Fluorescence Color Change Research Articles

Lanthanide coordination polymer nanoparticles as a ratiometric fluorescence sensor for real-time and visual detection of tetracycline by a smartphone and test paper based on the analyte-triggered antenna effect and inner filter effect

Lanthanide coordination polymer nanoparticles (LML-Eu3+-GMP CPNPs) were fabricated as a ratiometric fluorescence sensor for real-time and visual assays of tetracycline (TC). The LML-Eu3+-GMP CPNPs were prepared by spontaneous self-assembly of Eu3+, luminol (LML) and guanosine 5′-monophosphate (GMP) at room temperature, which only emitted blue fluorescence dominated by LML, and no red characteristic fluorescence of Eu3+ was observed. In the presence of TC, TC can trigger the antenna effect (AE) and inner filter effect (IFE), the blue fluorescence of LML-Eu3+-GMP CPNPs is quenched by TC via IFE, and the red characteristic fluorescence of Eu3+ can be turned on through AE. When sodium citrate (Cit) is added to the sensing system, it can further enhance the red fluorescence of Eu3+. The dual-ligand CPNP sensor has a rapid fluorescence response, noticeable fluorescence color change, good selectivity, and high sensitivity with a detection limit of 3.4 nM. It was successfully applied to detect TC in honey, milk, lake water and tap water. Meanwhile, the portable smartphone and test paper were applied to develop POCT devices for real-time and visual detection of TC, which could offer a promising application for real-time and semiquantitative assays of TC.

Fluorescence-color-changing biomimetic tough films with simultaneous shape-deformation triggered by pH

Stimuli-responsive materials with complex practical functions that could imitate certain behaviors of living organisms have wide potential applications in frontier fields. However, the fabrication of stimuli-responsive films with simultaneous change in fluorescence color and shape in response to a single stimulus, especially by a simple fabrication strategy, remains a challenge. Herein, a simple hydrogel-film-post crosslinking strategy is proposed to prepare films that exhibit fluorescence change accompanying with shape deformation under pH stimulus. The synchronous changes are realized by the combination of dynamic boron chemistry and pH-sensitive lanthanide complexes. Under different pH conditions, the protonation/deprotonation of the ligands coordinated to Eu3+ ions could generate switchable on/off fluorescence behavior, while the association/dissociation of borate ester bonds between 3-aminobenzeneboronic acid (SA-PBA) and polyvinyl alcohol (PVA) could lead to macroscopic deformation. The existence of borate ester bonds is beneficial to the mechanical properties of composite films. Under pH stimulus, the film-based artificial flower could simulate the flowering of natural flowers accompanying with color changes and the film-based gripper could grasp object with a visual signal, which demonstrates that the SA-PBA/PVA/EuL films have great potential for wide application.

Tunable Thermofluorochromic Sensors Based on Conjugated Polymers

AbstractEven though thermofluorochromic materials are eternal candidates for their use in multiple applications, they are still limited as they require complex synthetic strategies to accomplish tunable optical properties and/or provide optical changes only over a very wide temperature range. By taking advantage of the high sensitivity of the optical properties of conjugated polymers and oligomers to the external environment, herein phase change material (PCM)‐based thermofluorochromic mixtures are created, where the solid‐to‐liquid transition of the PCM host triggers a sharp fluorescence color change of the dispersed polymers/oligomers. Fluorophore conjugation length, concentration, and PCM nature can be used to vary the spectral properties of the resulting materials along the visible region, covering a large part of the CIE 1931 color space. For the preparation of functional devices, this behavior can be directly transferred to the solid state by soaking or printing cellulose papers with the obtained thermofluorochromic mixtures as well as by structuring them into solid lipid particles that can be dispersed within polymer matrices. The resulting materials show very promising features as thermal sensors and anticounterfeiting labels.

