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In this context, we used the multicomponent Chichibabin pyridine synthesis reaction to synthesize a novel di(thiophen-2-yl) substituted and pyrene-pyridine fluorescent molecular hybrid. The computational (DFT and TD-DFT) and experimental investigations were performed to understand the photophysical properties of the synthesized new structural scaffold. The synthesized ligand displays highly selective fluorescent sensing properties towards Fe3+ ions when compared to other competitive metal ions (Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe2+, Hg2+, Na+, Ni2+, Pb2+, Sr2+, Sn2+ and Zn2+). The photophysical properties studies reveal that the synthesized hybrid molecule has a binding constant of 2.30 × 103 M−1 with limit of detection (LOD) of 4.56 × 10−5 M (absorbance mode) and 5.84 × 10–5 M (emission mode) for Fe3+ ions. We believe that the synthesized pyrene-conjugated hybrid ligand can serve as a potential fluorescent chemosensor for the selective and specific detection of Fe3+ ions. [ABSTRACT FROM AUTHOR]

Accurate detection of copper ions is crucial since it is an essential trace element. Carbon quantum dots (CQDs) were prepared from apricot leaves using a hydrothermal method. These CQDs, which generated a reference signal, were combined with glutathione-bound gold nanoclusters (GSH-AuNCs) synthesized by the reduction of chloroauric acid to form a ratiometric fluorescent probe. The probe exhibited fluorescence emission at 450 nm and 568 nm. The determination of Cu(II) was performed through visual analysis of the color change and the intensity ratio (I450/I568) of the emission peaks. Orange fluorescent GSH-AuNCs responded to Cu(II) with fluorescence, and the blue fluorescent CQDs were chemically inert. The probes changed color from pink to purple to blue in response to different concentrations of Cu(II). The linear range of the fluorescence probe for Cu(II) was 0 to 120 µmol/L, and the limit of detection (LOD) was 0.65 µmol/L. This study has demonstrated that the probe provided good selectivity for detecting Cu(II) in water and has potential practical application. [ABSTRACT FROM AUTHOR]

The detection of pH and water is critical in the life sciences and chemical industries. The yellow fluorescent carbon dots (CDs) synthesized by solvothermal method using neutral red (NR) as carbon source, ethylenediamine (EDA) as nitrogen source and ethanol as solvent was studied. It was found that the carbon dots (NR-EDA-CDs) could produce double emission peaks when the excitation wavelength was in the range of 310~370 nm. Therefore, a method for the detection of pH and water with a double ratio fluorescence probe based on a single luminant was established. The carbon dots were characterized by high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy, infrared spectroscopy and X-ray photoelectron spectroscopy. The results showed that the carbon dots are spheroidal in shape, with an average particle size of 3. 6 nm and obvious graphite structure. It was found that the carbon dots has good stability, photobleaching resistance and salt tolerance at the excitation wavelength of 365 nm. In phosphate buffer solution, pH in the range of 4. 15~8. 55 has a good linear relationship with the fluorescence intensity ratio of 581 and 449 nm (F581/ F449), and its coefficient (R²) is 0. 986. The pH ratio fluorescent probe has the characteristics of wide linear range and good reversibility. At the same time, it was found that the content of water in DMSO is linear with F485/ F585 in the range of 0. 6%~50% (V (H2O) / V (DMSO)), R² is 0. 996, and the detection limit is 0. 18% (V (H2O)/ V (DMSO)) . The double ratio fluorescent probe provides a new method for the detection of pH and water. [ABSTRACT FROM AUTHOR]

A novel coumarin–naphthalimide‐based ratiometric fluorescent probe, called XPT, was synthesized with the aim of achieving high sensitivity and anti‐interference for N2H4 detection. The probe XPT consists of coumarin species and naphthalimide species, which act as the energy donor and acceptor, respectively. The phthalimide group functions as the recognition unit for N2H4. Without the presence of hydrazine, the naphthalimide remains in a non‐fluorogenic phthalimide mode, disrupting the FRET signal. However, the phthalimide group undergoes the Gabriel reaction to an amine, which induces FRET and consequently causes a shift in the emitted fluorescence from 468 to 528 nm when N2H4 was added. The results of the study demonstrated that XPT exhibits high sensitivity with a limit of detection 2.2 μM, as well as selectivity. Furthermore, it is remarkable that the distribution of N2H4 in real water samples can be monitored by XPT. [ABSTRACT FROM AUTHOR]

