Fluorescence Color Research Articles

Fluorogenic Monitoring of α-Amylase in Human Urine for Straightforward Diagnosis of Pancreatic Diseases.

In this study, we developed a sensitive method for monitoring α-amylase using a fluorogenic approach based on the host-guest complexation between an amphiphilic pyrenyl derivative (1) and γ-cyclodextrins (γ-CDs). The compound 1 self-assembles into nanofibrils in aqueous solutions. Upon the introduction of γ-CD, compound 1 forms an inclusion complex with it. This complex then participates in the formation of a 2 : 2 complex with another complex, leading to strong excimer fluorescence. Upon interaction with α-amylase, γ-CD undergoes hydrolysis, leading to the regeneration of nanofibrils, which is accompanied by a decrease in excimer fluorescence and an increase in monomeric fluorescence. This ratiometric fluorescence color change enables the sensitive detection of low levels of α-amylase in human urine, offering a practical approach for early screening of pancreatic-related diseases.

Hybrid metal halide family with color-time-dual-resolved phosphorescence for multiplexed information security applications

Luminescent materials with engineered optical properties play an important role in anti-counterfeiting and information security technology. However, conventional luminescent coding is limited by fluorescence color or intensity, and high-level multi-dimensional luminescent encryption technology remains a critically challenging goal in different scenarios. To improve the encoding capacity, we present an optical multiplexing concept by synchronously manipulating the emission color and decay lifetimes of room-temperature phosphorescence materials at molecular level. Herein, we devise a family of zero-dimensional (0D) hybrid metal halides by combining organic phosphonium cations and metal halide tetrahedral anions as independent luminescent centers, which display blue phosphorescence and green persistent afterglow with the highest quantum yields of 39.9 % and 57.3 %, respectively. Significantly, the luminescence lifetime can be fine-tuned in the range of 0.0968–0.5046 μs and 33.46–125.61 ms as temporary time coding through precisely controlling the heavy atomic effect and inter-molecular interactions. As a consequence, synchronous blue phosphorescence and green afterglow are integrated into one 0D halide platform with adjustable emission lifetime acting as color- and time-resolved dual RTP materials, which realize the multiple applications in high-level anti-counterfeiting and information storage. The color-lifetime-dual-resolved encoding ability greatly broadens the scope of luminescent halide materials for optical multiplexing applications.

Ratiometric Fluorescence Depending on In/Out Isomerism of Host‐Guest Conjugate Having a Fluorosolvatochromic Dye

Host‐guest conjugate is a promising strategy for providing outstanding molecules. Herein, we designed host‐guest conjugate HG1, which comprises a hydrophilic host unit, tetraaza[2.2.1.2.2.1]paracyclophane CPX2with a microhydrophobic cavity, and a guest unit, 2,3‐naphthalimide fused with two benzothiophenes G1 exhibiting fluorosolvatochromism, linked with an oxyethylene chain. HG1 initially showed a fluorescence band at 585 nm in MeOH/H2O (1/499 v/v); however, this band decreased with time, and instead, a new band at 430 nm appeared. The CIE chromaticity diagram showed that the fluorescent color changed from yellow‐orange to blue via white. NMR analysis of HG1 in methanol‐d4 exhibited different signals of the G1 unit between the blue and yellow fluorescent structures. The blue fluorescent structures showed asymmetrical signals assigned as the G1 unit, affected by the cavity environment of the CPX2 unit. Consequently, HG1 can form two conformations: In‐form and Out‐form. In In‐form, the G1 unit is inside the hydrophobic cavity of the CPX2 unit and shows blue fluorescence. In Out‐form, the G1 unit is outside the CPX2 unit and shows yellow fluorescence in an aqueous solvent. Therefore, HG1 performs as a ratiometric fluorophore depending on the in/out isomerism of the host‐guest conjugate.

