Acidic pH-Activatable Visible to Near-Infrared Switchable Ratiometric Fluorescent Probe for Live-Cell Lysosome Targeted Imaging

Ratiometric fluorescence sensor based on deep learning for rapid and user-friendly detection of tetracycline antibiotics

The detection of tetracycline antibiotics (TCs) in food holds great significance in minimizing their absorption within the human body. Hence, this study aims to develop a rapid, convenient, real-time, and accurate detection method for detecting antibiotics in an authentic market setting. A colorimetric fluorescence sensor was devised for tetracycline detection utilizing PVA aerogels as the substrate. Its operating principle is based on the IFE effect and antenna effect. A detection device is designed to capture fluorescence images while deep learning was employed to aid in the detection process. The sensor exhibits high responsiveness with a mere 60-s requirement for detection and demonstrates substantial color changes(blue to red), achieving 99% accuracy within the range of 10-100 μM with the assistance of deep learning (Resnet18). Real sample simulation tests yielded recovery rates between 95% and 130%. Overall, the proposed strategy proved to be a simple, portable, reliable, and responsive solution for rapid real-time TCs detection in food samples.

Acidic Lysosome-Anchoring Croconium-Based Nanoplatform for Enhanced Triple-Mode Bioimaging and Fe3+-Triggered Tumor Synergistic Therapy

Metal-modulated croconium dyes with multimodal-imaging and synergistic therapy in the tumor microenvironment have exhibited great potential in tumor theranostics. However, their unideal structure optimization always weakened the efficacy of near-infrared fluorescence-photoacoustic (NIRF/PA) imaging and photothermal therapy (PTT). Here, we screened croconium dye containing two indole groups with better NIRF/PA imaging and PTT in their family, linked to two morpholine rings, and obtained CR-736, as a lysosome-targeting and Fe3+-modulated agent. The established CR-736-Fe3+ nanoplatform was accurately delivered to the breast tumor site, released CR-736 and Fe3+ in the lower acidic lysosome microenvironment, and activated pH-responsive NIRF/PA/magnetic resonance imaging and PTT. Furthermore, ferroptosis generated hydroxyl free radicals and lipid peroxide by consuming GSH and H2O2 by dint of the accumulation of Fe3+ in tumor cells, which resulted in the inhibition of the expression of heat shock proteins and the concomitant recovery of PTT. The synergistic therapy of PTT, ferroptosis, and chemodynamics was further optimized to the maximal extent in tumor lysosome acidic microenvironment and proved both in vitro and a mouse tumor model. This study opens a new avenue in designing excellent and unique croconium-based nanoplatforms, synergizing multiple tumor theranostic methods, and further optimizing the theranostic effects in tumor microenvironment.

Organic fluorophores-based molecular probes with dual-fluorescence ratiometric responses to in-vitro/in-vivo pH for biosensing, bioimaging and biotherapeutics applications

In recent years, organic fluorophores-based molecular probes with dual-fluorescence ratiometric responses to in-vitro/in-vivo pH (DFR-MPs-pH) have been attracting much interest in fundamental application research fields. More and more scientific publications have reported the exploration of various DFR-MPs-pH systems that have unique dual-fluorescence ratiometry as the signal output, in-built and signal self-calibration functions to improve precise detection of targets. DFR-MPs-pH systems possess high-performance applications in biosensing, bioimaging and biomedicine fields. This review has comprehensively summarized recent advances of DFR-MPs-pH for the first time. First of all, the compositions and types of DFR-MPs-pH are introduced by summarizing different organic fluorophores-based molecule systems. Then, construction strategies are analyzed based on specific components, structures, properties and functions of DFR-MPs-pH. Afterward, biosensing and bioimaging applications are discussed in detail, primarily referring to pH sensing and imaging detection at the levels of living cells and small animals. Finally, biomedicine applications are fully summarized, majorly involving bio-toxicity evaluation, bio-distribution, biomedical diagnosis and therapeutics. Meanwhile, the current status, challenges and perspectives are rationally commented after detailed discussions of representative and state-of-the-art studies. Overall, this present review is comprehensive, in-time and in-depth, and can facilitate the following further exploration of new and versatile DFR-MPs-pH systems toward rational design, facile preparation, superior properties, adjustable functions and highly efficient applications in promising fields.