To find a convenient, rapid and accurate measurement of lead (Pb2+) content in tobacco flavors, blue carbon dots (CDs) were used as a signal probe due to their fluorescence response to Pb2+. At the same time, a fluorescent material that does not react with Pb2+ and exhibits different fluorescence color was used as a reference probe. By adjusting the mixing ratio of the above two materials, a ratiometric fluorescence probe was constructed and used for visual quantitative analysis of Pb2+ mass frations in tobacco flavor samples. The results showed that: 1) Under ultraviolet irradiation, as the mass fraction of Pb2+ increased from 0 to 20 mg/kg, there was a distinct color transition of the probe solution from blue to pink. The mass fraction of Pb2+ showed on a good linear relationship with the fluorescence intensity ratio (I460/I580) with a limit of detection (LOD) as low as 1.32 µ g/L. 2) The probe demonstrated rapid response capability with detection completed within 5 min, and showed an excellent selectivity and interference resistance. 3) The fluorescence color change could be identified by the Red/Green/Blue (RGB value) color mode by smartphones, then a standard working curve corresponding to RGB values and Pb2+ mass fraction was established to simplify the analysis process and realize rapid detection of Pb2+ with LOD of 7.04 µg/L. 4) The average recoveries ranged from 91.14% to 103.80%, and the relative standard deviations (RSDs) were from 3.01% to 5.23%. This method is simple, fast and accurate, and realizes the rapid visual quantitative detection of Pb2+ mass fraction in tobacco flavor samples. [ABSTRACT FROM AUTHOR]

A precisely designed dual-color biosensor has realized a visual assessment of thymidine kinase 1 (TK1) mRNA in both living cells and cell lysates. The oligonucleotide probe is constructed by hybridizing the antisense strand of the target and two recognition sequences, in which FAM serves as the donor and TAMRA as the acceptor. Once interacting with the target, two recognition strands are replaced, and then the antisense complementary sequence forms a more stable double-stranded structure. Due to the increasing spatial distance between two dyes, the FRET is attenuated, leading to a rapid recovery of FAM fluorescence and a reduction of TAMRA fluorescence. A discernible color response from orange to green could be observed by the naked eye, with a limit of detection (LOD) of 0.38 nM and 5.22 nM for spectrometer- and smartphone-based assays, respectively. The proposed ratiometric method transcends previous reports in its capacities in visualizing TK1 expression toward reliable nucleic acid biomarker analysis, which might establish a general strategy for ratiometric biosensing via strand displacement. [ABSTRACT FROM AUTHOR]

The accumulation of heavy metal ions in the human body sharply affects health, drawing global attention. Consequently, there is an urgent need to develop environmentally-friendly and non-toxic metal ion fluorescent sensing probes. Herein, two fluorescent probes based on Cs–Bi–Cl perovskite quantum dots (PeQDs) with distinct structures, namely Cs 3 BiCl 6 :Eu3+ (3-1-6-E) and Cs 3 Bi 2 Cl 9 :Eu3+ (3-2-9-E), were successfully synthesized by using the ligand-assisted re-precipitation (LARP) method for detecting Cu2+ and Fe3+ ions in ethanol. Both PeQDs exhibit polychromatic emission, including feature emission around 505 nm and distinctive emission from Eu3+ ions in the long-wavelength region, making them suitable for ratiometric fluorescent probes. Significantly, both probes displayed excellent linear relationship with correlation coefficients of 0.998 (3-1-6-E) and 0.985 (3-2-9-E), respectively. The limit of detection (LOD) reached 6.23 μM (3-1-6-E) and 4.55 μM (3-2-9-E). Notably, the 3-2-9-E quantum dots (QDs) successfully detected Fe3+ ions in ethanol, owing to their unique photo-quenching and photo-recovery phenomena. The detection results exhibited excellent linear fitting, with a correlation coefficient of 0.996 and a low LOD of 3.6 μM. Furthermore, compared to undoped PeQDs, Eu3+ ion-doped PeQDs demonstrate strongly enhanced luminescence intensity and excellent photo-stability. This work expands the potential applications of lead-free PeQDs while simultaneously improving their luminescent properties. [ABSTRACT FROM AUTHOR]

Nanoclusters for fluorescence detection are generally comprised of rare and expensive noble metals, and the nanoclusters based on more affordable transition metal have attracted increasing attention. This study designed a ratiometric fluorescent probe to detect dopamine (DA), an important neurotransmitter. With carbon dots encapsulated within silica (CDs@SiO2) as the reference, the emitted reference signal was almost unchanged due to the protection of inert silicon shell. Meanwhile, copper nanoclusters modified with 3-aminophenyl boronic acid (APBA-GSH-CuNCs) provided the sensing signal, in which the phenylboric acid could specifically recognize the cis-diol structure of DA, and caused the fluorescence quenching by photoinduced electron transfer. This dual emission ratiometric fluorescent probe exhibited high sensitivity and anti-interference, and was able to selectively responded to DA with a linear range of 0–1.4 mM, the detection limit of 5.6 nM, and the sensitivity of 815 mM−1. Furthermore, the probe successfully detected DA in human serum samples, yielding recoveries ranging from 92.5% to 102.7%. Overall, this study highlights the promising potential of this ratiometric probe for detecting DA. [ABSTRACT FROM AUTHOR]

