Coumarin-hemicyanine-based far-red to near-infrared fluorescent probes: A new generation of fluorescent probe design platform

Advancements in small molecule fluorescent probes for the detection of formaldehyde in environmental and food samples: A comprehensive review

Formaldehyde (FA), a hazardous substance with carcinogenicity and mutagenicity, necessitates sensitive and accurate detection methods for protecting public health and the environment. While numerous reviews have explored FA fluorescent probes, the current literature predominantly emphasizes biological systems, leaving a gap in addressing FA's roles in environmental monitoring and food safety. This review discusses recognition mechanisms for FA detection, including 2-aza-Cope rearrangement, methylenehydrazine reaction, formimine formation, and other mechanisms. Furthermore, this review underscores the practical applications of these probes in real-world contexts, namely their incorporation into test strips, hydrogels, and membranes for environmental monitoring and food safety. Moreover, this review highlights future directions for developing intelligent detection systems that combine fluorescent probes with data processing algorithms and artificial intelligence technologies. By synthesizing the current knowledge in this area, this review aims to stimulate future research and advancements in FA detection technology, ultimately contributing to improved environmental management and public health protection.

Dye-sensitized lanthanide-doped upconversion nanoprobes for homocysteine sensing in human serum and living cells via a spatial optimization strategy

Homocysteine (Hcy) is an established risk factor for cardiovascular and neurodegenerative diseases, making its real-time detection critical for maintaining physiological balance and monitoring disease progression. However, developing probes that specifically recognize Hcy with a high signal-to-background ratio remains a significant challenge. In this study, we present a novel upconversion nanoprobe for Hcy detection, which integrates NIR cyanine dyes (CyPd) with β-NaGdF4:Yb20%,Er2%@NaGdF4:Yb10%,Nd10% upconversion nanoparticles (UNs). CyPd, featuring α,β-unsaturated ketone and pyridine functional groups, serves as both an efficient energy donor and a recognition antenna for the UNs. Benefiting from a hydrogen bonding-assisted two-site strategy of CyPd, coupled with highly efficient energy transfer from CyPd to UNs, the nanoprobe demonstrates high selectivity and sensitivity for Hcy in aqueous solutions, achieving a low detection limit of 0.19 μM. Importantly, the nanoprobe exhibits excellent performance in human serum, with recovery rates ranging from 97.9% to 103.2% and a low relative standard deviation of less than 3.51%. Furthermore, it was successfully applied for both exogenous and endogenous Hcy bioimaging. This innovative nanoprobe offers a promising tool for the accurate and efficient detection of Hcy, with potential applications in disease diagnosis and monitoring.

A chitosan-based sensing membrane for on-site and sensitive dual-channel portable detection and efficient adsorption of Pb2+ in groundwater

The presence of lead ion (Pb2+) in groundwater poses a serious risk to human health, even at low levels. Therefore, it is essential to develop a new strategy for both selective detection and effective removal of Pb2+ in groundwater, which has been rarely reported. Here, we developed a multi-functional chitosan-based fluorescent sensing membrane (CM-L/CG) by using a casting method for the sensitive/selective detection and removal of Pb2+ in groundwater. The CM-L/CG membrane can be integrated into the portable laser-induced fluorescence spectrometer (LIFs) for on-site detection of Pb2+, with a low detection limit of 1.02 ppb. Moreover, the CM-L/CG membrane demonstrates an outstanding 99 % removal rate and an adsorption capacity of 247.6 mg g-1 for Pb2+ and the adsorption process is mainly controlled by chemisorption. Importantly, the CM-L/CG membrane enables the real-time and on-site detection of Pb2+ in groundwater samples via a smartphone-based RGB (Red Green Blue) color analysis-assisted portable platform and portable LIFs-based platform, achieving acceptable results. This dual-functional fluorescent sensing membrane represents a breakthrough in environmental monitoring technology, offering a comprehensive solution for sensitive detection and efficient removal of Pb2+ from groundwater.