Cerium Vanadate Nanozyme with pH-Dependent Dual Enzymatic Activity for Glioblastoma Targeted Therapy and Postradiotherapy Damage Protection

Nanocatalytic therapy is an emerging technology that uses synthetic nanoscale enzyme mimics for biomedical treatment. However, in the field of neuroscience, achieving neurological protection while simultaneously killing tumor cells is a technical challenge. Herein, we synthesized a biomimic and translational cerium vanadate (CeVO4) nanozyme for glioblastoma (GBM) therapy and the repair of brain damage after GBM ionizing radiation (IR). This system exhibited pH dependence: it showed potent Superoxide dismutase (SOD) enzyme activity in a neutral environment and Peroxidase (POD) enzyme activity in an acidic environment. In GBM cells, this system acted in lysosomes, causing cellular damage and reactive oxygen species (ROS) accumulation; in neuronal cells, this nanozyme could undergo lysosomal escape and nanozyme aggregation with mitochondria, reversing the mitochondrial damage caused by IR and restoring the expression level of the antiapoptotic BCL-2 protein. Mechanistically, we believe that this distribution difference is related to the specific uptake internalization mechanism and lysosomal repair pathway in neurons, and ultimately led to the dual effect of tumor killing and nerve repair in the in vivo model. In summary, this study provides insight into the repair of brain damage after GBM radiation therapy.

Design of an Acidic pH-Activated NIR Fluorescent Convertible Rhodamine-Hemicyanine Probe-Peptide Conjugate for Living Cancer Cell Active Targeted Selective Tracking of Lysosomes

We have synthesized an acidic pH-activatable dual targeting ratiometric fluorescent probe-peptide conjugate using the SPPS protocol on Rink amide AM resin. Living carcinoma cell specific active targeting, successive cell penetration, and selective staining of lysosomes are accomplished. Real-time monitoring of lysosomes, 3D, and multicolor cancer cell imaging are also attained. The de novo design consists of the integration of multifunctionality into a single molecular scaffold, e. g., RGDS peptide residue to target cancer cell surface overexpressed receptor αVβ3 integrin, live-cell penetrating organic unsymmetrical rhodamine-hemicyanine chromophore comprising a lysosome targeting morpholine group, and an acidic pH openable spiro-lactam ring for a visible-to-NIR switchable ratiometric response. Water-soluble fluorescent probe-peptide conjugate exhibits intramolecular spirolactamization at basic pH through Arg amide N. The visible spirolactam state predominantly exists at physiological and basic pH and can be switched to the highly conjugated NIR open amide state (λem=735 nm) through spiro-lactam ring opening triggered by acidic pH with a huge bathochromic shift (Δλabs=336 nm, ΔλFL=265 nm). Moreover, pH-sensitive ratiometric optical switching is achieved. This in situ acidic cancer cell lysosome activatable multifunctional fluorophore-peptide conjugate shows augmented molar absorptivity, enhanced quantum yield, and improved fluorescence lifetime at acidic lysosomal pH; negligible cytotoxicity; and dual targeted ratiometric imaging capability of living cancer cell selective lysosomes with a pKa value of 5.1.