2‐Aryl‐1H‐benz[de]isoquinolinium Ions: Cationic Dyes Displaying Mechanochromism and Crystallochromism

Abstract2‐Aryl‐5,8‐di‐tert‐butyl‐1H‐benz[de]isoquinolinium tetrafluoroborates were synthesized and crystalized to form yellow to orange crystals. Absorption and fluorescence maxima (λABS and λFL‐SL) of the compounds in CH2Cl2 depend on the electronic and steric properties of the aryl ring substituents and closely match those arising from theoretical calculations. λABS and λFL‐SL values of the compound possessing bulky 2,6‐diisopropylphenyl substituents are the shortest among the substances because of sterically promoted retardation of conjugation between the isoquinolinium and aryl ring planes. In contrast, solid‐state fluorescence maxima (λFL‐SD) of the compounds are not closely correlated with the electronic properties of the aryl substituents. Furthermore, one crystalline form of both the 4‐trifluoromethylphenyl and 4‐nitrophenyl derivatives exhibit mechanochromic and crystallochromic behavior reflected in absorption and fluorescence color changes. X‐ray diffraction and crystallographic analysis reveal that the solid state photophysical properties of these substances are related to different molecular stacking interactions occurring in different crystalline forms.

A ratiometric fluorescence platform based on carbon dots for visual and rapid detection of copper(II) and fluoroquinolones.

A simple smartphone-integrated ratiometric fluorescent sensing system for visual determination of copper ions (Cu2+) and fluoroquinolones (FQs) was developed based on carbon dots (CDs) which were synthesized through the high-temperature pyrolysis of citric acid. In this system, with the fluorescence resonance energy transfer effect between CDs and 2,3-diaminophenazine (oxOPD), the detection of Cu2+ and ciprofloxacin (CIP, an example for FQs) was realized. Cu2+ catalyzes the oxidation of OPD to form oxOPD with yellow fluorescence, resulting in the quenching of CDs. In addition, CIP can inhibit the catalytic activity of Cu2+ and induce the recovery of CDs fluorescence. Under the excitation of 400nm, the changes of CDs fluorescence at 472nm and oxOPD fluorescence at 556nm were monitored. The detection results showed that the sensing system exhibited good selectivity and sensitivity to Cu2+ and CIP with the limit of detection of 2.32 × 10-8mol L-1 and 0.2ngmL-1, respectively. In addition, a smartphone was developed as a portable analyzer to capture the change of fluorescence color and quickly analyze the concentration of Cu2+ and CIP. The proposed smartphone-based sensing platform has satisfactory sensitivity, and it has application prospects for detecting Cu2+ and FQs in food safety monitoring.

Fluorescence and Colorimetric Dual-Mode Ratiometric Sensor Based on Zr-Tetraphenylporphyrin Tetrasulfonic Acid Hydrate Metal-Organic Frameworks for Visual Detection of Copper Ions.

As a special heavy metal ion, copper ions (Cu2+) play an indispensable role in the fields of environmental protection and safety. Their excessive intake not only easily leads to diseases but also affects human health. Therefore, it is particularly important to construct a facile, effective, and highly selective Cu2+ probe. Herein, a novel Zr-tetraphenylporphyrin tetrasulfonic acid hydrate (TPPS) metal-organic framework (ZTM) was fabricated using TPPS as the ligand and exhibited strong red fluorescence with a high quantum yield of 12.22%. In addition, we designed a ratiometric fluorescent probe by introducing green fluorescein isothiocyanate (FITC), which was not subject to environmental interference and had high accuracy. When exposed to different amounts of Cu2+, the fluorescence emission at 667 nm from ZTMs is remarkably quenched, while that at 515 nm from FITC is enhanced, accompanied by a change in the solutions' fluorescence color from red to green under a UV lamp. Besides, the ZTMs solutions display an excellent ratiometric colorimetric response for Cu2+ and produce an obvious color change (from green to colorless) that is visible to the naked eye. The fabricated ZTMs@FITC fluorescent probe exhibits distinguished performance for Cu2+ detection with linear ranges of 0.1 to 5 μM and 5 to 50 μM, as well as a low detection limit of 5.61 nM. Moreover, a colorimetric sensor based on ZTMs exhibits a good linear range from 0.1 to 20 μM for Cu2+ with the detection limit of 4.96 nM. Furthermore, the dual-signal ratiometric sensor has significant specificity for Cu2+ and is successfully applied for monitoring Cu2+ in water samples, which proves its practical application value in the environment and biological systems.