Ultra sensor based on color and UV-excited fluorescence images for predicting quality attributes of Shine-Muscat grape bunches at different maturity stages

Fruit maturity at harvest is a major factor in determining its quality. In this study, external skin color of grape has been utilized to predict their chemical content and, in turn, the maturity of the fruit. Measurements of the chemical content such as Brix and acidity were made on ten bunches of “Shine Muscat” grapes at three different harvest periods (immature, mature, and overmature). Using a machine vision system, color and UV-excited fluorescence images of grape berries and bunches were taken during the respective harvest stages. Acquired images were processed using ImageJ to obtain RGB values. Rratio and a*/b* are strongly related to Brix and sugar-to-acid ratio of grape fruit, with regression coefficients of 0.5626 and 0.5180, repectively. It was found that a* color index was the best predictor of grape bunch maturity. Furthermore, discriminant analysis has shown that color images of grape berries perform better than 365 nm fluorescence images.

Triggering dual-mode dynamic optical responses by anchoring carbon dots on MnO2 hollow spheres

Multi-mode responsive optical materials with versatile application prospects for optical sensing, optoelectrical devices, and information encryption are highly desired. Here we integrate fluorescent carbon dots onto the hollow MnO2 spheres, and modulate the interaction between them to achieve a water-stimulated responsive system with dual-mode dynamic signals in both fluorescence and structural color. The composite film shows a structural color shifting from blue to green as well as displays a fluorescence “on” in the presence of trace water, with both changes capable of being reversibly switched up to 10 times. The amide bond between the two components enables the controllable dispersion and aggregation of the carbon dots which is essential to the reversibility. Fabrication of several security labels with separate information in structural color and fluorescence channels demonstrates the application potential of the composite. This work provides a concise route to develop new multi-mode responsive optical materials for applications in anti-counterfeiting, sensing, and coding.

Rapid assessment of acetophenone using an anti-interfering triple-emission Ln3+-functionalized HOF@MOF sensor

The development of high-performance sensors for rapidly detecting acetylacetone (AP) in water samples is necessary because its release into the environment can result in many vital problems for human health and environment. Herein, we first designed a hybrid by integrating HOF with ZIF-8 through a sequential growth strategy. By separately introducing blue-emitting SiQDs and green- and red-emitting Tb3+ and Eu3+ into ZIF-8 and HOF, the resultant ZIF-8@SiQDs@HOF@Eu3+@Tb3+ comprised three emission peaks at 484, 545 and 620 nm, all of which could be employed as switch-off responsive peaks to low concentrations of AP with a detection limit of 0.79 ppm. However, in environments with high concentrations of AP, a turn-on signal at 484 nm was observed. Thereupon, the ratiometric fluorescence intensity of the ternary emission varied within different concentration ranges, accompanied by the fluorescence color evolution from red to salmon to plum to purple to final blue. Moreover, a portable sensing film was fabricated for rapid warning, sensitive and visual determination of AP in complicated environments. Therefore, this triple-emission sensor with wide color variations and strong anti-interference advantages could promote further research to improve the selectivity, sensitivity and inherent self-correction of multimodal fluorescence detection and the ease of sensing operation.

Ligand-assisted reprecipitation synthesis of highly luminescent and stable CsPbBr3@SiO2 nanoparticles with formation kinetics analysis

Cesium lead bromide (CsPbBr3) perovskite nanocrystals are becoming a popular alternative to chalcogenide quantum dots because of their bright green fluorescence and high color purity. However, owing to the poor stability caused by their highly ionic nature and the dynamic binding of long-chain capping ligands, their practical applications are limited. Although (3-aminopropyl)triethoxysilane (APTES) is a frequently used insulating material for wrapping CsPbBr3nanocrystals, it often causes surface etching. To address this issue, we introduced oleic acid into the anti-solvent toluene to inhibit the etching effect of APTES using a modified room-temperature ligand-assisted reprecipitation process. We utilized in situ time-dependent photoluminescence measurements to study the formation kinetics of CsPbBr3nanocrystals and determine the optimal ligands ratio. This innovative approach enables precise control over CsPbBr3@SiO2nanoparticles synthesis, yielding uniformly shaped nanocrystals with a silica shell, a consistent size around 10.17 ± 1.6 nm, and enhanced photoluminescence quantum yields ranging from 90% and 100%. The photoluminescence lifetimes of our CsPbBr3@SiO2nanoparticles were significantly prolonged owing to a reduction in non-radiative recombination. This boosts their stability in thermal and polar solvent environments, making them superior candidates for use in photonic devices.