In the ratiometric fluorescent (RF) strategy, the selection of fluorophores and their respective ratios helps to create visual quantitative detection of target analytes. This study presents a framework for optimizing ratiometric probes, employing both two-component and three-component RF designs. For this purpose, in a two-component ratiometric nanoprobe designed for detecting methyl parathion (MP), an organophosphate pesticide, yellow-emissive thioglycolic acid-capped CdTe quantum dots (Y-QDs) (analyte-responsive), and blue-emissive carbon dots (CDs) (internal reference) were utilized. Mathematical polynomial equations modeled the emission profiles of CDs and Y-QDs in the absence of MP, as well as the emission colors of Y-QDs in the presence of MP separately. In other two-/three-component examples, the detection of dopamine hydrochloride (DA) was investigated using an RF design based on blue-emissive carbon dots (B-CDs) (internal reference) and N-acetyl L-cysteine functionalized CdTe quantum dots with red/green emission colors (R-QDs/G-QDs) (analyte-responsive). The colors of binary/ternary mixtures in the absence and presence of MP/DA were predicted using fitted equations and additive color theory. Finally, the Euclidean distance method in the normalized CIE XYZ color space calculated the distance between predicted colors, with the maximum distance defining the real-optimal concentration of fluorophores. This strategy offers a more efficient and precise method for determining optimal probe concentrations compared to a trial-and-error approach. The model's effectiveness was confirmed through experimental validation, affirming its efficacy. [ABSTRACT FROM AUTHOR]

As a biothiol, cysteine (Cys) is essential to both physiological and pathological processes and has been associated with many diseases, including neurological disorders, rheumatoid arthritis, and renal dysfunction. Therefore, the development of a high‐performance probe for detecting Cys levels can help prevent and diagnose disease. In this study, a ratiometric fluorescent probe based on a novel fluorophore was developed for detecting Cys, and it showed high specificity and a rapid response time toward Cys. This probe demonstrates excellent biocompatibility and has been utilized effectively for the imaging of Cys in living cells. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescent probe for hypoxanthine (Hx) detection was established based on the mimic enzyme and fluorescence characteristics of cobalt-doped graphite-phase carbon nitride (Co doped g-C3N4). In addition to emitting strong fluorescence, the peroxidase activity of Co doped g-C3N4 can catalyze the reaction of O-phenylenediamine and H2O2 to produce diallyl phthalate which can emit yellow fluorescence at 570 nm. Through the decomposition of Hx by xanthine oxidase, Hx can be indirectly detected by the generating hydrogen peroxide based on the measurement of fluorescent ratio I (F570/F370). The linear range was 1.7–272.2 mg/kg (R2 = 0.997), and the detection limit was 1.52 mg/kg (3σ/K, n = 9). The established method was applied to Hx detection in bass, grass carp, and shrimp, and the data were verifi ed by HPLC. The result shows that the established probe is sensitive, accurate, and reliable, and can be used for Hx detection in aquatic products.

Sensors for which the output signal is an intensity change for a single-emission peak are easily disturbed by many factors, such as the stability of the instrument, intensity of the excitation light, and biological background. However, for ratiometric fluorescence sensors, the output signal is a change in the intensity ratio of two or more emission peaks. The fluorescence intensity of these emission peaks is similarly affected by external factors; thus, these sensors have the ability to self-correct, which can greatly improve the accuracy and reliability of the detection results. To accurately image glutathione (GSH) in cells, gold nanoclusters (AuNCs) with intrinsic double emission at wavelengths of 606 nm and 794 nm were synthesized from chloroauric acid. With the emission peak at 606 nm as the recognition signal and the emission peak at 794 nm as the reference signal, a near-infrared dual-emission ratio fluorescence sensing platform was constructed to accurately detect changes in the GSH concentration in cells. In vitro and in vivo analyses showed that the ratiometric fluorescent probe specifically detects GSH and enables ultrasensitive imaging, providing a new platform for the accurate detection of active small molecules. [ABSTRACT FROM AUTHOR]

The desirable properties of the sophisticated fluorescent pH probe are ratiometric detection properties and a wide detection range. In this study, three types of fluorophores with different fluorescence properties were assembled on a DNA origami nanostructure. DNA nanostructure has the advantage of being a scaffold that can assemble different types of fluorophores with control over their number and position. The defined number of three different fluorophores, i.e., pH-sensitive fluorescein (CF) and Oregon Green (OG), and pH-insensitive tetramethylrhodamine (CR), assembled on the DNA scaffold provided a ratiometric fluorescent pH probe with a wide pH detection range that could cover the variation of intracellular pH.

By serving dipyridylic acid (DPA) and 2,5-dihydroxyterephthalic acid (DHTA) as the biligands, a novel lanthanide (Eu3+) metal–organic framework (MOF) namely Eu-DHTA/DPA was prepared for specific Hg2+ fluorescence determination. The dual-ligand approach can endows the resulting luminescent MOF with dual emission of ratiometric fluorescence and uniform size. Eu3+ produces intense red fluorescence when activated by the ligand DPA, while the other ligand DHTA produces yellow fluorescence. Under 273 nm excitation, the presence of Hg2+ in the monitoring environment causes an increase in the intensity of the DHTA fluorescence peak at 559 nm and a decrease in the intensity of the Eu3+ fluorescence peak at 616 nm. Hg2+ effectively quenches the fluorescence emission of the central metal Eu3+ in Eu-DHTA/DPA at 616 nm through a dynamic quenching effect. This recognition process occurs due to the coordination of Hg2+ with ligands such as benzene rings, carboxyl groups, and pyridine N in three-dimensional space. Hg2+ was detected by measuring the ratio between two fluorescence peaks (I559 nm/I616 nm) within the range 2—20 μM, achieving a remarkably low detection limit of 40 nM. The established ratiometric fluorescence method has been successfully applied to the determination of Hg2+ in industrial wastewater of complex composition. The method plays a crucial role in the rapid and sensitive monitoring of Hg2+ in real environmental samples. The recoveries ranged from 92.82% to 112.67% (n = 3) with relative standard deviations (RSD) below 4.8%. This study offers a convenient and effective method for constructing probes for Hg2+ monitoring, with practical applications in environmental monitoring. [ABSTRACT FROM AUTHOR]

