Fluorescence Color Change Research Articles

Non-conjugated polymer dots for fluorometric and colorimetric dual-mode detection of quercetin

Due to the biochemical and pharmacological activities, the convenient and effective detection of quercetin (Qc) is very important for biochemistry, pharmaceutical chemistry and clinical medicine. A kind of non-conjugated polymer dots (NCPDs) was used as a versatile and sensitive dual-mode optical output for Qc detection, which was synthesized by hyperbranched poly(ethylenimine) (PEI) and l-threonine via environmentallyfriendly way. The dual-mode method proposed in this work had high sensitivity and definiteselectivity for Qc detection. Additionally, it was convenient for the naked eyes to observe the fluorescence brightness and color change.

High-Performance Trichloroacetic Acid Sensor Based on the Intramolecular Hydrogen Bond Formation and Disruption of a Specially Designed Fluorescent o-Carborane Derivative in the Film State.

Discriminative and sensitive detection of environmentally important and health-related trichloroacetic acid (TCA) suffers from various problems such as bulky instruments and time-consuming operation as well as complex sample processing. Herein, we present a rapid, sensitive, and specific method for the detection of gaseous TCA using a fluorescent single-molecule array. An o-carborane-based benzothiazole derivative (CB-BT-OCH3) with specific fluorescence properties was specifically designed and utilized to fabricate a film-based single-molecule array. It was revealed that the fluorescent film is photochemically stable and extremely sensitive to TCA vapor, depicting an observable fluorescence color change from green to blue. The experimental detection limit is 0.2 ppm, which is lower than the safety limit (1 ppm) required by the threshold limit values and biological exposure indices. In addition, the film could show detectable intensity change within 0.2 s. On the basis of multiple signal responses, a conceptual two-channel-based fluorescent TCA sensor was developed. Importantly, the proposed conceptual sensor paves a new route to the development of specific fluorescent film-based sensor arrays with a single fluorophore as sensing units.

Smartphone-based fluorometer for pH detection using green synthesized carbon dots

As a group of heavy-metal-free fluorescent nanomaterials, carbon dots (CDs) have recently received a growing interest as they have high optical absorption activity and are chemically stable, biocompatible, and less toxic. In this paper, the green synthesis of stable CDs by hydrothermal and pyrolysis methods from Parmigiano-Reggiano is performed. An intrinsically emitted fluorescence results from simultaneous generation and the surface passivation of CDs by the mentioned techniques. The responses of hydrothermal CDs to pH occur by emission wavelength at 430 nm under 365 nm excitation. When the pH is increased from 2–12, its emission fluorescence intensity will be reduced. The pH was also analyzed real time by developing a smartphone-based portable recognition platform consisting of an instrument and a self-designed APP called “Image Analyser”. The fluorescence color change of CDs caused by the pH was recorded by the camera of the smartphone and color of pictures was analyzed by APP. The results of both methods are similar, so the CDs based recognition platform are highly practically and efficient tool as they could analyze pH with outstanding functionality, as examined in this study in different samples.

Amphiphilic Conjugated Polyelectrolyte-Based Sensing System for Visually Observable Detection of Neomycin with High Sensitivity

To detect neomycin, one of the common antibiotics in the environment and in food and which may pose harm to human health, a fluorescence sensing system based on an amphiphilic conjugated polyelectrolyte (CPE) was constructed. The CPE, PFPE-COONa, with poly[fluorenyl-alt-p-phenyleneethynylene] (PFPE) as the backbone and carrying four pendant hydrophilic carboxylate groups and two long hydrophobic alkoxyl chains in each repeat unit, was successfully synthesized. The photophysical study found that PFPE-COONa emission was solvent dependent, displaying a 58 nm red shift in wavelength and a nearly 150-fold enhancement in intensity for the emission maximum, by varying the ratios of the mixed solvent. Based on an understanding of the photophysics, the sensing condition was optimization to dissolve PFPE-COONa in the THF/H2O mixed solvent with a ratio of 1:1. The sensing system displayed excellent sensing performance toward neomycin at a neutral pH value. The blue-to-green fluorescence color change of the polymer solution, which can be clearly observed by the naked eye, upon around 0.7 μM of neomycin and the limit of detection (LOD) was calculated to be 0.78 nM. In addition, other possible interferents had no significant influence on the detection of neomycin. The mechanism study confirmed that the polymer aggregation, which induced strong electrostatic static interaction between the carboxylate groups of high density in the polymer and the dense positively charged primary amino groups in neomycin, was the main reason for such a visually fluorescent color change. This study provides a general strategy for the future design of sensing systems for organic pollutants.