Ratiometric fluorescence probe based on carbon dots and p-phenylenediamine-derived nanoparticles for the sensitive detection of manganese ions.

A ratiometric fluorescence probe based on carbon quantum dots with 420nm emission (bCQDs) and a p-phenylenediamine-derived fluorescence probe with 550nm emission (yprobe) is constructed for the detection of Mn2+. The presence of Mn2+ results in the enhanced absorption band at 400nm of yprobe, and the fluorescence of yprobe is significantly enhanced based on the chelation-enhanced fluorescence mechanism. The fluorescence of bCQDs is then quenched based on the inner filtration effect. The ratio (I550/I420) linearly increases with the increase of Mn2+ concentration within 2.00 × 10-7-1.50 × 10-6M, and the limit of detection is 1.76 × 10-9M. Given the fluorescence color changing from blue to yellow, the visual sensing of Mn2+ is feasible based on bCQDs/yprobe coupled with RGB value analysis. The practicability of the proposed method has been verified in tap water, lake water, and sparkling water beverage, indicating that bCQDs/yprobe has promising application in Mn2+ monitoring.

Samarium, nitrogen co-Doped carbon dots for detection of Epinephrine: Theoretical and experimental

In this study we have developed a highly sensitive optical sensor for the detection of epinephrine using carbon dots co-doped with samarium and nitrogen (Sm,N-CDs) with a very low detection limit of 28.1 nM and a broad linear dynamic range from (0–105 nM). Various techniques were employed to characterize the synthesized material, aiming to understand its morphological and physicochemical characteristics. The synergistic effect of the synthesized Sm,N-CDs demonstrated excellent optical performance, high selectivity and photostability. Additionally, good recovery findings were obtained when the sensor’s viability for Epinephrine detection in biological fluid samples that had been spiked was evaluated. In addition, we have developed an smartphones-based sensor to record the solution’s fluorescent color shift as it is being sensed. Using a mobile phone application to examine the green, red, and blue values from these photos, the comparable LOD was found to be 17.21 μM in a (0–90 μM) wide linear range of concentration. This straightforward, affordable, and quick screening device is highly demanding for the on-the-spot identification of the analytes at remote locations where advanced instrumentation is typically unavailable. Density functional theory was used to examine energy, stability, band gap, and how Ep interacted with the Sm,N-CDs nanoparticles.

Bioimaging research of a turn-on homodimer fluorescent probes for pH and viscosity: A new turn-on strategy

A turn-on homodimer fluorescent probe (BL) that responded to pH and viscosity was facilely synthesized based on homo-FRET. The probe exhibited strong fluorescence intensity and color changes in alkaline pH. In addition, the probe's fluorescence had altered with changes in viscosity. What's more, Mitochondrial localization and pH bioimaging in E. coli cell experiments confirmed that BL was a novel multifunctional probe that could be applied to mitochondrial-targeted fluorescence imaging under normal conditions and real-time fluorescence imaging of E. coli under alkaline conditions.

Engineering a new quinoline based chromo − fluorogenic chemosensor for consecutive sensing of Cu2+ and N–acetyl–L–cysteine: Applications in Smartphone platform, real samples and living cell bioimaging

A new quinoline based chromo − fluorogenic chemosensor (QMEH) was designed for the sequential recognition of Cu2+ and N–acetyl–L–cysteine (NAC) in DMSO:H2O (50:50, v/v) medium. Excellent visual color changing and fluorescence quenching of QMEH with gradually adding of Cu2+ were monitored with highly selective binding stoichiometry (1:1), which might be resulted from a chelation enhanced quenching (CHEQ) phenomenon. Next, the Cu2+−enhanced absorbance and − quenched emission of QMEH were fully recovered by NAC through the displacement approach. The QMEH−Cu2+ complex structures showed obvious color changes by the adding of NAC from ’’bright yellow’’ to ’’noncolored’’ under daylight and from ’’noncolored’’ to ’’blue’’ under UV−cabinet, respectively. The gradual addition of NAC to the QMEH−Cu2+ solution induced its absorbance and emission recovery with low detection limits of 65.88 μM and 6.32 μM, respectively. To assess the importance of method parameters, the validation study was carried out using diverse analytical parameters. Moreover, thanks to the superior sensing performance and the low cytotoxicity ability of QMEH, it was used for the Smartphone platform, natural spring waters and the sequential bioimaging of Cu2+ and NAC in hepatocellular carcinoma cells.