The desirable properties of the sophisticated fluorescent pH probe are ratiometric detection properties and a wide detection range. In this study, three types of fluorophores with different fluorescence properties were assembled on a DNA origami nanostructure. DNA nanostructure has the advantage of being a scaffold that can assemble different types of fluorophores with control over their number and position. The defined number of three different fluorophores, i.e., pH-sensitive fluorescein (CF) and Oregon Green (OG), and pH-insensitive tetramethylrhodamine (CR), assembled on the DNA scaffold provided a ratiometric fluorescent pH probe with a wide pH detection range that could cover the variation of intracellular pH. [ABSTRACT FROM AUTHOR]

The global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus has necessitated rapid, easy-to-use, and accurate diagnostic methods to monitor the virus infection. Herein, a ratiometric fluorescence enzyme-linked immunosorbent assay (ELISA) was developed using Si-fluorescein isothiocyanate nanoparticles (FITC NPs) for detecting SARS-CoV-2 nucleocapsid (N) protein. Si-FITC NPs were prepared by a one-pot hydrothermal method using 3-aminopropyl triethoxysilane (APTES)-FITC as the Si source. This method did not need post-modification and avoided the reduction in quantum yield and stability. The p-nitrophenyl (pNP) produced by the alkaline phosphatase (ALP)-mediated hydrolysis of p-nitrophenyl phosphate (pNPP) could quench Si fluorescence in Si-FITC NPs via the inner filter effect. In ELISA, an immunocomplex was formed by the recognition of capture antibody/N protein/reporter antibody. ALP-linked secondary antibody bound to the reporter antibody and induced pNPP hydrolysis to specifically quench Si fluorescence in Si-FITC NPs. The change in fluorescence intensity ratio could be used for detecting N protein, with a wide linearity range (0.01–10.0 and 50–300 ng/mL) and low detection limit (0.002 ng/mL). The concentration of spiked SARS-CoV-2 N protein could be determined accurately in human serum. Moreover, this proposed method can accurately distinguish coronavirus disease 2019 (COVID-19) and non-COVID-19 patient samples. Therefore, this simple, sensitive, and accurate method can be applied for the early diagnosis of SARS-CoV-2 virus infection. [ABSTRACT FROM AUTHOR]

Peroxynitrite (ONOO−) is a transient and reactive oxidant with significant roles in numerous biological processes. Research has established a correlation between excessive mitochondrial ONOO− production and various diseases. As such we developed a mitochondria-targeting, fluorescence-based ratiometric probe using a boronate group for ONOO− recognition and coumarin as the fluorophore. The probe exhibited a 615 nm far-red emission, and a new fluorescence emission at 475 nm developed upon adding ONOO−.The probe possessed high sensitivity and selectivity for ONOO− detection with distinct ratiometric fluorescent output and a low detection limit of 11 nM. Significantly, Probe 1 could monitor ONOO− level fluctuations in biological systems due to its superior spectral properties and low toxicity. Notably, probe 1 has been effectively used for imaging in live HepG2 cells, zebrafish, Arabidopsis thaliana , and liver injury mouse tissues. [Display omitted] • A COUPY-based fluorescent probe with deep red emission was developed. • The probe can detect ONOO− via a ratiometric output. • The probe can be used for imaging changes of ONOO− in vivo. • The probe was used to monitor ONOO− change in plant cells under Cd2+ stress. [ABSTRACT FROM AUTHOR]

Phosgene is a suffocating toxic gas that seriously threatens human health and public security. With this research, we developed a simple ratiometric fluorescent probe (1) bearing indole and benzimidazole moieties as the sensing sites and employed it for the aggregation-induced emission-based (AIE-based) detection of phosgene. It was the first time that the probe could detect phosgene in an almost pure aqueous solution (f w = 99.5 %). Probe 1 had AIE-activity, and the maximum emission peak was 392 nm with increasing water fraction (0–99.5 %). When reacting with phosgene, the emission peak at 392 nm gradually decreased, while a new peak appeared at 449 nm and continued to increase with increasing water fraction (0–99.5 %). Probe 1 exhibited a rapid response toward aqueous phosgene with high selectivity and sensitivity (limit of detection being 23.8 nM). Additionally, we fabricated 1 -loaded test strips for gas phosgene detection, enabling dual-channel detection under 245 nm and 365 nm hand-held UV lamps. Finally, this probe was used to monitor phosgene in bionic samples. [Display omitted] • A ratiometric phosgene fluorescence probe 1 based on AIE properties was obtained. • Probe 1 is the first fluorescence probe to detect phosgene in a 99.5 % aqueous medium. • Probe 1 can rapidly, sensitively, and selectively detect phosgene in the solution phase. • 1 -loaded test strips were applied to dual-channel monitor gas phosgene. • Probe 1 can image the trace amount of phosgene in biological sample. [ABSTRACT FROM AUTHOR]