Carbon dots as versatile nanomaterials in sensing and imaging: Efficiency and beyond

Carbon dots (CDs) have emerged as a versatile and promising carbon-based nanomaterial with exceptional optical properties, including tunable emission wavelengths, high quantum yield, and photostability. CDs are appropriate for various applications with many benefits, such as biocompatibility, low toxicity, and simplicity of surface modification. Thanks to their tunable optical properties and great sensitivity, CDs have been used in sensing as fluorescent probes for detecting pH, heavy metal ions, and other analytes. In addition, CDs have demonstrated potential as luminescence converters for white organic light-emitting diodes and light emitters in optoelectronic devices due to their superior optical qualities and exciton-independent emission. CDs have been used for drug administration and bioimaging in the biomedical field due to their biocompatibility, low cytotoxicity, and ease of functionalization. Additionally, due to their stability, efficient charge separation, and low recombination rate, CDs have shown interesting uses in energy systems, such as photocatalysis and energy conversion. This article highlights the growing possibilities and potential of CDs as adaptable nanomaterials in a variety of interdisciplinary areas related to sensing and imaging, at the same time addressing the major challenges involved in the current research and proposing scientific solutions to apply CDs in the development of a super smart society.

Carbon Dots: Synthesis, Characterizations, and Recent Advancements in Biomedical, Optoelectronics, Sensing, and Catalysis Applications

Carbon nanodots (CNDs), a fascinating carbon-based nanomaterial (typical size 2-10 nm) owing to their superior optical properties, high biocompatibility, and cell penetrability, have tremendous applications in different interdisciplinary fields. Here, in this Review, we first explore the superiority of CNDs over other nanomaterials in the biomedical, optoelectronics, analytical sensing, and photocatalysis domains. Beginning with synthesis, characterization, and purification techniques, we even address fundamental questions surrounding CNDs such as emission origin and excitation-dependent behavior. Then we explore recent advancements in their applications, focusing on biological/biomedical uses like specific organelle bioimaging, drug/gene delivery, biosensing, and photothermal therapy. In optoelectronics, we cover CND-based solar cells, perovskite solar cells, and their role in LEDs and WLEDs. Analytical sensing applications include the detection of metals, hazardous chemicals, and proteins. In catalysis, we examine roles in photocatalysis, CO2 reduction, water splitting, stereospecific synthesis, and pollutant degradation. With this Review, we intend to further spark interest in CNDs and CND-based composites by highlighting their many benefits across a wide range of applications.

Monophenyl luminescent material with dual-state emission and pH sensitivity for cell imaging

Dual-state emission (DSE) luminescent materials are a newly discovered category of luminescent materials that exhibit efficient light emission in multiple states, including dilute solutions, highly concentrated solutions, aggregated states and solid states. These materials effectively address the aggregation-caused quenching (ACQ) observed in traditional organic luminescent materials with large conjugated planes, as well as the limitations of aggregation-induced emission (AIE) materials, which typically do not emit light in dilute solutions. The design and development of DSE luminescent materials for organelle imaging applications has attracted considerable interest. In this context, this study presents the design and synthesis of a novel luminescent compound, DMSS-AM, characterised by intramolecular hydrogen bonding and a D-π-A structure. As a monophenyl luminescent material, DMSS-AM exhibits DSE properties with fluorescence quantum yields of 22.1% in solution and 14.0% in the solid state. In particular, it exhibits unique pH-responsive properties, facilitating the targeted detection of lysosomal pH changes. Confocal laser scanning microscopy imaging of cells demonstrated that DSE emitters at both low and high concentrations do not affect image quality for bio-imaging applications. This advance is expected to significantly broaden the applicability of DSE luminescent materials in future applications.

Design and Application of Fluorescent Probes to Detect Cellular Physical Microenvironments

The microenvironment is indispensable for functionality of various biomacromolecules, subcellular compartments, living cells, and organisms. In particular, physical properties within the biological microenvironment could exert profound effects on both the cellular physiology and pathology, with parameters including the polarity, viscosity, pH, and other relevant factors. There is a significant demand to directly visualize and quantitatively measure the fluctuation in the cellular microenvironment with spatiotemporal resolution. To satisfy this need, analytical methods based on fluorescence probes offer great opportunities due to the facile, sensitive, and dynamic detection that these molecules could enable in varying biological settings from in vitro samples to live animal models. Herein, we focus on various types of small molecule fluorescent probes for the detection and measurement of physical parameters of the microenvironment, including pH, polarity, viscosity, mechanical force, temperature, and electron potential. For each parameter, we primarily describe the chemical mechanisms underlying how physical properties are correlated with changes of various fluorescent signals. This review provides both an overview and a perspective for the development of small molecule fluorescent probes to visualize the dynamic changes in the cellular environment, to expand the knowledge for biological process, and to enrich diagnostic tools for human diseases.