Advancing quantitative PCR with color cycle multiplex amplification.

Quantitative PCR (qPCR) is the gold standard for detection and quantitation of known DNA targets, but the scarcity of spectrally distinct fluorophores and filter sets limits the number of detectable targets. Here, we introduce color cycle multiplex amplification (CCMA) to significantly increase the number of detectable DNA targets in a single qPCR reaction using standard instrumentation. In CCMA, presence of one DNA target species results in a pre-programmed pattern of fluorescence increases. This pattern is distinguished by cycle thresholds (Cts) through rationally designed delays in amplification. For example, we design an assay wherein Staphylococcus aureus sequentially induces FAM, then Cy5.5, then ROX fluorescence increases with more than 3 cycles between each signal. CCMA offers notably higher potential for multiplexing because it uses fluorescence permutation rather than combination. With 4 distinct fluorescence colors, CCMA theoretically allows the detection of up to 136 distinct DNA target sequences using fluorescence permutation. Experimentally, we demonstrated a single-tube qPCR assay screening 21 sepsis-related bacterial DNA targets in samples of blood, sputum, pleural effusion and bronchoalveolar lavage fluid, with 89% clinical sensitivity and 100% clinical specificity, showing its potential as a powerful tool for advanced quantitative screening in molecular diagnostics.

Eu3+-functionalized covalent organic framework for ratiometric fluorescence detection and adsorption of tetracycline and information steganography.

Functional materials with organic/inorganic composites as the main matrix and rare earth ion complexes as the guest have shown a very broad application prospect for antibiotic sensors. However, Eu3+-complex often relies on a single fluorescence response signal, which is susceptible to changes in the detection environment and cannot simultaneously detect and remove tetracycline (TC). Herein, green fluorescent covalent two-dimensionalorganic framework (COF-TD) is synthesized, followed by modification of Eu3+ to synthesize COF-TD@Eu3+. In the ratiometric sensor, Eu3+ serves as the recognition site and specific response probe for TC, while COF-TD is the fluorescence reference and carrier for Eu3+. Due to the antenna effect, TC enhances the red fluorescence of Eu3+, while the green fluorescence of COF-TD remainsalmost stable. Based on the change of fluorescence intensity and fluorescence color from green to red, the efficient ratiometric sensing can be finished in 1min. The developed method shows high sensitivitywith a detection limit of 0.3μM and highselectivity to TC which makes the methodapplicableto detect TC in traditional Chinese medicine preparations. In addition, due to the high specific surface area of COFs and specific adsorption sites, COF-TD@Eu3+ also shows good performance for TC removal. The findings show that the maximum adsorption capacity is 137.3mgg-1 and the adsorption equilibrium is reached in 30min. Smartphone assisted COF-TD@Eu3+ for both ratiometric fluorescence detection and detecting the absorption ofTC is proposed for the first time. The molecular cryptosteganography that transforms the selective response of COF-TD@Eu3+ to binary strings is anticipated to advance utilization of nanomaterials in logic sensing and information safety.

A Self‐Calibrating Sensing Platform Based on Amine‐Responsive Excitation Wavelength‐Dependent Fluorescent Polymers for Real‐Time and Visual Detection of Food Freshness

AbstractAccurate assessment of food freshness is critical to maintaining human health. However, the complex environment of food usually leads to false‐positive measurements result. Therefore, the development of sensing platforms with self‐calibration for accurate detection of food freshness in complex environments is essential. Here, using the green fluorescence‐emitting FITC‐ene and the red fluorescence‐emitting DBA‐ene‐Eu3+ as fluorescent units, fluorescent polymeric materials P1‐P4 with excitation wavelength‐dependent (254 and 365 nm, matched with standard UV lamp) emission are prepared. P1‐P4 responded rapidly to biogenic amines (BAs). Among them, P3 exhibits the widest linear range, and the most noticeable fluorescence color change (from orange‐red to yellow‐green) under 254 nm excitation and enhanced green fluorescence under 365 nm excitation. The changes of P3‐prepared labels at different excitation wavelengths can be utilized to rapidly evaluate the food's freshness. Furthermore, by using a smartphone to read the Red/Green/Blue values of the labels, the total volatile basic nitrogen (TVBN) values can be output to quantitatively evaluate the food freshness, and the output TVBN values at different excitation wavelengths are utilized for mutual calibration to improve the accuracy of the estimation results. This self‐calibrating sensing platform is fast and nondestructive, which provides an effective method for the accurate evaluation of food freshness.