The mechanism of SO 2 detection by the HBT-EMBI probe was elucidated through the TDDFT level, and the ratiometric emission peaks were attributed from a new perspective. [Display omitted] • The keto configuration is more stable than the enol for HBT-EMBI-HSO 3 -. • The introduction of HSO 3 - does not inhibit the ICT process of HBT-EMBI. • The ESIPT process of HBT-EMBI-HSO 3 - is suppressed, with the barrier of 10.9 kcal/mol. Sulfur dioxide (SO 2), a toxic air pollutant, can have harmful effects on human health when inhaled or when it forms bisulfite in the body. In the present work, a ratiometric fluorescent probe, 2-(2′-hydroxyphenyl)benzothiazole-3-ethyl-1,1,2-trimethyl-1 H -benzo[e]indolium (HBT-EMBI), was selected to study the mechanism of SO 2 derivatives detection. This study provides insights into the attributions of ratiometric fluorescence through hydrogen bond dynamics, electronic excitation properties, radiation rates, and excited state intramolecular proton transfer (ESIPT) processes using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) level. The results confirm that the large Stokes shifts and broad emission spectra of the HBT-EMBI probe are associated with its intramolecular charge transfer (ICT) characteristics and hydrogen bonding-driven ESIPT processes, respectively. After the addition reaction between the probe and HSO 3 −/SO 3 2−, the conformational populations of HBT-EMBI-HSO 3 − transfer abnormally from enol configurations to more stable keto configurations, which leads to a distinguished change in the visible color and the ratiometric fluorescence signal, and is not due to the blockage of the ICT process of HBT-EMBI-HSO 3 −, as previously reported. This work provides a new perspective on the mechanism of detection of SO 2 derivatives by ESIPT fluorescent probes. [ABSTRACT FROM AUTHOR]

A creatively designed and constructed a multifunctional ratiometric fluorescence probe is reported by assembling glutathione (GSH)-protected gold nanoclusters (AuNCs) with fluorescein-doped mesoporous silica nanoparticle (FS) for the detection of Cu2+ and Ag+ ions, which could eliminate most interferences by self-calibration. Under the excitation at 450 nm, the fluorescence connected with AuNCs can rapidly respond by quenching or enhancement, respectively, for Cu2+ and Ag+ ions, while the fluorescein isothiocyante (FITC) fluorescence served as reference with negligible change. The fluorescence intensity ratio showed good linear relationships with Cu2+ and Ag+ concentrations in the range 0.5–10 μM and 0.1–8 μM, respectively. The detection limits were as low as 140 nM and 60 nM for Cu2+ and Ag+ ions, respectively. The color change induced by fluorescent intensity ratio variation could also be employed for visual discrimination. The AuNC-embedded FS (FS-Au) nanoprobe was successfully used for Cu2+ and Ag+ ion determination in drinking water and intracellular Cu2+ imaging, which exhibits promising prospects in cost-effective and rapid determination of both Cu2+ and Ag+ with good sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

Coronavirus disease 2019 (COVID-19) highlights the importance of rapid and reliable diagnostic assays for the management of virus transmission. Here, we developed a one-pot hydrothermal method to prepare Si-FITC nanoparticles (NPs) for the fluorescent immunoassay of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein (N protein). The synthesis of Si-FITC NPs did not need post-modification, which addressed the issue of quantum yield reduction during the coupling reaction. Si-FITC NPs showed two distinct peaks, Si fluorescence at λem = 385 nm and FITC fluorescence at λem = 490 nm. In the presence of KMnO4, Si fluorescence was decreased and FITC fluorescence was enhanced. Briefly, in the presence of N protein, catalase (CAT)-linked secondary antibody/reporter antibody/N protein/capture antibody immunocomplexes were formed on microplates. Subsequently, hydrogen peroxide (H2O2) and Si-FITC NPs/KMnO4 were injected into the microplate together. The decomposition of H2O2 by CAT resulted in remaining of KMnO4, which changed the fluorescence intensity ratio of Si-FITC NPs. The fluorescence intensity ratio correlated significantly with the N protein concentration ranging from 0.02 to 50.00 ng/mL, and the detection limit was 0.003 ng/mL, which was more sensitive than the commercial ELISA kit with a detection limit of 0.057 ng/mL. The N protein concentration can be accurately determined in human serum. Furthermore, the COVID-19 and non-COVID-19 patients were distinguishable by this method. Therefore, the ratiometric fluorescent immunoassay can be used for SARS-CoV-2 infection diagnosis with a high sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

As an essential component of reactive oxygen species (ROS), peroxynitrite (ONOO - ) plays an indispensable role in redox homeostasis and signal transduction, with anomalous levels implicated in various clinical conditions. Therefore, accurate and rapid detection of intracellular ONOO - levels is crucial for revealing its role in physiological and pathological processes. In this study, we developed a ratiometric fluorescent probe to detect ONOO - levels in biological systems. The probe demonstrated a fast reaction rate (within 15 min), outstanding selectivity, high sensitivity (limit of detection=13.32 nM), and stability in the presence of ONOO - . The proposed probe was successfully used for visualizing endogenous ONOO - in living cells and tracking changes in intracellular ONOO - levels during drug-induced hepatotoxicity using ratiometric fluorescence., (© 2025 Wiley-VCH GmbH.)

