Fluorescence Color Change Research Articles

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.

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.

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.

A novel biomass carbon dots ratiometric fluorescence probe coupled with molecularly imprinted polymer for selective detection of aflatoxin B1

The accumulation of Aflatoxin B1 (AFB1) in food and crops can pose significant hazards to human health. Consequently, there has been extensive attention paid to the development of a rapid and reliable method for detecting AFB1 in food. In this context, a ratiometric fluorescence probe (DE-MIPs) was prepared using dual-emission fluorescent carbon dots (CDs) coupled with the molecular imprinting technique for visual detection of AFB1. The dual-emission CDs consisted of red fluorescence biomass CDs (R-CDs) wrapped by molecularly imprinted cavities (R-CDs@MIPs), which served as a response signal, and pure blue emission biomass CDs (B-CDs) as a reference signal. Due to the specific quenching effect of AFB1 on red fluorescence while leaving blue fluorescence unaffected, there was a gradual decrease in the fluorescence intensity ratio (I670/I437) and a distinct shift in fluorescence color from red to blue as the concentration of AFB1 increased. The ratiometric probe demonstrated excellent linearity in detecting AFB1 within the concentration range of 0.1–200 ng/mL, with a detection limit (LOD) of 0.05 ng/mL. Furthermore, the practicality of DE-MIPs was validated by successfully detecting AFB1 in vegetable oil, with desirable recoveries from 89.0% to 107.4%. Furthermore, the integration of a smartphone as colorimetric reader enabled rapid AFB1 detection by capturing changes in fluorescence color. Overall, the development of this ratiometric probe offers a novel perspective for the facile and efficient identification of AFB1 in complex food samples.

A Ratiometric Fast-Response Fluorescent Probe Based on Dicyanoisophorone for Monitoring HClO in Paper Test Strips and Living Mice.

A new dicyanoisophorone-based ratiometric fluorescent probe NOSA was synthesized and characterized. It showed a fast fluorescence response to HClO with the emission color change from dark green to bright red. NMR, IR, and HRMS suggested that the detection of NOSA to HClO may originate from the hydroxyl deprotection reaction by HClO on the molecule NOSA, which caused a red-shift of fluorescence. The probe NOSA displayed high selectivity and excellent anti-interference performance with a limit of detection at 3.835 × 10-7M. The convenient paper test strips were successfully obtained and applied to the detection of HClO based on fluorescence color change with the varied NaClO concentration. Moreover, spiked recovery experiments in real water samples indicated that the probe NSOA could quantitatively detect HClO, and the fluorescence bio-imagings in vivo were carried out, and HClO detection in biosystems using NOSA was realized.

Smartphone-assisted fluorescent sensor for the visualization and quantitative detection of doxycycline and L-arginine

A novel smartphone-assisted fluorescent sensor based on europium/zirconium metal-organic framework (Eu0.5/Zr0.5-MOF) was developed for the fast and sensitive determination of doxycycline (DOX) and L-arginine (Arg). After the addition of DOX, the fluorescence of Eu0.5/Zr0.5-MOF was quenched owing to the inner filter effect (IFE). When Arg was introduced into the Eu0.5/Zr0.5-MOF@DOX complex system, the fluorescence was recovered because the interaction between Arg and Eu0.5/Zr0.5-MOF@DOX weakened the IFE. Moreover, the Eu0.5/Zr0.5-MOF produced continuous fluorescence color changes for the visual measurement of DOX and Arg. The fluorescent probe for DOX and Arg offered broad linear ranges of 0.05–80 and 0.1–60 μg/mL, respectively, with detection limits as low as 2.07 and 67.5 ng/mL. The proposed method was successfully applied to monitor DOX in eggs and Arg in human serum. This work provides a powerful platform for the real-time and visual analysis of DOX and Arg in food and biological samples.

Lanthanide metal-organic frameworks as ratiometric fluorescent probes for real-time monitoring of PFOA photocatalytic degradation process