A smartphone-based supramolecular biosensor for portable and rapid detection of buprofezin in real food samples

Buprofezin (BUP) is an insect growth regulator widely used in agriculture to control hemipteran pests, particularly the melon aphid, Aphis gossypii, due to its efficiency and low toxicity. Although approved by the Chinese government, its maximum residue limit (MRL) in food is strictly regulated, and conventional techniques for detecting BUP have several limitations. Our study reports successful BUP detection using a supramolecular fluorescent probe DP@ALB, constructed with chalcone-based fluorescent dye DP and albumin as the host. The probe offers advantages such as low cost, visual signal output with high fluorescence color variation, rapid response, and high sensitivity. Additionally, portable test strips enable convenient on-site BUP detection and simplifying field monitoring of spiked real samples. The study achieves precise qualitative and quantitative BUP analysis in grape fruit, groundwater, and soil with satisfactory recoveries. Further, the biological applicability of sensor for the in vitro detection of BUP in L929 living cells was demonstrated. This research breakthrough overcomes the limitations of traditional analytical methods, offering an efficient and reliable approach for food and environmental monitoring and pesticide residue detection.

Novel benzothiazole-based fluorescent probe for efficient detection of Cu2+/S2− and Zn2+ and its applicability in cell imaging

BackgroundIn recent years, environmental pollution has been increasing due to the excessive emission of toxic ions, which has caused serious harm to human health and ecological environment. There are various methods for detecting Cu2+, S2− and Zn2+, but the traditional ion detection methods have obvious disadvantages, such as poor selectivity and long detection time. Therefore, it is still crucial to develop simple, efficient and rapid detection methods. ResultsA fluorescent probe based on benzothiazole, (E)-N'-(3-(benzo[d]thiazol-2-yl)-2-hydroxy-5-methylbenzylidene)-3,4,5-tris(benzyloxy)benzohydrazide (BT), was designed and synthesized. It was characterized using ESI-MS, 1H NMR, and 13C NMR. BT can be used as a chemosensor to detect Cu2+, S2− and Zn2+ in CH3CN/H2O (7:3, v/v, pH = 7.4, HEPES buffer: 0.1 M), with detection limits of 0.301 μM, 0.017 μM, and 0.535 μM, respectively. At an excitation wavelength of 320 nm, BT exhibits an “on-off-on” response to Cu2+/S2− and enhanced fluorescence response to Zn2+, with a change in fluorescence color from orange to green. The coordination ratio of ions to the probe was determined to be 1:1 through Job's plot and hydrogen spectral titration. The recognition mechanism was discussed in conjunction with theoretical calculations. Furthermore, the probe has been successfully used in test strips and medical swabs colorimetry, as well as live cell imaging. SignificanceThe probe BT lays the foundation for the design and synthesis of multifunctional fluorescent probes. As a portable detection method, probe BT was used to detect Cu2+, S2− and Zn2+ on strips. Furthermore, the probe was applied to biological cells to detect target ions with low cytotoxicity and excellent cell permeability. This indicating that it can be used as a potential candidate for tracking Cu2+ and S2− in clinical diagnostics and biological systems.

