Fluorescence Color Change Research Articles

An activatable AIEgen for imaging of endogenous H2S: Reticulation based H2S gas sensor

Novel 2,4-dinitrophenylether functionalized hydroxybenzothiazole derivative (HBT 3) has been synthesized and characterized for selective and rapid detection of H2S in aqueous medium, gas phase and live cells. The H2S induced thiolysis of 2,4-dinitrophenylether leads to morphological transformation in HBT 3 from spherical to reticulate with aggregation induced emission (AIE + ESIPT) at 550 nm (greenish yellow aggregates) as evidenced by optical, DLS, NMR and AFM studies. The HBT 3 can specifically detect H2S with limits of detection as low as 0.45 and 1.22 µM in CH3CN; 2.9 µM and 6.8 µM in 70% HEPES buffer–CH3CN solution. The HBT 3 based solution- and solid- supported point-of-care testing (POCT) kits have been explored for detection of 75–400 ppm H2S gas; 2.4 µg H2S with fluorescence color change from non-fluorescent to fluorescent yellow. HBT 3 has been successfully utilized for endogenous and exogenous detection of H2S in live L929 cells.

Smartphone coupled, solution, solid and vapour phase sensing of nerve agent mimic by 1,8-naphthalimide derived Schiff base

A 1,8-naphthalimide based Schiff base, SAL, comprising of n-butyl-1,8-naphthalimide and 2-hydroxysalicyaldehyde as fluorophore and receptor units, respectively, has been utilized for the efficient detection of nerve agent mimic, diethyl chlorophosphate (DCP). Upon interaction with DCP, blue shift in the UV–vis band and enhancement in emission peak of SAL was observed with detection limit of 15.4 µM based on fluorescence titration data. The sensor was capable to selectively detect various concentrations of DCP by naked eye as well as fluorescent color change in solid, solution and vapour phase in the presence of stockpile of other competitive analytes. Further, the colorimetric changes were coupled with the smartphone via a color detector app for the cost-effective, convenient and on-site detection of DCP.

A novel colorimetric fluorescence probe for the sensitive and selective detection of hypochlorite and its bioimaging in living cells

Hypochlorite (ClO−) is a well-known redox regulator among reactive oxygen species and plays a crucial role in bacterial disinfection and body immunity. Therefore, there is a high demand for an analytical technique to monitor ClO− under physiological conditions. Herein, a novel fluorescence probe, RES-DPPT, was developed for detecting ClO−. This probe employs diphenylphosphinothioyl unit as the recognition group and resorufin as the fluorescent platform. RES-DPPT has high sensitivity and specificity, rapid response, and wide pH tolerance for monitoring ClO−. Additionally, RES-DPPT undergoes colorimetric and fluorescence color changes in the solution, which can be observed by the “naked eye.” Furthermore, RES-DPPT is successfully able to detect exogenous and endogenous ClO− in living cells.

A smartphone-assisted paper-based ratio fluorescent probe for the rapid and on-site detection of tetracycline in food samples

Rapid, sensitive and portable analytical methods for on-site detection of tetracycline (TC) in food samples is of critical importance for food safety and public health. In this study, a dual-emission ratio fluorescent probe (Gd0.9@Eu0.1) was prepared and utilized for the detection of tetracycline (TC) by observing the fluorescence color change from blue to red. The detection process exhibits a wide linear range (0–52.0 μM), good selectivity and low detection limit (14 nM). A paper-based probe and a colorimetric card was constructed for the visual detection of TC. Furthermore, a novel and portable detection platform combining smartphone and test strip was exploited for the quantitative and on-site detection of TC in real pork sample. The developed method was validated through intra- (n = 5) and inter-day (n = 2) measurements, as well as comparison with a traditional HPLC method. These statistical result validate the reliability and accuracy of the developed method. This intelligent detection platform represents a promising approach for the rapid, sensitive and visual detection of TC in food samples.