Herein, a facile, environmental-friendly, and sustainable strategy for efficient separation, conversion, and utilization of lignocellulose components was developed. Lignocellulose components were separated by green deep eutectic solvent (DES). The extracted lignin had potential for downstream production of aromatic chemicals and was used to synthesize lignin-doped carbon dots (CDs) in a ratiometric fluorescent probe for detecting biogenic amines (BAs) that were generated from food spoilage. The preparation of CDs provided an efficient strategy to convert biomass waste into carbon-based nanomaterials. This probe exhibited a sensitive, rapid, and linear response to BAs with a low detection limit of 0.045 μM. The retained cellulose with the crystal I structure was used to prepare cellulose nanofibers (CNFs) via oxidation and mechanical treatment. Furthermore, the CNFs were used as a matrix to fabricate CDs/CNFs films for real-time and visual food freshness monitoring. From biomass waste to rational applications, this study not only expanded the comprehensive utilization of lignocellulose in a green and environment-friendly manner but also demonstrated the prospects of CDs-based composite films in on-site monitoring of food quality and safety. [ABSTRACT FROM AUTHOR]

The lysosome is the typical acidic organelle involved in many biological processes, the fluctuation of its pH influences its normal digestive function and even the fate of the cells. To conveniently detect and visualize lysosomal pH changes during heatstroke, we designed and synthesized a lysosomal‐targeted ratiometric pH‐sensitive fluorescent probe TCF‐LysopH. TCF‐LysopH showed an ideal pKa value (pKa=6.12) in the lysosomal pH range during heatstroke (5.00–7.00), rapid response for the changes of pH in real‐time, reversible pH switching ability, good selectivity, low cytotoxicity, and excellent lysosome‐targeting ability. The large Stokes shift of 110 nm allows us to apply the probe for fluorescence imaging in MCF‐7 cells. The probe has much better photostability (only less than 20 % decrease in intensity for 15 min irradiation) than LysoTracker Green. The fluorescence intensity became higher with the increase of pH, which is consistent with the tendency of the lysosomal pH change during heatstroke. Importantly, TCF‐LysopH was applied to measure the change of lysosomal pH during heatstroke in live cells, the results prove once again that the pH of the lysosome is increased during heatstroke. Thus, TCF‐LysopH was successfully developed as a practical and useful tool to provide a better understanding of the complicated mechanisms between lysosome pH change and heatstroke. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) as small molecular signal messenger plays key functions in numerous biological processes. The imaging detection of intracellular hydrogen sulfide is of great significance. In this work, a ratiometric fluorescent probe BH based on an asymmetric BODIPY dye for detection of H2S was designed and synthesized. After the interaction with hydrogen sulfide, probe display colorimetric and ratiometric fluorescence response, with its maximum emission fluorescence wavelength red-shifted from 542 nm to 594 nm, which is attributed to the sequential nucleophilic reaction of H2S leading to enhanced molecular conjugation after ring formation of the BODIPY skeleton. A special response mechanism has been fully investigated by NMR titration and MS, so that the probe has excellent detection selectivity. Furthermore, probe BH has low cytotoxicity and fluorescence imaging experiments indicate that it can be used to monitor hydrogen sulfide in living cells. [ABSTRACT FROM AUTHOR]

The rapid, sensitive, and selective detection of ascorbic acid (AA) is of significance in medical assays and diagnostics. In this work, a new aminoperylenediimide (APDI) derived ratiometric fluorescent probe based on the specific redox reaction of cobalt oxyhydroxide (CoOOH) and AA was constructed. APDI exhibited dual fluorescence emission peaks at 549 and 596 nm with an excitation wavelength of 494 nm. In the presence of CoOOH, the dual fluorescence could be quenched. The dominant fluorescence quenching mechanism was caused by the inner filter effect. Using the red emission as a reference, the fluorescence intensity ratio (F549/F596) was linearly correlated with the concentration of AA over a range of 0.05 to 1 μM. The limit of detection for AA was found to be 17 nM. Importantly, the probe was successfully used to detect AA in living cells. Therefore, this high sensitivity and selectivity strategy could directly survey the AA levels in real samples. [ABSTRACT FROM AUTHOR]