Fluorescence Ratio Nanoprobe Consisting of a Carbon Nanodots-Quantum Dots Composite for Visual Detection of Folic Acid in Dry Milk Powders

Folic acid (FA) is a vitamin essential for human physiology; thus, rapid, accurate, and sensitive methods for its detection and quantification in different biological samples are necessary. A fluorescent ratiometric nanoprobe (the complex composed of quantum dots and carbon dots) based on carboxyl-modified quantum dots (QDs) and amino-modified graphene-based carbon dots (CDs) has been developed for the visual determination of folic acid (FA). The nanoprobe is the composition in which QDs were covalently bonded with CDs. Red and blue fluorescence of nanoprobe can be selectively quenched and enhanced by FA, respectively. Thus, the nanoprobe is capable to generate clearly visible fluorescence color change from pink to blue upon exposure to UV light. Depending on the color change and its intensity, FA can be identified, and their concentrations can be determined. The sensor prepared based on the nanoprobe demonstrated good selectivity and sensitivity toward FA with exceptionally low detection limit equal to 0.039 μM. We also prepared a paper-based sensor to demonstrate convenient and simple approach to visually detect FA. Thus, the nanoprobe demonstrated feasibility of rapid real-time quantitative FA detection; considering its simple, effective, and practicality, expectedly it can be used for practical application.

Development of General Methods for Detection of Virus by Engineering Fluorescent Silver Nanoclusters.

Viruses have caused significant damage to the world. Effective detection is required to relieve the impact of viral infections. A biomolecule can be used as a template such as deoxyribonucleic acid (DNA), peptide, or protein, for the growth of silver nanoclusters (AgNCs) and for recognizing a virus. Both the AgNCs and the recognition elements are tunable, which is promising for the analysis of new viruses. Considering that a new virus such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) urgently requires a facile sensing strategy, various virus detection strategies based on AgNCs including fluorescence enhancement, color change, quenching, and recovery are summarized. Particular emphasis is placed on the molecular analysis of viruses using DNA stabilized AgNCs (DNA-AgNCs), which detect the virus's genetic material. The more widespread applications of AgNCs for general virus detection are also discussed. Further development of these technologies may address the challenge for facile detection of SARS-CoV-2.

Humidity‐Responsive Liquid Crystalline Network Actuator Showing Synergistic Fluorescence Color Change Enabled by Aggregation Induced Emission Luminogen

AbstractImitating the structures and behaviors of natural creatures is of great significance to scientists to explore novel materials for practical applications. However, the design and fabrication of biomimetic devices with complex and outstanding performances is still on the way. A bilayer film composed of liquid crystalline networks (LCN) film and hydrochromic aggregation‐induced‐emission molecule‐doped hydrophilic layer is prepared. Under different relative humidity, the composite film can deform and change fluorescence color simultaneously. The influence of the content of the hydrophilic matrix on the fluorescent property and humidity‐responsive behaviors of the bilayer film is investigated. Thanks to the mechanical anisotropy provided by uniform‐aligned LCN film, different modes of deformation of the bilayer film are achievable, like bending, curling, and twisting. More importantly, due to the independence of the LCN film and the non‐mesogenic molecules brought by this bimorph strategy, complex alignment of the LCN film and modification by immiscible molecules are realized in a single LCN actuator. Based on the functional composite film, artificial flowers showing synergistic blooming and shape‐changing is prepared. By regulating the molecular alignment of the LC mesogens of the LCN film, the artificial flowers can imitate various blooming behaviors of natural flowers like confederate jasmine and jade lotus.

Silicon nanoparticles-based ratiometric fluorescence platform: Real-time visual sensing to ciprofloxacin and Cu2+

In this work, a silicon nanoparticles (Si NPs)-based ratiometric fluorescence sensing platform was conveniently fabricated by simply mixing fluorescent Si NPs as co-ligands and reference signal with lanthanide metal ion Eu3+ as response signal. The introduction of ciprofloxacin (CIP) remarkably turned on the characteristic fluorescence of Eu3+ at 590 nm and 619 nm through the “antenna effect”. At the same time, the blue emission of Si NPs at 445 nm kept comparatively stable. A good linear relationship between the ratio fluorescence intensity and CIP concentration in the range of 0.211–132.4 μM with a limit of detection (LOD) of 89 nM was obtained. In the presence of Cu2+, the fluorescence emission of Eu3+ was sharply turned off because of the stronger coordination ability of Cu2+ with CIP, which guaranteed the sequential detection of Cu2+. Meanwhile, the distinct fluorescent color change from bright blue to red, then back to blue, enabled naked-eye visual detection of CIP and Cu2+ in the solution phase and on paper-based test strip, and was successfully applied to determine the levels of CIP in complicated food samples with high sensitivity.