Synthesis, LC self-assembly and photophysical behavior of stimuli responsive cyanostilbene-based hexacatenar mesogens with multicolour switching

A novel series of cyanostilbene-based hexacatenar mesogens consisting of two cyanostilbene units and one central pyridine in the π-conjugated rigid core were obtained by Suzuki coupling and Knoevenagel reactions. POM, DSC, SAXS, UV–vis spectrophotometer and fluorescence spectrophotometer were employed to explore the liquid crystalline, photophysical and stimuli responsive properties. All the biscyanovinyl diphenylpyridine-based hexacatenars can self-assemble into rectangular columnar phase with P2mm symmetry in bulk state. All the mesogens display weak solvatochromism due to the weak intramolecular charge transfer (ICT) and aggregation-induced enhanced emission (AIEE) due to non-planar structure and the long π-conjugated core. Temperature inducing hypochromatic shifts of fluorescence spectra, fluorescence quenching and the change in fluorescence color due to the phase transition and molecular planarization was well demonstrated. In addition, volatile acids could induce reversible changes of dual solid color, dual fluorescence color, fluorescence quantum yield and fluorescence lifetime owing to the protonation and deprotonation of pyridine. DFT analysis demonstrated that the protonation could induce more distinct molecular distortion and ICT, causing bathochromic-shifted absorption and emission spectra. Therefore, the introduction of different functional building blocks into liquid crystalline molecules is beneficial for the development of multifunctional materials.

A sensitive fluorescence sensor based on a glutathione modified quantum dot for visual detection of copper ions in real samples.

Copper (Cu2+), as a heavy metal, accumulates in the human body to a certain extent, which can induce various diseases and endanger human health. Rapid and sensitive detection of Cu2+ is highly desired. In present work, a glutathione modified quantum dot (GSH-CdTe QDs) was synthesized and applied in a "turn-off" fluorescence probe to detect Cu2+. The fluorescence of GSH-CdTe QDs could be rapidly quenched in the presence of Cu2+ through aggregation-caused quenching (ACQ), resulting from the interaction between the surface functional groups of GSH-CdTe QDs and Cu2+ and the electrostatic attraction. In the range of 20-1100nM, the Cu2+ concentration showed a good linear relationship with the fluorescence decline of the sensor, and the LOD is 10.12nM, which was lower than the U.S. Environmental Protection Agency (EPA) defined limit (20μM). Moreover, aiming to attain visual analysis, colorimetric method was also used for rapidly detecting Cu2+ by capturing the change in fluorescence color. Interestingly, the proposed approach has successfully been applied for the detection of Cu2+ in real samples (i.e., environment water, food and traditional Chinese medicine) with satisfactory results, which provides a promising strategy for the detection of Cu2+ in practical application with the merits of being rapid, simple and sensitive.

A novel diarylethene-based fluorescence sensor for Zn2+ detection and its application

A series of fluorometric sensors of Zn2+ have been synthesized due to the significant function of Zn2+ in the human body and environment. However, most of probes reported for detecting Zn2+ have high detection limit or low sensitivity. In this paper, an original Zn2+ sensor, namely 1o, was synthesized by diarylethene and 2-aminobenzamide. When Zn2+ was added, the fluorescence intensity of 1o increased by 11 times within 10 s, along with a fluorescence color change from dark to bright blue, and the detection limit (LOD) was calculated to be 0.329 μM. According to Job’s plot curves, the binding mode of 1o and Zn2+ was measured as 1:1, which was further proved by 1H NMR spectra, HRMS and FT-IR spectra. The logic circuit was designed to take advantage of the fact that the fluorescence intensity of 1o can be controlled by Zn2+, EDTA, UV and Vis. In addition, Zn2+ in actual water samples were tested, in which the recovery rate of Zn2+ was between 96.5 % and 109 %. Furthermore, 1o was successfully made into a fluorescent test strip, which could be used to detect Zn2+ in the environment economically and conveniently.