A dopamine-functionalized carbon nanodot (C-dots) ratiometric fluorescence probe for hypochlorite (ClO−) detection is reported. Fluorescent C-dots with maximal emission at 420 nm are synthesized via the hydrothermal synthesis of 3-hydroxyphenylboric acid at 160 °C for 8 h. After modified with dopamine for 5 min, the obtained dopamine-functionalized C-dots exhibit two maximal fluorescence emissions at 420 nm and 460 nm. Fluorescent intensity at 460 nm gets quenched with the addition of ClO− and fluorescent intensity at 420 nm is almost unaffected. Therefore dopamine-functionalized C-dots can be used as ratiometric fluorescence probe for highly sensitive detection of ClO−. The ratio of fluorescent intensity at 460 nm and 420 nm (I460nm/I420nm) has a linear relationship with the concentration of ClO− from 2 μM to 60 μM and limit of detection (LOD) of 0.6 μM. It shows high selectivity for the detection of ClO− toward other anions (SO42−, Cl−, NO3−, S2−, CO32−), metal ions (Mg2+, Ba2+, Ag+, Fe3+, Ca2+, Na+, Cr6+, Cr3+, Hg+), or other substances such as H2O2, glutamate, cysteine, and citric acid. When it is utilized in ClO− detection in tap water, the average recoveries are from 95.7% to 103.2% with the relative standard deviations (RSDs) lower than 5%. [ABSTRACT FROM AUTHOR]

A novel ratiometric fluorescent probe was constructed for sensitive assay of hydrogen peroxide (H2O2) and glucose, which utilized the synergistically enhanced effects of Ce3+ and Fe2+ on copper nanoclusters (CuNCs) and coumarin. In the CuNCs-Ce3+/Fe2+-coumarin system, Ce3+ triggered the aggregation-induced emission phenomenon of CuNCs, and Fe2+ catalyzed the Fenton reaction to efficiently yield hydroxyl radical (•OH). In the presence of H2O2, the 625-nm red fluorescence of CuNCs was sharply quenched owing to the oxidation of CuNCs to Cu(II) by •OH, but the 460-nm blue fluorescence of 7-hydroxycoumarin from the oxidation of coumarin by •OH dramatically increased. Based on the reversible changes in two fluorescence signals, a satisfactorily ratiometric probe was constructed for H2O2 assay with a detection limit (LOD) of 0.6 μM accompanied by a visual color variation from red to blue. For glucose assay, this ratiometric probe gave a linear range of 3.2–160 μM and LOD of 0.96 μM owing to the oxidization of glucose to yield H2O2 in the presence of glucose oxidase and O2. Overall, the newly developed ratiometric probe shows a great prospect in real applications for visual assay of H2O2 and glucose by our naked eyes.

[Display omitted] • An ICT-FRET-based fluorescent probe for the ratiometric detection of HNO has been reported. • The probe displays high sensitivity and high selectivity for HNO. • The probe had been applied for the ratiometric detection of HNO in A549 cells. Nitroxyl (HNO) is an important reactive nitrogen that is associated with various states in physiology and pathology and plays a unique function in living systems. So, it is important to exploit fluorescent probes with high sensitivity and selectivity for sensing HNO. In this paper, a novel ratiometric fluorescent probe for HNO was developed utilizing intramolecular charge transfer (ICT) and fluorescence resonance energy transfer (FRET) mechanisms. The probe selected coumarin as energy donor, naphthalimide as energy receptor and 2-(diphenylphosphino)benzoate as the sensing site for detecting HNO. When HNO was not present, the 2-(diphenylphosphino)benzoate unit of the probe restricted electron transfer and the ICT process could not occur, leading to the inhibition of FRET process as well. Thus, in the absence of HNO the probe displayed the intrinsic blue fluorescence of coumarin. When HNO was added, the HNO reacted with the 2-(diphenylphosphino)benzoate unit of the probe to yield a hydroxyl group which resulting in the opening of ICT process and the occurring of FRET process. Thus, after providing HNO the probe displayed yellow fluorescence. In addition, the probe showed good linearity in the ratio of fluorescence intensity at 545 nm and 472 nm (I 545 nm /I 472 nm) with a concentration of HNO (0.1–20 μM). The probe processed a detection limit of 0.014 μM and a response time of 4 min. The probe also specifically identified HNO over a wide pH scope (pH = 4.00–10.00), including physiological conditions. Cellular experiments had shown that this fluorescent probe was virtually non-cytotoxic and could be applied for ratiometric sensing of HNO in A549 cells. [ABSTRACT FROM AUTHOR]

The rapid detection of pyrosulfites in food chemistry is crucial to food safety and health. Here, a coumarin-type ratiometric fluorescent probe was developed based on the Michael addition reaction to detect sodium pyrosulfite (Na 2 S 2 O 5). The probe exhibited high selectivity and fast response (t 1/2 = 6 s) to Na 2 S 2 O 5 and a low detection limit (26 nM). Because of its excellent ratiometric response performance, the probe was successfully applied to measure the amount of Na 2 S 2 O 5 in preserved fruits. Colour information analysis and formula calculations were performed to quickly determine the sodium pyrosulfite amount in an actual sample by using a smartphone. Therefore, the intelligent strategy of combining the sensing process and smartphone provides a convenient and efficient method for the fast monitoring of sodium metabisulfite in actual food. [Display omitted] • A coumarin-type ratiometric fluorescent probe was synthesized to detect Na 2 S 2 O 5. • The probe identified Na 2 S 2 O 5 with fast response time (t 1/2 = 6 s) and low detection limit (26 nM). • Using RGB analysis and formula application, the Na 2 S 2 O 5 content can be calculated. • Smartphone-based on-site detection of Na 2 S 2 O 5 in actual samples was achieved. [ABSTRACT FROM AUTHOR]