Ratiometric fluorescent probes for pH mapping in cellular organelles

The intracellular pH (pHi) in organelles, including mitochondria, endoplasmic reticulum, lysosomes, and nuclei, differs from the cytoplasmic pH, and thus maintaining the pH of these organelles is crucial for cellular homeostasis. Alterations in the intracellular pH (ΔpHi) in organelles lead to the disruption of cell proliferation, ion transportation, cellular homeostasis, and even cell death. Hence, accurately mapping the pH of organelles is crucial. Accordingly, the development of fluorescence imaging probes for targeting specific organelles and monitoring their dynamics at the molecular level has become the forefront of research in the last three decades. Among them, ratiometric fluorescent probes minimize the interference from the excitation wavelength of light, auto-fluorescence from probe concentration, environmental fluctuations, and instrument sensitivity through self-correction compared to monochromatic fluorescent probes, which are known as turn-on/off fluorescent probes. Small-molecular ratiometric fluorescent probes for detecting ΔpHi are challenging yet demanding. To date, sixty-two ratiometric pH probes have been reported for monitoring internal pH alterations in cellular organelles. However, a critical review on organelle-specific ratiometric probes for pH mapping is still lacking. Thus, in the present review, we report the most recent advances in ratiometric pH probes and the previous data on the role of mapping the ΔpHi of cellular organelles. The development strategy, including ratiometric fluorescence with one reference signal (RFRS) and ratiometric fluorescence with two reversible signals (RFRvS), is systematically illustrated. Finally, we emphasize the major challenges in developing ratiometric probes that merit further research in the future.

Multifunctional Theranostic Probe Based on the Pim-1 Kinase Inhibitor with the Function of Tracking pH Fluctuations during Treatment

Currently, kinase inhibitors have been applied in the diagnosis or treatment of cancer with their unique advantages. It is of great significance to develop some comprehensive theranostic reagents based on kinase inhibitors to improve the performance of reagents for biomedical applications. Besides, tracking changes in the intracellular environment (e.g., pH) during cancer development and drug delivery is also critical for cancer research and treatment. Therefore, it is an urgent desire to design some novel multifunctional reagents based on kinase inhibitor strategies that can trace changes in the microenvironment of cancer cells. In this paper, a multifunctional theranostic reagent based on Pim-1 kinase inhibitor 5-bromobenzofuran-2-carboxylic acid is proposed. The theranostic probe binds to tumor-specific Pim-1 kinase, releases strong fluorescence, and produces cytotoxicity, thus achieving cell screening and killing effects. Furthermore, the probe can specifically target lysosomes and sensitively respond to pH. It can be used to track the pH changes in the intracellular environment under conditions of autophagy and external stimulation, as a visual tool to monitor pH fluctuations during cancer treatment. In conclusion, this simple but multifunctional theranostic reagent proposed in this work is expected to provide a promising method for cancer diagnosis and therapy.

Water-solubility croconic acid-bisindole dye with morpholine ring for tumor NIRF/PA imaging and photothermal therapy activated by lysosome pH-response

A novel croconic acid-bisindole dye CR-630 with a morpholine ring showed good water-solubility and obvious lysosome-targeting. The protonation of the nitrogen atom in the indole and lysosome-targeting of morpholine ring let it exhibit stronger pH-responsive NIR/PA imaging and photothermal effect in the lysosome acidic microenvironment (pH 4.0-5.5) than in the tumor acidic microenvironment. In the animal study, compound CR-630 could NIRF/PA image in the tumor tissues in 1.5-2.0 h, effectively inhibit the growth of the tumor, and even ablate the tumor at the drug dose of 1 mg/kg. It also demonstrated good biosafety. This study gives a new idea to develop water-solubility organic dyes with lysosome targeting, stronger pH-responsive NIRF/PA imaging and PTT for breast cancer.

