Lysosome triggered near-infrared fluorescence imaging of cellular trafficking processes in real time

Integrated anti-vascular and immune-chemotherapy for colorectal carcinoma using a pH-responsive polymeric delivery system

Colorectal carcinoma (CRC) has become one of the most prevalent malignant tumors and exploring a potential therapeutic strategy with diminished drug-associated adverse effects to combat CRC is urgent. Herein, we designed a pH-responsive polymer to efficiently encapsulate a stimulator of interferon genes (STING) agonist (5,6- dimethylxanthenone-4-acetic acid, termed ASA404) and a common clinically used chemotherapeutic agent (1-hexylcarbamoyl-5-fluorouracil, termed HCFU). Investigations in vitro demonstrated that polymer encapsulation endowed the system with a pH-dependent disassembly behavior (pHt 6.37), which preferentially selected cancerous cells with a favorable dose reduction (dose reduction index (DRI) of HCFU was 4.09). Moreover, the growth of CRC in tumor-bearing mice was effectively suppressed, with tumor suppression rates up to 94.74%, and a combination index (CI) value of less than one (CI = 0.41 for CT26 cell lines), indicating a significant synergistic therapeutic effect. Histological analysis of the tumor micro-vessel density and enzyme-linked immunosorbent assay (ELISA) tests indicated that the system increased TNF-α and IFN-β levels in serum. Therefore, this research introduces a pH-responsive polymer-based theranostic platform with great potential for immune-chemotherapeutic and anti-vascular combination therapy of CRC.

A NIR-Fluorochrome for Live Cell Dual Emission and Lifetime Tracking from the First Plasma Membrane Interaction to Subcellular and Extracellular Locales

Molecular probes with the ability to differentiate between subcellular variations in acidity levels remain important for the investigation of dynamic cellular processes and functions. In this context, a series of cyclic peptide and PEG bio-conjugated dual near-infrared emissive BF2-azadipyrromethene fluorophores with maxima emissions at 720 nm (at pH > 6) and 790 nm (at pH < 5) have been developed and their aqueous solution photophysical properties determined. Their inter-converting emissions and fluorescence lifetime characteristics were exploited to track their spatial and temporal progression from first contact with the plasma membrane to subcellular locales to their release within extracellular vesicles. A pH-dependent reversible phenolate/phenol interconversion on the fluorophore controlled the dynamic changes in dual emission responses and corresponding lifetime changes. Live-cell confocal microscopy experiments in the metastatic breast cancer cell line MDA-MB-231 confirmed the usability of the dual emissive properties for imaging over prolonged periods. All three derivatives performed as probes capable of real-time continuous imaging of fundamental cellular processes such as plasma membrane interaction, tracking endocytosis, lysosomal/large acidic vesicle accumulation, and efflux within extracellular vesicles without perturbing cellular function. Furthermore, fluorescence lifetime imaging microscopy provided valuable insights regarding fluorophore progression through intracellular microenvironments over time. Overall, the unique photophysical properties of these fluorophores show excellent potential for their use as information-rich probes.

Cytoplasmic Ca2+ influx mediates iron- and reactive oxygen species-dependent ferroptotic cell death in rice immunity

Iron- and reactive oxygen species (ROS)-dependent ferroptosis occurs in plant cells. Ca2+ acts as a conserved key mediator to control plant immune responses. Here, we report a novel role of cytoplasmic Ca2+ influx regulating ferroptotic cell death in rice immunity using pharmacological approaches. High Ca2+ influx triggered iron-dependent ROS accumulation, lipid peroxidation, and subsequent hypersensitive response (HR) cell death in rice (Oryza sativa). During Magnaporthe oryzae infection, 14 different Ca2+ influx regulators altered Ca2+, ROS and Fe2+ accumulation, glutathione reductase (GR) expression, glutathione (GSH) depletion and lipid peroxidation, leading to ferroptotic cell death in rice. High Ca2+ levels inhibited the reduction of glutathione isulphide (GSSG) to GSH in vitro. Ca2+ chelation by ethylene glycol-bis (2-aminoethylether)-N, N, N', N'-tetra-acetic acid (EGTA) suppressed apoplastic Ca2+ influx in rice leaf sheaths during infection. Blocking apoplastic Ca2+ influx into the cytoplasm by Ca2+ chelation effectively suppressed Ca2+-mediated iron-dependent ROS accumulation and ferroptotic cell death. By contrast, acibenzolar-S-methyl (ASM), a plant defense activator, significantly enhanced Ca2+ influx, as well as ROS and iron accumulation to trigger ferroptotic cell death in rice. The cytoplasmic Ca2+ influx through calcium-permeable cation channels, including the putative resistosomes, could mediate iron- and ROS-dependent ferroptotic cell death under reduced GR expression levels in rice immune responses.

Water-Soluble Small Organic Fluorophores for Oncological Theragnostic Applications: Progress and Development

Cancer is one of the major noncommunicable diseases, responsible for millions of deaths every year worldwide. Though various cancer detection and treatment modalities are available today, many deaths occur owing to its late-stage detection and metastatic nature. Noninvasive detection using luminescence-based imaging tools is considered one of the promising techniques owing to its low cost, high sensitivity, and brightness. Moreover, these tools are unique and valuable as they can detect even the slightest changes in the cellular microenvironment. To achieve this, a fluorescent probe with strong tumor uptake and high spatial and temporal resolution, especially with high water solubility, is highly demanded. Recently, several water-soluble molecules with emission windows in the visible (400-700 nm), first near-infrared (NIR-I, 700-1000 nm), and second near-infrared (NIR-II, 1000-1700 nm) windows have been reported in literature. This review highlights recently reported water-soluble small organic fluorophores/dyes with applications in cancer diagnosis and therapeutics. We systematically highlight and describe the key concepts, structural classes of fluorophores, strategies for imparting water solubility, and applications in cancer therapy and diagnosis, i.e., theragnostics. We discuss examples of water-soluble fluorescent probes based on coumarin, xanthene, boron-dipyrromethene (BODIPY), and cyanine cores. Some other emerging classes of dyes based on carbocyclic and heterocyclic cores are also discussed. Besides, emerging molecular engineering methods to obtain such fluorophores are discussed. Finally, the opportunities and challenges in this research area are also delineated.