The extensive use of fluoride in agriculture, industry, medicine, and daily necessities has raised growing concerns about fluoride residue. To date, real-time visual detection and efficient removal of fluoride ions from water remain greatly desirable. Herein, nano-CAU-10-NH 2 @RhB is introduced as a ratiometric fluorescent probe and efficient scavenger for the intelligent detection and removal of fluoride ions. CAU-10-NH 2 @RhB is readily obtained through one-pot synthesis and exhibits high sensitivity and selectivity for real-time fluoride ion detection, with a naked-eye distinguishable color change from pink to blue. A portable device for point-of-care testing was developed based on color hue analysis readout using a smartphone. A quantitative response was achieved across a wide concentration range, with a detection limit of 54.2 nM. Adsorption experiments suggest that nano-CAU-10-NH 2 @RhB serves as an efficient fluoride ion scavenger, with a fluoride adsorption capacity of 49.3 mg/g. Moreover, the mechanistic study revealed that hydrogen bonds formed between fluoride ions and amino groups of CAU-10-NH 2 @RhB are crucial for the detection and adsorption of fluoride ions. This analysis platform was also used for point-of-care quantitative visual detection of fluoride ions in food, water, and toothpaste. [Display omitted] • Ratiometric fluorescence detection and high effective adsorption of fluoride ions. • Real-time and visual detection of fluoride ions with remarkable color change. • Portable devices and smartphone-based automated intelligent analysis. • Quantitative and semi-quantitative point-of-care testing. • User-friendly and cost-effective accessible for real-sample analysis. [ABSTRACT FROM AUTHOR]

Lipids play a crucial role in the growth and development of organisms. However, the lack of effective chemical tools for lipid imaging has hindered a comprehensive understanding of the dynamic changes in lipid content and types in organisms. Here, we introduce a brightness-constant, lipid droplet-targeting ratiometric fluorescent probe called PAA for visualizing dynamic lipid changes during zebrafish growth and development. PAA was an ultra-stable dimer composed of two carbonylpyrenes. Despite variations in polarity, its absorption spectra, quantum yield and fluorescence brightness remained consistent. However, only fluorescence emission wavelength underwent redshift with increasing polarity. These properties enabled stable lipid imaging throughout the entire live zebrafish and allowed for the identification of lipid polarity using ratiometric fluorescence. Furthermore, PAA revealed changes of lipid composition in developing zebrafish. From 3–5 days post fertilization (dpf), zebrafish with undeveloped digestive organs exhibited a gradual decrease in overall lipid content and a reduction in lipid polarity. Subsequently, as the digestive organs fully developed (6–8 dpf), zebrafish were fed with paramecium, resulting in a gradual increase in overall lipid content and lipid polarity. Moreover, starvation experiments indicated that overall lipid content and polar lipids increased in zebrafish fed with paramecium. The successful application of PAA in visualizing lipid dynamics in zebrafish provides new avenues for studying lipid physiology and pathophysiology in living systems. [Display omitted] • The emission of PAA red-shifts with increased polarity, but the intensity remains unchanged. • Selective fluorescence imaging of lipid droplets enables imaging of lipids in zebrafish. • Visualize dynamic lipid changes during zebrafish growth and development. • Identification of lipid polarity using ratiometric fluorescence. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four fluorescent probes are synthesized for highly sensitive detecting malononitrile. • Their optical properties and detection performances are compared comprehensively. • Nopinyl-based chemosensor exhibits excellent capability and is applied in bioimaging. Malononitrile is a very important chemical material and has wide application fields in production of medicines, pesticides, and extraction of gold. However, its nonnegligible hypertoxicity inspired researchers to develop more efficient analysis techniques to sensitively and selectively detect malononitrile. Nopinone derivatives initiated by our research group have been developed as a class of organic fluorescent chemosensors for identifying multiple analytes in recent years. Different heterocyclic compounds based on nopinone were designed and synthesized to be applied in the fields of environmental analysis, food detection and bioimaging. Nevertheless, the comparison research on the optical properties of fluorescent compounds containing the nopinyl matrix with other structural analogs including alkyl, cyclohexyl and phenyl groups was deficient. Herein, four 4-(1 H -imidazol-2-yl)benzaldehyde-based ratiometric fluorescent chemosensors based on o -dimethyl cyclohexyl, phenyl and nopinyl units for recognizing malononitrile were designed and developed, and their differences in the optical properties and detection performances were investigated by using spectral analysis combined with theoretical calculations. Moreover, the nopinone-based 4-(1 H -imidazol-2-yl)benzaldehyde fluorescent chemosensor NMZQ was successfully applied in the dual channel fluorescence bioimaging of malononitrile in living HeLa cells and zebrafish, which attributed to its outstanding spectral property and detection performance. [ABSTRACT FROM AUTHOR]