Two-phase activated colorimetric and ratiometric fluorescent sensor for visual detection of phosgene via AIE coupled TICT processes

In this paper, we specifically designed and synthesized an excellent colorimetric and ratiometric fluorescent sensor DPA-CI for rapid and convenient detection of the highly toxic phosgene. DPA-CI was developed by incorporated a diphenylamine (DPA) and a 2-imine-3-benzo[d]imidazole as the enhanced push–pull electronic structure into the coumarin fluorophore matrix. The sensor DPA-CI towards phosgene sensing exhibited both visible colorimetric and ratiometric fluorescent color change in solution and in gaseous conditions with TICT and AIE mechanism respectively, which can be easily distinguished by using the naked eye. Also, the sensor DPA-CI showed splendid sensing performance such as excellent selectivity, rapid response (less than 8 s in THF and 2 min in gaseous condition), and fair sensitivity (limit of detection less than 0.11 ppm in gaseous condition and 0.27 μM in solution). The design strategy based on enhanced push–pull electronic structure with AIE and TICT properties will be helpful to construct a solid optical sensor with excellent potential application prospects for portable and visual sensing of gaseous phosgene through distinct color and ratiometric fluorescence change by the naked eyes.

N-hydroxypropyl substituted 4-hydroxynaphthalimide: Differentiation of solvents and discriminative determination of water in organic solvents

A naphthalimide-based fluorophore (HONIOH) was designed by introducing a hydroxy unit into the 4th position of the aromatic core and a hydroxypropyl unit into the N-imide site. Photophysical properties of HONIOH were highly dependent on solvents, which was ascribed to the excited state proton transfer (ESPT) coupled with intramolecular charge transfer (ICT) mechanism. Further studies demonstrated that HONIOH can be used to recognize N, N-dimethylformamide (DMF) qualitatively and differentiate methanol from ethanol. Three control compounds were synthesized, their photophysical properties were investigated in various solvents, and experimental results revealed that hydroxyl and hydroxypropyl units contribute to the solvents differentiation ability of HONIOH. In addition, HONIOH was successfully applied as a colorimetric, fluorescent probe for the discriminative detection of trace water in organic solvents, such as fluorescence turn-on response accompanied by fluorescent color changes from light yellow to purple in DMF, and fluorescence turn-off response and blue to yellow fluorescent color changes in acetonitrile, tetrahydrofuran, and acetone. We believe that N-substituted 4-hydroxynaphthalimide derivatives may find widespread applications in chemical and biochemical sensing and imaging.

A highly-sensitive “turn on” probe based on coumarin β-diketone for hydrazine detection in PBS and living cells

Herein, a new “turn on” fluorescent probe C-1 is developed to specifically detect hydrazine using coumarin nucleus as the fluorophore and β-diketone as the recognition group. The probe shows high selectivity towards hydrazine over other common ions and amine-containing species, as well as good water solubility and quantitative detectability of hydrazine in concentration range of 1–200 μM. The detection limit is as low as 1.89 ppb, which is lower than the threshold set by EPA (10 ppb). Probe-coated filter papers are confirmed to detect gaseous hydrazine successfully through obvious fluorescence color changes. In addition, the probe has been verified to detect hydrazine in actual water environment and living cells.

Synthesis, structure and properties of luminescent Cd(II) coordination polymers based on imidazole-decorated tetraphenylethylene

Two new cadmium(II) luminescent coordination polymers (CPs), [Cd(L)Cl2]·3DMF (1) and [Cd(L)(DMA)(H2O](ClO4)2·5DMA (2) (L = 1,1,2,2-tetrakis(4-(1H-imidazol-1-yl)phenyl)ethene, DMF = N,N-dimethylformamide, DMA = N,N-dimethylacetamide), were synthesized under solvothermal conditions. Crystallographic analyses reveal that 1 and 2 have different two-dimensional (2 D) network structures. Both 1 and 2 show mechanochromic properties with fluorescent color change from blue to blue-green under UV light. In addition, 1 can be potentially utilized as mechanochromic material as well as a sensor for detection of DMF, exhibiting reversible mechanochromic luminescence with color changes and self-repairing behavior by grinding and soaking in DMF under UV irradiation. Furthermore, 1 can act as potential fluorescence materials for sensing Fe(III).