A novel pH-activated AIEgen probe for dynamic lysosome tracking and high-efficiency photodynamic therapy

A novel AIEgen molecular probe (N-3QL) with typical AIE effects, good biocompatibility, lysosome targeting, pH activation, excellent photostability, and high brightness was synthesized using two simple synthetic steps. Spectroscopic and cytotoxicity experiments indicate that N-3QL can not only be used for the dynamic monitoring of cancer cell lysosomes, but also for photodynamic therapy (PDT) ablation of cancer cells.

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.

Oxygen and pH responsive theragnostic liposomes for early-stage diagnosis and photothermal therapy of solid tumours

The development of cancer treatment is of great importance, especially in the early stage. In this work, we synthesized a pH-sensitive amphiphilic ruthenium complex containing two alkyl chains and two PEG chains, which was utilized as an oxygen sensitive fluorescent probe for co-assembly with lipids to harvest a liposomal delivery system (RuPC) for the encapsulation of a photothermal agent indocyanine green (ICG). The resultant ICG encapsulated liposome (RuPC@ICG) enabled the delivery of ICG into cells via a membrane fusion pathway, by which the ruthenium complex was localized in the cell membrane for better detection of the extracellular oxygen concentration. Such characteristics allowed ratiometric imaging to distinguish the tumour location from normal tissues just 3 days after cancer cells were implanted, by monitoring the hypoxia condition and tracing the metabolism. Moreover, the pH sensitivity of the liposomes favoured cell uptake, and improved the anti-tumour efficiency of the formulation in vivo under NIR irradiation. Assuming liposomal systems have fewer safety issues, our work not only provides a facile method for the construction of a theragnostic system by combining phototherapy with photoluminescence imaging, but hopefully paves the way for clinical translation from bench to bedside.

Asymmetric aza-BODIPY photosensitizer for photoacoustic/photothermal imaging-guided synergistic photodynamic/photothermal therapy

Cancer synergistic therapy usually shows improved therapeutic efficacy with low side effects. In this contribution, an aza-BODIPY-derived photosensitizer NBDP with asymmetric structure and the periphery phenyl ring modified with bromine atom was designed and synthesized for synergistic photothermal therapy (PTT) and photodynamic therapy (PDT). Photosensitizer NBDP exhibited good singlet oxygen (1O2) generation capacity (1.43 times higher than that of ICG), and NBDP NPs showed an outstanding photothermal conversion efficiency (η) of 46.0% under 660 nm photoirradiation. Guided by in vivo photoacoustic (PA) imaging, NBDP NPs were found to targetedly accumulate in the tumor tissues in 6 h. All results showed that the aza-BODIPY-derived photosensitizer NBDP had great potential for PA/photothermal imaging-guided synergistic PTT/PDT.

The in vivo drug delivery pattern of the organelle-targeting small molecules

Eukaryotic cell organelles sustain the life of cells. Their structural changes and dysfunctions can cause abnormal physiological activities and lead to various diseases. Molecular imaging technology enables the visualization of subcellular structures, cells, organs, and the whole living body's structure and metabolism dynamic changes. This could help to reveal the pharmacology mechanisms and drug delivery pathway in vivo. This article discusses the relationship between organelles and human disease, reviews recent probes targeting organelles and their behavior in vivo. We found that mitochondria-targeting probes prefer accumulation in the intestine, heart, and tumor. The lysosome-targeting probe accumulates in the intestine and tumor. Few studies on endoplasmic reticulum- or Golgi apparatus-targeting probes have been reported for in vivo imaging. We hope this review could provide new insights for developing and applying organelle-targeting probes.

Intracellular lipophilic network transformation induced by protease-specific endocytosis of fluorescent Au nanoclusters

The understanding of the endocytosis process of internalized nanomedicines through membrane biomarker is essential for the development of molecular-specific nanomedicines. In various recent reports, the metalloproteases have been identified as important markers during the metastasis of cancer cells. In particular, MT1-MMP has provoked concern due to its protease activity in the degradation of the extracellular matrix adjacent to tumors. Thus, in the current work, we have applied fluorescent Au nanoclusters which present strong resistance to chemical quenching to the investigation of MT1-MMP-mediated endocytosis. We synthesized protein-based Au nanocluster (PAuNC) and MT1-MMP-specific peptide was conjugated with PAuNC (pPAuNC) for monitoring protease-mediated endocytosis. The fluorescence capacity of pPAuNC was investigated and MT1-MMP-mediated intracellular uptake of pPAuNC was subsequently confirmed by a co-localization analysis using confocal microscopy and molecular competition test. Furthermore, we confirmed a change in the intracellular lipophilic network after an endocytosis event of pPAuNC. The identical lipophilic network change did not occur with the endocytosis of bare PAuNC. By classification of the branched network between the lipophilic organelles at the nanoscale, the image-based analysis of cell organelle networking allowed the evaluation of nanoparticle internalization and impaired cellular components after intracellular accumulation at a single-cell level. Our analyses suggest a methodology to achieve a better understanding of the mechanism by which nanoparticles enter cells.

