oxidizability, which can accelerate the Au NBPs etching and accompany with vivid color changes and localized surface plasmon resonance (LSPR) blue shift. On the basis of this, the proposed colorimetric glucose assay accomplishes a dynamic range of 0.05–90 μM with detection limit of 0.02 μM, which is almost three orders of magnitude lower than that (10 μM) based on gold nanorods (Au NRs). Moreover, the approximate glucose levels can be intuitively and conveniently judged by the color changes with naked eye. Most importantly, visually distinguish between healthy people and diabetic patients by naked eye dispense with any sophisticated instrument is the most important highlight of this colorimetric assay, indicating the available potential for diagnosis. To the best of our knowledge, this is the first report of colorimetric assay using Au NBPs as etching substrates for visually analysis of glucose.

Noble Metal Nanoparticle-Based Multicolor Immunoassays: An Approach toward Visual Quantification of the Analytes with the Naked Eye.

Noble metal nanoparticle-based colorimetric sensors have become powerful tools for the detection of different targets with convenient readout. Among the many types of nanomaterials, noble metal nanoparticles exhibit extraordinary optical responses mainly due to their excellent localized surface plasmon resonance (LSPR) properties. The absorption spectrum of the noble metal nanoparticles was mostly in the visible range. This property enables the visual detection of various analytes with the naked eye. Among numerous color change modes, the way that different concentrations of targets represent vivid color changes has been brought to the forefront because the color distinction capability of normal human eyes is usually better than the intensity change capability. We review the state of the art in noble metal nanoparticle-based multicolor colorimetric strategies adopted for visual quantification by the naked eye. These multicolor strategies based on different means of morphology transformation are classified into two categories, namely, the etching of nanoparticles and the growth of nanoparticles. We highlight recent progress on the different means by which biocatalytic reactions mediated LSPR modulation signal generation and their applications in the construction of multicolor immunoassays. We also discuss the current challenges associated with multicolor colorimetric sensors during actual sample detection and propose the future development of next-generation multicolor qualification strategies.

A near-infrared BODIPY-based fluorescent probe for ratiometric and discriminative detection of Hg2+ and Cu2+ ions in living cells

A near-infrared distyryl boron dipyrromethene-based sensor bearing one bis(1,2,3-triazole)amino receptor has been synthesized. This probe selectively and quickly binds to Hg2+ and Cu2+ ions in CH3CN/H2O (5:1 v/v) and exhibits remarkably blue-shifted absorption and fluorescence bands due to the inhibition of the intramolecular charge transfer process. The fluorescence changes of this probe upon binding to Hg2+ or Cu2+ ion are totally different, undergoing a ratiometric fluorescence enhancement (for Hg2+) or a fluorescence quenching (for Cu2+) mechanism. The corresponding vivid color changes can be easily seen by the naked eye. This probe was further introduced into Hela cells for living cell imaging and found to discriminate Hg2+ and Cu2+ ions through two near-infrared fluorescence emission channels. These overall results indicate that this Click-derived near-infrared BODIPY-based probe is potentially useful for ratiometric and discriminative detection of Hg2+ and Cu2+ ions in solutions and living cells.