Synthesis of Near-Infrared-Absorbing Anionic Heptamethine Cyanine Dyes with Trifluoromethyl Groups

A novel anionic heptamethine cyanine (HMC) dye with two trifluoromethyl groups that selectively absorb near-infrared light is synthesized. When contrasted with previously studied anionic HMC dyes with substituents such as methyl, phenyl, and pentafluorophenyl groups, the trifluoromethylated dye displays a red-shifted maximum absorption wavelength (for instance, 948 nm in CH₂Cl₂) along with enhanced photostability. Furthermore, HMC dyes with broad absorption in the near-infrared region are synthesized by combining a trifluoromethylated anionic HMC dye with a cationic HMC dye as a counterion.

Orange-Emissive Carbon Dots with High Photostability for Mitochondrial Dynamics Tracking in Living Cells

Mitochondria play significant roles in maintaining a stable internal environment for cell metabolism. Hence, real-time monitoring of the dynamics of mitochondria is essential for further understanding mitochondria-related diseases. Fluorescent probes provide powerful tools for visualizing dynamic processes. However, most mitochondria-targeted probes are derived from organic molecules with poor photostability, making long-term dynamic monitoring challenging. Herein, we design a novel mitochondria-targeted probe based on carbon dots with high performance for long-term tracking. Considering that the targeting ability of CDs is related to surface functional groups, which are generally determined by the reaction precursors, we successfully constructed mitochondria-targeted O-CDs with emission at 565 nm through solvothermal treatment of m-diethylaminophenol. The O-CDs are bright with a high quantum yield of 12.61%, high mitochondria-targeting ability, and good stability. The O-CDs possess a high quantum yield (12.61%), specific mitochondria-targeting ability, and outstanding optical stability. Owing to the abundant hydroxyl and ammonium cations on the surface, O-CDs showed obvious accumulation in mitochondria with a high colocalization coefficient of up to 0.90 and remained steady even after fixation. Besides, O-CDs showed outstanding compatibility and photostability under various interruptions or long-time irradiation. Therefore, O-CDs are preferable for the long-term tracking of dynamic mitochondrial behavior in live cells. We first observed the mitochondrial fission and fusion behaviors in HeLa cells, and then, the size, morphology, and distribution of mitochondria in physiological or pathological conditions were clearly recorded. More importantly, we observed different dynamics interactions between mitochondria and lipid droplets during the apoptosis and mitophagy processes. This study provides a potential tool for exploring interactions between mitochondria and other organelles, further promoting the research on mitochondria-related diseases.

Three near-infrared and lysosome-targeting probes for photodynamic therapy (PDT)

Lysosome, an organelle which contains a number of hydrolases and hydrogen ions, plays a crucial role in cellular survival and apoptosis. If selectively destroy lysosomes membrane, inner hydrolases and hydrogen ions will leak and induce cell death. In this work, three lysosome-targeting fluorescent probes (HCL 1-3, heptamethine cyanine lysosomal-targeting probe) were designed, synthesized and developed for photodynamic therapy. Piperazine and N, N-dimethyl structures made HCL 1-3 have good lysosome targeting ability while Pearson's correlation coefficients reached 0.85, 0.87 and 0.78. It can be concluded from MTT test, HCL 1-3 have high photo cytotoxicity and low dark cytotoxicity from MTT test. Calcein/PI staining assays also supported cytotoxicity of HCL 1-3 under light conditions. In vivo experiments, HCL 2 accumulated in tumor and a strong fluorescence signal was observed at 12 h post injection. All results showed that our experiments provide help and new ideas for cyanine dyes in cancer treatment.