Constant Conversion Rate of Endolysosomes Revealed by a pH-Sensitive Fluorescent Probe

Endolysosome dynamics plays an important role in autophagosome biogenesis. Hence, imaging the subcellular dynamics of endolysosomes using high-resolution fluorescent imaging techniques would deepen our understanding of autophagy and benefit the development of pharmaceuticals against endosome-related diseases. Taking advantage of the intramolecular charge-transfer mechanism, herein we report a cationic quinolinium-based fluorescent probe (PyQPMe) that exhibits excellent pH-sensitive fluorescence in endolysosomes at different stages of interest. A systematic photophysical and computational study on PyQPMe was carried out to rationalize its highly pH-dependent absorption and emission spectra. The large Stokes shift and strong fluorescence intensity of PyQPMe can effectively reduce the background noise caused by excitation light and microenvironments and provide a high signal-to-noise ratio for high-resolution imaging of endolysosomes. By applying PyQPMe as a small molecular probe in live cells, we were able to reveal a constant conversion rate from early endosomes to late endosomes/lysosomes during autophagy at the submicron level.

Superior biocompatible carbon dots for dynamic fluorescence imaging of nucleoli in living cells

The nucleolus is a newly developed and promising target for cancer diagnosis and therapy, and its imaging is extremely significant for fundamental research and clinical applications. The unique feature, i.e., high resolution at the subcellular level, makes the fluorescence imaging method a powerful tool for nucleolus imaging. However, the fluorescence imaging of nucleoli in living cells is restricted by the limited availability of fluorescent agents with specific nucleolus-targeting capability and superior biocompatibility. Here, promising carbon dots (CDs) with intrinsic nucleolus-targeting capability were synthesized, characterized and employed for dynamic fluorescence imaging of nucleoli in living cells. The CDs exhibit a high fluorescence quantum yield of 0.2, excellent specificity and photostability, and superior biocompatibility, which were systematically demonstrated at the gene, cellular and animal levels and confirmed by their biological effects on embryonic development. All these features enabled CDs to light up the nucleoli for a long time with a high signal-to-noise ratio in living cells and monitor the nucleolar dynamics of malignant cells in camptothecin (CPT) based chemotherapy. Their excellent optical and biological features as well as general nucleolus-targeting capability endow CDs with great potential for future translational research.

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.

A multicomponent reaction platform towards multimodal near-infrared BODIPY dyes for STED and fluorescence lifetime imaging

We report a platform combining multicomponent reaction synthesis and automated cell-based screening to develop biocompatible NIR-BODIPY fluorophores. From a library of over 60 fluorophores, we optimised compound NIRBD-62c as a multimodal probe with suitable properties for STED super-resolution and fluorescence lifetime imaging. Furthermore, we employed NIRBD-62c for imaging trafficking inside cells and to examine how pharmacological inhibitors can alter the vesicular traffic between intracellular compartments and the plasma membrane.

Bichromatic Imaging with Hemicyanine Fluorophores Enables Simultaneous Visualization of Non-alcoholic Fatty Liver Disease and Metastatic Intestinal Cancer

Simultaneous detection of different diseases via a single fluorophore is challenging. We herein report a bichromatic fluorophore named Cy-914 for the simultaneous diagnosis of non-alcoholic fatty liver disease (NAFLD) and metastatic intestinal cancer by leveraging its NIR-I/NIR-II dual-color imaging capability. Cy-914 with a pK_a of 6.98 exhibits high sensitivity to pH and viscosity, showing turn-on NIR-I fluorescence at 795 nm in an acidic tumor microenvironment, meanwhile displaying intense NIR-II fluorescence at 914/1030 nm under neutral to slightly basic viscous conditions. Notably, Cy-914 could sensitively and noninvasively monitor viscosity variations in the progression of NAFLD. More importantly, it was able to simultaneously visualize NAFLD (ex/em = 808/1000-1700 nm) and intestinal metastases (ex/em = 570/810-875 nm) in two independent channels without spectral cross interference after topical spraying, further improving fluorescence-guided surgery of tiny metastases less than 3 mm. This strategy may provide an understanding for developing multi-color fluorophores for multi-disease diagnosis.

Recent Progress in Second Near-Infrared (NIR-II) Fluorescence Imaging in Cancer

Cancer continues to be one of the leading causes of death worldwide, and its incidence is on the rise. Although cancer diagnosis and therapy have advanced significantly in recent decades, it is still a challenge to achieve the accurate identification and localization of cancer and to complete tumor elimination with a maximum preservation of normal tissue. Recently, second near-infrared region (NIR-II, 1000-1700 nm) fluorescence has shown great application potential in cancer theranostics due to its inherent advantages, such as great penetration capacity, minimal tissue absorption and scattering, and low autofluorescence. With the development of fluorescence imaging systems and fluorescent probes, tumor detection, margin definition, and individualized therapy can be achieved quickly, enabling an increasingly accurate diagnosis and treatment of cancer. Herein, this review introduces the role of NIR-II fluorescence imaging in cancer diagnosis and summarizes the representative applications of NIR-II image-guided treatment in cancer therapy. Ultimately, we discuss the present challenges and future perspectives on fluorescence imaging in the field of cancer theranostics and put forward our opinions on how to improve the accuracy and efficiency of cancer diagnosis and therapeutics.

Excited state lifetime modulation in semiconductor nanocrystals for super-resolution imaging

We report on proof of principle measurements of a concept for a super-resolution imaging method that is based on excitation field density-dependent lifetime modulation of semiconductor nanocrystals. The prerequisite of the technique is access to semiconductor nanocrystals with emission lifetimes that depend on the excitation intensity. Experimentally, the method requires a confocal microscope with fluorescence-lifetime measurement capability that makes it easily accessible to a broad optical imaging community. We demonstrate with single particle imaging that the method allows one to achieve a spatial resolution of the order of several tens of nanometers at moderate fluorescence excitation intensity.