Near-infrared fluorescent probes based on naphthyridine derivatives for mitochondrial nucleic acid imaging

Most current nucleic acid-responsive fluorescent probes are enhanced ones with short emission wavelengths. Therefore, the development of novel near-infrared, turn-on response nucleic acid fluorescent probes is of great significance. Herein, three cationic fluorescent dyes 1a-1c were synthesized by reacting naphthalidine salt with suitable aldehydes. These probes exhibited excellent photostability, maintaining over 95% of their absorption rate after 5 h of irradiation. Notably, probes 1a-1c exhibited an OFF-ON fluorescence response to DNA and RNA. The maximum emission wavelength could reach the near-infrared region (661-762 nm), with large Stokes shifts (153-222 nm) upon binding to DNA/RNA. The fluorescence intensity was enhanced 143 fold and 127 fold for 1b upon interaction with DNA and RNA, respectively. Co-staining and nucleic acid digestion assays showed that probes 1a-1c could target the mitochondria of fixed cells with low cytotoxicity. These findings may be useful for the early screening of genetic mutations related to mitochondrial diseases.

Fabrication of a Redox-Reversible Near-Infrared Fluorogenic Probe for Ferroptosis Process Monitoring and the Early Diagnosis of Diabetes

Ferroptosis is a type of cell death triggered by the iron-dependent accumulation of lipid peroxides in cells. Diabetes, a chronic metabolic disorder characterized by hyperglycemia, can lead to various health complications. The process of ferroptosis and the progression of diabetes are closely linked to redox homeostasis, which is regulated by the levels of reactive oxygen and sulfur species. Currently, there are no fluorescent probes available to monitor changes in redox homeostasis during ferroptosis and diabetes. Here, we report the first endeavor to create a reversible near-infrared fluorogenic (NIRF) probe for monitoring the process of ferroptosis reversal and precise diabetes diagnosis. In vitro data demonstrated that NIR-CSTe could cyclically and reversibly detect ONOO- and GSH up to four times with minimal loss in fluorescence intensity. With the help of NIR-CSTe, we observed that HT-1080 cells, induced to undergo ferroptosis by erastin after being washed with PBS for 24 h and then treated with ferrostatin-1, showed a recovery in intracellular GSH levels. In contrast, treatment with deferoxamine did not yield similar results. Lastly, NIR-CSTe was also utilized for the early diagnosis and efficacy assessment of diabetes in relation to ONOO-/GSH redox balance, with results illustrating that the combined administration of metformin and empagliflozin was more effective than using either drug alone. Thus, this smart probe holds significant potential as an essential tool for clinical diagnosis and treatment of diseases associated with redox homeostasis.

NIRFluor: A Deep Learning Platform for Rapid Screening of Small Molecule Near-Infrared Fluorophores with Desired Optical Properties

Small molecule near-infrared (NIR) fluorophores play a critical role in disease diagnosis and early detection of various markers in living organisms. To accelerate their development and design, a deep learning platform, NIRFluor, was established to rapidly screen small molecule NIR fluorophores with the desired optical properties. The core component of NIRFluor is a state-of-the-art deep learning model trained on 5179 experimental big data. First, novel hybrid fingerprints including Morgan fingerprints, physicochemical properties, and solvent properties were proposed. Then, a powerful deep learning model, multitask fingerprint-enhanced graph convolutional network (MT-FinGCN), was designed, which combines fingerprint information and molecule graph structure information to achieve accurate prediction of six properties (absorption wavelength, emission wavelength, Stokes shift, extinction coefficient, photoluminescence quantum yield, and lifetime) of different small molecule NIR fluorophores in different solvents. Furthermore, the "black-box" of the GCN model was opened through interpretability studies. Finally, the well-trained models were placed on the web platform NIRFluor for free use (https://nirfluor.aicbsc.com).