Carbon dots/Ag nanoclusters-based fluorescent probe for ratiometric and visual detection of Cu2+

A fluorescent probe, N-doped carbon dots/Ag nanoclusters (N-CDs/AgNCs), was designed and synthesized successfully based on fluorescence inner filler effect (IFE) for the ratiometric and visual detection of Cu2+. Due to the IFE, the as-prepared probe exhibited a weak blue emission at 455 nm and a strong red emission and 665 nm. After adding Cu2+, the red fluorescence can be quenched because of the strong chelating interaction between GSH and Cu2+, whereas the blue fluorescence could be recovered because of the weakening of the IFE, accompanying by a remarkable fluorescence color change from pink to blue under a UV light. Under optimized experimental conditions, the N-CDs/AgNCs probe showed excellent selectivity to Cu2+ and a good linear relationship between the fluorescence intensity proportion (I665/I455) and Cu2+ concentration in the range of 0 to 60 μM with a detection limit of 0.13 µM. Further, N-CDs/AgNCs could be used for detecting Cu2+ in tap water and lake water. These results showed that the IFE ratiometric fluorescent probe may provide a new idea for the visualization and semiquantitative detection of Cu2+ and imply that it has great potential to detect Cu2+ in real environment water samples.

Ratiometric pyrene-based fluorescent sensor for on-site monitoring of formaldehyde in foods and living cells

A ratiometric pyrene-based fluorescence sensor PN was developed for visual detection of formaldehyde (FA) by featuring homoallylamino group as specific recognition site. Sensor PN undergo a unique FA-triggered 2-aza-Cope rearrangement, which resulted in monomer-excimer conversion in a ratiometric manner accomplished with distinguishable fluorescent color change from blue to violet. Due to the advantage of high selectivity, fast response (< 100 s), low detection limit (18 μM), wide quantitative detection range (0.018–4 mM) and large ratio enhancement (up to 10-fold), PN has been successfully applied for detecting FA in diverse food samples. Notably, novel portable devices based on paper chip and alginate gel were constructed and realized visual quantitative detection of liquid and gaseous FA, as well as nondestructive monitoring volatile FA variation of real food samples during their shelf life, which were verified with the aid of chemometrics. Most importantly, sensor PN has been proven to be capable of fluorescence imaging of FA in living cells. Therefore, the impressive sensor PN is expected to provide advice and insights in the field of food safety and biological systems analysis.

Anisotropic Bi-Layer Hydrogel Actuator with pH-Responsive Color-Changing and Photothermal-Responsive Shape-Changing Bi-Functional Synergy.

Stimuli-responsive color-changing and shape-changing hydrogels are promising intelligent materials for visual detections and bio-inspired actuations, respectively. However, it is still an early stage to integrate the color-changing performance and shape-changing performance together to provide bi-functional synergistic biomimetic devices, which are difficult to design but will greatly expand further applications of intelligent hydrogels. Herein, we present an anisotropic bi-layer hydrogel by combining a pH-responsive rhodamine-B (RhB)-functionalized fluorescent hydrogel layer and a photothermal-responsive shape-changing melanin-added poly (N-isopropylacrylamide) (PNIPAM) hydrogel layer with fluorescent color-changing and shape-changing bi-functional synergy. This bi-layer hydrogel can obtain fast and complex actuations under irradiation with 808 nm near-infrared (NIR) light due to both the melanin-composited PNIPAM hydrogel with high efficiency of photothermal conversion and the anisotropic structure of this bi-hydrogel. Furthermore, the RhB-functionalized fluorescent hydrogel layer can provide rapid pH-responsive fluorescent color change, which can be integrated with NIR-responsive shape change to achieve bi-functional synergy. As a result, this bi-layer hydrogel can be designed using various biomimetic devices, which can show the actuating process in the dark for real-time tracking and even mimetic starfish to synchronously change both the color and shape. This work provides a new bi-layer hydrogel biomimetic actuator with color-changing and shape-changing bi-functional synergy, which will inspire new strategies for other intelligent composite materials and high-level biomimetic devices.

A dual-state-emission chalcone-based supramolecular probe for ratiometric detection of penconazole in environmental samples

Penconazole (PEN) is a systemic triazole fungicide widely pulverized on fruits and vegetables to control powdery mildew disease. PEN has various hazardous effects on mammalians primarily through PEN-induced excessive generation of reactive oxygen species, which may cause metabolic disorders, cancer, etc. Therefore, development of an effective analytical method for PEN is of great importance for the environmental safety and human health. In the present work, we report a supramolecular fluorescent probe OPyCH@ALB constructed by selecting of a dual-state-emission chalcone as the indicator and albumin as the host, for the first time, successfully realizing the ratiometric detection of PEN. This probe is capable of detecting PEN with rapid response (10 s), high sensitivity (LOD = 0.28 μM, 76 ppb), high selectivity, and a visible fluorescence color change from green to red. Based on this probe, the portable paper-based test strips, which enable the on-site monitoring of PEN without the involvement of any complicated testing apparatus, were fabricated. Furthermore, this probe was used to realize the qualitative and quantitative analysis of PEN in ground water and soil with high accuracy, and successful achieved on-site recognition of PEN on the surface of grapes. We expect that this method will be applied as a convenient and affordable tool for the rapid monitoring of PEN at the point-of-use, such as in residential, agricultural, and food production settings.