Cancer Cell Membrane Labeling Fluorescent Doppelganger Enables In Situ Photoactivated Membrane Dynamics Tracking via Two-Photon Fluorescence Imaging Microscopy

Various suborganelles are delimited by lipid bilayers, in which high spatial and temporal morphological changes are essential to many physiological and pathological processes of cells. However, almost all the amphiphilic fluorescent molecules reported until now are not available for in situ precise tracking of membrane dynamics in cell apoptosis. Here, the MO (coumarin pyridine derivatives) was devised by engineering lipophilic coumarin and cationic pyridine salt, which not only lastingly anchored onto the plasma membrane in dark due to appropriate amphipathicity and electrostatic interactions but also in situ reflected the membrane damage and heterogeneity with secretion of extracellular vesicles (EVs) under reactive oxygen species regulation and was investigated by two-photon fluorescence lifetime imaging microscopy. This work opens up a new avenue for the development of plasma membrane staining and EV-based medicines for the early diagnosis and treatment of disease.

One Scaffold, Different Organelle Sensors: pH-Activable Fluorescent Probes for Targeting Live Microglial Cell Organelles

Targeting live cell organelles is essential for imaging, understanding, and controlling specific biochemical processes. Typically, fluorescent probes with distinct structural scaffolds are used to target specific cell organelles. Here, we have designed a modular one-step synthetic strategy using a common reaction intermediate to develop new lysosomal, mitochondrial, and nucleus-targeting pH-activable fluorescent probes that are all based on a single boron dipyrromethane scaffold. The divergent cell organelle targeting was achieved by synthesizing probes with specific functional group changes to the central scaffold resulting in differential fluorescence and pK_a . Specifically, we show that the functional group transformation of the same scaffold influences cellular localization and specificity of pH-activable fluorescent probes in live primary microglial cells with pK_a values ranging from ∼3.2-6.0. We introduce a structure-organelle-relationship (SOR) framework to target nuclei (NucShine), lysosomes (LysoShine), and mitochondria (MitoShine) in live microglia. This work will result in future applications of SOR beyond imaging to target and control organelle-specific biochemical processes in disease-specific models.

Role of Azole Drugs in Promoting Fungal Cell Autophagy Revealed by an NIR Fluorescence-Based Theranostic Probe

Autophagy, a widespread degradation system in eukaryotes, plays an important role in maintaining the homeostasis of the cellular environment and the recycling of substances. Optical probes for the tracking of autophagy can be used as an effective tool not only to visualize the autophagy process but also to study autophagy-targeted drugs. Various molecule probes for autophagy of cancer cells emerge but are very limited for that of fungal cells, resulting in the lack of research on antifungal drugs targeting autophagy. To address this issue, we report an azole NIR fluorescence-based theranostic probe AF-1 with antifungal activity that is sensitive to autophagy-associated pH. The unique design of this probe lies in the introduction of both the pH-sensitive fluorophore with a detection range matching the pH range of the autophagy process and the conserved core structural fragment of azole drugs, providing a strategy to investigate the relationship between antifungal drug action and autophagy. As such, AF-1 exhibited excellent spectral properties and was found to target and induce the autophagy of the fungal cell membrane while maintaining moderate antifungal activity. Of note, using this theranostic probe as both a dye and drug, the autophagy process of fungi was visualized in a ratiometric manner, revealing the role of azole antifungal drugs in promoting autophagy to induce fungal cell apoptosis.

Femtosecond Spectroscopy and Nonlinear Optical Properties of aza-BODIPY Derivatives in Solution

The fast relaxation processes in the excited electronic states of functionalized aza-boron-dipyrromethene (aza-BODIPY) derivatives (1-4) were investigated in liquid media at room temperature, including the linear photophysical, photochemical, and nonlinear optical (NLO) properties. Optical gain was revealed for nonfluorescent derivatives 3 and 4 in the near infrared (NIR) spectral range under femtosecond excitation. The values of two-photon absorption (2PA) and excited-state absorption (ESA) cross-sections were obtained for 1-4 in dichloromethane using femtosecond Z-scans, and the role of bromine substituents in the molecular structures of 2 and 4 is discussed. The nature of the excited states involved in electronic transitions of these dyes was investigated using quantum-chemical TD-DFT calculations, and the obtained spectral parameters are in reasonable agreement with the experimental data. Significant 2PA (maxima cross-sections ∼2000 GM), and large ESA cross-sections ∼10^-20  m² of these new aza-BODIPY derivatives 1-4 along with their measured high photostability reveal their potential for photonic applications in general and optical limiting in particular.

Interfacial Biomaterial-Dentin Bacterial Biofilm Proliferation and Viability Is Affected by the Material, Aging Media and Period

Biomaterial−dentin interfaces undergo degradation over time, allowing salivary, tissue fluid, and bacterial movement between the root filling or restoration and dentin. This study aims to investigate the effect of aging in simulated human salivary/bacterial/blood esterases (SHSE) on proliferation and viability of Enterococcus faecalis biofilm within the dentin interface with four materials used to fill/restore the endodontic space. Root canals of human anterior teeth were prepared and filled with gutta-percha and one of the following: self-cured resin composite (BisfilTM 2B, Bisco, Schaumburg, IL, USA) with either self-etch (SE) (EasyBond) or total-etch (TE) (ScotchbondTM, 3M, Saint Paul, MN, USA) methacrylate-based adhesives, epoxy-resin sealer (AH Plus®, Dentsply Sirona, York, PA, USA), or bioceramic sealer (EndoSequence® BC Sealer™, Brasseler USA, Savannah, GA, USA). Specimens were aged in SHSE or phosphate-buffered saline (PBS) for up to 360 days, followed by cultivation of steady-state E. faecalis biofilm. Depth and viability of interfacial bacterial biofilm proliferation were assessed by confocal laser scanning microscopy and live/dead staining. Data were analyzed using three-way ANOVA and Scheffe’s post hoc analyses. Initial depths of biofilm proliferation were similar among material groups (p > 0.05). All groups showed significantly deeper biofilm proliferation with increased aging period (p < 0.05). SHSE aging increased interfacial biofilm depth for TE, SE and BC (p < 0.05) but not AH. For unaged interfaces, BC exhibited the lowest ratio of live bacteria, followed by AH, TE, and SE (p < 0.05). Interfacial bacterial biofilm proliferation and viability were dependent on the biomaterial, aging media, and period.