A novel BODIPY-based fluorescent probe for naked-eye detection of the highly alkaline pH

A novel alkaline pH-responsive probe based on an asymmetric aza-BODIPY was synthesized in a one-pot Schiff base formation reaction. This pH-sensitive probe comprises an asymmetric aza-BODIPY as the luminescent core, with a benzothiazole moiety connected via an imine bond serving as the recognition site. The probe exhibits a turn-off fluorescence response upon exposure to alkaline pH (9.6-12.4), while a bathochromic band in the absorption emerges due to its extended π-conjugation system, accompanied by a visible colorimetric change from yellow to orange to red. Furthermore, the probe responds linearly in the highly alkaline region, with a pKa of 11.65. The recognition mechanism of the probe towards alkaline pH relies on the deprotonation of the imine group on the aza-BODIPY core, leading to an enhanced degree of π-electron conjugation. The quenched fluorescence intensity is attributed to the increased non-radiative decay of the deprotonated form of the probe. The probe demonstrates high reliability for practical applications due to its photostability and reversibility. This study provides new insights into the design of probes for detecting high alkaline pH levels.

Developing a vanillin-derived imidazo-pyridin-containing fluorescent probe for imaging cysteine in living pulmonary cells under oxygen supply variation

In this work, derived from vanillin and imidazo-pyridin backbone, a fluorescent probe IPV-Cys was developed for imaging the cysteine (Cys) level in living pulmonary cells under oxygen supply variation. By mimicking the oxygen supply variation in both the solution test and cellular imaging, the optical performance and imaging effect of IPV-Cys was investigated. In the solution system, the oxygen supply variation caused no impact on the reporting signals. The fluorescence reporting signal intensity at 490 nm suggested the enhancement along with the increase of the Cys concentration. The advantages of IPV-Cys included relatively high sensitivity, high stability, and high selectivity. On the basis of the low cyto-toxicity, IPV-Cys achieved the monitoring the endogenous Cys level in in living pulmonary cells and the impact of the oxygen supply variation by reporting fluorescence signals. The information here was meaningful for both the pre-clinical diagnosis and surgical techniques.

Nitrile-aminothiol bioorthogonal near-infrared fluorogenic probes for ultrasensitive in vivo imaging

Bioorthogonal chemistry-mediated self-assembly holds great promise for dynamic molecular imaging in living organisms. However, existing approaches are limited to nanoaggregates with 'always-on' signals, suffering from high signal-to-background ratio (SBR) and compromised detection sensitivity. Herein we report a nitrile-aminothiol (NAT) bioorthogonal fluorogenic probe (CyNAP-SS-FK) for ultrasensitive diagnosis of orthotopic hepatocellular carcinoma. This probe comprises a nitrile-substituted hemicyanine scaffold with a cysteine tail dually locked with biomarker-responsive moieties. Upon dual cleavage by tumor-specific cathepsin B and biothiols, the 1,2-aminothiol residue is exposed and spontaneously reacts with nitrile group for in situ intramolecular macrocyclization, enabling near-infrared fluorescence (NIRF) turn-on as well as self-assembly. In living male mice, such 'cleavage-click-assembly' regimen allows for real-time and ultrasensitive detection of small cancerous lesions (~2 mm in diameter) with improved SBR (~5) and extended detection window (~36 h), outperforming conventional clinical assays. This study not only presents NAT click reaction-based fluorogenic probes but also highlights a generic dual-locked design of these probes.

D-π-A type fluorescent dyes: Effect of π-bridge units on optical and G4 DNA binding properties

Fluorescent solvatochromic dyes that are sensitive to the nature of local microenvironmental, have been explored as probes in applications ranging from the imaging biomolecules to understanding of basic biomolecule functions. To expand the scope of fluorescent solvatochromic dyes for G-quadruplex (G4) DNA structures, and to illustrate the relationship between structure and properties, three newly designed D-π-A type fluorescent dyes were synthesized by introducing diarylimidazole to carbazole skeleton linked to benzene, furan or thiophene π-conjugated bridge and connected with pyridinium acceptor, respectively. Their structural characteristics, optical properties, and G4 DNA binding properties were discussed in detail. In general, the incorporation of furan and thiophene as π-conjugated bridges leads the better conjugation and molecular coplanarity with more efficient intramolecular charge transfer (ICT) effect compared with benzene bridge. The fluorescence intensities induced upon interaction were found that TP-6 with thiophene π-conjugated bridge had the strongest response toward G4 DNAs. In addition, the application of this dye as a fluorescent agent for living cell imaging was also demonstrated.