Acidic pH-Triggered Live-Cell Lysosome Specific Tracking, Ratiometric pH Sensing, and Multicolor Imaging by Visible to NIR Switchable Cy-7 Dyes

We have demonstrated an efficient synthetic route with crystal structures for the construction of acidic pH-triggered visible-to-NIR interchangeable ratiometric fluorescent pH sensors. This bioresponsive probe exhibits pH-sensitive reversible absorption/emission features, low cytotoxicity, a huge 322 nm bathochromic spectral shift with augmented quantum yield from neutral to acidic pH, high sensitivity and selective targeting ability of live-cell lysosomes with ideal pK_a , off-to-on narrow NIR absorption/fluorescence signals with high molar absorption coefficient at acidic lysosomal lumen, and in-situ live-cell pH-activated ratiometric imaging of lysosomal pH. Selective staining and ratiometric pH imaging in human carcinoma live-cell lysosomes were monitored by dual-channel confocal laser scanning microscope using a pH-activatable organic fluorescent dye comprising a morpholine moiety for lysosome targeting and an acidic pH openable oxazolidine ring. Moreover, real-time tracking of lysosomes, 3D, and multicolor live-cell imaging have been achieved using the synthesized pH-activatable probe.

pH-Switched Near-Infrared Fluorescent Strategy for Ratiometric Detection of ONOO- in Lysosomes and Precise Imaging of Oxidative Stress in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is well-known as a kind of autoimmune disease, which brings unbearable pain to the patients by multiple organ complications besides arthritis. To date, RA can be hardly cured, but early diagnosis and standard treatment can relieve symptoms and pain. Therefore, an effective tool to assist the early diagnosis of RA deserves considerable attention. On account of the overexpressed ONOO^- during the early stage of RA, a near-infrared (NIR) receptor, Lyso-Cy, is proposed in this work by linker chemistry to expand the conjugated rhodamine framework by cyanine groups. Contributed by the pH-sensitive spiral ring in rhodamine, receptor Lyso-Cy has been found to be workable in lysosomes specifically, which was confirmed by the pH-dependent spectra with a narrow responding region and a well-calculated pK_a value of 5.81. We presented an excellent ratiometric sensing protocol for ONOO^- in an acidic environment, which was also available for targeting ONOO^- in lysosomes selectively. This innovative dual-targeting responsive design is expected to be promising for assisting RA diagnosis at an early stage with respect to the joint inflammatory model established in this work at the organism level.

Norsquaraine endowed with anticancer and antibacterial activities

BACKGROUND

Photodynamic therapy (PDT) is a method for the treatment of cancer. Furthermore, PDT can also be used for the eradication of bacteria. The photo-sensitizing drug, a.k.a photosensitizer, is critical for the success of PDT. Although norsquaraines are analogs of squaraine dyes, they are overlooked as photosensitizers.

METHODS

In this work, synthesis, characterization, bioimaging and in vitro PDT applications of a new norsquaraine dye 1 were described. We also prepared nanoparticles from norsquaraine 1 and Pluronic F127 to obtain 1@F127.

RESULTS

Norsquaraine 1 boosted the generation of reactive oxygen species over a wide range of pH (pH 8.0, 7.0, 6.0, and 2.2.). Furthermore, 1 was internalized by epidermoid laryngeal carcinoma Hep-2 (Hep-2) cells and used for fluorescence imaging. Remarkably, norsquaraine 1 destroyed most of the cancer cells (ca. 77% to 89%) after illumination with red light. Most strikingly, 1 successfully inhibited the growth of Methicillin-resistant Staphylococcus aureus (MRSA) upon illumination. Last but not least, photodynamic sterilization of tomato juice, an acidic beverage, was feasible using 1 as a photo sterilizer. Nano formulation of 1 with Pluronic F127 provided 1@F127 nanoparticles. It is lucid that 1@F127 nanoparticles permeate into Hep-2 cells and boost the generation of ROS upon illumination.

CONCLUSION

Norsquaraine 1 shows superior features as a photosensitizer pertinent to PDT in a wide range of pH. This norsquaraine is endowed with anticancer and antibacterial activities. Which should be further evaluated.