Quantifying Phase Behaviour in Model Food Composites Using 3D Confocal Laser Scanning Microscopy

There is an increasing demand for the design of complex bio-composites with customized structural characteristics for use in processed food products. Phase behaviour of these mixtures determines textural properties, encouraging the pursue of a rapid technique that can accurately quantify it. The present work tests the efficacy of confocal laser scanning microscopy (CLSM) coupled with image analysis software (Imaris), for the quantification of phase behaviour in complex tertiary systems. In doing so, it develops phase separated gels of agarose and gelatin supporting inclusions of canola oil. The polysaccharide was replaced with whey protein isolate (WPI) and the topology of the tertiary dispersion with gelatin and canola oil was also examined. Reproducible phase volume estimates were obtained, including those of the lipid phase, which were a close match to the actual concentrations added to the hydrocolloid gel. The approach could offer an alternative to the rheological estimation, via theoretical blending law analysis, of phase volumes in bio-composites.

Graphical Abstract

Synthesis and photophysical properties of nitrated aza-BODIPYs

A series of nitrated aza-BODIPYs on the 2- and 6-positions were regioselectively synthesized and their photophysical properties were examined.

Modular Design of High-Brightness pH-Activatable Near-Infrared BODIPY Probes for Noninvasive Fluorescence Detection of Deep-Seated Early Breast Cancer Bone Metastasis: Remarkable Axial Substituent Effect on Performance

We herein report a series of high-brightness pH-activatable near-infrared (NIR) BODIPY probes for high-contrast intravital imaging of deep-seated early breast cancer bone metastasis by harnessing the axial substituent effect. These probes exhibit tunable pK _a, higher brightness, and antiquenching capabilities in aqueous solution, which can be simultaneously adjusted by axial steric substituents. The optimized probe BODO-3 bearing axial dimethyl substituents exhibited a higher pK _a value of 5.6 and a brighter NIR fluorescence under tumor acidic pH, showing 10.3-fold and 6.5-fold enhanced brightness (εΦ) at pH 5.5 and 6.5, respectively. Due to the higher brightness, BODO-3 with a brilliant NIR emission at 700 nm allows for deep optical penetrations of 5 and 8 mm at pH 6.5 and 4.5, respectively. Meanwhile, covalent functionalization with glucose (BODO-3-Glu) could further enhance breast cancer and its soft tissue metastasis imaging in vivo. Notably, covalent functionalization with bisphosphonate (BODO-3-PO ₃ H ₂ ) allowed the successful targeting and visualization of deep-seated bone metastases of breast cancer with a high tumor to normal contrast of 8/1, outperforming X-rays in early detection. This strategy may provide insights for designing high-brightness activatable NIR probes for detecting deep-seated tumors and metastases.

Radiative lifetime of a BODIPY dye as calculated by TDDFT and EOM-CCSD methods: solvent and vibronic effects

The radiative emission lifetime and associated S₁ excited state properties of a BODIPY dye are investigated with TDDFT and EOM-CCSD calculations. The effects of a solvent are described with the polarizable continuum model using the linear response (LR) approach as well as state-specific methods. The Franck-Condon (FC), Herzberg-Teller (HT) and Duschinsky vibronic effects are evaluated for the absorption and emission spectra, and for the radiative lifetime. The transition energies, spectra shapes and radiative lifetime are assessed with respect to experimental results. It is found that the TDDFT transition energies are overestimated by about 0.4-0.5 eV, whereas EOM-CCSD improves the vertical emission energy by about 0.1 eV in comparison to TDDFT. The solvatochromic and Stokes shifts are better reproduced by the state-specific solvation methods, which show that these methods are more suited than the LR model to describe the solvent effects on the BODIPY dye. The vibronic effects lead to an increase of the radiative lifetime of about 0.4 to 1.0 ns depending on the theoretical approach, which highlights the importance of such effects. Moreover, the HT effects are negligible on both the spectra and lifetime, which demonstrates that the FC approximation is accurate for the BODIPY dye. Finally, the comparison with experimental data shows that the radiative lifetimes predicted by EOM-CCSD and TDDFT have comparable accuracy.

BODIPY derivatives as fluorescent reporters of molecular activities in living cells

Fluorescent compounds have become indispensable tools for imaging molecular activities in the living cell. 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is currently one of the most popular fluorescent reporters due to its unique photophysical properties. This review provides a general survey and presents a summary of recent advances in the development of new BODIPY-based cellular biomarkers and biosensors. The review starts with the consideration of the properties of BODIPY derivatives required for their application as cellular reporters. Then review provides examples of the design of sensors for different biologically important molecules, ions, membrane potential, temperature and viscosity defining the live cell status. Special attention is payed to BODPY-based phototransformable reporters.

The bibliography includes 339 references.

1,7-Di-tert-butyl-Substituted aza-BODIPYs by Low-Barrier Rotation to Enhance a Photothermal-Photodynamic Effect

1,7-Di-tert-butyl-substituted aza-BODIPYs (tBu-azaBDP) were successfully obtained for the first time. The structures of tBu-azaBDP and Ph-azaBDP were confirmed by X-ray crystal analysis, and tBu-azaBDP 2 is more twisted than Ph-azaBDP 5. tBu-azaBDPs have significant photo-stability and enhanced water solubility. tBu-azaBDPs possess excellent optical properties, such as high molar extinction coefficients, broad full width half maxima, and large Stokes shifts, which is comparable to those of the parent dye Ph-azaBDP. Although the low-barrier rotation of the distal -tBu groups in tBu-azaBDPs results in low quantum yield, photothermal conversion efficiency and singlet oxygen generation ability of tBu-azaBDPs are more effective than those of Ph-azaBDP, which is highly desirable for a photothermal-photodynamic therapy agent.