Smartphone-Aided Fluorescence Detection of Cardiac Biomarker Myoglobin by a Ratiometric Fluorescent AuNCs-QDs Nanohybrids Probe with High Sensitivity.

Simple and sensitive detection of cardiac biomarkers is of great significance for early diagnosis and prevention of acute myocardial infarction (AMI). Here, a ratiometric fluorescent nanohybrids probe (AuNCs-QDs) was synthesized through the coupling of bovine serum albumin-functionalized gold nanoclusters (AuNCs) with CdSe/ZnS quantum dots (QDs) to realize simple and sensitive detection of cardiac biomarker myoglobin (Mb). The AuNCs-QDs probe shows pink fluorescence under UV light, with two emission peaks at 468nm and 630nm belonging to QDs and AuNCs, respectively. Importantly, the presence of Mb caused fluorescence quenching of the blue-emitting QDs, thereby inhibiting the fluorescence resonance energy transfer (FRET) process between QDs and AuNCs, and reducing the fluorescence intensity ratio (F468/F630) of AuNCs-QDs probe effectively. As the concentration of Mb increases, the ratiometric fluorescent probe also exhibits a visible fluorescence color change. The detection limit was as low as 4.99μg/mL, and the response of the probe to Mb showed a good linear relationship up to 0.52mg/mL. Moreover, the probe has excellent specificity for Mb. Besides, the AuNCs-QDs has been applied to detect Mb of urine samples. More importantly, we also developed an AuNCs-QDs probe modified smartphone-aided paper-based strip for on-site monitoring of Mb. As far as we know, this is the first report of a smartphone-aided paper-based strip for on-site quick monitoring of Mb, which provides a useful approach for AMI biomarker monitoring and may can be extended to other medical diagnostics.

Visualizing stimulus-responsive dual-ligand fluorescent probes for hypochlorite: A novel strategy for real application in tap water.

As an effective ingredient of disinfectants, ClO- inevitably remains in water, which induces potential health hazards such as lung damage and kidney disease. In this study, we synthesized stimulus-responsive dual-ligand luminol-Tb-GMP coordination polymer nanoparticles (luminol-Tb-GMP CPNPs) as highly selective fluorescent probes for the real-time and visual detection of ClO- . CPNPs consist of Tb3+ , a nuclear metal, that coordinates with GMP and luminol, an auxiliary ligand. GMP can be oxidized by ClO- and damage its structure, resulting in fluorescence quenching of CPNPs. The two-ligand CPNPssensor has a rapid fluorescent response, significant fluorescent color change, and high sensitivity, with a linear range of 2-18 μM and a detection limit of 0.14 μM. It has been successfully used to detect ClO- in tap water, fountain water, and drinking water. Simultaneously, the portable filter paper strip was prepared to expand the range of applications outside the laboratory, which will provide a promising application for the real-time and semiquantitative analysis of ClO- .

A core–shell structure ratiometric fluorescent probe based on carbon dots and Tb3+ for the detection of anthrax biomarker

A novel core–shell structure ratiometric fluorescent probe was developed, which can selectively and sensitively detect 2,6-dipicolinic acid (DPA) as an anthrax biomarker. Carbon dots (CDs) was embedded into SiO2 nanoparticles, which was acted as an internal reference signal. Tb3+ with green emission was connected to the carboxyl functionalized SiO2, which was acted as a responsive signal. With the addition of DPA, the emission of CDs at 340 nm was unchanged, while the fluorescence of Tb3+ at 544 nm was enhanced by the antenna effect. In the concentration range of 0.1–2 μM, the fluorescence intensity ratio of I544/I340 showed a good linear relationship with the concentration of DPA, and the limit of detection (LOD) was 10.2 nM. In addition, the dual-emission probe showed an obvious fluorescence color change from colourless to green with increasing DPA under UV light, which enabled visual detection.