Smartphone as a simple device for visual and on-site detection of fluoride in groundwater

Developing a portable device for visual and on-site detection of fluoride in groundwater is highly anticipated. In this paper, 2-(tert-butyl-diphenylsilanyloxy)−5-nitro-1H-benzoimidazole (1) has been rationally designed via a silanization reaction for self-calibration detection of fluoride, and the detection limit was calculated as 0.11 μM. The contact of 1 with fluoride would induce the cleavage of Si-O bond and trigger the emergence of excited state intramolecular proton transfer (ESIPT) process, and then the enol-like emission at 437 nm decreased accompanying with the increase of keto-like tautomerism emission at 550 nm. More importantly, considering the demand of field detection for fluoride in groundwater and combining the function of smartphone to obtain the chroma of photos. The chroma value of the fluorescence color changes from blue to yellow could be conveniently determined through a color recognizer application installed in smartphone. The device can accurately reflect the concentration of fluoride by analyzing the chroma value. The test in actual water samples confirmed that the simple device based on smartphone could be used efficiently for visual, on-site and accurate detection of fluoride in groundwater.

An aroylhydrazone-containing diarylethene derivative derived chemosensor for colorimetric and fluorimetric dual sensing Cu2+

A diarylethene derivative with an aroylhydrazone unit was designed and synthesized as a colorimetric and fluorimetric dual responsive sensor for Cu2+ with high selectivity and rapid response. Connecting 7-diethylamino-3-hydrazide-coumarin moiety and 2-pyridyl-containg diarylethene provided an intramolecular charge transfer (ICT) system with affluent binding site (N^N^O), which was developed for the selective and sensitive detection of Cu2+ by dual colorimetric and fluorimetric responses. A clear Cu2+-induced ratiometric colorimetric sensor with color change from light yellow to orange red and on-off fluorescence with fluorescence color change from bright cyan to deep teal was constructed. At the same time, colorimetric and fluorimetric responses to Cu2+ were both achieved at the photostationary state. Based on the obvious color change, the sensor was used for the fabrication of test strips that can be used as the standard cards for detecting Cu2+. This study is expected to facilitate and broaden the application of diarylethene derivative in tracing Cu2+ in future work.

Benzimidazole-functionalized fluorescent probe for rapid detection of 2,4,6-trinitrophenol and Ag+ in semiaqueous medium

In this study, a simple fluorescent chemosensor with good fluorescence properties was synthesized, and was used to develop a sensitive and selective sensor, for the determination of 2,4,6-trinitrophenol (TNP) and Ag+ in THF/H2O medium, based on the fluorescence quenching mechanism. Fluorescence quenching experiments revealed that the fluorescence intensities of the resulted probe were linear with the concentrations of TNP and Ag+ in the concentration range of 3.0?5.0 and 2.0?5.0 ?mol dm-3, with the detection limit of 1.36 and 0.82 ?mol dm-3, respectively. At the same time, accompanied with fluorescent color change under 365 nm UV light irradiation. This has demonstrated that the compound can act as a potential candidate for a ?naked-eye? rapidly detector for Ag+ and TNP in soils and aquatic systems.

Dynamic tuning of metal–ligand coordination through water molecules to induce multicolor fluorescence variations for humidity monitoring and anti-counterfeiting applications

We proposed a simple and effective strategy to construct a luminescent ratiometric RH sensor that can exhibit fluorescence color changes from blue to yellow upon increasing the RH.

Red-to-blue paper-based colorimetric sensor integrated with smartphone for point-of-use analysis of cerebral AChE upon Cd2+ exposure.