A Hybrid Nanogel to Preserve Lysosome Integrity for Fluorescence Imaging

Fluorescence imaging of lysosomes provides a powerful tool to probe the lysosome physiology in living cells, yet the continuous light exposure inevitably causes lysosome damage and phototoxicity, which remains a formidable challenge. Here the long-term lysosome tracking with minimized photodamage was realized using a multifunctional nanoprobe, a platinum nanoparticle, and a quinacrine co-loaded nanogel. To construct the hybrid nanogel, cisplatin first functioned as cross-linker to withhold all components and then was reduced to a platinum nanoparticle in situ by ethanol. The platinum nanoparticle enabled a long-term quinacrine fluorescence imaging of lysosome by scavenging the light induced reactive oxygen species which could damage lysosomal membranes.

Intriguing Heteroleptic ZnII bis(dipyrrinato) Emitters in the Far-Red Region With Large Pseudo-Stokes Shift for Bioimaging

Novel heteroleptic ZnII bis(dipyrrinato) complexes were prepared as intriguing emitters. With our tailor-made design, we achieved far-red emissive complexes with a photoluminescence quantum yield up to 45% in dimethylsulfoxide and 70% in toluene. This means that heteroleptic ZnII bis(dipyrrinato) complexes retain very intense emission also in polar solvents, in contrast to their homoleptic counterparts, which we prepared for comparing the photophysical properties. It is evident from the absorption and excitation spectra that heteroleptic complexes present the characteristic features of both ligands: the plain dipyrrin (Lp) and the π-extended dipyrrin (Lπ). On the contrary, the emission comes exclusively from the π-extended dipyrrin Lπ, suggesting an interligand nonradiative transition that causes a large pseudo-Stokes shift (up to 4,600 cm-1). The large pseudo-Stokes shifts and the emissive spectral region of these novel heteroleptic ZnII bis(dipyrrinato) complexes are of great interest for bioimaging applications. Thus, their high biocompatibiliy with four different cell lines make them appealing as new fluorophores for cell imaging.

Fluorescent Amphiphilic Quaternized β-Chitin: Antibacterial Mechanism and Cell Imaging

Fluorescent materials span multiple applications from biological probes and chemical sensing to optoelectronic systems. Although great efforts have been made toward developing classes of fluorescent materials, 100,000+ traditional fluorescent dyes still suffer from the obstacle of aggregation-caused quenching (ACQ). Thus, designing fluorescent materials with excellent optical performance from ACQ luminogens remains challenging. In this work, we prepared fluorescent amphiphilic quaternized β-chitin (QC-F) via nucleophilic addition between the amino groups of QC and isothiocyanate groups of fluorescein isothiocyanate (FITC). Due to the covalent anchoring of the QC backbone, steric hindrance of the bulky acetamido groups, electrostatic repulsion of the quaternary ammonium groups, and homogeneous distribution of FITC units, the FITC units were spatially and electronically isolated, and the QC-F series exhibited unique fluorescent behaviors. The QC-F series could be used to observe their interactions with microbial cells through fluorescence imaging to gain insights into the QC antibacterial mechanism. Moreover, with their favorable cytocompatibility, the QC-F series are also suitable for cell imaging. Thus, the present work will broaden the applications of chitin and conventional ACQ luminogens.

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

Here, we have designed and synthesized acidic pH-activatable visible to NIR switchable ratiometric pH-sensitive fluorescent dye. The design consists of a cell-permeable organic probe containing a lysosome targeting morpholine functionality and an acidic pH-activatable oxazolidine moiety. The visible closed oxazolidine form (λ_abs 418 nm) can be switched to the highly conjugated NIR Cy-7 form (λ_abs 780 nm) through ring opening of the oxazolidine moiety at acidic pH. This switching of the ratiometric fluorescent probe is highly reversible and can be controlled by pH. NMR, UV/vis, and fluorescence spectroscopies allowed monitoring of pH switching behavior of the probe. This bioresponsive in situ acidic organelle activatable fluorophore showed reversible pH-switchable ratiometric optical properties, high photostability, huge bathochromic emission shift of 320 nm from basic to acidic pH, off-to-on narrow NIR absorption and emission bands with enhanced molar extinction coefficient at lysosomal pH, good quantum yield, low cytotoxicity, and targeted imaging ability of live cell lysosomes with ideal pK_a. The report demonstrated ratiometric imaging with improved specificity of the acidic lysosome while minimizing signals at the NIR region from nontargeted neutral or basic organelles in human carcinoma HeLa and A549 as well as rat healthy H9c2(2-1) live cells, which is monitored by confocal laser scanning microscopy.

Two birds with one stone: A highly sensitive near-infrared BODIPY-based fluorescent probe for the simultaneous detection of Fe2+ and H+ in vivo

Ferrous ion (Fe²⁺) plays an essential role in many physiological and pathological processes, and its cellular metabolism is closely related to acidic pH. However, the lack of multifunctional Fe²⁺ probes has hindered the further study of Fe²⁺ in vivo. Herein, we report a dual-responsive near-infrared (NIR) fluorescent probe BODIPY-Fe for the simultaneous of Fe²⁺ and H⁺ in vivo by harnessing the N-oxide strategy and photoinduced electron transfer (PeT) mechanism. BODIPY-Fe exhibited NIR fluorescence at 671 nm, rapid response to Fe²⁺ within 90 s, and high sensitivity of low LOD of 292 nM towards Fe²⁺. Moreover, BODIPY-Fe could sensitively and selectively detect Fe²⁺ and H⁺ in the lysosomes of living cells simultaneously. Notably, BODIPY-Fe was able to noninvasively visualize Fe²⁺ and H⁺ in vivo, showing "ON-OFF-ON" NIR fluorescence signal changes. This work demonstrates that BODIPY-Fe has great potential to promote the simultaneous imaging of Fe²⁺ and H⁺ in biological systems.