PH Oscillator-Driven Jellyfish-like Hydrogel Actuator with Dissipative Synergy between Deformation and Fluorescence Color Change.

Development of soft actuators with complex practical functions is significant for imitating the behaviors of living organisms. However, it is still a challenge to fabricate artificial soft actuators with jellyfish-like synergistic deformation and fluorescence color change (SDFC) and autonomous dynamic behavior, but such a system could obviously endow the classic soft actuators with more functions. Herein, we proposed to utilize tetra(4-pyridylphenyl)ethylene (TPE-4N) luminogen with pH-responsive aggregation-induced emission (AIE) to fabricate the AIE active hydrogel, which could be further employed to obtain an anisotropic bilayer soft actuator based on strong interfacial adhesion with acrylic acid (AA) gels. Furthermore, artificial flower-shape actuators showing SDFC behaviors were demonstrated. On the basis of these findings, jellyfish-inspired autonomous gel actuators driven by a pH oscillator have been fabricated, in which periodical SDFC behaviors completely regulated by the system itself without repetitive on/off switches of external stimuli were well synchronized with the pH oscillator. The described combination of nonlinear chemistry and responsive hydrogels actuator opens pathways toward out-of-equilibrium SDFC devices with autonomous behavior useful for biomimetic fields.

Real-Time Loop-Mediated Isothermal Amplification (LAMP) Method for Quantitative Salmonella Typhi Detection Based on ViaB Gene

Background & Objective: There is a vast range of diseases caused by Salmonella including gastroenteritis, enteric fever, bacteraemia, and focal infection. Salmonella infection is usually transmitted to humans by consuming foods or water contaminated with animal or human waste. This study aims to design a quantitative-LAMP method for real-time detection of Salmonella enterica serovar Typhi (S. Typhi), the causative agent of Typhoid fever. Materials & Methods: A new LAMP primer set was designed and used based on the ViaB gene to specifically detect S. Typhi. The genome of some Salmonella-related and non- Salmonella-related bacteria was subjected to the LAMP assay for detection of S. Typhi to evaluate its analytical specificity, its analytical sensitivity and limit of detection (LOD). Further, turbidity in tubes was measured by a turbidimeter, and then a standard curve was depicted by plotting (Tt) time threshold values against the logarithm of ViaB gene copy number and this standard curve helped the researchers a lot to obtain a quantitative method. Results: The Salmonella Typhi LAMP assay specifically assessed the ViaB gene. It was shown that the analytical sensitivity of the assay was 0.28 fg using agarose gel electrophoresis or amplification plots in Loop amp real-time turbidimeter system, whereas the amplification was 2.8 fg under direct observation of fluorescent color changes. In the proposed methods, the lower limit of detection (LLOQ) of the assays was ~1 and 8 copies of the ViaB gene, respectively. In the LAMP assay for the quantitative detection of Salmonella Typhi, the linear correlation (r2= 0.97) was calculated between the log copy number and Tt values. Conclusions: The Salmonella Typhi LAMP assay is a simple and accurate tool to detect the causative agent of Typhoid fever that may be designed for clinical laboratories.

Tunable Fluorescence and Afterglow in Organic Crystals for Temperature Sensing.

The modulation of the properties of emission from multiple emission states in a single-component organic luminescent material is highly desirable in data anticounterfeiting, information storage, and bioapplications. Here, a single-component luminescent organic crystal of difluoroboron diphenyl β-diketonate with controllable multiple emission colors is successfully reported. The temperature-dependent luminescence experiments supported by high-level theoretical calculations demonstrate that the ratio of the fluorescence between the monomer and excimer and the phosphorescence maxima of the excimer can be effectively regulated. In addition, the temperature-dependent fluorescence and afterglow dual-emission color changes provide a new strategy for the design of highly accurate double-checked temperature sensors.