Visual monitoring of hydrazine in food and environmental samples by wearable probe

Hydrazine is a poisonous compound that has been widely applied in the agricultural and chemical industry, leading to serious environmental pollution. Thus, the detection of hydrazine remained extremely important for ensuring food safety and environmental protection. Considering the importance of hydrazine detection for human health, a novel colorimetric/fluorescent probe (TPB) for the detection of hydrazine in various samples has been developed. In the presence of hydrazine, TPB emits a blue emission band at 452 nm with high sensitivity (limit of detection equal to 40 nM), ultrafast detection (less than 10 s), broad working pH range (6 -10), and strong anti-interference capabilities. These excellent performances have been exploited to fabricate hydrogel-based sensing labels (test kits, cotton swabs, glass rods, and gloves), which allowed the detection of hydrazine traces in soil, earthworms, plant samples, and living cells. This work presents a novel sensing approach for future research, aiming to develop a novel fluorescent probe exploiting the ICT process for the detection of hydrazine.

A unique near-infrared fluorescent probe based on dual-DNP binding sites for rapid monitoring of hydrogen sulfide in food samples and living cells

A new NIR fluorescent probe (DCIQ-2DNP), which combined the thiolysis of dinitrophenyl (DNP) ether and DNP-marked electron-deficient quaternary carbon, was reported for the first time for detection of H2S. The DCIQ-2DNP probe showed an NIR emission signal (740 nm), a large Stokes shift (128 nm), and rapid monitoring of hydrogen sulfide (within 60 s) in food samples and living cells.

Large stokes shift and near-infrared fluorescent probe for bioimaging and evaluating the HClO in an rheumatoid arthritis mouse model

It is crucial to identify aberrant HClO levels in living things since they pose a major health risk and are a frequent reactive oxygen species (ROS) in living organisms. In order to detect HClO in various biological systems, we created and synthesized a near-infrared fluorescent probe with an oxime group (-C = N-OH) as a recognition unit. The probe DCMP1 has the advantages of fast response (10 min), near-infrared emission (660 nm), large Stokes shift (170 nm) and high selectivity. This probe DCMP1 not only detects endogenous HClO in living cells, but also enables further fluorescence detection of HClO in living zebrafish. More importantly, it can also be used for fluorescence imaging of HClO in an rheumatoid arthritis mouse model. This fluorescent probe DCMP1 is anticipated to be an effective tool for researching HClO.

Near-infrared and multifunctional fluorescent probe enabled by cyanopyridine cyanine dye for bisulfite recognition and biological imaging