A novel indene-chalcone-based fluorescence probe with lysosome-targeting for detection of endogenous carboxylesterases and bioimaging

An indene-chalcone-based fluorescence probe 1 was synthesized and characterized. Under physiological conditions (containing 5% DMSO), probe 1 showed satisfactory stability with a low background signal and recognized carboxylesterases (CEs) based on the catalytic hydrolysis of ester groups, releasing a significant green fluorescence. Probe 1 presents several features including a short response time (within 20 min), low detection limit (1.3 × 10^-4 U/mL) and large stokes shift (over 155 nm). Notably, commercial lysosomal dye co-staining experiments illustrated the lysosomal localization function of 1, with the probe also being used for cell and zebrafish imaging of endogenous CEs.

A near-infrared probe for the real-time detection of lysosomal pH in living cells under "wash free" conditions

Lysosomal pH is an important indicator for the physiological state of eukaryotic cells. The real-time detection of intracellular lysosomal pH is critical for understanding and studying many physiological and pathological processes of cells. Herein, we designed and synthesized a series of novel pH sensors, namely W1, W2 and W3. By comparing the spectroscopic properties of the three molecules and their ability to target lysosomes in living cells, a specific probe W1 was selected for the quantitative analysis of lysosomal pH changes in live cells. W1 shows a fast, sensitive and highly selective red fluorescence response to an acidic pH value. The pK_a value of W1 is 5.84, and the fluorescence intensity ratios of I₇₄₃/I₆₈₀ under acidic conditions show a good linear relationship with the pH value. In addition, W1 shows a 100-fold difference in fluorescence from an extracellular environment to an intracellular environment, allowing it to be used as a "wash free" staining probe to visualize the pH change of lysosomes. W1 was further applied to detect the changes of lysosomal pH during apoptosis and mitophagy. Thus, W1 is expected to be a potentially useful tool for monitoring the changes of lysosomal pH in cell-related physiological or pathological states.

Construction of Red Fluorescent Dual Targeting Mechanically Interlocked Molecules for Live Cancer Cell Specific Lysosomal Staining and Multicolor Cellular Imaging

We have designed and synthesized red fluorescent mechanically interlocked molecules with dual targeting functionality for live cancer cell specific active targeting followed by selective internalization and imaging of malignant lysosomes along with real-time tracking, 3D, and multicolor cellular imaging applications.

Basic Fluorescent Protonation-Type pH Probe Sensitive to Small ΔpKa of Methanol and Ethanol

An optical pH probe is a simple and effective tool for determining an accurate pH value in its localized area. However, basic pH probes with pK_BH+ values above 8 have rarely been reported, although many components with high pK_a such as arginine play important roles in vivo. Herein, we introduce novel colorimetric and fluorescent basic probes 1-5, which are designed using push-pull-type aminoquinoline and aminobenzoquinoline fluorophores, with pK_BH+ values ranging from 8.4 to 9.9. After the basicity of the remarkably sensitive basic probe 4 was tuned, it was able to successfully distinguish between the pK_a values of MeOH (15.5) and EtOH (15.9), thus displaying selective protonation and fluorescence enhancement in MeOH over EtOH. Our pH probes can be used to detect MeOH poisoning in commercial EtOH products such as hand sanitizers, providing an effective solution to this problem observed during the COVID-19 pandemic.

An AIE-Active probe for detection and bioimaging of pH values based on lactone hydrolysis reaction

Cellular pH homeostasis is essential for many physiological and pathological processes. pH monitoring is helpful for the diagnosis, treatment and prevention of disorders and diseases. Herein, we developed a ratiometric fluorescent pH probe (TCC) based on a coumarin derivative containing a highly active lactone ring. TCC exhibited a typical AIE effect and emitted blue fluorescence under weak acidic condition. When under weak basic condition, the active lactone moiety underwent a hydrolysis reaction to afford a water-soluble product, which gave red-shifted emission. The emission color change from blue through cyan and then to yellow within pH 6.5-9.0 which is approximate to the biological pH range. And the fluorescence color change along with pH value is reversible. Furthermore, TCC was successfully utilized in the detection of the intracellular pH change of live HeLa cells, which indicated that TCC had practical potential in biomedical research.