Herein, combined with a pervasive smartphone installed with a color recognition app, dual-responsive CDs@Eu/GMP ICPs were designed as a red-to-blue paper-based colorimetric sensor for the point-of-use analysis of cerebral acetylcholinesterase (AChE) upon Cd2+ exposure. Blue-emitting CDs with multi-functional groups as guests were encapsulated into the network of Eu/GMP ICPs to obtain CDs@Eu/GMP ICPs with the sensitized red fluorescence of Eu3+. With the presence of thiocholine (TCh), derived from acetylthiocholine (ATCh) hydrolyzed by AChE, the coordination environment of the CDs@Eu/GMP ICPs was interrupted, leading to the collapse of the CDs@Eu/GMP ICP network and the corresponding release of guest CDs into the surrounding environment. Consequently, the sensitized red fluorescence of Eu3+ decreased and the blue fluorescence of the CDs increased. This obvious red-to-blue fluorescent color changes of CDs@Eu/GMP ICPs on test paper could then be integrated with the smartphone for point-of-use analysis of cerebral AChE upon Cd2+ exposure, which not only offers a new analytical platform for a better understanding of the environmental risk of Alzheimer's Dementia (AD), but also holds great potential in the early diagnosis of AD even at the asymptomatic stage with the decrease in CSF AChE as an early biomarker.

Water Pollution Control and Treatment Based on Quantum Dot Chemical and Biological High‐Sensitivity Sensing

Inorganic pollutants in water can have an important impact on ecosystems and human health, so the development of rapid and sensitive detection methods for typical inorganic pollutants in water samples is important for understanding the pollution status of the water environment, as well as water pollution prevention and protection of drinking water safety. Fluorescence sensing technology has the advantages of fast response, high sensitivity, simple operation, and low cost but still has the problems of low quantum yield, cumbersome construction process, and limited practical applications. Based on the excellent fluorescence properties, a series of fluorescence sensing was constructed for the rapid, highly sensitive, and selective detection of various typical inorganic pollutants in water. And the related fluorescence sensing mechanism was investigated in this paper. In this paper, nitrogen/sulfur codoped carbon quantum dots (N, S‐CQDs) were prepared for the sensitive and selective detection of sulfide and ferric ion. The blue fluorescent N, S‐CQDs were prepared by a one‐step hydrothermal method using ammonium citrate and L‐cysteine as raw materials, which have excitation wavelength dependence and fluorescence quantum yield of 16.1% for the selective detection of sulfides with a detection limit (S/N = 3) of 11.0 nM (about 0.35 μg/L). CQDs with significantly higher fluorescence quantum yields (69%) and no excitation dependence were prepared when citric acid was used instead of ammonium citrate and were used for the selective detection of ferric ion with a detection limit of 14.0 nM (~0.8 μg/L). The method has been successfully applied to the determination of total phosphorus in surface water and human urine, and the fluorescence color change of the dual‐emission sensing can be used for the naked‐eye identification and semiquantitative detection of phosphate.

Folding fluorescent probes for self-reporting transesterification in dynamic polymer networks.

Dynamic exchange reactions in covalent adaptable networks (CANs) are difficult to probe directly via various macroscopic mechanical methods. Herein, we report a fluorescent strategy for directly reporting the dynamic bond exchange in transesterification-based CANs by using folding molecular probes. The folding probes (PDI-dimers) consist of two perylene diimide (PDI) cores, a spacer of dynamic esters between the two PDI cores, and reactive terminal groups. During transesterification in CANs, the PDI-dimers unfold their PDI excimers to show a sharp fluorescent color change from orange to bright yellow. This visual strategy is demonstrated by a crosslinked thiol-Michael network (TMN) and poly(4-hydroxybutyl acrylate) network (PHBA). The dynamic behaviors like stress relaxation and self-stiffening in these CANs can be directly read out via the change of fluorescent color. This method can provide quantitative information and show spatiotemporal resolution and therefore, can be applied to probe various dynamic chain exchange mechanisms in crosslinked materials.

Combination of imine bond and samarium emitter enables turn-off fluorescence detection of hydrazine in vapor and water samples

The development of convenient and efficient fluorescence techniques is of great significance for selective detection and precise determination of biotoxic N2H4 in human health and environmental sciences. By the pre-organization-assisted template synthesis, disclosed here is a luminescent Sm(III) macrocycle-based probe Sm-2m bearing dynamic imine bonds as recognition moieties which provides the selective and ratiometric turn-off fluorescence sensing for N2H4 over various amine species based on the N2H4-induced structure transformation. This fluorescent sensing process finished within 20 min shows the low limit of detection (0.18 μM, 7.2 ppb) and wide linear sensing range (0–60.0 μM). Furthermore, probe Sm-2m is also be used to quantitatively determine N2H4 in vapor gas and water samples through fluorescence color changes, which are evaluated by the Sm-2m-impregnated test paper strips and RGB value outputs. Finally, our proposed smartphone-based analytical method gives satisfactory N2H4 detection results. It is thus believed that this work can shed some lights on development of optical probes and detection techniques for N2H4, even other hazardous chemicals.