Late-stage functionalisation of alkyne-modified phospha-xanthene dyes: lysosomal imaging using an off-on-off type of pH probe

Near-infrared (NIR) fluorescent molecules are of great importance for the visualisation of biological processes. Among the most promising dye scaffolds for this purpose are P[double bond, length as m-dash]O-substituted phospha-xanthene (POX) dyes, which show NIR emission with high photostability. Their practical utility for in vitro and in vivo imaging has recently been demonstrated. Although classical modification methods have been used to produce POX-based fluorescent probes, it is still a challenge to introduce additional functional groups to control the localisation of the probe in cells. Herein, we report on the development of POXs that bear a 4-ethynylphenyl group on the phosphorus atom. These dyes can subsequently be functionalised with azide-tagged biomolecules via a late-stage Cu-catalysed azide/alkyne cycloaddition (CuAAC) reaction, thus achieving target-selective labelling. To demonstrate the practical utility of the functionalised POXs, we designed a sophisticated NIR probe that exhibits a bell-shaped off-on-off pH-response and is able to assess the degree of endosomal maturation.

Highly Photostable Fluorescent Tracker with pH-Insensitivity for Long-Term Imaging of Lysosomal Dynamics in Live Cells

Visualizing and tracking lysosomal dynamic changes is crucially important in the fields of physiology and pathology. Most currently used pH-dependent small-molecule lysotrackers and sensors usually fail to visualize and track the changes due to (1) their leakage from lysosomes when the lysosomal pH increases and (2) their low photostability. Therefore, it is of significant interest to develop lysosomal probes for visualizing and tracking lysosomal dynamics independent of pH fluctuations and with high photostability. Herein, we found that the popular dicyanomethylene-4H-pyran (DCM) derivative DCM-NH₂ can selectively target and label lysosomes with bright red fluorescence regardless of pH changes. The fluorescence enhancement in lysosomes has probably resulted from their microenvironment of polarity and viscosity. Compared with the commonly used commercial lysosomal molecular probes (LysoTracker Deep Red (LTDR) and LysoTracker Red DND-99), DCM-NH₂ was demonstrated to exhibit a much stronger tolerance in lysosomes against various treatments and microenvironmental changes, and lysosomal membrane permeability could not cause DCM-NH₂ to lose imaging of their targets as well. Moreover, DCM-NH₂ exhibited a superior anti-photobleaching ability and low (photo-) cytotoxicity, which, along with pH-insensitivity, ensured its capability of long-term visualizing and tracking lysosomal dynamics. Lysosomal dynamic events such as the kiss-and-run process, fusion-fission, and mitophagy were successfully recorded with DCM-NH₂. Our study thus confirms that DCM-NH₂ is highly competitive for lysosomal imaging by overcoming the limitations of the commercial LysoTrackers and highlights the unexplored application of DCM-NH₂ in bioimaging.

Near-Infrared Fluorescent Probe Activated by Nitroreductase for In Vitro and In Vivo Hypoxic Tumor Detection

Tumor hypoxia is correlated with increased resistance to chemotherapy and poor overall prognoses across a number of cancer types. We present here a cancer cell-selective and hypoxia-responsive probe (fol-BODIPY) designed on the basis of density functional theory (DFT)-optimized quantum chemical calculations. The fol-BODIPY probe was found to provide a rapid fluorescence "off-on" response to hypoxia relative to controls, which lack the folate or nitro-benzyl moieties. In vitro confocal microscopy and flow cytometry analyses, as well as in vivo near-infrared optical imaging of CT26 solid tumor-bearing mice, provided support for the contention that fol-BODIPY is more readily accepted by folate receptor-positive CT26 cancer cells and provides a superior fluorescence "off-on" signal under hypoxic conditions than the controls. Based on the findings of this study, we propose that fol-BODIPY may serve as a tumor-targeting, hypoxia-activatable probe that allows for direct cancer monitoring both in vitro and in vivo.

Poly(amino acid)s-based star AIEgens for cell uptake with pH-response and chiral difference

Chiral aggregation-induced emission luminogens (AIEgens) are the new-generation chiral sensors that regulate chiral signals from the molecular level to the macroscopic assembly. Expanding applications of chiral AIEgens and in-depth understanding of their chiral recognition in biological systems are meaningful. Herein, two star chiral AIEgens, consisting of tetraphenylethene (TPE) as core and poly(N-acryloyl-L(D) valine) (PLV or PDV) as arms, were precisely synthesized via atom transfer radical polymerization (ATRP) technique and named TPE-PLV and TPE-PDV. They possessed typical AIE characteristics and exhibited an increase in concentration-dependent fluorescence intensity. The two AIEgens were pH-responsive and had strong AIE-related emission in acidic solution. Importantly, AIEgens can enter the living cells by ATP dependent endocytosis, then light them up. The interactions between the AIEgens and living human hepatocarcinoma (HepG2) cells revealed that the internalization process of TPE-PLV and TPE-PDV was both chiral-dependent and pH-responsive. This novel strategy for synthesizing poly(amino acid)s functionalized AIEgens could inspire the development of promising fluorescent materials with chirality.