The assessment of perfluorooctanoic acid (PFOA) photocatalytic degradation usually involves tedious pre-treatment and sophisticated instrumentation, making it impractical to evaluate the degradation process in real-time. Herein, we synthesized a series of lanthanide metal-organic frameworks (Ln-MOFs) with outstanding fluorescent sensing properties and applied them as luminescent probes in the photocatalytic degradation reaction of PFOA for real-time evaluation. As the catalytic reaction proceeds, the fluorescence color changes significantly from green to orange-red due to the different interaction mechanisms between the electron-deficient PFOA and smaller radius F− with the ratiometric fluorescent probe MOF-76 (Tb: Eu = 29:1). The limit of detection (LOD) was calculated to be 0.0127 mM for PFOA and 0.00746 mM for F−. In addition, the conversion rate of the catalytic reaction can be read directly based on the chromaticity value by establishing a three-dimensional relationship graph of G/R value-conversion rate-time (G/R indicates the ratio between green and red luminance values in the image.), allowing for real-time and rapid tracking of the PFOA degradation. The recoveries of PFOA and F− in the actual water samples were 99.3–102.7% (RSD = 2.2–4.4%) and 100.7–105.3% (RSD = 3.9–6.8%), respectively. Both theoretical calculations and experiments reveal that the detection mechanism was attributed to the photoinduced electron transfer and energy transfer between the analytes and the probe. This method simplifies the sample analysis process and avoids the use of bulky instruments, and thus has great potential on the design and development of quantitative time-resolved visualization methods to assess catalytic performance and reveal mechanisms.

Synthesis, crystal structure and photophysical properties of a dinuclear MnII complex with 6-(di-ethyl-amino)-4-phenyl-2-(pyridin-2-yl)quinoline.

A new quinoline derivative, namely, 6-(di-ethyl-amino)-4-phenyl-2-(pyridin-2-yl)quinoline, C24H23N3 (QP), and its MnII complex aqua-1κO-di-μ-chlorido-1:2κ4 Cl:Cl-di-chlorido-1κCl,2κCl-bis-[6-(di-ethyl-amino)-4-phenyl-2-(pyridin-2-yl)quinoline]-1κ2 N 1,N 2;2κ2 N 1,N 2-dimanganese(II), [Mn2Cl4(C24H23N3)2(H2O)] (MnQP), were synthesized. Their compositions have been determined with ESI-MS, IR, and 1H NMR spectroscopy. The crystal-structure determination of MnQP revealed a dinuclear complex with a central four-membered Mn2Cl2 ring. Both MnII atoms bind to an additional Cl atom and to two N atoms of the QP ligand. One MnII atom expands its coordination sphere with an extra water mol-ecule, resulting in a distorted octa-hedral shape. The second MnII atom shows a distorted trigonal-bipyramidal shape. The UV-vis absorption and emission spectra of the examined compounds were studied. Furthermore, when investigating the aggregation-induced emission (AIE) properties, it was found that the fluorescent color changes from blue to green and eventually becomes yellow as the fraction of water in the THF/water mixture increases from 0% to 99%. In particular, these color and intensity changes are most pronounced at a water fraction of 60%. The crystal structure contains disordered solvent mol-ecules, which could not be modeled. The SQUEEZE procedure [Spek (2015 ▸). Acta Cryst. C71, 9-18] was used to obtain information on the type and qu-antity of solvent mol-ecules, which resulted in 44 electrons in a void volume of 274 Å3, corresponding to approximately 1.7 mol-ecules of ethanol in the unit cell. These ethanol mol-ecules are not considered in the given chemical formula and other crystal data.

A ratiometric fluorescence and colorimetry dual-signal sensing strategy based on o-phenylenediamine and AuNCs for determination of Cu2+ and glyphosate.

A ratiometric fluorescence sensing strategy has been developed for the determination of Cu2+ and glyphosate with high sensitivity and specificity based on OPD (o-phenylenediamine) and glutathione-stabilized gold nanoclusters (GSH-AuNCs). Water-soluble 1.75-nm size GSH-AuNCs with strong red fluorescence and maximum emission wavelength at 682nm were synthesized using GSH as the template. OPD was oxidized by Cu2+, which produced the bright yellow fluorescence oxidation product 2,3-diaminophenazine (DAP) with a maximum fluorescence emission peak at 570nm. When glyphosate existed in the system, the chelation between glyphosate and Cu2+ hindered the formation of DAP and reduced the fluorescence intensity of the system at the wavelength of 570nm. Meanwhile, the fluorescence intensity at the wavelength of 682nm remained basically stable. It exhibited a good linear relationship towards Cu2+ and glyphosate in water in the range 1.0-10 µM and 0.050-3.0µg/mL with a detection limit of 0.547 µM and 0.0028µg/mL, respectively. The method was also used for the semi-quantitative determination of Cu2+ and glyphosate in water by fluorescence color changes visually detected by the naked eyes in the range 1.0-10 µM and 0.30-3.0µg/mL, respectively. The sensing strategy showed higher sensitivity, more obvious color changes, and better disturbance performance, satisfying with the detection demands of Cu2+ and glyphosate in environmental water samples. The study provides a reliable detection strategy in the environment safety fields.