Carbocyanine-Based Fluorescent and Colorimetric Sensor Array for the Discrimination of Medicinal Compounds

Array-based optical sensing is an efficient technique for the determination and discrimination of small organic molecules. This study is aimed at the development of a simple and rapid strategy for obtaining an optical response from a wide range of low-molecular-weight organic compounds. We have suggested a colorimetric and fluorimetric sensing platform based on the combination of two response mechanisms using carbocyanine dyes: aggregation and oxidation. In the first one, the analyte forms ternary aggregates with an oppositely charged surfactant wherein the dye is solubilized in the hydrophobic domains of the surfactant accompanied with fluorescent enhancement. The second mechanism is based on the effect of the analyte on the catalytic reaction rate of dye oxidation with H2O2 in the presence of a metal ion (Cu2+, Pd2+), which entails fluorescence waning and color change. The reaction mixture in a 96-well plate is photographed in visible light (colorimetry) and the near-IR region under red light excitation (fluorimetry). In this proof-of-concept study, we demonstrated the feasibility of discrimination of nine medicinal compounds using principal component analysis: four cephalosporins (ceftriaxone, cefazolin, ceftazidime, cefotaxime), three phenothiazines (promethazine, promazine, chlorpromazine), and two penicillins (benzylpenicillin, ampicillin) in an aqueous solution and in the presence of turkey meat extract. The suggested platform allows simple and rapid recognition of analytes of various nature without using spectral equipment, except for a photo camera.

A cationic amphiphilic tetraphenylethylene derivative with hydrochromic sensitive property: Applications in anti-counterfeiting ink and rewritable paper

Since the discovery of aggregation induced emission (AIE) phenomenon, various stimuli-responsive materials have been rapidly developed, but there are still great challenges in the application of ink printing due to the bad water solubility. In this research, a new cationic amphiphilic TPE-functionalized pyridine salt (TPE-OTs) was designed, which shows good water solubility and hydrochromic properties. The optical properties of the compound have been studied, which is equipped with the typical AIEE characteristics and TICT effect. The compound can self-assemble to form aggregates with a particle size of about 30 nm in water. What is more, the compound is responsive to the environmental humidity, whose fluorescent color changes from green to yellow as the humidity gradually increased. Based on this characteristic, we applied it to the fluorescent anti-counterfeiting ink, realizing the protection and encryption of information.

Rapid detection of the E198A mutation of carbendazim-resistant isolates in Colletotrichum gloeosporioides by loop-mediated isothermal amplification

Apple bitter rot is a serious agricultural disease caused by Colletotrichum gloeosporioides. In recent years, carbendazim-resistant C. gloeosporioides strains bearing an E198A point mutation in the β-tubulin gene (GAG to GCG) have emerged, threatening global apple production. As such, rapidly detecting the presence of this E198A mutation in C. gloeosporioides isolates is essential in order to monitor the spread of this pathogen and to prevent outbreaks of disease. Herein, we developed a simple loop-mediated isothermal amplification (LAMP) approach to detecting the E198A mutation in C. gloeosporioides isolates from ‘Gala’ apple samples. This optimized LAMP protocol was sufficient to establish the E198A genotype of a given isolate following a 60 min incubation at 63 °C by using four specific primers. The results of this reaction could be interpreted visually based on a fluorescent yellow-green color change upon the addition of the SYBR Green I dye, and were additionally confirmed via gel electrophoresis. Importantly, this LAMP assay was capable of rapidly and reliably detecting apples that were infected with carbendazim-resistant isolates harboring this E198A mutation. In conclusion, this LAMP assay in this study can rapidly, specifically, and sensitively detect cases of apple bitter rot caused by C. gloeosporioides isolates harboring the E198A mutation.

Fluorescence Colour Control in Perylene-Labeled Polymer Chains Trapped by Nanotextured Silicon.

The ability to modulate, tune, and control fluorescence colour has attracted much attention in photonics-related research fields. Thus far, it has been impossible to achieve fluorescence colour control (FCC) for material with a fixed structure, size, surrounding medium, and concentration. Here, we propose a novel approach to FCC using optical tweezers. We demonstrate an optical trapping technique using nanotextured Si (black-Si) that can efficiently trap polymer chains. By increasing the laser intensity, the local concentration of perylene-labelled water-soluble polymer chains increased inside the trapping potential. Accordingly, the excimer fluorescence of perylene increased while the monomer fluorescence decreased, evidenced by a fluorescence colour change from blue to orange. Using nanostructure-assisted optical tweezing, we demonstrate control of the relative intensity ratio of fluorescence of the two fluorophores, thus showing remote and reversible FCC of the polymer assembly.