Benzothiadiazole-Substituted Aza-BODIPY Dyes: Two-Photon Absorption Enhancement for Improved Optical Limiting Performances in the Short-Wave IR Range

Aza-boron dipyrromethenes (aza-BODIPYs) presenting a benzothiadiazole substitution on upper positions are described. The strong electron-withdrawing effect of the benzothiadiazole moiety permits enhancement of the accepting strength and improves the delocalization of the aza-BODIPY core to attain a significant degree of electronic communication between the lower donating groups and the upper accepting groups. The nature of the intramolecular charge transfer is studied both experimentally and theoretically. Linear spectroscopy highlighted the strongly redshifted absorption and emission of the synthesized molecules with recorded fluorescence spectra over 1000 nm. Nonlinear optical properties were also investigated. Strong enhancement of the two-photon absorption of the substituted dyes compared with the unsubstituted one (up to 4520 GM at 1300 nm) results in an approximately 15-20 % improvement of the optical power limiting performances. These dyes are therefore a good starting point for further improvement of optical power limiting in the short-wave IR range.

Nanoplastics as a Potential Environmental Health Factor: From Molecular Interaction to Altered Cellular Function and Human Diseases

The problem of plastic pollution is becoming increasingly important and has attracted great interest in the last few years. Polystyrene is one of the most used plastic types in the food and beverage industry, medical and laboratory devices. Increased plastic production and increased food, water, and air pollution and contact with nanoplastics may cause long-lasting changes and predispose to adverse developmental and degenerative diseases through mechanisms that are not yet understood.

The aim of this article is to provide an overview of current knowledge to plastics, especially polystyrene, and their impact on the human health. In particular, we discuss the major sources of plastic waste, polystyrene surface chemistry, as well as mechanisms by which plastics degrade in the environment. We also provide an insight into cellular uptake mechanism and the molecular interaction of polystyrene nanoparticles and human cells. This review offers scientists and clinicians useful information and could be used as a starting point for more in-depth analysis of nanoplastics as a potential environmental health factor.

Base-induced multi-state fluorescence of a trefoil-shaped salicylaldehyde azine derivative

Base-induced four-state fluorescence is demonstrated in a trefoil-shaped salicylaldehyde azine derivative bearing multiple acidic protons.

Facile synthesis of graphene quantum dots from glucan and their application as a deoxidizer and in cell imaging

A facile and effective route to synthesize graphene quantum dots for cell imaging and as a deoxidizer by using glucan as a precursor is developed. AuNPs are successfully synthesized by mixing of graphene quantum dots and Au(III) salts without any additional reductants. The reducing driving force of these graphene quantum dots is much weaker than that of strong reducing agents such as NaBH4. The sizes of the as-synthesized AuNPs are much larger, with an average size of 15 nm. Notably, this size range is specifically useful and optimal for the application of AuNPs in biomedical applications. In addition, the as-synthesized graphene quantum dots are also successfully applied in cell imaging.

Near-infrared fluorescent probes: a next-generation tool for protein-labeling applications

The development of near-infrared (NIR) fluorescent probes over the past few decades has changed the way that biomolecules are imaged, and thus represents one of the most rapidly progressing areas of research. Presently, NIR fluorescent probes are routinely used to visualize and understand intracellular activities. The ability to penetrate tissues deeply, reduced photodamage to living organisms, and a high signal-to-noise ratio characterize NIR fluorescent probes as efficient next-generation tools for elucidating various biological events. The coupling of self-labeling protein tags with synthetic fluorescent probes is one of the most promising research areas in chemical biology. Indeed, at present, protein-labeling techniques are not only used to monitor the dynamics and localization of proteins but also play a more diverse role in imaging applications. For instance, one of the dominant technologies employed in the visualization of protein activity and regulation is based on protein tags and their associated NIR fluorescent probes. In this mini-review, we will discuss the development of several NIR fluorescent probes used for various protein-tag systems.

A Small-Molecule AIE Chromosome Periphery Probe for Cytogenetic Studies

The chromosome periphery (CP) is a complex network that covers the outer surface of chromosomes. It acts as a carrier of nucleolar components, helps maintain chromosome structure, and plays an important role in mitosis. Current methods for fluorescence imaging of CP largely rely on immunostaining. We herein report a small-molecule fluorescent probe, ID-IQ, which possesses aggregation-induced emission (AIE) property, for CP imaging. By labelling the CP, ID-IQ sharply highlighted the chromosome boundaries, which enabled rapid segmentation of touching and overlapping chromosomes, direct identification of the centromere, and clear visualization of chromosome morphology. ID-IQ staining was also compatible with fluorescence in situ hybridization and could assist the precise location of the gene in designated chromosome. Altogether, this study provides a versatile cytogenetic tool for improved chromosome analysis, which greatly benefits the clinical diagnostic testing and genomic research.

A common genetic variant in zinc transporter ZnT2 (Thr288Ser) is present in women with low milk volume and alters lysosome function and cell energetics

Suboptimal lactation is a common, yet underappreciated cause for early cessation of breastfeeding. Molecular regulation of mammary gland function is critical to the process lactation; however, physiological factors underlying insufficient milk production are poorly understood. The zinc (Zn) transporter ZnT2 is critical for regulation of mammary gland development and maturation during puberty, lactation, and postlactation gland remodeling. Numerous genetic variants in the gene encoding ZnT2 (SLC30A2) are associated with low milk Zn concentration and result in severe Zn deficiency in exclusively breastfed infants. However, the functional impacts of genetic variation in ZnT2 on key mammary epithelial cell functions have not yet been systematically explored at the cellular level. Here we determined a common mutation in SLC30A2/ZnT2 substituting serine for threonine at amino acid 288 (Thr288Ser) was found in 20% of women producing low milk volume (n = 2/10) but was not identified in women producing normal volume. Exploration of cellular consequences in vitro using phosphomimetics showed the serine substitution promoted preferential phosphorylation of ZnT2, driving localization to the lysosome and increasing lysosome biogenesis and acidification. While the substitution did not initiate lysosome-mediated cell death, cellular ATP levels were significantly reduced. Our findings demonstrate the Thr288Ser mutation in SLC30A2/ZnT2 impairs critical functions of mammary epithelial cells and suggest a role for genetic variation in the regulation of milk production and lactation performance.