A novel fluorescence sensor film for hydroquinone based on a graphene quantum dots-nano activated carbon composite

A novel film sensor, composed of graphene quantum dots-nano activated carbon, chitosan, and PVA, offers a simple and effective hydroquinone (HQ) detection. This film exhibits impressive HQ adsorption under ambient conditions (room temperature, pH 7, 3 h) and utilizes a readily observable fluorescence color change for quantification. Upon HQ binding, the film's fluorescence color shifts from yellow-green to blue, enabling a linear detection range of 1.0–150 mg⋅L−1 based on intensity analysis of the blue component (B value). Calibration curves generated on the same day (n = 3) exhibit high precision, with standard deviations of the linear equation parameters below 0.014 and a low detection limit of 0.5 mg⋅L−1. The film exhibits exceptional stability, retaining its color and performance for up to 20 days. This stability is further corroborated by recovery experiments utilizing HQ-spiked water samples at concentrations of 2.5 mg⋅L−1 and 40 mg⋅L−1, where recoveries of 106 % and 95 % were achieved, respectively. These results demonstrated the sensor's reliable quantification capabilities. Notably, the sensor exhibited insignificant interference from commonly co-existing substances such as ethanol, ascorbyl glucoside, arbutin, kojic acid, and methylene blue. However, Cu²⁺, Fe³⁺, and catechol did cause some interference. This versatility, coupled with its straightforward operation, makes the film sensor a promising candidate for on-site HQ detection in diverse environmental monitoring applications.

A dual-response ratiometric fluorescent sensor by europium-doped silicon nanoparticles for fluorescent and smartphone imaging detection of tetracycline

Given the threat to human health posed by the abuse of tetracycline (TC), the development of a portable, on-site methods for highly sensitive and rapid TC detection is crucial. In this work, we initially synthesized europium-doped silicon nanoparticles (SiEuNPs) through a facile one-pot microwave-assisted method. Due to its blue-red dual fluorescence emission (465 nm/621 nm), which was respectively attributed to the silicon nanoparticles and Eu3+, SiEuNPs were designed as a ratiometric fluorescent sensor for TC detection. For the dual-signal reverse response mechanism: TC quenched the blue emission from silicon nanoparticles through inner filter effect (IFE), and enhanced the red emission through “antenna effect” (AE) between TC and Eu3+, the nanoprobe was able to detect TC within a range of 0.2–10 μM with a limit of detection (LOD) of 10.7 nM. Notably, the equilibrium detection time was only 1 min, achieving rapid TC detection. Furthermore, TC was also measured in real samples (tap water, milk and honey) with recoveries ranging from 95.7 % to 117.0 %. More importantly, a portable smartphone-assisted on-site detection platform was developed, enabling real-time qualitative identification and semi-quantitative analysis of TC based on fluorescence color changes. This work not only provided a novel doped silicon nanoparticles strategy, but also constructed a ratiometric sensing platform with dual-signal reverse response for intuitive and real-time TC detection.

Multiresponsive Bilayer Hydrogel Actuator with Switchable Shape Morphing Capability and Visible Color/Fluorescence Change.

Bilayer hydrogels, endowed with multiresponsive and switchable color-changing properties, have garnered significant attention for bioinspired artificial intelligent materials. However, the design and fabrication of such hydrogels that can fully mimic the adaptation of the live organism, i.e., simultaneous changes in shape, fluorescent, and/or visible color, still remain significant challenges. Herein, a multiresponsive (e.g., temperature, salt, and pH) and multiadaptive (shape, fluorescent color, and visible color changes) hydrogel was fabricated by employing monomers featuring pH-responsive fluorescence 4-(2-(4-(dimethylamino) phenyl)-1-isocyanovinyl) phenol (DP) and switchable color-changing 4-(2-sulfethyl) -1-(4-vinylbenzyl) pyridinium betaine (VPES). The bilayer hydrogel comprises a temperature- and pH-responsive gel layer, poly(N-isopropylacrylamide-co-2-(dimethylamino) ethyl methacrylate), along with a pH-, temperature-, and salt-responsive gel layer, poly(acrylamide-co-2-(dimethylamino)ethyl methacrylate-co-VPES)@DP. Due to the opposite swelling/shrinking behavior between the two layers, the prepared hydrogel exhibits shape changes in response to thermal, salt, and pH stimuli, along with switchable fluorescent color and visible color change that originate from DP and polyVPES, respectively. Apart from multiresponsive behavior, this hydrogel also shows an excellent antifatigue property and high sensitivity, which makes it hold significant potential in many applications. We anticipate that this strategy to realize multiresponsive capability in this work can also inspire the design of the biomimetic smart materials.