SO2 derivatives, sulfite/bisulfite, are widely employed in both the food processing and drug synthesis industries. Despite their widespread application, excessive levels of sulfite/bisulfite can negatively impact human health. Most probes for detecting sulfite/bisulfite are restricted by their fluorescence within the visible spectrum range and poor solubility in aqueous solution, which limit their use in food testing and biological imaging. Herein, a near-infrared probe comprising of the cyanopyridine cyanine skeleton, 4-((Z)-2-((E)-2-chloro-3-(2-cyano-2-(1-methylpyridine-4(1H)-ylidene)ethylidene)cyclohex-1-en-1-yl)-1-cyanovinyl)-1-methylpyridin-1-ium (abbreviated as CCP), was developed. This probe enables precise quantification of bisulfite (HSO3-) in almost pure buffered solutions, showing a near-infrared fluorescence emission at 784 nm with an impressively low detection limit of 0.32 μM. The probe stands out for its exceptional selectivity, minimal susceptibility to interference, and strong adaptability. The probe CCP utilizes the CC bond to trigger a near-infrared fluorescence quenching reaction with HSO3- via nucleophilic addition, which effectively disrupts the large delocalization within the molecule for accurate HSO3- identification. Moreover, the probe has been successfully applied in detecting HSO3- in various food products and living cells, simplifying the measurement of HSO3- content in water samples. This advancement not only enhances the analytical capabilities but also contributes to ensuring food safety and environmental protection. ENVIRONMENTAL IMPLICATION: SO2 derivatives including sulfite/bisulfite, serving dual roles as preservatives and antioxidants, have widespread application across various sectors including food preservation, water sanitation, and the pharmaceutical industry. Despite their widespread application, excessive levels of sulfite/bisulfite can affect human health. Developing methods for precisely and sensitively detecting sulfite/bisulfite in food products and biological samples is important for ensuring food safety and environmental protection. Here, a sensitive near-infrared and multifunctional fluorescent probe in a 99.9 % buffered solution, along with water gel encapsulation, has been successfully applied for the detection of bisulfite in food, authentic water samples, and biological cells.

Development of Novel Fluorescent Probes for Specific Detection of Hypochlorous Acid

Hypochlorous acid (HClO) is widely used in everyday life for bleaching and disinfecting tap water, and also in human metabolism, where it plays an important role in destroying foreign bacterial invaders and pathogens as well as immune defense and cellular functioning maintenance. Abnormal levels of hypochlorous acid have the potential to cause joint inflammation, neuronal degeneration, and even life-threatening cancer. Specific identification and effective detection of hypochlorous acid are important for monitoring human health and the environment. In recent years, organic fluorescent probes have attracted much attention because of their simple synthesis, easy operation, high sensitivity, and high specificity, and a variety of hypochlorous acid fluorescent probes based on low-cost, easy-to-operate, and rapid identification have been developed. In this paper, we review the fluorescent probes that have been developed in the past five years for the specific recognition of hypochlorous acid based on different fluorophores, such as triphenylamine, coumarin, 1,8-naphthalize, etc., as well as recognition units, such as N-N dimethyl thiosemicarbazone, and describe how the probes and hypochlorous acid interact for identification in the same manner as other fluorescent probes. In addition, the reaction mechanism between the probe and hypochlorous acid, the fluorescence change of the probe, and the detection limit are described to illustrate the progress in the detection of hypochlorous acid in recent years and to provide ideas for the development of hypochlorous acid fluorescent probes in the future.

Dynamic insights into mitochondrial function: Monitoring viscosity and SO2 levels in living cells

Mitochondria, central organelles pivotal for eukaryotic cell function, extend their influence beyond ATP production, encompassing roles in apoptosis, calcium signaling, and biosynthesis. Recent studies spotlight two emerging determinants of mitochondrial functionality: intramitochondrial viscosity and sulfur dioxide (SO2) levels. While optimal mitochondrial viscosity governs molecular diffusion and vital processes like oxidative phosphorylation, aberrations are linked with neurodegenerative conditions, diabetes, and cancer. Similarly, SO2, a gaseous signaling molecule, modulates energy pathways and oxidative stress responses; however, imbalances lead to cytotoxic sulfite and bisulfite accumulation, triggering disorders such as cancer and cardiovascular anomalies. Our research focused on development of a dual-channel fluorescent probe, applying electron-withdrawing acceptors within a coumarin dye matrix, facilitating monitoring of mitochondrial viscosity and SO2 in live cells. This probe distinguishes fluorescence peaks at 650 nm and 558 nm, allowing ratiometric quantification of SO2 without interference from other sulfur species. Moreover, it enables near-infrared viscosity determination, particularly within mitochondria. The investigation employed theoretical calculations utilizing Density Functional Theory (DFT) methods to ascertain molecular geometries and calculate rotational energies. Notably, the indolium segment of the probe exhibited the lowest rotational energy, quantified at 7.38 kcals/mol. The probe featured heightened mitochondrial viscosity dynamics when contained within HeLa cells subjected to agents like nystatin, monensin, and bacterial lipopolysaccharide (LPS). Overall, our innovative methodology elucidates intricate mitochondrial factors, presenting transformative insights into cellular energetics, redox homeostasis, and therapeutic avenues for mitochondrial-related disorders.