Molecular engineering of fluorescence probe for real-time non-destructive visual screening of meat freshness.

Spoiled meat poses a great challenge to food security and human health, which should be addressed by the early monitoring and warning of the meat freshness. We herein exploited a molecular engineering strategy to construct a set of fluorescence probes (PTPY, PTAC, and PTCN) with phenothiazine as fluorophore and cyanovinyl as recognition site for the facile and efficient monitoring of meat freshness. These probes produce an obvious fluorescence color transition from dark red to bright cyan in response to cadaverine (Cad) through the nucleophilic addition/elimination reaction. The sensing performances were elaborately improved to achieve quick response (16s), low detection limit (LOD=3.9nM), and high contrast fluorescence color change by enhancing the electron-withdrawing strength of cyanovinyl moiety. Furthermore, PTCN test strips were fabricated for portable and naked-eye detection of Cad vapor with fluorescence color change from crimson to cyan, and accurate determination of Cad vapor level with RGB color (red, green, blue) mode analysis. The test strips were employed to detect the freshness of real beef samples, and demonstrated a good capability of non-destructive, non-contact and visual screening meat freshness on site.

Structures, photophysical properties, and optical sensing of zinc– and copper–salicyaldimine complexes

Metal–salicyaldimine complexes [M(sal-3-py)2] (1, M = Zn; 2, M = Cu), where Hsal-3-py = 3-(salicylideneimino)pyridine, have been synthesized. Nuclear magnetic resonance (NMR) spectroscopy and mass spectroscopy (MS) indicated that 1 and 2 both have a ML2-type discrete molecular structure in the solution and amorphous phases. Single-crystal X-ray diffraction analysis and X-ray powder diffraction (XRPD), however, proven that 1 and 2 both possess an extended two-dimensional sql layer net in the crystalline phase. The electronic absorption spectra of 1 and 2 in MeOH exhibited intense intraligand charge transfer (ILCT) transitions in the UV region (200–340 nm) and metal–ligand charge transfer (CT) transition in the visible region (380–400 nm). The emission spectra of 1 displayed a cyan fluorescence band at 480 nm in solid-state and a green fluorescence band at 502 nm in MeOH solution. Optical detection of 1 in MeOH toward Cu2+, Al3+, and Cr3+ ions showed remarkable changes in electronic absorption spectra and ON–OFF–ON fluorescence color change from green to blue light emission. The sensing processes involves two stages, i.e., direct central metal displacement for Cu2+ detection and analyte-induced decomplexation for Al3+/Cr3+ detection, and subsequently further recognition through the 3-pyridyl functions of the salicyaldimine ligands. Further, 1 displayed remarkable fluorescence color change from green light in MeOH to cyan light in H2O, being potential candidate as H2O probe in methanol.

Three‐Output Naked‐Eye High Temperature Organic Film Threshold Thermometers Based on Non‐Invasive Chemical Reaction

AbstractHigh‐contrast and stably visualized ambient or luminescent color‐switching can be achieved by thermal‐induced non‐invasive chemical reaction for naked‐eye threshold temperature indication. The clear and visible output signal of these indicators arises from the large absorption/emission spectral changes upon heating. However, such chemical reactions are difficult to realize in solid‐state, especially in the high‐temperature region. Herein, a series of naked‐eye high‐temperature threshold film indicators have been developed based on the solid‐state in situ thermal decomposition reaction of difluoroboron β‐diketonate derivative. These thermosensitive films feature three high‐contrast visible outputs of ambient thermochromism, fluorescence color change, and luminescence ON/OFF switching, which can be easily detected with the naked eye. The PR‐PS film of (E)‐4‐(2‐(6‐bromopyren‐1‐yl)vinyl)‐2,2‐difluoro‐6‐phenyl‐2H‐1λ3,3,2λ4‐dioxaborinine (PR) doped in polystyrene (PS) polymer matrix achieved high sensitivities related to change of ratiometric luminescence and fluorescence intensity up to 230%°C−1 and 1.85%°C−1, respectively. Furthermore, the polymer matrix with different glass transition temperatures enables programmable tuning of threshold temperature from 120 to 180 °C. These thermosensitive films show clear and high‐contrast color changes and emission turn‐off in real‐time with consistent air stability, high photostability, and waterproofing property. This shows considerable potential in outdoor robust high‐temperature threshold sensing and information storage.