Pyrene‐based ratiometric fluorescent chemosensor for sensitive detection of hypochlorite in a perfect aqueous solution

AbstractWe synthesized a pyrene‐based sensitive fluorescent chemosensor, TPA‐Cl ((E)‐N,N,N‐trimethyl‐2‐oxo‐2‐(2‐(pyren‐1‐ylmethylene)hydrazinyl)ethan‐1‐aminium chloride), to detect hypochlorite in a perfect aqueous solution. TPA‐Cl showed high selectivity for hypochlorite through fluorescence color change from sky blue to blue. The detection limit for hypochlorite was calculated as 0.27 μM, which is a quite low value. Moreover, the presence of other anions or ROS hardly hindered the sensing of hypochlorite by TPA‐Cl. Furthermore, TPA‐Cl could be applied successfully as a test kit for the simple recognition of hypochlorite. Surprisingly, TPA‐Cl is the first pyrene‐based fluorescent chemosensor that can detect ClO− by using the TPA‐Cl‐coated test kit. Moreover, TPA‐Cl could achieve the quantification of ClO− in various environmental water samples. The hydrolytic cleavage and oxidation mechanism of TPA‐Cl by hypochlorite was elucidated through UV–vis and fluorescent spectroscopy, 1H NMR titration, ESI‐MS analysis and DFT calculation.

A ratiometric fluorescent sensor based on S-doped BCNO quantum dots and Au nanoclusters combined with 3D-printing portable device for the detection of malachite green.

Sulfur-doped BCNO quantum dots (S-BCNO QDs) emitting green fluorescence were prepared by elemental doping method. The ratiometric fluorescence probe with dual emissions was simply established by mixed S-BCNO QDs with gold nanoclusters (GSH-Au NCs). Because the emission spectrum of Au NCs (donor) at 615nm overlapped well with the ultraviolet absorption of malachite green (MG), fluorescence resonance energy transfer (FRET) can be achieved. When the concentration of MG increased, the fluorescence intensity (F495) of S-BCNO QDs decreased slowly, while the fluorescence intensity (F615) of Au NCs decreased sharply.The fluorescence intensity ratio of F615/F495 decreased with the increase of MG. By plotting the F615/F495 values against MG concentration, a sensitive and rapid detection of MG was possible with a wide detection range (0.1-50 µM) and a low detection limit of 10 nM. Due to the accompanying fluorescence color change from pink to blue-green, it can be used for visual detection. A three dimensional-printing device utilizing digital image colorimetry to capture color changes through the built-in camera, enables quantitative detection of MG with a good linearity between the values of red/green ratioand MG concentrations at the range 1-50 µM. This sensing platform had a range of advantages, including high cost-effectiveness, portability, ease of operation, and high sensitivity. Furthermore, the sensing platform was successfully applied tothe detection of MG in real water sample and fish samples, thereby verifying the reliability and effectiveness of this sensing platform in water quality monitoring and food safety.

Novel ratiometric fluorescent probe with large Stokes shift for selective sensing and imaging of Zn2+ in live cell

A novel ratiometric fluorescent probe, namely 5-[(3-dicyanoylidene −5.5-dimethyl) cyclohexenyl-1-ethenyl] salicylaldehyde-3′-hydroxybenzohydrazone (DCSH) is presented for the selective sensing of Zn2+ ion in acetonitrile/water (2/3, pH 7.4) solution. Introducing Zn2+ ions notably caused the peak emission of DCSH to shift from 560 nm to 646 nm, accompanied with a significant enhancement of its intensity. A vivid change in fluorescence color from yellow to red facilitated the immediate identification of Zn2+ ions by visual observation. DCSH exhibits substantial Stokes shifts (110 and 196 nm), rapid detection capability (within 10 s) and high sensitivity to Zn2+ ions, achieving a limit of detection of 31.2 nM. The response mechanism is supposed to involve the block of C = N bond isomerization and excited state intramolecular proton transfer (ESIPT) along with the enhancement of fluorescence through chelation (CHEF) effect. DCSH was effectively utilized for ratiometric fluorescence imaging to monitor exogenous Zn2+ concentrations in HeLa cells. Significantly, DCSH is capable of monitoring elevated levels of Zn2+ ion during apoptosis induced by L-Buthionine sulfoximine (BSO).