Syntheses and Applications of Coumarin-Derived Fluorescent Probes for Real-Time Monitoring of NAD(P)H Dynamics in Living Cells across Diverse Chemical Environments

Fluorescent probes play a crucial role in elucidating cellular processes, with NAD(P)H sensing being pivotal in understanding cellular metabolism and redox biology. Here, the development and characterization of three fluorescent probes, A, B, and C, based on the coumarin platform for monitoring of NAD(P)H levels in living cells are described. Probes A and B incorporate a coumarin-cyanine hybrid structure with vinyl and thiophene connection bridges to 3-quinolinium acceptors, respectively, while probe C introduces a dicyano moiety for replacement of the lactone carbonyl group of probe A which increases the reaction rate of the probe with NAD(P)H. Initially, all probes exhibit subdued fluorescence due to intramolecular charge transfer (ICT) quenching. However, upon hydride transfer by NAD(P)H, fluorescence activation is triggered through enhanced ICT. Theoretical calculations confirm that the electronic absorption changes upon the addition of hydride to originate from the quinoline moiety instead of the coumarin section and end up in the middle section, illustrating how the addition of hydride affects the nature of this absorption. Control and dose-response experiments provide conclusive evidence of probe C's specificity and reliability in identifying intracellular NAD(P)H levels within HeLa cells. Furthermore, colocalization studies indicate probe C's selective targeting of mitochondria. Investigation into metabolic substrates reveals the influence of glucose, maltose, pyruvate, lactate, acesulfame potassium, and aspartame on NAD(P)H levels, shedding light on cellular responses to nutrient availability and artificial sweeteners. Additionally, we explore the consequence of oxaliplatin on cellular NAD(P)H levels, revealing complex interplays between DNA damage repair, metabolic reprogramming, and enzyme activities. In vivo studies utilizing starved fruit fly larvae underscore probe C's efficacy in monitoring NAD(P)H dynamics in response to external compounds. These findings highlight probe C's utility as a versatile tool for investigating NAD(P)H signaling pathways in biomedical research contexts, offering insights into cellular metabolism, stress responses, and disease mechanisms.

Role of Alkali Cations in DNA-Thioflavin T Interaction

This study investigates the role of alkali cations in modulating the interaction between deoxyribonucleic acid (DNA) and Thioflavin T (ThT) in dilute and condensed phases. The emission characteristics of ThT were analyzed in the presence of double-stranded DNA and G-quadruplex structures with a focus on the effects of four cations: sodium, potassium, calcium, and magnesium. The ThT emission in double-stranded DNA was influenced by direct DNA binding and steric hindrance within the hydration shell of DNA, which was modulated by the presence of alkali cations. Lasing spectroscopy experiments further highlighted ThT sensitivity to the spatial arrangement of water molecules in the DNA hydration shell. Lasing was exclusively observed in the presence of Mg2+ in the G-quadruplex structure, suggesting that the parallel propeller configuration of G4 provides an optimal environment for ThT light amplification. This study highlights the critical role of cations in DNA-dye interactions and reaffirms the significance of ThT in biophysical studies.

Visulization of peroxynitrite variation for accurate diagnosis and assessing treatment response of hepatic fibrosis using a Golgi-targetable ratiometric fluorescent probe