A colorimetric/ratiometric chemosensor based on an aggregation-induced emission strategy for tracing hypochlorite in vitro and in vivo

Excessive levels of hypochlorite (ClO−) negatively affect environmental and biological systems. Thus, it is essential to develop sensors that can identify ClO− in various systems such as the environment and living organisms. In this study, we report the development and evaluation of a novel aggregation-induced emission (AIE) strategy-based colorimetric and ratiometric fluorescent chemosensor 2,2′-(((1E,1′E)-[2,2′-bithiophene]− 5,5′-diylbis(methanylylidene))bis(hydrazin-1-yl-2-ylidene))bis(N,N,N-trimethyl-2-oxoethan-1-aminium) chloride (BMH-2∙Cl) for detecting ClO−. BMH-2∙Cl enabled highly selective ClO− detection through a color change from yellow to colorless and a fluorescence color change from turquoise to blue in a perfect aqueous solution. BMH-2∙Cl exhibited low limits of detection (2.4 ×10−6 M for colorimetry and 2.9 ×10−7 M for ratiometric fluorescence) for detecting ClO− with a rapid response within 5 s. The detection mechanism for ClO− and an AIE property change of BMH-2∙Cl were demonstrated by 1H NMR titration, ESI-MS, variation of water fraction (fw) and theoretical calculations. In particular, we confirmed not only the practicality of BMH-2∙Cl by using test strips, but also demonstrated the potential for efficient ClO− detection in biological and environmental systems such as real water samples, living zebrafish and bean sprouts.

Simple method for visual detection of nitrite using fluorescence and colorimetry by poly (tannic acid) nanoparticles

The nitration reaction of nitrite and phenolic substances was first used to identify and detect NO2− by taking fluorescent poly (tannic acid) nanoparticles (FPTA NPs) as sensing platform. With the low cost, good biodegradable and convenient water-soluble FPTA NPs, a fluorescent and colorimetric dual modes detecting assay was realized. In fluorescent mode, the linear detection range of NO2− was 0–36 μM, the LOD was as low as 3.03 nM, and the response time was 90 s. In colorimetric mode, the linear detection range of NO2− was 0–46 μM, and the LOD was as low as 27 nM. Besides, a smartphone with FPTA NPs@ agarose hydrogel formed a portable detection platform to test the fluorescent and visible color changes of FPTA NPs for NO2− sensing as well as for accurate visualization and quantitative detection of NO2− in actual water and food samples.

Construction of ratiometric fluorescent nanosensors based on carbon dots dual emission strategy for high-sensitivity visual detection of Ag+

ABSTRACT Water-soluble purple fluorescent carbon nanodots (P-CDs) were synthesised using 2-phenylphenol, and red fluorescent carbon dots (R-CDs) were prepared from o-phenylenediamine and phosphoric acid. Based on the fluorescence quenching effect of Ag+ on carbon quantum dots, and additionally introducing a red light-emitting quantum dot with excellent performance and high quantum yield, a dual emission ratiometric fluorescent nanosensor (P-CDs/R-CDs) was established. The semi-quantitative detection of silver ions can be realised. Under the excitation light of 254 nm and 365 nm, the fluorescence spectrum shows double emission fluorescence peaks at 343 nm and 626 nm, which originate from the fluorescence emission of the synthesised C-dots and the additionally introduced C-dots, respectively. The relationship between the ratio of the intensity of the two emission peaks F343/F626 and the concentration of silver ions realises the analysis and detection of silver ions. The linear detection range of this method was 0.096–10 μM, and the detection limit (LOD, S/N = 3) was 32 nM. In addition, the method can also perform naked-eye visual detection according to the fluorescence colour change of the probe under ultraviolet light, and realise the rapid monitoring of Ag+ on site. The P-CDs/R-CDs ratiometric fluorescence sensor provides a new method for the detection of Ag+ and promotes the development of heavy metal ion sensing.