Selective and sensitive detection of bilirubin by Fe3+-mediated porphyrin red fluorescence "on-off-on" sensing platform

Bilirubin (BR) serves as a crucial clinical marker for jaundice and liver dysfunction, making its quantitative detection amidst numerous biomolecular interferences of paramount importance. In this work, 5, 10, 15, 20-tetrakis(4-methoxycarbonylphenyl)porphyrin (TPPCOOMe) was utilized as the fluorophore, and Fe3+ was used as the mediator to achieve quantitative detection of BR in human serum through the "on-off-on" fluorescence signal change. The non-fluorescent metalloporphyrin complex TPPCOOMe@Fe3+ generated by the interaction between Fe3+ and TPPCOOMe served as the fluorescence sensing platform. With the addition of BR, the good binding ability between BR and Fe3+ released TPPCOOMe into the sensing medium and restored red fluorescence, while creating conditions for the redox reaction between BR and Fe3+. The fluorescence probe exhibited a good linear relationship with BR in the concentration range of 0–8 μM, the detection limit was as low as 14 nM and the response time was 2 min. Furthermore, a test paper strip-based sensor coupled with a smartphone color-read App was employed to test the fluorescence color changes of TPPCOOMe@Fe3+ for BR sensing, and this intelligent sensing platform had been successfully achieved for the actual detection of BR in human serum without the influence of other metal ions and important biomolecules.

Multi-Stimuli-Responsive Fluorescent Molecule with AIE and TICT Properties Based on 1,8-Naphthalimide.

A multi-stimuli responsive fluorophore, named NBDNI, was developed by constructing a 1,8-naphthalimide derivative in which a rotatable electron-donating N,N-dimethylaniline group attached to its 4-position. This molecular structure endowed NBDNI with aggregate-induced emission (AIE) and twisted intramolecular charge transfer (TICT) properties, enabling remarkable fluorescence changes in response to multiple external stimuli: (i) sensitivity to polarity in various solvent systems and polymer matrix; (ii) significant fluorescence response and excellent linearity towards temperature changes in solution; (iii) distinct switch of fluorescence color upon acid and base treatments; (iv) reversible mechanochromism behavior in the solid state. Moreover, the mechanisms underlying the aforementioned stimuli-responsive phenomena have been proposed based on comprehensive systematic measurements. Furthermore, preliminary applications such as fluorescence thermometry and acid/base test paper have been demonstrated. This research will bring about new opportunities for the development of novel stimuli-responsive luminescent materials.

Easy and fast detection of S2− by a new benzothiazole-based fluorescent probe in environmental, biological and food systems

The detection of S2− is required because of its harmful effects on human health. This led us to strategically design a new benzothiazole-based fluorescent chemosensor BTP (2-(benzo[d]thiazol-2-yl)-4,6-dichlorophenol). This sensor undergoes a fluorescence color change from orange to green in the presence of S2− via the deprotonation of phenol in near-perfect water. The detection limit for S2− reached 0.78 μM and BTP could selectively probe S2− over other competing analytes. The process whereby BTP responds to S2− was suggested to be improved intramolecular charge transfer (ICT), as was demonstrated by extensive DFT calculations. Particularly, BTP was successfully applied to detect S2− in zebrafish, real water, and beverage samples. Further, test strips coated with BTP were used to monitor the S2− released in raw meat. BTP is the first benzothiazole-based chemosensor developed to detect the S2− released from various types of food samples. The proposed method offers a novel tool for measuring S2− in biological and environmental systems, as well as the food quality under on-site conditions.

Jellyfish-Inspired Visual and Sensory Bubbling Robots with Automatic 3D Morphable Films for Underwater Environmental Interactions.

Coelenterates, such as Atolla jellyfish, are capable of integrating color, communication, and motion in a sophisticated manner, thereby enabling them to function as intelligent biological systems that can adapt to the challenges of the underwater environment. Extensive efforts have been dedicated to exploiting underwater visual, sensory, actuating, or combined systems. However, current biomimetic soft systems are still limited by the lack of comprehensive, integrated functional skins that can automatically deform, dynamically sense, and further send color signals when diving into underwater conditions. Here, we propose the synthetic soft skins composed of assembled entangled carbon nanotube networks and fluorescent unit-embedded elastomers which can be applied in a suspended form to allow autonomic 3D deformation, real-time perception, and dynamic fluorescence color transformation. The capabilities of the sensory and color display thresholds were controlled through the entanglement density of carbon nanotubes and the suspended area. As a demonstration, the soft thin skin was integrated into an artificial jellyfish robot, enabling the realization of a closed-loop feedback system for dynamic sensory processing, signal processing, and further 3D morphing-induced fluorescent color change, demonstrating significant potentials in underwater visual display, danger warning, and environmental exploration.