Hepatic fibrosis (HF) is caused by persistent inflammation, which is closely associated with hepatic oxidative stress. Peroxynitrite (ONOO-) is significantly elevated in HF, which would be regarded as a potential biomarker for the diagnosis of HF. Research has shown that ONOO- in the Golgi apparatus can be overproduced in HF, and it can induce hepatocyte injury by triggering Golgi oxidative stress. Meanwhile, the ONOO- inhibitors could effectively relieve HF by inhibiting Golgi ONOO-, but as yet, no Golgi-targetable fluorescent probe available for diagnosis and assessing treatment response of HF through sensing Golgi ONOO-. To this end, we reported a ratiometric fluorescent probe, Golgi-PER, for diagnosis and assessing treatment response of HF through monitoring the Golgi ONOO-. Golgi-PER displayed satisfactory sensitivity, low detection limit, and exceptional selectivity to ONOO-. Combined with excellent biocompatibility and good Golgi-targeting ability, Golgi-PER was further used for ratiometric monitoring the Golgi ONOO- fluctuations and screening of ONOO- inhibitors from polyphenols in living cells. Meanwhile, using Golgi-PER as a probe, the overexpression of Golgi ONOO- in HF and the treatment response of HF to the screened rosmarinic acid were precisely visualized for the first time. Furthermore, the screened RosA has a remarkable therapeutic effect on HF, which may be a new strategy for HF treatment. These results demonstrated the practicability of Golgi-PER for monitoring the occurrence, development, and personalized treatment response of HF.

A near-infrared fluorescent probe for rapid and on-site detection of sulfur dioxide derivative in biological, food and environmental systems

Emission of toxic gaseous sulfur dioxide (SO2) and its derivative bisulfite (HSO3-) from various industrial applications, like food processing, transportation, and the coking process, has raised substantial concerns regarding environmental quality and public health. The probes for specific and sensitive detection of SO2 derivatives plays an essential role in their regulation, and ultimately mitigating their environmental and health implications, but the one that can detect SO2 derivatives onsite by end users remains limited. Herein, we report a new near-infrared fluorescence probe (SL) for rapid and onsite detection of SO2 derivative, HSO3- in industrial wastewater, food samples and for sensing its interaction with biological organisms. The SL is developed through coupling of quinolinium and coumarin moiety through an electron deficit CC bond that can specifically react with HSO3- via a Michael addition. By recording the blue shift of absorption and emission spectra, SL can sensitively detect HSO3- (limit of detection, 38 nM) in aqueous solution within 40 s SL is biocompatible, can be used for evaluating toxicity of SO2 derivatives in living organisms. The preparation of SL-stained test paper allows the colorimetric/fluorometric analysis for quantification of HSO3- onsite in food, river and coking wastewater samples using a smartphone. The successful development of SL not only provides a new tool to investigate HSO3- in biological, food and environmental systems, but also potentially promotes the application of fluorescence technique for rapid and onsite analysis of real-world samples by end users.

Exploring Structural-Photophysical Property Relationships in Mitochondria-Targeted Deep-Red/NIR-Emitting Coumarins

Organic fluorophores operating in the optical window of biological tissues, namely in the deep-red and near-infrared (NIR) region of the electromagnetic spectrum, offer several advantages for fluorescence bioimaging applications owing to the appealing features of long-wavelength light, such as deep tissue penetration, lack of toxicity, low scattering, and reduced interference with cellular autofluorescence. Among these, COUPY dyes based on non-conventional coumarin scaffolds display suitable photophysical properties and efficient cellular uptake, with a tendency to accumulate primarily in mitochondria, which renders them suitable probes for bioimaging purposes. In this study, we have explored how the photophysical properties and subcellular localization of COUPY fluorophores can be modulated through the modification of the coumarin backbone. While the introduction of a strong electron-withdrawing group, such as the trifluoromethyl group, at position 4 resulted in an exceptional photostability and a remarkable redshift in the absorption and emission maxima when combined with a julolidine ring replacing the N,N-dialkylaminobenzene moiety, the incorporation of a cyano group at position 3 dramatically reduced the brightness of the resulting fluorophore. Interestingly, confocal microscopy studies in living HeLa cells revealed that the 1,1,7,7-tetramethyl julolidine-containing derivatives accumulated in the mitochondria with much higher specificity. Overall, our results provide valuable insights for the design and optimization of new COUPY dyes operating in the deep-red/NIR region.