Fluorescence Colour Control in Perylene‐Labeled Polymer Chains Trapped by Nanotextured Silicon

AbstractThe ability to modulate, tune, and control fluorescence colour has attracted much attention in photonics‐related research fields. Thus far, it has been impossible to achieve fluorescence colour control (FCC) for material with a fixed structure, size, surrounding medium, and concentration. Here, we propose a novel approach to FCC using optical tweezers. We demonstrate an optical trapping technique using nanotextured Si (black‐Si) that can efficiently trap polymer chains. By increasing the laser intensity, the local concentration of perylene‐labelled water‐soluble polymer chains increased inside the trapping potential. Accordingly, the excimer fluorescence of perylene increased while the monomer fluorescence decreased, evidenced by a fluorescence colour change from blue to orange. Using nanostructure‐assisted optical tweezing, we demonstrate control of the relative intensity ratio of fluorescence of the two fluorophores, thus showing remote and reversible FCC of the polymer assembly.

Molecular Aggregation Dynamics via a Liquid-like Cluster Intermediate during Heterogeneous Evaporation as Revealed by Hyperspectral Camera Fluorescence Imaging.

A hyperspectral camera (HSC) is a camera with great potential to obtain spectral information at each pixel, together with spatial imaging. HSC fluorescence imaging enables the molecular aggregation dynamics of the evaporative crystallization process to be followed in real-time. The key intermediate liquid-like cluster state for the two-step nucleation mechanism is visualized by the fluorescence color changes of mechanochromic luminescent dibenzoylmethanatoboron difluoride derivatives. Three types of emissive species (Crystal, BG-aggregates, and Amorphous) are generated from monomers in solution (low order and density) via liquid-like cluster (high density and low order) during solvent evaporation. These emissive species have partially different aggregated states based on fluorescence decay and fluorescence excitation spectral measurements. In terms of crystallization dynamics, our results indicate that it is important not only to generate supersaturated states but also to maintain the survival time of the liquid-like cluster. Moreover, we demonstrate that HSC fluorescence imaging can be a powerful tool for visualizing heterogeneous molecular aggregation processes.

A confined carbon dot-based self-calibrated fluorescence probe for visible and highly sensitive moisture readouts

Excellent luminescent materials are essential for high-performance fluorescent nanosensors. Here, a new-type of self-calibrated humidity sensor is established through monitoring the fluorescent color change of carbon dots (CDs) confined in sodium hydroxide (CDs@NaOH). The CDs are prepared by a facile and rapid microwave-assisted heating method using citric acid, urea, and NaOH as precursors. The confinement effect from the NaOH reduces the nonradiative transition and suppresses the aggregation-induced quenching of the CDs in the solid. Compared with other sensors based on CD fluorescent visualization, the sensor has good linearity and a wide humidity-detection range from 6.9% to 95.4%. With the increased relative humidity, the fluorescence color of the sensor changes from green to blue. The proposed sensing mechanism is due to the breaking and reforming of hydrogen bonds and proton transfer occurring at the CD-NaOH matrix interfaces. These findings suggest a potential role for the spatial confinement effect and may provide an avenue for developing highly sensitive humidity readouts.

A Novel and Reactive Fluorescent “Turn‐on” Probe Based on Benzimidazole Derivative for Selective CN−Detection

AbstractA novel fluorescent probeLbased on benzimidazole derivative for selective CN−detection was designed and synthesized, and its structure was identified by spectral analysis. In DMSO/H2O (v/v=7 : 3, pH=9) solvent system, the fluorescence intensity forLenhances and the color change from yellow to colorless and purple was immediately observed at 426 nm, but there was no obvious color change when other anions instead of CN−was added to the system. The mechanism on CN−recognition was also studied by1H NMR, IR, MS analysis and theoretical calculations. The probeLfor CN−detection exhibited high sensitivity, and the molar ratio and lowest detection limit was 1 : 1 and 8.2×10−7 mol L−1, respectively. In addition, the probeLcould be successfully applied to the detection of CN−in bitter almond, and was also used as a test paper, which indicated that the probeLmight conveniently carried out the quick identification and detection of cyanide ion in the environment and food samples through its fluorescent color change under UV lamp.