Aromatic fluorine atom-induced highly amine-sensitive trimethine cyanine dye showing colorimetric and ratiometric fluorescence change

The prepared ring-perfluorinated trimethine cyanine dye 2a has a significantly higher response to n-hexylamine than the non-fluorinated dye 2b, and exhibited a dual change in the solution and on filter paper and fluorescence color at widely shifted wavelengths, visible to the naked eye.

Real-Time and High-Fidelity Tracking of Lysosomal Dynamics with a Dicyanoisophorone-Based Fluorescent Probe

The development of high-performance probes that can visualize and track the dynamic changes of lysosomes is very important for the in-depth study of lysosomes. Herein, we report that a dicyanoisophorone-based probe (named DCIP) can be used for high-fidelity imaging of lysosomes and lysosomal dynamics. DCIP can be easily prepared and shows strong far-red to near-infrared emissions centered at 653 nm in water with a huge Stokes shift (224 nm), high quantum yield (Φ = 0.15), high pKa value (∼8.79), and good biocompatibility. DCIP also shows good cell permeability and can label lysosomes rapidly with bright fluorescence without a time-consuming washing process before imaging. DCIP also possesses good photostability and negligible background, making it effective for long-term and high spatiotemporal resolution (0.44 s of exposure) imaging of lysosomes. Moreover, DCIP achieved high-fidelity tracking of lysosomal dynamics at an extremely low concentration (1 nM). Finally, we also demonstrated that DCIP could real-time track the interactions of lysosomes with other organelles (damaged mitochondria as a model) and image the drug-escape processes from lysosomes. All of the results show that DCIP holds broad prospects in lysosome-related research.

Lighting up Individual Organelles With Fluorescent Carbon Dots

Cell organelles play crucial roles in the normal functioning of an organism, therefore the disruption of their operation is associated with diseases and in some cases death. Thus, the detection and monitoring of the activities within these organelles are of great importance. Several probes based on graphene oxide, small molecules, and other nanomaterials have been developed for targeting specific organelles. Among these materials, organelle-targeted fluorescent probes based on carbon dots have attracted substantial attention in recent years owing to their superior characteristics, which include facile synthesis, good photostability, low cytotoxicity, and high selectivity. The ability of these probes to target specific organelles enables researchers to obtain valuable information for understanding the processes involved in their functions and/or malfunctions and may also aid in effective targeted drug delivery. This review highlights recently reported organelle-specific fluorescent probes based on carbon dots. The precursors of these carbon dots are also discussed because studies have shown that many of the intrinsic properties of these probes originate from the precursor used. An overview of the functions of the discussed organelles, the types of probes used, and their advantages and limitations are also provided. Organelles such as the mitochondria, nucleus, lysosomes, and endoplasmic reticulum have been the central focus of research to date, whereas the Golgi body, centrosome, vesicles, and others have received comparatively little attention. It is therefore the hope of the authors that further studies will be conducted in an effort to design probes with the ability to localize within these less studied organelles so as to fully elucidate the mechanisms underlying their function.

Fluorescent Benzothiadiazole Derivatives as Fluorescence Imaging Dyes: A Decade of New Generation Probes

The current review describes advances in the use of fluorescent 2,1,3-benzothiadiazole (BTD) derivatives after nearly one decade since the first description of bioimaging experiments using this class of fluorogenic dyes. The review describes the use of BTD-containing fluorophores applied as, inter alia, bioprobes for imaging cell nuclei, mitochondria, lipid droplets, sensors, markers for proteins and related events, biological processes and activities, lysosomes, plasma membranes, multicellular models, and animals. A number of physicochemical and photophysical properties commonly observed for BTD fluorogenic structures are also described.