Electrofluorochromic Hydrogels by Oligothiophene-Based Color-Tunable Fluorescent Dye Doping.

Soft electronic materials hold great promise for advancing flexible functional devices. Among the various soft materials available, hydrogels are particularly attractive for soft electronic device development due to their inherent properties, including transparency, shape adaptability through swelling/deswelling, and self-healing capabilities. Transparent hydrogels contribute to the creation of advanced smart devices such as sensors, smart windows, and anticounterfeiting technologies. Poly(vinyl alcohol) hydrogels are used as a platform for creating electrofluorochromic (EFC) devices in combination with oligothiophene-conjugated benzothiazole derivatives (OCBs) as fluorescent emitters. OCBs demonstrated excited-state intramolecular proton transfer (ESIPT) behavior with a large Stokes shift and emission changes responsive to solvent polarity and pH stimuli. Even in the solid state, OCBs exhibited strong fluorescence emission across a wide range of colors from blue to red, making them exceptionally well-suited for EFC device development. Their quantum yields in the powder state were obtained between 2.3% and 19.9%. Through the incorporation of OCBs into a PVA hydrogel (OCB@PVA), we achieved the successful fabrication of flexible EFC devices, including electronic paper and smart panels. When electric potentials (-2.4 and +2.4 V) were applied in OCB@PVA, fluorescence color changes were observed by an electrochemically induced pH change owing to electrohydrolysis of water. These devices demonstrated the potential of OCB@PVA hydrogels in the realm of flexible electronics. They could be used to create innovative and versatile devices with stimuli-responsive fluorescence properties.

Portable hydrogel kit based on Michael addition reaction for (E)-2-hexenal gas detection

Plants exhibit rapid responses to biotic and abiotic stresses by releasing a range of volatile organic compounds (VOCs). Monitoring changes in these VOCs holds the potential for the early detection of plant diseases. This study proposes a method for identifying late blight in potatoes based on the detection of (E)-2-hexenal, one of the major VOC markers released during plant infection by Phytophthora infestans. By combining the Michael addition reaction with cysteine-mediated etching of aggregation-induced emission gold nanoclusters (Au NCs), we have developed a portable hydrogel kit for on-site detection of (E)-2-hexenal. The Michael addition reaction between (E)-2-hexenal and cysteine effectively alleviates the etching of cysteine-mediated Au NCs, leading to a distinct fluorescence color change in the Au NCs, enabling a detection limit of 0.61 ppm. Utilizing the superior loading and diffusion characteristics of the three-dimensional structure of agarose hydrogel, our sensor demonstrated exceptional performance in terms of sensitivity, selectivity, reaction time, and ease of use. Moreover, quantitative measurement of (E)-2-hexenal was made easier by using ImageJ software to transform fluorescent images from the hydrogel kit into digital data. Such method was effectively used for the early detection of potato late blight. This study presents a low-cost, portable fluorescent analytical tool, offering a new avenue for on-site detection of plant diseases.

Visual lambda-cyhalothrin detection using yellow carbon dots molecularly imprinted polyvinylidene fluoride fluorescent membrane

Due to its common use as an insecticide during agricultural production, residual lambda-cyhalothrin (LC) in food and the environment presents a significant human health risk. Developing an accurate LC detection method that does not require pretreatment remains a challenge. This study developed a novel yellow carbon dots molecularly imprinted (YCDs@MIPs) polyvinylidene fluoride (PVDF) composite (YCDs@MIPs@PVDF) fluorescent membrane for rapid visual LC detection. This method required no pretreatments during analysis since the LC could be specifically adsorbed when the samples passed through the YCDs@MIPs@PVDF membrane, causing fluorescence quenching, while matrix-interfering components could be removed for the porous structure of the membrane. A smartphone was used for rapid visual LC detection based on membrane fluorescence color changes in a dark-box ultraviolet analyzer. In food with a 15 % PVDF content and 6 mL added YCDs@MIPs, LC was quantitatively detected in a broad concentration range (5–500 μg/L) with a limit of detection (LOD) of 0.039 μg/L to 0.16 μg/L, which was lower than the strictest EU2019/92 limit of 10 μg/L. The analysis time was reduced from over 8 h when using the GB 23200.121–2021 and GB/T20769–2008 national standard methods to 30 min, while the analytical procedure decreased from six steps to two. The visual detection strategy combining the YCDs@MIPs@PVDF composite fluorescent membrane with a smartphone provided a new rapid detection technique for composite membrane purification and fluorescence signal output function.