Color-changing fluorescent DNA probe containing solvatochromic Dansyl-nucleoside surrogate for sensing local variation of DNA duplex

A novel Dansyl-nucleoside surrogate (Dns) based on (±)-trans-4-(hydroxymethyl) piperidin-3-ol was designed and synthesized. The Dns exhibited excellent solvatochromic properties. About 90 nm of red-shift accompanied color change from green to orange could be achieved with an increase of solvent polarity. The Dns was incorporated into oligodeoxynucleotide by phosphoroamidite chemistry. Two kinds of Dns-incorporated fluorescent DNA probes were designed and synthesized for sensing variation of DNA duplexes based on color-changing manner. As a result, the color-changing DNA probe not only can detect complementary oligonucleotide, but also can distinguish mismatch flanked in Dansyl/nucleobase pair by naked eye. Moreover, the change of fluorescence color of sample solutions could be captured by smartphone, and the photographs could be digitalized by image-processing software. Thus, the Dns-incorporated fluorescent DNA probe is expected to open the way to point-of-care assays in the future.

A highly selective fluorescence and absorption sensor for rapid recognition and detection of Cu2+ ions in aqueous solution and film.

A fluorescence and absorption chemosensor (SAAT) based on 5-(hydroxymethyl)-salicylaldehyde (SA) and o-aminothiophenol (AT) was designed and synthesized. SAAT in DMSO-HEPES (20.0 mM, v/v, 1:99, pH = 7.0) solution shows a highly selective and sensitive absorption and an 'on-off' fluorescence response to Cu2+ ions in aqueous solutions over all other competitive metal ions including Na+ , Ag+ , Ba2+ , Ca2+ , Cd2+ , Mg2+ , Zn2+ , Cr3+ , Al3+ , Hg2+ , K+ , Mn2+ , Ni2+ , Sr2+ , Tb3+ and Co2+ . SAAT exhibits ratiometric absorption sensing ability for Cu2+ ions. Importantly, SAAT also can sense Cu2+ ions using fluorescence quenching, the fluorescence intensity of SAAT showed a good linear relationship with Cu2+ concentration, and the detection limit of Cu2+ was 0.34 μM. The results of Job's plot, Benesi-Hildebrand plot, mass spectra, and density functional theory calculations confirmed that the selective absorption and fluorescence response were attributed to the formation of a 1:1 complex between SAAT and Cu2+ . SAAT in test film could identify Cu2+ in water samples using the intuitive fluorescence colour change under a UV lamp. SAAT has great application value as a selective and sensitive chemosensor to discriminate and detect Cu2+ ions.

Highly sensitive, selective, and reusable nanofibrous membrane-based carbon polymer dots sensors for detection of Cr(VI) in water

Core-shell structured fluorescent carbon polymer dots (CPDs) were covalently incorporated onto poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibers to fabricate novel nanofibrous membrane sensors to detect trace amount of heavy metal ions in drinking water systems. The membrane sensor was assembled in a syringe filter cell as a sensor unit together with a volumetric syringe, and fluorescent color changes of the sensors responding to concentrations of Cr(VI) can be identified by naked eyes. The sensor system possesses features of instant detection, low cost, environment-friendliness, and high sensitivity to quantitative measure Cr(VI) in a concentration range of 1–50 ppb, which is much lower than federal permissible limit of Cr(VI) in drinking water. Moreover, the used sensor could be refreshed and reused for many times without obvious fluorescence loss and nanofibrous membrane damage by simply exposing to a 20 μM Vitamin C (VC) solution. The fluorescent color changes of the sensors could be read by an App on a smartphone, which is facile, convenient and suitable for more accurate household operation, showing great prospect for instant on-site detection of Cr(VI) in drinking water.